274

Pollution is defined as unfavourable alteration of our surroundings. Water is

an essential commodity for survival. It has the property to dissolve many substances

in it, therefore it can easily get polluted. High concentration of heavy metals in

surface water generally associated with industrial discharges. According to the World

Health Organization (WHO), the metals of most immediate concern are Aluminium,

Chromium, Iron, Cobalt, Copper, Nickel, Cadmium & Mercury1.

Water pollution has focused the attention of both the scientific community and

the public on environmental problems. It not only affects the health and welfare of

people and organisms, but it also damages vegetation and properties2

According to Mason3 there are five major types of toxic pollutants known to man:

1) Metals arising from industrial processes and some agricultural application

(lead, copper, nickel and zinc)

2) Organic compounds, originating from industrial, agricultural and some

domestic sources (herbicides, PCB's, organochloride pesticides, chlorinated

aliphatic hydrocarbons, organometallic compounds and phenols)

3) Gases (ammonia and chlorine)

4) Anions ( cyanides, fluorides, sulphides and sulphites)

5) Acids and alkalis

Amongst the pollutants contaminating water bodies, metals play an important

role 4.

Metals are elements found naturally in aquatic ecosystems due to various

processes such as weathering and erosion5. Some of these metals are essential to

living organisms in trace amounts (for example copper and zinc). Essential trace

elements have a narrow optimal concentration range for growth and reproduction,

both in excess and shortage can be detrimental to organisms6 with unusually high

concentrations becoming toxic to aquatic organisms7. Metals are present in very low

concentrations in natural aquatic ecosystems8 usually at the nanogram to microgram

per liter level, but recently the occurrence of especially heavy metals in excess of

natural loads, has become an increasing concern9-10 for aquatic ecosystem 'health'.

Heavy metals are part of a group of elements, whose hydrochemical cycles have been

accelerated to a great extent by man5. The most important heavy metals in water

pollution are zinc, copper, lead, cadmium, mercury, nickel and chromium5,11-12.

Metals are introduced into the environment by a wide range of natural and

275

anthropogenic sources7 and with anthropogenic being either domestic or industrial.

Heavy metals are often present at elevated concentrations in aquatic ecosystems, due

to

1) the rapid growth in population9-12,

2) an increase in industrialization6,9

3) the increase of urbanization and socio- economic activities, exploration and

exploitation of natural resources,

4) extension of irrigation and other modern agricultural practices, as well as

5) the lack of environmental regulations9.

Consequently aquatic organisms are exposed to the elevated levels of metals6,

levels not previously encountered8, posing a great threat to aquatic organisms in

particular, and to the whole ecosystem in general13-14.

An accelerated release of heavy metals into the aquatic environment poses

serious water pollution problems because of their toxicity15 persistence and

bioaccumulation in food chains16. Due to their adverse effects on aquatic ecosystems,

it is important to identify the sources and measure the discharges of heavy metals into

systems nationwide9. Metals and pesticides, in particular, have an inclination to

accumulate and undergo food chain magnification17. It is thus also important to

monitor the bioaccumulation of these metals in a system, in order to assess the

possible impact on human health (fish consumed) and organism health (exposure to a

pollutant or consumption by predators)18. Despite progress made in environmental

waste management, heavy metals still pose immense health hazards to humans and

biota. Metal pollution is an important worldwide problem, which is growing at an

alarming rate.4 Unlike other classes of pollutants, which can be biodegraded and

destroyed completely, metals are non-biodegradable7 and can neither be created nor

destroyed. However, these metals might be altered into more toxic forms or

complexed to more stable and less toxic compounds5. In an aquatic environment metal

toxicity can be influenced by various a biotic environmental factors such as oxygen,

calcium/water hardness19-21, pH and temperature5,18-20

Contamination of aquatic ecosystems with heavy metals should be monitored and

controlled21. Ecosystems are examined for heavy metal pollution by using chemical or

biological assays. Chemical measurements of heavy metals in water, although

sensitive, not provide bioavailability information of the metals22.

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The random discharge of various wastes, pollute most ecosystems and affect

survival and physiological activities of organisms in these systems17. In natural

waters, metal ions occur as free aqueous ions, complexes with organic/inorganic

ligands or adsorbed onto the surfaces of particles23 and most metals are taken up in the

ionic form18. Free metal ions cause more serious damaging effects on aquatic

organisms than their more complex forms17. The duration of exposure of a specific

concentration of toxin can influence whether it will kill an aquatic organism19.

Nickel toxicity to aquatic life depends on the species, pH, water hardness and

other environmental factors27. According to Nebeker28, nickel has been shown as

moderately toxic to fish and aquatic invertebrates when compared to other metals.

The tolerance limit of Nickel in drinking water is 0.01mg/L beyond this limit it can

cause lung's, nose and bone cancer. It's poisining can cause deziness, headache,

nausia and vomitting, chest pain, dry cough and shortness of drug, rapid respiration

and extreme weakness, therefore, it is neccessary to remove Nickel (II) from waste

water before releasing it in to streams26.

Copper is an essential trace element to plants, animals and even humans29. It is

in fact a required element for all living organisms, and although the absolute

concentration of copper is usually low in nature, it occurs in adequate quantities for

growth in all aquatic environments30.

In animals, copper is important for bone formation, maintenance of myclin within the

nervous system, synthesis of haemoglobin, a component of key metalloenzymes, plus

it forms an important part of cytochrome oxidase and assorted other enzymes

involved in redox reactions in cells31,32. It is essential for cellular metabolism, where

its concentration is well regulated5 but becomes toxic at elevated levels. Iron (III) is

also toxic at higher concentration.

Dissolved oxygen, hardness, temperature, pH, and chelating agents can

increase the toxicity [Cu2+]8. Organic and inorganic substances can easily complex the

cupric form of copper, which is the most common speciation of this metal and it's then

adsorbed on to particulate matter. Therefore, the free ion is rarely found except in

pure acidic soft water33. The chemical speciation of copper strongly depends on the

pH of water, copper in water, precipitates at high pH (alkaline) and is thus not toxic,

whilst at low pH (acidic) it is mobile, soluble and toxic8.

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Chromium are generally found into predominant forms as trivalent and

hexavalent state in industrial waste waters. Cr (VI) is hazardous than Cr(III) in

biological activities. The permiscible limit for Cr (VI) in drinking water is 0.05 ppm34

beyond this limit it affects the human health causes skin rashes upsets stomach,

creates respiratory problems weaken immune system, damages kidney and liver alters

genetic material, creates lung cancer and even leads to death36.

In recent years, increasing awareness of the environmental impact of heavy

metals has promoted a demand for the purification of industrial wastewaters prior to

discharge into natural waters. This has led to the introduction of more strict legislation

to control water pollution, such as the National Environmental Quality Standards37.

In advanced countries, removal of heavy metals in wastewater is normally

achieved by advance technologies such as ion exchange, chemical precipitation. Ultra

filtration, or electrochemical deposition do not seem to be economically feasible for

such industries because of their relatively high costs. Therefore, there is a need to look

into alternatives to investigate a low-cost method, which is effective and economic.

Recently a great deal of interest in the research for removal of heavy metals

from industrial elements have focused on to use of vegetable waste, agricultural by

products and also building waste material as adsorbents. They have been recognised

as an emerging technique for the de-pollution of heavy metal polluted streams38-39, as

the vegetable waste, agricultural by products building waste material are capable of

binding heavy metals by adsorption, chelation and ion exchange40-42.

In the present work, we have carried out the adsorption studies of the heavy

metal ions like Copper, Nickel, Iron and Chromium onto the easily available cut

material (building waste material) of Marble (M), Red Kotta (R), Kadappa (K) and

Granite (G) available from the units where cutting process of it was carried out at

negligible cost. The powder were collected processed and finally used as adsorbents

for the removal of these metal ions.

Literature survey reveals that the work carried by different researchers36-37

showed the effective and efficient adsorbative capacity of adsorbent after treatment

with acid. It gave us an idea whether acid treated MRKG can work and give good

adsorption results. Surprisingly acid treated MRKG showed encouraging results of

adsorption of metal ions from solution. It appears acid treatment of adsorbent increase

278

surface porosity, surface area, surface activity and surface roughness. The observation

also corroborated by the studies of acid treatment on bentonite and soil 43-44.

The adsorption efficiency depends on interfacial tension between metal ion

and MRKG and surface activity of the adsorbent. The water binding forces become

lower after the acid treatment and may increase the hydrophobacity of the adsorbent

surface45. Overall this situation may be helping easy diffusion of metal ions towards

the surface and increase in surface activity resulting into higher adsorption. In other

sense, as the metal ion solution coming in contact with surface of adsorbent, initially

the intermolecular forces of metal ion and surface of the adsorbent are strong and may

weaken towards saturation. This phenomenon also confirmed from 'L' type Giles

isotherm and also based on kinetic and thermodynamic parameters suggest a weak

chemi- adsorption. The present study aimed at to find the effect of treatment of

adsorbent with mineral acids viz H2SO4. As acid treatment creates an ideal condition

for facile adsorption of metal ions to the surface.

4.1 Effect of pH

The removal of metal ions from aqueous solution as the latter effects the

surface is related to the pH of the solution degree of ionisation and the species of

adsorbate41.

Quek et.al46 during their work showed the removal of metals by sago waste

which decreased with decrease in pH of the solution. The solution of optimum pH

value was taken into consideration during the work to avoid precipitation of metals at

higher pH value and which defeat the purpose of employing adsorption47-48.

According to Mohammod et.al49 pH 5 maximizes the exposure of negative

sites of the adsorbents through dissolution of more protons and thus enhances the

adsorption capacities as the surface oxide functions as ligands for metal ions while

adsorption is attributed solely to chemical interaction namely inner-sphere

complexation. The adsorption of metals found to be strongly dependent on the pH of

the solution demonstrates that the optimum pH for the adsorption of Cu, Pb were

about 5 which was rather acidic50 .

At low pH (<3) there was excessive protonation of the active sites at carbon

surface and this often refuses the formation of links between metal ions and the active

site. At moderate pH & values (3-6) linked H+ is released from active sites and

279

adsorbed amount of metal ions is generally found to be increase. At higher pH values

(>6) the precipitation is dominant or both ion exchange and aqueous metal hydroxide

formation (not necessarily precipitation ) may become significant mechanism in the

metal removal process this condition is often not desirable as the metal precipitation

could lead to a misunderstanding for the adsorption capacity. And in practice, metal

precipitation is generally not a stabilized form of heavy metal as the precipitation can

some time be very small in size and upon the neutralization of the effluents from the

waste water plant, the solubility of the metals increases resulting in a recontamination

of the waste outlet stream51. At low pH value the surface of the adsorbent would be

closely associated with hydronium ion (H3O+) which hinders the access of metal ions

by repulsive forces, to the surface functional groups, consequently decreasing the

percentage of metal removal.

In the present investigation the adsorption of Nickel, Copper, Iron and

Chromium carried on the surface MRKG as adsorbent by varying the pH and

keeping the initial concentration of adsorbate and amount of adsorbent constant. The

result are presented in Table No. 1.0.3, 2.0.3, 3.0.3, 4.0.3, 5.0.3, 6.0.3, 7.0.3 and 8.0.3

for Nickel Table Nos 1.1.3, 2.1.3, 3.1.3, 4.1.3, 5.1.3, 6.1.3, 7.1.3 and 8.1.3 for Copper

Table Nos. 1.2.3, 2.2.3, 3.2.3, 4.2.3, 5.2.3, 6.2.3, 7.2.3 and 8.2.3 and for Iron Table

Nos. 1.3.3, 2.3.3, 3.3.3, 4.3.3, 5.3.3, 6.3.3, 7.3.3 and 8.3.3 for Chromium and the

Summarised adsorbed values are presented in short in the tabular form.

The adsorption capacities at varying pH (2-7) showed increase in adsorption of

metal ions as shown in figure 4.1.1 (A),(B) to 4.1.4(A),(B) and our findings are in

good agreement with singh et.al58.

Fig. 4.1.1(A) : Effect of pH on Adsorption of Untreated Marble Powder (M)

Fig. 4.1.1(B) : Effect of pH on Adsorption of Treated Marble Powder (M)

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Poor adsorption of metal ions at lower pH is apparent due to the higher

concentration of H+ ions present in the reaction mixture which compete with the M2+

ions during ion-exchange reaction on adsorbent. Further at higher pH the decrease in

adsorption may attributed to the formation of soluble complexes. 58-59

The removal of heavy metal by adsorption has been reported to be

significantly affected by the solution60-61. The solution pH plays a vital role in the

removal of heavy metals as the acidity of solution pH is one the most important

parameters controlling the uptake of heavy metals from wastewater and aqueous

solution.62

According to Najua et.al62 the uptake and percentage removal of copper from

the aqueous solution strongly affected by the pH of the solution which was in strong

Fig. 4.1.2(A) : Effect of pH on Adsorption of Untreated Red Kotta (R)

Fig. 4.1.2(B) : Effect of pH on Adsorption of Treated Red Kotta (R)

Fig. 4.1.3(A) : Effect of pH on Adsorption of Untreated Kadappa (K)

Fig. 4.1.3(B) : Effect of pH on Adsorption of Treated Kadappa (K)

Fig. 4.1.4(A) : Effect of pH on Adsorption of Untreated Granite (G)

Fig. 4.1.4(B) : Effect of pH on Adsorption of Treated Granite (G)

281

agreement with Kannan et.al60-61. The uptake of copper increased from 0.11 mg/g to

1.20 mg/g when the pH increased from pH=2 with 0.96 mg/g and 1.07 mg/g

adsorption capacity at pH=5 respectively, after that the capacity of adsorption

decreases slightly in pH range of 6 to 9.

The minimum adsorption observed at low pH (pH 2) may be due to the fact

that the higher concentration and higher mobility of H+ ions present favoured the

preferential adsorption of hydrogen ions compared to Cu (II) ions.63 It would be

plausible to suggest that at lower pH value, the surface of the adsorbent is surrounded

by hydronium ions (H3O+) thereby preventing the metal ions from approaching the

binding sites of the adsorbent64, thus at higher H+ concentration, the biosorbent

surface becomes more positively charged and the attraction between biomass and

metal cations gets reduced65 In contrast, as the pH increases, more negatively charged

surface becomes available thus facilitating greater copper removal. It is commonly

agreed that the adsorption of metal cations increases with increasing pH as the ionic

species become less stable in the solution.

However, at higher pH values (pH 6, pH 7, pH 8 and pH 9) there is a decrease

in the adsorption capacity. This is due to the occurrence of copper precipitation. At

pH 6 there are three species present in solution as suggested by Elliot et.al66. Cu2+ ion

in very small quantities and Cu(OH)+ and Cu(OH)2 in large quantities. Three species

are adsorbed at the surface of adsorbent by ion exchange mechanism with the

functional groups present in adsorbent or by hydrogen bonding67. The removal of

metal ions increases with increase in pH 6.0 to 10.0 even without adsorbent; this may

be due to the formation of metal hydroxide precipitation68-73.

According to Esmaeili et.al74 the pH of the aqueous solution is an important

controlling parameter in the adsorption process which is in good agreement with

Asmal et.al75 . The study of effect of pH on copper biosorption on activated carbon

was carried at room temperature by varying the pH of copper solution. The uptake of

copper (II) showed an increase with an increase in pH from 1.0 to 4.0. The lowest

uptake at higher pH value was probably due to the formation of anionic hydroxide

complexes. The effect at higher pH values may be attributed to the ligands such as

carboxylate and sulfonate groups could uptake fewer metal ions76.

Obh et.al77 showed that sour-sop seeds had a decrease in the adsorption rate for

Cu2+ and Zn2+ ions and an increase in the adsorption rate of Pb2+ and Ni2+ ions, when

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the pH of the synthetic waste water was between the value of 5 and 7. When

alkalinity increased that is from pH value of 7 to 9 there was further decrease in the

rate of adsorption by Sour-sop seeds for Cu2+, Zn2+, Pb2+ and Ni2+ ions in the synthetic

waste water. Results showed highest rate of adsorption by sour-sop seeds was 69 %

removal for Ni2+ ions in the synthetic waste water at pH vlue of 7. with increase in

pH from 5 to 9, the degree of protonation of the adsorbent functional group decreased

gradually and hence removal was decreased. A close relationship between the surface

basis of the adsorbents and the anions is evident, where the interaction between

oxygen free Lewis basic sites and the free electrons of anions, as well as the

electrostatic interactions between the anions and the protonated sites of the adsorbents

are the main adsorption mechanism78-80.

The effect of pH can be explained to the availability of negative charged

groups at the biosorbent surface and is necessary for the sorption of metals to

proceed81-82, which is at the highly acidic pH 2 is unlikely as there is a net positive

charge in the system due to H+ and H3O+. In such a system H+ complete with metal

ions51 resulting in a active sites to become protonated to the virtual exclusion of metal

binding on the adsorbent surface83-84 . i.e. at higher H+ concentration, the adsorbent

surface becomes more positively charged reducing the attraction between adsorbent

and metal cations84 In contrast, as the pH increases, more negatively charged surface

becomes available thus facilitating greater metal uptake85.

In our findings the adsorption of metals Nickel (II), Copper (II), Iron (III) and

Chromium (VI) on to the surface of MRKG adsorbent exhibit a drastic decrease in

metal affinity at low pH condition. pH of medium affects the solubility of metal ions

and ionization state of the functional groups86.

The increase in metal removal with increase in pH can be explained on the

basis of a decrease in comptition between proton (H+) and metal cations for the same

functional groups. The decrease in positive charge surface as pH increases would

result in lower electrostatic repulsion between the surface of adsorbent and metal

ions87.

In our present investigation activated carbon adsorbent acts as a negative

surface and attracts the positively charged metal ions. Generally the net positive

charge decreases with increasing pH value leads in the decrease in repulsion between

the adsorbent surface and metal ions and thus improving the adsorption capacity85 .

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The efficiency of adsorption of metal ions on to the surface of treated MRKG was

found to be higher than when compared with untreated MRKG. The order of

adsorption of metal ions on to the surface of MRKG are enlisted below as

For Nickel : (Untreated) : K < M < R < G, (Treated) : R < K < M < G; For Copper :

(Untreated) : M < K < R < G, (Treated) : M < K < G < R; For Iron : (Untreated) : M

< G < K < R, (Treated) : K < G < R < M & For Chromium : (Untreated) : G < K <

R < M, (Treated) : G < K < M < R.

4.2 Effect of Variation in adsorbent dose

Adsorption process is affected by surface properties such as surface area and

polarity. A large specific surface area is preferable for providing large adsorption

capacity, but the creation of a large internal surface area in a limited volume

inevitably gives rise to large numbers of sized pores between adsorption surfaces88.

The size of micropores determines the accessibility of adsorbate molecules to the

adsorption surface. Therefore, pore size distribution of micropore is an important

property for adsorptivity of adsorbents89. The existence of macropores serves as

diffusion path of adsorbate molecules from outside the granule to the micropores in

fine powders and crystals and can be used to classify adsorbents88. These properties

are possessed both by conventional and non-conventional adsorbents and are capable

of removing heavy metals from solution. In addition non conventional adsorbents

contain cellulose which is made up of repeating units of D-glucose as a major

component of cell walls. The polar hydroxyl groups on the cellulose could be

involved in chemical reaction and hence bind heavy metals from solutions90.

In the present investigation the adsorption of metals Nickel (II),

Copper (II), Iron (III) and Chromium (IV) was carried out on the surface of different

amount (1g, 2g, 3g, 4g, and 5 g) of MRKG adsorbent at constant temperature

concentration of metals and are presented in Table No's 1.0.2, 2.0.2, 3.0.2, 4.0.2,

5.0.2, 6.0.2, 7.0.2 and 8.0.2 for adsorption of Nickel Table No's 1.1.2, 2.1.2, 3.1.2,

4.1.2, 5.1.2, 6.1.2, 7.1.2 and 8.1.2 for adsorption of Copper Table No's 1.2.2, 2.2.2,

3.2.2, 4.2.2, 5.2.2, 6.2.2, 7.2.2 and 8.2.2 for adsorption of Iron Table No's1.3.2,

2.3.2, 3.3.2, 4.3.2, 5.3.2, 6.3.2, 7.3.2 and 8.3.2 for adsorption of Chromium.

The present study reveals that as the adsorbent dose is increased from 1.0 g to

5.0 g there is an increase in the adsorption of metal on to the MRKG adsorbent

284

Fig. 4.2.1(A) : Effect of Adsorbent dose on Adsorption of Untreated Marble Powder (M)

Fig. 4.2.1(B) : Effect of Adsorbent dose on Adsorption of Treated Marble Powder (M)

Fig. 4.2.2(A) : Effect of Adsorbent dose on Adsorption of Untreated Red Kotta (R)

Fig. 4.2.2(B) : Effect of Adsorbent dose on Adsorption of Treated Red Kotta (R)

Fig. 4.2.3(A) : Effect of Adsorbent dose on Adsorption of Untreated Kadappa (K)

Fig. 4.2.3(B) : Effect of Adsorbent dose on Adsorption of Treated Kadappa (K)

Fig. 4.2.4(A) : Effect of Adsorbent dose on Adsorption of Untreated Granite (G)

Fig. 4.2.4(B) : Effect of Adsorbent dose on Adsorption of Treated Granite (G)

285

surface see figure 4.2.1(A),(B) to 4.2.4(A),(B) and it is good agreement with the

earlier reported work91.

Maximum adsorption of metal was observed at higher dose of MRKG

adsorbent and the adsorption of metals onto the surface of it and can be shown in the

order as : For Nickel : (Untreated) : R < M < K < G, (Treated) :R < K < M < G, For

Copper : (Untreated) : G < K < M < R, (Treated) : G < K < M < R, For Iron :

(Untreated) : K < R < G < M, (Treated) : K < G < R < M For Chromium :

(Untreated) : R < M < G < K, (Treated) : R < K < M < G.

Thus for Nickel maximum adsorption was found at untreated and treated

Granite (G) surface, for Copper maximum adsorption was found at untreated and

treated Red Kotta (R), for Iron maximum adsorption was found at untreated and

treated Marble Powder (M) and for Chromium maximum adsorption was found at

untreated Kadappa (K) and treated Granite (G).

Farooqui et.al91 showed that the percentage removal of heavy metal ions (Cr

(II), Ni(II) and Fe(II) increase with the increase in adsorbent dosage but then becomes

constant. A maximum removal of about 99 % was reported on adsorbent dosage of

5g / 100 ppm. The increase in adsorption with increase in adsorbent dosage may be

due to the increase in the availability of active sites which may be attributed to the

increase in the effective surface area of the adsorbent61. Srinivas et.al92 during their

investigation observed the effect of dosage of the adsorbent on the varied amount of

adsorbent dose showed that with increase in adsorbent dose, adsorption of (Cd, Zn)

metal ion also increased contact area.

The dependence of heavy metal adsorption on the varied amount of activated

charcoal was studied by Bikermann et.al93. by keeping the concentration of heavy

metal ions solution constant, and reported that increase in adsorption was with

increase in the amount of charcoal (adsorbent). The effect of adsorbent dosage on the

percentage removal of Cr (VI) at various initial Cr (VI) concentration were carried by

Bandyopadhyay et.al94 and reported that the percentage removal increases sharply

initially with the increase in adsorbent dosage but beyond a value of 1.7 gm / 100 ml,

the percentage removal reached almost a constant value. Kannan et.al95 showed the

percentage removal of copper by low cost carbonaeous adsorbent and showed the

percentage removal of copper found to increase with increase in the dose of

adsorbent. This may be attributed to the increased availability of active adsorption

286

sites and surface area resulting from the conglomeration of the adsorbents especially

at higher adsorbent dose96 .

The plot of percentage removal of copper versus dose of adsorbent were found

to be exponential for all adsorbents indicating that the amount of copper adsorbed

varied in accordance with a fractional power term of the dose of adsorbent (for

example [dose]n where n = fraction ). This suggests that the adsorbed copper either

blocked the access to the initial pores or caused particles to aggregate, thereby

reducing the active site availibility80. According to Najua et.al62 adsorbent dosage are

important parameter, which influences the extent of metal uptake from the solution.

The amount of metal uptake increased from 0.86 mg/g with 0.5g adsorbent upto 1.08

mg/g with 1 g adsorbent. Prior to that it was apparant that the percent removal of

copper increases as the adsorbent dosage increase from 0.5g to 1.0 g due to the limited

availability of the number of adsorbing species for a relatively large number of

surface sites on the adsorbent at higher dosage of adsorbent. It is plausible that with

the higher dosage of adsorbent there would be greater availability of exchangeable

sites for metal ions97. The reduction in adsorbent dosage in the suspension at a given

metal concentration enhances the metal / adsorbent ratio, thus increase the metal

uptake per unit adsorbent98-99. The sharp decrease in adsorption capacity may be

attributed to the overcrowding of adsorbent particles100. More over the high adsorbent

dosage could impose a screening effect of the dense outer layer of the cells, thereby,

shielding the binding sites from metals101. The effect of adsorbent dosage i.e. increase

adsorbent concentration increased the percent removal of metal which may be

attributed to the availability of more surface functional groups and surface area at

increasing dosage is directly proportional to metal adsorption102-104.

Oboh et.al77 showed that the adsorbent dose of 1.0 g there was an increase in

the adsorption rate. The large the surface area, the larger the amount of metal ion

adsorbed. It may be attributed to the increase in the available binding sites in the

biomass (adsorbent) for the complexation of the heavy metals105, it explains the high

percent removal of the heavy metals.

Viriya et.al and others106-108 during their study varied adsorbent concentration

from 0.1 to 1 g /30 ml of synthetic waste water and studied the effect of biomass on

the sorption kinetics of heavy metals ions (Cu++and Pb++)at pH= 5. The results

reported shows that the equilibrium concentrations for both metals decreased with

287

increasing biomass doses for a given initial Cu2+ and Pb2+ concentration. The results

were anticipated because increasing adsorbent doses provided a greater surface area

which could accommodate a higher quantity of heavy metals and due to the

equilibrium limitations the quantity of metal being adsorbed for a certain surface area

of adsorbent decreased.

The increased carbon dosage (adsorbent), increased the adsorption of Nickel

(II) from aqueous solution, it was reported that for removal of 30 mg/L of Nickel (II),

the maximum adsorbent dose (carbon dose) required was 80 mg/50 ml; it may be

attributed to availability of more surface area and functional group109.

Patil et.al and others57 showed percent removal of Ni (II) ions was higher in

case of Powered Activated Charcoal followed by Powered Babhul Charcoal. The

removal of Ni (II) ions by Powered Activated Charcoal and Powered Babhul Charcoal

found to increase 51 % and 98.2 % and 40.6 to 84 % respectively, with an adsorbent

dose varying from 0.5 g/l to 5.09/l. However with the further increase in adsorbent

dose there was no appreciable increase in Nickel removal it is in good agreement with

our finding. In the present investigation the removal of heavy metal ions on SAT-

MRKG are enlisted as Nickel 78.40 %, Copper-75 % , Iron-70.00 % and Chromium -

77.70 %.

Whereas UNT-MRKG removed Nickel 65.60 %, Copper 60.20 %, Iron 38.00

% and Chromium 66.93 %. Hence it is concluded that SAT-MRKG is the best

adsorbent than UNT-MRKG.

4.3 Effect of Initial concentration of Metal Ion

The feasibility and efficiency of a adsorption process not only depends on the

properties of the adsorbents, but also on the concentration of the metal ion solution.

The initial metal concentration provides an important driving force to overcome all

the mass transfer resistances of the metal between aqueous and solid phase110-113.

There are many factors which contributes to the adsorbate concentration effect. The

first and most important one is that adsorption sites remain unsaturated during the

adsorption reaction the second cause is aggregation / agglomeration of adsorbent

particles at higher concentrations. Such aggregation leads to a decrease in the total

surface area of the adsorbent particles available for adsorption and an increase in the

288

diffusional path for adsorption and an increase in the diffusional path length114.

Addagalla et.al115 during their adsorption study of copper and Zinc, showed that

adsorption process was affected as the removal of heavy metals was stable and then

decreases with increase in the heavy metals concentration it may be attributed to

initial adsorption of metal ions fully at the active sites on adsorbent later on no free

sites available for adsorption.

In the present investigation during the adsorption of Nickel, Copper, Iron and

Chromium on the surface of MRKG adsorbent by varying initial concentration of

adsorbate (Ni, Cu, Fe, Cr) is given in the Table No's 1.0.4, 2.0.4, 3.0.4, 4.0.4, 5.0.4,

6.0.4, 7.0.4 and 8.0.4 for adsorption of Nickel Table No's 1.1.4, 2.1.4, 3.1.4, 4.1.4,

5.1.4, 6.1.4, 7.1.4 and 8.1.4 for adsorption of Copper Table No's 1.2.4, 2.2.4, 3.2.4,

4.2.4, 5.2.4, 6.2.4, 7.2.4 and 8.2.4 for adsorption of Iron Table No's 1.3.4, 2.3.4,

3.3.4, 4.3.4, 5.3.4, 6.3.4, 7.3.4 and 8.3.4 for adsorption of Chromium given in tabular

form, Our findings shows that as concentration of adsorbate is increased there is

increase in adsorption process and are enlisted in figures 4.3.1 (A),(B) to 4.3.4(A),(B)

which is in good agreement with the finding of Esmaeili et.al74.

Fig. 4.3.1(A) : Effect of Initial Concentration on Adsorption of Untreated Marble Powder (M)

Fig. 4.3.1(B) : Effect of Initial Concentration on Adsorption of Treated Marble Powder (M)

Fig. 4.3.2(A) : Effect of Initial Concentration on Adsorption of Untreated Red Kotta (R)

Fig. 4.3.2(B) : Effect of Initial Concentration on Adsorption of Treated Red Kotta (R)

289

In a low solution concentration Sodium Chloride had little influence on the

adsorption capacity. At higher ionic strength the adsorption chromium of ion on

Babhul Bark Charcoal increased due to the partial neutralization of the positive charge

on the carbon surface and a consequent compression of the electrical double layer by

the Chloride anion. The chloride ion can also enhance adsorption of chromium ion

on Babhul Bark Charcoal by pairing of their charges and hence reducing the repulsion

between the chromium ions adsorbed on the surface69-71. This indicates carbon to

adsorb more of positive chromium ion.

Najua et.al62 during their investigation, showed that adsorption capacity of

Palmkernel adsorbent increased from 0.23 to 1.09 mg/g as the metal concentration

increases in the electrostatic interaction between the copper ions (adsorbate) and the

adsorbent active sites and it can be explained by the fact that more adsorption sites

were covered as the metal ion increases116. Beside higher initial concentration lead to

Fig. 4.3.3(A) : Effect of Initial Concentration on Adsorption of Untreated Kadappa (K)

Fig. 4.3.3(B) : Effect of Initial Concentration on Adsorption of Treated Kadappa (K)

Fig. 4.3.4(A) : Effect of Initial Concentratio on Adsorption of Untreated Granite (G)

Fig. 4.3.4(B) : Effect of Initial Concentration on Adsorption of Treated Granite (G)

290

an increase in the affinity of the copper ions towards the active sites117. The decline in

the adsorption capacity attributed to the availability of smaller number of surface sites

on the adsorbents for a relatively larger number of adsorbing species at higher

concentration81. It was in good agreement with the finding of Han et.al116 .

Tariq et.al117 during the their investigation studied the effect of various initial

concentration on adsorption of metal ions (Copper (II) and Iron (III)) on to the surface

of adsorbent (Pine Fruit Powder) and concluded that adsorption increases with

increase in the concentration of metal ions. It may be attributed to lower

concentration, the ratio of initial number of metal ions to the available surface area at

lower concentration which is minimum and thus subsequently the fractional

adsorption become independent of initial concentration. However, at higher

concentration the available sites of adsorption becomes fewer and hence the

adsorption of metal ions is dependent upon initial concentration.

The effect of initial concentration to metal removal that percentage of Cr (VI)

(metal) uptake was found to be increase with initial adsorbate concentration59. This

may be attributed to the fixed adsorbent dose the total available adsorption sites which

remain invariable for all the concentration checked. Hence, the percentage removal of

chromium has shown significant decrease with the increase in the initial adsorbate

concentration it is in good agreement of with findings of Barros et.al119.

The metal adsorbed is higher for greater values of initial metal ion

concentration or the percentage adsorption is more for lower concentration of metal

ions and decreases with increasing initial metal ion concentration118. This is attributed

to more efficient utilization of the adsorptive capacities of the adsorbent due to greater

driving force (by a higher concentration gradient pressure)120-121

Srinivas et.al92 studied the effect of initial concentration of metal ion in

effluent solutions and reported that the conc. of heavy metal ions (Cd,Zn) varied from

0.5 to 50 ppm, with the increase in initial concentration of metal in the solution

increased the amount of adsorption and found to be in the exponential phase. Kannan

et.al122 carried adsorption study of Copper (II) and suggested low cost effective

adsorbent in place of commercial activated charcoal. The decrease in the extent of

removal of copper (in %) with the increase in the initial concentration which may be

attributed to the reduction in immediate adsorption and due to the lack of available

291

active sites for the high initial concentration of copper similar results were also

reported by Ramprasad et.al123.

4.4 Effect of Contact Time

The adsorption process, contact time plays a vital role, irrespective of the

other, experimental parameters that affects the adsorption Kinetics124. The removal of

copper by adsorption on low cost carbonaceous adsorbents was found to be rapid at

the initial stage of contact time and then it becomes slow and stagnant with increase in

the contact time. A major proportion of the total copper removal may be attributed to

immediate solute adsoption on to the surface of adsorbent with subsequent slow

removal of the remaining amount of Copper125.

Oboh et.al126 during their adsorption study of Copper, Nickel, Zinc and Lead

showed that adsorption process gets affected as the percentage removal of metal ions

from synthetic waste water increases with time.

Madhavakrishnan et.al127 during their finding studied the effect of agitation

time on the percent removal of Ni (II) by Ricinus Communis Pericap Activated

Carbon (RCP) carbon and showed that the percent removal increase with increase in

agitation time and attains equlibrium within 70 min for all the concentration studied

(10mg./L to 40mg/L). The curves obtained were single, smooth and continous till the

saturation of Ni(II) on activated carbon surface.

The effect of agitation time on various concentration of Chromium solution

(25 to 125 mg/L) were carried by Dhanakumar et.al128 and reported that the removal

rate was rapid during first 10 minutes of agitation. Then the rate slowed down

gradually until it attained an equilibrium beyond which there was no significant

increase in the rate of removal.

In the present investigation during the adsorption of Nickel (II), Copper (II),

Iron (III) and Chromium (IV) on the surface of MRKG adsorbent by varying contact

time is given in the Table No.s 1.0.1, 2.0.1, 3.0.1, 4.0.1, 5.0.1, 6.0.1, 7.0.1 and 8.0.1

for adsorption of Nickel, Table No.s 1.1.1, 2.1.1, 3.1.1, 4.1.1, 5.1.1, 6.1.1, 7.1.1 and

8.1.1 for adsorption of Copper, Table No.s 1.2.1, 2.2.1, 3.2.1, 4.2.1, 5.2.1, 6.2.1, 7.2.1

and 8.2.1 for adsorption of Iron, Table No.s 1.3.1, 2.3.1, 3.3.1, 4.3.1, 5.3.1, 6.3.1,

7.3.1 and 8.3.1 for adsorption of Chromium given in tabular form as in Chapter 3.

292

In our present investigation with increase in contact time between adsorbent

and adsorbate adsorption process also increased and is shown in figures 4.4.1 (A),(B)

to 4.4.4 (A),(B).

The effect of contact time on adsorption if Ni, Cu, Fe, and Cr onto the surface

of MRKG during our study found to be in the range as shown below

For Nickel :(Untreated): M<R<K<G, (Treated): K<R<M<G, For Copper :

(Untreated) : R<K<G<M, (Treated) : K<G<R<M, for Iron (Untreated): K<R<G<M,

(Treated) : G<M<K<R, for Chromium : (Untreated) : K<M<G<R, (Treated) :

K<G<R<M

Fig. 4.4.1(A) : Effect of Contact Time on Adsorption of Untreated Marble Powder (M)

Fig. 4.4.1(B) : Effect of Contact Time on Adsorption of Treated Marble Powder (M)

Fig. 4.4.2(A) : Effect of Contact Time on Adsorption of Untreated Red Kotta (R)

Fig. 4.4.2(B) : Effect of Contact Time on Adsorption of Treated Red Kotta (R)

Fig. 4.4.3(A) : Effect of Contact Time on Adsorption of Untreated Kadappa (K)

Fig. 4.4.3(B) : Effect of Contact Time on Adsorption of Treated Kadappa (K)

293

4.5 Adsorption Kinetics

Kinetics of adsorption describing solute uptake rate, which in turn governs the

contact time of adsorption process, is one of the important characteristics defining the

efficiency of adsorption. The important physico-chemical studies which helps in the

evaluation of the basic qualities of a good adsorbent are adsorption kinetics and

equilibrium 129.In order to estimate the adsorption capacity of the adsorbent

accurately, it is important to allow sufficient time for the experiment system to reach

equilibrium.The pseudo-first order equation of Lagergren as cited by Ho et.al130 and

was employed for studying the adsorption kinetics. The pseudo-first order equation of

Lagergren is generally expressed as follows :

dqt = k1 (qe – qt) dt

where qe = 0 , qt = qt, are the adsorption capacity at equilibrium and at time 't'

respectively (mg / g) and K1 is the rate constant of pseudo first order adsorption (min-

1). After integration and applying boundary conditions from t = 0 to t = t and qt = 0

to qt = qt' . The integrated form of equation becomes. log (qe – qt) = log qe - k1 t /

2.303

The equation is applicable to experimental results generally differs from a true

first order equation in two ways. The parameter K1 (qe – qt ) does not represent the

number of available sites. The parameters log qe is an adjustable parameter and often

is found not equal to the intercept of a plot of log ( qe – qt ) against t of a plot. of log

(qe – qt) against t 131. In order to fit equation log (qe – qt) = log qe – k1 t/2.303 to

experimental data, the equilibrium sorption capacity, qe must be known.

Fig. 4.4.4(A) : Effect of Contact Time on Adsorption of Untreated Granite (G)

Fig. 4.4.4(B) : Effect of Contact Time on Adsorption of Treated Granite (G)

294

In many cases qe is unknown and as chemisorption tends to become

unmeasureably slow, the amount adsorbed is still significantly smaller than that the

equilibrium amount. However in this case, the plot of log (qe – qt) versus t gives a

straight line confirming the applicability of first order rate expression of

Lagergren129,132-133. In the present investigation adsorption kinetics were determined

by using Lagergren equation132. The values of rate constants were determined

graphically as well as by fitting into Lagergren equation for MRKG, it was observed

that rate constant is independent of concentration of adsorbate with some exception

and it is given in tabular form for MRKG. From the table of adsorption after applying

various condition it can be concluded that the rate constant is independent of initial

concentration of adsorbate with some exception and it ranges from 2.428 x 10-2 per

minute to 3.120 x 10-2 per minute for adsorption Nickel on MRKG, 2.012 x 10-2 to

3.321 x 10-2 per minute for adsorption of copper on MRKG and 2.170 x 10-2 to 4.750

x 10-2 per minute for Iron on MRKG and 1.892 x 10-2 to 3.612 x 10-2 per minute for

Chromium. Also during the kinetics study at various pH, the results showed as pH

increases rate of adsorption (rate constant) increases this may be attributed to the

competition between H+ ion and metal ion for adsorption on the surface of MRKG.

In order to know the effect of adsorbent dose viz by varying the amount of

adsorbent (1g, 2g, 3g, 4g and 5g respectively) the kinetics were carried by keeping the

other parameter constant and it was observed that the rate constant increases with

increase in the quantity of adsorbent which indicates that adsorption depends on

surface area of adsorbent and, therefore, increase in quantity furnishes more surface

area and hence as adsorption increases at the same time, rate of adsorption also

increases. Thus it can be concluded that the rate constant Kr depends on pH and

amount of adsorbent and is independent of concentration of adsorbate.

The effect of temperature on adsorption used to calculate energy of activation

and the data fitted to Arrhenius equation.

K = Ae–Ea/RT.

295

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Metals on to the Surface of MRKG adsorbent.

Nickel Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 2 3 4 5 6 7 25oC 30

oC 35

oC 40

oC 45

oC 100 ppm

200 ppm

300 ppm

400 ppm

500 ppm

Marble

Powder

Untreated 2.961

x10-2

3.018

x10-2

3.236

x10-2

3.420

x10-2

3.420

x10-2

2.063

x10-2

2.322

x10-2

2.678

x10-2

2.779

x10-2

2.912

x10-2

2.942

x10-2

3.70

x10-2

3.746

x10-2

3.840 3.942 3.976 2.428 2.511 2.601 2.771 2.841

Treated 3.102 3.148 3.428 3.512 3.512 3.062 2.424 2.718 2.819 3.102 3.102 3.812 3.846 3.94 4.01 4.027 3.147 2.781 2.712 2.812 2.942

Rajasthan

Red

Kotta

Untreated 2.724 2.991 3.097 3.248 3.248 2.012 2.149 2.342 2.549 2.888 2.978 3.501 3.670 3.777 3.812 3.903 2.342 2.412 2.555 2.813 2.940

Treated 2.814 3.120 3.124 3.314 3.314 2.142 2.216 2.416 2.629 3.001 3.108 3.617 3.781 3.888 3.916 4.012 3.142 2.678 2.678 2.946 3.416

Kadappa Untreated 3.002 3.301 3.167 3.274 3.274 2.116 2.420 2.777 2.942 3.012 3.112 3.800 3.812 3.944 4.012 4.125 2.411 2.671 2.670 2.910 2.946

Treated 3.112 3.402 3.247 3.341 3.341 2.178 2.512 2.814 3.102 3.146 3.217 3.903 3.942 4.012 4.132 4.215 2.516 2.712 2.714 3.142 3.176

Granite Untreated 3.107 3.426 3.340 3.421 3.421 2.412 2.517 2.918 3.210 3.212 3.324 3.746 3.801 3.896 3.977 4.011 2.525 2.617 2.723 2.841 2.940

Treated 3.208 3.517 3.417 3.517 3.517 2.618 2.719 3.120 3.517 3.614 3.719 3.816 3.914 3.927 4.101 4.112 2.628 2.712 2.814 2.942 3.120

296

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Metals on to the Surface of MRKG adsorbent.

Copper Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 2 3 4 5 6

25oC 30 oC 35 oC 40 oC 45 oC 100 200 300 400 500

Marble

Powder

Untreated 1.152 x10-2

1.205

x10-2

1.261 1.324 1.395

2.132 2.421 3.012 3.189 3.986 1.103 1.142 1.185 1.25 1.44 2.012 2.612 2.712 2.810 3.104

Treated

2.102 x10-2

1.231

x10-2

1.262 1.262

x10-2

1.228 3.012 3.104 3.546 3.782 4.011 1.363 1.491 1.591 1.767 1.909 2.146 2.721 2.914 3.142 3.571

Rajasthan

Red Kotta

Untreated 1.487 1.567 1.657 1.705 1.757 2.406 2.567 3.425 3.589 4.024 2.039 2.055 2.072 2.062 2.200 2.314 2.819 2.914 3.120 3.342

Treated 2.085 2.085 2.217 2.251 2.310 3.148 3.502 3.794 3.842 4.146 3.124 3.195 3.195 3.351 3.593 2.346 2.917 3.012 3.041 3.402

Kadappa Untreated 1.016 1.199 1.132 1.199 1.304 2.012 2.126 2.546 3.001 3.214 1.473 1.572 1.685 1.781 1.892 2.132 2.432 2.567 2.689 3.011

Treated 2.350 2.421 2.588 2.636 2.862 2.421 2.510 2.642 3.114 3.316 1.672 1.961 2.018 2.321 2.444 2.242 2.761 2.876 2.946 3.101

Granite Untreated 1.127 1.139 1.215 1.240 1.265 2.564 2.678 3.412 3.449 4.012 1.721 1.842 2.431 2.679 3.00 2.117 2.712 2.841 2.896 2.978

Treated 3.000 3.105 3.850 3.500 3.758 3.500 3.888 4.750 4.946 5.001 3.671 3.721 3.891 3.912 3.912 2.272 2.842 2.941 2.942 3.321

297

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Metals on to the Surface of MRKG adsorbent.

Iron Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 1 2 3 4 5 6 25oC 30

oC 35

oC 40

oC 45

oC 100 200 300 400 500

Marble

Powder

Untreated 1.153 x10-2

1.184 1.26 1.250 1.285 1.410 1.638 2.169 2.340 2.678 2.897 1.876 1.978 2.120 3.123 2.120 2.170 2.234 2.734 2.840 2.973

Treated 1.673 x10-2

2.102 2.230 2.540 2.734 1.670 1.890 2.210 2.420 2.784 3.820 1.976 2.110 2.240 3.212 2.240 2.290 2.340 2.840 2.920 3.110

Rajasthan

Red Kotta

Untreated 1.312 x10-2

1.615 1.712 1.814 1.912 1.520 1.748 2.240 2.520 2.748 3.120 2.140 2.210 2.240 3.214 2.240 2.340 2.346 2.840 2.950 3.120

Treated 1.840 2.312 2.410 2.630 2.840 1.880 1.910 2.312 2.520 2.840 3.230 2.420 2.400 2.510 3.340 2.510 3.140 3.678 3.890 4.104 4.112

Kadappa Untreated 1.216 1.520 1.670 1.720 1.812 1.420 1.640 2.138 2.410 2.670 2.712 1.742 1.841 2.001 3.103 2.001 2.016 2.140 2.640 2.729 2.840

Treated 1.342 1.782 1.894 1.940 2.132 2.140 2.170 2.240 2.560 2.782 2.812 2.140 2.210 2.432 3.143 2.432 2.142 2.432 2.846 2.946 3.240

Granite Untreated 1.420 1.620 1.840 1.940 2.413 1.680 2.140 3.120 3.240 3.340 2.560 2.740 2.840 3.210 3.314 3.210 3.516 4.146 24.276 4.300 4.540

Treated 2.640 2.740 2.840 2.470 2.560 2.780 2.250 3.230 3.310 3.410 3.520 2.840 2.940 3.319 3.413 3.319 3.618 4.240 4.347 4.470 4.750

298

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Metals on to the Surface of MRKG adsorbent.

Chromium Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 1 2 3 4 5 25oC 30 oC 35 oC 40 oC 45 oC 100 200 300 400 500

Marble

Powder

Untreated 1.110 x10-2

1.054 1.810 1.940 1.981 1.782 1.840 2.140 2.321 2.317 2.417 2.516 3.149 3.724 3.432 1.892 2.246 2.427 2.526 2.873

Treated

1.140 x10-2

1.782 1.940 2.143 2.413 2.140 2.140 3.120 3.240 3.341 3.347 3.357 3.417 3.841 3.910 2.170 2.399 2.470 2.870 2.940

Rajasthan

Red Kotta

Untreated 1.410 x10-2

1.512 1.920 2.111 2.413 2.417 2.514 2.620 2.724 2.842 2.514 2.614 2.814 3.012 3.142 1.940 2.310 2.516 2.610 2.940

Treated 1.520

x10-2

1.617 2.110 2.320 2.512 2.514 2.610 2.720 2.811 2.849 2.614 2.712 2.910 3.142 3.246 2.130 2.416 2.617 2.710 3.120

Kadappa Untreated 1.001

x10-2

1.062 1.720 1.814 1.878 1.641 1.730 2.014 2.214 2.142 2.314 2.417 2.619 2.719 2.840 1.740 1.810 1.940 2.111 2.146

Treated 1.114

x10-2

1.124 1.817 1.912 1.941 1.723 1.841 2.146 2.312 2.216 2.412 2.517 2.714 2.812 2.912 1.840 1.942 2.160 2.217 2.214

Granite Untreated 1.524

x10-2

1.670 1.837 1.927 1.949 1.799 1.840 1.910 2.142 2.214 2.717 2.812 2.913 2.914 3.120 3.130 3.240 3.317 3.411 3.512

Treated 1.620

x10-2

1.940 2.140 2.210 2.317 2.410 2.642 2.712 2.242 2.312 2.812 2.917 3.014 3.140 3.217 3.210 3.417 3.418 3.516 3.612

299

where Ea is energy of activation, R is gas constant and T is temperature. The

equation is modified as,

log K = log A – Ea / 2.303 RT

The plot of log k Vs. 1/T gave a straight line with negative slope and used to

calculate energy of activation and is presented in tabular form as follows

Adsorbent Untreated Marble (M)

Untreated Red Kotta

Untreated Kadappa

Untreated Granite

Nickel 4007.496J 2538.911J 7942.235 J 796.521 J

Copper 3607.32 J 1705.436 J 6414.29 J 7122.7 J

Iron 3607.33 J 2291.910 J 2843.351 J 3561.37 J

Chromium 2311.06 J 3312.45 J 3209.061 J 1123.937 J

Adsorbent Treated Marble (M)

Treated Red Kotta

Treated Kadappa

Treated Granite

Nickel 1608.360 7457.812 2355.098 689.2970

Copper 1277.114 8537.711 1072.240 1014.799

Iron 2169.890 946.739 9573.357 8807.690

Chromium 833.499 1146.739 5744.14 2699.747

The Ea value for adsorption of metal on to the surface of MRKG, it was

observed for adsorption of Chromium Ea value was smaller which may be attributed

to the higher binding of Chromium ions on the surface of treated marble. The energy

barrier is less and, therefore its rate of adsorption is higher.

In our finding and from calculated value of Ea the adsorption capacity of

untreated MRKG for Nickel, Copper, Iron & Chromium can be given as for Nickel

(Untreated): K>M>R>G, (Treated): R>K>M>G, for Copper (Untreated): G>K>M>R,

(Treated) : R>M >K >G, for Iron (Untreated):M>G>K >R, (Treated): K>G>M>R, for

Chromium (Untreated): R>K>M>G, (Treated): K>G>R>M.

Thus, in general to understand the mechanism of adsorption, thermodynamic

parameters along with energy of activation is important.

The dispersion force between metal ion and adsorbent during adsorption at

equilibrium increases with increase in initial concentration which may be attributed to

the positively charged ion approaching the adsorbent surface inducing negative charge

300

on it and hence attraction between the two dipoles lowers potential energy between

them and brings adsorption134 .

Kinetic curves are single, smooth and continuous and the saturation expected

to occur indicates a monolayer adsorption of metal ion on the adsorbent surface,

initally adsorption of metal ion increases but gradually slows down when approaches

equilibrium. These behaviours are quite common and attributed to the saturation of

the available adsorption sites135.

The study showed that the rate of metal uptake by the adsorbent was rapid and

about 60-75 % or more Ni, Cu and Fe and Cr accumulated on the adsorbent within 30

minutes. Results indicates removal efficiency increased with an increase in contact

time before equilibrium is reached. This could be attributed to the greater availability

of various functional group on the surface of the adsorbents which are required for

interaction with anions and cations. This improved the binding capacity and the

process proceed rapidly. Our findings are in good agreement with Olayinka and

others136-137. The decline in adsorption in later stages may be attributed to a large

vacant surface sites available for adsorption and after some time the remaining vacant

surface sites may be difficult to occupy due to repulsive forces between solute

molecules of the solid and the adsorbent similar results were also reported by different

researchers 134-136, 138-140.

4.6 Effect of Temperature

Temperature plays a major role in the adsorption of heavy metals on adsorbent

surface. Although, the magnitude of the heat effect for the adsorption process is one

of the most important creteria for the efficient removal of heavy metals from the

waste water. Temperature changes will affect a number of factors which are

important in heavy metal ion adsorption. Some of the factors include

I) The stability of the metal ion species initially placed in a solution.

II) The stability of micro-organism-metal complex depending on the adsorbent

(biosorption) sites.

III) The effect of temperature on the micro-organism cell wall configuration.

IV) The ionisation of chemical moieties on the cell wall141.

The temperature has two major effects on the adsorption process. One is that

increasing the temperature will increase the rate of adsorbate diffusion across the

301

external boundary layer and in the internal pores of the adsorbate particles because

liquid viscosity decreases as temperature increases and the other one is that it effects

the equilibrium capacity of the adsorbate depending on whether the process is

exothermic or endothermic142-143.

In the present investigation the adsorption of Nickel, Copper and Iron and

Chromium carried on the surface of MRKG as adsorbent by varying the temperature

as 35, 40 and 450c and keeping the initial concentration of adsorbate and amount of

adsorbent constant. The result are presented in Table No's 1.0.3, 2.0.3, 3.0.3, 4.0.3,

5.0.3, 6.0.3, 7.0.3 and 8.0.3 for adsorption of Nickel Table No's 1.1.3, 2.1.3, 3.1.3,

4.1.3, 5.1.3, 6.1.3, 7.1.3 and 8.1.3 for adsorption of Copper Table No's 1.2.3, 2.2.3,

3.2.3, 4.2.3, 5.2.3, 6.2.3, 7.2.3 and 8.2.3 for adsorption of Iron Table No's 1.3.3,

2.3.3, 3.3.3, 4.3.3, 5.3.3, 6.3.3, 7.3.3 and 8.3.3 for adsorption of Chromium given in

tabular form as in chapter 3.

The temperature dependence of adsorption process is of complex nature

thermodynamic parameter like heat of adsorption and the energy of activation plays

an important role in predicting the adsorption behavior and both are strongly

temperature dependent144.

In our present work heavy metal uptake increased on the surface of MRKG

with increase in temperature are shown in figure 4.6.1 (A),(B) to 4.6.4 (A),(B). Our

finding is supported by Sivakumar and others144.

Suleman Paiser et.al145 studied the effect of temperature by keeping all other

parameter constant, temperature was varied from 250C to 500C. The adsorption of

chromium increased with increase in temperature upto 400C and started decreasing

with increase in temperature which may be attributed to change in the texture of

adsorbent and thus it reduces the sorption capacity at high temperature. Adsorbent

contains more than one type of sites for metal binding. The effect of temperature on

each site is different and contributes to overall metal uptake. The effect of

temperature on adsorption also depends on the heat of adsorption. Usually for

physical adsorption heat of adsorption is negative, adsorption reaction is exothermic

and preferred at lower temperature. For chemisorption the overall heat of adsorption

is combination of heat of various reactions taking place at adsorption sites. It depends

on type of metal and adsorbent. This was attributed to the different behaviour of lead

and chormium uptake with temperature during investigation.

302

Fig. 4.6.1(A) : Effect of Temperature on Adsorption of Untreated Marble Powder (M)

Fig. 4.6.1(B) : Effect of Temperature on Adsorption of Treated Marble Powder (M)

Fig. 4.6.2(A) : Effect of Temperature on Adsorption of Untreated Red Kotta (R)

Fig. 4.6.2(B) : Effect of Temperature on Adsorption of Treated Red Kotta (R)

Fig. 4.6.3(A) : Effect of Temperature on Adsorption of Untreated Kadappa (K)

Fig. 4.6.3(B) : Effect of Temperature on Adsorption of Treated Kadappa (K)

Fig. 4.6.4(A) : Effect of Temperature on Adsorption of Untreated Granite (G)

Fig. 4.6.4(B) : Effect of Temperature on Adsorption of Treated Granite (G)

303

Farooqui et.al91 during their study on low cost processed adsorbent concluded

that temperature increase the adsorption properties decreases. At 250C the adsorption

decreases to 77 % by the leaves of cauliflower, it may attributed the to process being

exothermic. The decreases in adsorption with rise of temperature may be due to the

enhanced capacity of the Fe(II) ion from the surface of adsorbent. Gundugan et.al146

also study the effect of temperature by varying it between 100C to 300C on adsorption

of copper onto peat at constant concentration and reported that with increase in

temperature from 120C to 300C very small amount (1.033%) adsorbed indicating the

negligible effect of temperature on copper adsorption on to the surface of peat.

Bansal et.al147 studied the effect of temperature on adosorption of Chromium from the

sample solution with different temperature ie. 28,32 and 420C respectively, it was

observed that adsorption of heavy metal (chromium) increases with the decrease in

temperature this is in agreement with Farooqui et.al91, The low temperature gave

maximum adsorption and adsorption increases in the order as 200C > 320C > 400C.

The increased adsorption at higher temperature during the present

investigation may be attributed to acceleration of some originally slow step, creation

of some new activation sites on adsorbent surface, decrease in the size of adsorbing

species, this could well occur due to progressive desolution of the metal ion as the

solution temperature increases our findings is in good agreement with the finding of

different researchers115,148-149.

4.7 Adsorption Isotherm

The capacity of adsorption isotherm is fundamental and plays an important

role in determination of the maximum capacity of adsorption. It also provides a

panorama of the course taken by the system under study in a concise form, indicating

how efficiently a adsorbent will adsorb and allows an estimate of the economic

viability of the adsorbents commercial applications for the specified solute62. It is a

graphical representation showing the relationship between the amount adsorbed by a

unit weight of adsorbent and the amount of adsorbate remaining in a test medium at

equilibrium115. It maps the distribution of adsorbable solute between the liquid and

solid phases at various equilibrium concentration150. The Langmuir and Freundlich

models are the most widely used models in the case of adsorption of metal ions by

adsorbents even though the metal uptake may not exactly follows the monolayer

304

adsorption mechanism. The Langmuir adsorption isotherm has been used

traditionally to quantify and contrast the performance of different adsorbents. The

Langmuir Isotherm is based on the assumptions:

I) All sites are equivalent

II) Adsorption results in a monomolecular layer of coverage.

III) A molecule is adsorbed on a site independent of the neighbouring adsorbed

molecules.

IV) Coverage is independent of binding energy145. and

V) Constant temperature.

The rate of attachment to the surface should be proportional to a driving

force times an area. The driving force is the concentration of fluid and the area is the

amount of bare surface. The affinity between the adsorbent and the different metals

quantified by fitting the obtained adsorption values to the Langmuir isotherm. In this

case, the following form of the Langmuir equation is applied

q = qmax ( b Ce ) 1 + b Ce

Where qmax is the maximum adsorption uptakes per unit mass of adsorbent in mg/g,

Ce is the equilibrium concentration of heavy metals ion in mg/C and b is the

Langmuir constant of adsorption, qmax and b calculated from the intercept and the

slope of plots.

The Freundlich modell51 is perhaps the most popular adsorption model for a

single solute system and is an empirical relation equation based on the distribution of

solute between the solid phase and aqueous phase at equilibrium.

The linear form of the Freundlich equation is x/m = K Ce1/n

Where x is concentration of metal ion adsorbed, Ce is equilibrium concentration of

metal ion in solution. K and 1/n are empirical constants and have been calculated

from intercept and slope of the plots. A larger value for 1/n indicates a larger change

in effectiveness over different concentration. Also, when 1/n >1,O. The change in

adsorbed concentration is greater than the change in the solute concentration152. The

Freundlich equation is empirical equation with no basis in theory which assumes an

305

exponential variation in site energies and also assumed that surface adsorption is not

rate limiting step153.

The Freundlich model as observed in fig. I B found to be linear the coefficient

of correlation value (r2) was high. It is in good agreement with the findings of Shilpi

et.al154. Values of Freundlich constants are depicted in Table no. I B adsorption. A

smaller value of 1/n indicates better adsorption mechanism and formation of relating

stronger bond between adsorbate and adsorbent148-151.

Nasim129 during their adsorption study on removal of Cd (II) metal showed a

larger value for 1/n indicating a larger change in effectiveness over different

equilibrium concentration, also when 1/n is greater than 1 , the change in adsorbed

concentration is greater than the change in the solute concentration once the

coefficents have been determined x/m can be calculated for all concentration131.

The linear plot between 1/Ce and 1/qe for Nickel (II), Copper (II) and Iron

(III) and Chromium indicates the validity of Langmuir adsorption isotherm

consequently suggesting the formation of monolayer coverage of the adsorbate on the

surface of the adsorbent in the concentration range studied. The values of qm and Ka

determined from the slopes and intercepts of the plots and are reported in Table No.

IIB, The Langmuir plots had a good correlation coefficients152. Isotherm data reveals

that the adsorption process follows both Freundlich and Langmuir isotherm and that

the adsorption is favourable. The Langmuir equation and Freundlich model describes

the isotherm of Nickel (II), Copper (II) and Iron (III) and Chromium (VI) adsorption

with high correlation coefficient (R2 =0.99)130.

The dimensionless equilibrium parameter R is defined by Hall152. i.e.

RL = 1 / 1 + b Co

where b is Langmuir constant (1/mg) and Co is the initial concentration (mg/L).

'R' values observed are given in Table I B and are found to be in the range between

Zero to One favourable adsorption155. Our findings are in good agreement with Patil.

306

Adsorbate Marble Powder

Rajasthan Red Kotta

Kadappa Granite

Nickel 0.0072 0.0103 0.0120 0.0104

Copper 0.0107 0.0105 0.0110 0.0106

Iron 0.0108 0.0106 0.0109 0.0102

Chromium 0.0110 0.0105 1.0102 0.0103

Table IB : Dimensionless Equilibrium parameter (Rl) for metal ions

The dimensionless equilibrium parameters also called separation factor 156 is

indicate of adsorption phenomenon, was divided into four class

Class

I RL > 1 Adsorption unfavourable

II RL = 1 Linear

III RL = 0 Irreversible

IV 0 < RL < 1 Favourable

The value of RL during our investigation lied between 0.0072 to 0.01, which

indicates, that the adsorption of metals (Ni, Cu, Fe and Cr) are favourable on MRKG

which is in good agreement with the findings of Bandyopandyay et.al35.

4.8 Thermodynamics Parameters

Thermodynamic Parameters evaluated the nature of adsorption of adsorbate

and its magnitude during adsorption process.

The change in standard Gibbs free energy (�G), standard enthalpy change

(�H) and standard entropy change (�S) to be calculated using the following

equation.

�G = - RT lnk ... 1

�H = R (ln K2/K1 ) T1 T2 /(T1 – T2) ... 2

�S = (�H - � G) / T ... 3

307

where R is the gas constant, K, K1 and K2 are equilibrium constants at temperature T,

T1 and T2 respectively. Numerical values of equilibrium calculated by using equation

K = CBe / CAe

where Be and Ae are the equilibrium concentrations of heavy metals cations on the

adsorbent and adsorbate respectively. The calculated thermodynamics parameters for

the adsorption of Nickel (II), Copper(II) and Iron(III) and Cromium (VI) on to the

surface of MRKG are given in the Table No. IIIB.

The negative values of �G are indicative of the spontaneous nature of the

process. Entropy has been defined as the degree of chaos of the system and the

positive of �S reflects adsorption of Nickel (II), Copper(II) and Iron(III) and

Cromium (VI).

The negative value of �H shows the exothermic nature of Nickel (II),

Copper(II) and Iron(III) and Cromium (VI) on to the surface of MRKG. Our

observation are supported by the work carried by Soon–Yong et.al158.

The large negative value of �G shows the spontaneity of the adsorption

process of heavy metal ions. The decrease in the value of �G with increase in

temperature indicates adsorption process in endothermic and thus it is favoured with

increase in temperature159. The negative values of �G validate the feasibility of the

adsorption process and the spontaneity of adsorption of adsorbate on to adsorbent160.

The positive values of �S if positive suggest increase in randomness at the

solid / solution interface during the adsorption similar results were observed during

present investigation. The positive value of �H shows endothermic nature of

adsorption process observed by Kavitha160-61 and the negative value of �H shows

exothermic nature of adsorption process.

According to Laura162

(I) �G value upto – 15 KJ/ Mole are connected with the physical interaction

between adsorption sites and metal ion (Physical adsorption)

308

(II) �G values more than –30 KJ/mole involves charge transfer from

adsorbent surface to the metal ion to form a co-ordination bond.

(Chemical adsorption).

The �G values obtained in this study for metals ions Nickel (II), Copper(II)

and Iron(III) are below than – 15 KJ / mole. indicating that the adsorption

mechanism is the physical interaction between adsorption sites and metal ion

(physical adsorption) which is in good agreement with the findings of Laura et.al162.

The positive values of �S suggest increased randomness at the solid-liquid

interface during the adsorption of metal ion. The adsorbed solvent (water) molecules,

which are displaced by the adsorbed species, gain more translational entropy than is

lost by the adsorbate ion. Furthermore, before the adsorption process takes place the

adsorbate ions are heavily solvated (The system is more ordered) and this order is lost

when the ions are adsorbed on the surface, due to the release of solvated water

molecules.

309

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322

Dyes are chemicals which on binding with a material will give colour to the

material. Dyes are ionic, aromatic organic compounds with structures including aryl

rings which have delocalised electron systems. The colour of a dye is provided by the

presence of chromophore group. A chromphore is a radical configuration consisting

of conjugated double bonds containing delocalized electrons. Other common

chromophoric configurations includes azo (-N-N-), carbonyl (=C=O); carbon

(=C=C=); carbon-nitrogen (>C=NH or –CH=N-); nitroso (-NO or N-OH); nitro (NO2

or = NO-OH); and sulphur (C=S). The chromogen, which is the aromatic structure

normally containing benzene, naphthalene or anthracene rings, is part of a

chromogen-chromophore structure along with an auxochrome. The presence of

ionising groups known as auxochromes results in a much stronger alteration of the

maximum absorption of the compound and provides a bonding affinity. Some

common auxochrome groups include – NH2, -COOH, -HSO3, -OH1. A detailed

classification of dyes including some structures is provided in The Colour Index

(C.I.)2.

Coloured dye wastewater arises as a direct result of the production of the dye

and also as a consequence of its use in the textile and other industries. There are more

than 100,000 commercially available dyes with over 7 x105 tonnes of dyes produced

annually3. It is estimated that 2% of dyes produced annually are discharged in effluent

from manufacturing operations whilst 10% was discharged from textile and associated

industries4. Use of reactive dyes is increasing5 . The rapid growth rate in the use of

reactive dyes is due to the increasing use of cellulosic fibres and the technical and

economic limitations of other dyes used for these fibres5-6.

Neglecting the aesthetic problem, the greatest environmental concern with

dyes is their absorption and reflecting of sunlight entering the water which interferes

with the growth of bacteria to level insufficient to biologically degrade impurities in

the water7. Colour in effluents can cause problems in several ways: dyes can have

actual and/or chronic effects on exposed organisms depending on the exposure time

and dye concentration; dyes are inherently highly visible meaning that concentrations

as low as 0.005 ppm capture the attention of both the public and the authorities8; dyes

absorb and reflect sunlight entering water and so can interfere with the growth of

bacteria and hinder photosynthesis in aquatic plants9.

323

4.9 Colour Adsorption

Adsorption techniques for wastewater treatment have become more popular in

recent years owing to their efficiency in the removal of pollutants to stable for

biological methods. Adsorption can produce high quality water while also being a

process that is economically feasible10. Decolourisation is a result of two mechanisms

– adsorption and ion exchange9 and is influenced by many factors including

dyes/sorbent interaction, sorbent surface area, particle size, temperature, pH and

contact time.

Consequently, the removal of pollutants from aqueous effluents is of

significant environmental, technical and commercial importance. Different process for

removal of dye from industrial wastewaters has been reported in the past11-14. Over the

years the adsorption process has emerged as a viable and effective alternative to most

of these conventional treatment techniques which are rather expensive. A large

number of low-cost adsorbents have been utilized for the removal studies of dyes and

the search for more cheaper and effective adsorbents still continues unabated.

In the present work, the adsorption studies of some dyes namely Methylene

Blue, Methylene Red and Malachite Green were carried on to naturally occuring and

easily available low cost adsorbents viz. Marble (M.), Rajasthan Red Kotta (R),

Kadappa (K), Granite (G) building waste material naturally dried, powered, processed

and finally used as adsorbent for the removal of these dyes. Literature survey reveals

that the work carried by different researchers15-16 showed the effective and efficient

adsorbative capacity of acid treated adsorbent. It gives us an idea whether acid treated

can work and give good adsorption results. Surprisingly acid treated MRKG showed

encouraging results of adsorption of acid dyes from solution. It appears, acid

treatment of adsorbent MRKG increase surface porosity, surface area, surface activity

and surface roughness. The observation also corroborated by the studies of acid

treatment on bentonite and soil17-18 The adsorption efficiency depends on interfacial

tension between acid dye, and MRKG, surface activity of the adsorbent. Our studies

on MRKG shows that there is an great increase in adsorption capacity of adsorbent in

removal of an ionic dye solution after treatment of adsorbent. This can be attributed to

increase in surface activity of adsorbent and the dye solution in contact with surface

of adsorbent, initially the intermolecular forces of dye, and surface of the adsorbent

are strong and becomes weak towards saturation. It was confirmed from 'L' type

324

Giles19 isotherm. The present study is aimed to find the effect of treatment of

adsorbent with mineral acids viz. H2SO4 creates an ideal condition for facile

adsorption of acid dyes to the surface.

4.10 Effect of pH

The pH of the medium has been found to play an important role in deciding

not only the extent but some times even the actual nature of adsorption of given

system20. It is therefore, necessary to make the proper adjustment in the pH of a

system to obtain the desired results. Studies employing dyes or ionic species as the

adsorbate and various adsorbents of common use (e.g. metal, their oxides and

hydroxides, clay, mineral, charcoal and plant material) indicate that the choice of the

pH range for favourable adsorption depends on the adsorbate-adsorbent pair. Both

acidic and basic media of pH range were found to be suitable for different adsobate-

adsorbent system. With some system large adsorption was seen in acidic medium

while with some other system basic medium was found suitable. The acidic medium

favoured21-22 the adsorption of chloride, sulphate onto soil and number of paraffin

chains onto cotton and wool. Similar results have also been observed using dyestuffs

as the adsorbate. The large adsorption of Acid Green Anthraquinone onto the surface

of organo silicia23 crystal violet onto polymer24 chrome dye onto activated carbon25 ,

fly ash26, acid dyes on neutral alumina27 and acid dyes on rice husk ash28.

On the other hand, in many cases especially with cationic types of adsorbate,

basic medium was found to be favourable for large desorption. Examples of such are

the adsorption of bromocresol green and bromothymol blue onto polymer23 synthetic

basic dyes onto activated sludge29 several heavy cations (dodecyltrimenthyl

ammonium and cetyltrimethyl ions) onto silica. An increase in adsorption of Acid Red

– 14 and Reactive blue –14 onto silica-magnesia mix gel30as well as in the adsorption

of basic dyes Methylene blue, Crystal violet, Malachite green and Rhodamine B on

iron oxide, silica and other materials31-35. In some cases the adsorption was found to

be maximum at a certain pH value. Such result have been observed by the adsorption

of congo red onto wollastonite36 ostrazone blue BG-onto polyester. The results show

two maxima37 as well as no marked variation in the amount adsorbed over an

appreciable pH range are also known. It has been reported38 that there is no such

325

change in the amount adsorbed in the adsorption of acid dyes onto polymer as a result

of variation in the pH of solution.

In the present investigation a known amount of the adsorbent was kept in

contact with a fixed volume of dye solution of which the pH was pre-adjusted for

definite value. The necessary pH of the solution was obtained using hydrochloric acid

and sodium hydroxide respectively for acidic and basic range of pH. For the

adjustment of pH of the dye solution, calculated volumes of standard solution of acid

or alkali were used. The volume were adjusted in such a way, which on addition to a

fixed volume, that were excepted to give required pH in the resulting dye solution.

Before use in the adsorption experiments the pH of the experimental solution was

measured using a glass electrode with the help of an electronic digital pH meter

(Equiptronic 203). The sample solutions withdrawn at various time intervals were

used for measuring the corresponding concentration of the residual dye solution, value

then obtained were employed for the estimation of the amount adsorbed on to the

surface. As the adsorbent is treated with dilute acid, the residual pH lies in between 5

to 5.5. Hence necessary precautions were taken while adjusting the pH of the solution

during experiment. For sake of, convenience the experiment were carried out using

pH electrode deep in the solution to get perfect value of pH. Experiments at higher pH

(7.20) were carried out by adding little quantity of base to adjust the pH properly with

desired value.

As the aim of the present experiments was to see the influence of pH on the

time rate study of adsorption, the necessary precaution were taken while adjusting the

pH of solution i.e. there was no change in colour appearance of the dye under these

extreme conditions40-41. Therefore, for the present study as all the dyes are acidic

dyes, the selection of the pH value were restricted with a conveniently small range 2

to 7. However the selection is based on trial experiments of colour appearance and

change in concentration. In the present investigation the adsorption of Methylene

Blue, Methylene red and Malachite Green onto the surface of MRKG. The

consolidated results for adsorption of acid dyes with change in pH are summarised in

table No.9.0.3, 10.0.3, 11.0.3, 12.0.3, 13.0.3, 14.0.3, 15.0.3, 9.1.3, 10.1.3, 11.1.3,

12.1.3, 13.1.3, 14.1.3, 15.1.3, 9.2.3, 10.2.3, 11.2.3, 12.2.3, 13.2.3, 14.2.3, 15.2.3

respectively in section B of chapter 3.

326

In the present investigation maximum adsorption of methylene blue,

methylene red and malachite green on to the surface of MRKG adsorbent at high pH

condition. The efficiency of adsorption of dyes onto the surface of treated MRKG was

found to be higher than when compared with untreated MRKG. The order of

adsorption of dyes onto the surface of MRKG are enlisted below as: For Methylene

Blue : (untreated): R<G<K<M ; (Treated): R<K<G< M ; Methylene Red :

(Untreated): M<R<G<K ;(Treated): M<G<R<K ; Malachite Green:

(Untreated):G<M<K<R ;(Treated): M<K<R<G.As the pH increased from 2 to 7,there

was increased in adsorption of dyes onto the surface of MRKG,as shown in fig 4.10.1

(A),(B) to 4.10.4(A),(B). Our findings has a good support of the results reported by

Ahmed and others46-50.

Fig. 4.10.1(A) : Effect of pH on Adsorption of Untreated Marble Powder (M)

Fig. 4.10.1(B) : Effect of pH on Adsorption of Treated Marble Powder (M)

Fig. 4.10.2(A) : Effect of pH on Adsorption of Untreated Red Kotta (R)

Fig. 4.10.2(B) : Effect of pH on Adsorption of Treated Red Kotta(R)

327

The adsorption at lower pH may be attributed to the increase in concentration

of hydrogen ion in dye solution which neutralizes hydroxyl group in the vicinity of

adsorbent surface, and facilitates the diffusion of dye molecule toward the surface of

adsorbent. Similarly diminished adsorption were reported by Bahadur et.al27 . At

higher pH due to the availability of large number of OH- ion and consequently the

diffusion barrier is increased which results into poor adsorption. In the present finding

at higher pH there is a change in order of reaction with change in pH, which suggest

the role of adsorbent as it may be leaching out at higher pH as the adsorbent is

building waste material consisting mainly various organic components , therefore our

studies restricted to the higher pH level upto 7.20.

Arunima et.al42 during their investigation of neem leaves powder (NLP) as

adsorbent for removal of methylene blue found that the pH of the medium does not

have much effect on adsorption of methylene blue on NLP. It is likely that the surface

of NLP particles are neither acidic nor basic and the cationic dye, methylene blue

Fig.4.10.3(B): Effect of pH on Adsorption of Treated Kadappa (K)

Fig. 4.10.4(A) : Effect of pH on Adsorption of Untreated Granite (G)

Fig. 4.10.4(B): Effect of pH on Adsorption of Treated Granite (G)

Fig. 4.10.3(A) : Effect of pH on Adsorption of Untreated Kadappa (K)

328

seems to have equal preference for the adsorption sites at all pH values. Mehmet

Dogan et.al43 studied adsorption isotherms at various pH's (3,5,7,9, and 11) and

reported that the adsorbed amount of acid yellow 49 on decreased with increase in pH

values. The surface is positive at low pH and is negative at higher pH. As the pH of

dye solution becomes lower than pH = 6.6, the association of dye anion with more

positively charge surface.

Alok Mittal et.al44 during their investigation carried pH measurements in the

pH range 2-6 and found that with increase in pH a decrease in the adsorption of the

dye over feathers (adsorbent) was observed. The maximum uptake of the dye took

place around pH 2.0 and beyond pH 4.0 the adsorption of the dye was almost

negligible. Thus pH 2.0 was selected for all subsequent studies. A continuous

decrease in the adsorption with increasing pH indicates possibility of development of

positive charge on the Hens feathers, which inhibits the adsorption of dye over it.

Ubale et.al45 during their adsorptions study of phenol on Goda sand found that

there is increased adsorption with increase in pH which may be attributed to the

binding of phenol molecules to the Goda sand (adsorbent) whereas lower adsorptions

may be attributed to the presence of excess hydrogen ion which lowers binding of

phenol molecules on Goda Sand.

4.11 Effect of adsorbent dose

Effect of adsorbent dose plays an important role in standardising the

adsorption process with quantification of adsorbate solution and the adsorbent. The

series of experiments with different amount of approximate concentration. The

adsorbent treated with acid due to its increase high adsorption capacity moderate

amount of adsorbent ranging from 1.0 g to 5.0 g required for 100 ml. The actual

amounts adsorbed at equilibrium with saturation time is given in table No. 9.0.2,

10.0.2, 11.0.2, 12.0.2, 13.0.2, 14.0.2, 15.0.2, 16.0.2, 9.1.2, 10.1.2, 11.1.2, 12.1.2,

13.1.2, 14.1.2, 15.1.2, 16.1.2, 9.2.2, 10.2.2, 11.2.2, 12.2.2, 13.2.2, 14.2.2, 15.2.2,

16.2.2 of section B Chapter 3.

The adsorption of Methylene Blue, Methylene Red and Malachite Green on to

the surface of various dose of MRKG adsorbent and its removal in percentage after 60

minutes is shown in figures 4.11.1 (A),(B) to 4.11.4 (A),(B).

329

In the present investigation adsorption of organic dyes on the different amount

of Untreated and Treated MRKG adsorbent shows that with increase in the amount of

adsorbent dose adsorption also increase it is in good agreement with the work reported

by Yamin Yasin et.al51.

The extent of the adsorption in the system is determined by a number of

factors of which the availability of the active adsorption sites and concentration of the

dye solution are the most important. The adsorbent employed in the present study are

in the powdered form and have been activated appropriately at suitable temperature

and thus capable of providing excessive opportunity for large adsorption52. The

maximum removal of Phenylacetic acid (PAA) by adsorption on activated charcoal

(AC), tea powder (TP) and saw dust (SD) was found to be enhanced on increased

amount of adsorbent53.

Fig. 4.11.1(A) : Effect of Adsorbent Dose on Adsorption of Untreated Marble Powder (M)

Fig. 4.11.1(B) : Effect of Adsorbent Dose on Adsorption of Treated Marble Powder (M)

Fig. 4.11.2(A): Effect of Adsorbent Dose on Adsorption of Untreated Red Kotta(R)

Fig. 4.11.2(B): Effect of Adsorbent Dose on Adsorption of Treated Red Kotta(R)

330

The adsorption study of phenol on Goda sand and maximum removal of

phenol with increase in adsorbent dose was reported and may be attributed to increase

in the availability and of the active sites due to the increase in the surface area45. The

increased amount of adsorbent, increases adsorption site, though the number of dye

molecule present in the solution remains constant. On the other hand, the dye

molecule gets easily adsorbed due to the increase in adsorption sites with increased

amount of adsorbent. Thus it can cause a rapid decline in the concentration of dye

solution i.e. maximum removal of dye54. Rachakornkiji et.al55 during the study of

removal of dyes using bagasse flyash observed that the removal efficiency of reactive

dye increases rapidly with increase in the concentration of the adsorbent due to the

greater availability of the exchangeable sites or surface areas at higher concentration

of the adsorbent56-57. The present study reveals that with increase in the amount of

MRKG adsorbent dose i.e. from 1g to 5g, there is an increase in the adsorption of

Fig. 4.11.3(B) : Effect of Adsorbent Dose on Adsorption of Treated Kadappa (K)

Fig. 4.11.3(A) : Effect of Adsorbent Dose on Adsorption of Untreated Kadappa (K)

Fig. 4.11.4(A) : Effect of Adsorbent Dose on Adsorption of Untreated Granite (G)

Fig. 4.11.4(B) : Effect of Adsorbent Dose on Adsorption of Treated Granite (G)

331

dyes (Methylene Blue, Methylene Red and Malachite Green) onto the surface of

Untreated and Treated MRKG.

It was found that maximum adsorption of methylene blue onto the surface of

Untreated Marble powder (M),the percentage removal was 66.16 and on the treated

surface of granite (G),the percentage removal was 84.62. The order of adsorption of

methylene blue onto the surface 5g of Untreated MRKG was of the order K<G<R<M

and Treated MRKG was of the order K<M<G<R.

For Methyelene Red maximum adsorption recorded onto the surface of

untreated Granite (G), it was found to be 60.67 percent and minimum onto the surface

of Untreated Kadappa (K) and was 47.50 percent. In case of treated adsorbent

maximum adsorption recorded onto the surface of treated red kotta (R) it was found to

be 71.98 percent and minimum on treated granite (G) was 64.00 percent. The order

of adsorption of methylene red on to the surface of 5g of untreated MRKG was of the

order K<M<R<G and treated MRKG was of the order M<G<K<R.

Similarly, for Malachite Green maximum adsorption recorded onto the surface

of untreated granite (G) and treated marble power (M) was 56.67 and 64.50 percent

respectively whereas minimum adsorption recorded onto the surface of untreated

kadappa (K) and treated kadappa(K) was 33.34 and 43.00 percent respectively. The

order of adsorption of malachite green on to the surface of 5g untreated MRKG was

the order K<R<M<G and treated MRKG was the order K<G<R<M.

4.12 Effect of Initial Concentration

The adsorption of dyes onto MRKG is rapid in the beginning, slow down later

on and finally reached towards the equilibrium. A large fraction of the total amount

of dye is found to be adsorbed with in a few minutes of time. Thus 40-45 % of the

total amount of dye is observed to be removed from solution with in 20-30 minutes.

The total time to attain the equilibrium depends on the nature of the adsorbent as well

as adsorbate. But to have the comparative study and by keeping in view that the

adsorbent is a building waste material 100 ml of dye solution was kept in contact with

0.9 gm of adsorbent at constant temperature for kinetic study and care has been taken

to maintain agitation constant in all the experiments. The attainment of the

equilibrium was on the basis of reaction carried out on dilute solutions and the

saturation time found to be dependent on the amount of adsorbent. The variation in

332

the concentration of the dye solution (0.5 to 5.0 x 10-5M) does not show any

measurable change in the equilibrium time though the variation in uptake is observed

at intermediate stages are in the range of (0.5 to 5.0 x 10-5M). These concentration

ranges follows the Lambert Beer's law58. Generally adsorption consists of diffusion

of dye molecule from bulk solution to the surface, adsorption of the dye molecule on

to the surface and layer formation on the surface of adsorbent. Mostly the adsorbed

dye content gradually increases constantly upto certain time limit and finally attains

the equilibrium indicating a saturated adsorption59-60. The time growth of uptake

increase with concentration of dye solution. The increase adsorption of the adsorbate

onto adsorbent may be due to increase in surface activity and due to micelle formation

or the aggregation of dye molecule in the concentration range studied. Similar results

have also been reported by several workers61-62 .

Thus, on varying the concentration of dyes (Methylene Blue, Methylene Red,

Malachite Green) from (1.0 x 10-5 to 5.0 x 10-5 M) the amount adsorbed onto the

surface of MRKG randomly increased and the consolidated results are given in Table

9.0.4, 10.0.4, 11.0.4, 12.0.4, 13.0.4, 14.0.4, 15.0.4, 16.0.4, 9.1.4, 10.1.4, 11.1.4,

12.1.4, 13.1.4, 14.1.4, 15.1.4, 16.1.4, 9.2.4, 10.2.4, 11.2.4, 12.2.4, 13.2.4, 14.2.4,

15.2.4, 16.2.4 respectively and the amount adsorbed during the investigation in terms

of percentage removal of dye are shown in figures 4.12.1 (A),(B) to 4.12.4(A), (B).

Saiful et.al63 during their adsorption study of removal of dye from aqueous

solution by using sugar bagasse reported that with increase in the concentration of dye

solution, there was a decrease in percentage removal of dye even though the amount

of dye adsorbed increased64-67, the findings are in good agreement with our findings

Fig. 4.12.1(A) : Effect of Initial Concentration on Adsorption of Untreated Marble Powder (M)

Fig. 4.12.1(B) : Effect of Initial cncentration on Adsorption of Treated Marble Powder (M)

333

4.13 Effect of Contact Time

The removal of dye by adsorption process using MRKG was found to be

rapid at the initial stage of contact time and then related with increase in contact time

of adsorbent and adsorbate. It may be attributed to the strong binding forces between

dye molecules and the adsorbent MRKG. Our finding are in good agreement with

the findings reported by Yamin et.al68. Hussain et.al69 during their study used

carbonized straw as adsorbent for the removal of Methylene Blue and reported that

with increase in contact time of adsorbent-adsorbate system, adsorption increased but

Fig. 4.12.2(A) : Effect of Initial Concentration on Adsorption of Untreated Red Kotta (R)

Fig. 4.12.2(B) : Effect of Initial Concentration on Adsorption ofTreated Red Kotta (R)

Fig. 4.12.3(A) : Effect of Initial Concentration on Adsorption of Untreated Kadappa (K)

Fig. 4.12.3(B) : Effect of Initial Concentration on Adsorption of Treated Kadappa (K)

Fig. 4.12.4(A) : Effect of Initial Concentration on Adsorption of Untreated Granite (G)

Fig. 4.12.4(B) : Effect of Initial Concentration on Adsorption ofTreated Granite (G)

334

after 120 minutes of contact time, adsorption Methylene blue was almost constant

adsorbent. The findings were in good agreement with Vinod et.al70.

In the present investigation the adsorption of Methylene Blue, Methylene Red

and Malachite Green onto the surface of MRKG. The consolidated results for

adsorption are enlisted in Table Nos. 9.0.1, 10.0.1, 11.0.1, 12.0.1, 13.0.1, 14.0.1,

15.0.1, 16.0.1, 9.1.1, 10.1.1, 11.1.1, 12.1.1, 13.1.1, 14.1.1, 15.1.1, 16.1.1, 9.2.1,

10.2.1, 11.2.1, 12.2.1, 13.2.1, 14.2.1, 15.2.1, 16.2.1 respectively in section B Chapter

3 and the variation in the adsorption process is shown in figures 4.13.1 (A) (B)to

4.13.4 (A) (B).

Fig. 4.13.1(A) : Effect of Contact Time on Adsorption of Untreated Marble Powder (M)

Fig. 4.13.1(B) : Effect of Contact Time on Adsorption of Treated Marble Powder (M)

Fig. 4.13.2(A) : Effect of Contact Time on Adsorption of Untreated Red Kotta (R)

Fig. 4.13.2(B) : Effect of Contact Time on Adsorption of Treated Red Kotta (R)

335

Maximum adsorption of Methylene Blue has found to be on the surface of

untreated and treated Kadappa (K) (57.34 % and 67.00 % respectively); Whereas,

maximum adsorption of Methylene Red was onto the surface of untreated and treated

Marble Powder (M) (63.34 and 69.43 % respectively). Malachite Green showed

higher affinity to the surface of untreated and treated Red Kotta (K) was (51.67 % and

67.50 % respectively). The results is indicative of maximum adsorption capacity of

MRKG used in the present investigation for removal of organic dye.

4.14 Adsorption Kinetics

Kinetics of adsorption describes the solute uptake rate which in turns govern

residence time or sorption reaction. It is one of the important characteristics in

defining the efficiency of adsorption71.

Adsorption is a widely used process for interpreting the equilibrium amount

between adsorbent and adsorbate72. A study of adsorption kinetics is desirable as it

provides information about the mechanism of adsorption which is important for the

Fig. 4.12.3(A) : Effect of Contact Time on Adsorption of Untreated Kadappa (K)

Fig. 4.13.4(A) : Effect of Contact Time on Adsorption of Untreated Granite (G)

Fig. 4.13.4(B) : Effect of Contact Time on Adsorption of Treated Granite (G)

Fig. 4.12.3(B) : Effect of Contact Time on Adsorption of Treated Kadappa (K)

336

efficiency of the process. Successful application of the adsorption demands

innovation of cheap easily available and abundant adsorbents of known kinetics

parameters and adsorption characteristics73. In order to examine the controlling

mechanism of the adsorption process pseudo first order equation were used to test the

experimental data. A simple kinetics analysis of adsorption is the pseudo first order

rate expression of the Lagergren equation74-76. It gives the average value of the rate

constant K for adsorption of dye (adsorbate) onto MRKG (adsorbent) and can be

calculated in the form

dq = K1 (qe – qt) ..... (1) dt

Where K1 is the rate constant of pseudo – order adsorption (m-1) and qe and qt are the

amount of dye adsorbed per gram MRKG (mg/g MRKG) at equilibrium and time 't'

respectively. After definite integration by applying the initial condition qt = 0 at t =

0 and q = qt and t = t, equation 1 becomes

log (qe – qt) = log qe – (k1 / 2.303) t . ................... (2)

A straight line of log (qe – qt) versus 't' suggests the applicability of the kinetic models

which allows computation of the adsorption rate constant also shown by Sreelatha

et.al77.

The adsorption rate is attributed to several diffusion steps, the first step is the

transport of the adsorbate from the bulk solution to the outer surface of the adsorbent

granule by molecular diffusion. This is called film diffusion. The film diffusion term

is used to describe resistance of the mass transfer at the surface of the particle. The

concentration gradient in the liquid film around the granule is the driving force in film

diffusion. Film diffusion has importance in solution containing high adsorbate to

solvent ratios and can be rate controlling. If adequate provision were not made to

include this in the basic diffusion equation then the analytical solution of these

equation would be grossly in error78-81. The second step termed intraparticle diffusion

invities transport of the adsorbate into the interior sites by diffusion within the pore

filled liquid, which is called pore diffusion and migration along the solid surface of

337

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Dyes on to the Surface of MRKG adsorbent.

Methylene Blue Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 1 2 3 4 5 25oC 30 oC 35 oC 40 oC 45 oC 100 200 300 400 500

Marble

Powder

Untreated 1.624 x10-2

1.635 1.714 1.940 1.981 1.881 1.923 2.220 2.321 2.423 2.321 2.654 3.136 3.724 3.325 1.984 2.224 2.657 2.726 2.865

Treated 1.996 x10-2

2.003 2.226 2.143 2.426 2.143 2.113 3.213 3.240 3.362 3.113 3.352 3.422 3.751 3.845 2.132 2.325 2.520 2.650 2.654

Rajasthan

Red Kotta

Untreated 1.468 x10-2

1.521 1.882 2.311 2.475 2.317 2.152 2.523 2.724 2.856 2.392 2.842 2.863 3.110 3.652 1.885 2.225 2.254 2.780 2.795

Treated 1.897

x10-2

1.998 2.321 2.340 2.645 2.634 2.263 2.632 2.811 2.873 2.632 2.956 2.920 3.231 3.654 2.125 2.386 2.367 2.800 3.332

Kadappa Untreated 1.432

x10-2

1.448 1.902 1.964 2.110 1.643 2.123 2.210 2.214 2.151 2.653 2.932 2.632 2.732 2.765 1.654 1.752 1.685 2.321 2.265

Treated 1.789

x10-2

1.886 2.426 2.912 2.994 1.693 2.312 2.122 2.312 2.232 2.553 2.652 2.865 2.787 2.842 1.457 1.354 2.630 2.325 2.321

Granite Untreated 1.346

x10-2

1.398 2.001 2.223 2.120 1.819 1.960 1.932 2.142 2.254 2.842 2.992 2.932 2.696 3.001 3.212 3.114 3.217 3.623 3.425

Treated 1.846

x10-2

1.942 2.225 2.263 2.317 2.263 2.442 2.413 2.242 2.363 2.836 2.932 3.016 3.210 3.105 3.212 3.254 3.329 3.628 3.712

338

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Dyes on to the Surface of MRKG adsorbent.

Methylene Red Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 1 2 3 4 5 25oC 30 oC 35 oC 40 oC 45 oC 100 200 300 400 500

Marble

Powder

Untreated 1.140 x10-2

1.754 1.814 1.940 1.981 1.781 1.825 2.220 2.333 2.420 2.101 2.220 2.316 2.339 2.425 1.989 2.001 2.157 2.226 2.365

Treated 1.520 x10-2

1.920 2.121 2.413 2.416 2.041 2.052 3.213 3.120 3.120 3.002 3.125 3.111 3.251 3.355 2.162 2.327 2.535 2.650 2.714

Rajasthan

Red Kotta

Untreated 1.001 x10-2

1.320 1.432 2.001 2.413 2.013 2.201 2.523 2.424 2.625 2.136 2.262 2.744 2.420 2.652 1.776 1.852 2.294 2.180 2.415

Treated 1.527

x10-2

1.627 1.731 2.450 2.445 2.134 2.263 2.235 3.221 3.353 3.221 3.216 3.320 3.276 3.465 2.224 2.386 2.637 2.863 2.846

Kadappa Untreated 1.620

x10-2

1.442 1.655 2.212 2.551 2.113 2.123 2.232 2. 452 2.751 2.253 2.273 2. 324 2.703 2.765 1.854 1.945 2.392 2.389 2.565

Treated 1.789

x10-2

1.652 1.846 2.635 2.842 2.193 2.312 2.412 3.552 3. 386 3.353 3.652 3. 650 3.387 3.541 2.457 2.543 2.711 2.925 2.921

Granite Untreated 1.446

x10-2

1.625 2.331 2.226 2.612 2.219 1.960 2.319 2.511 2.851 2.372 2.392 2. 328 2.742 2.881 1.912 2.113 2.519 2.441 2.625

Treated 1.794

x10-2

1.969 2.225 2.768 2.967 2.267 2.442 2.563 3.564 3.963 3.441 3.832 3. 679 3.400 3.601 3.012 2.667 2.891 3.002 3.001

339

Adsorption Kinetics

Values of Rate Constants (Kr) by fitting into Lagergron equation for adsorption of Dyes on to the Surface of MRKG adsorbent.

Malachite Green Adsorbent Dose pH Temperature Initial Concentration

1g 2g 3g 4g 5g 1 2 3 4 5 25oC 30 oC 35 oC 40 oC 45 oC 100 200 300 400 500

Marble

Powder

Untreated 1.341 x10-2

1.824 1.832 1.884 1.911 1.672 1.736 2.011 2.113 2.337 2.135 2.232 2.441 2.537 2.625 1.647 1.898 1.917 2.154 2.224

Treated 1.356 x10-2

2.130 2.221 2.413 2.513 1.730 1.862 2.239 2.312 2.559 3.012 3.220 3.331 3.401 3.611 2.142 2.327 2.537 2.620 2.717

Rajasthan

Red Kotta

Untreated 1.221 x10-2

1.643 1.526 1.653 2.101 1.889 1.902 2.326 2.424 2.674 2.264 2.312 2.544 2.632 2.725 1.777 2.001 2.129 2.180 2.346

Treated 1.427

x10-2

2.103 2.226 2.450 2.607 1.941 2.013 2.532 2.964 3.111 3.341 3.318 3.426 3.513 3.702 2.254 2.385 2.637 2.773 2.786

Kadappa Untreated 1.120

x10-2

1.447 1.685 1.763 2.213 2.013 2.123 2.635 2.796 2.714 2.367 2.371 2. 610 2.724 2.867 1.819 2.154 2.225 2.226 2.463

Treated 1.588

x10-2

2.315 2.347 2.635 2.721 2.119 2.213 2.712 2.968 3. 197 3.435 3.516 3. 593 3.627 3.816 2.359 2.544 2.711 2.825 2.811

Granite Untreated 1. 004

x10-2

1.526 1.775 1.658 2.413 2.132 2.316 2.819 3.111 2.812 2.427 2.419 2. 738 2.819 2.919 1.967 2.223 2.317 2.364 2.561

Treated 1.813

x10-2

2.013 2.645 2.768 2.867 2.203 2.442 2.963 3.217 3.263 3.561 3.635 3. 712 3.722 3.879 2.906 2.621 2.891 2.990 3.000

340

the pore, which is called surface diffusion. As these two transport processes act in

parallel, the more rapid controls the overall rate of transport. The third step is

adsorption of the solute on the active sites on the adsorbent surface, since the

adsorption process is very rapid it does not influence the overall kinetics. The overall

rate of adorption process, therefore, can be controlled by the slowest step, which

would be either film diffusion or internal diffusion79.

The kinetic data reveals that adsorption follows the first order reaction kinetics

and from pH study it can be concluded that in acidic media the dye removal

percentage is higher our finding is in good agreement with Mumin et.al82. The

decrease in adsorption rate which may be explained on the basis of aqua complex

formation and subsequent acid base dissociation at solid solution interface. Any

surface creates a charge (positive or negative) on its surface83. This charge are

proportional to the pH of that solution that surrounds the oxide particle. Thus it can

be concluded as pH increases, rate of adsorption decreases it may be due to the

competition between H+ ions and acid dyes for adsorption considered by increasing

the adsorbent dose from 1 g to 5 g by keeping other parameters constant, it was found

that rate constant increases i.e the removal efficiency of dye increases. The number of

available adsorption sites increases which furnishes more adsorption and, therefore,

rate constant (k1) also increases our finding are in good agreement with Mumin et.al

and Others 82-84.

Lodha et.al85 studied and showed the effect of variation in the amount of

adsorbent on the contact time for a constant initial concentration. It was observed that

maximum removal of methylene blue took place within the first few minutes ; while

equilibrium was obtained in about 2 hours. The removal of dye significantly

increased when more rice husk was added because more active sites were made

available for adsorption. It is important to note that short contact times indicate that

the predominant mechanism of adsorption is chemisorption and hence the process is

irriversible78 .

The rate constant K1 at different temperature were applied to estimate the

activation energy of the adsorption of dyes onto MRKG by Arrhenius equation86.

lnK = lnA – Ea ... (3) RT

341

Where Ea, R and A refers to the Arrhenius Activation Energy the gas constant and the

Arrhenius factor respectively. The slope of the plot of log K1 versus 1/T was used to

evaluate Ea as listed below in the tabular form.

The Ea value for adsorption of dyes (Methylene Blue, Methylene Red and

Malachite Green) it was found in the range of 1033.94 J to 7926.916 J.

The minimum value of 1033.94 J was for Malachite Green untreated Red

Kotta (R) system whereas 421.710 was the minimum value for Malachite Green in

Treated Marble Powder (M) system which may be attributed to lesser energy barrier

and therefore comparatively rate of adsorption was higher. The maximum value

7926.916 J is found to in Malachite Green untreated Granite 888.4.027 J is found to in

the Methylene Red - Treated Marble Powder (M) system which indicates

comparatively low rate of adsorption may be attributed to more energy barrier during

adsorption.

Ea (Energy of Activation for Dyes)

Adsorbent Untreated

Marble (M) Untreated Red

Kotta Untreated Kadappa

Untreated Granite

Methylene Blue

2872.071 7084.440 3431.687 5284.611

Methylene Red 4154.929 6798.543 3829.428 4805.932 Malachite

Green 5361.199 1033.94 2297.657 7926.916

Adsorbent Treated Marble (M)

Treated Red Kotta

Treated Kadappa

Treated Granite

Methylene Blue

1991.302 3293.308 6127.08 4122.022

Methylene Red 8884.0273 3791.134 1891.306 2316.804

Malachite Green

421.710 1053.09 8424.74 1014.798

342

4.16 Effect of Temperature

Temperature is one of the most important factors, which determines the extent

of adsorption of given system. Its influence in deciding the actual alternation is both

positive and negative, and depends on the nature of interaction involved. In general,

the level of adsorption at any particular concentration usually decreases with increase

in temperature, i.e., the over all process is exothermic87-88. A lowering of temperature

is favourable for large adsorption in the case where physical adsorption is

predominant. On the other hand in chemisorptions or in activated adsorption, an

elevated temperature is preferred. Many workers89-92 reported the decrease in

adsorption with increase in temperature as well as many of them also reported the

increase in adsorption with increase in temperature93-94. Results indicating no

appreciable alternation in the amount adsorbed due to variation in temperature are

also known95. Temperature also plays an important role on the rate of adsorption.

Generally rate is found to be increase with temperature96-98. For chemisorptions

Taylor et.al99 described that the increase in rate proceeds exponentially. An increase

in the rate of adsorption has been reported from the liquid phase, with the adsorption

of Basic Yellow onto activated Carbon100 Methylene Blue, Crystal Violet and

Malachite Green onto Iron oxide showed enhanced adsorption rate with

temperature101, the increase in adsorption of polyacrylamide onto Fuller's earth with

temperature has been reported by Bajapi and coworker54. The results from adsorption

of Alizarin Red on Chitin show increase in rate of adsorption with increase in

temperature as the temperature enhances the rate102. The effect of temperature has

moderate effect on the adsorption of reactive dyes on to eggs membrane103-104.

Gupta104 and co-workers studied the effect of temperature on the adsorption of basic

dye Rhodamine-B and Methylene Blue from aqueous solution using bagasse fly ash.

Study of influence of temperature on the rate of adsorption of dyes has been

mostly restricted to the textile fabrics used as the adsorbents. It was of interest

therefore, to make such measurement using MRKG as an adsorbent. This study is

helpful in the determination of the alternation in the extent of the adsorption as well as

computing the corresponding energy of activation involved in the process105-116. In

case of hydrogenation the adsorption of hydrogen on platinum and palladium was

found to be increased with increased in temperature.

343

The details of adsorption of Methylene Blue, Methylene Red and Malachite

Green onto the surface of MRKG adsorbent with variation, in temperature is given

Table Nos. Table 9.0.5, 10.0.5, 11.0.5, 12.0.5, 13.0.5, 14.0.5, 15.0.5, 16.0.5, 9.1.5,

10.1.5, 11.1.5, 12.1.5, 13.1.5, 14.1.5, 15.1.5, 16.1.5, 9.2.5, 10.2.5, 11.2.5, 12.2.5,

13.2.5, 14.2.5, 15.2.5, 16.2.5.

The adsorption of acid dyes onto the surface of MRKG increased with

increase in temperature and the percentage removal of acid dyes from aqueous after

sixty minutes is shown in fig. 4.16.1 (A),(B) to 4.16.4 (A),(B).

Arumina et.al42 showed during their investigation that adsorption of dyes

increased on the surface with increase in temperature. The effect of temperature on

adsorption has always been a very complex process and the net effects are likely to be

determined by the adsorbent - adsorbate interaction107. The effect of temperature on

adsorption show that the process is dominated by chemisorptive bond formation

between the adsorbate and the adsorbent, but some physical adsorption cannot be

entirely ruled out. The adsorption sites of the surface of the are expected to be

heterogenous, non-specific and non-uniform as in case of many other adsorbent108-109.

G. Annadurai et.al52 used the rearranged Langmuir isotherm for different temperatures

like 30, 45 and 600C and the amount of dye adsorption was fitted as a function of

temperature in isotherm equation. An increase in temperature adsorption. The

variation in dye adsorption at higher temperature was found to be greater compared

to that at a lower temperature.

Mahir Akan et.al75 studied the adsorption isotherms at different temperature

and showed that the adsorption capacity of acid yellow increases with increase in

temperatures. This may be due to increase in the mobility of the large dye ions with

increasing temperature. An increasing number of molecules may also acquire

sufficient energy to undergo an interaction with active sites at the surface, furthermore

increasing temperatures may produce a swelling effect within the internal structures of

the sepiolite enabling large dyes to penetrate further. This indicates that the adsorption

process becomes more favourable with increase in temperature109-111.

344

Fig. 4.16.1(A) : Effect of Temperature on Adsorption of Untreated Marble Powder(M)

Fig. 4.16.1(B) : Effect of Temperature on Adsorption of Treated Marble Powder (M)

Fig. 4.16.2(A) : Effect of Temperature on Adsorption of Untreated Red Kotta (R)

Fig. 4.16.2(B) : Effect of Temperature on Adsorption of Treated Red Kotta (R)

Fig. 4.16.3(A) : Effect of Temperature on Adsorption of Untreated Kadappa(K)

Fig. 4.16.3(B) : Effect of Temperature on Adsorption of Treated Kadappa (K)

Fig. 4.16.4(A) : Effect of Temperature on Adsorption of Untreated Granite (G)

Fig. 4.16.4(B) : Effect of Temperature on Adsorption of Treated Granite (G)

345

The increase in the adsorbed mass with increase in temperature can be

explained by the fact that increase in temperature reduces the intermolecular forces

between the water molecule which are adsorbed at the interface portion of the

adsorbent which leads to the surface of the adsorbent become more active, this

facilitates diffusion of dye molecules towards the surface of adsorbent easily which

show the increased in adsorption with increase in temperature. As the adsorption

appears to be of physical type it is reasonable to consider that the involved

intermolecular forces are strengthened at lower temperature which finally results in an

increased adsorption. At lower temperature the possibility of agglomeration of dye

molecule may not be ruled out as postulated by several workers in the case of the

adsorption of several dyes111-112. Obviously in the agglomerated state the dye –

molecule will be adsorbed to a greater extent.

At higher temperature the escaping tendency of the molecules from the solid

to the bulk phase may increase due to the increased solubility of the adsorbate in the

solution phase113. This results in a lower adsorption at higher temperature similar type

of results have also been obtained elsewhere114-115. In several investigation116,

however an increase in the adsorption capacity has been observed which is attributed

to either an increase in the number of active sites on the adsorbent or strentghening of

the bonds between the adsorbate and adsorbent. According to Bhattacharya et.al117

the percentage adsorption increase with increase in adsorption temperature. This

points to an endothermic nature of the adsorption process118-120.

Raghuvanshi et.al57 during their kinetic study of methylene blue bioadsorption

on baggase reported the rate of dye uptake increases from 78.09% to 86.35% with

rising temperature at 30oC to 50oC since the adsorption rate increase as the diffusion

coefficient rises with temperature120.

In our findings the adsorption of acid dyes (Methylene Blue, Methylene Red,

and Malachite Green) onto the surface of MRKG adsorbent increases with an increase

in temperature, the percentage removal of Methylene Blue at 313 K from aqueous

solution by Untreated MRKG adsorbent is of the order K<R<M<G and Treated

MRKG adsorbent is of the of order R<K<M<G. Thus Methylene Blue at both

temperature (Maximum and Minimum) shows affinity to the surface of untreatead and

treated Marble Powder (M). Similarly, adsorption of Methylene Red on to the

surface of Untreated MRKG at 303K follows the order as K<G<M<R and at 313 K

346

the order of adsorption on Treated MRKG follows the order as M<G<R<K. The

adsorption of Malachite Green onto the surface of Untreated MRKG at 303 K was

found to be in the order as K<G<R<M and at 313 K the order of adsorption on

Treated MRKG surface was observed in the sequence as K<M<G<R. In short it can

be concluded with increase in temperature adsorption of acid dyes increase onto the

surface of MRKG adsorbent which is in good agreement with Mahir and

Others43,75,119,120.

4.17 Adsorption Isotherm

Among the factors, which determine the extent of adsorption, the

concentration of the adsorbate solution is one of the chief determinants. Any change

in this factor is seen to affect not only the extent but in some cases also the nature of

adsorption. The actual variation of the amount adsorbed with concentration (Pressure

in case of gases) at a constant temperature is expressed by relation usually known as

adsorption isotherm. The adsorption isotherm is graphical representation of amount

of substance adsorbed against the residual concentration of the adsorbate in the

solution. Several such isotherms both obtained empirically as well as derived on

theoretical basis have been proposed from time to time; represent the observed results.

Many of these, despite their successful adsorption in specific cases, are found

inadequate in system of diverse nature or in simple cases also specially when applied

over wide range of experimental parameters.

Initially most of the isotherms were derived for the adsorption of gases onto

solid surface118 but they were also found successful in representing the other

adsorption process, especially the adsorption of dyes onto solids surfaces28,34,122. The

amount of solute adsorbed by one gram of the adsorbent under a given set of

condition is expressed usually as,

X = f (C) or f (P)

Where C = concentration (P is pressure in case of gas) of the adsorbate solution. In

the adsorption of dyes by commonly used solid adsorbents isotherm of different

nature have been reported by several workers123. This includes even those showing

regular and then sometimes a rise again, as well as those showing interrupted rise well

defined constant adsorption isotherm all showing an increase in the amount

347

adsorbed123. In the present study a small variation in temperature (i.e.50C) is

considered for each run. Such a small change in temperature does not appear to

affect the general nature of the isotherm though individual values of the amount

adsorbed varied. MRKG as adsorbent at higher temperature is favourable for large

adsorption for Methylene Blue, Methylene Red and Malachite green as the

temperature increased from 35oC to 45oC.

The adsorption data for a wide range of adsorbate concentration and adsorbent

doses were analyzed using Langmuir and Freundlich isotherms in order to find the

adsorption capacity of MRKG adsorbate.

Freundlich Theory :

A fairly satisfactory empirical isotherm, which can be applied to adsorption of

gases with considerable successes but have been used principally for adsorption from

solution, has been discussed by H. Freundlich124. He suggested that the ratios of the

amount of solute adsorbed onto a given mass of adsorbent to the concentration of the

solute in the solution are not constant at different concentration of solutions. If qe is

the amount of solute adsorbed mg per gram of adsorbent and Ce is the equilibrium

concentration in the solution, the empirical relation is;

x m = qe = KFCe

1/n

Where,

KF = rough measure of adsorption capacity (intensity of adsorption)

n = empirical constant.

The linear form of the equation is;

log qe = log KF + 1 log Ce

n The values of KF and 1/n are calculated from the intercept and slope of the plot of

log qe Vs. log Ce respectively.

According to Lodha85, the Freundlich log plot is linear which may be

attributed to the fact that Freundlich equation the concentration of dye on the

adsorbent increases as the dye concentration in liquid increases. The experimental

observation reported too suggests that the isotherm plateau is not reached even at very

high concentration of the adsorbent. The favourable adsorption process reported is

348

also indicated by the fact the value of n is less than 1. Moosa et.al125 studied the

sorption capacities of rice bran for benzene, toluene, etheylbenzene and cumene for

different isotherms and accordingly the Freundlich adsorption isotherm gave an

empirical expression encompassing the surface heterogeneity and the exponential

distribution of energies82. The Freundlich isotherm124 tested and was found that for

each BTEC components, a straight line was obtained. The slope of the straight line

gave the values of 1/n which were less than 1 indicating the intensity of adsorption.

The value of 1/n showed that the removal of BTEC by rice bran was effective at lower

concentration and the intercept yield the adsorption capacity.

The result obtained tested for the applicability of Freundlich adsorption

isotherm. The straight line plots of log qe Vs. log Ce for the adsorbent MRKG and

show its applicability. The values for the Freundlich constants KF and 1/n calculated

from the intercepts and slopes of the above-mentioned plots are given in Table No.

1A. The Freundlich isotherm was verified by using least square fit and regression

analysis and computer programming in EXCEL. The value of regression co-efficient

r2 was calculated and represented in the following Table I-A. The value are very

close to 1.0 which indicate that good corelation exists, between log x/m and log C.

Langmuir Theory :

Langmuir121 suggested a theory to describe the adsorption of gaseous

molecules. on a metal surface. The Langmuir adsorption isotherm has been found

suitable to many sorption processes and it can used to explain the sorption of dyes on

to solid surfaces. According to this theory, it is that the surface of solid is made up of

elementary sites. For the solid liquid interface the saturated monolayer can be

represented by the following expression,

Ce = 1 + Ce qe Qob Qo

Where,

Qo and b = are Langmuir constant related to capacity and energy of adsorption,

respectively. The values of Qo and b are calculated form the slope and intercept of

plot of Ce/qe Vs. Ce, respectively.

The basic assumption in the Langmuir isotherm is that adsorption takes place

at specific sites on the adsorbent and once a site is occupied no further adsorption can

take place at that site. This implies that at saturation the adsorbent is covered

uniformly by a layer of molecules126.

349

The Langmuir model121 represents monolayer adsorption on a set of distinct

localized adsorption sites having the same adsorption energies no interaction between

adsorbed molecules. The plot yield a straight line for all the organics investigated,

indicating that the Langumuir sorption model is followed by the sorption data very

well. The values of maximum adsorption capacity calculated from the slopes of the

linear plots whereas the values of enthalpy of adsorption (b) estimated from the

intercepts of the plot. Hussain et.al127 during their adsorption study of organic acid on

to the surface of chemically processed animal charcoal reported the data obtained

during findings was fitted for Langmuir Isotherm and found to be linear indicative of

applicability of Langmuir equation.

The data obtained from the present isotherm study of most the systems also fit

well the modified Langmuir isotherm. The linear plots of Ce / qe Vs. Ce (Fig. IIA) for

MRKG at various temperatures suggests the applicability of Langmuir isotherm. The

values of Langmuir isotherm constant Qo and b are determined from the slopes and

intercepts of the respective plots and are given in Table No. II A. The isotherm

constant Qo is a measure of the amount of dye adsorbed when the monolayer is

completed. Theoretically the values of Qo should remain constant over the

temperature studied. However, a small variation in Qo values is seen with rise of

temperature. The values of Qo are also related to capacity of adsorption. The values

of b are related the energy of adsorption. From above data of Langmuir isotherm

constants the formation of monolayer has been confirmed in the present system.

The essential characteristic of the Langmuir isotherm is expressed in terms of

dimensionless constant separation factor or equilibrium factor R1

R L = 1___

1 + b Ce

This parameters indicates the nature of the isotherm as under

RL value Type of Isotherm

RL > 1 Unfavourable

RL = 1 Linear

O < RL < 1 Favourable

R = 0 Irreversible

350

The adsorption of acid dyes is favourable onto the surface of MRKG as the

RL value in the present study falls in the type 0 < RL < 1 and the range found to

0.009 to 0.010 and is in good agreement with findings of Lodha et.al85.

4.18 Thermodynamic Parameters

The term Gibbs free energy (∆G) is the fundamental criterion of

spontaneity128. It is calculated from isotherm curves indicates the adsorption of dyes

onto MRKG. The negative value of free energy (∆G) indicates high affinity of dye to

the MRKG surface and indicate feasibility of the process and the spontaneous nature

of the adsorption128-133.

For adsorption of dye on to MRKG surface the negative values of ∆H gives

the idea about the nature of reaction i.e. exothermicity134-135. And the positive value

indicates that adsorption process in them is not a exothermic reaction which it is a

physical adsorption or weak chemical adsorption. The positive value of ∆H during

adsorption process may be attributed to the disruption of water-water hydrogen

bonding in the structural water cluster142 . A entropy change (∆S) found to be positive

for adsorption of dye onto the surface of MRKG it may be attributed to the dye

molecules which are highly solvated in solution and on adsorption on MRKG leads to

release the solvent molecule136. Also when acid dyes are dissolved in water. Water

molecules tend to form more structural cluster surrounding the hydrophobic nonpolar

moiety (NPM) of the acid dyes and plays a significant role in determining the

adsorption capacity of a specific system137-138. Thereby, when acid dyes is moved

from water to the resin phase, the water cluster surrounding the NPM of the acid dyes

anion breaks down and may lead to an increase of overall entropy130. Positive value

of ∆S indicates increased randomness at the interface, this could also be attributed to

the size of the dye molecules as a single dye molecule displaces lot of water

molecules from the adsorbent surface, as it is very large in size compared to water

molecule132.

The negative value of entropy change (∆S) during adsorption process may be

attributed in terms of restriction of the moment of the molecule to two dimension on

351

the surface as against three dimension in the table. In other words a decrease in

entropy change is indicative of the decrease in randomness of the system132-135.

The values of thermodynamics parameters are given in Table No.III. reveals

that dye adsorption MRKG is favour at lower temperature130. The thermodynamic

parameter calculated from isotherm curves indicate that the adsorption of dyes onto

MRKG with negative values of free energy (∆G) indicating high affinity of dye to the

surface, and negative values of enthalpy (∆H) gives the idea about the nature of

reaction i.e. exothermicity and randomness can be explained on the basis of negative

values of entropy (∆S).

Lodha et.al85 during their investigation calculated and reported the average

values of thermodynamics parameters ∆H, ∆S and ∆G. The values demonstrates a

spontaneous and favourable adsorption process found positive indicating endothermic

process. The relatively small values point to the formation of weak chemisorptive

bonds between methylene blue and rice husk surface. Similarly the value of standard

entropy change (∆So) are also not very large which indicates that the interaction does

not lead to a considerable change in surface configuration upon the adsorption. The

negative values of standard Gibbs energy change (∆Go) in all the cases are indicative

of the spontaneous nature of the interaction without requiring large activation energy

of adsorption. Each of the thermodynamic parameter is in narrow range of values for

all adsorbent and therefore, it may be concluded that the thermodynamic process

involved in the dye / husk interaction for all the adsorbents are more or less uniform

in nature.

Daruwala et.al111 showed during their investigation the negative value of ∆H,

∆S and ∆G. indicative of exothermic and spontaneous process and suggesting no

structural changes at the solid-liquid interface with weak bond formation between

adsorbent and adsorbate139. The observation reported indicates that rice bran is very

effective for the removal of fat soluble substances and has potential application for the

removal of organic compounds. The negative values of ∆G is a indicative of a

spontaneous process with high affinity of the dye to the surface of the adsorbent128.

Exothermicity may be explained on the basis of negative values of the enthalpy

change (∆H) in the adsorption phenomenon. A negative entropy change (∆S) may

be understood in terms of restriction of the movement of the molecules to two

dimension on the surface as against three dimensions in the bulk. In other words a

352

decrease in entropy change is indicative of the decrease in the randomness of the

system.

Daniel et.al140 reported brilliant red H.E. – 38 dye sorption mechanism on

activated charcoal as a spontaneous process. The apparent entropy change values

were almost constant over the temperature range the positive entropy characterized an

increased disorder of the system, due to the loss of water which is surrounding the dye

molecule at the sorption on the activated charcoal. It can be suggested that the

driving force for sorption process is an entropy effect. This observation were

demonstrated by other experimental results concerning organic compound sorption

mechanism141.

The adsorption enthalpy in our findings for MRKG system found to negative

indicative of exothermic process, ∆G decreases from -3.22 KJ to 4.0 KJ/mole with

increase in temperature from 30o C to 45oC Negative value of ∆Go indicates that the

adsorption process is favourable and spontaneous in nature. Our finding is in good

agreement with the findings of Sivakumar et.al134. Mishra et.al142 during their

adsorption study of dyes on low cost Mahna cake (MOC) reported that an increase in

∆G with temperature suggested high adsorption of dye at lower temperature. The

negative values of ∆H for dye adsorption indicates that the reaction is exothermic143.

Rasheed Khan144 during their adsorption study of methylene blue and malachite

green from aqueous solution on the surface of wool carbonizing waste reported values

of ∆G and ∆S were random for both dyes adsorption process and found to be

spontaneous at lower temperature145. According to Smith et.al143 the positive values

of ∆H indicates adsorption process endothermic and negative value of ∆S suggest the

probability of favourable adsorption.

According to Jayswal147 ∆G value depends on several factors such as

temperature and heat consumed released upon the uptake of the cationic dye. In their

study the ion exchanger used was amorphous in nature, thus it was expected that all

sorption sites may be energetically equivalent. The incoming cationic dye could first

occupy most favourable sites. As adsorption proceeds the sites becomes progressively

less favourable. The overall ∆G values is a result from the contribution of the above

mentioned factors. Depending on the predominant factors ∆G values vary in each

case. The negative value of ∆H indicates adsorption of dyes are exothermic in

nature148. Jayswal et.al147 also concluded that the decrease in the value of ∆S was

353

attributed to higher uptake of the dyes which is a result of high ∆S in the external

aqueous phase and a lower ∆S in adsorbent phase149-150.

354

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