Batch Adsorption of Fluoride Using Low Cost Adsorbents ... 3/Issue 6/IJESIT201406_34.pdfISSN: 2319-5967 ISO 9001:2008 Certified International Journal of Engineering Science and Innovative

ISSN: 2319-5967

ISO 9001:2008 Certified International Journal of Engineering Science and Innovative Technology (IJESIT)

Volume 3, Issue 6, November 2014

257

Batch Adsorption of Fluoride Using Low Cost

Adsorbents Prepared From Corncob and

Acacia Nilotica Stalk by KOH Activation C.B.Shivayogimath

1, M.N.Hiremath

2, Lokeshappa

3

1 Professor and Head, Dept of Civil Engineering, B.E.C. Bagalkot, Karnataka, India,

2Associate Professor, Department of Civil Engineering, AITM, Bhatkal-581320, Karnataka, India.

3Professor, Department of Civil Engineering, UBDTCE, Davanagere

Abstract; This work was focused on the batch mode adsorption of fluoride on low cost adsorbents. Granular activated

carbons were prepared from corn cob (CGAC) and Acacia Nilotica stalk (ACAG) by KOH activation, these prepared

activated carbons and processed broken waste tiles granules (TBAG) were used as solid phase material in the batch mode

of fluoride adsorption. Activated carbon and precursor material were analyzed for physical, elemental and proximate

analyses and the effect of carbonization temperatures for 600, 700, 800 and 900°C was examined. Batch mode Adsorption

study was carried out under various operational conditions, and results were compared with commercial activated

alumina (CAAG). It was observed that BET surface area and pore volume of the prepared activated carbon were found to

be 940 m2/g and 81 % for corn cob (CGAC), 1065 m2/g and 83% for acacia nilotica stalk (AGAC) and 365 m2/g and

83% for broken waste tile granules(TBAG) respectively at a carbonization of 800°C. The results show that agro residue

corn cob and Acacia nilotica trees/plants which are regarded as one of the worst weeds because of its invasiveness,

potential for spread, and economic and environmental impacts, can be used as a promising low cost precursor for the

production of activated carbon.. Batch adsorption studies reveals , that Experimental data on batch study reveals that

CAAG shown maximum fluoride removal of 92 % followed by 83 %, 81 % and 48 % for CAAG, AGAC, CGAC and

TBAG respectively. Equilibrium isothermal models of Frendlich and Langmuir fits well for the fluoride adsorption.

Index Terms: Fluoride, isotherms, batch mode, Activated Carbon, BET Surface Area.

I. INTRODUCTION

Pure water is scarce and is not easily available to all. The water may be contaminated by natural sources or by

domestic and industrial effluents. One such contaminant is fluoride. Fluoride is a salt of the element fluorine.

Fluorine is the most highly reactive element of halogen family. Small amounts of it are found in seawater, bone,

teeth and in ground water mainly as fluoride ion.[1]. The latest estimate by UNICEF 1999 suggests that around

200 million people, from among 25 countries the world over, are affected by dreadful fate of fluorosis [2]. India

and China the most populous countries of the world, are the worst affected. India is plagued with various water

quality problems due to profile contaminants mainly of geogenic origin and fluoride stands first among them.

The weathering of primary rocks and leaching of fluoride containing minerals in soils yield fluoride rich

groundwater in India which is generally associated with low calcium content and high bicarbonate ions. Rural

India which constitutes the bulk (70%) of the total population is deprived of such interventions. The population

in major parts of rural India is mainly dependent on the groundwater as an only available source of drinking

water. As a matter of quality of the groundwater is concerned it is often found to be contaminated with fluoride,

arsenic, iron, and salts. In recent years, fluoride affected health problems has emerged as major issue in rural

India

Fluoride – World Scenario

Fluoride problem is not only confined to Indian sub continent, it is global problem .The latest information shows

that fluorosis is an endemic public health problem in 25 other nations around the globe as shown in the fig1.1

The total number of people affected is not known, but conservative estimate would number in the tens of

millions.

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Fig 1.1 Countries with Endemic Fluorosis [Source Unicef Website]

Fluoride – An Indian Scenario

India is one among the 25 nations in the world, where fluoride contaminated groundwater is creating health

problems. A report of UNICEF (1999)[4] confirms the fluoride problem in 177 districts of 20 states of India as

shown in fig1.2, (WHO 2004) [6]. Andhrapradesh is also one of the fluorosis endemic states. Today India is the

seventh largest, second most populous country in the world with a land mass of 3.29 million square km with

more than 1.04 billion people [Planning Commission report]. Total population of India will exceed 1330 million

in 2020 with water consumption expected to move up by 20-40%. India possesses 16% of the world‟s

population but just 4% of its water resources. Though, surface water in India is scarce and groundwater is deep

and difficult to reach (UNICEF 2002) [4], almost 90% of drinking water needs are met with from groundwater

only. The scarcity of groundwater and presence of excess fluoride can be treated as the two most critical issues

in the Indian systems of sustainable drinking water supply.

Fig 1.2 Fluoride Map Of India. (Source CGWB 2009)

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The fluoride problem in India is primarily of hydro geochemical origin. It has been observed that low calcium

and high bicarbonate alkalinity favour high fluoride content in groundwater [7-8].Though drinking water is the

major contributor (75–90% of daily intake), other sources of fluoride poisoning are food, industrial exposure,

drugs, cosmetics, etc. Endemic fluorosis remains a challenging and extensively studied national health problem

in India. In 1991, 13 of India‟s 32 states and territories were reported to have naturally high concentrations of

fluoride in water [9], but this had risen to 20 by 1999 [10]. The most seriously affected areas are Andhra

Pradesh, Punjab, Haryana, Rajasthan, Gujarat, Tamil Nadu and Uttar Prades [11-12]. The highest concentration

observed to date in India is 48 mg/L in Rewari District of Haryana [10]. The high concentrations in groundwater

are a result of dissolution of fluorite, apatite and topaz from the local bedrock, and [13] noted the general

negative correlation between fluoride and calcium concentrations in Indian groundwater. Table 1.1 Districts Endemic for Fluorosis in Indian States [14]

SL

N0

STATE DISTRICTS ENDEMIC FOR FLUOROSIS FLUORIDE LEVEL

1 Andhra Pradesh Cuddapah, Hyderabad, Krishna, Medak, Warangal

Ananthapur, Karimnagar,Kurnool, Nalgonda

Prakasam , Chittoor , Guntur, Khammam, Mahbubnagar

,Nellore and Rangareddy

0.4 - 29.0 mg/L

2 Assam Karbi Anglong ,Nagaon 1.6 - 23.4 mg/L

3 Bihar Rohtas, Gaya, Nawada, Munger, Jamual and Bhagalpur 0.2 - 8.32 mg/L

4 Chattisgarh Durg and Dhandewala information awaited

5 Delhi West Zone ,North West Zone, East Zone, North East Zone,

Central Zone, South Zone and South West Zone

0.2 - 32.0 mg/L

6 Gujarat Ahmedabad, Amreli, Anand,Nadiad, Banaskatha, Bharuch,

Bhavnagar, Dahod, Gandhinagar, Jamnagar, Kutchh,

Junagarh, Mehsana, Navsari, Godhara, Patan, Porbandar,

Rajkot ,Narmada, Sabarkantha, Surat, Surendranagar,

Vadodara and Valsad

1.5 - 18.0 mg/L

7 Haryana Rewari, Faridabad, Karnal, Sonipat, Jhind, Gurgaon,

Mohindragarh, Rohtak, Kurukshetra, Kaithal, Bhaiwani and

Sirsa

0.2 - 48.32 mg/L

8 Jammu &

Kashmir

Doda 0.5 -4.21 mg/L

9 Jharkhand Deoghar, Pakur, Palamu,Sahabganj and Girdh 0.5 - 14.32 mg/L

10 Karnataka Dharwad, Gadag, Bellary, Belgaum, Raichur, Bijapur,

Gulbarga, Chitradurga, Tumkur Chikmagalur, Mandya ,

Bangalore Rural, Mysore, Mangalore, Shimoga and Kolar

0.2 - 7.79 mg/L

11 Kerala Palghat, Alleppy and Vamanapuram 0.2 - 5.40 mg/L

12 Madhya

Pradesh

Shivpuri, Jubua, Mandla, Dindori, Chhindwara, Dhar,

Vidhisha, Seon, Sehore, Raisen Mandsour, Neemuch,

Ujjain and Gwalior

1.5 - 4.20 mg/L

13 Maharashtra Bhandara, Chanderpur, Buldhana, Jalgaoun, Nagpur, Akola,

Amravati, Nanded, Sholapur Yavatmal

0.11 - 10.00 mg/L

14 Orissa Angul, Dhankanal, Boudh,,Nayagarh, Puri, Balasore,

Bhadrak, Bolangir, Ganjam Jagatsinghpur, Jajpur,

Kalahandi, Keonjhar, Khurda, Koraput,Mayurbhanj, Pulbani

and Rayagada

0.6 - 9.2 mg/L

15 Punjab Mansa, Faridkot, Bhatind, Muktsar, Moga, Sangrur,

Ferozpur, Ludhiana, Amritsar, Patiala Ropar, Jalandhar,

Fategarh, Sahib, Kapurthala, Gurdaspur, Hoshiarpur and

Nawanshahar

0.4 - 42.0 mg/L

16 Rajasthan Bhilwara, Ajmer, Sirohi, Tonk, Nagaur, Jalor, Jodhpur,

Sawai Madhopur, Dausa, Jaipur Sikar , Alwar, Churu,

Bharatpur, Jhunjhunun, Jaisalmer, Barmer, Pali , Rajsamand,

Banswara, Dungarpur, Bikaner, Dholpur, Karauli, Udaipur,

Chittaurgarh, Kota, Bundi, Jhalawar Ganganagar,Baran

and Hanumangarh

0.10 - 10.0 mg/L

17 Tamil Nadu Krishnagir, Dharmapuri, Erode, Salem, Coimbatore,

Thiruchirapally, Madurai,Vellore and Virudunagar

0.1 - 7.0 mg/L

18 Uttaranchal information awaited information awaited

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Literature survey reveals that, Several defluoridation techniques namely precipitation, membrane process,

electrolytic ion exchange and adsorption onto various adsorbents have been evaluated both in field and

laboratory, owing to various drawbacks like lower efficiency, no applicability on mass scale and higher costs

associated with conventional defluoridation techniques, adsorption based fluoride removal systems are emerging

as the feasible option, Among these methods, adsorption is the most convenient, effective, and economical,

especially for point-of-use applications[15-16]. Several adsorbent materials have been tried in the past to find

out an efficient and economical defluoridating agent. Activated alumina, activated carbon, activated alumina

coated silica gel, calcite, activated saw dust, activated coconut shell carbon and activated fly ash, groundnut

shell, coffee husk, rice husk, magnesia, serpentine, tricalcium phosphate, bone charcoal, activated soil sorbent,

carbon, etc., are different adsorbent materials reported in the literature. Hence in this present work,

defluoridation using activated carbons prepared from locally available Corn cob and Acacia nilotica stalk along

with broken waste mangalore tiles granules are prepared, characterized and used as adsorbents for batch mode

adsorption for the removal fluoride in drinking water.

Abatement of Fluorosis

The abatement of fluorosis through the treatment of drinking water in rural areas is a very difficult task because

of economical and technological restrictions. Defluoridation of water is the only measure to prevent fluorosis

where there is no scope for alternative source, and various different defluoridation methods/techniques have

been developed [19]. However, few among all these methods cannot be easily implemented in areas where the

problems occur. This section gives a brief overview of various defluoridation methods. Defluoridation processes

can be broadly classified into four main categories:

(i) Adsorption methods: in these methods sorbents such as bone charcoal, activated alumina, and clay are

used in column or batch systems.

(ii) Ion exchange methods: these methods require expensive commercial ion exchange resins.

(iii) Co-precipitation and contact precipitation methods: these methods co precipitate fluoride ions with

for example aluminum sulfate and lime (Nalgonda technique) ,or precipitate fluoride ion, for

example with calcium and phosphate compounds.

(iv) Membrane processes: these include reverse osmosis, electro dialysis and nanofiltration methods.

The last one is very promising for large scale pilot plants in the future. Taking into consideration all the realities

of the problem as outlined in this short review, the provision of an affordable and technologically simple

solution must obviously lie in empowering the local communities to construct feasible defluoridation systems

from local and readily available materials. There is thus a need for developing low cost methods to remove

fluoride from water. The removal of fluoride using locally available clays was studied in many countries where

the problem occurs and the development of laboratory scale defluoridation columns to study the efficiency of

fluoride removal using different sorbents is recommended for local communities.

It is well known that application of fluoride removal techniques constitutes big challenge in third world

countries. Unfortunately, of the 25 countries in the world with severe fluoride problems most have low

economies. Then only complementary approach to be developed in the future depending on the utilization of

locally available low cost sorbents for adsorption of fluoride.

II. MATERIALS AND METHODS

Raw Materials

The first precursor material used was corncob. Dried whole corncobs which were crushed and

separated from pith/chaff are sieved to mesh size 12x16 (1.2-0.7 mm) as precursor material that is corn-

cob granules of 1.2-0.7 mm grain sizes were obtained from Venkateshwara Agro Products, Pvt Ltd,

Gadag.

The second precursor material used was acacia nilotica stalk, Acacia Nilotica trees are growing

abundantly in entire north Karnataka region as weed and which is generally being used as a fuel wood

19 Uttar Pradesh Varanasi, Kaunauj, Pratapgarh, Farukhabad, Raebareily,

Unnao and Hardoi

0.2 - 25.0 mg/L

20 West Bengal Birbaum, Bankura, Malda, Purulia, 24 South Parganas,

Dakshin Dinajpur and Uttar Dinajpur

1.1 - 14.47 mg/L

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by the local poor people. The precursor material i.e. acacia nilotica stalk of 4-6 mm in diameter was

cut into length of 10-20 mm in size, was collected from the field of Mundaragi area of Gadag district.

The broken tiles were collected locally and it was washed several times to remove earthy matter and

finally was washed with distilled water. These were air dried and ground manually to the desired mesh

size of 20x40

Materials for Solid Phase

Granular Activated carbon produced from the corncob (CGAC), acacia nilotica stalk (AGAC) and commercial

activated carbon in the form of activated alumina (CAAG) and natural broken waste tiles granules (TBAG) were

used as the adsorbent. For typical experiment desired fraction of activated carbon was washed with distilled

water in order to remove the fines, dried and required quantity of was soaked overnight in distilled water for

aeration. Activated carbon thus de aerated was used as the solid phase in batch and column adsorption of

fluoride.

Materials for Liquid Phase

Synthetic fluoride solution was used as liquid phase in all the experiments. Test standard solutions were

prepared by appropriate dilution of the freshly prepared stock solutions.

Preparation of fluoride solution

1. Stock solution was prepared by adding 221 mg of anhydrous sodium fluoride and diluted to 1000ml

with distilled water.

2. Then standard solution was prepared by taking 100ml of prepared stack solution and diluted to 1000ml

with distilled water.

Chemicals and Reagents Used

All the chemicals and reagents used were of analytical grade and procured from Merc Specialties Private

Limited, Mumbai. Following are the chemicals used in this study.

Potassium Hydroxide (KOH Pellets)

Hydrochloric acid of 3 N (HCL)

Instruments Used

Instruments which were used in the studies are briefly discussed below. List of Instruments and their

Manufacturers

1. Magnetic Stirrer Remi Equipments, New Delhi

2. Digital Weight Balance Sartouier, Gottingen, Germany

3. Muffel Furnace

4. Heating Oven

5. Peristaltic Pump Murhopye Scientific Company, Mysore

III. PREPARATION AND CHARECTERIZATION OF ACTIVATED CARBON

Preparation of Granular Activated Carbon from Corn Cob and Acacia Nilotica Stalk by KOH Activation

Chemical impregnation was done by dissolving 25g of KOH pellets in 1 liter of distilled water, then oven dried

Cooled precursor materials such as is corn-cob granules and acacia nilotica stalk pieces of 100 grams were

thoroughly mixed separately in a beaker containing the KOH solution, and agitated on a magnetic stirrer at 80

for 1 hour; after one hour of impregnation , the beaker is taken out of the magnetic stirrer and material is

strained out, cooled and washed 4 to5 times with distilled water till we get pH of washed water near to 7. Then

the washed precursor material is dried in the oven by keeping them for 24 hours at 110± 5 ; after 24 hours, the

oven dried material were taken out of oven and cooled to room temperature, then the material is kept in the

muffle furnace for carbonization process at 600 for 2 hour. After two hours of carboneous process the

materials were taken out, cooled and then activated by keepingt in a beaker which contains 3N HCl, for 30 min

at 80 on a magnetic stirrer, after this once again the said material is washed with distilled water for 4 to 5

times or till one get pH of washed water near to7. Then the material is kept in a oven for 12 hours under 110±

5 for drying. After 12 hours of oven drying, material is taken out of the oven and used for further studies. The

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procedure is repeated for different temperatures of 600,700, 800 and 900 separately to assess the effect of

carbonization temperature on characteristic properties of prepared activated carbons.

Activation of Waste Tile Granules

Chemical activation was impregnated with potassium hydroxide (KOH) to remove inert material present in

it.15g of KOH pellets were dissolved in 1 liter of distilled water then the oven dried and cooled precursor

material granules of broken waste tiles was thoroughly mixed with KOH solution in a beaker and kept on

magnetic stirrer at 80 for 1 hour. Then the beaker taken out of the magnetic stirrer and cooled and

washed 4 to5 times with distilled water till we get pH of washed water to nearly 7. Washed precursor

material was kept in the oven for 24 hours at 110±5 , after 24 hours the oven dried material were taken

out from oven and a l lo w i t to coo l . These granules were kept in beaker which contains 0.2N HCl for 30

min at 80 on magnetic stirrer. After that once again the said material was washed with distilled water

for 4 to 5 times or till we get pH of washed water as 7.Then the material is dried out and kept in a oven for

12 hours under 110± 50

.

Fig 1.3 Processed Waste broken tiles granules

Fig 1.4 Images of (a) maize (b) corn cob (c) corn cob granules (d) prepared activated carbon

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Fig 1.5 Images of (a) Acacia Nilotica Tree (b) Precursor material (c) Oven dried precursor material (d) Prepared

Granular activated carbon

CHARACTERIZATION OF PREPARED GRANULAR ACTIVATED CARBON The porous properties of the prepared activated carbons were analyzed to observe developed SEM images as

replica of their porous surfaces and surface area analysis were carried out using a scanning electron microscope

JSM -5610LV and gas sorption analyzer NOVA 22OO, Quatachroma respectively. Other tests on moisture

content, ash content and iodine number were carried out as per the standard test procedures, of ARE 2752: 1995

20]. Tests were conducted at NITK Suratkal , and results are presented in tables from

1.3 -1.7

EXPERIMENTAL SETUP FOR BATCH ADSORPTION

For batch adsorption studies, conical flask of 250 ml capacity with tight fitting rubber cock to avoid evaporation

or spilling of during agitation, was used for agitation of the adsorb ate solution (fluoride solution) with the

adsorbent (Activated Carbon). Adsorption experiments were conducted in different batches for the adsorbents,

where the adsorbent bed height/dose, pH of the solution, initial ion fluoride concentration and flow rate were

changed for the different sets of experiments

(a) (b) Fig 1.6 (a) Schematic diagram (b) Photographic image of the batch adsorption experimental set up

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Batch Adsorption Study

The batch adsorption studies include the effect of various experimental conditions such as pH, initial

concentration, adsorbent dosage, contact time, agitation speed and equilibrium isothermal modeling at room

temperature and the kinetics of adsorption at different temperatures in 250 ml conical flask containing 100 ml

solution of fluoride. The influence of pH, rotation speed, adsorbent dosage, initial fluoride ion concentration and

contact time on the sorption rate is discussed by means of typical graphs from 1.11 -1.15 in result and discussion

section.

Kinetics study was carried out by adding 0.1 g of adsorbent into a series of 250 ml conical flask containing 100

ml solution of fluoride and was shaken in a mechanical shaker, After this the samples were centrifuged and the

concentrations were analyzed in a fluoride electrode (Orion meter). Each experiment continued until equilibrium

conditions were reached when no further decrease in the fluoride concentration was measured. The equilibrium

adsorption capacity was calculated from the following relationship.

V

(1)

Where,

qe (mg/g) is the equilibrium adsorption capacity,

Ce is the fluoride concentration at equilibrium (mg/L),

V is the volume of solution (L) and w is the weight of adsorbent (g)

Batch Adsorption Isothermal Models The quantity of adsorbate that can be taken up by an adsorbent is a function of both the characteristics and

concentration of adsorbate and the temperature. The characteristics of the adsorbate that are of importance include;

solubility, molecular structure, molecular weight, polarity, and hydrocarbon saturation. Generally, the amount of

material adsorbed is determined as a function of the concentration at a constant temperature, and the resulting

function is called an adsorption isotherm models. Equations that are often used to describe the experimental isotherm

data were developed by –

Freundlich

Langmuir and

Branauer, Emmet and Teller (BET Isotherm)

Of the three, the Freundlich isotherm is used most commonly to describe the adsorption characteristics of activated

carbon used in water and waste water treatment, derived empirically in 1912, the Freundlich isotherm is defined as

follows:

(i) Freundlich Isotherm

The linear form of the Freundlich isotherm is,

nCkmx /1*/ (2)

Taking log on both sides

Log x/m = log k + 1/n Log C

Where, x/m = amount of sorbate adsorbed per unit weight of adsorbent at equilibrium,

X = Amount of adsorbate removal (mg/L)

M = Mass or weight of the adsorbent

C = Equilibrium concentration of adsorbate in solution.

K = An empirical constant related to sorption capacity

n = An empirical constant related to sorption intensity.

The equation is of the type Y = C + m*X.

Where, C = Log10 k

Y = Log10 x/m,

(3)

X = Log10 C and m = 1/n

(4)

The plot of, log X/M versus log C gives a straight line with slope 1/n and intercept = log K, knowing slope and

intercept 1/n and “K” are calculated.

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Experimental data are often plotted in this manner as a convenient way of determining whether removal of materials

from solution is accomplished by adsorption and as a means of evaluating the constants “K” and “n”.

(ii) Langmuir Isotherm

The Langmuir theory based on the belief that adsorption is a type of chemical combination or process of the

adsorbed layer which is unimolecular

The theory assumes

1. That there is a uniform energy of adsorption on the surface.

2. That maximum adsorption corresponds to a saturated monolayer of solute molecules on the surface

and

3. That there is no transmigration of adsorbate in the plate of the surface.

The Langmuir Isotherm is used to describe single – layer adsorption and the linear from the Langmuir‟s

isotherm is.

x/m = a b c / (1 + b c)

(5) Or

C/ (x/m) = 1/ab + c/a

Where, x/m = Amount of adsorbate adsorbed per unit weight of adsorbent

C = Equilibrium concentration of adsorbate in solution after adsorption or saturated concentration.

„a‟ are empirical constants.

The equation is of the type

Y = C + mX,

(6)

Where C = 1/ab and m = 1/a. the plot of C/ (X/M) versus C produces a straight line graph The value of

constants 1/b and 1/ab can be calculated by intercept and slope.

1/ ab = intercept; slope = 1/a

Intercept = 1/b x slope; b = slope / intercept.

The plot of linearised Langmuir isotherm [C/ (x/m) versus C],

From graphs „a‟ and „b‟ are evaluated by knowing slope and intercept. This can further be authenticated by

least square analysis.

The essential characteristics of Langmuir Isotherm can be expressed in terms of dimensionless constant separation

factor of equilibrium parameter as,

R = 1/[(1 + a) C0]

Where R = Co-relation coefficient

a = Langmuir constant and

C0 = Initial solute concentration (mg/L)

From the above equation it has been given parameter indicating the shape of the isotherms is as follows.

Table 1.2 Parameter indicating shape of Isotherm

VALUES OF R TYPE OF ISOTHERM

R > 1 Unfavourable

R = 1 Linear

0 < R > 1 Favourable

R = 0 Irreversible

IV. RESULTS AND DISCUSSIONS

Surface morphology examined by SEM images given in fig 1.8-1.10 clearly revealed the surface texture and

porosity of the adsorbent with holes and small openings found on the surface indicating that it would increase

the contact area and facilitate pore diffusion during adsorption, it was also observed that material carbonized at

800 was fragmented and highly porous surface texture compared to other SEM images. The effect of

activation temperature clearly shows that as the carbonization temperature increases surface area also increases

this is because, at lower temperature chemical residues left in the carbon block the pore structure, even washed

with acid after carbonization process, thereby reducing pore volume. It was also observed that at 900 there is

little reduction in the surface area this is because, higher temperature leads to excess carbonization, excess

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carbonization leads to the formation more ash there by produces larger diameter pores by pore widening and

pore collapse, this also result in a decrease of surface area.

The SEM was used to get proper images to determine structure and distribution of pores that are present on

the surface of the processed waste broken tiles granules; it also determines the nature of the size of the pore.

From fig 1.8-1.9 it was evident that 20x40 mesh sized granules had larger pores.

Effect of pH The adsorption of fluoride was studied over a pH range of 2.5 to 7.5 as shown in Fig 1.11. The effect of pH on

fluoride adsorption was studied at an initial fluoride concentration (C0) of 5 mg/L with an adsorbent dose (m) of

1 g/L. It was seen from Fig 1.11 that the fluoride removal increased with decrease in pH values and as the pH

was increased from 2.5 to 7.5, the fluoride removal efficiency was decreased considerably for all the adsorbents.

The adsorption of other ions gets affected due to the strong affinity for H+ and OH

- ions on the adsorption sites.

Because of higher H+ ion concentrations at lower pH the negative charges on the adsorbent surface get

neutralized. This is in turn reduces the hindrance to diffusion of negatively charged fluoride ions and gives rise

to the more active surface for adsorption [21]. However, no appreciable increase in fluoride removal was

observed within a pH range of 2.5 to 4.5. It may be ascribed to the fact that initially at lower pH, the formation

of weak hydrofluoric acid took place which retards the rate of fluoride adsorption. The maximum fluoride

removal was achieved at a pH of 4.5. Therefore an initial pH of 4.5 were selected for the rest of the adsorption

study.

Experimental Conditions:

Initial concentration 5 mg/L

Adsorbent Dose 1g/l

Contact Time 90 Min

Agitation speed 120 rpm

Effect of Initial Ion Concentration

The effect initial fluoride ion concentration on the adsorption of fluoride is shown in Fig 1.12. It was quite

evident from that the percentage fluoride removal was decreased with the increase in initial concentration of

fluoride. At higher fluoride concentration the availability of active sites on the adsorbent is less which causes

lower adsorption efficiency [22]. The maximum fluoride removal was achieved at initial concentration of 3.0

g/L. So it can be concluded that the percentage uptake is highly dependent on initial concentration of fluoride

ions.


pH 4.5

Adsorbent Dose 1g/l

Contact Time 90 Min


Effect of Agitation Speed

The effect of agitation speed on the adsorption of fluoride was studied over a agitation speed range of 30 to 150

rpm. It was quite evident from fig 1.13 that the uptake of fluoride ions increased with the increase in the

agitation speed. It was further revealed that maximum fluoride removal was achieved at agitation speed of 120

rpm. So it can be concluded that the percentage uptake is highly dependent on agitation speed of the batch

reactor, this is because of the resistance to the mass transfer which mainly lie around the surface of adsorbent

and breaks down with increasing agitation speed, as a result of this more ions penetrates into the adsorbents with

ease.


pH 4.5

Initial ion concentration 1mg/L

Adsorbent dose 3.0 g/L

Contact time 120 min

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Effect of adsorbent dosage The percentage uptake of fluoride as a function of adsorbent dose at an initial F

- ion concentration is shown in

fig 1.14 .The percent removal of fluoride increased with increase in adsorbent dose and a maximum removal

was obtained with an adsorbent dose of 3 g/l. The higher removal capacity at higher adsorbent dose attributed to

the availability of more effective surface area of the prepared adsorbent for adsorption [23].


pH 4.5


Contact Time 90 Min


Effect of Contact Time The effect of agitation time on the adsorption of fluoride ions is shown in Fig 1.15. It was quite evident that the

uptake of fluoride ions increased with the lapse of time. It was further revealed that maximum fluoride removal

was achieved at 120 minute. So it can be concluded that the percentage uptake is highly dependent on initial

concentration of fluoride ions. The plot of the fluoride ions uptake versus time curves is single, smooth and

continuous leading to saturation which indicates the possible monolayer coverage of fluoride ions on the surface

of the adsorbent [24].


pH 4.5


Adsorbent dose 3.0 g/L


Table 1.3 Elemental Analysis of Corncob and Acacia nilotica stalk the Precursor Materials

Properties Carbon Hydrogen Oxygen Nitrogen

Corn cob 44% 7.0% 47% 0.4%

Acacia nlotica stalk 48% 6.0% 44% 0.4%

Table 1.4 Charecterization of Prepared CGAC

S. NO. TEST CONDUCTED AT 600 AT 700 AT 800 AT 900

1. Ash content % 6.8 6.2 3.9 6.4

2. Moisture content % 4.3 3.6 2.8 3.4

3. Surface area m2/g 565 672 940 888

4. Iodine number 410 580 860 810

5. Pore Volume 34% 49% 81% 78%

Table 1.5 Surface area, ash content and moisture content of AGAC

SL.NO. CHARACTERISTIC AT 6000C AT 7000C AT 8000 C AT 9000 C

1 Ash content % 5.8 4.9 3.7 4.4

2 Moisture content % 4.1 3.8 2.4 3.5

5 Surface area m2/g 590 880 1065 910

6 Iodine number 480 720 980 840

7 Pore Volume 44% 61% 83% 68%

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Table 1.6 Chemical Characterization of Broken tiles granules

Chemical

Composition

Sio2 Fe2 03 CaO MgO Al2O3 SO3

Value in % 72.9 3.70 2.00 0.80 14.51 0.55

Table 1.7 Charecterization of broken tiles granules

Charecteristics

property

Ash content Moisture content Surface area Iodine Number Pore Volume

Value s 6.8% 4.5% 365 m2/g 245 28%

Fig 1.7 SEM Images of granular activated carbon carbonized at 800 0C of Corncob (CGAC)

Fig 1.8 SEM Images of granular activated carbon carbonized at 800 0C of Acacia Nilotica (AGAC)

Fig 1.9 SEM image of Processed Waste broken tiles granules

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Fig 1.10 Effect of pH Fig 1.11 Effect of initial concentration

Fig 1.12 Effect of Agitation speed

Fig 1.13 Effect of adsorbent dose Fig 1.14 Effect of contact time

Equilibrium Isothermal Modeling

The distribution of fluoride between the liquid phase and the solid phase is a measure of the position of equilibrium

in the adsorption process and can be expressed by isothermal modeling. The relationship between the amount of a

substance adsorbed at constant temperatures and its concentration in the equilibrium solution is called as the

adsorption isotherm [25].Several models have been published in the literature to describe experimental data for

adsorption isotherms, with the Langmuir and Frendlich models being frequently employed. In our work, both

models were used to describe the relationship between the amount adsorbed by TBAG, AGAC, CGAC and CAAG

and its equilibrium concentration.

Data obtained for adsorption are presented in fig 1.16 to fig 1.23 to compare the fitting of frendlich and Langmuir

isotherms respectively, with the equilibrium data. It can be seen that, the frendlich isotherm fits the data better than

the Langmuir isotherm as evidenced by the higher correlation coefficient for the former compared to the later.

Estimated values of the model parameters are given in 1.16 to fig 1.23. It can be observed from the tables 1.8 -1.9

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that values of correlation coefficient for frendlich isotherms are in the range of 0.966 to 0.977, where as for langmuir

the values are in the range of 0.749 to 0.827. It clearly indicates that frendlich isotherms fit well fluoride adsorption

equilibrium

Frendlich Isothermal Modeling

Fig 1.15 Fit for Frendlich isothermal model for TBAG

Fig 1.16 Fit for Frendlich isothermal model for AGAC

Fig 1.17 Fit for Frendlich isothermal model for CA

Fig 1.18 Fit for Frendlich isothermal model for CGAC

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Langmuir Isothermal Modeling

Fig 1.19 Fit for Langmuir isothermal model for TBAG

Fig 1.20 Fit for Langmuir isothermal model for AGAC

Fig 1.21 Fit for Langmuir isothermal model for CGAC

Fig 1.22 Fit for Langmuir isothermal model for CAAG

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Table 1.8 Experimental parameters of Frendlich Equilibrium isothermal model

Adsorbents Studied Value of

„ n „

Value of constant

„KF‟

Coefficient correlation value „R2‟

TBAG 0.43 2.44 0.977

AGAC 0.73 0.11 0.977

CGAC -0.95 0.61 0.947

CAAG 1.63 0.43 0.966

Table 1.9 Experimental parameters of Langmuir Equilibrium isothermal model

Adsorbents

Studied

Value of

„ K „

Value of constant

„Q0‟

Coefficient correlation value „R2‟

TBAG 0.44 1.47 0.827

AGAC 0.13 -1.06 0.836

CGAC 0.11 -0.753 0.793

CAAG 0.19 -1.91 0.749

V. CONCLUSION

Following are the conclusions drawn from the present investigation on „Batch Adsorption of Fluoride using Low

Cost Adsorbents Prepared from Corncob and Acacia Nilotica Stalk by KOH Activation‟

It was revealed from the studies, that low cost adsorbents AGAC and CGAC prepared from acacia

nilotica stalk and corn cob have the higher potential for removing fluoride from drinking water,

It was revealed from the studies, that indigenous raw materials and agro residues like, corn cob and

inferior wood stalks of Acacia Nilotica, can profitably be exploited and used as potential raw materials

(precursor materials) for the preparation of highly porous „Activated Carbon‟, which is now a day‟s

assuming ever increasing importance, in the light of growing awareness in our society against the

menace of environmental pollution.

From the above study it can be concluded that highly porous Granular Activated carbon with surface

area of 1065 m2/g and 940 m2/g can be produced from acacia nilotica stalk corn cobs respectively. To

produce carbon with high surface area and pore volume KOH treatment is a preferred route of

activation. For KOH activation the temperature between 750-790°C is optimum for getting highly

porous carbon with pore size, after which the widening of pores begins and product starts becoming

more and more mesoporous.

It was also revealed from the cost analysis, that cost of the prepared low cost adsorbents

TBAG,AGAC,CGAC and CAAG are Rs.160/Kg, Rs.275/Kg, Rs.265/Kg and Rs.965/Kg

respectively, have proved to be cost effective compared to the commercial activated carbon.

The operational parameters such as pH, initial fluoride concentration, adsorbent dose and contact time

were found to have an effect on the adsorption efficiency of TBAG, CGAC, AGAC and CAAG.

Experimental data on batch study reveals that CAAG shown maximum fluoride removal of 92 %

followed by 83 %, 81 % and 48 % for CAAG, AGAC, CGAC and TBAG respectively.

Values of correlation coefficient for frendlich isotherms are in the range of 0.966 to 0.977, where as for

langmuir the values are in the range of 0.749 to 0.827. It clearly indicates that frendlich isotherms fit well

fluoride adsorption equilibrium

It was revealed from the study, that adsorption process is highly dependent on pH and works best only in a

narrow pH range (4-6). High concentration of total dissolved salts (TDS) can result in fouling of the

alumina bed. The regeneration is required after every 4–5 months and effectiveness of adsorbent for

fluoride removal.

ACKNOWLEDGEMENT

The authors acknowledge the Head of the department of Material Science, NITK, Surathkal, for providing help

in undertaking surface area analysis, particle size analysis and SEM report.

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