Cover page corrected - 1shodhganga.inflibnet.ac.in/bitstream/10603/36248/14... · using LCV (Leuco crystal violet) by the modification of reported procedure [007]. Working standards

CHAPTER 8

REUSABILITY OF ADSORBENTS

8.1. Introduction

8.2. Experimental

8.3. Reusability of adsorbents after desorption of arsenic (III)

8.4. Reusability of adsorbents after desorption of antimony (III)

8.5. Reusability of adsorbents after desorption of vanadium (V)

8.6. Conclusions

Chapter 8: Reusability of Adsorbents

[348]

8.1 Introduction

he austere health alarm has constrained to think over the maximum contamination

level of metals that are toxic in nature and present in drinking water. The World

Health Organization has assigned maximum contamination level of 0.005µgml-1

for antimony in drinking water. The Bureau of Indian Standards has assigned 0.2µgml-1

as maximum contamination level for vanadium (V) whereas the U.S. Environmental

Protection Agency (USEPA) recently revised the previous maximum contaminant level

(MCL) for arsenic in drinking water from0.05µgml-1

to 0.01µgml-1

in response to new

health effects studies [001].

The new arsenic standard for drinking water will require thousands of drinking water

systems to install arsenic removal treatment processes or modify their existing treatment

to meet the new standard.

A handful of technologies including ion exchange, lime softening, coagulation,

filtration/membrane processes etc. have been adopted for the remedy but adsorption has

been observed to emerge as qualifying for best available technology for the removal of

toxic metal [002].

Advances in adsorption technology have been lately made to meet the demands. The

application of adsorption has expanded rapidly because of sharply rising environmental

requirements.

T

REUSABILITY OF ADSORBENTS

CHAPTER

8


[349]

Desorption of inorganic contaminantsfrom the adsorbent is rapidly gaining recognition

owingto its importance to the fate, toxicity, and transport ofcontaminantsin the

environmental system. The release of toxic metal/s from the adsorbent in significant

concentrations, either in the environmentalor biotic mediums, would be a risk for living

organisms. Thus, going hand-in-hand with these advances,thedesorptionof metal ions

from the adsorbents andreversible adsorption of arsenic on adsorbent have been

investigated which translate into better performance successfully contributing to the

regeneration of adsorbent and thus the reusability of adsorbent.

The mobility of toxic metal in water depends on water quality variables and desorption

from the adsorbent found in the aqueous phase [003,004]. A relatively significant

number of studies have considered the role of phosphate for its chemical similarities to

arsenic and antimony [005]. Since most drinking water distribution systems contain

many iron particles, such as corrosion by-products from corroding iron distribution

pipes, it is reasonable to assume that they could adsorb metal ions over time if arsenic is

present in the distribution system water. But the release of metal ion back into the

distributed water due to changes either in hydraulic (mechanical) or chemical processes

(such as pH) resulting in elevated levels of toxic metal ion exposure at the consumers’

taps poses concern. “Metal release” could be par metal-containing particles in the water.

Thus, with the limited knowledge related to release of soluble metal ions from

adsorbents, the objectives of this research were to: (1) examine the effect of contact

time on the desorption of toxic metal ion from adsorbents; (2) investigate the effect of

sodium hydroxide on the soluble release of metal ion from adsorbent into the water; (3)

investigate the effect of orthophosphate on the soluble release of metal ion from

adsorbent into the water.

The Chapter examinesdesorption of respective toxic metals from adsorbent/s under

optimized conditions and the study of the desorption efficiency of adsorbent and hence

the reusability of adsorbent/s for purification of water from toxic metal/s.


[350]

8.2 Experimental

8.2.1 Materials and methods

� Preparation of stock solutions

Leucocrystal violet solution (250µgml-1

) was prepared by adding 250mg of leucocrystal

violet (4,4’,4”-methylidynetris-(N,N’-dimethyl aniline)) in 200ml of double distilled

water and 3·0ml of 85·0% phosphoric acid to a volumetric flask and shaken gently until

it gets dissolved. The volume of the solution was made up to 1liter in a standard

volumetric flask.

Potassium iodate (1·0%) was prepared by dissolving 1·0gram of potassium iodate in

100ml of double distilled water. The volume of the solution was made up to 100ml in a

standard amber volumetric flask.

� Methodology for the desorption of metal ions

The adsorbent/s (0·1gram) used for adsorption of 100µgml-1

of the respective metal ion

(arsenic (III), antimony (III) and vanadium (V)) was separated from the solution by

filtration using Whatman filter paper and washed gently with water to remove

unadsorbed metal ion. The spent adsorbent was agitated for equilibrium time with 50 ml

of desorption media. Two desorption media were prepared (i) using 0·1MNaOH

solution (ii) using 0·1M potassium dihydrogen phosphate with phosphate as the

desorbing ligand to ensure a large excess of phosphate with respect to total metal ion.

The desorbed metal ion was estimated using UV-VIS spectrophotometry.

� Spectrophotometric methodology for the determination of metal ion/s

The concentration of the respective metal/s was determined spectrophotometrically

using LCV (Leuco crystal violet) by the modification of reported procedure [007].

Working standards were prepared by appropriate dilution of the stock solution. A 0·5M

solution hydrochloric acid and sodium hydroxide (obtained from Qualingens) were

prepared. An aliquot of the sample containing 0·16 – 1·6µgml-1

of respective metal ion

was taken in a 25ml volumetric flask. Then 2·0ml of potassium iodate was added


[351]

followed by the addition of 1·0ml of hydrochloric acid solution. The reaction mixture

was gently shaken followed by the addition of 1·0ml of LCV solution and 4-5 drops of

2·0N sodium hydroxide solution. The solution was kept in a thermostat maintained at

40°C for 5 minutes. The pH of the aliquot obtained was maintained at pH 5·5-6·5 (for

arsenic (III)) pH 6·0 (for antimony (III)) and pH (8·0) for vanadium (V). The volume

was made up to 25ml with double distilled water in a standard volumetric flask. The

absorbance was measured at λmax (592 nm) against a reagent blank.

The concentration of metal ion in the supernatant was estimated spectrophotometrically.

A linear calibration graph, absorbance vs. concentration of the crystal violet produced

from the reaction of liberated iodine with LCV, which is directly proportional to the

concentration of metal ion in solution. The concentration of metal in each unknown

solution was calculated from the calibration curve. The reagent blank does not indicate

any noticeable absorbance at the chosen wavelength. The percentage of the metal

adsorbed was calculated using Equation 8.1:

% metal ion adsorbed = [(Ci – Ce) / Ci] ×100 (8.1)

Amount of metal ion adsorbed (qe) was calculated from the relationship

qe = {(Ci – Ce) × V}/m (8.2)

where Ci was the initial concentration of metal ion (µgml-1

), Ce was the final

concentration of metal ion in solution after equilibrium was attained (µgml-1

), V was the

volume of the metal ion solution (l) and m was the mass of the adsorbent (g) used.

8.3 Reusability of adsorbents after desorption of arsenic (III)

8.3.1 Desorption of arsenic (III) using 0·1MNaOH

The optimum contact time required for desorption of respective metal ion was

investigated wherein the amount of arsenic (III) desorbed from the adsorbent was

obtained from batch experiment. The adsorbent (arsenic (III) adsorbed) was exposed to

desorption medium during 60-1500 minutes using 0·1M NaOH as desorbent and

studied with respect to time.


[352]

Figure 8.1. Desorption of arsenic (III) from (a) MMT, (b) MMT-1, (c) MMT-2, (d) MMT-

3, (e) CHITO-B, (f) MMT-4, (g) MMT-5 using NaOH

0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

% A

s (

III)

Deso

rbed

Contact Time/minutes

0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

% A

s (

III)

De

so

rbe

d


0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

55

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

5

10

15

20

25

30

35

40

45

50

55

% A

s (

III)

Deso

rbed


(a) (b)

(c) (d)

(e) (f)

(g)


[353]

The desorption of arsenic (III) from MMT was observed to increase from 1·20% to

29·00% during the contact time of 60 minutes and 720 minutes respectively after which

no appreciable increase in desorption was observed. Desorption of arsenic (III) from

MMT-1 was observed to increase from 8% to 30% with increase in contact time from

60 minutes to 720 minutes respectively. The desorption of arsenic (III) from MMT-2

was observed to increase from 10% to 39% during the contact time of 60 minutes and

900 minutes respectively. The arsenic (III) desorbed from MMT-3 was observed to

increase from 11% to 34% during the contact time of 60 minutes and 720 minutes

respectively as shown in Figure 8.1(d).

The desorption of arsenic (III) from MMT-4 was observed to increase from 5% to 44%

during the contact time of 60 minutes and 720 minutes respectively. The arsenic (III)

desorbed from CHITO-B was observed to increase from 9% to 51% during the contact

time of 60 minutes and 600 minutes respectively as shown in Figure 8.1(f). The arsenic

(III) desorbed from MMT-5 was observed to increase from 2% to 58% during the

contact time of 60minutes and 600 minutes respectively. Thus, CHITO-B shows the

minimum contact time required for maximum desorption of arsenic (III).

Hence, an optimized time of 720 minutes can be framed out from the batch experiment

of desorption with respect to time.

� Reusability of adsorbent

Desorption of arsenic (III) from MMT using 0·1M NaOH was observed to be 21%

during first cycle that decreased up to 6% during the fifth cycle. MMT was again

exposed to 100µgml-1

of arsenic (III) solution after every desorption cyclewherein the

adsorption capacity of MMT was observed to decrease from 90% to 14% in the second

cycle as shown in Figure 8.2. The total amount of arsenic (III) retained by MMT after

five cycles was observed to be 2862µg.


[354]

Figure 8.2. Reusability of adsorbent (a) MMT, (b) MMT-1, (c) MMT-2, (d) MMT-3,

(e) CHITO-B, (f) MMT-4, (g) MMT-5

No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

% %

% %

%

% %

No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5No. of Cycles No. of Cycles

No. of Cycles No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As(III) Adsorbed

As (III) Desorbed

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (II) Desorbed

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As(III) Adsorbed

As (III) Desorbed

(e) (f)

(g)

(a) (b)

(c) (d)


[355]

The MMT-1 and MMT-2 were found to desorb 30% and 39% arsenic (III) respectively

in the first desorption cycle when the arsenic (III) adsorbed adsorbents were treated

with desorbent medium. After first desorption cycle, the adsorption capacity of MMT-1

and MMT-2 was observed to decrease from 97% to 17% and 99% to 20% respectively

in the second cycle as shown in Figure 8.2. The total amount of arsenic (III) retained by

MMT-1 and MMT-2 after five cycles was observed to be 2212µg and 2294µg

respectively.The MMT-3 was found to desorb 34% of arsenic (III) during first cycle

when the metal ion adsorbed adsorbent was treated with desorbent medium. The

adsorbent was then exposed to 100µgml-1

of arsenic (III) solution wherein the

adsorption efficiency of was observed to decrease from 98% to 24% in the second cycle

as shown in Figure 8.2. The total amount of arsenic (III) retained by MMT-3 after five

cycles was observed to be 2968µg.

The MMT-4 and CHITO-B were found to desorb 44% and 45% arsenic (III) when the

metal ion adsorbed adsorbents were treated with desorbent medium. After first

desorption cycle the adsorbent was again exposed to 100µgml-1

of arsenic (III) solution

wherein the adsorption efficiency was observed to decrease from 98% to 35% in MMT-

4 and 93% to 29% in CHITO-B respectively in the second cycle as shown in Figure

8.2. The total amount of arsenic (III) retained by MMT-4 and CHITO-B after five

cycles was observed to be 3147µg and 3149µg respectively.

Table 8.1. Total amount of arsenic (III) retained after five adsorption - desorption cycles

S.No. Adsorbent Arsenic (III) retained

µg

01 MMT 2445

02 MMT-1 2294

03 MMT-2 2212

04 MMT-3 2988

05 MMT-4 3147

06 CHITO-B 3149

07 MMT-5 3307


[356]

The MMT-5 was found to desorb 58% of arsenic (III) when metal ion adsorbed

adsorbent was treated with desorbent medium. After first desorption cycle the adsorbent

was again exposed to 100µgml-1

of arsenic (III) solution wherein the adsorption

capacity of MMT-5 was observed to decrease from 98% to 34% in the second cycle.

The total amount of arsenic (III) retained by MMT-5 after five cycles was observed to

be 3307µg (Table 8.1).

8.3.2 Desorption of arsenic (III) using 0.1M potassium dihydrogen phosphate

The desorption of arsenic (III) from the adsorbent had been investigated from batch

experiment with respect to time. The adsorbent was exposed to desorption medium

during 60-1500 minutes using 0·1M potassium dihydrogen phosphate.

The desorption of arsenic (III) from MMT was observed to increase from 12% to 35%

with an increase in contact time of 60 minutes and 600 minutes respectively. The

desorption of arsenic (III) from MMT-1 was observed to increase from 10% to 42%

during the contact time of 60 minutes and 600 minutes respectively. The MMT-2 was

observed to show increase in desorption from 12% to 46% during the contact time of 60

minutes and 900 minutes respectively. The MMT-3 was observed to show an increase

in desorption from 12% to 34% during the contact time of 60 minutes and 600minutes

respectively as shown in Figure 8.3.

The desorption of arsenic (III) from MMT-4 was observed to increase from 10% to

44% during the contact time of 60 minutes and 720 minutes respectively. The

desorptionof arsenic (III) from CHITO-B was observed to increase from 11% to 45%

during contact time of 60 minutes and 600 minutes respectively. The MMT-5 was

observed to show an increase in desorption from 10% to 44% during the contact time of

60 minutes and 720 minutes respectively.


[357]

Figure 8.3. Desorption of arsenic (III) from (a) MMT, (b) MMT-2, (c) MMT-1,

(d) MMT-3, (e) CHITO-B, (f) MMT-4, (g) MMT-5 using phosphate

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Ad

so

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


0 200 400 600 800 1000 1200 1400 1600

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% A

s (

III)

Deso

rbed


(a) (b)

(c) (d)

(e) (f)

(g)


[358]

� Reusability of adsorbents

Desorption of arsenic (III) from the adsorbents using dihydrogen phosphate at high

arsenic (III) loading was investigated within the contact time of 600 minutes wherein

desorption from MMT was observed to be 35% that decreased up to 14% after five

cycles.

The MMT-1 and MMT-2 were found to desorb 42% and 46% arsenic (III) respectively

when the adsorbents (arsenic (III) adsorbed) were interacted with desorbent medium.

After first desorption cycle the adsorbent was again exposed to 100µgml-1

of arsenic

(III) solution wherein the adsorption capacity of MMT-1 and MMT-2 was observed to

decrease from 97% to 28% and 99% to 35% respectively in the second cycle as shown

in Figure 8.4. The total amount of arsenic (III) retained by MMT-1 and MMT-2 after

five cycles was observed to be 3008µg and 2797µg respectively as shown in Table 8.2.

The MMT-3 was found to desorb 64% of arsenic (III) when the metal ion adsorbed

adsorbent was treated with desorbent medium.

The MMT-4 and CHITO-B were found to desorb 70% and 60% arsenic (III) when the

metal ion adsorbed adsorbents were treated with desorbent medium. After first

desorption cycle the adsorption capacity of MMT-4 and CHITO-B was observed to


in Figure 8.4.

The total amount of arsenic (III) retained by MMT-4 and CHITO-B after five cycles

was observed to be 3800µg and 3847µg respectively. The MMT-5 was found to desorb

73% of arsenic (III) when metal ion adsorbed adsorbent was treated with desorbent

medium. After first desorption cycle the adsorbent was again exposed to 100µgml-1

of

arsenic (III) solution wherein the adsorption capacity of MMT-5 was observed to

decrease from 98% to 39% in second cycle [Figure 8.4]. The total amount of arsenic

(III) retained by MMT-5 after five cycles was observed to be 3333µg.


[359]

Figure 8.4. Reusability of adsorbent (a) MMT, (b) MMT-2, (c) MMT-1, (d) MMT-3,


No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (III) Desorbed


0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (III) Desorbed

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (III) Desorbed

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (III) Desorbed


% %

% %

%

No. of Cycles

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

As (III) Adsorbed

As (III) Desorbed

(g)

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5No. of Cycles

%

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5

No. of Cycles

%

(a) (b)

(c) (d)

(e) (f)


[360]

Table 8.2. Total amount of arsenic (III) retained after five adsorption - desorption cycles

8.4 Reusability of adsorbents after desorption of antimony (III)

8.4.1 Desorption of antimony (III) using 0·1M NaOH

The optimum contact time of desorption of antimony (III) was investigated with respect

to time from batch experiment. The adsorbent was exposed to desorption medium during

60-1500 minutes and desorption of antimony (III) was investigated using 0·1M NaOH.

The desorption of antimony (III) from MMT was observed to increase from 2% to 28%

with an increase in contact time of 60 minutes and 720 minutes respectively. The

MMT-1 was observed to increase from 11% to 34% during the contact time of 60

minutes and 720 minutes respectively. The MMT-2 was observed to show an increase

in desorption from 9% to 35% during the contact time of 60 minutes and 900 minutes

respectively. The desorption of antimony (III) from MMT-3 was observed to increase

from 10% to 31% during the contact time of 60 minutes and 720 minutes respectively

as shown in Figure 8.5.

The desorption of antimony (III) from MMT-4 was observed to increase from 19·% to

45% during the contact time of 60 minutes and 720 minutes respectively. The desorption

of antimony (III) from CHITO-B was observed to increase from 13% to 42% during the

contact time of 60 minutes and 900 minutes respectively as shown in Figure 8.5.

Desorption of antimony (III) from MMT-5 was observed to increase from 10% to 43%

during the contact time of 60 minutes and 600 minutes respectively.

S.No. Adsorbent Arsenic (III) retained

µg

01 MMT 3625

02 MMT-1 3008

03 MMT-2 2797

04 MMT-3 3296

05 MMT-4 3800

06 CHITO-B 3847

07 MMT-5 3333


[361]

Figure 8.5. Desorption of antimony (III) from (a) MMT, (b) MMT-1, (c) MMT-2,

(d) MMT-3, (e) CHITO-B, (f) MMT-4, (g) MMT-5 using NaOH

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed

Conact Time/minutes

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% S

b (

III)

Deso

rbed


(a) (b)

(c) (d)

(e) (f)

(g)


[362]

Thus, the contact time of 720 minutes has been observed as the optimum time of

contact for maximum desorption.


Desorption of antimony (III) using 0·1MNaOH during contact time of 600 minutes was

performed repeatedly to investigate the reusability of adsorbent. The desorption of

antimony (III) was observed to be 28% that decreased up to 4% during five cycles.

After each desorption cycle the adsorbent was again exposed to 100µgml-1

of solution

of antimony (III) wherein the adsorption efficiency of MMT was observed to decrease

from 82% to 23% in the second cycle as shown in Figure 8.6. The total amount of

antimony (III) retained after five cycles was observed to be 2123µg.

The MMT-1 and MMT-2 were observed to show desorption efficiency of 34% and

35% of antimony (III) respectively when the adsorbents (antimony (III) adsorbed) were

treated with desorbent medium as shown in Figure 8.6. The adsorbent was again

exposed to 100µgml-1

of antimony (III) solution wherein the adsorption efficiency of

MMT-1 and MMT-2 was observed to decrease from 90% to 15% and 95% to 24%

respectively in the second cycle. The total amount of antimony (III) retained by MMT-1

and MMT-2 after five cycles was observed to be 3068µg and 2809µg respectively as

shown in Table 8.3. The MMT-3 was found to desorb 31% of antimony (III) when the

adsorbent (antimony (III) adsorbed) was treated with desorbent medium. The adsorbent

was again exposed to 100µgml-1

of antimony (III) solution wherein the adsorption

capacity of was observed to decrease from 97% to 22% in the second cycle. The total

amount of antimony (III) retained by MMT-3 after five cycles was observed to be

3381µg.

The MMT-4 and CHITO-B were found to desorb 45·00% and 42·00% antimony (III)

when the metal ion adsorbed adsorbents were treated with desorbent medium. In the

second cycle the adsorbent was again exposed to 100µgml-1

of antimony (III) solution

wherein the adsorption capacity of MMT-4 and CHITO-B was observed to decrease

from 98% to 38% and 96% to 24% respectively in the second cycle. The total amount

of antimony (III) retained by MMT-4 and CHITO-B after five cycles was observed to

be 2890µg and3008µg respectively.


[368]

The MMT-4 and CHITO-B were found to desorb 49% and 64% antimony (III) when

the metal ion adsorbed adsorbents were treated with desorbent medium. After first


of antimony (III)

solution wherein the adsorption capacity of MMT-4 and CHITO-B was observed to


in Figure 8.8. The total amount of antimony (III) retained by MMT-4 and CHITO-B

after five cycles was observed to be 2871µg and 2757µg respectively. The MMT-5 was

found to desorb 48% of antimony (III) when metal ion adsorbed adsorbent was treated

with desorbent medium. After first desorption cycle the adsorbent was again exposed to

100µgml-1

of antimony (III) solution wherein the adsorption capacity of MMT-5 was

observed to decrease from 95% to 20% in the second cycle as shown in Figure 8.8. The

total amount of antimony (III) retained by MMT-5 after five cycles was observed to be

2981µg [Table 8.4].

Table 8.4. Total amount of antimony (III) retained after five adsorption - desorption cycles

S.No. Adsorbent Antimony (III) retained

µg

01 MMT 2636

02 MMT-1 2078

03 MMT-2 2441

04 MMT-3 3213

05 MMT-4 2871

06 CHITO-B 2757

07 MMT-5 2981

8.5 Reusability of adsorbents after desorption of vanadium (V)

8.5.1 Desorption of vanadium (V) using 0·1M NaOH

The optimum contact time required for desorption of vanadium (V) was investigated

wherein the adsorbent was exposed to desorption medium for 60-1500 minutes and

desorption of vanadium (V) was studied using 0·1MNaOH with respect to time.


[369]

Figure 8.9. Desorption of vanadium (V) from (a) MMT, (b) MMT-2, (c) MMT-1,

(d) MMT-3, (e) CHITO-B, (f) MMT-4, (g) MMT-5 using NaOH

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 200 400 600 800 1000 1200 1400 1600

0

10

20

30

40

50

60

70%

V(V

) D

es

orb

ed

Contact time/minutes

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 200 400 600 800 1000 1200 1400 1600

0

10

20

30

40

50

60

70

%v

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

Deso

rbed


(a) (b)

(c) (d)

(g)

(e) (f)


[370]

The desorption of vanadium (V) from MMT was observed to increase from 9·00% to

46·00% during the contact time of 60 minutes and 720 minutes respectively. The

percentage of vanadium (V) desorbed from MMT-1 was observed to increase from

11·00% to 49% during the contact time of 60minutes and 720 minutes respectively. The

desorption of vanadium (V) from MMT-2 was observed to increase from 9% to 55%


The desorption of vanadium (V) from MMT-3 was observed to increase from 10% to

31% during the contact time of 60minutes and 720minutes respectively as shown in

Figure 8.9.

The desorption of vanadium (V) from CHITO-B was observed to increase from 12% to

67% during the contact time of 60 minutes and 720 minutes respectively as shown in

Figure 8.9. The MMT-5 was observed to show an increase in desorption efficiency

from 10% to 55% during the contact time of 60 minutes and 720 minutes.


The investigations of reusability of adsorbent by desorption of vanadium (V) using

0·1M NaOH shows the desorption efficiency of 46% in first cycle that decreased up to

12% after five cycles.

The MMT-1 and MMT-2 were found to desorb 49% and 55% vanadium (V) when the

adsorbents (vanadium (V) adsorbed) were treated with desorbent medium.After first


of vanadium (V) solution

wherein the adsorption capacity of MMT-1 and MMT-2 was observed to decrease from

97% to 40% and from 98% to 46% respectively in the second cycle as shown in Figure

8.10. The total amount of vanadium (V) retained by MMT-1 and MMT-2 after five cycles

was observed to be 3783µg and 3449µg respectively.

The MMT-3 was observed to desorb 58% vanadium (V) when the metal ion adsorbed

adsorbents were treated with desorbent medium.After first desorption cycle the

adsorbent was again exposed to 100µgml-1

of vanadium (V) solution wherein the

adsorption capacity of MMT-3 was observed to decrease from 99% to 45% in the

second cycle as shown in Figure 8.10. The total amount of vanadium (V) retained by

MMT-3 after five cycles was observed to be 3405µg.


[371]

Figure 8.10. Reusability of adsorbents (a) MMT, (b) MMT-2, (c) MMT-1, (d) MMT-3, (e)

CHITO-B, (f) MMT-4, (g) MMT-5

%

V (V) Adsorbed

V (V) Desorbed

No. of Cycles

%

V (V) Adsorbed

V (V) Desorbed

No. of Cycles

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

(g)

(c)

(e)

(f)

(a)

(d)

(b)


[372]

The MMT-4 and CHITO-B were observed to desorb 55% and 68% vanadium (V) when

the metal ion adsorbed adsorbents were treated with desorbent medium. The adsorption

capacity of MMT-4 and CHITO-B was observed to decrease from 99·9% to 49% and

96% to 46% respectively in the second cycle as shown in Figure 8.10.

The total amount of vanadium (V) retained by MMT-4 and CHITO-B after five cycles

was observed to be 2893µg and 2882µg respectively.


adsorbents were treated with desorbent medium.


of vanadium

(V) solution wherein the adsorption capacity of MMT-5 was observed to decrease from

99% to 48% in the second cycle as shown in Figure 8.10. The total amount of

vanadium (V) retained by MMT-5 after five cycles was observed to be 3026µg.

Table 8.5. Total amount of vanadium (V) retained after five adsorption - desorption cycles

S.No. Adsorbent Vanadium (V) retained

µg

01 MMT 2636

02 MMT-1 3783

03 MMT-2 3449

04 MMT-3 3405

05 MMT-4 2893

06 CHITO-B 2882

07 MMT-5 3026

8.4.3 Desorption and Reusability of adsorbents using 0·1M dihydrogen phosphate

� Desorption of vanadium (V) using 0·1M dihydrogen phosphate

The optimum contact time required for desorption of vanadium (V) was investigated

wherein the adsorbent was exposed to desorption medium for 60-1500 minutes and

desorption of vanadium (V) using 0·1M potassium dihydrogen phosphate.


[373]

Figure 8.11. Desorption of vanadium (V) from (a) MMT, (b) MMT-1, (c) MMT-2, (d)

MMT-3, (e) CHITO-B, (f) MMT-4, (g) MMT-5 using dihydrogen phosphate

0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


0 300 600 900 1200 1500

0

10

20

30

40

50

60

70

% V

(V)

De

so

rbe

d


(a) (b)

(c) (d)

(g)

(e) (f)


[374]

The desorption of vanadium (V) from MMT was observed to increase from 10% to

32% during the contact time of 60 minutes and 720 minutes. The percentage of

vanadium (V) desorbed from MMT-1 was observed to increase from 11% to 42%




percentage of vanadium (V) desorbed from MMT-3 was observed to increase from 10%

to 42% during the contact time of 60 minutes and 600 minutes respectively as shown in

Figure 8.11.



desorption of vanadium (V) from CHITO-B was observed to increase from 19% to 70%

during the contact time of 60 minutes and 600 minutes respectively as shown in Figure

8.11. The MMT-5 was observed to show an increase in desorption from 9% to 60%



The investigations of reusability of adsorbent by desorption of vanadium (V) using

0·1M dihydrogen phosphate shows the desorption efficiency of 32% in first cycle that

decreased up to 9% during fifth cycle.

The MMT-1 and MMT-2 were found to desorb 42% and 45% vanadium (V) when the

metal ion adsorbed adsorbents were treated with desorbent medium during first cycle.


of vanadium

(V) solution wherein the adsorption capacity of MMT-1 and MMT-2 was observed to

decrease from 97% to 37% and from 97% to 38% respectively in the second cycle as

shown in Figure 8.12. The total amount of vanadium (V) retained by MMT-1 and

MMT-2 after five cycles was observed to be 2316µg and 3149µg respectively.


[375]

Figure 8.12. Reusability of adsorbents (a) MMT, (b) MMT-1, (c) MMT-2, (d) MMT-3,


%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

%

No. of Cycles

V (V) Adsorbed

V (V) Desorbed

(a) (b)

(c)

(d)

(g)

(e)

(f)


[376]


adsorbents were treated with desorbent medium. After first desorption cycle the

adsorbent was again exposed to 100µgml-1

of vanadium (V) solution wherein the

adsorption capacity of MMT-3 was observed to decrease from 98% to 40% in the

second cycle as shown in Figure 8.12. The total amount of vanadium (V) retained by

MMT-3 after five cycles was observed to be 2315µg.

The MMT-4 and CHITO-B were observed to desorb 63% and 70% vanadium (V) when

the metal ion adsorbed adsorbents were treated with desorbent medium. After first


of vanadium (V)

solution wherein the adsorption capacity of MMT-4 and CHITO-B was observed to


in Figure 8.12.

The total amount of vanadium (V) retained by MMT-4 and CHITO-B after five cycles

was observed to be 3317µg and 3800µg respectively [Table 8.6].

The percentage of vanadium (V) desorbed from MMT-2 was observed to increase from

9% to 55% during the contact time of 60 minutes and 900 minutes respectively. The

percentage of vanadium (V) desorbed from MMT-3 was observed to increase from 10%

to 31% during the contact time of 60 minutes and 720 minutes respectively as shown in

Figure 8.12.

Table 8.6. Total amount of antimony (III) retained after five adsorption - desorption cycles

S.No. Adsorbent Vanadium (V) retained

µg

01 MMT 2630

02 MMT-1 2316

03 MMT-2 3149

04 MMT-3 2315

05 MMT-4 3140

06 CHITO-B 3800

07 MMT-5 3317


[377]

8.6 Conclusions

The need to the development of a methodology wherein the adsorbent has maximum

possible adsorption capacity and reusability after desorption of toxic metal has been

investigated and attained.

The minimum contact time required for maximum desorption of arsenic (III) has been

observed to be 720 minutes using 0·1M NaOH whereas 600minutes using 0·1M

potassium dihydrogen phosphate. CHITO-B shows minimum time required (480

minutes) for maximum desorption of arsenic (III) then MMT-4 possibly due to presence

of weakly bound arsenic (III) to CHITO-B and hence faster desorption rate. An

appreciable decrease in desorption has been observed after 900 minutes due to the

unavailability of more desorption sites.

It has been observed that during first desorption cycle an appreciable amount of arsenic

(III) remain unadsorbed possibly due to strong bond with adsorbent. The amount of

arsenic (III) desorbed from MMT, CHITO-B, MMT-4 and MMT-5 was found to be

almost same as in the second, third, fourth and fifth cycle thus directing towards some

loosely bound arsenic (III) that could be removed in every step after adsorption. The

amount of arsenic (III) desorbed from MMT-1, MMT-2 and MMT-3 has been observed

to be little more than the amount adsorbed using NaOH as desorbent.

It has been observed that dihydrogen phosphate proved to be an efficient desorbent that

reduced the optimum contact time to 600 minutes and was observed to be capable of

desorbing the arsenic inaccessible to NaOH. During first desorption cycle an

appreciable amount of arsenic (III) remains unadsorbed which is in the order MMT-4>

MMT-5> CHITO-B> MMT-1. After the first cycle the amount of arsenic (III) desorbed

has been observed to be approximately same as the amount adsorbed. The efficiency of

phosphate could be due to the analogous structure of phosphate to arsenate.

Dihydrogen phosphate proved to be an efficient desorbent for antimony (III) wherein

the optimum contact time of 720 minutes was observed to be capable of desorbing

maximum antimony (III) inaccessible to NaOH. During first desorption cycle an

appreciable amount of antimony (III) remains unadsorbed which is in the order CHITO-


[378]

B> MMT-5> MMT-4> MMT-2. After the first cycle the amount of antimony (III)

desorbed has been observed to be approximately same as the amount adsorbed.

The improved efficiency of phosphate could be due to the analogous structure of

phosphate to arsenate and antimonate [008].

The minimum contact time required for maximum desorption of vanadium (V) has been

observed to be 720 minutes using 0.1M NaOH. An appreciable decrease in desorption

has been observed after 900minutes due to the unavailability of desorption sites.

It has been observed that during first desorption cycle an appreciable amount of

vanadium (V) remain unadsorbed possibly due to strong bond with adsorbent. The

amount of vanadium (V) desorbed from MMT, CHITO-B, MMT-4 and MMT-5 was

found to be almost same as in the second, third, fourth and fifth cycle thus directing

towards some loosely bound vanadium (V) that could be removed in every step after

adsorption. The amount of vanadium (V) desorbed follows the order as CHITO-B>

MMT-5 > MMT-3> MMT-4 using 0·1M NaOH. It has been observed that NaOH was

more efficient for desorption of vanadium (V) than dihydrogen phosphate. The high

desorption of vanadium (V) shows that the adsorption of vanadium (V) is a reversible

processwhich is possible by change in water pH.


[379]

References

[001] Federal Register (2001)

[002] Smith, E., Naidu, R., Alston, A. M. (2002) J. Environ. Qual,. 31, 557-563.

[003] Saada, A., Breeze, D., Crouse, S., Cornu, S., Baranger, P. (2003a)

Chemosphere, 51, 757-763.

[004] Preseah, S., Andreas, KK. (2011) J. Contaminant Hydrology, 126 216-225.

[005] Hingston, F. J., Posner, A. M., Quirk, J. P. (1971) Faraday Soc., 52, 334-342.

[006] Meng X., Korfiatis, G.P., Christodoulatis, C., Bank, S. (2001) Water Research,

34, 2805-2810.

[007] Stollenwerk, K. G., Breit, G. N., Welch, A. H. Yount, J. C., Whitney, J. W.,

foster, A. L., Uddin. M. N., Majumdar, R. K., Ahmed, N. (2007) Sci. Total

Environ., 379, 133-150.

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Cover page corrected - 1shodhganga.inflibnet.ac.in/bitstream/10603/36248/14... · using LCV (Leuco crystal violet) by the modification of reported procedure [007]. Working standards