paper on fluoride for tms 2011

8/4/2019 Paper on fluoride For TMS 2011

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REMOVAL OF FLUORIDE FROM WASTE WATER OF ALUMINIUM SMELTER BY ALUMINIUM

ION LOADED ION EXCHANGE RESIN

Email:[email protected]

Abstract

Strong Acid Cation resin has sulphonic acid functional group (H+ form) possesses appreciable defluoridation

capacity and it has been enhanced by chemical modification into Al 3+ form by loading of Aluminium ions in H+ form

of resin. The defluoridation Al3+ forms was found to be 480 mg F/kg, at 15 mg/L initial fluoride concentration. The

nature and morphology of sorbents are characterized using XRD, FTIR and SEM analysis. The fluoride sorption was

explained using the Freundlich, Langmuir and RedlichPeterson isotherms models. The calculated thermodynamic

parameters such as G, H, S and sticking probability (S*) explains the nature of sorption. Comparison was alsomade by the elution capacity of this resin in order to select a cost effective material. A Defluoridation Plant is in

service at aluminium smelter of National Aluminium Company to treatment the waste water for removing Fluoride

and reutilise the water to minimise the water loss.

Keywords: Cation resin; Modification; Defluoridation; Adsorption; Complexation

1. Introduction

Fluoride pollution of water can occur due to

smelting activity of alumina with cryolite to production

of aluminium or geochemical processes [1]. The removal

of fluoride from water is one of the most important issues

due to the effect on human health and environment.

Fluoride in drinking water may be beneficial or

detrimental depending on its concentration [2]. One such

preventive measure is defluoridation of water. Availabletechniques for the removal of fluoride belong to the

following three major categories viz., adsorption,

chemical precipitation and ion exchange. Among the

methods, adsorption technology is economical and

efficient method for producing high quality of water. In

recent years, a variety of adsorbents like metal loaded

adsorbents [1], activated alumina [3], chitosan beads [4],

composites [5], activated carbon [6], clay [7],

hydroxyapatite [8], etc., have been identified as the

promising defluoridating agents. Though defluoridation

of the material is an important criterion, it is also

necessary to consider the other factors like flow rate,

acceptability by the users, ease of operation, etc., while

designing the column for the success of technology.

In the present study a commercial cation

exchanger with sulphonic acid group namely CSA-9 of

Doshion ltd, India which removes fluoride by means of

adsorption have been modified into Al3+ forms in order

to enhance the defluoridation. The aluminium metal ions

exchanged with the sulphonate group of resin and have

shown promising results. It has been reported that the

adsorption capacity of fluoride on aluminium

impregnated carbon is 35 times higher than that of plain

activated carbon.

The original resin which is in H+ form converted

to Al3+ forms of resins for the defluoridation capacity

under various equilibrating conditions like contact time,initial fluoride concentrations, pH, temperature. The

fluoride removal by these resins was explained using

equilibrium. Best regenerator was also suggested for the

continuous use of these sorbents. These fundamental data

were useful in selecting the most suitable material for

fluoride removal from the waste water of Aluminium

smelter plant and reutilisation.

2. Materials and methods

2.1. Materials

A cation resin with sulphonic acid group (H+

form) was collected from Doshion Ltd., Ahamedabad,

India. This resin having H+ as an ion exchange resin was

washed with distilled water and dried at oven at 50 C

and has been modified into Al3+ forms as follows. The

Al3+ form of resin was prepared by treating 5% (w/v)

Al2(SO4)3 for 24 h, then the resin was washed with

distilled water till it attains neutral pH and dried at 50 C

for 12 h. The dried resin samples were used for the

sorption studies. All other chemicals employed were of

analytical reagent grade and were used without

purification. Double distilled water was used for

preparing all the solutions. For the field study, fluoride-

containing water was collected from waste water pond ofaluminium smelter plant.

2.2. Sorption experiments

Defluoridation experiments were carried out by

batch equilibration method in duplicate. In a typical case,

1 g of the sorbent was added to 50 ml of NaF solution of

initial concentration 10 mg/L. The contents were shaken

thoroughly using a constant temperature bath with a

shaker. The solution was then filtered and the residual

fluoride concentration was measured. Adsorption studies

were carried out in a temperature controlled water bath

shaker. The effect of initial fluoride concentration with

different temperatures at 20 to 40oC on sorption rate was

studied at the following initial fluoride concentrations

viz., 2, 4, 6, 8 and 10 mg/L by keeping the mass of

A.K.Sharma

National Aluminium Company Limited

NALCO BHAVAN

BHUBANESWAR 751013

ORISSA, INDIA.

B.K.Padhi

R&D Laboratory, Alumina Refinery,

National Aluminium Company Limited,

DAMANJODI-763008

ORISSA, INDIA.


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sorbent as 1 g and volume of fluoride solution as 50 ml at

pH 7.

2.3. Analysis

The concentration of fluoride was measured

using expandable ion analyzer EA 940 with the fluoride

ion selective electrode BN 9609 (Orion, USA). The pHmeasurements were done with the same instrument with

pH electrode. All other water quality parameters were

analyzed by using standard methods [9]. The surface

morphology of the resins was visualized by SEM with

LEO model. The SEM enables the direct observation of

the surface microstructures of the Al3+ loaded fresh and

fluoride-sorbed resins. FTIR spectra of the resins were

recorded with BRUKER model by mixing resin with

KBr. The results of FTIR were used to confirm the

functional groups present in the resins.

3. Results and discussion

3.1. Characterization of sorbents

The FTIR spectra (Fig. 1) of cationic resin with

sulphonic acid functional group in the form of Al3+ show

different spectral bands. The FTIR spectral data of the

fresh Al3+ form and fluoride-sorbed Al3+ form is shown

where the stretching frequency at 1121 and 1045 cm-1

corresponds to the presence of SO Al stretching

and the stretching frequency at 775 cm-1 indicates the

presence of Al O stretching in Al3+ form. The

difference in the SO stretching frequencies of

Al3+ form also confirms their change during

modification. This is also further confirmed by pHzpc

values in which the structural changes were indicated by

the shifting of pHzpc values for Al

3+

form it is 6.7.

Fig.1. FTIR spectra of Al3+ form resin and Fluoride

treated Al3+ resin

SEM images of the resins before and after

Aluminium ion sorption of H+ form and Al3+ form are

shown in Fig. 2a and b, respectively. The SEM pictures

of fluoride-sorbed Al3+ form is shown in Fig. 2c. The

alteration of the surface morphology in the fluoride-

sorbed resins indicates the sorption of fluoride occurs

ontothe sorbents.

Fig. 2 (a). SEM micrographs of H+ form

Fig. 2 (b). SEM micrographs of Al3+ form

Fig. 2 (c). SEM micrographs of fluoride-sorbed Al3+

form.

X-ray Diffraction studies of Al3+

adsorbed cationresin shows (Fig. 3 B) the aluminium ions are present as

amorphous in nature. From the diffraction pattern there is

no sharp peak was found but the peak at 2 value of 7.5and 17.5 reveals that the aluminium ions were exchanged

with the hydrogen ion of resin. The presence of

aluminium ion was analysed after treating the resin with

2% H2SO4. It was found that 16% of aluminium ions are

adsorbed by the resin. The XRD of fluoride exchanged

resin shows (Fig. 3 A) there were some developed peaks

at 2 value of 7.5, 17.5, 17.8, 28.1, 37.6 and 47.1 aredue to the presence of aluminium hydroxy fluoride.

When the fluoride adsorbed resins were regenerated with

5% (w/v) Al2(SO4)3 solution the similar pattern of XRD

was found as shown in Fig. 3.


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Fig. 3. XRD of Al3+ form resin and Fluoride adsorbed

Al3+ form resin

3.2. Effect of contact time

The effect of fluoride exchange capacity of

sorbents with contact time was studied using 10 mg/L as

initial fluoride concentration with neutral pH at roomtemperature to find out a minimum time of contact

needed to attain maximum fluoride exchange capacity.

The sorption of fluoride has been investigated as a

function of time in the range of 550 min. Fig. 4 shows

the variation of fluoride exchange capacity with time. It

is evident that the fluoride exchange capacity of all the

sorbents increases sharply with increasing time and reach

saturation after 40 min in the case of Al3+ forms.

Therefore, Al3+ forms were found to be appropriate for

maximum adsorption and were used in all subsequent

measurements.

0.06

0.08

0.1

0.12

0.14

0.16

5 1 0 1 5 20 2 5 30 35 4 0 4 5 50 5 5 6 0

Time (min)

FluorideRemovalCapacity(mgF-/g

)

Al3+ form

Fig. 4. Effect of contact time for Fluoride uptake by Al3+

form resin.

3.3. Influence of pH

The pH of the medium is an important variable

for the adsorption of fluoride on the adsorbents [10]. The

effect of pH on fluoride adsorption by the sorbents was

studied at five different pH levels viz., 3 to 8 by keeping

other parameters like contact time, dosage and initial

fluoride concentration as constant at 30 oC. Various pH

of the working solution were controlled by adding

HCl/NaOH solution. Fig. 5 explains the variation of

fluoride exchange capacity as a function of pH and it is

observed that the fluoride exchange capacity of all the

resins studied is not influenced by the pH of the medium

and hence it is decided that the pH has no significant

role. Similar type of results was observed when the

modified chitosan beads were used as the sorbent for

defluoridation [4]. For further experiments neutral pH

was maintained for sorption studies.

1.5

2

2.5

3

3.5

1.5 3.5 5.5 7.5

pH

FluorideUptake(mg/g)

Fig. 5. Effect of pH for Fluoride uptake by Al3+ form

resin.

3.4. Influence of the sorbate concentration

The effect of fluoride exchange capacity on

different initial fluoride concentrations viz., 2, 4, 6, 8 and

10 mg/L with neutral pH at 30 oC were studied and are

shown in Fig. 6. The fluoride exchange capacity of the

sorbents increases with increase in the initial fluoride

concentration. It is evident from Fig. 5 that the modified

forms of resins have higher fluoride exchange capacity.

In most of the time the fluoride level in drain water foundto have a maximum of 10 mg F ( /L. Hence, for further

studies the initial concentration of fluoride was fixed as

10 mg/L.

0

0.2

0.4

0.6

0.8

1

0 2 4 6 8 10 12

Fluoride concentration (mg/L)

FluorideR

emovalcapacity(mgF-/g)

Al3+ form

Fig. 6. Effect of concentration on removal of Fluoride by

Al3+ form resin.

3.5. Effect of temperature

Sorption studies were carried out at different

temperatures 20 to 40 oC with initial fluoride

concentration 10 mg/L by keeping all other factors as

constant. At higher temperature the mobility of fluoride

ions increased so that the complex formation increased.


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The effect of temperature for Al3+ form is shown in

Fig.7. It has been observed that the fluoride exchange

capacity of Al3+ form is influenced by the temperature

due to the complex formation with Al3+ ions there by

resultant in to higher removal of fluoride occurs. This

indicates that temperature is dependent on fluoride

removal.

2.5

2.7

2.9

3.1

3.3

3.5

3.7

3.9

15 20 25 30 35 40 45

Temperature (oC)

FluorideUptake(mg/g)

Fig. 7. Effect of temperature on the fluoride removal by

Al3+ form resin.

3.6. Sorption isotherms

To quantify the sorption capacity of the resins

studied for the removal of fluoride, three isotherms

namely Freundlich, Langmuir and RedlichPeterson

isotherms have been adopted.

3.6.1. Freundlich isotherm

The linear form of Freundlich [11] isotherm is

represented by the equation,Log Qe = log kf+ (1/n) log Ce (1)

Where,Qe is the amount of fluoride adsorbed per unit

weight of the sorbent (mg/g), Ce is the equilibrium

concentration of fluoride in solution (mg/L), kf is a

measure of adsorption capacity and 1/n is the adsorption

intensity. The plot of log Qe vs. log Ce (Fig. 8 ) is linear

which indicates the applicability of Freundlich isotherm.

The constants kf and 1/n of Freundlich isotherm for the

Al3+ type of sorbent is given in Table 1. Adsorption

process is favourable when the value of 1/n lies between

0.1 and 1, the value of n lies between 1 and 10. This

condition is obeyed by all the types of resins suggesting

fluoride gets sorbed by these resins. The values ofkfwere

found to be almost constant in all the temperaturesstudied for the resins.

0.6

0.7

0.8

0.9

1

1.1

1.2

0.8 1 1.2 1.4 1.6 1.8

log Ce

logQe

Fig. 8. Freundlich adsorption isotherm for fluoride

removal by Al3+ form resin.

3.6.2. Langmuir isotherm

Langmuir [32] isotherm model can be

represented by the equation:

Ce/Qc = 1/Qob + Ce/Qo (2)

where Qo is the amount of adsorbate at completemonolayer coverage (mg/g), which gives the maximum

sorption capacity of sorbent and b (mg/L) is the

Langmuir isotherm constant that relates to the energy of

adsorption were calculated from the slope and intercept

of the plot Ce/Qe vs. Ce (Fig. 9). The value of b

increases with increasing temperature confirms that

fluoride sorption takes place more readily with increase

in temperature. Langmuir model effectively described the

sorption data with r2 values >0.99.

In order to find out the feasibility of the isotherm,

the essential characteristics of the Langmuir isotherm can

be expressed in terms of a dimensionless constant

separation factor or equilibrium parameter, RL [12]

RL= 1/1+bCo (3)

where b is the Langmuir isotherm constant and Co is the

initial concentration of fluoride (mg/L). The RL values

between 0 and 1 indicate favourable adsorption for all

temperatures studied (cf. Table 1).

0

1

2

3

4

5

6

7

8

9

0 10 20 30 40 50Ce

Ce

/Qe

Fig. 9. Langmuir adsorption isotherm for fluoride

removal by Al3+ form resin.

3.6.3. Rate Constant

The specific rate constant kf for the adsorption of

fluoride ion on the resins was determined by Lagergan

equation [17].

Log (qe-q)= Log qe (kf /2.303) t (4)

Where qe and q (mg/g) are amounts of fluoride ion

adsorbed at equilibrium and time t, respectively. The

straight line plot (Fig. 10) of Log (qe-q) vs t at 30oC

indicated the validity of Lagergan equation for the

present system and explained that the process followed

first order kinetics. The values of kfwere calculated from

the slope of the plot and were 0.05191/min.


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0

0.1

0.2

0.3

0.4

0.5

0.6

0 10 20 30 40 50 60 70Time (min)

Log(qe-q)

Fig. 10. Validity of Lagergan equation for fluoride

removal by Al3+ form resin

3.7. Thermodynamic treatment of the sorption process

Thermodynamic parameters associated with theadsorption viz., standard free energy change (G),

standard enthalpy change (H), standard entropychange (S) and sticking probability (S*) werecalculated using Khan and Singh method, vant Hoff

equation and Horsfall and Spiff method [12], [13] and

[14]. The negative values of G confirm the feasibilityof the process and the spontaneous nature of sorption

with a high preference for fluoride sorption onto resins.

The positive value of H indicates the reaction is

endothermic in nature. The positive value of S whichis a measure of randomness at the solid/liquid interface

during fluoride sorption indicates the adsorption process

is irreversible and stable. The values of S* for all the

forms are very close to zero indicating that the nature ofadsorption is electrostatic attraction in which Al3+ forms

it is ionic.

3.8. Mechanism of fluoride removal by the sorbents

The fluoride removal capacity of these sorbents

may be controlled by adsorption mechanism rather than

ion exchange as they are cationic resins. When H+ form

is in contact with Al3+ solutions, the respective metal ions

gets exchanged for H+ ion by ion exchange mechanism.

The metal ions in the matrix will attract fluoride by

means of electrostatic adsorption and strong Lewis acid

base interaction [15] and [16]. All the sorbents

selectively retains fluoride as it is the hardest Lewis baseand the ions loaded into the resin are hard Lewis acids.

The possible mechanism of fluoride removal by Al3+

forms is shown in Fig. 11. The type of electrostatic

adsorption in Al3+ forms it is ionic. Among the sorbents,

Al3+ form possesses slightly higher fluoride exchange

capacity than the other two forms since it removes

fluoride by complexation mechanism also, in addition to

electrostatic adsorption because it is a strong Lewis acid,

possesses higher valency and chelating efficiency.

Fig. 11. Mechanism of fluoride removal by the Al3+ form

of cationic adsorbents.

3.9. Column operation

The performance of Al3+ cation resin in

continuous column operation was studied by conductingloading runs using 250 ml bed volume of resin and

influent having 15 mg/l fluoride ion concentration. The

capacity of resin for 1 mg/l leakage at different influent

flow rates such as 5 B.V./h, 10 B.V./h and 15 B.V./h

were determined. As the flow rate increased the

adsorption rate decreased because of lesser contact time

with resin.

Al3+ form of resins used in our study are also

tested with field sample taken from different drains of

Aluminium smelter plant area. The results of these trials

are presented in Table 1. It is evident from the result that

all the sorbents can be effectively employed for removing

the fluoride. There is no significant change in the levels

of other water quality parameters. In fact, the levels ofmost of the water quality parameters have been reduced

by these resins, in addition to fluoride. The modified

forms of resins give better results than H+ form.

Table 1. Field trial results of the sorbents.

Water quality

parameter

Before

treatment

After treatment

with Al3+ resin

F- (mg/L) 15.2 0.56

pH 7.2 6.8

Cl- (mg/L) 56.8 55.2

Total hardness

(mg/L)

125.0 120.0

Total Dissolvesolids (mg/L)

523 486

Na+ (mg/L) 54.2 53.5

3.10. Regeneration of exhausted sorbents

The exhausted resins were eluted using eluents

viz., HCl, H2SO4, NaOH and Al2(SO4)3 5% (wt/v).

Mineral acids elute fluoride as HF and NaOH as NaF. All

the regeneration experiments were carried out at room

temperature. The elution capacities of these forms of

resins were studied using 0.1 M HCl, 0.1 M H2SO4 and

0.1 M NaOH. Out of these four eluents, Al 2(SO4)3 5%

(wt/v) has been identified as the best eluent as it has 99%elution capacity while HCl, H2SO4 and NaOH have 90%,

80% and 75% elution capacities, respectively. After

regeneration, the sorbents can be reused for fluoride

removal. After regeneration of fluoride exhausted Al3+

form of resin the effluents can be reutilised by adjusting

the concentration of Al2(SO4)3 to 5% (wt/v) by adding

required Al2(SO4)3 and utilised for regeneration of

fluoride removal resin.

4. Conclusions

In general all the forms of resins possess

reasonably good defluoridation efficiency. The fluoride

exchange capacity of these sorbents is independent of pHof the medium and unaltered in the presence of co-anions

present in the medium. Al3+ form has higher fluoride

exchange capacity among the sorbents studied. The


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mechanism of fluoride removal by the sorbents is mainly

controlled by chemisorption. The sorption process

follows Freundlich, Langmuir and RedlichPeterson

isotherms. The values of thermodynamic parameters

indicate that the fluoride removal is spontaneous and

endothermic in nature. The rate of the reaction of all the

forms is controlled by first-order and particle diffusion

kinetic models. Field trial results indicate that thesesorbents can be effectively used to remove the fluoride

from water. Al2(SO4)3 5% (wt/v) has been identified as

the best eluent for the regeneration of the sorbents. This

type of result could definitely throw more light in

selecting best sorbent for fluoride removal for other

Aluminium smelters.

Acknowledgements

The authors are grateful to the management of

NALCO for kind permission to publish the paper and

also implementations of process know how for plant

operation to utilise the waste water which is free from

Fluoride ions.

References

[1] L. Fang, K.N. Ghimire, M. Kuriyama, K. Inoue, K.

Makino, Removal of fluoride using some lanthanum(III)-

loaded adsorbents with different functional groupsand

polymer matrices, J. Chem. Technol. Biotechnol. 78

(2003) 10381047.

[2] WHO,WHOGuidelines for DrinkingWater Quality,

vol. 1,World Health Organisation,Geneva, 1993, pp. 45

46.

[3] S. Meenakshi, Studies on Defluoridation of Water

with a Few Adsorbents and Development of an

Indigenous Defluoridation Unit for Domestic Use,

Ph.D.Thesis, Gandhigram, Tamil Nadu, India, 1992.

[4] N. Viswanathan, C. Sairam Sundaram, S. Meenakshi,

Removal of fluoride from aqueous solution using

protonated chitosan beads, J. Hazard. Mater. 169 (2009)

423430.

[5] C. Sairam Sundaram,N. Viswanathan, S.

Meenakshi,Uptake of fluoride by

nanohydroxyapatite/chitosan, a bioinorganic composite,

Bioresource Technol. 99 (2008) 82268230.

[6] S. Meenakshi, C. Sairam Sundaram, R. Sukumar,

Enhanced fluoride sorption by mechanochemically

activated kaolinites, J. Hazard. Mater. 153 (2008) 164

172.

[7] C. Sairam Sundaram, N. Viswanathan, S. Meenakshi,

Defluoridation chemistry of synthetic hydroxyapatite atnano scale: equilibrium and kinetic studies, J. Hazard.

Mater. 155 (2008) 206215.

[8] APHA, StandardMethods for the Examination

ofWater andWasteWater,American Public Health

Association,Washington, DC, 2005.

[9] S. Meenakshi, Anitha Pius, G. Karthikeyan, B.V.

Appa Rao, The pH dependence of efficiency of activated

alumina in defluoridation of water, Indian J.

Environ.Prot. 11 (1991) 511513.

[10] H.M.F. Freundlich, Uber die adsorption in lsungen,

Z. Phys. Chem. 57A (1906) 385470.

[11] T.W. Weber, R.K. Chakravorti, Pore and solid

diffusion models for fixed bed adsorbers, J. Am. Inst.

Chem. Eng. 20 (1974) 228238.[12] S. Meeenakshi, N. Viswanathan, Identification of

selective ion exchange resin for fluoride sorption, J.

Colloid Interf. Sci. 308 (2007) 438450.

[13] A.A. Khan, R.P. Singh, Adsorption thermodynamics

of carbofuran on Sn(IV) arsenosilicate in H+, Na+ and

Ca2+ forms, Colloids Surf. 24 (1987) 3342.

[14] M. Horsfall, A.I. Spiff, Effects of temperature on the

sorption of Pb2+ and Cd2+ from aqueous solution by

caladium bicolor (wild cocoyam) biomass, Electron.J.

Biotechnol. 8 (2005) 162169.

[15] F. Helfferich, Ion Exchange, McGraw-Hill, New

York, 1962.

[16] A. Dabrowski, Z. Hubicki, P. Podkoscielny, E.

Robens, Selective removal of the heavy metal ions from

waters and industrial waste waters by ion-exchange

method, Chemosphere 56 (2004) 91106.

[17] Y.C.Sharma, G.S.Gupta,G.Prasad, D.C.Rupaniwar,

Water,Air,Soil Pollut. (1990) 49,69.

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