Bio-adsorbents derived from Coconut fiber (Manju et al, 1997), eucalyptus bark (Sarin et al, 2006) , maple sawdust (Yu et al, 2003), Hevea brasilinesis sawdust activated carbon ( Karthikeyan et al, 2005), waste tealeaves and rice husk (Shyamala et al, 2005), neem sawdust (Vinodhini et al, 2009), Ficus benghalensis L.powder ( Nageswara Rao et al 2011), marine algae Graciliria edulis (Thilalai Natarajan, et al, 2011) and natural diatomite (Menderes Koyuncu et al, 2011), have been explored for controlling Chromium. Vandana Swarnkar et al (2011) probed HDTMA-Exchanged zeolites and comparative studies using different adsorbents have also been made (Meena et al 2003; Kothiyal, et al 2011).

The present work is a thorough study on the optimization of extraction conditions such as pH, time of equilibration and sorbent concentration, for the removal of Chromium (VI) from polluted waters using biomaterials derived from the leaves, barks or stems of Annona squamosa, Cassia Auriculata and Ficus religiosa.

METIRIALS AND METHODS:

All chemicals used were of analytical grade. 500 ppm stock solution of Chromium (VI) was prepared and was suitably diluted as per the need. 0.25 % Diphenyl carbazide solution was prepared in 50% of acetone.

A: Adsorbents:

Of the various bio-adsorbent derived from plants tried for the removal of Chromium from synthetically prepared polluted waters by optimizing various physicochemical parameters such as pH, conc. of sorbent and time of equilibration, it has been observed that the leaves, barks or stems and their ashes of Annona squamosa, Cassia auriculata and Ficus religiosa, have affinity towards the Chromium (VI) ions.

Annona squamosa is a small well-branched shrub that bears edible fruits called sugar-apple and it is a species of the genus Annona and belongs to Annonaceae family. It grows well at lower altitudes. Cassia auriculata is a common shrub that grows in dry regions in Asia. It belongs to Fabaceae family and is widely used in traditional medicine as a cure for rheumatism, conjunctivitis and diabetes. Ficus religiosa, or Bo-Tree is large dry season-deciduous or semi-evergreen tree grow up to 30 meters. It is a species of banyan fig native to South Asia and belongs to the Moraceae family and is considered as sacred by Hindus and Buddhists.

The leaves, stems or barks of Annona squamosa, Cassia auriculata and Ficus religiosa were cut or scrapped, washed with tap water, followed by distilled water and then sun dried. The dried materials were powdered to a fine mesh of size: <75µ and activated at 105^oC in an oven and then employed in this study. Further, these plant materials were burnt to ashes which were also employed in this work.

B: Adsorption experiment:

Batch system of extraction procedure was adopted (Gerard Kiely, 1998; Metcalf and Eddy, 2003; Trivedy, 1979). Carefully weighted quantities of adsorbents were taken into previously washed 1 lit/500 ml stopper bottles containing 500ml/250ml of Potassium Dichromate solution of predetermined concentrations. The various initial pH values of the suspensions were adjusted with dil HCl or dil NaOH solution using pH meter. The samples were shaken vigorously in mechanical shakers and were allowed to be in equilibrium for the desired time. After the equilibration period, an aliquot of the sample was taken for Chromium determination. Chromium (VI) was determined Spectrophotometrically by using “Diphenyl Carbazide” method (Arthur I Vogel, 1961).

Estimation of Chromium (VI): An aliquot amount of Chromate sample was taken in a 50ml volumetric flask. To it 1ml of 6N Conc. H₂SO₄ solution and 1ml of Diphenyl Carbazide solution were added successively and the solution was then diluted to the volume and mixed well. Then O.D. of the developed color was measured against blank at 540 nm using U.V. and Visible Spectrometer. Thus obtained O D value was referred to a standard graph (drawn between O.D and Concentration) prepared with known amounts of Chromium by adopting the method of Least Squares to find concentration of Chromium in unknown solutions.

The sorption characteristics of the said adsorbents were studied with respect to the time of equilibration, pH and sorbent dosage. The results obtained were presented in the Graph Nos. A: 1-3; B: 1and2; C: 1and2.

C: Effect of Interfering Ions:

The synthetic mixtures of foreign ions and Chromium (VI) were so made that the concentration of the former ions were maintained at fivefold excess than the latter. Then at optimum extraction conditions, Chromium (VI) was extracted as per the procedure detailed above. Percentage of extraction was calculated and the results are presented in the Table No. 1.

D: Applications:

The procedures developed were applied to some real samples from industrial sewages of tannery industries in Hyderabad and Chrome plating industries in Chennai. The results obtained were presented in the Table 2.

RESULTS AND DISCUSSION:

The effects of various physicochemical parameters such as pH, time of equilibration and sorption concentration on the extraction of Chromium (VI) have been presented in the Graph No. A: 1.1 to 1.4, A: 2.1 to 2.4, A: 3.1 to 3.4; B: 1 and 2; C: 1 and2).

It can be inferred that the % of extraction is time and pH dependent. With increase in time % of extraction increases at a fixed pH for a fixed adsorbent and after certain time (varies from sorbent to sorbent), the extractability remains constant, i.e. an equilibrium state has been reached. In other words, there will not be any further adsorption after certain time of equilibration time (vide Graph Nos. A: 1 to 3). As for example, in the case of Annona squamosa leaves, at pH: 2, % of extraction is 98.2% at 5hrs, 95.0% at 4.0 hrs, 90.0% at 3 hrs, 86.0% at 2.0 hrs, 82.0% at 1hr.(vide Graph No.A:1). The same trend is noticed in the case of other sorbents.

Table 1: Effect of Interfering Ions on the Extractability of Chromium (VI) with different Bio-sorbents

S.No	Adsorbent and its Concentration	Maximum Extractability at optimum conditions	% removal of Chromium (VI) in presence fivefold excess of interfering ions at optimum conditions: Conc. of Chromium(VI): 50ppm
S.No	Adsorbent and its Concentration	Maximum Extractability at optimum conditions	SO₄^2-	NO₃^2-	Cl^-	P0₄^3-	F^-	CO₃^2-	Ca²⁺	Mg²⁺	Cu²⁺	Zn²⁺	Ni²⁺
1	Powder of Annona squamosa leaves 2.5gm/l	98.2% pH:2, 5.0 hrs	76.4%	83.1%	86.2%	77.2%	91.6%	89.2%	92.6%	94.7%	98.5%	99.5%	98.6%
2	Powder of Cassia auriculata leaves 3.5gm/l	94.0% pH:2, 6.0hrs	78.3%	89..8%	92.0%	68.7%	93.2%	87.0%	93.6%	92.9%	91.3%	92.8%	90.0%
3	Powder of Ficus religiosa leaves 3.0gm/l	99.0% pH:2, 5.0hrs	70.4%	96.2%	97.4%	71.9%	98.7%	88.1%	98.5%	96.5%	96.0%	97.0%	98.0%
4	Ash of Annona squamosa leaves 2.0g/l	99.0% pH:2, 5.0 hrs	72.5%	83.3%	86.4%	70.3%	92.6%	85.2%	93.0%	93.5%	95.5%	92.5%	91.0%
5	Ash of Cassia auriculata leaves3.0g/l	96.0% pH:2, 5 .0hrs	78.4%	90.5%	82.3%	73.4%	95.1%	84.8%	95.5%	94.0%	93.3%	92.8%	97.0%
6	Ash of Ficus religiosa leaves 2.5g/l	100% pH:2, 5 hrs	78.2%	91.3%	91.8%	74.5%	97.3%	82.5%	100%	100%	100%	100%	100%
7	Bark Powder of Annona squamosa 1.5gm/l	100.0% pH:2, 5.0 hrs	73.9%	89.2%	83.1%	70.1%	79.3%	86.2%	96.2%	96.8%	97.2%	98.4%	99.1%
8	Bark Powder of Cassia auriculata 2.5gm/l	98.0% pH:2, 6.0hrs	75.3%	91.3%	86.7%	71.5%	93.3%	84.6%	99.3%	92.0%	94.0%	91.0%	95.0%
9	Bark Powder of Ficus religiosa 2.0gm/l	100.0% pH:2 5.0hrs	76.0%	90.1%	88.0%	70.3%	91.3%	88.4%	100%	100%	100%	100%	100%
10	Bark Ash of Annona squamosa 1.0gm/	100.0% pH:2, 4.0 hr	73.2%	84.4%	88.3%	71.2%	97.3%	86.4%	100%	100%	100%	100.0%	100%
11	Bark Ash of Cassia Auriculata 2.0gm/ l	99.0% pH:2, 5 .0hrs	73.2%	84.1%	96.7%	70.2%	98.1%	87.8%	99.1%	95.4%	96.8%	98.1%	97.0%
12	Bark Ash of Ficus religiosa 1.5gm/l	100% pH:2, 4.0 hrs	71.4%	96.1%	97.2%	72.7%	99.3%	81.1%	100%	100%	100%,	100%	100%

Table No: 2: Extractability of Chromium in Different Industrial Effluents and Natural Lake Samples using Bio-sorbents

Bio-Sorbent	% of Extractability of Chromium (VI) in diverse Samples (actual Conc. of Chromate is shown in parenthesis)
	Tannery Industry effluents			Chrome plating Industry effluents			Lake Samples (Chromate is fed)
	Sample-1 (25.0 ppm)	Sample-2 (32.5 ppm)	Sample-3 (41.5 ppm)	Sample-4 (36.5 ppm)	Sample-5 (50.1 ppm)	Sample-6 (44.0 ppm)	Sample-7 (20 ppm)	Sample-8 (18 ppm)	Sample-9 (29 ppm)
Leaves powder of Annona squamosa.:at pH:2; Equilibration time: 5.0 hrs and sorbent concentration: 2.5 gm/lit	86.5%	93.1%	85.0%	85.2%	85.5%	90.0%	96.5%	92.0%	91.2%
Leaves powder Cassia Auriculata. at pH:2; Equilibration time: 6.0 hrs and sorbent concentration: 3.5 gm/lit	88.0.%	92.2%	88.3%	86.0%	84.2%	87.2%	91.0%	91.5%	92..5%
Leaves powder of Ficus Religiosa . :at pH:2; Equilibration time: 5 hrs and sorbent concentration: 4.0 gms/lit	90.4%	90.6%	87.2%	90.0%	88.2%	91.5%	90.0%	9.3%	92.5%
Bark powder of Annona squamosa . :at pH:2; Equilibration time:5.0 hrs and sorbent concentration: 1.5 gm/lit	91.0%	92.0%	82.5%	91.4%	81.4%	85.5%	96.2%	88.6%	89.5%
Bark powder of Cassia Auriculata :at pH:2; Equilibration time: 6 hrs and sorbent concentration: 2.5gms/lit	92.0%	90.5%	83.5%	92.0%	85.0%	86.5%	90.3%	87.5%	87.5%
Bark powder of Ficus Religiosa . at pH:2; Equilibration time: 5.0 hrs and sorbent concentration: 2.0 gm/lit	92.4%	88.5%	85.3%	90.2%	87.7%	92.5%	86.5%	87.5%	88.5%
Ashes of Leaves of Annona squamosa . :at pH:2; Equilibration time: 5.0 hrs and sorbent conc.: 2.0 gms/lit	94.0%	90.4%	90.0%	91.6.%	88.4%	93.5%	90.5 %	93.5%	93.5%
Ashes of Leaves of Cassia Auriculata . :at pH:2; Equilibration time: 6.0 hrs and sorbent concentration: 3.0 gm/lit	92.6%	91.5%	88.5%	87.0%	84.2%	93.5%	88.3%	86.0%	90.5%
Ashes of Leaves powder : Ficus Religiosa . at pH:2; Equilibration time: 5.0 hrs and sorbent concentration: 2.5 gm/lit	93.0%	87.2%	87.5%	85.5%	85.7%	94.5%	90.8%	90.0%	92.6%
Bark ashes of: Annona squamosa :at pH:2; Equilibration time: 4.0 hrs and sorbent conc.: 1.0 gm/lit	94.0%	86.2%	84.5%	83.0%	81.1%	89.5%	88.5%	92.5%	90.9%
Bark ashes of Cassia Auriculata : at pH:2; Equilibration time: 5.0 hrs and sorbent conc. 2.0 gm/lit	88.9%	89.1%	86.5%	83.5%	84.3%	88.5%	86.5%	89.0%	93.8%
Bark ashes of Ficus Religiosa . :at pH:2; Equilibration time: 4.0 hrs and sorbent concentration: 1.5 gm/lit	91.7%	92.1%	90.2%	90.5%	89.6%	90.0%	87.0%	85.5%	92.5%

With Bark powder of Ficus religiosa, 100.0%, 85.0%, 68.0%, 48.0% and 32.0% extraction of Chromium(VI) have been observed at pH: 2,4, 6,8 and 10 respectively at an equilibration period of 5 hrs while with their ashes 100.0%, 87.0%, 74.0%, 45. 0% and 33.0% have been noted at an equilibration period of 4 hrs.

The maximum % of extractability is found to be marginally more with ashes of leaves than with raw powders of leaves. In most of the adsorbents, more than 90.0% extractability is observed even at 2 hrs of equilibration. (vide Graph Nos. A: 1-3).

Equilibration time needed for the maximum extraction of Chromium (VI) is found to be less for ashes of barks than raw bark powders. With the ashes of barks of Annona squamosa, Cassia Auriculata and Ficus religiosa, the equilibration time needed for maximum extraction is found to be 5 hrs, 6 hrs and 5hrs, respectively at optimum pH:2 while with their ashes, the optimum equilibration times are found to be 4 hrs, 5 hrs and 4 hrs respectively (vide Graph Nos. A: 1.2, 2.2, 3.2, and A: 1.4, 2.4, 3.4). However, in most of these sorbents, considerable amounts of Chromium have been found to be extracted even at 2 hrs of equilibration time.

The optimum sorbent dosage for maximum extraction of Chromates is found to be in the order:

Leaves > Leaves ash > Barks > Barks ashes : with Annona squamosa, the optimum dosage is found to be respectively 2.5 gms/lit, 2.0 gms/lit, 1.5 gms/lit and 1.0gm/lit ; with Cassia auriculata, 3.5 gm/lit, , 3.0 gms/lit, 2.5 gms/lit and 2.0 gms/lit; with Ficus religiosa, 4.0 gms/lit, 2.5 gms/lit, 2.0 gms/lit and 1.5 gm/lit (Vide Graph No.C:1.1and1.2).

The maximum percentage of extraction at optimum conditions of pH and sorbent dosage are found to be 98.2%, 94.0% and 99.0% with leaves powders of Annona squamosa, Cassia auriculata and Ficus religiosa (vide Graph Nos.A:1.1,2.1and3.1) and 99.0%, 96.0% and 100.0% with their ashes respectively (vide Graph No. A: 1.3, 2.3 and3.3). With bark powders of Annona squamosa, Cassia auriculata and Ficus religiosa, the maximum % of extractions are found to be respectively 100.0%,98.0% and100.0% (vide Graph Nos.A:1.2,2.2and3.2) while with their ashes 100.0%, 99.0% and 100.0% respectively (vide Graph Nos .A: 1.4,2.4 and3.4).

Interfering Ions: The effect of fivefold excess of foreign ions on the extractability of Chromate ions, has been studied and the results are presented in Table No. 1.

Cations have envisaged marginal effect. Sulphates and phosphates have interfered while rest of the anions taken for study, have almost no effect.

DISCUSSION:

To understand the extraction characteristics, surface morphology of these bio-sorbents have to be taken into account. The functional groups present in these lingo celluloses’ materials are either –OH-or -COOH groups. These groups dissociate at high pH values imparting negative charge to the surface and so electrostatic thrust for positively charged ions prevails on the surface at high pH conditions. But as the pH decreases, the dissociation of functional groups is not favored and further, protination occurs. This resulting positive charge at the interface, imparts thrust for anions at low pH condition. Chromate being an anion is adsorbed by these materials at low pHs and thus results in higher % of removal. As pH increases, the deprotination occurs and hence the affinity of the adsorbent towards the Chromate decreases and thus resulting in low % removal of Chromate ions.

The decrease in the rate of adsorption with the progress in the equilibration time, may be due to the more availability of adsorption sites initially and are progressively used up with time due to the formation of adsorbate film on the sites of adsorbent and thus resulting in decrease in capability of the adsorbent.

Applications:

The procedures developed in this work have been applied for samples collected from the effluents of Tannery and Chrome plating industries. The results obtained have been presented in the Table No: 2. It can be inferred that the procedures are remarkably successful.

CONCLUSIONS:

1. Leaves, stems or barks of Annona Squamosa, Cassia auriculata and Ficus religiosa have been found to be effective in the extraction of Chromate from polluted waters at low pH values.

2. Physicochemical parameters such as pH, time of equilibration and sorbent concentration have been optimized for the maximum removal of Chromate.

3. More than 94.0% of Chromate extraction is noted from simulated waters in all the sorbents of study at optimum conditions of extraction.

4. Fivefold excess of common foreign cations has marginal effect on the extraction. Sulphate and Phosphate are interfering while the rest of the anions of study have almost ‘nil’ effect.

5. The procedures developed are successfully applied for some industrial samples.

ACKNOWLEDGEMENT:

The authors thank UGC for financial aid for conducting this research work.

REFERENCES:

1. Ahmed M.T., Taha S. Chaaban T., Akretche D., Maachi R. and Dorange G. 2006. Desalination 419-420.

2. Amir, Hossein Mahvi, Dariush, Naghipur, Forugh, Vaezi and shahrokh, Nazamara., 2005. Tea waste as an adsorbent for heavy metal removal from industrial waste waters. American Journal of Applied Sciences., 2(1), 372-375.

3. Arenas, L.T., Lima E.C., Santos A.A., Vaghetti J.C.P.,. Costa T. M.H. and. Benvenutti E.V. 2007. Colloids and Surfaces A: Physicochemical and Engineering Aspects: 297, 240-248.

4. Arthur I Vogel. 1961. A Text book of Quantitative Inorganic Analysis including elementary Instrumental analysis, 3^rd Edition, ELBS., 792.

5. Asha Lata Singh 2008. E-J of Science and Technology, 1-16.

6. Cavaco S.A. Fernandes S., Quina M.M. and Ferreira L. 2007. J. Hazardous Materials: 144, 634-638.

7. Chen S.S., Cheng C.Y., Li C.W., Chai P.H. and Chang Y.H. 2007. J. Hazardous Materials: 142, 362-367.

8. Chubar, Natalia, Carvalho, Jorge R. and Neiva Correia, M.J. 2003. Cork Biomass as Biosorbent for Cu(II), Zn(II) and Ni(II). Colloids and Surfaces A :Physicochemical and engineering aspects 230(1-3), 57- 65.

9. Cristian Covarrubias, Renan Arriagada Jorge Yanez, Rafael Garcia; Maria Angelica;, SD Barros; Pedro Arroyo and Euardo Falabella Sousa-Aguia .2005. J of Chemical Technology and Bio-technology. 80(8), 899-908.

10. Dahbi S., Azzi M,. Saib N. M De la Guardia R. Faure and. Durand R 2002. Anal Bioanal Chem 374, 540-546.

11. Dakiky, M. Khamis,M., Manassra A. and Mereb M. 2002.Advances in Environ. Res. 6, 533-540.

12. Dinesh Mohan and Charles U. Pittman Jr. 2006. Activated carbons and low cost adsorbents fro remediation of tri and hexavalent chromium from water, J of Hazardous Materials” 137(2), 762-811.

13. Divya Jyothi M., Rohini Kiran K. and Ravindhranth K. 2011. IJABPT 2(4), 330-51.

14. Divya Jyothi M., Rohini Kiran K. and Ravindhranth K. 2012. ESAIJ, 7(2), 47-56.

15. Gerard Kiely. 1998. Environmental Engineering, McGraw-hall International Editions.

16. Gupta S. and Babu B.V. 2009. Chemical Engineering Journal 150, 352-365.

17. Hanumantha Rao Y., Kishore M. and Ravindhranath K. 2011. International J of Plant, Animal and Environmental Science, 1(3).

18. Hanumantha Rao Y., Kishore, M. and Ravindhranath K. 2011. IJABPT. 2(4), 2011, 323-29.

19. Imran Ali and V. K. Gupta V.K. 2006. Nature London: 1, 2661-2667.

20. Imran Ali. 2010 . Sepn. and Purfn. Rev. 39, 95-171.

21. Iqbal M., Saeed A., Akhtar N. and Petiolar N. 2002. Felt-sheath of palm: a new biosorbent for the removal of heavy metals from contaminated water, Bio Resource Technology: 81(2) 153-155.

22. Kamaludeen S.P.B., K.R. Arunkumar K.R.,Avudainayagam S. and .Ramasamy K. 2003. Ind. J .E. Exp. Bio 41, 972.

23. Karthikeyan T., Rajgopal S. and . Miranda L.R. 2005. J. Hazardous Materials: B 124, 192-199.

24. Kothiyal N.C. Deepak Pathamia and Chetan Chauhan 2011. Electronic J of Environment, Agricultural, Food Chemistry 10(9), 2900-2912.

25. Kowalski Z.1994. J. Hazardous Materials: 37, 137-144.

26. Kumar P.A., .Ray M. and Chakraborty S. 2007. J. Hazardous Materials 143, 24-32.

27. Lenore S., Clesceri Arnold E. Greenberg and Andrew D Easton (Editors).1998. Standard Methods for the Examination of Water and Wastewater,20th Edition, American Public Health Association, 3-65.

28. Loukidou, M.X., Zouboulis, A.I., Karapantsios T.D. and Matis K.A. 2004. Colloids and Surfaces A: Physicochemical and Engineering Aspect 242, 93-104.

29. LuzE. De-Bastan and Yoav Bashan. 2004. Recent advances in removing phsophorous from waste water and its future use as fertilizer (1997-2003). Water Research 38, 4222-4246, - a review article and other reference in it.

30. M. Galinnato M., .Moody K. and Piggin C.M.1999. Upland rice weeds of south and Southeast Asia IRRI. Philippines.

31. Majeti N.V. and. Kumar R. 2000. A review of chitin and chitosan applications. React. Funct. Polym. 46, 1–27.

32. Manju G. N. and T.S. Anirudhan T.S. 1997. Indian J. Environ. Health: 39 , 289-98.

33. Meena A. and Rajagopal C. 2003. Indian Journal of Experimental Biology 10, 72-78.

34. Menderes Koyuncu and Riza Kul A. .2011. J. Chem. Pharm. Res. 3(1) 297-303.

35. Metcalf and Eddy. (revised by George Techobanoglous, Franklin L.Burton and H. David Stensel). 2003 Wastewater Engineering: Treatment of Reuse. 4^th Edition, McGraw Hill Co., New York.

36. Mohan D,. Singh K.P and Singh V.K. 2005. J. Chemical Technol. Biotechnol.: 44, 1027-1042.

37. Mohan D., Singh K.P. and .Singh V.K. 2006.. J. Hazardous Materials. B135: 280-295.

38. Nageswara Rao L. and Prabhakar G. 2011. J. Chem. Pharm. Res 3(6), 73-87.

39. Oklieimen F.E. and Onyenkpa V. U. (1989). Bio Waste 29 11.

40. Orhan, Y and Buyukgungor 1993. Removal of heavy metals by using Agricultural wastes. Water Sci. Technol. 28, 247-255.

41. Parameswari E., Lakshmanan A. and T.Thilagavathi 2009. Australian Journal of Basic and Applied Sciences 3 (2 ), 1363-1368.

42. Preetha B. and Viruthagiri T. 2007. Biochem. Engineering J 34, 131-135.

43. Rajeev Upadhya 1992. J of Indian Pollution Control 8, 81-84.

44. Sandhya Babel and Tonni Agustions Kurniawan .2003. . Low Cost adsorbents fro heavy metals uptake from contaminated water : a review. J of hazardous materials: 97, 219-243.

45. Santiago I., Worland V.P., Cazares E.R. and Cadena F .1995. 47^th Purdue Industrial Waste Conference Proceedings: 669-710.

46. Sarin V and.Pant K. K 2006. Bioresource Technol 97,15-20.

47. Shrihari S. and Raghavendra S.K. 2003. Pol. Res.: 22(4) 507.

48. Shukla A., Zhang Y. H., Dubdey P., Margrave J.L and Sukla S.S. 2002. The role of sawdust in the removal of unwanted materials from water. J. Hazard Mater 95,137-152.

49. Shyamala R. Sivakamasundari S. and Lalitha P. 2005. J of Industrial Pollution Control 21(1), 31-36.

50. Singh D.K. and B. Srivastava B. 2000. Ind. J. of Industrial Polltion Control 16(1), 19-24.

51. Suneetha M. and Ravindhranath K. 2012. Der Pharma Chemica, 4 (1), 214-227

52. Thillai Natarajan S., Jayaraj R. Jeyasingh Thanara and Martin Deva Prasath P.2011. J. Chem. Pharm. Res. 3(2), 595-604.

53. Thomas L. Eberhardt, Soo-Hong Min James, Han S. Phosphate removal by refined aspen wood fiber treated with carboxymethyl cellulose and ferrous chloride 2006.Bioresource Technology 97, 2371-2376.

54. Trivedy R.K. 1979 Pollution Management in Industries, Environemental Publicatons, Karad, India.

55. US Department of Health and Human Services 1991. Profile for Chromium, Public Health Service Agency for Toxic substances and Diseases, Washington, DC.

56. US Patent: 3835042 (Sept 1974) 5000852 (March 1991) and 7105087 (Sept 2006); Great Britain 1394909 (Sep 1975); Switzerland: 575347 (March 1976); France:2192071 (Nov 1976);Canada: 1026472 (Feb 1978).

57. Vandana Swarnkar, Nishi Agrawal and Radh Tomar. 2011. J. Chem. Pharm. Res. #(3), 520-529.

58. Vasanthy M Sangeetha M. and Kalaiselvi R. 2004 . J of Industrial Pollution Control 20, 37-44.

59. Vinodhini V. and Nilanjana Das. 2009. American-Eurasian J of Scientific Research 4(4), 324-329 . ( references in it)

60. Yu, L.J., Shukla, S.S. Dorris, K.L, Shukla A. and Margrave J.L. 2003. J. Hazardous Materials, 100, 53-63.

Received on 10.01.2013 Modified on 17.01.2013

Asian J. Research Chem. 6(2): February 2013; Page 121-130

INTRODUCTION: