9] had been based solely on ICP, which measures total chromium. The authors had assumed that all Cr(VI) is retained after passing through the column, and had not considered the possibility of reduction to Cr(III). Reduction may indeed not

Figure 4. Amount of chromium removed in mg/g (q) by trimmed original wool as function of Ce, the equilibrium concentration of Cr(VI). Adsorbent dosage = 8.0 g/L, T = 25.0˚C, shaking speed = 150 rpm.

Figure 5. Langmuir isotherm for Cr(VI) and total chromium using original wool as adsorbent in long term mode (5 days). Adsorbent dosage = 8.0 g/L, pH = 1.5, T = 25.0˚C, shaking speed = 150 rpm.

Figure 6. Langmuir isotherm for Cr(VI) and total chromium using original wool as adsorbent in short term mode (contact time 3 h). Adsorbent dosage = 8.0 g/L, pH =1.5, T = 25.0˚C, shaking speed =150 rpm.

Table 2. Langmuir parameters (b, Q and R2) for total chromium and Cr(VI) for short term and long term equilibration periods, with original wool as adsorbent. Adsorbent dosage = 8.0 g/L, T = 25.0˚C, shaking speed =150 rpm.

Table 3. Freundlich isotherm parameters (Kf, n and R2) for total chromium and Cr(VI) for short and long term modes using trimmed wool as adsorbent. Adsorbent dosage = 8.0 g/L, T = 25.0˚C, shaking speed =150 rpm.

occur when the contact time between wool and the eluent is very short. Under such conditions, all forms of chromium are essentially removed. However, when solutions containing Cr(VI) were left in contact with wool in the column for longer periods, the first fraction contained higher concentrations of total chromium, and this can now be attributed to the presence of Cr(III). To verify this conclusion, 100 ppm Cr(VI) solution was applied to a column packed with original wool and eluted at a constant rate of 2.0 ml/min. 100 ml fractions of eluents, representing short term equilibration were collected for four successive overnight periods, with the elution stopped at the end of each day, thereby allowing long term equilibration of Cr(VI) on wool. The data for total chromium and Cr(VI) are presented in Figure 7. Virtually, the only form of chromium eluted overnight is Cr(III). This corroborates the finding that upon prolonged exposure on wool, Cr(VI) undergoes reduction to Cr(III).

3.5. FTIR Spectroscopy

Figure 8 displays FTIR spectra of wool before and after adsorption of Cr(VI). The very weak peak at 939 cm1 in free wool becomes much more pronounced in wool loaded with chromium for long term contact, due to the oxidation of wool by Cr(VI). This peak can be attributed to S=O bonds that form when cystine in wool is oxidized. A similar assignment has been reported for wool oxidized by UV irradiation [31] . This finding supports the proposed mechanism for removal of Cr(VI) by wool from aqueous solution (Equation (1)).

3.6. Electron Dispersive X-Ray Spectroscopy (EDS)

Scanning electron microscopy (SEM) was employed to study the surface of wool before and after loading with chromium. In order to obtain the elemental analysis of the surface, EDS spectra were recorded for both samples (Figure 9). Inspection of this figure reveals that chromium is retained on wool at the end of the long term contact time, with the appearance of a chloride peak from HCl.

Figure 7. Mass of chromium species in eluted fractions. Fraction volume = 100 ml, total applied volume = 2.5 L, pH of applied solution = 1.5, wool mass 26.0 g, wool depth = 29.0 cm. T = 25.0˚C.

Figure 8. FTIR spectra of free wool (bottom) and wool loaded with ionic chromium species (top).

Figure 9. EDS results for original free wool (top) and wool loaded with ionic chromium species (bottom).

4. Conclusion

The affinity of wool for Cr(VI) varies with contact time and pH. For short contact times, the Langmuir adsorption isotherm was obeyed with no detectable change in the oxidation state. However, removal percentages did not exceed 90%. Long contact times resulted in more than 99% removal of Cr(VI). A 2-step mechanism for this removal is proposed. The first involves fast adsorption of Cr(VI) on wool and the second a slow catalytic reduction of Cr(VI) to Cr(III), followed by desorption of Cr(III) into solution. The surface of wool before and after adsorption was characterized by FTIR and EDS and the results with the suggested mechanism. The optimum parameters for this significant improvement in Cr(VI) removal and hence its environmental remediation can now be identified as pH 1.5, contact time of at least 5 days, and a minimum adsorbent dosage of 8.0 g/L. For the short term study, pH 2.0 was selected so as to provide comparison with previous results. Cr(VI) adsorption follows the Langmuir adsorption isotherm with Q = 64.5. This high capacity of wool for Cr(VI) provides a practical solution for the removal of Cr(VI) from industrial wastewater. A plant can be constructed consisting of a batch adsorption reactor with a 5-day retention time in which Cr(VI) is mostly removed. The effluent could then subjected to pH 10.0 at which Cr(III) precipitates as hydroxide which can be recovered by sand filtration for further reuse.

Acknowledgements

This research was supported by the American University of Sharjah, Grant FRG12-2-10.

References

  1. Parikh, N. and Mashru, R. (2010) Estimation of Trace Amounts of Chromium(III) in Various Multivitamin Pharmaceutical Formulations. International Journal of Pharmacy and Biological Sciences, 1, 388-394.
  2. Kotas, J. and Stasicka, Z. (2000) Chromium Occurrence in the Environment and Methods of Its Speciation. Environmental Pollution, 107, 263-283. http://dx.doi.org/10.1016/S0269-7491(99)00168-2
  3. Dakiky, M., Khamis, M., Manassra, A. and Mer’eb, M. (2002) Selective Adsorption of Cr(VI) in Industrial Wastewater Using Low-Cost Abundantly Available Adsorbents. Advances in Environmental Research, 6, 533-540. http://dx.doi.org/10.1016/S1093-0191(01)00079-X
  4. Ezebuirol, P., Gandhi, J., Zhang, C., Mathew, J., Ritter, M. and Humphrey, M. (2012) Optimal Sample Preservation and Analysis of Cr(VI) in Drinking Water Samples by High Resolution Ion Chromatography Followed by Post Column Reaction and UV/Vis Detection. Journal of Analytical Sciences, Methods and Instrumentation, 2, 74-80. http://dx.doi.org/10.4236/jasmi.2012.22014
  5. Udy, M.J. (1956) History of Chromium. In: Udy, M.J., Ed., Chromium. Vol. I. Chemistry of Chromium and Its Compounds, Reinhold, New York, 1-13.
  6. Zhou, X., Korenaga, T., Takahashi, T., Moriwake, T. and Shinoda, S. (1993) A Process Monitoring Controlling System for the Treatment of Wastewater Containing Chromium(VI). Water Research, 27, 1049-1054. http://dx.doi.org/10.1016/0043-1354(93)90069-T
  7. Tiravanti, G., Petruzzelli, D. and Passino, R. (1997) Pretreatment of Tannery Wastewaters by an Ion Exchange Process for Cr(III) Removal and Recovery. Water Science and Technology, 36, 197-207. http://dx.doi.org/10.1016/S0273-1223(97)00388-0
  8. Seaman, J.C., Bertsch, P.M. and Schwallie, L. (1999) In Situ Cr(VI) Reduction within Coarse-Textured, Oxide-Coated Soil and Aquifer Systems Using Fe(II) Solutions. Environmental Science & Technology, 33, 938-944. http://dx.doi.org/10.1021/es980546+
  9. Khamis, M., Jumean, F. and Abdo, N. (2009) Speciation and Removal of Chromium from Aqueous Solution by White, Yellow and Red UAE Sand. Journal of Hazardous Materials, 169, 948-952. http://dx.doi.org/10.1016/j.jhazmat.2009.04.053
  10. Dahbi, S., Azzi, M. and de la Guardia, M. (1999) Removal of Hexavalent Chromium from Wastewaters by Bone Charcoal. Fresenius’ Journal of Analytical Chemistry, 363, 404-407. http://dx.doi.org/10.1007/s002160051210
  11. Kongsricharoern, N. and Polprasert, C. (1996) Chromium Removal by a Bipolar Electrochemical Precipitation Process. Water Science and Technology, 34, 109-116. http://dx.doi.org/10.1016/S0273-1223(96)00793-7
  12. Pagilla, K. and Canter, L.W. (1999) Laboratory Studies on Remediation of Chromium-Contaminated Soils. Journal of Environmental Engineering, 125, 243-248. http://dx.doi.org/10.1061/(ASCE)0733-9372(1999)125:3(243)
  13. Chakravarti, A.K., Chowdhury, S.B., Chakrabarty, S., Chakrabarty, T. and Mukherjee, D.C. (1995) Liquid Membrane Multiple Emulsion Process of Chromium (VI) Separation from Wastewaters. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 103, 59-71. http://dx.doi.org/10.1016/0927-7757(95)03201-N
  14. Lin, C.F., Rou, W. and Lo, K.S. (1992) Treatment Strategy for Cr(VI)-Bearing Wastes. Water Science and Technology, 26, 2301-2304.
  15. Aksu, Z. and Kutsal, T. (1990) A Comparative Study for Biosorption Characteristics of Heavy Metal Ions with C. vulgaris. Environmental Technology, 11, 979-987. http://dx.doi.org/10.1080/09593339009384950
  16. Leyva-Ramos, R., Fuentes-Rubio, L., Guerrero-Coronado, R. and Mendoza-Barron, J. (1995) Adsorption of Trivalent Chromium from Aqueous Solutions onto Activated Carbon. Journal of Chemical Technology and Biotechnology, 62, 64-67. http://dx.doi.org/10.1002/jctb.280620110
  17. Samantaroy, S., Mohanty, A.K. and Misra, M. (1997) Removal of Hexavalent Chromium by Kendu Fruit Gum Dust. Journal of Applied Polymer Science, 66, 1485-1494. http://dx.doi.org/10.1002/(SICI)1097-4628(19971121)66:8<1485::AID-APP9>3.0.CO;2-A
  18. Namasivayam, C. and Yamuna, R.T. (1995) Adsorption of Chromium (VI) by a Low-Cost Adsorbent: Biogas Residual Slurry. Chemosphere, 30, 561-578. http://dx.doi.org/10.1016/0045-6535(94)00418-T
  19. Singh, D.B., Rupainwar, D.C. and Prasad, G. (1992) Studies on the Removal of Cr(VI) from Wastewater by Feldspar. Journal of Chemical Technology and Biotechnology, 53, 127-131. http://dx.doi.org/10.1002/jctb.280530204
  20. Manassra, A., Khamis, M., Ihmied, T. and Eldakiky, M. (2010) Removal of Chromium by Continuous Flow Using Wool Packed Columns. Electronic Journal of Environmental, Agricultural and Food Chemistry, 9, 651-663.
  21. Vinodhini, V. and Nilanjana, D. (2009) Mechanism of Cr(VI) Biosorption by Neem Sawdust. Journal of Scientific Research, 4, 324-329.
  22. Qurie, M., Khamis, M., Manassra, A., Ayyad, I., Nir, S., Scrano, L., Bufo, S. and Karamam, R. (2013) Removal of Cr(VI) from Aqueous Environments Using Micelle-Clay Adsorption. Scientific World Journal, 2013, Article ID: 942703. http://dx.doi.org/10.1155/2013/942703
  23. Zghida, H., Baouab, M. and Gauthier, R. (2003) Sorption of Chromium Oxy-Anions onto Cationized Ligno-Cellulosic Materials. Journal of Applied Polymer Science, 87, 1660-1665. http://dx.doi.org/10.1002/app.11596
  24. EPAA (1992) Chromium Hexavalent (Colorimetric), EPA Method 7196A1992. http://www.epa.gov/osw/hazard/testmethods/sw846/pdfs/7196a.pdf
  25. Fiol, N., Escudero, C. and Villaescusa, I. (2008) Chromium Sorption and Cr(VI) Reduction to Cr(III) by Grape Stalks and Yohimbe Bark. Bioresource Technology, 99, 5030-5036. http://dx.doi.org/10.1016/j.biortech.2007.09.007
  26. Daneshvar, N., Salari, D. and Aber, S. (2002) Chromium Adsorption and Cr(VI) Reduction to Trivalent Chromium in Aqueous Solutions by Soya Cake. Journal of Hazardous Materials, 94, 49-61. http://dx.doi.org/10.1016/S0304-3894(02)00054-7
  27. Nakano, Y., Takeshita, K. and Tsutsumi, T. (2001) Adsorption Mechanism of Hexavalent Chromium by Redox within Condensed-Tannin Gel. Water Research, 35, 496-500. http://dx.doi.org/10.1016/S0043-1354(00)00279-7
  28. Tan, W.T., Ooi, S.T. and Lee, C.K. (1993) Removal of Chromium(VI) from Solution by Coconut Husk and Palm Pressed Fibers. Environmental Technology, 14, 277-282. http://dx.doi.org/10.1080/09593339309385290
  29. Singh, D.K., Saksena, D.N. and Tiwari, D.P. (1994) Removal of Chromium(VI) from Aqueous Solutions. Indian Journal of Environmental Health, 36, 272-277.
  30. Cho, N.S., Aoyama, M., Seki, K., Hayashi, N. and Doi, S. (1999) Adsorption by Coniferous Leaves of Chromium Ions from Effluent. Journal of Wood Science, 45, 266-270. http://dx.doi.org/10.1007/BF01177738
  31. Millington, K. and Church, J. (1997) The Photodegradation of Wool Keratin II. Proposed Mechanisms Involving Cysteine. Journal of Photochemistry and Photobiology B: Biology, 39, 204-212. http://dx.doi.org/10.1016/S1011-1344(96)00020-6

NOTES

*Corresponding author.

Journal Menu >>