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Langmuir 2001, 17, 4256-4260
Chromium Adsorption by Chitosan Impregnated with Microemulsion T. N. de Castro Dantas,* A. A. Dantas Neto, M. C. P. de A. Moura, E. L. Barros Neto, and E. de Paiva Telemaco Universidade Federal do Rio Grande do Norte, UFRN/PPGEQ, Campus Universita´ rio, 59.072-970 Natal/RN, Brazil Received August 4, 2000. In Final Form: April 10, 2001 Removal of chromium(III) from aqueous solutions by chitosan impregnated with a microemulsion was investigated. The modified chitosan showed a remarkable increase in chromium sorption capacity as compared to an untreated sample. Dynamic column experiments were performed to study the influence of pH, concentration, and the presence of others metal ions (copper and nickel) in the chromium solutions. The adsorption process is pH-dependent, and the amount of Cr(III) retained increases with increasing heavy metal initial concentration. It can be observed that the best bed efficiency was for copper, followed by chromium and then nickel. The nature of chromium(III) adsorption equilibrium at different temperatures (30, 40, and 50 °C) was investigated, and the Freundlich and Langmuir isotherm models were applied to fit the experimental data. The uptake process obeys the Langmuir isotherm. Following the adsorption step, the desorption process was carried out using several eluant solutions. The best results were obtained using strongly acidic solutions as eluants.
Introduction
Scheme 1. Structure of Chitosan
Most heavy metals are well-known toxic and carcinogenic agents and, when discharged in wastewater, represent a serious threat to human populations and the fauna and flora of receiving water bodies. Currently, many industries use heavy metals in the processing of raw materials, and consequently, the discharge of these metals into aquatic bodies and sources of drinking water has begun to be strictly controlled. The wastes of the textile, leather tanning, and electroplating industries are chromium-rich in hexavalent and/or trivalent forms of the metal. The hexavalent form is more hazardous than the trivalent form; however, the reduction of chromium(VI) to chromium(III) within cells and the binding of the metal to proteins and nucleic acids elevate the toxic potential of both forms.1-3 Sorption technology, including physical and chemical adsorption and ion-exchange process technologies have the potential to treat waters and industrial residues. In the adsorption process, atoms or ions (adsorbates) contained in a fluid phase diffuse to the surface of a solid (adsorbent), where they are chemically bound to the surface or held there by intermolecular forces.4 The search for cheap and efficient unconventional adsorbents to remove heavy metal ions has been the purpose of many investigations.2,5-11 In a previous paper,12
a treatment aimed at adsorbing a microemulsion on diatomaceous earth to remove chromium(III) was developed. The adsorbent used in the present experimental procedure is chitosan (Scheme 1). It was obtained by the deacetylation of chitin, a natural carbohydrate biopolymer extracted from the shells of arthropods such as shrimps, lobsters, and crabs. Brazil’s Northeast Region is rich in arthropods, and as the shells constitute a byproduct of industry, chitosan can be obtained from them very cheaply and with the advantage of being harmless to human beings.13,14 Microemulsions are applied for many purposes. They are thermodynamically stable, isotropic, and macroscopically homogeneous dispersions of two immiscible fluids, generally oil and water, stabilized with surfactant molecules either alone or mixed with a cosurfactant such as a short-chain alcohol.15-19
* Author to whom correspondence should be addressed. E-mail:
[email protected]. (1) Pe´rez-Candela, M.; Martı´n-Martinez, J. M.; Torregrosa-Macia´, R. Water Res. 1995, 29, 2174-2180. (2) Ajmal, M.; Rao, R. A. K.; Siddiqui, B. A. Water Res. 1996, 30, 1478-1482. (3) Tobin, J. M.; Roux, J. C. Water Res. 1998, 32, 1407-1416. (4) Seader, J. D.; Henley, E. J. Separation Process Principles; John Wiley & Sons: New York, 1998; pp 778-779. (5) Sun, G.; Shi, W. Ind. Eng. Chem. Res. 1998, 37, 1324-1328. (6) Lo´pez-Delgado, A.; Pe´rez, C.; Lo´pez, F. A Water Res. 1998, 32, 989-996. (7) Dimitrova, S. V.; Mehandgiev, D. R. Water Res. 1998, 32, 32893292. (8) Ajmal, M.; Khan, A. H.; Ahmad, S.; Ahmad, A.Water Res. 1998, 32, 3085-3091.
(9) Ferro-Garcı´a, M. A.; Rivera-Utrilla, J.; Bautista-Toledo, I.; Moreno-Castilla, C. Langmuir 1998, 14, 1880-1886. (10) Gupta, G.; Torres, N. J. Hazard. Mater. 1998, 57, 243-248. (11) Namasivayam, C.; Senthilkumar, S. Ind. Eng. Chem. Res. 1998, 37, 4816-4822. (12) Castro Dantas, T. N.; Dantas Neto, A. A.; Moura, M. C. P. A. Proceedings of the International Conference of Urban Pollution Control Technology (ICUPCT); Poon, C. S., Li, X. L., Eds.; Hong Kong Institution of Engineers: Hong Kong, 1999; pp S1-S6. (13) Baggio, C. O.; Stadler, E.; Laranjeiras, M. C. M. Rev. Quı´m. Ind. 1989, 672, 9-13. (14) Takatsuji, W.; Yoshida, H. Ind. Eng. Chem. Res. 1998, 37, 13001309. (15) Kahlweit, M.; Busse, G.; Faulhaber, B. Langmuir 1995, 11, 15761583. (16) Qutubuddin, S.; Miller, C. A.; Fort, T., Jr. J. Colloid Interface Sci. 1984, 101, 46-58.
10.1021/la001124s CCC: $20.00 © 2001 American Chemical Society Published on Web 06/07/2001
Cr(III) Adsorption Microemulsion-Impregnated Chitosan Table 1. Granule Size of the Chitosan Supplied Tyler (mesh)
size (mm)
% retained
28 48 65 100 150 200 250 325 400 0.99) than the Freundlich model. CTM’s adsorption capacity was found to increase with temperature. The capacities determined through batch experiments (85.99 mg/g) were smaller than those obtained in column experiments (130.22 mg/g). This can be explained by the pH and concentration gradients developed along the length of the column, improving the sorption processes. Tests accomplished with a solution containing a mixture of heavy metals allowed us to conclude that CTM adsorbs copper best, followed by chromium and then nickel. The aqueous mineral acids proved to be effective eluants, as an almost total solubilization of the adsorbent was observed, which prevents its utilization. LA001124S
