Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by An, J.-H. Articles by Dultz, S. Search for Related Content GeoRef GeoRef Citation

ADSORPTION OF Cr(VI) AND As(V) ON CHITOSAN-MONTMORILLONITE: SELECTIVITY AND pH DEPENDENCE

Institute of Soil Science, Leibniz University of Hannover, Herrenhäuser Str. 2, D-30419 Hannover, Germany

^* E-mail address of corresponding author: dultz{at}ifbk.uni-hannover.de

Montmorillonite modified with the cationic biopolymer, chitosan, has, in weak acidic solutions, protonated amine groups which act as anion-adsorption sites. Due to the specific surroundings of the adsorption sites and diffusion paths in the interlayer of chitosan-montmorillonite, preferential adsorption of certain anions is likely. In the present study, the adsorption properties for the inorganic anions Cr(VI) and As(V) were determined, taking into account solution pH and competitive adsorption in the presence of Cl^– and SO₄^2–. Chitosan-montmorillonite was prepared by adding an amount of chitosan equivalent to 500% of the cation exchange capacity (CEC) at pH 5 and 75°C. The resulting anion exchange capacity was ~0.34 mol_c/kg. The adsorption properties for As(V) and Cr(VI) were determined with the batch technique at pH 3 to 9. Adsorption isotherms were fitted to the Langmuir and Dubinin-Radushkevich equations and judged quantitatively by the correlation coefficient. To describe the competitive adsorption, the selectivity (S) was determined by the ratio of amounts of anions A and B adsorbed (q_A/q_B) in a binary system. The ionic species adsorbed, i.e. either Cr(VI) or As(V), depended on the pH, as did the degree of protonation of the amine groups, and this played a decisive role in the amount of anions adsorbed. The maximum amount of Cr(VI) adsorbed was 180 mmol/kg at pH 3.5, whereas for As(V) it was 120 mmol/kg at pH 4.0 to 5.0. The adsorption process of Cr(VI) and As(V) fit well to the Langmuir isotherm. By increasing the concentration of the competitive anion, Cl^–, in solution, the amount of Cr(VI) and As(V) adsorbed remained almost constant, whereas SO₄^2– had a more pronounced competitive effect. At concentration ratios of 0.5 and 1 for SO₄^2– to Cr(VI) and As(V), respectively, the sorption capacity decreased by 10 and 25%, respectively. The sequence of the selectivity was: Cr(VI)>SO₄^2–>As(V)>Cl^–. Chitosan-montmorillonite showed a high selectivity for Cr(VI), which adsorbed chemically. Despite the lower affinity for As(V) and physical adsorption, the adsorption capacity was relatively high.

Key Words: Anion Adsorption • Arsenate • Chitosan-montmorillonite • Chromate • Selectivity