Adsorption kinetics of chromium(III) removal from aqueous solutions using natural red earth

摘要

Laboratory-scale-simulated experiments were carried out using Cr(Ⅲ) solutions to identify the Cr(Ⅲ) retention behavior of natural red earth (NRE), a natural soil available in the northwestern coastal belt of Sri Lanka. The effects of solution pH, initial Cr(Ⅲ) concentration and the contact time were examined. The NRE showed almost 100 % Cr(Ⅲ) adsorption within the first 90 min. [initial [Cr(Ⅲ)] = 0.0092-0.192 mM; initial pH 4.0-9.0]. At pH 2 (298 K), when particle size ranged from 125 to 180 urn the Cr(Ⅲ) adsorption data were modeled according to Langmuir convention assuming site homogeneity. The pH-dependent Cr(Ⅲ) adsorption data were quantified by diffused layer model assuming following reaction stoichiometries: 2 > AlOH_(s) + Cr (OH)_(2(aq))~→ (>AlO)_2Cr_(s)~+) + 2H_2O log K 15.56 2 >FeOH_(s)+ Cr(OH)_(2(ap))~+→ (>FeO)_2Cr_(s)~+ + 2H_2O log K 5.08. The present data showed that NRE can effectively be used to mitigate Cr(Ⅲ) from aqueous solutions and this method is found to be simple, effective, economical and environmentally benign.