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Background & Aims of the Study: Since the chromium (VI) is a toxic, carcinogenic and non-biodegradable element and can accumulate in the tissues, the presence and release of this element through the effluents is associated with dangerous effects on life cycle. Thus, it should be removed from the effluents. In the present study, biosorption of Cr(VI) from aqueous solutions using Rice husk was investigated.

Materials and Methods: The various parameters such as pH, initial Cr(VI) ion concentration, adsorbent dose, and contact time were optimized in batch adsorption system. The experimental data were modeled by Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The pseudo-first order, pseudo-second order and intraparticle diffusion models were used to describe the kinetic data.

Results: The results indicated that Cr(VI) removal efficiency increases by increasing of contact time and adsorbent dosage. Langmuir models demonstrated the best fit of the adsorption data. The maximum adsorption capacity was 38.4 mg/g at optimum conditions of pH 5.0, contact time of 75 min, temperature of 30 ◦C and biomass dose of 5 g/L. The best correlation was provided by the second-order kinetic model.