Application of optimal mixture design in aluminum-dolomite composite for Cr(VI) removal from aqueous solution

An effective aluminum-dolomite composite, developed with a mixture of dolomite, bentonite, sawdust, and AlCl 3 , has been used for Cr(VI) removal from aqueous solution. Optimal mixture design method was used to determine the optimum mixture proportions by evaluating both chromium removal efficiency and mechanical strength. It was found that the optimum adsorption capacity and strength can be achieved with the proportion of 4.90 g dolomite, 3.12 g bentonite, 1.48 g sawdust, and 0.50 g AlCl 3 (10 g in total). Batch experiments were carried out using the composite revealed that 92% removal efficiency for Cr(VI) was occurred at pH 6 and room temperature (20°C). The adsorption kinetic and isotherm data well agreed with the pseudo-first-order kinetic and the Freundlich isotherm models, respectively. The co-existing anions (chloride, nitrate, and acetate) had slight negligible influence, and sulfate could significantly decrease the Cr(VI) adsorption efficiency. The aluminum- dolomite composite is a cost-effective adsorbent for Cr(VI) removal from aqueous solution, especially from low-level (<50 mg/L) sulfate solution, and no secondary pollution was observed after adsorption process.