Taguchi design for optimization of the removal of chromium(VI) by impregnated bentonite (K+) from aqueous solution

Abstract

Adsorption of very toxic Cr(VI) was studied by liquid–solid extraction by natural bentonite impregnated with potassium hydroxide (KOH). The optimization procedure was performed using L9 Taguchi design. The combined effect of the two process parameters are the initial Cr(VI) concentrations in aqueous solutions (10–4 – 8 × 10–4 M) and the amount of bentonite (K+) (0.1–0.4 g). The optimum conditions for adsorption are the initial Cr(VI) concentrations 10–4 (M) (level 1) and the amount of bentonite (K+) 0.4 (g) (level 3). Analysis of the signal-to-noise ratio was used to determine important parameters that help in the adsorption process. Several kinetics and isotherms were evaluated using non-linear models such as pseudo-first-order and pseudo-second-order; Langmuir and Freundlich models. Langmuir isotherm and pseudo-second-order model explained the removal mechanism among the models evaluated, which infers that the removal followed chemisorption. The results show that the removal of chromium is mainly affected by the initial Cr(VI) concentrations, followed by the adsorbent amount 7.41 mg/g removal of Cr(VI) under optimal conditions with the removal of 10–4 M of chromium at pH 5.02 with 0.4 g bentonite (K+) for 30 min and 300 rpm. The optimization procedure performed using the L9 Taguchi design provides access to industrial-scale Cr(VI) rejection processing.