Abstract
AbstractThe effectiveness of rice husk–activated carbon (RHAC) in the adsorption of Cr(VI) from an aqueous solution was investigated. The adsorbent was prepared, characterized, and subjected to optimization, kinetics, and thermodynamics studies. Optimization was done using response surface methodology (RSM) based on the Box–Behnken design. Accordingly, optimum adsorption factors obtained were shaking speed of 176.90 rpm, adsorbent dosage of 1.96 g, and initial concentration of 50.12 mg/L for 93.49% removal of Cr(VI) at a desirability of 1.00. The maximum adsorption capacity obtained was 98.14 mg/g. An equilibrium adsorption isotherm model and a kinetic model of Cr(VI) on RHAC were fitted to experimental data. The data were well represented by the Freundlich adsorption isotherm model, with R2 of 0.9956, which presumes an energetically heterogeneous surface. Furthermore, the adsorption kinetic data were well described by the pseudo‐second order model with R2 range of 0.9969–0.9997, indicating a high agreement between experimental and calculated values. Finally, thermodynamic parameters such as mean Gibbs free energy (∆G) showed that adsorption of Cr(VI) ions onto RHAC was spontaneous and endothermic under examined conditions. In this view, RHAC is a viable adsorbent for the optimum removal of Cr(VI) ions from wastewater.
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