Response surface modelling of Cr6+ adsorption from aqueous solution by neem bark powder: Box–Behnken experimental approach

The main aim of this study is to investigate the combined effect of different operating parameters like adsorbent dose, initial Cr6+ concentration and pH on the removal of Cr6+ from aqueous solution using neem bark powder (NBP). A series of batch experiments were performed to find out the adsorption isotherms and kinetic behaviour of Cr6+ in the aqueous solution. The adsorption process was examined with three independent variables viz. NBP dosage, initial Cr6+ concentrations and pH. Seventeen batch experiments designed by Box–Behnken using response surface methodology were carried out, and the adsorption efficiency was modelled using polynomial equation as the function of the independent variables. Based on the uptake capacity and economic use of adsorbent, the independent variables were optimized by two procedures. The desirability of first and second optimization procedures were found to be 1.00 and 0.84, respectively, which shows that the estimated function may well represent the experimental model. The kinetic study indicated that the rate of adsorption confirms to the pseudo-second-order rate equation. Thermodynamics study indicated that the adsorption process was spontaneous and endothermic in nature. The surface texture changes in NBP were obtained from FT-IR analysis. The optimized result obtained from RAMP plots revealed that the NBP was supposed to be an effective and economically feasible adsorbent for the removal of Cr6+ from an aqueous system.