Response surface methodological approach for optimizing the removal of cadmium from aqueous solutions using pistachio residues biochar supported/non-supported by nanoscalezero-valent iron

Abstract

Abstract A three-level Box–Behnken model (BBM) under response surface methodology (RSM) was used to optimize the removal of cadmium (Cd) ion by pistachio residues biochar (PRB) and PRB supported by nanoscale zero-valent iron (PRB-nZVI) from aqueous solutions. Optimization experiments were carried out by evaluation of the effect of four variables (initial Cd concentration, initial solution pH, adsorbent dosage, and contact time) at three levels (high, medium, and low), and one category contained two variables (PRB and PRB-nZVI). For this purpose, a total of 58 experimental runs were set and the experimental data were fitted to the empirical second-order polynomial model of a suitable degree. The physical and chemical structure results of the adsorbents confirmed the formation of nZVI (with diameters ~35 nm) on the PRB surface. The results showed that the new composite of biochar (PRB-nZVI) exhibited higher Cd removal efficiency compared with PRB from aqueous solutions. The existence of functional groups and nZVI on the surface of PRB-nZVI could be better than PRB for Cd removal in aqueous solutions by the processes of sorption, precipitation, and co-precipitation. Numerical optimization revealed that the optimum removal (96.58%) was obtained at an initial Cd concentration of 25.99 mg L−1 (pH 6.58), adsorbent dose (PRB-nZVI) of 0.55 g L−1, and contact time of 34.11 min, with desirability of 1. Based on the results, it is recommended that PRB-nZVI can be effectively used for the removal of Cd from a contaminated aqueous solution with varying chemical and physical conditions.