Optimization of Cadmium Removal from Aqueous Solutions Using Walnut-shell Residues Biochar Supported/unsupported by Nanoscale Zero-valent Iron through Response Surface Methodology

Using various biochars to remove heavy metals (HMs) from aqueous solutions has been in-creased in recent years. It is believed that the use of nanocompounds in biochars surface structure may increase the efficiency of contaminants removal. Therefore, this research tries to investigate the efficiency of walnut-shell biochar (WSB) alone or supported by nanoscale zero-valent iron (WSB-nZVI) on cadmium (Cd) removal in aqueous solution controlled by four variables including initial Cd concentration, initial solution pH, contact time, and adsorbent dosage by Box Behnken design under response surface methodology. The results of present study showed that WSB-nZVI has a significant priority on WSB of Cd removal efficiency in aqueous solutions. The existence of functional groups on the surface of WSB via precipitation and adsorption processes, as well as nZVI formed on the WSB-nZVI via generating adsorption and complexation processes, have increased the ability Cd removal than WSB raw adsorbent. The maximum predicted Cd removal efficiency based on the pro-posed model was 99.72% with desirability of 1, in initial Cd concentration of 70.78 mg L-1, pH of 6.92, adsor-bent dose of 0.56 g L-1 and contact time of 40.42 min.