Abstract
—This study applied Response Surface Methodology (RSM) to investigate the interaction between Calcium Hypochlorite (HTH) concentration, Sodium Chloride (NaCl) concentration and contact time on the leaching of silver (Ag) from PCB e-waste. A Central Composite Design (CCD) was generated by Minitab, which was used to guide the experimental procedure and optimize the process parameters. The outcome of the experimental results highlight that the extraction of silver relies on the chloride ion concentration and contact duration. The contour plot and surface plots demonstrated minimal silver extraction (<0.05) at low NaCl concentrations (<2.0 M) and short contact times (<150 min), while optimum extraction (0.18-2.0, ~ 20% recovery) occurred at NaCl = 2.5-3.0 M, HTH = 0.20-0.25 M, contact time = 200 – 250 min. Beyond these ranges, the response plateaued, suggesting equilibrium controlled kinetics. The observed trends align with chloride complexation mechanisms involving the formation of AgCl-2 and AgCl2-3 species. The results confirm that chloride-based systems enhance silver dissolution efficiency while reducing the environmental footprint compared to cyanide leaching. Overall, the RSM approach effectively optimized the process parameters, establishing a robust foundation for future scale up and integration of chloride-assisted silver recovery within sustainable metallurgical processing frameworks .