Validation of Bromide Leaching through Response Surface Methodology and Separation of Gold from Waste Printed Circuit Boards

The daily consumption of gold is increasing worldwide; however, its availability from conventional ores is reducing. Alternatively, the presence of gold in waste electrical and electronic equipment (WEEE) is nearly 100 times higher than in natural ore. Therefore, the possibility of the recovery and separation of gold from waste printed circuit boards of obsolete mobile phones is studied in the present work. Initially, the optimization of parameters for the quantitative gold leaching from metal clads of PCBs with halide salts at acidic conditions is studied through response surface methodology. Three factors (parameters), viz. temperature, time and stirring speed are altered during the experiments based on the central composite design (CCD). Leaching parameters have been optimized with the help of the second-order empirical equations and analysis of variance (ANOVA) for maximum gold dissolution. The selective recovery and separation of gold from leach liquor have been achieved with solvent extraction with an organic amide as extractant followed by cementation with zinc powder. The separated gold powder has also been analyzed with XRD and SEM-EDS to check the purity and homogeneous elemental distribution. The statistical design of experiments and separation processes for the effective recovery of gold corroborates the economic feasibility of the proposed process.