Strategies for recovery of copper and gold as single constituents or an alloy: Selective separation and adsorption-coupled incineration of the bulk metal-loaded adsorbents

To recover useful metals from waste PCBs, environmentally friendly bioleaching has recently attracted attention. Accordingly, distinct protocols are required to adequately recover the bioleached metals. Herewith, we present strategies to separate and recover copper and gold from a bioleached solution of waste PCBs. Polyethylenimine-polyacrylic acid composite adsorbents (PPCAs) were screened from among different candidate adsorbents. By only adjusting the mixing ratio of PEI and PAA, it was possible to recover gold and copper as single constituents or an alloy. A two-step strategy was designed, leading to the successful separation of copper and gold, first through selective adsorption of copper and then by bulk adsorption of copper and gold. The experimental maximum equilibrium uptakes of copper by PPCA-2 and PPCA-7 were 667±0.06 and 587±0.16 mg g⁻¹, respectively. The pseudo-first- and pseudo-second-order models fitted the kinetic data of copper better than gold. Following incineration, the adsorbents were characterized for examining the crystallinity and atomic energy states of the metals. Consequently, XRF analysis revealed that the copper-gold alloy ash contained 96.7±0.40% Cu and 1.73±0.26% Au. This study would be helpful for future studies that would aim at the separation and recovery of metallic minerals from bioleachates.