Green Process of Metal Recycling: Coprocessing Waste Printed Circuit Boards and Spent Tin Stripping Solution

Electronic waste (e-waste), including waste printed circuit boards (PCBs), has caused global concern owing to its potential environmental pollution and rich resource content. Previous studies have indicated that urban mining for metals recycling can decrease energy consumption and pollutants emission compared to the extraction of metals from natural minerals. During the production of PCBs, a large amount of spent tin stripping solution (TSS) is simultaneously generated, containing the significant amounts of metal ions and residue nitric acid. In this study, the coprocessing of waste PCBs and spent TSS at room temperature was proposed and investigated, with the aim of developing an environmentally sound process to address these problems. This coprocessing approach proved to be effective. 87% of the Sn–Pb solder, 30% of the Cu, 29% of the Fe, and 78% of the Zn was leached from waste PCBs with spent TSS after 2 h, at room temperature. Moreover, approximately 87% of the electronic components were dismantled from waste PCBs. About 99% of the Sn, Pb, Fe, Cu, and Zn were recovered from the leaching solutions by chemical precipitation. The proposed green process has substantial advantages over traditional recovery methods of heating waste PCBs, in terms of both material and energy efficiency

Mixed Potential Plays a Key Role in Leaching of Chalcopyrite: Experimental and Theoretical Analysis

The mixed potential plays a key role in leaching of chalcopyrite. Therefore, the impact of Fe²⁺ and Fe³⁺ on chalcopyrite leaching was investigated in this work. Simultaneously, the chalcopyrite passive film was studied by applying cyclic voltammetry (CV), potentiodynamic, potentiostatic, and Tafel polarization. X-ray photoelectron spectroscopy (XPS) was used to analyze the products formed during the electrochemical treatment of chalcopyrite. Furthermore, the band theory was used to analyze the oxidation and reduction of chalcopyrite. High copper extraction percentage was obtained at a low mixed potential or ratio of Fe³⁺/Fe²⁺. The empty states of chalcopyrite overlapped with filled states of Fe²⁺; chalcopyrite captured electrons from Fe²⁺ and was reduced to chalcocite, which was very easily oxidized by Fe³⁺. The Fe dissolves preferentially from the chalcopyrite surface in the potential range from 475 to 700 mV and leave behind a S₂^2– and S_<i>n</i>^2– passive film. The chalcopyrite transpassive dissolution occurs above 700 mV