Selective extraction of precious metals in the polar aprotic solvent system: Experiment and simulation.

The traditional hydrometallurgical process is the mainstream technology to recover precious metals from e-waste, which usually adopts strong acid/base and strong oxide with high environmental cost and energy consumption. In the present study, the selective extraction of precious metals was simulated and experimented with DMF as the solvent and Cl- ions provided by CaCl2 and CuCl2 (oxidizing agent). The leaching and precipitation rates of precious metals (Au, Ag, Pd) can reach more than 98% under optimization conditions. Kinetic data shows that the control model of the leaching process on precious metals was determined by linear fitting of the shrinkage model. The complex trace precious metals were extracted selectively using dimethylglyoxime and deionized water as precipitators by the leaching-precipitation-cycle method. Meanwhile, the waste liquid produced by this reaction process could be cyclically utilized. Furthermore, the leaching mechanism of precious metals was proposed. DMF could be complexed with the metals as well as coordination ions (Cl-), which can reduce the redox potentials. Cu(II) could be easily reduced to Cu(I) in the DMF system due to the higher second ionization energy of copper, which is not influenced by the hydration effect, thus shifting the equilibrium to the metal leach side. Oppositely, the addition of water promoted the conversion of Cu(I) to Cu(II) since the higher hydration energy of Cu(II) compensates for the second ionization energy. This research opens up a new path of sustainable development and provides basic theory and practical experience for environmentally friendly recovery of precious metals from e-waste.

Recovery of silver from crystal silicon solar panels in Self-Synthesized choline Chloride-Urea solvents system.

Traditional acid-base leching technology is the primary technology to recycle silver from crystal silicon solar panels, which is fussy and often employs poisonous/harmful chemicals. In the present study, silver was easily recycled from photovoltaic panels in self-synthesized. Deep-Eutectic Solvents System (DESs) without pretreatments and the reaction system could be cyclically utilized. The leaching and precipitation rate can reach 99% under the optimized conditions. In addition, the kinetic results showed that the leaching of silver followed the classical shrinkage core model, in which chemical reaction was the rate-controlling step and the apparent activation energy for leaching process is 172.36 kJ·mol-1. In the recycling process, Cu2+ acted as the oxidant, and the redox potential of Cu2+ in the DES system is much higher than that in aqueous system. Besides, the HNMR and FTIR analysis indicate that the intermolecular hydrogen bond formed in the DES mixed system, which would raise the melting and boiling point of the mixed system, and would be conducive to the following silver leaching process. Furthermore, the metal complex generation mechanisms were proposed in the present study, and urea plays not only an aprotic solvent which cannot solvate Cl-, but also the ligand which can complex with the metals as well as Cl- which can reduce the redox potentials and shift the equilibrium to the silver leaching side. In summary, this study can provide theoretical foundation and practical experience for recycling precious metals from waste crystal silicon solar panels environmentally efficient and cost-effective.