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.