Selective Step-by-Step Extraction of Precious Metals from Electronic Waste in Non-Aqueous Solvent Systems

Traditional hydrometallurgical technology is the mainstream technology to recycle precious metals from electronic waste. However, this method is cumbersome and often employs toxic/harsh chemicals. In the present study, the mono-metal (gold, silver, palladium) recycling system was firstly studied in dimethylformamide (DMF) which has the advantages of high solubility, low solvation effect, and excellent coordination interaction. The leaching-precipitation parameters were optimized which showed the precious metal leaching and precipitation rate could reach over 98% under the optimized conditions. Furthermore, the leaching kinetic results show that all three metals follow the classical shrinking core model with chemical reaction being the rate-controlling step. The apparent activation energies for leaching process of gold, silver and palladium were 107.13 kJ·mol -1 , 34.59 kJ·mol -1 , 67.75 kJ·mol -1 , which means gold is quite difficult to leach while silver is relatively easy. On this basis, we reported a selective extraction of compound metals in non-aqueous solvent systems, and obtained the productions of gold, silver chloride and palladium with dimethylglyoxime using leaching-precipitation-recycling process step by step. Furthermore, the metal complex generation mechanisms were proposed in the present study, DMF plays not only an aprotic solvent which cannot solvate Cl - , but also the ligand and can complexed with the metals as well as Cl - which result in the redox potentials reduce and move the equilibrium to the metal leaching side. In a word, this research could provide a fundamental basis as well as practical guidance for recycling precious metals environmentally, and could further consider the application of selective extraction of precious metals from electronic waste