An integrated and sustainable hydrometallurgical process for enrichment of precious metals and selective separation of copper, zinc, and lead from a roasted sand

摘要

This study developed an efficient and sustainable hydrometallurgical process for the enrichment of gold and silver and the stepwise separation of copper, zinc, and lead from sulfated roasted sand of waste printed circuit board smelting ash. Selective separation of copper and zinc was achieved by water leaching, and silver dispersion was reduced by controlling the amount of NaCl added during the leaching process. The results of the water leaching showed that the copper and zinc leaching rates were 99.85% and 99.47%, respectively, whereas the loss rate of silver was 2.1% with optimal leaching parameters. The high-chloride-complex method was used to study the efficient conversion and separation of lead from the leached residue, and the leaching kinetics and conversion mechanism of lead were discussed. The results showed that under the optimal conditions, the leaching rate of lead was 99.79%. Leaching kinetics analysis showed that lead leaching in the high - chlorine system was controlled by a chemical reaction; the apparent activation energy was 53.63 kJ/mol. After the leaching of copper, zinc, and lead, 1.66% Ag and 213 g/t Au were enriched in the leached residue; and the precious metal enrichment goal was reached. The chlorinated leachate showed good recycling performance, and a lead leaching rate of 97.93% was obtained after three circulations. After cooling, crystallization, and purification, lead chloride with a purity of 99.89% and high economic and industrial value was obtained from the lead-rich leachate. This process has favorable and sustainable industrial application prospects.