Controllable Production of Ag/Zn and Ag Particles from Hydrometallurgical Zinc Solutions

Ag/Zn and Ag particles have been successfully produced from electrolytes simulating zinc process solutions containing a high zinc concentration (65 g/L) and a negligible silver concentration (0.5-50 ppm) using a facile and sustainable electrodeposition-redox replacement (EDRR) method. Results show that the particle size and chemical composition of the deposited Ag/Zn and Ag particles can be readily controlled by varying the operating parameters such as replacement time and agitation. Electrochemical quartz crystal microbalance (EQCM) studies supported with SEM-EDS and TEM results indicate that the EDRR process consists of three regions: (I) zinc pulse deposition; (II) redox replacement between the Ag+ ions and the deposited Zn, formation of a Zn/Ag alloy structure, and competing Zn oxidation by H+ ions; and (III) further replacement between Ag+ ions and Zn (alloy) formed in the previous stage and possible silver reduction by hydrogen. The Zn (alloy) has a higher reduction potential which hinders the competing H+ reduction and sequentially improves the utilization efficiency of the sacrificial metal (Zn). Furthermore, by using the EDRR method, Ag/Zn particles could be successfully obtained from solutions with an extremely low Ag concentration of 0.5 ppm. The promising results demonstrate the feasibility of producing Ag-based functional materials utilizing trace amounts of Ag from zinc process solutions.