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

    Year: 2021

    Journal: ACS Sustain. Chem. Eng., Volume 9, JUN 21, page 8186–8197

    Authors: Wang, Zulin; Hannula, Pyry-Mikko; De, Swarnalok; Wilson, Benjamin P.; Vapaavuori, Jaana; Yliniemi, Kirsi; Lundstrom, Mari

    Organizations: Academy of Finland [322214, 334818, 319691, 297962]; Aalto University; Chinese Scholarship Council (CSC); Ella and Georg Ehrnrooth Foundation

    Keywords: Electrodeposition; Redox replacement; Precious metal; Circular economy; Bimetallic particles

    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.
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