Improved Metal Circular Economy-Selective Recovery of Minor Ag Concentrations from Zn Process Solutions

Silver is a metal widely applied in renewable energy applications and therefore subject to resource scarcity. The paper presents a new approach for recovering silver from zinc-containing solutions mimicking hydrometallurgical base metal process solution. By nature, silver present in ores or concentrates is more noble than zinc and not effectively leached into the sulfate media during zinc hydrometallurgical processing. This paper presents a novel approach for concentrating and recovering silver present in minor amounts in zinc sulfate media. The electrodeposition–redox replacement (EDRR) method was investigated in synthetic zinc sulfate solutions ([Zn] = 60 g/L, [Ag] = 1 ppb–250 ppm, [H2SO4] = 10 g/L) containing silver as low as 1 ppb. The deposited metal coating was analyzed by electrochemical techniques and SEM-EDS. As a result, an enrichment of silver as nano- and microparticles on electrodes was evident. With the application of multiple EDRR steps (n = 160), the method was shown to result in a high purity Ag layer (Ag/Zn ratio ≈ 1500 in the product) from solution with minor Ag content (Ag/Zn ratio ≈ 0.0017 in solution). Moreover, at the concentration levels studied, the EDRR method was shown to outperform conventional electrowinning (EW).