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Recovery of High-Purity Silver from Spent Silver Oxide Batteries by Sulfuric Acid Leaching and Electrowinning

A sustainable and effective sulfuric acid based process with the combination of facile acid leaching and electrowinning has been developed for the recovery of valuable elements from spent silver oxide batteries. Results suggest that the dissolution of elementary Ag was markedly promoted by the presence of MnO2 in the spent silver oxide batteries. Also, H2O2 was added to support an improved Mn and Ag extraction after 240 min of leaching. In the leaching step, 97% of silver as well as over 99% of Mn and Zn could be extracted under the optimum conditions: 1 mol/L H2SO4, a leaching temperature of 70 °C, an S/L ratio of 50 g/L, addition of 3 v/v % H2O2 at 240 min and a total leaching time of 270 min. Ultra-pure silver (Ag w/w% ≥ 99.98 %) was further recovered from the pregnant leaching solution (PLS) by potentiostatic electrowinning. Under the optimum deposition potential of -0.10 V and after 4 h of electrowinning, the silver recovery reached 98.5% with a high energy efficiency of 98.7%. Simultaneously, 5.6% Mn was recovered on the anode in the form of MnO2. Overall, these promising results suggest feasibility in the recycling of silver oxide batteries in sulfuric acid media.