Selective zinc recovery from spent alkaline batteries via multistage leaching with ammonium salts

The recycling of metals from spent alkaline batteries is essential for their proper management and for promoting sustainable battery consumption. Hydrometallurgical recycling techniques, such as leaching, are becoming important in batteries recycling. In this study, Zn has been selectively recovered from the black mass (BM) of spent alkaline batteries via chelating leaching using ammonium salts as chelating agents in single and multistage leaching units. The effect of leaching agent concentration, temperature, solid/liquid (S/L) ratio, a neutral leaching pretreatment and addition of ammonium hydroxide (NH₄OH) to the leaching solution on the selective Zn extraction was studied. Results of single-stage leaching revealed a maximum Zn extraction efficiency of 69.3 ± 0.4 wt % using a 2M ammonium carbonate ((NH₄)₂CO₃) solution at 25 °C and S/L ratio of 1/10 (g of BM/mL of solution). The addition of NH₄OH 1M increased Zn extraction to 79.0 ± 1.9 wt %. These single leaching conditions were used to test three multistage leaching systems: solid-flowing in series, liquid-flowing in series and solid-liquid countercurrent. The recovery efficiency was maintained and sometimes it was improved in multistep configurations, reaching a maximum recovery efficiency of nearly 90 wt%. Additionally, cumulative zinc extraction across the multistage leaching setups was as follows: 145.6 g Zn/kg BM in the 3-unit-solid-flowing in series, 433.5 g Zn/kg BM in the 4-unit-liquid-flowing in series, and 132.46 g Zn/kg BM in two-unit countercurrent leaching. These concentrations were obtained using a raw BM containing 240.9 g Zn/kg BM. These results show that zinc can be selectively extracted from matrices containing other metals, allowing the development of efficient and cost-effective methods for recycling resources from spent batteries.