Process for the recycling of alkaline and zinc–carbon spent batteries

In this paper a recycling process for the recovery of zinc and manganese from spent alkaline and zinc–carbon batteries is proposed. Laboratory tests are performed to obtain a purified pregnant solution from which metallic zinc (purity 99.6%) can be recovered by electrolysis; manganese is recovered as a mixture of oxides by roasting of solid residue coming from the leaching stage. Nearly 99% of zinc and 20% of manganese are extracted after 3 h, at 80 °C with 10% w/v pulp density and 1.5 M sulphuric acid concentration. The leach liquor is purified by a selective precipitation of iron, whereas metallic impurities, such as copper, nickel and cadmium are removed by cementation with zinc powder. The solid residue of leaching is roasted for 30 min at 900 °C, removing graphite completely and obtaining a mixture of Mn3O4 and Mn2O3 with 70% grade of Mn. After that a technical-economic assessment is carried out for a recycling plant with a feed capacity of 5000 t y−1 of only alkaline and zinc–carbon batteries. This analysis shows the economic feasibility of that plant, supposing a battery price surcharge of 0.5 € kg−1, with a return on investment of 34.5%, gross margin of 35.8% and around 3 years payback time.