Zinc metal extraction from alkaline battery waste by pyrochemistry

Purpose and goal
A pyro-chemical process with low CO2 emission for the extraction of zinc from spent alkaline batteries was developed. The process efficiency increased and the carbon footprint sharply decreased when H2 gas was used as a reducing agent. The waste feeding amount determined as the critical factor to control the efficiency in the case of scale-up the process, if horizontal static furnace is preferred. Gas analyses revealed that the exhaust gas of the process was dominated by CO and CO2, but other minor gases, which can be treatable, were also detected in the exhaust gas flow.

Structure and implementation
The project investigated the extraction of zinc from battery waste by a developed pyro-chemical process and systematically analysed the effects of the type and amount of the reducing agent, process time and waste feeding amounts to optimise the conditions for high recovery amount and low CO2 emission. Energy consumption and exhaust gas emission of the optimised process were analysed. The process carbon footprint is lesser than the lowest value of industrial zinc process considering that using green energy sources. The zinc particles has submicron size and it is a market-ready product.

Results
The zinc recovery amount reached 99% at 950 °C for 60 minute process time by adding carbon as a reducing agent. Although extra carbon increased the zinc recovery, the CO2 gas emission of the process also rose. When H2 gas was used, 99.7 and 99.8% of the zinc extracted from the waste at 950 °C for 45 and 60 minute process times, respectively, and the CO2 emission was minimized. Zinc and manganese oxide particles were prepared in the process. The project results show that industrial scale pyro-chemical process can be economically and environmentally feasible for the recovery of zinc from spent batteries.