Mechanisms and Kinetics for Pyrometallurgical Recovery of Zinc and Manganese Oxides from Spent Alkaline and Zinc-C Batteries

Abstract

The recycling of spent alkaline and Zinc-C batteries is essential for sustainable resource management and environmental protection. With the rising global demand for batteries, particularly in electric vehicles and energy storage systems, efficient recovery of valuable metals such as Zn and Mn has become increasingly important. While hydrometallurgical processes have been extensively studied, research on the kinetics and mechanisms of pyrometallurgical recovery, particularly carbothermal reduction, remains limited. This study investigates the carbothermal reduction process of black powder obtained from spent alkaline and Zinc-C batteries through both isothermal and non-isothermal experiments. A vertical tubular furnace equipped with a balance chamber was used to conduct thermogravimetric analysis, while gas analysis was performed to monitor CO and CO2 evolution. Isothermal experiments were conducted between 800 and 1300 degrees C, while non-isothermal experiments covered a temperature range of 25 to 1300 degrees C at heating rates of 5, 10, 15, and 20 degrees C/min. The reaction kinetics followed a two-dimensional diffusion model, confirming that CO gas generated in the process acted as a reducing agent. The isothermal activation energy was determined to be 14.3 J/mol, while the non-isothermal activation energy was 43.3 J/mol. Additionally, the reaction mechanisms and phase transformations of Zn and manganese oxides were analyzed across different temperature ranges. The findings provide crucial insights into optimizing process conditions for efficient and eco-friendly recovery of Zn and MnO from spent batteries, contributing to the advancement of circular economy strategies in battery recycling.