Zinc metal extraction from alkaline battery waste by pyrochemistry

Research Project, 2016 – 2017

Zinc (Zn) is one of the most economically important industrial metal after iron, aluminum and copper. It is widely used in several applications such as in metallurgy, electrical, chemical, defense and oil industries due to its anti-corrosion characteristic, chemical and mechanical properties. However, Zn is currently accepted as one of the endangered elements that may have potentially restricted reserve in the next century. Therefore, the reclaiming of Zn from various waste streams became an important subject for the sustainable Zn supply. Furthermore, the recycling of Zn reduces the energy requirement to nearly a quarter of the energy consumed for the primary production, as well as carbon footprint to one out of five, and also minimizes the environmental impact of Zn mining. Alkaline and zinc-carbon (Zn-C) battery black mass can be a significant secondary source for Zn. However Zn extraction from the battery waste is still a challenge and innovative alternatives should be developed for environmental and sustainable industry.

In the project, Zn was extracted from spent alkaline and zinc-carbon batteries by pyro-chemistry process using carbon (C) or hydrogen (H2) as a reducing agent. The thermodynamics of the pyro-chemical process was studied using the HSC Chemistry 5.11 software to determine the parameters to reach the higher Zn recovery amount, lowest energy consumption and lowest CO2 emission. The Zn extraction amount reached to 99.8% 60 min process time using 5%H2-N2 gas mixture as a reaction atmosphere. The C analyses show that the reduction reactions dominated by H2(g) and carbon footprint of the optimal process was calculated as 0.48 g CO2/ g Zn under the assumption of using green energy sources for the process.