Countercurrent leaching of lithium-ion battery waste under ambient conditions

• Room temperature leaching requires longer extraction time. • The overall processing time can be improved by counter current leaching. • Higher solid loading with comparable extraction efficiency is achieved. • Under optimized conditions the residue quality is improved to near 95 % graphite. Lithium mixed metal oxides from waste lithium-ion batteries or black mass can be effectively leached at room temperature with mineral acid and controlled addition of reducing agent. But at lower temperature and relatively higher solids loading, the time required for near complete dissolution of the value elements Li, Mn, Co, and Ni becomes longer due to the gradual decrease of chemical activity over time. To further improve the process, and lower the time required for acceptable efficiencies, and better suit a practical and continuous industrial adaptation recirculation or recycling the liquor and leach residues in part mode was evaluated. The current work utilizes 2 M sulfuric acid at room temperature as a lixiviant and controlled addition of hydrogen peroxide as reducing agent. True counter current leaching uses evaluated by reusing the leach liquor to effectively maximize the total solid to liquid ratio and substantially minimize the overall leach time. In addition, a two-step recirculating batch process was also evaluated to reuse both the solid and liquor effectively improving the combined leaching efficiency and the carbon quality in the final residue. Extraction of 97–99 % of Co and near 100 % of Mn, Ni and Li were achieved and the final leach residue by-product was 95 % C.