A zero-liquid discharge process to recover all critical metals from spent NCM111 cathode material of end-of-life lithium-ion batteries: statistically optimized leaching with formic acid and in-situ crystallization

A green chemistry process has been developed to recycle cathode material from end-of-life lithium ion batteries. NCM111 (LiNi1/3Co1/3Mn1/3O2) was completely leached with 13 M formic acid to produce two groups of salts with different solubilities: sparingly soluble cobalt, manganese, and nickel (CMN) formates and highly soluble lithium formate. During leaching, CMN formate salts exceeded their solubility limit in the pregnant leach solution (PLS) and crystallized. Mixed CMN formate salts were recovered by filtering the PLS. Lithium was completely recovered by evaporating the filtered PLS then thermally decomposing the lithium formate obtained in air to lithium carbonate. The purity of the lithium carbonate was 98.1 wt%. The leaching process was optimized through response surface methodology experiments. The minimum time required to completely leach NCM111 with 13 M formic acid was 30.8 h. Optimum leaching conditions were L/S = 2.81 mL/g (equivalent to S/L = 356 g/L) and T = 95 °C. During leaching, 98% of CMN formate salts exceeded their solubility limit and crystallized from the PLS. The recycling process is simple and generates no liquid or solid waste products. The only reagent is 13 M formic acid. The only by-products are water vapour, which can be condensed and reused, and carbon dioxide gas.