Two-step leaching process and kinetics for an eco-friendly recycling of critical metals from spent Li-ion batteries

With growing awareness to protect the urban environment and fulfill the soaring demand for critical metals, recycling of postconsumer Li-ion batteries has become imperative to deal in a sustainable manner. In this context, a two-step leaching of the exhausted LiNixCoyMnzO(2) cathode material was studied by sequential application of both organic and mineral acids. To optimize the experimental parameters of both steps, leaching was conducted using the L25 orthogonal array design. In the first-step leaching, lithium and copper was selectively leached into oxalic acid at the optimal condition of C2H2O4 (OA), 0.25 M; pulp density (PD1), 10%; H2O2 dosage (HPD1), 0.5%; temperature (T-1), 80 degrees C; and time (t(1)), 90 min. The parametric influences for achieving more than 99% efficiency of lithium and copper followed the order: t(1) > HPD1 > OA > PD1 > T-1 and t(1) > T-1 > OA > HPD1 > PD1, respectively. Residual metal-oxalates of cobalt, nickel, and manganese were subsequently dissolved into sulfuric acid solutions. Approximately 99% of all remaining metals could be leached at the optimal condition of H2SO4 (SA), 3.0 M; pulp density (PD2-), 6%; H2O2 dosage (HPD2), 2%; temperature (T-2), 60 degrees C; and time (t(2)), 120 min. The parametric influences on sulfuric acid leaching of metals followed the order as: SA > HPD2 > t(2) > PD2 > T-2. Leaching followed logarithmic rate law and exhibition of the diffusion-controlled mechanism was revealed through the values of apparent activation energy determined to be E-a(Li), 9.7 kJ/mol; E-a(Cu), 22.3 kJ/mol; E-a(Co), 9.5 kJ/mol; E-a(Ni), 11.2 kJ/mol; and E-a(Mn), 6.2 kJ/mol. This study successfully demonstrated the applicability of OA in the selective leaching of LiNixCoyMnz-type cathode materials, eliminating the need for copper and lithium separation from leach liquor of SA-medium. The present process offers two-fold advantages that securing the secondary supply for critical metals, and providing an environmentally sustainable route for waste valorization in a circular economy.

Automated summary

The study demonstrated the effectiveness of a two-step leaching process using organic and mineral acids for recycling exhausted Li-ion batteries, offering a sustainable solution for protecting the urban environment and fulfilling the demand for critical metals. The process optimized experimental parameters and successfully achieved high efficiency in leaching lithium, copper, cobalt, nickel, and manganese from the cathode material. This approach not only secures a secondary supply of critical metals but also provides an environmentally sustainable route for waste valorization in a circular economy.