The impact of chlorides on NMC leaching in hydrometallurgical battery recycling

Abstract

The current paper studies the impact of chlorides on NMC111 (LiNi1/3Mn1/3Co1/3O2) leaching mechanism. Experiments were conducted in chloride (HCl) and mixed sulfate–chloride (H2SO4–NaCl) solutions as well as in sulfate solution (H2SO4, reference), in the absence of external reductants. The results suggest no major differences in the leaching performance between studied lixiviants at 30 °C (∼75% for Li, ∼35% for Co, Ni, Mn), and increasing the temperature to 80 °C mainly improved the dissolution of lithium (>90% in all lixiviants). However, the leaching behavior of manganese was found to be different – in sulfate solutions, Mn precipitated as MnO2 with only 6% Mn left in solution after 2 h (at 80 °C), whereas in chloride-containing solutions, dissolved Mn remained soluble (30–40% extraction). The presence of chlorides also supported cobalt and nickel extraction, the mixed H2SO4–NaCl system resulting in extractions of 55% for Co and 58% for Ni at 80 °C. The increase in the dissolutions is suggested to be explained by the experimentally verified reaction between Cl- ions and NMC111, resulting in Cl2 formation and simultaneous NMC dissolution. The results indicate that hydrometallurgical battery recycling processes may face challenges with manganese extraction to solution when operating at increased temperatures, and that the presence of chloride ions can help to mitigate such difficulties by inhibiting unwanted precipitation of manganese compounds, producing Cl2 gas as a result. Nevertheless, as the final extractions were low even in the most effective lixiviant (55% Co, 58% Ni, 39% Mn at 80 °C), the use of additional reductants is necessary to ensure high metal leaching efficiencies also in such chloride-containing systems.