The interference of copper, iron and aluminum with hydrogen peroxide and its effects on reductive leaching of LiNi_1/3Mn_1/3Co_1/3O₂

Copper and iron are known to be effective alternative reducing agents to H₂O₂ in Li-ion battery leaching. The aim of this work is to study the effect of added H₂O₂ on its overconsumption to the side reactions such as oxidation of copper, iron, and aluminum in leaching of NMC 111 active material. The interactions between the reducing agents separately were first investigated (T = 30 °C, [H₂SO₄] = 2 M, t = 120 min). Elemental copper was found to be a less efficient reducing agent (78%) compared to aluminum (100%) in terms of Fe³⁺ reduced to Fe²⁺. Nevertheless, copper exhibited much higher rate of iron reduction than aluminum. Additionally, aqueous copper ions were found to cement on aluminum surface and redissolve in the presence of iron, thus acting as the metallic reducing agent. In contrast, in the presence of H₂O₂ ferrous iron and copper were rapidly oxidized resulting in the consumption of all reducing agents. These effects were confirmed also during the leaching of NMC (T = 30 °C, [H₂SO₄] = 1.5 M, t = 120 min), which demonstrated that the leaching efficiency markedly decreased (∼63%) in the presence of H₂O₂ and Cu when compared to H₂O₂ alone (∼78%). Furthermore, results from NMC leaching showed that when copper-iron reductant or H₂O₂ were added separately, a much higher leaching efficiency was achieved (∼66% and ∼78%, respectively) in contrast to being added together (∼58%).