A comparative study of discharging and leaching of spent lithium-ion battery recycling

[Display omitted] •Reductants promote the selective leaching of valuable metals from spent batteries.•Hydrazine sulfate assures selective extraction of Li, Mn, Ni, and Co in acid media.•Reductive acid leaching guarantees an elevated Cu0and Al0 remotion (≥90 %).•In alkaline media Li and Al leaching is directly affected by pH variation.•In alkaline media, additional species formation influences Li selective extraction. Accelerated production of lithium-ion batteries (LIBs) implies an increase in the raw materials demand, especially for metals like lithium, cobalt, and nickel. Spent LIBs recycling guarantees the regeneration and reincorporation of valuable materials into the manufacturing industry; therefore, recycling methods and techniques must be optimized. In this investigation, alkaline and reductive acid leaching processes were evaluated and compared in order to determine the effect of parameters such as pH, temperature, and reagents concentrations to achieve selective leaching processes. This study demonstrated that strongly alkaline solutions (NaOH) do not ensure selective lithium and aluminum dissolution. Also, a solid compound, LiAl2(OH)6OH(s) can be formed at pH ∼14, negatively affecting the lithium extraction. On the other hand, reductive acid leaching, with acid sulfuric and hydrazine sulfate (H2SO4 + N2H6SO4) solutions resulted in an efficient system, extracting ≥90 % of Ni, Co, and Mn at 40 °C. Hydrazine is essential as a reductant, although it must be added in excess (40 % excess with respect to the Co, Ni, and Mn content) to suppress copper dissolution. Furthermore, this work demonstrated the possibility of processing the entire spent LIBs sample once the discharge and crushing stages were concluded, avoiding physical separation, without affecting the leaching efficiency and contributing to process economy.