Separation of base metals from reduction smelt-alloy of spent lithium-ion batteries by ferric sulfate leaching, cementation, solvent extraction and oxidative precipitation

We propose a hydrometallurgical process to recover Ni, Co, Cu, Mn, and Fe from ferric sulfate synthetic leaching solution whose composition was similar to the real leach liquor of spent lithium-ion batteries (LIBs). Copper(II) was completely separated by cementation with iron powder at room temperature for 20 min. Afterward, H2O2 was added to the raffinate to oxidize Fe(II) to Fe(III). Multi-stage cross-current extraction with 2.0 M D2EHPA and stripping with 60% aqua regia completely removed iron from the solution. The separation of Mn(II) over Co (II) and Ni(II) was carried out by oxidative precipitation, in which Mn(II) was oxidized to MnO2 at the molar ratio NaClO to Mn(II) of 4.0 at pH 3.0. Following this, most of Co(II) together with 11% of Ni(II) were coprecipitated from the Mn(II) free filtrate at the molar ratio of NaClO to Co(II) of 7.0. From the filtrate containing Ni(II) of pH 3.0, the Ni(II) ions were completely recovered using Na2C2O4 as a precipitant at the same molar ratio of oxalate to Ni(II). Continuous experiments at the optimum condition of each step verified that Cu(II), Fe(III), and Mn(II) were completely separated by cementation, solvent extraction, and oxidative precipitation. The proposed process for base metal recovery from spent LIBs offers several advantages, such as low energy requirements and products with high purity.