Removal of iron and aluminum from hydrometallurgical NMC-LFP recycling process through precipitation

There is a need to develop removal strategies for typical battery impurities–iron and aluminum–from actual hydrometallurgical recycling solutions. In this work, the investigated solution originated from lithium nickel manganese cobalt oxide (NMC) rich black mass, while iron phosphate (LFP) was used as an in situ reductant. It was found that the presence of phosphate ions supported selective iron precipitation already at pH = 2.0 (T = 60 °C, t = 3 h, NaOH), with nearly complete iron removal (97.8 %). The precipitate was rich in iron (21.5 wt%) and phosphorus (13.4 wt%); it also contained 0.7 wt% Ni and 0.3–0.4 wt% Mn, Co, Al, and Li. It is suggested that the presence of phosphate in minor amounts may cause this co-precipitation of battery metals. With the aim of combined precipitation of iron (100 %) and aluminum (91.0 %), the pH was increased up to 4.5. Although 90.8 % of fluoride precipitated, the remaining fluorides may have kept the aluminum partially in soluble form as Al-F complexes. The formed precipitate had lower iron (18.4 wt%) and phosphorus (11.4 wt%) content, whereas the impurity contents and thus the battery metals losses were slightly higher: Ni, Mn, Co, Al, and Cu were each between 1.1–1.9 wt% and Li and F < 1 wt%. In the precipitates investigated, iron was found predominantly as iron phosphate (FePO₄), whereas a minor fraction also precipitated as iron fluoride (FeF₃). The precipitated aluminum existed mainly as AlOOH. The results presented here will help to build iron and aluminum removal strategies for industrial battery recycling solutions, and also provide insights into the dominant iron and aluminum phases forming the precipitates.