Separation and recovery of rare earth from waste nickel-metal hydride batteries by phosphate based extraction-precipitation

Abstract

A novel type of extraction-precipitation strategy based on phosphate was developed to recover rare earth (RE, i.e., La, Ce, Nd, and Pr) from waste nickel-metal hydride (NiMH) batteries. This method does not require saponification and organic solvents. The novel phosphates, i.e., dibenzyl phosphate (DBP), diphenyl phosphate (DPP), triphenyl phosphate (TPP) were studied as extraction-precipitants. DBP has high precipitation efficiencies for RE3+, which can reach 97.84%, 100%, 100% and 99.77%, respectively. In addition, the precipitation efficiencies of Mn2+, Co2+ and Ni2+ are less than 1.75%. DBP-RE has the largest particle size (D10 = 52.6 μm, D50 = 135.35 μm, D90 = 296.08 μm), which is much larger than the precipitations formed by NH4HCO3, H2C2O4, CaO and MgO. The larger precipitation particle sizes contribute to improving the solid-liquid separation efficiency. With 3 mol/L hydrochloric acid, the stripping efficiency of DBP-RE reaches 98.60%, and the purity of recovered RE is 99.85%. The regenerated DBP can be directly used for the recycling extraction. Therefore, the novel extraction-precipitation strategy is a green and sustainable separation method.