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

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 mu m, D50 = 135.35 mu m, D90 = 296.08 mu m), 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. (c) 2021 Published by Elsevier B.V. on behalf of Chinese Society of Rare Earths.

Automated summary

A new extraction-precipitation strategy based on phosphate has been developed for the recovery of rare earth elements from waste nickel-metal hydride batteries. This method eliminates the need for saponification and organic solvents. The novel phosphates, particularly dibenzyl phosphate (DBP), exhibit high precipitation efficiencies for rare earth elements and contribute to improved solid-liquid separation.