Lanthanide Sulfate Recovery by Synergistic Dimethyl Ether and Na2SO4 Fractional Crystallization.

Abstract

Lanthanides (Lns) are important to many technologies including magnets used in high-efficiency traction motors and generators. While commonly occurring in the environment and industrial waste streams, Ln are generally present at low concentrations. This work demonstrates synergistic Ln recovery from an aqueous magnet leachate to single ppm concentrations using Na₂SO₄ addition and subsequent dimethyl ether-driven fractional crystallization (DME-FC) treatment. It is found that combining DME-FC with low concentrations of Na₂SO₄ (≈0.1 M) results in synergistic isolation of Lns while making use of Na₂SO₄, an excessive byproduct of hydrometallurgical metal production. Combined Na₂SO₄ + DME reduces Ln metal ion (Pr, Nd, Sm, Gd, Dy, and Ho) solubilities by 700-27,000x with final concentrations ranging from 2 ppm to 200 ppm. Separately, Na₂SO₄ 0.1 M provides a 10-200x reduction and DME provides a 90-1,400x reduction in Ln solubilities. Final Ln concentrations of the combined process are 99.8% lower than what is achieved with each individual process.