Selective enrichment of rare earth ions from high-magnesium/calcium leaching solutions via extraction-precipitation

Magnesium sulfate is widely used as a leaching agent in ionic adsorption rare earth (RE) ore mining, but it produces leachates containing high concentrations of Mg²⁺ and Ca²⁺ and only trace levels of rare earth ions (RE³⁺), which leads to low-purity RE products and difficult enrichment. Here, we adopt an extraction-precipitation strategy using recyclable complexing agents—glyphosate (Gly), hydroxyethylidene diphosphonate (HEDP), creatine phosphate (CP), and ethylenediamine tetramethylenephosphonate (EDTMP)—to concentrate dilute RE₂(SO₄)₃ and further obtain a concentrated RECl₃ product. The results showed that at pH 3.5, with RE: CP molar ratio of 1:2, CP achieved higher precipitation efficiency for RE³⁺ than Gly, HEDP, and EDTMP. CP enabled the selective separation of RE 3+ (La, Nd, Y, Yb) from Mg²⁺ and Ca²⁺, enriching RE to 198.73   g·L⁻¹ in a single step, which is 933.65 times higher than that in the original solution. Meanwhile, the purity of the RE products reached 99.33%. This outstanding performance was further validated using actual mine leaching solutions, where the RE³⁺ concentration reached 261.57   g·L⁻¹. In addition, CP can be effectively recovered and reused. Overall, this method provides a simple, efficient, and environmentally friendly approach for high-purity RE recovery from impurity-rich leachates.