Recovery of rare earth elements from CaCl2 and MgSO4 leach solutions of ion-adsorbed rare earth deposits

Abstract

The serious ammonia-nitrogen pollution from ion-absorbed rare earth deposit (IAD) has attracted widespread attention. This study aims at improving the extraction process to achieve efficient and clean extraction of rare earths (RE). The extraction-precipitation strategy based on long-chain saturated fatty acids as precipitants was successfully used to selectively recover RE from CaCl2 and MgSO4 leach solutions of IADs. Extraction-precipitation mechanism of lauric acid (LAA) for RE was determined to be cation exchange. Under the optimum conditions, the RE in CaCl2 leach solution and MgSO4 leach solution of IADs were extracted on pilot scale. The precipitation percentage (E%) of RE reaches more than 95% in 5 min. The obtained precipitates have large particles and good hydrophobicity. The loss of LAA in raffinate is less than 0.015 g/L, so the raffinate can be recycled for the leaching of IAD without further treatment. After stripping with 6 mol/L HCl at 55 °C for 10 min, two concentrated solutions with the concentrations of 190.2 g/L RE (REO = 225.5 g/L) and 165.2 g/L RE (REO = 197.2 g/L) were obtained respectively. The purities of REO in the RE concentrated solutions are more than 95%. After 5 cycles, the performance of regenerated LAA has no obvious change. In the field of RE enrichment from IAD non-ammonium leaching solution, the extraction-precipitation strategy based on LAA reveals the advantages of low cost, simple operation, high efficiency, sustainability and low energy consumption. This strategy has shown its application potentials in the field of large-scale and short-process RE leach solution enrichment.