Separation of Phosphorus from Mixed Rare Earth Concentrate for Enrichment of REEs

The traditional rare earth extraction process generates a large amount of radioactive waste or alkaline wastewater, which has become an important constraint to rare earth production in recent years. In this study, the differences in solubility between rare earth sulfates and phosphoric acid and the high selectivity of tributyl phosphate (TBP) for phosphoric acid were exploited. The preliminary separation of phosphorus from rare earths was achieved in three stages of counter-current leaching under the low liquid-to-solid (L/S) ratio of 1:1, 323 K, with 98% of P while 2% of rare earth oxide (REO) entering into the solution. Subsequently, the dissolved phosphorus was selectively extracted by TBP. In total, 81% of P was extracted by five-stage cross-flow extraction under the organic-to-aqueous (O/A) ratio of 5:1, 298 K, leaving rare earths (REEs) in the raffinate. The extraction mechanism of low-concentration phosphoric acid in this system was investigated by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR) spectroscopies. Finally, the residual solid phase of the counter-current leaching process was leached with dilute sulfuric acid to recover the rare earths, and 97% of the REO was recovered to the solution. The whole process realizes the separation and extraction of rare earth and phosphorus resources, reduces the production of radioactive waste, and provides the possibility of green production of rare earths.