Beneficiation of rare earth elements contained in phosphogypsum using sequenced treatment process

Abstract

Concerns regarding the availability of rare earth elements (REEs) and the depletion of natural resource reserves have made it necessary to look for a significant breakthrough that may pave the way for the mining of several low-grade deposits and secondary resources. Phosphogypsum (PG) is one of the promising alternatives to preserve a steady flow of REEs and mitigate the loss of natural reserves. Nonetheless, the low concentration of REEs in PG implies the necessity of an enrichment step prior to any extraction attempt. To tackle the difficult challenges of REEs concentration from diluted phosphate-derived by-products, this study concentrated on determining the likely speciation of REEs and their beneficiation, as well as conducting an economic assessment of the potential industrial value of REEs present in PG. It was found that the alkaline solubilization of the gypsum phase of PG using Na4EDTA favored the beneficiation of different qualities of PG. Moreover, it was found that the abatement of residual undesirable phases by mineral acid (HF) for quartz (SiO2) elimination, or pyrometallurgical process, improved the enrichment of REEs in the residual concentrate. A REEs concentration of 4390.23 ppm and 4317.55 ppm were achieved after sequenced alkaline, neutral, and acidic treatment of low-grade PG (238.22 ppm); and sequenced alkaline, neutral, and pyrometallurgical treatment of high-grade PG (389.75 ppm), respectively. Furthermore, an elementary assessment of REEs speciation revealed that REEs could potentially be present as insoluble rare earth fluorides (REF3) and/or rare earth phosphates (REPO4).