Recovering rare earth elements from phosphogypsum using a resin-in-leach process: Selection of resin, leaching agent, and eluent

Phosphogypsum (PG) is an attractive secondary raw material for rare earth elements (REEs) because it is abundant and contains significant amounts of REEs. Herein, the resin-in-leach (RIL) process for REE recovery from PG was studied, and the factors affecting the yield and selectivity of conventional leaching and RIL are discussed based on the batch equilibrium data obtained using four different lixiviants, H2SO4, HCl, H3PO4, and NaCl. It was found that the chelating resin enabled the use of a low H2SO4 concentration (1 g/L) in the RIL process. The REE recovery yield and purity in the single-stage RIL process were higher when the chelating resin was used than when strong acid resins were used. The difference was significant in the multistage cross-current RIL process, where a loading of 19.2 g(REE)/kg(resin) and up to 20% purity were obtained with the chelating resin (vs. 3% in strong acid resin) after four stages. It is concluded that neither the breaking of the PG structure, nor the adsorption of calcium by the resin is necessary to enhance REE recovery. Considering the available literature and patents, this is a promising finding. REEs can be eluted from strong cation exchangers using a saturated sodium chloride solution, while EDTA or concentrated hydrochloric acid is required in the case of a chelating resin. However, Ca and REE can be further separated during elution of the chelating resin.