Production of Pr+Nd fraction from phosphogypsum by resin-in-leach and dynamic anion exchange separation

Abstract

Industrial phosphogypsum (PG), a byproduct from phosphoric acid production, is an attractive source of rare earth elements (REEs). In this work, a complete REE recovery process starting from authentic industrial waste PG is demonstrated. Selective extraction of REEs from calcium-containing matrix was achieved using a chelating resin in a resin-in-leach process (RIL). By combining HCl washing with alkaline methylglycinediacetic acid (MGDA) regeneration of the loaded resin, a high-purity (98.3%) Ca-free mixture was obtained. The resulting MGDA–REE mixture contained a high proportion of Ce (~ 45%) relative to the other REEs. Cerium(III) was selectively removed by oxidation with H2O2 to precipitate Ce(OH)4. The concurrent effect of the oxidizer on MGDA was also studied to evaluate ligand stability. To enhance the purity of individual MGDA-REE complexes, strong-base anion (SBA) resin combined with dilute HCl elution was used for chromatographic separation. The separation was based on differences in the stabilities of the complexes. A two-step separation process was introduced to obtain the main product, a Pr+Nd mixture. After the first separation step, the purity of Pr+Nd product fraction reached 87.9%. A second step further improved the purity, yielding a final Pr+Nd fraction with purity of 96.1%. Additionally, a La-containing fraction with a purity of 74.4% was obtained as a secondary product. These products can subsequently be converted into the corresponding oxides via oxalate precipitation followed by calcination.