REE extraction from phosphoric acid, phosphoric acid sludge, and phosphogypsum

Abstract

Phosphate rock is considered a secondary source of rare earth elements (REE), which are usually found in isomorphism substitution with Ca2+ ion. It approximately assays 0·01–0·1% (100–1000 μg g−1). Large tonnages of phosphate ore are mined and processed annually to manufacture commercial grade phosphoric acid indicating that REE extraction from phosphate beneficiation and chemical processing streams may have an economic value. In this work, REE were extracted from phosphoric acid by ion exchange resin using both direct and counter current methods while REE cocrystallised with phosphogypsum (PG) was digested by a mixture of concentrated sulphuric acid and recycled phosphoric acid, followed by extraction with DEHPA solvent. It was found that Heavy Rare Earth Elements (HREE) (Y, Gd, Tb, Dy, Er, Ho, Yb, Tm, and Lu) represented more than 70% of the REE dissolved in phosphoric acid while the critical REE (CREE) (Y, Nd, Eu, Tb, and Dy) constitute 45% of the distribution. Phosphogypsum has higher acids insoluble (A.I.) and phosphate (P2O5) than phosphoric acid sludge (PAS). The main impurities in PG are P2O5, AI, and CaO, while A.I., Al2O3, and P2O5 are the main PAS impurities. Phosphoric acid sludge leaching by nitric acid was more efficient than sulphuric acid even with higher acid strength and lower solids percentage; nitric and sulphuric acid leaching efficiency was approximately 58 and 49% for nitric and sulphuric acid, respectively. Rare earth elements extraction from phosphoric acid by ion exchange resin was not significantly affected by temperature change within the range 25–82°C but approximately 18% reduction was observed when extraction temperature was increased from 10 to 25°C. It was also found that REE-extraction efficiency increased with increasing resin dosage; approximately 65 and 28% extraction efficiency were achieved with 7 and 3 kg resin/t of phosphoric acid, respectively.