Enrichment of rare earths in magnesium sulfate leach solutions of ion-absorbed ores by extraction-precipitation

Abstract

Magnesium sulfate (MgSO4), a leaching agent for ion-absorption rare earth (RE) ores, can reduce the production of ammonia nitrogen wastewater and supply magnesium (Mg) for soil. Three novel solid extractants, i.e., 2,2′-(1,4-phenylenebis(oxy))dioctanoic acid (PPBOA), 2,2′-(1,2-phenylenebis(oxy))dioctanoic acid (OPBOA) and 2,2′-(1,3-phenylenebis(oxy))dioctanoic acid (MPBOA) were synthesized and used to enrich RE by extraction-precipitation strategy, which showed better selectivity and faster equilibrium. The precipitation rates of PPBOA, OPBOA and MPBOA on RE could reach 95.1%, 93.5% and 96.7% at the large liquid/solid phase ratio (450/1). Meanwhile, the purities of RE in the stripping solutions reached 96.1 wt%, 94.1 wt% and 96.2 wt%. Chemical oxygen demand (COD) values of raffinates from OPBOA and MPBOA were 56 mg/L and 69 mg/L, being lower than that of China national emission standard (100 mg/L). The concentration of enriched RE solution by MPBOA was 238.0 g/L, solid extractant and MgSO4 raffinate could be recycled.