Simultaneous recovery of rare earth elements and phosphorus from phosphate rock by phosphoric acid leaching and selective precipitation: Towards green process

Abstract

Phosphate rock has been considered as one of the potential promising resources for rare earth elements (REEs). But the cost issues and the technical challenges caused by the low content of REEs in ores did hinder the further development of REEs recovery technologies. In order to explore a green process for the recovery of REEs from phosphate rock, this study investigates the effects of phosphoric acid concentration, liquid-to-solid ratio (L/S ratio), leaching time and temperature on the leaching efficiencies of the major components from phosphate rock. A REEs recovery of 94.3% and a phosphorus recovery of 95.3% are achieved under the optimal conditions of attacking phosphate rock using 30%P2O5 acid with an L/S ratio of 10:1 and a stirring speed of 250 r/min at 25 °C for 4 h. Then, the selective precipitation of REEs with 81.3% REEs recovery is realized by heating up the leaching solution from 25 to 90 °C and keeping for 4 h. Thereafter, more than 95% phosphoric acid is recovered by H2SO4 and high purity gypsum, more than 95% CaSO4 (tested by XRF), is also produced at the same time. Ultimately, a green process that leaches phosphate rock with H3PO4, selectively precipitates REEs from leaching solution by heating up, recovers H3PO4 with H2SO4 is proposed. Compared with REE recovery in traditional processes, this process owns the merits of simple operation, energy saving and minimum wastes.