Simultaneous leaching of rare earth elements and phosphorus from a Chinese phosphate ore using H₃PO₄

Abstract

Although phosphate rock has been considered as a potential new rare earth elements (REEs) resource, the recovery of REEs from phosphate rock is impeded by technical challenges and cost issues. This study investigated the effects of operation conditions on the leaching efficiencies of REEs and phosphorus from Zhijin phosphate ore, a large phosphate deposit in China. The leaching process overtime was also studied by chemical analysis, scanning electron microscope with energy dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD). The results indicated that the REEs from Zhijin phosphate ore were mainly present in fluorapatite and dolomite, and REEs had similar trends of leaching efficiency to those of phosphorus and magnesium. Under the conditions of 25 wt% phosphoric acid concentration in the initial pulp, a weight ratio of liquid to solid of 12 mL/g, a temperature of 60°C, an agitation speed of 220 rpm, and leaching time of 120 min, REEs and phosphorus leaching efficiencies of 97.8% and 99.7% were obtained. Most parts of dissoluble substances were decomposed within 30 min. Chemical analysis, SEM-EDS, and XRD results indicated that leaching efficiencies of minerals in Zhijin phosphate ore increased following the order: quartz, aluminosilicate, pyrite, fluorapatite, dolomite, and calcite.

Leaching of rare earths from Abu Tartur (Egypt) phosphate rock with phosphoric acid

“…It could be revealed that the increase in phosphoric acid concentration from 5 to 25 wt.-% P 2 O 5 drastically improves the leaching efficiency of REEs. The increase of the H + ions in the solution as the phosphoric acid concentration increases supports the results obtained [35,62]. By increasing the phosphoric acid concentration to >25 wt.-%, the REEs leaching efficiency decreases sharply.…”

“…The results from the preliminary experiments (Fig. 4A) as well as other reports show that the equilibrium of the leaching reaction is achieved after 360 min [32,40,62]. This result is inconsistent with the obtained data from the DoE methodology.…”

“…This is due to the decrease in the solution bulk density, which causes an increase in the migration of different ions to the liquid medium [32,35]. The same trend has been observed during the dissolution of REEs and P from phosphate rock using phosphoric acid [35,62]. Further increase in the liquid/solid ratio >6 mL/g has only a slight impact on the REEs leaching efficiency.…”

“…This indicates that the leaching rate of the reaction starts rapidly until ~360 min (equilibrium time), then the rate of reaction becomes very slow (Plateau shape). The same behavior has been reported for the leaching of P and REEs from an iron-rich fluorapatite concentrate [32], and phosphate ore from China [35,62]. The reaction dissolution time was thus kept at 360 min in further experiments.…”

“…4C). The increase in the phosphoric acid concentration (up to 30 wt.-% P 2 O 5 ) also enhances the REEs dissolution efficiency, which can be attributed to an increase of H + ion concentration as a result of the increase of the phosphoric acid concentration, which positively influences the leaching process [40,62]. The least positive effect parameter on the leaching efficiency is the residence time, which can be due to the fast dissolution reaction.…”