Abstract
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.
Highlights
Rare earth elements (REEs) have been considered as the critical materials in the world due to their specialized application in many modern technologies [1,2]
A small amount of REEs are present as particle inclusions such as monazite, xenotime, allanite, and carbonate in apatite, which result in difficulty in REEs dissolution during the leaching process [5]
In the phosphoric acid concentration range studied, the increased trends of REEs and P2O5 leaching efficiency were almost the same, which is consistent with the fact that in phosphate ore, REEs present majorly in the form of isomorphous substitution for Ca and deposit as the REE phosphate [22]
Summary
Rare earth elements (REEs) have been considered as the critical materials in the world due to their specialized application in many modern technologies [1,2]. Due to a global supply shortage and strengthening demand of REEs, the exploration and processing of new sources (known as secondary sources) of REEs are necessary [3]. Phosphate rock is the most significant secondary REEs resource [4], and it contains 0.046 wt% REEs on average [5]. About 50 million tons of rare earths are stored in phosphate resources worldwide, nearly one hundred thousand of which are mined annually in the production of phosphate rock [6]. REEs occur primarily in the form of isomorphous substitution for Ca and deposit as the REE-francolite that can be released into leaching solution by mineral acids [7]. A small amount of REEs are present as particle inclusions such as monazite, xenotime, allanite, and carbonate in apatite, which result in difficulty in REEs dissolution during the leaching process [5]
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