Optimization and modeling of rare earth element leaching from Khouribga phosphate rock using response surface methodology

In Khouribga (Morocco), about 7.2 Mt of phosphate rock is mined annually, and most is used to manufacture fertilizers, phosphoric acid, and for exports. Extracting rare earths elements (REEs) from phosphate rock enhances their supply, improves the quality of phosphoric acid, protects the environment, and adds value to this crucial natural resource. In this regard, we are interested to develop efficient, selective, and applicable methods for processing phosphate in order to extract rare earth elements. Here, we report the characterization of Khouribga phosphate rock and the response-surface optimization of bench-scale hydrochloric-acid of its rare earth elements leaching. HCl concentration (3.7–37.0% w/v), temperature (50–100 °C), and contact time (5–45 min) were studied. The Phosphate rock contained 633 ppm total REEs, with yttrium as the dominant quantified element (427 ppm). The model identified 75 °C, 25 min, and 20.35% HCl as a predicted operating point; the six design center-point runs at these conditions gave a mean measured yield of 86.86 ± 2.05% ( n = 6). These results demonstrate the feasibility of a laboratory-scale leaching process under the conditions examined; which could be applied, after further verification, to rare earth element extraction at a phosphate rock beneficiation.