Leaching and recovery of phosphate and rare earth elements from an iron-rich fluorapatite concentrate: Part I: Direct baking of the concentrate

The present study is focused on the leaching and recovery of phosphate and Rare Earth Elements (REEs) from the Esfordi phosphate concentrate (Yazd province, Iran), which contains 16.31% P, 37.13% Ca, 2.91% Fe, 3% F, 0.3% Cl, and the TREE content is 1.2%. Cerium, lanthanum and neodymium account for 82% of the total rare earth content. Fluorapatite, magnetite and calcite-dolomite, with 88.7%, 4.8% and 2.3%, respectively, are the predominant minerals in the concentrate. Monazite (1.2%), apatite and xenotime (0.2%) are the main REE-bearing minerals. A process was designed for the simultaneous recovery of phosphate and REEs form flourapatite concentrate. Through direct sulphuric acid baking of the concentrate, maximum Ce, La, Nd and Y recoveries of 85.5 ± 3.0%, 85.2 ± 2.4%, 83.8 ± 2.1% and 84.8 ± 2.0%, were achieved, respectively, at an acid to ore ratio of 2.9, temperature of 270 °C and digestion time of 110 min. The phosphate precipitation method was used as an effective method to separate iron and phosphate from rare earths. By increasing the Fe 3 + P O 4 3 − ratio from 0.11 to 2 and gradually increasing the pH to 3.5, 98% of iron, 45% of Ca and all the Th precipitated out of solution. Subsequently, a total of 97% of rare earth elements were precipitated from solution by conventional bicarbonate precipitation to obtain a mixed concentrate containing 22.4% rare earth elements. The carbonate concentrate thus produced by using the mentioned novel process contained considerable amounts of calcium and sulfur. For this reason, a selective leaching stage is proposed to leach the calcium and phosphate from the concentrate prior to the acid baking process. This has been investigated in the part II of this research.