Effect of planetary ball milling and solid sodium hydroxide on dissolution of rare earth elements from weathered residual rare earth ores

The rare earth elements (REEs) are a group of 17 chemically similar metallic elements. The REEs are usually divided into light (LREEs) and heavy rare earth elements (HREEs). Since REEs have essential role in advanced industries, demand for REEs is expected to continue or even increase in future. Since China became predominating global supplier of REEs, the rest of the world is confronted with supply risk and intensively investigates new resources of REEs. As a part of the worldwide research trend, the weathered residual rare earth ore have been proposed for the study. The characteristic of this ore is that the rare earth minerals in this ore are very fine grinded. Because of this, hydrometallurgical processes are studied to recovery REE in this study. The objective of this study is to compare the effect of planetary ball milling without and with solid sodium hydroxide on dissolution of REEs from weathered residual rare earth ore by sulfuric acid. To achieve this, the planetary ball milling without and with solid sodium hydroxide was studied. The structural change of the ore by planetary ball milling without and with solid sodium hydroxide was investigated using x-ray absorption fine structure (XAFS) analysis. Because of REEs concentration in the ore, the targets of XAFS analysis were cerium K and LIII-edges and yttrium K-edge. The leaching experiments after planetary ball milling were conducted using 1 mol/dm³ sulfuric acid for 24 hours. Obtained results indicate that dissolution of LREEs exceeded 90 % due to planetary ball milling without and with solid sodium hydroxide. In case of HREEs, however, comparable dissolution was achieved only in case of planetary ball milling with solid sodium hydroxide. This trend was confirmed by structural changes of the ore investigated by XAFS analysis.