Metallurgical Processing and the Effect of Ethylenediaminetetra-Acetic Acid in Extraction and Separation of Rare-Earth Elements by Solvent Extraction with Di-2Ethylhexyl Phosphoric Acid

A study was conducted to determine the amenability to extraction of the rare earth elements (REE) and the effect of ethylene diamine tetra-acetic acid (EDTA), a chelating agent, on their separation in di-2ethylhexyl phosphoric acid (DEHPA) solvent extraction systems. To physically concentrate the ore, a screening process was used, and was successful in concentrating the rare earth elements hosted within the minerals in the fine size fractions, with higher grades in the minus 500 mesh (-25 microns) portion. The pre-concentrate was upgraded from a head grade of 13.8% to 19.1% REE using the simple screening process. Recoveries averaging 96% total rare earths were obtained in the leach tests with 20% hydrochloric acid at 90°C. Experiments of solvent extraction with DEHPA in kerosene were performed using the leachate produced in the leaching experiments. Different concentrations of EDTA were added to the aqueous phase prior to mixing with the organic. Addition of EDTA improves the percentage extraction and separation factors for some heavy rare-earth elements. Data from percent extraction and separation factors show noticeable sensitivity to concentrations of EDTA. It was observed that erbium (Er) and ytterbium (Yt) display the highest percent extractions of 84% and 92%, respectively.