Separation of heavy rare earth elements from calcium and light rare earth elements extracted from Estonian phosphorite ore by acid leaching and subsequent liquid extraction has been conducted and analyzed. For initial leaching, nitric acid, hydrochloric acid, and orthophosphoric acid with different concentrations have been utilized. For the final separation of heavy rare earth elements, a liquid extraction with bis(2-ethylhexyl) phosphate (D2EHPA) or 2-ethylhexyl hydrogen-2-ethylhexyl phosphonate (P507) at different acidic concentrations has been applied. After leaching and extraction, all samples were characterized using the inductively coupled plasma mass spectrometry method (ICP-MS/MS). Optimal conditions for both extracting agents have been established. All rare earth elements + Y have been recovered in acid leaching, and heavy rare earth elements (elements Gd-Lu) have been selectively recovered by D2EHPA with 5 M nitric acid leaching and by P507 with 1 M nitric acid leaching. The presence of Sc has not been detected in Estonian phosphorite ore.

Various heavy rare-earth separation strategies for separating light rare-earth elements and calcium have been evaluated in this study. Estonian phosphorite ore (fluorapatite) was dissolved in either 2 M nitric or hydrochloric acid, and the leachate was partially saponified thereafter with 2 M NaOH. The acid leachate was extracted with diluted NaOH-saponified D2EHPA using kerosene or toluene as solvents. The calculated extraction efficiencies and selectivities were compared with those reported in previous extraction studies using undiluted pure D2EHPA in strongly acidic media. It was found that extraction efficiencies are higher with diluted and saponified D2EHPA. However, separating heavy rare earth elements from light rare earth elements and calcium does not appear viable under mildly acidic conditions with diluted, saponified D2EHPA. Thus, for the most selective heavy rare-earth separations, extraction from strongly acidic media with pure D2EHPA appears to be a superior option.