Estonian phosphorite ore contains trace amounts of rare earth elements (REEs), many other d-metals, and some radioactive elements. Rare earth elements, Mo, V, etc. might be economically exploitable, while some radioactive and toxic elements should be removed before any other downstream processing for environmental and nutritional safety reasons. All untreated hazardous elements remain in landfilled waste in much higher concentration than they occur naturally. To resolve this problem U, Th, and Tl were removed from phosphorite ore at first using liquid extraction. In the next step, REE were isolated from raffinate. Nitrated Aliquat 336 (A336[NO₃]) and Bis(2-ethylhexyl) Phosphate (D2EHPA) were used in liquid extraction for comparison. An improved method for exclusive separation of radioactive elements and REEs from phosphorite ore in 2-steps has been developed, exploiting liquid extraction at different pH values.

The combined chemical extraction of rare earth elements from acid solutions and electrochemical separation of yttrium by electrodeposition from Estonian phosphorite ore samples containing rare earth elements has been conducted using ionic liquids at room temperature. It is shown that bis(2-ethylhexyl) phosphate can be used to selectively extract yttrium from other low rare earth elements, constituting the basis for further extraction. Electrochemical deposition can then be applied to the concentrated extraction product to separate valuable Y from the more abundant elements, such as Ca, from the natural sample. The addition of Bi salt to the working solution significantly aids REE’s deposition. It is shown that this extraction method can be highly efficient as well as selective when well-controlled different electrodeposition conditions are applied.

The chemical extraction of rare-earth elements (REEs) from Estonian graptolite-argillite (GA) and phosphate rock (Phosphorite, PH) samples has been conducted and analyzed. For the initial leaching process, HCl and HNO₃ with different concentrations were used to extract REEs from GA and PH. Different extraction agents, including ionic liquids, were examined for the extraction of REEs from acidic aqueous solutions in the liquid–liquid extraction step. After leaching and extraction, all samples were characterized using the inductively coupled plasma mass spectrometry method (ICP-MS/MS). The highest REE extraction efficiencies from GA were established with 1-ethyl-3-methyl imidazolium diethyl phosphate (EMImDEPO₄) and from PH using bis(2-ethylhexyl) phosphate (D2EHPA).

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.