Development of solvent extraction process for erbium purification

A solvent extraction process based on organophosphorus extractant EHEHPA has been developed to raise the purity of erbium from ~20 to >85% in the product solution. The challenging task of upgrading erbium value in a host of chemically similar heavy rare earths present in a concentrate (% composition: Dy₂O₃: 58.72, Er₂O₃: 21.45, Ho₂O_3: 13.33, Tm₂O₃: 0.67, Yb₂O₃: 4.74 and Y₂O₃: 1.09) was accomplished by careful selection of process parameters such as aqueous feed acidity, EHEHPA concentration, total rare earths concentration in feed solution, phase ratio, scrubbing agent, and so forth. Under optimised conditions, a multi-stage counter-current and scrubbing test runs raised the purity of erbium to >85% with >95% recovery in the product strip solution. Amongst the various scrubbing agent, 0.025M Er₂O₃ at 1.2M HCl was found to be superior.