Selective Separation of Nd, Dy, Pr, and Tb from Synthetic Leaching Solution of Rare Earth Elements using Solvent Extraction and Ultrasonically Generated Emulsion Droplets

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Authors
Yildiz, Deniz
Keyword
Rare Earth Elements , Solvent Extraction , Emulsification , Critical Elements , Cyanex 572 , D2EHPA
Abstract
Rare Earth Elements (REE) have characteristic features making them irreplaceable in modern applications. As developing countries become more environmentally conscious, there is a growing need for green technologies that utilize critical metals like REE, resulting in a significant shift away from traditional energy sources. In hydrometallurgical processes for purifying REE from concentrated solutions, the Solvent Extraction (SX) technique plays a vital role in separating and ensuring the purity of the elements. It is widely utilized in the industry owing to its high extraction capacity and easy applicability. However, several challenges are faced when SX is operated to treat solutions with a low concentration of metal ions. These challenges include phase disengagement, solvent loss, high capital expenditures, and increased consumption of solvents. The drawbacks associated with using conventional separation techniques, i.e., SX, have directed special attention toward alternative methods. Emulsion droplets stand out by creating a larger surface area, increasing the mass transfer capacity. This study aims to present the outcomes of two distinct experiments; the first involves a synergistic SX process using Cyanex 572 and D2EHPA, this work is the first to use Cyanex 572 and D2EHPA together on the synergistic effect. The second involves an ultrasonic-based SX process utilizing Cyanex 572 droplets to minimize the drawbacks of conventional SX. The findings of this study suggest that a mixture of 50% Cyanex 572 and 50% D2EHPA, employed at pH 0.25, could be the ideal combination for achieving selective separation. Nevertheless, it is noteworthy that using sole Cyanex 572 resulted in even higher single-stage extraction percentages of dysprosium (Dy) and terbium (Tb), at 99.33% and 98.97%, respectively. The results obtained from the SX process employing sole Cyanex 572 indicate that Heavy Rare Earth Elements (Dy, Tb) exhibit a superior extraction rate at all aqueous/organic ratios. Specifically, extraction rates ranging from 98.65% to 99.39% for Dy and 98.92% to 99.41% for Tb were observed. Conversely, the extraction rate for Light Rare Earth Elements (LREE) remained relatively low (ranging from 15.18 %- 43.82 for Nd and 6.91 % - 37.77% for Pr). This finding is promising in achieving selective separation between HREE and LREE, which was a principal objective of this study. However, during the SX experiments with Cyanex 572 droplets, it was found that the LREE extraction rate remained high across different A/O ratios due to the augmented surface area generated by ultrasonic means.
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