Rare earth recovery and separation using diglycolamides

International audienceRare earth elements (REE) have become essential for our modern economy, in relation to the development of new energy and communication technologies. Depending on their technical-economic efficiency and environmental footprint, hydrometallurgical processes enabling the recovery of separated elements could be of particular interest.Typically these processes include a first pre-treatment (crushing, milling and sieving) and an acidic leaching step (with eventual selective precipitation sub-steps), followed by a solvent extraction (SX) step aimed at the separation and purification of REE. Recently, diglycolamides (DGA) appeared as a very interesting group of extractants for the selective recovery of trivalent REE from nitric acid solutions, particularly in the presence of transition metal ions commonly found in various waste products. In this work, the TODGA extractant was successfully used for designing an efficient REE recovery process. The process integrates the mechanical and physico-chemical treatment of waste, followed by a solvent extraction step for the recovery and intra-separation of REE. Based on the experimental batch data, a phenomenological model has been elaborated taking into account the various distribution equilibria. The model has been implemented in our simulation code and used for calculation of various flowsheets, which have been tested at our pilot facility using compact continuous counter-current mixer-settlers. Experimental SX and modeling data allowing the recovery of >99.95% pure Dysprosium solution will be discussed in this paper. Preliminary technical-economic assessment and life-cycle analysis have also been conducted. Following this first successful demonstration, several novel dissymmetrical DGA have been developed and their solvent extraction behaviour in different acid media has been studied. Indeed, most processes use symmetrical DGA such as TODGA. The present work improves upon the classic design and demonstrates that novel dissymmetrical extractants display a remarkable improvement on REE extraction efficiency compared to reference TODGA in various acid media. Furthermore, the REE separation factors towards major impurities such as Fe3+ are substantially enhanced.The development of novel DGA with increased efficiency paves the way for the recovery and separation of high value REE from different streams. This opens new market opportunities since the effluent treatment has often an important impact either in the CAPEX or the OPEX of a solvent extraction plant. With some DGA extractants adapted to sulfuric acid media, the resulting effluent treatment plant could be cheaper than it would be using nitric acid media. Furthermore, their enhanced performance at low concentration should reduce the price of reagents in the OPEX