Abstract
Abstract Obtaining rare earth elements (REE) is a complicated task, due mainly to the difficulty of separating and purifying them. Solvent extraction is the most widely used technique for separating REE, and the most common extractants used are organophosphorus acids. The low selectivity of this technique leads to the need for a high number of extraction cells. To increase the selectivity and separation and avoid the practice of saponification of the extractant, the use of complexing agents has been studied, such as low-molecular-weight and biodegradable weak organic acids. The objective of this research was to study the separation of the rare earth elements Gd and Eu by the solvent extraction technique using the organophosphonic extractant 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (P507). Assays were performed using non-saponified and saponified P507 extractant and adding lactic acid to the aqueous phase prior to extraction. Experimental factorial planning was used to study the effect on the extraction and separation of the Eu and Gd of the variables extractant concentration, initial feed pH, saponification degree, and lactic acid concentration. The greatest Gd extractions were obtained when lactic acid was added to the feed solution. Also, saponification of the extractant and lactic acid addition improved the Gd/Eu separation. The number of stages required to extract Gd using McCabe-Thiele diagrams was estimated, whether or not the solution was conditioned with lactic acid. The largest extraction percentage was obtained by adding lactic acid in a continuous counter-current extraction assay, achieving 94% Gd extraction.
Highlights
The rare earth elements (REE) constitute the group of lanthanides in addition to the elements Y and Sc, and can be found widely distributed throughout the earth’s crust (Gupta, 2004)
The effects and the response surfaces for Gd extraction and the Gd/Eu separation factor in the P507 extraction tests with the addition of lactic acid to the aqueous phase, as a function of the lactic acid concentration and feed pH, are shown in respectively in the Figures 9, 10, 11 and 12
It can be concluded that both saponifying the extractant and adding lactic acid to the aqueous feed increase the Gd extraction and improve the separation of the Gd/Eu pair when using P507 as extractant
Summary
The rare earth elements (REE) constitute the group of lanthanides (atomic number between 51 and 71) in addition to the elements Y and Sc, and can be found widely distributed throughout the earth’s crust (Gupta, 2004). These elements have great economic importance due to the large number of applications in high-technology industries (Lapido-Loureiro, 2011). Solvent extraction (SX) or liquidliquid extraction using liquid organic extractants is currently one of the main techniques for industrial-scale separation, purification and concentration of metals, including REE.
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