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and room temperature, the extraction isotherm/McCabe–Thiele diagram predicted five theoretical stages and 35-40 g/L of loading capacity. Finally, stripping the ...
EXTRACTION OF RARE EARTHS FROM CHLORIDE SOLUTIONS TO A NITRATE IONIC LIQUID BY THE NEUTRAL EXTRACTANT CYANEX 923 Mercedes Regadío1, Koen Binnemans1 1KU

Leuven, Dept of Chemistry, Celestijnenlaan 200F, 3001 Heverlee. Belgium [email protected]

The rare-earth elements (REEs) are listed as critical metals in Europe due to their high economic value (increasing demand in motors, electronics, renewal energy and catalysts) and supply risks (>95% sourced from China) (1). Solvent extraction (SX) is currently the most important process for separating and obtaining REEs. First, a leaching solution with the dissolved elements (aqueous feed phase) is intensively mixed with a solvent (organic phase), which selectively extracts only the desired element/s. Then, the process is reversed by contacting the loaded organic phase with an acidic aqueous strip solution that recovers the desired element/s back out of the solvent. For this purpose, large amount of organic solvent and acids are required. In the present work, a more environmentally friendly approach is tested using “split-anion extraction” (2). The organic phase consisted of Cyanex® 923 (extractant) added to the quaternary phosphonium ionic liquid (IL) Cyphos® IL-101 in its nitrate form (diluent). The aqueous phase consisted of a synthetic feed solution that simulates the composition of a HCl releachate originated from Kringlerne REE deposit in Greenland (77 g/L of REE chlorides) in a 2.5 M CaCl2 matrix. Addition of Cyanex® 923 to the nitrate IL has two major advantages. Firstly, the loading capacity of the organic phase substantially increased due to the strong interactions of the phosphine oxides in Cyanex® 923, with the Lewis acidic REE. Secondly, the extraction sequence across the lanthanide series was changed from a negative one (La more extracted than Lu) to a positive one (La less extracted than Lu), with Y behaving similarly to Pr-Nd. This is convenient since La, Ce, Pr, Nd and Y make up the 77 w% of the total REE, and they will remain in the aqueous phase after SX, what reduces the organic phase consumed and the extraction stages needed for their full separation from the rest of heavier REE. For completing such a separation at a volume ratio aqueous:organic 1:1 and room temperature, the extraction isotherm/McCabe–Thiele diagram predicted five theoretical stages and 35-40 g/L of loading capacity. Finally, stripping the loaded organic phase with water (1:1 v:v) is possible, with almost 100% recovery of the previously extracted REE (Sm to Lu), after one stage. Using ILs instead of molecular organic diluents (volatile, flammable and nonelectrically conductive) and stripping with water instead of acids leads to safer and environmentally friendlier solvent extraction processes. Acknowledgements: These results has received funding from the European Community’s Seventh Framework Programme ([FP7/ 2007-2013]) under grant agreement n°309373. This work reflects only the author’s view, exempting the Community from any liability. References 1. European Commission (2010). Report of the Ad hoc Working Group on defining critical raw materials. Critical raw materials for the EU. 2. K. Larsson, K. Binnemans, Hydrometallurgy, 156(2015)206–214.