Investigating the use of an ionic liquid for rare earth mineral flotation*

Common collectors for rare earth mineral (REM) flotation, which include carboxylates and hydroxamates, face problems such as being non-selective and sensitive to impurity ions. A type of ionic liquid (IL), tetraethylammonium mono-(2-ethylhexyl)2-ethylhexyl phosphonate ([N-2222][EHEHP]), has been investigated previously for rare earth elements (REE) solvent extraction, and was proven to be selective and effective. In this work, [N-2222][EHEHP] was evaluated as a collector in bastnasite (a primary REM source for REE production) flotation for the first time. The results were compared with quartz and hematite, two common gangue minerals in REM deposits. Zeta potential measurements and Fouriertransform infrared spectroscopy (FT-IR) were completed to investigate the surface chemical properties involved in the flotation of these minerals using this collector. The findings were compared with microflotation results. FT-IR and zeta potential measurements suggest adsorption of the collector's phosphonate group onto bastnasite and hematite, likely through chemisorption; whereas for quartz, the minimum microflotation recovery is likely due to no adsorption of IL on its surface. Microflotation results show higher collectability of [N-2222][EHEHP] for hematite than bastnasite, the latter only shows appreciable recovery at pH 5 with elevated dosage of IL (500 g/t). To achieve better separation, a two-stage flotation scheme was designed and evaluated by bench scale flotation on a synthetic mineral mixture. The concentrates and tails were analyzed by magnetic separation, and it is found that bastnasite recovery over 90% with maximum upgrade ratio 1.7 can be achieved with elevated collector dosage. (c) 2020 Chinese Society of Rare Earths. Published by Elsevier B.V. All rights reserved.

Automated summary

A study evaluated an ionic liquid as a collector in bastnasite flotation, showing higher collectability for hematite than bastnasite. A two-stage flotation scheme was designed for better separation, achieving over 90% bastnasite recovery with a maximum upgrade ratio of 1.7.