Hydrometallurgical Flowsheet Options for Treatment of Wicheeda Lake Flotation Concentrate: Acid Bake Versus Caustic Crack

Abstract.

Defense Metals is currently developing the Wicheeda rare earth element (REE) carbonatite deposit in British Columbia, Canada. The deposit is dominated by gangue carbonates, including ankerite and dolomite, while the REE-bearing minerals include bastnaesite/parisite/synchysite and monazite, hosting primarily light rare earths, including praseodymium and neodymium. This paper presents the results from a metallurgical testwork programme conducted on flotation concentrate samples produced during a flotation pilot plant at SGS Lakefield. The concentrate samples assayed 40–50% TREO and contained approximately 21% monazite and 64% REE fluorocarbonates.

From 2019 to 2021, a hydrometallurgical flowsheet was developed employing caustic conversion of REE phosphates and fluorocarbonates followed by hydrochloric acid leaching capable of extracting 90–92% REE into the leach solution. The leach solution was treated in a series of impurity removal processes to remove elements, such as iron, aluminium, phosphate, and thorium. REEs were recovered from the purified solution via precipitation. In late 2021, testwork was initiated investigating alternative treatment options. Preliminary acid bake testwork yielded improved metallurgical extraction performance (> 95% PrNd) and showed the potential to reject thorium into the leach residue.

The paper and presentation will provide updated results of the caustic crack and acid bake processes and comparisons between the two routes in terms of metallurgical performance (extraction, reagent consumption) and process simplicity. Mineralogical characterization of leach residues will be used to explain the metallurgical performance of the two process routes.