Mass balance study of a multistage process for the purification of a fluorspar by-product from a rare earth element carbonatite deposit

Abstract

Fluorspar, also known as fluorite (CaF2), is commercially important in metallurgical (e.g. used as slag viscosity modifier), ceramic (e.g. used to manufacture glass), and chemical industries (e.g. production of commercial HF). In the present study, a process has been developed to produce a ceramic grade fluorspar by-product from a rare earth element (REE)-bearing carbonatite deposit. The objective of the present study was to conduce a mass balance assessment of a CaF2 by-product purification process as well as an economic evaluation of the final flotation step to determine the advantage/limitation of this additional step to improve the purity of CaF2 from metallurgical to ceramic grade. After an initial flotation step to produce feed, the fluorspar purification process consisted of four steps. Firstly, a magnetic separation step was conducted to pre-concentrate the fluorspar into a non-magnetic fraction, while concentrating Fe- and REE-bearing minerals in the magnetic fraction. Secondly, the non-magnetic fraction was subjected to an acid leaching step to solubilize carbonates. Thirdly, the leached solid was treated again by magnetic separation to remove the further liberated REE-bearing minerals from the fluorspar minerals. Finally, a flotation step was performed to depress silicate minerals in the tailings fraction and thus to improve fluorspar grade in the concentrate. The purity of fluorspar increased from 15.6% in the feed (no commercial value, residue to be disposed of) to 95.1% in the final product (ceramic grade). According to the mass balance calculations, approximately 98.6 g of ceramic grade CaF2 was recovered from 1 kg of feed material and the output/input ratio of fluorspar was estimated at 94.0%. The costs of the flotation process develop to improve the purity of CaF2 from metallurgical to ceramic grade were estimated at 194 $CAD.t−1, while the revenue to be generated by the ceramic grade fluorspar obtained were estimated at 244 $CAD.t−1, indicating that the additional flotation step is economically feasible and beneficial to the company, not only to upgrade fluorspar by-product (from commercial to ceramic grade), but also to generate a profit of at least 50 $CAD.t−1.