With the addition of rare earth elements to the critical minerals list for Canada, USA and the EU, the importance of a domestic source for Canada has increased significantly. Nechalacho is the only rare earth element (REE) project in production in Canada. In order to extract current and future REE deposits, an understanding is needed of the potential release of harmful elements as a result of mining and weathering processes. The objective of this research is to investigate the dissolution rate and mechanism of the fluorocarbonate ore minerals bastnaesite REE(CO3)F and parasite CaCe2(CO3)3F2. The results will indicate the possible extent of release of REE’s, fluoride, uranium and thorium that have the potential to be released to the near-surface environment during on-site crushing and ore sorting. The Nechalacho deposit, previously known as the Thor Lake deposit, is located approximately 100 km southeast of Yellowknife, Northwest Territories, Canada. This rare earth deposit has mineralization hosted in an assemblage of alkaline syenite and granite with intense hydrothermal alteration. In 2021, a demonstration project extracted ore from the T Zone bastnaesite-quartz-fluorite pegmatite with only physical upgrading of ore on site. For our experiments, we disaggregated pegmatite samples to concentrate the bastnaesite-parasite and ran batch experiments to monitor element release with time to assess dissolution rates as a function of initial fluid pH. Bastnaesite-parisite concentrate was added to reactors with initial solution pH of 2, 4 and 9 and sampled daily over two-weeks. These results will characterize the reactivity of the bastnaesite-parisite concentrate and shape future experiments to be run in this project. Additional experiments will determine the effect of fluid composition, temperature, grain size, and variation in mineral composition on mineral dissolution rates and rate of REE, U and Th release.
X-ray diffraction (XRD) analysis was utilized to determine the bulk mineralogy of the samples used in the batch experiments. The XRD results confirm the presence of fluorite and quartz in the samples used in the batch experiment, which could not be separated from the bastnaesite and parisite. The electron microprobe analyses of the ore indicate that the bastnaesite contains on average (n = 91) 18.0 wt% La2O3, 36.1 wt% Ce2O3, and 12.6 wt% Nd2O3. The parasite contains on average (n = 53) 13.7 wt% La2O3, 28.4 wt% Ce2O3, and 10.8 wt% Nd2O3. Previous research has focussed on the leaching of REE’s from these ore minerals using strong acids at elevated temperature to optimize REE release. This research aims to characterize the ore minerals and provide knowledge of the reaction mechanisms applicable to surface water environmental conditions.