AMERICAN RARE EARTHS LIMITED American Rare Earths announced results from a metallurgical study on leaching extraction of REE from Halleck Creek ore by low temperature, direct acid leaching. The U.S. Department of Energy?s Office of Energy Efficiency and Renewable Energy (?EERE?) awarded a three-year (2022-2025) research contract to Phinix, LLC with American Rare Earth and Virginia Tech as team members. This metallurgical study was carried out by researchers at the Department of Mining and Minerals Engineering at Virginia Tech.
These positive results further confirm the findings of the metallurgical testwork carried out by Wood PLC1 which were previously announced by ARR. Technical Summary: Under the direction of Wencai Zhang, Ph.D., Dr. Wei Liu and doctoral candidate Zhongqing Xiao performed leaching testwork and published the results (Liu, et. al., 2024) at Virginia Tech for the project.
Virgnia Tech used finely ground sample material from the Halleck Creek Project, p80 = 47.9 µm, that was concentrated using magnetic separation to produce a mixed rare earth concentrate (?Concentrate?). The leaching testwork compared the effects of a variety of acids, acid concentrations, temperatures, solid/liquid ratios, and particle sizes, collectively known as ?leach kinetics?, on the recoverability of REE from the Concentrate. Virginia Tech demonstrated that approximately 80% of REE were extracted from the Concentrate using 1 M sulfuric acid at 75° C for 2 hours.
Importantly, this work shows that the REE can be successfully recovered using mildly acidic, readily available chemicals at low temperatures which might decrease capital and operating costs and potentially reduce environmental impacts of the project. The study also demonstrated that the amorphous crystalline structure of the Halleck Creek allanite due to the metamictization of the allanite over geologic time further enhances the leachability of the ore. This phase of testwork focused on the leaching kinetics of the Concentrate.
During this stage of the EERE project, Virgnia Tech did not attempt to isolate discrete rare earth elements. As the project continues, Virginia Tech will focus on isolating discrete REE. Allanite is the primary REE bearing mineral at the Halleck Creek project.
Importantly, allanite is less refractory than monazite or bastnaesite, as monazite and bastnaesite cannot be leached using low-temperature acid tank leaching. No significant silica gel formation was observed during leaching. Allanite from Halleck Creek exhibits ?metamict?, amorphous texture, resulting from decomposition of the crystalline structure of the mineral due to low-level decay of uranium and thorium over a 1.4-billion-year period.
The amorphous nature of the Allanite appears to enhance REE leaching. Virginia Tech performed leach tests on allanite concentrates at elevated temperatures. Virginia Tech hypothesizes that allanite recrystalizes at higher temperatures, and reduces the ability to leach REE from the Concentrate.
A novel, comprehensive allanite review paper prepared by leading researchers on allanite leaching supports this hypothesis and highlights the potential of allanite as an REE ore mineral (Xiao and Zhang, 2024). The allanite review paper also suggests that future metallurgical research focusing on separation and leaching is needed (Xiao and Xhang, 2024).
