Significant progress is being made at American Rare Earths Ltd (ASX:ARR, OTCQB:ARRNF)'s Halleck Creek Rare Earths Project in Wyoming, with the company reporting good results from leach testing from the Cowboy State Mine. Testing has delivered robust recoveries for both light and heavy rare earth elements. Key outcomes include praseodymium and neodymium recoveries of 85% and 84%, respectively, and encouraging results for terbium (52%) and dysprosium (46%).
Further, impurity levels in leachate — particularly iron and aluminium — have been significantly reduced, with concentrations approximately five times and nearly three times lower than earlier tests. The company has selected atmospheric tank leaching as the preferred processing method, citing lower energy and reagent use compared to alternatives like acid-bake.
The tests are a significant milestone in technically de-risking the project, having confirmed the optimal leach conditions and the preferred configuration for the Pre-Feasibility Study (PFS) flow sheet.
Results indicate leach parameters that could deliver favourable processing outcomes, including reduced energy consumption and effective front-end impurity removal.
This development represents a critical step towards producing rare earth magnet oxides from Halleck Creek ore.
Leach testing campaign confirms optimal recovery pathway
An extensive leach testing program was conducted on ore from the Cowboy State Mine at SGS’s laboratory in Ontario, Canada. Twenty-five tests evaluated multiple leaching strategies, including atmospheric tank leach, acid-bake/water leach and counter-current leach methods. Atmospheric tank leaching (ATL) emerged as the preferred method, based on performance, cost efficiency and suitability for large-scale processing.
Of the 18 ATL trials conducted, test AL16 was identified as optimal. This test used a blend of 80% unaltered concentrate from gravity spiral and IRMS separation, and 20% fines processed via WHIMS. The ore was ground to 100% passing 53 microns. At 400 kilograms of sulfuric acid per tonne and 90°C over eight hours, AL16 achieved extraction rates of 85% for praseodymium and 84% for neodymium.
Reduced impurities improve processing efficiency
Compared to prior testing conducted for the Scoping Study, the updated leach tests delivered a significant drop in impurity levels. Iron concentrations in the leachate fell by 80%, aluminium by 65%, and other elements including sodium, potassium, titanium and phosphorus also showed substantial reductions.
This improvement is attributed to enhanced concentrate preparation. The newer process, which includes gravity spiral separation and IRMS, removed more iron- and aluminium-bearing minerals — such as hematite and magnetite — before leaching. As a result, downstream processing may require fewer reagents, leading to reduced operational costs and improved environmental outcomes.
Testing supports scalable and cost-effective processing
The ATL method was favoured for its relative simplicity and scalability. In contrast, acid-bake and counter-current leach methods involved higher reagent use, equipment complexity, and capital costs. Acid-bake trials, conducted at up to 300°C, did not offer improved rare earth element recoveries and introduced higher levels of aluminium, iron and magnesium into solution.
Counter-current leach testing yielded strong results, particularly for heavy rare earths, but required substantially higher acid dosages and double the filtration infrastructure. This complexity and potential cost increase led to ATL being confirmed as the preferred leach path for the Pre-Feasibility Study.
Next steps
SGS is progressing with impurity removal trials using the optimal leachate produced under AL16 conditions. These tests will support finalisation of the mineral processing flow-sheet and guide the design of pilot-scale trials.
American Rare Earths is focused on developing a sustainable and economically robust rare earth supply chain from Halleck Creek. The project's low impurity levels, high leach recoveries and efficient processing route position it strongly as a potential long-term supplier of rare earth magnet materials critical to global decarbonisation and advanced technologies.