Namibia Critical Metals president Darrin Campbell says the hydrometallurgical tests at the Lofadal project in Namibia form the basis for a prefeasibility study report expected later this year.
Namibia Critical Metals is developing the Tier-1 Heavy Rare Earth Project, Lofdal, a globally significant deposit of the heavy rare earth metals dysprosium and terbium in Namibia.
The Lofdal Project is fully permitted with a 25-year mining licence.
The hydrometallurgical scale-up and mini pilot plant test work led to the production of a high-purity rare earth element (REE) carbonate product at the “Lofdal 2B-4” heavy rare earth (HREE) project.
The company used the pilot-scale test work at SGS Lakefield, which resulted in a simplified flow sheet.
The pilot test work removes crude REE precipitation, re-leach, and thorium solvent extraction, which significantly simplifies and reduces overall reagent consumption.
Tests were conducted using a 93 kg pilot plant flotation concentrate sample with an average grade of 2.65% TREO produced at SGS Lakefield, using run-of-mine material from the Lofdal Area 4 starter pit.
Benchscale hydrometallurgical tests showed recoveries of around 94% terbium (Tb) and dysprosium (Dy) using a two-stage acid bake process at 300°C and 650°C.
The SGS pilot rotary kiln was used to scale from static acid baking to continuous testing in short 6-8 hour commissioning campaigns and a longer 72-84 hour pilot campaign.
The calcines produced in the acid bake campaigns were combined and water-leached batch-wise. The pregnant leach solution (PLS) was subsequently used in a series of bench-scale and continuous liquor treatment tests.
The original flowsheet consisted of Impurity Removal (IR), Crude Rare Earth Carbonate Precipitation (RP), Re-Leaching (RL) of the crude carbonate precipitate to produce a concentrated REE liquor, followed by Uranium IX and Thorium SX, and final REE recovery as calcined oxalate or carbonate.
Current test work has shown that a significantly simplified flowsheet consisting of two stages (primary and secondary) of impurity removal/neutralisation, followed by Uranium IX and two stages (primary and secondary) of REE carbonate precipitation, can produce high-grade HREE carbonate.
Under optimum operating conditions, continuous high temperature (600°C) sulphation in the SGS rotary kiln yielded high HREE dissolution (90–94% Tb and Dy). A composite water leach liquor was produced containing around 1.6 g/L REE and co-extracted impurities such as thorium, uranium, scandium, iron, and aluminium.
Batch testwork was used to show that two stages of impurity removal using magnesium carbonate were able to remove practically all (below analytical detection limits) thorium, scandium, iron, aluminium, and some of the uranium at minimum losses of HREE (~ 2%). Uranium was removed by ion exchange (UIX) using a conventional strong base anion resin with negligible co-extraction of HREE.
The UIX barren liquor was used in a mini-pilot plant where REE-carbonate was recovered in two stages (primary and secondary) of precipitation using sodium carbonate. Overall recovery of REE was almost quantitative, and around 0.5 kg of REE carbonate precipitate was produced, containing 3.24% dysprosium, 0.44% terbium, and 19.3% yttrium. Thorium impurities of the product are <0.5 g/t Th.
Standalone re-leach tests confirmed that any HREE co-precipitated in the Secondary Neutralisation (SN) stage and Secondary Rare Earth Precipitation was quickly recovered (>99.7%) using excess acidity contained in the Water Leach (WL) PLS. No additional acid is required.
Removing the original crude REE precipitation, re-leach (RL), and thorium solvent extraction (ThSX) unit operations forms a significant simplification and reduces overall reagent consumption.
The Japan Organization for Metals and Energy Security (JOGMEC) has committed an additional C$550,000 budget for Namibia Critical Metals.
The latest commitment made as part of JOGMEC’s fiscal year ended March 31, 2025, brings the organisation’s total expenditure commitments to over $15 million.
Campbell said the pilot-scale hydrometallurgical test work is for the “Lofdal 2B-4” pre-feasibility study.
Campbell said the SGS again demonstrated their ability to innovatively modify the flow sheet, resulting in further simplification and reduced reagent consumption.
“Our engineering and financial team will now evaluate the detailed results. It will form the basis of the PFS report expected later this year as we work to mitigate increased inflationary costs from our November 2022 PEA,” he said.
