This 2022 preliminary economic assessment outlines the proposed processing route for the Wicheeda rare earth project, comprising a flotation concentrator and a hydrometallurgical plant.
Report context
The Wicheeda project technical report, dated January 2022, describes a preliminary economic assessment (PEA) for a rare earth deposit. Material from the project is envisioned to be processed in a flotation concentrator to produce a rare earth flotation concentrate, which would then be sold into the market for the first four years of operation and subsequently processed in a hydrometallurgical plant to produce a mixed REE precipitate. The report presents conceptual flowsheets and preliminary process design criteria, with metallurgical testwork having been conducted on composites containing about 4.8% TREO.
Processing route
Flotation Concentrator
The proposed concentrator flowsheet will include three-stage crushing, ball mill grinding, rougher and scavenger flotation, and three stages of cleaner flotation at elevated temperature to produce a final flotation concentrate containing 40-50% TREO. The flotation concentrate will be thickened to about 55% solids and then filtered to about 9% moisture. The filtered concentrate will be weighed, sampled and bagged in super-sacks containing 1,000-2,000 kg of concentrate.
Crushing: Run-of-mine material will be hauled to the primary crusher. Primary crushed material will be conveyed to a double-deck secondary screen, with oversize conveyed to a secondary cone crusher. Discharge from the secondary crusher will be conveyed to a tertiary screen, with oversize conveyed to a tertiary cone crusher operating in closed circuit with the tertiary screen. Secondary and tertiary screen undersize (-9.5 mm) will be conveyed to a fine material bin feeding the grinding circuit.
Grinding Circuit: The circuit will consist of a single stage ball mill operating in closed circuit with a cluster of hydrocyclones to produce a final grind size of 80% passing (P80) 106 µm.
Reagent Conditioning and Flotation Circuit: Cyclone overflow from the grinding circuit will be conditioned in a three-stage conditioning circuit with required reagents at 80-85°C. The first stage conditioner will adjust slurry pH to 9.5-10 with soda ash, the second stage will condition with depressants for gangue minerals (F220 and Na2SiF6), and the third stage will condition with mineral collector and activator. The conditioned slurry will advance to rougher flotation. Rougher tailing will be further conditioned before scavenger flotation. Rougher and scavenger concentrates will be combined and conditioned before advancing to three stages of cleaner flotation.
Concentrate Thickening and Filtration: Final flotation concentrate will be thickened in a high-rate thickener to about 55% solids and filtered with a pressure filter to about 9% moisture.
Tailing Thickening: Final flotation tailing will be thickened to about 60% solids in a high-rate thickener and pumped to the tailings storage facility.
Recovery Estimate
Metallurgical test programs on composites containing about 4.8% TREO reported laboratory REO recoveries of 85% into flotation concentrates containing almost 49% TREO. It is noted that actual mined grades will be significantly lower. During the first 10 years of production, plant feed will range from about 2.1% to 3.0% TREO. Due to these lower feed grades, REO recovery has been discounted to 80% into concentrates containing 43% TREO for the first 10 years. For production years 11-16, plant feed grades will decline from about 1.9% to 1.2% TREO, with further discounting applied. The report states that confirmatory testwork on material representing planned mine production grades and mineral content will be required during the next phase of metallurgical testwork.
Hydrometallurgical Plant
The hydrometallurgical plant processes flotation concentrate received as moist filter cake. The flowsheet includes gangue leach, caustic crack, rare earth leach, impurity removal, rare earth precipitation, and HCl regeneration circuits.
Gangue Leach Circuit: Flotation concentrate is received at 290 t/d and passed through surge system into gangue leach tanks with two-hour residence time. Regenerated acid is fed to maintain terminal pH of 3.0 at 50°C. Leached slurry is thickened, pressure filtered, and washed. Filter cake feeds the caustic crack circuit, while pregnant solution is reacted with limestone slurry to pH 5 and sent to Mg-Mn precipitation.
Caustic Crack Circuit: Gangue leach residue is slurried with regenerated 50% NaOH solution at 150°C through agitated tanks providing four hours retention time. Discharge slurry is diluted, cooled, filtered and washed. The filter cake feeds the REE acid leach circuit. The filtrate is reacted with slaked lime in causticization reactors providing six hours residence time. Precipitate is removed and sent to waste; filtrate is evaporated back to 50% NaOH and recirculated.
Rare Earth Leach Circuit: Caustic crack residue is reacted with regenerated HCl at 50°C in reactors providing four hours residence time. Acid maintains terminal free acid of 30 g/L. Leach slurry is treated with H2O2, limestone to pH about 3, and SO4 to precipitate impurities. After filtration, pregnant leach solution is treated with NaHS to remove Pb and Zn. Impurity-free PLS is reacted with high-purity lime to precipitate REE hydrate, which is filtered, washed, partially dried, and placed in FIBC for transport.
HCl Regeneration: CaCl2 solutions from gangue leach and REE leach circuits are combined and agitated with lime slurry to pH 9 to precipitate Mg, Mn, and other metals. Purified CaCl2 solution is evaporated to about 450 g/L CaCl2, cooled and reacted with H2SO4, precipitating CaSO4 and forming 20% HCl solution used in the leach circuits.
Waste Handling: Waste streams are generated in gangue leach, causticization, REE impurity removal, Mg/Mn removal, and CaCl2 conversion. Filter cakes will be blended and transported back to the mine site for combination with flotation tailings.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Mine production rate | tpy | 1,800,000 | Design |
| Mill design capacity | tpd | 5,000 | Design |
| Life of mine TREO grade | % | 2.3 | Design |
| Crushing product P80 | mm | 9.5 | Design |
| Ball mill, feed F80 | µm | 9,500 | Design |
| Ball mill, product P80 | µm | 106 | Design |
| Bond ball mill work index (BWI) | kWh/t | 9.3 | Testwork |
| Abrasion Index, Ai | – | 0.007 | Testwork |
| Rougher-scavenger flotation temperature | °C | 80 – 85 | Design |
| Rougher-scavenger flotation pH | – | 9.5 | Design |
| Cleaner flotation temperature | °C | 80 – 85 | Design |
| Cleaner flotation pH | – | 8.5 | Design |
| Flotation retention times scale factor | – | 2.5 | From laboratory testwork |
| Flotation concentrate grade | % TREO | 40 – 50 | Design target |
| Concentrate filter cake moisture | w/w% | 9 | Design |
| Tailings thickener underflow density | w/w% | 55 | Design |
| Metallurgical testwork composite grade | % TREO | 4.8 | Testwork |
| Laboratory REO recovery | % | 85 | Testwork |
| Laboratory concentrate grade | % TREO | 49 | Testwork |
| Discounted REO recovery (years 1-10) | % | 80 | Design |
| Discounted concentrate grade (years 1-10) | % TREO | 43 | Design |
| Hydrometallurgical recover (REE to precipitate) | % | 87.0 | Design |
| Concentrate tonnage to hydromet plant | t/a | 100,465 | Design |
| REE content of dried precipitate | % TREO | 76 | Design |
Project website: https://www.defensemetals.com/wicheeda-property
Note: Flotation retention times are scaled by a factor of 2.5 from laboratory testwork. Discounted recovery and concentrate grades show adjustments for lower plant feed grades compared to testwork composites.
Technical qualifications
The report states that plant feed grades during the first 10 years of production will range from about 2.1% to 3.0% TREO, compared to metallurgical testwork composites containing about 4.8% TREO. Due to these lower feed grades, REO recovery has been discounted from the 85% laboratory recovery to 80% into concentrates containing 43% TREO for the first 10 years. Plant feed grades will continue to decline during production years 11-16 from about 1.9% to 1.2% TREO, with further discounting applied. The report explicitly states that confirmatory testwork on material representing planned mine production grades and mineral content will be required during the next phase of metallurgical testwork to confirm achievable REO recovery and concentrate grades.
Source: Wicheeda PEA NI 43-101 Technical Report, January 2022, Sections 17 Recovery Methods, 17.1 Flotation Concentrator, 17.1.1 Flotation Concentrator Description, 17.1.2 Recovery Estimate, 17.2 Hydrometallurgical Plant, 17.2.1 Plant Flowsheet and Design Criteria, 17.2.2-17.2.6
