The 2024 feasibility study for the Dasa Uranium Project defines a process plant designed to treat 365,000 dry tonnes per annum of uranium ore using a pugging and curing leach route followed by solvent extraction and peroxide precipitation.
Report context
This document is derived from the NI 43-101 technical report titled "Dasa Uranium Project, Feasibility Study, NI 43-101 Technical Report" dated 28 February 2024. The report details the recovery methods and process plant design for the Dasa Uranium Project based on laboratory and pilot plant test work. The process design is currently in execution, with the execution design not yet complete and costing still in progress. All financial evaluations retain 2021 costing and have not been updated for this feasibility study.
Processing route
Process selection and basis
The process route selected for the Dasa Plant is similar to Orano operations at Arlit in Niger, which process a similar ore type. Laboratory and pilot plant test work confirmed the process design parameters. The pugging and curing process has been successfully applied at the Cominak and Somair operations.
The process utilises the addition of high strength lixiviant and oxidative chemicals (sulphuric acid and nitric acid) to create aggressive reaction conditions in a low moisture feed. This promotes uranium leaching characteristics with limited dissolution of undesirable gangue elements like silica, which would otherwise have negative downstream process implications.
The design development followed a logical sequence including process design basis, block flow diagram, mass balance, mechanical equipment list, process flow diagrams, piping and instrumentation diagrams, process control philosophy, water balance, and process description.
Trade-off studies
Three trade-off studies were completed as part of process options selection: dry milling processing, final product precipitation, and tailing disposal.
Dry milling options: The study evaluated High Pressure Grinding Rolls (HPGR), Vertical Shaft Impactor (VSI), and Semi Autogenous Grinding (SAG) technologies. Mineralogical characterisation of the ore indicated that quartz is the primary gangue mineral with a coarse grain size, while uranium-containing minerals are fine-grained and hosted within the matrix holding quartz particles together. The SAG mill achieved the highest weighted total score (138) compared to HPGR (60) and VSI (118) based on technical risk, combined capital and operating costs, flowsheet complexity, ease of construction, technology maturity, and maintenance requirements. SAG was recommended because it offers greater control flexibility to minimise overgrinding of quartz and promotes polishing effects on coarse quartz particles.
Final product precipitation options: Three reagents were assessed: magnesia, ammonia, and hydrogen peroxide. From test work completed, hydrogen peroxide precipitation produced a product with the highest uranium grade at 76% U by mass, compared to 60% for ammonia and 52% for magnesia. The peroxide product also demonstrated extremely fast filtration rate and coarse particle size. The overall annual cost of the peroxide system was at least 30% lower than either magnesia or ammonia.
Tailings disposal options: The study evaluated dry stacking by conveyor, dry stacking by trucking, and wet disposal by piping. Over the life of mine, dry stacking by conveyor had the least total net present cost at $10,524,843 compared to wet tailings piping at $14,777,713 and dry stacking by truck at $14,150,645. Dry stacking was recommended.
Process design criteria
The Dasa Plant has a design capacity of 365,000 dry tonnes per annum based on a plant availability of 86%. The overall uranium recovery is 94.15%. The plant uses single stage crushing with a jaw crusher, dry SAG milling with screens, pug leaching with 10 minutes residence time in the pug drum and 3 hours curing time, belt filtration, solvent extraction with 4 extraction stages, 3 scrub stages, and 3 strip stages, sodium di-uranate (SDU) precipitation, and uranyl peroxide precipitation with hydrogen peroxide.
Process description
Run of Mine Pad: Haul trucks deliver ore to the RoM pad where it is either direct tipped to the RoM bin or dumped onto blending stockpiles. A front-end loader reclaims and trams ore from stockpiles to maintain relatively constant feed grade, acid consumption, and filtration characteristics.
Crushing Circuit: A single tip with a dedicated RoM bin and a single jaw crusher in open circuit. The RoM ore (F100 500 mm) is loaded into a 70 tonne RoM bin. After crushing, material reports to the crushed ore stockpile.
Dry Grinding and Classification: The milling circuit is configured as a dry SAG mill in closed circuit with dry screens. The SAG mill is equipped with a variable speed drive to manage variations in feed hardness. The air heating and drying system uses steam from the acid plant with diesel fed burners providing final heating requirements.
Pug Leach and Curing: Pugging is carried out in a revolving pugging drum where sulphuric acid, oxidant (sodium nitrate and nitric acid), and a small amount of water are added to achieve a total liquid/solids ratio of about 0.15. Retention time in the drum is 10 minutes. Curing occurs on two 2.4 m wide conveyor belts with a total length of 270 m and belt speed of 0.025 m/s, giving a residence time of 3 hours. After curing, dissolution is carried out in agitated slurry tanks at a solid-to-liquid ratio of 1:1.
Solid-Liquid Separation: Two 75 m² belt filters operating in parallel. The filtered pregnant leach solution is clarified using a pin bed clarifier and stored in two 500 m³ tanks with twenty-four-hour storage capacity. Each horizontal vacuum filter has 3 wash stages to limit soluble losses.
Solvent Extraction: A conventional solvent extraction treatment uses a tertiary amine (Alamine 336 at 8.7% v/v) dissolved in kerosene (Exxsol D80 at 84.4% v/v) with modifier (Exxal 13 at 7.0% v/v). Four mixer-settlers are used at extraction step, three at scrub step, and three at stripping step. At least 50% of the raffinate solution is discharged to evaporation ponds for disposal due to build-up of impurity metals.
Sodium Di-Uranate Precipitation: Five tanks in series provide a total residence time of 5 hours at 60°C. Caustic soda is the precipitation agent. The barren strip liquor is recycled back to strip after carbonate concentration adjustment.
Uranyl Peroxide Precipitation: Five mechanically agitated tanks with 6.5 hours residence time. The precipitation process uses seed recycle to provide nucleation sites. The resultant uranyl peroxide is dried between 120°C and 180°C in a kiln prior to packaging.
Final Product Drying and Packaging: Thickened slurry is centrifuged to produce a dewatered product containing 60% solids, then dried at 120°C to 180°C. The uranium drying and packaging plants are contained in sealed rooms maintained under slight negative pressure.
Key reported parameters
| Parameter | Units | Value | Basis |
|---|---|---|---|
| Ore throughput | dry t/a | 365,000 | Design |
| Plant availability | % | 86 | Design |
| Plant throughput (daily average) | dry t/d | 1,000 | Design |
| Plant capacity (design) | dry t/h | 50 | Design |
| Uranium grade (design) | % | 0.45 | Design |
| Overall uranium recovery | % | 94.15 | Design |
| Primary crusher type | , | Jaw Crusher | Design |
| RoM feed size, F100 | mm | 500 | Design |
| Crushing product size, P80 | mm | 80 | Design |
| SAG mill product, P95 | mm | 0.6 | Design |
| Pug leach solids content | % m/m | 85 | Design |
| Pug drum residence time | min | 10 | Design/testwork |
| Curing time | h | 3 | Design |
| Belt filter flux | t/h/m² | 0.504 | Design |
| Solvent extraction stages | , | 4 extraction / 3 scrub / 3 strip | Design |
| Raffinate bleed | % v/v | 52 | Design |
| SDU precipitation residence time | h | 5 | Design |
| SDU precipitation temperature | °C | 60 | Design |
| UP precipitation residence time | h | 6.5 | Design |
| Raw water consumption (process plant) | m³/h | 41.0 | Design |
| Milling circuit type | , | Dry SAG with screens | Design |
| Final product | , | Uranyl peroxide (UO₄·2H₂O) | Testwork |
| Precipitation reagent | , | Hydrogen peroxide | Testwork/trade-off |
| Precipitation product uranium grade | % m/m | 76 | Testwork (bench scale) |
| Tailings disposal method | , | Dry stacking by conveyor | Trade-off |
| Climatic conditions (conveyor distance) | m | ~1,000 | Design assumption |
| Tailings tonnage | t/d | ~500 | Design assumption |
| Tailings solids content | % m/m | 80 | Design assumption |
| Precipitate filtration rate | , | Extremely fast | Testwork (hydrogen peroxide) |
| Precipitate particle size | , | Coarse | Testwork (hydrogen peroxide) |
| SDU process filtration characteristics | , | Improved with fluid bed reactor | New testwork |
Project website: https://globalatomiccorp.com/Operations/Uranium/Dasa-Project/default.aspx
Technical qualifications
The plant design is currently in execution and the design has been optimised with detailed vendor information, but the execution design is not complete and costing is still in progress. The previous plant design remains for the feasibility study and is within the design accuracy required. Trade-off financial evaluations have not had their costs updated but keep the 2021 costing unaltered. The only changes to the design relate to tailings solids now all reporting to the tailings storage facility rather than partially to a backfill plant, and some infrastructure items now detailed under infrastructure.
The belt filters have been designed to handle ore variability, which requires limited clays in feed ore, prevention of overgrinding, careful reagent addition, and washing of solid tails with clean raffinate solution. The SDU process test work identified unfavourable settling and filtration characteristics, but new test work using fluid bed reactor technology has demonstrated superior filtration characteristics incorporated in the final design.
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*Source: Dasa Uranium Project, Feasibility Study, NI 43-101 Technical Report, 28 February 2024, Sections 17.1–17.6.*
