This report presents preliminary process design criteria and recovery methods for uranium, with conceptual considerations for lithium and potassium, supporting the May 2016 mineral resource estimate update.
Report context
The report documents preliminary process design work performed for the Chilcuno Chico, Quebrada Blanca, Tantamaco and Isivilla deposits, as presented in the GBM PEA and reported in the May 2016 technical report update to include lithium and potassium. The process design criteria are preliminary, with major equipment items costed on a non-optimised basis and the balance of costs estimated on a ratio basis, as is normal at this study level.
Processing route
Process design criteria
The preliminary process design is based on a 10-year mine life assumed for planning purposes, with plant operations scheduled at 24 hours per day. The plant design throughput is calculated at 1,463 tonnes per hour. The selected leach method is heap leaching, drawing reference from the Plateau Uranium operation, with the leach pad designed to accommodate 6 cells and a heap height of 7 metres. Uranium recovery is proposed via ion exchange, with precipitation using ammonium hydroxide. Overall leach recovery is calculated at 88%.
The planned process plant is situated at an altitude nominally in the range of 4,100 to 4,700 metres above sea level, a factor which has been incorporated into design considerations for generators, combustion machinery, pumping and electrical infrastructure.
Crushing
Testwork results indicate an optimum heap leach feed size for uranium extraction of 50 mm. The ore will be crushed in two stages. Primary crushers, in the form of sizers, will reduce particle size from 100% passing 600 mm to 80% passing 126 mm. Material will be conveyed overland to the plant and stockpiled ahead of secondary crushing. Secondary crushers, also sizers, will reduce the ore to 80% passing 42 mm, representing a nominal 100% passing 50 mm, operating in open circuit. Crushed ore will be conveyed to a fine product stockpile.
Heap preparation, stacking and leaching
The leach pad will be prepared with layers of fill, aggregate and impervious geomembranes, with collection piping installed above the upper membrane level. A final thick layer of aggregate will protect the membrane and collection piping during stacking and reclamation.
Fine crushed ore will be reclaimed from the stockpile and conveyed to the heap leach site, where it will be stacked continuously to a height of 7 metres in a single lift across 6 cells. Stacking rates for the entire pad are matched to cell leaching and drain cycle times, allowing continuous operation of stacker and reclaimer.
Irrigation piping on the stacked heap will distribute sulphuric acid leach solution. The heap will initially be irrigated with intermediate leach solution (ILS), followed by barren leach solution (BLS). The ILS from the initial leach pad will be collected in the pregnant leach solution (PLS) pond and pumped to the recovery plant. Sulphuric acid levels in the ILS will be monitored with fresh acid added as required. After leaching, the heap will be washed with water, which is stored, reused and neutralised with lime. Reclaimed ore will be transported to the tailings storage facility.
Uranium recovery
The PLS will be pumped to a recovery circuit comprising cationic ion exchange resin columns where dissolved uranium is loaded onto the resin. The resulting solution is returned to the barren leach solution pond. Uranium is stripped from the resin using concentrated sulphuric acid, followed by stripping with ammonium sulphate and precipitation with ammonium hydroxide. The ammonium diuranate (ADU) precipitate will be thickened ahead of filtration, drying and drumming of the final yellowcake product.
Proposed recovery of lithium and potassium
Metallurgical testwork on lithium and potassium recovery is considered by the preparer to be at a conceptual level only. However, on the basis of that testwork, it is envisaged that sulphuric acid dissolution of uranium will also dissolve both lithium and potassium, with recovery from the same PLS. Testwork leach solutions indicate potential for lithium carbonate precipitation and production, as well as potassium sulphate. Additional lithium leach testwork will be required to refine the process route and establish reliable quantities, qualities, acid consumption figures and production costs.
This proposed route implies that only lithium and potassium mined and treated as part of the uranium operation would be recovered, and that the operation would be unlikely to apply a lithium or potassium cut-off grade. These implications have been considered in the assessment of reasonable prospects of economic extraction.
Services and reagents
Estimated annual active power demand for the processing plant is 13.4 MW, requiring approximately 6,200 MWh averaged on a monthly basis. The total energy requirement is split: infrastructure 6%, processing 82%, and tailings 12% of total plant power requirement.
A preliminary water balance, based entirely on general meteorological information and limited site-specific data, indicates a net inflow requirement of 150 m³/hr of raw water for sustained operations.
Primary reagents specified for the process include:
- Dilute sulphuric acid for leach solution supplementation
- Lime slurry for leach neutralisation in the ponds area
- Concentrated sulphuric acid for ion exchange eluant
- Ammonium hydroxide for precipitation, manufactured on site from ammonia gas feedstock
- Sodium hydroxide to trim pH ahead of ammonium hydroxide addition
All reagents will be stored separately with dedicated offloading and delivery infrastructure to prevent contamination or incorrect delivery. The reagent storage area will be located away from other infrastructure and fabricated from suitable materials of construction.
For lithium and potassium extraction, the most significant additional services required would be precipitation agents, with further work required to determine these requirements.
Key reported parameters
| Parameter | Value | Unit | Basis |
|---|---|---|---|
| Life of Mine | 10 | Years | Assumed |
| Plant operating hours | 24 | Hours/day | Assumed |
| Plant design throughput | 1,463 | Tonne/hour | Calculated |
| Leach method | Heap leach | , | Plateau Uranium reference |
| Leach pad cells | 6 | Per leach pad | Calculated |
| Leach heap height | 7 | m | Calculated |
| Recovery method | Ion exchange | , | Refer Section 13 |
| Precipitation method | Ammonium hydroxide | , | Assumed |
| Overall leach recovery | 88 | % | Calculated |
| Crushed product size (primary) | 80% passing 126 | mm | Testwork/design |
| Crushed product size (secondary) | 80% passing 42 | mm | Testwork/design |
| Nominal heap feed size | 100% passing 50 | mm | Testwork optimum |
| Plant altitude range | 4,100–4,700 | m above sea level | Site condition |
| Annual active power demand | 13.4 | MW | Preliminary design |
| Monthly energy requirement | 6,200 | MWh | Estimated |
| Net raw water inflow | 150 | m³/hr | Preliminary estimate |
| Infrastructure power share | 6 | % | Estimated |
| Processing power share | 82 | % | Estimated |
| Tailings power share | 12 | % | Estimated |
Project website: https://americanlithiumcorp.com/macusani-uranium-project-peru/
Technical qualifications
The process design is preliminary and based on non-optimised equipment selection, with only major items costed and the balance of costing performed on a ratio basis. The water balance is based entirely on general meteorological information and limited site-specific data. Lithium and potassium recovery testwork is at a conceptual level only, and additional leach testwork is required to refine the process route and establish reliable potential quantities, qualities, acid consumption and production costs. The proposed recovery route for lithium and potassium implies that only material mined and treated as part of the uranium operation would be recovered, limiting the ability to apply separate cut-off grades.
Source: Mineral Resource estimates for the Chilcuno Chico, Quebrada Blanca, Tantamaco and Isivilla Deposits (update to include lithium and potassium), Report No. C-MYI-PUI-1647-990, May 2016, Sections 17.1–17.4.
