Taseko's 2014 pre-feasibility design took Aley carbonatite ore from a 10,000 tonne per day concentrator through leaching, calcining and an aluminothermic converter to standard grade ferroniobium.
The Aley niobium project sits in northeastern British Columbia, in the Omineca Mining Division, about 20 km northeast of the head of the Ospika Arm of Williston Lake. Aley Corporation, a wholly owned subsidiary of Taseko Mines Limited, owned 100% of the property. Taseko's technical report, with an effective date of September 15, 2014, set out a pre-feasibility level mine plan for a conventional open pit feeding a 10,000 tonne per day processing plant. The project was at the development stage, and the report does not give a construction start date. Its product was to be ferroniobium made on site from pyrochlore, fersmite and columbite in the Aley carbonatite.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Mill average throughput | 10,000 | t/d | Design basis |
| Annual tonnage | 3,650,000 | t/a | Design basis |
| Design processing rate | 439 | t/h | Process plant |
| Plant availability | 92 | % | Overall processing plant |
| Design feed grade | 0.50 | % Nb2O5 | Matches reserve grade |
| Design process plant recovery | 71 | % | Locked cycle test basis |
| Design overall site recovery | 65.3 | % | To ferroniobium |
| Ferroniobium production | 298 | Mkg/yr | Design criteria table |
| Ferroniobium grade in tests | 63 | % Nb | Test work result |
| Average leach recovery in tests | 95 | % | All leach tests |
| Mineral reserves | 83,815 | kt | Proven and probable at 0.50% Nb2O5 |
| Production schedule | 24 | years | Final 4 years from stockpile |
| Grinding product size | 50 | µm | 80% passing |
| Site connected power | 31.3 | MW | Operational peak 22.2 MW |
Overview
The recovery method rests on test work at two laboratories. SGS in Burnaby, British Columbia, supplied the basis for comminution, concentration and concentrate leaching, and Taseko produced that design. Xstrata Process Support in Sudbury, Ontario, supplied the basis for concentrate preparation and conversion, which Ausenco Minerals and Metals designed.
Run-of-mine ore passes through a single crushing stage to a coarse ore stockpile. A SAG mill, a ball mill and a tower mill grind it fine. A concentrator then upgrades the niobium, and the concentrate goes to leaching. Calcining follows, and the calcine is converted to ferroniobium in batch aluminothermic reactions. Concentrator waste is pumped as sand slurry to a sand storage management facility, while converter waste goes to secure containment. The report treats the flotation and leach conditions as proprietary and confidential, so it describes the equipment without the chemistry.
Key Process Stages
Crushing
Haul trucks tip ore onto a vibrating grizzly ahead of a 350 HP primary jaw crusher. Grizzly undersize goes straight to a conveyor, and oversize returns to the jaw. The crusher produces 80% passing 150 mm. A belt carries the product to a coarse ore stockpile with 15,000 t of live capacity beside the concentrator building.
Grinding
Three 25 HP apron feeders reclaim ore at 10,000 tpd into a 24 foot SAG mill. A 2.4 m by 6.1 m screen returns oversize to the SAG feed. Screen undersize is pumped to a primary cyclone cluster. Underflow feeds an 18 foot by 27 foot ball mill with the same motor size as the SAG mill, and the ball mill discharges back to the cyclone feed pump box.
Primary cyclone overflow at 140 µm goes to a secondary cyclone cluster. Its underflow feeds a 4,500 HP tower mill, which grinds to 80% passing 50 µm. The crushing and comminution areas hold more than 250 pieces of equipment and draw a peak of 12,500 kW. The largest drives are the 4,000 kW SAG mill, the 4,000 kW ball mill and the 3,400 kW vertical grinding mill.
Concentration
The concentrator uses magnetic separation, direct flotation, thickening and filtration. Magnetic separators handle up to 360 m3/h. Flotation tank cells range from 160 m3 down to 10 m3, with retention times from 76 down to 27 minutes. Thickeners run from 50 m to 15 m in diameter, and vertical plate filters complete the circuit. Over 170 pieces of equipment draw a peak of 6,100 kW. Waste streams are thickened and combined before pumping to the sand storage facility, and the concentrate is thickened for the leach plant.
Leaching
Leaching runs in tanks from 350 m3 down to 4 m3, with a designed reaction time of 16 hours. The circuit also includes acid regeneration. Residues are thickened in 15 m thickeners and filtered on belt filters, and the overflow and filtrate are recycled. All materials of construction are chosen for an acid environment. More than 210 pieces of equipment draw a peak of 1,700 kW. The filtered residue drops onto a conveyor that feeds the calciner.
Conversion to ferroniobium
The converter treats 100 t/d of leach residue. A screw feeder takes residue from a storage bin into a rotary kiln, which runs continuously. The calcine is cooled, stored and weighed into bulk bags, and kiln off-gas is cooled and treated.
Reagent preparation, reaction and metal finishing run 12 hours a day. Aluminum powder, iron, lime, fluorspar and sodium nitrate are mixed with the calcine in batches of about 6,800 kg. Each batch goes into a refractory-lined reactor vessel set in sand on a rail car. Under the reaction hood a fuse sets off the reaction, which lasts 10 to 15 minutes. Aluminum reduces the niobium and iron to ferroniobium, and the alumina reports to the refuse. The molten refuse is tapped into containers on rails for cooling and disposal. The metal cools partly in the vessel and then fully in a cooling area.
In the metal finishing plant the alloy is sampled, then crushed and screened through mobile reversible conveyors and screens from 30 mm to 2 mm. It is sized and packed to customer specifications. Dust from finishing is recycled to reagent preparation.
Additional Interesting Data and Summary
The proven reserve is 44,272 kt at 0.52% Nb2O5 and the probable reserve 39,543 kt at 0.48% Nb2O5, at a cut-off of 0.30% Nb2O5. The pit has a life-of-mine strip ratio of 0.5 to 1. In the last four years of the 24 year schedule, all mill feed comes from stockpile.
Power was to arrive on a proposed 150 km, 138 kV line from Mackenzie. The crushing and process plant take up to 18.6 MW of peak power, and the leach and converter plants up to 2.7 MW. Natural gas heats buildings and process streams, at an average of 81,700 GJ per year for buildings and 537,500 GJ per year for process streams including the calciner.
Process water comes back from the sand storage facility on a floating barge with four 250 HP vertical turbine pumps, which feed a 4,000 m3 fresh water tank. Thickener overflows are recycled in the plant. The process plant and converter are designed to run 24 hours a day, 365 days a year.
Cominco found pyrochlore at Aley in the early 1980s. Taseko acquired the project in 2007 and, from 2011, concentrated on metallurgical testing and a workable ferroniobium process.
Key Processes
- Single stage jaw crushing to a coarse ore stockpile
- SAG and ball milling with a tower mill for fine grinding to 50 µm
- Magnetic separation and direct flotation to a niobium concentrate
- Acid leaching of the concentrate with acid regeneration
- Rotary kiln calcining of the leach residue
- Batch aluminothermic reduction to ferroniobium
- Crushing, screening and packing of the alloy
- Sand slurry disposal with water reclaim by barge
Source: Technical Report on Mineral Reserves at the Aley Project, British Columbia, Canada, September 15, 2014.
Project website: Aley Project
