The Ajax Project 2016 Technical Report describes a proposed 65,000 t/d copper-gold processing plant designed around crushing, high-pressure grinding rolls, ball milling, and flotation to produce a copper concentrate with associated gold recovery.
Report context
This report, dated February 19, 2016, presents the recovery methods and process design for the Ajax Project. The processing plant is proposed to treat 23,725,000 dry tonnes of copper-gold ore annually, or 65,000 t/d, producing approximately 250,000 dry tonnes of concentrate per year grading 25% Cu and containing approximately 14.65 g/t Au. The ore processing scheme is based on metallurgical testwork program results described in Section 13 of the report, with a simplified process flow diagram (Figure 17-1), detailed mass and water balance, and process design criteria developed for the flowsheet.
Processing route
Primary Crushing and Stockpiling
Run-of-mine ore will be delivered to the primary gyratory crusher by 300 tonne haul trucks and fed directly to a 450 tonne capacity covered dump pocket. Large rocks not passing the 1,500 mm by 2,800 mm primary gyratory crusher opening will be broken with a permanently installed hydraulic rock breaker. Dust generated by dumping and rock breaking will be contained and collected by a dry dust collection system at the primary crusher dump area.
Crushed ore from the primary crusher, at P80 of 150 mm, is transferred via an apron feeder to the covered coarse ore stockpile feed conveyor. The stockpile provides surge capacity with a live capacity of 40,000 tonnes and total capacity of 200,000 tonnes, allowing uninterrupted feed to the downstream secondary crushing circuit. Reclaim is accomplished by four apron feeders located in a tunnel under the stockpile, each equipped with variable frequency drives. Two feeders can accommodate the full production rate, though all four can operate simultaneously.
Secondary and Tertiary Crushing
Coarse ore is conveyed to a feed bin with 360 tonnes live capacity at the head of the cone crusher screening circuit. Individual belt feeders draw material onto a 4.2 m by 8.5 m double-deck vibrating screen. Screen oversize (nominally +50 mm) is fed to the cone crusher feed bin with 175 tonnes live capacity, while undersize discharges to the fine ore stockpile feed conveyor. Tramp metal protection is provided by a feed metal detector that activates a diverter chute to an outside bunker.
Two 900 kW MP1250 cone crushers operate in closed circuit, with material returned to the screening circuit. A dry dust collection system controls dust emissions, with captured fines returned to the first cone crusher screen feed conveyor.
The covered fine ore stockpile provides 20,000 tonnes live capacity and 100,000 tonnes total capacity, formed as a 32 meter high conical pile. Three apron feeders with 75 kW variable frequency drives reclaim material to the HPGR feed bin conveyor. A weightometer and particle size camera provide process control data, while a belt magnet protects downstream equipment from tramp metal.
Tertiary Crushing with HPGR
The tertiary crushing circuit consists of two HPGR units and two HPGR screens in closed circuit configuration. Material is received in a 360 tonne HPGR feed bin with steep tapered walls, mass flow design, and 25 mm thick liners, located inside the crushing building to prevent freezing. Two variable speed belt feeders deliver material to the HPGRs, with an intermediary conveyor allowing placement of a metal detector and diverter gate to automatically bypass tramp metal. Two 2.4 m diameter roll class HPGRs receive feed with F80 of 45 mm and reduce it to P80 of 15 mm.
HPGR screens separate oversize particles requiring further crushing from particles passing to the cyclone feed pumpbox. Screens are double deck multi-slope units with 7 mm wide apertures, and water sprays aid separation. Screen oversize returns via conveyor to complete the closed circuit, with a diverter gate providing operational flexibility for bypassing to an outdoor bunker.
Ball Mill Grinding Circuit
Two parallel ball mill trains, each operating in closed circuit with a cluster of hydrocyclones, grind ore to a target P80 of 214 µm. Each circuit treats 1,472 t/h of new feed. Cyclone feed pumpboxes (281 cubic meters) receive combined HPGR screen undersize and ball mill discharge, with slurry pumped by 2,000 kW cyclone feed pumps to cyclone clusters of twelve 840 mm diameter cyclones each (ten operating, two standby). Cyclone underflow at 78% solids by weight flows by gravity to the ball mill feed chute.
Each ball mill is 7.9 m diameter by 13.4 m long, equipped with dual pinion drives powered by two variable frequency drives with 9,000 kW low synchronous motors. Ball mills are protected from tramp metal by ball mill magnets positioned on the discharge, with collected chips discharged to a scats bunker.
Flotation and Regrind
Cyclone overflow at 35% solids by weight with P80 of 214 µm flows to rougher flotation. Each ball mill line feeds its own rougher train comprising six 300 m³ forced air tank flotation cells, each with 265 kW motors and variable frequency drives, providing approximately 28 minutes retention time. Collector, frother, and promoter are added to the feed box with provisions for additional reagents in the third and fifth cells. Froth cameras monitor cell performance with imaging software and expert systems for optimization.
Rougher concentrate undergoes primary regrind in a vertically stirred mill operating in closed circuit with a cyclone cluster at 250% recirculating load. The primary regrind mill is 4,500 hp, with twenty-five 375 mm diameter cyclones (22 operating, 3 standby) classifying the product to P80 of 40 µm. Cyclone underflow is returned to the mill, with a fraction diverted to the gravity gold concentration circuit.
A portion of the primary regrind cyclone underflow is processed through a gravity circuit to maximize recovery of fine gravity gold, with the concentrate combined with copper concentrate at the concentrate thickener. Regrinding to approximately 20 µm is required to fully liberate copper bearing material, achieved through secondary regrind prior to cleaner flotation.
Concentrate Dewatering and Tailings
Copper concentrate is dewatered by thickening and filtration before placement in a concentrate stockpile, with reclaim by front-end loader to concentrate trucks for shipment to the Port of Vancouver. Final flotation tailings are disposed of as thickened tailings slurry into a tailings storage facility, with process water recycled from the tailings thickener overflow and supplemented by recovered water from the tailings storage facility and concentrate thickener overflow. Fresh water is used for pump gland seal service, reagent preparation, gravity concentrator fluidization, and process water makeup.
Key reported parameters
| Item | Units | Value | Basis |
|---|---|---|---|
| Design throughput | dmt/y | 23,725,000 | Design |
| Design throughput | t/d | 65,000 | Design |
| Copper grade | % | 0.3 | Design |
| Gold grade | g/t | 0.2 | Design |
| Ore density | kg/m³ | 2,790 | Design |
| Crushing work index (average) | – | 8.57 | Testwork |
| HPGR index | – | 2.92 | Testwork |
| Ball mill work index (Bond average) | – | 23.59 | Testwork |
| SMC (A x b) | – | 34.47 | Testwork |
| Abrasion Index | – | 0.24 | Testwork |
| Primary crushing availability | % | 70 | Design |
| Secondary crushing availability | % | 85 | Design |
| Tertiary crushing availability | % | 92 | Design |
| Milling and concentration availability | % | 92 | Design |
| Primary crushing nominal capacity | dmt/h | 3,869 | Design |
| Secondary crushing nominal capacity | dmt/h | 3,186 | Design |
| Tertiary crushing nominal capacity | dmt/h | 2,944 | Design |
| Milling nominal capacity | dmt/h | 2,944 | Design |
| Primary crushing feed size F80 | mm | 745 | Design |
| Tertiary crushing product P80 | mm | 3.25 | Design |
| Primary grinding circuit product P80 | µm | 214 | Design |
| Regrind circuit product P80 | µm | 40 | Design |
| Overall copper recovery | % | 85.9 | Testwork/design |
| Overall gold recovery | % | 85.1 | Testwork/design |
Project website: https://kghm.com/en/our-business/projects-under-development/ajax
Technical qualifications
The process design relies on several specific testwork programs documented in Section 13 of the report. HPGR design criteria show testwork conducted by the equipment supplier. Grinding mills were sized based on Bond Work Index data for ball mills, with the primary regrind mill also using Bond Work Index data. The secondary regrind mill was sized based on Signature test data from laboratory testwork and confirmed by the supplier. Flotation cells were sized based on optimum flotation times determined during bench and pilot scale test campaigns, using typical design parameters and scale-up factors.
The secondary crushing circuit is arranged so that two feeders can accommodate the full production rate, though all feeders may operate simultaneously. The HPGR screen oversize return conveyor normally returns material to close the circuit, but a diverter gate provides bypass capability to maintain partial feed should both HPGRs be down. Ball mill grinding circuits are each capable of treating 1,472 t/h of new feed, with cyclone underflow at 78% solids by weight. The primary regrind cyclone cluster comprises twenty-five 375 mm diameter cyclones with 22 operating and 3 standby.
Dust control measures include dry dust collection systems for the primary crusher and cone crusher areas, with captured fines returned to appropriate feed conveyors. Chemical suppression systems supplement dust control, and ventilation fans sweep the covered stockpile and tunnel atmospheres. The HPGR screen feed bin is designed with steep tapered walls, mass flow design, and interior heating to mitigate freezing effects, with 25 mm thick liners on inner walls.
The report provides the process design criteria for the proposed plant but does not include detailed mass and water balance data in the sections reviewed, nor does it address construction schedules, capital or operating costs, or economic analysis.
Source: Ajax Project Updated Technical Report, February 19, 2016, Section 17 Recovery Methods.
