The Preliminary Economic Assessment for the Decar Nickel Project in British Columbia, Canada, details a processing plant that uses only physical separation methods to recover nickel from awaruite ore, based on metallurgical test work conducted by SGS.
The Decar Nickel Project is an advanced-stage development project located in British Columbia, Canada. The processing strategy outlined in the Preliminary Economic Assessment (PEA) is predicated entirely on physical separation methods, using the high specific gravity and magnetic susceptibility of the nickel-iron mineral awaruite. This design choice precludes the need for chemical or hydrometallurgical recovery processes. The performance of the gravity and magnetic separation equipment is based on bench-scale test work conducted by SGS, which investigated the recovery of nickel from the Decar awaruite deposit.
The plant is designed to process 40 Mt/a of run-of-mine (ROM) material. The process flowsheet includes three stages of crushing and grinding, a single stage of magnetic separation, a regrind stage using tower mills, and a final gravity concentration step using Knelson concentrators. All crushing is performed dry, and the final concentrate is dewatered and dried before transport. The PEA states that no test work has yet been conducted to determine how the concentrate grade might vary with changes in head grade, and as such, the Project is assumed to produce a concentrate with a constant grade.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Plant Throughput | 40 | Mt/a | 115 kt/d |
| Average Feed Grade | 1,182 | g DTR nickel/t | Not stated |
| Nickel Concentrate Production | 269 | kt/a | Not stated |
| Nickel Concentrate Grade | 13.5 | % total nickel | Constant grade assumed |
| DTR Nickel Recovery | 75 to 85 | % | Targeting 82% |
| Total Nickel Recovery | 37 to 42 | % | Corresponds to DTR recovery |
| Bond Ball Mill Work Index | 15 | kWh/t | Assumed; no comminution test work conducted |
| Regrind Size | 70 | µm | In tower mill |
| Primary Grind Size | 600 | µm | Nominal |
| Crushing Product Size | 13 | mm | Tertiary crushing product |
| Magnetic Separator Feed Solids | 30 | % solids | Not stated |
| Magnetic Separator Concentrate Solids | 70 | % solids | Not stated |
| Knelson Concentrator Feed Solids | 30 | % solids | Not stated |
| Knelson Concentrator Concentrate Solids | 70 | % solids | Not stated |
| Final Concentrate Moisture (Filter) | 9 | % | After rotary disk filter |
| Final Concentrate Moisture (Dryer) | 5 | % | After diesel-fired dryer |
| Process Electrical Demand | 92.5 | MW | Scaled from a similar model process |
| Dryer Diesel Demand | 1.5 | million L/a | Not stated |
| Thickener Underflow Solids | 65 | % solids | Not stated |
| Thickener Diameter | 184 | m | Minimum; three required |
| Tails Settling Rate | 0.7 | m²/t/day | Assumed; no settling tests conducted |
| Filter Unit Capacity | 800 | kg/h/m² | Assumed; similar to magnetite |
Overview
The Decar project’s orebody is characterized by the presence of awaruite, a naturally occurring nickel-iron alloy. The beneficiation process is designed around the mineral's physical properties rather than its chemical composition. All unit operations selected for the flowsheet use either gravity or magnetic separation. The process performance criteria for these separators were established through test work performed by SGS. A "Nickel Value in Use Study" conducted by Hatch Ltd. used synthetic process concentrates with 15% and 4% total nickel to assess marketability, though the process is expected to produce a concentrate with 13.5% total nickel.
Key Process Stages
The process design is based on the flowsheet presented in the PEA, which consists of several distinct stages. Run-of-mine material is first reduced in size through a series of primary, secondary, and tertiary crushers. This crushed material is then fed to primary ball mills for wet grinding to a nominal size of 600 µm. The primary grinding circuit operates in open circuit with trommels to prevent oversized material from advancing.
Following grinding, the slurry is processed in a single stage of wet magnetic separation. The magnetic separators, which feature drums with an 85 mm diameter and 3,175 mm length, are fed with a slurry containing 30% solids. They are designed to produce a concentrate with 70% solids, and their performance criteria represent reasonable name plate values comparable to SGS test results. The magnetic concentrate is then diluted and fed to tower mills for regrinding to 70 µm.
The final stage of beneficiation uses Knelson concentrators, which are gravity separation devices. These units process a 30% solids slurry and produce a concentrate with 70% solids. To recover the collected concentrate, the Knelson concentrators periodically shut down one to three times per hour, necessitating a surge tank upstream. Each concentrator is designed to recover 2.4% of the feed mass and 67% of the total nickel. The concentrate is then dewatered using a rotary disk filter to achieve 9% moisture, and finally dried to 5% moisture in a diesel-fired dryer before being stored in a covered warehouse with seven days of capacity. From there, the concentrate is trucked to a rail spur and shipped to a west coast port.
Reject material from the magnetic and gravity separation stages forms the tailings stream. This tailings slurry is thickened using three large thickeners, each at least 184 m in diameter, to recover water for recycling. The thickener underflow, at 65% solids, is disposed of in a Tailings Management Facility (TMF). The process is entirely physical and requires only minor amounts of flocculant and descaling agents, quantities of which could not be estimated.
Additional Interesting Data and Summary
The PEA notes several design assumptions and identifies areas for future study. The Bond ball mill work index of 15 kWh/t was assumed, as no comminution test work had been completed at the time of the report. Equipment sizing was based on Tetra Tech's internal references and vendor discussions. The crushing plant would be large, with a potential requirement for approximately eight standard cone crushers and 12 short-head cone crushers. Similarly, the primary grinding stage would require three large ball mills.
The report suggests that future studies should evaluate alternative grinding options such as semi-autogenous grinding (SAG) mills and high-pressure grinding rolls (HPGR). For the regrind circuit, the tower mills are preferred due to lower operating and installation costs, smaller floor space requirements, and reduced noise and over-grinding, but the use of ball mills in closed circuit with hydrocyclones should be considered in future design work. Additional test work is also recommended to determine the required filtering area for the concentrate dewatering stage.
The PEA includes a preliminary look at the marketability of the concentrate. A study by Hatch used concentrate grades of 15% and 4% total nickel to determine "value in use," while this process is expected to produce a constant 13.5% total nickel concentrate. The projected concentrate is likely to have a composition that falls between the two grades tested by Hatch. The process design assumes a constant concentrate grade since no test work has yet been conducted to establish the relationship between head grade and concentrate grade.
Key Processes
- Communition: Three-stage crushing (gyratory, standard cone, short-head cone) followed by primary ball milling to 600 µm, and tower mill regrinding to 70 µm.
- Magnetic Separation: A single stage of wet drum magnetic separators to produce a rougher concentrate, exploiting the magnetic properties of awaruite.
- Gravity Concentration: Knelson concentrators for the final beneficiation stage, recovering a significant portion of the nickel into a high-grade gravity concentrate.
- Dewatering and Drying: Rotary disk filtration to achieve 9% moisture, followed by a diesel-fired dryer to reach 5% moisture for product transport and storage.
Source: Preliminary Economic Assessment – Decar Nickel Project, 2023.
Project website: Preliminary Economic Assessment – Decar Nickel Project
