The 2025 feasibility study for the Matawinie Graphite Mine details a processing plant designed to produce a high-purity graphite concentrate from a 4.23% feed grade, supported by 2024 lock cycle test work.
The 2025 feasibility study for the Matawinie Graphite Mine presents the engineering design for a mineral processing facility intended to produce 105,882 dry tonnes of graphite concentrate per year. The design basis for the plant is an ore feed with a head grade of 4.23% C(g), which represents the average over the life of mine. The concentrator is designed to treat a nominal 7,804 dry tonnes per day, operating at a nominal rate of 325 dry tonnes per hour, with an assumed operating availability of 90%. A design factor of 4.2% was applied to the crushing and comminution equipment, 20% for most other processing equipment, and 25% for the slurry pumps.
The flowsheet is based on a combination of well-established processes, including primary crushing, semi-autogenous grinding, ball milling, conventional flotation, polishing, and stirred media milling. The overall metallurgical design targets a final concentrate grade of 97.5% C(t), assuming a total carbon content in the concentrate equal to the graphite carbon content, as the processing of ore eliminates other carbon sources. The average graphite recovery for design purposes is set at 93%, corresponding to an average weight recovery of 4.13%. The plant design was updated based on test work performed at the NMG demonstration plant, as well as results from external laboratories and supplier test facilities. The foundational metallurgical parameters for the design were derived from 2024 lock cycle test work, which may be subject to change depending on ore composition.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Nominal Ore Processing Rate | 2,563,728 | dry tpy | |
| Nominal Concentrator Ore Processing Rate | 7,804 | dry tpd | |
| Ore Moisture | 5.0 | % | |
| Graphite Ore Grade C(g) (average over LOM) | 4.23 | % | |
| Crusher Operating Time | 37.5 | % | |
| Nominal Ore Crushing Rate | 780 | dry tph | |
| Concentrator Operating Time | 90 | % | |
| Nominal Ore Processing Rate | 325 | dry tph | |
| Final Graphite Concentrate Grade C(t) | 97.5 | % | |
| Final Graphite Concentrate Recovery | 93 | % | |
| Total Graphite Production (nominal) | 105,882 | dry tpy | |
| Total Graphite Production (average over LOM) | 103,328 | dry tpy |
Project website: https://nmg.com/updated-feasibility-study/
Overview
The mineral processing facility is designed around a conventional flowsheet comprising crushing, grinding, flotation, polishing, and stirred media milling. The design integrates metallurgical test work, supplier simulations, and operational experience from the NMG demonstration plant. The plant’s main objective is to produce a high-purity graphite concentrate, with the process water and tailings management strategies designed to support continuous 24-hour operation. Design criteria were refined through multiple stages of metallurgical testing, and the equipment sizing was based on the final mass balance, flowsheet, and layout considerations.
Key Process Stages
The primary crushing circuit consists of two identical lines, each equipped with a grizzly feeder and a jaw crusher. The crushing circuit is designed to operate during the daytime, 16 hours per day, on weekdays only. Fines from the grizzly feeder bypass the crusher and are combined with the crusher product. A stockpile is incorporated into the design to provide a constant and stable feed to the downstream grinding circuit, ensuring the plant can maintain operations when the crusher is not running.
The grinding circuit is comprised of a SAG mill and a ball mill operating in a closed circuit with hydrocyclones. The SAG mill is driven by a 3,000 kW variable-frequency drive motor. The cyclone cluster consists of nine 400 mm cyclones, with seven in operation and two spares. Cyclone overflow is directed to a trash screen to remove wood chips. The design of the SAG mill and vibrating screen circuit is based on ore comminution characteristics, while the ball mill, cyclone, and rougher/scavenger flotation circuit design is based on test work, supplier simulations, and demonstration plant operational experience.
The flotation process is a multistage operation. Rod mill or ball mill discharge is directed to a rougher/scavenger flotation circuit. Fuel oil and methyl isobutyl carbinol are added as collector and frother. The rougher/scavenger concentrate is sent to a polishing mill, after which the upgrading process continues in cleaning stages. Four cleaning stages are conducted in series, and the upstream cleaners are comprised of 2 x 10 m³ mechanical flotation cells. Tailings from cleaners 1, 3, 5, and 7 are sent to a cleaner scavenger circuit, which consists of 2 x 20 m³ mechanical flotation cells. Final cleaning is accomplished in flotation columns, with the concentrate from the 2nd flotation column being considered final concentrate and pumped to the concentrate thickener. The design of the SMMs, cleaning flotation cells, and columns is based on test work, supplier input, and NMG demonstration plant data.
Final concentrate handling includes a concentrate thickener and filtration. The concentrate is dewatered to a filter cake, with the filter presses equipped with a maximum of 98 plates each. The pressed graphite is then handled in a product loadout system that uses tandem 1 m³ pneumatic sending vessels in an alternating sequence, conveying the graphite to a receiving bin. From this bin, the graphite is blown to two parallel screening lines to produce four distinct size fractions: +50 mesh (+300 μm), -50 to +80 mesh (-300 to +180 μm), -80 to +150 mesh (-180 to +106 μm), and -150 mesh (-106 μm).
Tailings are managed using separate circuits for potentially acid generating and non-acid generating materials. The tailings dewatering circuit includes one PAG tailings thickener, one PAG tailings press filter, one NAG tailings thickener, and two NAG tailings press filters. The PAG tailings thickener is designed to produce an underflow at 62-65% solids, which is then pumped to the tailings desulphurization circuit. The combined concentrate from the sulphide flotation and magnetic separation circuits is filtered. Thickener overflow water is recovered to the process water system.
Reagent systems are designed to support the flotation and dewatering processes. The expected total PAX consumption is 621 kg per day. Lime is not required for graphite recovery but can be added at various locations to maintain a pH between 6.5 and 8 to prevent metal leaching. Two flocculant systems, a small one for the graphite concentrate thickener and a larger system for the other three thickeners, are included. Compressed air is supplied by blowers, with two compressors in normal operation and one on standby. The process water tank has a capacity of 409 m³, and the fresh water tank, fed by treated reclaim water, has a capacity of 300 m³.
Additional Interesting Data and Summary
The design criteria specified a top size for run-of-mine material that can be managed by the comminution circuit, with a confirmed crusher supplier recommendation on grizzly feeder and chute opening. The process design encompasses water balances for both winter and summer seasons. The plant includes a pH control system across multiple locations to manage metal leaching. The material handling design allows for the production of screened concentrate in four size products to meet customer needs, providing flexibility in the final product slate.
Key Processes
- Crushing: Grizzly feeders and jaw crushers in two parallel lines
- Grinding: SAG mill and ball mill in closed circuit with hydrocyclones
- Flotation: Rougher/scavenger and four-stage cleaning circuits using mechanical cells and columns
- Polishing: Stirred media mills for concentrate regrinding and impurity removal
- Dewatering: Concentrate and tailings thickeners, followed by pressure filtration
- Tailings: Separate PAG and NAG dewatering and desulphurization circuits
- Reagent Handling: Systems for flotation reagents, flocculant, frother, and pH modifiers
Source: 2025 Feasibility Study for the Matawinie Graphite Mine, 2025.
Project website: 2025 Feasibility Study for the Matawinie Graphite Mine
