This report describes the proposed graphite concentration process for the Lac Guéret project, including the design basis, process description, and key parameters for the Baie-Comeau facility.
Report context
The Lac Guéret Graphite Project 2018 Technical Report, dated December 2018, presents a feasibility study update. It describes a concentration plant designed for the Baie-Comeau site, which is separate from the mine at Lac Guéret. The report details the process design criteria and equipment areas.
Processing route
Overall approach
A team composed of Soutex and Mason Graphite personnel developed an industrial concentration process designed to treat on average 190 ktpy of ore and produce 52 ktpy of graphite concentrate. The process includes crushing, grinding, flotation with polishing circuits, filtration, drying, screening, and bagging. The concentrator operates at a nominal 24.1 tph with multiple process areas located at Baie-Comeau; only mining occurs at the Lac Guéret site.
Crushing
The crushing area includes one raw ore stockpile with 40,000 t capacity, a primary crusher with an apron feeder, and a crushed ore bin with about 8.5 hours retention. The primary crusher operates on average 1,268 h/y at 11.7% utilization, processing ROM ore with a top size of approximately 600 mm at a nominal rate of 150.0 tph, reducing ore to P80 ~75 mm.
Grinding and flotation
The primary grinding and flotation area consists of a SAG mill, SAG mill classification screen, rougher flotation cells, a rod mill, rod mill classification screen, and scavenger flotation cells. SAG mill discharge is screened; oversize recirculates and undersize feeds the rougher flotation. Rougher concentrates go to the first polishing circuit. Rougher flotation tails feed the secondary grinding rod mill, with oversize recirculated and undersize sent to scavenger flotation.
Polishing and cleaning flotation
The polishing area includes four polishing mills, two banks of cleaning flotation cells, eight flotation columns, and four concentrate wet screens. Rougher and scavenger concentrates are combined and undergo a sequence of polishing and cleaning flotation. Tailings from each stage are pumped to the tailings thickener, while concentrates are collected in a thickener before filtration. Process water from dewatering steps is recycled.
Concentrate filtration, drying, and commercial screening
The filtration and drying area includes one concentrate filter, one concentrate dryer, and one wet scrubber. Concentrate from the thickener underflow feeds a filter feed tank with eight hours residence time before filtration. Dried concentrate is stored in a silo before commercial sieving. The commercial screening area includes four concentrate screens, with two screen lines capable of generating up to ten finished products directed to finished product bins. The bagging area has three bulk bag packaging stations, one small bag packaging station, and one wrapping station.
Tailings treatment
All flotation tailings are collected in a pump box and pumped to a thickener to reach 62% solids, with decanted water sent to the raw water pond. Thickened pulp goes to a filter feed tank before a pressure filter produces a cake containing 15% humidity. The cake is stockpiled and trucked to the tailings management facility where it is spread and compacted.
Plant services and utilities
Reagents used include collector, frother, dispersant, flocculent, hydrated lime, and caustic soda. The collector is delivered in tanker trucks; frother in 1,000-litre totes; dispersant and flocculent in big bags; hydrated lime in big bags added to the SAG mill feed chute; caustic soda in 1,000-litre totes used in the dryer wet scrubber. Process water is sourced from recycled thickener overflows and the raw water tank. Potable water is used for human consumption and fire suppression.
Total power load is evaluated at 11.3 MW including all electrical power; process power is estimated at 7.2 MW including drying. An emergency generator provides power to critical equipment such as thickeners during power failures.
Key reported parameters
| Parameter | Units | Value |
|---|---|---|
| Ore throughput | tpy | 189,620 |
| Concentrate production | tpy | 51,865 |
| Overall weight recovery | % | 27.4 |
| Process facility service life | y | 25 |
| Plant operating time | % | 90.0 |
| Primary crusher operating time | % | 11.7 |
| ROM total carbon (average) | % Cg | 27.8 |
| ROM total carbon (annual max) | % Cg | 31.2 |
| ROM total carbon (annual min) | % Cg | 25.4 |
| ROM sulphur (average) | %S | 9.4 |
| ROM specific gravity | , | 2.9 |
| ROM moisture | % w/w | 5.0 |
| ROM maximum particle size (F100) | mm | 630 |
| Final concentrate grade +50 mesh | % Cg | 96.0 |
| Final concentrate grade -50 to +80 mesh | % Cg | 96.0 |
| Final concentrate grade -80 to +150 mesh | % Cg | 96.0 |
| Final concentrate grade -150 mesh | % Cg | 92.2 |
| Final concentrate average grade | % Cg | 93.7 |
| Carbon global recovery | % | 92.31 |
| Crushed ore feed tonnage (per crusher) | tph | 150.0 |
| SAG mill feed tonnage | tph | 24.1 |
| Concentrator operating schedule | h/y | 7,884 |
| Tailings cake moisture | % | 15 |
| Tailings thickener density | % solids | 62 |
| Process power requirement | MW | 7.2 |
| Total site power load | MW | 11.3 |
Project website: https://nmg.com/acquisition-lac-gueret/
Technical qualifications
The 92.3% recovery represents the average over 25 years of operation, taking into account a lower recovery of 87.5% for the ramp-up during production Year 1; from production Year 2, the recovery will be 92.5%. Ore transportation is planned to stop during the spring (generally April and May) when the forest road is softer, though reduced-tonnage transport may be maintained during the thaw period. The design accounts for the recovery of elemental sulphur from the concentrate dryer gas stream, which requires precipitation in a quench box and venturi scrubber with neutralization of sulphur dioxide in a packed bed scrubber with caustic soda.
Source: Lac Guéret Graphite Project , NI 43-101 Technical Report, Feasibility Study Update, December 2018.
