This report details the processing design for the North American Lithium Project, based on the existing plant, historical operations, and current testwork.
Report context
This April 2023 report defines the recovery methods for the North American Lithium Project, which is based on the existing plant that was placed on care and maintenance in early 2019 and restarted concentrator operations in Q1 2023. The design incorporates historical operational data, metallurgical testwork, and equipment information from suppliers.
Processing route
Crushing and sorting
The primary crushing system includes an apron feeder sized at 6,100 mm × 1,219 mm for a daily throughput of 4,588 tpd, feeding a jaw crusher equipped with a 149 kW motor. The crusher is designed for a feed size of 309 mm and a product P80 of 94 mm, with an expected utilization of 65%.
A two-deck vibrating screen receives the jaw crusher product with a nominal feed size F80 of 94 mm. The top deck opening is 75 mm and the bottom deck opening is 20 mm. Top deck oversize reports to the primary ore sorter while bottom deck oversize reports to two secondary ore sorters. Screen undersize with P80 of 13 mm is directed to the tertiary crusher.
The primary and secondary ore sorters receive feed with a Li2O grade of 1.04%, with waste rejection estimated at 50% and feed upgraded to approximately 1.10% Li2O. The reject grade is estimated at 0.43% Li2O. The crushing circuit lithium recovery, including sorting, is 95.6%.
Grinding
The grinding circuit consists of an open-circuit rod mill followed by a ball mill in closed circuit with stack sizer screens. The rod mill has an installed power of 970 kW and reduces feed from a P80 of 13,000 µm to 1,050 µm at a nominal feed rate of 4,200 tpd. Six stack sizer screens divide the stream into oversize with P80 of 970 µm reporting to the ball mill, and undersize with P80 of 200 µm reporting to desliming. The ball mill reduces screen oversize and returns product to the screens for classification.
Desliming, magnetic separation, and flotation
The grinding circuit undersize reports to a desliming stage consisting of 17 operating cyclones plus two on stand-by, with an overflow cut size (D50) of 10 µm. Cyclone underflow passes through six attrition scrubbers, each with a volume of 13 m³ and retention time of approximately 16 minutes at a nominal flowrate of 206 m³/h.
The attrition scrubber discharge is processed in a low-intensity magnetic separator (LIMS) to remove ball mill chips. Slurry is diluted to approximately 29% solids by weight. One double-drum counter-rotation wet LIMS, providing a magnetic field strength of 950 gauss, handles this duty. The non-magnetic stream reports to two 13,000 gauss wet high-intensity magnetic separators (WHIMS) in series, with magnetic waste sent directly to the tailings thickener. The lithium recovery from desliming and WHIMS is 88.5%.
The deslimed stream is conditioned in a high-density conditioning tank with reagents at a retention time of 16.4 minutes and nominal slurry flowrate of 176 m³/h. Rougher flotation consists of three 30 m³ tank cells, followed by scavenger flotation in three additional 30 m³ tanks. The cleaning circuit comprises three stages: 18 conventional cells of 8.5 m³ each in the first stage, 13 conventional cells of 5.1 m³ each in the second stage, and 19 conventional cells of 2.8 m³ each in the third stage. First cleaner tailings report to the tailings cyclone; second and third cleaner tailings are recirculated internally.
Third cleaner concentrate reports to a concentrate storage tank with agitator, then to a belt filter producing concentrate at approximately 8% moisture by weight.
Tailings management
Tailings from the concentrator are collected in a final tailings tank. Scavenger and first cleaner tailings are pumped to a dewatering cyclone, with underflow at 48.9% solids by weight and a flow rate of 167 m³/h reporting directly to the final tailings tank. Cyclone overflow combines with first desliming cyclone residue, LIMS rejects, and WHIMS rejects and is pumped to an 18.3 m diameter steel-constructed thickener. Thickener underflow at 50% solids by weight and 34.8 tph solids is pumped to the final tailings tank at 47.7 m³/h.
A future tailings filter plant is scheduled for start-up in 2025, with two recessed plate filter presses (one operating, one on standby) designed to bring filter cake moisture below 15%. Filtrate and wash water are collected and pumped to a clarifier, with overflow partially treated through a multi-media filter for reuse as filter wash water and gland seal water.
Reagents and consumables
Primary reagents include collector (Custofloat 7080) at 1,118 tpy for rougher and scavenger flotation, dispersant (F220) at 354 tpy for attrition scrubbing and cleaners, soda ash at 181 tpy for pH control in the high-density conditioning tank, and flocculant (Flomin 920) at 61 tpy for thickening. Grinding media consumption is 949 tpy of 75 mm rods and 849 tpy of 50 mm balls.
Electrical distribution
The plant receives 4.16 kV power through one 5/6.7 MVA transformer/switchgear unit. Grinding mill motors are fed at 4.16 kV. Most 600 V power is generated through double-ended switchgear arrangements using 3/4 MVA transformers. The future tailings filtration plant will be fed through a 13.8 kV overhead power line with step-down transformers and switchgear.
Key reported parameters
| Criterion | Unit | Value |
|---|---|---|
| Crushing Plant Availability | % | 65 |
| Concentrator Availability | % | 93 |
| Total ROM Mine Feed | tpy | 1,557,000 |
| Concentrator Ore Feed | tph | 175 |
| Concentrator Ore Feed Per Year | tpy | 1,425,690 |
| Rod Mill Feed Grade | % Li2O | 1.10 |
| Concentrate Production | tph | 22.65 |
| Concentrate Production | tpy | 184,511 |
| Concentrate Grade (design) | % Li2O | 5.82 |
| Concentrate Grade (first four years) | % Li2O | 5.40 |
| Concentrate Iron Content (target) | % Fe | < 1.00 |
| Concentrate Humidity | % H2O | 8.0 |
| Concentrator Lithium Recovery | % | 66.3 |
| Crushing and Sorting Lithium Recovery | % | 96.5 |
| Desliming and WHIMS Lithium Recovery | % | 88.5 |
| Flotation Lithium Recovery | % | 78.4 |
| Concentrator Personnel | employees | 86 |
| Concentrator Salaried Staff | employees | 28 |
| Concentrator Hourly Workers | employees | 58 |
| Natural Gas Assured Supply | sm³/h | 3,400 |
| Natural Gas Consumption (crusher building heating) | sm³/month | 52,470 |
Technical qualifications
The report notes that other process modifications are still being developed, including the addition of a crushed ore storage dome to increase ore retention capacity and a tailings filter plant scheduled for start-up in 2025. Peak winter natural gas loads are expected to exceed the assured supply of 3,400 sm³/h; Énergir is investigating network expansion, and alternatives including LNG make-up or partial propane supply may be required if expansion does not materialize. The report relies on reagent consumption rates based on flotation testwork. The concentrator currently has permits for 3,800 tpd throughput, with procedures underway to increase authorization to a maximum of 4,500 tpd; the current mass balance is based on nominal rod mill feed of 175 tph or 4,200 tpd.
Source: Sayona Mining Limited, NI 43-101 Technical Report, Definitive Feasibility Study for the North American Lithium Project, April 2023, Sections 17.1, 17.2, 17.3.3, and 17.3.7.
