Whabouchi Lithium Mine and Shawinigan Electrochemical Plant — 2019 Technical Report

The 2019 technical report describes the proposed processing facilities for the Whabouchi spodumene concentrator and the Shawinigan electrochemical plant, with design criteria based on testwork.

Report context

The February 2018 NI 43-101 technical report on the feasibility study for the Whabouchi Lithium Mine and Shawinigan Electrochemical Plant, issued by Nemaska Lithium Inc., presents the recovery methods and process design for the two integrated facilities. The Whabouchi concentrator is located 675 m north east of the open pit mine. The Shawinigan Electrochemical Plant is located in the City of Shawinigan, Quebec. The report documents proposed design parameters, historical testwork results, and the basis for process flow sheets and mass balances.

Processing route

Whabouchi Concentrator

Crushing and ore sorting

The concentrator is designed to produce a nominal 215,022 tonnes of spodumene concentrate per year at 6.25% Li₂O from an ore feed averaging 1.53% Li₂O. The run-of-mine mineralized material, containing 19.1% spodumene with 2% moisture, is dumped into a hopper and fed via apron feeder into a jaw crusher. The primary crusher discharge, with P80 of 95 mm, is screened on a double deck coarse ore screen. Top deck oversize is returned to a second jaw crusher in closed circuit. Bottom deck oversize (−80 mm +10 mm) is conveyed to ore sorters operating by X-Ray Transmission identification. The ore sorting area screens the feed at 35 mm; coarse ore sorter feed is −80 mm +35 mm and fine ore sorter feed is −35 mm +10 mm. Rejected waste is stockpiled for removal, while accepted material is transported to the fine crushing facility.

Fine crushing comprises a double deck vibrating screen and a two-stage cone crusher circuit. Secondary cone crushers (standard) crush top deck oversize to P80 of 21 mm; a tertiary short head cone crusher crushes bottom deck oversize to P80 of 12.7 mm. The final crushed product, with P80 of 5.8 mm and 100% passing 9 mm, is conveyed to a fine ore stockpile in a dome.

Dense media separation

The fine ore is screened on a double deck vibrating screen with 2.0 mm top deck and 0.85 mm bottom deck openings. Screen undersize (−0.85 mm) bypasses the DMS system to the fine muscovite removal circuit. Oversize (−9.0 mm +0.85 mm) goes to coarse muscovite removal via a hydraulic separator. The hydraulic separator overflow is screened; oversize reports to final tailings, while underflow and screen undersize are pumped via a dewatering screen to the DMS feed bin.

The DMS circuit uses a two-stage dense media separator unit. The rougher stage consists of two 510 mm diameter cyclones operating at a cut point specific gravity of 2.70, producing rougher floats (DMS tailings) and rougher sinks. The cleaner stage uses one 510 mm diameter cyclone at a cut point specific gravity of 2.96, producing cleaner floats (DMS middlings) and cleaner sinks (DMS concentrate). The DMS concentrate is dried in a rotary dryer to less than 1% moisture, then treated by dry magnetic separation (low intensity followed by rare earth high intensity) to produce the first portion of final spodumene concentrate at above 6.6% Li₂O.

Grinding and flotation

The DMS middlings are ground in a 2.4 m diameter by 2.7 m EGL grate discharge ball mill (250 kW) to a P80 of 640 µm, then combined with fine ore screen undersize for fine muscovite removal. The ground product feeds cyclones for densification, then a hydraulic separator for fine muscovite removal. Desliming is performed in a cyclone cluster, followed by wet magnetic separation (low intensity at 950 Gauss and wet high intensity at 13,000 Gauss) to remove paramagnetic material.

The spodumene flotation circuit consists of de-sliming, attrition scrubbing, and two stages of flotation. Attrition scrubbing uses four cells of 2.5 m³ each with dispersant and caustic soda at pH 12. Coarse flotation (−850 µm +200 µm) is performed in a 1.8 m diameter by 3.7 m high HydroFloat separator after conditioning with sulfuric acid (pH 8) and spodumene collector. The HydroFloat concentrate is screened at 250 µm; oversize at 5.52% Li₂O goes to the concentrate dewatering circuit.

Fine flotation (−200 µm +20 µm) uses two 2.5 m diameter by 8.0 m high flotation columns (rougher and cleaner) after conditioning with sulfuric acid (pH 8) and spodumene collector. The rougher column tailings go to the tailings thickener; rougher concentrate feeds the cleaner column. Cleaner column concentrate grades 6.37% Li₂O. Cleaner tailings are recycled to the de-sliming cyclones.

Concentrate dewatering and tailings

The flotation concentrate is thickened to 62% solids in a 6.0 m diameter high rate thickener, then filtered to less than 8% moisture using a 350 m² vertical plate pressure filter. The filtered concentrate combines with dried DMS concentrate on a conveyor; the blended concentrate has expected moisture less than 5%. The combined product is stored in a 4-day concentrate stockpile dome, then transported by road truck to Chibougamau for rail transport to Shawinigan.

Tailings from DMS, dry magnetic separation, mica hydroseparation, de-sliming, wet magnetic separation, HydroFloat, and column flotation are dewatered by a combination of screen dewatering, thickening in a 10.6 m diameter inclined plate settler to 61% solids, and pan filtration to 15% moisture. Filtered tailings are stored in a 1-day tailings storage dome and transported by haul truck to the co-disposal area with mine waste.

Concentrator mass balance and water

The concentrator processes 2,824 dry tonnes of ore per day requiring 279 m³/d of makeup water. Tailings are dewatered to about 12% moisture for dry stacking. The concentrator operates at 92% availability; the DMS section at 80%; the crusher at 66.7%. The DMS circuit recovers 36.7% of total feed spodumene; the flotation circuit recovers 48.6%; total spodumene recovery is 85.3%. DMS concentrate production is 86,641 dry tonnes per year; flotation concentrate production is 128,432 dry tonnes per year.

Shawinigan Electrochemical Plant

Plant design and feed

The electrochemical plant is designed for a feed rate of 215,022 dry tonnes per year of spodumene concentrate (42% DMS concentrate, 58% flotation concentrate) to produce 33,000 tonnes per year of lithium carbonate equivalent (LCE). The plant can vary lithium hydroxide monohydrate production from 50% to 100% of total Li units and lithium carbonate powder from 0% to 50% of total Li units. The plant operates 24 hours per day, 7 days per week, with 85% availability.

Thermal conversion and acid bake

Concentrate arrives by 92-tonne railcars, is discharged into a receiving hopper, and conveyed to a stockpile. A front-end loader reclaims concentrate through a crushing system reducing top size from 9.5 mm to less than 2 mm, then to a concentrate silo with 18 hours live capacity. The concentrate is preheated in three pre-heating cyclones, then calcined at 1,000 to 1,100°C in a natural gas fired flash calciner to convert alpha-spodumene to beta-spodumene. The roasted concentrate is cooled in cooling cyclones and a water-cooled indirect cooler, then stored in a roasted concentrate silo. Hot flue gases are sent to a baghouse for dust removal.

Beta-spodumene is mixed with sulfuric acid in a pug mixer and sent to an acid-bake kiln. The heat allows reaction of oxides with sulfuric acid to produce sulfates, primarily lithium sulfates and minor amounts of select impurity sulfates.

Leaching, purification, and electrolysis

The acid bake product is mixed with water in the concentrate leach step, then separated on a belt filter to remove gangue (aluminum-silicate). The pregnant leach solution undergoes three purification and filtration steps: primary impurity removal, secondary impurity removal, and tertiary impurity removal, followed by ion exchange polishing to remove trace calcium. These steps remove excess acid, calcium, silicon, iron, aluminum, manganese, and magnesium.

The polished solution feeds electrolyzers where lithium sulfate is converted to lithium hydroxide (catholyte solution) and sulfuric acid (anolyte solution). The anolyte is sent to sulfuric acid concentration and recycled to the pug mixer with fresh make-up acid.

Crystallization and final products

The catholyte is sent to lithium hydroxide monohydrate (LHM) crystallization. A double crystallization process produces pure LHM crystals and condensate that is fully re-used. A small bleed stream from LHM crystallization is sent to treatment where lithium is recovered and sodium and potassium are purged. LHM crystals are dried for sale. Up to 50% of LHM crystals can be converted to lithium carbonate in a dedicated circuit for sale as final product. Overall lithium recovery is reported as 95.9%.

Key reported parameters

Technical qualifications

The process design and criteria are based on a feasibility study prepared for Nemaska Lithium Inc. The overall lithium recovery for the electrochemical plant is based on laboratory results and extensive mass balance modeling. The concentrator weight recovery of 20.9% and spodumene recovery of 85.3% are average figures based on testwork on representative samples. Plant availability of 85% for the electrochemical plant is estimated based on benchmarks with comparable industries and high-level availability analysis. The report states that as of the date of the technical report, no commercial off-take agreements for concentrate sales were in place; two commercial off-take agreements for LCE products totalling about 14,000 LCE were in place, valid between 42 and 60 months from start of commercial production.

Source: Nemaska Lithium Inc., NI 43-101 Technical Report – Feasibility Study on the Whabouchi Lithium Mine and Shawinigan Electrochemical Plant, February 2018.