Preliminary Economic Assessment (PEA) #3 — Tamarack North Project

This article presents the processing routes and design criteria for the Tamarack North Project as described in the January 2021 Preliminary Economic Assessment.

Report context

The January 2021 Preliminary Economic Assessment #3 (PEA #3) on the Tamarack North Project by Talon Metals Corp. describes processing designs for the Tamarack mineralized material. The report presents three processing routes considered at this stage, with the concentrator section identical for all three scenarios. Process design criteria were generated based on an average daily mill feed rate of 3,600 tpd and a maximum annual head grade of 2.40% Ni and 1.08% Cu.

Processing route

Three processing scenarios

Three different processing routes are being considered: the Ni Concentrate Scenario, representing a conventional processing approach comprising a concentrator that produces Cu and Ni concentrates shipped to smelters; the Ni Sulphate Scenario, which includes a hydrometallurgical plant to transform Ni concentrate into a value-add product with only Cu concentrate shipped to a smelter; and the Ni Powder Scenario, where Ni concentrates are used to produce refined Ni powder for the EV market with Cu concentrate shipped to a smelter.

Concentrator design

The flotation process design for all processing routes comprises bulk rougher flotation followed by cleaning of the bulk rougher concentrate. The upgraded rougher concentrate is subjected to Cu/Ni separation, generating separate Cu and Ni concentrates. The bulk rougher tailings are treated in a desulphurization stage to produce a low-mass, high-sulphur tailings stream and a high-mass, low-sulphur tailings product. For the Ni Concentrate and Ni Powder Scenarios, the Ni concentrate represents the final output of the metallurgical facility.

The crushing circuit comprises primary jaw crushing, secondary cone crushing, and ball mill grinding. The grinding circuit product is subjected to bulk rougher flotation, followed by cleaning of the bulk rougher concentrate and a Cu/Ni separation circuit. The concentrates are thickened and filtered separately and shipped to different smelters via rail. The desulphurization flotation stage comprising a magnetic separator recovers most remaining sulphides into a high-sulphur tailings stream for use as paste backfill.

Mineralized ROM material with an F100 of 153 mm is reduced to a product size P80 of 17 mm in two crushing stages. The crushing circuit comprises a jaw crusher operated in open circuit followed by a cone crusher operated in closed circuit with a vibrating screen. The two-stage crushing circuit operates at approximately 70% utilization and a design factor of 25%, equating to a feed capacity of approximately 267.9 tph. The cone crusher product is transferred to two fine ore bins with a combined capacity of 3,000 m³ to decouple the crushing and grinding circuits.

Mineralized material is transferred to a 5.7 m x 8.7 m EGL ball mill operated in closed circuit with classifying hydrocyclones to generate a flotation circuit feed with a P80 of 100 µm. The ball mill cyclone overflow gravitates to bulk rougher flotation cells at a mass flow rate of 163.0 tph. Sulphide collectors SIPX and PAX and frother MIBC are added to the flotation feed box. Bulk rougher flotation is carried out in tank cells with a volume of 4 x 160 m³, corresponding to a retention time of approximately 72 minutes. The pH of the slurry is lowered to 7.0 in the last tank cell using sulphuric acid.

Bulk rougher tailings gravitate to a magnetic separator with a low-intensity magnetic field strength of 0.115T. The non-mags represent the low-sulphur tailings stream and the magnetic fraction is combined with the bulk cleaner 1 scavenger tailings to form the high-sulphur tailings product.

The bulk rougher concentrate is transferred to bulk cleaner 1 flotation comprising 3 x 50 m³ tank cells with a combined retention time of 14 minutes. The bulk cleaner 1 concentrate is subjected to one additional stage of cleaner flotation in 3 x 30 m³ tank cells with a combined retention time of 12 minutes. The bulk cleaner 2 concentrate presents the Cu/Ni separation feed.

Bulk cleaner 2 concentrate is directed to a Cu/Ni separation regrind mill cyclone. The regrind mill operates in closed-circuit to reduce the P80 from 60 µm to 25 µm prior to Cu/Ni separation using a VTM-400-WB Vertimill. Lime is added to maintain a pH of 12.0 to promote Cu and Ni mineral separation in 2 x 30 m³ tank cells with a combined retention time of 12 minutes.

Cu/Ni separation tailings represent the Ni concentrate. The Cu/Ni separation concentrate is treated in two additional cleaning stages: Cu cleaner flotation with 2 x 5 m³ tank cells and a retention time of 10 minutes, and Cu recleaner with 2 x 5 m³ tank cells and a retention time of 10 minutes. The pH is controlled at 12.0 in both cleaning stages.

The two concentrates are transferred to high rate thickeners. Plant sizing was performed for peak daily Ni and Cu concentrate production levels of 675 tpd and 93 tpd respectively at a mill feed rate of 3,600 tpd. Both thickeners have been designed for the peak expected production demand plus a 20% design factor for concentrate tonnage. Thickened slurries are pumped to pressure filters. Dewatered filter cakes are stockpiled and reclaimed using a front-end loader into rail cars for shipment to smelters for the Ni Concentrate Scenario.

Daily average low-sulphur and high-sulphur tailings production levels of 2,561 tpd and 587 tpd respectively are anticipated at a feed rate of 3,600 tpd. The two tailings streams are transferred to high rate thickeners sized for maximum annual production plus a 20% design factor. High-sulphur tailings will be used in the paste backfill recipe. Low-sulphur tailings will be primarily used in the paste backfill recipe blended with high-sulphur tailings, with the balance of low-sulphur tailings filter cake placed into a CFTF.

Hydrometallurgical plant design (Ni Sulphate Scenario)

The Ni Sulphate Scenario treats the Ni concentrate in a pressure oxidation (POX) autoclave followed by two stages of neutralization, Cu removal, Ni and Co solvent extraction (SX), and Mg precipitation. Process design criteria were generated based on an average daily hydrometallurgical plant feed rate of 475 tpd and an average Ni concentrate head grade of 10.2% Ni, 0.23% Co, and 1.06% Cu. The hydrometallurgical plant has been designed to operate at approximately 85% utilization with an average feed rate of 19.8 tph of Ni concentrate.

The Ni concentrate is repulped in a 4.5 m x 8.0 m agitated tank at a solids concentration of 10% w/w. The slurry is heated to approximately 70°C using direct steam before being pumped into a 5 m x 23 m autoclave operating at a temperature of 150°C with a maximum allowable working pressure of 580 kPa (absolute). The autoclave retention time is 90 minutes and it operates at a pH of 1.2. Chloride ions are added as a catalyst at a concentration of 2 g/L. Extraction rates for POX leach are 99.5% for Ni, 99.4% for Co, and 88.9% for Cu.

The leach residue consists mainly of goethite (~50%), hematite (~25%), and elemental sulphur (~15%). Impurities include Fe (~413,000 mg/L), Al (~3,300 mg/L), Mn (~270 mg/L), Cr (~210 mg/L), and Zn (~190 mg/L). Impurity removal is performed in two stages with a target pH of 3.25 in the first stage and a target pH of 4.75 in the second stage.

Almost all Fe and chromite are precipitated in the first neutralization stage with Ni, Co, and Cu losses of less than 0.1%, 0.2%, and 3.6% respectively. Secondary neutralization further lowers Fe and Al concentrations to below the detection limit. Cu removal uses NaHS at approximately 240% stoichiometric to precipitate remaining Cu ions as Cu sulphide.

The Cu-free solution is subjected to SX using Versatic 10 as the extractant and Exxsol D80 as the diluent. The loaded organic is stripped and the pregnant aqueous phase containing Ni and Co is treated in a Co SX circuit using Cyanex 272 as the extractant. Co is loaded onto Cyanex 272 while Ni remains in the aqueous phase.

The aqueous phase after Co SX is treated in a crystallizer to precipitate Ni as Ni sulphate hexahydrate. The crystallizer discharge is thickened, dewatered in a pressure filter, dried, and bagged in one tonne bulk bags. The Co solution is treated with NaHS to precipitate Co as a sulphide, dewatered, dried, and bagged.

The barren leach solution undergoes Mg removal by raising pH to 9.0 using lime. The thickener overflow is returned to re-pulp Ni concentrate. The filter cake is combined with the high-sulphur tailings stream.

Energy, water, and consumables

Total concentrator plant energy requirements from major mechanical equipment were established at 8,153 kW, with a total connected power of 9,784 kW. Operational power draw is projected to be 85% of connected power or 8,316 kW. Total water requirements of the grinding and flotation circuit are estimated at 543.0 m³/h. Freshwater requirement to make up the water deficit is 117.0 m³/h.

For the hydrometallurgical plant, total connected power is estimated at 6,000 kW with operational power draw anticipated at 5,100 kW. Total water requirements are estimated at 30 m³/h or 1.67 m³/t of Ni concentrate.

Reagent types and dosages for the concentrator were established in metallurgical programs conducted at XPS Sudbury and SGS Lakefield in 2019 and 2020. Reagent consumption rates include SIPX at 215 g/t, PAX at 230 g/t, MIBC at 150 g/t, lime at 2,150 g/t, and flocculant at 30 g/t. Grinding media consumption includes primary ball mill balls at 0.99 kg/t of mill feed, bulk rougher concentrate Vertimill media at 0.31 kg/t, and Cu/Ni separation Vertimill media at 0.57 kg/t.

For the hydrometallurgical plant, reagent types and dosages were established in the 2020 hydrometallurgical program up to the Cu precipitation stage, with the balance developed from similar operations.

Major equipment

The concentrator major equipment list includes: Metso C120 jaw crusher, Metso HP6 cone crusher, inclined screen (31 m² screening surface), 3,000 m³ fine ore bin, 5.7 m x 8.7 m ball mill (4,200 kW), 4 x 160 m³ bulk rougher flotation cells, LIMS magnetic separator (0.115 T), Vertimill VTM-250-WB for bulk cleaner regrind, 3 x 50 m³ bulk 1st cleaner flotation cells, 3 x 50 m³ bulk 1st cleaner scavenger flotation cells, 3 x 30 m³ bulk 2nd cleaner flotation cells, Vertimill VTM-400-WB for Cu/Ni separation regrind, 2 x 30 m³ Cu rougher tank cells, 2 x 5 m³ Cu cleaner tank cells, 2 x 5 m³ Cu recleaner tank cells, 20 m diameter Ni concentrate high-rate thickener, Ni concentrate pressure filter (130 m²), 7 m diameter Cu concentrate high-rate thickener, Cu concentrate pressure filter (22 m²), 18 m diameter HS tailings high-rate thickener, 36 m diameter LS tailings high-rate thickener, and 200 m² LS tailings belt filter.

The hydrometallurgical plant major equipment list includes: Ni concentrate repulp agitated tank, brick-lined autoclave leach circuit, primary neutralization agitated tanks with belt filter and three-stage wash, secondary neutralization agitated tanks with four-stage CCD, Cu removal agitated tanks with four-stage CCD, Ni and Co SX mixer-settlers, Co SX mixer-settlers, Ni sulphate circuit crystallizer with thickener, dryer, and bagging system, Co sulphide circuit agitated tanks with thickener, belt filter, dryer, and bagging system, and Mg removal agitated tanks with thickener.

Key reported parameters

Technical qualifications

The process design criteria were developed from a range of sources including Talon Metals, Metpro recommendation, Metpro calculation, DRA input, metallurgical testing, standard industry practice, and vendor recommendation. The SX circuits and the Mg precipitation circuit were designed using available engineering data of similar projects. Grinding media and liner consumption were calculated based on an estimated Bond abrasion index corresponding to the 70th percentile of abrasiveness of more than 2,000 samples tested at SGS, as no Bond abrasion index data is presently available for the Tamarack mineralization. Detailed equipment specifications for the hydrometallurgical plant were developed for the front end up to Cu sulphide precipitation based on testwork results; all other equipment sizing was determined by comparison of the proposed circuit with similar plants. The balance of reagent dosages for the hydrometallurgical plant beyond the Cu precipitation stage was developed from similar operations.

Source: Talon Metals Corp. – Preliminary Economic Assessment #3 on the Tamarack North Project, Document Number G4932-RPT-01, Revision 0, 08 Jan 2021, sections 17.0–17.10.