This 2018 pre-feasibility study presents a proposed concentrator flowsheet for the PAK lithium project, developed from locked-cycle testwork and designed for year-round operation with seasonal road access.
Report context
This pre-feasibility study for the Frontier Lithium PAK project, dated April 2018 (Project #16622-01), describes the proposed processing facilities based on metallurgical testwork performed at the XPS Consulting and Testwork Facility in Falconbridge, Ontario. The report documents a viable flowsheet for the production of technical and chemical grade spodumene concentrates, derived primarily from locked-cycle test iteration FRON-12, and provides the basis for mill design and capital cost estimation.
Processing route
Flowsheet development
A series of locked-cycle tests were performed at the XPS Consulting and Testwork Facility, the results of which were used to derive the preliminary process flowsheet and mass balance. Changes in the flowsheet were completed up to the 12th iteration of the locked-cycle test (FRON-12) and were primarily related to stabilization of the circuit as well as improvements in the removal of contaminants and improvement in concentrate grade as stated by the guiding technical specification for the concentrate. The preliminary circuit configuration has been built on the learnings from testwork and configured to mitigate risk associated with the process.
General processing plant descriptions were based primarily on locked-cycle (FRON-12) work. This resulted in the development of a viable flowsheet for the production of technical and chemical grade spodumene concentrates and served as the basis for both the mill design model and capital cost estimate. Information from the resultant processing plant model as well as vendor budget pricing contribute to the overall capital and operating cost estimates.
The technical concentrate is expected to contain a grade of 7.15% Li2O, representing 73.7% of the lithium in mill feed in 39.5% of the mass. The chemical concentrate had a grade of 7.14% Li2O, representing 7.6% of the lithium in mill feed in 4.1% of the mass. The technical and chemical concentrates met their respective specifications for contaminant elements, with the exception of iron and tantalum, which were not removed in the process demonstration exercise due to restricted availability of mass. Subsequent testing on larger samples showed substantial upgradeability of tantalum (and reduction of contaminant levels) by means of Knelson gravity separation, as well as reduction of iron by means of WHIMS separation to acceptable limits.
Combined lithium recovery in the milling circuit to saleable products was 81.3%. The feed to flotation (FRON-12) had been DMS-upgraded, with the FRON-12 blend representing 92.8% of the lithium in ore. Adjusted recoveries on an ore basis become: technical grade 68.4%, chemical grade 7.0%, combined products 75.4%.
The concentrator will operate on a 24 hours per day basis, 7 days per week, and 335 days per year, which equates to a planned availability of 92%.
Primary and secondary crushing
The crushing circuit is designed to reduce ROM ore with a moisture content of maximum 5% and an F80 of 300mm to feed the mill concentrator at a P80 of 13mm. ROM ore is transported by truck from the open pit and dumped into a hopper prior to the primary crusher, where it is reduced to a P80 size of 150mm. The ROM ore top size will be controlled by blast fragmentation to below 400mm minus, thereby avoiding the use of a grizzly section prior to the primary. A 895x660mm feed opening crusher has been selected to handle maximum lump size, which is lightly loaded at closed-side setting of 100mm. The primary crusher is a 75HP jaw-type, with a minimum operating capacity of 125 tph. A 12-hour operating day for the crusher is assumed.
From the primary crusher, crushed ore drops onto a double-deck screen which classifies undersize to bypass the secondary crusher. Deck sizes for the double deck screen have been selected at 25mm and 15mm respectively. The double deck screen is 1.5m wide and 4.8m long, and is in open configuration to lower the machine load of the secondary crusher. The secondary crusher is a 120HP cone type, with a predicted operating capacity of 71 tph at a closed side setting of 25mm. Both undersize from the double-deck screen and product of the secondary crusher report to a load-out conveyor that carries the ore through a heated gallery to the fine ore storage bin.
A belt magnet is located on the load-out conveyor to remove tramp ferrous material. A belt weigh scale on the load-out conveyor tracks the production rate of the crushing plant. A baghouse collects dust at the ore transfer points within the primary crusher building, which reports to the tail end of the load-out conveyor. A sump pit is provided to collect wash-up residue, designed to be emptied periodically by vacuum truck.
Fine ore storage
The fine ore storage bin is designed to provide storage of concentrator feed ore prior to the concentrator, and capacitance between the crushing circuit and concentrator to allow for day shift ore handling only to feed the crusher complex which operates on a continuous basis. Ore discharged from the primary and secondary crusher circuit is fed to the fine ore storage bin via the crusher circuit load-out conveyor. The fine ore bin is 6.2m diameter x 7.2m high, corresponding to a design capacity of 600 tons. A hydraulically actuated press-frame / chain gate system will control the outlet flow from the bin feeding the concentrator feed conveyor. The bin and conveyor transfer points will be enclosed within a heated bin house structure to eliminate the possibility of freeze/hang-ups during the winter months.
Dense media separation
The dense media separation (DMS) circuit has been incorporated at the front end of the concentrator facility as a method to remove barren material from the feed, resulting in a reduction of comminution energy prior to flotation and an upgraded mill feed. A two-stage DMS (coarse and fine) has been carried based on testwork and pro-forma calculations.
Coarse DMS plant design parameters include: feed rate (max) up to 40 tph; nominal feed rate 34 tph; nominal feed size range -13 + 2.0 mm; maximum feed particle size 38 mm; separator d50 cut-point density 2.7 to 3.1 SG; DM separator two stage 300mm Condor; medium ferrosilicon 270D (milled); estimated medium consumption 200-300 g/t DMS feed. The selected coarse modular system includes a two-stage, 300mm diameter separator, one 1.8m x 3.6m drain/rinse screen with 1.0mm aperture panels, and a dense media recovery system. The wet drum magnetic separator will be 0.9m diameter x 1.2m wide.
Fine DMS plant design parameters include: feed rate (max) up to 15 tph; nominal feed rate 7 tph; nominal feed size range -2 + 5.0 mm; maximum feed particle size 25 mm; separator d50 cut-point density 2.7 to 3.1 SG; DM separator two stage 250mm Condor; medium ferrosilicon 270D (milled); estimated medium consumption 300-400 g/t DMS feed. The selected fine modular system includes a two-stage, 250mm diameter separator, one 1.2m x 3.6m drain/rinse screen with 0.5mm aperture panels, and a dense media recovery system. The wet drum magnetic separator will be 0.9m diameter x 1.2m wide.
The coarse DMS feed screen rejects (>2mm) report to the coarse DMS separator. Sinks from the separator report to the tertiary crusher, to be reduced to an F80 of 2mm prior to primary grinding. Floats from the coarse DMS proceed to the integral floats screen and subsequent magnetic separation prior to reporting to the DMS tailings stockpile. The coarse DMS feed screen accepts (undersize) report to the fine DMS feed screen. The fine DMS feed screen rejects (>300µm) report to the fine DMS separator. Sinks from the separator report to the primary ball mill discharge stream after magnetic separation. Floats from the fine DMS proceed to the integral floats screen, then magnetic separation prior to reporting to the DMS tailings stockpile. It is estimated that the combined DMS plant will require 0.3 tonnes of ferrosilicon per day to maintain proper level of dense media within the circuit. Further testing will be required at the next stage of study to confirm.
Grinding
The grinding circuit is designed to produce feed slurry fine enough for effective flotation. The primary and secondary ball mills work in concert to produce a particle size of P80 = 200 µm for feed to a cyclopak unit prior to mica flotation. Design product size was set to a P80 = 150 µm as a conservative measure. The primary ball mill is in open-circuit with the discharge of the tertiary crusher. The tertiary crusher is a 120HP cone type, with a predicted operating capacity of 22 tph at a closed side setting of 4mm.
A primary and secondary ball mill comminution circuit has been carried based on testwork and pro-forma calculations. Feed material is lithium ore with specific gravity 2.75 and abrasion index 1.08 g. The primary ball mill has capacity of 22 dry TPH, ball mill work index 14.7 kWh/T, feed size F80 = 2 mm, product size P80 = 0.3 mm. The secondary ball mill has capacity of 31 dry TPH, ball mill work index 17.7 kWh/T, feed size F80 = 0.3 mm, product size P80 = 150 microns.
The primary ball mill is a 2.2 m diameter x 3.0 m long unit with a 200 HP installed motor and variable frequency drive. The discharge of the primary mill reports to the secondary ball mill pumpbox. To minimize working capital, both the primary and secondary mills will have identical installed motors. However, length of the secondary mill had to be longer to meet product requirements. The secondary ball mill is in closed configuration with a double deck feed screen, a 1.8m x 3.6m unit of similar construction as the coarse DMS feed screen. The secondary ball mill is a 2.2 m diameter x 3.5 m long mill with a 200 HP installed motor with a variable frequency drive.
Product of the secondary ball mill will be pumped to a de-sliming cyclone cluster consisting of ten 50mm diameter cyclones. Cyclone overflows are classified slimes (<10µ) and report to the tailings thickener. The underflow will feed a Knelson gravity separator prior to reporting to a low intensity magnetic separator (LIMS) and wet high intensity magnetic separator (WHIMS) prior to the first stage of (mica) flotation. Placement of the LIMS and HIMS within the overall circuit will be confirmed at the next stage of study, which will involve pilot plant testing to predict the most efficient arrangement. In practice, there is pragmatic evidence that the LIMS and WHIMS placement would be after pH depression prior to the mica flotation circuit. It is also anticipated that further de-sliming using an additional cyclone cluster prior to the next stage of flotation may be of benefit.
Mica flotation circuit
The mica flotation circuit is designed to remove undesired mica from the spodumene ore and therefore increase final Li2O concentration destined for flotation plant feed. The mica flotation circuit consists of two 8.5m3 rougher mechanical cells in series, equipped with 11 kW agitators. Feed will report to the roughers at a grind P80 of 200µ, reduced to a pH of 3.5 using sulphuric acid. Additional reagents introduced at the rougher stage are Flotigam EDA and Oleylamine. Rougher float products will report to two 1.4m3 cleaner mechanical cells in series, equipped with 3.7 kW agitators. Attrition scrubbing is required to clean the mineral surfaces and will produce more slimes prior to the next stage of flotation. The combined mica rougher and cleaner tails will continue to feed forward to a series of four 8m3 conditioning tanks equipped with 11kW agitators. Mica rougher float product will report to the mica cleaner cells. The float product from the cleaner cells will constitute the mica concentrate which will be pumped to the tailings thickener for disposal.
Spodumene flotation circuit
The spodumene flotation circuit is designed to produce high concentration spodumene concentrate. The circuit consists of a single 8.5m3 rougher mechanical cell, equipped with a 11 kW agitator. Feed to the rougher will be increased to a target pH of 8.5 using NaOH. Additional reagents introduced at the rougher stage are Flotigam FS/2 and Oleic acid as a collector. Rougher float products will report to two 1.4m3 rougher cleaner mechanical cells in series, equipped with 3.7 kW agitators. The rougher tails will continue to feed forward to a series of four 8.5m3 scavenger tanks equipped with 11kW agitators. Float products from the rougher scavengers will report to a scavenger cleaner circuit consisting of two 1.4m3 mechanical cells in series, also equipped with 3.7 kW agitators. Both rougher cleaner and scavenger cleaner float products will report to the conditioning stage prior to the final stage of flotation, phosphate flotation. Rougher scavenger tails will be pumped to the tailings thickener for disposal.
Phosphate flotation circuit
The phosphate flotation circuit is designed to remove phosphate from the spodumene concentrate to produce the high grade (technical) spodumene as well as a phosphate concentrate which comprises the chemical grade spodumene concentrate. The circuit consists of two 1.4m3 rougher mechanical cells, equipped with 3.7 kW agitators. Feed to the rougher will be maintained to a target pH of 8.5 using NaOH. Additional reagents introduced at the rougher stage are WW82 Dextrine prior to reverse flotation of phosphates from spodumene. The rougher tails will continue to feed forward to the spodumene concentrate thickener circuit. Rougher float products will report to two 1.4m3 phosphate cleaner mechanical cells in series, equipped with 3.7 kW agitators. Float products from the phosphate cleaner will be dewatered and handled as a separate chemical grade concentrate.
Concentrate thickening, dewatering and storage
Final concentrate from the phosphate rougher and cleaner tails are fed to a 7m diameter high rate concentrate thickener, where the feed slurry at 8% w/w is mixed with flocculant (30g/T) and thickened to a target solids concentration of 67% w/w. Thickened concentrate is pumped to a pressure concentrate filter, where the solids content is further increased to a target of 90% solids w/w. Discharge from the pressure filter is conveyed in an enclosed stockpile for bulk storage prior to being transported off-site for further refining. The bulk storage facility is sized to stage 60,000T of concentrate and is of dimension 37m wide x 151m long (5522m2). Thickener overflow and filter filtrate is collected and recycled back to the process.
Reagents and process water
Reagents will be stored dry, when possible, onsite prior to being prepared and stored in a separate area adjacent to the concentrator facility for distribution to the process. Reagents will be prepared using a dedicated process water unique to flotation zones (mica, spodumene, and phosphate) to avoid cross-contamination and other unfavorable effects. Make-up to process water systems will be accomplished by reclaim of supernatant liquid from the tailings pond as well as direct make-up from the adjacent lake. Required reagents per the study include: Flotigam EDA (120 kg/day, 40,200 kg/yr), Flotigam 10022 (60 kg/day, 20,100 kg/yr), MIBC (120 kg/day, 40,200 kg/yr), Flotinor 10060 (252 kg/day, 84,420 kg/yr), combined Oleic Acid + S2 (588 kg/day, 205,800 kg/yr), H2SO4 (240 kg/day, 84,000 kg/yr), NaOH (165 kg/day, 55,275 kg/yr), Dextrine WW82 (60 kg/day, 20,100 kg/yr), and Ferrosilicon DMS media (300 kg/day, 100,500 kg/yr).
Water supply
Four separate water supply systems will be provided to support operations for the concentrator: three process water supply systems, and one TMF reclaim water supply system. Process water will be supplied to a process/fire water storage tank from the water treatment plant located adjacent to the concentrator building. Process water will primarily be used for fire water for emergency use, cooling water for mill lubrication systems, gland water for the slurry pumps, concentrate filter wash water, and reagent make-down. The process/fire water tank will be equipped with a standpipe for process water suctions, ensuring the tank always holds at least a 2 hours supply of fire water. One potable water supply system for the entire mill complex will be located adjacent to the concentrator, with treatment including chlorination, filtration, and colour removal.
Reclaim water will be supplied to the reclaim water storage tank adjacent to the concentrator. Barge-mounted pumps at the TMF will pump the reclaimed water directly to the storage tank. The overflow solution from the concentrate thickener will also be reused by pumping it to the reclaim storage tank. Reclaim water will be used for DMS, primary ball mill circuit dilution, and secondary grinding mill circuit dilution.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Average production mill feed | 45 tpd of ore | Design basis |
| DMS rejection rate | 31% of mill feed | Design expectation |
| Comminution and flotation throughput (design) | 30.8 tph | After DMS rejection |
| Primary crusher capacity (minimum operating) | 125 tph | Design specification |
| Secondary crusher predicted operating capacity | 71 tph (CSS 25mm) | Design estimate |
| Tertiary crusher predicted operating capacity | 22 tph (CSS 4mm) | Design estimate |
| Primary ball mill work index | 14.7 kWh/T | Testwork basis |
| Secondary ball mill work index | 17.7 kWh/T | Testwork basis |
| Primary ball mill product size (design) | P80 = 0.3 mm | Design specification |
| Secondary ball mill product size (design) | P80 = 150 microns (conservative), P80 = 200 µm (flotation feed) | Design specification |
| Technical concentrate grade | 7.15% Li2O | Expected from testwork |
| Chemical concentrate grade | 7.14% Li2O | Expected from testwork |
| Combined lithium recovery in milling circuit | 81.3% | Locked-cycle test FRON-12 |
| Adjusted combined recovery (ore basis) | 75.4% | Calculated from testwork |
| Concentrator annual operating days | 335 days/yr (92% availability) | Design basis |
| Fine ore bin capacity | 600 tons | Design specification |
| Concentrate bulk storage capacity | 60,000T (37m x 151m) | Design specification |
| Concentrate filter target solids | 90% w/w | Design specification |
| Concentrate thickener target underflow | 67% w/w | Design specification |
Project website: https://www.paklithiumproject.com/
Technical qualifications
This article is based solely on the 2018 pre-feasibility study report (Project #16622-01, April 2018) for the Frontier Lithium PAK project. The metallurgical testwork described was performed at the XPS Consulting and Testwork Facility in Falconbridge, Ontario, using locked-cycle tests. The report notes that further testing will be required at the next stage of study to confirm certain parameters, including DMS ferrosilicon consumption and the optimal placement of LIMS and WHIMS within the circuit, which will involve pilot plant testing. The technical and chemical concentrates met their respective specifications for contaminant elements with the exception of iron and tantalum, which were not removed in the process demonstration exercise due to restricted availability of mass; subsequent testing on larger samples showed substantial upgradeability. The report does not provide operating history, current project status, ownership details, or economic performance data.
Source: Frontier Lithium PAK NI 43-101 Pre-Feasibility Study, Project #16622-01, April 2018, Sections 17.1 through 17.13.
