This NI 43-101 technical report, dated June 2014, describes the proposed mineral processing flowsheet for the recovery of magnetite and ilmenite concentrates from the Southwest and Armitage pits.
Report context
The June 2014 NI 43-101 Technical Report presents the feasibility study for the Southwest and Armitage pits, detailing the proposed processing route for run-of-mine ore. The report includes results from testwork performed at COREM in Québec City and at SGS in Lakefield, Ontario, which supported the selection of a beneficiation process flowsheet. The process flowsheets were designed by combining information from laboratory and pilot plant experiments, engineering experience on similar projects, and supplier input.
Processing route
Crushing and Ore Handling
Run-of-mine ore will be delivered by trucks with a 226-tonne capacity to two dump points located at a 54” x 75” gyratory crusher. The crusher was sized with a utilization of 65%, having a 2,335 tph (dry) instantaneous capacity. A hydraulic rock breaker will be installed adjacent to the crusher, and the crusher will be equipped with a main shaft positioning system. Crushed rocks, ranging from 0–12” in size, will pass through a surge pocket with a minimum 2-truck capacity. Crushed rock will be reclaimed by an 84” wide apron feeder directing material to a belt conveyor approximately 200 m long sized to handle 2,350 tph.
A stage of secondary crushing is necessary to maximize SAG mill throughput. A 1,000 HP cone crusher will reduce incoming oversize particles from the classification screen from a P80 of approximately 190 mm to 50 mm. The transfer conveyor from the gyratory crusher will feed a storage bin with 10 minutes of live retention time. A vibrating feeder will feed a double-deck screen with openings of 180 mm and 50 mm. A bypass chute allows tramp metal to bypass the screen and also allows bypass of the secondary crusher during maintenance. Screen undersize falls onto a crushed ore collecting conveyor; screen oversize is directed to the cone crusher feed.
The crushed ore will be transported via belt conveyor to a stockpile measuring 46 m by 115 m with a live storage capacity of approximately 9 hours. Five belt feeders will reclaim the crushed material, each capable of providing half of the full 1,576 tph feed (dry basis) to the reclaim belt conveyor.
Primary Grinding (SAG Circuit)
The SAG mill will be 36 ft in diameter x 17.25 ft long (flange to flange) with a total installed power of 15,000 kW. Forged steel balls, 5 inches in diameter at a total ball charge of 11–14% (v/v), will be used for grinding. A variable frequency drive (VFD) will be used for grinding control.
SAG discharge will be sent to a scalping screen; oversize goes to the recycle conveyor. Scalping screen undersize will be pumped to multi-slope screens. Multi-slope classification screen undersize will report to a pump-box and be pumped to magnetic cobbing; oversize is recycled to the SAG mill. A density meter will control process water addition to the pump-box feeding the magnetic separators, ensuring 40% (w/w) slurry density. An eight-way distributor will feed each magnetic separator feed box.
Primary Magnetic Separation (Cobbing)
Eight single-drum counter-rotation wet low intensity magnetic separators (diameter x width = 1,219 x 3,810 mm) will treat a design rate of 1,686 tph of ground ore at -3.0 mm (D100). Non-magnetic tailings will be collected in a large launder. The cobber tails will be separated into coarse and fine fractions using hydrocyclones. The magnetic concentrate will be sent by gravity to the ball mill discharge slurry pump-box.
Secondary Grinding
The cobber magnetic concentrate, along with ball mill discharge, will pass through a cyclone cluster. Overflow will continue to a second stage of magnetic separation. Underflow (U/F) at 75–80% (w/w) solids will be returned to the ball mill feed chute. The recirculating load in the ball mill closed circuit is taken to be 250%. The cyclone cluster, with 800 mm diameter cyclones, was designed with two spare cyclones per four operating cyclones to handle a potential 350% recirculating load.
A ball mill sized at 21 ft in diameter x 35 ft long (flange to flange) will achieve the desired re-grind size of P80 = 75 µm. The ball mill was sized to handle a design tonnage where 50% of the cobber feed reports to the ball mill. Nominally, 39% weight recovery from cobbing to the ball mill would be expected. The ball mill will have an installed power of 8,950 kW (12,000 HP) and will be equipped with a VFD.
Cleaning Magnetic Separation
Overflow from the ball mill circuit cyclones will be pumped to an eight-way distributor (2 blanks) feeding the secondary magnetic separation stage. Six double-drum, counter-current type, wet low intensity magnetic separators (diameter x width = 1,219 x 3,810 mm) will clean the cobber magnetic concentrate. The cleaning stage consists of two drums: a cleaner and a re-cleaner. Secondary magnetic separation tailings will be sent to the Fe non-mag SMS fines pump-box.
Magnetite Concentrate Desulfurization
The secondary magnetic separator concentrate will be fed to a flotation circuit consisting of six tank cells arranged in a 2-2-2 series configuration. A collector (PAX) and a frother will be added in a pre-conditioning tank. The sulphide flotation product will overflow into launders and be sent to the tailings thickener pump-box. The flotation underflow is the upgraded, desulfurized magnetic concentrate.
Magnetite Concentrate Dewatering
The upgraded magnetite concentrate will be fed to a 22 m diameter insulated concentrate thickener located outside the plant. The thickener will also receive filtrate from the drum filters and will be equipped with an auto-dilution system to dilute feed concentration to 17–19% solids by weight. The thickener underflow will have a 65–75% (w/w) solid maximum (design at 75%) and will be pumped to a filter feed agitated slurry tank.
From the filter feed agitated slurry tank, slurry will be pumped by four VFD slurry pumps, each feeding a drum filter with 80 m² of filtration area. Four drum filters will be required with steam addition to obtain a filter cake with 5.5% moisture. Each filter unit was designed to handle approximately 110 tph of filter cake at the targeted maximum moisture. Four vacuum pumps connected to a common header will produce the required vacuum.
Ilmenite Beneficiation
The tailings from the magnetite beneficiation circuit will be separated into fine (-106 µm) and coarse (+106 µm) material. The coarse fraction will pass through multi-stage gravity separation via spirals. The gravity concentrate will then be ground via ball mill in closed circuit with hydrocyclone classification. The fine material from the magnetite circuit will be dewatered and sent to a multi-stage gravity spiral circuit. The concentrate from the fine gravity circuit will be combined with the hydrocyclone overflow from the coarse concentrate regrind. The combined flow will pass through multi-stage magnetic separation before being sent to multi-stage flotation.
The froth from the flotation circuit will be dewatered via a thickener and drum filtration. Acidified tailings from flotation stages will be neutralized prior to being combined with non-acidified tailings. Coarse and fine tailings will both be pumped to treatment ponds.
Cobber Tailings Cyclone
Cobber non-magnetic tailings will be collected in a pump-box before being pumped to a single cluster of cyclones. The cyclones will separate material into +106 µm particles (underflow) and -106 µm particles (overflow). Coarse underflow will be sent to the coarse spirals circuit. Fine overflow will be sent to the SMS tailings pump-box and combined with non-magnetic fines from the SMS stage. The cyclone cluster includes three operating cyclones under nominal flow conditions with a fourth cyclone serving as a spare.
Coarse Tailings Gravity Circuit
Coarse tailings from the magnetite beneficiation plant will be pumped to a multi-stage spiral separation circuit. Incoming solids will be diluted, and wash water will be added to each spiral as per conditions determined in the spiral selection study performed at COREM. Tailings will be sent to a pump-box, then to coarse tailings cyclones, before being sent to a coarse tailings basin. Concentrate will be directed to a regrind circuit.
Fine Tailings Gravity Circuit
Fine non-magnetic tailings from the magnetite beneficiation plant will first be sent to a stage of dewatering cyclones to reach the target slurry density as per spiral selection studies performed at COREM. Four clusters of cyclones will each house 32 operating cyclones with four spares and eight blanked-off spots. The 150 mm diameter cyclones will dewater the incoming fine tailings and produce an underflow with most of the +20 µm solids.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Gyratory crusher instantaneous capacity | 2,335 tph (dry) | Design |
| Gyratory crusher utilization | 65% | Design |
| SAG mill dimensions | 36 ft diameter x 17.25 ft long | Design |
| SAG mill installed power | 15,000 kW | Design |
| SAG mill ball charge | 11–14% (v/v), 5-inch forged steel balls | Design |
| Reclaim belt conveyor feed rate | 1,576 tph (dry basis) | Design |
| Crushed ore stockpile live capacity | Approximately 9 hours | Design |
| Cobbing magnetic separators | 8 units, single-drum, 1,219 x 3,810 mm | Design |
| Cobber design feed rate | 1,686 tph at -3.0 mm (D100) | Design |
| SAG mill feed slurry density | 40% (w/w) | Design |
| Ball mill dimensions | 21 ft diameter x 35 ft long | Design |
| Ball mill installed power | 8,950 kW (12,000 HP) | Design |
| Ball mill product size | P80 = 75 µm | Design |
| Ball mill recirculating load | 250% (design), 350% (capacity) | Design |
| Weight recovery from cobbing to ball mill | 39% (nominal) | Design expectation |
| Secondary magnetic separators | 6 units, double-drum, 1,219 x 3,810 mm | Design |
| Flotation cells | 6 tank cells in 2-2-2 configuration | Design |
| Concentrate thickener diameter | 22 m | Design |
| Thickener underflow solids | 65–75% (w/w) maximum (design at 75%) | Design |
| Thickener feed dilution | 17–19% solids by weight | Design |
| Drum filter area per unit | 80 m² | Design |
| Drum filter production per unit | Approximately 110 tph filter cake | Design |
| Filter cake moisture target | 5.5% (with steam addition) | Design |
| Cobber tailings cyclone split | +106 µm (coarse), -106 µm (fine) | Design |
| Fine tailings dewatering cyclones | 4 clusters, 32 operating + 4 spare + 8 blanked per cluster | Design |
| Fine tailings cyclone diameter | 150 mm | Design |
Technical qualifications
The report states that the process flowsheets were designed by combining information collected during laboratory and pilot plant experiments, BBA’s experience on similar projects, and supplier input. The ball mill was sized in order to handle a design tonnage where 50% of the cobber feed reports to the ball mill; fluctuations in Satmagan and potential poor-liberation could lead to higher ball mill tonnages. The recirculating load in the ball mill closed circuit is taken to be 250%, but the cyclone cluster was designed to handle a potential 350% recirculating load under nominal conditions. The report notes that three drum filters could handle the design tonnage but would require increased steam to reduce residual moisture to 5.5%. The 20% excess capacity designed into the ilmenite plant serves to handle daily fluctuations in feed due to the incoming feed being a tailings stream and higher tonnages in low grade years.
Source: NI 43-101 Technical Report, Feasibility Study of the Southwest and Armitage Pits, June 2014, Sections 1.18 and 17.
