This technical report describes the conceptual process design for recovery of magnetite concentrate and production of acid pellets from the Block 103 deposit, based on metallurgical testwork and BBA’s reference project experience.
Report context
This June 2013 NI 43-101 Technical Report for Cap-Ex Iron Ore Ltd. presents the results of a Preliminary Economic Assessment (PEA) for the Block 103 Project. The report documents the recovery methods developed at a conceptual level for processing iron ore from the Block 103 deposit to produce a saleable acid pellet product. The process design basis, mass and water balances, and equipment sizing are preliminary and based on testwork results, handbook references, BBA’s experience on other reference projects, and vendor information. The 30-year initial life of operation is assumed for this PEA Study.
Processing route
Process design basis
Magnetic Fe (MagFe) will be recovered as a fine magnetic concentrate suitable as pellet feed. Plant design provides for the production of 16 Mt/y of concentrate feeding two pelletizing lines, with final pellet production estimated at approximately 16.6 Mt/y of acid pellets. The metallurgical performance forecast was derived from testwork executed to characterize the northern and eastern sectors of the deposit, based on an assumed particle size distribution typical of magnetic concentrators and in line with the liberation size determined from metallurgical testwork.
Ore crushing, conveying and storage
Ore from the mine will be delivered by truck to four dump points at the primary crusher building. Based on ore grindability testwork and vendor recommendation, two 1,600 mm × 2,900 mm (63″ × 114″), 750 kW (1,000 hp) gyratory crushers would provide the required crushing capacity, reducing ore to a P80 of 135 mm. Crushed ore is collected in surge pockets and fed to two tripper conveyors discharging onto an uncovered rectangular stockpile with a live capacity of approximately 12 hours (100,000 tonnes). Crushed ore is reclaimed onto four SAG mill feed conveyors, each fed by three variable speed apron feeders, with mill feed tonnage controlled by belt weigh scale signals.
Grinding and screening
Primary grinding is performed by four dual-pinion SAG mills with variable speed, active front-end type electric drives. Preliminary SAG mill sizing was performed using data from the SGS grindability testwork. Four 11,580 mm × 6,100 mm (38′ × 20′) dual-pinion SAG mills, each powered by two 10,000 kW (13,400 hp) motors for a total of 20,000 kW (26,800 hp), are assumed adequate for primary grinding. The SAG mill product is assumed as P100 = 2 mm and P80 = 1 mm.
Mill discharge is screened using a two-stage screening circuit with primary single-deck horizontal scalper screens (5 mm aperture) and secondary classification banana-type single-deck screens (2 mm aperture). Oversize from both stages is recirculated to the SAG mills.
Magnetic separation and regrind circuit
The flowsheet is based on staged wet, low intensity magnetic separation (LIMS) concentration. The classification screen undersize slurry is fed to three cobber LIMS lines, each feeding eight 1,220 mm × 3,660 mm (48″ × 144″) counter-rotation single drum cobber LIMS (twenty-four units total). Cobber concentrate is pumped to 900 mm diameter hydrocyclones (twenty-four units total) producing an overflow P95 of 106 μm directed to finisher LIMS, and underflow directed to three regrind ball mills.
Ball mill discharge feeds thirty rougher LIMS units (1,220 mm × 3,660 mm counter-rotation single drum). Finisher LIMS concentrate feeds twenty-six stack-sizer type screens (five-deck, urethane, 75 μm cut size, seventy-six screens total). Oversize returns to ball mills; undersize proceeds to twelve dewatering LIMS units. Finisher concentrate is fed to twenty-seven 1,220 mm × 3,660 mm counter-current double drum finisher LIMS.
Regrind ball mill sizing assumed a feed F80 of 1,000 μm and product P80 of 150 μm, using grindability data from testwork and vendor handbook data. The selected regrind ball mill is a 7,620 mm dia. × 11,740 mm (25′ × 38.5′), dual-pinion drive, with each pinion driven by a 7,500 kW (10,000 hp) fixed speed motor. Three such ball mills are required.
Tailings dewatering and pumping
Tailings from cobber LIMS are dewatered using hydrocyclones. Rougher LIMS and finisher LIMS tailings, along with cobber LIMS dewatering hydrocyclone overflow, are collected into three 45 m diameter tailings thickeners (one per line). Underflow is pumped to pump boxes collecting coarse tailings from cobber dewatering cyclone underflow. Tailings are pumped through 560 mm (22″) diameter rubber-lined pipelines with four stages of pumping (932 kW/1,250 hp each) for final disposal to the TMF. Three pipelines with four pumps each (twelve pumps total), all operating, are provided, with a fourth back-up line to be installed at full capacity.
Pellet plant
The pellet plant is designed as two lines, each receiving 8 Mt/y of concentrate slurry (total 16 Mt/y) producing 16.6 Mt/y of acid pellets. Pellet plant capacity was derived from discussions with vendors based on their experience with similar ores. The induration technology is based on straight grate design.
Concentrate reception and dewatering: Concentrate from dewatering LIMS is pumped to agitated holding tanks (two total), then to fourteen vertical vacuum disc filters (seven per line). Filter cake is directed to storage bins.
Additives grinding: Only bentonite is required for acid pellet production. Coarse bentonite is received, stored, and ground in a roller mill to 80% -74 μm, pneumatically transported to storage bins.
Mixing area: Concentrate filter cake and bentonite are blended in horizontal drum mixers with water addition to achieve required %-solids and consistency. Provision is made for addition of sodium hydroxide as needed.
Balling: Mixed material is transported to the balling area with twenty-eight 7.5 m diameter balling discs (fourteen per line). Green pellets discharge onto individual reversible collecting belts, then to main collecting conveyor. Double-deck roller screens (one per line) remove oversize and broken pellets, returning them to the mixed material stream.
Induration: Two straight grate induration machines (4 m wide, 816 m² area each) harden the green pellets. Drying occurs in two stages (updraft followed by downdraft). Pellets are preheated, then fired at approximately 1,270°C. Cooling is accomplished in two stages by updraft ambient air. Gas cleaning uses electrostatic precipitators on main gas streams and wet scrubbers at feed and discharge. A trade-off study comparing straight grate to rotary kiln design is advised for the next study phase.
Product discharge and load-out: Fired pellets discharge onto conveyors feeding a common exterior pellet load-out silo (32,000 tonnes capacity). The silo acts as buffer for loading 100 tonne gondola railcars. Two exterior emergency stockpiles are provided, with reclaim capability to the load-out silo.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Head grade MagFe | 18.6% | Metallurgical testwork |
| Head grade Mag | 25.7% | Metallurgical testwork |
| Concentrate weight recovery | 24.9% | Metallurgical testwork |
| Magnetic Fe recovery | 93.0% | Forecasted from testwork |
| Concentrate total Fe | 69.5% | Forecasted |
| Concentrate SiO2 | 3.36% | Forecasted |
| Concentrate P100 | 75 μm | Forecasted |
| Concentrate P80 | 41 μm | Forecasted |
| Concentrate -45 μm | 87% | Forecasted |
| Estimated pellet total Fe | 67.0% | Estimated |
| Estimated pellet SiO2 | 3.50% | Estimated |
| PEA initial life of operation | 30 years | PEA Study assumption |
| ROM feed | 64.3 Mt/y | Design basis |
| Primary crusher feed | 64.3 Mt/y, 9,780 t/h nominal (11,247 t/h design) | Design |
| Concentrator feed (including cobbing) | 64.3 Mt/y, 8,150 t/h nominal (9,372 t/h design) | Design |
| Concentrate production to pellet plant | 16.0 Mt/y, 2,029 t/h nominal (2,334 t/h design) | Design |
| Tailings generated | 48.3 Mt/y, 6,120 t/h nominal (7,039 t/h design) | Design |
| Pellet production | 16.6 Mt/y, 2,108 t/h nominal | Design |
| Crusher utilization | 75% | Design assumption |
| Concentrator utilization | 90% | Design assumption |
| Pellet plant utilization | 90% | Design assumption |
| Design factor | ±15% to nominal | Design assumption |
| Primary crusher | Two 1,600 mm × 2,900 mm gyratory, 750 kW each | Vendor recommendation and testwork |
| SAG mills | Four 11,580 mm × 6,100 mm, dual-pinion, 2 × 10,000 kW each | Preliminary sizing from testwork |
| Regrind ball mills | Three 7,620 mm dia. × 11,740 mm, dual-pinion, 2 × 7,500 kW each | Preliminary sizing from testwork and vendor data |
| Cobber LIMS | Twenty-four 1,220 mm × 3,660 mm counter-rotation single drum | Preliminary design |
| Rougher LIMS | Thirty 1,220 mm × 3,660 mm counter-rotation single drum | Preliminary design |
| Finisher LIMS | Twenty-seven 1,220 mm × 3,660 mm counter-current double drum | Preliminary design |
| Tailings thickeners | Three 45 m diameter | Preliminary design |
| Balling discs | Twenty-eight 7.5 m diameter (14 per line) | Design |
| Induration machines | Two straight grate, 4 m wide, 816 m² each | Vendor technology package |
| Pellet load-out silo | 32,000 tonnes | Design |
Project website: https://www.cap-ex.ca/projects/block-103/
All values reported on dry-tonne basis. SAG mill sizing assumes adequate power for nominal tonnage and nominal ore hardness; throughput will vary with ore hardness.
Technical qualifications
Equipment sizing is preliminary and generally based on a combination of testwork results, handbook references, BBA’s experience on other reference projects, and vendor information. The SAG mills specified (11,580 mm × 6,100 mm twin pinion configuration) are available from vendors but none are presently in operation; wrap-around type mills are currently in operation but at higher cost. Further vendor discussions are required to validate SAG mill choice.
Pellet plant capacity was derived from discussions with vendors based on their experience with similar ores; testwork to confirm pellet quality and production rate will be required in the next study phase. The pellet plant design is based on vendor technology packages incorporating process equipment within prescribed battery limits.
A trade-off study comparing straight grate to rotary kiln induration design is advised for the next study phase.
The mass and water balance presented is for nominal hourly production rates; major process equipment sizing and selection were done based on design values that include a ±15% design factor.
Source: Block 103 Project , 2013 Technical Report, Cap-Ex Iron Ore Ltd., NI 43-101 Technical Report, June 2013, Section 17 Recovery Methods.
