This report details the proposed processing route for iron mineralization at the Lake St Joseph Property, based on metallurgical testwork and process design criteria for an integrated concentrator, pellet plant and hot briquetted iron facility.
Report context
The process design and flowsheet development for the Rockex Project, described in the 26 October 2015 technical report for the Lake St Joseph Iron Property, is based on the metallurgical test program performed at SGS and described in Section 13.0 of that report. Processing of the Rockex iron mineralization is based on production of an iron concentrate in a processing facility located at Lake St Joseph, about 100 km northeast of Sioux Lookout and 350 km northwest of Thunder Bay on Lake Superior in Ontario. The pelleting and briquetting plant will be located at Sioux Lookout nearby the railroad. Unless otherwise noted, all weight and throughput are in dry tonnes.
Processing route
Beneficiation Overview
The iron in the run-of-mine (ROM) will be concentrated using gravity separation, magnetic separation and desliming. As determined by test results, the spiral separators will have a weight recovery of 15.3 percent while magnetic separators will recover 12.3 percent and the desliming will produce a further 7.0 percent for a total of 34.6 percent weight recovery. The process design is based on the results from metallurgical test work (see Section 13 of the report). The ROM average production will be 17.3 million tonnes per year (Mtpy) to yield 6.0 Mtpy of pellet feed at 66.3 percent iron.
Crushing and Stockpiling
Run of mine, containing 28.9 percent iron, 45.5 percent silica and 5 percent moisture, is dumped directly into a gyratory crusher by mine haul trucks. The crusher discharge product has a particle size of 80 percent less than 175 mm. The conical crushed material stockpile has a total capacity of approximately 74,000 tonnes and a live capacity of about 30,000 tonnes. The feed is reclaimed by two conveyors, each with three apron feeders, and discharged onto the SAG mill feed conveyor.
Primary Grinding and Classification Circuit
The SAG mill will operate at a pulp density of 65 percent solids by mass in a closed circuit with two vibrating screens. Screens oversize is conveyed to a diverter where a part is diverted to feed the pebble mill next to the SAG mill. The majority of the SAG circulating load is returned to the SAG mill feed conveyor along with fresh grinding media. The screen undersize product will have a particle size P80 of 1,700 µm and will be pumped to the secondary grinding circuit.
Secondary Grinding and Gravity Separation
The SAG mill screen undersize will be pumped to three parallel closed-loop ball mill circuits. The slurry is pre-classified via cyclones, with the cyclone underflow reporting to the secondary grinding ball mills. The cyclone overflows are pumped to gravity separation circuits for silica removal. The cyclone overflow of each ball mill circuit has a P80 of 88 µm and is pumped to three gravity separation circuits each composed of two stages of spiral gravity separators, rougher and cleaner. The rougher concentrate will be fed by gravity to the cleaner spirals located directly underneath. The rougher tails are final tails and are pumped to the tailings thickener. The cleaner concentrate is a final concentrate, about 44.3 percent of the total concentrate, and has a target grade of 66.5 percent iron and about 5.0 percent silica, and is pumped to the concentrate thickener and pipeline feed circuit. The cleaner tailings, containing 25.1 percent iron and 50.5 percent silica, are pumped to the tertiary grinding circuits prior to further beneficiation. For each of the three ball mill lines, the rougher spirals are grouped in 21 banks of 10 double start spirals for a total of 420 rougher spirals per line or 1,260 for the three rougher circuits. Each cleaner spiral bank is located directly under the corresponding rougher bank but is composed of only eight double start per bank.
Tertiary Grinding and Magnetic Separation Circuit
The cleaner spiral tails contain magnetite particles that are associated with silica. The cleaner spiral tails are directed to two tertiary ball discharge pump boxes for further classification via cyclones and regrinding. The cyclone underflows are returned to the two mills while the overflows, with particle size P80 of 27 microns, are directed to 14 rougher LIMS (1.2 m by 3.8 m). The rougher tails are pumped to 12 single drum cleaner magnetic separators for further recovery of iron units. The rougher and cleaner concentrates are piped to the finisher ball mill where they are mixed with the mill discharge and are pumped to a cyclone cluster. As a final liberation step, the cyclone underflow is reground in the finisher ball mill in closed circuit with cyclone. The cyclone overflow, with a particle size P80 of 18 microns, is further concentrated by three double drum finisher LIMS and is pumped to a desliming thickener. The magnetite concentrate from desliming thickener underflow is a final concentrate and is pumped to the final concentrate thickener. The magnetic separation concentrate represents about 35.5 percent of the total concentrate and will have an average grade of 66.9 percent iron and 5.2 percent silica.
Final Desliming
The cleaner and finisher LIMS tails contain unliberated iron oxides. The slurry is conditioned and fed to the primary desliming thickener which separates liberated silicates from the iron oxides via differential settling rates. The silicates, referred to as the slimes, report to the thickener overflow and are pumped to final tailings, while the denser iron oxides settle out and report to the thickener underflow. The underflow is fed to closed circuit pebble mill. The pebble mill further liberates silicates from the iron oxide particles. The cyclone overflow has a P80 of 18 microns and reports to the final three desliming thickeners. Each stage removes further slimes which further upgrades the iron oxides which report to the underflow. The concentrate is pumped to the final concentrate thickener. The desliming circuit concentrate will represent 20.2 percent of the total concentrate and will have a grade of 64.9 percent iron and 5.81 percent silica.
Final Tailings Circuit
The final tailings consist of the combined spirals, magnetic and desliming tails. These are thickened to 50 percent solids and pumped to the tailings pond located south of the concentrator building. About 80 percent of the water in the thickened tailings slurry is returned as reclaimed water to the plant. The remaining water is trapped in the tailings or is lost via either evaporation or percolation. The thickener overflow is pumped to the process water tanks. The final tailings have 8.8 percent iron and 66.8 percent silica grade.
Pellet Feed Storage and Reclamation and Car Loading
An overhead tripper conveyor creates a pellet feed stockpile of 60,000 tonnes representing slightly over three days of nominal operation. This will be stored in a covered facility. The pellet feed is reclaimed using a 3,000 tonnes per hour (tph) drum type reclaimer. The reclaim pellet feed is transported to the pellet plant. A pipeline transports the pellet feed from the mine site to Sioux Lookout.
Pellet Plant
Bentonite will be used as the pelletizing binder. Bentonite will be reclaimed from a bentonite storage facility and charged to a storage bin in the grinding building, withdrawn by belt feeder and fed to a vertical roller mill. A dynamic separator within the mill returns coarse particles directly to the mill; finer particles are lifted out of the mill in a gas stream and are collected by a cyclone and bag filter and discharged through rotary valves into an aerated storage silo. Part of the cleaned air is returned to the mill. The bentonite will be pneumatically transported to bins in the mixer area of the 6 Mtpy pellet plant.
Based on needs and requirements, limestone will be ground to pelletizing fineness in a wet ball mill in closed circuit with hydrocyclones. The flux will be reclaimed from limestone stockpile and conveyed to a storage bin, withdrawn from the bin by feeder and fed into a ball mill with an installed power of 2,600 kW. Water will be added to give an in-mill density of 75 percent solids by weight. Ball mill discharge is collected in a pump box, diluted to approximately 50 percent solids and pumped to a hydrocyclone cluster. Coarse underflow is returned to the feed of the mill, while the overflow is pumped to the flux agitated storage tank. Limestone slurry is pumped from the storage tank to the induration machine discharge conveyor by variable speed pump. One flux grinding facility will serve both pellet plants.
The concentrate slurry will be received at the pellet plant at approximately 65 percent by weight of solids from a pipeline. The slurry will be fed directly to the slurry tank, which has a total maximum storage of 8 hours. Steam will be injected into the slurry storage tank to maintain slurry temperature at approximately 45°C. The concentrate is then pumped to a filter line at a measured rate.
The concentrate is pumped to a pressure distributor and dewatered in six vacuum disc filters with a seventh filter on standby. Six vacuum pumps will be provided. Three snap blow compressors, common to all filters, will provide air for cake release. The filter cake is transferred via conveyor to the filter cake bins in the mixing station. Filtrate and filter boot drain is pumped back to the thickener. Distributor and filter boot overflow slurry is returned by gravity to the filter feed tank.
Bentonite will be fed to the mixer feed by a screw feeder. Concentrate is withdrawn from cake bins by feeders and discharged into the mixer. The filter cake and binder are mixed in a horizontal mixer, with a spare mixer provided in case of breakdown. The mixed material will be transported by belt conveyor to the balling area. Reject green balls from the green ball screening system will be added to the mixed material downstream of the mixer.
A conveyor distributes the mixed material and green ball returns into nine balling discs feed bins. The mixed material will be continuously discharged from the balling feed bins and fed into nine balling discs. Each disc discharges on individual belt conveyors that discharge onto a common collecting conveyor, which distributes the green pellet across a wide belt. The wide belt feeds onto a double deck roller screen to remove oversize and undersize. Green pellet fines will be recycled together with crushed oversize to the mixed material stream.
The pellets will be hardened on a Straight Grate Induration machine. Green pellets will be dried in two stages. The dried pellets will be preheated to a progressively higher temperature to calcine the flux and to initiate magnetite oxidation. The pellets will then be fired at approximately 1,270°C to provide recrystallization and slag bonding which will give the pellets adequate strength. A short section designated as after-firing allows the heat front to completely penetrate to the bottom of the bed without the application of additional high temperature heat. Cooling is accomplished in two stages by passage of ambient air supplied by a cooling air fan. The cooled pellets leave the induration machine at 100°C or less. Five process fans provide process gas flow. The cooling air fan forces ambient air through the pellet bed. In the first cooling section, the air leaving the top of the bed is ducted through a direct recuperation header. Process gas from the second cooling stage is transported by the updraft-drying fan to the updraft drying section of the grate.
Product pellets discharged from the segregation bin will be transported by conveyor to the pellet stockyard. The estimated stockpile area has two stockpiles for a total size of 150 m by 1,200 m, to handle production of 6 Mtpy and storage. Pellet products will be reclaimed by a slewing type bucket reclaimer. The reclaimed iron pellet products will be transported from the stockpile to the car loader by a conveyor system operating at 3,000 tph.
Pellets discharged from each induration machine will be transported to a natural segregation bin. Larger pellets will segregate to the sides of the bin and will be allowed to overflow a side chute to return as hearth layer. Tramp material and agglomerates are prevented from being recycled in the hearth layer by use of a static grizzly screen. Product pellets will be discharged from the bottom of the bin.
Process gas from the hood exhaust and windbox exhaust systems are cleaned for particulate matter by dry electrostatic precipitators. The dust collected will be slurried with water and pumped to the waste reclaim area. Dust from the electrostatic precipitators will be slurried with process water and collected together with slurry from scrubbers and washdown and pumped to thickeners. Thickener underflow is then sent to the filter feed tanks and thus all waste materials are returned to the process. Thickener overflow is returned to the process water tank.
Auxiliary systems and infrastructure for the pellet plant include natural gas for the induration process, the pilot burners and the air heater of the bentonite grinding system. Steam is required for fuel oil and slurry heating as well as building heating. Water systems are provided for machinery cooling, gland and spray water, process water system and fire-fighting. A centralized system for the generation of plant compressed air and instrument air will be provided.
Hot Briquetted Iron (HBI) Plant
The Rockex HBI Plant will utilise gas-based direct reduction processes and will have capacity of 4.3 Mtpa at an expected metallization of 94 percent iron. The pellet product is fed to a shaft-based reduction furnace. The feedstock is prepared to adjust the size to the requirement in the reduction furnace, requiring screening for separation to adjust the particle size downward.
The process gas is formed to generate H2 and CO to remove the oxygen from the ore. Coal is also added to the process gas to actuate in the reduction. Natural gas enters the reduction furnaces and is heated to the required temperature for reduction of the oxide feed.
Once reduced, the product is hot briquetted to produce HBI and then cooled prior to storage in piles. The hot briquetting is performed in a shaft-based furnace, where the pellets product is introduced through a proportioning hopper at the top of the shaft furnace. As the ore descends through the furnace by gravity flow, it is heated and the oxygen is removed from the iron by counter flowing gases which have a high H2 and CO content. With a screw the hot feed is pushed into the nip between two counter rotating rollers of the briquetting machine. Pockets in the synchronously rotating rollers form the briquettes. This process occurs at high temperatures of 700°C and high pressing forces of 120 kN per cm active roller width. The continuous string of briquettes leaving the rollers is guided by a heavy chute and is separated into mostly singles, for example by a rotor with impact bars. Briquettes from fine material, produced in fluidized bed processes, may also be separated in a rotating tumbling drum.
The entire plant for hot briquetting consists of: a briquetting press with screw feeder and material supply; a briquette string separator (impact separator or tumbling drum); a hot screen for elimination of fines which occur during briquetting and separation; a product cooler; a bucket elevator for recirculation of fines to the briquetting press; and chutes and accessories.
The final product is stockpiled and after reclaiming will be transported from the stockpile to the car loader by a conveyor system operating at 3,000 tph. The reclaimed HBI product is loaded in a unit train of 90 cars of 100 tonnes capacity each.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Total ROM processing rate | Mtpy | 17.3 | Design |
| Crusher operating time | % | 65 | Design |
| Nominal crushing rate | t/h | 3,044 | Design |
| Concentrator operating time | % | 90 | Design |
| Nominal processing rate | t/h | 2,198 | Design |
| Shipping facility operating time | % | 90 | Design |
| Nominal concentrate (pellet feed) production rate | t/h | 761 | Design |
| Total weight recovery | % | 34.6 | Testwork average |
| Spiral separation weight recovery | % | 15.3 | Testwork |
| Magnetic separation weight recovery | % | 12.3 | Testwork |
| Desliming weight recovery | % | 7.0 | Testwork |
| Spiral separation iron concentrate production | Mtpy | 2.66 | Design |
| Magnetic separation iron concentrate production | Mtpy | 2.13 | Design |
| Desliming concentrate production | Mtpy | 1.21 | Design |
| Total iron concentrate (pellet feed) production | Mtpy | 6.00 | Design |
| Total iron pellets production | Mtpy | 6.00 | Design |
| Total HBI production | Mtpy | 4.30 | Design |
| Average ROM iron grade | % Fe | 28.9 | Testwork |
| Average ROM silica grade | % SiO2 | 45.5 | Testwork |
| Pellet feed target grade | % Fe | 66.3 | Design |
| Pellet feed target silica | % SiO2 | 5.23 | Design |
| Spiral cleaner concentrate target grade | % Fe | 66.5 | Testwork |
| Spiral cleaner concentrate target silica | % SiO2 | 5.0 | Testwork |
| Magnetic separation concentrate average grade | % Fe | 66.9 | Testwork |
| Magnetic separation concentrate average silica | % SiO2 | 5.2 | Testwork |
| Desliming circuit concentrate grade | % Fe | 64.9 | Testwork |
| Desliming circuit concentrate silica | % SiO2 | 5.81 | Testwork |
| Final tailings grade | % Fe | 8.8 | Design |
| Final tailings silica grade | % SiO2 | 66.8 | Design |
| Concentrator design capacity average operating rate | tpd | 52,752 | Design |
| Nominal throughput rate of iron material | t/h | 2,198 | Design |
| Slurry pipeline nominal throughput rate | t/h | 761 | Design |
| Concentrator fresh water requirement | m³/h | 581 | Design |
| Reclaim water from tailings pond | m³/h | 1,150 | Design |
| Process water demand from thickener overflow | m³/h | 14,360 | Design |
| Plant total power requirement | MW | 180 | Design |
| Concentrator process areas power | MW | 75 | Design |
| Pellet and HBI plants power | MW | 100 | Design |
| Sioux Lookout area power | MW | 4.8 | Design |
| Infrastructure and losses power | MW | 16.6 | Design |
| Equipment sizing design factor | % | 15 | Design |
| HBI expected metallization | % Fe | 94 | Design |
| HBI briquetting temperature | °C | 700 | Design |
| HBI briquetting pressing force | kN/cm roller width | 120 | Design |
| Concentrator pellet feed stockpile capacity | tonnes | 60,000 | Design |
| Pellet stockyard area | m by m | 150 x 1,200 | Design |
| Car loader and reclaim conveyor rate | tph | 3,000 | Design |
| Unit train capacity | cars x tonnes/car | 90 x 100 | Design |
Project website: https://rockexmining.com/s/Lake_St_Joseph.asp.html
Technical qualifications
The process design and flowsheet development for the Rockex Project is based on the metallurgical test program performed at SGS and described in Section 13.0 of this report. The concentrator weight recovery of 34.6 percent is an average figure based on the test work results and may vary depending on the mineralization composition. The process plant mass balance has been calculated based on the developed flowsheet and the process design criteria. A detailed process design criteria has been developed for the purposes of the PEA. The concentrator, pellet plant and HBI plant facilities will operate for 24 hours per day, 7 days per week and 52 weeks per year at an expected 90 percent utilisation. All throughput rates are based on the production of 6.0 Mtpy of concentrate (pellet feed), pellets and 4.3 Mtpy HBI.
Source: Lake St Joseph Iron Property , 2015 Technical Report, ROCKEX Mining Corporation, Updated PEA including HBI Process for the Lake St Joseph Iron Property, 4284/M03802A, October 26th, 2015, Section 17 Recovery Methods and subsections.
