The Silver Yards processing plant employs dry and wet process streams to produce lump, sinter fines, and ultra-fines from direct shipping iron ores in the Schefferville area.
Report context
This technical report, dated April 12, 2013, provides a resource update for the Schefferville Area Direct Shipping Iron Ore Projects. The processing infrastructure described is the Silver Yards plant, located at the former Silver Yards marshalling area just north of the James North deposit. Labrador Iron Mines (LIM) operates the facility, which processes ore from multiple deposits in the region.
Processing route
Process design basis
The process design is based on mineralogy and equipment testing performed as described in Section 13 of the report. Laboratory testing and flowsheet development was completed by SGS Lakefield prior to design installation and operation of the wet plant. The Silver Yards plant was designed by DRA Americas and installed and built by a local engineering company from Labrador City. No chemicals are used in the processes.
Two process streams
LIM employs two separate process streams for mined ore depending on the feed head grade. The dry crushing and screening process is used to classify higher grade ores (>58% Fe, average 62% Fe). The wet process (crushing, scrubbing, screening, hydrosizing, magnetic separation, filtration) is used to upgrade lower grade ores (<58% Fe) into products that are over 62% Fe in content.
The dry process operates from April through November. The wet process plant operates from May through October. The seasonal operation is dictated by the freezing of finer iron ore products.
Silver Yards wet plant , Phase I and II
Commissioning of the wet plant commenced in April 2011 and production started in June 2011. The plant was built with two parallel lines operating as modular units. Phase I consisted of a washing and screening plant to produce two products: lump and sinter fines. The plan for the first year was to only wash and screen the higher grade blue ore material, while higher silica blue and yellow ore was stockpiled for later treatment.
Phase II, completed during summer 2011, consisted of the installation of a fines recovery system including a Floatex Density Separator on the (−600μm +150μm) fraction and an FLSmidth Pan Filter to dry the product to a moisture content of less than 8%.
Primary crushing area
Run-of-mine ore from the pits is delivered via off-highway end dump trucks to the primary mobile crushing plant. The ROM feed has a top size of 600 mm. Approximately 50% of the feed bypasses the primary crushing as it is already minus 100 mm. The primary crushing plant is not enclosed.
Tumbling scrubbers area
The discharge from the primary crusher is conveyed via a surge bin to three lines starting with a tumbling scrubbers circuit. The purpose of this step is to beneficiate the ore by incorporating water to wash the clay fines from the ore materials. The scrubbers are sized at 2,100 mm × 5,000 mm each, each with 90 kW power installed.
Primary screening area
The discharge from the tumbling scrubbers proceeds to the primary screening circuit. The primary screening units are double deck screens with openings of 25 mm and 1 mm, sized at 1,840 mm × 4,870 mm. Oversize material (+25 mm) on the top deck is sent to the secondary crushing circuit. Undersize material (+1 mm, −25 mm) is conveyed to the lump ore screening area. Material (−1 mm) from the bottom deck is sent to the secondary screening circuit.
Lump ore screening area
The oversize of the second deck from the primary screens (+1 mm, −25 mm) is fed to a single lump ore screen with the same size as the primary screens (1,840 mm × 4,870 mm). The lump ore screen deck has an opening of 8 mm. Oversize material (+8 mm, −25 mm) is stockpiled as a final lump product. Screen undersize (+1 mm, −8 mm) along with the oversize of the secondary screens is transported to a stockpile as a final sinter fines product.
Secondary crushing area
The oversize (+25 mm) from the primary screening circuit is transferred to the secondary crushing circuit. The secondary crusher is a standard 4 1/4 foot Symons cone crusher. The product from the cone crusher is recirculated back to the primary screening circuit.
Secondary screening area
The undersize (−1 mm) from the primary screening circuit is pumped to the secondary screening circuit, which consists of two four-deck and one five-deck Derrick Screens (type 2SG48-60R). The oversize material (+300 μm for higher grade material and +600 μm for lower grade material) from the secondary screens is conveyed to the sinter fines stockpile.
Fines recovery plant
In summer 2011, new equipment was installed to recover the (−600 μm/−300 μm) fraction. This equipment includes two stages of desliming via cyclones, a Floatex Density Separator, and filtration equipment. The undersize material (+100 μm, −600 μm) from the secondary screen is pumped to the two-stage desliming cyclones. The undersize material (−100 μm) from the Floatex Separators is dewatered in a 4,000 mm diameter, 10 m² filtering area FLSmidth Dorr Oliver Heavy Duty Horizontal Pan Filter (type HPF 10 m²) to a moisture of approximately 8% and then stockpiled as a sinter fines product.
Silver Yards wet plant , Phase III expansion
Phase III of the Silver Yards plant involves the installation of an additional parallel process stream similar to the two existing lines, which will increase the plant throughput capacity. Additionally, a Wet High Intensity Magnetic Separator (WHIMS) on the slimes fraction will produce ultra-fines, which will be combined with the final sinter fines product. This will improve the overall concentrate recovery. As a result of metallurgical test work carried out in 2010, it has been shown that the iron ore recovery can be increased by the incorporation of additional process equipment.
Work was carried out during 2012. Completion of the Phase III expansion was deferred in late 2012 but resumed again in April 2013 and was commissioned in June 2013.
The WHIMS will further process the (−150 μm, +20 μm) overflow of the Floatex Separator and the underflow of the secondary desliming cyclone to produce a third product , ultra fines. The product will be subsequently dewatered in a vacuum disc filter.
Product storage
Iron ore products from the beneficiation process are conveyed from the plant to respective radial stackers. Lump ore product and sinter fines products are stockpiled separately. An area of approximately 4,300 m² is available for clean ore storage, providing total capacity of approximately 20,000 tonnes. Drainage from the ore stockpiles is managed through site grading and ditching.
Rejects disposal area
The existing historically mined and flooded Ruth Pit, located north of the Silver Yards plant, is used as a final plant rejects disposal area. The undersize material from the secondary screening circuit (−100 μm) and the filtration filtrate are combined and pumped as slurry approximately 2.9 km via an above-ground, 300 mm diameter HDPE pipeline to the Ruth Pit, which has a surface area of 61.5 ha and depth of 120 m. An emergency disposal/storage area within the Silver Yards area is also designed to provide room in case the reject fines pipeline or beneficiation process equipment needs to be purged.
Dry classifying system
The throughput capacity of the dry classifying system with two lines in operation is 1,000 tonnes per hour or approximately 20,000 tonnes per day at mechanical availability of approximately 85%. One line provides crushing and screening, while the other line is used for screening only. Mass yield of higher grade ores (>58% Fe) is approximately 100%, while mass yield for lower grade ores (<58% Fe) is approximately 65%. The rejects from the dry process can be processed in the wet plant for secondary recovery.
Product specifications
Product specifications for the James ore body are described in the report. The product mix and specifications table reports Fe content ranges and SiO₂ content ranges for lump, sinter fines, and ultra-fines products.
| Product | Fe (%) | SiO₂ (%) |
|---|---|---|
| Lump | 62–64 | 5–7 |
| Sinter fines | 61–63 | 5–8 |
| Lump (alternate) | 63–65 | 4–6 |
| Ultra fines | 62–66 | 5–8 |
Project website: https://www.labradorironmines.ca/project.php
Process recoveries , Silver Yards plant
Based on existing testing and engineering design and short operating experience, the recoveries for Phase I (processing blue ore only) were: lump 15.0%, sinter fines 30.0%, total recovery 45.0%.
With Phase II equipment inclusion, the density separation and filtering process was planned to recover part of the previously treated rejects fraction (−600μm) and increase recovery by about 13.2%. Phase II recoveries: lump 15.0%, sinter fines 48.0%, total recovery 63.0%. Experience in 2011 and 2012 indicates these recoveries are practical.
Phase III equipment was expected to add ultra fines or pellet feed (+25 μm, −100 μm) at approximately 12.2% recovery, for a combined overall recovery of 75% to 80%, based on tests of blue ore only: lump 15%, sinter fines 48%, ultra fines 17%, total recovery 80%. The current process parameters are estimated based on equipment test results and operating experience for the blue ore and assume the high silica ores will be more difficult to process compared to the standard blue ore.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Wet plant throughput (Phases I+II) nameplate | 400 tonnes per hour | Design |
| Wet plant throughput (Phases I+II) operating | Approximately 8,000 tpd | Design at 85% availability |
| Wet plant throughput (Phases I+II+III) nameplate | 600 tonnes per hour | Design (proposed) |
| Wet plant throughput (Phases I+II+III) operating | 12,000 tpd | Expected at 85% availability |
| Dry plant throughput (two lines) | 1,000 tonnes per hour / 20,000 tpd | Design at 85% availability |
| Mechanical availability (all streams) | Approximately 85% | Design assumption |
| Mass yield wet Phases I+II | Approximately 60%–63% | Historical (short operating experience) |
| Mass yield wet Phases I+II+III | Approximately 75%–80% | Expected |
| Mass yield dry (high grade >58% Fe) | Approximately 100% | Design/historical |
| Mass yield dry (low grade <58% Fe) | Approximately 65% | Design/historical |
| Total recovery Phase I (blue ore) | 45% | Historical (short operating experience) |
| Total recovery Phase II | 63% | Historical (experience in 2011-2012) |
| Total recovery Phase III | 75%–80% | Expected (based on blue ore tests) |
| Product moisture (pan filter) | <8% | Design |
| Lump product size | +8 mm −25 mm | Design |
| Sinter fines product size | +1 mm −8 mm | Design |
| Ultra fines product size | +15 μm −150 μm (Phase III) | Design |
Technical qualifications
The process design is based on mineralogy and equipment testing as described in Section 13 of the report. Laboratory testing and flowsheet development was completed by SGS Lakefield prior to design installation and operation of the wet plant. Metallurgical test work carried out in 2010 showed that iron ore recovery could be increased by incorporation of additional process equipment. Phase III expansion work was carried out during 2012, deferred in late 2012, resumed in April 2013, and commissioned in June 2013. Process recoveries for Phase I and II are based on short operating experience. Phase III recovery estimates are based on tests of blue ore only; the report assumes high silica ores will be more difficult to process compared to standard blue ore.
Source: Schefferville Area Direct Shipping Iron Ore Projects Resource Update, April 12, 2013, Section 17: Recovery Methods.
