This report details the proposed processing route for the Dumont Nickel Project, based on design criteria established in June 2012.
Report context
Report 2139-RPT-003, Revision 0, dated 22 June 2012, presents the recovery methods section for the Dumont Nickel Project. The document outlines the proposed process plant design for treating run-of-mine ore to produce nickel concentrate and tailings. The report addresses the general processing strategy, design criteria, unit process selection, and equipment sizing for a plant to be built in two phases, initially at 50 kt/d with provision for expansion to 100 kt/d.
Processing route
General processing strategy
The proposed process plant and associated service facilities will process ROM ore delivered to primary crushers to produce nickel concentrate and tailings. The proposed process encompasses crushing and grinding of the ROM ore, desliming via a hydrocyclone circuit, slimes flotation, nickel sulphide rougher flotation, nickel sulphide cleaning flotation, magnetic recovery of sulphide rougher tailings, regrind of magnetic concentration and sulphide 1st cleaner tailings, and nickel alloy rougher and cleaner flotation.
Concentrate will be thickened, filtered, and stored on site prior to being loaded onto railcars or trucks for transport to third-party smelters. The slimes flotation tailings, magnetic separation tailings, alloy rougher tailings, and alloy 1st cleaner scavenger tailings will be combined and thickened before placement in the tailings storage facility.
Plant design basis and phasing
The process plant will be built in two phases. Initially, the plant will be designed to process 50 kt/d with allowances for a duplicate process expansion to increase plant capacity to 100 kt/d. Common facilities will include concentrate thickening and handling, and reagent storage and preparation.
The key criteria selected for the base plant (50 kt/d) and expansion plant (100 kt/d) designs are: a nominal base plant treatment rate of 50 kt/d and a nominal expansion plant treatment rate of 50 kt/d for a combined 100 kt/d treatment rate; design availability of 92% (after ramp-up), which equates to 8,059 operating hours per year, with standby equipment in critical areas; and sufficient plant design flexibility for treatment of all ore types at design throughput.
Comminution circuit
The comminution circuit design was determined through evaluation of variability comminution testwork performed at SGS-Lakefield. Testwork provided a crusher work index, Bond ball and rod mill indices, Bond abrasion index, SMC, and JK Axb values for the selected samples. Ausenco elected to use the 75th percentile of each of these values in the design.
For each 50 kt/d plant, Ausenco selected one 11.6 m (38 ft) diameter SAG mill and two 7.9 m (26 ft) diameter ball mills. The circuit is designed to achieve the design throughput for design competency ore, with potential for increased throughputs for softer ores. An overall plant availability of 92% or 8,059 h/a is nominated, considered an industry standard for a large, multi-train flotation plant with moderately abrasive ore.
Crushing and stockpile
Ore from the open pit is crushed using a primary gyratory crusher (assisted with a rock breaker) to a crushed product size of nominally 80% passing (P80) 101 mm. Crushed ore is fed onto the covered stockpile feed conveyor. A covered conical stockpile of crushed ore with a live capacity of 18 h is provided, with three apron feeders, each capable of feeding 60% of the full mill throughput.
Grinding and classification
A 22 MW SAG mill, 11.6 m diameter (38 ft) with 6.7 m EGL (22 ft), utilizes a trommel screen for classification and oversize recirculation. Two 12 MW ball mills, 7.9 m diameter (26 ft) with 11.0 m EGL (36 ft), operate in closed circuit with hydrocyclones, grinding to a product size of nominally 80% passing (P80) 150 µm.
Desliming circuit
A two-stage desliming circuit via hydrocyclones is specified. The first stage splits mass with a cut size (D50c) of 40 µm. The second stage splits mass with a cut size (D50c) of 10 µm. Hydrocyclone sizes for each stage are 400 mm and 100 mm, respectively.
Flotation circuit design
The flotation circuit comprises multiple stages with specified residence times. Slimes flotation consists of two trains of six 300 m³ forced air tank flotation cells per train to provide 30 minutes of retention time. Nickel sulphide rougher flotation consists of two trains of seven 300 m³ forced air tank flotation cells per train to provide 60 minutes of retention time. Nickel sulphide 1st cleaner, 2nd cleaner, and 3rd cleaner flotation are specified, with residence times of 15, 12, and 12 minutes respectively. Magnetic sulphide flotation provides 36 minutes of retention time. Awaruite roughers provide 60 minutes, with alloy 1st cleaners at 18 minutes, alloy 1st cleaner scavenger at 18 minutes, and alloy 2nd cleaners at 15 minutes.
Magnetic separation
The flowsheet includes magnetic recovery of sulphide rougher tailings, with regrind of magnetic concentration and sulphide 1st cleaner tailings.
Concentrate handling and tailings disposal
Nickel concentrate thickening operates at a flux of 0.25 t/m²/h, with filtration at 450 kg/m²/h. Tailings thickening operates at 0.75 kg/m²/h, with underflow density at 40% w/w.
Key reported parameters
| Criteria | Unit | Design 50 kt/d | Design 100 kt/d |
|---|---|---|---|
| Crusher feed | kt/d | 50 | 100 |
| Mt/a | 18.25 | 36.50 | |
| Crusher availability | % | 75 | 75 |
| Crusher throughput | t/h | 3,019 | 6,039 |
| Mill/flotation availability | % | 92 | 92 |
| Mill throughput | t/h | 2,264 | 4,529 |
| Bond ball mill work index (BWI) | kWh/t | 20.7 | 20.7 |
| Bond rod mill work index (RWI) | kWh/t | 15.7 | 15.7 |
| Bond crusher work index (CWI) | kWh/t | 15.3 | 15.3 |
| Specific gravity | t/m³ | 2.57 | 2.57 |
| Grind size P80 | µm | 150 | 150 |
| Head grade (design) | % Ni | 0.35 | 0.35 |
| % S | 0.10 | 0.10 | |
| % Fe | 5.71 | 5.71 | |
| Sulphide nickel recovery (design) | % | 56 | 56 |
| Alloy nickel recovery (design) | % | 4 | 4 |
| Overall nickel recovery (design) | % | 60 | 60 |
| Flotation residence times | |||
| Slimes flotation | min | 30 | 30 |
| Sulphide roughers | min | 60 | 60 |
| Sulphide 1st cleaners | min | 15 | 15 |
| Sulphide 2nd cleaners | min | 12 | 12 |
| Sulphide 3rd cleaners | min | 12 | 12 |
| Magnetic sulphide | min | 36 | 36 |
| Awaruite roughers | min | 60 | 60 |
| Alloy 1st cleaners | min | 18 | 18 |
| Alloy 1st cleaner scavenger | min | 18 | 18 |
| Alloy 2nd cleaners | min | 15 | 15 |
| Reagent consumptions | |||
| PAX | g/t | 140 | 140 |
| MIBC | g/t | 19 | 19 |
| Cytec 65 (frothing agent) | g/t | 6 | 6 |
| Calgon | g/t | 50 | 50 |
| CMC | g/t | 25 | 25 |
| Sulphuric acid (H2SO4) | kg/t | 8 | 8 |
| Copper sulphate (CuSO4) | g/t | 30 | 30 |
| Flocculant | g/t | 30 | 30 |
| Media consumption | |||
| SAG mill media | t/a | 1,087 | 2,175 |
| Ball mill media | t/a | 1,831 | 3,662 |
| Regrind mill media | t/a | 283 | 565 |
Project website: http://docs.openinfo.gov.bc.ca/d70769413a_response_package_fin-2013-00353.xls
Technical qualifications
The design head grade of 0.35% Ni was selected prior to final completion of the mine plan; however, it represents roughly 95% of the peak quarterly head grade. Additionally, 0.35% Ni falls in the 95th percentile of all quarterly maximum head grades. The report states that the design head grade value will be revisited in the next phase of study.
The comminution circuit design was based on evaluation of variability comminution testwork, with Ausenco electing to use the 75th percentile of each value in the design.
The report notes that given the low abrasion index of the Dumont ore, the nominated availability of 92% is likely conservative.
The process plant flowsheet design was conceptually based on those of comparable large flotation plants and then confirmed or altered based on trade-off studies and metallurgical testwork.
Source: 2139-RPT-003, Recovery Methods section, 22 June 2012.
