The 2015 PEA Technical Report for the Wellgreen Project describes a proposed process plant design that uses bulk flotation to produce a copper-nickel concentrate, with potential for supplementary magnetic recovery of metals from flotation tails.
Report context
The Wellgreen Project 2015 PEA Technical Report, effective February 2, 2015, presents a preliminary economic assessment that includes a proposed processing route for the project. The report details process design criteria and equipment sizing based on testing and industry standards. The report states that testing has not been fully evaluated for all aspects of the proposed flowsheet and that some design parameters require further definition at the pre-feasibility stage.
Processing route
Proposed Process Description
The proposed process plant design will use a primary crusher followed by two-stage crushing in closed circuit with screens to produce feed for a single stage ball mill. Flotation concentrate will be thickened and vacuum filtered to produce concentrate for shipment by truck. Flotation tails will be discharged to the tails facility.
Testing indicates that a flowsheet to produce a bulk copper-nickel concentrate, supplemented by magnetic recovery of flotation tails, will maximize recovery of valuable metals. Testing also indicates that early activation of the nickel is needed to achieve maximum possible nickel recoveries. Previous reports that detailed sequential flotation in intermediate stages of grinding have not been replicated.
Testing efforts to produce a separate copper concentrate using sequential flotation resulted in nickel recoveries up to 10% lower than those realized from bulk flotation. In addition, bulk flotation followed by copper-nickel separation also had a detrimental impact on overall recoveries. Therefore, for the purposes of this PEA, bulk flotation producing a bulk concentrate for direct sale has been pursued.
Primary Crushing
The primary crusher will be a 60-89, 600-kW gyratory crusher. Run of mine material will be trucked directly to the gyratory crusher. Mineralized material will normally be directed to the crusher feed stockpile, which is covered to reduce snow and rain addition. The gyratory crusher will produce 165 mm product and be capable of receiving material up to 1.2 m in size. A rock breaker will be used to break up larger material delivered from the pit.
Crushing
Crushing to produce ball mill feed will be performed in two stages. Both stages will be MP1000 or equivalent crushers drawing 1,000 kW each. The first crusher will receive material from a screen that removes material suitable for tertiary crushing and material at final size. The product from the secondary crusher and the mid-sized material will combine with the product from the tertiary crusher. This material will be screened to produce tertiary crusher feed and final ball mill feed, directed to the fine material bin. The tertiary feed will fall into a tertiary feed bin, and a feeder will allow choke feeding of the tertiary crusher. Final crushed product will be directed to fine material bins that will feed the grinding circuit. The fine material bins will have a total capacity for 12 hours of grinding operation. Bulk density of the mineralization at 50% voids will be 1.61 tonnes per cubic meter, and for 12 hours of production or 13,500 tonnes, the required volume is 21,000 m³.
Grinding
Grinding will be by single stage ball mills. Two mills will be required at this tonnage rate, and the mills will operate in parallel. It is possible to operate the mills in series as well with minor piping changes. Optimization of the layout will be considered at the pre-feasibility stage. The design p80 is 75 microns. Crushing plant product is projected to be 12,700 microns. The design circulating load is 300% to produce a cyclone overflow at 30% solids. The mills will be 7.6 m diameter by 10.4 m, drawing 10.5 megawatts of power. The mill will operate in closed circuit with cyclones, and feed from the fine material bins will be directed to the mill discharge pump box to avoid overgrinding.
Rougher Flotation
Rougher flotation will be via a bank of four 300 cubic meter tank cells. This will provide 24 minutes retention time and a carrying capacity of less than 1 mtph/m². This is considered conservative, and hence the circuit will be able to respond well if feed grade increases. Each cell will draw 300 kW. Total flotation concentrate tonnages have been calculated using a head grade of 0.5% nickel and 0.5% copper with 80% recovery of both to assure that the subsequent equipment will not be undersized. Total flotation tailings tonnages have been calculated using a head grade of 0.2% nickel and 0.2% copper with 60% recovery of both to assure that downstream equipment will not be undersized. Using these criteria for design purposes, the mass flow to flotation concentrate is 165 mtph, and the mass flow to flotation tailings is 1,030 mtph.
Magnetic Separation
Magnetic separation units have not yet been sized for the project. It is anticipated that four units per line will be needed, each drawing 50 kW. Magnetic separation tails, being non-magnetic material, will be directed to final tails. The design mass flow for magnetic separation is the case where rougher concentrate mass is at a minimum, resulting in a magnetic concentrate mass flow of 124 mtph. Magnetic concentrate will be reground, and testing to determine the optimum grind size has not yet been completed. For design purposes, 40 microns with a work index of 19.0 has been used, requiring a 4.1 m x 5.1 m ball mill drawing 1,200 kW.
Magnetic Concentrate Flotation
Magnetic concentrate will be floated in four 20 m³ tank cells drawing 20 kW each.
Regrind
Magnetic concentrate and bulk rougher concentrate will be reground in a 400 kW tower mill.
Cleaner Flotation
Cleaner flotation will be in three stages. The tails from the first cleaner are final tails. Each subsequent stage may return to the previous stage or to the magnetic concentrate flotation feed. Each stage will consist of four 10 m³ tank cells, for a total of 12 cells, drawing 10 kW each.
Dewatering
Testing to confirm dewatering equipment sizes has not yet been completed. An allocation of 500 kW for dewatering equipment is added to the equipment list, including thickening, vacuum filtration and ancillary equipment. The estimated mass of concentrate to be dewatered is 2.5% of the fresh feed or 27.4 mtph. At this time, a thickener diameter of 30 meters will be used, which is considered conservative.
Key reported parameters
| Parameter | Value | Units | Basis |
|---|---|---|---|
| Annual tonnage | 9,125,000 | dmt | Design (nominal capacity) |
| Nominal daily tonnage | 25,000 | dmt | Design (name plate capacity) |
| Design daily tonnage | 26,400 | dmt | Design (equipment sizing) |
| Ball mill circuit discharge (P80) | 75 | microns | Design |
| Grinding circuit feed (F80) | 12,700 | microns | Design |
| Ball mill circuit circulating load | 300 | % | Design |
| Bond ball work index | 19.0 | kWhr/mt | Testwork basis |
| Ball mill power (each) | 10,500 | kW | Design |
| Ball mill size (each) | 7.6 m x 10.4 m | , | Design |
| Rougher flotation retention time | 24 | minutes | Design |
| Rougher flotation cell volume (each) | 300 | m³ | Design |
| Rougher concentrate mass (high grade) | 164.5 | mtph | Design |
| Magnetic concentrate mass | 123.7 | mtph | Testwork (preliminary) |
| Final concentrate mass | 2.5 | % of fresh feed | Design |
| Primary crusher motor size | 600 | kW | Design |
| Cone crusher motor size (each) | 1,000 | kW | Design |
| Magnetic regrind mill power | 1,200 | kW | Design |
| Concentrate regrind mill power | 400 | kW | Design |
| Bulk density at 50% voids | 1.61 | tonnes/m³ | Testwork |
| Specific gravity of mineralized material | 3.22 | none | Testwork |
Project website: https://www.wellgreenplatinum.com/
Technical qualifications
The report contains several limitations that affect the accuracy and completeness of the process design. Industry standard availabilities have been used for this PEA, and it is recommended that this factor be more fully defined at the pre-feasibility study. Testing indicates that there is potential for improved recoveries of metals, particularly PGMs, by magnetic treatment of the final flotation tails, but the exact nature of this process has not been fully evaluated and has not been included in the economic evaluation at this time. Magnetic separation units have not yet been sized for the project. Testing to determine the optimum grind size for magnetic concentrate regrinding has not yet been completed. Testing to confirm dewatering equipment sizes has not yet been completed. The report also states that previous reports that detailed sequential flotation in intermediate stages of grinding have not been replicated.
Source: Wellgreen Project , 2015 PEA Technical Report, Effective Date February 2, 2015.
