This report details the proposed processing changes for the VAULT expansion at the Vanscoy Potash Operations, which will increase annual production from 1,800,000 tonnes to 2,800,000 tonnes of product.
Report context
This technical report presents the recovery methods for the VAULT expansion at Vanscoy Potash Operations (VPO). The existing plant has a long processing history, and the amenability of the ore body to recover and concentrate potash has been well established. The process improvements introduced by the VAULT expansion are supported by bench and pilot scale test work, and industry proven technology with a minimum of one year of successful use within the potash industry has been used in the design.
Processing route
Ore Storage
Ore will be hoisted from underground at a nominal rate of 1,800 tonnes per hour, typically operating for 16 hours per day. A total of 35,000 tonnes of ore storage capacity will be available on surface. The existing 5,000 tonnes of live ore storage will be maintained, and an additional manual reclaim facility with a 30,000 tonne capacity will be built. Ore will be direct fed from the hoist or reclaimed from storage at a nominal mill feed rate of 1,084 tonnes per hour.
Crushing and Attrition Scrubbing
The crushing circuit is designed to prepare the ore for downstream processing by reducing the material size to 95% less than 9.5mm. Crushing and scrubbing will be accomplished in two stages. Primary crushing will use a single stage of two parallel roll crushers. The ore will then be combined with saturated process brine to produce a slurry for primary attrition scrubbing in two parallel banks of six 972 ft³ scrubbing cells. The discharge from the primary scrubbers will be screened, with the undersized material reporting to primary deslime cyclones and the oversize going to secondary crushing using one stage of three parallel cagepakors. The secondary crushing discharge will return to the primary scrubber feed. Secondary scrubbing will use two parallel banks of six 444 ft³ scrubbing cells, with the discharge sent to secondary deslime screens.
Slimes Separation
Slimes separation will remove fine potash particles from the primary cyclone overflow and separate them from unwanted insoluble material. The flow will be passed over trash screens, then sent to an inclined plate hydro-classifier. This represents a major upgrade from the current process, which uses insoluble flotation. The hydro-classifier will separate insoluble material by controlling the up flow velocity through the unit, using a dispersing agent to maximize removal of insoluble material and minimize loss of fine potash particles. The hydro-classifier underflow will report to scavenger flotation, while the overflow goes to a 115-foot diameter slimes thickener for brine recovery.
Fines and Coarse Rougher Flotation
The split between fines and coarse rougher flotation occurs at the secondary deslime screens, with the +20 mesh material reporting to coarse rougher flotation and the -20 mesh reporting to fines rougher flotation. Prior to flotation, the feed slurry will be conditioned with a depressant to coat residual insoluble material, followed by potash collector, flotation oil promoter, and frother.
Cleaner and Re-cleaner Flotation
Fines flotation concentrate, along with coarse rougher concentrate screen undersize, will go through cleaner flotation. The concentrate will then go to re-cleaner flotation. In the existing East plant, cleaner tails will join the fine rougher tails and feed to the coarse roughers. In the expanded West plant, cleaner tails will report to the regrind rougher cyclones. Re-cleaning will use conventional cells in the East plant and pneumatic column flotation in the West plant.
Scavenger Flotation
Scavenger flotation will recover fine potash particles from the hydro-classifier underflow, the cleaner flotation tails, and the product centrifuge effluent cyclone overflow. Three parallel 15-foot by 30-foot pneumatic column cells will be used. The concentrate will be debrined and go to crystallization, while tails will report to the fine salt thickener.
Regrind Circuit
The regrind circuit will recover potash from the coarse rougher flotation tails that is not sufficiently liberated. The circuit will use screening, crushing, and re-floating, with flotation cells using stepped banks for reagent conditioning. The regrind circuit will be a closed circuit, with regrind flotation tails screened and recycled back to the feed.
Crystallization
The crystallization circuit will convert low grade fine material to high grade product through differential crystallization. The existing crystallization circuit will continue to be used, taking feed from the scavenger column flotation cells and fine dust from product loading operations. Modifications to the circuit will focus on improving heat recovery.
Product Centrifuges, Drying, Sizing, Compaction, and Loadout
The existing centrifuges will continue to be used, and two additional centrifuges will be installed in the new circuit. Product drying will use fluidized bed dryers, with the two existing dryers staying in service and one additional dryer being installed. After drying, product will be sized to produce non-premium product, with material not meeting specification sent to compaction. The existing three compaction plants will stay in service, and two additional plants will be built. The loadout circuit will be modified to replace the existing air classification system with high capacity screens, and a separate truck loading facility will be built. The designed loading rate is 275,000 tonnes per month.
Key reported parameters
| Parameter | Design Value | Basis |
|---|---|---|
| Annual production rate | 2,800,000 tonnes | Proposed design |
| Existing annual production rate | 1,800,000 tonnes | Historical operating data |
| Ore grade range | 22.0% K₂O to 25.5% K₂O | Proposed design |
| Average expected ore grade | 24.6% K₂O | Proposed design |
| Nominal milling rate | 1,084 tonnes per hour | Proposed design |
| Average product grade | 60.6% K₂O | Historical operating data |
| Product grade specification | >60.0% K₂O | Product specification |
| Design product split – premium | 75% (2,100,000 tonnes per annum) | Proposed design |
| Design product split – non-premium | 25% (700,000 tonnes per annum) | Proposed design |
| Design recovery | 87% | Proposed design (supported by bench and pilot scale test work) |
| Hoisting rate | 1,800 tonnes per hour | Proposed design |
| Hoist operating hours | 16 hours per day | Proposed design |
| Total ore storage capacity | 35,000 tonnes | Proposed design |
| Existing live ore storage | 5,000 tonnes | Historical operating data |
| Additional manual reclaim capacity | 30,000 tonnes | Proposed design |
| Crushing product size | 95% less than 9.5mm | Proposed design |
| Slimes thickener diameter | 115 feet | Proposed design |
| Scavenger flotation cells | Three 15 x 30 foot pneumatic column cells | Proposed design |
| Water consumption | 945 gallons per minute maximum | Proposed design |
| Electrical power consumption increase | 200% | Proposed design |
| Loading rate | 275,000 tonnes per month | Proposed design |
Project website: https://www.nutrien.com/about/our-business/locations?tab=potash
Technical qualifications
The report states that the amenability of the VPO ore body to recover and concentrate potash has been well established by the long processing history of the plant. Given the remarkable continuity of the Prairie Evaporite Formation potash beds, the relative ease of concentration is not expected to change. The process improvements introduced by the VAULT expansion are supported by bench and pilot scale test work. Industry proven technology with a minimum of one year of successful use within the potash industry has been used in the design. The only additional reagent that will be required will be a dispersing agent for the new hydro-classifier, which has been used in other conventional potash mining processes and meets all regulatory requirements. All other reagents will remain the same, with their consumption rate improving or remaining the same.
Source: Vanscoy Potash Operations , VAULT Expansion Technical Report, Section 17 Recovery Methods.
