This report details the proposed design, process description, and summer 2021 construction status for a 146,000-tonne-per-annum granular potash processing plant using solution mining and crystallization pond recovery.
Report context
This NI 43-101 Technical Report, dated November 30, 2021, summarizes detailed engineering and mine life review for the Milestone Phase I Project, prepared for Western Potash Corp. by March Consulting Associates Inc. The report describes a processing plant designed to produce 146,000 tonnes of granular potash annually, scheduled to operate 7,500 hours per year, with the wellfield capable of operating 8,000 hours per year. Normal wellfield operation to supply sufficient brine for full production would be 6,024 hours per year.
Processing route
Solution mining and brine circulation
The process begins with NaCl-saturated brine (solvent) from the cooling pond, which is heated to an injection temperature of up to 100°C and injected through wells into up to six solution mining caverns at a total rate of 300 m³/h. Production brine returns to surface through a production well and is transported via pipeline to the crystallization pond, where the brine is allowed to cool close to ambient temperature. KCl (MOP) precipitates upon cooling because KCl solubility decreases with falling temperature while NaCl solubility remains almost constant. The crystallization pond brine, depleted of a portion of KCl, is re-heated to 100°C and pumped back to the solution mining caverns as solvent in a closed loop through a central brine/solvent distribution system.
Carnallite in the ore is readily dissolved during solution mining, resulting in MgCl₂ in the cavern brine. The MgCl₂ content is controlled by purging a small stream of crystallization pond return brine to a disposal well, maintaining MgCl₂ content of the cavern brine at up to 2.5% w/w. The plant recovery of KCl from cavern brine to product is expected to be 96.3%.
Crystallization pond
The 503 m × 225 m crystallization pond is located east of the process plant. Brine enters at the southwest corner and is recovered from the central-west side. Surface-run pipes connect the pond with the process plant. The pond has an active surface area of 6 ha and contains total brine inventory of 225,000 tonnes, with non-recoverable inventory of 19,000 tonnes as pond floor cover. Pond feed brine flow is 300 m³/h at an average temperature of 47.9°C. Pond discharge brine flow is 309 m³/h with average temperature of 0.7°C. Average pond discharge brine KCl content is 83.0 g/L.
Debrining and drying
Potash precipitate is recovered using a dredge which pumps slurry to the processing plant for de-brining. Debrining consists of three steps: primary solid/fluid separation using a hydrocyclone, major fluid removal using a screen bowl centrifuge, and drying of solids in a rotary dryer. Dredge slurry flow is 150.3 m³/h at 10% w/w solids. The hydrocyclone underflow is expected to be 40–50% w/w solids, with overflow at 3–5% w/w solids. The centrifuge produces cake at 95.7% w/w solids with 4.3% moisture, and centrate at 2.0% w/w solids. Overflow from the hydrocyclone and centrate from the centrifuge are recirculated to the crystallization pond.
The rotary dryer is designed for product discharge temperature greater than 200°C, with residual moisture in product at a target of 0.05% and maximum of 0.1%.
Compaction plant
Dryer discharge product and recycled fines and dust from the compaction circuit are fed to a feed bin providing surge capacity. From the feed bin, MOP powder is fed by a force feeder system to a twin-roll compactor to form flake. Flake is broken by a flake-breaker crusher and fed to a bi-level primary screen separating oversize and undersize from midsized product particles. Oversize is fed to a cage mill and recycled to the primary screen; undersize is recycled to compaction feed. Midsized particles from the primary screen are fed to a polishing screen, where the midsize stream becomes the granular product. Oversize from the polishing screen is fed to the cage mill and recycled to the primary screen; undersize is recycled to compaction feed.
Granular product from the polishing screen is weighed on a weigh belt and treated with an oil-amine-colorant dedusting reagent mixture in a mix box before being conveyed to product storage. Dust collection is provided by a baghouse and fan system.
Major mechanical equipment
The process plant is a steel-clad building 25 m × 33 m and 15 m tall, housing hydrocyclone, centrifuge, rotary dryer with dust collection, water/slurry/brine/reagent pumps and tanks, and brine heat exchangers. The compaction building is 15 m × 15 m and 35 m tall, housing material handling equipment, compactor and flake breaker, product screens, and cage mill. The product storage and loadout building is 52.5 m × 27 m and 12 m tall.
Major equipment includes: nine piston injection pumps (Westpower), two plate heat exchangers (Inproheat Industries Ltd), one submerged combustion brine heater (Inproheat Industries Ltd), one hydrocyclone (Weir Minerals), one product centrifuge (Industrial Machine, screen bowl style), one rotary dryer (Heyl Patterson, co-current rotary style), one compactor (Ludman Industries with force feeder and flake breaker), one dredge (Dredge Yard, floating mobile with excavation head and onboard slurry pump), material handling systems (Continental Conveyor), and product loadout equipment (Tundra Process Solutions).
Key reported parameters
| Parameter | Unit | Design | Basis |
|---|---|---|---|
| Annual production | t | 146,000 | Design capacity |
| Plant operating hours | h/yr | 7,500 | Scheduled operation |
| Wellfield operating hours | h/yr | 8,000 | Capability |
| Normal wellfield hours for production | h/yr | 6,024 | For full production |
| Cavern injection temperature | °C | up to 100 | Design |
| Total injection rate | m³/h | 300 | Design |
| Number of solution mining caverns | up to 6 | Design | |
| Cavern brine MgCl₂ content | % w/w | up to 2.5 | Control target |
| KCl recovery from cavern brine to product | % | 96.3 | Expected |
| Crystallization pond area | ha | 6 | Active surface area |
| Pond feed brine temperature | °C | 47.9 | Average, design |
| Pond discharge brine temperature | °C | 0.7 | Average, design |
| Pond discharge brine KCl | g/L | 83.0 | Average, design |
| Dredge slurry flow | m³/h | 150.3 | Design |
| Dredge slurry solids | % w/w | 10 | Design |
| Hydrocyclone underflow solids | % w/w | 40–50 | Design range |
| Centrifuge cake solids | % w/w | 95.7 | Design |
| Centrifuge cake moisture | % w/w | 4.3 | Design |
| Dryer discharge temperature | °C | >200 | Design |
| Product residual moisture target | % | 0.05 | Target |
| Product residual moisture maximum | % | 0.1 | Maximum |
| Pond solids PSD passing 48 mesh (295 μm) | % | 50 | At dryer discharge, design |
| Pond solids PSD passing 100 mesh (147 μm) | % | 7 | At dryer discharge, design |
Project website: https://westernresources.com/Milestone-Phase-I
Technical qualifications
This article summarizes the proposed design and process description as presented in the 2021 Technical Report. No operating data from a fully commissioned plant is presented; the process parameters represent design criteria and expected performance. The plant status as of summer 2021 is reported as partially constructed, with the solution mining system completed and operational, while process and compaction areas required completion of mechanical, piping, chutework, electrical, and instrument installation. The storage and loadout building required all areas except foundations to be constructed. Over 85% of tagged equipment was on-site at that time. No subsequent construction or operational updates are provided in this report.
*Source: NI 43-101 Technical Report Summarizing Detailed Engineering and Mine Life Review, Milestone Phase I Project, prepared for Western Potash Corp., March Consulting Associates Inc., November 30, 2021, Section 17: Recovery Methods.*
