Pilot Testing | Potassium Sulfate Crystallization

The Client's Needs

Polyhalite core sample and potassium sulfate crystals from ICP and Veolia Pilot Testing
Polyhalite core sample and potassium sulfate crystals from ICP and Veolia Pilot Testing

ICP's Ochoa Mine Project is projected to produce approximately 714,000 tons per year of SOP (K2SO4) from polyhalite ore for greater than fifty years as concluded in a feasibility study.

Another part of the feasibility study was the demonstration of a unique process, based on research that dated back nearly a century, to produce SOP economically while maintaining a high-quality, specialty fertilizer product.

The crystallization of the brine developed after ore processing is critical to both the cost of production and the desired product quality. A process would need to be developed and validated to confirm the commercial design.

The Solution

ICP selected Veolia Water Technologies to refine the process due to their experience in the industry and overall development capabilities for crystallization process design using HPD® Technology. A seriesof tests were conducted to simulate various stages of the proposed flowsheet with the goal of validating the overall design.

This testing was performed at Veolia's HPD® Evaporation and Crystallization Research and Development Center in order to replicate the full process. This facility is fully equipped for full analytical, bench-scale and pilot-scale testing.

Testing Objectives

The objectives of the test program were as follows:

  • Verify operating parameters of the calcined polyhalite leach process and confirm the composition of feed to the Veolia process equipment.
  • Perform pilot testing on leonite dissolution and preconcentration to study the precipitation of calcium sulfate (CaSO4) solids at pilot scale and to prepare SOP crystallizer feed.
  • Pilot testing of SOP crystallization to produce samples.
  • Optimize leonite crystallization to maximize recovery of leonite and ultimately, the final product.

Testing Description

  • Calcined ore is fed to ICP's countercurrent leaching process. This produces a brine rich in potassium and magnesium sulfates with some impurities that includes sodium chloride and calcium sulfate.
  • The leach brine is then fed to a dissolution tank in which leonite solids, produced later in the process, are dissolved. Producing this potassium and magnesium-based mineral and recycling the solids maximizes overall production of SOP. This recovers as much K2SO4 as possible from the process purge stream.
  • A seeded, mechanical vapor re-compression HPD® (MVR) Crystallizer then provides bulk water removal from the leonite enriched brine. The controlled seeding prevents scaling of heat transfer surfaces while aiding in precipitation of CaSO4 - based solids from solution.
  • Following a filtration step to remove precipitated solids, the second crystallizer (SOP crystallizer) produces a slurry of pure SOP. The slurry is sent to a centrifuge from which the solids are fed to a dryer that yields a granular, crystalline product.
  • The purge from the SOP crystallizer, containing potassium, is sent to the multiple-effect leonite crystallization system. It is composed of three stages of crystallization to efficiently recover leonite from the purge stream. The leonite slurry is sent to a centrifuge and the solids are then fed back into the production loop to be combined with the leach brine at the beginning of the process.