IC Potash Corp. is revolutionizing the sulfate of potash (SOP) industry by expanding upon research that was originally conducted by the U.S. Bureau of Mines (USBM) from the 1920s to 1940s. The USBM research was a result of the government’s mandate to reduce American dependence on imports after Germany stopped shipping potash to the U.S. during World War I.
ICP’s unique process, called the Ochoa Process, utilizes polyhalite, water and energy to produce three main products – soluble SOP, standard SOP, and granular SOP – as well as several other potential by-products.
ICP has invested more than US$10 million to validate the research performed by the USBM, and later the Potash Corporation of America (PCA), and continues to conduct advanced test work and trade-off studies to enhance knowledge and to optimize process efficiency and economics.
The process refined by ICP is expected to result in the production of SOP in the bottom quartile for cost, with manageable capital costs.
As noted above, extracting potash from polyhalite (K2SO4•MgSO4•2CaSO4•2H2O) dates back to the 1920s. At that time, the USBM confirmed the process to convert polyhalite into SOP fertilizer, but the discovery and exploitation of naturally-occurring deposits of sylvite, or MOP, in the Carlsbad district reduced the urgency for polyhalite development. Consequently, the polyhalite deposits in southeastern New Mexico have remained untouched to this day.
Now that SOP has become the preferred fertilizer for the fruit, vegetable, tobacco and potato industries, and for agriculture in saline and dry soils due to its low chloride index, the potential to develop SOP from polyhalite is receiving renewed attention.
ICP’s Technical Team has greatly advanced the test work done by the USBM and PCA. The Process Flow Diagram has been optimized to ensure production of high quality, low cost SOP. Recent mineral processing test work includes:
The Ochoa Process incorporates six unit operations, each of which is standard in the mineral and chemical processing industries. These six unit operations, explained below, have been optimized to make the process more robust and energy efficient.
Step 1 - Crushing
Raw polyhalite ore is processed through closed circuit crushing to produce a minus 10 mesh product. Ore is initially passed through roll crushers followed by cage paktors with a screen deck, producing 440 tons of crushed ore per hour. The crushing operation is performed wet, followed by leach tanks and belt filtration/washing to remove sodium chloride from the ore.
Roll crushers and cage paktors are used in most potash operations.
Step 2 - Calcination
The crushed ore is fed into multiple fluidized bed calciners, where it is dried and heated to 480 degrees Celsius.
This modifies the polyhalite crystal structure, making the potassium and magnesium sulfates soluble in hot water.
Calcination using fluidized beds is done throughout the industrial mineral industry.
Step 3 - Leaching
Calcined solids enter a two-stage counter-current leach circuit where potassium and magnesium sulfates are leached using water at atmospheric boiling.
The slurry is fed to hydro-cyclones where the underflow is fed to solid bowl centrifuges to separate leached polyhalite from the potassium- and magnesium-rich liquor. The solids consist primarily of anhydrite, which hydrate to gypsum on the dry-stack tailings pile. The leach liquor is fed to the crystallization circuit for SOP.
Counter-current leaching is a common unit operation used in many mineral industries.
Step 4 - Crystallization
The potassium and magnesium-rich brine enters the crystallization circuit in a leonite dissolver tank.
Leonite is a crystallized mineral produced in the later stages of the process, composed of potassium and magnesium sulfate, and brought forward in the system to increase the recovery of potassium sulfate.
Following the leonite dissolver, the liquor enters a Mechanical Vapor Recompression (MVR) evaporator to remove water, increasing the SOP concentration to near-saturation, after which it is passed into the SOP crystallizer.
An MVR crystallizer continues to evaporate water to the point that SOP crystallizes, resulting in the recovery of approximately 89% of the SOP in solution.
The next stage of crystallization utilizes Multiple Effect Evaporators (MEE) to produce the mineral leonite. This leonite is then recirculated back to the leonite dissover to achieve optimal potassium recovery.
MEE technology has been used in chemical processing industries since the late 1800s, and MVR technology has been used since the 1960s.
Step 5 - Drying
The SOP crystal products are fed into fluidized bed dryers prior to the final granulation/compaction step.
Fluidized bed dryers are commonly used in the mineral processing industry for their increased efficiency.
Step 6 – Granulation/Compaction
Three SOP products will be produced, including soluble SOP which requires only screening and crushing; standard-grade SOP which requires only screening; and granular SOP which is produced by crushing and pan granulation using a binder, followed by screening to produce an industry-standard granular product.