SOP Production.

Sulfate of potash (SOP) is not a naturally occurring mineral and is produced by chemical methods. Only a few of these processes exist, and the Ochoa process is projected to be one of the lowest cost methods worldwide.

Process Method World Capacity Process Inputs Products
Mannheim 60%
  • MOP
  • Sulfuric Acid
  • Energy
  • SOP
  • HCI
MOP & Kieserite 25%
  • MOP
  • Kieserite
  • Energy
  • SOP
  • Magnesium Chloride
Salt Lakes 15%
  • Lake Brines
  • Energy
  • SOP
  • Magnesium Chloride
  • NaCl
Ochoa -
  • Polyhalite
  • Water
  • Energy
  • SOP

 

Mannheim Process

The most common method of producing potassium sulfate is the Mannheim process, which is the reaction of potassium chloride with sulfuric acid at high temperatures. The raw materials are poured into the center of a muffle furnace heated to above 600ºC. Potassium sulfate is produced, along with hydrochloric acid, in a two-step reaction via potassium bisulfate. This method for creating SOP accounts for 50% to 60% of global supply. The Mannheim process is also the most expensive of the processing techniques due to the high input costs associated with purchasing MOP and sulfuric acid.

Potassium Chloride and Sulfate Salts

Potassium chloride can be reacted with various sulfate salts to form a double salt that can be decomposed to yield potassium sulfate. The most common raw material employed for this purpose is sodium sulfate. Sodium sulfate, either in the form of mirabilite (also known as Glauber's Salt) or sulfate brine, is treated with brine saturated with MOP to produce glaserite. The glaserite is separated and treated with fresh MOP brine, decomposing into potassium sulfate and sodium chloride. These methods of production are the second greatest source of global supply at 25% to 30%.

Naturally Occurring Brines

Some operations produce SOP from the salt mixtures harvested from natural brines. Three companies produce potassium sulfate in such a way on a large scale: GSL Minerals (Great Salt Lake, Utah), SQM (Salar de Atacama, northern Chile) and Luobupo Potash (Lop Nur, northwest China). This method requires brines with high sulfate levels such as those found within these salt lakes. The sulfate is typically present in the harvest salts in the form of the double salt kainite, which is converted to schoenite by leaching with sulfate brine. The leach process is hampered by high sodium chloride content in the harvest salts and the halite is first removed by flotation. After thickening, the schoenite is decomposed by simply adding hot water, whereupon the magnesium sulfate enters solution leaving SOP crystals. This process is currently the lowest cost method to make SOP. As lakes with sufficient brine mineral levels are rare, this method only accounts for 15% to 20% of global supply.

Ochoa Process

IC Potash Corp.'s Ochoa process will convert polyhalite into SOP using unit operations common to the industrial minerals industry. Processing polyhalite to produce SOP involves the following steps: crushing and washing, calcination, leaching, crystallization, and granulation.