Unlike MOP, SOP is not a naturally occurring mineral and must be produced by chemical methods. The following paragraphs outline these production methods in more detail and the table below summarizes the primary and secondary sources of SOP including percentage of world capacity, process inputs, products produced, and cost per long ton of production.
|Process Method||World Capacity||Process Inputs||Products||Cost Per LT|
|MOP and Kieserite||25%||
The most common method of producing potassium sulphate is the Mannheim Process, which is the reaction of potassium chloride with sulphuric acid at high temperatures. The raw materials are poured into the centre of a muffle furnace heated to above 600ºC. Potassium sulphate is produced along with hydrochloric acid in a two-step reaction via potassium bisulphate. 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 sulphuric acid. This means that the final product costs about $500 per ton.
Potassium chloride can be reacted with various sulphate salts to form a double salt that can be decomposed to yield potassium sulphate. The most common raw material employed for this purpose is sodium sulphate. Sodium sulphate, either in the form of mirabilite (also known as Glauber's Salt) or sulphate brine, is treated with brine saturated with MOP to produce glaserite. The glaserite is separated and treated with fresh MOP brine, decomposing into potassium sulphate and sodium chloride. These methods of production are the second greatest source of global supply at 25% to 30%. The cost of these processes are approximately $350 per ton or higher.
Some operations produce SOP from the salt mixtures harvested from natural brines. Three companies produce potassium sulphate 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, north-west China). This method requires brines with high sulphate levels such as those found within these salt lakes. The sulphate is typically present in the harvest salts in the form of the double salt kainite, which is converted to Schoenite by leaching with sulphate 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 sulphate 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 and costs approximately $200 per ton.
The IC Potash processes to convert polyhalite into SOP will use unit operations common to the industrial minerals industry. Processing polyhalite to produce SOP and SOPM involves 7 main steps: primary crushing of the ore, wet grinding and halite salt removal, calcination, leaching, evaporative crystallization of SOP, evaporative crystallization of SOPM, drying, and granulation of the products. This method is expected to have an operating cost of approximately $162 per long tonne or $147 per short ton.