SOP (Potassium Sulphate, (K2SO4),) is an essential fertiliser for high-value, chloride sensitive crops such as fruit, vegetables, avocados, coffee beans, grapes, tree nuts, cocoa, anything grown under glass and in arid and acidic soils. It provides plants with the essential nutrients of potassium (K) and sulphur (S). It can also be known as Potassium Sulphate and has the chemical formula (K2SO4),.
It is predominantly used as a fertiliser for global food production and is often considered the fourth macro nutrient alongside potassium, nitrogen (N) and phosphorus (P).
SOP is a mineral fertiliser and a valuable tool in crop management by positively influencing crop yield and quality. SOP nutrients play an important role in the development of proteins, enzymes and vitamins, as well as improving plant photosynthesis and growth.
It improves nutritional value, taste and appearance (size, colour, and scent), fruit’s resistance to deterioration during transport and storage and its suitability for industrial processing. SOP can improve the uptake of phosphorus, iron, and other micronutrients and helps the plant to be more resistant to drought, frost, insects and many diseases. In sandy soils it can also reduce leaching of cations such as calcium and potassium.
SOP has little to no chloride and a low Salt Index (SI) when compared to alternatives, such as muriate of Potash (MOP) which contains 45% chloride, making it particularly important in semiarid regions with salinity problems and for those crops sensitive to chloride such as;
In these crops, SOP cannot be substituted with MOP, making demand inelastic.
Muriate of Potash (Potassium Chloride) is a cheaper, more abundant source of potash, BUT it contains almost 50% chloride which is detrimental to chloride-sensitive crops and arid soils. It also contains no sulphur.
There are three principle methods of producing SOP:
About 35% of the world’s SOP production is produced from natural brines via solar evaporation. It is a relatively low-cost primary production method, although there are a limited number of operations where geological endowment, logistics and environmental factors align. The weighted-average cost of production for primary producers is approximately US$260/t.
Natural brines, such as that being explored for by Trigg Mining, are the only source of SOP to be certified as organic. For organic certification SOP must come from natural sources with little or no processing, such as solar evaporation.
Potassium chloride (MOP) can be reacted with various sulphate salts, such as sodium sulphate, to produce a double salt and then decomposed to yield potassium sulphate (SOP). Around 20% of the global SOP production comes from this process.
With little over one half of the world’s SOP requirements produced from brines (35%) and reacted salts (20%) a synthetic process is required to meet total demand. The process to synthetically manufacture SOP is known as the Mannheim process. In this method, potassium chloride (MOP or KCl), is reacted with sulphuric acid (H2SO4) by heating in a furnace at temperatures of approximately 800oC to produce SOP and hydrochloric acid (HCl). A secondary process is then required to produce a soluble grade product.
The weighted average cost of production for secondary producers in 2017 was approximately US$320/t and is highly dependent on the input costs of MOP and sulphuric acid.