Sulphur is a key raw material for the fertilizer industry and its single largest end use is in the manufacture of phosphate fertilizers in the form of sulphuric acid. Sulphur is also used in the production of carbon disulphide, sulphur dioxide and phosphorous pentasulphide; pulp and paper uses; and rubber vulcanizing. Agronomically, sulphur is an essential element in forming protein, vitamins, enzymes, and chlorophyll in plants, and nodule development in legumes. It has been called the “fourth nutrient” and in 2014 China was its main consumer, followed by the United States.
World sulphuric acid supply is of some 250 Mt H2SO4, and it is produced from sulphur, oxygen and water via the contact process. The major growth drivers for sulphuric acid are the global consumption of phosphoric acid, titanium dioxide, hydrofluoric acid, ammonium sulfate manufacture, and for uranium processing and metallurgical applications.
Crops have different sulphur sensitivities: alfalfa, canola, and clover are very responsive to sulphur, while cereal crops such as wheat and corn are less responsive.
Soil with less than one percent organic matter is prone to sulphur deficiencies; soil with greater than 5 % organic matter is usually unresponsive to sulphur. Sulphur deficiency is usually seen when the soil has less than 10 ppm of soluble sulphur, and it has a retarding effect on plant growth.
Elemental sulphur has at least 85% S, and there are different types of fertilizers also containing sulphur: ammonium sulphate has some 24% S, ammonium thiosulphate 26%, SSP 12%, magnesium sulphate 14%, potassium sulphate 18%, potassium thiosulphate 17%, sulphur coated urea 10% S. Elemental sulphur is also used as a pesticide or fungicide.
Sulphur is commonly incorporated to both granular compound fertilizers and bulk-blended fertilizers in the form of AS, SSP, or calcium phosphate. Most of the fertilizer sulphur applied to soils comes from sulphate-containing fertilizers. But the most concentrated sulphur carriers are the fertilizers containing elemental sulphur.
Many NPK formulations contain sulphur, but the amount has decreased with the trend towards higher analysis fertilizers.
Plant requirements for sulphur are equal to or exceed those for phosphorus. It is one of the major nutrients essential for plant growth, root nodule formation of legumes and plants protection mechanisms. Sulphur application rates in typical fertilization practices usually range from 5 to 20 pounds of sulphur per acre.
For the production of 1 tonne of 100% H2SO4 sulphuric acid, they are required 0.33 tonnes of sulphur (or 0.76 tonnes pyrites 48% S).
Most of the sulphur production comes from the processing of fossil fuels, sulphur mined in its elemental form has declined over the last decade to less than two percent of world production.
Iron pyrites (FeS2) have typically 40-53% S, pyrrhotite minerals (Fe6S7) 40%, gypsum (CaSO4.2H2O) 19%, and anhydrite (CaSO4) 24%.
Around 90% of the global sulphur production is by-product and only some 10% is elective. The largest producers are China and the United States, followed by Russia and Canada.
The sulphur trade is dominated by the imports to China.
In 2014 China imported some 10.2 million tonnes S and the main suppliers were West Asia, eastern Europa and Central Asia, Japan, Canada, and the United States.
The Chinese sulphur imports are mainly geared to the southwestern provinces of Yunnan, Sichuan, and Guizhou, mostly for usage in the compound phosphate fertilizer factories. The majority of the Chinese sulfacid manufacturers are small producers. The pyrite process accounted for some 80% in the mid-nineties, but its proportion has been decreasing steadily since then, being less than half in the early current decade.
Resources of elemental sulphur in evaporite and volcanic deposits and sulphur associated with natural gas, petroleum, tar sands, and metal sulfides amount to about five billion tonnes. The main sulphur reserves are located in Canada, the United States, Poland, Iraq, China, Saudi Arabia, Mexico, Spain, Italy, France, Japan, and others. The sulphur in gypsum and anhydrite is almost limitless, and some 600 billion tonnes of sulphur is contained in coal, oil shales, and shale rich in organic matter, tar sands, but low-cost methods have not been developed to recover sulphur from these sources. The domestic sulphur resource is about one-fifth of the world total. Sulphur supplies should be adequate for the foreseeable future.