Pyrites is the name of a group of minerals that are compounds of metals from the group of tin, nickel, iron, cobalt, platinum. Compounds can be both sulfur and arsenic, and antimony or selenium.
Pyrite firing suggests that the feedstock has a light color, metallic luster, hardness from 3 to 7. Iron or sulfur pyrite (formula FeS2), it is pyrite, is a valuable technical raw material from which sulfur dioxide is obtained (production in chambers). In appearance, the mineral represents a mass of small crystals of the correct form of a yellowish-gray color with a hardness of 6-6.5. The composition of pure pyrites includes about 47 percent iron and about 53 percent sulfur.
Pyrite firing is accompanied by a series of chemical reactions, the first of which decomposes the mineral into iron sulfide and sulfur in a vapor state (at a temperature of about 500 ° C). Then the sulfur vapor burns, giving sulfur dioxide, and iron sulfide gives an oxide or nitrous oxide. Moreover, the sulfide does not burn out completely, forming a "cinder", which may include fayalite and other substances, depending on the impurities in the feedstock.
Calcined pyrite may produce a certain amount of SO3 mixed with SO2 in the gas phase. This substance acts on the equipment in a corrosive way, therefore, to reduce SO3, the gas temperature at the outlet of the furnace equipment should be about 850 ° C, and then quickly drop to 400 ° C.
Sulfur pyrite burning is practiced in many countries since this element is among the widespread. In Russia, this mineral is mined at the Soymenskaya dacha, the Kalitvinsky deposit, near Kushva, at the Theological factories, in the Caucasus, in the Ryazan and Smolensk regions, and in other places. Abroad Spanish deposits are especially famous (especially Aguas Tenidas, where the material does not contain copper, but has a high sulfur content), in addition, exploitation is carried out in the USA, France, Norway, Sweden. Arsenic species of this substance are often mixed with pyrites in nature, which gives a very harmful impurity in the production in chambers. Therefore, manufacturers are trying to use pure raw materials. For example, Russian factories in St. Petersburg operate on Swedish pyrites.
Iron pyrite (as well as sulfur pyrite ) is fired in furnaces, where raw materials are fed through a screw or nozzle. Then it mixes with the mass of solid material that is already in the unit (in a fluidized bed on the grate, under which air is supplied from below), after which chemical reactions occur that produce gas (is discharged) and cinder (is poured partially through special pipes). Excessive heat is also removed from the oven using water cooling elements.
Pyrite firing will be successful if the contact surface of the raw material with air is large enough. Therefore, the mineral is often processed in a pulverized state (in appropriate furnaces), when the particle size is so small that oxygen freely penetrates into the mass of the substance. In addition, the temperature regime is important, because minerals of this class are often sintered at temperatures above 900 ° C. To solve this problem, processing in the form of a dust-air mixture is also used, which allows burning of raw materials at temperatures up to 1000 ° C, which increases production efficiency.