Ferrous sulphate: physical and chemical properties, production, application

Ferrous sulphate is a chemical compound that is extremely common in nature and is widely used in various spheres of economic activity. There are two- and three-valence modifications of this substance. The first variety, also called iron vitriol, is an inorganic binary non-volatile compound having the formula FeSO ₄ . Externally, this chemical compound is a transparent crystalline hydrate of a light greenish-blue color, having a high degree of hygroscopicity and solubility in the aqueous medium. In a vacuum, FeSO ₄ decomposes with high intensity, complete decay occurs at a temperature of about 700 ° C.

Divalent iron sulfate serves as a widely used reagent, crystallized from solutions at room temperature in the form of FeSO ₄ ∙ 7H ₂ O heptahydrate, which is a pale blue substance. With prolonged storage, it is weathered, turning into a white powdery substance, and in the open air it gradually turns yellow due to oxidative processes. The weathering of iron sulfate is explained by the fact that there is one molecule of outer-sphere water in its structure, which easily leaves the crystal lattice.

Trivalent anhydrous iron sulfate is a light yellow, paramagnetic, extremely hygroscopic crystalline substance of the monoclinic syngony. It is capable of forming orthorhombic and hexagonal structural modifications. Trivalent iron sulphate crystallizes well from various solutions in the form of a variety of hydrate compounds containing up to ten water molecules. When slowly heated, it turns into anhydrous salt, which decomposes well into hematite and sulfuric anhydrite at a temperature of about 650 ° C. Like many other salts of triply charged cations, ferrous sulphate forms alum, crystallizing in the form of pale violet octahedra. This substance is a good reducing agent for the Ag + ion, which has strong oxidizing properties. Trivalent iron sulphate, the hydrolysis of which is observed during boiling of the solution in which it is contained, exists in nature mainly in jarosite (mineral).

In industry, this substance is produced primarily as a by-product in metal processing plants from various pickling solutions used to remove scale from steel products. This substance can also be isolated by calcination of pyrites or marcasites with NaCl in air. Another way to synthesize this is by heating the iron oxide in the salts of sulfuric acid. In laboratory practice this compound is isolated from Fe (OH) ₂ .

Much curiosity is caused by the fact that iron sulphate was discovered on Mars in 2009 by the "Spirit" spacecraft, from which scientists concluded that strong oxidation processes occur on the surface of the planet. Due to the very low density of this substance, the rover is so deeply bogged down in its deposits that it even touched a part of the body of deep layers of Martian soil.

On Earth, iron sulphate, due to its ability to hydrolyze along with aluminum alum, is used as a flocculant in the process of purification of drinking water. Forming flakes of hydroxide, this chemical compound adsorbs many harmful impurities. Also this substance has found wide application in medicine, where it is used as a curative and preventive remedy for iron deficiency anemia.

In the agricultural sector, iron sulphate is used for chemical land reclamation, control of pests of cultivated plants, destruction of mosses, lichens, weeds and spores of parasitic fungi. In gardening, ferrous sulphate is used to feed fruit trees as a catalyst for the formation of chlorophyll. The most sensitive to the lack of this substance is apple, pear, plum and peach.

In industry, ferrous sulphate is widely used in the textile industry, where it serves as an important component of ink and various mineral paints. Also this substance is a good preservative of wood. Some so-called waste iron sulphate solutions are processed into insulating materials such as ferron and ferrigips, which are a mixture of hydrates of this compound with various excipients.