Carbonate of barium
Barium carbonate BaCO3 occurs naturally in the form of witherite, mainly in some lead luster deposits in northwestern England. Usually, witherite crystallizes in the rhombic system and is isomorphic to aragonite and strontianite (above 811 ° C, the hexagonal modification is stable, and above 982 ° C, the cubic modification). A white precipitate of barium carbonate precipitates from aqueous solutions with the simultaneous presence of Ba2 + and CO32- ions. The initial product for the technical preparation of BaCO3 is heavy spar BaSO4, which, when heated to 600-800 ºC in the presence of coal, is reduced to barium sulfide:
BaSO4 + 2С = ВаS + 2СО2.
Carbon dioxide is passed into the aqueous sulfide solution, resulting in the formation of barium carbonate according to the reaction:
ВаS + СO2 + Н2O = ВаСО3 + Н2S.
You can also heat finely ground heavy spar with a concentrated solution of potassium carbonate at increased pressure; the reaction occurs:
ВаSO4 + К2СO3 = ВаСO3 + К2SO4.
Barium carbonate removes CO2 at a much higher temperature than carbonates of other alkaline earth metals; only at 1400 ° C the CO2 pressure over barium carbonate reaches atmospheric. Since barium carbonate begins to bake even below this temperature and, as a result, loses its porosity, it is very difficult to completely decompose it only by heating.
Barium carbonate, in addition to obtaining other barium compounds from it, they are used for the manufacture of special types of glasses (low-melting, heavy and characterized by a high refractive index), as well as in ceramic production. To obtain BaO, an important starting material for the preparation of BaO2, natural witherite is especially suitable, which is calcined at an angle, while for other purposes artificially prepared barium carbonate is preferred as the cheaper one.
Barium carbonate is slightly more soluble in water than calcium and strontium carbonates. Its saturated aqueous solution has an alkaline reaction as a result of hydrolysis. With salts, solutions of which, due to hydrolysis, have a strongly acidic reaction [aluminum, iron (III) or chromium salts], barium carbonate suspended in water reacts, resulting in the release of CO2 and precipitation of the corresponding metal hydroxides. This is sometimes used in analytical chemistry to separate trivalent metals of the ammonium sulfide group from divalent ones. The solubility of barium carbonate, like the solubility of other carbonates of the alkaline earth group, slightly increases in the presence of ammonium salts. Quite a significant amount of it dissolves in water,