Barium Sulfate

Barium sulfate, $$BaSO_4$$, is a white crystalline solid that is insoluble in water (solubility product $$K_{sp} = 1.1 \times 10^{-10}$$). The main commercial source of barium sulfate is the mineral baryte, which is normally highly impure. Baryte is reduced by heating with coke to barium sulfide, $$BaS$$:

$BaSO_4 + 4 C \rightarrow BaS + 4 CO$

Barium sulfide is soluble in water can be easily converted to oxide, carbonate, and the halides. In order to produce highly pure barium sulfate, barium sulfide or barium chloride is treated with sulfuric acid:

$BaS + H_2SO_4 \rightarrow BaSO_4 + H_2S$

$BaCl_2 + H_2SO_4 \rightarrow BaSO_4 + 2 HCl$

Barium sulfate belongs to the most insoluble sulfates. Its low solubility results in many important applications, such as contrast agent in x-ray imaging, detection of $$Ba^{2+}$$ ions, or the detoxification of barium salt solutions.

Most of the synthetic barium sulfate is used as a white pigment (together with $$TiO_2$$ or $$ZnS$$) for paints. One particular inorganic pigment called lithopone is a combination of barium sulfate and zinc sulfide.