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Barium silicate is an insoluble, orthorhombic mineral with a melting point of 1604 °C. It is used in the manufacture of optical glass and ceramics, and is also a useful flux for ceramic applications. It is a colorless, brittle, odorless, water-soluble salt with a high refractive index, which exhibits low optical attenuation. It is very soluble in hydrochloric acid, but very insoluble in cold and hot water. It is extremely poisonous when ingested, and is irritant if it comes into contact with the skin.
In the present invention, there is disclosed a commercially feasible process for producing barium silicate containing water-soluble barium values from barite in rotary kilns without contamination of the barium silicate product with sintering or fusion, whereby a significant portion of the water-insoluble material is readily leached to produce barium hydroxide. This process uses a slurry of finely divided silica, diatomaceous earth or recycled barium metasilicate leach residue as a starting source of silicon dioxide for the decomposition of barite with which it is combined to form the barium silicate.
The barium silicate is fed continuously into a calcining zone maintained at temperatures from about 1400 to about 1500 °C in the presence of a critical controlled slightly reducing atmosphere, whereby only small amounts, preferably less than 2% of barium sulfide are formed in the resulting barium silicate reaction product.
This reducing atmosphere is created by the combustion of natural gas at a temperature higher than the normal melting point of barium carbonate. The control of the atmosphere composition is important because an excess of reducing gases (i.e. H and CO) causes some melting to occur while a deficiency of gases (i.e. O2) decreases the reaction rate.