Barium: Source and Preparation
The abundance of barium is 0.0425% in the Earth’s crust. The main commercial source of barium is baryte (also called barite, barytes or heavy spar, BaSO4) with deposits in numerous parts of the world.
Source of barium
An alternative commercial source, far less significant than baryte, is witherite (BaCO3). The main deposits can be found in England, Romania, and the former USSR. The baryte reserves are estimated between 0.7 and 2 billion tons. Baryte production has risen since the second half of the 1990s. China accounts for more than 50% of this output, followed by India, Morocco, the United States, Turkey, Iran, and Kazakhstan. The barium mineral, benitoite (BaTi(Si3O9)), occurs as a very rare blue fluorescent gemstone and is the official state gem of California.
Preparation of barium
The mined ore is washed, crushed, classified, and separated from quartz. If the quartz penetrates too deeply into the ore, or the iron, zinc, or lead content is unusually high, then froth flotation is utilized instead. The product is a 98% pure baryte (by mass); the purity should be no less than 95%, with a minimal content of iron and silicon dioxide. It is subsequently reduced by carbon to form barium sulfide.
The water-soluble barium sulfide forms the starting material for other compounds: reacting BaS with oxygen produces the sulfate, with nitric acid the nitrate, with carbon dioxide the carbonate, etc. The nitrate can be thermally decomposed to produce the oxide. Barium metal is produced by reduction with aluminum at 1100C. The first step is the production of the intermetallic compound BaAl4.
BaAl4 as an intermediate, which is then reacted with barium oxide to produce the metal. In this reaction not all barium is reduced though. The remaining barium oxide reacts with the formed aluminum oxide.
Barium vapor is condensed and packed into molds in an atmosphere of argon. This process is used commercially, producing ultrapure barium. Normally sold barium has a purity of about 99%, with the major impurities being strontium and calcium (up to 0.8% and 0.25%, respectively) while other impurities are less than 0.1%. A comparable reaction with silicon at 1200℃ produces barium and barium metasilicate. Electrolysis is not utilized as barium readily dissolves in molten halides and the product is rather impure.
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