Barium Compounds - Occurrence and Production

Occurrence and Production

The abundance of barium is 0.0425% in the Earth's crust and 13 µg/L in sea water. The main commercial source of barium is barite (also called barytes or heavy spar), which is a barium sulfate mineral. Its deposits are spread all over the world. The only other commercial source is far less important than barite; it is witherite, a barium carbonate mineral. Its main deposits are located in England, Romania, and the former USSR.

Barite, left to right: appearance, graph showing trends in production over time, and the map showing shares of the most important producer countries in 2010.

The barite reserves are estimated between 0.7 and 2 billion tonnes. The maximum production was achieved in 1981, at 8.3 million tonnes, and only 7–8% of it was used to make barium or its compounds. The barite production has again risen since the second half of the 1990s: from 5.6 million tonnes in 1996 to 7.6 in 2005 and 7.8 in 2011. China accounts for more than 50% of this output, followed by India (14% in 2011), Morocco (8.3%), US (8.2%), Turkey (2.5%), Iran and Kazakhstan (2.6% each).

The mined ore is washed, crushed, classified, and separated from quartz. If the quartz penetrates too deep into the ore, or the iron, zinc, or lead content is abnormally high, then froth flotation methods are applied. The product is a 98% pure barite (by mass); the purity should be no less than 95%, with a minimal content of iron and silicon dioxide. It is then reduced by carbon to barium sulfide:

BaSO₄ + 2 C → BaS + 2 CO₂↑

The water-soluble barium sulfide is the starting point for other compounds: dissolved BaS upon reaction with oxygen gives the hydroxide, with nitric acid the nitrate, with carbon dioxide the carbonate, and so on. The nitrate can be thermally decomposed to yield the oxide. Barium metal is produced by reduction with aluminium at 1100 °C (~2000 °F). The intermetallic compound BaAl₄ is produced first:

3 BaO + 14 Al → 3 BaAl₄ + Al₂O₃

It is an intermediate, which reacts with barium oxide to give the metal. Note that not all barium is reduced.

8 BaO + BaAl₄ → Ba↑ + 7 BaAl₂O₄

The remaining barium oxide reacts with the formed aluminium oxide:

BaO + Al₂O₃ → BaAl₂O₄

and the overall reaction is

4 BaO + 2 Al → 3 Ba↑ + BaAl₂O₄

The thus produced barium vapor is collected at the cooler part of the apparatus and then packed into molds under argon atmosphere. This method is used commercially and can yield ultrapure barium. Commonly sold barium is about 99% pure, with main impurities being strontium and calcium (up to 0.8% and 0.25%) and other contaminants contributing less than 0.1%.

A similar reaction with silicon at 1200 °C (~2200 °F) yields barium and barium metasilicate. Electrolysis is not used because barium readily dissolves in molten halides and is rather impure when isolated with this method.