Barium
The most common naturally occurring minerals of barium are barite (barium sulfate, BaSO4) and witherite (barium carbonate, BaCO3), both being insoluble in water. Barium's name originates from the alchemical derivative "baryta", which itself comes from Greek βαρύς (barys), meaning "heavy." Barium was identified as a new element in 1774, but not reduced to a metal until 1808, shortly after electrolytic isolation techniques became available.
Barium has only a few industrial applications. The metal has been historically used to scavenge air in vacuum tubes. It is a component of YBCO (high-temperature superconductors) and electroceramics, and is added to steel and cast iron to reduce the size of carbon grains within the microstructure of the metal. Barium compounds are added to fireworks to impart a green color. Barium sulfate is used as an insoluble heavy additive to oil well drilling fluid, and in purer form, as X-ray radiocontrast agents for imaging the human gastrointestinal tract. Soluble barium compounds are poisonous due to release of the soluble barium ion, and therefore have been used as rodenticides.
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.
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 1,100 °C (2,010 °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 1,200 °C (2,190 °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.
Gemstone
A barium-containing mineral benitoite (barium titanium silicate) occurs as a very rare blue fluorescent gemstone, and is the official state gem of California.
| Symbol | Ba | |
| Atomic Number | 56 | |
| Atomic Weight | 137.327 | |
| Oxidation States | +2 | |
| Electronegativity, Pauling | 0.89 | |
| State at RT | solid | |
| Melting Point, K | 1002 | |
| Boiling Point, K | 1910 |
Appearance and Characteristics
Harmful effects:
Barium compounds that are water or acid soluble are highly poisonous. Barium powder can ignite spontaneously in air.
Barium sulfate, used in x-ray imaging, is highly insoluble in water, and is therefore nontoxic and completely removed from the digestive tract.
Characteristics:
- Barium is a metallic element chemically resembling calcium but more reactive. It is a soft, silvery metal and when cut it quickly turns a black color due to the formation of barium oxide, (BaO).
- It is also highly reactive with water or alcohol.
- When present in compounds barium exists usually in the Ba2+, divalent state.
- Barium dissolves in most aqueous acids except sulfuric acid, due to the formation of an insoluble protective layer of barium sulfate.
- Barium is most commonly found as the mineral barite (BaSO4) and witherite (BaCO3)
Uses of Barium
- Barium is used as a “flashed getter” in vacuum tubes to remove the last traces of gases.
- Barium is an important element in yttrium barium copper oxide (YBCO) superconductors.
- An alloy of barium with nickel is used in sparkplug wire.
- Barium sulfate (barite) is used to increase the contrast in x-ray imaging of the digestive system.
Barium is used in medicine to detect abnormalities in the digestive system.
The reaction between ammonium thiocyanate and barium hydroxide octahydrate is endothermic. As a result, the temperature will drop quickly. This causes the beaker to freeze to the wooden board.
