Barium

Barium is a chemical element on the periodic table whose symbol is Ba and its atomic number is 56. An alkaline earth metal, barium is the 18th most common element, occupying about 2,000 parts of the Earth's crust. Its atomic mass is 137,327. Its melting point is 725 °C, its boiling point is 1,640 °C, and its relative density is 3.5. Its main ore is barite.

Chemical properties

Reacts with copper and oxidizes rapidly in water. The element is so reactive that it does not exist in a free state in nature, although it also occurs in the form of iron or sulfur that is not soluble in water. Some of its compounds are considered diamonds.

Main features

A sample of pure barium preserved in mineral oil.

Barium is a metallic element that is chemically similar to calcium, but more reactive. This metal oxidizes very easily when exposed to air and is highly reactive with water or alcohol, which produces hydrogen gas. Burning with air or oxygen, it produces not only barium oxide (BaO), but also peroxide. Compounds of this heavy element are noted for their high specific gravity. This is the case of the most common barium mineral, barite (barium sulfate, BaSO₄), with a high density (4.5 g/cm³).

Physical properties

Boiling point: 1869.85 °C Melting Point: 726.85 °C Density: 3.62 g/cm^-3 Silver colour. Smell: odorless. Appearance: solid, brittle and soft. Any barium salt, exposed to the fire of the Bunsen burner (the most suitable for this experiment), colors the flame an intense green, even more than that of copper. It is about the third lowest quantum jump (precisely the fire coloring phenomenon) behind cesium and rubidium.

Applications

• The barium is used in pyrotechnia, like many other elements of the A groups.
• The metal bar has few practical applications, although it is sometimes used to coat electric conductors on electronic devices and on automotive systems.
• Barium nitrate is used in fireworks, and barium carbonate in rat poisons (through intake).
• Barium sulfate (BaSO)₄) is used in conjunction with lignin and black smoke as an expander for the manufacture of negative electrodes of lead-acid batteries, also used as filling material for rubber, paint and linoleum products.
• Also known as Barita or Baritina, due to its high density, is used as drilling mud in oil wells.
• A form of barium sulfate, being opaque to the X-rays, is used as a coating in the X-ray rooms or also diluted in water as a radiological contrast to examine X-ray structures, especially in the gastrointestinal system.
• Barium oxide (BaO) is part of the high-quality mineral glass lenses used, for example, in optical instruments.
• Barium titanium is used in the manufacture of ceramic microphones used in the form of piezoelectric glass.
• The hexagonal ferrite of barium (BaFe₁₂O₁₉) is used in nanostructured composite materials to increase the magnetic properties of the same, since it makes the coercive field of the nanocomposite grow.

History

Sir Humphry Davy, who first isolated the barium

Alchemists in the Middle Ages already knew some barium minerals. Pebbles of the mineral barite, found in Bologna, Italy, used to be known as the Bologna stones. Alchemists were attracted to them because after exposure to light, they glow for years. The phosphorescent properties of baryte heated with organic compounds were described by V. Casciorolus in 1602.

Carl Scheele identified baryte (barium sulfate) as containing a new element in 1774, but he could not isolate barium, only barium oxide. Johan Gottlieb Gahn also isolated barium oxide two years later in similar studies. The oxidized barium was originally called barota, after Guyton de Morveau, a name that was changed by Antoine Lavoisier to the current baryta, which derives from the Greek barys which means "heavy", in attention to the great density of many of its compounds. Also in the 18th century, English mineralogist William Withering observed a heavy mineral in the Cumberland lead mines, now known as You know it was a Witerite. Barium was first isolated by electrolysis of molten barium salts in 1808, by Sir Humphry Davy in England.

Davy, by analogy with calcium named barium after barite, with the final "-ium" signifying a metallic element. Robert Bunsen and Augustus Matthiessen obtained pure barium by electrolysis from a molten mixture of barium chloride and ammonium chloride.

The production of pure oxygen in the Brin process was a large-scale application of barium peroxide in the 1880s, before being superseded by electrolysis and fractional distillation of liquefied air in the early 1900s. In this process barium oxide reacts at 700 C with air to form barium peroxide, which decomposes above 500 C releasing oxygen:

2 BaO + O₂ 2 2 Bao₂

In 1908, barium sulfate was first applied as a radiological contrast agent in X-ray images of the digestive system.

Abundance and production

The abundance of barium is 0.0425% in the earth's crust and 13 μg/L in seawater. The main commercial source of barium is barite (also called barite or heavy spar), a barium sulfate mineral, with deposits in many parts of the world. Another commercial source, much less important than barite, is witherite, barium carbonate. The main deposits are in Great Britain, Romania and the former USSR.

Barita. From left to right: look, chart showing production trends over time, and map showing the contributions of the most important producer countries in 2010.

Reserves of baryte are estimated at between 0.7 and 2 billion tons. The maximum world production was 8.3 million tons in 1981, but only 7–8% was used for barium metal. Baryte production has increased since the second part of the 1990s, with 5.6 million tons in 1996 to 7.6 in 2005 and 7.8 in 2011. China accounts for more than 50% of this production, followed by India (14% in 2011), Morocco (8.3%), USA (8.2%), Turkey (2.5%), Iran and Kazakhstan (2.6% each).

The extracted mineral is washed, crushed, classified and separated from the quartz. If the quartz penetrates too deeply into the ore, or the iron, zinc, or lead content is abnormally high, then the froth flotation process is used.. The product is a 98% (by mass) pure barite; the purity must not be less than 95%, with a minimum content of iron and silicon dioxide. It is then reduced with carbon to barium sulphide:

BaSO₄ + 2 C → BaS + 2 CO₂

Water-soluble barium sulfide is the starting point for other compounds: treatment of BaS with oxygen produces the sulfate, with nitric acid the nitrate, with aqueous carbon dioxide the carbonate, and so on. Nitrate it can be thermally decomposed to produce the oxide. The metallic barium is produced by reduction with aluminum at 1100 °C. The intermetallic compound BaAl₄ is produced first:

3 BaO + 14 Al → 3 BaAl₄ + Al₂O₃

BaAl₄ is an intermediate product that reacts with barium oxide to produce the metal. Note that not all of the barium is reduced.

8 BaO + BaAl₄ → Ba↓ + 7 BaAl₂O₄

The remaining barium oxide reacts with the aluminum oxide formed:

BaO + Al₂O₃ → BaAl₂O₄

and the general reaction is

4 BaO + 2 Al → 3 Ba↓ + BaAl₂O₄

Barium vapor is condensed and packed into molds under an argon atmosphere. This method is used commercially and produces ultrapure barium. { {rp|3}} Commonly sold barium is approximately 99% pure. %, with the 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 degrees Celsius (2,192.0 °F) produces barium and barium metasilicate. Electrolysis is not used because barium dissolves easily in molten halides and the product is quite impure.

Natrolite benite crystals. The mineral bears the name of the San Benito River in San Benito County (California, USA), where it was first found.

Like a precious stone

The mineral of barium, benitoite (barium titanium silicate), occurs as a very rare blue fluorescent gemstone and is the official state gem of California.

Barium in seawater

Barium exists in seawater as the Ba²⁺ ion with an average oceanic concentration of 109 nmol/kg. Barium also exists in the ocean as BaSO₄, or barite. Barium has a profile similar to that of a nutrient with a residence time of 10,000 years.

Barium shows a relatively constant concentration in upper-ocean seawater, except for regions of high river inflow and regions with strong upwelling. There is little depletion of barium concentrations in the ocean isotopic values of barium show basin-scale equilibria rather than local or short-term processes.