The first recorded report of a barium mineral is from the early seventeenth century. Alchemist Vincenzo Casciarolo of Bologna, Italy, found some stones that glowed in the dark after heating and exposure to sunlight. This mineral, the "Bologna stone" now called barite (right), was dense and high in sulfur content, which properties might make it suitable for transmuting into gold. Several men therefore investigated the mineral and its phosphorescence, sometimes secretly, over the course of the next hundred years.
Barite is now known to be barium sulfate. Experiments on barite continued into the eighteenth century, the early age of chemistry. Swedish chemist C. W. Scheele in 1774 reduced barite to its oxide (barium oxide). This white alkaline powder was widely suspected to contain a new element. The metal itself, barium, was produced by Humphry Davy in 1808 by means of electrolysis, the same tool he used to isolate several other elements.
Mining and Production
Barium is obtained primarily from the mineral barite, which is widely distributed. Nine million tonnes of barite were mined in 2014, mainly from China (44%) and India (17%). As the most common use of barium is barite itself, most of the mineral is simply crushed, ground, and purified. Barium the metal is produced by converting barite to the oxide and then treating with aluminum or silicon at high temperature.
Properties and Uses
The word barite comes from the Greek for "heavy", and barium sulfate is indeed dense. The metal itself is only moderately dense, however. Barium is quite reactive, combining with oxygen or water. It must therefore be stored under mineral oil. Barium is soft, silver-white, and electrically conductive.
Barite or barium sulfate is dense, insoluble, and fairly inert as well as nonmagnetic. It is used worldwide as drilling mud in the creation of oil and gas wells. It can also be the aggregate in heavy concrete or as a paint filler. Barite is also familiar for its use in contrast x-rays (see below).
The metal barium reacts with most gases. Consequently, a bit of barium in a cathode ray tube (CRT) will take up stray atoms in the vacuum. Barium carbonate may also be found lining CRTs, where it blocks x-rays from leaking. As CRTs fall out of use, this need for barium fades away. Incidental amounts of barium are used as an alloy in bearings, spark plugs, and various other applications.
Barium burns green. Various shades of green are produced by barium compounds in fireworks.
Health and Medicine
Barium sulfate is familiar to most people as the edible or enema paste introduced before an intestinal x-ray. Barium sulfate is nonreactive and safe; its density makes the filled intestines stand out on an x-ray or cat scan.
Barium itself is a heavy metal, but it is always encountered as a compound. The water-soluble compounds are poisonous, but the others are not.