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Sr
Strontium
by Jonathan Buhalis

History

In the late 18th century, the element barium had recently been identified in minerals such as witherite. Around 1787, a mineral from Strontian in Scotland was brought to Edinburgh and thought to be a kind of witherite. But, the physician Dr. Adair Crawford and his assistant William Cruickshank analyzed this new mineral and found distinct differences between it and barium compounds. Crawford concluded "it is probable that the Scotch mineral is a new species of earth".

A few years later, Scottish chemist Thomas Charles Hope confirmed these differences. The mineral named strontianite dissolved differently in water from barium, it made different crystals, and it burned red in a flame rather than barium green. It fell to the great English chemist Sir Humphry Davy to isolate the metal itself using his tool of electrolysis. The year was 1808, and by then all new metals gained the suffix -ium. Thus, Davy named this new metal strontium.

Strontium was in high demand for about twenty-five years starting in 1870. Germany's sugar beet industry worked out a method of extracting sugar from the beet molasses by using strontium hydroxide. The strontium was precipitated from the mixture and recycled, but inevitable losses created an ongoing need for strontium minerals. Well before World War I, however, the price of sugar fell to where simpler processing techniques had to take over.

Mining and Production

celestite mineralThe most significant strontium mineral is celestite, which is strontium sulfate. Celestite and other such minerals are mined on a small scale. About 318,000 tonnes of strontium equivalent ore was extracted in 2014, with the top producers being Spain and China (52% and 31%, respectively).

For commercial purposes, strontium carbonate is more useful than the sulfate. Celestite ore is therefore treated with sodium carbonate. Alternatively, it is roasted and dissolved in water into which carbon dioxide is therefore injected. The result of either process is the desired carbonate.

Properties and Uses

As a metal lying between calcium and barium on the periodic table, strontium has properties similar to both. It is a soft, silvery metal that tarnishes quickly in air. It reacts vigorously with water and combines readily with the nonmetals to form a variety of salts and other minerals.

Strontium itself has few commercial uses. It is occasionally added to aluminum alloys.

strontium red fireworksStrontium iron compounds are used to make strong ceramic magnets. Strontium titanate is a clear crystal used in optics to spread white light into a spectrum. Strontium carbonate burns deep red in fireworks (right).

The largest use of strontium, however, is in the front glass of cathode ray tubes. A CRT in action generates x-rays, and strontium oxide in the glass blocks this without compromising the transparency of the tube. This demand has been the major application of strontium for several decades, but CRTs are being replaced by flat-panel displays. History therefore repeats itself as strontium goes out of fashion.

Biological

As strontium behaves chemically very much like calcium, it finds its way into the bones of the human body. This has been studied extensively and seems to present no health risk. Small amounts of strontium in the bones may, in fact, be beneficial. The drug strontium ranelate is used to treat osteoporosis in many countries, though not in the United States.

One strontium-related danger concerns its isotope strontium-90. Strontium-90, written 90Sr, is a form created by nuclear fission, such as the above-ground nuclear tests of the 1950s or the 1986 Chernobyl disaster. This radioactive isotope also finds its way into bones, where it can cause cancer. The half-life of 90Sr is 29 years.

Another radioactive strontium isotope, strontium-89, is used medically because it is incorporated into bone. Strontium chloride containing 89Sr is injected into patients with bone cancer, and the radioactive strontium is preferentially taken up by sites of fast-growing bone, which are the cancer sites. The radiation helps manage pain.

(c) 2007-2016 Virtual Wall Street
Content by Jonathan Buhalis
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