Strontium: From Sugar Beet To Dirty Bombs

April 26, 2011

This versatile metal may provide investors with unrealized opportunities.

 

One of the first major commercial uses of strontium (in the form of strontium hydroxide (Sr(OH)2) was to extract sugar from sugar beet. And, indeed, up until the early part of the last century, more than 100,000 tonnes of the metal's hydroxide was used each year for this purpose.

But strontium's purpose has recently expanded. Having more recently been vital to the production of old-fashioned, cathode ray tube (CRT) color TV screens, with the growing dominance of flat panels, its two main uses in the U.S. are now in the manufacture of glass and ferrite ceramic magnets, and pyrotechnics and signals. It is still used extensively, though less so, in China (a major strontium producer) in the production of CRT TVs.

 

Strontium - End Uses 2010

Source: U.S. Geological Survey (USGS)

 

And then there is the famous radioactive isotope of strontium—strontium-90 (90Sr), probably the only context in which most people have heard of the metal. While widely used as such an isotope both in medicine and industry (see Radioisotopes: A Market In Decay?), it is probably better known as the pernicious byproduct both of nuclear tests (fallout) and nuclear fusion (radioactive waste and spent fuel rods).

Strontium also plays a significant role in a number of films—not least, in 1954, as the material responsible for bringing Godzilla back to life!

More recently, however, fears have been expressed about its potential use as a source of radioactivity in a dirty bomb. It appears that, in the erstwhile Soviet Union, the isotope was used extensively in radioisotope thermoelectric generators, many of which now remain unaccounted for. One can only be somewhat relieved at the difficulty of effectively constructing such a weapon using the stuff.

 

Overwhelming Abundance

Perhaps surprisingly, strontium is quite abundant in the Earth's crust, comprising some 0.04 percent thereof, and standing at No. 15 in the ranking of all the elements.

While the metal is present in a number of different minerals, it is only economically viable to extract strontium from two minerals bearing the element: celestite (strontium sulfate—SrSO4) and strontianite (strontium carbonate—SrCO3).

As, according to the USGS, the global demand for strontium has dropped significantly since its peak in 1997, a number of countries have radically reduced production; some, like Turkey, have ceased production altogether. Having produced as much as 18,000 tonnes of strontium minerals as recently as 2005, it stopped production after 2008. And going forward, Spain's production is expected to diminish significantly after the closure, in early 2010, of Bruno SA's Montevive mine in Granada, a major celestite mine and refinery. (The family had managed the operation since 1956.)

 

Celestite - World Production (Tonnes)

Source: USGS

 

Also according to the USGS, the only country's celestite industry projected to grow over the next several years is that of Iran—a major supplier to China.

Although, in terms of volume, China is the world's largest producer of strontium minerals—in contrast with other producing countries—the quality of its celestite is lower and its reserves smaller.

Of the handful of producers in China, the most important is Nanjing Welbow Metals Co., Ltd. (RSM) founded in 1990 and based in Nanjing.

 

Practical Application

Although not currently vital, several of the metal's properties make it difficult to replace in a number of applications. And some others may lead to its increased use in other, less familiar, applications.

Because of its extreme reactivity both to oxygen and water, strontium is not found in nature in its metallic form. And in order to be stored safely, the metal must be kept under a hydrocarbon liquid—away from water or air—to prevent oxidation.

As a pure metal, strontium has few practical uses. One, however, is as an additive to aluminum to improve its machinability. Another is as an alloy in certain aluminum and magnesium alloys. According to Metallurg (a producer of "strontium aluminium master alloys"), "As an additive to Al-Si casting alloys, strontium improves strength, enhances mechanical properties and disperses porosity as it modifies the eutectic structure. The modified alloy displays a finer, less needle-like microstructure."

In this context, BMW has been a noted user of strontium metal, including it in magnesium-aluminum-strontium alloys (AJ-alloys) for the crankcases in its inline six-cylinder engines launched in 2004. Such crankcases contribute to weight savings in the front end of automobiles.

Research work done at the University of Saarland as long ago as 2009 demonstrated that: "... Merely adding a few parts per million of strontium completely changes the three-dimensional silicon network and ultimately leads to a significant increase in the strength of the engine block."

That said, it's the compound form of strontium that is most commonly used.

 

Strontium carbonate: Hard ferrite magnets are, typically, manufactured using either barium or strontium carbonates. Strontium ferrite magnets, in addition to being cheap, also have a number of useful properties, including:

 

  • Low density
  • Resistance to corrosion
  • Good resistance to demagnetization
  • Effective even at high temperatures

 

Ferrite magnets are commonly used in such applications as:

 

  • Crafts
  • Holding-magnet systems
  • Loudspeakers
  • Magnetic couplings
  • Magnetic therapy
  • Motors (e.g., windshield wipers)
  • Novelties
  • Sensors
  • Toys

 

The metal's carbonate can also be used (as a "getter") to remove unwanted lead when zinc is produced electrolytically.

Strontium oxide: Together with strontium carbonate, these two are used as substitutes for barium and lead in ceramic glazes. In addition, strontium oxide is used to impart both strength and hardness to glass. And because of the ability of strontium glass to absorb ultraviolet and X-rays, it has commonly been used in CRTs.

Strontium nitrate: Together with the metal's carbonate, chloride, oxalate, peroxide and sulfate, strontium nitrate can be, and is, used to provide a vibrant red color in pyrotechnics. In the civilian world they are used, for example, in fireworks and road flares. In the military world, they are used in such things as flares and tracer ammunition.

Strontium phosphate: Fluorescent lights employ phosphors using strontium phosphate (Sr3(PO4)2), for example, strontium magnesium phosphate and calcium strontium phosphate.

Strontium chromate: According to ChemicalLand21.com, strontium chromate "is used as rust- and corrosion-resistant pigment in paints, varnishes and oil colors. It is used in water based wash primers, metal conditioners or in aluminium flake coatings, either alone or in combination with basic zinc chromate (solvent and vinyl based wash primer). Strontium chromate has also been used as an additive to control the sulfate content of solutions in electrochemical processes." Strontium chromate is, however, now classified as a carcinogen in humans.

 

Other Forms, Other Uses

Strontium is used in several other applications in other forms. One in particular may turn out to be of interest in the future.

Two of the isotopes of strontium—strontium-89 (89Sr) and strontium-90 (90Sr)—have been used in the treatment of certain types of cancer. Separately, strontium-90 is used in thickness gauges and thermoelectric generators. These last have been used in space applications, navigation beacons and remote weather stations.

Strontium ranelate has been successfully been used in treatment of osteoporosis to reduce risk of bone fracture patients suffering from the disease.

Finally, strontium titanate (SrTiO3) can be a very good substrate for semiconductors. As distributor Sigma-Aldrich describes the material: "It is an excellent substrate from the epitaxial growth of many oxide this (sic) [thin] films and high-temperature superconductors." The company also describes it as having "applications in optical windows and as a high-quality sputtering target."

Indeed, a number of research establishments, including the Oak Ridge National Laboratory in the U.S., have undertaken exploration of its use in semiconductors, especially in the context of attempting to make transistors smaller and faster. For transistors, strontium titanate "exerts a stronger influence on the transistor's conductivity than silicon dioxide, the gate electrode can take up less space, compressing the area between the source and drain electrodes and shortening the distance the electrons would travel."

At the Center for Integrated Nanotechnologies at the Los Alamos National Laboratory in New Mexico, some exciting results were published earlier this year based on research that explored certain properties of terahertz metamaterials fabricated on strontium titanate single-crystal substrates.

Strontium may play a role in the field of energy; in particular, batteries. Scientists at the University of Erlangen-Nuremberg in Germany recently published an interesting paper on the use of strontium titanate in solid oxide fuel cells (SOFCs).

Finally, at the end of 2010, scientists at the University of Pittsburgh announced that they had been able to create "a nanoscale light sensor that can be combined with near-atomic-size electronic circuitry to produce hybrid optic and electronic devices with new functionality." The substrate used was strontium titanate.

 

Opportunities In Strontium

Albeit the world's second-largest producer of celestite, there is now only a single miner extracting the mineral in Spain—Solvay Minerales SA, itself owned by the large chemical concern Solvay of Belgium.

In China, the world's largest producer of celestite, there are a number of celestite producers. But the country still needs to import the mineral to fulfill its production needs.

Since Solvay is certainly neither a pure strontium play, nor is its activity in the metal a major part of the company's business—and with no investable mining companies in China for which strontium is a major part of their businesses—there seems to be little opportunity to invest in either the mining of celestite or the production of strontium.

For those interested in following the metal, however, keeping an eye on the areas in which promising research is currently taking place may throw up some interesting, albeit indirect, possibilities in the metal.

 

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Lipmann Walton & Co Ltd

U.S. Geological Survey (USGS)

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