Strontium

Strontium is a chemical element with the symbol Sr and atomic number 38. It is a soft, silver-white yellowish metallic element that is very chemically reactive. When strontium is exposed to air, it forms a dark layer of oxide on its surface.

Strontium is found in nature mainly in two minerals: celestine and strontianite. These minerals are mined to obtain the element. Both strontium and strontianite are named after the village of Strontian in Scotland, where the mineral was first discovered in 1790 by Adair Crawford and William Cruickshank. It was recognized as a new element the following year because of its distinctive crimson-red flame test color.

In 1808, the element was first isolated as a metal by Humphry Davy using a process called electrolysis. During the 1800s, strontium was often used in making sugar from sugar beets. Later, it became very important for making the glass screens of old television cathode-ray tubes. Today, as televisions have changed to newer technologies, the use of strontium has decreased a lot.

Natural strontium, mostly made up of the isotope strontium-88, is stable and not harmful to health in small amounts. However, a synthetic form called strontium-90 is radioactive and can be dangerous. It is one of the harmful parts found in nuclear fallout, because the body absorbs it in a similar way to calcium.

Characteristics

Strontium is a soft, silvery metal with a pale yellow color. It is very reactive, similar to the metals calcium and barium, which are next to it in the periodic table. It melts at 777 °C and boils at 1377 °C.

Strontium reacts with water to make strontium hydroxide and hydrogen gas. It also burns in air to form strontium oxide and strontium nitride. When freshly cut, it turns yellow quickly as it reacts with air. Strontium is often stored in oil to keep it from reacting.

Isotopes

Main article: Isotopes of strontium

Natural strontium is a mix of four stable isotopes: ⁸⁴Sr, ⁸⁶Sr, ⁸⁷Sr, and ⁸⁸Sr. The most common is ⁸⁸Sr, making up about 82.6% of all natural strontium. Some isotopes of strontium are used in medicine, while others can be found in fallout from nuclear weapons.

History

Strontium is named after the village of Strontian in Scotland, where it was first found in old mines.

In 1790, scientists noticed that minerals from Strontian behaved differently from others. They named these minerals strontianite because they were special and unlike anything seen before. Later, in 1808, a scientist named Sir Humphry Davy managed to separate the element strontium for the first time.

For many years, strontium was used in making sugar from sugar beets. It was important in factories until new methods replaced it. During tests of nuclear weapons, scientists learned that a form of strontium called strontium-90 was created, and they studied how it might affect health because it behaves like calcium in the body.

Occurrence

See also: Category:Strontium minerals

Strontium is found in nature quite often. It is the 15th most common element on Earth, making up about 360 parts per million in the Earth's crust. We find it mainly in two minerals: celestine (SrSO₄) and strontianite (SrCO₃). Celestine is more common in large enough amounts to mine, but strontianite is more useful when it is used in products.

In water, strontium acts a bit like calcium. It mixes with other minerals and sticks to soil particles. In the ocean, strontium is found at a level of about 8 mg/L, which is much less than calcium but more than another element called barium.

Production

Strontium is mainly produced from a mineral called celestine. As of January 2024, the top producers are Spain and Iran, each producing around 200,000 tons, followed by China and Mexico.

To make strontium, celestine is changed into a compound called carbonate. This is done by either using a special liquid or heating it with coal. The result is a dark material that is then dissolved in water. Adding a gas to this solution creates strontium carbonate.

The metal form of strontium is made by heating strontium oxide with aluminium. It can also be made in smaller amounts using a process called electrolysis.

Strontium is considered a critical material in the European Union, with most of it coming from Spain.

Applications

The main use of strontium was in making glass for old colour televisions. It helped stop harmful invisible rays called X-rays from escaping. But now, as we use new types of screens, this use has gone down.

Because strontium acts like calcium in our bodies, scientists can study it in old bones to learn where people lived long ago. This helps us understand how ancient people moved and lived.

Strontium also makes fireworks glow a bright red and is used in some glow-in-the-dark toys. It can even help people with sensitive teeth when added to special toothpaste.

Radioactive strontium

Some forms of strontium can give off helpful energy for treating pain caused by certain types of cancer. Another form can provide power for special scientific tools, though it needs careful handling because of the energy it releases.

Biological role

Chemical compound

Acantharea, a group of tiny sea creatures, build intricate skeletons using strontium sulfate. In living things, strontium can sometimes act like calcium. In our bodies, most of the strontium we take in ends up in our bones. The amount of strontium compared to calcium in our bones is very small, similar to the amount in our blood.

The human body treats strontium almost like calcium. Stable forms of strontium can be a health concern because we usually take in about two milligrams of it each day. Strontium acts much like calcium, and a lot of it collects in our bones. In adults, it mainly sticks to the outside of bones. In children, whose bones are still growing, strontium might be used to help build strong bones. Over time, strontium can dissolve from bones and move through the bloodstream, either to be used again by growing bones or to be removed from the body.

The time it takes for the body to remove strontium can vary widely, from a few weeks to many years. On average, it is thought to take about 18 years for the body to remove half of the strontium. How quickly it is removed can depend on a person’s age and gender because of differences in how bones work.

There is a medicine called strontium ranelate that helps bones grow stronger and can reduce certain types of broken bones. However, it can also increase the risk of blood clots and serious heart problems, so its use is now limited. Even though there are restrictions, some supplements still contain strontium. There isn’t much research on the safety of taking strontium chloride by mouth, so people with a history of blood clotting issues should avoid it.

When put on the skin, strontium can help reduce irritation and speed up the healing of the skin’s protective barrier.

Nuclear waste

Strontium-90 is a special kind of material made in nuclear reactors used for nuclear power. It is a big part of the tricky waste from these reactors and old fuel. It takes about 29 years for half of it to change and become less harmful, but it can still take hundreds of years to become safe. If people drink water or eat food with this material, it might increase the chance of some health problems.

Scientists are looking for ways to clean up this material. Some tiny water plants, called algae, have shown they can pick out strontium from water. This could help treat water from nuclear sites. Studies with different types of algae suggest these tiny plants might be useful for cleaning up radioactive wastewater.