Strontium is a chemical element with atomic number 38 in the periodic table. It’s the 15th most plentiful metal found in Earth’s crust with 0.034% ppm natural occurrence. Being a member of the alkaline earth metals group of the periodic table, this lithophile metallic element has two valence electrons present in the outermost shell.
Strontium is a trace mineral whose function resembles the one of calcium in the human body. The strontium-90 radioisotope is one of the most frequently found radioactive forms in the debris left after a nuclear catastrophe or nuclear fission. In addition, strontium salts are colored in a bright red color which is popularly used for emergency lights and fireworks.
Chemical and Physical Properties of Strontium
The symbol in the periodic table of elements: Sr
Atomic number: 38
Atomic weight (mass): 87.62 g.mol-1
Group number: 2 (Alkaline earth metals)
Period: 5 (s-block)
Color: Pale yellow color with a silvery luster
Physical state: Solid at room temperature
Half-life: From less than 25 milliseconds to 28.9 years
Electronegativity according to Pauling: 1.0
Density: 2.6 g.cm-3 at 20°C
Melting point: 777°C, 1431°F, 1050 K
Boiling point: 1377°C, 2511°F, 1650 K
Van der Waals radius: 0.215 nm
Ionic radius: 0.113 nm (+2)
Most characteristic isotope: 86Sr, 87Sr, 88Sr
Electronic shell: [Kr] 5s2
The energy of the first ionization: 549.2 kJ.mol-1
The energy of the second ionization: 1064 kJ.mol-1
Discovery date: In 1790 by Adair Crawford and William Cruickshank
With the periodic table symbol Sr, atomic number 38, atomic mass of 87.62 g.mol-1, and electron configuration [Kr] 5s2, strontium is a soft, yellow alkaline-earth metal with a silvery luster. It reaches its boiling point at 1377°C, 2511°F, 1650 K, while the melting point is achieved at 777°C, 1431°F, 1050 K. This member of the alkaline earth metals family of elements in the periodic table has an electronegativity of 1.0 according to Pauling, whereas the atomic radius according to van der Waals is 0.215 nm.
This silvery metal has a high refractive index and burns with a distinctive red color flame. When dissolved in liquid ammonia, it forms a dark blue solution. Strontium metal occurs in three crystalline allotropic forms with transition points at 235°C and 540°C. It’s softer than calcium and harder than barium.
Being an alkaline earth metal, strontium tarnishes rapidly upon exposure to air and produces volatile reactions when it comes into contact with H2O. Due to this reason, strontium must be isolated and kept away from both air and water when stored.
How Was Strontium Discovered?
When the Irish chemist and physician Adair Crawford (1748 – 1795) first attempted to determine the specific heats of the gaseous elements, he conducted a series of experiments. During his scientific work, his attention was caught by a mineral sample obtained from a lead mine near the small town of Strontian in Argyll, Scotland.
At that time, his fellow colleagues were considering beryllium and strontium as the same element. They had labeled the mineral ‘strontites’, while its oxides were known as ‘strontia’. Crawford had a reserved opinion on what was labeled as barium carbonate. He and his fellow colleague William Cruickshank held the belief that the new mineral was, in fact, a completely different and new substance.
In 1790 Crawford and Cruickshank succeeded in providing scientific proof for their claims, by which they became the first discoverers of element 38 – strontium (Sr).
All chemicals that have been derived from alkaline earth elements were isolated in their pure form by Sir Humphry Davy. In 1808 he managed to obtain the pure forms of magnesium, calcium, strontium, and barium, by applying the method of electrolysis. He had previously used electrolysis with great success in the purification process of the elements potassium and sodium.
How Did Strontium Get Its Name?
Strontium is named after a Scottish village called Strontian.
Where Can You Find Strontium?
Strontium is the 15th most commonly occurring chemical element in Earth’s crust, but it’s never found free in nature. The naturally occurring forms of element 38 can be traced in sediments, rocks, water, air, and soil.
Element 38 can always be found in natural water systems. Since this substance is highly soluble in water, it is released to groundwater as those minerals dissolve. The main natural sources of strontium are the minerals putnisite (SrCa₄Cr₈³⁺(CO₃)₈(SO₄)(OH)₁₆·25 H₂O), celestite (SrSO4), and the carbonate strontianite (SrCO3).
Strontium metal is typically prepared by electrolysis of the fused chloride that is mixed with potassium chloride. Also, it can be prepared by reduction of strontium oxide with aluminium in a vacuum. After this, the resulting substance is exposed at a temperature in order to produce pure strontium by the distillation process.
The world’s leading commercial producer of strontium is China, while the biggest strontium mines are located in the UK, Turkey, Mexico, and Spain. Annually, more than 140,000 tons of strontium are mined worldwide.
List of Strontium Minerals
The following is a list of minerals from which strontium can be obtained by mining:
- Celestine (mineral)
- Strontian process
Strontium in Everyday Life
- Strontium-85 isotope is applied in radiography for the bone imaging medical procedures;
- Low levels of strontium are used in the treatment of patients suffering from osteoporosis;
- Element 38 is the main component in the manufacturing of red signal flares (flare guns), emergency flares, and phosphors as a result of its brilliant red salts.
- Strontium carbonate (SrCO3) and strontium nitrate (Sr(NO3)2) are the most commonly used strontium compounds in the manufacturing of fireworks. They not only give them a vivid red color but also stabilize the fireworks compounds.
- When used as an alloying agent for aluminum or magnesium in cast engine blocks and wheels, strontium supports both the resistance and machinability of the metal;
- Applied in the TV picture tubes, strontium blocks the X-rays that are emitted;
- Strontium is widely used in the process of manufacturing ferrite magnets, as well as in the zinc refinement process;
- Apart from being highly radioactive and dangerous, strontium-90 isotope has also a beneficial role as a radioactive tracer in cancer therapy;
- Radioactive strontium-89 is administered intravenously (by IV) to both prostate cancer and advanced bone cancer patients in order to relieve the bone pain;
- By emitting beta-rays, strontium may generate electricity for space vehicles, remote weather stations, as well as for navigation buoys;
- The world’s most accurate atomic clock has been made with strontium atoms.
- Strontium chloride hexahydrate can be used in toothpaste for sensitive teeth. Some toothpaste brands include up to 10% of total strontium chloride hexahydrate by weight in their products.
Strontium and Health
The human body makes use of strontium as a trace mineral in a similar way it uses calcium. Namely, strontium is also accumulated mainly in the bones and other bone structures, i.e. teeth. When it’s absorbed by the bone tissue instead of calcium, strontium can destroy the bone marrow and trigger mutation of the cells which can cause cancer.
While strontium exposure may cause deformed bones and teeth in children, this trace mineral seems to have a beneficial effect in adults. For this, it is administered as a therapy in osteoporosis (bone mineral loss) patients which helps them increase the bone mineral density. However, strontium does not support the formation of new bone tissue.
According to a study published by the National Library of Medicine, a special form of strontium labeled as ‘strontium ranelate’ can increase bone formation and prevent bone loss when used in postmenopausal women with osteoporosis. Strontium ranelate acts through dual mechanisms of resorption inhibition by osteoclasts and maintaining or stimulating bone formation by osteoblasts
Furthermore, strontium ranelate may act as an anti-osteoporosis agent that significantly reduces both vertebral and nonvertebral fractures. In patients with vertebral osteopenia, strontium ranelate reduced the risk of vertebral fracture in 3 years by 40%. Also, the study provided scientific evidence showing that administration of this strontium compound decreased the risk of vertebral fractures in 1488 women aged between 80 and 100 years. In this study group, strontium ranelate had lowered the vertebral fractures risk by 59% in one year, and by 32% over 3 years.
However, another research conducted by the American Bone Health Organisation claims that the aforementioned benefits of strontium in bone health may be exaggerated and can no longer be used to treat osteoporosis. This decision was mainly based upon the occurrence of many serious negative side effects, such as nausea, diarrhea, headache, and skin irritation. For this reason, strontium ranelate has not been approved by the Food and Drug Administration (FDA) in the United States.
On the other hand, natural strontium citrate is widely used as a supplement in the preventive treatment of osteoporosis, as well as in the treatment of patients suffering from osteopenia (reduction of protein and mineral content of bone tissue).
This trace mineral can be found in some foods that we include in our everyday diet, such as:
- Pasteurized milk;
Foods that contain high levels of calcium are also good sources of strontium. The strontium amount in fruits or vegetables depends on the amount of this chemical element found in the soil where they have been grown. The estimated daily intake of strontium is 1–5 milligrams per day. While vitamin D and magnesium support better strontium absorption in our bodies, hypercalcemia may inhibit it.
Being similar to calcium when it comes to bone health, strontium supplements are possibly beneficial in patients with osteoporosis, as well as in post-menopausal women prone to bone fractures. On one hand, strontium may increase our ability to absorb calcium in our bones and kidneys by activating the calcium-sensing receptor of the cells.
Furthermore, strontium supports bone formation and bone health. Finally, this trace mineral improves the bones’ fracture resistance, could possibly prevent bone pain, and may promote good digestive health by increasing vitamin absorption.
However, strontium intake via food is always a better idea, than taking strontium supplements that may trigger some severe and life-endangering side effects:
- Cognitive problems;
- Liver inflammation;
- Blood clots;
- Skin reactions.
How Dangerous Is Strontium?
Strontium chromate is an extremely toxic compound that may lead to lung cancer. Strontium salts may trigger severe reactions upon skin contact, in the form of allergies and rashes. In addition, the radioactive isotope strontium-90 of this chemical element is able to deprive the body’s tissues of oxygen and lead to anemia and bone cancer.
In cases when exposure to high levels of naturally occurring strontium occurs during the periods of infancy and childhood, element 38 can affect bone growth and cause irregularly developed teeth, as well as weak bones in children.
When extremely high levels of strontium are accumulated in a body of a child, a condition labeled as ‘strontium rickets’ occurs. This disease characterizes the formation of abnormally thicker and shorter bones in the legs of children that further progresses as bone deformation. As a result, walking and all other physical activities become more difficult for the child.
The dust made of strontium metal can spontaneously ignite when exposed to air, which poses a fire hazard.
In addition, the non-radioactive isotopes of strontium are considered to be non-toxic, unlike the salts and radioisotopes of this chemical element.
Environmental Effects of Strontium
Since strontium occurs naturally in our environment, it can be found everywhere around us: in the air, soil, drinking water, foods, dust, etc. The geological, biological, aquatic systems, as well as the air can be polluted with strontium via nuclear tests and waste, the milling processes, phosphate fertilizers, and burning of coal.
Owing to the fact that most of the strontium compounds are highly soluble in water, natural aquatic systems, as well as the drinking water, can be easily contaminated by this chemical substance. According to the United States Environmental Protection Agency (EPA), strontium in drinking water poses a health risk when the concentration levels of this chemical reach above 4000 parts per billion (4mg/L). Water contaminated with strontium has no odor or taste, which makes it difficult for this chemical to be detected without laboratory testing.
Isotopes of Strontium
There are 35 isotopes of strontium. Naturally occurring strontium (38Sr) consists of four stable isotopes: 84Sr (0.56% abundance), 86Sr (9.86% abundance), 87Sr (7.0% abundance), and 88Sr (82.58% abundance).
Strontium-87 is a radiogenic form of element 38, i.e. it has nuclei produced by a process of radioactive decay. The 32 unstable isotopes of strontium decay undergo a beta– decay into strontium’s neighboring elements in the periodic table: yttrium (element below Sr) and rubidium (element above Sr).
Despite the fact that naturally occurring strontium (38Sr) has a stable electron structure, the synthetically produced strontium-90 form is highly radioactive and unstable.
Radioactivity of Strontium-90
The radioactive isotope strontium-90 represents a by-product of nuclear reactors. It’s mostly present in nuclear fallout. Together with the cesium-137 isotope, this strontium form is one of the two major and most abundant radioactive products of nuclear fission or nuclear accidents, such as the ones in Fukushima Daiichi, Chernobyl, or Techa River.
Having a half-life of 28.9 years, strontium-90 is the longest living form of element 38, as well as the most dangerous one. Namely, this radioactive form of strontium can be easily absorbed in the bones of infants and children, thus leading to adverse health effects and poor bone health.
Since the beta-radiation emitted by strontium-90 has a short range, it can be highly dangerous if it is ingested or inhaled. Once in the body, this radioactive isotope of strontium accumulates in the bones and changes their cellular mechanism, thus triggering deformities and bone tumors.
|Z||N||Isotopic mass (Da)
[n 2][n 3]
[n 6][n 7]
[n 8][n 4]
|Natural abundance (mole fraction)|
|Excitation energy||Normal proportion||Range of variation|
|73Sr||38||35||72.96597(64)#||>25 ms||β+ (>99.9%)||73Rb||1/2−#|
|β+, p (<.1%)||72Kr|
|74Sr||38||36||73.95631(54)#||50# ms [>1.5 µs]||β+||74Rb||0+|
|75Sr||38||37||74.94995(24)||88(3) ms||β+ (93.5%)||75Rb||(3/2−)|
|β+, p (6.5%)||74Kr|
|77Sr||38||39||76.937945(10)||9.0(2) s||β+ (99.75%)||77Rb||5/2+|
|β+, p (.25%)||76Kr|
|84Sr||38||46||83.913425(3)||Observationally Stable[n 9]||0+||0.0056||0.0055–0.0058|
|86mSr||2955.68(21) keV||455(7) ns||8+|
|89Sr[n 11]||38||51||88.9074507(12)||50.57(3) d||β−||89Y||5/2+|
|90Sr[n 11]||38||52||89.907738(3)||28.90(3) y||β−||90Y||0+|
|97Sr||38||59||96.926153(21)||429(5) ms||β− (99.95%)||97Y||1/2+|
|β−, n (.05%)||96Y|
|98Sr||38||60||97.928453(28)||0.653(2) s||β− (99.75%)||98Y||0+|
|β−, n (.25%)||97Y|
|99Sr||38||61||98.93324(9)||0.269(1) s||β− (99.9%)||99Y||3/2+|
|β−, n (.1%)||98Y|
|100Sr||38||62||99.93535(14)||202(3) ms||β− (99.02%)||100Y||0+|
|β−, n (.98%)||99Y|
|101Sr||38||63||100.94052(13)||118(3) ms||β− (97.63%)||101Y||(5/2−)|
|β−, n (2.37%)||100Y|
|102Sr||38||64||101.94302(12)||69(6) ms||β− (94.5%)||102Y||0+|
|β−, n (5.5%)||101Y|
|103Sr||38||65||102.94895(54)#||50# ms [>300 ns]||β−||103Y|
|104Sr||38||66||103.95233(75)#||30# ms [>300 ns]||β−||104Y||0+|
|105Sr||38||67||104.95858(75)#||20# ms [>300 ns]|
List of Strontium Compounds
Element 38 typically adopts the oxidation states +2 in a chemical reaction. It occurs in a divalent oxidation state in all of its compounds. Strontium is highly soluble in water. This property can be also transferred to some of the compounds in which strontium participates.
The most frequently prepared compounds that include strontium are listed below:
- Bismuth strontium calcium copper oxide
- Lanthanum strontium cobalt ferrite
- Lanthanum strontium manganite
- Strontium acetate
- Strontium aluminate
- Strontium barium niobate
- Strontium bromate
- Strontium bromide
- Strontium carbonate
- Strontium chlorate
- Strontium chloride
- Strontium chromate
- Strontium fluoride
- Strontium hexaboride
- Strontium hydride
- Strontium hydroxide
- Strontium iodide
- Strontium nitrate
- Strontium nitride
- Strontium oxalate
- Strontium oxide
- Strontium perchlorate
- Strontium peroxide
- Strontium ranelate
- Strontium ruthenate
- Strontium sulfate
- Strontium sulfide
- Strontium titanate
5 Interesting Facts and Explanations
- The radiogenic 87Sr is a daughter-isotope of 87Rb isotope. The half-life of this rubidium isotope is even three times longer than the current age of our Universe (4.88 × 1010 years).
- Almost 99% of all strontium in the human body is accumulated in the bones.
- Strontium is very much like the elements barium and calcium regarding its physical and chemical properties.
- The drinking water that is drawn from bedrock aquifers rich in strontium minerals has an especially high strontium saturation.
- Every five years, EPA examines the strontium levels in drinking water in the United States according to the Third Unregulated Contaminant Monitoring Rule testing, which is required by the 1996 Safe Drinking Water Act (SDWA) amendments.