Strontium - Sr
Strontium (Sr) is a chemical element with atomic number 38. This page summarises its properties, uses and environmental context, with notes for water and process-treatment engineers.
Properties · Uses and occurrence · Health · Environment · Water and treatment
Chemical properties of strontium
| Symbol / atomic number | Sr / 38 |
|---|---|
| Group / period / block | 2 / 5 / s |
| Standard atomic weight | 87.62(1) |
| Electron configuration | [Kr] 5s2 |
| Common oxidation state(s) | +2 |
| Density (20 °C) | 2.64 g cm−3 |
| Melting point | 777 °C |
| Boiling point | 1377 °C |
| Electronegativity (Pauling) | 0.95 |
| Non-bonded atomic radius | 0.249 nm |
| First ionisation energy | 549.47 kJ mol−1 |
| Representative isotopes | 84Sr, 86Sr, 87Sr, 88Sr |
| CAS registry number | 7440-24-6 |
Standard atomic weight follows CIAAW. Parentheses indicate uncertainty in the final quoted digits. Other physical and atomic data follow the Royal Society of Chemistry. Non-bonded atomic radii are method-dependent.
Strontium: properties, uses and occurrence
Strontium compounds are used in ferrite magnets, specialty glass and ceramics, and to produce red colors in flares and fireworks. Natural strontium has four stable isotopes; radioactive strontium-90 is a distinct fission product and should not be confused with stable strontium.
Health and safety
Strontium can follow calcium pathways in the body, but effects depend on isotope, compound, concentration and exposure. Strontium-90 is radioactive; most naturally occurring strontium is stable. Assess drinking-water results against applicable local guidance.
Strontium in the environment
Strontium occurs naturally in minerals including celestite (SrSO4) and strontianite (SrCO3). Dissolution and mobility depend on mineral form and water chemistry, including the presence of calcium and carbonate.
Strontium in water and treatment
Dissolved Sr2+ can be relevant in groundwater treatment. Full-scale studies have reported removal by cation exchange softening and lime softening, with performance varying by source water and operating conditions. Lime-softening removal tracked calcium removal; conventional coagulation and filtration alone generally removed little strontium in bench studies. Assess pH, calcium, alkalinity, dissolved inorganic carbon, blending and residuals, and confirm performance with representative testing. See Lenntech's strontium-in-water information.
Strontium page last reviewed: by Lenntech.
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