Sulphur - S
Sulfur (also spelled sulphur) is a yellow nonmetal found in minerals and living matter. In water treatment, sulfur-bearing species such as sulfide, sulfate and sulfite have different chemistry, hazards and treatment needs.
Chemical properties · Uses and occurrence · Health effects · Environmental effects · Water and treatment
Chemical properties of sulfur
| Symbol / atomic number | S / 16 |
|---|---|
| Group / period / block | 16 / 3 / p |
| Standard atomic weight interval | [32.059, 32.076] |
| Electron configuration | [Ne] 3s2 3p4 |
| Common oxidation states | −2, +2, +4 and +6 |
| Density (rhombic sulfur) | 2.07 g cm−3 |
| Melting point | 115.21 °C |
| Boiling point | 444.61 °C |
| Electronegativity (Pauling) | 2.58 |
| Non-bonded atomic radius | 0.180 nm |
| First ionisation energy | 999.6 kJ mol−1 |
| Stable isotopes | 32S, 33S, 34S and 36S |
| History | Known since antiquity |
| CAS registry number | 7704-34-9 |
Atomic weight follows CIAAW. Intervals reflect natural isotopic variation; parentheses indicate uncertainty in the final digits. Other properties follow RSC unless noted. Atomic radii depend on their definition.
Properties, uses and occurrence
Sulfur occurs in several forms, commonly as yellow crystals. It is recovered from natural deposits and as a by-product of processing oil and natural gas. Much elemental sulfur is converted to sulfuric acid, which is used in fertiliser manufacture and many industrial processes.
Sulfur is also present in minerals such as gypsum and in biological molecules. Sulfur, sulfate and sulfide are related chemically but are not interchangeable names.
Health effects of sulfur compounds
Elemental sulfur is not equivalent to hydrogen sulfide (H2S), sulfur dioxide (SO2), sulfite or sulfate. Hydrogen sulfide is a highly toxic gas that can occur around sewers, wastewater systems and other oxygen-poor environments; smell is not a reliable safety monitor. Sulfur dioxide is an irritating gas, while sulfate in ordinary water is a different dissolved ion. Assess each compound and exposure separately.
Sulfur in the environment
Sulfur cycles through rocks, soils, water, organisms and the atmosphere. Microbial activity can convert sulfate to sulfide under reducing, oxygen-poor conditions. Oxidation of sulfur-containing fuels can release sulfur dioxide, which contributes to acid deposition.
Sulfur species in process water
In water, sulfur may occur as sulfate, dissolved sulfide (including H2S and HS− depending on pH), sulfite, thiosulfate or particles of elemental sulfur. Sulfide can cause odour and corrosion problems and may release hazardous H2S to air.
Options for sulfide control include aeration or other gas transfer, chemical oxidation, and precipitation with suitable metal salts. Each process has different residuals and operating requirements; aeration transfers H2S to off-gas and does not make the hazard disappear. Sulfate may need a different process, such as membrane treatment or ion exchange, when its reduction is required. Test the actual sulfur species, pH, dissolved oxygen and water chemistry before selecting treatment.
Sulfur page last reviewed: by Lenntech.
Back to the periodic table of elements.