In which solvent does sulfur dissolve?

The sulfur concentration in sea water is around 870-930 ppm, while river water generally only contains around 4 ppm of the element. In inorganic form, the sulfur in water comes mainly as SO42-, but also as HSO4- and in the greatly reduced forms HSO3-, SO3, SO2 and HS- in front. There is also NaSO in sea water4- contain.

How and in which compounds does sulfur react with water?

Elemental sulfur is stable in water, so it does not react with it. This is indeed the case with some sulfur compounds. One example is sulfur dioxide, which reacts to form sulphurous acid when it is introduced into water. The reaction equation then reads:

SO2 + H2O -> H2SO3

Sulfur trioxide even shows explosive reactions when it comes into contact with water and forms sulfuric acid. Sulfuryl chloride reacts violently with water to form the aggressive chlorosulfonic acid. The compound reacts with a lot of water to form hydrogen chloride and sulfuric acid.

Water solubility of sulfur and / or its compounds

Sulfur itself is insoluble in water. Heavy metal sulfides are also considered to be almost insoluble. On the other hand, hydrogen sulfide is 94 g / L soluble in water and sulfur hexafluoride has a water solubility of 40 mg / L. Sulphates also usually have a high solubility in water.

Solubility and how it can be influenced

How can sulfur get into the water?

Sulfur already gets into the various environmental areas via the natural sulfur cycle and thus also into the water. For example, it occurs near volcanoes. Some minerals also contain sulfur, such as chalcopyrite, bornite or millerite. It is also a component of gypsum as a sulphate. In this way it gets into mineral springs and waters. Sulfur can also be found in sediments with a high organic content, mainly in the form of sulfides. However, the element also occurs in nature in elemental form. Hydrogen sulfide is a component of natural gas and organosulfur compounds from coal and petroleum.
However, sulfur is also used in a commercial field. The main source is then hydrogen sulfide from natural gas. The element is often found in pesticides, and pure sulfur was previously used as a fungicide. As an additive in cattle feed, the sulfur-containing amino acid methionine ensures that milk and meat also contain this substance in higher concentrations. Sulfur dioxide kills bacteria, has an antioxidant effect and protects food, especially vegetables, fruit and wine, from losing color. The element can also be present in flavor enhancers and sweeteners. Other sulfur compounds are processed in the pharmaceutical industry, and penicillin also contains the element.
One of the most well-known uses of sulfur is the vulcanization of rubber. But this element is also used in steel production. For example, some types of steel have about 0.2-0.3% sulfur added to make them easier to process. Concrete can contain sulfur, which in this case makes the material more resistant to corrosion.
In the chemical industry, sulfuric acid is both produced and processed. It is the most widely used chemical in industry. Hydrogen sulfide can be used as a bleaching agent. The element is also found in antifreeze, gunpowder, fireworks, solvents and batteries and is used in the production of paper, matches, cellophane, lubricants, paints and enamel.
The combustion of coal, natural gas and crude oil, which produces sulfur dioxide, also plays a major role in the release of sulfur into the environment. For example, coal has a sulfur content of 2-3%. The roasting of sulfur-containing ores and metals also contributes to this. However, modern technologies make it possible to convert sulfur dioxide from metal production into sulfuric acid, and heating oil now also contains less sulfur.
Sulphate can leak in large quantities from inadequately secured landfills for household waste, construction waste and hazardous waste. It can act as an indicator substance, as other substances were often also released into the soil and water when it appeared.
The radioactive isotope 35S is used as a tracer in research.

What environmental problems can water pollution with sulfur cause?

The sulfur cycle is the most disturbed natural cycle. The element is essential for all types of organisms, among other things because it is contained in many proteins.
Sulfur is a major component of the soil. Normal air-dry soils also contain 200-2000 ppm of the element. In the upper soil horizons it is largely organically bound. Bogs and marshes can have a sulfur content of as much as 35,000 ppm, and this value is often exceeded in gypsum soils.
A sulfur concentration of around 0.06-1% of its dry matter can be found in plant material. A deficiency in this element, which they absorb in the form of sulfate, is rather rare. In most cases, too much sulfur can be tolerated relatively well. However, it can lead to a dark green coloration of the leaves and reduce crop yields. However, the harmful effect is more due to the osmotic effect, since sulfate is very soluble. It is therefore assigned a high potential for spreading. If there is a very high level of sulphate in the soil, gypsum is often formed which, on the other hand, is only sparingly soluble and in turn limits the harmfulness. Damage occurs more frequently in waterlogged soils, since under these conditions sulphate can be reduced to sulphide, which as hydrogen sulphide has a negative effect on plants.
Plants are also sensitive to sulfur dioxide. Even a concentration of 1-2 ppm can disrupt the photosynthesis process. The gas is also one of the causes of acid rain and acid winter smog.
Sulfur dioxide gas, which occurs naturally in low concentrations but is released in large quantities by human activities, dissolves in raindrops, producing sulphurous acid (SO2 + H2O -> H2SO3). Another possibility is the previous oxidation to sulfur trioxide, which forms sulfuric acid in water (SO3 + H2O -> H2SO4). The acid rain causes acidification of the soil, which in turn leads to damage to the plants, and a higher acid content of water bodies. For example, some types of fish can reproduce more poorly. Acidification can be counteracted by liming. If this does not happen, it is also possible that metal ions are released from rocks by the acid and can even destroy animal life.
Sulfur itself is not considered to be hazardous to water. On the other hand, some sulfur compounds can cause greater damage in bodies of water. Sulfuryl chloride, for example, is one of the substances that are slightly hazardous to water, whereas carbon disulfide poses an even greater threat to natural waters. As for the toxicity of sulfur, it has an LD50-Value of> 5000 mg / kg when taken orally by the rat. This value indicates the lethal dose at which 50% of a population die.
Other sulfur compounds are more likely to play a role in environmental problems in the atmosphere. For example, sulfur hexafluoride is a compound with a global warming potential that is about 10,000 times greater than that of carbon dioxide. Of course, the greenhouse effect also has an impact on aquatic ecosystems.
Incidentally, some bacteria get their energy from the oxidation of sulfur. They are completely independent of sunlight, occur on the sea floor and in water in rocks and are referred to as lithotrophic ("living on stones").
Sulfur has four stable and six unstable, thus radioactive, isotopes.

What health effects can sulfur cause in water?

The sulfur concentration in the human body is around 2000 ppm. It is an essential element that is vital for humans in the form of the amino acid methonine. Sulfur is also found in other amino acids. They can form so-called disulfide bridges between peptides, which are mainly found in keratin, which is made up of hair and nails. The element is also contained as a component of coenzymes, vitamins, mucopolysaccharides and sulfuric acid esters.
The daily intake of the element is around 900 mg, mainly in the form of proteins from meat, fish and soy. A deficiency in the sulfur-containing vitamin B1 leads to beriberi disease, which can manifest itself in tremors, irritability, nerve paralysis and even heart failure.
Elemental sulfur is relatively non-toxic to humans, but this is not true for all of its compounds. It passes unchanged through the stomach, but in large quantities it can be converted into hydrogen sulfide in the intestine and have a laxative effect. Sulphate leads to a change in the taste of the food from a concentration of about 300-400 mg / L and above 600 mg / L it has a laxative effect. The sulphite ion is considered to be about 20 times more toxic than the sulphate ion. Sulfuric acid has a corrosive effect and if taken orally if about 5 ml leads to death from stomach burns. Carbon disulfide, on the other hand, mainly affects the nervous system, and sulfur dioxide narrows the airways and is a highly irritating substance that is toxic to the lungs and is also very reactive and can thus inhibit enzymes. Hydrogen sulfide is also a poisonous gas. Other sulfur compounds can act on the DNA and thus be carcinogenic.

Which water purification technologies can be used to remove sulfur?

Sulphate can be found in natural waters in concentrations of around 5-200 mg / L. A value of 250 mg / L should not be exceeded in drinking water either, as this can impair the taste and have a laxative effect.
High sulphate levels can primarily be reduced by treating with lime. Other coagulation options exist and ion exchangers, reverse osmosis, distillation and electrodialysis can also be used.
In sewage treatment plants, sulfur compounds are broken down with the help of sulfur-oxidizing bacteria. The sulfate ion can act as an electron acceptor and be reduced to hydrogen sulfide. This can in turn be removed with the help of aeration, oxidation or adsorption on activated carbon. Oxidation to remove sulfur compounds can be achieved through the use of chlorine, ozone, permanganate, or hydrogen peroxide.

The EU drinking water directive specifies a maximum sulfate concentration of 250 mg / L. The German Drinking Water Ordinance even has a stricter value of 240 mg / L.

Comparison of drinking water standards

References


To the periodic table of the elements

To the overview of the elements and water