The sulfur cycle It is the process of circulation of this chemical element on planet Earth. This process is expressed in a series of stages or phases that include the biosphere, lithosphere, atmosphere and hydrosphere..
Thus, a particle of sulfur on Earth passes through the soil and rocks, air, water and living beings. This movement is constantly repeated, moving from one environment to another.
Sulfur is an element with a yellow color and an unpleasant odor, whose main reservoirs are in the lithosphere. These are found mainly in the deposits of fossil fuels such as coal and oil, dissolved in ocean waters and forming part of living beings..
The sulfur cycle is very important, because this chemical element plays an essential role for life, both favoring or threatening living beings, depending on the substances it forms and where it is found..
Being part of essential amino acids, enzymes and chlorophyll, sulfur is vital for the existence of living organisms. At the same time as a pollutant, it is part of acid rain and can become a negative factor for life.
This chemical element is a non-metal, represented by the letter “S”, yellow, greenish-yellow, orange, yellowish-brown or gray. Furthermore, it is brittle, soft, with a silky or resinous sheen and an unpleasant odor. When sulfur burns, it produces a blue flame and releases sulfur dioxide which is a toxic gas..
The sulfur cycle is a biogeochemical cycle, that is, this element circulates between living organisms and the environment. It is also a gas-type cycle, since it forms gases, having an important phase in the atmosphere..
In turn, chemical changes occur in these processes, since it can combine with oxygen and other compounds. This cycle guarantees the availability of sulfur, giving continuity to life on the planet, because this element is a macronutrient.
Like any biogeochemical cycle, the sulfur cycle presents deposits, flows, and composition and phase changes. In this case, the main sulfur deposits are in the lithosphere, especially in fossil fuels such as coal and oil..
In the same way, there are a series of flows that cross in different directions between the atmosphere, the soil, the water and the living beings. Sulfur is found in this flow in various states, both gaseous, solid, and dissolved in water..
Similarly, sulfur assumes different chemical forms, for example calcium sulfate (CaSO4) and magnesium sulfate (MgSO4). Other forms are sulfur dioxide (SOtwo), sulfuric acid (HtwoSW4), carbon sulfide (CStwo), hydrogen sulfide (HtwoS) and soluble sulfate ions (SO4two-).
The phases or stages through which sulfur passes in its cycle do not follow a strict sequence. That is, sulfur can pass from the soil to living organisms and from these back to the soil.
It can also pass from the ground to the air and back to the ground or from the air to the water, from here to living organisms and back to the ground..
Mineral sulfur is found in rocks rich in this element, such as mineral coal. Also gypsum deposits (calcium sulfate), when decomposed, can generate sulfur deposits in the soil.
Oil is another compound that is deposited in geological layers and contains sulfur. Similarly, in the deposits of magma or molten rock in the interior of the Earth, sulfur abounds.
Sulfur reaches the soil by the decomposition of living beings, acid rain or the sedimentation of mineral sulfur. On the other hand, it leaves the ground in three fundamental ways: volcanic activity, natural extraction by living beings or human extraction..
Volcanoes expel sulfur-rich gases such as sulfur dioxide and also lava, which, among other components, contains this mineral. In addition, bacteria and plants absorb sulfur-rich compounds from the soil for their nutrition..
On the other hand, humans extract compounds with sulfur to generate energy or to use them in industry. This activity produces waste gases that contain this element, which pass into the atmosphere. For example, coal and oil are sulfur-rich compounds that are extracted from the earth..
Sulfur reaches the atmosphere through volcanic activity and oceanic hydrothermal vents, which release it in the form of the gas called sulfur dioxide (SOtwo). This gas is colorless, irritating and has a pungent odor..
Additionally, sulfur dioxide arises from man-made sources such as thermoelectric plants, car exhausts, and factories. Upon contact with the water vapor in the clouds, the SOtwo produces sulfuric acid that condenses in water droplets and precipitates.
Thus it falls dissolved in rainwater or snow, reaching the ground or bodies of water (rivers, lakes, oceans). Sulfur is also incorporated into the atmosphere as hydrogen sulfide due to bacterial activity both in the soil and in the water..
Sulfur enters the biological phase when it is incorporated into food chains, which occurs when it is absorbed by bacteria and plants both in the soil and in the water. It is absorbed as sulfate ions dissolved in water and then transformed into sulfides by reduction.
Once absorbed, it goes on to integrate the proteins that form the bodies of bacteria and plants. These in turn are consumed by other organisms, which in this way obtain the sulfur they require for their nutrition..
For example, plants absorb sulfur, herbivorous animals consume plants, and these in turn are consumed by carnivores. Therefore, sulfur travels throughout the food web..
When animals expel their feces, the remains of proteins and other compounds contained therein carry sulfur. In the same way, the death of living beings is a way to return sulfur to the soil or (in the case of aquatic organisms) to the water.
Upon death, decomposing organisms incorporate sulfur back into the soil in the form of hydrogen sulfide. The sulfur then oxidizes and forms sulfates again, which can be absorbed by plants..
There are also bacteria that process decomposing organic matter in swamps and release hydrogen sulfide into the air. Hence the characteristic smell that swampy areas have.
Sulfur reaches water bodies carried by runoff water that washes it from the ground. Similarly, it can fall directly from the air in the form of acid rain..
It is also incorporated into the oceans from the deep sea through submerged hydrothermal vents, which expel sulfur-rich compounds..
Once in the water, it is used as an energy source by sulfur-processing bacteria and absorbed by elements of plankton. In this way, it penetrates food webs, since bacteria and plankton are consumed by other marine beings.
The sulfur cycle is of vital importance, since it guarantees the recycling and availability of this fundamental element for living beings.
Sulfur is part of the amino acids that are the constituents of proteins, such as methionine, cysteine and cystine that are synthesized by plants. As well as other fundamental compounds for the metabolism of all living beings, such as coenzyme A.
Similarly, sulfur is part of the production of chlorophyll, which is the compound that allows transforming solar energy into food..
Elemental sulfur has a great economic value, since it is used in the manufacture of various products for industrial and domestic use. Among them the sulfuric acid that is used in batteries for motor vehicles.
It is also used in the manufacture of gunpowder, in the bleaching of paper and in the vulcanization of tires.
Sulfur compounds, such as sulfur dioxide and sulfur trioxide, emitted by industries, thermoelectric plants and vehicles, are pollutants. These compounds when hydrated in the atmosphere form sulfuric acid and sulfurous acid that precipitate as acid rain..
This process results in the acidification of bodies of water and negatively affects life..
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