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The Sulphur Cycle

It’s in the air, it’s all around us yet none of us really understand its importance and significance on our Earth. Yes im talking about Sulphur (or the Sulphur Cycle).

Sulphur is one of the most important, common and ubiquitous elements on earth existing as a non-metallic solid in its pure form, yellow in colour and found in many organic and inorganic compounds. It is found throughout the environment in soil, air and also rocks all the way through to plants and animals. Sulphur is present in amino acids such as cysteine and methionine meaning that as humans we have a little bit of sulphur in us from these amino acids that are of course found in the proteins we make.

Plants get their sulphur supply from micro-organisms in the soil and water around them which they can then obviously convert into useable forms from their growth and development. Animals will obtain their supply from eating plants and other animals (eachother). And, just like any liveable organism, these plants and animals will eventually die leaving micro-organisms to break them down releasing the basic elements back into the ground, for example carbon, nitrogen, phosphates and of course sulphur.

So what we have is a cycle within a cycle when it comes to a plant or animals growth using sulphur to build their own proteins, all the way to when that same plant or animal dies and decomposes which releases sulphur back into the environment in the form of sulphur salts, sulphide, sulphate esters and sulphonates.

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Sulphur cycle. Source: Google creative commons.

Apart from plants and animals contributing to the sulphur cycle, what else does? There are sulphates in water which often are converted (or reduced) to sulphur derivatives such as sulphides by certain microorganisms and aquatic plants. Micro-organisms living in such aquatic environments will either reduce or oxidise (or do both) sulphur already present. Another member of the sulphur cycle is volcanoes. When a volcano erupts this is usually accompanied by the release of hydrogen sulphide gas from sulphide mineral deposits, and also sulphur dioxide which can be extremely dangerous. Around volcanoes it is not uncommon to find deposited sediments of sulphur as minerals, or find buried Iron sulphide (known as pyrite) in these sediments.

Volcanic sulphur and underground sulphur contributes to our global supply even today and there are even chemical processes that many companies/industries use as a standard to syphon off Sulphur for distribution. The way this works is that the industrial sulphur is obtained as a by-product of natural gas and refinery processes, generating an efficient method to capture most of this sulphur by purifying it (getting it simply as sulphur) from other compounds.

The last most important contributor to the release of sulphur is human activity. As a species we have been emitting just about everything into our own atmosphere for the sake of advancement for centuries. Mining, metal processing plants and burning fossil fuels release hydrogen sulphide gas and sulphur dioxide into the atmosphere. This sulphur will then react with whatever water is already in the air producing sulphuric acid and sulphur salts. These newly formed compounds will return to Earth usually in the form of acid rain and disrupt local communities, creating chemical imbalance, killing fish and plant life. However atmospheric pollution does lend a hand, contributing to cloud formation  and absorbing UV light which in a way helps offset the temperature caused by the greenhouse effect.

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Sulphur Cycle Diagram. Source: Google creative commons.

Sulphur Cycle Diagram

Back in the olden days when old school mining was around sulphur was mined for use in making black gunpowder, to name one application. Nowadays its used in so many different industries such as in consumer products for example making matches and insecticides and also for use in fertilizers, an additive in gardens and fruit preservation.

Sulphur, just like Carbon and Nitrogen, is vital in all life processes.

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