The Sulfur Cycle

The Sulfur Cycle

The Sulfur Cycle

The sulfur cycle is the collection of processes by which sulfur moves to and from minerals, waterways and living systems.

The Steps

1. Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (H2S), elemental sulfur, as well as sulfide minerals.

-The weathering of rocks releases stored sulfur

2. Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate (2H2SO4).

2S + H2O + 3O2 ---> 2H2SO4.

Once in sulfate, plants can incorporate sulfur into proteins allowing it to run through the food chain

3.Reduction of sulfate to sulfide by sulfur bacteria

4.Incorporation of sulfide into organic compounds

Natural sources release sulfur into the atmosphere (volcanic eruptions, breakdown of organic matter, and evaporation of water

Hydrogen Sulfide

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Sulfuric Acid

Sulfur enters the atmosphere from several sources. Hydrogen sulfide (H S) is a colorless, highly poisonous gas with a rotten-egg smell and it's released from active volcanoes and from organic matter broken down by anaerobic decomposers in flooded swamps, bogs, and tidal flats.

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In the atmosphere, DMS is converted to sulfur dioxide, some of which in turn is converted to sulfur trioxide gas (SO ) and to tiny droplets of sulfuric acid (H SO ). DMS also reacts with other atmospheric chemicals such as ammonia to produce tiny particles of sulfate salts. These droplets and particles fall to the earth as components of acid deposition.

Volatile Dimethyl Sulfide

Certain marine algae produce large amounts of volatile dimethyl sulfide, or DMS (CH SCH ). Tiny droplets of DMS serve as nuclei for the condensation of water into droplets found in clouds

In this way, changes in DMS emissions can affect cloud cover and climate.

Sulfur Dioxide

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Sulfur dioxide (SO ) is a colorless and suffocating gas which also comes from volcanoes.

Sulfate

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Why Is Sulfur Important?

Particles of sulfate (SO ) salts, such as ammonium sulfate, enter the atmosphere from sea spray, dust storms, and forest fires. Plant roots absorb sulfate ions and incorporate the sulfur as an essential component of many proteins.

What we do...

It is essential for the functioning of proteins and enzymes in plants, and the animals that depend on the plants for sulfur

• we burn sulfur-containing coal and oil to produce electric power
• we refine sulfur-containing oil (petroleum) to make gasoline, heating oil, and other useful products
• we extract metals such s copper, lead, zinc from sulfur-containing compounds in rocks that are mined for these metals.

Acid Deposition

Sulfur comes back into the atmosphere in acid rain, which along with other air pollutants can harm trees and aquatic life.

Reservoirs

Human Activities

- Largest physical reservoir is the Earth´s crust where sulfur is found in gypsum and pyrite.

-Largest biologically useful sulfur is found in the ocean as sulfate anions 2.6g/L), dissolved hydrogen sulfide gas, and elemental sulfur

Other Reservoirs:

-Freshwater (sulfate, hydrogen sulfide, and elemental sulfur)

-Land (sulfate)

Atmosphere (sulfur oxide (so2), methane sulfuric acid(CH3SO3), volcanic activity releases hydrogen sulfide into the air

We have affects the sulfur cycle by releasing large amounts of sulfur dioxide into the atmosphere. We release sulfur into the atmosphere in three ways.