Sulphur cycle

Sulphur cycle

1. Sulfur Cycle Most sulfur is buried in rocks and minerals underground Hydrogen sulfide (H 2 S) and sulfur dioxide (SO 2 ) are released by volcanoes. The most reduced forms of sulfur are the sulfides, such as the odourus gas hydrogen sulphide (H 2 S) . Like the ammonium ion of the nitrogen cycle, this is a reduced compound that generally forms under anaerobic conditions.

2. SULFUR CYCLE

3. Steps of the sulfur cycle are: Mineralization of organic sulfur into inorganic forms, such as hydrogen sulfide (H2S), elemental sulfur , as well as sulfide minerals. Oxidation of hydrogen sulfide, sulfide, and elemental sulfur (S) to sulfate (SO 4 (2 - )). Reduction of sulfate to sulfide. Incorporation of sulfide into organic compounds (including metal-containing derivatives).

4. Sulfur Cycle SO 4 -2 Sulfate Reduction (Assimilitory) Organic Sulfur H 2 S Mineralization Sulfur Oxidation Sulfate Reduction (Dissimilitory) Elemental Sulfur Sulfur Oxidation Sulfur Reduction

5. SO 4 -2 ATP APS 2 ADP 2 ATP SO 3 -2 S 3 O 6 S 2 O 3 -2 Sulfate Reduction

6. Sulfur Reduction Thiosulfate Disproportionation S 2 O 3 -2 + H 2 O SO 4 -2 + HS - + H + S + H 2 HS - + H +

7. HUMAN IMPACTS TO SULFUR CYCLE Approximately 1/3 of all sulfur emitted into atmosphere comes from human activities. Burning sulfur containing coal and oil to produce electric power ( SOx = acid deposition). Convert sulfur -containing metallic ores into free metals such as copper, lead, and zinc releasing sulfur dioxide into the environment. Refining petroleum – ( SOx emissions) Smelting to convert sulfur compounds of metallic minerals into free metals (Cu, Pb , Zn) Industrial processing.

8. IMPORTANCE OF SULFUR CYCLE Sulfur is a component of most proteins and some vitamins. Sulfate ions (SO 4 2- ) dissolved in water are common in plant tissue. They are part of sulfur-containing amino acids that are the building blocks for proteins. Sulfur bonds give the three dimensional structure of amino acids. Many animals, including humans, depend on plants for sulfur-containing amino acids.

9. Sulfur Cycle  Sulfur cycle is the natural cycle which includes the mineralization of organic sulfur to sulfide, oxidation of this to sulfate, and reduction of this to sulfide followed by microbial incorporation of this into organic compounds.

10. Sulfur Cycle The sulfur cycle includes both gases and solids. Hydrogen sulfide gas (H 2 S) is released into the atmosphere by volcanic eruptions , hot springs , and the anaerobic decay of sulfur-containing biological material in swamps, bogs, and tidal flats. Certain marine algae produce dimethyl sulfide, (CH 3 ) 2 S, a volatile compound that enters the atmosphere as tiny droplets. Sulfur dioxide gas is released into the atmosphere by volcanoes and also forms when dimethyl sulfide reacts with oxygen gas. The burning of fossil fuels, such as coal and oil releases sulfur dioxide into the atmosphere.

11. Sulfur Cycle Sulfur dioxide reacts with atmospheric oxygen to produce sulfur trioxide (SO 3 ). Some sulfur trioxide reacts with tiny water droplets to form sulfuric acid (H 2 SO 4 ). Sulfur oxides also react with ammonia to produce tiny particles of ammonium salts. The winds carry droplets of sulfuric acid and particles of sulfate salts, which then fall to the earth in acid deposition. By adding sulfur compounds to the air, the use of fossil fuels increases the rate of acid deposition. All living things require sulfur to make proteins.

12. Sulfur Cycle Plants get sulfur by taking up ions of sulfate salts (SO 4 2- ) from the soil. Animals get sulfur by eating plants, and all living things release sulfur compounds when they decay. Decomposition releases sulfate salts (SO 4 2- ), which can be taken up by plants, as well as gaseous hydrogen sulfide.

13. Sulfur Cycle Some hydrogen sulfide enters the atmosphere. But when decay occurs in an oxygen-free environment, anaerobic bacteria break down hydrogen sulfide and release sulfur gas (S 2 ). Oxygen-requiring bacteria can incorporate sulfur into sulfate salts, which can be taken up by plants and enter the food chain once again.