WHAT IS THE SULFUR CYCLE?
☺ The Sulfur Cycle is the transfer and transformation of
sulfur compounds throughout the atmosphere, biosphere,
pedosphere, and hydrosphere.
☺ Sulfur is an important nutrient for organisms as it
makes up a significant part of certain amino acids,
proteins and other biochemicals.
☺ Much of the sulfur in the present environment
originated from deep sedimentary rocks and soil but due
to human interference, it has been released onto the
surface.
PATHWAY OF MOVEMENT
The sulfur cycle mainly consists of the movement of sulfur compounds from
sedimentary rocks and soil to surface systems such as plants or coal
factories, to the atmosphere, then back down to the ocean and soil through
precipitation.
☺ Sulfur is mainly found in soil and sediment in the form of inorganic
sulfur (S), sulfates (SO42–), reduced sulfur (H2S) and sulfides (S2−).
☺ Weathering and groundwater then bring the sulfur closer to the surface.
☺ The sulfur can be moved in two ways:
☺ Uptake by plants, providing them important nutrients
☺ Consumption by humans through coal & fossil fuel mining
☺ Factories burning and processing fossil fuels emit SO2 into the
atmosphere, which is then converted into sulfate and sulfuric acid.
☺ Through acid precipitation, sulfur is redistributed to the biosphere and
hydrosphere, settling into the soil and water, which will eventually
continue onto the next steps of the cycle.
☺ Sulfur is also released through the digestion and excretion of living
organisms.
IMPACT OF HUMANS
☺ Human action has had a major effect on the sulfur cycle. As farming
techniques and practices of humans has developed throughout the years,
more sulfur in the soil has been released into the atmosphere as dust due
to grazing and plowing of land, and river diversion. Sulfur has also been
released by the decrease of plants covers that would restrict wind erosion
in arid regions from human technology.
☺ Due to the drilling, burning and pumping of fossil fuels and coal in the
pedosphere, large amounts of sulfur, originally meant to maintain in deep
soil and sediments, have been released into the environment. There is an
increase of oxidized sulfur (SO4) in the global cycle at the expense of the
storage of reduced sulfur in the Earth’s crust.
☺ SO2 is released as an air pollutant through the production of fossil fuels
and forms sulfuric acid (H2SO4) as a result of interacting with the water
in the atmosphere. This reaction creates acid precipitation, which can
damage both man-made and natural systems.
☺ Sulfur is also applied to land as fertilizer, as it is an essential
biological element.
CHEMICAL EQUATIONS
H2S + 2CO2 + 2H2O → 2CH2O + 2H+ + SO42−
(Sulfur Oxidation)
Hydrogen Sulfide
Formaldehyde
Sulfate
2CH2O + SO42− → 2HCO3− + HS− + H+
(Sulfur Reduction)
Formaldehyde + Sulfate -> Hydrogen Carbonate