SULFUR DIOXIDE
SO2
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Sulfur is a yellow non-metallic element, Atomic number 16, atomic weight 32.06. It is polymorphic. The rhombic form melts at 112.8oC and the monoclinic form melts at 119oC.   A rubber like form of sulfur forms around 200oC. Sulfur boils at 444oC.   It burns readily in air to form sulfur dioxide. 
Sulfur dioxide is a colorless gas with a choking odor. It is formed by the oxidation of sulfur and its compounds. Some equations for the production of SO2 include:
S + O2 ------> SO2
4 FeS2 + 11 O2 -----> 2 Fe2O3 + 8 SO2
Na2SO3 + 2 H+ ----> H2O + 2 Na+ + SO2
FeS2 is pyrite or "fool's gold". It is a common impurity in soft coal
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The burning of sulfur or sulfur containing materials such as sulfides is the most common way to generate Sulfur Dioxide.

The picture on the left shows molten Sulfur, the element, burning in air with a characteristic blue flame to give SO2.

S + O2 ------> SO2
The SO2 in the atmosphere comes mainly from:
  1. Burning of high sulfur hydrocarbons such as eastern soft coal in power plants or use of high sulfur fuel in diesel trucks.
  2. Volcanic activity
Currently, not much can be done about Volcanic activity.
However, SO2 emissions from power plants can be reduced by:
    a. Removing SO2 from the smokestack emissions.
    b. Removing sulfur and sulfides from coal before burning.
    c. Switching to a sulfur free fuel.

Sulfur Dioxide which is recovered from smokestacks can be converted into Sulfuric Acid which can be sold.
2 SO2 + O2 + 2 H2O -----> 2 H2SO4
The conversion of SO2 to H2SO4 is a slow but spontaneous reaction.
Sulfuric Acid is a major component in "Acid Rain"

©RWK 1997