http://www.ehow.com/how_5700758_extract-sulfur-gypsum.html
Roast the gypsum moderately in an oven, causing it to give off its "waters of hydration."
CaSO₄·2H₂O ' CaSO₄ + 2 H₂O'
The anhydrous calcium sulfate can then be processed further to obtain a separation or extraction of its sulfur content.
2
Heat the gypsum in a kiln to 600 to 900 degrees C in the presence of a reducing atmosphere such as hydrogen or carbon monoxide to produce calcium oxide and sulfur dioxide. Using hydrogen, for example,
CaSO₄ + H₂ ' CaO + H₂O + SO₂
Thus the gypsum is converted to calcium oxide (lime) and sulfur dioxide, both very useful products. The sulfur dioxide can then be further processed in at least two commercially profitable ways.
Read more: How to Extract Sulfur From Gypsum | eHow.com
http://www.ehow.com/how_5700758_extract-sulfur-gypsum.html#ixzz1TpAHj1kP