Gypsum is a naturally occurring form of calcium sulfate, CaSO₄·2H₂O. It is used in the building trade for gypsum board, also called drywall, and is an ingredient in plaster of Paris. It is made of the elements calcium, sulfur, oxygen and hydrogen. The sulfur can be removed from the gypsum by a series of chemical steps including use of a heat, reducing agents and catalysts.
Instructions
1. 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.
3. Employ a catalyst made up of vanadium pentoxide and an alkali metal sulfate supported on small silica beads at high temperature. The sulfur dioxide will be converted into sulfur trioxide, which is to be dissolved in 98 percent sulfuric acid. That sulfur trioxide reacts with the 2 percent moisture to form additional sulfuric acid.
4. Catalytically reduce the sulfur dioxide into elemental sulfur. The U.S. Department of Energy describes the use of a cerium oxide catalyst to reduce a mixture of sulfur dioxide and carbon monoxide to form sulfur and carbon dioxide. In this reaction, the carbon monoxide is oxidized to carbon dioxide; hence the overall reaction is a reduction-oxidation reaction, or REDOX.
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