Gypsum board, also known as wallboard, sheetrock or most commonly drywall, is the most common form of finish wall sheathing. Common drywall is made of gypsum plaster sandwiched between two thick layers of paper, and makes for a very smooth finish. As with many other materials, the gypsum industry has found a way to incorporate recycled materials into drywall, which makes for a less energy intensive product, while also keeping a by-product of coal-fired power plants out of the landfill.
In 1970, the U.S. Congress implemented the Clean Air Act, which was designed to protect and improve the nation's air quality and the stratospheric ozone layer. This law was amended in 1990, and one of the amendments required power plants to reduce their sulfur dioxide emissions. To comply with this law, chemical scrubbers are used to remove sulfur from the flue gases of coal-fired power plants. According to Environmental Building News, the chemistry of this process is really elegant: sulfur dioxide in the flue gases reacts with the calcium carbonate to produce calcium sulfite, and this calcium sulfite is converted into gypsum by oxidizing it with water. The by-product of this process is synthetic gypsum, also known as flue-gas-desulfurization (FGD) gypsum, which is nearly chemically identical to virgin gypsum that is extracted from gypsum mines.
In the 1990s the gypsum industry recognized that using synthetic gypsum could not only save them money, but that there were also environmental benefits of the by-product. Whereas natural gypsum is obtained from gypsum mines, synthetic gypsum can be used to replace this limited resource, and gypsum companies can save energy by locating their production facilities near synthetic gypsum producing power plants. If the gypsum industry wasn't using this by-product in drywall, the FGD would just be sent to a landfill.
Many companies are now using synthetic gypsum exclusively in their drywall, or a blend of natural and synthetic — more than half of all drywall companies use some form of synthetic gypsum, and almost all of the drywall factories built in the last decade are synthetic gypsum facilities.
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