In the years since passage of the Ambient Clean Air Act of 1970, and its 1977 amendments, impoundment of FGD waste has involved hundreds of millions of tons of solids and the purchase of about 40 percent of its weight in lime, or 70 percent limestone. In addition to the costs of reagent and disposal, tens of thousands of acres of land have been removed from productive use to accommodate the wastes created. For example, earlier low solids sludge impoundments for a 2000 MW power plant required about 500 acres for disposal of combined FGD and fly ash solids for a 30-year plant life. Such impoundments impose the risk of continuous leaching of environmentally undesirable constituents into the groundwater and streams. C. A stoichiometric excess of lime and carbon in the initial mixtures enhances the rate of iron production and increases the degree of reaction completion.
Further research is required to reduce the sulfur content in the iron to meet steelmaking standards.