Minerals Information
Lime is a basic chemical that ranked fifth in total production in the United States in 1990. Its major uses are in steelmaking; pulp and paper manufacturing; construction; and the treatment of water, sewage, and smokestack emissions (flue gas desulfurization).
Lime is manufactured by calcining (burning) high-purity calcitic or dolomitic limestone at temperatures ranging from 980ø C to 1,320ø C. It is never found in a natural state. The calcination process drives off the carbon dioxide, forming calcium oxide (quicklime). The subsequent addition of water creates calcium hydroxide (hydrated lime). The term "lime" refers primarily to six chemicals produced by the calcination process followed by hydration where necessary. They are (1) quicklime or calcium oxide (CaO), (2) hydrated lime or calcium hydroxide [Ca(OH)2], (3) dolomitic quicklime (CaOùMgO), (4) type N dolomitic hydrate [Ca(OH)2ùMgO], (5) type S dolomitic hydrate [Ca(OH)2ù;Mg(OH)2], and (6) dead-burned dolomite. Lime can also be produced from other calcareous materials such as aragonite, chalk, coral, marble, and shell.
The last 20 years have witnessed three major market shifts and a tremendous increase in prices. The synthetic soda ash industry disappeared, decreasing annual lime consumption by more than 3 million metric tons. The steel industry expanded in the 1970's reaching a peak consumption rate of more than 8 million metric tons per year, but then shrank in the 1980's, causing a dramatic drop in consumption to current levels of about 4.6 million metric tons per year. Passage of the Clean Air Act in 1970 created the flue gas desulfurization market, which has grown steadily until it is the second largest market for lime in the United States. The large jump in prices during the 1970's was the result of the energy crisis. Fuel is generally the largest cost of operation in a lime plant utilizing rotary kilns.