HOW LIME IS PRODUCED
The four basic steps in the production of lime are:
(1) Quarrying or mining. Limestone is extracted in both underground and surface mines. Lime-quality limestone must be carefully identified and extracted to maintain its purity.
(2) Stone preparation. This step includes crushing and screening, and in many cases, washing to remove impurities.
(3) Calcining. Limestone, which is primarily composed of calcium carbonate, is heated to convert the calcium carbonate into calcium oxide. In the United States, this process is generally carried out in either large rotary kilns or vertical shaft kilns. Because of the high temperatures required (exceeding 1800 degrees F.), calcining is an energy-intensive process. The product of the calcining process is quicklime, which can be used as "pebble lime," or may be crushed or pulverized, depending on its intended use.
(4) Hydrating. Hydrated (or slaked) lime is produced by reacting quicklime with water in continuous hydrators. The end product is a fine dry powder, or, with additional water, pumpable milk of lime.