High-purity refractory "dolomite" (frequently called Doloma) and lower purity fettling grade "dead-burned dolomite" (usually referred to as DBD) are both manufactured by calcining dolomitic limestone. The method is similar to the manufacture of ordinary lime, except that the burning time is longer and temperatures considerably higher (in the range of 1600 - 1850º C). High purity doloma is fired in rotary or shaft kilns to the upper end of the temperature range without the addition of impurities. The lower-purity DBD is fired in rotary kilns to the lower end of the temperature range, and iron oxides are added during calcinations to stabilize the resulting hard-burned quicklime against decomposition from moisture. High purity doloma is used to manufacture refractory bricks employed in cement and lime rotary kiln linings, and in steel ladles and refining vessels. DBD is used for the manufacture of monolithic patching and repair materials for steel furnaces.
Large quantities of light-burned dolomitic lime are also employed in the production of synthetic refractory grade Magnesia (MgO). The quicklime is slaked in a magnesium chloride brine, precipitating magnesium hydroxide. The mag-hydroxide is calcined and fired into dense, high-purity magnesium oxide. Refractory magnesia is used in the production of linings for cement and lime kilns, in addition to steel ladles and furnaces.
Stabilized zirconium oxide (ZrO2) is produced by the addition of about 3% lime during the fusion or sintering process, and is widely used for analysis crucibles and thermocouple tubes, in addition to crucibles and furnaces used for the production of high-temperature aero-space alloys.
One form of silica brick, a specialized refractory used for lining coke ovens and glass furnaces, is made by thoroughly mixing ground silica (usually quartzite) with the addition of ½ to 3 percent milk-of-lime as a sintering (firing) aid. This mixture is formed into various shapes and then fired in kilns.
Lime serves a myriad of uses in the food industry. Some examples:
Dairy Industry--When cream is separated from whole milk, lime water is often added to the cream to reduce acidity prior to pasteurization when butter is produced. The skimmed milk is next acidified to separate casein. The casein is mixed with lime and a small amount of sodium fluoride to produce calcium caseinate, a form of glue. Fermentation of the remaining skimmed milk (whey) and the addition of lime forms calcium lactate, which is marketed as a medicinal or acidified to produce lactic acid.
Glue and Gelatin--Waste materials from rendering plants are treated with lime in slurry form. This process swells the collagen, thereby facilitating subsequent hydrolysis. After liming, the treated stock is washed to remove lime, albumin, and mucin. The washed stock is dried, and the final product is sold as glue or gelatin.
Baking Industry--In the preparation of a common type of baking powder, monocalcium phosphate is required as an ingredient. This is made by reacting pure phosphoric acid with a high calcium lime.
Fruit and Vegetables--In the controlled atmospheric storage of fruit and vegetables, bags of hydrated lime are placed on racks in the storage room to absorb CO2 that exudes from the ripening fresh produce. In this manner a higher ratio of oxygen to CO2 is maintained, permitting vegetables and fruit to be stored fresh for much longer periods. When placed in close proximity to the produce, carbon dioxide penetrates easily through the multiwall paper bags into the lime. For apples lime consumption averages about 1 to 1.5 lb./bushel. Pears, plums, and tomatoes, in addition to apples, have been stored in this way in Canada and the Northeastern U.S., as well as in Oregon and Washington. In California this technique is commonly employed in storing lettuce.
Miscellaneous--All quality tortillas are treated with lime. Corn is first soaked in milk-of-lime before its conversion to cornmeal. Lime is also used in the burgeoning corn chip business. The refuse, grape lees, from wineries is treated with lime, precipitating calcium tartrate, which is sold as such or converted to tartaric acid. Several prominent recipes for making watermelon pickles require the melon rind be soaked in milk-of-lime.
Back...
