The chemical industry uses lime in the production of a variety of chemicals including sodium alkalis, calcium carbide, cyanimide, citric acid, petrochemicals, propylene glycol glycerin, magnesia, calcium hypochlorite, and many others. These chemicals, in turn, are used in virtually every product in the United States.
A growing use for lime is the production of precipitated calcium carbonate, which is used in the production of paper, paint, ink, plastic, rubber, and some foods. The paper industry uses lime as a causticizing agent, for bleaching, and to produce PCC for their use.
These and other key uses of lime, such as for sugar refining, refractories, and other food industries are discussed in this area.
The Chemical Uses of Lime
Lime is a basic industrial chemical that is used as a component in many other chemical processes.
Alkalis
Alkali plants with access to natural soda ash use the “lime-soda process” to manufacture caustic soda (sodium hydroxide). Sodium carbonate (soda ash) reacts with lime slurry to form caustic soda and precipitated calcium carbonate as co-products.
Calcium Carbide and Cyanimide
Calcium carbide, the oldest source of acetylene, is formed by mixing quicklime and coke and heating to a temperature of 2000 degrees C. Molten carbide is continuously removed from the furnace and, upon solidifying, is crushed and ground to the desired size. Calcium cyanamide, a nitrogen fertilizer, is made by heating calcium carbide in the presence of nitrogen. Acetylene gas is generated from carbide by adding water, yielding a waste-hydrated lime.
Citric Acid
Lime is used in the purification of citric acid. Hydrated lime is added to a solution of citric acid that has previously been filtered to remove suspended solids. Calcium citrate is precipitated and removed. Citric acid can later be regenerated from the calcium citrate by reacting it with sulfuric acid to precipitate calcium sulfate.
Magnesia
Lime is used in the two major processes to manufacture magnesia (magnesium oxides): the seawater process and production from brines. In the seawater process, milk of lime precipitates magnesium hydroxide (Mg(OH)2) from seawater. Where dolomitic lime is used, up to half of the Mg(OH)2 derives from the lime. So too, in the production of Mg(OH)2 from brine, lime acts as a precipitant.
Calcium Hypochlorite
Calcium hypochlorite bleaches are produced by reacting lime with chlorine. These bleaches are widely used as swimming pool chemicals and in paper production.
Calcium Magnesium Acetate
Dolomitic lime is reacted with acetic acid to produce calcium magnesium acetate (CMA), a de-icing chemical. CMA is not corrosive and is very compatible with the environment. It is much less damaging to road surfaces and automotive parts than salt. It is effective in melting ice at very low temperatures and is not toxic to vegetation.
Miscellaneous Chemical Uses
Lime is employed in the manufacture of many other inorganic and organic chemicals and pharmaceuticals. Most of the calcium organic and inorganic salts are produced by reacting the various acids with lime (the base). Among the most important inorganic products that use lime are calcium phosphates (mono, di, and tri), fluoride, bromide, ferrocyanide, and nitrate. Lime is used in the manufacture of organics such as calcium acetate, stearate, oleate, tartrate, lactate, citrate, benzoate, and gluconate.
Lime is also used as a neutralizing agent in the manufacture of chrome chemicals (bichromate); for purification of salt brines; to aid in the concentration of glucose and dextrin; to make metallic calcium; as soda-lime, an absorbent and gas purifier; and for countless other minor or isolated purposes, such as for CO2 absorption, as a desiccant, etc.
Lime is used in the production of ethylene or propylene glycol via the chlorohydrin process. Ethylene gas, obtained readily from petroleum refineries, is chlorinated to form ethylene dichloride, which in turn is reacted with lime to produce ethylene glycol.
Industrial Uses of Lime
Sugar Refining
Hydrated lime is essential to the production of sugar from both sugar cane and sugar beets. It is also used to purify sugar from other sources, such as maple or sorghum, although these are produced in much smaller quantities.
Sugar cane and sugar beets are harvested and processed with water to form raw juice, which has a low pH and contains dissolved impurities. Hydrated lime is added to the juice to raise the pH and to react with the impurities to form insoluble calcium organic compounds that can be removed. Excess lime is removed by carbonation or by the addition of phosphoric acid. This process may be repeated several times depending on the purity of the final product required.
Refractory Products
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 production 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 kilns to the upper end of the temperature range without the addition of impurities. High-purity doloma is used to manufacture refractory bricks employed in cement and lime rotary kiln linings and in steel ladles and refining vessels. 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. DBD is used for the manufacture of monolithic patching and repair materials for steel furnaces.
Large quantities of light-burned dolomitic lime are used in the production of synthetic refractory grade magnesia (MgO). The quicklime is slaked in 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 adding about 3% lime during the fusion or sintering process. ZrO2 is widely used for analysis crucibles and thermocouple tubes in addition to crucibles and furnaces used for the production of high-temperature aerospace 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.
Food Industry
Lime serves a myriad of uses in the food industry. Some examples include:
Dairy Industry
When cream is separated from whole milk during the production of butter, lime water is often added to the cream to reduce acidity prior to pasteurization. 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. Afterward, 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, lime is required as an ingredient. This baking powder 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 ripening fresh produce. The co-location of hydrated lime in the storage room maintains a higher ratio of oxygen to CO2, permitting vegetables and fruit to be stored fresh for much longer periods. When placed near the produce, carbon dioxide penetrates easily through the multi-wall 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 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 corn chip business. Grape leaves from wineries are treated with lime to precipitate calcium tartrate, which is sold as such or converted to tartaric acid. Several recipes for making watermelon pickles require the melon rind to be soaked in milk-of-lime.
Precipitated calcium carbonate (PCC) is an innovative product derived from lime, which has many industrial applications. PCC is made by hydrating high-calcium quicklime and then reacting the resulting slurry, or “milk-of-lime”, with carbon dioxide. The resulting product is extremely white and typically has a uniform narrow particle size distribution. PCC is available in numerous crystal morphologies and sizes, which can be tailored to optimize performance in a specific application.
Use of PCC in the Paper Industry
With the alkaline conversion of the uncoated freesheet market and the continuing trend toward alkaline vs. acid process papermaking in the coated ground wood, and paperboard markets, PCC is well established as a filler and coating pigment for premium quality paper products. PCC is typically produced in slurry form at satellite plants located near paper mills. PCC enhances the optical properties and print characteristics of paper products, improves paper machine productivity, and can reduce papermaking costs through the replacement of more expensive pulp fiber and optical brightening agents. Constantly improving quality targets make the brightness of paper, and thus PCC, an increasingly important factor.
Use of PCC in Polymer Applications
PCC also finds many industrial uses due to its ability to achieve small particle sizes and special crystal shapes. In rigid polyvinyl chloride (PVC), such as vinyl siding and fencing, PCC increases impact strength with some of the smaller particles able to replace expensive impact modifiers. Nano PCCs (less than 0.1 micron in size) control viscosity and sag in automotive and construction sealants, such as PVC plastisols, polysulfides, urethanes, and silicones. In paint, PCC’s unique particle shapes improve hiding and allow reductions in titanium dioxide levels.
Use of PCC in Healthcare Applications
An effective acid neutralizer, PCC is often used in calcium-based antacid tablets and liquids. Being high in calcium content, PCC enables the formulation of high-dosage calcium supplements and multi-vitamin/mineral tablets. The small particle sizes and special particle shapes contribute to the development of good-tasting calcium-fortified foods and beverages.
Lime is an important commodity for the pulp and paper industry. Most pulp and paper facilities operate their own kilns and regenerate lime after use. Thus, this industry is primarily a market for “make-up” lime from commercial manufacturers.
Sulfate Process
By far, the largest application of lime in pulp manufacture is as a causticizing agent in sulfate (Kraft) plants. Here, the waste sodium carbonate solution is recovered and reacted with high calcium lime to generate caustic soda for reuse in the process. Most large sulfate plants recover about 90-98 percent of the lime by dewatering the waste calcium carbonate mud, and then calcining it in rotary kilns.
Sulfite Process
Sulfite plants use quicklime to prepare calcium bisulfite, an acid-cooking liquor used to digest or dissolve the non-cellulosic constituents of wood chips (paper and pulp stock). This process is on the wane due to waste disposal problems.
Bleaching
In pulp manufacturing processes, the interaction of lime and chlorine is used in the preparation of calcium hypochlorite bleach liquor. Calcium hypochlorite, the oldest known and lowest-cost bleach, is used extensively to bleach the pulp to the desired degree of whiteness.
Miscellaneous
Lime is used in the treatment of pulp and paper mill liquid wastes as a coagulant in color removal, a filtration conditioner, and, to a lesser extent, as a neutralizing agent. It is also used in the recovery of valuable by-products from pulp and paper mill wastes. It is used commercially to recover alcohol, calcium lignosulfonate, and yeast.