Lime and the paper industry
Lime, primarily known as calcium oxide (CaO), is a crucial industrial chemical with various applications across multiple sectors, including the paper industry. Derived mainly from limestone and other high-calcium materials, lime is produced through the heating of these materials, resulting in a highly reactive compound that can combine with water to form hydrated lime. In the paper industry, lime plays a vital role in the pulping process, where it aids in the removal of impurities and helps in the production of high-quality paper products.
Lime is also instrumental in chemical preparation, as it is involved in the production of calcium compounds essential for various processes in papermaking. Additionally, its reactivity and ability to neutralize acids make it effective in treating wastewater generated from paper production, ensuring environmental compliance. Beyond its applications in the paper industry, lime is widely used in manufacturing glass, porcelain, and construction materials, showcasing its versatility as a fundamental industrial resource. Understanding lime's role in these processes highlights its importance to both the paper industry and broader industrial applications.
Lime and the paper industry
Where Found
Lime is a manufactured product not found in nature. It is usually derived from the common rocks limestone, dolomitic limestone, and dolostone, although it can also be produced from other high-calcium materials such as marble, aragonite, chalk, shell, and coral.
Primary Uses
An essential industrial chemical, lime is used in the manufacture of steel, pulp and paper, glass and porcelain, and chemicals. It is a component of construction materials such as plaster, mortar, stucco, and whitewash. It is also used in conditioning acidic soils, softening water, and treating wastewater and smokestack emissions.
Technical Definition
Lime (also known as quicklime, caustic lime, or calcia) is a common term for the chemical compound calcium (CaO). The name is often applied to several related compounds, including hydrated or slaked lime (calcium hydroxide, Ca(OH)2); dolomitic quicklime (CaO˙·MgO); type N (Ca(OH)2·MgO) and type S (Ca(OH)2·Mg(OH)2) dolomitic hydrates; and refractory lime, also called dead-burned or hard-burned lime. When pure, lime occurs as colorless, cubic crystals or in a white microcrystalline form; often impurities such as iron and oxides of silicon, aluminum, and magnesium are present. Lime has a specific gravity of 3.34, a melting point of 2,570° Celsius, and a boiling point of 2,850° Celsius.
Description, Distribution, and Forms
A highly reactive compound, lime combines with water to produce the more stable hydrated lime. This reaction, known as slaking, produces heat and causes the solid almost to double in volume. At temperatures around 1,650° Celsius, lime recrystallizes into the coarser, denser, and less reactive refractory lime. When heated to approximately 2,500° Celsius, lime is incandescent.
Lime is a highly reactive manufactured compound that is an essential part of many industrial processes. An alkali, it dissolves in water to produce a caustic, basic solution. Lime is typically obtained from limestone, although other natural substances that are high in calcium are also used as raw materials for lime manufacture. In 2023, the United States produced 17 million tons of lime and quicklime, while the total world production approached 343 million metric tons.
History
Use of lime in construction dates back at least to the ancient Egyptians, who, between 4000 and 2000 BCE, employed it as a mortar and plaster. The Greeks, Romans, and Chinese used it in construction, agriculture, textile bleaching, and hide tanning. One of the oldest industries in the United States, lime manufacture began in colonial times. While the use of lime increased with the Industrial Revolution, it remained largely a construction material until the early twentieth century, when it became a crucial resource for the rapidly growing chemical industry.
Obtaining Lime
Lime may be prepared from a variety of naturally occurring materials with a high calcium content. While lime is commonly obtained from limestone, a sedimentary composed chiefly of calcite (calcium carbonate, CaCO3), it can also be derived from dolostone, a similar sedimentary rock that is predominantly dolomite (CaMg(CO3)2), or from rock with an intermediate composition (dolomitic limestone). Lime is also produced from marble, aragonite, chalk, shell, and coral (all mostly calcium carbonate). Because the raw materials for lime manufacture are plentiful and widespread, lime is produced all over the world, with production facilities generally located near the sources for the raw materials.
When calcium carbonate is heated in a masonry furnace to about 1,100° Celsius, it breaks down into lime and carbon dioxide. Heating dolomite in this fashion produces dolomitic quicklime and carbon dioxide. Approximately 100 metric tons of pure yields 56 metric tons of lime. Adding water to stabilize lime or dolomitic quicklime yields the hydrated (slaked) form. Dolomite is typically used to make refractory (dead-burned) lime, which involves heating the materials to temperatures around 1,650° Celsius.
Uses of Lime
A fundamental industrial chemical, lime is used in the manufacture of porcelain and glass, pigments, pulp and paper, varnish, and baking powder. It is employed in the preparation of calcium carbide, calcium cyanamide, calcium carbonate, and other chemicals; in the refining of salt and the purification of sugar; in treating industrial wastewater, sewage, and smokestack effluent; and in softening water. In it is used in and in concentrating ores. Lime and other calcium compounds are used in liming, a method for treating acidic soils. The application of lime to soil neutralizes acidity, improves soil texture and stability, and enriches the soil’s nitrogen content by increasing the activity of soil microorganisms that secure nitrogen from the air. Lime’s incandescent properties are employed in the Drummond Light, or limelight, in which a cylinder of lime is heated with the flame of an oxyhydrogen torch to produce a brilliant white light. Mixed with sand and water, lime serves as a mortar or plaster. The lime hydrates in combination with water; the mortar hardens quickly as the hydrated lime reacts with carbon dioxide in the air to form calcium carbonate. Dolomitic quicklime is used to produce a hard, strong, and elastic stucco.
Uses of hydrated lime include soil liming, sugar refining, and chemical preparation. In leather tanning, hydrated lime is used to remove hair from hides. In construction, it is used to increase the durability of mortar, plaster, and stucco. Hydrated lime in a highly dilute solution is whitewash. Filtering whitewash yields lime water, used in medicine as a burn treatment and as an antacid, and in chemistry as a reagent. Dolomitic hydrates are used as a in the manufacture of glass.
Dead-burned lime is a refractory material, able to withstand contact with often corrosive substances at elevated temperatures. Refractory lime is a component in tar-bonded refractory brick, which is used in the construction of the basic oxygen furnaces employed in steelmaking.
Bibliography
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