Hydrated lime

Some carbonates are important industrial chemicals. Calcium carbonate occurs naturally in several forms, including limestone, and is used in the production of quicklime, calcium oxide CaO, slaked (or hydrated) lime, calcium hydroxide Ca(OH)2 and cement. 

Maintenance of conditions ia the culture environment that keep stress to a minimum is one of the best methods of a voiding diseases. Vacciaes have beea developed agaiast several diseases and more are under development. Selective breeding of animals with disease resistance has met with only limited success. Good sanitation and disiafection of contaminated faciUties are important avoidance and control measure. Some disiafectants are Hsted ia Table 6. Poad soils can be sterilized with burnt lime (CaO), hydrated lime [Ca(OH)2], or chlorine compounds (12). 

Protein-Based Adhesives. Proteia-based adhesives are aormaHy used as stmctural adhesives they are all polyamino acids that are derived from blood, fish skin, caseia [9000-71 -9] soybeans, or animal hides, bones, and connective tissue (coUagen). Setting or cross-linking methods typically used are iasolubilization by means of hydrated lime and denaturation. Denaturation methods require energy which can come from heat, pressure, or radiation, as well as chemical denaturants such as carbon disulfide [75-15-0] or thiourea [62-56-6]. Complexiag salts such as those based upon cobalt, copper, or chromium have also been used. Formaldehyde and formaldehyde donors such as h exam ethyl en etetra am in e can be used to form cross-links. Removal of water from a proteia will also often denature the material. 

Calcium. Calcium is the fifth most abundant element in the earth s cmst. There is no foreseeable lack of this resource as it is virtually unlimited. Primary sources of calcium are lime materials and gypsum, generally classified as soil amendments (see Calcium compounds). Among the more important calcium amendments are blast furnace slag, calcitic limestone, gypsum, hydrated lime, and precipitated lime. Fertilizers that carry calcium are calcium cyanamide, calcium nitrate, phosphate rock, and superphosphates. In addition, there are several organic carriers of calcium. Calcium is widely distributed in nature as calcium carbonate, chalk, marble, gypsum, fluorspar, phosphate rock, and other rocks and minerals. 

Most carbide acetylene processes are wet processes from which hydrated lime, Ca(OH)2, is a by-product. The hydrated lime slurry is allowed to settle in a pond or tank after which the supernatant lime-water can be decanted and reused in the generator. Federal, state, and local legislation restrict the methods of storage and disposal of carbide lime hydrate and it has become increasingly important to find consumers for the by-product. The thickened hydrated lime is marketed for industrial wastewater treatment, neutrali2ation of spent pickling acids, as a soil conditioner in road constmction, and in the production of sand-lime bricks. 

Nicotine is used as a contact insecticide for aphids attacking fmits, vegetables, and ornamentals, and as a fumigant for greenhouse plants and poultry mites. Nicotine sulfate is safer and more convenient to handle and the free alkaloid is rapidly Hberated by the addition of soap, hydrated lime, or ammonium hydroxide to the spray solution. Nicotine sprays commonly contain 0.05—0.06% nicotine, and nicotine dusts, 1—2% nicotine. 

Combinations of lignite flyash from North Dakota and hydrated lime can increase the strength and durabiHty of soils. The lime content varies from 2—7% and 1ime flyash ratio from 1 1 to 1 7 (61). Lignite flyash can also be used as a partial replacement for Portland cement to produce strong, durable concrete (62). 

The term lime also has a broad coimotation and frequently is used in referring to limestone. According to precise definition, lime can only be a burned form quicklime, hydrated lime, or hydraiflic lime. These products are oxides or hydroxides of calcium and magnesium, except hydraiflic types in which the CaO and MgO are chemically combined with impurities. The oxide is converted to a hydroxide by slaking, an exothermic reaction in which the water combines chemically with the lime. These reversible reactions for both high calcium and dolomitic types are Quicklime... 

Puilding lime may be quick or hydrated lime, but usually coimotes the latter, where the physical characteristics make it suitable for ordinary or special stmctural purposes (see Building materials, survey). 

Chemical lime is a quick or hydrated lime used for one or more chemical or industrial appHcations. Usually chemical lime has a relatively high chemical... 

Finishing lime is a refined hydrated lime, milled to make it suitable for plastering, particularly the finish coat. Putty derived from this hydrate possesses unusually high plasticity. 

Hydraulic hydrated lime is a chemically impure form of lime with hydraiflic properties of varying extent. It contains appreciable amounts of sflica, alumina, and usually some iron, chemically combined with much of the lime. Hydraiflic hydrated lime is employed solely for stmctural purposes. 

Mason s lime is a hydrated lime used in mortar for masonry purposes. 

Quicklime is usually white of varying intensity, depending on chemical purity some species possess a slight ash-gray, buff, or yellowish cast. Invariably quicklime is lighter in color than the limestone from which it is derived. Hydrated limes, except for hydrauHc and impure hydrates, are extremely white in color, invariably whiter than their quicklimes. 

Odor. Except for highly carbonaceous species, most limestones are odorless. Quick and hydrated limes possess a mild odor that is characteristic but difficult to describe except that it is faintly musty or earthy, not offensive. 

Texture. All limestones are crystalline, but there is tremendous variance in the size, uniformity, and arrangement of their crystal lattices. The crystals of the minerals calcite, magnesite, and dolomite are rhombohedral those of aragonite are orthorhombic. The crystals of chalk and of most quick and hydrated limes are so minute that these products appear amorphous, but high powered microscopy proves them to be cryptocrystalline. Hydrated lime is invariably a white, fluffy powder of micrometer and submicrometer particle size. Commercial quicklime is used in lump, pebble, ground, and pulverized forms. 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

Other Reactions. Dry hydrated lime adsorbs halogen gases, eg, CI2 and F2, to form hypochlorites and fluorides. It reacts with hydrogen peroxide to form calcium peroxide, a rather unstable compound. At sintering temperatures, quicklime combines with iron to form dicalcium ferrite. 

Although most lime is sold as quicklime, production of hydrated lime is also substantial. This product is made by the lime manufacturer in the form of a fluffy, dry, white powder, and its use obviates the necessity of slaking. Small lime consumers caimot economically justify the additional processing step that hydration entails. 

The manufacture of hydrated lime proceeds by the slow addition of water to cmshed or ground quicklime in a premixing chamber or a vessel known as a hydrator, both of which mix and agitate the lime and water. The amount of water added is critical. Too much water makes it impossible, or too cosdy, to produce the desired dry form too Httle water leaves hydration incomplete, causing degraded quaUty, namely, chemical instabiUty and stmctural unsoundness. 

Lime. The total toimage of quicklime and hydrated lime sold and used in 1992 was 16.2 x 10 t. Captive lime accounted for 11% of this total, nearly the same percentage as captive limestone. Captive lime production decreased drastically since the 1970s, falling from 6.7 x 10 t in 1973 to 1.82 X 10 in 1992. Whereas commercial lime production was at an all time high in 1992, total lime (commercial lime plus captive lime) was 18% below that... 

In recent years, lime treatment has been advocated for corrosion control by removing lead and copper from distribution systems, mainly by raising the pH to around 7.5, which prevents these heavy metals from solubilizing. This type of treatment is appHcable to all water suppHes, and especially for small systems. Itinvolves the use of hydrated lime, generally deHvered in bags (see Water). 

Hydrated lime is also used to stabilize the calcium sulfite—sulfate sludge derived from thickeners at SO2 scmbbing plants that use limestone—lime. Hydrated lime (2—3%) is added to react with the gypsum sludge and flyash or other added siHceous material. Under ambient conditions the lime and siHca serve as a binder by reacting as calcium siHcates so that the material hardens into a safe, nonleaching, stable, sanitary landfill or embankment fill. 

Miscellaneous. Both whiting and hydrated lime are used as diluents and carriers of pesticides, such as lime—sulfur sprays, Bordeaux, calcium arsenate, etc. The most widely used bleach and sterilizer, high test calcium hypochlorite, is made by interacting lime and chlorine (see Bleaching AGENTS). Calcium and magnesium salts, such as dicalcium phosphate, magnesium chloride, lithium salts, etc, are made directly from calcific and dolomitic lime and limestone. 

The lower equivalent weight of magnesium hydroxide compared to caustic soda, hydrated lime, and soda ash reduces the stoichiometric amounts necessary to neutralize a given amount of acid. Depending on relative alkah costs, magnesium hydroxide can offer the advantage of lower chemical costs. 

A diagram for one implementation of this process (61,62) is shown in Eigure 11. Recovered potassium sulfate is converted to potassium formate [590-29 ] by reaction with calcium formate [544-17-2] which is made by reacting hydrated lime, Ca(OH)2, and carbon monoxide. The potassium formate (mp 167°C), in hquid form, is recycled to the combustor at about 170°C. Sulfur is removed as soHd calcium sulfate by filtration and then disposed of (see... 

Tricalcium phosphate, Ca2(P0 2> is formed under high temperatures and is unstable toward reaction with moisture below 100°C. The high temperature mineral whidockite [64418-26-4] although often described as P-tricalcium phosphate, is not pure. Whidockite contains small amounts of iron and magnesium. Commercial tricalcium phosphate prepared by the reaction of phosphoric acid and a hydrated lime slurry consists of amorphous or poody crystalline basic calcium phosphates close to the hydroxyapatite composition and has a Ca/P ratio of approximately 3 2. Because this mole ratio can vary widely (1.3—2.0), free lime, calcium hydroxide, and dicalcium phosphate may be present in variable proportion. The highly insoluble basic calcium phosphates precipitate as fine particles, mosdy less than a few micrometers in diameter. The surface area of precipitated hydroxyapatite is approximately... 

Tricalcium Phosphate. Commercial tricalcium phosphate (TCP) is actually an amorphous basic calcium phosphate close to hydroxyapatite in composition. Because of its extremely low solubiUty in water, TCP is precipitated almost quantitatively from dilute phosphate solutions with a slurry of hydrated lime. TCP is separated by dmm-, spray-, or flash-drying the TCP slurry, with or without intermediate sedimentation or filtration steps. It is used as an industrial-grade flow conditioner and parting agent. 

Causticization, the reaction of hydrated lime [1305-62-0], Ca(OH)2, with sodium carbonate to regenerate sodium hydroxide and precipitate calcium carbonate, is an important part of the Bayer process chemistry. 

Synthetic magnesia is most often produced from seawater, known as seawater magnesia. Seawater contains approximately 1294 ppm Mg. Synthetic magnesia can also be produced from brine wells or lakes which have much higher concentrations of magnesium. Regardless of the source of magnesium, the sea or brine water is treated with hydrated lime, Ca(OH)2, that precipitates Mg(OH)2 ... 

Gold Lime Softening. Precipitation softening accompHshed at ambient temperatures is referred to as cold lime softening. When hydrated lime, Ca(OH)2, is added to the water being treated, the following reactions occur ... 

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