Quicklime production

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. 

Quicklime Production (section 14.2). This is a significant use of limestone in industrialised countries. 

Bulk density. This depends on the mean apparent density of the particles and on the voidage between them. The latter is related to the particle size distribution and particle shape. Most commercial screened quicklime products have bulk densities in the range 900 to 1200 kg/m. Inclusion of fines, which fill the interstices, can increase the bulk density by 30 %. 

Hardness. Most commercial quicklime products have a hardness of 2 to 3 Mohs. The value for dead-burned dolomite is in the range 3 to 5 Mohs [13.1]. 

Table 18.2 summarises the physical tests for quicklime products specified by various standards [18.2,18.3,18.5]. 

Table 18.3. Chemical analysis of quicklime products by traditional methods.

The principles of sampling slaked lime products are similar to those described in section 6.2 for limestone and section 18.3 for quicklime products. Definitions of the terms increment, sample, spot sample, composite sample and laboratory sample are given in the Glossary and Fig. 6.1 illustrates how they are related. 

As with limestone, minimising wastage is an important factor in the economics of quicklime production. Integrated hme works often feed surplus grades to a hydrating plant or to a ground lime plant. Products which cannot be used are often blended into selected products, or sold as agricultural lime. 

When quicklime products are applied to the land, the first reaction is slaking. This produces finely divided calcium hydroxide and enables relatively coarse kibbled lime (a screened grade) to be used effectively. Some of the hydrated lime dissolves and produces a rapid increase in soil pH, within a week or two. The remainder of the lime carbonates, reacts relatively slowly, and keeps the pH in the required range for a prolonged period. The duration of that period depends on the rate of application, the nature of the soil and the rate of lime loss. 

In the context of global warming, the emission of large amounts of carbon dioxide from quicklime production merits careful consideration. The thermal decomposition of CaCOa and MgCOa inevitably produces up to 0.75 t of C02/t of lime. The quantity of CO2 produced from combustion, is 0.2 to 0.45 t/t of lime, depending on the composition and calorific value of the fuel, and the specific heat requirement of the kiln. 

The rotary kiln has become extremely important in lime processing, and is used to burn a large portion of dolomitic quicklime production. More than half of all industrial quicklime is made in rotary kilns. The rotary is particularly useful for making the hard burned grade of quicklime that must contain a minimum amount of unburned limestone. 

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. 

Extremely dry (or super-dry ) ethyl alcohol. The yields in several organic preparations e.g., malonic ester syntheses, reduction with sodium and ethyl alcohol, veronal synthesis) are considerably improved by the use of alcohol of 99-8 per cent, purity or higher. This very high grade ethyl alcohol may be prepared in several ways from commercial absolute alcohol or from the product of dehydration of rectified spirit with quicklime (see under 4). 

Acid rhodamines are made by the iatroduction of the sulfonic acid group to the aminoxanthene base. The preferred route is the reaction fluorescein (2) with phosphorous pentachloride to give 3,6-dichlorofluoran (fluorescein dichloride) (23), which is then condensed with a primary aromatic amine in the presence of 2inc chloride and quicklime. This product is then sulfonated. For example, if compound (23) (fluorescein dichloride) is condensed with aniline and the product is sulfonated. Acid Violet 30 Cl45186) (24) is produced. 

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... 

Many lime plants are able to reduce the impurities in their lime product by careful screening and selecting of stone for burning. Because 9 kg of limestone produce only 5 kg of quicklime, the percentage of impurities in a quicklime is nearly double that in the original stone. Analyses of typical samples of high calcium, magnesian, and dolomitic limestones found in the United States are Hsted in Table 1. 

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. 

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... 

Calcium Oxide. Also called lime or quicklime (4,5), calcium oxide [1305-78-8] (Class 1, nonregenerative), is relatively iaexpensive. It is prepared by roasting calcium carbonate (limestone) and is available ia a soft and a hard form according to the way ia which it was burned. For desiccant service, soft-burned lime should always be used. Calcium oxide is most commonly used to dehydrate Hquids and is most efficient when it can be heated to speed the reaction rate. The reaction product is calcium hydroxide, which cmmbles as it picks up moisture. 

The product, calcium hydroxide, is commonly known as slaked lime because, as calcium hydroxide, the thirst of lime for water has been quenched (slaked). Slaked lime is the form in which lime is normally sold because quicklime can set fire to moist wood and paper. In fact, the wooden boats that were once used to transport quicklime sometimes caught fire in the heat of reaction when water seeped into their holds. An aqueous solution of calcium hydroxide, which is slightly soluble in water, is called lime water. It is used as a test for carbon dioxide, with which it reacts to form a suspension of the much less soluble calcium carbonate ... 

Groundnut oil, in soap making, 22 735 Ground quicklime, 75 28 production of, 75 54-56 quality control for, 75 70 uses for, 75 61-62... 

Iron(II) porphyrin complexes, four-coordinate, 14 552-553 Iron(III) porphyrin complexes, 14 554 Iron porphyrins, 14 552-555 Iron(II) porphyrins, 14 553 Iron(III) porphyrins, 14 553 Iron(IV) porphyrins, 14 554 Iron production quicklime in, 15 61 sulfur use in, 23 591 Iron removal, in municipal water treatments, 26 124 Iron salts... 

Magnesia-base refractories, 15 425 Magnesian quicklime, 15 28 Magnesia products, 15 323 Magnesioferrite, in chromite, 6 474 Magnesioriebeckite, 3 288-289 Magnesite, 15 321, 387, 389-390... 

Solid bodies, flows past, 11 753-757 Solid-bound photosensitizing dyes, 9 518 Solid bowl centrifuges, 16 659-660 Solid-burned quicklime, 15 29 Solid by-products... 

Steel mill products, United States shipments of, 23 313t Steel mills, scrap grades used by, 21 413 Steel phosphating, 15 251 Steel-plate printing, 14 329 Steel-pouring pit refractories, 21 5111 Steel production, 23 247-248 quicklime in, 15 61 sulfur use in, 23 591 Steel products, 23 311 net shipments of, 23 312t Steel quenching... 

Calcium carbonate occurs in nature as hmestone in various forms, such as marble, chalk, and coral. It is probably the most widely-used raw material in the chemical industry. It has numerous apphcations, primarily to produce cement, mortars, plasters, refractories, and glass as budding materials. It also is used to produce quicklime, hydrated lime and a number of calcium compounds. It is produced either as powdered or precipitated calcium carbonate. The latter consists of finer particles of greater purity and more uniform size. They also have many important commercial apphcations. Various grades of precipitated calcium carbonate are used in several products, such as textiles, papers, paints, plastics, adhesives, sealants, and cosmetics. 

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