Quicklime processing

The next step is to establish, as clearly as possible, the quality of the quicklime required, in terms of % CaCOa, sulfur, reactivity and other key parameters, as well as the lead grade in terms of particle size. The impact of the design of the quicklime processing plant on product quality should not be overlooked (see chapter 17). 

Ib/ft ). Again, dolomitic limes average about 4% denser than their high calcium counterparts. The severity of the calcination process largely determines the porosity of a quicklime the higher the temperature of calcination and the longer its duration, the more the porosity declines. 

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. 

Alkalies. In the 1960s, 3.2-34 x 10 t /yr of lime was captively produced by the U.S. alkaH industry for manufacturing soda ash and sodium bicarbonate via the Solvay process. Electrolytic process caustic soda and natural soda ash (trona) from Wyoming have largely replaced the Solvay process. Three of the trona producers in Wyoming now purchase quicklime for producing caustic soda. 

Precipitated Calcium Carbonate. Precipitated calcium carbonate can be produced by several methods but only the carbonation process is commercially used in the United States. Limestone is calcined in a kiln to obtain carbon dioxide and quicklime. The quicklime is mixed with water to produce a milk-of-lime. Dry hydrated lime can also be used as a feedstock. Carbon dioxide gas is bubbled through the milk-of-lime in a reactor known as a carbonator. Gassing continues until the calcium hydroxide has been converted to the carbonate. The end point can be monitored chemically or by pH measurements. Reaction conditions determine the type of crystal, the size of particles, and the size distribution produced. 

Quicklime is less easy to handle, and swells considerably on hydration. It is cheap, however, and is often used on open trays to protect process equipment, machinery, furnaces, etc. during shut-down periods. If it is accidentally flooded with water, the slurry of hydrated lime provides an alkaline medium in which uncoated steel surfaces will remain without rusting. 

This process, usually carried out in a kiln and at a temperature well above 600°C, seems to have been practiced as early as the Stone Age (Gourdin and Kingery 1975). Quicklime is a basic component of calcareous cement. Before the cement can be prepared, however, it is essential to slake (disintegrate and break up) the quicklime by the addition of water water reacts with quicklime to form slaked lime, composed of calcium hydroxide ... 

Oxygen solubility, in aeration water treatment, 26 153-154 Oxygen sources, for fermentation, 44 25 Oxygen steelmaking, quicklime requirements for, 45 68 Oxygen steelmaking processes, 23 255-260 Oxygen transfer, 26 153... 

Liming an acidic lake is similar to the process many people use to maintain a pH balance in their soil for lawn maintenance. Plants have an optimum pH range in which they strive. Acidic conditions often develop in soils for several reasons. Rain tends to leach away basic ions, weak organic acids develop from the carbon dioxide produced by decaying organic matter, and strong acids, such as nitric acid, can form when ammonium fertilizers oxidize. To neutralize these acids, different forms of lime such as quicklime, CaO, and slaked lime, Ca(OH)2, are used to neutralize the acid and increase the pH of the soil. Table 13.9 shows how much fertilizer is wasted when applied to... 

The chemists or alchemists gradually acquired a knowledge of the various salts produced by the action of acids on nitrum and of the transformations of the various salts from one form to another, by the action of acids on the different salts—e.g. sulphuric acid on sodium chloride. The carbonates of the alkalies were called mild alkalies to distinguish them from the caustic alkalies. It was known quite early that the caustic alkalies are obtained by the action of quicklime on the mild alkalies for example, the Latin Geber 7 and Albertus Magnus of the thirteenth century knew that the ash of plants furnished a caustic alkali when treated with quicklime and water. The process is essentially that employed to-day. 

Before charging the retorts, the ore is reduced to a coarse powder, then mixed with quicklime, and shovelled in. Six or seven hundredweight of the mixture, a sufficient charge for eaeh retort, can, with a proper amount of heat, be worked off in about three hours. The process is continuous, and, with an efficient staff of workmen, oould he daily made, by using nine such retorts, to decompose six tons of the mixture—a quan-tfty which, if the ore was rich like that of the Idrinn or Almaden mines, would equal twelve hundred to a ton of mercuiy daily. 

David Macbride, a prominent surgeon of Dublin, was the next to contribute to the chemistry of gases. He published a work entitled Experimental Essays in 1764. Macbride was especially interested in the fermentation processes in the animal body. Knowing that fixed air was an important product of these fermentations, he was led to investigate fixed air. His book consists of five essays, two of which, On the nature and properties of fixed air, and On the dissolvent power of quicklime, contain his contribution to the knowledge of fixed air. 

Calcium Oxide. [CAS 1305-78-8], CaO (quicklime), white solid, mp 2,570CC. reacts with H.O 10 form calcium hydroxide with the evolution of much heal reacts with H2O vapor and COi of the atmosphere to form caleium hydroxide and carbonate mixture (slaked lime) formed by heating limestone at high temperature (800=C) and removal of CCL. This process is conducted industrially in a lime kiln. 

E. C. C. Baly and H. M. Duncan studied the decomposition of ammonia by means of a hot platinum wire. Two types of ammonia may be prepared—an inactive and an active modification—which are decomposed to different extents by the same quantity of energy. The active form is obtained by the slow withdrawal of ammonia from a cylinder containing the compressed gas by warming the cone. aq. soln. and drying the gas by quicklime and by isothermal evaporation of the liquefied gas at its b.p. The inactive form is obtained by the rapid evaporation of the liquefied gas. The inactive gas slowly recovers its activity on remaining in contact with the liquefied gas. The same effect can be produced by gently warming the gas by means of a platinum wire heated at 200°. In order to observe these phenomena, the platinum wire must be activated in the same way as is customary in W. Ostwald s process for the catalytic oxidation of ammonia in air to nitric acid. Alternatively,... 

Figure 13.7 The calcium oxide produced from this process is known as quicklime or lime and is used in large quantities in the manufacture of soda glass.

Most of the basic oxides may also be prepared by heating the carbonates, a class of salts afterwards to be discussed. The carbonates of the alkali metals, however, are not thus decomposed like their hydroxides, they may be volatilised without decomposition. But all other carbonates are decomposed by exposure to a red heat. The process has already been described as a method of manufacturing quicklime. Most carbonates, however, do not require the same high temperature a dull red heat suffices. And the oxides do not, as a rule, recombine with the carbon dioxide expelled, as does lime hence there is no danger of re-carbonating the oxide. 

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