Carbon dioxide reaction with calcium hydroxide

E7.13 Reaction of Calcium Hydroxide Solution with Carbon Dioxide... 

In paintings, the heahng effect can be the result of the formation of a calcium carbonate (CaCOj) heahng film via the chemical reaction of released calcium hydroxide (CaOH) with carbon dioxide (COj) in the air when the coating is damaged. 

Problem The conversion reaction of quicklime or caustic lime (CaO) to slaked or hydrated lime (Ca (OH)2), is historically an important process. After limestone CaC03 is heated at a temperature of about 1000°C, calcium oxide CaO is produced this calcium oxide reacts with water to form calcium hydroxide Ca (OH)2 this can be used to regenerate limestone again by the reaction with carbon dioxide forming once again calcium carbonate CaC03 ( lime circulation ). 

Reaction with carbon dioxide. In practice, quicklime reacts with carbon dioxide under ambient conditions. This is because commercially-produced quicklime always contains sufficient calcium hydroxide (produced by reaction with atmospheric water vapour in the cooling zone of the lime kiln) for carbon dioxide to be absorbed by the hydroxide (equation 13.1). That reaction releases water, which is available to react with more quicklime to produce more hydroxide etc, until the quicklime is fully converted into calcium carbonate (equation 13.2), see section 19.2. 

Reactions with acid gases. In practice, quicklime reacts with acidic gases under ambient conditions. This is because commercially-produced quicklime always contains sufficient calcium hydroxide for the gases to react with the hydroxide (compare with reaction with carbon dioxide). 

The durability of steel bars depends on the passivation developed by the alkaline environment of the material. It is provided by the calcium hydroxide of the concrete and causes a pH level of about 12-14 pH. The chemical reaction with carbon dioxide supplied by air lowers the pH level and reaches a depassivation under a pH level of 10. Besides the reduced strength of the corroded steel the ferrous oxide expands and causes the concrete to flake off. The initiation of eorrosion can be retarded by increasing the thickness of the concrete layer above the steel bars. Structural elements need a minimum thickness of 60 to 80 mm in order to achieve an economically reasonable durability. 

The Solvay process involves a series of partial reactions. The first step is calcination of calcium carbonate to form lime and CO2. Lime is converted to calcium hydroxide. The most crucial step of the process involves reacting brine solution with carbon dioxide and ammonia to produce sodium bicarbonate and ammonium chloride. Sodium bicarbonate converts to sodium carbonate. The calcium hydroxide and ammonium chloride react to form calcium chloride as the by-product. The partial reactions are shown below ... 

Hard-core RMs of carbonate-alkylaryl sulfonates (OCABS) are prepared by reaction of carbon dioxide with calcium or magnesium oxide (or hydroxide) in the presence of a surfactant (Delfort et al., 1995 Mansot et al., 1993a). Because of their alkaline reservoir they are able to neutralize the acidic by-products resulting from oxidation of oil and from fuel combustion products (blow-by). 

If all went well, cloudiness happened. When you blow bubbles into clear calcium hydroxide, it turns cloudy. When you pour clear calcium hydroxide into clear carbonated soda, the solution turns cloudy. The explanation for both of these is that you observed an acid-base reaction. In each case, the cloudiness came from the interaction of an acid—carbonic acid (H COj)—and a base—calcium hydroxide. A carbonated soda already has carbonic acid in it. When you blow bubbles into calcium hydroxide, the carbon dioxide (CO ) from your breath interacts with the water in the calcium hydroxide solution to form H COj. Here s the balanced equation for the interaction of carbonic acid and calcium hydroxide ... 

The mode of action of lime as a bonding agent is based on the reaction of calcium hydroxide with carbon dioxide in the air ... 

Tip The calcium hydroxide can be suspended in the Erlenmeyer flask with a little water gaseous carbon dioxide is added, and it is then closed off with a stopper and glass tube. If the flask is connected to a syringe which is filled with carbon dioxide, it is then possible to see the reaction of calcium hydroxide with the gas the piston is sucked into the syringe. This experiment can simulate the setting and reaction of calcium mortar in the air. 

In the absence of calcium hydroxide, quicklime only reacts with carbon dioxide at temperatures above about 300 °C and below 800 °C. This reaction can occur in the cooling zone of lime kilns under abnormal conditions. It results in carbonation of quicklime at the surface of the pores, and can give abnormally low reactivities for a given mean apparent density. 

Carbon dioxide. Calcium hydroxide reacts readily with carbon dioxide in the absence of water at all temperatures below its dissociation temperature (equation 19.1). It should be noted that the reaction of quicklime with carbon dioxide below 300 °C only proceeds in the presence of calcium hydroxide. The water released by equation (19.1) is available to hydrate more calcium oxide (19.2), and thereby permits further carbonation to occur. 

The reaction of calcium hydroxide with carbon dioxide is ... 

II) The reaction of calcium hydroxide solution (limewater) with carbon dioxide is the basis of the limewater test for CO2. During the reaction, a white precipitate is produced. Name the precipitate and write an ionic equation for the reaction. 

This carbon dioxide-free solution is usually treated in an external, weU-agitated liming tank called a "prelimer." Then the ammonium chloride reacts with milk of lime and the resultant ammonia gas is vented back to the distiller. Hot calcium chloride solution, containing residual ammonia in the form of ammonium hydroxide, flows back to a lower section of the distiller. Low pressure steam sweeps practically all of the ammonia out of the limed solution. The final solution, known as "distiller waste," contains calcium chloride, unreacted sodium chloride, and excess lime. It is diluted by the condensed steam and the water in which the lime was conveyed to the reaction. Distiller waste also contains inert soHds brought in with the lime. In some plants, calcium chloride [10045-52-4], CaCl, is recovered from part of this solution. Close control of the distillation process is requited in order to thoroughly strip carbon dioxide, avoid waste of lime, and achieve nearly complete ammonia recovery. The hot (56°C) mixture of wet ammonia and carbon dioxide leaving the top of the distiller is cooled to remove water vapor before being sent back to the ammonia absorber. 

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. 

Neutralization Acidic or basic wastewaters must be neutrahzed prior to discharge. If an industry produces both acidic and basic wastes, these wastes may be mixed together at the proper rates to obtain neutral pH levels. Equahzation basins can be used as neutralization basins. When separate chemical neutralization is required, sodium hydroxide is the easiest base material to handle in a hquid form and can be used at various concentrations for in-line neutralization with a minimum of equipment. Yet, lime remains the most widely used base for acid neutr zation. Limestone is used when reaction rates are slow and considerable time is available for reaction. Siilfuric acid is the primary acid used to neutralize high-pH wastewaters unless calcium smfate might be precipitated as a resmt of the neutralization reaction. Hydrochloric acid can be used for neutrahzation of basic wastes if sulfuric acid is not acceptable. For very weak basic waste-waters carbon dioxide can be adequate for neutralization. 

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 ... 

An intimate mixture ot 274 grms. of rubidium iron alum, or 260 grms. of rubidium aluminium alum with 100 grms. of calcium carbonate, and 27 grms. of ammonium chloride, is heated in a nickel crucible to a dull red heat until ammonia vapours are no longer evolved, and then the temp, is raised to redness. The product is ground with a litre of cold water for 15 minutes filtered by suction and washed with 400 c.c. of water, added in small portions at a time. The combined sulphuric acid is precipitated by the addition of barium hydroxide, and the filtered liquid boiled while a stream of carbon dioxide is passed through the soln. If the soln. loses its alkaline reaction, and yet retains some calcium, a little rubidium carbonate must be added to precipitate calcium carbonate. The soln. is then treated with hydrochloric acid and evaporated. 

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