Calcium carbonate—See Limestone

At about the same time that the Birkeland-Eyde process was developed, the Frank-Caro cyanamide process was commercialized (14). In this process limestone is heated to produce lime, which then reacts with carbon in a highly energy-demanding reaction to give calcium carbide. Reaction with N2 gives calcium cyanamide [150-62-7] which hydrolyzes to ammonia and calcium carbonate (see Cyanamides). 

This process is directly coupled to the manufacture of quicklime. Milk of lime is obtained by slaking and then carbon dioxide, produced by the calcining of limestone, is passed into the suspension forming calcium carbonate (see Sections 5.3.2.3 and 5.3.2.4). 

In vino veritas ( there is truth in wine ) implies that, suitably lubricated, a person may be more likely to confess all. However, the German apothecary Johann Friedrich Meyer (1705-1765) might well have said In colds veritas ( there is truth in chalk ) since it is through calcium carbonate (chalk limestone) that he discovered his acidum pingue—said to be the general principle innate in all bodies, the principle in fire, and the component of all acids (see Figure 178). And... 

Whitening (1601) A finely divided form of Calcium Carbonate obtained by milling high-calcium limestone, marble, shell, or chemically precipitated calcium carbonate. See Limewashing. 

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. 

The composition of the particles is related to that of the source rocks. Quartz sand [composed of silica (silicon dioxide)], which makes up the most common variety of silica sand, is derived from quartz rocks. Pure quartz is usually almost free of impurities and therefore almost colorless (white). The coloration of some silica sand is due to chemical impurities within the structure of the quartz. The common buff, brown, or gray, for example, is caused by small amounts of metallic oxides iron oxide makes the sand buff or brown, whereas manganese dioxide makes it gray. Other minerals that often also occur as sand are calcite, feldspar and obsidian Calcite (composed of calcium carbonate), is generally derived from weathered limestone or broken shells or coral feldspar is an igneous rock of complex composition, and obsidian is a natural glass derived from the lava erupting from volcanoes see Chapter 2. 

Calcinating limestone (composed of calcium carbonate) removes its volatile component (carbon dioxide) and results in the formation of quicklime (composed of calcium oxide) (see Textbox 33). 

FIGURE 44 Weathering. A weathered sandstone column. Calcite (composed of calcium carbonate) is dissolved by rain and groundwater (see Textbox 73). When stone in which calcite is a main component as, for example, sandstone, limestone, and marble, is in contact with water for long periods of time, it is weathered and partly or entirely dissolved. Pollutants such as sulfur dioxide are fundamental in accelerating the weathering and dissolution process. When sulfur dioxide, for example, dissolves in rainwater, it forms sulfuric acid, a strong acid that, at ambient temperatures, rapidly dissolves calcium carbonate. 

Lime (calcium oxide, CaO) is used in the manufacture of mortar. It is manufactured in large quantities in Europe (see Figure 4.6) by heating limestone (calcium carbonate, CaCOs). 

In Chapter 13, we shall see that limestone (calcium carbonate) is a substance which can be used to neutralise soil acidity. Powdered limestone is used as it neutralises the acidity faster than if lumps of limestone are used. Why do you think this is the case ... 

When acid gets on limestone, the calcium carbonate is broken apart. Calcium ions and carbon dioxide gas are two of the things that are formed. The bubbles you see in the bowl with the vinegar are carbon dioxide. The bubbles form on the surface of the chalk. The chalk in the vinegar gets smaller because the acetic acid in the vinegar breaks the calcium carbonate in the chalk apart. Acid rain can hurt statues and buildings in the same way. 

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of... 

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