Calcium oxide from calcite

The choice of selected raw materials is very wide, but they must provide calcium oxide (lime), iron oxide [1309-37-1/, siHca, and aluminum oxide (alumina). Examples of the calcereous (calcium oxide) sources are calcium carbonate minerals (aragonite [14791-73-2] calcite [13397-26-7] limestone [1317-65-3] or mad), seasheUs, or shale. Examples of argillaceous (siHca and alumina) sources are clays, fly ash, mad, shale, and sand. The iron oxide commonly comes from iron ore, clays, or mill scale. Some raw matedals supply more than one ingredient, and the mixture of raw matedals is a function of their chemical composition, as deterrnined by cost and availabiHty. 

Calcium oxide (CaO, lime, quicklime, unslaked lime) is differentiated from calcium hydroxide [Ca(OH)2, slaked lime, hydrated lime] and limestone (CaC03, calcite, calcium carbonate, marble chips, chalk) by formula and by behavior. A saturated solution of calcium oxide in water is called limewater and a suspension in water is called milk of lime. 

In the model mixture studies calcium acetate was observed to react with pyrite at 750° and 1000°C to generate anhydrite XRD peaks of greater intensity than those observed for the system of calcite reacting with pyrite (Table II, Systems A and B). Sulfur fixation by calcium released from calcium acetate by pyritic sulfur was greater than in the calcite case probably due to the similar tanperatures at which calcium acetate decomposes and pyrite oxidizes (400° to 500°C). Calcite, on the other hand, does not decompose until higher temperatures (900°C) therefore the calcium necessary to form anhydrite is not as readily available. Most of the SO2 formed by oxidation of pyrite would be lost to the atmosphere by the time calcite decomposes. 

In system F calcite was used as a calcium source for the formation of gehlenite. The reaction did not proceed as completely as with calcium acetate, as inferred from two observations 1) some of the calcium remained as calcium oxide upon decomposition of... 

All raw materials purchased by glass producers have to pass very stringent requirements for composition and particle size distribution. Silica is from sand and alumina is from the clay. Boric oxide is from colemanite and boric acid. Limestone or calcite is for calcium oxide. The summary is given in Table 9.1. 

Surfactant level varies from 10-15% in low-priced bars to 20-30% in premium bars. Where a combination of surfactants is used, as in the Philippines, typically a mixture of alcohol sulfate and LAS is used in a ratio of 50 50-85 15. Bars containing only AS as the surfactant are very brittle and need a high amount of humectants such as glycerine or addition of hydrotropes to reduce the brittleness. STPP/TSPP level ranges from 0-3% in low-priced bars to 15-30% in premium bars. The moisture level in the bars varies from 3 to 12%, carbonates typically from 10 to 25%, and fillers such as calcite, talc, and clay fill the rest of the formulation. Because the presence of free water in the bars can lead to mushiness during production or use, a variety of desiccants and adsorbent materials have also been added to bars to control the moisture. Examples include phosphorous pentoxide, sulfuric acid, boric acid, and calcium oxide as well as a variety of clays. 

Chemical decomposition reactions, in which a solid reactant is heated to produce a new solid plus a gas, are commonly used for the production of powders of simple oxides from carbonates, hydroxides, nitrates, sulfates, acetates, oxalates, alkoxides, and other metal salts. An example is the decomposition of calcium carbonate (calcite) to produce calcium oxide and carbon dioxide gas ... 

According to the Colour Index (1971), synthetic calcite can be produced industrially in two ways (1) from conversion of calcium oxide, and (2) as a precipitate of calcium chloride with sodium carbonate. The resultant compound was often used as a base for lake pigments and as an extender for others. However, see calcium carbonates group for a fuller discussion of synthesis. The Colour Index designation for this pigment is Cl 77220/Pigment White 18. The term whiting also may refer to a synthetic calcimn carbonate. 

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. 

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