Limestone carbonate

The principle of fluidised bed combustion with simultaneous desulphurisation is based on the thermal decomposition of limestone carbonates to yield oxides which then react with the sulphur oxide products of combustion of both inorganic and organic sulphur compounds in the hydrocarbon fuel. 

Calcium occurs mainly as calcium carbonate and calcium silicate on earth s crust both are found in limestone. By heating the limestone, carbon dioxide is driven away to obtain calcium oxide. Because of its abundance in nature, it is an inexpensive raw material and is used in various industries including in cement manufacture to tooth pastes. It is available in dilferent grades based on the particle size, purity, and reactivity. 

Kendall C. G. St. C., Sadd J. L. and Alsharhan A. R. (1994) Holocene marine cement coatings on beach-rocks of the Abu Dhabi coast-line (UAR) analogues for cement fabrics in ancient limestones. Carbon. Evapor. 9, 119-131. 

Considerable effort was concentrated on evaluating the effect of concrete composition on k Q for the storage array. Local concrete is high in basalt and low in limestone (carbon). The differences in aggregates used for ordinary concrete were found to change keff by as much as 250 mllli-k between extremes. 

A reviewer was concerned with the possible inclusion of carbonate carbon during oxalate formation. We cannot totally rule out a jfraction of the oxalate carbon arising from dissolved carbonate. But, limestone carbon cannot be the sole source of the oxalate carbon because of the C-14 content. The conversion of carbonate carbon to oxalate carbon would result in an oxalate radiocarbon age older than the true age and our conclusion that the accretion layer is not 30,000-40,000 years old would still be valid. Russ et al. (22, 22, 25) and Watchman et al. (26-28) obtained radiocarbon results that suggest oxalate does not contain " C-free carbon by the superposition of multiple oxalate and known age pictograph paint layers. Furthermore, the oxalate value of -11.67%o is closer to atmospheric (-7.8%o) than to marine carbonates ( 0 %o). 

Rainwater for instance will pick up atmospheric COg and react with calcium carbonate (limestone) to form a soluble substance, calcium bicarbonate. This reaction gives water its natural hardness . 

The alkali metals of Group I are found chiefly as the chlorides (in the earth s crust and in sea water), and also as sulphates and carbonates. Lithium occurs as the aluminatesilicate minerals, spodimene and lepidolite. Of the Group II metals (beryllium to barium) beryllium, the rarest, occurs as the aluminatesilicate, beryl-magnesium is found as the carbonate and (with calcium) as the double carbonate dolomite-, calcium, strontium and barium all occur as carbonates, calcium carbonate being very plentiful as 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. 

The process of extraction requires first smelting (to obtain the crude metal) and then refining. In smelting, iron ore (usually an oxide) is mixed with coke and limestone and heated, and hot air (often enriched with oxygen) is blown in from beneath (in a blast furnace). At the lower, hotter part of the furnace, carbon monoxide is produced and this is the essential reducing agent. The reduction reactions occurring may be represented for simplicity as ... 

In combination, carbon is found as carbon dioxide in the atmosphere of the earth and dissolved in all natural waters. It is a component of great rock masses in the form of carbonates of calcium (limestone), magnesium, and iron. Coal, petroleum, and natural gas are chiefly hydrocarbons. 

Mixed with sand it hardens as mortar and plaster by taking up carbon dioxide from the air. Calcium from limestone is an important element in Portland cement. 

Acetylene was discovered m 1836 by Edmund Davy and characterized by the French chemist P E M Berthelot m 1862 It did not command much attention until its large scale preparation from calcium carbide m the last decade of the nineteenth century stim ulated interest m industrial applications In the first stage of that synthesis limestone and coke a material rich m elemental carbon obtained from coal are heated m an electric furnace to form calcium carbide... 

In a similar vein, mean seawater temperatures can be estimated from the ratio of 0 to 0 in limestone. The latter rock is composed of calcium carbonate, laid down from shells of countless small sea creatures as they die and fall to the bottom of the ocean. The ratio of the oxygen isotopes locked up as carbon dioxide varies with the temperature of sea water. Any organisms building shells will fix the ratio in the calcium carbonate of their shells. As the limestone deposits form, the layers represent a chronological description of the mean sea temperature. To assess mean sea temperatures from thousands or millions of years ago, it is necessary only to measure accurately the ratio and use a precalibrated graph that relates temperatures to isotope ratios in sea water. 

Historically, soda ash was produced by extracting the ashes of certain plants, such as Spanish barilla, and evaporating the resultant Hquor. The first large scale, commercial synthetic plant employed the LeBlanc (Nicolas LeBlanc (1742—1806)) process (5). In this process, salt (NaCl) reacts with sulfuric acid to produce sodium sulfate and hydrochloric acid. The sodium sulfate is then roasted with limestone and coal and the resulting sodium carbonate—calcium sulfide mixture (black ash) is leached with water to extract the sodium carbonate. The LeBlanc process was last used in 1916—1917 it was expensive and caused significant pollution. 

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. 

In addition to the principal equations discussed, several others occur which may be of importance, including calcination of calcium carbonate (limestone), which takes place in the upper shaft at 800—870°C,... 

Definitions. In addition to showing varying degrees of chemical purity, limestone assumes a number of widely divergent physical forms, including marble, travertine, chalk, calcareous mad, coral, shell, ooHtes, stalagmites, and stalactites. AH these materials are essentially carbonate rocks of the same approximate chemical composition as conventional limestone (2—4). 

The carbonate minerals that comprise limestone ate calcite [13397-26-7] (calcium carbonate), which is easily the most abundant mineral type aragonite [14791-73-2] (calcium carbonate) dolomite [17069-72-6] (double carbonate of calcium and magnesium) andmagnesite [13717-31 -5] (magnesium carbonate). Individual limstone types ate further described by many common names (1). Some of this nomenclature is repetitious and overlapping. The following terms ate in common use in Europe and the United States. 

Cementstone is an impure (usually argillaceous) limestone, possessing the ideal balance of siUca, alumina, and calcium carbonate for Portiand cement (qv) manufacture. When calcined it produces a hydrauHc cementing material. 

Chemical-grade limestone is a pure type of high calcium or dolomitic limestone used by the chemical-process industry or where exacting chemical requirements ate necessary. It contains a minimum of 95% total carbonate. In a few areas of the United States this minimum may be extended to 97 or 98%. 

Dolomitic limestone contains considerable MgCO. A tme dolomitic stone contains a ratio of 40—44% MgCO to 54—58% CaCO. However, the term is mote loosely used to denote any carbonate rock that contains mote than 20% MgCO. It varies in color, hardness, and purity. 

Dluxstone is a pure form of limestone used as flux or purifier in metaHurgical furnaces. It can be high calcium, magnesian, or dolomitic, providing it contains at least 95% carbonate. 

Fossiliferous limestone is a general term for any carbonate stone in which the fossil stmcture is visually evident. 

Hydraulic limestone is an impure argillaceous carbonate somewhat akin to cementstone, except that it may contain mote MgCO, and usually it produces cement-like materials of lower hydrauHcity. 

Whiting at one time coimoted only a very fine form of chalk of micrometer sizes but the term is now used more broadly to include all finely divided, meticulously milled carbonates derived from high calcium or dolomitic limestone, marble, shell, or chemically precipitated calcium carbonate. Unlike all of the above natural forms of limestone, it is strictly a manufactured product. 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

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