Limestone CaCO

A fluidized bed is an excellent medium for contacting gases with sohds, and this can be exploited in a combustor because sulfur dioxide emissions can be reduced by adding limestone, CaCO, or dolomite, CaCO MgCO, to the bed. 

Other Processes. Other methods iaclude reaction of lime, (CaO) with hydrogen cyanide (24) and reaction of limestone, (CaCO ), with ammonia (25). 

A number of chemical reactions occur in the absorber beginning with the reaction of limestone (CaCO,) with the SO, to form calcium sulfite (CaSO,). The calcium sulfite oxidizes to calcium sul-... 

Dolomitization is the process by which limestone (CaCO,) is transformed into dolomite CaMg (CO,). During the transformation (which occurs under pressure), crystal reorientation occurs, which results in porosity in dolomite. 

Limestone CaCOs, sedimentary rock formed by the accumulation of shells or corals... 

The manufacture of Portland concrete consists of three basic steps—crushing, burning, and finish grinding. As noted earlier, Portland cement contains about 60% lime, 25% silicates, and 5% alumina with the remainder being iron oxides and gypsum. Most cement plants are located near limestone (CaCOs) quarries since this is the major source of lime. Lime may also come from oyster shells, chalk, and a type of clay called marl. The silicates and alumina are derived from clay, silicon sand, shale, and blast-furnace slag. 

Lime is obtained by calcination of dolomite, CaCOs MgCOs, or limestone, CaCOs, under controlled conditions to remove all CO2. After bicarbonate removal, the seawater is then treated with calcium hydroxide, slaked dobme or sodium hydroxide to precipitate magnesium hydroxide ... 

Calcium compounds, essential for the formation of bones and teeth, are obtainable from limestone (CaCOs), gypsum (CaS04-2H20), and fluorite (CaF2) for use in water treatment, agriculture, construction (concrete), and the chemical industry, for which lime (CaO) is the least expensive source of alkali. Calcium is the third most common cation in seawater (400 mg kg-1). 

The impact of water hardness due to calcium or magnesium ions on detergents was explained in Section 7.3.1 The source of most Ca2+ and Mg2+ in hard water is the dissolution of limestone (CaCOs) or dolomite [CaMg(COs)2]. Magnesium carbonate is fairly soluble (1.26 mmol L 1 at ambient temperature), but CaCOs is much less so (0.153 mmol L 1). However, if the water contains dissolved CO2 (as indeed it will if it is exposed to the air see Exercise 14.9), the relatively freely soluble Ca(HCOs)2 forms, and the limestone slowly dissolves away ... 

Lime (calcium oxide) is widely used in the production of cement, steel, medicines, insecticides, plant and animal food, soap, rubber, and many other familiar materials. It is usually produced by heating and decomposing limestone (CaCOs), a cheap and abundant mineral, in a calcination process ... 

The term lime normally covers both limestone (CaCO ) and quicklime (CaO), which is produced from it by calcination. Slaked lime [Ca(OH)2l is formed by reacting quicklime with water. 

The burning of limestone, CaCOs CaO + CO2, goes only 70% to completion in a certain kiln. 

Limestone (CaCOs) is converted into CaO in a continuous vertical kiln (see Fig. P5.23). Heat is supplied by combustion of natural gas (CH4) in direct contact with the limestone using 50% excess air. Determine the kilograms of CaCOa that can be processed per kilograms of natural gas. Assume that the following average heat capacities apply ... 

Calcium nitrate, CaNO i, made by running the crude nitric acid through a series of granite beds filled with limestone (CaCO t) until the liquid contains under 0.5 per cent free HNOs. The liquor is neutralised with lime, evaporated in vacuum pans until of 1.9 sp. gr., and allowed to solidify. It is then either exported in drums, or ground up and put into casks, being sold as Norwegian saltpetre. It is reddish-brown to black. It is further described on p. 12. 

Oxidizing gas and slag-forming materials, such as silica (Si02) sand, lime (CaO), limestone (CaCOs), dolomite (CaO-MgO), or calcium fluoride (CaF2) are added to the still-molten raw silicon in a refinement step. Less noble elements than silicon are oxidized and dissolved in the slag, which is removed. To avoid excessive heat losses, some of the silica can be provided directly by oxidation of some of the silicon melt instead of sand. Carbon is removed from the melt in the form of SiC precipitates. 

The sequence is as follows, (a) Sulfur dioxide, made by burning sulfur or roasting pyrite (FeS2), is passed over wet limestone (CaCOs) until a total of 7% SO2 has dissolved ... 

Limestone (CaCOs) and dolomite (CaCOs MgCOs), which are widespread on Earth s surface, often enter the water supply. According to Table 4.2, calcium carbonate is insoluble in water. However, in the presence of dissolved carbon dioxide (from the atmosphere), calcium carbonate is converted to soluble calcium bicarbonate [Ca(HC03)2] ... 

The industrial manufacturing processes for iron and steel can be summarized as follows. Iron ore is mixed with limestone (CaCOs) and coke in a blast furnace in which temperatures vary from 750 to 2250 K. Carbon is converted to CO in the highest temperature zone, but both C and CO may reduce the iron ore ... 

A bed of limestone, CaCO, along the Verde River, Arizona. 

Problem A chemical engineer injects limestone (CaCOs) into the hot flue gas of a coalburning power plant to form lime (CaO), which scrubs SO2 from the gas and forms gypsum (CaS04 2H20). Find Kc for the following reaction, if CO2 pressure is in atmospheres ... 

The interplay of acid-base, solubility, and complex ion equilibria is often important in natural processes, such as the weathering of minerals, the uptake of nutrients by plants, and tooth decay. For example, limestone (CaCOs) will dissolve in water made acidic by dissolved carbon dioxide ... 

The problem of sulfur dioxide pollution is further complicated by the energy crisis. As petroleum supplies dwindle and the price increases, our dependence on coal will grow. As supplies of low-sulfur coal are used up, high-sulfur coal will be used. One way to use high-sulfur coal without further harming the air quality is to remove the sulfur dioxide from the exhaust gas by means of a system called a scrubber before it is emitted from the power plant stack. A common method of scrubbing involves blowing powdered limestone (CaCOs) into the combustion chamber, where it is decomposed to lime and carbon dioxide ... 

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