Calcium emission from

The abatement of fluorine emissions and disposal of by-product calcium sulfate from phosphoric acid plants are environmental concerns. 

Formation of emissions from fluidised-bed combustion is considerably different from that associated with grate-fired systems. Flyash generation is a design parameter, and typically >90% of all soHds are removed from the system as flyash. SO2 and HCl are controlled by reactions with calcium in the bed, where the lime-stone fed to the bed first calcines to CaO and CO2, and then the lime reacts with sulfur dioxide and oxygen, or with hydrogen chloride, to form calcium sulfate and calcium chloride, respectively. SO2 and HCl capture rates of 70—90% are readily achieved with fluidi2ed beds. The limestone in the bed plus the very low combustion temperatures inhibit conversion of fuel N to NO. ... 

Sulfur dioxide emissions from power plants can be reduced by spraying a water solution of calcium hydroxide directly into the smokestack. This "scrubbing" operation brings about the reaction... 

The use of the lignin fraction is much more cumbersome currently the best-known chemical of a real commercial importance is vanillin, which is obtained by oxidation of the black liquor. Another example is a product called spray-dried lignosulfonate (as sodium salt) obtained from the older, acidic sulfite pulping process. It is sold as a commercial product primarily as a concrete additive for enhanced strength. Since the cement industry is one of the big contributors of carbon dioxide emissions (due to the production of calcium oxide from calcium carbonate), the use of this renewable, wood-derived product not only is fossil-carbon neutral in itself but also reduces carbon dioxide emission due to the diminished need for cement in large infrastructures made of concrete. 

Figure 24, The basic principle used in atomic absorption. The sample is sprayed into the flame, and the calcium and magnesium emission from the lamp is absorbed. The extent of absorption is measured on the detector arm translated in terms of concentration.

As light emission from aequorin is dependent on Ca2+, the protein has been widely employed for determination of this ion. In particular, the protein was used in the past in the highly sensitive measurement of intracellular calcium concentration in several kind of cells [16]. More recently immobilized aequorin was used to develop an optical biosensor for measurement of calcium ions in complex... 

A protein of similar molecular weight to that of rat oncomodulin, rat and rabbit parvalbumins, S100, and the vitamin D-dependent calcium-binding proteins has been isolated from chicken gizzard smooth muscle. In this case, however, the fluorescence emission from the four tyrosine residues is quenched by Ca2+ binding.(160) The decrease in fluorescence intensity was used to suggest that there are two different classes of Ca2+binding sites. 

The results of the PCA from each subset are similar except that the data subsets which did not either Include the meteorological data or normalize the data to reduce meteorological variability (subsets 2 and 3) were not able to separate several of the components probably due to the atmospheric masltlng effect. Information on the wind direction and rainfall quantity dependence of seasalt and metals Is obtained when meteorological data are Included In the analysis. From the standpoint of separation of chemical factors the fourth subset (normalization to fractional composition) provided the best resolution of the data. Using deposition or concentrations, a component that Indicated a combined Influence of sulfate, nitrate, lead and calcium emission sources was resolved Into separate components when the fractional composition data were analyzed by PCA. 

Figure 3. Effect of scatter from calcium emission on the observed background signal in the region of the zinc, I = 213.9-nm line. Note that the borosilicate glass filter prevents any visible radiation from entering the spectrometer CSSj.

Emission spectroscopy utilizes the characteristic line emission from atoms as their electrons drop from the excited to the ground state. The earliest version of emission spectroscopy as applied to chemistry was the flame test, where samples of elements placed in a Bunsen burner will change the flame to different colors (sodium turns the flame yellow calcium turns it red, copper turns it green). The modem version of emission spectroscopy for the chemistry laboratory is ICP-AES. In this technique rocks are dissolved in acid or vaporized with a laser, and the sample liquid or gas is mixed with argon gas and turned into a plasma (ionized gas) by a radio frequency generator. The excited atoms in the plasma emit characteristic energies that are measured either sequentially with a monochromator and photomultiplier tube, or simultaneously with a polychrometer. The technique can analyze 60 elements in minutes. 

S02 emissions from sulfuric acid plants are controlled in spray towers. Effluent gases contain less than 0.5 percent S02. The S02 emissions have to be controlled (or recovered as elemental sulfur by, for example, the Claus process). An approach is to absorb the S02 in a lime (or limestone) slurry (promoted by small amounts of carboxylic acids, such as adipic acid). Flow is in parallel downward. The product calcium salt is sent to a landfill or sold as a by-product. Limestone is pulverized to 80 to 90 percent through 200 mesh. Slurry concentrations of 5 to 40 percent have been used in pilot plants. 

In environmental analysis, flame photometry is most widely used for the determination of potassium, which emits at 766.5 nm. It is also often used for the determination of sodium at 589.0 nm, although spectral interference problems (see Chapter 3) then may be encountered in the presence of excess calcium because of emission from calcium-containing polyatomic species. Molecular species are more likely to be found in cooler flames than in hotter flames. Some instruments use single, interchangeable filters, while others have three or more filters, for example for the determinations of potassium, sodium and lithium,... 

The reaction of various metal oxides with hydrogen chloride and the reverse reactions have been extensively smdied [47] the reaction behavior of hydrogen chloride with various bivalent and trivalent metal oxides has been reported. Sakata et al. reported the spontaneous degradation of municipal waste plastics at low temperature [48] and also the dechlorination of chlorine compounds from PVC mixed plastics-derived oil using solid sorbents [22], Courtemanche and Levendis [49] reported the control of HCl emission from the combustion of PVC by in-fumace injection of calcium-magnesium-based sorbents at gas temperatures of 850 and 1050°C. In the present study, the adsorption temperature 350°C was found to be optimum for the complete removal of hydrogen chloride at moderate concentrations (1820 ppm). 

B. Conrtemanche and Y. A. Levendis, Control of the HCl emissions from the combustion of PVC by in-fumace injection of calcium-magnesium-based sorbents, Env. Eng. Set, 15, 123-135 (1998) and references therein. 

Concrete is a highly alkaline environment because of the high concentration of calcium oxide or calcium hydroxide. The pH is greater than 12, which protects the steel-reinforcing bars used in the building from corrosion. Carbonation occurs when carbon dioxide reacts with the calcium carbonate and the pH of the environment drops to around 9. In this situation, carbonation becomes rapid, especially in industrialised areas and towns where there is a lot of exhaust emission from traffic. Acrylic coatings have become a versatile choice to overcome the problem of carbonation. 

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