Limestone sensitivity

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. 

Resins filled with ground limestone to levels of 80% by weight are useful in soHd cast products. The fillers reduce sensitivity to brittle fracture and improve modulus, but have Httle effect on general strength properties (Table 8). 

Kalk-echtlieit. /. fastness to lime, -einlagerung, /. calcareous deposit, -eisengranat, m. lime-iron garnet, andradite. -eisenstein, m, ferruginous limestone, kalkempfindlich, a. sensitive to lime. Kalkempfindlichkeit, /. sensitiveness to lime, kalken, kalken, v.t. lime. 

Acid deposition and the associated particulate nitrates and sulfates are implicated in the deterioration of certain sensitive ecosystems, decreased visibility, negative human health effects, and increased degradation of certain stone building materials and cultural resources, especially those made of limestone and marble. Fine particulate nitrate and sulfate particles... 

The sensitivity of AN to initiation by heat may be increased or decreased by the presence of certain inorganic impurities. For instance, small amts of Cu increase sensitivity to heat because of the formation of a small amt of copper nitrite, which causes instability (Ref 90). The formation of Cu nitrite also was reported in Mellor, v 7 (Ref 16). Mellor also reports that the presence of Fe, Al or especially Zn in powdered form lowers the temperature required for the decompn of AN. Kast (Ref 31) reported that the presence of KMn04 in powdered form may cause the spontaneous heating of AN. Investigations conducted at Pic Arsn showed that different Cr compds such as the oxide and nitrate catalyze the decompn of AN, and in some cases explosions occurred at temps as low as 200°. Among the inorganic substances which lessen the sensitivity of AN to heat are clay, kiesel-guhr, powdered limestone etc. The same effect was expected of Amm sulfate until the disaster at Oppau in 1921 (Refs 15a 15b) rendered the safety of such a mixt uncertain. Amm sulfate had been used for many years as a desensitizer for AN in fertilizers and it was considered that such mixts could not be... 

The materials known to be sensitive to such attack are primarily those presenting a relatively thin facade of a substance that reacts readily with dilute acids (especially sulfuric). These include zinc (galvanized steel), certain paints, unprotected carbon steel. Copper (bronze) and carbonate stones (marble, limestone, some sandstones) may be attacked by acids, but their "sensitivity" will depend on the stock thickness and the intended service life. In the case of outdoor sculpture, for example, works of permanent value will be "sensitive" to deposited acids. 

While the development of flue gas clean-up processes has been progressing for many years, a satisfactory process is not yet available. Lime/limestone wet flue gas desulfurization (FGD) scrubber is the most widely used process in the utility industry at present, owing to the fact that it is the most technically developed and generally the most economically attractive. In spite of this, it is expensive and accounts for about 25-35% of the capital and operating costs of a power plant. Techniques for the post combustion control of nitrogen oxides emissions have not been developed as extensively as those for control of sulfur dioxide emissions. Several approaches have been proposed. Among these, ammonia-based selective catalytic reduction (SCR) has received the most attention. But, SCR may not be suitable for U.S. coal-fired power plants because of reliability concerns and other unresolved technical issues (1). These include uncertain catalyst life, water disposal requirements, and the effects of ammonia by-products on plant components downstream from the reactor. The sensitivity of SCR processes to the cost of NH3 is also the subject of some concern. 

Equation (7) indicates that the relative effectiveness of Mg2+ and Ca2+ in inhibiting the limestone dissolution rate depends on the ratio of Mg2+ concentration to Ca2+ concentration. On the other hand, the sensitivity of limestone dissolution rate to the Mg2+ concentration is determined by the Ca2+ concentration. As indicated by Equation (7), when the minimum ratio ( Mg/0Ca) 0 5 is required... 

This effect is relatively small until the total magnesium ion concentrations reach about 1000 ppm. o The effect of Mg2+ concentration on limestone dissolution rate can be explained by a surface adsorption model. The adsorption of Mg2+ reduces the limestone dissolution rate because the surface is partially blinded by the adsorbed magnesium ions. The competitive adsorption of calcium and magnesium ions was described by a mathematical model based on the Langmuir adsorption isotherm. The model was used to explain the sensitivity of limestone dissolution rate to magnesium ion concentration under limestone DA operating conditions. 

Experimental determination of He diffusion was attempted by Duddridge et al. (1991), who injected He-rich gas at a depth of 35 m into permeable limestones cut by a fault. They recorded a pulse of He in shallow soil gas 5-20 hours later within 10 m of the fault suboutcrop and up to 53 hours later 20 m from the fault suboutcrop. However, the concentration increase recorded (0.032 ppm) is well within the error of the analytical system (mass spectrometer with constant pressure inlet, as discussed below, and analytical sensitivity of 0.030 ppm), the data are patchy with many samples showing no pulse, and there is no estimate of background variation or the effect of changing environmental conditions. Conclusions about diffusion rates based on these data may not be reliable. 

Marble and limestone surfaces were exposed to atmospheric conditions at four eastern U.S. sites and were monitored for changes in surface chemistry, surface roughness/re-cession, and weight. The effect of acid deposition, to which calcareous materials are especially sensitive, was of particular interest. Results are described for the first year of testing, and aspects of a preliminary equation to relate damage to environmental factors are discussed. Thus far, findings support that acid deposition substantially damages marble and limestone surfaces. 

The deterioration of marble and limestone exposed both to anthropogenic acid deposition from the environment and to natural weathering is being assessed as one of the major activities of the Materials Effects Task Group of the National Acid Precipitation Assessment Program (NAPAP). There is much concern for the calcareous stone materials because of their widespread use as the exterior structure of commercial, institutional, and private buildings as well as in valued monuments and memorials. These calcium carbonate materials are especially sensitive to an acid environment. 

Reduced sensitivity of the system to limestone type and grind. Fine grinding of limestone is probably not required... 

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