Calcium carbonate CaCO formation

The formation of calcium carbonate (CaCOs), calcium sulfate, and barium sulfate scales in brine may create problems with permeability. Therefore it is advantageous that newly made fractures have a scale inhibitor in place in the fracture to help prevent the formation of scale. Formulations of hydraulic fracturing fluids containing a scale inhibitor have been described in the literature [1828]. 

Birds have evolved a chemical process that allows them to rapidly produce the calcium carbonate, CaCOs, required for eggshell formation. Research has shown that some chemicals, like DDT and PCBs, can decrease the amount of calcium carbonate in the eggshell, resulting in shells that are thin and fragile. 

Natural waters often contain relatively high levels of calcium ion, Ca, and hydrogen carbonate ion (bicarbonate), HCO3, from the leaching of minerals into the water. When such water is used commercially or in the home, heating of the water leads to the formation of solid calcium carbonate, CaCOs, which forms a deposit ("scale") on the interior of boilers, pipes, and other plumbing fixtures. 

The LSI is probably the most widely used indicator of cooling-water scale potential. It is purely an equilibrium index and deals only with the thermodynamic driving force for calcium carbonate scale formation and growth. It provides no indication of how much scale (CaCOs)... 

The kinetics of the formation of the magnesium hydroxide and calcium carbonate are functions of the concentration of the bicarbonate ions, the temperature, and the rate of release of CO2 from the solution. At temperatures up to 82°C, CaCO predominates, but as the temperature exceeds 93°C, Mg(OH)2 becomes the principal scale. Thus, ia seawater, there is a coasiderable teadeacy for surfaces to scale with an iacrease ia temperature. 

Removing a product from a system at equilibrium also makes Q < and leads to the formation of additional products. This behavior is commonly used to advantage in chemical synthesis. For example, calcium oxide (lime), an important material in the construction industry, is made by heating calcium carbonate in a furnace to about 1100 K CaCOs ( ) CaO (s) + CO2 (g) = (pco2 = 10 at 1100 K... 

The above-listed features of the formation of X-ray amorphous and crystalline products are observed in the decompositions of many other compounds. Haul and Schoning [41] applied an X-ray method (line-width technique) to study the structure of the decomposition products of dolomite as a function of temperature. The experiments were carried out both in vacuum and in a CO2 environment. In vacuum, decomposition proceeded to the CaO and MgO oxides, and in a CO2 environment, to CaCOs and MgO. This difference is reasonable. It originates from the calcium carbonate being more stable than the magnesium carbonate (the enthalpies of formation of CaCOs and MgCOg at 800 K are —1,154 and —1,045 kJ mol respectively). The size of the crystallites formed in vacuum [41] increased monotonically from 6nm for MgO and 13 nm for CaO to 120-140 nm with the temperature increasing within the range 700-1,000° C. (Oversaturation decreases in these conditions from 10 to 10 for MgO, and from 10 to 10 for CaO.)... 

Calcium carbonate has a solubility product of about 10" in slightly alkaline solutions. Figure 7.38 shows a titration curve for CaCb in NaCl solution when NaaCOs was added to precipitate the calcium ion [86]. There are four distinct regions on a curve. Region I is the neutralization of acid, and Region II is the formation of bicarbonate between pH 5 and 6. In Region HI, CaCOs precipitates when the pH exceeds about... 

In a further study, DiMasi and colleagues investigated the kinetics of amorphous CaCOs formation at a fatty acid monolayer interface using synchrotron X-ray reflectivity measurements [173]. In-situ experiments found three different parameters that control CaCOs mineralization in the presence of arachidic acid monolayers, PAA, and Mg + ions. Firstly, the crystal growth rate depends on the concentration of counterions and not on the polymer concentration in solution. Secondly, the soluble polymer only affects the lifetime of the amorphous calcium carbonate. And finally, the sole effect of Mg + is to delay the mineral film formation. These data thus suggest that competitive adsorption (e.g. Mg + vs. Ca +) is another parameter to consider in controlled mineralization processes. 

Scheme 1 a Aggregation mode of interlayer micelle-occluded nanocrystals, b Graphic presentation of the formation mechanism of CaCOs mesorings. Gray, calcium carbonate red, hydrophobic block blue, soluble neutral block yellow, charged block. The red arrow indicates the decreasing gradient of occluded polymer within the disklike structure. (Reproduced from [156], 2006, American Chemical Society)... 

Be(OH)2 is amphoteric, but the hydroxides of Mg, Ca, Sr, and Ba are basic. The basicity increases from Mg to Ba, and group 2 elements portray the usual trend that basic properties increase on descending a group. Solutions of Ca(OH)2, called lime water, are used to detect carbon dioxide. When C02(g) is bubbled through these solutions, they become opaque ( milky ), owing to the formation of a suspension of CaCOs. If additional CO2 is passed through these cloudy solutions, the turbidity dissipates and soluble calcium bicarbonate is formed from the excess CO2 (equation 25). 

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