Calcium thermodynamic data

In addition to end-member phases, such as fluorapatite and HA, several studies have reported thermodynamic data related to solid solutions of apatite with various cations involving substitutions like Ca-Mg, Ca-Cd, Ca-Pb and Ca-Sr [72-74]. The related enthalpies of mixing were obtained, and their variation versus composition was generally indicative of a non-statistical occupancy of the cationic sites of the apatitic structure. In some instances, the limits of cationic substitution for calcium were estimated (e.g. in the range 0.073-0.101 for Ca-Mg fluorapatites according to Ben Abdelkader et al. [74]). 

High temperature thermodynamic data are available only for three sulfites calcium, potassium, and sodium. Most sulfites are fairly unstable, decomposing at relatively low temperatures. The decomposition reactions are not always exactly known, with diverse decomposition products, including sulfur, being reported. There are two major decomposition reactions (1) decomposition to the oxide and S02, and (2) oxidation-reduction (disproportionation) to the sulfate and oxide and S02, i.e.,... 

EXAMPLE 22-4 The following thermodynamic data are given for the dissociation of calcium carbonate at 25°C AH = 178 kJ AG = 130 kJ AS° = 161 J/mole-deg. Estimate the temperature at which the dissociation pressure is 1 atm, ignoring the correction for heat capacity. 

Sulfur oxides in the FCC regenerator flue gas can react with these alkaline earth metals to form sulfates. On the basis of thermodynamic data, the formation of calcium and barium sulfates is favored over the formation of vanadates at typical regenerator conditions[l 1,12]. The other trap materials may or may not be affected by sulfur competition, depending on the SOx concentration and regenerator conditions. In any case, the effect of sulfur competition can not be overlooked when designing effective vanadium traps. 

The immiscibility region near the Si02 apex was neglected in the calculation as such behavior is not considered in the thermodynamic model. Furthermore, because of the lack of thermodynamic data, the crystallization of rankinite, tricalcium silicate, tricalcium aluminate, and calcium hexaaluminate was not included in the calculation. 

In making thermodynamic calculations to determine departure from equilibrium, thermodynamic data for pure stoichiometric calcite and dolomite were used. However, mineralogic and x-ray examination of aquifer material has shown that the calcite may have several mole percent magnesium the dolomite that occurs in the system is generally calcium-rich (13). Therefore, both of these minerals in the natural state have a higher free energy and hence a somewhat higher solubility than the pure minerals. Thus, part of the supersaturation that we have calculated may be more apparent than real. 

Fig. 4.43 The COj ions content in AFt vs. temperature, calculated basing on the thermodynamic data AFt is in equilibrium with the excess of calcite, calcium monocarboaluminate, port-landite and liquid phase (not shown in figure) (according to [123])...

Dob] Dobrovsky, L., Linzer, E., Unzeitigova, H., Analysis of the Fundamental Thermodynamic Data of Calcium Systems (in Czech), Shorn. Ved. Praci Vysok. Skoly Banske v Ostrava (Trans. Inst. Min. Metall. Ostrava Met Series), 1,1-20 (1988) (Calculation, Thermodyn., 31)... 

Fuj] Fujiwara, H., Tano, M., Yamamoto, K., Ichise, E., Solubility and Activity of Calcium in Molten Iron in Equilibrium with Lime and Thermodynamics of Calcium Containing Iron Melts , ISIJ Int, 35(9), 1063-1071 (1995) (Experimental, Phase Relations, Thermodyn., 23) [1995Jowl] Jowsa, J., Calcium and Oxygen in Liquid Iron-Discrepancies Between Thermodynamic Data and its Consequences (in Polish), Hutnik- Wiadomosci Hutnicze, 7, 246-250 (1995) (Calculation, 22)... 

It has been known for years though that calcium and sulfate ions in solution associate to form the aqueous molecule CaSO. Many studies have been done in an attempt to determine the effect of this association on the system (G2, G6, G13, G16. G17, G20, G23, G30. G32, G33. G44, G45, G46, G47, G55, G67, G72, G73). The Russian thermodynamic data compilation reflects this ... 

This Is about half the value of the solubility product calculated using the NBS data that assumes complete dissociation. Since the amount of calcium and sulfate ions in solution are so low and the association of the two to form an aqueous molecule would have little effect on the ionic strength, it may be decided to disregard the interaction. The large difference in the solubility products points out that care must be taken in matching the thermodynamic data to the modeling method chosen. 

Table 7.16 Thermodynamic data for calcium(ll) species at 25 °C and comparison with data available in the literature.

Table 7.19 Literature thermodynamic data for calcium species at 25 °C.

Dickinson, E., Semenova, M.G., Belyakova, L.E., Antipova, A.S., Il in, M.M., Tsapkina, E.N., Ritzoulis, C. (2001). Analysis of light scattering data on the calcium ion sensitivity of caseinate solution thermodynamics relationship to emulsion flocculation. Journal of Colloid and Interface Science, 239, 87-97. 

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