Dolomite CaMg

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. 

Wettability measurements show that most soil constituents are water wettable or hydrophilic,28 although calcium carbonates [calcite, CaC03, and dolomite, CaMg(C03)2] are slightly hydrophobic for example, the contact angle of water and heptane is 100 to 105°. Therefore, carbonaceous reservoirs are usually oil-wet. 

As a test of our ability to calculate activity coefficients in natural brines, we consider groundwater from the Sebkhat El Melah brine deposit near Zarzis, Tunisia (Perthuisot, 1980). The deposit occurs in a buried evaporite basin composed of halite (NaCl), anhydrite (CaSC>4), and dolomite [CaMg(CC>3)2]. The Tunisian government would like to exploit the brines for their chemical content, especially for the potassium, which is needed to make fertilizer. 

The waste contained about 3.5% dissolved solids, 1.7% chlorides, 0.4% sodium hydroxide, and tens to hundreds of ppm of chlorinated hydrocarbons and chlordane its pH was generally greater than 13 (Brower et al., 1989). At the time of drilling, analysis of formation samples indicated that the injection zone was composed of nearly pure dolomite [CaMg(CC>3)2]. The carbonate formation was thought to be safe for accepting an alkaline waste water because carbonates are considered stable at high pH. 

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 ... 

Vb Carbonates are used, for example, in masses for fine ceramics and in glazes. Well-known examples are calcite or calcspar CaC03 which is the main component of limestone, magnesite MgC03 and dolomite CaMg[C03]2. In coarse ceramics lime is added to clay to obtain yellow-firing bricks. 

Figure 3.2 Typical DTA trace showing the decomposition of dolomite (CaMg(C03)2). The endotherm peaked at 650°C corresponds to the decomposition of free MgC03 in magnesitic [1] dolomite. The endotherm peaked at 805°C coincides with the decomposition of dolomite CaMg(C03)2(,) = CaC03(,) + MgO( )+ C02(s). The final endotherm peaked at 920°C corresponds to the decomposition of calcite (freed from the previous dolomite decomposition) CaC03(,) = CaO(,j + C02(s).

In the absence of other substances, dolomite [CaMg(C03),] begins to decompose rapidly in air at about 750°C, giving initially periclase and a carbonate of higher Ca/Mg ratio. The decomposition temperature is much affected by the presence of other substances. 

This rule can be applied to both electronic and dielectric polarizabilities, but here we discuss the rule only insofar as it applies to dielectric polarizabihties. The molecular or oxide additivity rule has been applied to hydrates, to the compounds MTiOs where M = Mg, Ca, Sr, and Ba, to dolomite (CaMg(C03)2), zircon (ZrSi04), and spinel (MgAl204), to several titanates andzirconates andKMgFs, and to a variety of minerals. " ... 

XRD analysis has revealed the presence of several different types of carbonate minerals in liquefaction residues from a number of coals. Minerals identified included vaterite and calcite (two polymorphs of CaCO,) dolomite (CaMg[C03]2) and in the residue from a high sulfur coal (2.26 db), anhydrite (CaSO,) was identified. The types of mineral deposits formed depend not only on the coal but also on the reaction conditions. Our data indicates that whilst vaterite forms at low temperatures (380°C), as the temperature increases, the vaterite becomes progressively converted to calcite, the more stable form. After further increases in temperature, particularly at long reaction times, dolomite begins to form. 

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