Carbonates dolomite CaMg

The most common nonphosphalic accessory minerals associated with sedimentary phosphate rocks are quaife— clays, and two carbonates dolomite (CaMg(C03)2) and calcite (CaCOs). Carbonate-cemented phosphate rocks are particularly noteworthy because of their abundance. McClellan and Gremillion [14[ estimated that there are 3 tonnes of carbonate-cemented phosphate rock for every tonne of ore that could be handled by conventional milling and flotation processes (quartz- and clay-containing phosphate rocks). 

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. 

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. 

Divergent plate boundary Areas where adjacent tectonic plates are separating. A spreading zone. Dolomite A calcium-magnesium carbonate mineral, CaMg(C03)2-Dolostone A sedimentary carbonate rock primarily consisting of dolomite. 

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. 

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. 

The most abundant carbonate minerals in mine wastes are calcite [CaCOs], dolomite [CaMg(C03)2], ankerite [Ca(Fe,Mg)(C03)2], siderite [FeC03] or mixtures thereof. The dissolution of calcite can be described as... 

The regional distribution of hardness (i.e. Ca plus Mg) is shown in Fig. 4. This probably reflects the distribution of free carbonates in the sediments with areas of hard water reflecting their presence and low hardness areas reflecting their absence. The most probable carbonate minerals are calcite (CaCOs) and dolomite (CaMg(C03)2). The absence of pH and bicarbonate data from the National Hydrochemical Survey dataset means that saturation indices for these minerals could not be calculated. However, data from the three Special Study Areas (Smedley et al., 2001) suggest that there is both calcite and dolomite saturation, even slight supersaturation. 

Many carbonate minerals are found in the earth s crust. As a result, the waters of several lakes, rivers, and even oceans are in contact with these minerals. CaC03 is the primary component of limestone and marble, while dolomite (CaMg(C03)2) and magnesite (MgC03) are minerals found in other rock formations. 

Limestone (chiefly calcite, CaCOa) and dolomite rocks (chiefly dolomite, CaMg(C03)2) are exposed at about 20% of Earth s surface. Carbonate detritus, fossil shell materials, and carbonate cements are also common in noncarbonate sedimentary rocks and arid-climate soils. The carbonate minerals found in such occurrences, in decreasing order of importance, are calcite, dolomite, magnesian cal-cites (Cai jMgfCOa where jc is usually <0.2), aragonite (a CaCOa polymorph) and, perhaps, magnesite. As a rule of thumb, when such materials are present in silicate or aluminosilicate rocks or soils at a level of about 1 % or more, they will lend to dominate the chemistry of the soil or ground-water. This fact is extremely important when one is concerned about the ability of a rock to neutralize acid mine waters, other acid wastewaters, or acid rain. 

The relative dissolution rates between calcite and dolomite were also estimated for Bonanza field by examining the ratio of excess Ca to excess Mg in the post-treatment produced water. This ratio is 2.6 (Fig. 8). Assuming pure calcite (CaCOj) and pure dolomite (CaMg(C03)2>, this could only have resulted from the dissolution of 1.6 mol of calcite and 1 mol of dolomite, a calcite/dolomite dissolution ratio of 1.6. Assuming an impure calcite composition, the Ca/Mg ratio would result in a calcite/ dolomite dissolution ratio of approximately 1.9. Even though calcite is a minor component in the Tensleep reservoir, its relative contribution to the post-COj injection water is great. This is also despite the fact that the dolomite is more finely crystalline than the calcite, and would thus be expected to have a larger surface area exposed to the carbonated water. 

Calcium, element number 20, is a silvery-gray metal with a density of 1.55 g/cm3. The main source of calcium is seawater. Sedimentary materials that contain calcium include calcite, limestone, marble, and chalk (all of which are forms of calcium carbonate, CaC03), gypsum (CaS04 x 2H20), and dolomite (CaMg(C03)2). 

Calcite (CaCOj), dolomite (CaMg(COf)2)> and apatite (CafiF,OH)[POfifi. Carbonates of clay size are rather rapidly leached from humid soils. In arid regions, calcite accumulates. The phosphate remains in the clay phase after apatite decomposition, although in the form of Ca phosphates in alkaline soils or A1 and Fe phosphates in acid soils. 

The reaction of atmospheric carbon dioxide with water (the reverse of the second equation) is important in the weathering of rocks, and the formation of large carbonate deposits such as caldte, dolomite (CaMg(C03)2), and siderite (FeCOs). 

Dolomite rock is defined as a carbonate rock, containing calcite <50 %, dolomite >50 %. (Visser 1980). The term dolostone has been coined to avoid confusion with the mineral dolomite, CaMg (003)2, but has not gained general acceptance. 

Carbonates of alkaline-earth and other divalent metals are crystalline phases of noteworthy importance both in the earth sciences, as rock-forming minerals, and in chemical technology, as raw materials for a number of industrial processes. In particular, the calcite polymorph of CaCOs and dolomite, CaMg(C03)2, are present in huge quantities in the earth s crust as main constituents of limestones (sedimentary rocks), and are also important minerals of several metamorphic rocks. 

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