Solubility of carbonate minerals

Because of the great depth of the ocean, the most important physical property determining the solubility of carbonate minerals in the sea is pressure. The pressure dependence of the equilibrium constants is related to the difference in volume, AV, occupied by the ions of Ca and in... 

There are several ways one can write the solubility of carbonate minerals in water. Most useful are reactions written in terms of CO2 or H+. As noted earlier, carbon dioxide is the chief source of acidity in most natural waters. The reaction between calcite and CO2 is... 

Why is the solubility of carbonate minerals roughly proportional to the cube root of the CO2 pressure. 

How might increases in groundwater pollution affect the solubility of carbonate minerals ... 

Eqs. (4) and (11) show that an increase of proton activity a(H+) in the solution raises the solubility of carbonate minerals and lowers the solubility of CO2. A decrease in proton activity and subsequent increase in basicity, results in a precipitation of mineral carbonates. The decrease of the solubility of M C03, e.g. can be caused by a common anion introduced by dissolved sodium or potassium carbonate or bicarbonate salts. 

Most primary and secondary minerals found in soil systems are barely soluble in the soil solution. The amount of mass from the bulk phase to hydrated ions in soil solution is negligible compared to the total mass of the solid phase. In arid and semi-arid soils, concentrations of most trace metals in soil solution may be controlled by their carbonates and to some extent by their hydroxides. Other than carbonates, trace elements in arid and semi-arid soils may also occur as sulfate, phosphate or siliceous compounds, or as a minor component adsorbed on the surface of various solid phase components. The solubility of carbonates, sulfates and other common minerals of trace elements in arid and semi-arid soils will be discussed in Chapter 5. Badawy et al. (2002) reported that in near neutral and alkaline soils representative of alluvial, desertic and calcareous soils of Egypt, the measured Pb2+ activities were undersaturated with regard to the solubility of... 

Stolper E., Eine G., Johnson T., and Newmann S. (1987). Solubility of carbon dioxide in albitic melt. Amer. Mineral, 72 1071-1085. 

A central concept important in studies of the geochemistry of carbonate systems is that of carbonate mineral solubility in natural waters. It is the touchstone against which many of the most important processes are described. In the previous chapter, methods for the calculation of the saturation state of a solution relative to a given carbonate mineral were presented. In addition, equations were given for... 

Natural carbonate minerals do not form from pure solutions where the only components are water, calcium, and the carbonic acid system species. Because of the general phenomenon known as coprecipitation, at least trace amounts of all components present in the solution from which a carbonate mineral forms can be incorporated into the solid. Natural carbonates contain such coprecipitates in concentrations ranging from trace (e.g., heavy metals), to minor (e.g., Sr), to major (e.g., Mg). When the concentration of the coprecipitate reaches major (>1%) concentrations, it can significantly alter the chemical properties of the carbonate mineral, such as its solubility. The most important example of this mineral property in marine sediments is the magnesian calcites, which commonly contain in excess of 12 mole % Mg. The fact that natural carbonate minerals contain coprecipitates whose concentrations reflect the composition of the solution and conditions, such as temperature, under which their formation took place, means that there is potentially a large amount of information which can be obtained from the study of carbonate mineral composition. This type of information allied with stable isotope ratio data, which are influenced by many of the same environmental factors, has become a major area of study in carbonate geochemistry. 

Most studies of carbonate chemistry in deep sea sediment pore waters have, therefore, focused on the the apparent solubility behavior of carbonates in these sediments. The basic hypothesis is that because of the relatively fast reaction kinetics of carbonate minerals and generally low sedimentation rates in deep sea... 

Methods need to be developed to measure and determine the influences of factors such as strain, crystal geometry, dislocation density, low concentrations of coprecipitates, etc. on subtle solubility and reactivity differences of carbonate minerals. 

For these carbonates, the calculation of the saturation index gets more difficult. If, for instance, one considers the calcite/strontianite system, the solubility of both mineral phases is estimated by ... 

Some silicate minerals are also formed in a similar manner. The process is very slow, slower than even carbonate formation, because of the very low solubility of silicate minerals. In clay minerals, or in lateritic soils, silicates dissolve very slowly to form an intermediate product, silicic acid (H4Si04), which subsequently will react with other sparsely soluble compounds and form silicate bonding phases. Thus, a dissolution-precipitation process seems to be crucial to forming some silicate minerals. 

INFLUENCES ON THE SOLUBILITY AND SATURATION STATE OF CARBONATE MINERALS... 

Sec. 6.4 Influences on the Solubility and Saturation State of Carbonate Minerals... 

Carbonate mineral saturation can limit metal and carbonate concentrations even in sewage and landfill leachate polluted groundwaters. What would you expect the apparent CO2 pressure to be in such waters and why What about the solubility of carbonates under such conditions ... 

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