Water mineral equilibrium relationships

White (1995) found that the apparent thermodynamic supersaturation of silicate minerals in most soil pore waters resulted from excessive values for total dissolved aluminum. In reality, much of this aluminum is complexed with dissolved organics in shallow soils and does not contribute to the thermodynamic saturation state of silicate minerals. Solubility calculations involving low dissolved organic concentrations in deeper soil horizons and in groundwater appear to produce much clearer equilibrium relationships (Paces, 1972 Stefansson and Amorsson, 2000 Stefansson, 2001). 

Carbon dioxide and its carbonate minerals play an important role in environmental chemistry and atmospheric physics. In natural waters, atmospheric CO2 has a significant influence on pH, which varies from alkaline seawaters to acidic low mineral lakes, rivers, and soil water. In freshwaters and in oceans the equilibrium relationships between the carbon dioxide, the chemical and biological components, temperature, and the pH are complex functions. Chemical thermodynamics provide quantitative relationships between chemical energy, ionic reactions, solubilities, speciation, pH, and alkalinity. In natural systems these relationships are also complex functions of chemical and biological effects. 

Silica concentration in deep ground water in the granitic rock area (e.g., Kamaishi, Japan) is in equilibrium with SiOz mineral (chalcedony) (Fig. 1.27). Based on a coupled fluid flow-dissolution-precipitation kinetics model the relationship between residence time of deep ground water and A/M was derived, and the reasonable values of x is estimated to be more than 40 years (Shikazono and Fujimoto 2001). 

Figure 3.10 illustrates the important relationships among dissolved CO2 in water, dissolved carbonate species (HCOj, CO3"), and solid carbonate minerals, particnlarly limestone (CaCOj) and dolomite (CaCOj MgCOj). These species are very important in the chemistry of the hydrosphere. As examples, many minerals are deposited as salts of COj" ion and algae in water utilize dissolved CO2 and HCO3 in the synthesis of biomass. The equilibrium relationships among CO2 gas in the atmosphere, dissolved CO2 and carbonate species in water, and solid carbonate minerals largely determine the pH, alkalinity, and hardness of water. 

There existed oxidation-reduction reactions with the same reaction speed on the sulphide mineral surface in water. One is the self-corrosion of sulphide mineral. Another is the reduction of oxygen. If the equilibrium potential for the anodic reaction and the cathodic reaction are, respectively, E and, and the mineral electrode potential is E, the relationship among them is as follows ... 

Dixit and Biswas124 dealt with the relationship between H+ an OH- concentrations and adsorption of an anionic collector on a mineral surface and its flotability. They used the system zircon-Na oleate. If Na oleate is dissolved in water the following equilibrium sets up ... 

Several chemical reactions, including calcium carbonate and hydroxyapatite precipitation, have been studied to determine their relationship to observed water column and sediment phosphorus contents in hard water regions of New York State. Three separate techniques have been used to Identify reactions important in the distribution of phosphorus between the water column and sediments 1) sediment sample analysis employing a variety of selective extraction procedures 2) chemical equilibrium calculations to determine ion activity products for mineral phases involved in phosphorus transport and 3) seeded calcium carbonate crystallization measurements in the presence and absence of phosphate ion. 

This relationship is also fairly intuitive. Look at it this way. The number of phases is always at least one (a system with no phases is not very interesting). To define a system having only an aqueous solution phase (p = 1), we must specify each of the solutes in the water, or b — 1 quantities. If there is one mineral in equilibrium with the water (p = 2), it controls one basis species, and so reduces b by one, and similarly for all p mineral or gas phases. This is Phase Rule (3.34). But defining the equilibrium state is not usually enough. We want also to know the mass of each phase, so we need p extra data, giving Phase Rule (3.35), which says that for any system we need b pieces of information. These b pieces of information are... 

A simple method for estimating the pH-solubility relationship of bile acids and salts is to carry out aqueous acidometric titration of a bile salt in water with a stronger mineral acid [5,35], Once the molarities of bile salt and mineral acid are known, the titration curves provide a direct measurement of equivalence, equilibrium and metastable pH values, the pH at which precipitation of the HA species occurs (pHpp,), an estimate of the solubilities of the HA species in water (if the system is < CMC) or in water plus micelles (if the system is > CMC) and a calculation of the apparent pK (pATg). The methods, results and interpretation of such titration curves for the common bile salts, titrated with HCl, have been described in detail elsewhere [5,6]. 

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