Saturation index state

Fig. 8-2. Steady-state profiles of the saturation index, omegadel = omega-1, the dissolution rate, and the respiration rate.

Figure 8-5 plots the carbonate parameters in the steady state as a function of depth between 0 and 400 centimeters. The figure shows that the saturation index, dissolution rate, and respiration rate all are very close to zero at 400 centimeters. The results for this simulation therefore do not depend on the total thickness of the sedimentary column, provided that this total thickness exceeds 400 centimeters, a limit that depends on the rate at which respiration decreases with increasing depth. 

When the number of concentrations of the circulating water is in the order of 3-7, some of the salts dissolved can exceed their solubility limits and precipitate, causing scale formation in pipes and coolers. The purpose of the treatment of the cooling water is to avoid scale formation. This is achieved by the injection of sulfuric acid to convert Ca and Mg carbonates (carbonate hardness) into more soluble sulfates. The amount of acid used must be limited to maintain some residual alkalinity in the system. If the system pH is reduced to far below 7.0, it would result in an accelerated corrosion within the system. As stated earlier, scale formation and/or corrosion tendency is defined by the Saturation Index (Langelier Index) and Stability Index (Ryznar equation). 

The calculation of montmorillonite saturation index present at the end of each 0.5-pH interval from the kinetically generated solution composition and the equilibrium constant for the Aberdeen montmorillonite was presented on Figure 6. A rapid Increase in saturation at lower values of pH slowing at higher pH values is indicated. This behavior suggests that the rate of production of soluble cations is greater than the rate at which species required for montmorillonite precipitation are removed from solution. Note that it has not been stated that montmorillonite precipitates in the classical sense that is, as a simple crystalline substance. 

Symbol for liquid state of a substance Langelier of Saturation Index... 

In studies of the state of saturation of minerals in natural waters and in most of the geochemical computer codes, the saturation index (SI) is used. The index is defined as 5/= log,o((2/ eq). so that 5/ = 0 at equilibrium (at saturation) of the mineral with the solution. The saturation index and AG, are related through SI = AG,./(2.3026 RT). If the reaction is written with the mineral as the reactant, then when SI and AG, are both negative, the mineral is undersaturated and so will tend to dissolve. When both are positive, the mineral is supersaturated and will tend to precipitate from solution. 

It needs to be stated clearly that the conditions of saturation thus calculated in the process of water analyses are determined exclusively on the basis of the prevalent analytical data and the employed data available on equilibria. A mineral shown to be supersaturated must not immediately, or at a later instance, be precipitated from this solution, but can be formed, for example, when other conditions are fulfilled, e.g. such standing in relation to the reaction kinetics. At the same time, a mineral found to be anJersaturated does not have to become dissolved immediately or at a later time - after all, it is possible that this mineral will never come in contact with the solution. The result of such a model calculation should just be understood as the statement that certain minerals can be either dissolved or precipitated. It goes without saying that mostly such minerals are of particular interest that have a calculated saturation index close to zero, because this circumstance often refers to set equilibria and hence to corresponding reactions. 

For evaluating the direction of a reaction are used various values log(na./]C.°) -saturation index, SI., log(K7Hfl ) - disequilibrium index or Yla /K = Cl. -saturation state. At saturation state greater than 1 the solution is considered oversaturated, and less than 1, undersaturated relative to the products of the reaction. 

Chemical affinity A is associated with saturation index SI. and saturation state through the following equation... 

The saturation state of pore solution is described by the saturation index Q. This index indicates which process dominates. Q Is defined by... 

Aqueous species do not occur in pure form, because their solubility in water is limited [2]. The solubility is the maximum amount of a substance that can be dissolved in a solution [6]. The saturation index indicates the saturation state of a solution with respect to a mineral phase, which is given by... 

The log is known as the saturation index (S2) and indicates the state of saturation of the solution with respect to the mineral phase the situations are [37, 42, 43] If the lAP is smaller than the equilibrium constant, it indicates a tendency of dissolution, and if lAP is bigger than the equilibrium constant, it indicates a precipitation tendency of the mineral. 

It is also possible to estimate the spatial distribution of steady state concentration in chimney, giving temperature dependency of diffusion coefficient, D. The amounts of precipitation of minerals can be calculated from the saturation index that is obtained from the distribution of concentration of fluid in chimney. 

Due to the complexity of the precipitation process, the saturation index (SI) is calculated to estimate the calcium carbonate precipitation in water, and is used to describe the saturation state (from a thermodynamic point of view) of the aqueous phase composition versus different solids. It is widely used to estimate the potential precipitation of different solids from an equilibrated aqueous phase speciation. 

Saturation index calculations made as part of a species distribution problem allow an assessment to be made of the effect of organic acids on the likely state of heterogeneous equilibria in an aqueous system (see Drever 1988, for discussion and definitions). By comparing saturation indices for minerals in systematically different waters we can predict the likely behavior of these minerals in the presence of organic acids. The predictions about mineral stability vary with the precise constraints that are placed on the calculations, in particular whether the cations are constrained to be in equilibrium with a mineral phase or set as a total concentration, the temperature, the partial pressure of CO2, and the anionic composition of the water. Conclusions that differ from those presented here may be possible, nevertheless, some consistent trends emerge that are related to observations made in the preceding section about speciation. 

Following Wolery (1983), we utilize chemical affinity (A units of kcal) as a measure of mineral saturation state, which is defined as A = 2.303RT(SI) where SI is the conventional saturation index (see Drever 1988). 

Many attempts have been made to characterize the stabiUty of the colloidal state of asphalt at ordinary temperature on the basis of chemical analysis in generic groups. For example, a colloidal instabiUty index has been defined as the ratio of the sum of the amounts in asphaltenes and flocculants (saturated oils) to the sum of the amounts in peptizers (resins) and solvents (aromatic oils) (66) ... 

The fluorescent components are denoted by I (intensity) followed by a capitalized subscript (D, A or s, for respectively Donors, Acceptors, or Donor/ Acceptor FRET pairs) to indicate the particular population of molecules responsible for emission of/and a lower-case superscript (d or, s) that indicates the detection channel (or filter cube). For example, / denotes the intensity of the donors as detected in the donor channel and reads as Intensity of donors in the donor channel, etc. Similarly, properties of molecules (number of molecules, N quantum yield, Q) are specified with capitalized subscript and properties of channels (laser intensity, gain, g) are specified with lowercase superscript. Factors that depend on both molecular species and on detection channel (excitation efficiency, s fraction of the emission spectrum detected in a channel, F) are indexed with both. Note that for all factorized symbols it is assumed that we work in the linear (excitation-fluorescence) regime with negligible donor or acceptor saturation or triplet states. In case such conditions are not met, the FRET estimation will not be correct. See Chap. 12 (FRET calculator) for more details. 

Once the initial equilibrium state of the system is known, the model can trace a reaction path. The reaction path is the course followed by the equilibrium system as it responds to changes in composition and temperature (Fig. 2.1). The measure of reaction progress is the variable , which varies from zero to one from the beginning to end of the path. The simplest way to specify mass transfer in a reaction model (Chapter 13) is to set the mass of a reactant to be added or removed over the course of the path. In other words, the reaction rate is expressed in reactant mass per unit . To model the dissolution of feldspar into a stream water, for example, the modeler would specify a mass of feldspar sufficient to saturate the water. At the point of saturation, the water is in equilibrium with the feldspar and no further reaction will occur. The results of the calculation are the fluid chemistry and masses of precipitated minerals at each point from zero to one, as indexed by . 

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