Ion interaction theory

Example 3 When using the specific ion interaction theory, the relationship between the normal potential of the redox couple in a medium... 

In case of low charged species, and approximately below 3 mol kg 1 the Specific Ion interaction Theory (SIT) [29] can be applied for the calculations of activity coefficients. Data available on interaction coefficients are scarce. But, paradoxically for actinide ions such data are relatively well known. However, in certain cases, they can be estimated from the model developed by L. Ciaviatta [33,34],... 

The most common approach used by geochemical modeling codes to describe the water-gas-rock-interaction in aquatic systems is the ion dissociation theory outlined briefly in chapter 1.1.2.6.1. However, reliable results can only be expected up to ionic strengths between 0.5 and 1 mol/L. If the ionic strength is exceeding this level, the ion interaction theory (e.g. PITZER equations, chapter 1.1.2.6.2) may solve the problem and computer codes have to be based on this theory. The species distribution can be calculated from thermodynamic data sets using two different approaches (chapter 2.1.4) ... 

Nonideality in aqueous solutions (see Chapter 3) was ascribed to Coulombic attraction between K and CCions, and the ion-ion interaction theories were evolved for aqueous solutions. The electrostatic attraction between a pair of oppositely charged ions could overwhelm thermal jostling and result in the formation of ion pairs (see Section 3.8). 

Later modifications of this general approach became known as the specific-ion interaction theory (SIT) because of the explicit dependence... 

One advantage of the ion interaction theory is that it can be applied to solutions of different salinities, that is, to brines, seawaters with different salinities, and estuarine waters. While the ionic medium method provides a very simple solution to many problems, especially for the speciation of constituents in the open ocean, it cannot readily be applied to solutions of different salinity that is, brines, seawater, and estuarine waters must be treated as separate solvents (Pabalan and Pitzer, 1988). 

Truesdell-Jones Equations, Specific Ion-Interaction Theory... 

Bronsted-Guggenheim-Scatchard specific ion interaction theory (SIT) (cf. Grenthe and Wanner 1989 Giridhar and Langmuir 1991 Nordstrom and Munoz 1994) is an ion- and electrolyte-specific approach to activity coefficients, which is, therefore, theoretically capable of greater accuracy than the Davies equation. The general SIT equation for a single ion, i, can be written... 

Since a large part of the NEA-TDB project deals with the thermodynamics of aqueous solutions, the units describing the amount of dissolved substance are used very frequently. For convenience, this review uses M as an abbreviation of mol-dm for molarity, c, and, in Appendices B and C, m as an abbreviation of mol-kg for molality, m. It is often necessary to convert concentration data from molarity to molality and vice versa. This conversion is used for the correction and extrapolation of equilibrium data to zero ionic strength by the specific ion interaction theory, which works in molality units (c/ Appendix B). This conversion is made in the following way. Molality is defined as moles of substance B dissolved in 1 kilogram of pure water. Molarity is defined as Cg moles of substance B dissolved in (/ - c M) kilogram of pure water, where p is the density of the solution in kg-dm and the molar weight of the solute in kg-mof. ... 

One method takes into account the individual characteristics of the ionic media by using a medium dependent expression for the activity coefficients of the species involved in the equilibrium reactions. The medium dependence is described by virial or ion interaction coefficients as used in the Pitzer equations [73PIT] and in the specific ion interaction theory. 

The way in which the activity coefficient corrections are performed in this review according to the specific ion interaction theory is illustrated below for a general case of a complex formation reaction. Charges are omitted for brevity. 

When using the specific ion interaction theory, the relationship between the redox potential of the couple PuO /Pu " in a medium of ionic strength /, and the corresponding quantity at / = 0 should be calculated in the following way. The reaction in the galvanic cell ... 

Table B-4, Table B-5 and Table B-6 contain the selected specific ion interaction coefficients used in this review, according to the specific ion interaction theory described. Table B-4 contains cation interaction coefficients with Cl", CIO andNOj. Table B-5 anion interaction coefficients with Li, with Na or NH and with K. The coefficients have the units of kg-mol and are valid for 298.15 K and 1 bar. The species are ordered by charge and appear, within each charge class, in standard order of arrangement, cf. Section 11.1.8.

The ion-interaction theory in contrast to the above was developed by Pitzer (42) as an outgrowth of work done by Guggenheim (44). This phenomenological methodology was based on the concept that ions electrostaticly interact in solution and that these interactions were based on a statistical likelihood of collision, hence the ionic strength dependency. Several papers in this volume discuss aspects of the importance of this approach to modeling the chemistry of complex systems. 

Ion Interaction. Ion-interaction theory has been the single most noteworthy modification to the computational scheme of chemical models over the past decade this option uses a virial coefficient expansion of the Debye-Huckel equation to compute activities of species in high ionic strength solutions. This phenomenological approach was initially presented by Pitzer ( ) followed by numerous papers with co-workers, and was developed primarily for laboratory systems it was first applied to natural systems by Harvie, Weare and co-workers (45-47). Several contributors to the symposium discussed the ion interaction approach, which is available in at least three of the more commonly used codes SOLMNEQ.88, PHRQPITZ, and EQ 3/6 (Figure 1). 

Figure V-15 Extrapolation to / = 0 of experimental results for the formation of Zrp3 using the specifie ion interaction theory. The data refer to perchlorate media and are taken from [67NOR] ( ), [49CON/MCV] (o), [62BUS] (A) and [69NOR2] (T). The data from the first three of these studies have been recalculated in this review (see Appendix A and Table V-14). The dashed lines are back-propagated data using the 95% uncertainties in the stability constant and interaction coefficient to / = 5 mol-kg . ...

Extrapolation to / = 0 of experimental data for the formation of ZrOH using the specific ion interaction theory.105... 

---