Stability and solubility constants

The purpose of the current review was to critically evaluate the hydrolytic reactions of metal ions (cations) and select stability and solubility constants, where available, across the temperature range of 0-375°C. In carrying out the review, an attempt has been made to be as thorough as possible and utilise as much data as are available in the literature as possible. However, it is not feasible to review all data that have been published on a given metalion, and, undoubtedly, some studies have been missed. This certainly has not been by intention, and it is possible that the inclusion of some of these missing data may have led to different conclusions being reached for metals where little data exists. For those metals where substantial information is available, or for the protolysis constant of water, the exclusion of some data would unlikely affect the thermochemical data derived or the conclusions reached regarding the speciation of the metal ion. 

Stability and solubility constants were largely selected based on their consistency across a number of studies. The consistency may relate to where multiple data are available for a single set of conditions or one or more data are available for multiple conditions (i.e. either temperature or ionic strength). The temperature dependence of stability or solubility constants is based around the relationship of the constants with the inverse of absolute temperature assuming a constant heat capacity (whether zero or non-zero) and that for ionic strength is dependent on the relationship of the constants with respect to the specific ion interaction theory (standard or extended). The consistency is related to the agreement between the measured stability or solubility constants with respect to their uncertainties and the equation used to explain the temperature or ionic strength effects. 

Using the stability and solubility constants derived at zero ionic strength (25 C), a predominance speciation diagram is illustrated in Figure 7.13. The diagram... 

Thermodynamic parameters for the hydrolysis species of uranium(VI) and its oxide and hydroxide phases can be determined from the stability and solubility constants accepted in the present review together with the thermodynamic data for the oxide or hydroxide phases selected by either Grenthe et al. (1992) or GuUlaumont et al. (2003). The obtained thermodynamic values are listed in Table 9.7. 

The stability and solubility constants derived at 25 °C for zero ionic strength have been used to create a predominance speciation diagram for chromium(lll). The diagram is illustrated in Figure 11.30. The speciation behaviour illustrated in the figure is quite similar to that indicated by Rai, Sass and Moore (1987) for an ionic strength of 0.01 moll . These authors showed that the solubiUty of Cr(OH)j(s) increased at a pH between 11 and 12 due to the formation of Cr(OH) , as well as... 

The stability and solubility constants derived at 25 C for zero ionic strength have been used to create a predominance speciation diagram for cobalt(ll). The... 

A predominance speciation diagram for zinc(II) has been created from the stability and solubility constants derived at 25 C for zero ionic strength. The diagram is illustrated in Figure 11.98. Zincite, ZnO(s), has been used as the dominant soUd crystalline phase. A region does not exist where the polymeric species,... 

On the basis of the data utilised to produce Figure 12.1, the selected stability and solubility constant data for technetium(IV) are... 

Rard et al. (1999) give a Gibbs energy of formation for TcO(OH)2(aq) of AGf° = -(568.2 8.8) kJmol . The accepted stability and solubility constants and this Gibbs energy of formation lead to the following accepted thermodynamic values ... 

Brown and Sylva (1987) developed one of the best theories for the prediction of stability and solubility constants (Langmuir, 1997 Moriyamaef /., 2005). The unified theory of metal ion complexation (UTMIC), as it relates to hydrolysis species and phases, was described in Chapter 2. A variation of Eq. (2.86) is given in the following for the stability constant of the hydrolysis species... 

I 16 Prediction of Stability and Solubility Constants redefined according to... 

Figure 16.10 demonstrates that there is a linear free energy relationship between the stability and solubility constants. The slope derived from the line of best fit is -1.87 0.05, and the intercept is —40.2 0.6 the coefficient of determination is... 

Figure 16.10 Relationship between the stability and solubility constants for M(OH)g species and MOjls) phases.

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