Solid-solution equilibrium

The relationship between aluminous sepiolite and the magnesian form is not at all clear as yet. The question of whether or not aluminous sepiolite can be precipitated directly from solution should be posed since alumina concentration in alkaline solutions (pH 7-9) is assumed to be quite low. For the present, palygorskite should probably be considered as a phase produced through solid-solution equilibria due to its high alumina content. Possibly most sepiolites are produced in this way. Even the inonomineralic deposits in saline lakes or deep sea cores contain sepiolites with high alumina contents (Parry and Reeves, 1968 McLean, et al., 1972). 

Liquid-solid solution equilibria at constant pressure... 

Figure 10.5. Limiting curves for liquid solution-solid solution equilibria.

Akaogi M. and Akimoto S. (1977) Pyroxene-garnet solid-solution equilibria in the systems Mg4Si40i2-Mg3Al2Si30i2 and Fe4Si40i2-Fe3Al2Si30i2 at high pressures and temperatures. Phys. Earth Planet. Inter. 15, 90-106. 

An updated and expanded version of PHREEQC (version II) was published by Parkhurst and Appelo (1999). Version II has all of the capabilities of version I, and includes new routines for kinetically controlled reactions, solid-solution equilibria, fixed-volume gas-phase equilibria, variation of the number of exchange or surface sites in proportion to a mineral or kinetic reactant, diffusion or dispersion in one-dimensional (ID) transport, ID transport coupled with diffusion into stagnant zones, and isotope mole balance in inverse modeling. 

Krishnamurti, G. S. R., and Naidu, R. (2003). Solid-solution equilibria of cadmium in soils. Geoderma 113, 17-30. 

Establishment of solid/solution equilibria was followed as a function of time. Resulting equilibrium solutions were filtered through 0.45 pm filters, which might not have been sufficiently effective to retain small colloids. On the other hand, concentrations of dissolved Zr in the equilibrium solutions were determined by complexometry, which wouid not detect colloidal Zr. The solubility data were interpreted by presence of the dominant solution species Zr(OH)j and Zr2(OH) with complexation constants determined from the potentiometric titrations, using solubility constants of Zr(OH)4 as the only fitting variable. However, as can be seen in Figures D-6 to D-9 the experimental data can be equally well fitted by presence of polymeric species, for example by the presence of the two tetramers Zr (OH) and Zr4 (OH) 5. The results were not substantially influenced by NO3 complexation. In most cases, the contribution of NOj complexes represented less than 1% of the total speciation. A maximum of 17% N07 complexes is predicted for the most acid medium in 2 M NaN03. 

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