Kaolinite equilibria

Baviere et al. [41] determined the adsorption of C18 AOS onto kaolinite by agitating tubes containing 2 g of kaolinite per 10 g of surfactant solution for 4 h in a thermostat. Solids were separated from the liquid phase by centrifugation and the supernatant liquid titrated for sulfonate. The amount of AOS adsorbed is the difference between initial solution concentration and supernatant solution concentration at equilibrium. 

A proponent of "reverse weathering" suggested that gibbsite, kaolinite, and quartz exist in equilibrium according to the following equation. In equilibrium expressions for these reactions, water will appear as the activity, rather than concentration. The activity can be approximated by the mole fraction of water. What is the activity of water if this equilibrium is maintained Could this equilibrium exist in seawater, where the mole fraction of water is about 0.98 AG values (kj/mol) gibbsite — 2320.4 kaolinite — 3700.7 quartz —805.0 water —228.4. 

If alunite, K-mica and kaolinite (which are common minerals in the advanced argillic alteration) are in equilibrium, the concentration of H2SO4 can be estimated based on the experimental work by Hemley et al. (1969) the concentration of H2SO4 at 200°C and 300°C is 0.002 and 0.012 M, respectively. This may suggest that it is difficult to form such a high concentration of sulfate ion only by oxidation of H2S. 

Figure 1.96. Log /oj-pH diagram constructed for temperature = 200°C, ionic strength = 1, ES = 10 m, and EC = 10 m. Solid line represents aqueous sulfur and carbon species boundaries which are loci of equal molalities. Dashed lines represent the stability boundaries for some minerals. Ad adularia. Bn bomite, Cp chalcopyrite, Ht hematite, Ka kaolinite, Mt magnetite, Po pyrrhotite, Py pyrite, Se sericite. Heavy dashed lines (1), (2), and (3) are iso-activity lines for ZnCOs component in carbonate in equilibrium with sphalerite (1) 4 co3=0-1- (2) 4 ,co3=0-01- (3) 4 co3 =0-001 (Shikazono, 1977b).

Minerals in oxygen isotopic equilibrium with mixed fluid are feldspar for ore deposit/zone IV, and zone III/II, montmorillonite, and kaolinite for zone II/I, and montmorillonite for zone I/fresh rocks. 

Fig. 6.3. Saturation indices of Amazon River water with respect to various minerals (left) calculated directly from a chemical analysis, and (right) computed assuming that equilibrium with kaolinite and hematite controls the fluid s aluminum and iron content.

To construct an alternative model of Amazon River water, we assume that equilibrium with kaolinite (a clay mineral, Al2Si205 (OH)4) and hematite (ferric oxide, Fe203) controls the aluminum and iron concentrations ... 

Many mineralogic reactions involve exchange of cations or anions. Hence, geochemists commonly need to determine equilibrium lines in terms of activity ratios. Consider, for example, the reaction at 25 °C between the clay kaolinite [Al2Si205(0H)4] and the mica muscovite. The RXN commands... 

We further specify equilibrium with kaolinite [Al2Si205(0H)4], which occurs in at least some of the veins as well as in the altered wall rock. Since we know the fluid s potassium content (Table 22.1), assuming equilibrium with kaolinite fixes pH according to the reaction,... 

By this reaction, we can expect the modeled fluid to be rather acidic, since it is rich in potassium. We could have chosen to fix pH by equilibrium with the siderite, which also occurs in the veins. It is not clear, however, that the siderite was deposited during the same paragenetic stages as the fluorite. It is difficult on chemical grounds, furthermore, to reconcile coexistence of the calcium-rich ore fluid and siderite with the absence of calcite (CaCOs ) in the district. In any event, assuming equilibrium with kaolinite leads to a fluid rich in fluorine and, hence, to an attractive mechanism for forming fluorite ore. 

In a final application of kinetic reaction modeling, we consider how sodium feldspar (albite, NaAlSisOs) might dissolve into a subsurface fluid at 70 °C. We consider a Na-Ca-Cl fluid initially in equilibrium with kaolinite [Al2Si20s (OF )/ ], quartz, muscovite [KAl3Si30io(OH)2, a proxy for illite], and calcite (CaC03), and in contact with a small amount of albite. Feldspar cannot be in equilibrium with quartz and kaolinite, since the minerals will react to form a mica or a mica-like... 

Na -loess clay, where batch experiments were analyzed by X-ray diffraction and infrared and far-infrared measurements. The adsorption isotherm (Fig. 8.36) shows that loess clay is selective for cesium cations. The raw material contained a large amount of quartz, and the clay material was a mixture of kaolinite and an interstrati-fied iUite-smectite mineral as a result, equilibrium Cs" adsorption data are not consistent with a single site Langmuir model. Cesium adsorption on this particular soil clay occurs by cation exchange on sites with various cesium affinities. At low concentration, far-infrared spechoscopy shows the presence of very selective adsorption sites that correspond to internal collapsed layers. At high concentration, Cs MAS-NMR shows that cesium essentially is adsorbed to external sites that are not very selective. 

Toca, C.G. (1981) Desorption of phosphate from iron oxides in relation to equilibrium pH and porosity. Geoderma 26 203—216 Caillere, S. Gatineau, L. Henin, S. (1960) Preparation a Basse temperature d hematite alu-mineuse. Comp. Rend. 250 18—22 Cambier, P. Picot, C. (1988) Nature des lia-sions kaolinite-oxyde de fer au sein des mi-croagregats dun sol ferralitique. Sci. du Sol 28 223-238... 

Considering the compositions of the mixed layered minerals found in sedimentary rocks (Figure 25) it is obvious that magnesian-iron expandable dioctahedral minerals will be in equilibrium not uniquely with kaolinite but also in many instances with a magnesian-iron phase—either chlorite or an expanding trioctahedral mineral. In such a situation the slope in... 

When an expanding mineral is no longer stable, the iron content of the chlorite in equilibrium with illite will become more variable (Figure 49b). If chlorite is present due to a relatively high Fe/Fe + Mg content of a rock, it can occur with three other aluminous phases such as illite-montmorillonite and kaolinite. Thus the four-phase phyllosilicate assemblage common to argillaceous rocks can be accounted for by dividing the... 

The buffer capacity may be considered as defined for the incremental addition of a constituent to a closed system at equilibrium—e.g., adding a strong acid to a carbonate solution, C02 to a water solution in equilibrium with calcite, a strong acid to a sea water solution in equilibrium with both kaolinite and muscovite, etc. In general,... 

One set of aluminosilicate equilibrium relationships for which some quantitative data are available is depicted in Figure 5. This figure (25° C) is derived from information presented and discussed by Hemley (15), Feth, Roberson, and Polzer (8), and Garrels and Christ (11). The dual boundaries between potassium mica (muscovite) and kaolinite reflect the roughly estimated uncertainty in the equilibrium constant. The relationship of this boundary to actual K -H+ ratios in sea water may be... 

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