Kaolinite stability

MgO—K2O—Al2O2—SiO2—H2O system. In the stabUity-field diagram for the MgO—K2O—AI2O3— SiO2 H2O system (Fig. 15), it may be noted that all of the compositions of groundwater from the drift aquifers fall within the kaolinite stability field. However, compositions of groundwater from the bedrock aquifers also plot in the illite and Mg-chlorite fields. One possible interpretation of the distribution of these points is that a continuous spec-... 

Figure 2.61 Orthoclase and kaolinite stability fields in ground water.

Gangue minerals and salinity give constraints on the pH range. The thermochemical stability field of adularia, sericite and kaolinite depends on temperature, ionic strength, pH and potassium ion concentration of the aqueous phase. The potassium ion concentration is estimated from the empirical relation of Na+/K+ obtained from analyses of geothermal waters (White, 1965 Ellis, 1969 Fournier and Truesdell, 1973), experimental data on rock-water interactions (e.g., Mottl and Holland, 1978) and assuming that salinity of inclusion fluids is equal to ffZNa+ -h m + in which m is molal concentration. From these data potassium ion concentration was assumed to be 0.1 and 0.2 mol/kg H2O for 200°C and 250°C. 

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).

Limited silica fines stabilization data indicated that increasing copolymer molecular weight from 100,000 to 1,000,000 daltons had, if anything, a negative effect on silica fines stabilization. At a molecular weight of 1,000,000 daltons, this copolymer appeared to be more effective in stabilizing silica fines than silica/kaolinite, calcite, or hematite fines. However, the results may be due in part to the larger particle size and lower surface area of the silica fines (see Table II). 

When the DMAEMA content of NVP - DMAEMA copolymers was reduced from 20% to 8%, the silica fines stabilization effectiveness appeared to improve slightly. When the 80/20 NVP - DMAEMA copolymer was converted to a terpolymer containing 8% DMAEMA (CH SO, silica fines stabilization was substantially unaffected. However, stabilization of silica/kaolinite fines was greatly improved. This suggested that the interaction of polymer quaternary nitrogen atoms with anionic sites on mineral surfaces was important for the stabilization of migrating clays but a different interaction was important for the stabilization of silica fines. Calcite fines stabilization improved while hematite fines stabilization effectiveness decreased. This also indicated the nature of the adsorbed polymer - fine particle complex varied for different minerals. 

The consequence of these partial charges is that one surface of kaolinite is compatible with and attractive to the other surface. This results in increased stability of kaolinite and the formation of relatively stable structures. Some kaolinite particles can be larger than the 0.002 mm upper limit for clay Both surfaces also attract and hold water through these partial charges. The absorptive activity of kaolinite is associated with its surface electrons and partially positive hydrogens, and thus the two faces of kaolinite can attract anions, cations, water, and electrophilic and nucleophilic organic compounds. 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

Kaolinite is the main constituent in china clay used to make porcelain. The layers are largely held together by van der Waals forces. Bentonite is used in cosmetics, as a filler for soaps, and as a plasticizer, and it is used in drilling-muds as a suspension stabilizer. Bentonite and kaolinite clays are used, after treatment with sulfuric acid to create acidic surface sites, as petroleum cracking catalysts. Asbestos also has a layered structure (Section 12.13). 

Figure 4. Depth-temperature coordinates of apparent kaolinite upper stability in various pelitic rock sequences of Tertiary or younger age in deeply buried sediments. D = Dunoyer de Segonzac (1969) B = Browne and Ellis (1970) M = Muffler and White (1969) P = Perry and Hower (1970) S = Steiner (1968). Arrow indicates that kaolinite is stable to the greatest depth in the sequence.

Burnham, 1962 Keller and Hanson, 1968 Rose, 1970 Lowell and Guilbert, 1970 Keller, 1963). These studies indicate that kaolinite can be formed by hydrothermal alteration at the surface as well as to depths of several kilometers. Although information is lacking for low temperatures, intermediate conditions of pressure and temperature are known to permit the stability of the potassic mica-beidellite mixed layered composition series which excludes the stable coexistence of K-feldspar and kaolinite. If one accepts the argument that both beidellite-sodic and potassic are... 

The above use of "stable coexisting minerals" is of course based upon the fundamental consideration that the chemical system is "closed" that is, the chemical components K, Si and OH are "inert", their relative proportions, mass, in the system determines the phases formed. This can be assumed valid for many argillaceous sediments and rocks. However, in some geological environments, aqueous solutions containing alkalis and hydrogen ions in various concentrations (whose activities, therefore, are variables but constant throughout a given system) react with kaolinite or other minerals to influence its stability under otherwise constant physical and chemical parameters. 

Table 2 gives temperatures of montmorillonite stability which are established by the experiments reported. The most important criteria used is reaction reversal this lacking, length of the experiments and variety of starting material was taken into consideration. Two points are important among micas and other phyllosilicates only kaolinite, serpentine and muscovite are stable to very low temperatures. All trioctahedral 2 1 structures break down to expandable phases at low temperatures (bio-tites) or to 1 1 structures plus expandable phase (chlorites). 

It is instructive to compare the natural mineral assemblages with those in the simplified system which has been studied experimentally. The system muscovite-pyrophyllite is useful because it contains phases analagous to natural minerals. The system is dominated by two factors (1) the stability of the expandable phase (potassic beidellite) either alone or as a mixed layered phase (2) the stability of kaolinite in the presence of quartz. It appears from the data presented by Velde (1969) that the... 

Pelitic rocks investigated in the same areas where corrensites are formed during alpine metamorphism (Kiibler, 1970) revealed the absence of both montmorillonite and kaolinite but the illite or mica fraction was well crystallized as evidenced by measurement of the "sharpness" of the (001) mica reflection (Kiibler, 1968). This observation places the upper thermal stability of the expandable and mixed layered trioctahedral mineral assemblages at least 50°C. above their dioctahedral correlevants. This is valid for rocks of decidedly basic compositions where no dioctahedral clay minerals are present. 

V is characterized by kaolinite-illite-chlorite assemblages beyond the stability of an expanding mixed layered potassic dioctahedral mineral and below the thermal stability of pyrophyllite. The establishment of such conditions will be difficult in that the non-appearance of a mineral is a poor diagnostic and, as we have seen, kaolinite is frequently eliminated from sediments before its upper stability limit in the presence... 

VELDE (B.), 1968. The effect of chemical reduction on the stability of pyrophyllite and kaolinite in pelitic rocks. Journ. Sed. Petr. 

Second, Feth et al. (3) observe that the waters gain much of their silica in a few feet of travel, showing that it is the action of the high C02 water that produces "kaolinite. The rock minerals react, forming "kaolinite continuously in the system, and the "kaolinite controls the water composition by its presence. If the aluminum analyses were not so low, and hence analytically suspect, an attempt could be made to calculate an equilibrium constant for the substance formed. All that can be said at the moment is that the values of Si02 and Al concentrations and of pH are reasonable for those controlled by an aluminosilicate of the approximate stability of kaolinite. 

Figure 4. Silicate stability. KF, KM, G, K, and Q are K+-feld-spar, K+-mica, gibbsite, kaolinite, and amorphous silica, respectively. M and AB are montmorillonite and albite. W, S, FW, and SW represent areas of winter lake data, summer lake data, extracted fresh water sediments, and extracted sea water sediments, respectively...

May H.M., Kinniburgh D.G., Helmke P.A. and Jackson M.L. (1986) Aqueous dissolution, solubilities and thermodynamic stabilities of common aluminosilicate clay minerals Kaolinite and smectites. Geochim. Cosmochim Acta 50, 1667-1677. 

The interaction energy of neighboring DMSO molecules in the same interlayer space is about 0.95 kcal/mol. Despite these mutual interactions between DMSO molecules in the interlayer space of kaolinite, it was found that the interactions between the molecule and the surface of the kaolinite are the major contributors to the stabilization of the molecule. 

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