Illite solubility

Figure 9.13 Temperature dependence of the compositions of illitic solubility-controlling phases in the presence of kaolinite and quartz betweeen 25°C and 250°C. From S. U. Aja and P. E. Rosenburg in Clays Clay Minerals 40(3) 292-99. Copyright 1992. Used by permission.

Reaction with K-Bearing Minerals. WD experiments with mixtures of Na-Kinney and sparingly soluble K-minerals were undertaken to simulate natural conditions. When K-feldspar was shaken with Na-Kinney at room temperature without WD for as long as 1 year, no illite layers were found in the experimental product. Nor were illite layers formed when muscovite was shaken with Na-Kinney for... 

Phenolic compounds have also been oxidatively polymerized to humic substances by clay minerals (29) and by the mineral fraction of a latasol (66). After a 10-day equilibration period, montmoril-lonite and illite clay minerals yielded 44 to 47% of the total added phenolic acids as humic substances whereas quartz gave only 9%. Samples of a latasol yielded over 63% of the total amount, from mixtures in varied proportion, of mono-, di- and trihydroxy phenolic compounds as humic substances (66). Extractions of the reaction products yielded humic, fulvic, and humin fractions that resembled soil natural fractions in color, in acid-base solubility, and in infrared absorption spectra. Wang and co-workers (67) further showed that the catalytic polymerization of catechol to humic substances was, enhanced by the presence of A1 oxide and increased with pH in the 5.0 to 7.0 range. Thus the normally very reactive products of Itgnin degradation can be linked into very stable humic acid polymers which will maintain a pool of potentially reactive phytotoxins in the soil. 

Metal transport increases were also metal specific, following the sequence Zn > Pb > Cu for total metal elution and Zn > Cu > Pb for soluble metal elution. Overall, however, between 30 and 90% of Cu was transported in the soluble fraction, while >60% of Zn and Pb were transported in the colloid-sorbed fraction. This is generally consistent with the metal affinities of the different colloids in conjunction with OC content and colloid size differences. Average increases of total Cu transport in the presence of colloids were three-fold for kaolinitic, five-fold for illitic, and six-fold for montmorillonitic colloids compared to the controls. The respective average... 

FIGURE 2.4 BTCs for soluble Cu, Zn, and Pb eluted in the presence or absence (control) of soil colloids with montmorillonitic, illitic, or kaolinitic mineralogy. 

FIGURE 2.6 Desorbed (a) total and (b) soluble Pb elution in D-H20 (control) and colloid suspensions with montmorillonitic, mixed, or illitic mineralogy flushed through the soil monoliths. 

Initially in this study, it was planned to critically evaluate AG data for complex clays, including chlorite, illite, and the smectites. However, there is much evidence that these clays dissolve Incongruently so that the apparent equilibria in solution are determined by secondary phases, such as gibbsite, boehmite, amorphous silica, and ferric oxyhydroxldes. The smectites are frequently the dominant clays in the colloidal size fraction in natural sediments. They have very large exchange capacities, and exhibit wide chemical variations. Usually, one or more of these factors have not been considered in the experimental solubility work. Even if appropriate corrections could be made, it is uncertain whether a AG value so obtained would have applicability to natural systems. 

As hydrolysis of the silicates and aluminosilicates continued (equation 1), dissolved sodium ions were continually produced, and acid was consumed. The pH of the water gradually increased. Formation of kaolinite was replaced by formation of montmoril-lonite and finally by production of illite. Silica was more soluble than alumina and as aluminosilicates were attacked by the water a protective coating of A1(0H) formed around the particles. This coating helped transport mineral particulates to the sediment. The reactions indicated by equation 1 were replaced by the family of reactions indicated in equation 2, written using the hydrolysis of albite as an example. 

Reference [137] reports the absence of significant dissolution of illite. In contrast, [138] reports considerable release of Si and Al from illite. Dissolution of illite, that is, Al, Si, Ca, and Mg concentrations at pH 3-9, was studied in [139]. Dissolution of kaolinite at acidic pH was studied in [140]. Reference [141] reports the release of Si, Fe, Al, and Mg from montmorillonite as a function of pH. Concentrations of Si and Al in solution during titration of smectite are reported in [142]. Solubility of laponite is discussed in [143] and references therein. 

Moderately Alkaline Weak-Leaching Environment Only a portion of the mobile weathering products (silica, base cations) is lost by leaching in this situation. Aluminum and iron hydroxide are the least soluble weathering products, so these react with the soluble silica and base cations to produce 2 1 layer silicates, including dioctahedral smectites and illites. Chlorites can be formed in this situation as well. 

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