Soil Minerals in the Al₂O₃-SiO₂-H₂O System and a Theory of Their Formation

Abstract

Abstract-An attempt has been made to assemble the best thermodynamic information currently available for soil minerals in the AI.203-SiO2-H._,O system at 25~ and 1 atm. Montmorillonite is included by considering its aluminum silicate phase. Diagrams are presented so that the stability of the minerals can be visualized in relation to the ionic environment. Although the AI20:~-SiO2-H20 system is a very simple one compared to soils and sediments, the stability diagrams depict a mineral stability sequence and mineral pair associations that are in good agreement with natural relations.According to the stability diagram, mineral pairs that can form in intimate association are gibbsitekaolinite, kaolinite-montmorillonite, and montmorillonite-amorphous silica. Forbidden pairs are amorphous silica-kaolinite, amorphous silica-gibbsite, and montmorillonite-gibbsite. The formation of intimate mixtures of three or more of these minerals is also forbidden. The stability diagrams predict ion activity relationships that are in reasonable agreement with those obtained from soils and sediments.Amorphous silica probably limits high silica levels, with montmorillonite also forming at high silica levels. Kaolinite forms at intermediate and gibbsite at low silica levels. These minerals in turn probably control the activity of aluminum ions at a level appropriate to the pH. The formation of gibbsite, kaolinite, montmorillonite and amorphous silica appears to be controlled by a combination of kinetics and equilibria. That is, the kinetic dissolution of unstable silicates appears to control the H4SiO4 level. The new mineral(s) most stable at that H4SiO4 level appear to precipitate in response to solution equilibria.

Silicon nutrition and sugarcane production: A review1

“…Leaching of Si from the soil and plant uptake are also important in determining Si concentrations in soils (Kittrick, 1969). The concentration of soluble Si in soils is undoubtedly dynamic, where equilibrium conditions are the exception rather than the rule.…”

“…Others have suggested that amorphous Si coatings formed due to dehydration (McKeague and Cline, 1963c), kaolinite and montmorillonite (Kittrick, 1969), a surface aluminosilicate component (R) of variable composition (Weaver and Bloom, 1977), and/or opal (Wilding et al, 1979) might regulate the amount of Si in the soil solution. As monosilicic acid l oses water, it forms socalled silica gel until the proper moisture content is reached.…”

Authigenic Mineral Formation by Solodization

“…Energy-dispersive X-ray microanalysis (Fig. 5) (Vaughan 1978 (Lindsay 1979 (Table 8) were in the range for equilibrium solutions with smectite minerals (Kittrick 1969 …”

The element-release mechanisms of two pyrite-bearing siliciclastic rocks from the North German Basin at temperatures up to 90 °C under oxic and anoxic conditions

“…Amorphous ferrihydrite was modeled using the log K value from the SIT database, which is also included in the PhreeqC package, and the standard enthalpy of reaction (ΔH) from the LLNL database. Data for amorphous aluminum hydroxide were taken from Kittrick (1969). No ΔH values were available for amorphous aluminum hydroxide and manganese oxohydroxide, so no direct temperature dependence could be calculated for these two phases.…”

“…Data taken from the LLNL database, except log K of ferrihydrite (SIT database) and amorphous aluminum hydroxide (Kittrick 1969 …”