Aluminum oxyhydroxides products

In our weathering example (Table 7,2) kaolinite, rather than the aluminum oxyhydroxides, was the chief weathering product of the feldspars. This reflects the fact that the silica present in soil moisture and natural waters, generally, is high enough to stabilize kaolinite relative to the aluminum oxyhydroxides. This observation is better understood if we write the kaolinite dissolution reaction ... 

TABLE 12.7 Solubility products of some secondary aluminum oxyhydroxides and sulfate minerals observed resulting from the interaction of acid mine waters with geological materials... 

Aluminum is another abundant metal that is obtained from the ore bauxite, a mix of the minerals boehmite (aluminum oxyhydroxide) and gibbsite (aluminum hydroxide). The production of aluminum is very expensive because the bauxite must be heated with the compound cryolite to make a molten solution in which the aluminum is concentrated by an electric current. Aluminum is used in products such as cans, foil, windows, vehicles, and household items and mixed with other metals in alloys. 

The results of development work on processes indicate that the two main methods of preventing the duplex microstructure from forming appear to be fast-firing, or increasing the amount of / "-alumina at low temperatures. Based on these results, Duncan et al. [21] and Zyl et al. [22] have described production processes starting from aluminum oxyhydroxides or aluminum hydroxides as precursors for the synthesis of the solid electrolyte "-alumina. Duncan et al. described an alumina precursor which substitutes in part or wholly for a-alumina in an established slurry solution spray-drying process. As a precursor, hydrothermal boehmite, Cera hydrate, has been used. A calcination step is important at the begirming of the process. Boehmite was used both in the as-received condition and after calcination. The effect of the calcination temperature on the fired properties of /S"-alumina can be seen in Table 21.5. 

Silicate and aluminosilicate mineral-weathering reactions involve both H -ion attack on the mineral and hydration or hydrolysis of the product minerals (clays and metal oxyhydroxides) or product aqueous species. If the primary mineral contains aluminum, then clays may result from the weathering. If the primary mineral contains Fe(II) or other reduced metal ions, weathering may involve oxidation as well as hydrolysis. 

He has contributed to research on the interface between soil chemistry and mineralogy and soil biology. His special areas of research include the formation mechanisms of aluminum hydroxides and oxyhydroxides, the surface chemistry and reactivities of short-range-ordered precipitation products of Al and Fe, the influence of biomolecules on the sorption and desorption of nutrients and xenobiotics on and from variable charge minerals and soils, the factors that influence the sorption and residual activity of enzymes on phyllosilicates, variable charge minerals, organomineral complexes, and soils and the chemistry of arsenic in soil environments. 

---