Surface charge aluminosilicate minerals

The surface charge of aluminosilicate minerals may arise either from isomorphous cation substitution within the structure,... 

The most abundant and important of the aluminosilicate minerals in the earth s surface are the feldspars, which result from the substitution of aluminum for silicon in three-dimensional silicate networks such as quartz. The Al ions must be accompanied by other cations such as sodium, potassium, or calcium to maintain overall charge neutrality. Albite is a feldspar with the chemical formula NaAlSi308. 

Walther, J.V., Relation between rates of aluminosilicate mineral dissolution, pH, temperature and surface charge, Azw. J. Sci., 296, 693,1996. 

Perrott, K.W., Surface charge characteristics of amorphous aluminosilicates. Clays Clay Miner, 25,417, 1977. 

Buffering by aluminosilicate mineral decomposition. In moderately to strongly acid soils (pH < 5.5), variable-charge mineral surfaces as well as layer silicate edges accept protons to generate anion exchange sites, for example at A1 sites ... 

The major components of most soils are silicate and aluminosilicate minerals. Under natural conditions, these components have negative charges. Anionic pollutants are less attracted to negatively charged surfaces. The high solubility of anionic pollutants and low adsorptive capacity of soils can result in the persistence of high concentration of anionic pollutants, including d , Cr(VI), NOi, Se(VI), Se(IV), As(V), As(III),Tc(VII), Mo(VI), POi, F-, ClOj, and SOj (Blowes et aL, 2000). 

Taking this one step further, perhaps even an inorganic gene may have been provided by clay mineral sources. Earliest clay samples are of a mineral called montmorillonite that consists of sheets of aluminosilicates in which Fe2+, Fe3+ and Mg2+ are substituted for some of the Al3+, and Al3+ is substituted for Si4+. The oxygen content of the layers does not change and the alternative valencies allow the production of positive and negatively charged layers. Dramatically, Paecht-Horowitz and co-workers showed that the amino acid adenylate could be polymerised with up to 50 units on the montmorillonite surface in aqueous solution. Similar condensation reactions for carbohydrates on hydrotalcite surfaces have... 

The formation of edge charges of minerals have been discussed in Chapter 1, Section 1.3.21. It has been shown that aluminosilicates (including montmorillonite) have two types of surface (aluminol and silanol) sites, and their protolytic processes have been expressed by Chapter 1, Equations 1.54-1.56. For simplicity, the reaction equations are repeated here. For aluminol sites,... 

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