The rates of many heterogeneous reactions are dependent upon the mineral-water interfacial area. Examples include release of nutrients from primary minerals, rate of growth of authigenic minerals, adsorption and desorption of metal and organic contaminants on soil and sediment grains, neutralization of acid deposition by weathering reactions, oxidation and reduction of mmetal-containing phases and solutes, clumping of colloids or bacteria by electrostatic attraction, and photocatalytic degradation of organic pollutants at metal oxide surfaces (Davis et al., 1993; White and Brantley, 1995). Several workers have also shown that the surface area is a key parameter in predicting weathering rates using geochemical models (e.g. PROFILE) and soil chemistry under the influence of acid rain (Jönsson et al., 1995; Hodson et al., 1996, 1997a). Along with the permeability, the surface area is one of the most difficult physical parameters to quantify in extrapolating from the laboratory to the soil plot to the watershed (White and Peterson, 1990). Most models of solute transport in aquifers and in soils simply ignore the mineral-water surface area term by combining it with the kinetic rate constant into one fitting parameter, despite the fact that the specific surface area may vary over several orders of magnitude — 102–106 cm2/g as functions of grain size, mineralogy, oxide coating, weathering history, or biological effects, or as a combination of these factors. Despite the importance of the mineral surface area in many areas of geochemistry, little systematic effort has been expended to understand or predict this term for primary silicates (more work has been completed on the surface area of clays and simple oxides).
Weitere Kapitel dieses Buchs durch Wischen aufrufen
- Surface Area of Primary Silicate Minerals
S. L. Brantley
A. F. White
M. E. Hodson
- Springer Netherlands
- Chapter 14