Chemistry Reference
In-Depth Information
Dove and Elston,
898
this interfacial layer can be described by a triple layer surface com-
plexation model (TLM) as shown in Fig. 4.31. The interface consists of three electro-
statically charged regions, each with an associated electric potential and surface charge;
these are termed the
o,
and
d
planes. Hydrogen ions are permitted to coordinate with
the unsaturated sites of the interface at the innermost
o
layer. Sodium is positioned at
the layer or the
d
layer. The surface silicon-oxygen complex may have a different
chemical character depending on the adsorbed species. In a sodium chloride solution
the surface complexes can be represented as
and The concentration of each species depends on pH and salt concentration, and
the sum of the fractions of these surface species equals 1:
Calculation of the distribution of the species as a function of pH is shown in Fig. 4.32.
The rate of dissolution of silica is then determined by the number of reactive species.
