T. Hiemstra et Wh. Vanriemsdijk, A SURFACE STRUCTURAL APPROACH TO ION ADSORPTION - THE CHARGE-DISTRIBUTION (CD) MODEL, Journal of colloid and interface science, 179(2), 1996, pp. 488-508
An ion adsorption model for metal hydroxides has been developed which
deals with the observation that in the case of inner sphere complex fo
rmation only part of the surface complex is incorporated into the surf
ace by a ligand exchange reaction while the other part is located in t
he Stern layer. The charge distribution (CD) concept of Pauling, used
previously in the multi site complexation (MUSIC) model approach, is e
xtended to account for adsorbed surface complexes. In the new model, s
urface complexes are not treated as point charges, but are considered
as having a spatial distribution of charge in the interfacial region,
The new CD model can describe within a single conceptual framework all
important experimental adsorption phenomena, taking into account the
chemical composition of the crystal surface. The CD model has been app
lied to one of the most difficult and challenging ion adsorption pheno
mena, i.e,, PO4 adsorption on goethite, and successfully describes sim
ultaneously the basic charging behavior of goethite, the concentration
, pH, and salt dependency of adsorption, the shifts in the zeta potent
ials and isoelectric point (IEP), and the OH/P exchange ratio, This is
all achieved within the constraint that the experimental surface spec
iation found from in situ IR spectroscopy is also described satisfacto
rily. (C) 1996 Academic Press, Inc.