ABSTRACT
This chapter briefly discusses the state of the art for mineral and organic colloidal particles, followed by a general discussion on ion binding to homogeneous and to heterogeneous colloids. It showS that the effect of the concentration of the indifferent salt on the proton adsorption behavior can be used to assess an “appropriate” electrostatic model without a priori knowledge about the chemical heterogeneity. Chemical heterogeneity also leads to an affinity decrease with progressive adsorption since the higher affinity sites are mainly responsible for ion binding at low coverage and the lower affinity sites dominate the binding process at higher coverages. Ion binding to clays and metal (hydr)oxides has been studied intensively. The intrinsic chemical heterogeneity of a natural colloid derives from the presence of different types of reactive groups on the particle. The most simple approximation for a heterogeneous surface is to treat it as (pseudo-)homogeneous.
