| Abstract: |
Boron adsorption behavior on the clay minerals kaolinite, montmorillonite, and illite was investigated. Adsorption increased at low pH, exhibited a peak in the pH range 8 to 10, and decreased at high pH. It was assumed that B adsorbs by means of a ligand exchange mechanism with aluminol groups at the edges of the clay particles. The constant capacitance model was able to describe B adsorption on kaolinites over the entire pH range studied (3–12), using only one adjustable parameter: the boron surface complexation constant. The model was able to fit B adsorption on montmorillonites and illites using three adjustable parameters; however, the chemical significance of some of the surface complexation constants is uncertain. Silicon release to solution increased in the order: kaolinite ∦ illite < montmorillonite and exhibited a minimum in the pH range 8 to 9. Boron adsorption on kaolinites was reduced only slightly in the presence of added silicate despite considerable silicate adsorption. Boron adsorption on montmorillonites was unaffected by the presence of added silicate. It is suggested that B and silicate adsorb on specific sites and that little anion competition occurs. |
