Interaction of monomeric and polymeric species of metal ions with clay surfaces. II. Changes in surface properties of clays after addition of iron(III)

Abstract

The adsorption of poly [Fe(III)-OH] cation by claysurfaces led to flocculation of clay particles possibly by polymer bridging while the addition of iron(III) from hydrolysed ferric nitrate solutions resulted in flocculation and cementation by precipitated iron(III). Electrokinetically clays with adsorbed iron(III) behaved similarly to amorphous ferric hydroxides with positive mobilities below the point of zero charge (PZC). Polycations reversed the charge on the clay particles at maximum adsorption, which probably represents neutralization of charge due to surface hydroxyls. When hydrolysed ferric nitrate solutions were added to kaolinite and illite charge reversal occurred at pH values below 6. Adsorption of iron(III) resulted in a partial reduction of negative charge in clays. The reduction of negative charge in kaolinite and illite was close to the charge due to surface hydroxyls. The net charge estimated at all pH values corresponded with the electrophoretic mobility in all the iron(III) clay complexes except bentonite with adsorbed polycations.