Interparticle action and rheology of kaolinite-amorphous iron hydroxide (ferrihydrite) complexes

The complexes of kaolinite and amorphous iron hydroxides (ferrihydrite) initially prepared at pH 3.0 and 9.5 were brought to equilibrium at different pH values at pH 3–10. Bingham yield stress for the suspensions of the complexes have been examined as a function of pH. The complexes prepared at pH 3.0 and 9.5 both gave higher Bingham yield stress than the kaolinite in higher pH range, and the amorphous iron hydroxides in the complexes prepared at 9.5 were more effective in enhancing yield stress. The results are discussed in terms of the charge characteristics of the amorphous iron hydroxide and its association with the kaolinite surfaces by means of electron microscopy and zeta potential and surface area determinations.