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The surface and bulk properties of Al(III)/SiO2 and Fe(III)/SiO2 suspensions were determined as a function of prepared pH. The TEM results showed that Al(III) tends to form Al(OH)3 coatings on the surface of SiO2 while Fe(III) tends to form the discrete Fe(OH)2 phase in bulk solution with system pH increase. The charge reversals (CR) observed in the Al(III)/SiO2 system represent, in order of increasing pH, the point-of-zero charge (PZC) on the SiO2 substrate (CR1), the pH of surface nucleation of Al(OH)3 (CR2), and, at high pH, the PZC of the Al(OH)3 coating (CR3). The observed electrophoresis mobility of Fe(III)/SiO2 is the overall result contributed by negatively charged SiO2 and positively charged Fe(OH)3.

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