Surface electrochemical properties of red mud (bauxite residue): Zeta potential and surface charge density

The surface electrochemical properties of red mud (bauxite residue) from different alumina refineries in Australia and China were studied by electrophoresis and measuring surface charge density obtained from acid/base potentiometric titrations. The electrophoretic properties were measured from zeta potentials obtained in the presence of 0.01 and 0.001 M KNO3 over a wide pH range (3.5–10) by titration. The isoelectric point (IEP) values were found to vary from 6.35 to 8.70 for the red mud samples. Further investigation into the surface charge density of one sample (RRM) by acid/base potentiometric titration showed similar results for pHPZC with pHIEP obtained from electrokinetic measurements. The pHIEP determined from zeta potential measurements can be used as a characteristic property of red mud. The minerals contained in red mud contributed to the different values of pHIEP of samples obtained from different refineries. Different relationships of pHIEP with Al/Fe and Al/Si ratios (molar basis) were also found for different red mud samples.

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► Nature of Al minerals varies between Bayer and other process.
► Red mud samples showed the presence of both permanent and variable charge surface.
► Al/Fe, Al/Si (molar basis) influence IEP.
► Chemical composition of red mud can be used to predict IEP of red mud.