The use of zeta potential to investigate the interaction of oleate on hematite

• Zeta potential used to investigate interaction of oleate on hematite.
• From literature, presence of oleate causes a reduction in zeta potential.
• A natural hematite sample with low silica followed this trend.
• Presence of 2.5% silica drove zeta potential characteristics rather than oleate.
• Suggested mechanism involved two-stage adsorption process hematite/silica/oleate.

The aim of this paper was to investigate how the use of zeta potential measurements on the hematite–oleate system as a function of pH could provide additional information on this system. From the literature survey it was found that the presence of oleate causes a reduction in both the zeta potential and isoelectric point of hematite compared to their values in the absence of oleate. There have been a number of suggested mechanisms including the adsorption of soluble oleate solution species and precipitation of oleate salts and/or oleate colloids or micelles, depending on the pH and the concentration of oleate in solution. These phenomena were investigated using two hematite samples containing differing amounts of silica. The results for oleate addition to the hematite sample containing the lower amount of silica followed the anticipated trends indicating lower values of zeta potential and isoelectric point with increasing oleate addition. The situation for the hematite sample containing the higher amount of silica, even though it only contained 2.5% silica, was more complex. Although the increased addition of silica reduced the values of the zeta potential, there appeared to be a major influence of the silica driving the values of the zeta potential below those of the oleate at acid values of pH. It was proposed that this was due to a combination of the presence of silica and oleate, suggesting that the mechanism was the physical adsorption or heterocoagulation of colloidal hematite on fine silica followed by the adsorption of oleate species onto the hematite. An attempt was made to correct the equilibrium oleate concentration to account for the adsorption of oleate onto the surface of the hematite, but this was only significant at the very low addition rate of the oleate.

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