Executive Summary

MERIWA project M367 provides new information on particle surfaces in industrial liquors through zeta potential and acoustic measurements. A focus was the effect additives, and process conditions such as pH, temperature and ionic strength would have on the zeta potential. A substantial proportion of the work was in refining the methods used to measure zeta potential in concentrated electrolyte systems, and identifying the strengths and limitations of the Dispersion Technology DT1200 instrument. The DT1200 electroacoustic spectrometer, the first instrument of its type in Australia, was assessed using both model systems and industrial samples.

Industry based subprojects for Alcoa World Alumina, Worsley Alumina, and Tiwest Joint Venture were carried out, building on the earlier core M367 investigations. The subprojects included an examination of the effects of specific additives on the zeta potentials of gibbsite and sodium oxalate surfaces. Aspects of solids crystallisation were also examined. Other subproject investigations examined zeta potential changes in red mud during flocculation, and correlated titanium dioxide zeta potentials with processing stages during pigment production.

Measurements of zeta potentials in high ionic strength solutions were made using the DT1200 instrument, and showed substantial variation depending on the aqueous electrolyte. There was evidence of zeta potential and other differences occurring even when electrolyte concentrations were above 1 M. A higher instrument sensitivity would be required to routinely record zeta potential differences in the most concentrated industrial liquors (for example, over 3 M). The DT1200 in its current form is ideally suited for the measurement of the zeta potential of small particles less than 1 μm in systems with electrolyte levels of less than 1 M. This project showed that measurements outside that range were possible, although currently difficult.

The addition of oleic acid consistently made the zeta potential of gibbsite and sodium oxalate surfaces more negative, in both low and high electrolyte concentrations. Differences in zeta potentials were also observed for other additives, including sodium gluconate on gibbsite surfaces. Surface inactive species such as sodium succinate were found to have no significant effect on the zeta potential of gibbsite and sodium oxalate.

Zeta potential changes were not observed for red mud during flocculation, but differences in sound attenuation were observed. Solids crystallisation in mixed systems caused a shift in the recorded zeta potential for some sponsor samples, and sound attenuation could also be used to monitor crystallisation in relatively high solids slurries.

The DT1200 instrument was particularly capable of measuring the size of submicron particles, but was less effective for particle sizes above 30 μm. Similar zeta results were obtained for dilute electrolytes using the DT1200 and Acoustosizer, but the DT1200 could measure zeta potentials at higher electrolyte concentrations.

from: “Industrial applications using improved measurements of particle surface charge” MERIWA Report 253, E. Karakyriakos and V. Patrick, June 2005. ISBN 192098111X.