Surface potential of hematite particles in high concentration electrolytes: Electroacoustic measurements and suspension stability

The behavior of hematite particles and their surface charge in the presence of various electrolytes ranging from 10−3 to 10 mol L−1 has been investigated. Zeta potential measurements were performed using an electroacoustic device, and results showed that the nature of the alkaline cation in solution (Li+, Na+, K+, Cs+ or tetramethylammonium) leads to the presence or absence of a charge neutralization for higher concentrations. This behavior follows the indirect Hofmeister series (lithium has the strongest effect) and may be attributed to the hard or soft nature of the cation. This effect was also shown by experiments with various anions (OH−, Cl−, Br−, NO3−, ClO4−). Calculations using the classical DLVO theory predicted stability in agreement with the observed macroscopic behavior of the hematite suspensions, and most notably the rate and degree of sedimentation.