Electrosurface Properties of Schungite III Particles in Aqueous Electrolyte Solutions

Abstract

The kinetics of electrolyte extraction into water and the electrosurface properties (adsorption of potential-determining ions H+ and OH− and ζ potential) of five fractions of schungite III (particle sizes of < 5, 50–100, 160–400, 400–1000, and 1600–2500 µm) are studied in aqueous NaCl, CaCl2, and AlCl3 solutions at different pH values. It is shown that, in water and NaCl and CaCl2 solutions, the point of zero charge (PZC) of the particles with sizes of 50–100 and 160–400 µm is observed at pH 4.0 and is independent of the electrolyte concentration. The isoelectric point (IEP) for small (<5 µm) schungite III particles is observed at pH 2.8. The IEP position is independent of CaCl2 concentration, but it shifts to pH 2.4 when NaCl concentration increases to 0.1 M. The disclosed differences in the PZC and IEP values may be caused by different compositions of particles of different fractions. In a 10−5 M AlCl3 solution, schungite particles demonstrate three IEPs (pH 3.0, 4.5, and 7.4) due to different degrees of AlCl3 hydrolysis at different pH values.