2.4. Measurements of zeta-potential
The zeta-potentials were measured using a Zetasizer Nano Zs90
instrument. The suspensions with 0.01% concentration (mass fraction)
of the minerals were dispersed in a beaker for 1 h at room
temperature (25 C) in the presence of different concentration of
reagents. The pH sweep direction was 1.5–12. Three measurements
of zeta potential were run, and their averages were taken
as the final result.