Colloidal stability of silica and graphite in aqueous suspensions

In order to investigate the effect of surface wettability on colloidal stability, aggregation/dispersion behaviors of fine silica and graphite in aqueous suspensions have been investigated. It was found that hydrophobic graphite particles showed a high aggregation degree in low pH suspensions, while it showed very low aggregation degree in high pH suspensions due to the strong electrostatic repulsions between graphite particles. On the other hand, silica particles showed stable dispersion behaviors even under strong Van der Waals attraction in low pH suspensions, which could not be explained by DLVO theory. Solvation factor on hydrophilic silica particles was applied to prove the strong hydration of silica, and it is the hydration repulsion forces among silica particles that determined the stable dispersion of silica particles in a wide pH range. Therefore, it was concluded that hydration layers formed on hydrophilic mineral surfaces played an important role in colloidal stability.