Particle adhesion and removal in model systems. Part 1.—Monodispersed chromium hydroxide on glass

The interactions of monodispersed chromium(III) hydroxide particles of 0.28 µm diameter with glass were studied using the packed column technique. The particles were first adsorbed by passing the the sol through a bed containing glass beads at pH ∼ 3, at which conditions the particles and the beads are of opposite charge. Desorption was then studied as a function of pH by rinsing the column with solutions containing different electrolytes in varying concentrations. Optimum removal at low ionic strength occurred at pH 11.5, which is well above the point of zero charge of the colloidal chromium hydroxide particles. When the particles were adsorbed at pH 4 and ∼ 6, respectively, the removal was substantially less under otherwise identical conditions. The addition of NaNO3, NaF, Ca(NO3)2 and Co(dipy)3(ClO4)3 at the pH of optimum removal (11.5) of the rinse solution caused a decrease in desorption and, depending on ionic strength, eliminated altogether particle separation. The greater the counterion charge, the less salt was necessary to suppress desorption. These results are best explained in terms of double layer interactions between the particles and the substrate and no indication of chemical bonding could be detected.