Investigation of the permeability of humic molecules using zeta potential measurements

Zeta potential measurements have been performed on colloidal humate in the presence of differing concentrations of sodium ions at pH=6.0. A series of calculations has been performed in which the radius of the humic colloid was varied until the predicted surface potential was equal to the experimentally determined zeta potential. The results of the calculations showed that as the ionic strength increases, the apparent radius of the colloid decreases. Similar calculations in which a model colloid was treated as a rigid sphere, i.e., the radius of the colloid was kept constant, failed to simulate the observed zeta potential measurements.