Anion Exclusion On Transport In Columns of Variable Charged Minerals Using the Frequency Domain Approach.

Exclusion of nitrate anions from negatively charged surfaces was examined in different variable charged minerals when solution pH was higher than their points of zero charge.  The four minerals were gibbsite, goethite, hematite and kaolinite.  The column experiments were used to measure the transport of anion nitrate through the columns packed with the minerals.  The influent was designed as concentrations of nitrate varying as a sinusoidal function of time.  Based on the amplitude reduction and phase shift of the sines of nitrate concentrations, the solvent velocites were estimated using the frequency domain approach.  The velocities of the transport of nitrate in the negatively charged columns were 8%-16% higher than those of inert tracer in the columns.  The change of velocities of transport of nitrate was affected by the surface charge density.  This study provided a novel and accurate way to the study of anion exclusion on transport.