Kinetics of Ion-Pair Formation On the Surfaces of Variable Charged Minerals Coupled with Transport Processes Using the Frequency Domain Method.

The fate of nitrate in environment is affected by the kinetics of ion-pair forming on the surfaces of variable charge minerals coupled with transport process.  The objectives of this study were (1) to generate the coupled processes in column experiments packed with gibbsite, goethite and hematite, and (2) to estimate the reaction rates using the frequency domain method developed by Shuai and Yost (2007).   The input signals to the columns were designed as sinusoidal changes of nitrate at constant pH.  The input and output signals of nitrate and/or proton concentrations were monitored by UV/Vis and pH detectors.  A mathematical model was derived to describe the ion-pair forming at the variable charged surface and the coupled transport process described by Convection-Dispersion Equation (CDE). Results showed that the output signals were dominated by the desired frequency and thus the coupled processes in the columns were linear.  The estimated rates ion-pair forming at the surfaces of minerals were at the scale of min^-1.