PULSE-INJECTION CHROMATOGRAPHIC DETERMINATION OF THE DEPOSITION AND RELEASE RATE CONSTANTS OF COLLOIDAL PARTICLES IN POROUS-MEDIA

The packed column technique with injection of very short sample pulses was demonstrated in this study to be well suited for studying the mas s transfer coefficients of colloidal particles flowing through porous media. It has been used here to examine the deposition and release kin etics of model colloidal latex spheres with sulfate surface functional groups in packed soda-lime glass beads. Apart from the commonly obser ved process of particle removal by the beads, strong evidence of spont aneous detachment of the deposited particles from the bead surfaces wa s found without even changing solution chemistry or flow conditions. I n particular, the rate constants of the two processes were estimated f rom the measured particle breakthrough curves on the basis of the conv ection-dispersion equation coupled with a two-site first-order kinetic s model; the reversible site was used to account for the observed part icle release, while the irreversible site was assumed to be responsibl e for the apparent loss of particles in the column. Solution ionic str ength was found to have a significant effect on the deposition process . Upon increasing ionic strength, the particle deposition rate constan t showed transition from slow to fast regime, and this can be explaine d qualitatively using the DLVO theory. The particle release rate const ant was, however, seen to be almost independent of ionic strength. One of the main advantages of this pulse-injection technique over the tra ditionally used continuous step input method is that many repeat exper iments can be performed on the same column without causing significant blocking or filter ripening effects owing to the very small amount of particles injected into the column.