Fluorescence macrophotography as a tool to visualise and quantify spatial distribution of deposited colloid tracers in porous media

Abstract

Fluorescence macrophotography was used for the evaluation of colloidal transport and deposition in silica sand and sandy soil packed columns. With the fluorescence macrophotography technique, the number of microspheres and its macroscopic distribution on a column cross section is derived from an image of the fluorescence intensity of the surface. Column experiments with varying flow velocity and input concentration of microspheres lead to conditions with high deposition or high breakthrough of the colloids. In comparison with established microscopic fluorescent techniques the presented novel methodology was found to deliver similar estimates of particle concentrations and similar detection limits. Moreover, unlike with fluorescent microscopic method, the fluorescent macrophotography technique provides valuable information about the spatial distribution of microspheres. The Sulforhodamine-B, a frequently applied organic dye to label the microspheres, limits the applicability of fluorescence macrophotography technique due to self-quenching effects which occur at high particle concentration. At high proximity of the fluorescent microspheres self-quenching effects led to underestimation of microsphere concentration as well as incorrect depth profiles. Very recent developed microspheres, labelled with rare-earth-ion-chelate-complexes overcome this limitation.