Packed bed filtration of laponite sols

Abstract

Packed bed filtration experiments have been conducted to elucidate the transport behavior of laponite, a synthetic clay mineral with a platelet diameter ∼30 nm, which is representative of negatively charged natural colloids. When the filtration column was packed with quartz, glass beads, or sediments of glaciofluvial origin various detection techniques showed that laponite passes through these materials without sorption. γ-Alumina was found to have a small, ∼0.1 mg laponite per g filter, sorption capacity which increased with the number of (AlOH 2 +) surface groups. Electrolytes with ionic strengths < 0.002 M, corresponding to soft natural waters, did not influence these results. The sorption of laponite is reversible when new particles are introduced to the system. This fact was demonstrated using laponites labelled with different dyes at various flow rates and influent sol concentrations. Due to the highly porous nature of alumina, laponite particles are separated in the column from ionic contaminants by size exclusion. Ionic and molecular matrix diffusion in alumina beds were ascertained in breakthrough experiments using KCl and O 2 as flow tracers, whereas no such effect was observed for the other non-porous filter materials.