Transport and capture of submicron particles in a natural sand: short column experiments and a linear model

Abstract

The transport and capture of latex particles, considered as model colloids, in a column packed with a well-defined natural sand was studied. The shape of the breakthrough curves is analysed in terms of the effect of different operating conditions: flow rate, ionic strength, colloid particle size, and particle concentration. The results confirm the strong influence of flow rate and ionic strength on the retention of particles of a given diameter (0.21 μm). At a very low velocity and for an ionic strength superior to 10−3 M, the breakthrough curves of the particles have a characteristic shape with a time delay followed by a long tail. The retention as a function of colloid particle size is also pointed out. This leads to the establishment of a linear two-site adsorption model to simulate the observed phenomena. Two transfer times were calculated to characterise the capture phenomena associated with each site. One distinguishes fast trapping sites for which the transfer time is independent of flow rate, and the other, relatively slow sites for which the transfer time is inversely proportional to the flow. These sites are tentatively identified by observation of the deposit structure in the packed bed after an elution experiment.