Transport of iron oxide colloids in packed quartz sand media: Monolayer and multilayer deposition

The transport and deposition dynamics of hematite (alpha -Fe2O3) colloids i n packed quartz sand media are investigated. Column transport experiments w ere carried out at various solution ionic strengths, colloid concentrations , and flow velocities. A colloid transport model was proposed that includes the dynamics of blocking as well as multilayer deposition that takes place at high ionic strengths where particle-particle interactions are favorable . Blocking dynamics in the model are described by either Langmuirian adsorp tion (LA) or random sequential adsorption (RSA). Two important model parame ters-the particle-matrix collision efficiency and the ionic strength depend ent blocking (excluded area) parameter-are estimated from the colloid break through curves using a nonlinear optimization procedure. The collision (att achment) efficiency for particle-particle interactions, on the other hand, was determined independently from colloid aggregation rate measurements. At very low ionic strength, only monolayer deposition is observed and the RSA model gives a better description of the experimental data than the LA mode l. At higher ionic strengths, multilayer deposition becomes significant and both models yield comparable results. Calculated maximum surface coverages at low ionic strengths were in good agreement with experimentally observed values obtained by scanning electron microscopy. (C) 2000 Academic Press.