Laboratory experiments and mathematical modeling were used to explore the dynamics of kaolinite and Pb in water-saturated porous media. Batch adsorption experiments were used to obtain the adsorption isotherms of Pb onto kaolinite and quartz sand. Both kaolinite and sand adsorbed Pb from water, but the adsorption capacity of kaolinite was about 30 times higher than that of sand. Saturated sand columns were used to examine the transport behaviors of Pb and kaolinite. The presence of kaolinite in the saturated porous media enhanced the mobility of Pb. The presence of Pb on kaolinite and grain surfaces, however, reduced the transport of kaolinite. Additionally, an experiment in which clean kaolinite was passed through sand contaminated with Pb indicated that mobile kaolinite could scavenge the absorbed Pb from the sand surface to facilitate Pb transport. Simulations from the Langmuir model and an advective-dispersive transport model matched well with the experimental data collected from the batch adsorption and column breakthrough studies.

The transport of Pb(II) or Cd(II) in subsurface has been studied in the literature; however; their co-transport in porous media in presence of colloids has not been clearly understood. In this work, a series of column experiments were conducted to study Pb(II) and Cd(II) co-transport in saturated porous media under various experimental conditions with different combination of colloidal solution (montmorillonite colloid, manual loessial soil colloid and humic acid), flow rate (0.1, 0.5 and 1.0 ml min⁻¹) and sand grain size (0.4–0.8mm and 0.8–2.0mm). The results showed that increase of flow rate and grain size promoted the mobility of Pb(II) and Cd(II), furthermore, the presences of mobile colloids also enhanced the mobility of the two heavy metals, meanwhile, Cd(II) showed higher mobility than Pb(II) in the columns. Findings from this work enhanced current understanding of the competitive transport and colloid-facilitated transport of heavy metals in saturated porous media.