An experimental study of cotransport of heavy metals with kaolinite colloids

Highlights: • Low flow rate facilitated the transport of metals under the presence of kaolinite. • High flow rate facilitated the transport of metals under the presence of kaolinite. • Transport behavior of multi-metals was consistent with the competitive sorption. -- Abstract: Cotransport of heavy metals, Pb, Cu and Zn (multi-metal system), and transport of those metals (single-metal system) were investigated by performing laboratory soil column experiment under the presence of kaolinite colloids. Preequilibrated kaolinite colloids with heavy metal solution was injected to the column until 10 pore volumes under two different flow rates and three different concentration of kaolinite colloids. Heavy metal concentration in effluent showed that the mobility of Pb was facilitated as kaolinite colloids concentration (C_c0) increases under high flow rate while the mobility of Pb and Cu were retarded as C_c0 increases under low flow rate. In addition, optimized first order rate coefficient related to sand-heavy metal interaction and estimated bed efficiency of experimental breakthrough curves demonstrated that the presence of mobile kaolinite colloids delayed the adsorption of heavy metals to the sand and facilitated the transport. Colloid associated contaminant transport model used in this study was found to be well fitted to the experimental breakthrough curves with the parameters associated with observed heavy metal transport without kaolinite colloids and adsorption/desorption between the heavy metals and the mobile kaolinite colloids.