title: Colloid-facilitated transport of lead in natural discrete fractures.
abstract: Colloid-facilitated transport of lead (Pb) was explored in a natural chalk fracture with an average equivalent hydraulic aperture of 139 microm. Tracer solution was prepared by adding montmorillonite (100 mg L(-1)) and/or humic acid (HA) (10 mg L(-1)) to modified artificial rainwater containing dissolved Pb (21.4 mg Pb L(-1)), naturally precipitated PbCO(3) particles (16.4 mg Pb L(-1)) and LiBr (39.0 mg L(-1)). We found that Pb is only mobile when associated with colloids. PbCO(3) particles were not mobile in the fracture. The addition of HA to the montmorillonite suspension increased the suspension's mobility and therefore promoted the colloid-facilitated transport of Pb. The increases in pH and sodium absorption ratio induced by the chalk-tracer solution interactions appeared to increase the dispersion and mobilization of colloids entering the fracture. The dominant colloid-facilitated transport of Pb reported in this study has significant implications for risk assessment of Pb mobility in fractured rocks.
authors.affiliation: Department of Environmental Hydrology & Microbiology, Zuckerberg Institute for Water Research, J. Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, P.O. Box 192, Midreshet Ben-Gurion 84990, Israel.
authors.forename: Xiang-Yu
authors.initials: XY
authors.lastname: Tang
authors.forename: Noam
authors.initials: N
authors.lastname: Weisbrod
mesh_terms: D000327:Adsorption; D003102:Colloids / Q000737:chemistry*; D006812:Humic Substances; D057446:Hydrodynamics; D007854:Lead / Q000032:analysis / Q000737:chemistry*; D008956:Models, Chemical; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000737:chemistry
chemical_list: D003102:Colloids; D006812:Humic Substances; D012989:Soil Pollutants; D014874:Water Pollutants, Chemical; D007854:Lead