title: Influence of mineral colloids and humic substances on uranium(VI) transport in water-saturated geologic porous media.
abstract: Mineral colloids and humic substances often co-exist in subsurface environment and substantially influence uranium (U) transport. However, the combined effects of mineral colloids and humic substances on U transport are not clear. This study is aimed at quantifying U transport and elucidating geochemical processes that control U transport when both mineral colloids and humic acid (HA) are present. U-spiked solutions/suspensions were injected into water-saturated sand columns, and U and colloid concentrations in column effluent were monitored. We found that HA promoted U transport via (i) formation of aqueous U-HA complexes, and (ii) competition against aqueous U for surface sites on transport media. Illite colloids had no influence on U transport at pH5 in the absence of HA due to low mobility of the colloids. At pH9, U desorbed from mobile illite and the presence of illite decreased U transport. At pH5, high U transport occurred when both illite colloids and HA were present, which was attributed to enhanced U adsorption to illite colloids via formation of ternary illite-HA-U surface complexes, and enhanced illite transport due to HA attachment to illite and transport media. This study demonstrates that the combined effects of mineral colloids and HA on contaminant transport is different from simple addition of the individual effect.
authors.affiliation: Environmental Science Program, Faculty of Science, Memorial University, St. John's, Newfoundland and Labrador A1B 3X7, Canada.
authors.forename: Qing
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Department of Earth Sciences, Memorial University, St. John's, Newfoundland and Labrador A1B 3X5, Canada. Electronic address: tcheng@mun.ca.
authors.forename: Tao
authors.initials: T
authors.lastname: Cheng
authors.affiliation: Department of Earth Sciences, Memorial University, St. John's, Newfoundland and Labrador A1B 3X5, Canada.
authors.forename: Yang
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000327:Adsorption; D003102:Colloids / Q000737:chemistry*; D060587:Groundwater / Q000032:analysis*; D006812:Humic Substances / Q000032:analysis*; D008903:Minerals / Q000737:chemistry*; D016062:Porosity; D014501:Uranium / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D003102:Colloids; D006812:Humic Substances; D008903:Minerals; D014874:Water Pollutants, Chemical; C099089:illite; D014501:Uranium
keywords: Adsorption; Column experiments; Humic acid; Mineral colloids; Uranium transport