Co-transport of U(VI), humic acid and colloidal gibbsite in water-saturated porous media.
The release of uranyl from uranium tailing sites is a widely concerned environmental issue, with limited investigations on the effect of coexistence of various colloids. Gibbsite colloids extensively exist, together with ubiquitous humic substances, in uranium polluted waters at tailing sites, due to high concentration of dissolved Al in acid mine drainage. In this context, we investigated the co-transport of U(VI), gibbsite colloids and humic acid (HA) as a function of pH and ionic strength at a U(VI) concentration (5.0 × 10-5 M) relevant within mine tailings and related waste. It was found that, owing to electrostatic attraction, gibbsite colloids and HA associated with each other and transported simultaneously regardless of U(VI) presence. Besides the impact of pH and ionic strength, whether gibbsite colloids facilitated U(VI) transport depended on HA concentration. Gibbsite colloids impeded U(VI) transport at relatively low HA concentration (≤5 mg L-1), because associated colloids loaded with U(VI) were positively charged which favored colloid retention on negatively charged quartz sand in the column. U(VI) together with gibbsite colloids and low concentration HA was completely blocked at natural pH and/or high ionic strength. At relatively high HA concentration (20 mg L-1), however, the associated colloids showed negative zeta potential which facilitated U(VI) transport because of repulsion between negatively charged colloids and quartz sand. Meanwhile, high concentration of HA dramatically accelerated the transport of gibbsite colloids. These results implied that gibbsite colloids might imped U(VI) migration at uranium tailing sites unless the aquifers are enriched with abundant humic substances.
['Yang|Junwei|J|', 'Ge|Mengtuan|M|', 'Jin|Qiang|Q|', 'Chen|Zongyuan|Z|', 'Guo|Zhijun|Z|']
D000327:Adsorption D003102:Colloids D060587:Groundwater D006812:Humic Substances D008956:Models, Chemical D009994:Osmolar Concentration D016062:Porosity D011791:Quartz D012822:Silicon Dioxide D027981:Symporters D014501:Uranium D014867:Water D014875:Water Pollutants, Radioactive
U(VI) Humic acid Gibbsite colloids Transport