This study contributes to the mounting evidence showing that dissolved silicates (Si), common to natural surface waters, can profoundly affect contaminant transport in soil, sediments and groundwater. Here, we show that Si surface coverage and speciation can be affected by hydrogeochemical conditions. We find that dynamic flow-through conditions (2.98 cm/h and 14.92 cm/h) sustain monomeric Si species with loadings of up to ~0.8 Si/nm2 but that oligomeric species can form at the goethite surfaces under static (no-flow conditions). However, water flow variability or discontinuous flow led to higher Si loadings. While these monomeric species occupy no more than ~22 % of the reactive OH groups on goethite, they can effectively suppress NA binding, and therefore enhance NA mobility in dynamic conditions. Combining mass transfer kinetics and surface complexation modeling, we present a new transport model to account for the stepwise polymerization of Si on goethite and NA transport. This work reveals most overlooked aspect of silicate binding under water flow-through conditions, which can play a determining role on the surface speciation and transport of antibiotics in the environment. Our findings may have broader implications and could be extended to other organic compounds containing carboxylic and amine functional groups.
L. Zhou, W. Cheng, R. Marsac, JF. Boily, K. Hanna
Silicate surface coverage controls quinolone transport in saturated porous media
Journal of Colloid and Interface Science, 607, 2022, 347-356. https://doi.org/10.1016/j.jcis.2021.08.142
Khalil Hanna, Univ Rennes, ENSCR, ISCR-CNRS UMR 6226, F-35000 RennesFrance
khalil [dot] hannaensc-rennes [dot] fr
IUF (2017-2022); PICS CNRS (2018-2020); Swedish Research Council (2020-04853); ANR C-FACTOR (ANR-18-CE01-0008)
Published October 12, 2021