Wei Zhang - Transport and retention of colloidal particles in partially saturated porous media: Effect of ionic strength

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      Publication Details (including relevant citation   information): Zevi, Yuniati, Dathe, Annette, Gao, Bin,   Zhang, Wei, Richards, Brian K., Steenhuis, Tammo S., Water   Resour. Res., 2009, 45 (12), pp   W12403

      Abstract: We directly observed pore-scale   attachment of fluorescent synthetic polystyrene colloids (1.0 μm   diameter) in a partially saturated sand pack (pore space   saturation ranging from 0.7 to 0.9) at four solution ionic   strengths (0, 1, 100, 200 mmol NaCl). Sequential confocal laser   microscope images were analyzed to quantify colloid retention,   particularly at air-water meniscus-solid (AWmS) interfaces. We   concurrently measured effluent colloid concentrations to   determine overall matrix retention. Ionic strength had no effect   on meniscus contact angles (26.7 ± 3.7 degrees) or surface   tension (63–67 mN/m), both important components of the capillary   forces thought to play the primary role in retention at the AWmS   interfaces. AWmS interfaces attachment was greatest at 1 mmol,   with the 0 mmol ionic strength reducing attachment by half.   Increasing ionic strength to 100 and 200 mmol markedly decreased   colloid retention at the AWmS interfaces due to observed   increased competing attachment at grain surfaces (solid/water   interface) that reduced the number of colloids available for AWmS   interface attachment.

      Address (URL): http://dx.doi.org/10.1029/2008WR007322