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The adsorption of the U-232 radionuclide by biochar fibers in the sub-picomolar concentration range has been investigated in laboratory aqueous solutions and seawater samples. The adsorption efficiency (Kd values and % relative removal) of untreated and oxidized biochar samples towards U-232 has been investigated as a function of pH, adsorbent mass, ionic strength and temperature by means of batch-type experiments. According to the experimental data, the solution pH determines to a large degree the adsorption efficiency, and adsorbent mass and surface oxidation lead to significantly higher Kd values. The ionic strength and temperature effect indicate that the adsorption is based on the formation of inner-sphere complexes, and is an endothermic and entropy-driven process (ΔH° and ΔS° > 0), respectively. Regarding the sorption kinetics, the diffusion of U-232 from the solution to the biochar surface seems to be the rate-determining step. The application of biochar-based adsorbents to treat radioactively (U-232) contaminated waters reveals that these materials are very effective adsorbents, even in the sub-picomolar concentration range.

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Abstract. We use finite elements in space and a fully implicit scheme in time in

The steady, pressure-driven flow of a Herschel-Bulkley fluid in a channel is considered assuming that slip occurs on one wall only due to slip heterogeneities. Hence, the velocity profile is allowed to be asymmetric. The fully-developed solutions are derived and the different flow regimes are identified. The development of the flow is investigated numerically using the Papanastasiou regularization for the constitutive equation, a power-law slip equation, and finite element simulations. The combined effects of slip and the Bingham number are discussed. .