A benchmark for multi-rate surface complexation and 1D dual-domain multi-component reactive transport of U(VI)
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- Greskowiak, J., Gwo, J., Jacques, D. et al. Comput Geosci (2015) 19: 585. doi:10.1007/s10596-014-9457-4
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Nonequilibrium surface complexation reactions have been found to substantially affect U(VI) transport in natural porous media both in laboratory and field scale experiments. Nonequilibrium sorption behavior occurs on multiple time scales and is a result of diffusion-limited transport in immobile intra-grain and intra-aggregate pore water. Experimental data on U(VI) transport was successfully described with a recently developed reactive transport model that accounted for the nonequilibrium adsorption processes through the formulation of a multi-rate surface complexation model treating surface complexation as kinetic reactions. In the present work, a benchmark problem set has been developed for testing existing or newly developed reactive transport codes on their capability to simulate multi-rate surface complexation and dual-domain multi-component reactive transport of U(VI). The benchmark problem consists of three individual component problems on the basis of previous studies investigating the desorption of U(VI) from radionuclide-contaminated sediment from the Hanford 300A site, Washington, USA. Starting with a single-domain model considering constant hydrochemical conditions (component problem 1), the complexity of the model was stepwise increased. In the component problem 2 dual-domain first-order mass transfer was added. The principal problem also included dual-domain mass-transfer, but was further extended for changing hydrochemical conditions in the column’s inflow water, which resulted in drastic changes in the U(VI) desorption pattern due to surface complexation reactions. For the three individual component problems, the corresponding simulation results agree very well among four well-known and thoroughly tested independent reactive transport codes, indicating that the proposed benchmark problem set is a suitable test case.