Flow-enhanced kinetics of uranyl (UO2) transport into nano-porous silica gel

• Transport kinetics of uranyl into nanopourous silica is diffusion limited.
• Time constant depends on pore size.
• Kinetics is enhanced by two orders of magnitude with fluid flow.
• There is a critical saturation flow velocity.

Uranyl transport into nanoporous silica gel is limited in a static aqueous solution by slow natural diffusion to the open bonding sites. In order to make this process faster, the diffusion dependence was eliminated using pressure driven fluid flow. Uranyl transport and adsorption within nanoporous silica gel was measured using time-dependent fluorescent measurements in an aqueous solution. The transport kinetics was measured under two different conditions: static solution in a standard cuvette and flowing solution through the silica gel. It was determined that the kinetics of uranyl uptake within nanoporous silica gel depends strongly on the liquid flow velocity. Above a certain velocity, the adsorption kinetics increased by at least two orders of magnitude (from about 40 min to 2 s) in comparison to a static solution. In a static solution, the kinetics depends on the porosity of the silica gel, but this dependence was not observed when the liquid flow velocity exceeded a certain value. Flow-enhanced adsorption kinetics has potential applications for fast detection of trace levels of uranyl in water.

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