| The fate and transport two different kinds of nanoparticles; quantum dots and uranyl-silicates; has been examined and the role of some chemical and hydrodynamic conditions has been investigated. The findings revealed that quantum dot nanoparticles are mobile in the subsurface environment at typical groundwater pH and ionic strength. The impacts of the ionic strength and pH on the quantum dot particle mobility in porous media are related to two removal mechanisms, deposition and pore straining. In terms of physical factors, Brownian diffusion is the dominant mechanism of influence for the deposition in the saturated zone. Also, low pore flow velocity in a heterogeneous porous media results in higher removal of quantum dots compared to the one with a homogeneous sand grain size. Under unsaturated conditions, gas-water interface has been found as the main mechanism in terms of the mobility of quantum dots in comparison with the removal mechanisms of pore straining and deposition at solid-water interfaces. The ultimate effect of a non-ionic surfactant on the transport is related to both the surface tension and the steric repulsion between the quantum dot nanoparticles and different interfaces. Light transmission and fluorescence method revealed that the hue component of the emitted light was impacted by the air saturation besides the concentration level. Consequently, hue/intensity ratios can be used to determine the quantum dot nanoparticle concentration, incorporating the fluorescence of the quantum dots and the air saturation. The dissolved phase uranium is retarded at pH 6, and suspected to form a silicate containing precipitate at pH 11. Silica dissolution at high pH has been found to be higher than expected based on estimates from quartz dissolution but lower than the concentration that would be in equilibrium with quartz. On the contrary to our hypothesis, the uranyl silicate nanoparticles do not enhance the uranium transport. |
