Leakage of radioactive wastewater temporally stored in underground tanks can lead to the escape of heavy metals into the subsurface. A practical method to get rid of such risk is to provide the wastewater basic pH. As alkaline conditions favor the adsorption of heavy metals on common mineral surfaces, the adsorption retards the transport of heavy metals significantly. However, observations show that heavy metals within an alkaline solution can travel much faster than expected when the leakage occurs into an aquifer with acidic pH. It occurs because mixing induced by longitudinal and transverse hydrodynamic dispersion creates a low-pH zone within the reactive porous medium, which is unfavorable to adsorption of heavy metals, form a fast contaminant pulse that travels at the average groundwater velocity. Here, we show numerical simulations and experiments of fast pH-dependent of strontium (Sr2+) transport induced by both longitudinal and transverse dispersion. We performed experiments using a bead-pack containing silica (SiO2) and activated alumina (Al2O3), selected on the basis of its significant Sr2+ adsorption above pH 7 (Figure 1). Currently, we are performing experiments to verify our numerical simulations shown in Figure 2, which are performed under the conditions favoring fast pH-dependent transport, i.e., initial acidic pH in the system, followed by the injection in the lower half of the domain of a basic solution containing Sr2+.

Fast pH-dependent transport of heavy metals and radionuclides due to longitudinal and transverse dispersion

254th National Meeting (2017)

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