A SCALING MODEL FOR SCALING URANIUM SORPTION/DESORPTION PROPERTIES AND THEIR UNCERTAINTIES IN CONTAMINATED SEDIMENTS

A statistical approach was developed based on sediment grain size distribution to scale U(VI) sorption/desorption properties in sediments. The approach assumes that the mean and variance of U(VI) sorption/desorption properties in a sediment including labile U(VI) concentration, sorption site concentration, equilibrium surface complexation reaction constants, and sorption/desorption rate constants can be predicted from the corresponding properties in individual grain size fractions in the sediment. The approach concept and numerical implementation was demonstrated using multi-rate U(VI) desorption from a contaminated sediment from US Department of Energy’s Hanford site, Washington. Stirred flow-cell experiments were performed to derive U(VI) desorption data in the contaminated sediment and its individual grain size fractions. The flow-cell data were used to estimate the rate constants and their statistical properties for individual grain size fractions. The calibrated properties were then used to predict the rate constants and their statistical properties in the sediment, which were used to predict U(VI) desorption. The predicted U(VI) desorption was validated with the measured U(VI) desorption in the sediment. The developed approach can be used to upscale U(VI) sorption/desorption properties from laboratory to field using field-scale grain size distribution. The concept of the approach can also be applied to upscale other reaction properties.