An area of 1.4 km² of U(VI) contaminant plumes at levels above drinking water standards is present at the Hanford site, WA. Some U(VI) plumes has not dissipated as rapidly as predicted and many questions related to possible future migration of U(VI) remain unanswered. Hydraulically saturated column experiments were conducted to investigate U(VI) desorption and adsorption kinetics by applying stop-flow events of systematically increasing duration until U(VI) concentrations no longer increase during these events. Contaminated sediments that experienced long-term exposure to U(VI) contamination and electrolytes with different ([CO3]_TOT) concentrations and pH (8.05 and 8.90) were used to study the effect of carbonate on U(VI) transport and to simulate the mildly alkaline/calcareous conditions representative of the Hanford site where uranyl–carbonate and calcium–uranyl–carbonate complexes dominate aqueous speciation. Reaction based models for U(VI)-chemistry in these sediments were applied in a kinetic mode to the experimental data. A distributed rate model with rate coefficients that follow the gamma probability distribution, was used to describe the effluent data and to allow comparisons between calculated rates of U(VI) desorption/adsorption under different chemical conditions. Our results suggest that U(VI) fate and transport in the vadose zone and aquifer systems from which the sediments were obtained, are kinetically controlled and depend strongly on ([CO3]_TOT) aqueous concentration.