Insights into transport velocity of colloid-associated plutonium relative to tritium in porous media

Although faster transport velocities of colloid-associated actinides, bacteria, and virus than nonreactive solutes have been observed in laboratory and field experiments, some questions still need to be answered. To accurately determine the relative velocity (U-Pu/U-T) of Pu-239 and tritium representative of the bulk water, a conceptual model of electrostatic interactions coupled with the parabolic water velocity profile in pore channels is developed. Based on the expression for U-Pu/U-T derived from this model, we study the effects of water flow rates and ionic strengths on the UPu/U-T. Also, the velocity relationship between Pu, tritium and Sr2+ is explored. The results show that U-Pu/U-T increased fairly linearly with decreasing water flow rates; UPu/U-T declined approximately exponentially with increasing Na+ concentrations; the charge properties of colloid-associated Pu (negative), tritium (neutral) and Sr2+ (positive) had a close association with their transport velocities as U-Pu : U-T : U-Sr(2+) = 1.41 : 1 : 0.579.