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 (239)Pu 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 U(Pu)/U(T). Also, the velocity relationship between Pu, tritium and Sr(2+) is explored. The results show that U(Pu)/U(T) increased fairly linearly with decreasing water flow rates; U(Pu)/U(T) declined approximately exponentially with increasing Na(+) concentrations; the charge properties of colloid-associated Pu (negative), tritium (neutral) and Sr(2+) (positive) had a close association with their transport velocities as U(Pu) : U(T) : U(Sr)(2+) = 1.41 : 1 : 0.579.