Radioactive colloid advection in a sorbing porous medium: Analytical solution

Colloids are capable of increasing rates of hydrogeologic transport because (a) they can move faster on average than solute due to hydrodynamic chromatography, (b) they can be retarded less than solute by sorption onto rock, and (c) they can increase the apparent liquid-phase radionuclide concentration. Colloid formation might occur as water carrying radionuclide solute leaves the immediate vicinity of the waste package and encounters changing geochemical conditions. Also, colloids of less soluble waste species might form as the waste matrix around them dissolves and migrates away. The authors restrict the analysis in this paper to true colloids that are a solid phase of the radionuclide itself. Colloids can significantly increase the transport rates of contaminants under certain conditions, thereby reducing the containment ability of geologic disposal sites. Neglecting colloid/solute interaction is conservative but unrealistic. This study gives simple formulas for estimating the velocity of a colloid front and the maximum penetration distance of colloids that are in local dissolution equilibrium with solute