Dispersion stability and electrokinetic properties of intrinsic plutonium colloids: implications for subsurface transport.

Subsurface transport of Plutonium (Pu) may be facilitated by the formation of intrinsic Pu colloids. While this colloid-facilitated transport is stability gely governed by the electrokinetic properties and dispersion (resistance to aggregation) of the colloids, reported experimental data is scarce. Here, we quantify the dependence of zeta potential of intrinsic Fu(IV colloids on PH and their aggregation rate on ionic strength. Results indicate an si electric point of pH 8.6 and a critical coagulation concentration of 0.1 M of 1:1 electrolyte at pH 11.4. The zeta-Potelitial/PH dependence of the Pu(IV) colloids is similar to that of goethite and hematite colloids. Colloid interaction energy calculations using these, values reveal an effective Hamaker constant of the intrinsic Pu(IV) colloids in water of 1.85 x 10(-19) J corresponding to a relative permittivity of 6.21 and refractive of 2.33, in agreement with first principles calculations. This relatively high Hamaker constant combined with the positive charge of Pu(IV) colloids under typical groundwater aquifer conditions led to two contradicting hypotheses: (a) the Pu(IV) colloids will exhibit significant aggregation and deposition, leading to a negligible subsurface transport or (b) the Pu(IV) colloids will associate with the relatively stable native groundwater colloids, leading to a considerable subsurface transport. Packed column transport experiments supported the second hypothesis.