In order to accurately simulate the large-scale migration of plutonium in groundwater(a three-phase system),it is necessary to understand the interaction mechanisms between plutonium(Ⅳ),natural colloid,and granite(immobile media).The experimental results show that plutonium pseudo-colloids(i.e.,Pu(Ⅳ)sorbed on the surfaces of soil colloids)have the strong mobility(i.e.,the recovery percentage of plutonium after plutonium pseudo-colloids transported through columns filled with pore media,R).The mobility R increases with soil colloid concentration ρ(0≤ρ≤375.4 mg/L,1.3％≤R≤52.5％).The master complexation speciation of Pu(Ⅳ)on the surfaces of soil colloids is ≡SOPu(OH)3.The speciation percentage(＞95％)is positively correlated with the colloid concentration.The results of experiments and surface complexation calculations confirm that plutonium pseudo-colloids enhance the mobility of Pu(Ⅳ)and thus pose a greater risk of contaminating far-field waters than the dissolved Pu(Ⅳ).The calculations of DLVO interaction potential indicate that the trough depth of the second energy minima(Φmin2)between colloids and media deepens with increasing colloid concentrations.This attractive interaction potential results in an increase in the adsorptive deposition efficiency of plutonium pseudo-colloids on the media surfaces.The DLVO calculations are consistent with the observation:the mobility of plutonium pseudo-colloids become weak(375.4 mg/L＜ρ≤2017.8 mg/L,52.5％＜R≤12.7％).
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