title: Colloid-associated plutonium aged at room temperature: evaluating its transport velocity in saturated coarse-grained granites.
abstract: The fate and transport of colloidal contaminants in natural media are complicated by physicochemical properties of the contaminants and heterogeneous characteristics of the media. Size and charge exclusion are two key microscopic mechanisms dominating macroscopic transport velocities. Faster velocities of colloid-associated actinides than that of (3)H2O were consistently indicated in many studies. However, dissociation/dissolution of these sorbed actinides (e.g., Pu and Np), caused by their redox reactions on mineral surfaces, possibly occurred under certain chemical conditions. How this dissolution is related to transport velocities remains unanswered. In this study, aging of the colloid-associated Pu (pseudo-colloid) at room temperature and transport through the saturated coarse-grained granites were performed to study whether Pu could exhibit slower velocity than that of (3)H2O (UPu/UT <1). The results show that oxidative dissolution of Pu(IV) associated with the surfaces of colloidal granite particles took place during the aging period. The relative velocity of UPu/UT declined from 1.06 (unaged) to 0.745 (135 d) over time. Size exclusion limited to the uncharged nano-sized particles could not explain such observed UPu/UT <1. Therefore, the decline in UPu/UT was ascribed to the presence of electrostatic attraction between the negatively charged wall of granite pore channels and the Pu(V)O2(+), as evidenced by increasing Pu(V)O2(+) concentrations in the suspensions aged in sealed vessels. As a result of this attraction, Pu(V)O2(+) was excluded from the domain closer to the centerline of pore channels. This reveals that charge exclusion played a more important role in dominating UPu than the size exclusion under the specific conditions, where oxidative dissolution of colloid-associated Pu(IV) was observed in the aged suspensions.
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China. Electronic address: xiejinchuan@nint.ac.cn.
authors.forename: Jinchuan
authors.initials: J
authors.lastname: Xie
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Lin
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Mei
authors.initials: M
authors.lastname: Li
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Jihong
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Xiaohua
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Northwest Institute of Nuclear Technology, P.O. Box 69-14, Xi'an City, Shanxi Province 710024, PR China.
authors.forename: Yifeng
authors.initials: Y
authors.lastname: He
mesh_terms: D003102:Colloids / Q000737:chemistry*; D004784:Environmental Monitoring; D011005:Plutonium / Q000032:analysis / Q000737:chemistry*; D013535:Suspensions / Q000737:chemistry; D013696:Temperature; D014872:Water Movements; D014875:Water Pollutants, Radioactive / Q000032:analysis / Q000737:chemistry*
chemical_list: D003102:Colloids; D013535:Suspensions; D014875:Water Pollutants, Radioactive; D011005:Plutonium
keywords: Charge exclusion; Colloid; Granite; Plutonium; Size exclusion; Transport velocity