title: Interaction of rare earth elements and components of the Horonobe deep groundwater.
abstract: To better understand the migration behavior of minor actinides in deep groundwater, the interactions between doped rare earth elements (REEs) and components of Horonobe deep groundwater were investigated. Approximately 10 ppb of the REEs, i.e. Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm, and Yb were doped into a groundwater sample collected from a packed section in a borehole drilled at 140 m depth in the experiment drift of Horonobe Underground Research Laboratory in Hokkaido, Japan. The groundwater sample was sequentially filtered with a 0.2 μm pore filter, and 10 kDa, 3 kDa and 1 kDa nominal molecular weight limit (NMWL) ultrafilters with conditions kept inert. Next, the filtrate solutions were analyzed with inductively coupled plasma mass spectrometry (ICP-MS) to determine the concentrations of the REEs retained in solution at each filtration step, while the used filters were analyzed through neutron activation analysis (NAA) and TOF-SIMS element mapping to determine the amounts and chemical species of the trapped fractions of REEs on each filter. A strong relationship between the ratios of REEs retained in the filtrate solutions and the ionic radii of the associated REEs was observed; i.e. smaller REEs occur in larger proportions dissolved in the solution phase under the conditions of the Horonobe groundwater. The NAA and TOF-SIMS analyses revealed that portions of the REEs were trapped by the 0.2 μm pore filter as REE phosphates, which correspond to the species predicted to be predominant by chemical equilibrium calculations for the conditions of the Horonobe groundwater. Additionally, small portions of colloidal REEs were trapped by the 10 kDa and 3 kDa NMWL ultrafilters. These results suggest that phosphate anions play an important role in the chemical behavior of REEs in saline (seawater-based) groundwater, which may be useful for predicting the migration behavior of trivalent actinides released from radioactive waste repositories in the far future.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan. Electronic address: kiri@tagen.tohoku.ac.jp.
authors.forename: Akira
authors.initials: A
authors.lastname: Kirishima
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kuno
authors.affiliation: Horonobe Underground Research Center, Japan Atomic Energy Agency, Hokushin 432-2, Horonobe-cho, Hokkaido, 098-3224, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Amamiya
authors.affiliation: Kyoto University Research Reactor Institute, 2, Asashiro-Nishi, Kumatori-cho, Sennan-gun, Osaka, 590-0494, Japan.
authors.forename: Takumi
authors.initials: T
authors.lastname: Kubota
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kimuro
authors.affiliation: Horonobe Underground Research Center, Japan Atomic Energy Agency, Hokushin 432-2, Horonobe-cho, Hokkaido, 098-3224, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Amano
authors.affiliation: Horonobe Underground Research Center, Japan Atomic Energy Agency, Hokushin 432-2, Horonobe-cho, Hokkaido, 098-3224, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Miyakawa
authors.affiliation: Tono Geoscience Center, Japan Atomic Energy Agency, 1-64, Yamanouchi, Akiyo, Mizunami, Gifu, 509-6132, Japan.
authors.forename: Teruki
authors.initials: T
authors.lastname: Iwatsuki
authors.affiliation: Horonobe Underground Research Center, Japan Atomic Energy Agency, Hokushin 432-2, Horonobe-cho, Hokkaido, 098-3224, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizuno
authors.affiliation: Department of Nuclear Engineering, Kyoto University, Kyoto Daigaku-Katsura, Nishikyo, Kyoto, 615-8530, Japan.
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sasaki
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 1-1 Katahira 2-chome, Aoba-ku, Sendai, 980-8577, Japan.
authors.forename: Nobuaki
authors.initials: N
authors.lastname: Sato
mesh_terms: D005374:Filtration; D060587:Groundwater / Q000737:chemistry*; D007564:Japan; D013058:Mass Spectrometry / Q000379:methods*; D008674:Metals, Rare Earth / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D008674:Metals, Rare Earth; D014874:Water Pollutants, Chemical
keywords: Colloid; Deep groundwater; Horonobe underground research laboratory; Phosphate; Radioactive waste; Rare earth elements