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Journal Articles

Efficient condensation of organic colloids in deep groundwater using surface-modified nanofiltration membranes under optimized hydrodynamic conditions

Aosai, Daisuke*; Saeki, Daisuke*; Iwatsuki, Teruki; Matsuyama, Hideto*

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 495, p.68 - 78, 2016/04


 Times Cited Count:1 Percentile:2.45(Chemistry, Physical)

The transport of radionuclides by organic colloids in deep groundwater is one of the important issues for the geological disposal of high-level radioactive waste. Because of their low concentration, it is difficult to directly analyze organic colloids in deep groundwater. In this study, hydrodynamic conditions were optimized, and surfaces of nanofiltration membranes were modified using a cationic phosphorylcholine polymer for preventing membrane fouling. Deep groundwater, obtained at the Mizunami Underground Research Laboratory in Japan, was condensed. The recovery yield of the organic colloids in the deep groundwater condensation test at 5-fold condensation was improved from 62% to 92% by the optimized hydrodynamic conditions and membrane surface modification for prevention of membrane fouling. The composition of organic colloids in the condensates was analyzed using pyrolysis gas chromatography coupled with mass spectrometry.

Journal Articles

Concentration and characterization of organic colloids in deep granitic groundwater using nanofiltration membranes for evaluating radionuclide transport

Aosai, Daisuke*; Saeki, Daisuke*; Iwatsuki, Teruki; Matsuyama, Hideto*

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 485, p.55 - 62, 2015/11


 Times Cited Count:4 Percentile:11.59(Chemistry, Physical)

To analyze organic colloids in deep groundwater, concentration techniques using adsorption resins and reverse osmosis membranes have been widely applied, because their concentrations in deep groundwater are very low and detection of the organic colloids in raw groundwater is difficult. However, these techniques have respective disadvantages such as chemical disturbance and membrane fouling caused by cations. To overcome their disadvantages, we propose a new concentration method using nanofiltration membranes to concentrate organic colloids rapidly without chemical disturbance and to selectively remove monovalent and divalent ions, which may cause inorganic and/or organic fouling. Concentration performance of the NF and RO membranes for aqueous solutions for humic acids was evaluated using a laboratory-scale membrane test unit. The time course of permeate flux and concentration of humic acids were measured. These membranes were applied to the concentration of actual groundwater.

Journal Articles

Size and composition analyses of colloids in deep granitic groundwater using microfiltration/ultrafiltration while maintaining in situ hydrochemical conditions

Aosai, Daisuke*; Yamamoto, Yuhei*; Mizuno, Takashi; Ishigami, Toru*; Matsuyama, Hideto*

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 461, p.279 - 286, 2014/11


 Times Cited Count:9 Percentile:27.22(Chemistry, Physical)

In studies of colloids in deep groundwater, a serious problem exists because the properties of the colloids are influenced by changes in the chemistry of groundwater upon exposure to the atmosphere and pressure release during sampling. Then, ultrafiltration technique, while maintaining in situ hydrochemical conditions was developed. As the result of the investigation using the method at the Mizunami underground Research Laboratory (MIU), different types of colloids consisting of inorganic and organic substances were observed and complex formation between the colloids and REEs was suggested. Furthermore, characteristic partitioning of REEs depending on colloids size was observed in complex natural environments without chemical disturbance. The current findings are useful for understanding migration of radionuclides.

Journal Articles

Size and elemental analyses of nano colloids in deep granitic groundwater; Implications for transport of trace elements

Saito, Takumi*; Suzuki, Yohei*; Mizuno, Takashi

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 435(Sp.IAP2012), p.48 - 55, 2013/10

 Times Cited Count:16 Percentile:45.19(Chemistry, Physical)

Nano colloids in granitic groundwater obtained from a borehole located at the -300-m stage of the Mizunami Underground Research Laboratory were studied in terms of their size distributions by flow-field flow fractionation. In order to deal with relatively low concentrations of colloids, colloids were enriched first by ultrafiltration, and then by in-situ enrichment using a large injection loop and the slot flow technique. The size distributions of organic and inorganic constituents of colloids were measured by UV/Vis, fluorescence and inductively coupled plasma mass spectrometry, from which possible association of trace elements with host colloidal phases consisting of major elements and organic materials was discussed. Trace elements, namely, Sr, lanthanides (La, Ce, Eu, Lu), actinide elements (U, Th) and heavy metals (Cu, Zn and W), exhibited distinct size distributions, reflecting their preferential association with certain host colloidal phases.

Journal Articles

Transport behavior and deposition kinetics of humic acid under acidic conditions in porous media

Yamashita, Yuji*; Tanaka, Tadao; Adachi, Yasuhisa*

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 417, p.230 - 235, 2013/01

 Times Cited Count:10 Percentile:30.02(Chemistry, Physical)

Transport behavior of humic acid was studied from the aspects of colloidal stability. Deposition kinetics of purified Aldrich humic acid was investigated over a wide range of monovalent and divalent electrolyte concentrations at pH 3.0 by using packed-bed technique. Spherical glass beads with diameters of 0.2 mm were utilized as model collectors. Breakthrough curves of humic acid were measured with UV-VIS spectrophotometer. The values of C/C0 (C and C0 are the effluent and influent concentrations of humic acid, respectively) decreased with increasing electrolyte concentrations. Experimental collision efficiencies were determined from measured single collector efficiencies. The results are presented as stability curves, which is the logarithm of the collision efficiency as a function of the logarithm of salt concentration. Stability curves of humic acid obviously showed favorable and unfavorable regimes and critical deposition concentration in the presence of both electrolytes. As a consequence, it is indicated that transport behavior of humic acid is primarily controlled by electrostatic interaction between humic acids and collectors.

Journal Articles

Complexation of Am with size-fractionated soil humic acids

Nagao, Seiya*; Aoyama, Masakazu*; Watanabe, Akira*; Tanaka, Tadao

Colloids and Surfaces A; Physicochemical and Engineering Aspects, 347(1-3), p.239 - 244, 2009/09

 Times Cited Count:5 Percentile:12.92(Chemistry, Physical)

Humic substances play important role in geochemical behavior of trace elements such as actinides in aquatic environments. The association properties of Am with humic substances were studied on the basis of structural feature of humic substances. Humic acids prepared from three types of soils, and separated two humic acids with different structural features: fluorescence-poor and higher molecular size fraction, HA and fluorescence-rich and lower molecular size fraction, FL. The association experiments were carried out in a medium of 0.01M NaClO$$_{4}$$ solution at a humus concentration of 10 mg/l and pH 6-8. The dominant size fractions of Am in the presence of the HA were 450nm - 100k Daltons and 100k - 30k Daltons. On the other hand, Am was presented in the size of 30k - 10k Daltons in the FL. These results indicate that characteristics of size-fractionated humic acids are related association properties with Am.

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