X-ray inverse fluorescence approach for accurate determination of Fe valence in Fe-rich geological materials

Nakada, Ryoichi*; Okuda, Hanaya*; Suga, Hiroki*; Yamaguchi, Akiko; Takahashi, Yoshio*; Kawazoe, Takaaki*

Geochemical Journal, 29 Pages, 2026/00

https://doi.org/10.2343/geochemj.GJ26003

Iron undergoes redox transitions between ferrous (Fe) and ferric (Fe) states, playing a key role in various geoscientific processes from Earth's interior to surface environments. Partial fluorescence yield X-ray absorption near edge structure analysis (PFY-XANES) is widely used to evaluate iron valence, but it is susceptible to thickness and self-absorption effects in high-concentration samples. In this study, we applied the inverse fluorescence yield method (IPFY) to geological samples and demonstrated that it enables more accurate iron valence determination than PFY. IPFY-XANES suppressed overestimation of the Fe ratio and reduced thickness effects. This method is expected to be a powerful non-destructive tool for analyzing natural samples such as meteorites and high-pressure recovered specimens.

High stabilization of pentavalent uranium on magnetite nanoparticles evidenced by high-energy-resolution X-ray absorption spectroscopy

Yomogida, Takumi; Scaria, J.*; Fablet, L.*; Tokunaga, Kohei; Dei, Shuntaro; Higashi, Kotaro*; Kawamura, Naomi*; Takahashi, Yoshio*; Marsac, R.*

Chemical Communications, 61(91), p.17926 - 17929, 2025/11

https://doi.org/10.1039/D5CC04540A

This paper presents insights into the influence of magnetite stoichiometry (0 R = Fe(II)/Fe(III) 0.5) on the surface reduction of U(VI) to U(V) and U(IV), as a key parameter controlling U redox speciation in natural settings. Although R can readily change due to the oxidation of structural Fe(II) or proton/ligand-promoted dissolution, prior studies have not quantified U(V) when assessing these effects. We employed U L-edge HERFD-XANES spectroscopy to investigate the electronic structure of U on magnetite with varying stoichiometries and observed a peak splitting of U(V) on magnetite. Our results demonstrate the high stability of U(V) species under a wide range of conditions, and after 10 days on magnetite by the combination of MCR-ALS analysis. A key finding is that structural Fe(II), whose abundance depends on pH and redox conditions, plays a critical role for in the stabilization of U(V) on magnetite.

A Systematic understanding of adsorption reaction on clay minerals focusing on radium as a key element

Yamaguchi, Akiko; Okumura, Masahiko; Takahashi, Yoshio*

SPring-8/SACLA Research Frontiers 2024 (Internet), p.86 - 87, 2025/08

Adsorption reactions on clay minerals are important reactions that affect the environmental behavior of various elements, but due to their complexity, there are still many unresolved issues. In this study, we focused on radium, which has the largest ionic radius among alkaline earth metals, and performed the world's first extended X-ray absorption fine structure (EXAFS) measurement of radium adsorbed on clay minerals to clarify the adsorption structure of radium. The results for radium were compared with those for other elements, and the stability of the adsorption structure was evaluated by first-principles calculations to clarify the determinants of the adsorption structure of clay minerals.

Clay minerals and metal ions; Unraveling the behavior of metal ions from a microscopic perspective

Yamaguchi, Akiko; Yoshimura, Takashi*; Okumura, Masahiko; Takahashi, Yoshio*

Kinzoku, 95(6), p.506 - 514, 2025/06

Clay minerals control behaviors of metal ions in the soil because they are widespread in the earth's surface layer and have a large cation exchange capacity. Due to the complex structure of clay minerals, it is necessary to clarify their microscopic structure and chemical reactions in order to understand how they work. In this article, we describe a study that reveals the mechanism by which clay minerals adsorb metal ions through systematic extended X-ray absorption fine structure (EXAFS) measurements and first principles calculations.

Molecular geochemistry developed by fluorescence XAFS using high energy resolution fluorescence X-ray detection

Yomogida, Takumi; Takahashi, Yoshio*

Chikyu Kagaku, 59(1), p.1 - 10, 2025/03

https://doi.org/10.14934/chikyukagaku.59.1

X-ray absorption fine structure XAFS spectroscopy techniques, which are applicable to almost all elements, provide information on elemental valence and local structure with high elemental selectivity and high sensitivity. It has become an indispensable method in space geochemistry and environmental chemistry. This review presents examples of the application of fluorescence XAFS methods to elements that are difficult to detect by conventional methods, and examples where new chemical species information has been obtained by increasing the energy resolution of the X-ray fluorescence (XRF) detection system to obtain XAFS.

Adsorption structures and bonding states of cesium and barium adsorbed on various sites of vermiculite

Yamaguchi, Akiko; Okumura, Masahiko; Kawamura, Naomi*; Takahashi, Yoshio*

Science of the Total Environment, 964, p.178585_1 - 178585_13, 2025/02

https://doi.org/10.1016/j.scitotenv.2025.178585

There are many unresolved issues in the adsorption reactions of clay minerals. One of the reasons is the existence of multiple adsorption sites. It is known that the contribution of each adsorption site depends on the concentration of adsorbed ions, and there is a challenge in comprehensively correlate the results of atomic-level simulations that employ limited number of atoms and inevitably deal high-concentration samples with actual environmental samples where concentrations are orders of magnitude lower. In this study, we combined experiments using synchrotron radiation and first-principles calculations to comprehensively elucidate the systematic changes in the local structure of adsorption sites and adsorbed ions based on the adsorption concentration at the atomic level, and demonstrated that the interaction between adsorbed ions and clay minerals involves ionic bonding.

Interpretation of vertical migration and enrichment processes of rare earth elements (REEs) in ion-adsorption-type mineralization in Japan based on REE speciation analyses

Nagasawa, Makoto*; Shimizu, Yusuke*; Yamaguchi, Akiko; Tokunaga, Kohei; Mukai, Hiroki*; Aoyagi, Noboru; Mei, H.; Takahashi, Yoshio*

Chemical Geology, 670, p.122431_1 - 122431_25, 2024/12

https://doi.org/10.1016/j.chemgeo.2024.122431

Circular polarization measurement for individual gamma rays in capture reactions with intense pulsed neutrons

Endo, Shunsuke; Abe, Ryota*; Fujioka, Hiroyuki*; Ino, Takashi*; Iwamoto, Osamu; Iwamoto, Nobuyuki; Kawamura, Shiori*; Kimura, Atsushi; Kitaguchi, Masaaki*; Kobayashi, Ryuju*; et al.

European Physical Journal A, 60(8), p.166_1 - 166_10, 2024/08

https://doi.org/10.1140/epja/s10050-024-01392-6

Microbially formed Mn(IV) oxide as a novel adsorbent for removal of Radium

Tanaka, Kazuya; Yamaji, Keiko*; Masuya, Hayato*; Tomita, Jumpei; Ozawa, Mayumi*; Yamasaki, Shinya*; Tokunaga, Kohei; Fukuyama, Kenjin*; Ohara, Yoshiyuki*; Maamoun, I.*; et al.

Chemosphere, 355, p.141837_1 - 141837_11, 2024/05

https://doi.org/10.1016/j.chemosphere.2024.141837

In this study, biogenic Mn(IV) oxide was applied to remove Ra from mine water collected from a U mill tailings pond in the Ningyo-toge center. Just 7.6 mg of biogenic Mn(IV) oxide removed more than 98% of the Ra from 3 L of mine water, corresponding to a distribution coefficient of 10 mL/g for Ra at pH 7. The obtained value was convincingly high for practical application of biogenic Mn(IV) oxide in water treatment.

High sensitivity of a future search for effects of -odd/-odd interactions on the 0.75 eV -wave resonance in + forward transmission determined using a pulsed neutron beam

Nakabe, Rintaro*; Auton, C. J.*; Endo, Shunsuke; Fujioka, Hiroyuki*; Gudkov, V.*; Hirota, Katsuya*; Ide, Ikuo*; Ino, Takashi*; Ishikado, Motoyuki*; Kambara, Wataru*; et al.

Physical Review C, 109(4), p.L041602_1 - L041602_4, 2024/04

https://doi.org/10.1103/PhysRevC.109.L041602