Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2): a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust

Mamiko Yamashita Maeno, Hironori Ohashi, Kotaro Yonezu, Akane Miyazaki, Yoshihiro Okaue, Koichiro Watanabe, Tamao Ishida, Makoto Tokunaga, Takushi Yokoyama

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Abstract

It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth’s continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2− complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2− and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.

Original languageEnglish
Pages (from-to)211-218
Number of pages8
JournalMineralium Deposita
Volume51
Issue number2
DOIs
Publication statusPublished - Feb 1 2016

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dioxides
sorption
Anions
Sorption
manganese
anion
crusts
X ray absorption
Ions
crust
anions
X-ray spectroscopy
ion
X ray photoelectron spectroscopy
x rays
Redox reactions
fine structure
photoelectron spectroscopy
oxidation-reduction reactions
Iron oxides

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Sorption behavior of the Pt(II) complex anion on manganese dioxide (δ-MnO2) : a model reaction to elucidate the mechanism by which Pt is concentrated into a marine ferromanganese crust. / Maeno, Mamiko Yamashita; Ohashi, Hironori; Yonezu, Kotaro; Miyazaki, Akane; Okaue, Yoshihiro; Watanabe, Koichiro; Ishida, Tamao; Tokunaga, Makoto; Yokoyama, Takushi.

In: Mineralium Deposita, Vol. 51, No. 2, 01.02.2016, p. 211-218.

Research output: Contribution to journalArticle

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abstract = "It is difficult to directly investigate the chemical state of Pt in marine ferromanganese crusts (a mixture of hydrous iron(III) oxide and manganese dioxide (δ-MnO2)) because it is present at extremely low concentration levels. This paper attempts to elucidate the mechanism by which Pt is concentrated into marine ferromanganese crust from the Earth’s continental crust through ocean water. In this investigation, the sorption behavior of the Pt(II) complex ions on the surface of the δ-MnO2 that is a host of Pt was examined as a model reaction. The δ-MnO2 sorbing Pt was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) to determine the chemical state of the Pt. Hydrolytic Pt(II) complex ions were specifically sorbed above pH 6 by the formation of a Mn-O-Pt bond. XPS spectra and XANES spectra for δ-MnO2 sorbing Pt showed that the sorbed Pt(II) was oxidized to Pt(IV) on δ-MnO2. The extended X-ray absorption fine structure (EXAFS) analysis showed that the coordination structure of Pt sorbed on δ-MnO2 is almost the same as that of the [Pt(OH)6]2− complex ion used as a standard. Therefore, the mechanism for the concentration of Pt in marine ferromanganese crust may be an oxidative substitution (penetration of Pt(IV) into structure of δ-MnO2) by a reduction-oxidation reaction between Pt(II) in [PtCl4-n(OH)n]2− and Mn(IV) in δ-MnO2 through a Mn-O-Pt bond.",
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AU - Okaue, Yoshihiro

AU - Watanabe, Koichiro

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AU - Yokoyama, Takushi

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