Motoyuki Matsuo

Iron speciation in modern sediment from Erhai Lake, southwestern ChinaRedox conditions in an ancient environment

Abstract In a core of sub-aquatic sediment from Erhai Lake, southwestern China, 4 Fe species were identified as paramagnetic Fe3+, superparamagnetic Fe3+, hematite Fe3+, and paramagnetic high-spin Fe2+ using Mossbauer spectroscopy. The 120 cm core has a distinct lithological boundary at a depth of about 70 cm. Each Fe species has a distinctive distribution with depth. These results represent the redox conditions within the sediment, and also probably reflect the primary sedimentary environments. With increasing burial depth, hematite (Fe2O3) decreased, especially below depths greater than 25 cm, and finally disappeared at around 95 cm. The summed paramagnetic Fe3+ (superparamagnetic Fe3++paramagnetic Fe3+) did not change as much, only exhibiting a slight decrease at depths greater than 75 cm, about 5 cm beneath the lithological boundary within the core. The intensity of paramagnetic high-spin Fe2+ increased with depth. These vertical variations were in harmony with organic geochemical parameters such as TOC concentration, H-index and O-index, indicating that reducing conditions are strongly intensified in the sediment below 70 cm. The geological, organic geochemical and 14C data combined with the present Mossbauer spectroscopic study give a strong indication that the redox environment of Erhai Lake probably shifted rather rapidly from a deep reducing to a shallow oxic state at about 2 ka ago.

Iron speciation of sliding mud in Toyama Prefecture, Japan

Abstract It has been often observed that black mud recently formed and accumulated in slip planes that are closely associated with a progressing landslide in Japan. Mossbauer spectroscopy revealed that the composition of Fe species in the sliding mud is different from those in the debris rock and bedrock. The sliding mud contains more ferrous iron species, which indicates a relatively stronger reducing condition within the sliding zone than within the host rocks. In addition, the composition of Fe species, the total Fe and the volume of sliding mud also change with landslide development. Therefore, detailed Fe speciation in landslide profiles can be a useful approach to understanding the progress of a landslide and may also predict future sliding as well.

Neutron induced prompt gamma-ray and instrumental neutron activation analyses of urban estuarine sediments

Neutron induced prompt γ-ray analysis (PGA) and instrumental neutron activation analysis (INAA) have been applied to the sediments collected from the Tama River estuary in Tokyo, Japan. The vertical distribution of 24 elements in the sediments was determined and the factors goveming the vertical profiles have been discussed. Major elements are distributed depending on weathering that proceeds much with increasing depth. Cadmium is highly concentrated in the deeper layer where sulphate ion is reduced to hydrogen sulphide. The distribution of several rare earth elements is also presented

Reduction process of Cr(VI) by Fe(II) and humic acid analyzed using high time resolution XAFS analysis.

The initial reduction behavior of Cr(VI) to Cr(III) has not been clearly understood due to its rapid reduction reaction. In order to study the reduction process of Cr(VI) in detail, we applied quick X-ray absorption fine structure (QXAFS) analysis to observe how Cr(VI) was reduced to Cr(III) by Fe(II) and humic acid (HA) with time. The Cr(VI) concentration was analyzed every 60s, and the plots of ln(Cr(VI)/Cr(VI)0) versus time were used to evaluate the reduction process based on their linearity. Reduction by Fe(II) showed a linear relation, whereas reduction by HA showed a nonlinear relation. With combined Fe(II) and HA, the linearity was unlike those of Fe(II) and HA individually. The reduction rate was not constant. The structure of Fe(II) produced by HA during the Cr(VI) reduction was investigated by using Mössbauer spectroscopy, which showed that Fe(II) produced by HA reduction of Fe(III) had the same structure as the initial Fe(II). HA can reduce Fe(III) back to Fe(II), and reproduced Fe(II) reduces Cr(VI). For Cr(VI) reduction by combined Fe(II) and HA, each reductant contribute differently: Fe(II) directly contributes to the Cr(VI) reaction, whereas HA reduces both Cr(VI) and Fe(III).

Mössbauer spectroscopic characterization of iron compounds in paddy soil

Chemical states of iron and their vertical distribution in paddy soil, which was derived from weathered volcanic ashes, have been investigated by57Fe Mössbauer spectroscopy. The relative amount of paramagnetic Fe3+ has no dependence on depth, whereas that of magnetic Fe3+ decreases with an increase in depth. The paramagnetic Fe2+ can be divided into two fractions which show an opposite dependence on depth from each other. The depth profile of the iron components clearly reflects the chemical conditions characteristic of the paddy environment, and the origin of the iron components is also discussed.

Studies on intake of heavy metals by Bradybaena similaris, land snails, by XAFS measurement.

We have applied XAFS in order to determine both the chemical form and the place where heavy metals are stored in cultivated land snails. From Cu and Zn XANES spectra, the shells showed similar patterns as those of soft tissues and not like carbonates. This indicates that heavy metals are not completely taken into carbonate structures but are present within organic components in the shells. In addition, Cu XANES spectra of the samples showed low absorption edge-energy in the order of hepatopancreas, mantle, body, and shell. By comparing samples with standard reagents, each of which has only S- or O-ligand, it was found that the metals in hepatopancreas exist mostly as S-bound chemical components. To quantify the relative abundance of S-bound chemical component, partial least-squares (PLS) regression was applied. The PLS result indicated that for Cu, S-bound compound was higher in the order of hepatopancreas > mantle > body >shell.

Characterization of Natural Chromite Samples from Ophiolite Complexes in the Philippines by 57Fe Mössbauer Spectroscopy

Mössbauer spectroscopy was applied to natural chromite samples from ophiolite complexes in the Philippines. Chemical and structural characterization of the chromite samples was also carried out using X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and X-ray fluorescence spectrometry (XRF). The Mössbauer spectra of the samples consisted of quadrupole doublets ascribable to Fe3+ in octahedral site, Fe3+ in tetrahedral site, and Fe2+ in tetrahedral site. The relative percentage of Fe3+ and Fe2+ ions suggested that these Philippine samples were formed under relatively high oxygen fugacity.

Iron and sulfur speciation in some sedimentary-transformation- type of lead-zinc deposits in West Kunlun lead-zinc ore deposit zone, Northwest China

Redox conditions are very important for almost all geological processes including ore deposit formation. However, the direct measurement of redox potential (Eh) values for solid materials is difficult. The chemical speciation of redox sensitive elements is one factor which determines the redox conditions. In this study, four groups of ore samples and their host rocks were collected from four sites along the west Kunlun lead–zinc ore deposit zone in northwest China and the iron- and sulfur- species analyzed using Mössbauer spectroscopy and X-ray absorption near edge fine structure (XANES). The results showed systematical change in redox conditions between the ore rocks and their associated host rocks. All ore samples contained more reducing sulfur species than their corresponding host-rocks indicating significantly enhanced reducing conditions in the ore bodies than their host rocks. Such reducing conditions should be more favorable for the sulfidization of metal during the ore formation. In addition very small concentrations of ferrous iron were found in only some of the small samples. This may indicate the removal of iron during metal sulfide ore deposit formation.

Column chromatographic boron isotope separation at 5 and 17 MPa with diluted boric acid solution

Boron isotopic fractionation factor (S) between boron taken up in strongly basic anion exchange resin and boron in aqueous solution was determined by breakthrough column chromatography at 5 and 17 MPa at 25 degrees C, using 0.1 mM boric acid solution as feed solution. The S values obtained were 1.018 and 1.012, respectively, which were smaller than the value reported by using the same chromatographic method at the atmospheric pressure at 25 degrees C with the boron concentration of 10mM, but were larger than the values under the same condition with much higher concentration of 100 and 501 mM. Calculations based on the theory of isotope distribution between two phases estimated that 21% (5 MPa) and 47% (17 MPa) of boron taken up in the resin phase was in the three-coordinated B(OH)(3)-form, instead of in the four-coordinated B(OH)(4)-form, at high pressures even with a very diluted boric acid solution. We discussed the present results by introducing (1) hydration and (2) a partial molar volume difference between isotopic molecules. Borate may have been partially dehydrated upon transfer from the solution phase to the resin phase at high pressures, which resulted in smaller S values compared with those at the atmospheric pressure. Instead, it may be possible that the difference in the isotopic partial molar volume difference between B(OH)(3) and B(OH)(4)(-) caused the S value to decrease with increasing pressure.

Vertical distribution of elements in non-polluted estuarine sediments determined by neutron induced prompt gamma-ray and instrumental neutron activation analyses

Neutron induced prompt gamma-ray analysis (PGA) and instrumental neutron activation analysis (INAA) have been applied to the sediments collected from the Yasaka River estuary in Oita Prefecture, Japan. The vertical distribution of 33 elements in the sediments has been determined and compared with that in more polluted estuarine sediments. While the S content increased with increasing depth because of a sulphide accumulation under reducing condition, the increase in sulphide-forming elements such as Ag, Cd, Co and Zn was not observed in the deeper section of the Yasaka River estuarine sediments.