Natural speciation of Mn, Ni, and Zn at the micrometer scale in a clayey paddy soil using X-ray fluorescence, absorption, and diffraction

Abstract

The natural speciation of Mn (0.19 g/kg), Ni (46 mg/kg) and Zn (42 mg/kg) in the argillic horizon (120 cm depth, pH = 5.6) of an Ultisol from a paddy soil in northern Taiwan was investigated by advanced X-ray synchrotron techniques. Microchemical associations were imaged by synchrotron-based X-ray microfluorescence, host minerals were identified by standard and micrometer-resolved X-ray diffraction, and the local coordination environment of Mn, Ni, and Zn was probed using extended X-ray absorption fine structure (EXAFS) spectroscopy on a powdered sample and a soil thin section, and polarized EXAFS spectroscopy on a highly textured self-supporting clay film from the <2 µm fraction of the soil.

The concentration and distribution of selected heavy metals (Pb, Cd, Cu and Zn) in soils collected from the rice fields of MADA in Kedah, Malaysia

“…Mancheau et al [26] found that Zn In acidic to near-neutral aluminium-rich clayey paddy soils in Vietnam was predominantly bound to the hydroxyl-Al interlayers in the fine soil matrix. Similarly, paddy soils in the Kedah plain were sbundant in phyllosilicate minerals in the clay fractions such as kaolinite, smectite and mica [21], which in turn provide a good binder for Zn accumulation.…”

Structural characterization of terrestrial microbial Mn oxides from Pinal Creek, AZ

“…8). The variation in height of these specific features originates in the planarity of the manganese oxide layer; tall narrow peaks at these positions are characteristic of Mn oxides with undistorted hexagonal layer symmetry and low Mn(III) content (Manceau et al, 2002(Manceau et al, , 2005Webb et al, 2005b). These features arise from Mn-Mn-Mn multiple scattering, which dies away quickly as the Mn-Mn-Mn (i.e., linear adjacent Mn neighbors) angle bends away from 180°.…”

“…Natural marine and soil Mn oxides frequently have been reported to be poorly crystalline and to exhibit layer structures (Post, 1999;Manceau et al, 2005;Bodei et al, 2007). It is likely that such morphologies implicate biogenic origin.…”

“…It can thus be concluded that this nanoparticulate layered structural motif is characteristic of (but not necessarily unique to) laboratory biogenic Mn oxides. These conclusions lead one to question if environmental biogenic Mn oxides exhibit such characteristics (intriguingly, such features are frequently reported for poorly crystalline natural Mn oxides of possible biogenic origin (Post, 1999;Manceau et al, 2005;Bodei et al, 2007)). Establishing similarity between laboratory and environmental biogenic Mn oxides, were it to occur, would represent a significant step forward because it would provide the scientific basis to model the behavior of environmental Mn oxides based on data from laboratory studies.…”

Biogeochemistry of Nickel and Its Release into the Environment

“…Synchrotron-based XRF allows the establishment of elemental mappings of small-scale samples, with lateral resolutions in the µm range [34]. By combining different synchrotron X-ray techniques, such as X-ray diffraction, X-ray absorption fi ne-structure analysis (XAFS), and X-ray absorption near edge structure analysis (XANES), information on the mineral phase, the oxidation state and the nearest neighbour atom can be obtained [35][36][37].…”