HR: 0830h
AN: B21C-0725 [PDF]
TI: Structural Study Of Nickel- And Zinc-Doped Layer Type Manganese Oxides
AU: * Tommaseo, C E
EM: tommaseo@nature.berkeley.edu
AF: Departement ESPM, University of California, Hilgard Hall 235, Berkeley, CA 94720 United States
AU: * Tommaseo, C E
EM: tommaseo@nature.berkeley.edu
AF: Environmental Geochemistry Group, LGIT, University J. Fourier, BP 53,, Grenoble, 38041
France
AU: Manceau, A
EM: manceau@ujf-grenoble.fr
AF: Environmental Geochemistry Group, LGIT, University J. Fourier, BP 53,, Grenoble, 38041
France
AU: Lanson, B
EM: bruno.lanson@obs.ujf-grenoble.fr
AF: Environmental Geochemistry Group, LGIT, University J. Fourier, BP 53,, Grenoble, 38041
France
AU: Sposito, G
EM: gsposito@nature.berkeley.edu
AF: Departement ESPM, University of California, Hilgard Hall 235, Berkeley, CA 94720 United States
AB:
In order to understand better the mobility of trace elements in soils it is necessary to characterize the interactions of
these elements with the reactive mineral components of soils. We have studied the intercalation processes of Zn and Ni in the
oxide phases birnessite [layer type Mn(III,IV)O$_{2}$ oxide] and lithiophorite [MnO$_{2}$-Al(OH)$_{3}$ mixed-layer oxide],
which are found in ferromanganese nodules common in lakes, shallow marine environments, and the oceanic floor. Previously
Manceau, Lanson and coworkers have demonstrated that nickel is sequestered in soil ferromanganese nodules by substituting for
Mn$^{3+}$ in the manganese oxide sheet of lithiophorite and for Li$^{+}$ in the Al(OH)$_{3}$ sheet. In birnessite, on the
other hand, they found that Zn atoms are adsorbed in the interlayer above and below vacant octahedral sites, either
tetrahedrally and/or octahedrally coordinated.
In our studies, Zn and Ni doped lithiophorite and birnessite with varying concentrations of the doped metals were synthesized
in the laboratory to avoid the inherent complexity of natural samples. Different types of synthesis procedures had to be
chosen for the birnessite and lithiophorite samples in order to insert the two metals into the structures of these phases.
This reflects the differing insertion behavior of Zn and Ni and the corresponding different varieties of doped Ni and Zn in
the birnessite and lithiophorite structures. Structural characterization of the Zn and Ni doped manganese oxides was
performed with help of X-ray diffraction and EXAFS spectroscopy to determine precisely in which form and in which place in
the structure the metals occur. The higher quality of the EXAFS spectra (k-values up to 16 \AA$^{-1}$) of our synthetic
samples in comparison to those of natural samples allowed us to resolve interatomic distances that differed by less than 0.12
\AA. For example, Ni is octahedrally coordinated, sharing edges with the Mn octahedra in the birnessite structure at two
slightly different Ni-Mn distances. Independently of its doping concentration, Zn was found to be tetrahedrally coordinated
in both of the oxides investigated. The only exception to this trend was observed after replacing in the synthesis procedure
for lithiophorite a certain percentage of Li by Zn. In that case Zn can be intercalated in the structure both tetrahedrally
and octahedrally coordinated.
DE: 1615 Biogeochemical processes (4805)
DE: 4805 Biogeochemical cycles (1615)
SC: Biogeosciences [B]
MN: 2003 Fall Meeting