sorption is also very fast, equilibrium being reached within a few hours (e.g.,
Grangeon et al. 2017).
7.3.3 An Introduction to the Use of Powder X-Ray Diffraction
to Determine the Origin of Layer Charge
Most frequently, determination of a mineral structure is performed by refining it
powder X-ray diffraction (XRD) pattern using the Rietveld method. This is, in the
case of vernadite, complicated by turbostratism, which induces very particular XRD
patterns, containing only a few weak hk bands and 00l reflections. To circumvent
this difficulty of analysis, many studies made the use of alternative physical
methods, such as Fourier-transformed infrared (FTIR) spectroscopy, Raman spectroscopy, or synchrotron-based X-ray absorption spectroscopies, for example X-ray
Absorption Near-Edge Structure (XANES) or Extended X-Ray Absorption Fine
Structure (EXAFS). However, although useful and efficient, these methods only
provide a partial picture of the structure of the studied material. For example,
EXAFS typically probes the local order up to 6 Å around the central atom. In
addition, the nanocrystalline nature of vernadite may induce uncertainties in the
determination of the structural features responsible for vernadite reactivity, in
particular layer vacancies (Webb et al. 2005). Thus, these methods benefit from
the complementary use of XRD (and vice versa), which provides information at the
crystallite scale. To model XRD patterns, a specific method of analysis that is
capable of reproducing the patterns of turbostratic structures can be applied (Drits
and Tchoubar 1990; Plancon 1981, 2002). As exemplified in Fig. 7.6, this method is
capable of quantitatively reproducing the XRD patterns, and has sensitivity to main
vernadite layer structure characteristics, including crystallite size, lattice parameters,
and density of interlayer species adsorbed above layer vacancies. For more examples, and application to the study of trace metal sorption at vernadite surface, the
reader is referred to previous literature studies (Drits et al. 2007; Grangeon et al.
2008; Lafferty et al. 2010b; Lanson et al. 2008; Manceau et al. 2013). This example
demonstrates that a quantitative method of analysis of XRD patterns can be used to
quantitatively probe the structure of vernadite, and thus to help understanding the
reasons behind the exceptional reactivity of soil Mn oxides.
7.4 Potential Uses for Remediation
The specific properties of the Mn oxides can be used for decontamination and soil
remediation purposes. The use of both natural and engineered Mn oxides is
referenced for water treatment and soil remediation, as presented in the following
sections.
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
413
Grangeon et al. 2017).
7.3.3 An Introduction to the Use of Powder X-Ray Diffraction
to Determine the Origin of Layer Charge
Most frequently, determination of a mineral structure is performed by refining it
powder X-ray diffraction (XRD) pattern using the Rietveld method. This is, in the
case of vernadite, complicated by turbostratism, which induces very particular XRD
patterns, containing only a few weak hk bands and 00l reflections. To circumvent
this difficulty of analysis, many studies made the use of alternative physical
methods, such as Fourier-transformed infrared (FTIR) spectroscopy, Raman spectroscopy, or synchrotron-based X-ray absorption spectroscopies, for example X-ray
Absorption Near-Edge Structure (XANES) or Extended X-Ray Absorption Fine
Structure (EXAFS). However, although useful and efficient, these methods only
provide a partial picture of the structure of the studied material. For example,
EXAFS typically probes the local order up to 6 Å around the central atom. In
addition, the nanocrystalline nature of vernadite may induce uncertainties in the
determination of the structural features responsible for vernadite reactivity, in
particular layer vacancies (Webb et al. 2005). Thus, these methods benefit from
the complementary use of XRD (and vice versa), which provides information at the
crystallite scale. To model XRD patterns, a specific method of analysis that is
capable of reproducing the patterns of turbostratic structures can be applied (Drits
and Tchoubar 1990; Plancon 1981, 2002). As exemplified in Fig. 7.6, this method is
capable of quantitatively reproducing the XRD patterns, and has sensitivity to main
vernadite layer structure characteristics, including crystallite size, lattice parameters,
and density of interlayer species adsorbed above layer vacancies. For more examples, and application to the study of trace metal sorption at vernadite surface, the
reader is referred to previous literature studies (Drits et al. 2007; Grangeon et al.
2008; Lafferty et al. 2010b; Lanson et al. 2008; Manceau et al. 2013). This example
demonstrates that a quantitative method of analysis of XRD patterns can be used to
quantitatively probe the structure of vernadite, and thus to help understanding the
reasons behind the exceptional reactivity of soil Mn oxides.
7.4 Potential Uses for Remediation
The specific properties of the Mn oxides can be used for decontamination and soil
remediation purposes. The use of both natural and engineered Mn oxides is
referenced for water treatment and soil remediation, as presented in the following
sections.
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
413