these two types of minerals, with layered structures being the precursor of the tunnel
structures (e.g., McKenzie 1989), and many experiments were performed to better
understand the relationship between these two groups. The main results obtained are
summarized in this section.
7.2.3.1 Influence of the Chemical Composition of Layered Precursor
Studies performed in laboratory conditions regularly showed that the conversion
from phyllomanganate to tectomanganate is possible, and that the size of the
tectomanganate tunnels depends on the nature of the interlayer cation present in
the phyllomanganate precursor. For example, it was shown that Mg
2+ -saturated
precursors transform into synthetic todorokite, while Na
+
-saturated precursors produce synthetic cryptomelane. A few examples of the influence of the initial interlayer
cation, when of relevance for soils, on the nature of the obtained tectomanganate are
presented in Table 7.2.
Fig. 7.5 Back-scattered electron imaging of particles (top left) and (from top to bottom and left to
right), Si, O, Fe, Pb, and Mn EDS mapping in a carbonated soil contaminated by PbS particles after
3 months of aging in wet and temperate conditions
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
407
structures (e.g., McKenzie 1989), and many experiments were performed to better
understand the relationship between these two groups. The main results obtained are
summarized in this section.
7.2.3.1 Influence of the Chemical Composition of Layered Precursor
Studies performed in laboratory conditions regularly showed that the conversion
from phyllomanganate to tectomanganate is possible, and that the size of the
tectomanganate tunnels depends on the nature of the interlayer cation present in
the phyllomanganate precursor. For example, it was shown that Mg
2+ -saturated
precursors transform into synthetic todorokite, while Na
+
-saturated precursors produce synthetic cryptomelane. A few examples of the influence of the initial interlayer
cation, when of relevance for soils, on the nature of the obtained tectomanganate are
presented in Table 7.2.
Fig. 7.5 Back-scattered electron imaging of particles (top left) and (from top to bottom and left to
right), Si, O, Fe, Pb, and Mn EDS mapping in a carbonated soil contaminated by PbS particles after
3 months of aging in wet and temperate conditions
7 The Nature of Manganese Oxides in Soils and Their Role as Scavengers of Trace. . .
407