『Abstract
Todorokite is a common Mn oxide mineral in terrestrial and ocean-floor
environments, and it is commonly synthesized from layered Na-buserite.
Pyrophosphate, which is known to form strong complexes with Mn(III)
at a pH range of 1-8, was added to a suspension of Na-buserite
in order to sequester the available Mn(III) in Na-buserite. No
Mn(III)-pyrophosphate complex was formed in solution at pH 10,
and the treated Na-buserites were concerted completely to todorokite.
Significant transformation reductions were observed when Na-buserite
was treated with pyrophosphate solution at pH 7. The presence
of Mn(III) within the MnO6 octahedral sheets
of Na-buserite is critical for the transformation from layered
buserite to tunnel-structured todorokite at atmospheric pressure.
At lower pH, two effects are combined to reduce the amount of
Mn(III) in the layers: (1) the complexing power of pyrophosphate
is increased; and (2) the transformation from Na-buserite to H-birnessite,
which is concomitant with the migration of Mn(III) from layers
to the interlayer, and the partial disproportionation of Mn(III).
The results showed that Mn(III) played a key role in the transformation
of layered Na-buserite to tunnel-structures todorokite at atmospheric
pressure.
Key Words: Buserite; Mn oxide; Todorokite; Transformation; Refluxing.』
Introduction
Experimental
Preparation of Na-buserite
Treatments of Na-buserite using Na4P2O7 solutions
Ion-exchange of Na-buserite and subsequent conversion to todorokite
Methods of analysis
Measure of Mn(III)-pyrophosphate complex
X-ray diffraction analysis
Transmission electron microscopy measurement
Results
Effect of pH in Na4P2O7 solutions on the phase transformation from Na-buserite
to todorokite
Effect of Na4P2O7 concentration at pH 7 on the phase transformation
from Na-buserite to todorokite
Effect of Na4P2O7 treatment time on phase transformation from
Na-buserite to todorokite
Effect of reflux time on the phase transformation from Na-buserite
to todorokite
Discussion and conclusions
Acknowledgments
References