Cui,H., Qiu,G., Feng,X., Tan,W. and Liu,F.(2010): Birnessites with different average manganese oxidation states synthesized, characterized, and transformed to todorokite at atmospheric pressure. Clays and Clay minerals, 57(6), 715-724.

『大気圧下で合成され、特徴付けされ、轟石へ変化した、異なる平均マンガン酸化状態をもつバーネス鉱』

『Abstract
　Todorokite is a common manganese oxide mineral, with a tunnel structure, found in Earth surface environments, and is easily synthesized from layered birnessite. The aim of the current study was to prepare birnessites with different average manganese oxidation states (AOS) by controlling the MnO4-/Mn2+ ratio in concentrated NaOH or KOH. A series of (Na,K)-birnessites, Na-birnessites, and K-birnessites with different AOS was synthesized successfully in strongly alkaline media. The (Na,K)-birnessites and Na-birnessites prepared in NaOH clearly contained both large (500-1000 nm) and small (40-400 nm), plate-shaped crystallites. The K-birnessites prepared in KOH media consisted mostly of irregular (100-200 nm), plate-shaped crystallites. The degree of transformation of birnessite to todorokite at atmospheric pressure decreased as the AOS values of (Na,K)-birnessites and Na-birnessites increased from 3.51 to 3.80. No todorokite was present when a Na-birnessite with an AOS value of 3.87 was used as the precursor. Pyrophosphate, which is known to form strong complexes with Mn3+ at a pH range of 1-8, was added to a suspension of (Na,K)-birnessites in order to sequester the available Mn3+ in (Na,K)-birnessites. Removal of Mn3+ from birnessite MnO6 layers by pyrophosphate restricted transformation to todorokite - no (Na,K)-birnessite transformed to todorokite after pyrophosphate treatment. The interlayer K+ initially within (Na,K)-birnessites could not be completely ion-exchanged with Mg2+ to form todorokite at atmospheric pressure. No todorokite was forthcoming from K-birnessites even from those with small AOS values (3.50.

Key Words: AOS; Atmospheric pressure; Birnessite; Todorokite.』

Introduction
Materials
　Preparation of birnessites with different AOS values
　Pyrophosphate treatment of (Na,K)-birnessite and Mn(III)-pyrophosphate-complex measurement
　Mg2+-reflux treatment: MgCl2 treatment of birnessite and subsequent conversion to todorokite
Analytical methods
　Elemental analysis, AOS determination, and infrared (IR) analyses
　X-ray diffraction studies
　Transmission electron microscopy measurements
Results
　Characterization of synthetic birnessites
　Buserite formation by Mg2+ exchange
　Formation of todorokite by refluxing reaction
　The effect of Na4P2O7 on birnessite-to-todorokite transformation
Discussion
Summary
Acknowledgments
References


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