Clays and Clay Minerals, Vol. 57, No. 6, 715–724, 2009.
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Authors
Cui, Haojie
Qiu, Guohong
Feng, Xionghan
Tan, Wenfeng
Liu, Fan
Issue Date
2009
Type
Article
Language
Keywords
Periodicals , Geology , AOS , Atmospheric Pressure , Birnessite , Todorokite
Alternative Title
Birnessites With Different Average Manganese Oxidation States synthesized, Characterized, And Transformed To Todorokite At atmospheric Pressure
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) byco ntrolling 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 successfullyin stronglyalkaline media. The (Na,K)- birnessites and Na-birnessites prepared in NaOH clearlycontained 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+ initiallywi thin (Na,K)-birnessites could not be completelyion-excha nged withMg2+ to form todorokite at atmospheric pressure. No todorokite was forthcoming from K-birnessites even from those with small AOS values (3.50).
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Citation
Clays and Clay Minerals, Vol. 57, No. 6, 715–724, 2009.
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