Geochemical fates and unusual distribution of arsenic in natural ferromanganese duricrust

Preferential enrichment of arsenic in iron oxides relative to manganese oxides has been well documented. In this study, however, a distinct arsenic enrichment is revealed in natural ferromanganese duricrusts, which are commonly found in natural weathering profiles of manganese-bearing carbonate rock...

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Bibliographic Details
Published in:Applied geochemistry 2017-01, Vol.76, p.74-87
Main Authors: Liu, Huan, Lu, Xiancai, Li, Juan, Chen, Xiaoye, Zhu, Xiangyu, Xiang, Wanli, Zhang, Rui, Wang, Xiaolin, Lu, Jianjun, Wang, Rucheng
Format: Article
Language:English
Subjects:
Arsenic
EXAFS
Ferromanganese duricrust
Spatial distribution
μ-XRF
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Summary:Preferential enrichment of arsenic in iron oxides relative to manganese oxides has been well documented. In this study, however, a distinct arsenic enrichment is revealed in natural ferromanganese duricrusts, which are commonly found in natural weathering profiles of manganese-bearing carbonate rocks. In the studied ferromanganese duricrust covering Carboniferous carbonates at Qixia Mountain in eastern China, stromotalite-like structures composed by hematite, goethite, pyrolusite and hetaerolite have been observed. Electron microprobe analysis (EMPA) mapping and synchrotron-based micro-scanning X-ray fluorescence (μ-XRF) analyses reveal that the arsenic content in manganese oxides is elevated with respect to iron oxide phases. For example, the arsenic content of pyrolusite is approximately 5 times as much as that of hematite or hetaerolite. However, the highest arsenic content (0.58 wt% As2O5) occurs in 2.75 (±0.96, ±σ) μm micro-bands of hematite ((FexMnIII1-x)2O3, 0.75 
ISSN:0883-2927
1872-9134
DOI:10.1016/j.apgeochem.2016.11.012