Microscale Imaging and Identification of Fe Speciation and Distribution during Fluid鈥揗ineral Reactions under Highly Reducing Conditions
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- 作者：L. E. Mayhew ; S. M. Webb ; A. S. Templeton
- 刊名：Environmental Science & Technology
- 出版年：2011
- 出版时间：May 15, 2011
- 年：2011
- 卷：45
- 期：10
- 页码：4468-4474
- 全文大小：884K
- 年卷期：v.45,no.10(May 15, 2011)
- ISSN：1520-5851
文摘
The oxidation state, speciation, and distribution of Fe are critical determinants of Fe reactivity in natural and engineered environments. However, it is challenging to follow dynamic changes in Fe speciation in environmental systems during progressive fluid鈥搈ineral interactions. Two common geological and aquifer materials鈥攂asalt and Fe(III) oxides鈥攚ere incubated with saline fluids at 55 掳C under highly reducing conditions maintained by the presence of Fe0. We tracked changes in Fe speciation after 48 h (incipient water鈥搑ock reaction) and 10 months (extensive water鈥搑ock interaction) using synchrotron-radiation 渭XRF maps collected at multiple energies (ME) within the Fe K-edge. Immediate PCA analysis of the ME maps was used to optimize 渭XANES analyses; in turn, refitting the ME maps with end-member XANES spectra enabled us to detect and spatially resolve the entire variety of Fe-phases present in the system. After 48 h, we successfully identified and mapped the major Fe-bearing components of our samples (Fe(III) oxides, basalt, and rare olivine), as well as small quantities of incipient brucite associated with olivine. After 10 months, the Fe(III)-oxides remained stable in the presence of Fe0, whereas significant alteration of basalt to minnesotaite and chlinochlore had occurred, providing new insights into heterogeneous Fe speciation in complex geological media under highly reducing conditions.