کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
10565746 | 971963 | 2015 | 10 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Amorphous As-sulfide precipitates from the shallow-water hydrothermal vents off Milos Island (Greece)
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
شیمی
شیمی (عمومی)
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چکیده انگلیسی
Amorphous orpiment-like As-sulfides (As2S3) are the most common As phases precipitating in hydrothermal systems, yet there is a lack of information regarding their solid-state characterization. Using a combination of optical, SEM-EDS, micro-Raman and XANES/EXAFS applications, we investigated yellow-orange As- and S-rich sediments occurring in the shallow-water hydrothermal system off the coast of Milos Island, Greece. The precipitates have several morphologies, but are dominantly colloidal. Intriguing “biological” morphologies also exist (e.g., cell-like (~ 10 μm), spirals (~ 20 μm), and rounded “cinnamon bun” shapes (~ 20 μm)). SEM-EDS data indicated that the precipitates have an As:S ratio similar to orpiment (average = 0.58, range 0.51-0.63; n = 8). Micro-Raman spectra indicated that orange colored precipitates appear to be dominated by poorly crystalline and/or amorphous arsenic sulfides with micro-amounts of more crystalline orpiment and impure sulfur. The yellow sediments also contained crystalline elemental sulfur in the form S8. Bulk As K-edge XANES spectra of the As-sulfide precipitates proved a valence of As corresponding to orpiment-type (As2S3) compounds (â 1 to + 3). EXAFS fitting results indicated that the studied material exhibits an amorphous orpiment-like structure with As ions coordinated by 3 sulfur atoms (CN = 3.0). The As-S interatomic distance of the first shell is calculated at 2.279 Ã
and the Debye-Waller factor (Ï2) is 0.00427. These data suggest that the modeled structure of the studied precipitates is slightly S-deficient and ordered only in the first shell around As, resembling an orpiment-type structure, whereas higher shells are not present and must be disordered. The disorder phenomenon may be strictly produced either by the existence of occasional As-S-As bridges with As-As bonds or by the occurrence of As-O-As bridges, causing twisting of the AsS3 pyramids in the initial orpiment structure. This distortion in the higher coordination shells of the structural sheets creates the amorphous orpiment.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Marine Chemistry - Volume 177, Part 5, 20 December 2015, Pages 687-696
Journal: Marine Chemistry - Volume 177, Part 5, 20 December 2015, Pages 687-696
نویسندگان
A. Godelitsas, R.E. Price, T. Pichler, J. Amend, P. Gamaletsos, J. Göttlicher,