The Fate of Vanadium-Bearing Iron Oxyhydroxides in Marine Sediments: Integrating Gel-Based In Situ Mineral Probes with Synchrotron X-ray Fluorescence Microspectroscopy
Felicia J. Haase*, Ryo Sekine, Nicholas J. C. Doriean, Daryl L. Howard, David T. Welsh, Yun Wang, Jessica Hamilton, Donald E. Canfield, Enzo Lombi and William W. Bennett,
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引用次数: 0
Abstract
Vanadium (V) is a redox-sensitive trace metal often used as a paleoredox proxy in ancient marine sediments. However, our understanding of the early diagenesis of V is limited to laboratory-based simulations and bulk geochemical measurements of natural sediments. Microscale measurements are essential to exploring V geochemistry in organic-rich coastal sediments, where redox zonation changes over small spatial scales. Here, we describe an innovative in situ two-dimensional (2D) imaging approach to study redox-driven changes of V-bearing iron oxyhydroxides (lepidocrocite and ferrihydrite) in intertidal mudflat sediments of an Australian lagoon lake (Coombabah Lake, Queensland). Vanadium-bearing iron oxyhydroxides were suspended in a polyurethane-based hydrogel matrix, loaded on laser-cut acrylic probes, and exposed to mudflat sediments for up to 6 weeks. Changes in V speciation and Fe mineralogy were examined using synchrotron-based X-ray fluorescence (XRF) microspectroscopy for high-resolution chemical imaging of elemental (V, S, Fe) distributions combined with micro-X-ray absorption near-edge structure (μXANES) spectroscopy at the V and Fe K-edges for speciation analysis. Linear combination fitting of μXANES data revealed that solid-phase VV was reduced to VIV in the ferruginous zone of sediments and to a mixture of mainly VIV and some VIII (up to 10–20%) in the sulfidic zone, where the reduction correlated with the degree of sulfidation and conversion of the iron oxyhydroxides to FeS (up to 96%). The combination of gel-based mineral probes with synchrotron-based μXRF tools can unravel small-scale geochemical relationships and provide new insights into the early diagenesis of trace elements in marine sediments.
钒(V)是一种对氧化还原反应敏感的痕量金属,经常被用作古海洋沉积物中的古氧化还原替代物。然而,我们对钒的早期成因的了解仅限于实验室模拟和对天然沉积物的大量地球化学测量。在富含有机质的沿岸沉积物中,氧化还原分带会在较小的空间尺度上发生变化,因此微尺度测量对探索这些沉积物中的 V 地球化学至关重要。在这里,我们描述了一种创新的原位二维(2D)成像方法,用于研究澳大利亚泻湖(昆士兰州库姆巴湖)潮间带泥滩沉积物中含钒铁氧氢氧化物(鳞斑铁和铁酸盐)的氧化还原驱动变化。含钒铁氧氢氧化物悬浮在聚氨酯水凝胶基质中,装载在激光切割的丙烯酸探针上,并暴露在泥滩沉积物中长达 6 周。利用同步辐射 X 射线荧光 (XRF) 显微光谱对元素(V、S、F)分布进行高分辨率化学成像,并结合 V 和 Fe K 边缘的微 X 射线吸收近边结构 (μXANES)光谱进行标样分析,从而检测 V 标样和 Fe 矿物学的变化。μXANES数据的线性组合拟合显示,固相VV在沉积物的铁锈带被还原为VIV,在硫化带则被还原为主要是VIV和部分VIII(高达10-20%)的混合物,还原程度与硫化程度和铁氧氢氧化物转化为FeS(高达96%)相关。基于凝胶的矿物探针与基于同步辐射的μXRF工具相结合,可以揭示小尺度地球化学关系,并为海洋沉积物中微量元素的早期成因提供新的见解。
期刊介绍:
The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.