17:15 〜 18:45
[SCG48-P23] 化学浸出法による深海堆積物中の海水由来Os同位体分析手法の実験的検討
キーワード：遠洋性粘土、石灰質軟泥、Os同位体、層序年代、化学浸出法
Deep-sea sediments are widely attracting attention as a recorder of geochemical cycle in the Earth’s surficial system. Some types of sediments concentrate specific elements such as rare-earth elements and, thus, can be a new resource for the industrially critical materials [1,2], as well as a paleoenvironmental archive [3].
To reconstruct the (pale)oceanographic record from marine sediments and elucidate the concentration mechanism of rare-earth elements in pelagic clay, the depositional age is crucial information. The marine osmium (Os) isotope ratio has changed through the geologic time and the Os isotope stratigraphy was applied to determine the depositional ages of pelagic clay that hardly contain calcareous/siliceous microfossils [3]. The Os isotope ratio in seawater has been recorded in sediments as the hydrogenous component. In the Os isotope analysis for this purpose, various digestion and leaching methods have been used to extract the hydrogenous Os from the sediments. However, the Os fraction extracted by these methods, and whether their Os isotope ratios are equivalent to the seawater value, have not been quantitatively evaluated. Furthermore, to extend the valuable Os isotope dataset more easily, it is important to establish an efficient analytical protocol.
In this study, we aim to propose an appropriate and efficient method to extract hydrogenous Os from deep-sea sediments. Using pelagic clay and calcareous ooze samples, we implemented extraction experiments by chemical leaching methods with comparing the results to those with the inverse aqua regia digestion method. The concentration and isotope ratios of Os and rhenium (Re) were measured using a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS), and the chemical compositions of the residues and extracted solutions were analyzed using an ICP-QMS. We also analyzed changes in mineral composition by using XRD. Our results suggest that the chemical leaching method using 1 M HCl could effectively extract marine osmium from pelagic clay selectively. On the other hand, for calcareous ooze samples, the Os isotope ratios were almost identical regardless of processing protocols.
[1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Iijima et al. (2016) Geochemical Journal 50, 557-573. [3] Ohta et al. (2020) Scientific Reports 10, 9896.
To reconstruct the (pale)oceanographic record from marine sediments and elucidate the concentration mechanism of rare-earth elements in pelagic clay, the depositional age is crucial information. The marine osmium (Os) isotope ratio has changed through the geologic time and the Os isotope stratigraphy was applied to determine the depositional ages of pelagic clay that hardly contain calcareous/siliceous microfossils [3]. The Os isotope ratio in seawater has been recorded in sediments as the hydrogenous component. In the Os isotope analysis for this purpose, various digestion and leaching methods have been used to extract the hydrogenous Os from the sediments. However, the Os fraction extracted by these methods, and whether their Os isotope ratios are equivalent to the seawater value, have not been quantitatively evaluated. Furthermore, to extend the valuable Os isotope dataset more easily, it is important to establish an efficient analytical protocol.
In this study, we aim to propose an appropriate and efficient method to extract hydrogenous Os from deep-sea sediments. Using pelagic clay and calcareous ooze samples, we implemented extraction experiments by chemical leaching methods with comparing the results to those with the inverse aqua regia digestion method. The concentration and isotope ratios of Os and rhenium (Re) were measured using a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS), and the chemical compositions of the residues and extracted solutions were analyzed using an ICP-QMS. We also analyzed changes in mineral composition by using XRD. Our results suggest that the chemical leaching method using 1 M HCl could effectively extract marine osmium from pelagic clay selectively. On the other hand, for calcareous ooze samples, the Os isotope ratios were almost identical regardless of processing protocols.
[1] Kato et al. (2011) Nature Geoscience 4, 535-539. [2] Iijima et al. (2016) Geochemical Journal 50, 557-573. [3] Ohta et al. (2020) Scientific Reports 10, 9896.