Search results for "Geochemistry"

Uranyl sorption onto birnessite: A surface complexation modeling and EXAFS study

2014

This work investigates the mechanism of the uranyl interaction with birnessite, one of the most common layer-type MnO2 mineral at the Earth's surface, by coupling macroscopic (surface complexation experiments) and microscopic (EXAFS measurements) approaches. The sorption of uranyl on synthetic hexagonal birnessite, the low-pH birnessite form, was studied under various conditions of pH (3–6), electrolyte backgrounds (0.1 M NaClO4, NaNO3 and Na2CO3), and solid/liquid ratios (from 0.27 to 4.5 g/L). Sorption isotherms exhibit a complex form indicative of at least two types of sorption sites. EXAFS data reveal the presence of two equatorial O shells at ca. 2.32 Å and 2.46 Å for all the samples, …

Identification of metalloporphyrins extracted from the copper bearing black shale of fore sudetic monocline (Poland)

2006

Abstract Metalloporphyrins were isolated from copper-bearing black shale ores. The shale originates from the Lubin copper mine (Poland). The porphyrins have been extracted by way of a Soxhlet apparatus, and then purified using column chromatography. In order to identify the extracted porphyrins complexes UV–Vis, mass spectrometry and EPR analytical techniques have been used.

Magma and volatile supply to post-collapse volcanism and block resurgence in Siwi caldera (Tanna Island, Vanuatu arc)

2011

Siwi caldera, in the Vanuatu arc (Tanna island), is a rare volcanic complex where both persistent eruptive activity (Yasur volcano) and rapid block resurgence (Yenkahe horst) can be investigated simultaneously during a post-caldera stage. Here we provide new constraints on the feeding system of this volcanic complex, based on a detailed study of the petrology, geochemistry and volatile content of Yasur-Siwi bulk-rocks and melt inclusions, combined with measurements of the chemical composition and mass fluxes of Yasur volcanic gases. Major and trace element analyses of Yasur-Siwi volcanic rocks, together with literature data for other volcanic centers, point to a single magmatic series and p…

Special issue on pattern recognition techniques in data mining

2017

Peer Reviewed

Sedimentological and diagenetic influences on low permeability properties of the Middle Jurassic limestones (Paris Basin, France)

2009

A detailed sedimentological, geochemical and mineralogical study is carried out on the Early Bajocian to Early Callovian (Middle Jurassic) limestones of the Paris Basin. Deposits include 18 lithofacies which are stacked into 10 third-order depositional sequences. Our geochemical study including a compilation of bibliographic data allows us to refine the existing sea surface palaeotemperature pattern. A cooling from the latest Early Bajocian to the Late Bajocian and a subsequent warming from the earliest Callovian to the Early/Middle Callovian transition are described using a proxy of sea surface temperatures. Together with δ13C and mineralogical data, our new δ18O values suggest a palaeo-cl…

Solid-state compatibility of Ca:LaNbO4 with perovskite cathodes: Evidences from X-ray microspectroscopy

2022

The solid-state compatibility between calcium-doped lanthanum niobate and three perovskite cathode materials was investigated using two X-ray microbeam techniques, micro X-ray fluorescence and micro X-ray absorption spectroscopy. The cathode powders (lanthanum strontium ferrite, either cobalt or copper-doped, and lanthanum strontium cobaltite) in contact with the dense electrolyte pellet were annealed at 1150 degrees C for 12-144 h to simulate the effect of thermal stresses due to fabrication and long-term operation. As a result, several interdiffusion phenomena were then observed on the bilayer cross-sections: in particular, the chemical state and coordination environment of calcium, iron,…

Uptake of actinides by calcium silicate hydrate (C-S-H) phases

2018

Abstract The sorption of actinides (Th, U – Am) was studied in dependence of the solid-to-liquid (S/L) ratio (0.5–20.0 g/L) and the calcium-to-silicon (C:S) ratio. The C:S ratio was varied between 1.80 and 0.70 to simulate the changing composition of the C-S-H phases during cement degradation from high to low C:S ratios. The decrease of the calcium content in the C-S-H phases by time is accompanied by a decrease in pH in the corresponding suspensions from 12.6 to 10.2. X-ray photoelectron spectroscopy (XPS) of the C-S-H phases showed an increasing depletion of Ca on the surface with increasing C:S ratio in comparison to the composition of the solid phase as a whole. The sorption experiments…

Thin crust and exposed mantle control sulfide differentiation in slow-spreading ridge magmas

2017

Comparative high-resolution chemostratigraphy of the Bonarelli Level from the reference Bottaccione section (Umbria-Marche Apennines) and from an equ…

2006

The Bonarelli Level (BL) from the upper Cenomanian portion of the reference Bottaccione section (central Italy) is characterized by the presence of black shales containing high TOC concentrations (up to 17%) and amounts of CaCO3 near to zero. In the absence of carbonate and, consequently, of relative carbon- and oxygen-isotopic data, the elemental geochemistry revealed to be a very useful tool to obtain information about the palaeoclimatic and palaeoceanographic evolution of the Tethys Ocean during the OAE2. Based on several geochemical proxies (Rb, V, Ni, Cr, Si, Ba), the BL is interpreted as a high-productivity event driven by increasingly warm and humid climatic conditions promoting an a…

Investigating the impact of anthropogenic land use on a hemiboreal lake ecosystem using carbon/nitrogen ratios and coupled-optical emission spectrosc…

2019

Anthropogenic impacts on lake ecosystems have increased substantially towards the present. However, the strength and timing in most cases are not evaluated in detail, missing valuable information on the response and recovery of an aquatic system. In this study, we use the sediment total organic carbon/total nitrogen ratio (C/N) and inductively coupled-optical emission spectroscopy (ICP-OES) elements and the available information about the biological processes to explore anthropogenic land use impact on the lake ecosystem. As a case study we selected a hemiboreal lake Trikātas (Latvia, NE Europe). The Pearson correlation was used to statistically test the correlations of all variables. Our r…