With the aim to shed a light on this mechanism, two tremolite samples, one from Italy (Castelluccio) and one from USA (Maryland), immersed in a buffer solution (pH 7.4) with H2O2 were characterized by a multi-technique approach.
A particular focus lies on a discussion of processes (redox transformations, complexation, sorption, precipitation, dissolution, evaporation, diffusion, biological cycling) which are able to induce metal stable isotope fractionation in environmental systems.
Liquid water on equatorial Mars is inconsistent with large-scale climatic conditions. Humidity and temperature measurements by the Curiosity rover support the formation of subsurface liquid brines by hydration of perchlorates during the night.
Ath Godelitsas's insight:
Perchlorates are widespread on the surface of Mars and it is expected that liquid brines are abundant beyond equatorial regions where atmospheric humidity is higher and temperatures are lower.
XAS results show that Zn(II) adsorbs as tetrahedral and octahedral triple-corner-sharing complexes at layer vacancy sites when reacted with birnessite in the absence of Mn(II). Addition of aqueous Mn(II) causes no discernible change in Zn(II) surface speciation at pH 6.5, but triggers conversion of adsorbed Zn(II) into spinel Zn(II)1–xMn(II)xMn(III)2O4 precipitates at pH 7.5. This conversion is driven by electron transfer from adsorbed Mn(II) to structural Mn(IV) generating Mn(III) surface species that coprecipitate with Zn(II) and Mn(II).
The authors report results of chemical imaging experiments using environmental scanning electron microscopy (ESEM) and scanning transmission X-ray microscopy (STXM) to investigate the LLPS of micrometer-sized particles undergoing a full hydration-dehydration cycle.
The Kos-Nisyros volcanic centre is a long-active, Plio-Pleistocene magmatic system in the subduction zone along the easternmost edge of the active Hellenic volcanic arc in the Aegean Sea. Although today there are signs of relative quiescence in volcanic activity, active onshore fumaroles and shallow-sea hydrothermal vents persist on, amongst others, the island of Kos. The present study explores the large-scale imprint of hydrothermally sourced heavy metals and nutrients on the island’s coastal marine environment, based on geochemical data collected in September 2007 from hydrothermal waters and surficial nearshore sediments (<10 m water depth) at several vents in the Bros Thermi and Kephalos Bay hydrothermal fields.
Biotite and vermiculite can be directly applied as a promising and sustainable alternative to the use of classical K fertilizers, illite can be utilized in combination with soluble K fertilizers, whereas muscovite, phlogopite and smectite may not be suitable for plant growth.
The authors show through magnetic and spectroscopic measurements that the phototrophic Fe(II)-oxidizing bacterium Rhodopseudomonas palustris TIE-1 oxidizes magnetite (Fe3O4) nanoparticles using light energy.
The authors have analyzed -at nanoscale level- the calcite/clay assembly, the main constituents of argillite, under storage conditions and show the fragility of the montmorillonite with respect to calcite.
The processes that create economic-grade accumulations of metals above magma chambers are unclear. High-temperature laboratory experiments show that rapid reactions between magmatic gases and Earth's crust can trigger efficient metal deposition.
Ath Godelitsas's insight:
The authors use high-temperature laboratory experiments to show that a very rapid chemisorption reaction occurs between sulphur dioxide gas, a principal component of magmatic gas mixtures, and calcic feldspar, an abundant mineral in the arc crust. The chemisorption reaction generates the mineral anhydrite and hydrogen sulphide gas, and triggers deposition of metal sulphides.
Chabazite is typically synthesized in 1 M KOH solutions but also crystallizes in simulated young cement pore water, a pH 13 aqueous solution mainly containing K+ and Na+ cations. Its formation and stability in this medium was evaluated as a function of temperature (60 and 85 °C) over a timeframe of more than 2 years and was also asessed from a mechanistic point of view. Chabazite demonstrates excellent cation-exchange properties in simulated young cement pore water.
The main phases of the lower mantle, bridgmanite and ferropericlase, do not show any structural transitions at these depths, so only moderate and smooth viscosity variations are expected with depthto at least ~2,500 km. The reason for slab stagnation, which may also lead to the formation of chemically distinct reservoirs in Earth’s deep mantle, is therefore unclear. The authors have used synchrotron radial X-ray diffraction to measure in situ the deformation behaviour of ferropericlase at pressures of up to 96 GPa.
Above 80 GPa, in situ synchrotron infrared experiments show the unequivocal spectroscopic signature of the high-pressure phase of (Mg,Fe)CO3. Using ab-initio calculations, the authors assign the new infrared signature to C–O bands associated with tetrahedrally coordinated carbon with asymmetric C–O bonds. Tetrahedrally coordinated carbonates are expected to exhibit substantially different reactivity than low-pressure threefold coordinated carbonates, as well as different chemical properties in the liquid state.
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