Visual and in situ Raman spectroscopic observations of the liquid-liquid immiscibility in aqueous uranyl sulfate solutions at temperatures up to 420 °c

The phase behaviors of aqueous UO2SO4 solutions were investigated in situ with a microscope and a Raman spectrometer at temperatures from 25 to 420 °C. Results show that aqueous UO2SO4 solution separated into UO2SO4-rich (Urich) and UO2SO4-poor (Upoor) liquid phases coexisted with a vapor phase at =285.8 ± 0.5 °C. Both visual and Raman spectroscopic investigations suggest that a reversible strong UO2 2+-SO4 2- association was responsible for the liquid-liquid immiscibility in aqueous UO2SO4 solutions. Main evidences were summarized as: (1) the liquid-liquid phase separation temperature decreases with increasing UO2SO4 concentration up to 0.54 mol/kg, and then increased at greater concentrations, characterizing a lower critical solution temperature (LCST) at 285.8 °C ± 0.5 °C. LCST is commonly accepted as a diagnostic feature of polymer solutions; (2) analyses of the shapes of the Raman spectra of v1(UO2 2+) and v1(SO4 2-) bands show that the UO2 2+-SO4 2- association becomes stronger at elevated temperatures, especially in the immiscible Urich phase; and (3) with increasing temperature, the Urich phase becomes more concentrated, whereas the Upoor phase becomes more dilute, indicating that the hydration of UO2 2+ and SO4 2- cannot be maintained in the Urich phase. Destruction of the hydration spheres of UO2 2+ and SO4 2- further favors the ion association in the Urich phase. These results are important for describing similar sulfate solutions at elevated temperatures, especially under supercritical conditions

Program and abstract volume

This "workshop is aimed at bringing together martian mineralogists, geochemists, and other interested scientists to discuss the mineralogical and chemical evidence for hydrous environments and the potential insights into their nature that numerical modeling, laboratory experiments, theory, and spacecraft data analysis can provide."Lunar and Planetary Institute, National Aeronautics and Space Administrationscientific organizing committee, Susanne Schwenzer, David Kring, Stephen Clifford ; scientific organizing committee, Oleg Abramov ... [and others]PARTIAL CONTENTS: Delivery and Redistribution of Volatiles on Mars During the Basin-forming Epoch: An Overview--Impact-generated Hydrothermal Systems in Mafic to Ultramafic Noachian Crust on Mars--Geochemical Models of Reactions of Seawater and Meteoric Water with Basalt and Peridotite--The Duration of Chemical Weathering of Gusev Crater's Wishstone-Watchtower Sequence

Growth and structure of CaCO3

Organisms often employ non-classical crystallisation mechanisms to create the remarkable materials that are biominerals. These materials often surpass their synthetic counterparts in terms of physical properties, morphologies and structural organisation. The non-classical mechanisms employed include the controlled formation, transition and release of amorphous precursor material, and the oriented attachment/ nucleation of nano sized particulates. Combined, these strategies are capable of generating hierarchically ordered superstructures. Both of these mechanisms operate under ambient conditions in a physically delimited environment of body fluids, which enables precise regulation of the solution composition. This thesis describes a range of biomimetic studies which have investigated key aspects in the formation and structural organization of calcium carbonate. Of interest were the influence of additives and physical confinement on the formation and transformation of amorphous calcium carbonate (ACC). The studies revealed that both of these factors play key roles in controlling ACC crystallisation. Additives which inhibit crystallisation in solution can accelerate transformation of ACC in the solid state. This effect was observed for all of the larger molecules examined, while the small molecules retarded crystallisation in both solution and the solid state. Investigation of ACC crystallisation in confinement, in turn, demonstrated that ACC dehydrates prior to crystallizing even in solution, and that nucleation of the first crystal phase in solution must occur by dissolution/ reprecipitation. Studies were also performed to characterise the “ammonia diffusion method” which is widely used in the precipitation of calcium carbonate. Despite this, virtually nothing is known about the changes in solution conditions which occur during this process. The analysis showed that the supersaturation remains relatively high and constant throughout most of the process, which potentially enables multiple nucleation events to occur in a single experiment. These results were then used to develop a one pot method which offers comparable reaction conditions. Finally, Bragg coherent diffraction imaging (BCDI) was used to characterise calcite crystals precipitated on self-assembled monolayers (SAM), where these provide a mimic of the organic matrices used to control crystallisation in organisms. Initial observations of the growth and dissolution of calcite by BCDI allowed the visualization of the 3D dislocation network present within a single crystal. Examination of crystals grown on SAMs, in contrast, showed that a build-up strain causes the formation of a single dislocation loop, where this is correlated with the morphological development of the crystal

Assessing the relationship between the soil dielectric constant and electrical conductivity using 5TE sensors in the field conditions

Postprint (published version

Clay Mineral Transformations after Bentonite/Clayrocks and Heater/Water Interactions from Lab and Large-Scale Tests

This book, “Clay Mineral Transformations after Bentonite/Clayrocks and Heater/Water Interactions from Lab and Large-Scale Tests”, covers a broad range of relevant and interesting topics related to deep geological disposal of nuclear fuels and radioactive waste. Most countries that generate nuclear power have developed radioactive waste management programmes during the last 50 years to emplace long-lived and/or high-level radioactive wastes in a deep underground repository in a suitably chosen host rock formation. The aim is to remove these wastes from the human environment. If a site is properly chosen, a repository system comprising both natural and engineered barriers would provide a high level of protection from the toxic effects of the waste.The 17 papers published in this Special Issue show that bentonites and clayrocks are an essential component of the multi-barrier system ensuring the long-term safety of the final disposal of nuclear waste. The efficiency of such engineered and natural clay barriers relies on their physical and chemical confinement properties, which should be preserved in the long-term

The Origin and Early Evolution of Life

What is life? How, where, and when did life arise? These questions have remained most fascinating over the last hundred years. Systems chemistry is the way to go to better understand this problem and to try and answer the unsolved question regarding the origin of Life. Self-organization, thanks to the role of lipid boundaries, made possible the rise of protocells. The role of these boundaries is to separate and co-locate micro-environments, and make them spatially distinct; to protect and keep them at defined concentrations; and to enable a multitude of often competing and interfering biochemical reactions to occur simultaneously. The aim of this Special Issue is to summarize the latest discoveries in the field of the prebiotic chemistry of biomolecules, self-organization, protocells and the origin of life. In recent years, thousands of excellent reviews and articles have appeared in the literature and some breakthroughs have already been achieved. However, a great deal of work remains to be carried out. Beyond the borders of the traditional domains of scientific activity, the multidisciplinary character of the present Special Issue leaves space for anyone to creatively contribute to any aspect of these and related relevant topics. We hope that the presented works will be stimulating for a new generation of scientists that are taking their first steps in this fascinating field

Computational and experimental studies of selected magnesium and ferrous sulfate hydrates: implications for the characterisation of extreme and extraterrestrial environments

Magnesium sulfate hydrates are considered important rock-forming minerals on the outer three Galilean moons of Jupiter (i.e., Europa, Ganymede, Callisto) and, alongside ferrous sulfate hydrates, are promising candidate minerals for the widespread sulfate deposits that occur in the equatorial region of Mars. In such extraterrestrial environments, these minerals experience extreme high-pressure conditions in the interiour of the Galilean moons and low temperature conditions on the surface of these moons and Mars. The aim of this thesis is to understand the structural stability, compressibility, and thermal expansion of these compounds in such extreme environments and aid their identification in ongoing and future space missions. Most magnesium sulfate hydrates lack accurate reference elastic tensors, which hinders their seismological identification in lander missions on the icy moons of the outer solar system, as envisioned for the near future. In this thesis, the accuracy of recent advancements in density functional theory to predict the compressibility and elastic constants of icy satellite candidate minerals (i.e., epsomite (MgSO₄·7H₂O), gypsum (CaSO₄·2H₂O), carbon dioxide (CO₂), and benzene (C₆H₆)) was assessed by benchmarking them against experimental reference data from the literature. Key findings are that density functional theory calculations do not yield elastic constants accurate enough to be used as a reference for the seismic exploration of icy moons. However, the bulk compressibility of such materials is very accurately reproduced by density functional theory, which was therefore used to predict the compressibility of the icy satellite candidate minerals starkeyite (MgSO₄·4H₂O) and cranswickite (MgSO₄·4H₂O). Knowledge of the compressibility of such minerals is critical to model mantle processes (e.g., salt diaprisim, plate tectonics, subduction) and the density structure of the outer three Galilean moons. The thermal expansion and structural stability of three sulfate minerals (i.e., rozenite (FeSO₄·4H₂O), starkeyite, and cranswickite) was characterised for the first time using neutron diffraction. Cranswickite transforms to starkeyite at 330 K, well above the maximum surface temperature of 308 K hitherto reported on Mars. Starkeyite likely undergoes a structural phase transition at around 245 K. The structure of this proposed low-temperature polymorph could not be determined but would be of great interest since the temperature drops below 245 K on equatorial Mars at night-time. Starkeyite was also studied by means of synchrotron X-ray diffraction but suffered radiation damage. No phase transition was observed in rozenite from 290 – 21 K, which contrasts with Raman data reported in the literature, where sharpening of vibrational modes upon cooling was misinterpreted as mode splitting and evidence for two phase transitions at temperatures relevant to the Martian surface. First-principles phonon frequency calculations provide evidence supporting the absence of vibrational mode splitting. A workflow to obtain reliable reference Raman spectra for space exploration was proposed and an optical centre stick for the simultaneous acquisition of neutron diffraction and Raman spectroscopy data at the HRPD instrument was commissioned. Lastly, the structure of a polymorph of hexahydrite (MgSO₄·6H₂O), most recently proposed in the literature, was shown to be unambiguously wrong

Fluid-rock interactions in a carbon storage site analogue, Green River, Utah

Pagination differs from hardbound copy deposited in Cambridge University Library.Reactions between CO2-charged brines and reservoir minerals might either enhance the long-term storage of CO2 in geological reservoirs or facilitate leakage by corroding cap rocks and fault seals. Modelling the progress of such reactions is frustrated by uncertainties in the absolute mineral surface reaction rates and the significance of other rate limiting steps in natural systems. This study uses the chemical evolution of groundwater from the Jurassic Navajo Sandstone, part of a leaking natural accumulation of CO2 at Green River, Utah, in the Colorado Plateau, USA, to place constraints on the rates and potential controlling mechanisms of the mineral-fluid reactions,under elevated CO2 pressures, in a natural system. The progress of individual reactions, inferred from changes in groundwater chemistry is modelled using mass balance techniques. The mineral reactions are close to stoichiometric with plagioclase and K-feldspar dissolution largely balanced by precipitation of clay minerals and carbonate. Mineral modes, in conjunction with published surface area measurements and flow rates estimated from hydraulic head measurements, are then used to quantify the kinetics of feldspar dissolution. Maximum estimated dissolution rates for plagioclase and K-feldspar are 2x10-14 and 4x10-16 mol·m-2·s-1, respectively. Fluid ion-activity products are close to equilibrium (e.g. DGr for plagioclase between -2 and -10 kJ/mol) and lie in the region in which mineral surface reaction rates show a strong dependence on DGr. Local variation in DGr is attributed to the injection and disassociation of CO2 which initially depresses silicate mineral saturation in the fluid, promoting feldspar dissolution. With progressive flow through the aquifer, feldspar hydrolysis reactions consume H+ and liberate solutes to solution which increase mineral saturation in the fluid and rates slow as a consequence. The measured plagioclase dissolution rates at low DGr would be compatible with far-from-quilibrium rates of ~1x10-13 mol·m-2·s-1 as observed in some experimental studies. This suggests that the discrepancy between field and laboratory reaction rates may in part be explained by the differences in the thermodynamic state of natural and experimental fluids, with field-scale reactions occurring close to equilibrium whereas most laboratory experiments are run far-from-equilibrium. Surface carbonate deposits and cementation within the footwall of the local fault systems record multiple injections of CO2 into the Navajo Aquifer and leakage of CO2 from the site over ca. 400,000 years. The d18O, d13C and 87Sr/86Sr of these deposits record rapid rates of CO2 leakage (up to ~1000 tonnes/a) following injection of CO2, but rates differ by an order of magnitude between each fault, due to differences in the fault architecture. Elevated pCO2 enhances rates of feldspar dissolution in the host aquifer and carbonate precipitation in fracture conduits. Silicate mineral dissolution rates decline and carbonate precipitation rates increase as pH and the CO2 charge dissipate. The Sr/Ca of calcite cements record average precipitation rates of ~2x10-6 mol/m2/s, comparable to laboratory derived calcite precipitation rates in fluids with elevated Mn/Ca and Fe/Ca, at cc of ~1 to 3. This suggests that far-from-equilibrium carbonate precipitation, which blocks fracture conduits and causes the leaking system to self-seal, driven by CO2 degassing in the shallow subsurface, can be accurately modeled with laboratory derived rates. Sandstones altered in CO2 leakage conduits exhibit extensive dissolution of hematite grain coatings and are chemically bleached as a result. Measurements of Eh-pH conditions in the modern fluid, and modeling of paleo-Eh-pH conditions using calcite Fe and Mn concentrations, suggests that the CO2-charged groundwaters are reducing, due to their low dissolved O2 content and that pH suppression due to high pCO2 is capable of dissolving and transporting large concentrations of metals. Exhumed paleo-CO2 reservoirs along the crest of the Green River anticline have been identified using volatile hosting fluid inclusions. Paleo-CO2-charged fluids mobilized hydrocarbons and CH4 from deeper formations, enhancing the reductive dissolution of hematite, which produced spectacular km-scale bleached patterns in these sediment.This work was funded by a post-graduate research grant from Shell Global Solutions International awarded to Niko Kampman