Online Differential Thermal Isotope Analysis of Hydration Water in Minerals by Cavity Ringdown Laser Spectroscopy.

We have developed a new method for measuring the isotopic composition (δ18O and δD) of different types of bonded water (e.g., molecular water, hydroxyl) contained in hydrated minerals by coupling a thermal gravimeter (TG) and a cavity ringdown laser spectrometer (CRDS). The method involves precisely step-heating a mineral sample, allowing the separation of the different types of waters that are released at different temperatures. Simultaneously, the water vapor evolved from the mineral sample is analyzed for oxygen and hydrogen isotopes by CRDS. Isotopic values for the separate peaks are calculated by integrating the product of the water amounts and its isotopic values, after correcting for background. We provide examples of the application of the differential thermal isotope analysis (DTIA) method to a variety of hydrous minerals and mineraloids including gypsum, clays, and amorphous silica (opal). The isotopic compositions of the total water evolved from a set of natural gypsum samples by DTIA are compared with the results of a conventional offline water extraction method followed by CRDS analysis. The results from both methods are in excellent agreement, and precisions (1σ) for δ18O (±0.12‰) and δD (±0.8‰) of the total gypsum hydration water from the DTIA method are comparable to that obtained by the offline method. A range of analytical challenges and solutions (e.g., spectroscopic interferences produced by VOCs in natural samples, isotopic exchange with structural oxygen, etc.) are discussed. The DTIA method has wide ranging applications for addressing fundamental problems across many disciplines in earth and planetary sciences, including paleoclimatology, sedimentology, volcanology, water exchange between the solid earth and hydrosphere, and water on Mars and other planetary bodies

Prediction of equilibrium isotopic fractionation of the gypsum/bassanite/water system using first-principles calculations

The stable isotopes (18O/16O, 17O/16O and 2H/1H) of structurally-bound water (also called hydration water) in gypsum (CaSO4•2H2O) and bassanite (CaSO4•0.5H2O) can be used to reconstruct the isotopic composition of paleo-waters. Understanding the variability of the isotope fractionation factors between the solution and the solid α17Omineral-water, α18Omineral-water and αDmineral-water) is crucial for applying this proxy to paleoclimatic research. Here we predict the theoretical equilibrium fractionation factors for triple oxygen and hydrogen isotopes in the gypsum-water and bassanite-water systems between 0 ⁰C and 60 ⁰C. We apply first-principles using density functional theory within the harmonic approximation. Our theoretical results for α18Ogypsum-water (1.00347±0.00037) are in agreement with previous experimental studies, whereas Dgypsum-water agrees only at temperatures above 25 ⁰C. At lower temperatures, the experimental values of αDgypsumwater are consistently higher than theoretical values (e.g. 0.9749 and 0.9782, respectively, at 3 ⁰C), which can be explained by kinetic effects that affect gypsum precipitation under laboratory conditions at low temperature. We predict that α18Obassanite-water is similar to α18Ogypsum-water in the temperature range of 0 ⁰C to 60 ⁰C. Both α18Ogypsum-water and α18Obassanite-water show a small temperature dependence of ~0.0000122 per ⁰C, which is negligible for most paleoclimate studies. The theoretical relationship between α17Ogypsumwater and α18Ogypsum-water from 0 °C to 60 °C is 0.5274±0.00063. The relationship is very insensitive to temperature (0.00002 per ⁰C). The fact that α18O values of gypsum hydration water are greater than free water (α18Ogypsum-water >1) whereas αD values of gypsum hydration water are less than free water (αDgypsum-water <1) is explained by phonon theory. We conclude that calculations from first-principles using density functional theory within the harmonic approximation can accurately predict fractionation factors between structurally-bound water of minerals and free water.ER

Coupled measurements of δ¹⁸O and δD of hydration water and salinity of fluid inclusions in gypsum from the Messinian Yesares Member, Sorbas Basin (SE Spain)

We studied one cycle (Cycle 6) of gypsum-marl deposition from the Messinian Yesares Member in Sorbas Basin, Spain. The objective was to reconstruct the changing environment of deposition and its relation to astronomically-forced climate change. The δ1818O and δD of gypsum hydration water (CaSO4•2H2O) and salinity of fluid inclusions were measured in the same samples to test if they record the composition of the mother fluid from which gypsum was precipitated. Water isotopes are highly correlated with fluid inclusion salinity suggesting the hydration water has not exchanged after formation. The relatively low water isotope values and fluid inclusion salinities indicate a significant influence of meteoric water, whereas δ34S, δ18OSO4 26 and 87Sr/86Sr support a dominant marine origin for the gypsum deposits. The discrepancy between water and elemental isotope signatures can be reconciled if meteoric water dissolved previously deposited marine sulfates supplying calcium and sulfate ions to the basin which maintained gypsum saturation. This recycling process accounts for the marine δ34S, δ18OSO4 and 87Sr/86Sr signatures, whereas the low δ18O and δD values of gypsum hydration water and fluid inclusion salinities reflect the influence of freshwater. The cyclic deposition of gypsum and marl in the Yesares Member has previously been interpreted to reflect changing climate related to Earth’s precession cycle. We demonstrate that the δ18O, δD and salinity of the parent brine increased from low values at the base of Cycle 6 to a maximum in the massive gypsum palisade, and decreased again to lower values in the supercones at the top of the cycle. This pattern, together with changes in mineralogy (calcite-dolomite-gypsum), is consistent with a precession-driven change in climate with wettest conditions (summer insolation maxima) associated with the base of the calcium carbonate marls and driest conditions (summer insolation minima) during formation of the gypsum palisade.The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ERC Grant Agreement n. 339694 (Water Isotopes of Hydrated Minerals) to D. A. Hodell.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.epsl.2015.07.07

A review of the production cycle of titanium dioxide pigment

Titanium is a very important element for several industrial applications, being one of the ninth most abundant elements in the Earth’s crust (0.63% wt). In this work it will discuss the different mining and industrial activities involved in the production of titanium dioxide. The first step ana-lyzed will treat about the beneficiation mining process of titanium mineral, and secondly, it will discuss the two main processes of the TiO2 manufacturing (sulphate and chloride routes). In addi-tion, we will show different uses of the titanium dioxide pigment as filler in paper, plastics and rubber industries and as flux in glass manufacture, etc. Finally, we will show that the old wastes are currently called co-products since they were valorized, being commercialized by the Spanish industry of TiO2 production in different fields such as agriculture, civil engineering, or cement manufacturing.Government of Andalusia’s project “Characterization and modelling of the phosphogypsum stacks from Huelva for their environmental management and control” (Ref.: RNM-6300

Precise and accurate isotope fractionation factors (α17^{17}O, α18^{18}O and αD) for water and CaSO4_{4}·2H2_{2}O (gypsum)

Gypsum (CaSO$_{4}$·2H$_{2}$O) is a hydrated mineral containing crystallization water, also known as gypsum hydration water (GHW). We determined isotope fractionation factors (α$^{17}$O, α$^{18}$O and αD) between GHW and free water of the mother solution in the temperature range from 3 °C to 55 °C at different salinities and precipitation rates. The hydrogen isotope fractionation factor (αD$_{gypsum-water}$) increases by 0.0001 units per °C between 3 °C and 55 °C and salinities <150 g/L of NaCl. The αD$_{gypsum-water}$ is 0.9812 ± 0.0007 at 20 °C, which is in good agreement with previous estimates of 0.981 ± 0.001 at the same temperature. The α$^{18}$O$_{gypsum-water}$ slightly decreases with temperature by 0.00001 per °C, which is not significant over much of the temperature range considered for paleoclimate applications. Between 3 °C and 55 °C, α$^{18}$O$_{gypsum-water}$ averages 1.0035 ± 0.0002. This value is more precise than that reported previously (e.g. 1.0041 ± 0.0004 at 25 °C) and lower than the commonly accepted value of 1.004. We found that NaCl concentrations below 150 g/L do not significantly affect α$^{18}$O$_{gypsum-water}$, but αDgypsum-water increases linearly with NaCl concentrations even at relatively low salinities, suggesting a salt correction is necessary for gypsum formed from brines. Unlike oxygen isotopes, the αD$_{gypsum-water}$ is affected by kinetic effects that increase with gypsum precipitation rate. As expected, the relationship of the fractionation factors for $^{17}$O and$^{18}$8O follows the theoretical mass-dependent fractionation on Earth ($\textit{θ}$ = 0.529 ± 0.001). We provide specific examples of the importance of using the revised fractionation factors when calculating the isotopic composition of the fluids.This research was supported by the ERC WIHM Project [#339694] to DAH

Physical weathering of carbonate host-rock by precipitation of soluble salts in caves: A case study in El Orón-Arco Cave (Region of Murcia, SE Spain)

The dissolution of carbonate host-rock by freshwater in phreatic or vadose conditions is the most common mechanism for the formation of caves; however, circulation of saline solutions through carbonate materials and precipitation of soluble salts may also play an important role. We studied the stable isotope composition (δ18O and δ34S of sulfate, δ18O and δD of structurally-bound gypsum hydration water and 87Sr/86Sr) and salinity of fluid inclusions in gypsum speleothems found in El Orón-Arco Cave (Cartagena, SE Spain). We suggest that physical weathering of carbonate host-rock was driven by precipitation of soluble sea-salts (mostly gypsum and halite), and this process controlled the recent geomorphological evolution of the cave. The Triassic carbonate host-rock shows clear evidence for salt weathering, including gypsum/halite infillings in cracks of the bedrock, mechanical spalling of the carbonate, and detachment of rock fragments that lead to the formation cave voids and in-situ accumulations of piles of unsorted rubble. Sulfur and oxygen isotopes of gypsum sulfate (3.0‰ < δ18O < 11.6‰ and 16.7‰ < δ34S < 20.7‰) are generally lower than modern seawater sulfate and suggest contributions from a 34S-depleted source (i.e. oxidation of pyrite). The δ18O and δD of gypsum hydration water are relatively low compared to expected values for the evaporation of pure seawater to gypsum saturation, suggesting that gypsum precipitation involved a secondary calcium-sulfate source or recycling of gypsum from previous stages, along with mixing of seawater and meteoric water seepage to the cave. The 87Sr/86Sr in gypsum shows intermediate values between modern seawater and Triassic carbonate values because of interaction between the solution and the bedrock. The salinities of the speleothem-forming solutions are relatively high (13.2 ± 3.2 wt% eq. NaCl) compared to gypsum formed from evaporated brackish solutions (i.e. ~4–8 wt% eq. NaCl) and indicate dissolution of earlier evaporites before secondary gypsum precipitation. This cave-forming mechanism, which is related to saline water circulation and precipitation of evaporitic minerals, may be common in other coastal caves

Charge Transfer in Partition Theory

The recently proposed Partition Theory (PT) [J.Phys.Chem.A 111, 2229 (2007)] is illustrated on a simple one-dimensional model of a heteronuclear diatomic molecule. It is shown that a sharp definition for the charge of molecular fragments emerges from PT, and that the ensuing population analysis can be used to study how charge redistributes during dissociation and the implications of that redistribution for the dipole moment. Interpreting small differences between the isolated parts' ionization potentials as due to environmental inhomogeneities, we gain insight into how electron localization takes place in H2+ as the molecule dissociates. Furthermore, by studying the preservation of the shapes of the parts as different parameters of the model are varied, we address the issue of transferability of the parts. We find good transferability within the chemically meaningful parameter regime, raising hopes that PT will prove useful in chemical applications.Comment: 12 pages, 16 figure

Competition between polar and nonpolar lattice distortions in oxide quantum wells: new critical thickness at polar interfaces

Two basic lattice distortions permeate the structural phase diagram of oxide perovskites: antiferrodistortive (AFD) rotations and tilts of the oxygen octahedral network and polar ferroelectric modes. With some notable exceptions, these two order parameters rarely coexist in a bulk crystal, and understanding their competition is a lively area of active research. Here we demonstrate, by using the LaAlO₃/SrTiO₃ system as a test case, that quantum confinement can be a viable tool to shift the balance between AFD and polar modes and selectively stabilize one of the two phases. By combining scanning transmission electron microscopy (STEM) and first-principles-based models, we find a crossover between a bulklike LaAlO₃ structure where AFD rotations prevail, to a strongly polar state with no AFD tilts at a thickness of approximately three unit cells; therefore, in addition to the celebrated electronic reconstruction, our work unveils a second critical thickness, related not to the electronic properties but to the structural ones. We discuss the implications of these findings, both for the specifics of the LaAlO₃/SrTiO₃ system and for the general quest towards nanoscale control of material properties

Colored microbial coatings in show caves from the galapagos islands (Ecuador): first microbiological approach

The Galapagos Islands (Ecuador) have a unique ecosystem on Earth due to their outstanding biodiversity and geological features. This also extends to their subterranean heritage, such as volcanic caves, with plenty of secondary mineral deposits, including coralloid-type speleothems and moonmilk deposits. In this study, the bacterial communities associated with speleothems from two lava tubes of Santa Cruz Island were investigated. Field emission scanning electron microscopy (FESEM) was carried out for the morphological characterization and detection of microbial features associated with moonmilk and coralloid speleothems from Bellavista and Royal Palm Caves. Microbial cells, especially filamentous bacteria in close association with extracellular polymeric substances (EPS), were abundant in both types of speleothems. Furthermore, reticulated filaments and Actinobacteria-like cells were observed by FESEM. The analysis of 16S rDNA revealed the presence of different bacterial phylotypes, many of them associated with the carbon, nitrogen, iron and sulfur cycles, and some others with pollutants. This study gives insights into subsurface microbial diversity of the Galapagos Islands and further shows the interest of the conservation of these subterranean geoheritage sites used as show caves.Ministerio del Ambiente de Ecuador (Parque Nacional Galápagos)-PC-65-14Ministerio de Economía y Competitividad de España (MINECO) y el Fondo Europeo de Desarrollo Regional de la Unión Europea (FEDER)-CGL2016-75590-PPortuguese Foundation for Science and Technology. Fundação para a Ciência e a Tecnologia (FCT)-UID/Multi/04449/2019 HERCULES/U