Thermal stability and high-temperature behavior of the natural borate colemanite: An aggregate in radiation-shielding concretes

Colemanite is a natural borate that can be used as an aggregate in neutron-radiation shielding concretes. In this study, we report its thermal behavior, up to 500 degrees C, by describing: 1) its dehydration mechanisms and 2) its thermo-elastic parameters. The thermal expansion of colemanite is significantly anisotropic. The refined volume thermal expansion coefficient at ambient conditions is: alpha(V0) = 4.50(10).10(-5) K-1. The loss of structural H2O occurs at least from similar to 240 degrees C, and at T > 325 degrees C an irreversible amorphization occurs, followed by a complete dehydration. The potential implications on the use of colemanite as concrete-aggregate are discussed. (C) 2019 Elsevier Ltd. All rights reserved

Acid Mine Drainage and PTE distribution in a volcanic sulfur mine: the Thiorichia Mine, Milos Island, Greece

Acid Mine Drainage is a major environmental concern in sulfur-rich ore deposits and is widely studied in different geological contexts and for a variety of sulfide ore deposits. Milos volcanic sulfur mine represents in this picture a type of ore deposit whose acid mine drainage concern is little studied. Milos Island is an active volcano of the Hellenic volcanic arc, with a main caldera collapse structure and a widespread secondary activity. The island hosts seven active mines that exploit bentonite (with the biggest mine in Europe), perlite and pozzolan deposits and several abandoned sulfur, kaolin, barite and manganese mines. Such intense mining activity in a 160 km2 highly touristic island increases the importance of environmental studies for the sustainability of the island economy. Sulfur mining at Milos started in V century BC, but the first modern mining concession dates back to 1862 and led to the opening of the Thiorichia Mine on the Eastern shore of the island. The mining site comprised several tunnels, sulfur purification facilities and other buildings for workers accommodation and administration. Sulfur purification was gained firstly with the Calcaroni method and later with Gill four chambers furnace. Extraction declined in the second half of last century and the mine was definitely closed in 1981. During the field survey three different earthen materials were sampled: sands from the adjacent beach, stream sediments downstream from the purification plant and dumped material, close to the purification plant and uphill on the road leading to the mine. Beach samples are coarser (sandy gravels) due to wave erosion while both sediments and wastes fall in the range of sands and gravely sands. Acid Mine Drainage potential was assessed with ABA procedure and results show that beach sands have no acid potential due to complete leaching of sulfur while sediments and wastes have variable acid potential closely related to the degree of sulfur oxidation. Whole rock ICP analyses show that the highest environmental hazard for PTE is related to the high mercury content of stream sediments and wastes. XRD-powder diffraction analyses show that quartz represents the overwhelming mineral phase in all the samples analysed. Minor phases as alunite-like minerals, micas, elemental sulfur, opal and kaolinite-like minerals have also been detected. The present work shows that Acid Mine drainage and PTE concern studies in sulfur deposits are particularly difficult due to the complete decoupling between the acid potential production, strictly related to the elemental sulfur content of the materials, and the potential release of PTE in the environment, probably associated to secondary clay and alunite-like minerals

Renal effects and nephroprotection induced by SGLT2 inhibitor Empagliflozin in patients with Diabetes Mellitus: a literature review

Chronic kidney disease is a frequent comorbidity in patients with diabetes mellitus (DM) and it increases their cardiovascular risk; chronic hyperglycemia in patients with DM leads to direct and indirect disorders in kidney's structure and function, and it is the principal risk factor for the development of diabetic nephropathy and end-stage renal disease. In the current review, results of studies are exposed in which high tolerability of empagliflozin is exposed in diabetic patients with kidney disease. Empagliflozin by inhibiting SGLT2 provides a novel therapy with benefic effects, not only in glycemic control, but it also has cardiovascular and renal benefits, which they have been demonstrated in the EMPA-REG OUTCOME trial, and continue in evaluation in other studies

An in situ HT-HP single crystal X-ray diffraction study of armstrongite, a microporous zirconium silicate

Armstrongite, CaZr[Si6O15]\ub72H2O, is a natural \u201czeolite-like\u201d Zr-silicate with a heteropolyhedral framework consisting of SiO4 tetrahedra and ZrO6 octahedra that form cavities occupied by Ca-exchangeable cations (Mesto et al., 2014). The behavior at non ambient conditions of armstrongite from Khan Bogdo deposit (Gobi, Mongolia) was studied by in-situ High Temperature Single Crystal X-ray Diffraction (HT SCXRD), both in air and under dry conditions up to 500\ub0C and 375 \ub0C respectively, and by in-situ High Pressure Single Crystal X-ray Diffraction (HP SCXRD) using synchrotron X-ray diffraction data (collected up to 8.01 GPa), a diamond anvil cell and the mix methanol:ethanol:water as hydrostatic pressure-transmitting fluid. On heating an abrupt discontinuity in the trend of the cell parameters and unit-cell volume occurs at T = 275\ub0C in dry condition and at T = 450\ub0C in air. The cell volume decreased by ~7.5%, compared to that measured at RT, and is compatible with the loss of the two water molecules. The dehydrated phase (solved and refined at 275\ub0C only under dry conditions) exhibits the same space group (C2/m) as RT armstrongite, significantly shortened a and b cell dimensions, increased \u3b2 angle, and smaller unit-cell volume (a = 13.406(3), b = 13.752(3), c = 7.811(2) \uc5, \u3b2 = 110.22(3)\ub0, V = 1351.3(5) \uc53) with respect to the hydrated phase (a = 14.0135(7), b = 14.1234(6), c = 7.8388(4) \uc5, \u3b2 = 109.401(4)\ub0, V = 1463.4(1) \uc53) at RT. The process is also accompanied by the distortion of the cavities as a consequence of Ca splitting and positional disorder of tetrahedral framework oxygens. The dehydration/rehydration process of armstrongite is completely reversible as also found from previous HT XRPD investigation (Schingaro et al., 2018). HP SCXRD data show a first-order phase transition between 4.01(5) and 5.07(5) GPa. In the high-pressure polymorph, the unit-cell volume triplicates. The bulk compression of armstrongite is mainly accommodated through the tilting of both SiO4 tetrahedra and ZrO6 octahedra around the shared oxygen hinges. The high-P polymorph of armstrongite is found to be stiffer (KV0 increase of ~ 66%), and a remarkable change of the elastic anisotropic scheme occurs. No evidence of crystal-fluid interaction, with a selective sorption of molecules of the pressure-transmitting fluid through the cavities, was observed. Mesto, E., Kaneva, E., Schingaro, E., Vladykin, N., Lacalamita, M. & Scordari, F. (2014): Armstrongite from Khan Bogdo (Mongolia): crystal structure determination and implications for zeolite-like cation exchange properties. Am. Mineral., 99, 2424-2432. Schingaro, E., Lacalamita, M., Mesto, E. & Della Ventura, G. (2018): Thermal stability and dehydration of armstrongite, a microporous zirconium silicate. Micropor. Mesopor. Mat., in press

New insights into the monoclinic-to-orthorhombic phase transition in MFI-zeolites

The so-called ZSM-5 zeolites have a MFI-type structure, and are characterized by an Al-doped siliceous framework (Fig. 1), with the Si/Al ratio ranging from 10 to infinity; when this ratio exceeds 1000, the zeolite is typically known as \u201cSilicalite-1\u201d. The ZSM-5 zeolites exhibit a complex polymorphism, as they may crystallize either in the orthorhombic P212121 space group, or in the more common orthorhombic Pnma and even in the monoclinic P21/n11 space groups (usually referred to as ORTHO and MONO, respectively). A monoclinic (P21/n11)-to-orthorhombic (Pnma) phase transition (hereafter MOPT) has been reported in ZSM-5 zeolites,1,2 in response to different variables. Several variables, such as temperature, pressure, framework chemistry, concentration of defects, as well as the nature and the concentration of the sorbate, may stabilize the Pnma or the P21/n polymorphs.3-6 In particular, the temperature and pressure at which the MOPT occurs largely depends on the framework composition. In order to obtain new insights into the mechanism of the MOPT at varying chemical and pressure conditions, we synthesized six chemically distinct MFI-zeolites, with framework-Si partially replaced by Al or B (counterbalanced by Na or H as extra-framework cations, see Tab. 1). Then, by in situ synchrotron X-ray powder diffraction experiments with a diamond-anvil cell, the high-pressure behavior of the synthesized MFI-zeolites has been studied using methanol and silicone oil as pressure-transmitting fluids. All the investigated zeolites crystallized in the monoclinic P21/n11 space group and experienced the MOPT during compression. The Na-Silicalite-1 (Table 1), for example, underwent the monoclinic-to-orthorhombic phase transition at ~ 0.5 GPa in silicone oil and at ~ 0.4 GPa in methanol. A preliminary analysis suggests that, when compressed in the non-penetrating silicone oil, the doped MFI zeolites experience the MOPT at lower pressures than the Na-SiO2 silicalite

High-pressure cold methanol intrusion in MFI-zeolites

In the last decades, several efforts were devoted to explore the P-mediated intrusion of molecules in microporous compounds since this can lead to new routes of tailoring functional materials, bearing a potentially relevant technological impact. MFI-zeolites are also used as catalysts in some olefins-production processes, representing an appealing alternative to the high-energy demanding Steam Cracking process, which actually accounts for 95% of the total worldwide olefins production.1-3 The applicative importance of MFI-type zeolites is due to their unique structure formed by (Al,Si)O4 tetrahedra connected in such a way that a pore system, consisting of two intersecting channels, occurs within its zeolitic framework. The employment of zeolites as synthesis catalysts allows milder synthesis conditions, leading to a lower energy consumption and, therefore, lower greenhouse emissions. Furthermore, in recent years MFI-zeolites have been used in the promising methanol-to olefins synthesis process, which, being able to obtain olefins directly from methanol in place of oil bears a potential breakthrough industrial impact. It is worth to underline usually, at ambient conditions, only the surfaces of the zeolite crystallites are believed to be active in the methanol-to olefins process. However, induced by pressure, the methanol molecules may penetrate and diffuse through the zeolitic channels.4 This may bear a significant impact in the industrial applications of this zeolite as a catalyst, since a \u201ccold\u201d intrusion of methanol into the zeolite cavities might pave the way to increase the efficiency of the methanol-to-olefins conversion process. In this regard, we synthesized and then studied, by in situ synchrotron X-ray powder diffraction experiments, the high-pressure behavior of six MFI-zeolites with different chemical composition (reported in Tab. 1). Consistently with the previous studies,5 all the synthesized zeolites are monoclinic (space group P21/n11) at ambient pressure, although a monoclinic-to-orthorhombic phase transition (MOPT) is reported to occur at P > 1 GPa.5 Analyzing the pressure-volume data and the diffraction patterns, we were able to ascertain: i) all the MFI zeolites compressed in silicone oil have overall the same bulk compressibility (Fig. 1), ii) there are differences, among the different zeolites, in the magnitude of the methanol adsorption (e.g., Fig. 2), iii) the MOPT is influenced by both crystal chemistry and sorbate (methanol) loading. Overall, this study provides useful information about the optimal chemical composition of a potential MFI-catalyst in the methanol-to-olefins conversion process operating at high-pressure conditions

Methanol intrusion in MFI-zeolites at high pressure

MFI-zeolites are currently used as catalysts in some olefins-production processes, representing an appealing alternative to the high-energy demanding Steam Cracking process, which accounts for 95% of the total worldwide olefins production (Sadrameli 2016; Arvidsson et al., 2016). More recently, MFI-zeolites have been used in the promising methanol-to-olefins (MTO) synthesis process, which, being able to obtain olefins directly from methanol in place of oil, bears a potential breakthrough industrial impact. At ambient conditions, only the surfaces of the zeolite crystallites are believed to be active in the methanol-to olefins process. However, pressure may favour the intrusion and diffusion of methanol molecules through the zeolitic channels, as observed in other zeolites (Gatta et al., 2018). This phenomenon may bear a significant impact in the industrial applications of MFI zeolites as catalysts, as a \u201ccold\u201d intrusion of methanol into the zeolite cavities might pave the way to increase the efficiency of the MTO conversion process. In this regard, we have synthesized and investigated, by in situ synchrotron powder-XRD, the high-pressure behaviour of six MFI-zeolites with different chemical compositions (framework-Si partially replaced by Al or B and counterbalanced by Na or H as extra-framework cations), by using methanol and silicone oil (as a reference) as P-transmitting fluids, respectively. All the synthesized zeolites are monoclinic (space group P21/n11) at ambient pressure, although a monoclinic-to-orthorhombic phase transition (MOPT) is observed to occur at \uf07e P > 0.5 GPa. Based on the experimental X-ray diffraction patterns and on the high-P evolution of the unit-cell parameters, we ascertain that: i) all the MFI zeolites compressed in silicone oil (acting as non-penetrating fluid) have, overall, the same bulk compressibility, ii) pressure induces the intrusion of methanol through the structural voids and, among the different zeolites, the magnitude of the adsorption phenomenon is different, iii) the MOPT is influenced by both the crystal chemistry and the sorbate (methanol) loading. The experimental findings of this study represent the first step to select the optimal chemical composition of a potential MFI-catalyst for the MTO conversion process operating at high-pressure conditions. References: Arvidsson M., Haro P., Morandin M., Harvey S. 2016. Comparative Thermodynamic Analysis of Biomass Gasification-Based Light Olefin Production Using Methanol or DME as the Platform Chemical. Chem. Eng. Res. Des., 115, 182\u2013194. Gatta G. D., Lotti P., Tabacchi G. 2018. The Effect of Pressure on Open-Framework Silicates: Elastic Behaviour and Crystal\u2013fluid Interaction. Phys. Chem. Miner., 45, 115\u2013138. Sadrameli S. M. 2016. Thermal/Catalytic Cracking of Liquid Hydrocarbons for the Production of Olefins: A State-of-the-Art Review II: Catalytic Cracking Review. Fuel, 173, 285\u2013297

The elastic behavior of zeolitic frameworks : The case of MFI type zeolite under high-pressure methanol intrusion

The high-pressure behavior of six synthetic zeolites with the MFI topology, characterized by different chemical composition (framework-Si partially replaced by Al or B and counterbalanced by Na or H as extra-framework cations), has been investigated by in-situ powder synchrotron X-ray diffraction using silicone-oil and methanol as hydrostatic pressure-transmitting fluids. For each sample, the compressibility in silicone-oil has been found to be considerably higher than that in methanol. This difference in terms of bulk elasticity is due to the adsorption of methanol already at P < 0.1 GPa, with different magnitudes as a function of the sample crystal-chemistry. The high number of experimental pressure points allowed an accurate determination of the monoclinic-to-orthorhombic phase transition (MOPT), detected between 0.3 and 0.7 GPa in the samples compressed in silicone-oil, whereas the orthorhombic Pnma polymorph has been found to be stable already at 3c 0.1 GPa in four samples compressed in methanol. This suggests that the adsorption of methanol may increase the P-stability range of the orthorhombic Pnma phase. A comparative analysis of the effect of pressure on the methanol adsorption by MFI-zeolites with different chemical composition is provided, which offers potentially useful information on their application as catalysts in the methanol-to-olefins conversion processes and in industrial high-pressure processes

Host–Guest Hydrogen Bonding in High-Pressure Acetone Clathrate Hydrates: In Situ Single-Crystal X-ray Diffraction Study

The phenomenon of host–guest hydrogen bonding in clathrate hydrate crystal structures and its effect on physical and chemical properties have become subjects of extensive research. Hydrogen bonding has been studied for cubic (sI and sII) and hexagonal (sH) binary clathrates, while it has not been addressed for clathrate structures that exist at elevated pressures. Here, four acetone hydrate clathrates have been grown at high-pressure and low-temperature conditions. In situ single-crystal X-ray diffraction revealed that the synthesized phases possess already known trigonal (sTr), orthorhombic (sO), and tetragonal (sT) crystal structures as well as a previously unknown orthorhombic structure, so-called sO-II. Only sO and sII have previously been reported for acetone clathrates. Structural analysis suggests that acetone oxygens are hydrogen-bonded to the closest water oxygens of the host frameworks. Our discoveries show that clathrate hydrates hosting polar molecules are not as exotic as previously thought and could be stabilized at high-pressure conditions through hydrogen bonding

On the identification of hyperhydrated sodium chloride hydrates, stable at icy moon conditions

Sodium chloride is expected to be found on many of the surfaces of icy moons like Europa and Ganymede. However, spectral identification remains elusive as the known NaCl-bearing phases cannot match current observations, which require higher number of water of hydration. Working at relevant conditions for icy worlds, we report the characterization of three “hyperhydrated” sodium chloride (SC) hydrates, and refined two crystal structures [2NaCl·17H2O (SC8.5); NaCl·13H2O (SC13)]. We found that the dissociation of Na+ and Cl− ions within these crystal lattices allows for the high incorporation of water molecules and thus explain their hyperhydration. This finding suggests that a great diversity of hyperhydrated crystalline phases of common salts might be found at similar conditions. Thermodynamic constraints indicate that SC8.5 is stable at room pressure below 235 K, and it could be the most abundant NaCl hydrate on icy moon surfaces like Europa, Titan, Ganymede, Callisto, Enceladus, or Ceres. The finding of these hyperhydrated structures represents a major update to the H2O–NaCl phase diagram. These hyperhydrated structures provide an explanation for the mismatch between the remote observations of the surface of Europa and Ganymede and previously available data on NaCl solids. It also underlines the urgent need for mineralogical exploration and spectral data on hyperhydrates at relevant conditions to help future icy world exploration by space missions