1,721,006 research outputs found
Georesources, finding the perfect mixture between science and dissemination in PCTO activities
Full text linkThe critical role of georesources and the environmental footprint of human activities in
shaping the current and future society are sometimes overlooked by the public, especially by the
youngest generations. Mining is often associated with environmental threats and dangers while the
importance of georesources is greatly underestimated or, worse, neglected. This despite the fact that
responsible exploitation of georesources is a pivotal requirement to reshape the current economic
model into a more environmentally friendly while still maintaining a sustainable economic growth.
In the framework of PTCO (Paths for Transversal Skills and Orientation) activities we have organized
a 15-hours project aimed to sensibilize students to the needs and risks of mining activities.
Laboratories, movies, frontal lectures, thought experiments and the interactive visits to the Earth
Sciences facilities have been organized attempting to keep an informal context to obtain high levels
of engagement and participation. The project has so far been presented to 19 high school classes and
over 360 students. Following each cycle, students were invited to fill a three-minute anonymous
questionnaire to evaluate the project offering valuable insights for further improvement and
development of the activities. Not surprisingly, the most appreciated activity was at the lab facilities
at the department, which was deemed by the majority “too short”, highlighting the need to produce
more active-oriented environments to engage the students
Hydrated borates at non ambient conditions: pivotal experiments in the production of neutron shielding concretes.
Full text linkHydrated borates (e.g., colemanite, kernite, ulexite, borax, tincalconite) are the most common ore minerals of
boron, an important geochemical marker, in pegmatitic and granitic systems, for petrogenetic processes and a
strategic element in a series of technological applications. Hydrated borates have been listed as critical raw
materials by the EU [1], and they could be used as aggregate in neutron-shielding Sorel or Portland concretes,
enhancing the adsorption of concrete towards thermal neutrons. The main structural units in hydrated borates
are Bφx units (fundamental building blocks, i.e., tetrahedra and planar trigonal group where φ is an anion, O2-
or OH-
), connected in such a way to form clusters of polyions connected to alkaline/Earth alkaline (mainly
Na+
, K+
, Ca2+, Mg2+) polyhedra. In these structures, H2O molecules and OHform a complex and pervasive
hydrogen-bond network, which reinforce the connection between the polyions clusters and the cationspolyhedrons, playing a paramount role in the stability of the crystalline edifice [2, 3]. In the last 4 years, a
number of studies have been performed at high temperature and pressure unveiling phase transition driving
deformation mechanisms’ that lead to the formation of their high-pressure polymorphs. Critically, the pressure
at which hydrated borates undergo a phase transition is related to the water content of the mineral itself. The
aim of this contribution is to provide insides on the high-pressure behavior and structure evolution of selected
hydrate borate minerals. These studies at non ambient conditions are pivotal to produce neutron shielding tiles
of Sorel concretes
Inderborite : a comprehensive reinvestigation of its technological features
Full text linkInderborite is a hydrated borate (ideal formula:...) often found in lower fractions alongside with the
five most important boron commodities (i.e., colemanite, kernite, ulexite, borax, tincalconite).
Nowadays, Turkish mines produce more than 70% of the worldwide B-minerals (e.g., Sarikaya borate
deposits, Baysal, 1973). Hydrated borates have been listed as critical raw materials by the EU (EU
Commission, 2017), and, because of the high neutron cross-section of B-10, they could be used as
aggregates in neutron-shielding Sorel or Portland concretes, enhancing their adsorption towards
thermal neutrons. In the forthcoming decades, with the advent of fusion power plants, it is predicted
that substantial quantities of neutron-activated elements (e.g., beryllium or tungsten), will be
produced (Gonzalez de Vincente et al. 2022). The main goal of this projects was to: i) re-investigate,
by means of a multi-methodological approach, the crystal chemistry (with a focus on the B isotopic
composition and trace elements) and structure of inderborite (even based on a single-crystal neutron
diffraction experiment), ii) assess the stability range of inderborite with respect to pressure and
temperature even for potential industrial utilization of this borates, iii) describe the structural
evolution of inderborite, at the atomic scale, with increasing pressure and temperature
High-pressure phase trasition and crystal structure evolution of inderite, MgB3O3(OH)5 5H2O
Full text linkInderite, ideally [MgB3O3(OH)5∙5H2O], is a light (1.80 g/cm3) Na-free hydrated borate, discovered in the Inder deposit (Kazakhstan), which could be efficiently employed in radiation-shielding concretes due to its relatively high B2O3 content (⁓37 wt%). The crystal structure of inderite is made by [B3O3(OH)5]2- polyions, organized in 3-membered rings of 2 Bφ4 tetrahedra and one Bφ3 unit (where φ is an anion; O2-or OH-). Prior to any utilization, is advisable to correctly characterized the thermodynamic parameters of any aggregate, if used in neutron-shielding concretes, where temperature can increase due to the interactions with the highly energetic neutron beam. Overall, phase transitions occurring at different pressures (and temperatures) were discovered in all the hydrous borates investigated so far (e.g., [1, 2]), suggesting that the high-pressure stability of hydrated borates having polyions organized in isolated units (e.g., inderite) is directly correlated with the total H2O content of the mineral itself. Inderite is the ideal case-scenario to validate this model and here we report the results of this study that leads to: 1) track the isothermal compressional path, based on the experimental P-V data, 2) derive the elastic parameters, currently unavailable in the literature; 3) investigate the phase-stability field of inderite at high-pessure; 4) describe the high-pressure structural re-arrangement of inderite at the atomic scal
P-mediated crystal-fluid interaction in the ABC-6 zeolite group: the case of ERI, OFF and EAB topologies
No full textThe Pressure-mediated intrusion of molecules and solvated ions into the nano-cavities of microporous (or layered) materials is an efficent method to facilitate the mass transfer from fluids to crystalline solids. This phenomenon, which can be observed in both synthetic and natural zeolites, for example, could expand their industrial applications, develop new functional materials, and improve catalytic performance of these open-framework compounds. In addition, from a geological perspective, a comprehensive understanding of the crystal-fluid interaction induced by pressure may lead to a reassessment of the role played by zeolites as carriers of fluids during the early stages of subduction. It is worth noting that this class of open-framework silicates can contain up to 20 wt% of H2O. In this study, we have investigated the crystal-fluid interaction, driven by pressure, in three different natural zeolites belonging to the “ABC-6 group”: erionite (ERI framework, with a 6-membered ring sequence of AABAAC), offretite (OFF, sequence of AAB), and bellbergite (EAB, sequence of AABCCB). The aims of this study were twofold: 1) to determine the potential role of erionite as a fluid carrier during subduction, as one of the alteration minerals occurring in oceanic floor basalts, and 2) to compare the mechanisms adopted by structurally similar frameworks in accommodating bulk compression and adsorbing new molecules, as well as to determine the magnitude of the crystal-fluid interaction in structurally similar frameworks. Synchrotron XRD experiments were conducted on single crystals of natural erionite, offretite and bellbergite using a diamond anvil cell, both with potentially penetrating and non-penetrating pressure-transmitting fluids. The latters served as a reference for evaluating the crystal-fluid interaction, as the adsorption of new molecules reduces the bulk compressibility for the "pillar" effect exerted by the intruded guest species in the structural voids. The results revealed that erionite shows the largest adsorption capacity among the three zeolites. Moreover, the occurrence and magnitude of the crystal-fluid interaction phenomena were found to be strongly influenced by the H2O content in the hydrous pressure-transmitting fluids used in our experiments. In the case of offretite, liquid neon acted as penetrating fluid, with intruded atoms forming weak Van der Waals interactions with the extra-framework population. Natural bellbergite, on the other hand, shows limited intrusion of guest molecules from the pressure-transmitting fluids, highlighting the significant role of "secondary factors," such as the initial extra-framework content of the mineral, on crystal-fluid interaction phenomena
Pressure-mediated crystal-fluid interactions in natural erionite-K
No full textInvestigating the behaviour at high pressure of crystalline compounds with a microporous structure, e.g. zeolites, has experienced a boosted interest in the last two decades, especially due to the P-induced intrusion of molecules and ions into the structural nano-cavities from the P-transmitting fluids [1]. Zeolites have a consolidated history of technological and industrial applications, but the understanding of these P-induced phenomena may further expand their utilizations, opening the way for new routes for tailoring functional materials. In this study, we have investigated the behaviour of the natural zeolite erionite when compressed in non-penetrating and potentially penetrating fluids: i.e. those fluids made by molecules having a kinetic diameter that may allow their P-mediated adsorption into the zeolite structural cavities.
Erionite is a zeolite with a wide chemical variability in Nature, expressed as solid solutions among three end-members: erionite-Ca, erionite-Na and erionite-K.
Our sample, classified as erionite-K, has an average chemical formula: K2.31Na0.02Ca2.15Mg0.69Ba0.04Sr0.02Al9.00Si27.19O72·18.66(H2O). Erionite crystal structure is characterized by the presence of large cages (23-hedron, called “erionite-cage”), superposed along the c axis, hosting most of the extra-framework population.
We have conducted experiments by single-crystal X-ray diffraction under in-situ high-pressure conditions at the Xpress beamline of the Elettra Synchrotron, using an ETH-type diamond anvil cell (DAC) and ruby as P-calibrant. We have performed two P-ramps using different P-transmitting media: the first one using the non-penetrating silicone oil, up to 2.60(5) GPa, and the second one with the potentially penetrating methanol:ethanol:H2O = 16:3:1 (hereafter mew) mixture, up to 4.97(5) GPa. Using the EoSFit7c software, the P-V data obtained by the silicone oil ramp were fitted by a II order Birch-Murnaghan equation of state, yielding the following refined isothermal bulk modulus KV0 = 44(1) GPa (βV0 = KV0-1 = 0.0227(5), where βV0 is the bulk volume compressibility).
P-V data from the mew ramp (Fig. 1) show a significant decrease in compressibility, which unambiguously suggests the (irreversible) P-induced intrusion of H2O (and possibly alcohols) molecules. The adsorption seems to occur in three different steps, approximately around 0.2, 1.2 and 2 GPa. This behaviour is somehow surprising if we consider that the magnitude of the intrusion process is comparable with that of synthetic SiO2-ferrierite [2] and AlPO4-5 [3] zeolites, but in this case has been observed in a natural sample of erionite, with structural cavities filled by extraframework population.
Further experiments with different classes of potentially penetrating fluids will allow a full understanding and constraints of the P-induced adsorption phenomena in erionite
The role of temperature on the pressure-mediated adsorption in natural zeolites: the case of leonhardite
Full text linkWhile the high-pressure and high-temperature behavior of natural zeolites has been intensively studied in the
last decades, to the best of our knowledge, no in-situ X-ray diffraction studies have been performed combining
the effects of both. Experiments at these conditions could have crucial geological implications and potential
applications at the industrial level (e.g., high-P/T adsorption of alcohols compounds in zeolites to promote
methanol to olefins reaction). In this study, we present the results from the first pilot experiments, obtained
with an easy and reproduceable experimental set-up, performed with one of the most common natural zeolite,
i.e., laumontite ([(Ca4-xNax)Kx][Al8Si16O48]⋅(H2O)n, with n 16). This zeolite occurs in a wide range of natural
environments, including sedimentary deposits or volcanoclastic sequences interested by burial
diagenesis/metamorphism, as well as in hydrothermal vugs of volcanic rocks. Partially hydrated laumontite
(i.e., with 15 H2O molecules per unit cell) is often referred to as “leonhardite”. The behavior and adsorption
mechanisms of these minerals have been (already) well characterized at high-pressure by several authors(Gatta
et al. 2018; Comboni et al. 2018), leaving unexplored the effect induced by temperature increase. In-situ highpressure+high-temperature single-crystal synchrotron X-ray diffraction experiments were performed at the
ID15-b beamline, at the ESRF, Grenoble (France). Saltwater (0.35 wt% NaCl) was used as hydrostatic
pressure-transmitting fluid. The DAC was placed in a resistive heater, which allowed to increase the T up to
100(2)°C. Temperature was defined using a thermocouple placed very close to the P-chamber; T value was
consistent with what obtained by the analysis of the Au-powder pattern. In leonhardite, the temperature seems
to enhance the H2O adsorption, giving rise to a volume expansion at P <5 kbar. Above this pressure, the
compressibility becomes similar to that of fully hydrated laumontite [2]. Previous experimental findings
proved that leonhardite experiences a full hydration, at ambient PT conditions, only after about 24 hours,
whereas each data-point at high-PT required not more than 20 minutes: this further highlights the role played
by temperature on the kinetics of the P-mediated adsorption process (i.e., speeding up the adsorption process)
The role of temperature on P-induced crystal-fluid interaction : a study on LAU and HEU topologies
No full textNatural zeolites can be found in soil, oceanic basalts as well as sediments and diagenetic environments. Their peculiar reversible hydration property (i.e., the ability to adsorb and release H2O molecules) and the ability to overhydrate under pressure, make them suitable carriers of fluids in the upper Earth crust during the early stage of subduction. Despite the extensive study of high-pressure and high-temperature behavior of natural and synthetic zeolites over the last decades, few studies have yet combined the effects of both conditions. Experiments at combined high pressure and high temperature might provide valuable insights on the crystal-fluid interaction preocesses occurring in nature at the geological conditions of stability of zeolites, especially when these microporous compounds can act as carriers and moderators of the circulating fluids.
In this study, the in situ combined high-pressure and high-temperature behavior of two commonly occurring natural zeolites, heulandite and laumontite, was investigated. The P-induced crystal-fluid interaction of these two zeolites was studied at ambient-T by Comboni et al. [1] for laumontite and Seryotkin [2] for heulandite. These results have been used as benchmarks to evaluate the role of temperature on the crystal-fluid interaction. In-situ, HTHP single-crystal synchrotron X-ray diffraction experiments were conducted using a diamond anvil cell (DAC) surrounded by a resistive heater at the ID15b beamline at the European Synchrotron Radiation Facility in Grenoble (France). The setup allowed to reach temperatures of about 150(2)°C. Pressure was measured using the ruby fluorescence technique while temperature was monitored using a thermocouple located very close to the P-chamber, allowing a precise determination of both these variables. The results obtained were consistent with those calculated using the Au-powder pattern.
The results showed that temperature significantly increased the kinetics of H2O adsorption in laumontite, with respect to the compressional behavior at room conditions, leading to a volume expansion observable already at pressures < 5 kbar. It was previously found that laumontite hydrated at ambient conditions after 24 hours, while the presence of a temperature gradient reduced the time at about 15 minutes. Even for heulandite, the comparison with literature data suggests that a higher H2O adsorption rate was observed when the thermal gradient was applied.
References
[1] Comboni D., Gatta G.D., Lotti P., Merlini M. & Hanfland M. 2018. Crystal-fluid interactions in laumontite. Microporous Mesoporous Mater., 263, 86-95.
[2] Seryotkin, Y.V. 2015. Influence of content of pressure-transmitting medium on structural evolution of heulandite: Single-crystal X-ray diffraction study. Microporous and Mesoporous Mater., 214, 127-135
Crystal-fluid interactions in erionite-group zeolites under compression
No full textIn the last two decades many studies showed that hydrostatic compression is able to enhance or induce the intrusion of molecules (or solvated ions) into the structural nano-cavities of microporous materials, pointing out that this is a viable way to promote a mass transfer from fluids to structurally-incorporated molecules. A full understanding of this phenomenon in natural or synthetic zeolites might expand the number of their utilizations, e.g. tailoring of new materials, as catalysts in industrial processes [1,2]. In addition, this phenomenon bears an intrinsic relevance also in Earth Sciences, as zeolites may act as fluid carriers in the upper Earth crust, e.g. during the early subduction of oceanic sediments or altered basalts.
In this scenario, we focused on three natural zeolites, structurally characterized by six-membered rings of tetrahedra and belonging to the large group of ABC-6 open-framework materials: erionite, offretite and bellbergite. Erionite is a quite common zeolite in nature, where it forms in basaltic vugs, crystallizing from hydrothermal fluids. It shows an ERI-type framework, made by the repetition of AABAAC sequences of 6-membered rings of tetrahedra layers. Offretite (OFF framework type) shows an AAB sequence and is commonly intergrown with erionite, due the easy occurrence of stacking faults at B and C positions of the 6-membered rings layers. Bellbergite is a rather uncommon zeolite in nature, more famous for its synthetic counterparts [3], and shows an EAB framework with ABBACC sequence.
The crystal-fluid interactions during compression were investigated by means of in situ single-crystal X-ray diffraction, which allows to focus the study on the effects that interaction has on the crystal structure of zeolites. The experiments were performed at the ID15B beamline of the European Synchrotron Radiation Facility, using diamond anvil cells to apply hydrostatic pressures on the investigated samples and using different pressure-transmitting fluids: namely, the non-penetrating silicone oil and daphne oil 7575 and potentially penetrating methanol:ethanol:water 16:3:1 mixture, ethanol:water 1:1 mixture, methanol, distilled H2O and liquid Ne. As non-penetrating are intended those fluids which molecules have a kinetic diameter larger than the free diameter of the open-framework of the zeolite and, therefore, cannot be pressure-intruded into the crystal structure. The compressional experiments in non-penetrating fluids provide, therefore, a benchmark to which compare the behavior of the same microporous compound in a potentially penetrating fluid.
Among the investigated natural samples, erionite resulted to be the one with the highest magnitude of adsorption, as shown by Figure 1. The new adsorbed molecules act as “pillars” within the framework nanocavities, decreasing the compressibility of the structure, as it is clear comparing the unit-cell vs. pressure evolution of erionite compressed in silicone oil and methanol:ethanol:water (16:3:1) mixture, respectively (Figure 1). The obtained results also allow to conclude that the magnitude of the intrusion for a given zeolite is strictly related to the H2O content of the hydrous P-transmitting fluids, where the largest is the water fraction, the highest the magnitude of the intrusion and (sometimes) the lower the pressure at which it occurs. A comparison of the crystal-fluid interactions under pressure in natural erionite and in other synthetic zeolites (e.g. SiO2-ferrierite [4]), points out that the observed magnitude of intrusion in this study is surprisingly high for a natural zeolite, characterized by channels and cages already filled by extraframework cations and molecules. These results suggest that natural zeolites, despite being intrinsically less inclined to show pressure-induced crystal-fluid interaction with respect to synthetic ones, should not be a priori excluded as targets for the tailoring of new materials by exploiting hydrostatic compression, especially when a modest temperature is also applied. Moreover, the obtained results also suggest that the role of zeolites as fluid carriers or fluid moderators in the geological processes occurring in the upper Earth crust deserves a more comprehensive characterization for a full understanding.
Acknowledgements: ESRF is acknowledged for the provision of beamtime. The Italian Ministry of Education (MUR) is acknowledged for the support through the projects “PRIN2017—Mineral reactivity, a key to understand large-scale processes” (2017L83S77) and “Dipartimenti di Eccellenza 2023-2027”.
References (up to five):
[1] G.D. Gatta, P. Lotti, G. Tabacchi, Physics and Chemistry of Minerals 45, 2018, 115–138
[2] D. Comboni, F. Pagliaro, P. Lotti, G.D. Gatta, M. Merlini, S. Milani, M. Migliori, G. Giordano, E. Catizzone, I.E. Collings, M. Hanfland, Catalysis Today 345, 2020, 88–96.
[3] R. Aiello, R.M. Barrer, Journal of the Chemical Society A, 1970, 1470-1475.
[4] P. Lotti, R. Arletti, G.D. Gatta, S. Quartieri, G. Vezzalini, M. Merlini, V. Dmitriev, M. Hanfland, Microporous and Mesoporous Materials 218, 2015, 42-54
Pressure-driven phase transitions in hydrated borates
Full text linkHydrated borates (e.g., colemanite, ulexite, kernite and borax) are the most common ore minerals of boron, an important geochemical marker, in pegmatitic and granitic systems, for petrogenetic processes and a strategic element in a series of technological applications. Hydrated borates, which have been listed as critical raw materials by the EU [1], could be used as aggregate in neutron-shielding Sorel or Portland concretes, enhancing the adsorption towards thermal neutrons. In hydrated borates, the main structural units are Bφx units (tetrahedra and planar trigonal group where φ is an anion, O2- or OH-), connected in such a way to form clusters of polyions connected to alkaline/Earth alkaline (mainly Na+, K+, Ca2+, Mg2+) polyhedra. In these structures, H2O molecules and OH- form a complex and pervasive hydrogen-bond network, often enhancing the connection between the polyions clusters and the cations-polyhedrons, therefore playing a paramount role in the stability of the crystalline edifice [2, 3]. The aim of this contribution is to analyze and provide insides on the high-pressure behavior and structure evolution of several hydrate borate minerals, unveiling the phase transition driving deformation mechanisms that lead to the formation of their high-pressure polymorphs. A common pattern, that could be used to predict the high-pressure phase stability of this class of minerals, has been detected
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