Hydrothermal Solutions Research Articles

Piezoelectric assisted photocatalytic degradation of dyes by plasmon Ag nanoparticles modified Na0.5Bi0.5TiO3 nanospheres

Piezo-photocatalysis has attracted tremendous interest in dealing with organic pollutants. In this work, silver (Ag) nanoparticles modified Na0.5Bi0.5TiO3 nanospheres (hereinafter referred to as Ag-NBTO) were prepared by hydrothermal and chemical solution methods. Our results show that 98.6 % RhB is degraded in 120 min under the simultaneous excitation of ultraviolet light and ultrasound with the assistance of Ag-NBTO. The corresponding rate constant k is 0.0329 min−1, which is 10 times higher than that of Na0.5Bi0.5TiO3. The excellent piezo-photocatalytic performance may be attributed to the local surface plasmon resonance (LSPR) effect. This work offers great potential for eliminating environmental pollution and can be extended to other piezoelectric materials.

Paragenetic Association of Platinum and Gold Minerals in Placers of the Anabar River in the Northeast of the Siberian Platform

Areal placers of diamond and precious metals (platinum and gold) of unknown origin are widespread in the Anabar River basin on the northeastern part of the Siberian Platform. This article discusses the typomorphic features of palladium gold (porpezite) and ferroan platinum, which, in addition to fragmented individual grains, sometimes form close growths, which indicates their obvious genetic relationship. This can be used to delimit the primary sources of commercial components of complex placers by their genetic types. The composition of minerals was determined on a Camebax-Micro (Cameca, France) microprobe analyzer, and their microstructural relationships were studied using the scanning microscope JSM-6480LV JEOL. Determination of the structure and parameters of elementary lattices of minerals was carried out on the D8 Discover diffractometer. According to microprobe analysis, the Pd content in porpezite ranges from 0.73% to 12.83%, Ag does not exceed 2.75% and Cu reaches 3–4%. Considering the composition, such a gold–platinum mineral association from placers of the Anabar river is close to precious metals from placers of the Gulinsky massif, as well as Au–PGE ore occurrences related to ultramafic–mafic intrusions of other regions of the world. Complex gold–platinum-metal mineralizations are usually closely related to parent rocks and are often observed in sulfide and chromite ores of layered ultramafic–mafic intrusions with complex metasomatic and hydrothermal transformations. It is shown that in such cases gold and platinum form a magmatogenic paragenesis of minerals that coexist until the separation of hydrothermal solutions from magma, which, as a rule, transports Au and Ag with a small fraction of PGE from the fluid-ore-magmatic system in accordance with the model of the formation of gold–porphyry deposits. Within the Anabar diamond-bearing region, according to modern geophysical data, a significant number of local gravimagnetic anomalies associated with the presence of intrusive massifs of basic and alkaline-ultrabasic rocks in the cover and within the basement have been identified. This allows us to assume that the buried parent rocks of the Anabar Au–Pt placers may be located in both the Precambrian and Phanerozoic strata.

Geochronology, mineralogy, and geochemistry of tonsteins from the Pennsylvanian Taiyuan Formation of the Jungar Coalfield, Ordos Basin, North China

Altered volcanic ashes occur worldwide in coal-bearing sequences. The Carboniferous is one of the important coal-forming periods but the altered volcanic ashes within coals in China of this geological age have not been well studied. In this study, the nature of the partings in the No. 9 coal seam of the Pennsylvanian Taiyuan Formation from the Yaogou Mine, Jungar Coalfield, Ordos Basin, North China, was comprehensively investigated. Fifteen partings were identified as altered volcanic ashes based on the typical features, including thin but persistent bands, sharp contacts with the enclosing coals, vermicular and book-like kaolinite, angular quartz, and euhedral primary zircons, while some muscovite and detrital zircon grains in the samples indicate minor contribution of terrigenous debris. Two UPb zircon ages from the altered volcanic ashes at the top and bottom of the No. 9 coal constrain that the Taiyuan Formation in the studied area falls within the Gzhelian Stage of the Late Pennsylvanian. All the altered volcanic ashes were defined as tonsteins due to the relative abundances of kaolinite (> 50%). Furthermore, the TiO2/Al2O3 values suggest that the tonsteins have three magmatic origins, which were mostly felsic, with less intermediate and mafic. The trace elements of the enclosing coals, detrital intra-seam clay beds, floor, and roof were mainly sourced from the felsic-intermediate rocks. However, the elevated concentrations of Li, Ga, Zr, Nb, In, Sn, Hf, Ta, Pb, and Th may be related to the leaching of the tonsteins by (acidic) groundwater or hydrothermal solutions. This is supported by the dominant MREY enrichment patterns with positive Gd anomalies of the coals.

RARE EARTH FLUOROCARBONATES IN ROCKS OF THE SAFYANOVSKY COPPER-ZINC-PYRITE DEPOSIT (MIDDLE URALS)

For the first time, rare earth (REE)-fluorocarbonates were found in the ore-bearing rocks of the Safyanovsky copper-zinc-pyrite deposit (Middle Urals): synchysite, bastnasite, in association with fluorite, calcite, dolomite, barite, pyrite, sphalerite. Samples with REE-fluorocarbonate mineralization were found at a depth of 262 m in an altered near-ore zone of pyrite-carbonate-kaolinite-sericite-quartz composition in contact with massive pyrite-chalcopyrite and pyrite-sphalerite ores. It is assumed that REE-fluorocarbonates were formed from a hydrothermal solution together with fluorite and calcite. This event may be associated with a period of hydrothermal activity manifested at the post-collision stage of the development of the Ural folded system.

Composition and formation conditions of noble metal ores of the Koykar-Svyatnavolok sill (Republic of Karelia)

The Viksha iron ore deposit is confined to the Koykarsko-Sviatnavolok sill, where as a part of ore bodies, in addition to the main components - iron and titanium, it contains gold, platinum, and palladium. The purpose of this publication is to determine the type and patterns of noble metal mineralization in gabbro-dolerites of the Koykar-Svyatnavolok sill, to consider the mechanisms of accumulation and localization of precious metals in ore bodies. The repeated occurrence in the section of the intrusion of an association of two rock varieties of contrasting composition (high-iron - titanomagnetite gabbro-dolerites, and high-siliceous - granophyres), as well as the revealed petrographic, petrochemical and geochemical regularities, allow us to consider liquid stratification of magmatic melt as a mechanism for the formation of ore titanomagnetite horizons ( segregation). This liquid immiscibility led to the accumulation of noble metals in the high-iron fluidized liquate in accordance with distribution coefficients of nobel metals between silicate and oxide melts and between melt and fluid. The confinement of noble metal mineralization to sulfide, cobaltite-bornite-chalcopyrite accumulations in ore titanomagnetite horizons has been established, which corresponds to the low-sulfide noble metal type of mineralization. Precious metal mineralization is represented by both native mineral forms (arsenides, sulfoarsenides, antimonides and intermetallides of platinum group metals, gold and silver tellurides, electrum, native gold) and isomorphic impurities in bornite and cobaltite. The relationship between the formation of minerals bearing noble metals and the process of chloritization against the background of the transformation of protolith titanomagnetite is shown. A model for the concentration of precious metals from basaltoid melt in several stages is proposed: enrichment of fluidized high-iron ore liquat with precious metals; their accumulation in the residual fluid and in the sulfide liquid during the crystallization of ore liquat; their partial entry into the hydrothermal solution during fluid cooling and hydrothermal metasomatism of earlier crystals. The localization of noble metals occurred as the residual fluid cooled, due to the destruction of complex chloride and sulfide compounds with noble and non-ferrous metals and the crystallization of sulfide-precious metal paragenesis within the ore horizons.

Thorite inclusions in zircon of the monzogranite, Lower Nubia, SW Egypt

Abstract This report presents the results of a petrographical and mineralogical (optical microscopy, BSE-EDS image analysis) study of zircon in samples from the Lower Nubian monzogranite. The mineral occurs as smaller grains (< 80 μm) in a fine-grained quartz-feldspar-matrix, coexisting with other accessory minerals including biotite, clinochlore, titanite, and britholite-(Ce). Zircon is also present within biotite and britholite-(Ce), suggesting that it started crystallization at about the same time as these two minerals. Two types of thorite inclusions within zircon are reported in this study. Type 1 is widely distributed throughout the zircon grain, forming crystallites of which each is typically < 1 μm in size. Type 2 is relatively larger (5-15 μm) and occurs only in one part of the grain. For the thorite inclusions, three possible origins are briefly discussed: (1) exsolution of thorite from zircon; (2) dissolution/reprecipitation of zircon; and (3) growth syngenetically with zircon. Of these potential hypotheses, the syngenetic growth model seems more favorable for zircon-thorite intergrowths than the other two hypotheses. Thorite inclusions and their host zircons seem to have grown from magma rather than hydrothermal or supercritical solutions. Here, they have primary textures and consistent chemical compositions that are consistent with whole-rock geochemistry.

Trace element composition of fluorite from the Chumathang pegmatite deposit, eastern Ladakh, India

AbstractThe fluorite deposit of the Chumathang area of south‐eastern Ladakh, India, is hosted in pegmatite which cross‐cuts the Paleogene Chumathang granite. The rare earth element and yttrium (REE‐Y) and the trace element's composition of different colored (green, purple, and white) fluorite were investigated to understand its genesis. The green fluorite core is surrounded by purple fluorite, indicating that green fluorite crystallized earlier than the purple one. The white fluorite is mineralized with green fluorite, it does not exhibit any zoning like the other fluorite. The REE pattern of green and white fluorites is similar to those in the host pegmatite and associated Chumathang granite. ƩREE content in fluorite increases from green, white to purple. Fluorites in the study area are characterized by negative Ce suggesting partial reducing conditions during its formation. The Y/Y*, Ce/Ce*, and Eu/Eu* ratios show that fluorite records the compositional evolution of the hydrothermal solutions that transported the trace and REE from the host granite during the fluid–wall rocks interactions. The fluorite exhibits a positive Y anomaly which is suggestive of strong Y‐Ho fractionation in the fluid system. Chumathang fluorite show significant degrees of differentiation between terbium (Tb) and lanthanum (La) in all the purple, green, and white colored fluorite. The Tb/La and Tb/Ca ratios of the fluorites confirm the role of pegmatitic melt and hydrothermal fluid in the genesis of Chumathang fluorite.

МЕДИСТЫЕ СЛАНЦЫ ПРИКОЛЫМСКОГО ТЕРРЕЙНА (СЕВЕРО-ВОСТОК РОССИИ): МИНЕРАЛОГО-ГЕОХИМИЧЕСКИЕ ОСОБЕННОСТИ И УСЛОВИЯ РУДООБРАЗОВАНИЯ

Copper mineralization in the Magadan region (North-East of Russia) has been established in quartz-chloritoid and chlorite shales of the middle and upper Riphean of the Prikolymsky terrane. Compared to the upper crust, copper shales of the Oroek deposit are noticeably enriched in a narrow range of trace elements: Cu, Ag, Au, Rh, and Se, with enrichment factors ranging from 10-fold (Se, Rh) to 100-fold (Ag, Au) and even 1000-fold (Cu) suggesting, apparently, their synchronous involvement in ore formation. In addition, the studied samples are slightly enriched in Cd, Li, Co, Zn, V, U, Sc, Y, and REE. Copper shales show relatively flat rare earth element (REE) patterns similar to the chondrite-normalized pattern having no distinct positive or negative Eu anomalies and dominated by light lanthanides. The Ce/Ce* and Eu/Eu* values indicate that ore formation proceeded under oxidizing conditions. The obtained geochemical data show that the Riphean host rocks could serve as a source of trace elements and REE ore-forming fluids. In the ores, covellin and chalcocite are the main copper minerals; less common are roxbyite, idaite, nukundamite, spioncopite, chalcopyrite, silver-bearing (Ag about 1 wt. %) bornite and yarrovite, as well as native gold. Fluid inclusions in quartz suggest that copper mineralization was formed at temperatures of 212–190 °C and a pressure of 1 kbar, from hydrothermal solutions of medium salinity (from 13.8 to 12.4 wt. % eq. NaCl) and high density (0.95–0.98 g/cm3) saturated with chlorides of Ca, Mg, and K. The copper shales of the Prikolymsky terrane differ from sedimentary copper and copper shales of the African Belt by low Co and Ni contents and from the Kupfershifer by low concentrations of Pb and Zn. The obtained results can be used for prognosticating new deposits.

НОВЫЕ ДАННЫЕ О ГЕНЕЗИСЕ ГЮМУШЛУГСКОГО СВИНЦОВО-ЦИНКОВОГО МЕСТОРОЖДЕНИЯ НАХЧЫВАНСКОЙ АР АЗЕРБАЙДЖАНА

As a result of long-term geological and sedimentological investigation of the Gyumushlug stratiform lead and zinc deposit in the carbonate strata of the Middle Devonian and study of the geological structure of the Sharur massive of the territory and adjacent areas, it became possible to develop its sedimentary ore genesis. The source of metals for the formation of the deposit was not hypothetical hydrothermal solutions, as was confirmed by previous researchers, but polymetallic deposits and manifestations developed on the Baikal basement of the Zangezur microcontinent. The formation of ore deposits of the Gyumushlug tested a difficult and long path, amounting to several hundred million years. Three stages of ore formation were established: sedimento-logical-diagenetic; catagenetic with the participation of hot highly mineralized chloride-sulfate-calcium-magnesium groundwater; tectonic, which manifestate on the border of the Late Triassic and Early Jurassic as a result of the activation of the Early Alpine phase of tec-togenesis...

ЖЕЛЕЗОМАРГАНЦЕВЫЕ КОРКИ ГОРЫ ПЕТРА ВЕЛИКОГО И ХРЕБТА ВАСИЛЬКОВСКОГО (ЯПОНСКОЕ МОРЕ)

The structure and chemical composition of ferromanganese crusts formed on the sedimentary cover of the underwater volcanoes of Peter the Great Seamount and the Vasilkovsky Ridge, located near the continental slope of Primorye (Sea of Japan), have been studied. The crusts were formed as a result of cementation and precipitation of manganese hydroxides on the surface of the sediment. Signs of the hydrothermal nature of these formations are a very high value of titanium and low aluminum modules, low concentrations of non-ferrous and rare earth elements, and an excess of heavy REE contents over light ones. Ore matter was probably deposited in the Pleistocene-Holocene from post-volcanic hydrothermal solutions. Unlike the crusts deposited on basalts in the central parts of the Sea of Japan, these crusts do not contain inclusions of small grains of medium- and high-temperature mineral phases of non-ferrous metals.

Microwave-assisted hydrothermal solution process for accelerated formation of 3D hierarchical flowery anatase-TiO2 microspheres with excellent photocatalytic activity

A microwave-assisted hydrothermal solution synthesis methodology is used to prepare 3D hierarchical flowery TiO2 microspheres quickly and without calcination.

Геохимическая зональность рудной залежи Ново-Учалинского колчеданного месторождения (Южный Урал, Россия)

Novo-Uchaly essentially zinc (CZn>>CCu) VMS deposit is one of the largest in the Urals. Currently, it is under additional exploration by fans of underground drilling wells and mine workings. The paper describes a novel geochemical zonation of the sulphide deposit (the example of Cu, Zn, Au and In), discusses conditions of formation and factors that caused its complication. We carried geostatistical calculations in addition to the analysis of the zonation of the deposit. The ore deposit is represented by a large subvertical ribbon of a whimsical structure, inclined southward, which is confined to the wing of an inverted large anticlinal fold, cut by mafic dikes and characterized by a complex, combined geochemical zonality. The distribution of Cu and Zn is generally asymmetric. Copper-rich ores tend to the northern wedge of the deposit, and to the south, along its declination, the concentration of Zn increases, while Cu decreases, and the middle part of the deposit is represented by zinc-rich ores. In the section, copper maxima are more often noted in the footwall side of the deposit, and zinc — in the hanging side. The intrusion of a thick gabbro-diorite dyke and subsequent dynamometamorphism, including hydrothermal solutions, caused the redeposition of more mobile Cu in the near-contact zones of the dyke and areas of swell of the ore body thickness. Within the swell of the thickness of the deposit, in the hinge of the fold of the 2nd order, rich copper-zinc ores occur, which are enriched by Zn, Pb, Au, Ag, In, Ba and some other rare elements. The similarity of their behavior in ores is confirmed by their high positive pair correlation. In the ore body, the distribution patterns of gold and indium are rather symmetrical. High concentrations of gold and indium are confined to a sharp bend in the ore body, and small indium maxima occur in the footwall of the ore lode. As a result of dynamometamorphism, the deposit acquired a whimsical structure with the formation of thick swells; ores were significantly recrystallized, and locally enriched by non-ferrous and precious metals.

Geologic setting of the Pueblo Viejo Au–Ag–Cu-(Zn) mining district, Dominican Republic - Links to volcanic domes and volcanogenic massive sulfide mineralization

Geologic mapping at the Pueblo Viejo Au–Ag–Cu-(Zn) mine, Dominican Republic, and across the surrounding Pueblo Viejo district, reveals the geologic setting at the time of mineralization. Ore deposits consisting of disseminated sulfide, bedded massive sulfide, and high-grade massive sulfide veins formed (∼112 Ma) in a volcanic dome field during a period of extension across an emergent, intraoceanic island arc. Geologic maps reveal the links between volcanic domes and structure, hydrothermal alteration and mineralization, and ore deposits and gossans. Whole-rock geochemical data establish a tholeiitic signature for Early Cretaceous magmatism including the volcanic dome field. Northerly-striking, high-angle faults controlled the emplacement of volcanic domes and served as feeders for hydrothermal solutions. The largest ore deposits formed in a subsiding, marginal marine, volcano-sedimentary basin. Stacked intervals of bedded massive sulfide mineralization indicate that the basin was subsiding while mineralization was underway. Calc-alkaline dikes and plutons in the Pueblo Viejo district intruded at ∼88 Ma, well after mineralization had ended. Low-angle reverse faulting, greenschist facies metamorphism, and milky quartz veining and replacement were also Late Cretaceous (post-mineral) events. Ore deposits in the Pueblo Viejo district are best described as hybrid epithermal – VMS deposits, formed during a period of Early Cretaceous extension, tholeiitic volcanism, and volcanic dome emplacement in a shallow, marginal marine environment. Exploration for Au–Ag–Cu-(Zn) deposits like Pueblo Viejo should focus on intraoceanic island arcs, tholeiitic volcanic dome fields, extensional volcano-sedimentary basins, and VMS mineral occurrences.

Hydrothermal humification of lignocellulosic components: Who is doing what?

The humification behavior of lignocellulosic components (i.e., cellulose, hemicellulose and lignin) under acid-alkali two-step hydrothermal treatment was investigated with particular interest of revealing the contribution of single components as well as their interaction to hydrothermal humic acid (HHA). Lignin with its rich aromatic structures, had the highest HHA contribution (51.8 ± 1.0 wt%), while cellulose and hemicellulose only contributed 8.8 ± 1.6 wt% and 20.1 ± 4.4 wt% HHA yields, respectively. The conversion pathway of these components toward humification indicated that the hydrochar (HC) rather than the hydrothermal solution (HS) had higher humification capability under alkaline hydrothermal conditions because the hydrochar-derived HHA yields of 40.8 ± 2.0 wt% (cellulose), 66.2 ± 6.4 wt% (hemicellulose) and 55.4 ± 6.1 wt% (lignin) were achieved. In addition, co-hydrothermal treatment of cellulose, hemicellulose and lignin under this process improved the HHA production ascribing to the increased HC yield (23.1–53.1 %). The chemical characteristics of HHA products from lignocellulosic components (cellulose, hemicellulose, lignin) and their combinations were similar to the acknowledged natural humic acids. The hydrothermal humification of biowaste mainly passes through a top-down pathway (i.e., HHA forms from the oxidation of large fragments of hydrochar) as well as two bottom-up pathways (i.e., the soluble chemicals conduct the polymerization reaction for HHA production and react with the fragments from HC to synthesize the HHA). This study filled the lack of knowledge in the field of biowaste humification.

Petrography and geochemistry of the iron-rich rocks in the banded iron formation of the Chilpi Group, Central India: Implications on the level of oxygen in the Paleoproterozoic atmosphere before the “Proterozoic iron ore gap”

The Chilpi Group (2050–1850 Ma) in the Bastar Craton contains Banded Iron Formation (BIF) deposited immediately after the Great Oxidation Event but before the “Proterozoic iron ore gap”. Baseline geochemical data generated from this crucial period of Earth's history representing the transition from an initial high productivity period followed by productivity collapse, thereby delaying the evolution of biota, are interpreted in terms of the redox state of the ocean and atmospheric oxygen content. Presence of chamosite, greenalite and siderite in the ironstones of the Chilpi Group, identified during present analysis, provide valuable information regarding the redox state of the shallow sea. Geochemical analyses reveal high concentrations of Fe2O3total and SiO2 (average ~ 87.85 wt%) in iron-rich bands. Trace elements commonly enriched in detrital phases (e.g. Sc, Hf, Nb, Th and Zr) show good correlation with total REE concentration, but these have concentration below the cut-off limit defined for detrital sediments (except 3 samples). Higher concentration of these elements in greenalite/chamosite-rich samples indicates accumulation of these elements in greenalite/chamosite during primary precipitation. Most of the samples have low concentrations of Al2O3 (<5 wt%) and TiO2 (<0.5 wt%), but some chamosite-bearing samples show enrichments of Al2O3 (up to ~20 wt%). Post-Archean Australian Shale normalised rare earth elements with Y (REEY) patterns, showing a superchondritic Y/Ho ratio (average 32.15) and positive La, Gd and Y anomalies, indicate the preservation of seawater like signatures. Though a low positive Eu-anomaly, and Al/(Al + Fe + Mn) versus Fe/Ti plot suggest seawater signature with possible mixing of hydrothermal fluids and/or <10 % detrital components, preservation of seawater signatures and no involvement of high-temperature hydrothermal fluids are deduced from Eu/Sm versus Sm/Yb and Eu/Sm versus Y/Ho patterns. The Eu/Sm and Y/Ho ratios lower than the seawater and a mixing trend away from oceanic hydrothermal solution indicate possible mixing of freshwater with seawater for the observed REEY patterns. Redox-sensitive trace element ratios indicate a dysoxic to suboxic-anoxic condition in the depositional basin. Presence of oolitic textures and occurrence of chamosite support the shallow water (<60 m water depth) and anoxic condition in the depositional basin. The oxygen content of 10−3–10−5 times the present atmospheric level in the atmosphere is inferred for the period during the deposition of the BIF.

Low-Cost Antimony Selenosulfide with Tunable Bandgap for Highly Efficient Solar Cells.

About 10% efficient antimony selenosulfide (Sb2 (S,Se)3 ) solar cell isrealized by using selenourea as a hydrothermal raw material to prepare absorber layers. However, tailoring the bandgap of hydrothermal-based Sb2 (S,Se)3 film to the ideal bandgap (1.3-1.4eV) using the selenourea for optimal efficiency is still a challenge. Moreover, the expensive selenourea dramatically increases the fabricating cost. Here, a straightforward one-step hydrothermal method is developed to prepare high-quality Sb2 (S,Se)3 films using a novel precursor sodium selenosulfate as the selenium source. By tuning the Se/(Se+S) ratio in the hydrothermal precursor solution, a series of high-quality Sb2 (S,Se)3 films with reduced density of deep defect states and tunable bandgap from 1.31 to 1.71eV is successfully prepared. Consequently, the best efficiency of 10.05% with a high current density of 26.01 mA cm-2 is achieved in 1.35eV Sb2 (S,Se)3 solar cells. Compared with the traditional method using selenourea, the production cost for the Sb2 (S,Se)3 devicesis reduced by over 80%. In addition, the device exhibits outstanding stability, maintaining more than 93% of the initial power conversion efficiency after 30 days of exposure in the atmosphere without encapsulation. The present work definitely paves a facile and effective way to develop low-cost and high-efficiency chalcogenide-based photovoltaic devices.

Hydrothermally treated vermiculites: Ability to support products for CO2 adsorption and geological implications

The proposal of this research was to obtain products with higher porosity and specific surface area than the raw vermiculite for its possible application as a support material for CO2 adsorption. In addition, it was proposed to analyze the possible geological implications of the products resulting from the hydrothermal treatment of vermiculites in relation to their genesis. Hydrothermal treatment in the presence of CO2, at low temperature and pressure conditions, was carried out in two vermiculites from Uganda and China, with different behavior to thermal exfoliation and microwave irradiation. The untreated and treated samples were characterized by several techniques: X-ray diffraction (XRD) for obtaining the mineral composition; thermogravimetry (TG - DTG) for analyzing the thermal behavior; and BET isotherms for obtaining textural parameters. In addition, the hydrothermal solutions were characterized by the pH and the measuring of the lixiviated elements with inductively coupled plasma mass spectrometry (ICP-MS). Vermiculite can be a suitable support for CO2 adsorbents, based on the SBET and Qm values, and it is susceptible to carbonation. The hydrothermal treatment produced water loss in the expanded vermiculites by CO2 replacement; as consequence, amorphization occurred in the purer Ugandan sample, and vermiculitization occurred in the less pure sample from China.The vermiculitization process indicates that the geological origin of vermiculite may be hydrothermal from phlogopite.

Crustal waveguides of sedimentary deposits and conditions for their operation

The relevance of the article is determined by the need to develop the theory of crustal waveguides as a new look at the processes of formation of various hydrocarbon deposits. The purpose – identification of new structures – crustal waveguides – active fluid-saturated zones, within which certain types of traps for hydrocarbons can be formed. Research methods. The article analyzes literature sources that consider the phenomenon of oil formation as a result of the evolution of fluid-saturated zones of crustal waveguides and data from X-ray diffraction and electron microscopic analyzes of layered silicates. Results. The conditions for the operation of crustal waveguides are considered from the standpoint of the presence of free matter, methods of its delivery and energy sources, and features of the formation of their structure. The data of studies of the mineral composition of the rocks of the North-Tazovskaya depression of Western Siberia and the features of their hydrothermal-metasomatic alterations are presented. Minerals and their parageneses have been established, indicating the presence of hydrothermal processes accompanying crustal waveguides. The article argues that the processes of alteration of host rocks in various zones of crustal waveguides lead to the formation of special hydrocarbon traps of an unconventional type, established for deep Jurassic and pre-Jurassic deposits in the north of Western Siberia. The theory of crustal waveguides makes it possible to find the relationship between the formation of oil and gas fields and the geoenergetic aspects of the problem of the removal of intraterrestrial heat in various forms, the main of which is hydrothermal activity. The conclusions summarize the main provisions of the theory of crustal waveguides of sedimentary deposits, the conditions for their operation. The necessary conditions are: the presence of free matter in deep zones, energy sources of self-oscillations of the sedimentary strata and deep faults containing them as a result of unloading the stress field of a special kind, taking into account the depths of their formation. Conclusions are also drawn about the mineral composition of hydrothermal solutions associated with crustal waveguides, which affect host rocks and lead to the formation of a new type of metasomatic traps for hydrocarbons.

Enrichment of critical elements (Li-Ga-Nb-Ta-REE-Y) in the coals and host rocks from the Daping Mine, Yudongnan Coalfield, SW China

Critical elements in coals and host rocks have attracted much attention due to their growing demand and rising economic significance. This research reports new data of elevated critical elements and mineralogical characteristics of the coals and host rocks from the Daping Mine, Yudongnan Coalfield, neighboring to the previously reported coal-hosted Li and rare earth elements plus yittrium (REY) ore deposit of the Donggou Mine in the same coalfield. The coal in the Daping Mine is mainly a medium-volatile bituminous coal and characterized by a low-ash yield (Ad = 13.08–30.32 %, 19.65 % on average) and a high-sulfur content (1.75–9.25 %, 3.43 % on average). Critical elements including Li, Ga, Nb, Ta, REY are enriched in the coal. Minerals in the Daping coal are mainly clay minerals (including illite, mixed layer of illite/smectite (I/S), kaolinite, and chamosite) and pyrite, and to a lesser extent, calcite, anatase, and marcasite, with traces of zircon, celestite, and baddeleyite. Lithium is mainly associated with illite, and Ga, Nb, Ta, and REY also have an inorganic affinity. The terrigenous materials of the Daping coal were from the intermediate-felsic rocks at the top of the Kangdian Upland rather than the basalts. Hydrothermal solutions also make a great contribution to the enrichment of critical elements and minerals. High-temperature solutions (>200 °C) may be responsible for the weakly negative Eu anomalies. The coal ashes in the Daping Mine have significant concentrations of Li2O (2583 ppm on average), Ga (83.5 ppm on average), (Nb, Ta)2O5 (143 ppm on average), and REO (oxides of REY, 1125 ppm on average), all of which are higher than their respective cut-off grades. Moreover, the floor strata are enriched in these critical elements. Thus, the coal ashes and floor strata are potential resources for extraction of these critical elements.

Understanding the effect of sulfate ions on the hydrothermal curing of autoclaved aerated concrete

The addition of calcium sulfate in the preparation of autoclaved aerated concrete (AAC) leads to improved mechanical properties but the precise mechanism is not well constrained. To study this, the hydrothermal curing process was monitored quantitatively with and without sulfate addition using ex situ and in situ X-ray diffraction. Higher concentrations of sulfate ions delayed the formation of the intermediate C-(A)-S-H phase and the dissolution of quartz. Once the additional sulfate ions were depleted by hydroxylellestadite formation, C-(A)-S-H formation and quartz dissolution started simultaneously at higher rates. This delayed reaction is suggested to enhance the mechanical strength by i) improving the diffusion of silicate ions in hydrothermal solution, ii) improving the distribution of C-(A)-S-H and tobermorite crystallites, and iii) closing larger capillary pores in the range of 1–5 μm. This could explain some of the ambiguous results from previous studies and provide an opportunity to optimize the AAC production process.