High H2O Contents Research Articles

Low-Temperature NH3-SCR Technology for Industrial Application of Waste Incineration: An Overview of Research Progress

Selective catalytic reduction of nitrogen oxides with NH3 (NH3-SCR) was investigated deeper and deeper with poisoning factors such as H2O, SO2, heavy metals, etc. In order to remove the reheating process before the SCR reactor, the application trend of NH3-SCR technology in the non-power industry is concentrated on the condition of low temperature even ultra-low temperature. The present study summarizes the research process of SO2 and H2O resistance of NH3-SCR catalysts under low temperatures related to the working conditions of municipal solid waste incineration plants. In detail, the effects of a high content of H2O and low concentration of SO2 are reviewed. Other factors such as heavy metals, alkali, or alkaline earth metals in the reaction system, synergistic removal of NOx, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are addressed. Finally, the catalytic performance of assembled monolithic catalysts and pilot-scale experiments are also analyzed for the possibility of industrial application. Hopefully, in view of the questions outlined in this study, valuable insights could be taken into consideration for the development of NH3-SCR in waste incineration.

Crustal thickening and multipoint delamination for the ca. 90 Ma high-Sr/Y intrusions and the associated porphyry-skarn Cu-Au-Mo mineralization in the western central Lhasa terrane, Tibetan Plateau

The ca. 90 Ma (92−84 Ma) high-Sr/Y intrusions in the western central Lhasa terrane (WCLT) of the Tibetan Plateau record critical information about the late Mesozoic crustal architecture of the Lhasa terrane and may have provided favorable conditions for porphyry mineralization. However, conflicting geodynamic processes have been proposed, and their mineralization potential is unclear. Here, we report the newly discovered Banongzuosi porphyry-skarn Mo-Cu deposit and Qielong skarn Cu-Au and Rongqing porphyry-quartz vein-type Mo mineral prospects. They provide important constraints on the generation of the ca. 90 Ma high-Sr/Y magmas and their associated mineralization potential. Then, integrated studies of the ca. 90 Ma intrusions are performed to address the above issues. Dating shows that intrusions and mineralization in the three areas occurred at 92.4−84.1 Ma. Based on whole-rock geochemistry, the high-Sr/Y intrusions can be divided into low- and high-Mg#-Cr ones. Zircon Hf isotopic data indicate that both ancient and juvenile lower crust existed in the WCLT, with significant juvenile components in the high-Mg# and Cr-rich intrusions. The crustal thickness calculated from the zircon trace element data suggests that the WCLT had thickened crust (>64 km) with local areas thinned by lower crustal delamination at ca. 90 Ma. Regional thickening and local lower crustal delamination formed the low- and high-Mg#-Cr intrusions, respectively. Whole-rock and zircon trace element data reveal that most of the ca. 90 Ma high-Sr/Y intrusions are hydrous and oxidized. The thickened crust resulted in high H2O contents and fO2 of intrusions and promoted porphyry-skarn mineralization. However, crustal thinning and contamination by reduced Precambrian basement decreased the magma fO2 and hindered mineralization. The advantageous tectonic setting and high H2O and fO2 led to the ca. 90 Ma high-Sr/Y intrusions having the potential to form collisional porphyry-skarn Cu-Au-Mo deposits.

Research on the effect of CO2 and H2O on NO reduction of biomass char by the equivalent characteristic spectrum method via an on-line mass spectrometer

Despite extensive experimental studies on NO reduction by biomass char, the impact of high concentrations of CO2 and H2O on the NO-char reaction remains insufficiently understood. This study investigates the effects of CO2, H2O, and CO2+H2O atmospheres on NO reduction by biomass char in a micro-fluidized bed (MFB). Experiments were conducted at 900 °C, with CO2 concentrations ranging from 20 % to 80 % and H2O concentrations from 10 % to 40 %. The results show that increasing concentrations of CO2 and H2O accelerate the NO reduction rate. However, under high CO2 and H2O concentrations, both the maximum NO reduction efficiency and the mass consumption of nitrogen decrease. In a CO2 atmosphere, nearly all nitrogen from NO converts to N2, but this conversion efficiency declines in the presence of H2O. When both CO2 and H2O are present, H2O predominantly governs the NO consumption rate. Additionally, the apparent activation energy for NO reduction is higher in an H2O atmosphere compared to a CO2 atmosphere at similar concentrations.

Simulation of lithium hydroxide decomposition using deep potential molecular dynamics.

Chemical reactions and vapor-liquid equilibria for molten lithium hydroxide (LiOH) were studied using molecular dynamics simulations and a deep potential (DP) model. The neural network for the model was trained on quantum density functional theory data for a range of conditions. The DP model allows simulations over timescales of hundreds of ns, which provide equilibrium compositions for the systems of interest. Single-phase NPT simulations of the liquid show the decomposition of LiOH into lithium oxide (Li2O) and dissolved water (H2O). These DP results were validated by direct abinitio molecular dynamics simulations that confirmed the accuracy of the model with respect to reaction kinetics and equilibrium properties of the melt. The reactive vapor-liquid behavior of this system was subsequently studied using direct coexistence interfacial DP simulations. Partial pressures of H2O in the vapor are found to be in close agreement with available experimental measurements. By fitting temperature-dependent expressions for the reaction equilibrium and Henry's law constants, the equilibrium composition for any given initial composition and temperature can be quantitatively modeled. For high initial concentrations of Li2O or H2O, mixtures of LiOH + Li2O/H2O are found to undergo phase separation. The present study illustrates how DP-based molecular dynamics simulations can be used for quantitative modeling of multiphase reactive behavior with the accuracy of the underlying abinitio quantum chemical methods.

The genesis and mineralization potential of the Kunshan pluton in the Xuancheng district, Eastern China

The Xuancheng mineralization district (XMD) is an important part of the Middle-Lower Yangtze River Metallogenic Belt, and hosts a number of porphyry-skarn Cu poly-metal discoveries in recent years. The Kunshan pluton is located in the northeastern sector of the Xuancheng district, and is composed of fine-grained pyroxene diorite, coarse-grained pyroxene diorite and granodiorite. This study reports zircon LA-ICP-MS U-Pb chronology, whole-rock geochemistry and Sr-Nd isotope analysis of the Kunshan Complex pluton. The intrusions young from the fine-grained pyroxene diorite (137.2 ± 2.0 Ma), through the coarse-grained pyroxene diorite (136.1 ± 2.1 Ma) to the granodiorite (134.8 ± 2.2 Ma). All three stages of magmatic samples are high-potassium calc-alkaline to potassium dolerite series, they are enriched in light rare earth elements (LREE) and large ion lithophile elements such as Rb, Sr, and (Ba), but depleted in heavy rare earths elements (HREE), and high field strength elements such as Nb, Ta, Ti, and P. Their (87Sr/86Sr)i and (143Nd/144Nd)i values range from 0.706703 to 0.707618 and 0.512023 to 0.512064 respectively. The samples from the Kunshan complex pluton are consistently plotted the zone between the mantle evolution trending line and MLYB crust, which indicating the three-stage melt are derived from the crust-mantle mixed source, with closer to lithosphere mantle. All phases of the pluton were derived from the same magmatic source, likely the crust-mantle mixed zone between the lower Yangtze crust and enriched lithospheric mantle. The 3 stage melts formed Kunshan complex pluton gradually strengthen fractional crystallization (FC) during their emplacement process, while the late granodiorite melt with highest FC degree was the ore-forming intrusion, which is characterized with oxidized melt with low temperature, and high H2O content. After Compared with the mineralized granitoid intrusive rocks in the Middle-Lower Yangtze River Metallogenic Belt, it suggests that the late highly differentiated granitoids, like Kunshan granodiorite, are probably favorable metallogenic indications.

Experimental study and chemical equilibrium calculation on the mineral transformation of high-alkali coal under oxy-fuel condition

The study aimed to study the mineral transformation of high-alkali coal to address the ash-related issues in oxy-fuel combustion. However, the traditional ashing method alone is inappropriate to study the mineral transformation at the initial stage of coal combustion due to the high ashing temperature. Hence, both the plasma ashing method (<200 °C) and traditional ashing method (600–1200 °C) were employed in this research to prepare the ash samples for characterization. The plasma ashing method is an efficient way to determine the original minerals in coal because it can consume the organic matter at low temperature. The recirculation of flue gas in oxy-fuel combustion can lead to high SO2 and H2O concentrations, while their influences on mineral transformation need to be clarified. In this work, SO2 and H2O were injected into CO2 to simulate the recycled flue gas (RFG). Furthermore, the chemical equilibrium calculation was conducted besides multiple experimental tests to acquire more comprehensive information of mineral transformation. The results show that high sodium and calcium contents are determined in these high-alkali coals, and two of them are rich in iron. In O2/CO2 atmosphere, some sodium (e.g. NaCl) volatilizes into the gas phase and the others converts into aluminosilicates (e.g. NaAlSi3O8) during the heating process. The calcium salts (mainly CaCO3 and CaSO4) decompose and produce silicates, aluminosilicates, and magnesium silicates. The major iron-containing minerals are identified as FeS, FeS2, and Fe2O3. Both FeS and FeS2 are oxidized into Fe2O3 below 600 °C. Moreover, the kaolinite (Al2Si2O5(OH)4) in raw coals decomposes at low temperature (<600 °C). In O2/RFG atmosphere, the additions of SO2 and H2O enhance the sulfation of AAEMs (alkali and alkaline earth metals) and delay the decomposition of sulfates. The productions of some silicates, aluminosilicates, and magnesium silicates of AAEMs are inhibited to varying degrees, and there could be complicated salts containing sulfur (e.g. hauyne). The transformations of iron-containing minerals are little related to the presences of SO2 and H2O. This work obtained the transformations of main minerals in high-alkali coal under O2/CO2 and O2/RFG conditions, which helps to address the ash-related issues.

Experimental study on the ash deposition and NO emission of high-alkali coal under the staged O2/CO2 and O2/RFG conditions

The oxy-fuel combustion contributes to carbon capture, while the recirculation of flue gas brings about high concentrations of SO2 and H2O, which can affect the transformation of minerals in high-alkali coal. The staged oxy-fuel combustion, as an effective method for NOx reduction, can also change the ash deposition behavior of high-alkali coal. Two kinds of diluting agents, including pure CO2 for O2/CO2 combustion and simulated “recycled flue gas” (CO2, SO2, and H2O) for O2/RFG combustion, were employed in the present work. The ash deposition and NO emission of high-alkali coal during the staged oxy-fuel combustion were simultaneously studied under O2/CO2 and O2/RFG conditions. The conversion ratios of fuel-nitrogen to NO (CNO) and ash deposition efficiencies (Ed) at different stoichiometric ratios in primary combustion zone (SR1) and different oxygen concentrations were obtained. Afterwards, a series of tests were performed to further analyze the ash deposits. The experimental results show that as SR1 increases from 0.6 to 1.2, CNO jumps from 2.0 % to 23.5 % (O2/CO2 combustion) and from 1.9 % to 19.9 % (O2/RFG combustion). The additions of SO2 and H2O can reduce the NO emission. With the rising SR1, Ed under the O2/CO2 and O2/RFG conditions decreases from 4.0 % to 2.6 % and from 4.8 % to 2.1 %, respectively. At high SR1, the CaSO4 amount declines and the iron contributes less to the ash deposition. In O2/RFG combustion, the small sticky particles of sodium aluminosilicates on large particle surfaces reduce, and the large particles of calcium aluminosilicates shrink because some calcium produces CaSO4. Moreover, the exposure of ferrous iron to H2O helps its oxidization so iron is harder to cause severe adhesion. As O2 concentration rises from 21 % to 40 %, CNO shows an upward trend. Meanwhile, Ed under the O2/CO2 and O2/RFG conditions increases from 2.6 % to 3.7 % and from 2.3 % to 2.7 %, respectively. The present work is expected to provide some conducive information for the clean utilization of high-alkali coal and secure operation of boiler, as well as large-scale CO2 capture.

Volatiles and Redox Along the East African Rift

AbstractThe upper mantle under the Afar Depression in the East African Rift displays some of the slowest seismic wave speeds observed globally. Despite the extreme nature of the geophysical anomaly, lavas that erupted along the East African Rift record modest thermal anomalies. We present measurements of major elements, H2O, S, and CO2, and Fe3+/ΣFe and S6+/ΣS in submarine glasses from the Gulf of Aden seafloor spreading center and olivine‐, plagioclase‐, and pyroxene‐hosted melt inclusions from Erta Ale volcano in the Afar Depression. We combine these measurements with literature data to place constraints on the temperature, H2O, and fO2 of the mantle sources of these lavas as well as the initial and final pressures of melting. The Afar mantle plume is C/FOZO/PHEM in isotopic composition, and we suggest that this mantle component is damp, with 852 ± 167 ppm H2O, not elevated in fO2 compared to the depleted MORB mantle, and has temperatures of ∼1401–1458°C. This is similar in fO2 and H2O to the estimates of C/FOZO/PHEM in other locations. Using the moderate H2O contents of the mantle together with the moderate thermal anomaly, we find that melting begins at around 93 km depth and ceases at around 63 km depth under the Afar Depression and at around 37 km depth under the Gulf of Aden, and that ∼1%–29% partial melts of the mantle can be generated under these conditions. We speculate that the presence of melt, and not elevated temperatures or high H2O contents, are the cause for the prominent geophysical anomaly observed in this region.

An investigation on the H2O, unburned H2 and NO emission characteristics from a direct injection hydrogen engine

Hydrogen engines show great potential as a power source with good combustion performance, zero carbon emissions, and diverse sources. However, the exhaust emission characteristics with high water vapor (H2O) content have not yet been clarified. This study presents the exhaust emissions of a heavy-duty direct-injection hydrogen engine under various operational parameters, with a focus on the H2O content. The results reveal important exhaust emissions characteristics of the hydrogen engine, including lower exhaust temperature (200 °C–400 °C), higher unburned H2 emissions (up to 17100 ppm), less nitrogen oxide (NO) generation (<1000 ppm), and higher H2O content (6%–40%). Additionally, unburned H2 rises, and NO and H2O decrease as the excess air ratio (λ) increases. When λ is greater than 3, NO levels fall sharply to below 100 ppm. Optimal emissions performance is achieved with a 5 °CA BTDC ignition timing where low levels of H2, H2O, and NO are maintained. Increasing hydrogen injection pressure decreases H2 but raises exhaust temperature, H2O, and NO emissions. Excessively delaying hydrogen injection timing adversely affects the concentration gradient in the cylinder, increasing unburned H2 emissions. The best emissions performance is observed at a hydrogen injection timing of 110 °CA BTDC.

Fast, furious, and gassy: Etna's explosive eruption from the mantle

The 3930 BP Fall Stratified (FS) eruption at Mt. Etna is a rare example of a highly explosive eruption of primitive (picritic) magma directly from the mantle. The eruption produced ash plumes up to an estimated 20 km height, leading to a volcanic explosivity index (VEI) 4 (subplinian). Given its volatile-rich and primitive nature, the FS magma may have ascended rapidly from great depths to avoid fractionation and mixing within the extensive plumbing system beneath Etna. To determine the pressures from which the FS magma derived, we perform rehomogenization experiments on melt inclusions hosted in Fo90–91 olivines to resorb shrinkage bubbles and determine the initial H2O and CO2 in the melt. With measured CO2 concentrations of up to 9600 ppm, volatile solubility models yield magma storage pressures of 630–800 MPa. These correspond to depths of 24–30 km, which are comparable to the seismologically estimated Moho. Therefore, the magma's high CO2 concentration must come from carbon in the mantle (likely from subducted carbonates), as opposed to assimilation of shallow (<10 km) crustal carbonates.Diffusion modeling of H2O and forsterite zonation profiles in clear, euhedral, and crystallographically oriented olivines indicates rapid ascent of magma directly from its source region to the surface. Forsterite profiles exhibit a narrow rim of growth zoning but no detectable diffusional zoning, reflecting maximum ascent times of 1–5 days. Eighteen measured H2O profiles result in remarkably uniform decompression rates of 0.47 MPa/s (95% confidence interval of 0.16–1.28 MPa/s), which is among the fastest measured for basaltic-intermediate magmas. These decompression rates indicate that the final stage of magma ascent over the region in which H2O degasses (between the surface and ∼ 15 km) occurred extremely fast at ∼ 17.5 m/s. This eruption may provide a link between primary magma composition and eruption intensity: we propose that the unusually explosive nature of this picritic eruption was driven by high H2O and CO2 concentrations, which led to continuously rapid ascent without stalling, all the way from the Moho.

Revealing the mechanism of hydration on the CO2 kinetic adsorption of CaO surface via ReaxFF MD simulations with experiments

Hydration has been regarded as an effective method to improve the cyclic activity of CaO during the Calcium looping CO2 capture process, but its mechanism remains unclear. In this work, the hydration reaction of CaO surface and its underlying mechanism was studied by ReaxFF molecular dynamics simulation combing with TGA experiments. The effect of hydration on the initial CO2 adsorption rate showed a trend of promoting at low H2O degree and inhibiting at high H2O concentration. The CaO surface was easily passivated, and it can maintain its crystal structure and begin to distort at about 1.0 H2O monolayer contents. Hydration failed to promote the CO2 adsorption rate, inversely the CO2 adsorption process accelerated the diffusion of H ions inward the CaO lattice·H2O dissociation produced two hydroxyl groups: direct OwH and indirect OsH. Atomic density profiles showed that the direct hydroxyl pairs were always, and indirect OsH groups can consume surface oxygen active sites, reducing the initial rapid CO2 adsorption activity. On the pre-hydrated CaO surface, CO2 molecules were more likely to bind to solid oxygen active sites than OH groups. The H free radical diffused inside the lattice in the form of transition HO2 state, promoting the slow CO2 adsorption amount.

Geochemical Evidence of Water-Fluxed Crustal Melting in the Northern Colombian Andes

Abstract The compositions of crustal magmas are powerful tools for understanding the formation and differentiation of continents. However, the geochemical fingerprints that distinguish the two dominant mechanisms of crustal melting, namely dehydration and water-fluxed melting, are still controversial. To provide new insights into this problem, we discuss the petrogenesis of the Paipa Volcanic Complex (PVC), an isolated Quaternary volcanic field in the Colombian Eastern Cordillera. The PVC is characterized by peraluminous trondhjemite-like rhyolites with exceptionally high Na2O contents (~6 wt %), super-chondritic Nb/Ta (~27), elevated Sr/Y ratios (~120), spoon-shaped REE patterns, and enriched isotopic compositions that overlap with those of the local basement. They also exhibit high pre-eruptive H2O contents (~up to 9.5 wt %) and abundant Paleozoic zircon inheritances. We demonstrate that these characteristics are inconsistent with a process of intra-crustal differentiation from a mafic or intermediate mantle-derived precursor. Instead, we propose that the origin of the PVC is best explained by melting the local (meta)sedimentary basement under H2O-saturated conditions, at middle-crustal pressures (~1.3 GPa) and relatively low temperatures (~690–740°C), following the complete breakdown of plagioclase and biotite, and the formation of reactive peritectic amphibole. This scenario differs from the high-temperature dehydration melting conditions that have been widely proposed for the Andes and globally, which result in the production of water undersaturated magmas in equilibrium with anhydrous lithologies rich in plagioclase and/or garnet. Accordingly, we speculate that an external H2O flux was ultimately sourced from a buoyant, cold, and hydrated mantle wedge that was extensively metasomatized by fluids derived from the Nazca and Caribbean flat-slab fronts. These conditions depressed the asthenospheric mantle potential temperature, likely inhibiting mantle melting. In turn, they facilitated the infiltration and ascent of mantle-derived H2O through pre-existing crustal faults and shear zones. Our results indicate that water-fluxed melting could be a plausible mechanism for generating crustal magmas in orogenic regions where the availability of free H2O has been difficult to confirm.

Effectiveness of Ti-in-amphibole thermometry and performance of different thermometers across lower continental crust up to UHT metamorphism

Metabasites are important constituents of deep crustal sections and are the favored rock type for studying lower crustal amphibolite to granulite transitions. However, metapelites may develop a larger number of temperature-sensitive mineral assemblages and are particular useful when extreme ultrahigh temperature (UHT) conditions are envisaged. A recent calibration of the Ti-in-amphibole thermometer by Liao et al. (2021) was supposed to make thermometry on metabasites quick and easy to apply. However, their calibration is based on experiments which were not originally designed to investigate in detail the temperature dependence of Ti in amphibole. In addition, a possible effect of aTiO2 and/or pressure on the Ti content of amphibole was not fully taken into account. This resulted in a calibration uncertainty of ± 70 °C (2σ), much higher than that of other single-mineral thermometers. In this study we firstly test the newly calibrated Ti-in-amphibole thermometer across the mid to lower crustal section of the Ivrea–Verbano Zone (IVZ; NW Italy) and compare the performance of different thermometric techniques across the sequence. Ti-in-amphibole thermometry records increasing peak temperatures from amphibolite (600–700 °C), transition (750–800 °C) and granulite (850–950 °C) zones. Titanium content of amphibole may be modified by retrograde fluid influx returning temperatures c. 200–300 °C lower than in non-altered domains. The comparison reveals that Zr-in-rutile thermometer in pelitic granulites seems to be more prone to post-peak resetting than the Ti-in-amphibole thermometry in nearby mafic rocks. This behavior is also confirmed by amphibole analyses from other UHT localities, where the performance of Ti-in-amphibole thermometry is comparable with that of Al-in-orthopyroxene in pelitic granulites. However, Ti-in-amphibole temperatures are underestimated in rutile-bearing samples and this limitation is not solely restricted to rocks containing high H2O contents as previously thought. Derived constraints on the diffusivity of Ti through amphibole demonstrate the robustness of the Ti-in-amphibole thermometer to later thermal disturbances. However, ad-hoc experiments are still necessary to improve the accuracy and precision of calibration and to extend its applicability. This advance will make mafic granulites routine targets for studies devoted to understanding the regional extent of UHT metamorphism.

Review on Mercury Control during Co-Firing Coal and Biomass under O2/CO2 Atmosphere

Combining biomass co-firing with oxy-fuel combustion is a promising Bioenergy with Carbon Capture and Storage (BECCS) technology. It has the potential to achieve a large-scale reduction in carbon emissions from traditional power plants, making it a powerful tool for addressing global climate change. However, mercury in the fuel can be released into the flue gas during combustion, posing a significant threat to the environment and human health. More importantly, mercury can also cause the fracture of metal equipment via amalgamation, which is a major risk for the system. Therefore, compared to conventional coal-fired power plants, the requirements for the mercury concentration in BECCS systems are much stricter. This article reviews the latest progress in mercury control under oxy-fuel biomass co-firing conditions, clarifies the impact of biomass co-firing on mercury species transformation, reveals the influence mechanisms of various flue gas components on elemental mercury oxidation under oxy-fuel combustion conditions, evaluates the advantages and disadvantages of various mercury removal methods, and finally provides an outlook for mercury control in BECCS systems. Research shows that after biomass co-firing, the concentrations of chlorine and alkali metals in the flue gas increase, which is beneficial for homogeneous and heterogeneous mercury oxidation. The changes in the particulate matter content could affect the transformation of gaseous mercury to particulate mercury. The high concentrations of CO2 and H2O in oxy-fuel flue gas inhibit mercury oxidation, while the effects of NOx and SO2 are dual-sided. Higher concentrations of fly ash in oxy-fuel flue gas are conducive to the removal of Hg0. Additionally, under oxy-fuel conditions, CO2 and metal ions such as Fe2+ can inhibit the re-emission of mercury in WFGD systems. The development of efficient adsorbents and catalysts is the key to achieving deep mercury removal. Fully utilizing the advantages of chlorine, alkali metals, and CO2 in oxy-fuel biomass co-firing flue gas will be the future focus of deep mercury removal from BECCS systems.

Density functional theory study on the mechanism of water gas shift reaction catalyzed by molybdenum hexacarbonyl in aqueous solvent

The mechanism of the water gas shift reaction (WGSR) catalyzed by Mo(CO)6 in both gaseous and aqueous phases were analyzed using the density functional theory (DFT) method. This study indicates that aqueous phase slightly increased every energy barrier for each step along the reaction path. The turnover frequency (TOF) of the reaction was determined using the energy span model (ESM). The TOF value in the aqueous phase (2.48 × 10−16 s−1) is slightly lower than in the gas phase (6.08 × 10−16 s−1). Actually, the advantages of aqueous phase may be attributed to high solubility and concentration of H2O, CO, OH−. The study of temperature (300–900 K) on energy profile shows that the reaction rate of WGSR can be increased with the increase of temperature. This research filled the gap in understanding the mechanism for the WGSR in aqueous phase, provides a reasonable theoretical foundation for molybdenum-based catalysts development.

Volatiles in melt inclusions from lunar mare basalts: Bridging the gap in the H2O/Ce ratio between melt Inclusions in lunar pyroclastic sample 74220 and other mare samples

The H2O concentration and H2O/Ce ratio in olivine-hosted melt inclusions are high in lunar pyroclastic sample 74220 (H2O up to 1410 ppmw; H2O/Ce up to 77) but lower (H2O 10 to 430 ppmw; H2O/Ce 0.3 to 9.4) in all other lunar samples studied before this work. The difference in H2O concentration and in H2O/Ce ratio is absent for other volatile elements (F, S, and Cl) in melt inclusions in 74220 and other lunar samples. Because H2O (or H) is a critical volatile component with significant ramifications on the origin and evolution of the Moon, it is important to understand what causes such a large gap in H2O/Ce ratio between 74220 and other lunar samples. Two explanations have been advanced. One is that volcanic product in sample 74220 has the highest cooling rate and thus best preserved H2O in melt inclusions compared to melt inclusions in other samples. The other explanation is that sample 74220 comes from a localized heterogeneity enriched in some volatiles. To distinguish these two possibilities, here we present new data from two rapidly cooled lunar samples with glassy melt inclusions: olivine-hosted melt inclusions (OHMIs) in 79135 regolith breccia (unknown cooling rate but with glassy MIs similar in texture with those in 74220), and pyroxene-hosted melt inclusions (PHMIs) in 15597 pigeonite basalts (known high cooling rate, second only to 74220 and 15421). In addition, we also investigated new OHMIs in sample 74220. If the gap is due to the difference in cooling rates, samples with cooling rates between those of 74220 and other studied lunar samples should have preserved intermediate H2O concentrations and H2O/Ce ratios. Our results show that melt inclusions in 79135 and 15597 contain high H2O concentrations (up to 969 ppmw in 79135 and up to 793 ppmw in 15597) and high H2O/Ce ratios (up to 21 in 79135 and up to 13 in 15997), bridging the big gap in H2O/Ce ratio among 74220 and other lunar samples. Combined with literature data, we confirm that H2O/Ce ratios of different lunar samples are positively correlated to the cooling rates and independent of the type of mare basalts. We hence reinforce the interpretation that the lunar sample with the highest cooling rate best represents pre-eruptive volatiles in lunar basalts due to the least degassing. Based on Ce concentration in the primitive lunar mantle, we estimate that H2O concentration in the primitive lunar mantle (meaning bulk silicate Moon) is 121 ± 15 ppmw. Our new data also further constrain F/P, S/Dy and Cl/Ba ratios in lunar basalts and the lunar mantle. Estimated F, P, and S concentrations in the lunar primitive mantle are 4.4 ± 1.1 ppmw, 22 ± 8 ppmw, and 67-33+67 ppmw, respectively.

The relationship between iron redox states and H2O contents in back-arc basin basaltic glasses from the North Fiji Basin

Island-arc basalts (IAB) from convergent plate margins tend to have both higher iron oxidation states (higher Fe3+/Fe2+) and higher H2O contents than the mid-ocean ridge basalts (MORB) produced by seafloor spreading, which raises the question of whether these two characteristics are causally related. Back-arc basin basalts (BABB) may help with this question, in that they are products of seafloor spreading, like MORB, but sourced from supra-subduction mantle, like IAB. Here we examine the relationship between Fe3+/Fe2+ (determined by XANES spectroscopy) and H2O contents in BABB glasses from the North Fiji Basin (NFB). The glasses cover a range of compositions from 6.1 to 8.5 wt% MgO, and from 0.16 to 1.6 wt% H2O, and have also been analysed for trace elements and Sr-Nd-Pb-isotopes. Measured Fe3+/Fe2+ range from MORB-like to slightly higher values and are positively correlated with H2O and heavy-halogen contents (Cl, Br and I). The correlation is due to lower Fe2+ rather than higher Fe3+ compared to the MORB array. This suite of BABBs is not significantly enriched in trace elements other than H2O and the heavy halogens, with MORB-like Ba/Th and other incompatible-element ratios, suggesting that the H2O and halogens may have come from dehydration of subducted lithospheric serpentinites under subsolidus conditions. Na2O is unusually variable for a suite of samples from such a limited area, and is not correlated with H2O, precluding a relationship between H2O and degree of melting. The link between H2O and low Fe2+ may be explained by H2O-rich fluids entering the transcrustal magma plumbing system, where they increase the proportion of olivine and augite to plagioclase crystallizing during the crustal evolution of the magmas. In this situation, relatively small additions of H2O can have an enhanced effect on major-element chemistry if the crustal evolution proceeds by cycles of replenish-mix-tap-crystallize (RMTX) rather than by simple fractional crystallization without repeated replenishment and tapping. The absence of any increase in Fe3+ with H2O, together with the lack of any correlation between H2O and Fe3+/Fe2+ in MORB glasses generally, suggest that various mechanisms, including more extensive olivine fractionation, were responsible for elevating Fe3+/Fe2+ in H2O-rich basalts from convergent margin settings. Proxy methods based on concentrations of elements with redox-variable partition coefficients (V, Eu) are not sensitive enough to record the subtle variations in Fe3+/Fe2+ observable by XANES spectroscopy.

Effect of lithium on the atmospheric corrosion characteristics of TZM as the first-wall material in EAST

The effect of Lithium (Li) coating on the corrosion behavior of molybdenum-titanium-zirconium (TZM) alloy was investigated in low- and high-humidity air at room temperature (RT). Additionally, the corrosion mechanism was also studied through immersion tests in deionized water and LiOH solution. The test results confirm that the corrosion of the TZM alloy depends on the presence of H2O and O2, particularly H2O. In environments with high humidity, the TZM surface without Li coating easily undergoes oxidation, resulting in the formation of dark-green MoO3·xH2O. The Li coating significantly accelerates the surface oxidation of the TZM alloy because of its high absorptive properties for H2O, O2, and CO2, thereby generating Li2O, LiOH, and Li2CO3. These processes lead to a high content of O2 and H2O near the TZM surface, facilitating the formation of MoO3·xH2O. The immersion of TZM in water also leads to oxidative corrosion, which is more severe than that in high humidity air because of the dissolution of MoO3, causing the water to become dark-green. The oxidation of TZM in LiOH solution exhibits a behavior similar to that of water immersion. However, the corrosion in the LiOH solution is more severe because of the reaction between the surface oxide MoO3 and LiOH, which forms a colorless Li2MoO4, accelerating the corrosion process. This study offers valuable insights into the effective anti-corrosion strategies for the cleaning and storage of the TZM wall material in the EAST tokamak.

Effects of SO2 and H2O on the ash deposition and NO emission during oxy-fuel combustion of high-alkali coal

The oxy-fuel combustion is promising to realize the large-scale CO2 capture and effective reduction of nitric oxides. The recirculation of flue gas in oxy-fuel combustion can lead to high concentrations of SO2 and H2O, which probably affects the ash deposition of high-alkali coal because SO2 and H2O are important for the transformation of alkali and alkaline earth metals (AAEMs). In the present work, the effects of SO2 and H2O in recycled flue gas on the ash deposition and NO emission during the oxy-fuel combustion of high-alkali coal were experimentally evaluated in a vertical two-stage furnace system. The conversion ratio of fuel-nitrogen to NO (CNO) and ash deposition efficiency were measured, and then the ash deposits were subjected to a couple of tests for further analyses. The experimental results show that SO2 helps to reduce the NO emission and its impact on ash deposition depends heavily on its concentration. In the case with modest SO2 addition, the sulfations of sodium and calcium are enhanced to some extent. Consequently, the amount of small sticky particles (NaCl and sodium aluminosilicates) that attached to large particles decreases, and the large particles mainly made of calcium aluminosilicates become smaller and less sticky. The newly generated Na2SO4 and CaSO4 are insufficient to overcome the inhibiting effects, thus the ash deposition efficiency decreases. Under the condition of excessive SO2 addition, the sulfations are further promoted. The small particles rich in Na2SO4 and CaSO4 are substantially more, which can not only serve as the initial ash layer on the heating surface, but also strengthen the stickiness of large particles by attaching to their surfaces. Therefore, the ash deposition efficiency increases·H2O can reduce the NO emission, while it aggravates the ash deposition because H2O enhances the sulfation.

Crystallization of a hydrous magma ocean in the shallow lower mantle

The solidification of a deep magma ocean occurred early in Earth's history. Although the initial amount of H2O in Earth's magma ocean is predicted to be low (e.g., <3000 ppm), as an incompatible element it becomes highly enriched (e.g. >10 wt%) in the final few percent of crystallization. In order to understand how a hydrous magma ocean would crystallize at the top of the lower mantle, we determined liquidus phase relations in the MgO-FeO-CaO-Al2O3-SiO2-H2O system at 24 GPa. We find that the bridgmanite (brg) + stishovite (st) + melt and bridgmanite (brg) + ferropericlase (fp) + melt cotectic boundary curves trend to Mg-rich melt compositions with decreasing temperature and extend to very high H2O contents (∼80 mol% H2O). The brg+st+melt curve is a subtraction curve at < ∼18 mol% H2O and a reaction curve at higher H2O contents, whereas the brg+fp+melt is a subtraction curve throughout its length. The density of melts along the two cotectics leads to neutral buoyancy with respect to shallow lower mantle and transition zone minerals at H2O contents up to ∼25 mol%. A transient melt-rich layer can form at the top of the lower mantle during late-stage crystallization in a mushy magma ocean when melt percolation dominates. When crystallization exceeds ∼98%, hydrous melts (>25 mol% H2O) become buoyant and can percolate into and hydrate the mantle transition zone.