Sulfate Formation Research Articles

Carbon nitride nanosheets induce pulmonary surfactant deposition via dysfunction of alveolar secretion and clearance

Graphitic carbon nitride is a new type of carbon-based nanomaterial with superior properties and great potential for application, which raised great concerns about their environmental and occupational exposure. Graphitic carbon nitride has been reported to accumulate in the lung potentially, however, the respiratory hazard effect of graphitic carbon nitride is still unknown. In the present study, we reported that graphitic carbon nitride (g-CN) and its doped variant sulfur doped graphitic carbon nitride (S-g-CN) nanosheets inhalation induced pulmonary inflammation, increased the production of pulmonary surfactant in alveolar type II epithelial cells, accompanied by the upregulation of lipids transporter expression levels in alveolar macrophages to clear excessive pulmonary surfactant in the alveolar. Further investigation found that the internalization of g-CN and S-g-CN prevented lipid phagocytosis and metabolic processes in alveolar macrophages, ultimately leading to the deposition of proteins and phospholipids in the lung. Furthermore, we found that g-CN was more robust in inhalation toxicity compared to sulfur doped form, which meant the doping of sulfur in graphitic carbon nitride reduced hazardous effects on the respiratory system. In summary, our study demonstrated that inhalation of graphitic carbon nitride nanosheets caused the deposition of pulmonary surfactants in lung, providing an insightful reference for pulmonary toxicity assessment of graphitic carbon nitride.

Response Enhancement in High-Temperature H2S-Treated Metal Oxide Gas Sensors.

Metal oxide gas sensors (MOGS), crucial components in monitoring air quality and detecting hazardous gases, are well known for their poisoning effects when exposed to certain gas molecules, such as hydrogen sulfide. Surprisingly, our research reveals that high-temperature H2S treatment leads to an enhancement effect rather than response decay. This study investigates the time-decaying response enhancement, being attributed to the formation of metal sulfide and metal sulfate on the metal oxide's surface, enhancing the electronic sensitization. Such an enhancement effect is demonstrated for various gases, including CO, CH3CH2OH, CH4, HCHO, and NH3. Additionally, the impacts of H2S treatment on the response and recovery time are also observed. Surface compositional analysis are conducted with X-ray photoelectron spectroscopy. A proposed mechanism for the enhancement effect is elaborated, highlighting the role of electronic sensitization and the sulfide-sulfate component. This research offers valuable insights into the potential applications of metal oxide sensors in sulfide-presented harsh environments in gas sensing, encouraging future exploration of optimized sensor materials, operation temperature, and the development of hydrogen sulfide poisoning-resistant and higher sensitivity MOGS.

Impact on the incorporation of metals in physicochemical and antimicrobial properties in films based on arrowroot starcha

New biodegradable packaging has been developed from renewable sources, mainly of vegetable origin. Arrowroot starch has been recently used to produce high-quality biodegradable films capable of behaving well when incorporating oils, extracts, metal, and metal nanocomposites. The study aimed to verify the impact of incorporating metals in the sulfate and chloride forms in a biopolymeric matrix from arrowroot starch in terms of biodegradability, physicochemical and microbiological parameters. Different arrowroot films were produced to incorporate solutions with a concentration of 1 Mol L-1 of sulfate and chloride metals. The action of biodegradability in soil, UV transmittance, and visible light were observed in UV-Vis spectrophotometry and antimicrobial action on Escherichia coli, Staphylococcus aureus, Salmonella serovar Typhimurium, and Salmonella serovar Enteritidis. Good results were obtained, such as biodegradability time between 81.70 to 100 % (30 days), a low transmission rate of UV radiation and visible light between 250 to 890 nm, high capacity for bacterial inhibition between 22.08 to 10.05 mm for E. coli, among 25.59 to 11.10 mm for S. aureus, between 22.14 to 11.66 mm for S. serovar Typhimurium and between 21.11 to 8.26 mm for S. serovar Enteritidis. It is concluded that the biodegradable films of arrowroot starch incorporated with metals showed potential in all the evaluated tests, thus characterizing possible new products for different uses, such as low time available in the environment, preservation of the characteristics of special products, and antimicrobial capacity.

Extraction of arsenic from fine dust of copper smelters by reduction roasting with natural gas

One of the current trends in the complex processing of fine dust from copper smelters is their direct leaching with sulfuric acid. As practical results show, high reliable technological parameters are not achieved due to the high content of arsenic in dust. During sulfuric acid leaching of dust, arsenic is distributed between the lead cake and the solution at a ratio of 40 and 60%, respectively. The redistribution of arsenic between leaching products significantly reduces the technological performance and leads to the accumulation of arsenic in the technological scheme. The paper presents the results of comprehensive studies of the elemental and phase composition of fine dust from one of the copper smelters in Kazakhstan. In the initial dust, along with the main phases presented in the form of lead and zinc sulfate, the following typical components were found: oxides of copper, lead, zinc and copper and zinc ferrites. Arsenic is found in two forms—As(III) and As(V). The laboratory installation and technique for conducting reduction roasting of dust with natural gas are presented. The influence of roasting duration, temperature and natural gas consumption on the extraction of arsenic from dust was studied. It has been established that almost complete, up to 99%, extraction of arsenic from dust is achieved with optimal technological roasting parameters: duration τ = 40 min.; natural gas consumption is 1.5 times higher than the stoichiometrically required amount for the reduction of As2O5, and temperature 500 °C.

Hydrothermal carbonization of sewage sludge for hydrochar valorization: Role of feedwater pH on sulfur removal and transformation

Adjusting the pH value is a useful method to improve the hydrochar properties during hydrothermal carbonization (HTC). The distribution of various sulfur species in hydrochar is considered as an important parameter affecting its further utilization. Nevertheless, the detailed effects of pH on the redistribution of different sulfur forms are still unknown. This study investigated the sulfur transformation pathways during HTC of sewage sludge with different feedwater pH (0–14) at 220 °C. Both acidic and alkaline feedwater facilitate the conversion of organic sulfur from the hydrochar into the stable species in aqueous products (i.e., sulfate-S). The latter especially leads to a decreased sulfur retention ratio of 31.97 % at pH=0 and 60.13 % at pH=14. Under acidic conditions, organic sulfur species such as sulfone-S and aliphatic-S undergo enhanced cyclization to form aromatic-S/thiophene-S in aqueous and hydrochar products; additionally, the oxidation of sulfone-S predominates the generation of sulfate-S in aqueous products at pH < 1. Under alkaline conditions, the aromatic-S/thiophene-S can be further oxidized into sulfate-S in aqueous products at pH>13. Furthermore, the interaction between water-soluble sulfate-S and hydrolytic intermediates (i.e., glucose, heterocyclic compounds) is intensified at pH=14, resulting in increased formation of sulfone-S and sulfite-S in aqueous products. The insights gained from this study can offer guidance for controlling sulfur distribution during HTC by adjusting the feedwater pH.

Water–Rock reactions in the acid leaching of Uranium: Hydrochemical characteristics and reaction mechanisms

Acid in–situ leaching (AISL) mining is used to recover uranium from sandstone using sulphuric acid. However, the evolution of groundwater hydrochemistry, the water–rock reaction mechanisms, and their relationship remain elusive. To effectively address these issues, ore samples were obtained from a sandstone uranium deposit in Inner Mongolia in this work. Soaking tests at different sulphuric acid concentrations were performed to quantify the mining aquifer’s water–rock reaction processes (sulphuric acid and minerals) according to the hydrogeochemical composition analysis and inverse modelling. From our results, it was demonstrated that the water–rock interactions between the sulphuric acid and gangue minerals primarily affect the leachate’s chemical composition. The introduction of sulphuric acid efficiently facilitates the gangue mineral dissolution and the groundwater total dissolved solids (TDS) increases and enhances the formation of uranyl sulphate (predominantly UO2SO4 and UO2(SO4)22– and UO22+, thus stimulating uranium mobility. Mineral precipitation (mirabilite) is primarily responsible for the elevated TDS in the leachate. The leachate’s oxygenation mainly depends on the sulphuric acid concentration and Fe3+ concentration produced by hematite dissolution. During the AISL process, the dissolution of dolomite, calcite, FeO, hematite, pyrite, K–feldspar, anorthite, chlorite, and alunite take place in the groundwater system. In parallel, the precipitation of kaolinite, illite, Ca–Montmorillonite and mirabilite, accompanied by Na–K exchange and Na–Mg exchange occur. The dissolution of dolomite, calcite and illite and Na–Mg exchange mostly affects the hydrochemical evolution, as well as the leachate of Fe mainly from dissolved chlorite. The predominant precipitates were kaolinite and mirabilite, with their precipitation ability increasing with acidity. These findings highlight the importance of clarifying the relationship between the hydrochemical characteristics and the water–rock reaction mechanisms in AISL geochemical processes to elucidate the hydrochemical evolution and mineral corrosion characteristics of ore–bearing aquifers. Finally, K–feldspar, alunite, chlorite, anorthite and dolomite were obtained as the major acid–consuming minerals. Our work provides a novel evaluation method for the prediction of acid consumption that can be used for actual production.

(Invited) Probing the Reaction Microenvironment during Electrochemical Nitrate Reduction to Ammonia

Nitrate pollution of wastewater from agricultural runoff and industrial waste streams is common around the globe. Nitrate negatively impacts the environment through harmful algal blooms and can be dangerous for human consumption. Strict limits have been set on nitrate discharge and the concentration in drinking water (< 50 ppm). Nitrate is currently removed from water by conversion to nitrogen through a biological process that requires chemical inputs (e.g., methanol) and post-treatment to remove biomass and organics.Electrochemical reduction of nitrate (NO3RR) to ammonia can remove nitrate from water and is an alternative to Haber-Bosch (HB) ammonia production, a significant source of global CO2 emissions. Ammonia is an important chemical precursor with potential applications in sustainable energy as a fuel or H2 carrier, or can be used as a fertilizer in the form of ammonium sulfate. This research addresses the water–energy nexus by converting nitrate to a valuable product, off-setting the cost of water treatment, and reducing demand for HB.NO3RR can be done from small to large scales, use renewable electricity, and eliminate the need for expensive and hazardous chemicals. However, NO3RR processes must exhibit selectivity toward ammonia to avoid the formation of other undesired products and occur at a low overpotential to minimize operating costs from electricity. To address these challenges, we must understand the reaction environment at the electrode–electrolyte interface, where heterogeneous electrochemical reactions occur. We use in situ attenuated total reflectance–surface-enhanced infrared adsorption spectroscopy (ATR–SEIRAS) to investigate the adsorbed reactants, intermediates, and interfacial pH. We studied the repeatability of the technique for in situ interfacial pH measurement and recommend controls to the community when using this method. The ATR–SEIRAS results are correlated with electrochemical experiments measuring NO3RR selectivity, activity, and efficiency. NO3RR products are measured by ion chromatography and gas chromatography. Our results relate bulk electrolyte properties with interfacial properties, and interfacial properties with reaction activity and selectivity. This understanding could lead to the development of electrolyte engineering strategies to optimize ammonia production in electrochemical NO3RR.

Formation of Inorganic Sulfate and Volatile Nonsulfated Products from Heterogeneous Hydroxyl Radical Oxidation of 2-Methyltetrol Sulfate Aerosols: Mechanisms and Atmospheric Implications.

Chemical transformation of 2-methyltetrol sulfates (2-MTS), key isoprene-derived secondary organic aerosol (SOA) constituents, through heterogeneous hydroxyl radical (•OH) oxidation can result in the formation of previously unidentified atmospheric organosulfates (OSs). However, detected OSs cannot fully account for the sulfur content released from reacted 2-MTS, indicating the existence of sulfur in forms other than OSs such as inorganic sulfates. This work investigated the formation of inorganic sulfates through heterogeneous •OH oxidation of 2-MTS aerosols. Remarkably, high yields of inorganic sulfates, defined as the moles of inorganic sulfates produced per mole of reacted 2-MTS, were observed in the range from 0.48 ± 0.07 to 0.68 ± 0.07. These could be explained by the production of sulfate (SO4 •-) and sulfite (SO3 •-) radicals through the cleavage of C-O(S) and (C)O-S bonds, followed by aerosol-phase reactions. Additionally, nonsulfated products resulting from bond cleavage were likely volatile and evaporated into the gas phase, as evidenced by the observed aerosol mass loss (≤25%) and concurrent size reduction upon oxidation. This investigation highlights the significant transformation of sulfur from its organic to inorganic forms during the heterogeneous oxidation of 2-MTS aerosols, potentially influencing the physicochemical properties and environmental impacts of isoprene-derived SOAs.

Fertility and ecotoxicological condition of light gray forest soils of the Ivanovo region

The results oflong-term monitoring of light gray forest soil for agricultural purposesin theIvanovo region are presented, which was carried outto establish the level of fertility according to the mainagrochemical indicators, the content of mobile forms of trace elementsand sulfur, the ecotoxicological state according to the content ofgross and mobile forms of heavy metals, arsenic, caesium-137 andstrontium-90.The average values of the indicators, their levels ofchange and trends in changes in the metabolic and hydrolyticacidity of the soil, availability of organic matter, mobile formsof nitrogen, phosphorus, potassium, exchangeable calcium, magnesium and other bases,mobile forms of boron, copper, zinc, molybdenum, cobalt, manganese andsulfur have been established.According to the content of traceelements in the soil, the needs for the use ofmicronutrients are determined.Changes, concentrations and trends in the mobileforms of cadmium, lead, copper, zinc, nickel, chromium, mercury andarsenic in the soil have been determined.The study establishedbackground values, changes and trends in the specific activities ofcaesium-137 and strontium-90, the density of their contamination of thesoil of the site and the power of the exposuredose of gamma radiation.According to thePearson–Spearman correlation coefficients,the peculiarities of the influence of the content of organicmatter, the level of acidity and the capacity of cationexchange on the content of mobile forms of trace elements,sulfur, gross and mobile forms of metals and radionuclides wereestablished.

Constraining sulfur incorporation in calcite using inorganic precipitation experiments

The sulfur over calcium ratio (S/Ca) in foraminiferal shells was recently proposed as a new and independent proxy for reconstructing marine inorganic carbon chemistry. This new approach assumes that sulfur is incorporated into CaCO3 predominantly in the form of sulfate (SO42−) through lattice substitution for carbonate ions (CO32–), and that S/Ca thus reflects seawater [CO32–]. Although foraminiferal growth experiments validated this approach, field studies showed controversial results suggesting that the potential impact of [CO32–] may be overwritten by one or more parameters. Hence, to better understand the inorganic processes involved, we here investigate S/Ca values in inorganically precipitated CaCO3 (S/Ca(cc)) grown in solutions of CaCl2 − Na2CO3 − Na2SO4 − B(OH)3 − MgCl2. Experimental results indicate the dependence of sulfate partitioning in CaCO3 on the carbon chemistry via changing pH and suggest that faster precipitation rates increase the partition coefficient for sulfur. The S/Ca ratios of our inorganic calcite samples show positive correlation with modelled [CaSO40](aq), but not with the concentration of free SO42− ions. This challenges the traditional model for sulfate incorporation in calcite and implies that the uptake of sulfate potentially occurs via ion-ion pairs rather than being incorporated as single anions. Based on the [Ca2+] dependence via speciation, we here suggest a critical evaluation of this potential proxy. As sulfate complexation seems to control sulfate uptake in inorganic calcite, application as a proxy using foraminiferal calcite may be limited to periods for which seawater chemistry is well-constrained. As foraminiferal calcite growth is modulated by inward Ca2+ flow to the site of calcification coupled to outward H+ pumping, sulfate incorporation as CaSO40 ion-pair in the foraminifer’s shell also provides a mechanistic link for the observed relationship between S/Ca(cc) and [CO32–].

In-situ inhibition mechanism of SO3 formation over MoS2 modified V2O5/TiO2 catalyst within selective catalytic reduction process

The utilization of commercial vanadium-titanium based catalysts (V2O5/TiO2) within the selective catalytic reduction (SCR) process is a prominent contributor to the emergence of sulfur trioxide (SO3) in coal-fired boiler environments. The direct modification of vanadium-titanium based catalysts has big potential to be an efficacious strategy for in-situ inhibiting SO3 formation. This research evaluates the effectiveness of MoS2 modified V2O5/TiO2 catalyst on SO2 oxidation under diverse conditions, using controlled condensation for SO3 collection. The results showed that V2O5-MoS2/TiO2 catalysts outperformed conventional V2O5/TiO2 catalysts in inhibiting the oxidation from SO2 to SO3 between 200 and 400 °C, with optimal performance at 350 °C. No significant effect was observed on the catalytic oxidation of SO2 when the O2 concentration was lower than that of SO2, whereas the introduction of appropriate quantities of NO promoted the generation of SO3. The excessive inclusion of NH3 nearly doubled the SO3 generation rate, increasing it from 0.284 % to 0.434 %. The NO and NH3 mixture markedly reduced SO3 generation to 0.085 % at a 62 mL/min mixture concentration, just 30 % of the rate without the mixture. Following the reaction of SO2 and O2, the reacted catalyst exhibited reduced pore volume, enhanced thermochemical stability, and lower susceptibility to SO2 catalytic oxidation. The addition of low-valence sulfur improves catalyst reducibility, reduces V5+–OH reactions in various atmospheres, and decreases the formation of sulphate and gaseous SO3. The Mo-S-Mo group also effectively prevents the formation of HSO4− intermediates. Additionally, MoS2 reacts with SO3 via a reduction reaction, significantly lowering the SO3 levels. Finally, in diverse atmospheric conditions, the catalysts maintained their V5+ content and catalytic efficiency, thus improving SCR performance stability.

Can we reach consensus on the dominant sulfate formation pathway in China's haze?

Atmospheric sulfate aerosols contribute significantly to air pollution and climate change. Sulfate formation mechanisms during winter haze events in northern China have recently received considerable attention, with more than 10 studies published in high-impact journals. However, the conclusions from in-field measurements, laboratory studies, and numerical simulations are inconsistent and even contradictory. Here, we propose a physically based yet simple method to clarify the debate on the dominant sulfate formation pathway. Based on the hazes evolving in the synoptic scale, first, a characteristic sulfate formation rate is derived using the Eulerian mass conservation equation constrained by in situ observations. Then, this characteristic value is treated as a guideline to determine the dominant sulfate formation pathway with a 0D chemical box model. Our observation-derived results establish a linkage between studies from laboratory experiments and chemical transport model simulations. A convergent understanding could therefore be reached on sulfate formation mechanisms in China's wintertime haze. This method is universal and can be applied to various haze conditions and different secondary products.

Laboratory infrared spectra and fragmentation chemistry of sulfur allotropes

Sulfur is one of six life-essential elements, but its path from interstellar clouds to planets and their atmospheres is not well known. Astronomical observations in dense clouds have so far been able to trace only 1 percent of cosmic sulfur, in the form of gas phase molecules and volatile ices, with the missing sulfur expected to be locked in a currently unidentified form. The high sulfur abundances inferred in icy and rocky solar system bodies indicate that an efficient pathway must exist from volatile atomic sulfur in the diffuse interstellar medium to some form of refractory sulfur. One hypothesis is the formation of sulfur allotropes, particularly of the stable S8. However, experimental information about sulfur allotropes under astrochemically relevant conditions, needed to constrain their abundance, is lacking. Here, we report the laboratory far-infrared spectra of sulfur allotropes and examine their fragmentation pathways. The spectra, including that of cold, isolated S8 with three bands at 53.5, 41.3 and 21.1 µm, form a benchmark for computational modelling, which show a near-perfect match with the experiments. The experimental fragmentation pathways of sulfur allotropes, key information for astrochemical formation/destruction models, evidence a facile fragmentation of S8. These findings suggest the presence of sulfur allotropes distributions in interstellar space or in the atmosphere of planets, dependent on the environmental conditions.

Quantitative determination of sulfate sulfur in soils and sediments using the S-Kα and S-Kβ X-ray spectra and PLS regression

A new approach to the quantitative determination of sulfate sulfur in soils and sediments by wavelength-dispersive X-ray fluorescence spectrometry in combination with partial least squares (PLS) regression has been investigated. The quantitative analysis of sulfate sulfur was carried out by analyzing the spectra in the S-Kα and S-Kβ regions of sulfur spectral lines. The study shows that the differences in the spectra in both regions can be used for quantitative analysis of sulfate sulfur in the presence of sulfur in other forms. The obtained information can be used for quantitative express analysis of sulfur forms in objects of various nature.

Sulfur and nitrogen interaction affects onion yield and post-harvest quality

Ionic interactions affect the mineral composition of plants, which can cause nutritional disorders with reflections on yield, post-harvest quality, and food safety. Thus, this study evaluated the interaction between nitrogen (N) and sulfur (S) and its effects on onion production and post-harvest quality. The study was conducted in a completely randomized design, with a 3 × 5 factorial scheme and four replications. The treatments consisted of a combination of three S rates (0, 20, and 40 mg dm−3) and five N rates (0, 40, 60, 80, and 100 mg dm−3), applied in the form of calcium sulfate (CaSO4·2H2O) and urea, respectively. It was observed that the interaction between N and S negatively affected onion production, reducing the gain of both fresh and dry mass of the bulb. The N/S ratio ranged from 16.5 to 26.2 and was not influenced by the interaction between N and S. Onion pungency was classified as intermediate. The higher pungency value was obtained with the application of 100 mg dm−3 of N, and 40 mg dm−3 of S. The application of N when combined with 20 mg dm−3 of S contributed to increasing titratable acidity and soluble solids content of onion cv. Diamantina.

Phenotype-driven assessment of the ancestral trajectory of sulfur biooxidation in the thermoacidophilic archaea Sulfolobaceae.

Certain members of the family Sulfolobaceae represent the only archaea known to oxidize elemental sulfur, and their evolutionary history provides a framework to understand the development of chemolithotrophic growth by sulfur oxidation. Here, we evaluate the sulfur oxidation phenotype of Sulfolobaceae species and leverage comparative genomic and transcriptomic analysis to identify the key genes linked to sulfur oxidation. Metabolic engineering of the obligate heterotroph Sulfolobus acidocaldarius revealed that the known cytoplasmic components of sulfur oxidation alone are not sufficient to drive prolific sulfur oxidation. Imaging analysis showed that Sulfolobaceae species maintain proximity to the sulfur surface but do not necessarily contact the substrate directly. This indicates that a soluble form of sulfur must be transported to initiate cytoplasmic sulfur oxidation. Conservation patterns and transcriptomic response implicate an extracellular tetrathionate hydrolase and putative thiosulfate transporter in a newly proposed mechanism of sulfur acquisition in the Sulfolobaceae.IMPORTANCESulfur is one of the most abundant elements on earth (2.9% by mass), so it makes sense that the earliest biology found a way to use sulfur to create and sustain life. However, beyond evolutionary significance, sulfur and the molecules it comprises have important technological significance, not only in chemicals such as sulfuric acid and in pyritic ores containing critical metals but also as a waste product from oil and gas production. The thermoacidophilic Sulfolobaceae are unique among the archaea as sulfur oxidizers. The trajectory for how sulfur biooxidation arose and evolved can be traced using experimental and bioinformatic analyses of the available genomic data set. Such analysis can also inform the process by which extracellular sulfur is acquired and transported by thermoacidophilic archaea, a phenomenon that is critical to these microorganisms but has yet to be elucidated.

Reaction and deactivation mechanisms of a CeIn/HBEA catalyst with dual active sites for selective catalytic reduction of NOx by CH4

Methane selective catalytic reduction (CH4-SCR) technology has shown promise for controlling NOx emissions from natural gas generator sets. This study presents a highly efficient Ce30In15/HBEA catalyst featuring dual active sites, Al-O–(InO+)-Si site for CH4 activation and ceria oxygen vacancy (Ce3+-□) site for NOx activation. However, the CH4-SCR activity of this catalyst decreased in the presence of H2O, SO2, C3H6, and CO2. The inhibitory effects on CH4-SCR activity followed by the sequence: H2O > SO2 > C3H6 > CO2. In particular, H2O combined with Al-O–(InO+)-Si to form inactive In(OH)3-zz+ species and occupied Ce3+-□, preventing Ce4+-NO3–/NO2– formation. In/Ce sulfate formation via the reaction between SO2 and In/Ce active sites hindered CH4 and NOx adsorption and activation. The formed carbon deposits covered the active sites on the catalyst surface due to incomplete C3H6 oxidation. In comparison, the dual active sites were almost unaffected by CO2. Overall, this study provides a basis for the rational design of novel catalysts for CH4-SCR.

Insights into the Acidic Site in Manganese Oxide in Terms of the Sulfur and Water Tolerance of Low-Temperature NH3 Selective Catalytic Reduction.

A critical constraint impeding the utilization of Mn-based oxide catalysts in NH3 selective catalytic reduction (NH3-SCR) is their inadequate resistance to water and sulfur. This vulnerability primarily arises from the propensity of SO2 to bind to the acidic site in manganese oxide, resulting in the formation of metal sulfate and leading to the irreversible deactivation of the catalyst. Therefore, gaining a comprehensive understanding of the detrimental impact of SO2 on the acidic sites and elucidating the underlying mechanism of this toxicity are of paramount importance for the effective application of Mn-based catalysts in NH3-SCR. Herein, we strategically modulate the acidity of the manganese oxide catalyst surface through the incorporation of Ce and Nb. Comprehensive analyses, including thermogravimetry, NH3 temperature-programmed desorption, in situ diffused reflectance infrared Fourier transform spectroscopy, and density functional theory calculations, reveal that SO2 exhibits a propensity for adsorption at strongly acidic sites. This mechanistic understanding underscores the pivotal role of surface acidity in governing the sulfur resistance of manganese oxide.

Effect of different forms of calcium sulfate on the properties of cement

Abstract In our conditions, mainly flue gas desulfurization gypsum (FGD gypsum) is used as a cement setting regulator. When cement is ground, it decomposes into hemihydrate or even anhydrite as the temperature rises. The ground cement is placed in a storage silo where the increased temperature is compounded by increased pressure and the cement properties are affected by the moisture released and by the change in the phase composition of the setting regulator. Under laboratory conditions, hemihydrate and anhydrite II and III were prepared from one type of FGD gypsum. Their purity was monitored by X-ray diffraction analysis and differential thermal analysis. The prepared calcium sulfates were used in different proportions as setting regulators in the laboratory preparation of Portland cements. Technological properties such as strength and solidification were then determined for cements. The hydration process was monitored by the calorimetric method.

Quantification of Gypsum in Soils via Portable X-ray Fluorescence Spectrometry

Abstract This study explores the potential of X-ray fluorescence (XRF) as a rapid, nondestructive, and cost-effective technique for in situ sulfate quantification. Gypsum, the main source of sulfate in soils, reacts with calcium-based stabilizers to form expansive minerals, which reduces the long-term strength of the treated soil. Therefore, accurate detection of sulfate content prior to employing calcium-based chemical stabilization is important to mitigate the possibility of expansive mineral formation and ensure acceptable engineering behavior of the stabilized soil. Portable handheld XRF (PXRF) has shown the ability to estimate gypsum content accurately, utilizing calcium as a proxy. However, detecting sulfur, in the form of sulfite or sulfate remains challenging due to device sensitivity limitations. This research aims to address this limitation and develop a method for direct sulfur detection, enhancing the utility of PXRF for in situ sulfate quantification. Laboratory standards were created with known amounts of gypsum and portions were sent to a commercial laboratory for whole rock analysis. The remainder of the reference standards were used to calibrate several soil library standards within the PXRF. The calibrated PXRF was able to accurately detect the anhydrous form of gypsum, anhydrite (CaSO4), in these reference standards for contents ranging from 0 to 8 %. The proposed XRF-based approach offers the potential to revolutionize sulfate detection in soils, providing a rapid and reliable tool for assessing soil stability and optimizing chemical stabilization efforts. By enabling real-time, on-site analysis, this method holds promise for improving construction practices and reducing the risk of structural damage associated with soils containing sulfate-bearing minerals.