Thermogravimetric Mass Spectrometry Research Articles

Research on the Explosion Reaction Mechanism of Volatile Gases from Coal Dust Pyrolysis

ABSTRACT It is imperative to have an in-depth understanding of the coal dust explosion reaction mechanism to control and prevent coal explosions in the coal mining industry and promote the safe and efficient utilization of coal resources. The volatile gases are the primary components involved in coal dust explosion reactions. Therefore, studying the explosion reaction mechanism of volatile gases in coal dust is of great significance for revealing the process of coal dust explosion. This study conducted a thermogravimetric mass spectrometry (TG-MS) experiment to analyze the mass loss characteristics and volatile gas components during coal dust pyrolysis. Experimental results showed that the pyrolysis process of coal dust is mainly divided into three stages. The main components of volatile gases escaping from coal dust pyrolysis are CO, CH4, CO2, and H2O. Then, the Chemkin-Pro numerical simulation method was also introduced to analyze the mixture explosion reaction process of coal dust pyrolysis volatile gas. The sensitivity analysis and the rates of production analysis (ROP) of reactants, products, and intermediate products during the volatile gas explosion reaction were conducted. Furthermore, 14 components and 27 key elementary reactions involved in the reaction process were simplified and extracted. A simplified reaction pathway for the mixture explosion of coal dust pyrolysis volatile gas was constructed. This study introduces a novel approach to investigate the mechanism of homogeneous combustion of volatile gases in coal dust explosion reactions.

Influence of composite chloride salt retardant on the characteristics of coal spontaneous combustion and comprehensive evaluation methodology

ABSTRACT In this study, we aimed to improve the efficacy and longevity of single inhibitors. NaCl, CaCl2, MgCl2, and layered double hydroxides (LDHs) were selected as the inhibitory components for experimental study. The impact of the composite inhibitors on the spontaneous combustion characteristics of the coal was studied through temperature programmed experiment, thermal analysis experiments, thermogravimetric mass spectrometry and entropy weight method, and the optimal inhibitor was determined. The findings indicate that the apparent activation energy (E a ) of the coal sample, with the addition of inhibitors during the oxidation stage, was improved. E a of MgCl2 +1.0 LDHs + Coal was the highest (127.28 kJ/mol), i.e. 35.99 kJ/mol higher than that of the original coal. The inclusion of the inhibitor increased the characteristic ignition temperatures of the coal samples compared with the original coal. The highest ignition temperature was observed for MgCl2 +0.5 LDHs + Coal, reaching (323.98°C), i.e. 11.42°C higher than that of the original coal. The addition of inhibitors significantly inhibited the production of CO. Among the three chloride salts, MgCl2 exhibited the strongest inhibitory effect on CO production. According to the entropy weight method, MgCl2 +0.5 LDHs showed the best inhibitory effect. The results show that the composite halogen inhibitor can effectively inhibit the spontaneous combustion of coal.

Evaluation of the thermal hazard and pyrolysis mechanism of 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate via thermal analysis and DFT calculation: Effect of structural characteristics

Imidazole ionic liquid, as a green solvent, is one of the most widely used ionic liquids. Understanding its thermal safety characteristics and mechanism is the essential basis for its safe application. In this paper, the thermal hazard characteristics of two ionic liquids with typical structural characteristics are systematically studied, which were 1-allyl-3-methylimidazole nitrate and 1-propyl-3-methylimidazole nitrate ionic liquids. The thermal decomposition peculiarities of two ionic liquids were systematically analyzed by thermogravimetric analyzer, differential scanning calorimetry and accelerating rate calorimeter techniques, and the risk of thermal runaway is also evaluated. In addition, the pyrolysis products and microscopic pyrolysis mechanism of ionic liquids were studied via thermogravimetry-Fourier transform infrared spectroscopy, thermogravimetric mass spectrometry and density functional theory calculation, and the essential mechanism of thermal hazard were determined. The influence of substituent structure on the thermal hazard characteristics of imidazole nitrate ionic liquid was preliminarily analyzed from macroscopic experiment and microscopic mechanism two aspects. This study provides a theoretical basis for the safe application, design and development of imidazole nitrate ionic liquids.

Insight into the pyrolysis and gas generation behavior of silicomanganese slag and assessing its foaming abilities in foam glass ceramic

This paper proposes a novel route for the utilization of silicomanganese slag in the preparation of high-temperature foam ceramic materials, grounded in the unique characteristics of the slag. The phase evolution and gas generation mechanisms of silicomanganese slag was systematically investigated using thermogravimetric mass spectrometry (TG-MS), thermodynamic simulation, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Foam glass ceramic with a density of 291 ± 8 kg/m3 and a compressive strength of 2.83 ± 0.07 MPa was prepared using silicomanganese slag as a foaming agent. This research indicated that manganese and sulfur in the silicomanganese slag are critical contributors to gas generation. Manganese in the slag oxidizes to dimanganese trioxide (Mn2O3) before reaching 1000 °C, and at temperatures between 1000 and 1200 °C, trivalent manganese (Mn3+) converts to divalent manganese (Mn2+) and enters the pyroxene crystal, releasing oxygen (O2). Sulfur in the slag, captured by divalent calcium (Ca2+), forms a more stable calcium sulfate (CaSO4) during heating and enriches the slag particle surface. As the temperature exceeds 1000 °C, Ca2+ gradually integrates into the pyroxene, prompting the release of sulfate decomposition products, forming sulfur dioxide (SO2) and O2. A small fraction of unreacted CaSO4 enters the glass phase, forming fibrous crystals that enhance the compressive strength of the foam glass-ceramic through fiber reinforcement. The outcomes of this work offer new insights into the high-value utilization of silicomanganese slag and enrich the understanding of gas generation mechanisms in Mn-based and S-based foaming agents.

Waste control by waste: Extraction of valuable metals from mixed metallurgical dust by boiling furnace roasting

Electric arc furnace dust (EAFD) is a hazardous waste by-product generated during the process of electric furnace steelmaking, which is rich in valuable metal elements. In order to solve the problem of environmental pollution and resource utilization of EAFD, we propose a new process for medium-temperature suspension roasting EAFD and coke dry quenching dust to extract valuable metals. The thermodynamic properties and migration behavior of valuable elements involved in the reaction were analyzed using thermodynamic simulation software FactSage8.1 and thermogravimetric mass spectrometry. The mechanism and kinetic equation of the dezincification process were investigated using the Kissinger method and Coats-Redfern model. The impact of various parameters on the process efficacy and ash fusion characteristics of the material were investigated through boiling furnace experiments. The results demonstrate that elevating the reaction temperature and decreasing the zinc partial pressure is more favorable for reducing and separating zinc. The corresponding kinetic equations for the decomposition of ZnFe2O4 and reduction of ZnO are denoted as dα/dT = 1.69 × 1012exp (−3.37 × 104/T) and dα/dT = 6.76 × 106 exp (−2.08 × 104/T) × (1 − α) [−ln(1 − α)]3/4, respectively. The optimum reaction temperature was 1050 °C, the C/O ratio was 0.8, the reaction time was 40 min, and the ventilation rate was 3500 mL/min. Under these conditions, the material had no liquid phase agglomeration, and the removal rates of zinc and lead were 93.38 % and 98.14 %, respectively. The crude zinc dust with a zinc grade of 87.57 % and the alloy slag with an iron grade of 52.38 % was obtained. The new process utilizes the excellent heat transfer characteristics and fluidization conditions of the boiling furnace to efficiently realize the high-grade recovery of valuable metals in the EAFD, which provides new insights for the clean treatment of zinc-containing waste.

Carnallite double salt for thermochemical heat storage

The potential use of carnallite (KMgCl3·6H2O) for low temperature thermochemical heat storage has been evaluated. Carnallite is an incongruently soluble double salt and its possible decomposition and dehydration reactions have been carefully evaluated from available thermodynamic data and the phase diagram has been constructed. The dehydration and rehydration reactions have been experimentally studied and the reaction products have been characterized using thermogravimetric mass spectrometry, water vapor sorption, X-ray powder diffraction, scanning electron microscopy, Raman microscopy and calorimetry. The results of the experimental investigation of these reactions confirm the model predictions and clearly show that a thermochemical cycle including carnallite and its dihydrate (KMgCl3·2H2O) is very promising for low temperature domestic thermochemical storage. In comparison to both pure MgCl2·6H2O and also other salts mentioned in the literature, the double salt carnallite offers significant advantages. It has a higher deliquescence humidity and, thus, is much less sensitive to over-hydration and liquefaction. It can be easily dehydrated at only 100 °C and is much less prone to hydrolysis (HCl release). Carnallite has also a good reversibility between dehydration and hydration and the re-formation of carnallite by rehydration is easily achieved at low water vapor pressure and faster reaction rate than the hydration of MgCl2·2H2O to MgCl2·6H2O. The enthalpy of hydration is slightly higher for the hydration of KMgCl3·2H2O than for the hydration of MgCl2·2H2O. The only price to be paid is a slightly reduced storage density of the double salt due to its larger molar volume. However, the theoretical storage density of 1.52 kJcm−3 is still excellent. Also, carnallite is a low-cost material as it is available as industrial waste material or can be easily synthesized.

A coumarin-based optical probe for the quantitative determination of Fe3+ ions in water, petroleum crude oil, and catalyst samples; an experimental and theoretical investigation

A simple and sensitive optical probe, designated as "N-((9-benzyl-9H-carbazol-3-yl)methylene)-7-(diethylamino)-2-oxo-2H-chromene-3-carbohydrazide" was designed and synthesized for the accurate quantification of Fe3+ ions in water, milk, vegetables, petroleum crude oil, and catalyst samples in their prepared aqueous solutions. This probe (referred to as Probe-L) acts as a naked-eye chemosensor, at 254 nm, undergoing a noticeable color change from light yellow to medium dark brown in an aqueous medium. It exhibits exceptional selectivity for Fe3+ ions even in the presence of interfering elements such as Na+, K+, Ca2+, Mg2+, Ba2+, Cr3+, Mn2+, Co2+, Ni2+, Cu2+, Zn2+, Al3+, Cd2+, As3+, Sn2+, and Hg2+. To determine the sensitivity of Probe-L towards Fe3+, we conducted experimental tests and found that it can detect Fe3+ ions with a concentration as low as 0.001 ppm. Through Job's plot, Thermogravimetric, and high-resolution mass spectrometry (HRMS) studies, we confirmed the 1:1 binding interaction between Probe-L and Fe3+ ions. In addition, computational experiments were conducted to ascertain the optimal geometry for Probe-L and its metal complex. The results indicated an octahedral geometry and the calculated HOMO-LUMO energy gaps were found to be 2.49 eV. We conducted a comparative analysis of the quantitative results derived from Probe-L in assessing Fe3+ content across various samples, juxtaposing them with the outcomes obtained through the ICP OES technique. Significantly, our findings demonstrated a favorable concordance with the ICP OES results, indicating the viability of the new techniques for a wide range of practical applications.

Thermogravimetric analysis of co-combustion characteristics of sewage sludge and bamboo scraps combined with artificial neural networks

The increasing amount of sludge resources has brought great challenges to the ecological environment and sustainable development. Co-combustion of low calorific value sewage sludge and biosolid waste has become a new and effective way to treat sludge. The co-combustion characteristics of sewage sludge and bamboo scraps in air were studied by thermogravimetric mass spectrometry and artificial neural network. The thermogravimetric analysis of combustion at three different heating rates was performed with five different mixing ratios. Through comprehensive combustion index and cooperative analysis, it is concluded that the co-burning effect and cooperative effect of sludge and bamboo are better. Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose were used to calculate the apparent activation energy. The average activation energy of the sludge mixed with 75% bamboo scraps was the lowest (126.3 kJ mol−1) under the co-combustion condition. The ion current of combustion gas products during combustion was studied by mass spectrometry. Co-combustion can increase NOx and reduce SO2, and 75% bamboo slag mixed sludge has the least gas production. Finally, the prediction model of sludge co-combustion is established by artificial neural network, which provides a prospective guidance for the resource utilization of solid waste.

In-Line Co-Processing of Stainless Steel Pickling Sludge Using Argon Oxygen Decarburization Slag Bath: Behavior and Mechanism

Stainless steel pickling sludge (SSPS) is classified as hazardous solid waste, while Argon Oxygen Decarburization (AOD) slag is challenging to utilize due to the leaching toxicity of Cr. This study introduces a novel in-line co-processing technique for AOD slag and SSPS, parallel to the steelmaking process, aimed at metal recovery, sulfur fixation, and slag detoxification: pre-treatment-AOD slag bath approach. The transformations and migrations of sulfur and metal elements, such as Fe and Cr, in the co-processed mixture were analyzed using thermogravimetric–mass spectrometry (TG-MS) and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS). The results indicated that sulfur in SSPS could be transformed from CaSO4 to CaS under controlled low pre-reduction temperatures (below 800 °C), facilitating its stabilization in the slag and achieving a sulfur fixation rate of over 99%. Metal elements, including iron and chromium, first formed a small portion of spinel (FeCr2O4) during the pre-reduction phase, then Fe-Cr or Fe-Cr-C-based alloy particles were rapidly formed at high temperatures and in the presence of reducers in the slag bath (1550 °C), aggregating and growing spontaneously, ultimately achieving a metal recovery rate of over 95%. Furthermore, a reaction model for SSPS briquettes in the AOD slag bath was established to further reveal the mechanisms of sulfur, iron, and chromium stabilization and migration, thereby providing a basis for the harmless disposal of both materials. The product alloys are expected to be used as additives in stainless steel production, while the harmless slag could be safely utilized in the preparation of cementitious auxiliary materials.

Gasification Performance of Barley Straw Waste Blended with Lignite for Syngas Production under Steam or Carbon Dioxide Atmosphere

The gasification performance of lignite/barley straw mixtures for syngas production was investigated. The experiments were carried out under a steam or carbon dioxide atmosphere, in fixed-bed and thermogravimetric–mass spectrometry systems. The thermal behavior, reactivity, conversion, product gas composition, liquid and gaseous by-products and interactions between fuels were determined and correlated with the structural characteristics and inherent minerals in ashes, which were analyzed via mineralogical, chemical and fusibility tests. Devolatilization of the materials up to 600 °C resulted in the carbon enrichment of chars and a 30–90-fold increase in the specific surface area. Gaseous and liquid by-products with higher heating values of 5–7 MJ/m3 and 20–28 MJ/kg could offer valuable energy. Upon steam gasification up to 1000 °C, product gas was enriched in hydrogen and carbon monoxide. The syngas yield and heating value of the gas mixture were higher for barley straw fuel (0.77 m3/kg, 11.4 MJ/m3), which, when blended with the lignite, produced upgraded products. Upon carbon dioxide gasification up to 1000 °C, barley straw char exhibited a 3-times higher rate than the lignite, as well as higher conversion (94.5% vs. 62.9%) and a higher syngas yield (0.84 m3/kg vs. 0.55 m3/kg). Lignite/barley straw blends showed synergistic effects and presented higher gasification reactivity and conversion in comparison to lignite. The overall performance of lignite was improved with the steam reagent, while that of barley straw was improved with the carbon dioxide reagent.

Homogenizing microwave pyrolysis of oily sludge using nano-Fe3O4: volatile gas product analysis

: To improve the homogeneity of heating, the magnetic absorbing material Fe3O4 is considered to use in microwave pyrolysis of oily sludge. Therefore, the effect of Fe3O4 on the microwave pyrolysis of oily sludge is investigated based on gas volatile products. Thermogravimetric mass spectrometry result certifies that Fe3O4 will increase the weight-loss ratio from 13.0% to 14.1%. Also, the characteristic peak intensity of CO in gas products decreases from 5.41×10-10 A/g to 1.95×10-10 A/g, while H2O increases from 3.57×10-10 A/g to 7.32×10-10 A/g and CO2 increases from 6.87×10-10 A/g to 8.92×10-10 A/g. This is caused by the esterification of alcohols and esters and the reduction of Fe3O4 by CO. Based on the decrease in activation energy and enthalpy values of Stage Ⅱ and Ⅳ, it infers that Fe3O4 catalyzes the pyrolysis process of oily sludge to some extent. Similarly, gas chromatography-mass spectrometry results show that Fe3O4 can make the types of gas products increase. Especially, the number of molecular species increases from 5 to 46 under 200-300 ℃. Finally, a simple molecular dynamics simulation model is conducted, and the results are in agreement with the experimental results. This study shows that Fe3O4 improves the pyrolysis homogeneity and the pyrolysis efficiency also improves.

Gasification of organic solid waste for syngas: Physicochemical and conversion mechanism investigation

The syngas of organic solid waste (OSW) obtained through gasification is of great interest in energy and fuel production owing to its clean and environmentally friendly characteristics. In this study, the physicochemical properties of typical OSW were systematically studied, and the mechanism of the influence of OSW sample structure and composition on gasification behavior was studied by thermogravimetric mass spectrometry and gasification experiments. Scanning electron microscopy was used to observe the surface morphology of the samples, showing that waste wood chips (WWC) and Pennisetum giganteum (PG) have well-developed pore structures. Fourier transform infrared spectroscopy results indicated that polyurethane foam (PF) and polyethylene terephthalate (PET) have more oxygen-containing functional groups than WWC and PG. X-Ray diffraction showed that the order of crystallinity index was WWC > PET > PF > PG. X-ray photoelectron spectroscopy results showed the order of the surface alkali content was PG > PF > WWC. Furthermore, thermogravimetric and mass spectrometry experiments were used to explore the components released from volatiles during heating, demonstrating that WWC and PG produce mainly H2O, while PF and PET produce mainly CO2. Gasification experiments were carried out at different heating rates, and PET had the highest initial and final gasification temperatures. The distributed activation energy model was used to calculate the apparent activation energy, which was in the order WWC (153.7 kJ/mol) > PET (136.9 kJ/mol) > PG (81.2 kJ/mol) > PF (78.9 kJ/mol) and was consistent with the carbon ordering degree result.

Quantitative Contribution of Oxygen Vacancy Defects to Arsenate Immobilization on Hematite.

Hematite is a common iron oxide in natural environments, which has been observed to influence the transport and fate of arsenate by its association with hematite. Although oxygen vacancies were demonstrated to exist in hematite, their contributions to the arsenate immobilization have not been quantified. In this study, hematite samples with tunable oxygen vacancy defect (OVD) concentrations were synthesized by treating defect-free hematite using different NaBH4 solutions. The vacancy defects were characterized by positron annihilation lifetime spectroscopy, Doppler broadening of annihilation radiation, extended X-ray absorption fine structure (EXAFS), thermogravimetric mass spectrometry (TG-MS), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS). The results revealed that oxygen vacancy was the primary defect type existing on the hematite surface. TG-MS combined with EPR analysis allowed quantification of OVD concentrations in hematite. Batch experiments revealed that OVDs had a positive effect on arsenate adsorption, which could be quantitatively described by a linear relationship between the OVD concentration (Cdef, mmol m-2) and the enhanced arsenate adsorption amount caused by defects (ΔQm, μmol m-2) (ΔQm = 20.94 Cdef, R2 = 0.9813). NH3-diffuse reflectance infrared Fourier transform (NH3-DRIFT) analysis and density functional theory (DFT) calculations demonstrated that OVDs in hematite were beneficial to the improvement in adsorption strength of surface-active sites, thus considerably promoting the immobilization of arsenate.

Contamination Level Prediction: Progress in Species Separation by TGA/MS

Molecular contamination can be detrimental to spacecraft life expectancy as it may induce changes to the properties of the surfaces on which it deposits. In order to control these potential issues, manufacturers need to assess in-flight contamination levels in the quite early design phases, possibly leading to design changes or extra material bake-out to fulfil requirements. The accuracy of model assessments may thus have direct impacts on missions and costs. Prediction of outgassing and deposition at mission timescale is done by extrapolating short-term on-ground experimental results, by fitting the latter with some empirical or physical laws. Common methods are the power law interpolation (in isothermal conditions) or the residence time approach (with thermally activated time constants), which leads to exponential decays in isothermal conditions. Although they allow fitting the measured outgassed flux over few-day-long experiments, their extrapolation to ten or fifteen-year-long missions is more challenging. Validating empirical laws might involve long-term empirical comparisons, while obviously the validation of physical models should start with checking their physics. In spite of many years trying, a basic difficulty was yet found to block significant progress on physical validation. As long as measurements are limited to the total mass on QCMs it looks possible to fit data as a sum of almost any law, such as residence time or diffusion models e.g. for outgassing. Following this observation, a conclusion was drawn that the only way to discriminate between two different physics was to characterize contamination at chemical species level. Such characterizations are a prerequisite to unravel the physics at play during several phenomena: outgassing, deposit films dynamics, photochemistry, environment/ATOX interactions, etc. This innovative approach, presented herein, aims at identifying outgassed contaminants by means of coupled thermogravimetric analysis and mass spectrometry. For this purpose, this paper reports the successful species separation and identification of contaminants outgassed from a material used in space applications: the epoxy adhesive Scotchweld EC-9323-2.

Synergistic Effects between Lignin, Cellulose and Coal in the Co-Pyrolysis Process of Coal and Cotton Stalk.

In this work, Qiqunahu (QQH) coal, cotton stalk, cellulose and lignin extracted from cotton stalk were selected as raw materials to study the effects of the co-pyrolysis of coal and cotton stalk. Online thermogravimetric mass spectrometry (TG-MS) was used to analyse mass loss and gas release characteristics during co-pyrolysis. The results reveal that the mixture of cotton stalk and coal can significantly enhance the reactivity of the blends and promote the formation of effective gas. The cellulose in the cotton stalk promotes the generation of H2 and CO2 during the co-pyrolysis of coal and cotton stalks. Lignin promotes the production of CH4 and CO2. Cellulose and lignin show an inhibitory effect on the precipitation of small molecular weight hydrocarbon gases during co-pyrolysis. This study provides a better understanding for the co-pyrolysis of biomass and coal.

Exploring the key components of Au catalyst during CO oxidation using TG-MS and operando DRIFTS-MS

Nano-Au has a good catalytic activity for CO oxidation, but its catalytic mechanism is still not clear. Here, CO oxidation on Au2O3 and its thermal decomposition products were studied using thermogravimetric-mass spectrometry (TG-MS) and operando diffuse reflectance infrared Fourier transform spectroscopy-mass spectrometry (DRIFTS-MS) to explore the key active components of Au catalyst for CO oxidation. The TG-MS results showed that Au2O3 decomposed to AuO at 210 °C and Au at 375 °C and was oxidized to form Au oxide above 375 °C. When Au2O3 decomposed into AuxOy (x>y) above 210 °C, the CO oxidation activity obviously increased. Au atoms in the Au-Au system serve as electron donor and CO adsorption sites. Au atom is oxidized to AuO by the O atom from O2 decomposition following the Epling-Xu decomposition mechanism. A schematic diagram of the key components of Au2O3 catalysts during CO oxidation was proposed based on TG-MS and operando DRIFTS-MS analysis results.

Evolution of structural damage of solid composite propellants under slow heating and effect on combustion characteristics

Composite propellants are used to fabricate solid motors for space vehicles. The fundamental factor that affects motor safety is the structural damage in the propellant owing to slow heating in an abnormal storage or service environment. Hence, their thermal damage and combustion characteristics should be studied comprehensively. In this study, we investigated the combustion behaviours of hydroxyl-terminated polybutadiene/ammonium perchlorate/aluminium powder (HTPB/AP/Al) and hydroxyl-terminated block copolyether/AP/Al (HTPE/AP/AI) propellants under slow heating conditions. The pore structure was observed using scanning electron microscopy and micro-computerised tomography. Their weight loss behaviour, gaseous products, and pore structure evolution were analysed using thermogravimetric analysis, mass spectrometry, and Fourier-transform infrared spectroscopy. The influence of the pore structure on the combustion behaviour was studied by establishing the relationship between combustion and energy release rates. The weight loss rates of HTPB/AP/Al and HTPE/AP/Al before ignition were 34.5% and 16.1%, respectively. Upon heating, the HTPB binder decomposed to form pore channels, through which the gaseous products produced from the decomposition of AP were released, which increased the structural damage in this propellant. In contrast, upon heating, the HTPE binder liquefied and formed a coating on the AP particles, which slowed the structural damage in this propellant. Moreover, the calculated reaction intensity of HTPB/AP/Al was 4.16 times that of HTPE/AP/Al, indicating that larger pore channels increase the burning surface for combustion.

Effects of Pyrrhotite on the Combustion Behavior and the Kinetic Mechanism of Pyrite-Pyrrhotite Mixture Powders in the Air

In this study, we performed a comparative analysis of the combustion behavior of pyrite, pyrrhotite, and pyrite-pyrrhotite mixture (mixed mineral) powders in an air atmosphere. To study the influence of the pyrrhotite content in mixed mineral powders on the combustion behavior in the air, thermogravimetric mass spectrometry, X-ray diffraction analysis, and scanning electron microscopy were employed. The results indicated that pyrrhotite lead to a weight gain in the mixed minerals during the combustion process. Pyrrhotite particles are more easily adsorbed on the surface of pyrite particles during mixed mineral combustion due to their strong ability to absorb oxygen, which accelerates pyrite combustion. The weight loss of mixed minerals decreased during the combustion process with increasing pyrrhotite content, resulting from pyrite encapsulation by agglomerated and sintered pyrrhotite during combustion. The calculated kinetic parameters and phase analysis results suggested that pyrite combustion is consistent with the shrinking core mechanism, and in the combustion process, the irregular pyrite particle shrank into a spherical particle; the combustion products of pyrrhotite grew in a layer-by-layer manner. Pyrrhotite combustion corresponded to the three-dimensional diffusion mechanism, and mixed mineral combustion was dominated by the shrinking core mechanism and supplemented by the three-dimensional diffusion mechanism. SO2, as the main combustion product, was continuously generated and volatilized in the reaction, signifying that the combustion reaction of pyrite is a two-phase reaction involving gas and solid.

Synthesis of calcium carbonate-loaded mesoporous SBA-15 nanocomposites for removal of phosphate from solution.

Removal of phosphate from water is very crucial for protecting the ecological environment since massive phosphorus fertilizers have been widely used and caused serious water deterioration. Thus, we fabricated a series of calcium carbonate-loaded mesoporous SBA-15 nanocomposites with different Ca:Si molar ratio (CaAS-x) as phosphorus adsorbents via a simple wet-impregnation method. The multiply approaches including X-ray diffraction (XRD), N2 physisorption, thermogravimetric mass spectrometry (TG-MS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) were used to characterize the structure, morphology, and composition of mesoporous CaAS-x nanocomposites. The phosphate adsorption efficiency of the CaAS-x nanocomposites was studied through adsorption and desorption batch tests. Results showed that the increases of Ca:Si molar ratio (rCa:Si) improved the phosphate removal capacity of CaAS nanocomposites, especially CaAS with the optimum synthesis molar ratio of Ca:Si as 0.55 showed the high adsorption capacity of 92.0 mg·g-1 to high concentration of phosphate (> 200 mg·L-1). Note that the CaAS-0.55 had a fast exponentially increased adsorption capacity with increasing the phosphate concentration and correspondingly showed a much faster phosphate removal rate than pristine CaCO3. Apparently, mesoporous structure of SBA-15 contributed to high disperse of CaCO3 nanoparticles leading to the monolayer chemical adsorption complexation formation of phosphate calcium (i.e., =SPO4Ca, =CaHPO4-, and =CaPO4Ca0). Therefore, mesoporous CaAS-0.55 nanocomposite is an environmental-friendly adsorbent for effective removal of high concentration of phosphate in neutral contaminated wastewater.

Effect of addition of K2CO3 on the structure of coals with different ranks by FTIR and TG/MS

K2CO3 was considered as the effective catalyst on the pyrolysis performance of coal, however, its effect on coals with different ranks and coalification jumps is unknown until now. This study aims to explore the catalytic mechanism of K2CO3 on coals with different ranks. 8 coals with a vitrinite reflectance (Ro,max) ranging from 0.68% to 1.71% were catalyzed by K2CO3. Thermogravimetric-Mass spectrometry analyzer (TG/MS) and Fourier Transform Infrared (FTIR) spectroscopy were used to characterize the structural variation before and after the addition of K2CO3. FTIR results showed that the length of aliphatic chains (CH2/CH3) decrease and then increase with the turning point near Ro,max = 1.53%, the degree of condensation of aromatic ring (DOC),aromaticity (I) decreased and the concentration of aliphatic hydrogen (Hal/H) increased for all coal samples except for DQ coal (Ro,max = 1.53%) after the addition of K2CO3, indicating the abrupt changes occurred at Ro,max = 1.53%. TG/MS results showed that both the weight loss rate and the maximum weight loss rate temperature exhibit reflection changes near 0.68% and 1.2% of Ro,max. The evolution rate of hydrogen and ethane showed turning changes near Ro,max = 1.21%, while the evolution rate of methane and benzene present transitive changes near Ro,max = 1.53%. Ro,max = 1.21% and Ro,max = 1.53% are consistent with the second and the third coalification jump, respectively. Both TG/MS and FTIR results demonstrated that the effect of K2CO3 is related to coal rank, especially the coalification jump. K2CO3 may tend to act on CC structures furthermore promote the evolution of gaseous products during pyrolysis. The results provide deeply understanding for the coalification jumps and theoretical basis for the selection of suitable catalysts with different coal ranks.