Lignite Particles Research Articles

Experimental Study on Effects of Different Factors on Continuous Detonation of Superfine Lignite: Particle Size and Fuel Equivalent Ratio

ABSTRACT The Rotating Detonation Engine (RDE) is garnering attention for its high thermal cycle efficiency. In order to explore the detonation evolution of lignite/gas/oxygen gas-solid two-phase fuel in RDE, self-developed RDE(L:1000 mm) was used to study the detonation characteristics of lignite dust with ultra-fine particle size in methane/oxygen atmosphere, and the effects of ultra-fine particle size and equivalent ratio on detonation characteristics were explored, achieving stable propagation of rodtating detonation waves (RDW) with durations between 0.611 and 0.684s. The results indicate that the introduction of lignite dust significantly enhances the detonation effects compared to pure methane fuel. An increase in the overall equivalence ratio boosts the propagation velocity of RDW in methane-solid fuels, while a larger lignite dust particle size slows it down. Among ultrafine lignite powder sizes, a 1 μm particle size achieved the highest detonation wave speed. In terms of RDW propulsion, the impact of particle size and methane-solid fuel equivalence ratio on thrust mirrors their effect on detonation wave velocity. At a global equivalence ratio (GER) of 1.8, the specific impulse under different particle sizes was about 0.6 times that at a GER of 1.0, suggesting that an excess of fuel can reduce detonation effectiveness. The optimal specific impulse results were obtained with a lignite powder addition rate of 6 g/s, particle size of 1 μm, and GER of 1.0, reaching 4.6 kN·s·kg−1. The research results reveal the detonation process and detonation propagation law of lignite in methane/oxygen, especially for the future application of lignite in detonation energy release engineering.

Binding mechanism in bio-briquette prepared with wheat straw and lignite by mechanical thermal expression process

ABSTRACT In this study, bio-briquette was prepared with lignite and wheat straw by mechanical thermal expression (MTE) process and analyzed using an optical microscope (OM), scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscopy. Under the combined action of thermal and mechanical energy, the binding mechanism between lignite and biomass in bio-briquette was discussed. Results showed that the compressive strength of bio-briquette increased with the increase of pressure and temperature, which positively affected the bonding of material particles. Lignite particles were wrapped into the network formed by interconnected fibers of different lengths. During the MTE process, the liquid bridges were built among the biomass undergoing glass transition, water, and partially melted lignite, which became solid bridges after briquette formation, enhancing the compressive strength of bio-briquette.

Experimental Study on the Micro-Structure of Lignite and Its Explosive Solid Residue

ABSTRACT Lignite reserves in the world’s various coal reserves in the first place. To take a qualitative and quantitative analysis on the change characteristics of the microstructure of lignite before and after explosion, the explosive tests took four lignite samples as the research object and were carried out in the 20 L spherical explosive test system. The experimental study was carried out by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and Raman spectrometer to analyze the change characteristics of the surface morphology and macromolecular structure of lignite before and after explosion. The results indicated that compared with bituminous coal, the surface particles of lignite are less porous after explosion and the morphology is relatively complete. The rich aliphatic hydrocarbon and oxygen-containing structures in the range of 700–1800 cm−1 and 2800–3000 cm−1 contained in lignite were greatly reduced or disappeared after the explosion, while the mineral band at 536 cm−1 were more obvious and the band intensity became stronger. The area of D3 and D4 peak in Raman spectra decreased significantly after the explosion, which means that the CH3 and CH2 structures in the carbon structure of R-O-R’ (ether group) in lignite are significantly reduced. Besides, the intensity ratio of the sum of D3 peak and D4 peak to G peak ((ID3+ID4)/IG) of the solid product after explosion is reduced significantly, close to 0. The change can be applied of coal microstructure groups in the process of explosive reaction is helpful to reveal the reaction mechanism of pulverized coal explosion and provide a reference for identification and analysis the pulverized coal explosion accident.

Ignition characteristics of single coal particles under ammonia co-firing conditions

To meet the goal of an international carbon-neutral framework, the promotion of clean coal utilization occupies a vital position in reducing greenhouse gas emissions. Ammonia co-firing is considered as a potential strategy for future power generation to reduce fossil energy consumptions, soot, CO2 emissions, and hydrocarbon pollutants. In the present work, the ignition characteristics of single coal particles under ammonia (NH3) co-firing conditions were investigated. Particles were injected with NH3 or N2 into a hot flue gas environment at 1550 K generated by a CH4-fired Hencken burner. Temporally resolved images of CH* chemiluminescence and char thermal radiation were captured. Combining the signal profiles, ignition modes and characteristic times of single burning particles were studied with different coal types, carrying atmospheres, and O2 contents. When the carrier gas was replaced by NH3 atmosphere, the ignition delay time of all coal particles was greatly shortened, and the time interval from ignition to peak, as well as the combustible component burnout time, were both lengthened due to the promoted devolatilization and combustion reaction rates of coal particles caused by the NH3 flame. Concerning the ignition mode in the NH3-blended cases, the homogeneous ignition behaviors of the lignite particles were further enhanced, while the bituminous particles transitioned to the homogeneous-heterogeneous united ignition mode. As the O2 content in the flue gas increased, the ignition of all coal particles was advanced monotonously, and the chemiluminescence became more intense in both N2 and NH3 atmospheres.

Online monitoring of the burning characteristics of single pulverized coal particle in O2/N2 and O2/CO2 environments

The objective of this study is to compare the ignition and burning characteristics such as burnout times of volatiles and char, and ignition mechanism of single pul?verized coal particle burning in air (O2/N2) and oxy (O2/CO2) environments. An entrained flow reactor with photo detector has been employed for this study. This technique involves online monitoring of radiation emission from an individual coal particle. Individual particles of sub-bituminous or lignite coal particle with size in the ranges of 106-125 micron and 180-212 micron particles have been injected into an air (O2/N2) or oxy (O2/CO2) environment inside an entrained flow reactor. The oxygen concentration in the ambient gas is varied between 10%-50% by volume. The volatile and char burnout times have been obtained from time histories estimated from the radiation emitted by the particle. The results show an obvious increase in the burning rates of volatiles and char with increasing oxygen concentration. Further, when compared to N2 atmosphere, the burning rate and radiation intensity are found to be lower in CO2 atmosphere, especially at lower oxygen concentrations. An indication of the possible ignition mechanism has been outlined from the percentages of single and double peaks observed in the radiation emission histories. The complete experimental investigation shows that the burning rates of both volatiles and char are predominantly affected by the oxygen concentration, particle size and gas temperature. The theoretical results from a single particle model has been used to validate the trends and the combustion durations obtained from the present experimental study and is published as a separate manuscript.

Lignite Upgradation of Mae Moh Power Plant Thailand via Low – Temperature Pyrolysis

The lignite at Mae Mo mine in Lampang Thailand, which is the focus of this study is ranked as the lowest class in coal classification. The lignite is currently burned directly in boilers for electricity production, resulting in inefficiencies. The objective is to use low-temperature pyrolysis to improve the lignite. Lab-scale experiments were conducted using different lignite particle sizes (2.36 mm, 1.00 mm, and 0.25 mm) at temperatures ranging from 250-600°C and retention times of 0-60 mins. The best quality lignite was achieved processing a particle size of 2.36 mm at a temperature of 350°C and a retention time of 20 mins. The gross calorific value, fixed carbon, and char content increased with higher operating temperatures. Weight loss occurred between 300-600°C due to the degradation of volatile organic fractions and char formation. Ash and sulfur constituents increased in smaller coal sizes. The average gross calorific value of char was 23.04-27.19 MJ/kg. Lower operating temperatures, larger coal sizes, and sufficient retention time are recommended for the pyrolysis process to achieve optimal results.

The potential of polycyclic aromatic compounds as indicators for soil contamination by open-pit mining and utilization of lignite: a case study at Ptolemaida basin, Greece

The majority of Greek lignite fields and coal-fired power plants is accumulated in the centre of Western Macedonia in the Ptolemais-Amynteo region of Northern Greece (Ptolemaida basin). The corresponding environmental impact dominantly caused by the mining process itself but also due to the burning process of lignites needs to be considered. Therefore, this study aimed at assessing the potential of PAHs to trace the environmental impact of power plant and coal mining emissions on soil pollution in the Ptolemaida basin. Noteworthy, the study area exhibits some special features (e.g. geomorphological and meteorological conditions, well-defined emission sources) that allow to prove the suitability of PAHs as indicators for specific petrogenic contaminations. The different sets of PAH emission sources followed in this study (fly ashes, lignite dust, charred woody material) reflected the pollution as derived from the coal mining activities as well as agricultural measures. Different approaches from simple (total amount) to more complex fingerprinting (ring member classification; profiles of sulphur-/nitrogen- and oxygen-containing PACs) as well as the application of established specific PAH ratios revealed no significant correlation with the detected soil contamination or rather soil PAH profiles. However, the microscopic analyses contradicted this assumption, since relevant particle concentrations were evident for fly ash as well as lignite particles. Hence, a huge superimposition by a further PAH emission source is assumed, probably the exhaust fumes of car traffic. In general, the study demonstrated that the application of PAHs as source indicators in soil systems is very complex and needs a very thorough interpretation. Hence, the need of using additionally complementary parameters for an unambiguous emission source apportionment seems obvious.Graphical abstract

The non-isothermal drying characteristics of lignite and prevention strategies for structure damage

Structural damage to lignite during drying may cause dust explosions and pose a safety hazard. In this study, a prevention strategy for drying damage of lignite particles using non-isothermal drying processes is proposed. The isothermal and non-isothermal drying processes of lignite particles were systematically studied using drying curves, drying models, and water transfer coefficients. Temperature changes inside the particles were monitored, and the particle strength after drying was analyzed. The results revealed that the internal temperature of the particles suddenly increased towards the end of the drying period at 170 °C, and the corresponding water vapor pressure significantly increased, thereby increasing the driving force for water transfer during the later stages of drying. However, the water vapor pressure caused serious damage to the particles. For the non-isothermal drying process in which the temperature decreased from high to low, the free water was rapidly and massively removed under high temperature during the early stages of drying, and the vapor pressure decreased during the removal of pore water in the late stage of drying, which meant less damage was caused to the pore structure by the vapor pressure.

Mechanistic insight into the adsorption and interaction of lignite, organic ingredients, and dispersant in coal wastewater slurry

The conversion of coal gasification wastewater into coal wastewater slurry (CWWS) for combustion and gasification fuels is a promising approach that combines resource recovery with effective wastewater management. In this work, the influence of organic ingredients derived from coal gasification wastewater on the slurrying capabilities of lignite, particle dispersion/aggregation behavior, and adsorption characteristics between lignite and sodium methylene dinaphthalene sulfonate (NNO) in CWWS was thoroughly investigated. The interaction mechanism of lignite, NNO, and the organic ingredients in the slurry systems revealed subsequently by molecular dynamics (MD) simulations. Results indicated that the maximum solid concentration for coal gasification wastewater simulated by organic ingredients increased by 1.64% with a decrease in pseudo-plasticity and stability. The presence of dodecane, phenolic and heterocyclic nitrogen compounds caused the dissociation and coalescence of particles in the CWWS and further formation of creaming or clarifying layer. The adsorption processes of NNO and the organic ingredients on lignite particles exhibited competitive adsorption, following the pseudo-second-order kinetic and the Freundlich thermodynamic models. The adsorbed organic ingredients enhanced the hydrophobicity and electrostatic repulsion of the particle surface in CWWS, increasing the hydrophobic C-C/C-H content from 64.73% to 71.27%. Moreover, the MD simulation results revealed that the adsorption conformations at the lignite-water interface in CWWS changed from “single-point and single-layer” adsorption of NNO to “multi-point and multi-layer” adsorption of NNO and organic ingredients driven by hydrophobic effect, van der Waals force, π-π stacking effect, and hydrogen bonding.

Application a solid fuel mixture based on Bolshesyrsky lignite and birch wood waste in power plants

In this paper, we investigate the possibility of using a solid fuel mixture based on lignite from the Bolshesyrsky coal mine and birch wood waste in power plants, taking synergistic interactions between the mixture components into account. Simultaneous thermal analysis was used to determine the main combustion characteristics of lignite, biomass and their mixtures. Non-isothermal heating was performed at a rate of 20°C/min across the temperature range of 25–800°C under the air flow of 50 ml/min. The sample weight was about 6 mg. Proximate and elemental analyses of lignite and biomass samples were performed according to conventional methods. The advantages and disadvantages of converting power plants operated on solid fossil fuels to a solid fuel mixture of lignite and biomass are discussed. The main combustion characteristics of lignite, biomass and their mixtures were defined. The ignition temperature of the coke residue and biomass was found to comprise 365 and 299°C, respectively. The temperature of combustion completion for lignite and biomass was 551 and 464°C, respectively. In comparison with lignite, biomass burns at lower temperatures due to the high content of volatile substances. The addition of biomass to lignite was found to reduce both the ignition temperature of the coke residue and that of combustion completion. An analysis of the combustion process of volatile substances and coke residue established the presence of both positive and negative synergistic interactions between lignite and biomass particles, affecting the maximum combustion rate and the mixture reactivity. The results obtained can be applied when designing power plants operated on solid fuel mixtures of lignite and biomass.

Mechanical Properties and Brittleness Characterization Method of Low-Rank Coal and Its Char Particles under a Uniaxial Compression Test

The mechanical properties of low-rank coal and its char particles are of great significance in many energy and chemical process applications. The 2.8–4.0 mm narrow size range irregularly shaped particles of Shenhua sub-bituminous coal and Huolinhe lignite and their 800 °C chars were studied by using a uniaxial compression test. The results showed that their mechanical properties such as effective elastic modulus, crushing force, crushing energy, and tensile stress fitted well with Weibull and logistic distributions. Statistically, the strength of both kinds of coal chars was higher than that of raw coal. The distribution of mechanical parameters of lignite and its char particles was more dispersed and had a wider range of variation. The brittleness index composed of compressive stiffness and breakage energy could well describe the particle failure mode, and the brittleness of sub-bituminous coal was greater than that of lignite. Image-based particle size distribution analysis revealed that samples with higher brittleness and strength would produce less volume of fragments conforming to fractal distribution during the crushing process. This indicates that the crushing process of coal particles with brittleness and high strength is relatively fast and their cracks are not fully developed.

Can reductive deiodination improve the sorption of iodinated X-ray contrast media to aquifer material during bank filtration?

Iodinated X-ray contrast media (ICM) as well as their aerobic transformation products (TPs), are highly polar triiodobenzoic acid derivatives, ubiquitously found in the urban water cycle. Based on their polarity, their sorption affinity to sediment and soil is negligible. However, we hypothesize that the iodine atoms bound to the benzene ring play a decisive role for sorption, due to their large atom radius, high electron number and symmetrical positioning within the aromatic system. The aim of this study is to investigate, if the (partial) deiodination, occurring during anoxic/anaerobic bank filtration, improves the sorption to aquifer material. Tri, di, mono and deiodinated structures of two ICMs (iopromide and diatrizoate) and one precursor/TP of ICM (5-amino-2,4,6-triiodoisophtalic acid) were tested in batch experiments, using two aquifer sands and a loam soil with and without organic matter. The di, mono and deiodinated structures were produced by (partial) deiodination of the triiodinated initial compounds. The results demonstrated that the (partial) deiodination increases the sorption to all tested sorbents, even though the theoretical polarity increases with decreasing number of iodine atoms. Whereas lignite particles positively affected the sorption, mineral components decreased it. Kinetics tests show biphasic sorption for the deiodinated derivatives. We have concluded that iodine affects the sorption by sterical hindrance, repulsive forces, resonance and inductive effects, depending on the number and position of iodine, side chain characteristics and composition of the sorbent material. Our study has revealed an increased sorption potential of ICMs and their iodinated TPs to aquifer material during anoxic/anaerobic bank filtration as a result of (partial) deiodination, whereby a complete deiodination is not necessary for efficient removal by sorption. Furthermore, it suggests that the combination of an initial aerobic (side chain transformations) and a subsequent anoxic/anaerobic (deiodination) redox milieu supports the sorption potential.

Numerical optimization of combustion and NOX emission in a retrofitted 600MWe tangentially-fired boiler using lignite

In order to meet the ultralow emission standard of NOx, the combustion system of a 600 MWe tangentially-fired lignite boiler was retrofitted using air-staged combustion technology. The retrofit scheme is described in detail. Combustion and NOx emission characteristics of the original and retrofitted boiler were numerically studied and compared. Optimization simulations for retrofitted boiler were carried out under different over-fired air ratios. The moisture content in lignite was specially considered in simulations by simplified coal compositions method. The results show that the ignition of lignite particles is delayed due to the high moisture content. After retrofit, the temperature level in furnace rises owing to the reduction of total excess air coefficient in furnace, and the high temperature region moves upward due to the introduction of separated over-fire air. The NOx emission is reduced by approximately 40% through retrofitting, which proves that the low-NOx retrofit for the lignite-fired boiler is successful. With over-fired air ratio increasing from 15% to 25%, the NOx emission for retrofitted design decreases from 394 mg/Nm3 to 317 mg/Nm3 (at 6% O2). OFA ratio of 20% is the most economical case, and OFA ratio of 25% is the most environmentally friendly case. Taking NOx emission and boiler thermal efficiency into account, the practical operating condition with OFA ratio of 20% is optimal for retrofitted boiler. The results can be beneficial for the retrofit and practical operation of similar lignite-fired boilers.

Particle-scale heat and mass transfer processes during the pyrolysis of millimeter-sized lignite particles with solid heat carriers

• Devolatilization kinetics is coupled with the heat and mass transfer processes. • Evolution of pore structure in coal pyrolysis with solid heat carrier is included. • Multi-physical fields inside a lignite particle during pyrolysis is elaborated. • The intraparticle mass transfer mechanism influences the secondary reaction. The study of mesoscale solid fuel pyrolysis behavior is a key bridge between the microscopic reaction kinetics and macroscopic multiphase reaction flow in a reactor. In this work, a one-dimensional nonstationary model was developed in spherical coordinate system for the pyrolysis of millimeter-scale lignite particles with solid heat carriers, in which a modified multistep kinetic model (MSM) was coupled with a series of correlative transient heat and mass conservation equations in conjunction with the dusty gas model (DGM). The MSM for coal pyrolysis was modified by adding a set of kinetic equations of pseudo-elementary secondary reactions, making the kinetic model comparable to the Chemical Percolation Devolatilization model in terms of accuracy. In addition, a semiempirical submodel for the evolution of pore structure parameters (porosity, pore size, and permeability) was incorporated to obtain the precise mechanism of volatile species transport in the porous coal matrix. The modified MSM and pore evolution submodel were validated against literature data. The coupling effects between intraparticle transport processes and transient devolatilization kinetics were investigated. It was concluded that notable multiphysical fields (pressure, concentration, and velocity) emerged within lignite particles during pyrolysis, governed by the heating history. In addition, it should be noted that the direction and mechanism of volatiles transfer within porous lignite particles varied during pyrolysis, which can significantly affect secondary reactions. Flow reversal and shifts in the dominant mass transfer mode influenced the secondary reaction pathway, in addition to the impact of volatiles flow velocity on the reaction degree.

Experimental study of moisture effects on spontaneous combustion of Baiyinhua lignite from individual particles to stockpile

Evaporation and condensation of moisture affect dramatically the spontaneous combustion of lignite with high moisture content at low temperatures. Moisture migration between the lignite and the external environment of coal stockpile encompasses the scales of individual particles and stockpile. The cyclic moisture evaporation/condensation test was applied to investigate moisture migration of individual lignite particles at different particle sizes and temperatures. The wire-mesh basket test was selected primarily to analyze the heating process and critical self-ignition temperature of lignite stockpile. Results of the cyclic moisture evaporation/condensation test reveal that the moisture content of re-saturated lignite is much lower than that of the original one. Moisture content versus time showed a tendency to overlap in repeated moisture evaporation processes, and so did the repeated moisture evaporation processes. Therefore, a model of moisture migration of individual particles was built to describe the repeated moisture evaporation and condensation processes. The time factor determines the speed of moisture evaporation and condensation of individual lignite particles, being inversely proportional to ambient temperature and proportional to particle size, respectively. In the wire-mesh basket test, the heating process of the lignite stockpile can be divided into four stages, but the influence of moisture was more pronounced in stage II. Critical self-ignition temperature is proportional to particle size and increases linearly with moisture content. According to Frank-Kamenetskii theory, an increase in either particle size or moisture content can restrain the tendency of spontaneous combustion of Baiyinhua lignite stockpile.

Hydrogen production from low-rank coal by a two-step method combined subcritical depolymerization with supercritical gasification

High efficiency gasification of inferior brown coal to produce hydrogen is a research focus and difficulty for clean utilization of coal resources. Abundant intermolecular hydrogen bonds in brown coal induce cross-linking side reactions of coal molecules in the pyrolysis process, which inhibits the efficient gasification of lignite. Based on the high temperature and pressure visualization reactor, it was found that alkaline subcritical liquid water would destroy the hydrogen bond structure in lignite, thus leading to the depolymerization of lignite particles. Based on this phenomenon, the crosslinking side reaction in the pyrolysis process can be suppressed at the molecular level. Therefore, a two-step method combined subcritical depolymerization with supercritical gasification was proposed to achieve high-efficiency gasification of brown coal for hydrogen production (the carbon gasification efficiency reached 98 % at 650 ∼ 700 °C). This provides a theoretical basis for the scheme design of clean and efficient gasification hydrogen production from inferior brown coal in supercritical water.

Determining the flotation upgrading effect of shale oil on lignite via molecular dynamics simulation and experiment comparisons

ABSTRACT In this study, we combined experiments with molecular dynamics simulation to investigate the improvement of lignite flotation performance by shale oil and microscopic promotion mechanism. Through FTIR and GC/MS tests, our preliminary findings showed that shale oil contains polar groups and long-chain alkanes. Moreover, XPS tests confirmed that shale oil could render the C–C/C–H and cover the C–O, C=O and O=C–O functional groups. The induction time between lignite particles and shale oil bubbles was 15ms lower than that between kerosene bubbles. Besides, the flotation results indicated that shale oil could improve the yield and reduce the ash content of clean coal significantly. The molecular dynamics simulation results showed that shale oil molecules could preferentially adsorb on lignite pore surface and weak the direct adsorption and seepage of water molecules on lignite surface. This was consistent with the results of an analysis of the whole system’s relative concentration distribution and mean square displacement of water molecules. These data provide further evidence that shale oil can clearly improve the flotation recovery of low-rank coal, which is of great importance for the clean utilisation of low-rank coal.

Structural evolution of lignite from heterogeneous particles to homogeneous products during ruthenium ion catalytic oxidation depolymerization

Disclosing the structure evolution of lignite from heterogeneous particles to homogeneous products during depolymerization is of great significance to understand the depolymerization process of lignite. In this work, the structure evolution of lignite during ruthenium ion catalytic oxidation (RICO) depolymerization was studied. Special attention was paid on the changes of the size of lignite particles and molecular weight of the soluble products. The results showed that the depolymerization of lignite into benzene polycarboxylic acids (BPCAs) involved the conversion of lignite from microparticles into nanoparticles, which can be further depolymerized and released the soluble products into the solution. Around 93% of the organic matter in lignite can be converted from heterogeneous particles to homogeneous products. The molecular weight of the soluble products had a wide distribution from dozens of thousand Dalton to several hundred Dalton, indicating that the macromolecules released from lignite particles were gradually decomposed and formed a series of intermediate products. These results explain that why the composition of the depolymerization products is complex. Finally, the microstructural evolution process of lignite during depolymerization was speculated. Lignite particles mainly experienced the microparticles, nanoparticles, macromolecules, and then small molecules such as BPCAs. The formation of macromolecules proceeded fast and the subsequent formation of BPCAs from macromolecules was the rate-determining step. This work contributes deep insights into the structural evolution process of lignite during RICO depolymerization, and provides basic data for the regulation and control of the depolymerization process.

Effects of Moisture on the Ignition and Combustion Characteristics of Lignite Particles: Modeling and Experimental Study.

The influence of the moisture content on the ignition and combustion characteristics of lignite single particles was studied using an ignition model of single coal particles with moisture and experimental investigations in a visual drop tube furnace under the temperature of 1300 K. The moisture content and the lignite particle size were varied within the ranges of 0–20% and 75–250 μm, respectively. The images of the combustion process illustrated that higher moisture content caused a significant ignition delay. The probability of homogeneous ignition was greatest when the particle size was 125–150 μm and the moisture content was 5%. An ignition model was employed to explain the mechanism of the influence of moisture content on the ignition and combustion characteristics, which embedded the chemical percolation devolatilization model to increase the accuracy of predictions. The predicted results show that there was an overlap in the release of moisture and volatile matter from the lignite particle during the combustion at a high heating rate. The devolatilization rate increases with the increase of moisture, which explains the increase in the probability of homogeneous ignition and fragmentation. Both particle size and moisture content have two-sided effects on the ignition mode, which causes the complexity and irregularity of the ignition mode of particles with moisture.

Preparation of lignite-loaded nano-FeS and its performance for treating acid Cr(VI)-containing wastewater.

In this study, lignite-loaded nano-FeS (nFeS@Lignite) was successfully prepared by ultrasonic precipitation, and its potential for treating acid Cr(VI)-containing wastewater was explored. The results showed that the 40--80-nm rod-shaped nFeS was successfully loaded onto lignite particles, and the maximum adsorption capacity of Cr(VI) by nFeS@Lignite reached 33.08mg∙g-1 (reaction time = 120min, pH = 4, temperature = 298.15K). The adsorption process of Cr(VI) by nFeS@Lignite fitted the pseudo-second-order model and the Langmuir isotherm model, and thermodynamic results showed that the adsorption process was an endothermic process with an adsorption enthalpy of 28.0958kJ·mol-1. The inhibition intensity of coexisting anions on Cr(VI) removal was in the order of PO43- > NO3- > SO42- > Cl-, and the increase of ionic strength resulted in more pronounced inhibition. Electrostatic adsorption, reduction, and precipitation were synergistically engaged in the adsorption of Cr(VI) by nFeS@Lignite, among which reduction played a major role. The characterization results showed that Fe2+, S2-, and Cr(VI) were converted to FeOOH, S8, SO42-, Fe2O3, Cr2O3, and Fe(III)-Cr(III) complexes. This research demonstrates that nFeS@Lignite is a good adsorbent with promising potential for application in the remediation of heavy metal-contaminated wastewater.