Low-temperature Ashing Research Articles

Characterization of the melting behavior of high-temperature and low-temperature ashes

The flow behavior of high-temperature ash (HTA) and low-temperature ash (LTA) from room temperature to 1350°C was studied. The change of volume in the heating process was investigated by the heating stage microscope. The mineral matter composition and microstructure characteristics of HTA and LTA samples during the heating process were observed by X-ray diffraction and scanning electron microscope. The HTA and LTA samples shrink at the first heating stage, and then melt. With the increasing temperature, the minerals in HTA and LTA samples change and the flowability improves. The HTA and LTA samples show significantly spreading property. However, the shrinkage of HTA sample is different from that of LTA sample. The volume change of HTA sample is not obvious when the temperature is lower than 800°C, while the volume of LTA sample presents the continuous decrease. At the temperature range of 800–1000°C, the main minerals formed in LTA and HTA samples are augite and albite, respectively. Those mineral matter variations result in the obvious volume change of HTA and LTA samples. In addition, the microstructure of the samples shows that the shapes of particles in LTA are irregular and the surface of particles is coarse at lower temperature. With the increasing temperature, the attachments on the particle surface agglomerate, melt and accumulate. The variation of particles validates the change of flow behavior in the heating process.

Geochemistry and nano-mineralogy of feed coals, mine overburden, and coal-derived fly ashes from Assam (North-east India): a multi-faceted analytical approach

In order to address the scarcity of information on the nature and mode of occurrence of minerals and elements in coal, coal mine overburden and coal ashes from North-east India, and also the relations between coal mineralogy and ash chemistry, the petrology, mineralogy and nano-mineralogy, and ash chemistry of some industrially important high-sulfur coals, mine overburden materials and fly ash samples from Assam (India) have been evaluated. A combined approach, using petrography, low-temperature ashing plus X-ray diffraction (LTA-XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscope (HR-TEM), Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS), has provided new information on the mineralogy and nano-mineralogy of these sub bituminous coals and associated mine overburden. The presence of rare earth elements and yttrium (REY) in Northeast Indian coal, mine overburden and fly ash samples is also reported for the first time. The identification of these components may be significant from an economic point of view. Some Northeast Indian fly ashes, with REE oxides up to 1580ppm on an ash basis, might possibly represent sources for recovery of rare earth elements.

Investigation on the sintering behaviors of low-temperature lignite ashes

To investigate the sintering behaviors of lignite ashes, the 450 °C Xiaolongtan (XLT) and Huolinhe (HLH) lignite ash samples were analyzed by press-drop sintering technique, scanning electron microscope, and X-ray diffraction. The result shows the sintering temperature of XLT ash is lower than that of HLH, as a result of that base/acid (B/A) ratio of XLT is higher than that of HLH. The sintering temperatures of two lignite ashes under reducing atmospheres (H2 and CO) are lower than those under oxidizing atmospheres (CO2 and O2), which result from the effects of different iron states under different atmospheres. The sintering temperatures of two lignite ashes decrease with the increase in pressure. It decreases slightly in the range of low pressure, changes clearly in the range of 0.7–1.0 MPa, and changes slightly again with further increase in pressure. The sintering process of lignite ashes is proposed by the presentation of partial-melting phases, the generations of aggregates, and the densification of aggregates.

Understanding of mineralogy and residence of trace elements in coals via a novel method combining low temperature ashing and float-sink technique

For understanding the mineralogical characteristic and trace element affinities to specific minerals in coals, a combined method has been adopted and evaluated, which is low temperature oxygen-plasma ashing followed by float-sink density separation in bromoform. Mineral matter would be isolated from coals, and light (<2.89g/cm3) and heavy (>2.89g/cm3) mineral fractions would be separated from coal low temperature ash residues. Coals collected from three coalfields in China, namely Xiaolongtan (XLT), Huolinhe (HLH) and Yangquan (YQ), have been studied. Mineralogical characteristic of coals was characterized by X-ray diffraction and a field emission scanning electron microscope equipped with energy-dispersive X-ray spectroscopy. The distributions of trace elements in coals, low temperature ashes, and light and heavy mineral fractions were determined by inductively coupled-plasma mass spectrometry.The results show that minerals of different densities in coal can be successfully isolated and separated into two mineral fractions with the help of the combined method. Phase-mineral compositions in light mineral fraction of each coal are very similar to those in the respective low temperature ashes as a whole. Phases identified in the heavy mineral fraction are completely different from those in the low temperature ash and the light mineral fraction of each coal. Pyrite dominates in the heavy mineral fractions from the three coals, which constitutes up 48.7wt.%, 82.9wt.%, and 100wt.% in the heavy mineral fraction of YQ, XLT, and HLH coals, respectively. Pyrite particles mostly occur as euhedral crystals, which display well-defined shapes, such as pentagonal dodecahedra, tetrakaidecahedra, cubes, decahedra, and regular octahedra. Framboid and massive pyrite are also clearly observed. Trace elements Pb, Cd, Mo, Cu, Tl, Sn, Sb, and Zn have a strong affinity to pyrite; elements Ni and Co are likely to occur in pyrite or ankerite; elements Sr, Hf, Li, V, Ga, Rb, Ba, Nb, Cs, U, Th, and Zr are associated with clay minerals and quartz; rare earth elements are clearly associated with clay minerals.

Characterisation and comparison of biomass ashes with different thermal histories using TG-DSC

The present research is focused on the characterisation and comparison of biomass ashes from wood pellet with different thermal histories. One of the ashes is obtained in a muffle furnace until its mass stabilization reaching a temperature of 550 °C, low temperature ash (LTA); the other one came from an experimental fixed bed combustor after 4 h of stable combustion in which the temperature reached is above 1,000 °C, high temperature ash (HTA). The samples were studied using Thermogravimetry and Differential Scanning Calorimetry (TG-DSC) techniques, and they were subjected to a heating up to 900 °C under an inert atmosphere with the objective of perceiving the differences in their thermal behaviour. At these temperatures, complex phase transformations occur, related to decomposition of carbonates and formation of silicates. TG and DSC curves are compared and some differences in mass loss, temperature peaks and enthalpy associated to endothermic effects are detected and they are explained based on the different compositions of both samples obtained at different temperatures. Other techniques were applied for the determination of the chemical composition of the ashes; X-ray fluorescence and Scanning electron microscopy with energy dispersive X-ray spectroscopy showed the elements present in the ashes, and X-ray diffraction revealed the crystalline phases and confirms that LTA is mainly composed of carbonates, while HTA mostly consists of silicates.

Composition and mode of occurrence of minerals in Late Permian coals from Zhenxiong County, northeastern Yunnan, China

AbstractMinerals in the Late Permian coals from the Niuchang-Yigu mining area, Zhenxiong County, northeastern Yunnan, China, were investigated using optical microscopy and low temperature ashing plus X-ray diffraction (LTA + XRD). The results showed that minerals in the coal LTAs are mainly quartz, kaolinite, chamosite, mixed-layer illite/smectite (I/S), pyrite, and calcite, with trace amounts of marcasite, dolomite, and bassanite. The authigenic quartz generally occurs in collodetrinite or as a filling in cleats or cell cavities. This silica was mainly derived from aqueous solutions produced by the weathering of basaltic rocks in the Kangdian Upland and from hydrothermal fluids. The presence of β-quartz paramorph grains in collodetrinite probably indicates that these grains were detrital and came from a volcanic ash. Clay minerals are generally embedded in collodetrinite and occur as cell-fillings. Pyrite occurs as framboidal, anhedral, and euhedral grains and a cell-filling. The coals are high in pyrite and the high pyrite content probably results from seawater invading during the stage of peat accumulation. Calcite generally occurs as vein-fillings, indicating an epigenetic origin.

Organic matter removal for the analysis of carbon and oxygen isotope compositions of siderite

The measurement of stable carbon (C) and oxygen (O) isotope compositions in siderite from sediments and soils can be useful to constrain carbonate genesis processes and/or to reconstruct paleoclimates. In order to evaluate our ability to determine C and O isotope compositions of siderite in modern sediments and soils containing immature organic matter, we prepared and analyzed synthetic samples made of variable proportions of pure siderite and yeast (selected for representing an immature organic matter because of its potential high reactivity to H3PO4 digestion). Replicate analyses of CO2 produced by phosphoric acid (H3PO4) digestion of our pure siderite standard at 130°C provided δ13Csid and δ18Osid values of −12.3±0.1‰ and −16.2±0.3‰ (2σ) relative to PDB. Analysis of the synthetic sample mixtures shows δ13C and δ18O values undistinguishable from those of pure siderite within uncertainties, for proportion of yeast in the mixture equal to or lower than 10wt.% (corresponding to ~5wt.% of total organic carbon). In contrast, samples with proportions of yeast higher than 10wt.% were progressively shifted to more negative values (down to −21.8‰ for C and −19.6‰ for O) with increasing proportion of yeast, as a result of an increasing contribution of CO2 produced by the reaction of yeast with H3PO4 at 130°C. Although in the case of natural samples this organic matter CO2 contribution probably strongly depends on both organic matter source organisms and diagenetic history, our data indicate that the removal of organic matter prior to siderite analysis may be often required. We thus tested three different methods for organic matter removal on our synthetic samples, using either oxidation in solution with NaOCl or H2O2, or oxidation in low-temperature oxygen-plasma ashing system. For both methods based on oxidation in aqueous solution, we show that the determination of δ13C and δ18O is improved for concentration of yeast lower than 75wt.% in the “siderite–yeast” mixture but is still shifted to lower values by 4.1 and 0.7‰ for C and O respectively, for a yeast proportion higher than 75wt.%. Moreover, these two methods induce partial siderite dissolution, preventing determination of siderite content in the samples. The best method of yeast removal for coupled C and O isotopes analysis is the oxidation by low-temperature oxygen-plasma ashing, which strongly improves the accuracy of the δ13C and δ18O measurements and perfectly preserves siderite. In conclusion, any study of siderite isotope composition in organic-rich samples should include an evaluation of the need for organic matter removal using low-temperature oxygen-plasma ashing, the only method shown here to be efficient while preserving the siderite.

Combustion of Biosolids in a Bubbling Fluidized Bed, Part 1: Main Ash-Forming Elements and Ash Distribution with a Focus on Phosphorus

This is the first in a series of three papers describing combustion of biosolids in a 5-kW bubbling fluidized bed, the ash chemistry, and possible application of the ash produced as a fertilizing agent. This part of the study aims to clarify whether the distribution of main ash forming elements from biosolids can be changed by modifying the fuel matrix, the crystalline compounds of which can be identified in the raw materials and what role the total composition may play for which compounds are formed during combustion. The biosolids were subjected to low-temperature ashing to investigate which crystalline compounds that were present in the raw materials. Combustion experiments of two different types of biosolids were conducted in a 5-kW benchscale bubbling fluidized bed at two different bed temperatures and with two different additives. The additives were chosen to investigate whether the addition of alkali (K2CO3) and alkaline-earth metal (CaCO3) would affect the speciation of phosphorus, so the molar ratios targeted in modified fuels were P:K = 1:1 and P:K:Ca = 1:1:1, respectively. After combustion the ash fractions were collected, the ash distribution was determined and the ash fractions were analyzed with regards to elemental composition (ICP-AES and SEM-EDS) and part of the bed ash was also analyzed qualitatively using XRD. There was no evidence of zeolites in the unmodified fuels, based on low-temperature ashing. During combustion, the biosolid pellets formed large bed ash particles, ash pellets, which contained most of the total ash content (54%–95% (w/w)). This ash fraction contained most of the phosphorus found in the ash and the only phosphate that was identified was a whitlockite, Ca9(K,Mg,Fe)(PO4)7, for all fuels and fuel mixtures. With the addition of potassium, cristobalite (SiO2) could no longer be identified via X-ray diffraction (XRD) in the bed ash particles and leucite (KAlSi2O6) was formed. Most of the alkaline-earth metals calcium and magnesium were also found in the bed ash. Both the formation of aluminum-containing alkali silicates and inclusion of calcium and magnesium in bed ash could assist in preventing bed agglomeration during co-combustion of biosolids with other renewable fuels in a full-scale bubbling fluidized bed.

Geochemistry and nano-mineralogy of two medium-sulfur northeast Indian coals

The petrology, mineralogy, and inorganic geochemistry of two contrasting high-sulfur, vitrinite-rich subbituminous to bituminous coals from the North Eastern Region (NER) of India have been studied using a combination of optical microscopy, quantitative X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM/SAED), and chemical analysis techniques. The study reveals that the Fe nano-particles are present in Indian high-sulfur Tertiary coals including nano-pyrite, Fe-oxyhydroxides and a small amount of sphalerite. The pyrite is present as framboids and unsymmetrical cubic crystals (rhombohedral). They contain potentially hazardous elements viz. As, Pb, and Se measured by EDS techniques. Mineral-matter residues isolated from the coals by low-temperature oxygen-plasma ashing are dominated by carbonate minerals (calcite, dolomite, ankerite), pyrite and pyrite oxidation products (jarosite and coquimbite), kaolinite, illite, and quartz. Sulfate-bearing phases such as tschermigite, bassanite and gypsum are also present, probably as artifacts of the plasma-ashing process.

Characterization of Macromolecular Structure of Pyrolysis Products from a Colorado Green River Oil Shale

Volatile products from an oil shale from the Colorado Green River formation were studied by several methods. The oil shale was demineralized, and the resulting kerogen was also chemically analyzed. Both the oil shale and the demineralized kerogen were pyrolyzed at 10 K/min, and the pyrolysis products (light gas, tar, and char) were analyzed using 13 C NMR, XPS, GC/MS, and FTIR. Low temperature ashing was performed in order to compare pyrolysis yields of oil shale and demineralized kerogen on a dry ash-free basis. Volatile yields of approximately 75% were achieved in an oil shale retort and 79% in the kerogen retort on a daf basis, with over 60% of the kerogen converted to tar. A carbon aromaticity of 21% was determined for the demineralized kerogen based on the NMR analysis, with an average number of 8.4 aromatic carbons per cluster, 4.4 attachments per cluster, an average cluster molecular weight of 666 amu, and an average molecular weight per side chain of 128 amu. At elevated temperatures, carbon aromaticity in the residual char increased to 81%, with an increase in the number of aromatic carbons per cluster to 19, and a corresponding increase in the number of attachments per cluster during kerogen pyrolysis. The GC/MS analysis of tars showed significant amounts of alkane/alkene pairs of straight chain hydrocarbons ranging from 9 to 20 carbons in length. XPS data were obtained to identify the nitrogen and oxygen species present in the kerogen, showing that nitrogen mainly occurs as heteroatoms. The nitrogen and sulfur preferentially stayed in the char compared to carbon and hydrogen.

Trends in Asbestos and Non-asbestos Fibre Concentrations in the Lung Tissues of Japanese Patients with Mesothelioma

We aimed to elucidate changes in asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma over time. Lung tissues were obtained from 46 patients with mesothelioma who died or underwent surgery between 1971 and 2005. All of the patients had a history of occupational asbestos exposure. We classified patients into four groups according to the period during which their lung tissue was obtained. Asbestos and non-asbestos fibre concentrations were determined by transmission electron microscopy with energy-dispersive X-ray analysis using a low-temperature ashing procedure. From the 1970s to the 2000s, we observed a decrease in the geometric mean of total asbestos concentration (67.4-1.05 million fibres per gram dry lung), chrysotile concentration (25.0-0.66 million fibres per gram dry lung), amphibole asbestos concentration (21.3-0.76 million fibres per gram dry lung), and non-asbestos fibre concentration (326-19.3 million fibres per gram dry lung). The mean duration of asbestos exposure decreased from 33.7 to 17.6 years, and the mean duration since the last exposure increased from 0.3 to 21.5 years. The percentage of longer fibres to total fibres tended to increase over time, whereas the mean fibre length did not differ significantly. The present study suggested that asbestos and non-asbestos fibre concentrations in the lung tissues of Japanese patients with mesothelioma who have occupational histories of asbestos exposure may have decreased from the 1970s to the 2000s.

Evaluation of the combustion behaviour and ash characteristics of biomass waste derived fuels, pine and coal in a drop tube furnace

Currently there is an increasing interest on a new generation of low cost biomass fuels derived from human activities like wood and forestry residues, crop residues and refuse derived fuels (RDF) produced from municipal or industrial solid waste. The main objective of this study is to evaluate the combustion behaviour and ash characteristics of a number of these renewable fuels, namely rice husk, straw, coffee husk and RDF derived from municipal waste. For comparisons purposes, the study also includes a bituminous coal and pine branches. The study was carried out in a drop tube furnace (DTF), where data was obtained for gas temperatures, particle burnout, and carbon, hydrogen and nitrogen release along the reactor for the six solid fuels. The analysis of the experimental data included the use of both a one dimensional (1D) model and the Fluent. The results reveal that biomass fuels yield particle burnout values comparable to those of coal due to a number of factors that have opposite effects, mainly their higher volatile matter, which increases the burnout, and their higher moisture content and larger particle size, which decreases it. According to the 1D model, the residence time of the particles in the DTF is strongly affected by the particle size, but the number of size fractions considered has little influence on the calculated burnout. Moreover, the use of the Sauter mean or mass median diameters is not appropriated to represent the biomass particle sizes in model calculations. Predicted burnout with the 1D model is similar to those predicted by the Fluent. The ash composition of the fuels revealed that RDF might have some corrosion and slagging potential, while the use of rice husk and straw could induce slagging through the formation of low melting temperature ashes.

Analyses of Aluminum Structures in a Chinese Coal Ash and Its Slag by STMAS NMR

Double-quantum filter satellite-transition magic-angle spinning experiments were tentatively carried out by one high magnetic field solid-state nuclear magnetic resonance (800 MHz for 1H Larmor frequency) to analyze the local 27Al structure in minerals of coal ash and slag. A high magnetic field offered higher sensitivity and resolution; hereby, the inconspicuous resonances of satellite-transition magic-angle spinning were obtained successfully at less stringent conditions. An obvious single 6-coordinate 27Al resonance was detected in the low-temperature ash; structures in pre-molten ashes (as prepared at 815 and 1,000°C) located relatively integral and symmetric, while Al resonances in the ash prepared at 1,600°C after once completely molten demonstrated discrete and asymmetric distribution. Moreover, the detailed spatial correlations among various aluminum species in rapid quenching slag exhibited dispersive T-O-T structures with lower signal-to-noise ratio of resonances.

Transformation of Minerals in Coal and Biomass upon Heating and their Impacts on Co-Firing

Co-firing has been adopted as a major approach for the efficient use of biomass as an energy source in large scale for two decades. Such a practice contributes to the decarbonisation in power generation sector and therefore to the mitigation of CO2 emission. However, due to the differences in terms of thermal behaviors between biomass and coal, the co-firing of some biomasses with coal still presents many engineering problems, such as excessive fouling and slagging, which subsequently result in deteriorated boiler efficiency. The understanding of the transformation of minerals upon heating and how minerals originated in biomass affect ash fusion characteristics is of some significance for both design and operation purposes. In this study, low temperature ash (LTA) samples of biomass and coal were prepared and analyzed by using X-ray diffraction (XRD), scanning electron microscopy (SEM) coupled energy diffraction spectrum (EDS), the results of which were compared with their corresponding high temperature ash (HTA) samples. The transformation of minerals upon heating was therefore studied. The ash fusion characteristic temperatures of ash samples derived from different biomass and coal blends were investigated. The ash fusion characteristic temperatures show some additive behaviors.

Partitioning of mineralogical and inorganic geochemical components of coals from Santa Catarina, Brazil, by industrial beneficiation processes

Comparative studies of the mineral matter and trace elements in 12 pairs of run-of-mine (ROM) and clean-coal products from beneficiation plants in Santa Catarina, southern Brazil, have been carried out using low-temperature oxygen-plasma ashing, X-ray diffraction and chemical analysis techniques with the aim of evaluating the effect of coal preparation on the mineralogy and chemical composition of the final coal products. The results show that substantial reductions in mineral matter and ash percentages are associated with beneficiation of coals mined from the different deposits. These reductions are accompanied by changes in the percentages of Fe2O3 in the respective coal ashes, due to the reduction in the proportion of pyrite in the mineral matter, and also by a reduction in the percentage of Na2O, possibly due to ion exchange within the clay minerals. The relative proportions of quartz, clay minerals, and minor phases such as calcite and feldspar (mainly albite) within the mineral matter are not, however, significantly changed by the beneficiation processes.The concentrations of most trace elements in the beneficiation products are similar to the respective concentrations in the relevant ROM materials, or are reduced to an extent similar to that of the total mineral matter percentage for the respective coal samples. This suggests an association mainly with the clay-rich mineral matter. The concentrations of As and Pb, however, are reduced to a greater extent for most samples by the beneficiation processes, consistent with a pyrite association. Concentrations of Ge, U and Zr are higher in many of the clean coals than in the respective run-of-mine materials, suggesting the possibility of preferential association, at least for some deposits, with the organic-rich fractions of the coals concerned.

Research on Ultra-High Performance Concrete with Rice Husk Ash

Tests were carried out on the properties of Ultra-High Performance Concrete (UHPC) by partially or completely replacing Silica Fume (SF) by Low-temperature Rice Husk Ash (L-RHA) .The results show that the activity and adsorptive capacity of L-RHA is greater than SF; The compressive strength of UHPC is increased by both the filling effect and the secondary hydration effect for L-RHA, but only by the filling effect for SF. However, more than 10% dosage of L-RHA or SF reduces the early compressive strength of UHPC. The compressive strength of UHPC with two blends of L-RHA and SF with less than 10% dosage of each ingredient is higher than the one with only a blend of ingredient, L-RHA or SF.

Comparison of methods to obtain ash from coal of the Southwest of Colombia

The method for concentration of mineral matter at low temperature (about 250 °C), called Low Temperature Ash (LTA) was applied to a sample of coal from the mine “Las Mercedes” located in Colombia southwestern. This method provides better information about the content of mineral matter in natural coal (NC), removing the organic matter more efficiently without significant transformations of mineral phases present in that coal. These results were observed through Mossbauer spectra and X-ray patterns taken from samples of NC, (LTA) and the conventional method of High Temperature Ash (HTA). The results show that the LTA process provides more representative data of the mineral phases for natural coal than that using the conventional HTA process.

The effect of a new formaldehyde-free binder on the dissolution rate of glass wool fibre in physiological saline solution

The in-vitro dissolution rate of fibres is a good predictor of the in-vivo behavior and potential health effects of inhaled fibres. This study examines the effect of a new formaldehyde-free carbohydrate-polycarboxylic acid binder on the in-vitro dissolution rate of biosoluble glass fibres. Dissolution rate measurements in pH 7.4 physiological saline solution show that the presence of the binder on wool insulation glass fibres has no effect on their dissolution. There is no measurable difference between the dissolution rates of continuous draw fibres before and after binder was applied by dipping. Nor is there a measurable difference between the dissolution rates of a production glass wool sample with binder and that same sample after removal of the binder by low-temperature ashing. Morphological examination shows that swelling of the binder in the solution is at least partially responsible for the development of open channels around the glass-binder interface early in the dissolution. These channels allow fluid to reach the entire glass surface under the binder coating. There is no evidence of any delay in the dissolution rate as a result of the binder coating.

Mineral behavior of low-temperature lignite ashes under gasification atmosphere

To investigate the mineral behavior of lignite ashes under gasification conditions, 450 °C Xiaolongtan lignite ash samples (XLT-LTA) treated at different temperatures or pressures under reducing atmosphere (H2/CO2=1: 1, volume ratio) have been examined by means of an SC-444 apparatus, a scanning electron microscope with an energy dispersive X-ray detector (SEM-EDX), and by X-ray diffraction (XRD). The results showed the sulfur content in the XLT-LTA to be much higher than that in ashes prepared at 815 °C, as a result of the release of sulfur dioxide during the oxidization of pyrite. With increasing temperature, the XLT-LTA particles gradually agglomerate and form partially molten surface entities with obvious apertures, and the content of iron and calcium in the congeries or molten parts increases due to the fusion of fine ash particles with the enrichment of iron and the formation of low-temperature eutectics of calcium and iron. An increase of pressure restrains the decomposition of calcite and muscovite, and promotes the formation of iron minerals (e.g., hercynite, cordierite, and sekaninaite) and orthoclase. The content of amorphous material also increases with increasing pressure.

Occurrence and origins of minerals in mixed-layer illite/smectite-rich coals of the Late Permian age from the Changxing Mine, eastern Yunnan, China

Abstract Minerals in coals from the Changxing Mine of eastern Yunnan, southwestern China, were investigated using low temperature ashing plus X-ray diffraction (LTA + XRD), optical microscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDX). The results show that minerals in the Changxing coals include mixed-layer illite/smectite (I/S), quartz, kaolinite, dolomite, Mg-bearing siderite, anatase, ammonium illite, K-illite, calcite, and chamosite, as well as minor amounts of hematite, paragonite, K-feldspar, and an Al-hydroxide mineral (gibbsite?). The Changxing coals are typically rich in mixed-layer I/S, accounting for an average of 47.2% in their low temperature ashes. Mixed-layer I/S occurs mainly in two types: (1) lentoid as thin beds, and (2) fractures- or cells-fillings. The Type 1 is of terrigenous detrital origin and probably related to the weathering products of the Emeishan basalt, while the Type 2 is of epigenetic origin and precipitated from hydrothermal fluids of a mafic magma intrusion. The high K and poor Na in the Type 1 mixed-layer I/S indicate that it is in a higher evolution stage than the Type 2. Ammonium illite, K-illite, and paragonite are probably products of dissolution and recrystallization of mixed-layer I/S, while Mg-bearing siderite and partly chamosite are related to the Fe, Mg, Al, and Si released from the evolution of mixed-layer I/S.