Ash Yield Research Articles

Factors controlling the occurrence and distribution of iron in Bulgarian coals

Coal of varying age (Upper Carboniferous to Pliocene) and coalification rank (lignite to anthracite) from nineteen coal-bearing basins and deposits, belonging to 8 coal-bearing provinces from Bulgaria, were examined for the occurrence and distribution of Fe. For the majority of the coals, the average Fe concentrations vary from 1.1 to 10.2 wt% and are higher than the World’s average. An exception exists only for Karlovo and Dobrudzha Basins, where slight depletion of Fe (<1 wt%) was established. On contrary, carbonaceous shales from the majority of the basins show Fe depletion in comparison to the Clarke values for clays. Based on the negative correlations with the ash yields, organic affinity of the element can be suggested for most of the studied coals. An exception exists for the Burgas Basin, for which predominantly inorganic affinity of the element can be suggested, whereas for Stanyantsi, Samokov, Bobov Dol, Dobrudzha and Svoge Basins mixed organic/inorganic affinity of Fe can be presumed. The element most probably predominantly occurs in the form of organometallic compounds, especially in the coals that formed in preferentially acidic peat-forming environment. Nevertheless, small contribution from biogenic iron cannot be excluded. The mineral form of Fe is probably mainly associated with sulfides, carbonates, and sulfates, although the presence of Fe oxides, silicates and hydroxides is also established. The analysis of Fe occurrence and its organic/inorganic affinity in Bulgarian coals reveal the following controlling factors: i) Fe concentration within the basin’s provenance; ii) the type (i.e. terrigenous or groundwater) of element supply; and iii) environmental conditions during peat-formation.

Total Sulfur and Ash Yield of Tanjung Formation Coal in Sekako, Barito Basin, Central Kalimantan: Implication of Depositional Process

Tanjung Formation is one of the major coal-bearing deposit in the Barito Basin, Central Kalimantan. The distribution of total sulfur and ash yield in coal is closely related to the depositional environment. This study was to determine the total sulfur and ash yield and the interpretation of the dynamics of depositional process. Coal seam A and B generally have low to medium ash yield 2.82 to 9.23 (wt.%, db) and low total sulfur content of <1 (wt.%, db), except for the 6PLY1 coal sample which has total sulfur content that relatively high at 1.55 (wt.%, db). Coal samples 5PLY1A, 5PLY1B, 5PLY3, 5PLY5, 6PLY2, 6PLY4, 6PLY5, 6PLY7, and 6PLY9 which have low to medium ash yield and low total sulfur content <1% (wt.%, db) are formed in the topogeneous mire (freshwater swamp) in a fluvial environment. The total sulfur content was interpreted to be derived mainly from the parent plant materials. Meanwhile, the 6PLY1 coal sample which has an ash yield of 5.83 (wt.%, db) and total sulfur content of 1.55 (wt.%, db) formed in topogeneous mire in an environment that is invaded by sea water, and the total sulfur content were interpreted coming from the parent plant materials and the effect of seawater invasion which is rich in sulfate (SO4) compounds. It is also supported by the occurrence of syngenetic mineral content (framboidal pyrite) and epigenetic pyrite of 1.23 (vol.%).

Quantitative characterization of low-rank coal reservoirs in the southern Junggar Basin, NW China: Implications for pore structure evolution around the first coalification jump

Abstract The assessment of coalbed methane (CBM) reservoirs can provide insights into the evolution of the pore structure systems around the first coalification jump (FCJ). The southern Junggar Basin, a typical low-rank coal-bearing basin in northwestern China, has been of interest to scientists and policy-makers due to its abundance of CBM resources and favourable conditions for CBM enrichment. A total of 28 coal samples from the Middle Jurassic Xishanyao Formation collected from 11 sampling sites in the central segment of the southern Junggar Basin were analyzed in this study. These samples were quantitatively characterized and comprehensively evaluated using macroscopic to nanometer-scale methods including macroscopic coal description, proximate analysis, vitrinite reflectance measurements, maceral analysis, low pressure nitrogen adsorption (LPNA), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR). The results show that the Xishanyao low-rank coals are characterized by low moisture contents, low or low-medium ash yields (eastern and western parts), high volatile matter contents, moderate vitrinite contents, and high inertinite contents. The physical property of the Xishanyao coals generally displays heterogeneity, with the specific surface area, the total pore volume, the air permeability and the transverse relaxation time (T2) ranging from 0.116 to 15.983 m2/g, 0.461 × 10−3 to 13.37 × 10−3 cm3/g, 0.001 to 151.66 mD (0.987 × 10−6 to 0.149 μm2) and 1.44–174.22 ms, respectively. A new parameter, namely micropore volume proportion per unit nano-meter, is proposed. Micropore and transition pore volume per nm, specific surface area, total pore volume, DN1 and DN2 (LPNA fractal dimension) all first increase, then decrease and finally increase with rising coal rank, while the maximum and minimum values of the maximum vitrinite reflectance (Ro, max) occur at 0.58–0.59% and 0.65–0.66%. The boundary of Ro, max corresponding to the FCJ can be further defined from 0.5-0.6% to 0.58–0.59% based on the evolution of adsorption pore structures. Thus, pore structure parameters related to adsorption capacity are controlled predominantly by coal rank. In addition, tectonic deformation has a strong impact on seepage pore structure but only a slight impact on that of adsorption pore, which leads to an ambiguous correlation or a complex trend between mesopore, macropore content, DMIP (fractal dimension of MIP) and coal rank around the FCJ. This study reveals the complex variation of pore structure evolution of low-rank coals and the significant influence of the FCJ on physical properties of coalbed methane reservoirs.

Intermediate size fine coal beneficiation by Reflux ™ Classifier using statistical approach

The Reflux™ Classifier (RC) is the state-of-the-art liquid-solid fluidized bed gravity separator and its industrial acceptance and commercialization have been increasing in the coal preparation. Despite the significant advancement of this technology, optimization studies, which could be of paramount interest to the plant operator, were not found in the previously published literature. The objective of this research work is to develop a statistical model to predict the ash content and yield of the concentrate. Box-Behnken design of experiment was employed to analyze the gravity separation performance of the intermediate size coal fraction (0.25 × 2 mm). Three important operating parameters (bed setpoint, feed rate and fluidization water rate) were considered to study the separation efficiency of RC. To achieve minimum ash content with the maximum yield of concentrate, multi-response optimization was carried out using desirability approach to optimize the concentrate ash (%) and yield (%) simultaneously. The global optimum yield value of 50% concentrate was achieved with an ash content of 11.5%, at the bed density setpoint of 1100 kg/m3, feed rate of 5.9 l/min and water fluidized rate of 4.1 l/min. The influence of operating variables of the RC on ash content and yield of concentrate are presented and discussed in 3D surface plots. The developed statistical models for the ash content and yield of concentrate when tested were found to predict the yield with an average error of 5%. Partition curves showed that the separation density (ρ50) varied from 1.34 to 1.52 and the Ecart probable error (Ep) varied from 0.075 to 0.1 for the Reflux™ Classifier.

Occurrence and release of cadmium, chromium, and lead from stone coal combustion

Stone coal, which has high ash yield, low carbon content, and low calorific value, releases toxic elements during the combustion process. In this study, samples were collected from an open-pit stone coal mine in the southern Shaanxi province, China. A simulated combustion experiment and sequential chemical extraction were applied to investigate the enrichment, occurrence, and release of Cr, Cd, and Pb in raw stone coal and ash. The contents of Cr, Cd, and Pb in raw stone coal were larger than those reported for other coals in China and worldwide. The enrichment factors of Cr, Cd, and Pb in ash at different temperatures exceeded 0.7, with the exception of Cd at 1000 °C. This indicates that Cr, Cd, and Pb were first enriched at low temperature (below 600 °C) and then volatilized at high temperature due to the decomposition of clay minerals. The dominant forms of toxic elements in raw stone coal were Fe–Mn-bound Cr and Cd and carbonates of Pb. As the temperature increased, the organic forms decreased obviously, and the residual forms increased; however, the Fe–Mn-bound forms remained the dominant forms of Cr, Cd, and Pb.

Enrichment origin of critical elements (Li and rare earth elements) and a Mo-U-Se-Re assemblage in Pennsylvanian anthracite from the Jincheng Coalfield, southeastern Qinshui Basin, northern China

The Qinshui Basin is the largest reservoir of commercial coalbed methane in China. The No. 15 seam, one of the major coal seams for coalbed methane exploration in the Jincheng Coalfield, SE Qinshui Basin, has recently been found to be enriched in the critical element Li. This study further investigates the inorganic geochemistry of the No. 15 coal and associated rocks and reveals the enrichment origin of critical elements in these horizons. The Jincheng No. 15 coal is rich in Li, Mo, U, Se, Re, and rare earth elements and Y (REY). Concentrations of Mo, U, Se, and Re are higher in the two topmost coal benches, probably due to marine transgression in the early diagenetic stage after the peat had been established. The enrichment of Li and REY in a few lowermost coal benches is suggested to be derived from hydrothermal fluids that were related to magmatic activity (110–140 Ma) during the Yanshanian Orogeny (Late Jurassic-Early Cretaceous), or a Late Triassic-Early Jurassic abnormal thermal event occurring at 190–215 Ma. Light REY (La, Ce, Pr, and Nd) in the Jincheng No. 15 coal are predominantly associated with phosphate minerals. Heavier REY (Sm to Lu) show a mixed phosphate and organic affinity in the studied coal samples. Non-coal samples are characterized by light REY- and HREY-enrichment, which is probably inherited from the source material in the Trans North China Orogen.Trace elements in the coal can be highly enriched in the ash if the coal is combusted due to the low to medium ash yield of the coal. Critical elements, including Li, Ga, and REY, in the Jincheng No. 15 coal are considered as promising material for industrial recovery and have been previously under-estimated. On the other hand, environmentally sensitive elements including As, Hg, and Pb, while having concentrations within the normal range compared with average worldwide coals, can be highly enriched in the coal combustion residues if the coal is combusted, and thus careful consideration needs to be given to the utilisation of such coals.

Petrographic and mineralogical study of extended outcrops of lignite layers in Agbor area, southern Nigeria

Coal layers up to 1 m thick, exposed mainly on river banks in the vicinity of Agbor, Okhuokhuo and Ubiaja, Southern Nigeria, were examined by means of organic petrology, mineralogy and geochemistry, in order to gain coal quality data and understand the palaeoenvironmental conditions during peat accumulation in the broad area of the Ogwashi-Asaba Formation. The obtained results show that coal is of low-rank C; it overlies mainly claystone derived from flooding of branches of the palaeo-Niger River. The precursor peat was accumulating in mires under mesotrophic to ombrotrophic, anoxic conditions. The peat-forming vegetation represented mainly herbaceous plants with minor tree contribution. Though the number of studied samples is low, the distribution of the lignite layers extends further towards N.NW of the known lignite-bearing area. Taking into consideration the low ash yields of some samples, there are encouraging indications for notable lignite deposits of high quality. The mineralogical composition and the activity concentrations of 238U, 226Ra, 232Th and 40K exclude any severe environmental effect from coal exploitation. Due to all these promising evidences, a detailed exploration in these and between these outcrops is recommended in order to estimate the lignite potential hosted in this area.

Effects of silicon-aluminum additives on ash mineralogy, morphology, and transformation of sodium, calcium, and iron during oxy-fuel combustion of zhundong high-alkali coal

Zhundong coalfield with super-huge reserve is the largest integrated coalfield in China, while its high content of alkali and alkaline earth metals (AAEMs) gives rise to severe slagging and fouling problems during combustion. Previous studies have been conducted on the release and transformation behaviors of the AAEMs during air combustion of Zhundong coal but with little concern on iron. However, the effects of silicon-aluminum additives on oxy-fuel combustion of high-alkali coal have been rarely evaluated yet. The present study focused on the effects of four silicon-aluminum additives (Al2O3, SiO2, kaolin and diatomite) on the chemical form transformation of sodium (Na), calcium (Ca) and iron (Fe), ash morphology and mineralogy of Zhundong high-alkali coal during oxy-fuel combustion. Experimental results showed that the silicon-aluminum additives could increase the ash yield of Zhundong coal and hinder the release of Na, Ca and Fe, while various additives had different effects on the element transformation. Almost all the additives promoted the transformation of water-soluble sodium to insoluble form during oxy-fuel combustion and the amount of insoluble sodium was increased correspondingly. The variations of sodium present in forms of hydrochloric acid-soluble and ammonium acetate-soluble were highly related to coal type. Various silicon-aluminum additives exhibited different microstructures and mineral types, and the ways of retaining AAEMs were also different. With an increase in the proportion of diatomite additive, the sodium contents of water-soluble and ammonium acetate-soluble forms declined; however, the content of sodium in form of hydrochloric acid-soluble increased at first and then decreased. This work can provide a beneficial information to promote the clean, effective and safe utilization of Zhundong coals in large-scale.

Mineralogy and geochemistry of the Palaeogene low-rank coal from the Baise Coalfield, Guangxi Province, China

Some previous studies have investigated the enrichment origin of Sb and Cs in coal, but strong supportive evidence for the sources of the two elements in coal is still absent. The main aims of this study were to provide a better understanding of the geochemical and mineralogical characteristics of the Palaeogene No. 5 Coal from the Zhoujing coal mine, Baise Coalfield, Guangxi Province, southwestern China. The No. 5 Coal has a low rank (0.44% Ro,max; 46.96% volatile matter content), an average ash yield 19.37%, and a medium sulfur content (1.23% on average). The main minerals in the No. 5 Coal are kaolinite, illite, quartz, and pyrite. Bassanite (2CaSO4•(H2O)) was identified in the low-temperature ashes in varying proportions (2.7% - 37.6%). The mineralogy of the non-coal samples (partings, roof and floor strata) is similar to that of the coals but chlorite is additionally present and pyrite is largely absent in these non-coal samples. The modes of calcite occurrence in the partings indicates a terrigenous origin for this phase.Compared with average values for world low-rank coals, the No. 5 Coal is distinctively enriched in Sb (29.12 μg/g), Cs (9.71 μg/g), and U (15.61 μg/g). Compared with the average values for world clays, the parting and host rock samples have normal concentrations for most trace elements, with an exception of higher Sb (9.93 μg/g). The elevated Sb and Cs in the coal were derived from the detrital material shedding from the exposed middle Triassic strata, which host notable Au and Sb deposits in the surrounding region. The REY (rare earth elements and Y) distribution patterns for the coal benches, partings, roof and floor strata are generally characterized by enrichment in medium REY and positive Gd anomalies, both of which were due to acidic waters circulating within the coal basin. The mineral compositions and their association indicate that the depositional environment was weakly acidic at the early stage of peat accumulation and then changed to neutral or weakly alkaline in the later stage.

Desulfurization of Giral lignite of Rajasthan (Western India) using Burkholderia sp. GR 8–02

ABSTRACT Present investigation entails the results of desulfurization of high sulfur Giral (Rajasthan-India) lignite with the help of Burkholderia sp. GR 8–02. Total sulfur varies from 3.73% to 7.91%, where inorganic sulfur is 2.17–3.82%, pyritic and Sulfate sulfur is 0.90–2.42% and 0.47–2.84%, respectively. Chemical analysis, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM/EDS) were used in order to understand desulfurization. Bacterial treatment caused a significant reduction in total sulfur content ranging from 23.59% to 37.55%. Organic sulfur removal ranges from 11.06% to 20.54% while pyritic and Sulfate sulfur removal vary from 10.40–43.39% and 50.89–96.97%, respectively. In addition to desulfurization of lignite, the reduction in the ash yield and the volatile matter was also observed whereas there was a relative increase in the fixed carbon and elemental carbon content. Further, an increase in the gross calorific value from 3189 kcal/kg to 3482 kcal/kg was noticed.

Mineralogical and Environmental Geochemistry of Coal Combustion Products from Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, Northwest China

The mineralogical and geochemical characteristics of feed coals and coal combustion products (CCPs) from the Shenhuo and Yihua Power Plants in Xinjiang Autonomous Region, were studied by means of proximate analysis, Power X-ray diffraction (XRD), scanning electron microscopy with Energy Dispersive X-ray analyzer (SEM-EDX), inductively coupled plasma atomic emission spectrometry (ICP-MS) and inductively coupled plasma mass spectrometry (ICP-AES). The environmental geochemistry of CCPs was evaluated by Al-normalized enrichment factor as well as European Standard EN-12457 leaching test. Two feed coals have the characteristics of low sulfur content, medium to high volatiles matter yields, medium moisture content, super low to medium ash yield, medium to high calorific value and low mineral content. The main crystalline facies in fly ash and slag are quartz and mullite, with a small amount of calcite, and some unburned carbon. Hematite, SrSO4 and barite also can be observed in fly ashes by SEM. Typical plerophere occurs in fine fly ash rather than the coarse fly ash. The concentration of most trace elements in CCPs falls within the lower concentration range of European fly ashes. With respect to the partitioning behavior of trace elements during coal combustion, S is highly volatile, and Mg, Na, Zn, B, Co, As, Nb, Zr, Cu and K also show certain volatility, which may to some extent emit to the atmosphere. Furthermore, leaching experiments show that leachable concentrations of most of the potentially toxic elements in CCPs are low, and the CCPs fall in the range between inert and nonhazardous landfill material regulated by the 2003/33/EC Decision.

Palynology, organic petrology and geochemistry of the Bell coal bed in Western Kentucky, Eastern Interior (Illinois) Basin, USA

The Bell coal bed is one of the stratigraphically oldest coals (Atokan, Duckmantian) in the Illinois Basin that has been commercially mined and occurs near the Morrowan-Atokan boundary, which was a time of significant lithologic change in the basin. The Bell coal occurs as a series of discontinuous pods, in contrast to younger (Asturian) coals in the basin that are thicker and more extensive in occurrence. Thirty-two samples of coal and carbonaceous shale, collected from surface mine, outcrop, and drill core locations were analyzed geochemically, petrographically and palynologically to ascertain the origin of the Bell coal bed in western Kentucky.The Bell coal exhibits a great deal of variability in thickness and composition, both temporally and spatially. Based on ash yields, the Bell coal consists of intercalated layers of coal (≤25% ash), impure coal (>25 to <50% ash) and carbonaceous shale (≥50% ash). Sulfur contents vary significantly, from 0.2% to 10.0%. Petrographically, the Bell coal is mainly a high vitrinite coal (>80%, mmf), with telovitrinite occurring more frequently than detrovitrinite and gelovitrinite. Certain layers, however, contain elevated amounts of liptinite and inertinite. Among the inertinite macerals, examples of both fire (e.g., fusinite) and degradation (e.g., macrinite) origin are evident. Samples with elevated amounts of inertinite are commonly, though not exclusively, high in ash, indicating that some of the inertinite may be of allochthonous origin.Palynologically, the Bell coal is dominated by arborescent lycopod spores (avg. >70%), occurring primarily as Lycospora, with some samples containing increased proportions of spores and pollen from other Pennsylvanian plant groups. Samples with more heterogenous palynofloras commonly have elevated ash yields, indicating that some portion of the assemblages may be also of allochthonous origin.Collectively, the Bell coal is interpreted to have formed from a series of small, disconnected paleomires that were planar and topogenous with paleotopography having an influence on peat development. A planar, topogenous origin helps to explain the highly variable ash yields and sulfur contents. Accumulating peat, principally from arborescent lycopod source material, was mainly well-preserved, but punctuated with intervals marked by sediment influx, the development of more heterogeneous palynofloras and degradation and oxidation of the surficial peat by both biologic (decay) and abiotic (fire) processes.

Effects of 20 kHz ultrasound on coal flotation: The roles of cavitation and acoustic radiation force

Cavitation and acoustic radiation force are two main effects of ultrasound. In this study, ultrasonic pretreatment (UPT) and simultaneous treatment (UST) methods were applied to coal flotation. The ultrasonic effects were analyzed by measuring changes in ash content and yield of concentrate with or without ultrasound treatment. The decrease in ash content after UPT or UST was due to the cleaning effect of ultrasound. This effect is generated by the collapse of tiny bubbles trapped on the rough coal surfaces, as seen in images obtained by scanning electron microscopy (SEM). An improvement in recovery was only seen with the UST method. Properties of large bubbles, specifically their aggregation and shape, were influenced by ultrasound through the oscillation behavior and acoustic radiation force in the sound field, respectively. This work is expected to provide a novel perspective to the study of ultrasound-assisted flotation.

Mineralogical and geochemical characteristics of the Permian coal from the Qinshui Basin, northern China, with emphasis on lithium enrichment

Comprehensive information about the concentrations, distribution, and modes of occurrence of elements in coal are important from the environmental and economic point of view. Although a great number of previous studies have investigated the geology of coalbed methane in the Qinshui Basin, only a few studies focused on the inorganic constituents in coal. More specifically, the mode of occurrences of valuable element Li in the No. 3 Coal is still unclear, although Li was found enriched. In this study, we present mineral characteristics, as well as multi-element data on the Permian No. 3 Coal from the Sucun and Gaohe Mines, Changzhi City, southern Qinshui Basin. The studied coals are characterized by low- to medium-ash yield (Ad = 5.72%- 28.18%, 12.34% on average), low volatile matter yield (Vdaf = 8.49–15.17%, 10.96% on average), suggesting a low volatile bituminous coal to semi-anthracite. NH4-illite and kaolinite are the main minerals in the coals detected by XRD, and trace amount of minerals calcite, dolomite, quartz, pyrite and diaspore can also be found. The major elements of the studied No. 3 coals are dominated by SiO2 and Al2O3, ranging 2.49–16.45 wt% and 2.13–12.9 wt% (on a whole-coal basis), respectively. Li is enriched in the No. 3 coals (5 < CC < 10). Li in the studied coals is positively correlated with Al2O3, SiO2 and ash yield, with the correlation coefficients (r) of 0.86, 0.8, and 0.78, respectively. The sequential leaching results show that 96.6%–99.4% of Li in the coals was removed by HF. The proportion of Li present as the ion-exchange form and water soluble form accounts for <1.1% and < 0.29% of the total Li respectively in the coals. Li in the studied coals are probably bound to clay minerals kaolinite and illite, residing mainly in non-exchangeable positions, either in the octahedral or pseudo-hexagonal sites.

Coal-bed methane geology of the No. 2 coal seam in Fengfeng Coalfield, North China

The Fengfeng Coalfield is an important coal production base in the Hebei Province of North China. It has been reported that higher coal-bed methane (CBM) contents exist in this area showing good prospects for the exploration of CBM. However, there are few studies on CBM investigation in Fengfeng Coalfield. In order to better understand the geological controls on CBM in the Fengfeng Coalfield, geological surveys and laboratory experiments were conducted that included coal petrology analysis, proximate analysis, mercury intrusion, low-temperature liquid nitrogen adsorption, coal permeability analysis, and methane adsorption/desorption. The results show that the organic compositions are dominated by vitrinites, followed by inertinites, and minor liptinites. The CBM contents are range between 0.83 and 11.52 m3/t, with an average of 4.72 m3/t. The moisture contents are range from 0.76 to 2.54%, with an average of 1.21%, and the ash yields are range from 11.46 to 24.5%, with an average of 17.07%. Low-temperature nitrogen gas adsorption indicates the micropores provide most of the pore specific surface and the pore volume is mainly determined by small pores and mesopores. The geologic structures, coal-bearing strata, and the coal depositional environments were studied through field geological research and laboratory tests. The coals were deposited in a river-dominated shallow delta environment to form the mudstones or siltstones of the coal roof and floor that were used to seal the CBM. The CBM were mainly generated during stages of the Hercynian–Indosinian and the Early-Middle Yanshanian orogeny. Underground water flowed to the Dashucun Mine and its adjacent mines in the northeast of the Gushan Anticline to form a semi-closed hydrodynamic system that created the CBM emission and preservation. The coal rank increases from the southern to the northern areas. Then, it can be speculated that the CBM formation and preservation conditions in the north are better than in the south. The best prospective targets for CBM are in the northern areas. The results of this study may be useful for CBM exploration in North China.

Segmentation of multi-coal seam pore structure in single well profile and its sedimentary control: a case study of Well Y1 in Panguan syncline, western Guizhou, China

The pore structure of coal reservoirs is crucial for the occurrence and production of coalbed methane (CBM). Taking as an example the upper Permian coal-bearing strata profile of Well Y1 in Panguan syncline of western Guizhou, mercury intrusion porosimetry (MIP) and low-temperature N2 adsorption/desorption (LT-N2GA) experiments were carried out on samples from six main coal seams. Hysteresis coefficients of MIP and LT-N2GA were proposed. Fractal dimension of pore structure of each coal seam was calculated. The segmentation of pore structure of multi-coal seams was found. We found the total pore volume (TPV) and specific surface area (SSA) of coal were increased and then decreased as the increase of coal seam buried depth, which is characterized by two-segment distribution. The upper segment included the 7#, 10#, and 12# coal seams, whereas the lower segment contained the 18#, 19#, and 24# coal seams. The TPV, SSA, and MIP hysteresis coefficients and fractal dimension of seepage pore of the upper segment coal seams are larger than those of lower segment coal seams on the whole, while the LT-N2GA hysteresis coefficient, fractal dimension of adsorption pore, and fractal dimension of high-pressure stage of the upper segment are smaller than those of the lower segment. The coal seams in upper segment have more open pores, while the coal seams in the lower segment have more fine neck bottle pores or ink bottle pores. Taken together, these data demonstrated that the coal seams in the upper segment have higher adsorption and seepage capacity, and are more favorable for CBM development. The fundamental reason for the two-segment variation of TPV and SSA of six main coal seams is the symmetry of sedimentary facies in coal-bearing strata; moreover, the ash yield controls the TPV and SSA of coal seams, and the ratio of vitrinite to inertinite (V/I) controls the development of pores.

Separation performance of flotation column with dilution water in pulp zone

ABSTRACT Flotation columns show a good separation performance for fine coal slime and have been widely used in coal preparation plants. In this study, to reduce the ash content of the concentrate, dilution water was added to the pulp zone of the flotation column. Tailings discharge was also correspondingly increased to ensure the balance of coal pulp in the flotation column. The results indicate that ash content and yield of concentrate decrease with the increasing dilution water. The flotation efficiency index increases initially and then decreases as the rate of dilution water increases, and the highest flotation efficiency index is obtained at a dilution water rate of 0.18 cm/s, this indicates that appropriate addition of dilution water in the pulp zone improves the separation performance of the flotation column. In addition, the closer the dilution water is to the bottom of the flotation column, the better the separation performance of the flotation column becomes. Moreover, compared with a conventional flotation column with a feed pulp concentration of 40 g/L, the flotation column with dilution water has a similar pulp concentration in the pulp zone and shows a better separation performance.

Concentrations and modes of occurrence of some potentially valuable and toxic elements in the No. 5 coal from the Yanzishan Mine, Datong Coalfield, Shanxi Province, China

In this study, the mineralogical compositions, concentrations and occurrence modes of the elements in the No.5 coal from the Yanzishan Mine were investigated, using X-ray powder diffraction (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma mass spectrometry (ICP-MS), and scanning electron microscopy equipped with an energy-dispersive X-ray spectrometer (SEM-EDS). The No. 5 coal is characterized by high ash yield content (mean 32.30%) and low sulfur content (mean 0.47%). The minerals are mainly composed of kaolinite, quartz and pyrite, with a small proportion of illite, apatite, siderite, sphalerite and Ti-oxide. Compared with the Chinese coals, the No. 5 coal has much higher percentages of SiO2 (mean 16.22%) and Al2O3 (mean 14.57%) than other major oxides. Compared with the world hard coals and Chinese coals, the No. 5 coal is enriched in some potentially valuable (Al2O3, Li, Ge, Zr, and Hf) and toxic (Be, As, Se, Cd, and Pb) elements. Lithium and Hf are mainly associated with clay minerals; Be, Se, and Zr mainly have both inorganically and organically affinities; As mainly occurs as a sulfide form in pyrite; Cd is incorporated in clay minerals; and Pb has an affinity for both clay minerals and organic sulfur. All the coal samples are characterized by weakly positive or no pronounced Eu anomalies, indicating that the rare earth elements and yttrium (REY) likewise originated from granite of the Yinshan Oldland together with injection of the low temperature hydrothermal fluids.

Mineralogy, petrography and organic geochemistry of Miocene coal seams in the Kınık coalfield (Soma Basin-Western Turkey): Insights into depositional environment and palaeovegetation

The Kınık coalfield is located in the south-westernmost part of the Soma Basin in western Turkey and hosts all three Miocene coal seams (from bottom to top: kM2, kM3 and kP1). This study presents the coal-petrographical, mineralogical and organic geochemical features of samples collected from two deep cores. Samples from seam kM2 generally display low ash yields and high TOC content, whereas the kM3 and kP1 seams are characterized by relatively high ash yields and low TOC values. Furthermore, total S content of the kP1 is very high (up to 7.0%, on dry basis). The maceral composition, the coal facies diagrams, and the distributions of n-alkanes and diterpenoids indicate changes of depositional conditions and vegetation in the palaeomires of the kM2 seam during Early Miocene. The precursor peat of kM2 seam started accumulating under limnotelmatic conditions followed by pure telmatic ones. Consequently, initial mixed vegetation was replaced by a conifer-dominant assemblage in the palaeomires, in the upper parts of the kM2 seam.The coal facies indices and high concentrations of n-alkanes, along with the relatively low di-/ (di+tri-)terpenoid ratios, are indicators of the higher contribution of herbaceous species and minor abundance of conifers in the palaeomires of kM3 and kP1 seams. Nevertheless, the mineralogical composition of the kM3 and kP1 seams indicate increased clastic input and alkalinity in the palaeomires that could reduce preservation of organic matter. Thus, high ash yields and low TOC were obtained from these seams. In addition, sulphate-rich water supply along with synchronous pyroclastic air-borne input into the palaeomires caused elevated total S content of the kP1 seam.

A petrographic approach to a newly found lignite outcrop from Bilene (Gaza, Mozambique)

A Pleistocene coastal lignite outcropping between the Muândeje Lake (Maputo Province) and Nhachuendezo Lake (Gaza Province) was recognized during geological mapping performed in 2009. However, these outcrops started to be investigated only in 2017 through paleontological fieldwork under the PaleoMoz Project (www.paleomoz.org). Here the chemical and petrographic compositions of a coal sample from this locality are reported. This new occurrence represents the first lignite occurrence from coastal Mozambique. The lignite is a Low Rank C (Lignite C) coal with a huminite reflectance of 0.248%. The results show that the lignite has high ash yield (46.5%, d); volatile matter (65.2%, daf), carbon (57.3%, daf), hydrogen (5.3%, daf) and nitrogen (2.3%, daf) contents are according to the rank of this coal; and, low total sulphur (1.8%, d). The coal is richer in huminite (86%) than liptinite (10%) and inertinite (4%). The maceral analysis indicates that lignite's peat precursor derived mainly from herbaceous plants and Botryococcus algae deposited in a topogenous mire (fen) under mesotrophic anoxic conditions. The water level remained above the paleomire's surface.