Pb In Coal Research Articles

Process analysis of Pb transformation in the coal devolatilization stage

The transformation of Pb during coal devolatilization affects its emission characteristics. Herein, devolatilization experiments were conducted at 1100–1300 °C in a fixed-bed experimental system using four types of coal samples. The occurrences of Pb in coal and devolatilization products were characterized. The release ratio of Pb first increased and then stabilized with time. The Pb release ratio and rate were higher at higher temperatures. Pb in some coal samples was completely released at 1100 °C. Pb in coal was mainly in carbonate- and oxide-bound, sulfide-bound, and residual forms. During devolatilization, carbonate-, oxide-, and sulfide-bound Pb gradually disappeared. Organic-bound and residual Pb first increased and then decreased owing to the conversion of gaseous Pb into Char-Pb by char, according to further form analysis of residual Pb and the experiments of char retaining PbCl2 and PbO. The effects of different volatile components on residual Pb were compared, and H2S was found to significantly promote the release of residual Pb in coal. The transformation paths of Pb during coal devolatilization were proposed, including the release of original Pb in coal and the reversible conversion between gaseous Pb and Char-Pb. The results help understanding Pb emission and developing control techniques for coal-fired plants.

Migration Behaviors of As, Se and Pb in Ultra-Low-Emission Coal-Fired Units and Effect of Co-Firing Sewage Sludge in CFB Boilers

The migration behaviors of As, Se and Pb in ultra-low-emission coal-fired units were investigated and the effect of co-firing of sewage sludge and coal was explored in circulating fluidized-bed (CFB) boiler units. Samples of feed fuel including coal and sewage sludge, fly ash, bottom slag and desulfurization slurry were collected from five CFB units with a capacity between 150 MW and 350 MW and two pulverized coal boiler (PC) units with a capacity of 350 MW and 600 MW. The majority of As, Se and Pb in coal is released during coal combustion and enriched in fly ash. As, Se and Pb in fly ash and bottom slag are associated with inorganic matter, of which As, Se and Pb associated with silicates and aluminosilicates account for more than 60%. In the wet flue gas desulfurization (WFGD) unit, more than half of the As, Se and Pb migrates to the solid fraction and the concentrations of As, Se and Pb in fine solid particles are much higher than those in coarse solid particles and the liquid fraction. The proportions of exchangeable As, Se and Pb or associated with organic matter in gypsum are higher than those of fly ash and bottom slag. According to the two studied CFB units with blending ratios of sewage sludge below 10%, co-firing with sewage sludge has little effect on the migration and transformation characteristics of As, Se and Pb. Under a long-term acidic leaching environment, Pb in combustion by-products is in the range of low risk, while As and Se are in the range of medium risk.

Release characteristics of arsenic, selenium, lead and transformation of minerals during ashing process of coal

In this paper, two kinds of coal (Baiyinhualignite and coal usinginEzhou Power Plant) were selected to study the occurrence of heavy metals including arsenic (As), selenium (Se) and lead (Pb) in coal and their release behaviors during the ashing process. The influence of ashing conditions on the mineral conversion was also examined by the combination with the changes of minerals in coal. The burn-out temperature of the coal was determined fromthethermalweightlosscurve by extrapolation method, and then the coal sample was ashed according to the National Standard Method of China. The obtained ash samples were characterized by XRD, XRF, and TG-DTG to analyze the change characteristics of coal minerals at different ashing temperatures. The content and occurrence of As, Se and Pb in coal samples were extracted by sequential chemical extraction method. The heavy metals in the ash sample were extracted by HNO3 + HF, and the heavy metal content in the extract was detected by Inductively Coupled Plasma Mass Spectrometer (ICP-MS). The results show that the heavy metal in BYH coal is mainly As in the form of sulfide bound state, which leads to the increasing volatility of As with temperature easily. However, the heavy metal in EZ is mainly sulfide-bound Pb, which makes it easy torelease with temperature. Se in coal mainly exists in the form of organic bound state and sulfide bound state. During coal ashing, kaolin is gradually dehydroxylated into metakaolin and finally converted into mullite; pyrite is oxidized to form hematite; gypsum is dehydrated to form anhydrite. The release rate of heavy metals is greatly affected by the combustion temperature during the ashing process. High content of heavy metals in the sulfide bound state results in high release rate with increasing the temperature.

Experimental pyrolysis of metalliferous coal: A contribution to the understanding of pyrometamorphism of organic matter and sulfides during coal waste heaps fires

Thermal metamorphism of original coal adjacent to burning centers in coal waste heaps is a common phenomenon, and semi-coke and coke are formed during this process. In this study, changes taking place during the pyrolysis of both organic and inorganic constituents of coal in burning heaps are interpreted, and the volatility of major and trace elements is assessed. Experimental pyrolysis of bituminous coal from the coal and uranium Novátor Mine (Czech Republic) was carried out at temperatures of 200 °C, 500 °C, 700 °C and 900 °C. Changes occurring at various temperatures of pyrolysis in the coal matrix were studied by methods of coal petrography, organic and inorganic geochemistry. Due to the high contents of sulfides of Fe, Cu Zn and Pb in coal, changes in their chemical composition which occur during their melting were also studied.The results showed that with rising temperature the amount of gas produced during the pyrolysis increased significantly while the amount of released nitrogen from coal organic substance and CO2 decreased and, conversely, the H2 content was increasing significantly. The largest amount of tar originated at a temperature of 500 °C. Coke and semi-coke appeared in the solid residue already at a temperature of 500 °C and, as the temperature increased, its porosity and optical reflectance were gradually increasing. The results of gas chromatography/mass spectroscopy (GC/MS) showed that the pyrolysis was associated with a rapid decline in the extractability of solid products of pyrolysis. The maximum concentration of polycyclic aromatic hydrocarbons (PAHs) in coke was recorded at 500 °C (28.5 rel.% of identified compounds), and then dropped to 11 rel.% at 900 °C.The concentration of Hg in the solid residue after the pyrolysis declined significantly even at temperatures of <500 °C. At higher temperatures, apart from Hg, the amount of In, Sb, Tl, Zn, As, Mo, Sn, Pb, Se, Hg and Cd in the pyrolysis residuum gradually decreased, which corresponds to the presence of sulfides of the above elements in the mats of coal fire gas minerals (CFGM) on the surface of many burnt coal heaps.Galena was partially melted during the pyrolysis already at a temperature of 700 °C to form metallic Pb. However, a significant increase in the volume of melts occurred when the temperature reached 900 °C with the formation of mineral assemblage consisting of galena – metallic Pb – pyrrhotite – sphalerite – intermediate Cu-Fe solid solution phase (iss) – bornite. Consequently, the melting of sulfides during the pyrolysis can be one of the reasons for high volatility of some chalcophile elements in the processes of coal pyrolysis in burning heaps.

Spatial Macroscale Variability of the Role of Mineral Matter in Concentrating Some Trace Elements in Bituminous Coal in a Coal Basin—A Case Study from the Upper Silesian Coal Basin in Poland

As there are numerous claims that the mode of occurrence of trace elements in coal influences the quality of the substrates as well as the course and results of the coal preparation processes, it is necessary to analyse the differences in the mode of occurrence of the elements in coal within a coal basin or a coal deposit. With the use of concentration distribution functions and the Pearson correlation coefficient, it was concluded that (1) mineral matter plays a significant and nearly constant or constant role in concentrating V, Cr, Co, As, Rb, Sr, Ba, and Pb in coal; (2) organic matter plays a stable role in concentrating Sn; and (3) there are significant differences in the role of organic and mineral matter in concentrating Mn, Ni, Cu, Zn, Mo, Cd, and Sb in coal throughout the USCB (Upper Silesian Coal Basin). Moreover, there was observed a difference in the mode of occurrence of Cr, Mn, Co, Ni, Cu, Zn, Mo, Cd, Sn, and Sb in coal in the vertical profile of the USCB. At the same time, there were observed no differences and a stable significant role of mineral matter in concentrating V, As, Rb, Sr, Ba, and Pb in coal, while the role of the petrographic groups of the coal components in concentrating the elements in raw coal was differentiated. It is believed that the difference in the mode of occurrence of the trace elements in coal within coal seams and coal deposits is a geochemical regularity.

Exposure of heavy metals in coal gangue soil, in and outside the mining area using BCR conventional and vortex assisted and single step extraction methods. Impact on orchard grass

It was investigated that toxic metals (cadmium and lead) enhanced in coal gangue soil used for the reclamation of soil, creates adverse impacts on atmosphere. Presently the chemical fractionation of toxic metals in coal, inner and outer coal gangue soil samples of Lakhra coalfield were studied along with the impact on the orchard grass grown on coal gangue soil in a subside land of the coal mining area. The BCR sequential extraction scheme (BCR-SES) was carried out to determine the different chemical profiles of heavy metals in coal and coal gangue soil samples. For comparative purpose time saving conventional single step extraction (CSE) and vortex assisted single step extraction (VSE) schemes based on same working setting used BCR extraction scheme. The all three procedures were validated by a certified soil sample (BCR 483) and standard addition method in real samples. The total Cd and Pb in coal, soil and grass samples were determined prior to oxidize by acid mixture. The separation of each fraction of Cd, and Pb in all types of environmental samples by VSE could be completed in 30-120s. The extracted Cd and Pb concentrations in reducible fractions by CSE and VSE extraction procedure were 2.5-5% higher than those values gained through BCR-SES. About 71 and 50% of Cd and Pb in coal samples were observed in acid soluble, reducible and oxidizable fraction, respectively, whilst rest of Cd and Pb (29 and 50%) were found in residual phase. The orchard grass (Dactylis glomerata) grown on land reclaimed with OSG was analysed, the bioaccumulate Cd and Pb may create adverse impacts on grazing cattle.

Study on the Transformation of Arsenic and Lead in Pyrite During Thermal Conversion

The forms of arsenic (As) and lead (Pb) in coal have an important influence on their transformation during combustion. Considering that As and Pb in coal are partially associated with pyrite, pyrol...

Modes of occurrence of ecotoxic elements in coal from the Upper Silesian Coal Basin, Poland

Optical microscopy, x-ray diffraction and selective x-ray fluorescence spectrometry, SEM/EDS and laser ablation-micro-ICP-AES have been used to study the minerals and the concentrations of 15 trace elements in coal from the Upper Silesian Coal Basin. Mineral matter has a significant impact on the contents of V, Cr, Co, Cu, As, Rb, Sr, Cd, Ba and Pb in coal and organic matter on the contents of Ni, Zn, Mo, Sn and Sb in coal. Contents of V, Cr, Cu, Rb, Sr and Ba are most probably dependent on clay minerals and those of V and Rb on both clay minerals and vitrinite. Organic matter and carbonate minerals likely determine contents of Mn, and mineral matter and vitrinite likely determine contents of Co and Pb are probably influenced by sulphides. The bulk of the V, Cr, Mn, Co, Ni, Cu, Rb, Sr, Mo, Sb and Ba in the coal is probably of syngenetic origin. In contrast, the contents of Zn, As, Cd and Pb and, to a degree, those of Mn, Ni, Mo and Sb are epigenetic. Analysis results in the micro-area of minerals from bituminous coal reveal that the greater the heterogeneity of disulphides and of their association with carbonates and the more this heterogeneity applies to epigenetic minerals, the higher the contents of Ca, Cr, Mn, Ni, Zn, Cd and Pb. Diagenetic carbonates have higher contents of Cr, Mn and Ni, and smaller contents of Ca, Zn, Cd and Pb than the epigenetic minerals. These characteristics can be important from an ecological perspective; they identify which mineral matter components are best removed from coal to make it more suitable for combustion and in chemical processing.

The Petrography, Mineralogy and Geochemistry of Some Cu- and Pb-Enriched Coals from Jungar Coalfield, Northwestern China

The petrological, geochemical, and mineralogical composition of the Carboniferous-Permian coal deposit in the Jungar coalfield of inner Mongolia, Northwestern China, were investigated using optical microscopy and field emission scanning electron microscopy in conjunction with an energy-dispersive X-ray spectrometer (SEM-EDX), as well as X-ray powder diffraction, X-ray fluorescence, and inductively coupled plasma mass spectrometry. The Jungar coal is of high volatile C/B bituminous quality with 0.58% vitrinite reflectance and has a low sulfur content of 0.70% on average. Inertinite (mineral-free basis) generally dominates in coal from the lower part of the Shanxi formation, and vitrinite is the major maceral assemblage in the coal from the Taiyuan formation, which exhibits forms suggesting variation in the sedimentary environment. The Jungar coal is characterized by higher concentrations of copper (Cu) in No. 6 coal, at 55 μg/g, and lead (Pb) in No. 4 coal at 42 μg/g. Relative to the upper continental crust, the rare earth elements (REE) in the coal are characterized by light and medium–heavy REE enrichment. The minerals in the Jungar coal are mainly kaolinite, dickite, pyrite, calcite, siderite, quartz, and, to a lesser extent, gypsum and K-feldspar. The enrichment and occurrence of the trace elements, and of the minerals in the coal, are attributed to the fragmental parent rock during diagenesis and coalification. The main elements with high enrichment factors, Cu and Pb, overall exhibit a notably inorganic sulfide affinity and a weak organic affinity. Primary and epigenetic sedimentary environment and the lithology of the terrigenous parent rock are the key factors that influence the occurrence and formation of Cu and Pb in coal. The depositional environment is more influential in the formation of Cu than Pb in coal. Lead is more easily affected by the terrigenous factors than Cu when they are under a similar depositional environment.

Microwave digestion for the quantification of inorganic elements in coal and coal ash using ICP-OES

In this paper, microwave digestion conditions have been optimised to achieve complete recoveries for the ash-forming inorganic elements in coal and coal combustion fly ash, during the analysis by inductively coupled plasma optical emission spectroscopy (ICP-OES). The elements analysed include six major (Al, Ca, Fe, K, Mg and Na) and twelve trace (As, Ba, Be, Co, Cr, Cu, Li, Mn, Ni, Pb, Sr and V). Seven reference samples have been tested, including two standard coal references, SRM1632c and SARM19, their corresponding high-temperature ashes (HTAs), and three coal fly ash references, SRM1633c, SRM2690 and BCR38. The recoveries of individual elements in these samples have been examined intensively, as a function of the amount of hydrofluoric acid (HF, 0–2.0ml), microwave power (900W vs. 1200W) and sample mass (0.05g vs. 0.1g). As have been confirmed, the recoveries of these individual elements varied significantly with the microwave digestion condition, elemental type and sample property. For the coal references and their HTAs, the use of HF can be ruled out for most of the elements, except K associated with feldspar, Pb and V. In particular, the recovery of Pb in coal is highly sample-specific and thus unpredictable. The majority of elements in fly ash references require the use of 0.1–0.2ml HF for a complete recovery. Al in fly ash is the only exceptional element which gave incomplete recoveries throughout, suggesting the use of a complementary technique for its quantification. As has proven to be the only element inconsequential of sample type and digestion conditions, achieving complete recoveries for all cases. On the power parameter, using a higher power such as 1200W is critical, which has proved to be an ultimatum for the recovery of certain elements, especially in fly ash. Halving sample mass from 0.1g to 0.05g was also found to be insignificant.

Isotopic composition of lead in Czech coals

Abstract The content and isotopic compositions of lead (Pb) were studied on selected coal samples from the Czech Republic. Simultaneously, the forms of bonding of Pb in coal were studied using sequential extraction (1M ammonium acetate, 3 M HCl, 48% HF and 2 M HNO 3 ). Lead in most samples of bituminous and brown coal is mobilized by 3 M HCl, while sulphides are already oxidized in the studied samples at the beginning of the extraction (1 M ammonium acetate). Thus, Pb could be bonded in carbonates and oxides and also to sulphides present in the coal. Following decomposition of the sulphides, Pb is adsorbed on the remainder of the solid phase and is released only in the acidic medium of the second extraction solution (i.e. 3 M HCl). Bituminous coal contains an average of 33 mg/kg Pb, while brown coal contains an average of 8.9 mg/kg Pb. The 206 Pb/ 207 Pb ratio varies in the range 1.167–1.234 for bituminous and 1.172–1.24 for brown coal. No inverse proportionality of the Pb content and the 206 Pb/ 207 Pb ratio was observed in the studied samples and, thus, the Pb content in most samples is a result of the combination of lithogenic and ore Pb. Only several samples with high uranium contents exhibited a highly radiogenic 206 Pb/ 207 Pb ratio (> 1.3). It was not possible to demonstrate any statistical dependence between the operational defined speciation of Pb, the mineralogical composition and the Pb isotopic composition.

Evaluation of pyrolysis curves for volatile elements in aqueous standards and carbon-containing matrices in electrothermal vaporization inductively coupled plasma mass spectrometry

Pyrolysis curves in electrothermal atomic absorption spectrometry (ET AAS) and electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) have been compared for As, Se and Pb in lobster hepatopancreas certified reference material using Pd/Mg as the modifier. The ET AAS pyrolysis curves confirm that the analytes are not lost from the graphite furnace up to a pyrolysis temperature of 800 °C. Nevertheless, a downward slope of the pyrolysis curve was observed for these elements in the biological material using ETV-ICP-MS. This could be related to a gain of sensitivity at low pyrolysis temperatures due to the matrix, which can act as carrier and/or promote changes in the plasma ionization equilibrium. Experiments with the addition of ascorbic acid to the aqueous standards confirmed that the higher intensities obtained in ETV-ICP-MS are related to the presence of organic compounds in the slurry. Pyrolysis curves for As, Se and Pb in coal and coal fly ash were also investigated using the same Pd/Mg modifier. Carbon intensities were measured in all samples using different pyrolysis temperatures. It was observed that pyrolysis curves for the three analytes in all slurry samples were similar to the corresponding graphs that show the carbon intensity for the same slurries for pyrolysis temperatures from 200 °C up to 1000 °C.

Determination of Lead in Coal Using Direct Solid Sampling and High-Resolution Continuum Source Graphite Furnace Atomic Absorption Spectrometry

A method has been developed for the determination of Pb in coal using direct solid sampling (SS) and high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS GF AAS). The certified coal reference materials used in this study were ground in an agate mortar to particle size ≤50 µm. Mass aliquots between 0.1 and 1 mg were weighed onto pyrolytic graphite platforms, and inserted directly into the graphite tube. For pyrolysis temperatures lower than 600 °C, a continuous background due to radiation scattering at solid particles preceded the atomic signal, as the coal matrix could not be sufficiently eliminated under these conditions. An optimized pyrolysis temperature of 700 °C was adopted for Pb without the use of a modifier. The optimum atomization temperature was found to be 1700 °C. Under these conditions, interference-free determination could be performed with calibration against aqueous standards in 0.5% v/v HNO3. A total of six certified reference coal samples were analyzed, and the results obtained were all in good agreement with certified and informed values, respectively, according to a Student t-test at a 95% confidence level. A detection limit of 0.008 µg g−1 for Pb was obtained at the 217.000 nm resonance line, a value comparable to those obtained by other sensitive, but much more sophisticated techniques, showing that the absence of dilution in the SS-HR-CS GF AAS method allows at least equivalent detection performance.

Lead contents of coal, coal ash and fly ash

Flameless atomic absorption spectrometry is applied for the determination of Pb in coal, coal ash and fly ash. Lead concentrations in coal and coal ash ranging from respectively 7 to 110 µg g−1 and 120 to 450 µg g−1 are found. A mean concentration of 1520 µg g−1 in fly ash corresponding to a concentration of 117 µg m−3 in the effluent gas suggests the importance of coal combustion as an atmospheric source of Ph. The contribution of coal combustion to the total Pb emissions is conservatively estimated at 6%.