Concentration and distribution of trace elements in some coals from Northern China

The concentration, distribution and modes of occurrence of trace elements in thirty coals, four floors and two roofs from Northern China were studied. The samples were collected from the major coalfields of Shanxi Province, Shaanxi Province, Inner Mongolian Autonomous Region, and Ningxia Hui Autonomous Region. The concentrations of seventeen potential hazardous trace elements, including Hg, As, Se, Pb, Cd, Br, Ni, Cr, Co, Mo, Mn, Be, Sb, Th, V, U, Zn, and five major elements P, Na, Fe, Al, and Ca in coals were determined.Compared with average concentration of trace elements in Chinese coal, the coals from Northern China contain a higher concentration of Hg, Se, Cd, Mn, and Zn. They may be harmful to the environment in the process of combustion and utilization. Vertical variations of trace elements in three coal seams indicated the distributions of most elements in coal seam are heterogeneous. Based on statistical analyses, trace elements including Mo, Cr, Se, Th, Pb, Sb, V, Be and major elements including Al, P shows an affinity to ash content. In contrast, Br is generally associated with organic matter. Elements As, Ni, Be, Mo, and Fe appear to be associated with pyrite. The concentrations of trace elements weakly correlate either to coal rank or to maceral compositions.     

Abundances and modes of occurrence of trace elements in the Çan coals (Miocene), Çanakkale-Turkey

This study presents the concentrations and modes of occurrence of trace elements in 81 coal samples from the Çan basin of northwestern Turkey. The concentration of trace elements in coal were determined by inductively coupled plasma-mass spectrometry and inductively coupled plasma-atomic emission spectrometry. Additionally, traditional coal parameters were studied by proximate, ultimate, X-ray diffraction, and petrographic analyses. Twenty trace elements, including As, B, Ba, Be, Cd, Cu, Co, F, Hg, Mo, Ni, Pb, Sb, Se Sn, Th, Tl, U, V, and Zn, receive much attention due to their related environmental and human health concerns. The Çan coals investigated in this study are lignite to sub-bituminous coal, with a broad range of ash yields and sulphur contents. The trace element concentrations show variety within the coal seams in the basin, and the affinities vary among locations. The concentrations of B, Ba, Be, Cd, Cu, Co, F, Hg, Mo, Ni, Pb, Sb, Se, Sn, Tl, and Zn in Çan coals are within the Swaine's worldwide concentration range, with the exception of As, Th, U, and V. On the other hand, compared with world coals, the Çan basin coals have higher contents of As, B, Cu, Co, Mo, Pb, Th, U, V, and Zn. Based on statistical analyses, most of the trace elements, except for U, show an affinity to ash yield. Elements including As, Cd, Hg, Se, Cu, Mo, Ni, and Zn, show a possible association with pyrite; however, the elements Se, B, and Mo can be have both organic and inorganic associations.     

Geochemistry, mineralogy, and technological properties of the main Stephanian (Carboniferous) coal seams from the Puertollano Basin, Spain

This study is focused on the occurrence and distribution of mineral matter and major and trace elements in the high volatile bituminous coal from Puertollano (south-central Spain). The relationship between ash behaviour and inorganic composition, as well as the possible formation of fouling and slagging deposits in boilers during the conversion process, were investigated. The Puertollano coals do not exhibit plastic properties, despite their rank, probably because of their high ash and inertinite contents.The Puertollano coal has medium to low total S content (0.48% to 1.63% db, with a mean of 1.0% db) and is characterised by relatively high contents of Si, Pb, Sb, and Cs. Some elements such as As, Cd, Co, Cr, Cu, Ge, Li, Mn, Ni, W, and Zn are also present in relatively high contents. The enrichment in a number of heavy metals could be attributed to the common sulphide ores occurring near the Puertollano coal deposit.The following trace elements affinities are deduced: (a) sulphide affinity: As, Co, Cd, Cu, Ni, Sb, Tl, and Zn; (b) aluminum–silicate affinity: K, Ti, B, Co, Cr, Cs, Cu Ga, Hf, Li, Nb, Rb, Sn, Ta, Th, V, Zr, and LREE; (c) Carbonate affinity: Ca, Mg, Mn, and B; (d) organic affinity: B.The very high Si levels and the anomalous enrichment in Cs, Ge, Pb, Sb, and Zn shown by the Puertollano coals account for the high contents of these elements in the Puertollano fly ash when compared with the other Spanish coal fly ashes.The chemical composition of the high temperature ash (HTA) is consistent with the trend shown by the ash fusion temperatures (AFT) and also with the predictive indices related to slagging and fouling propensities. Thus, the ash fusion temperatures increase with high values of Al₂O₃ as well as with the decrease in Fe₂O₃, CaO, and MgO.     

Geochemistry of Permian Coal and Its Combustion Residues in Huainan Coalfield, China

INTRODUCTIONMany environmental problems may arise during coal min-ing and utilization. Among these prob1ems, much attention hasbeen paid to S(), and NO. emission during coal combustion.But the environmental effects produced by hazardous elementsduring coal mining and utilization are also important and de-serve to be studied (Goodazi, 1995; Finkelman, 1993; Valk-ovic, l983). For example, when coal wastes are used for landreclamation, the harmful elements in them may pollute water,soil an…     

Environmental assessment of elements and polyaromatic hydrocarbons emitted from a Canadian coal-fired power plant

A detailed assessment of elements was carried out at a power plant rated at approximately 760 MW of electricity using western Canadian subbituminous coal. The concentrations of elements of environmental concern (As, Cd, Cr, Hg, Ni, and Pb) in milled coals, ashes, stack-emitted materials. Speciation of As, Cr, and Ni were determined. The polyaromatic hydrocarbons (PAHs) emitted from the stack were also measured. The rates of input of elemental input for As, Cd, Cr, Hg, Ni, and Pb were 28, 0.94, 230, 0.44, 44, and 88 kg/day, respectively; of which only 0.16, 0.01, 0.40, 0.27, 0.15, and 0.04 kg/day, respectively, were stack emitted. The total stack emission of toxic elements is 1.02 kg/day, with Cr being the highest contributor to this group with 0.4 kg/day. However, Hg at 0.27 kg/day has the highest percentage rate of emission at about 60%, while Cd has the lowest at about 1%. The electrostatic precipitator (ESP) removes a significant portion of the elements indicated by their relative enrichment (RE) ratios greater than 0.7. The results show that most of the elements in milled coal are low compared to world coals and other Canadian milled coals.Mercury is mostly ( 81%) emitted as gaseous elemental mercury (GEM), with 19% as reactive gaseous mercury (RGM). Particulate mercury is very low and averages about 0.1% of the total mercury at this station. Most of the arsenic in the milled coal is primarily associated with pyrite or as arsenate in its less toxic form of As⁺⁵ (> 95%). In both bottom and fly ashes, more than 95% of the total arsenic is present as As⁺⁵. Chromium in the milled coal and bottom ash is mostly non-toxic (Cr⁺³). The more toxic Cr⁺⁶ comprise less than 5% of the total Cr in the ESP fly ash and the stack-emitted ash. Nickel in milled coal and ashes is in the form of non-toxic Ni⁺², predominantly in coordination with oxygen.The emitted PAHs include acenapthene, fluorene, 2-methyl-fluorene, phenathrene, anthracene, fluoanthene, and pyrene; which are emitted from stack at the combined rate of 3.6 g/day. The concentrations of elements of environmental concern (As, Cd, Hg, Ni, and Pb) emitted to the atmosphere by the power plant in the zone of maximum impact at ground level are lower than those listed in the Health Guidelines of the USEPA and Canadian National Air Pollution Surveillance. This is based on stable meteorological conditions, down wind from the power plant for a maximum distance of 3 km.     

Assessment of elemental content of milled coal,combustion residues,and stack emitted materials: Possible environmental effects for a Canadian pulverized coal-fired power plant

Two monitoring studies were carried out at four-year intervals on a power plant that uses western Canadian subbituminous coal and generates approximately 800 Mw/h of electricity. The distributions of elements of environment concern (As, Hg, Ni, Pb, and Cd) and elements of environmental interest (B, Ba, Be, Cl, Co, Cr, Cu, Mn, Mo, Th, Se, V, U, and Zn) in milled coals, power plant ashes, and emitted materials from the stack were determined using neutron activation analysis (NAA), Inductively Coupled Plasma Emission Spectroscopy (ICPES), and Inductively Coupled Plasma-Mass spectroscopy (ICP-MS) for most elements, Graphite Furnace Atomic Absorption (GFAA) for Pb, and Cold Vapor Atomic Absorption (CVAA) for Hg.The concentrations of most of elements in milled coal are low as compared to world coals and other Canadian milled coals. For example, in both studies mercury is within the lower range of world coal. Bottom ashes from both studies have low concentrations of As, Cd, Hg, Pb, and Zn, as well as low relative enrichment factors (RE) for the same elements, indicating that they were not enriched in the bottom ash. The ESP's remove most of the elements of environmental interest as indicated by their high RE ratios of greater than > 0.7.The rates of input of elements of environmental concern (As, Cd, Hg, Pb and Ni) for this station were 23.65, 1.24, 0.54, 98.2 and 95.2 kg/day, respectively, of which only 0.20, 0.02, 0.31, 0.48 and 0.36 kg/day were emitted from the stack. Thus only a small amount of these elements found in the milled coal was emitted while most were captured in the bottom and the ESP ashes. Nickel has the highest rate of emission (0.48 kg/day) within the elements of environmental concern group. However, the Ni emitted from this station does not belong to the toxic species. The element with the lowest rate of emission is Cd (0.02 kg/day). The total emission of elements of environmental concern is 1.37 kg/day, which is low as compared their ambient concentrations in either rural or urban air. The total rate of emission of B, Ba, Be, Co, Cr, Cu, Mn, Mo, Se, Th, U, V, and Zn is 56.51 kg/day and is mostly comprised of the total emission of Ba (21.73 kg/day) and Zn (19.14 kg/day).     

Petrographic, mineralogy, and geochemistry of coals of Pabedana, Kerman Province, Central Iran

This paper discusses the result of the detailed investigations carried out on the coal characteristics, including coal petrography and its geochemistry of the Pabedana region. A total of 16 samples were collected from four coal seams d2, d4, d5, and d6 of the Pabedana underground mine which is located in the central part of the Central-East Iranian Microcontinent. These samples were reduced to four samples through composite sampling of each seam and were analyzed for their petrographic, mineralogical, and geochemical compositions. Proximate analysis data of the Pabedana coals indicate no major variations in the moisture, ash, volatile matter, and fixed carbon contents in the coals of different seams. Based on sulfur content, the Pabedana coals may be classified as low-sulfur coals. The low-sulfur contents in the Pabedana coal and relatively low proportion of pyritic sulfur suggest a possible fresh water environment during the deposition of the peat of the Pabedana coal. X-ray diffraction and petrographic analyses indicate the presence of pyrite in coal samples. The Pabedana coals have been classified as a high volatile, bituminous coal in accordance with the vitrinite reflectance values (58.75–74.32 %) and other rank parameters (carbon, calorific value, and volatile matter content). The maceral analysis and reflectance study suggest that the coals in all the four seams are of good quality with low maceral matter association. Mineralogical investigations indicate that the inorganic fraction in the Pabedana coal samples is dominated by carbonates; thus, constituting the major inorganic fraction of the coal samples. Illite, kaolinite, muscovite, quartz, feldspar, apatite, and hematite occur as minor or trace phases. The variation in major elements content is relatively narrow between different coal seams. Elements Sc,, Zr, Ga, Ge, La, As, W, Ce, Sb, Nb, Th, Pb, Se, Tl, Bi, Hg, Re, Li, Zn, Mo, and Ba show varying negative correlation with ash yield. These elements possibly have an organic affinity and may be present as primary biological concentrations either with tissues in living condition and/or through sorption and formation of organometallic compounds.     

Coal combustion by-product quality at two stoker boilers: Coal source vs. fly ash collection system design

Fly ashes from two stoker boilers burning Pennsylvanian Eastern Kentucky high volatile A bituminous coal blends were examined for their petrology and chemistry. The source coals have similar trace element contents. One of the ash collection systems was retrofitted with a baghouse (fabric filter) system, collecting a finer fly ash at a cooler flue gas temperature than the plant that has not been reconfigured. The baghouse ash has a markedly higher trace element content than the coarser fly ash from the other plant. The enhanced trace element content is most notable in the As concentration, reaching nearly 9000 ppm (ash basis) for one of the collection units. Differences in the ash chemistry are not due to any substantial differences in the coal source, even though the coal sources were from different counties and from different coal beds, but rather to the improved pollution control system in the steam plant with the higher trace element contents.     

Trace elements in high-S subbituminous coals from the teruel Mining District, northeast Spain

The elemental composition of high temperature ash (750°C) and forms of S were studied in 25 coal seams from the Escucha Formation (Middle Albian) in the Teruel Mining District, northeast Spain. The principal analytical method was ICP-MS, but ICP-ES was also used in the determination of some trace elements. The analytical data show wide ranges of trace element cotnents among the coal seams studied, even in the vertical profile of a single coal seam. These wide ranges of the trace element concentrations are attributed to both syngenetic and epigenetic processes.When a comparison was made between the average trace element contents of the Teruel Mining District coals, and those of the average content in worldwide coals, the Teruel coals show slightly higher concentrations of Be and U, and lower concentrations of Ba, Cd, Mn, Pb, Sr and Zr. Further, three main groups of trace elements were differentiated on the basis of the inorganic/organic association: (1) trace elements with inorganic affinity; Ba, Ce, Co, Cr, La, Mn, Ni, Rb and Zr. Between these, Ba, Ce, Cr and Rb show a well defined correlation with the clay mineral content, and Co and Ni with pyritic-S content; (2) trace elements with an intermediate (mixed) affinity; As, Cd, Cu, Dy, Er, Eu, Gd, Ge, Ho, Lu, Mo, Nd, Pb, Pr, Sb, Sm, Sr, Tb, Th, Tm, U, Yb and Zn. In this group, As, Cd, Cu, Ge, Mo, Th, U and Zn show a weak trend associated with the mineral matter and Sr with the organic matter; and (3) Be shows an organic affinity. The high mineral matter content (21.3% HTA) of the Teruel coals may account for the great number of elements with inorganic affinity. This classification represents a general trend, but the results show that the affinities of some trace elements (e.g. As, Sb and Zn) may vary from one coal seam to another in the Teruel Mining District.     

晋北-宁北煤中痕量元素的地球化学特征

应用仪器中子活化 (INAA)、电感耦合等离子体原子发射光谱 (ICP- AES)和原子吸收光谱 (AAS)等方法测定了晋北-宁北一线 5对矿井、 2个露天矿、 5个电厂和 3个洗煤厂煤中环境敏感性痕量元素的含量;通过与中国土壤、其他地区煤以及世界范围煤中痕量元素含量进行对比,总结了研究区痕量元素的分布、富集特征,得知部分地区煤中 Hg、 Cd和 Se的含量较高,在燃烧利用过程中可能对环境造成影响.通过分析痕量元素与灰分、挥发分的相关性以及痕量元素间、痕量元素与 Al、 Fe和 Sp的相关、聚类特性,探讨了痕量元素间及其与矿物质间的亲合性及赋存特征.     

Geochemistry and Modes of Occurrence of Hazardous Trace Elements in the No. 11 Coal Seam, Antaibao Surface Mine, Shanxi Province

Concentrations of seventeen hazardous trace elements including As, Pb, Hg, Se, Cd, Cr, Co, Mo, Mn, Ni, U, V, Th, Be, Sb, Br and Zn in the No.ll coal seam, Antaibao surface mine, Shanxi Province were determined using Instrumental Neutron Activation Analysis （INAA）, Inductively Coupled Plasma Atomic Emission Spectrometry （ICP-AES）, Cold-Vapor Atomic Absorption Spectrometry （CV-AAS） and Graphite Furnace Atomic Absorption Spectrometry （GF-AAS）. Comparisons with average concentrations of trace elements in Chinese coal show that the concentrations of Hg and Cd in the No. 11 coal seam, Antaibao surface mine are much higher. They may be harmful to the environment in the process of utilization. The variations of the trace elements contents and pyritic suffur in vertical section indicated that： （a） the concentrations of As, Pb, Mn, and pyritic sulfur decrease from roof to floor; （b） the concentrations of Cr, Zn and Mo are higher in roof, floor and lower in coal seam; （c） the concentration of Br, Sb, and Hg are higher in coal seam and lower in roof and floor; （d） the concentrations of Mo, V, Th and AI vary consistently with the ash yield. Cluster analysis of trace elements, pyritic sulfur, ash yield and major elements, such as AI, Fe, P, Ca shows that： （a） pyritic sulfur, Fe, As, Mn, Ni, Be are closely associated and reflect the influence of pyrite; （b） Mo, Se, Pb, Cr, Th, Co, Ca and A! are related to clay mineral, which is the main source of ash; （c） U, Zn, V, Na, P maybe controlled by phosphate or halite; （d） Hg, Br, Sb and Cd may be mainly organic-associated elements which fall outside the three main groups. The concentration distribution characteristics of trace elements in coal seam and the cluster analysis of major and trace elements showed that the contents of trace elements in the No. 11 coal seam, Antaibao surface mine, are mainly controlled by detrital input and migration from roof and floor.     

Leaching characteristics of fly ash

The disposal of fly ash as a byproduct of thermic power stations, results in significant environmental problems. The leaching of coal fly ash during disposal is of concern for possible contamination, especially for the aquatic environment when ash is in contact with water. The aim of this study was to investigate the leaching behaviour of fly ashes currently disposed in Kemerkoy Power Plant (Turkey) fly-ash-holding pond. The studies were conducted with fly ashes from the electrostatic precipitators (fresh fly ash) and from the fly ash pond (pre-leached fly ash). The fly ashes has alkaline in nature and pH ranges between 11.9 to 12.2. The pre-leached fly ash exhibited lower EC values (7,400 µS) than the fresh fly ash (10,300 µS). In contrast to Fe and Pb, the elements such as Cr, Cd, Cu and Co did not leach from the fly ash. The Ca and Mn concentrations decreased with increasing temperature whereas, Na and K concentrations increased. The results showed that the most important effects of fly ash leaching were pH, Na, Ca, K, Fe, Mg, Mn and Pb.     

Trace elements and their variation along seam profiles of certain coal seams of Middle and Upper Barakar formations (Lower Permian) in East Bokaro coalfield,district Hazaribagh,Bihar, India

Trace-element data are presented for the first time for any coal seam in India, across a full working section, based on systematically collected channel samples of coal, together with their maceral composition. The trace-element variation curves along the seam profile are presented together with group maceral compositions of Kargali Bottom, Kargali Top, Kargali, Kathara, Uchitdih, Jarangdih Bottom, Jarangdih, and Jarangdih Top seams, East Bokaro coalfield. The Kathara and Uchitdih seams have also been sampled at two other localities and lateral variation in data in their trace-element and maceral compositions is also evaluated.The East Bokaro coals have: Ba and Sr > 1000 ppm; Mn < 450 ppm; Zr < 400 ppm; Ni and V < 250 ppm; Cr < 185 ppm; La < 165 ppm; Cu, Nb, and B < 125 ppm; Pb, Co and Y < 75 ppm; Ga, Sn, Mo, In and Yb < 15 ppm; Ag 2 ppm; and Ge 7 ppm. Petrographically, the coals are dominant in vitrinite (33–97%), rare in exinite (<15%), and semifusinite (0.8–49%) is the dominant inertinite maceral, with variable mineral and shaly matter (11–30%), graphic representation of trace elements versus vitrinite, inertinite, and coal ash indicates the affinity of (a) vitrinite with Cu, Ni, Co, V, Ga and B; (b) inertinite with Nb and B; and (c) coal ash (mineral matter) with Pb, Cu, Ni, La, Mn and Y; Ba, Cr, Sr, Zr, Cu and Ni are of organic as well as inorganic origins.The trend of the variation patterns and average compositions of the different seams are shown to be distinct and different. The variation along the same profile is inferred to be different for different seams of the coalfield.Trace-element data for certain coals of seams from different coalfields in the Gondwana basins of India are presented. There is a wide difference for each of these basins with respect to certain elements. This is suggestive of the proportions of Cu, Ni, V, Y, Ba, Sr, Cr, B, Zr and Ag, characterizing the different Gondwana Basins.     

Acid leaching of ash and coal: Time dependence and trace element occurrences

The leaching of coal and coal/asphaltite/wood-ashes in sulfuric acid (pH 1.0, 25 °C, S/L, 1:10) was studied as a function of time; acid consumption and extracted metal concentrations are presented. Whole coals consumed acid rapidly during the first few minutes, followed by slow acid consumption. Wood-, lignite-, and asphaltite-ashes consumed acid in two stages, the rapid phase extending < 30 min and the slow phase extended up to 10 days. The rapid phase was dominated by the dissolution of Ca, K and Mg ions for wood-ash, by Ca, Al and Mg ions for lignite-ash and Ca and Mg ions for asphaltite-ash. The sulfur concentration in solution and the concentrations of Ca, Fe, K, Mg, Na, P, Al and Mn in the aqueous phase verified the neutralizing capacity of the untreated ashes as well as the formation of insoluble sulfates in the residues. The slow phase kinetics differed for different fuels and exhibited leaching of several abundant elements—Fe, Al, K, Na and Mn. Trace elements (Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Th, U, V, Zn) sometimes required up to 32 h for maximal extraction from ashes. Suggestions are presented regarding the chemical nature of trace elements in the untreated coals and ashes and suitable residence times for economical industrial processes. We think it possible to combine bacteriological oxidation of sulfidic concentrates of acid leaching from ash of various qualities or even whole coals.     

Characteristics of Coal Ashes in Yanzhou Mining District and Distribution of Trace Elements in Them

In the process of combustion of coal organic and inorganic materials in it will undergo a complex variation.Part of thew will become volatiles and,together with coal smoke,enter into atmosphere,some will remain in micro-particulates such as ash and dust and find their way into atmosphere in the form of solid particles,and the rest will be retained in ash and slag.Coal ashes are the residues of organic and inorganic substances in coal left after coal combustion and the compostition of coal ashes in dependent on that of minerals and organic matter in coal.This paper deals with the chemical composition of coal ashes,the distribution of trace elements in them and their petrological characteristics,and also studies the relationship between the yield of coal ashes and the distribution of trace elements.In addition,a preliminary study in also undertaken on the factors that affect the chemical composition of coal ashes.As viewed from the analyses of coal ash samples collected from the Yanzhou mining district,it can be seen clearly that coal ashes from the region studied are composed chiefly of crystalline materials,glassy materials and uncombusted organic matter and the major chemical compositions are SiO2,Al2O3,Fe2O3,and CaO,as well as minor amounts of SO3,PWO5,Na2O,K2O and TiO2.During the combustion of coal,its trace elements will be redistributed and most of them are enriched in coal ashes.At the same time,the concentrations of the trace elements in flying ash are much higher than those of bottom ash,i.e.,with decreasing particle-size of coal ashes their concentrations will become higher and higher.So the contents of trace elements are negatively proportional to the particle-size of coal ashes.There has been found a positive correlation between the trace elements Th.V.Zn,Cu and Pb and the yield of coal ashes while a negative correlation between Cl and the yield of coal ashes.     

The leaching of trace elements from municipal solid waste incinerator bottom ash at different stages of weathering

For a proper assessment of the environmental impact of the utilisation and disposal of Municipal Solid Waste Incinerator (MSWI) bottom ash it is necessary to understand weathering processes and their effects on (trace) element leaching. The authors have investigated the processes that control the leaching of Cd, Pb, Zn, Cu, and Mo from 3 categories of bottom ash: (A) unweathered bottom ash (grate siftings and unquenched samples), (B) quenched/non-carbonated bottom ash (freshly quenched and 6-week-old samples), and (C) weathered bottom ash (1.5- and 12-year-old samples). Leaching experiments were performed in a pH-stat at a large range of pH values. The speciation code MINTEQA2 was used for subsequent modelling of precipitation/dissolution processes. The speciation of trace elements in weathered bottom ash was also investigated by microanalytical techniques. In A- and B-type bottom ash the general controlling processes are thought to be precipitation/dissolution of relatively soluble minerals or, in the case of Cu in particular, extensive complexation with dissolved organic C. At the “natural” pH of the samples, the leaching of Cd, Pb, Cu, Zn and Mo is generally significantly lower from C-type bottom ash than from less weathered types of bottom ash. This reduction in leaching is due to the neutralisation of bottom ash pH and the formation of less soluble species of these elements as weathering continues. In the more weathered (C-type) bottom ash trace element leaching does not seem to be solubility-controlled; although slow precipitation reactions cannot be totally excluded, it is hypothesised that the controlling mechanism in those samples is sorption to neoformed minerals.     

Mineralogy and geochemistry of feed coals and their combustion residues from the Cayirhan power plant,Ankara, Turkey

A total of 48 samples, feed (run-of-mine) coals and their combustion residues (fly ash and bottom ash) were systematically collected twice a week over a 4 week period (June 1998) from two boiler units (I and II) of the Cayirhan power plant (630 MW) that burns zeolite-bearing coals of late Miocene age. The feed coals are high in moisture (22.8% as-received) content and ash (44.9%) yield and total S content (5.1%), and low in calorific value (2995 kcal/kg). The mineralogy of the feed coals contains unusually high contents of the zeolites (clinoptilolite/heulandite and analcime), which are distributed within the organic matter of coal. Other minerals determined are gypsum, quartz, feldspar, pyrite, dolomite, calcite, cristobalite and clays. Common minerals in the crystalline phase of the combustion residues are anhydrite, feldspar, quartz, hematite, lime and Ca–Mg silicate. Minor and trace amounts of magnetite, cristobalite, maghemite, gehlenite, calcite and clinoptilolite/heulandite are also present in the combustion residues. Trace element contents of the feed coals, except for W, fall within the estimated range of values for most world coals; however, the mean values of Mn, Ta, Th, U and Zr are near maximum values of most world coals. Elements such as As, Bi, Ge, Mo, Pb, Tl, W and Zn are enriched more in the fly ash compared to the bottom ash.     

Petrology of subbituminous feed coal as a guide to the capture of mercury by fly ash—influence of depositional environment

The mercury and maceral content of subbituminous feed coals burned at six Canadian power plants was measured and compared to the mercury and carbon content of corresponding fly ashes. The fly ashes were collected from electrostatic precipitator (ESP) pollution controls used at the power plants. Four feed coals from the Upper Cretaceous to Tertiary age Scollard Formation were deposited in freshwater depositional environment and contain 35–44% inertinite. Two feed coals from the Upper Cretaceous age Horseshoe Canyon Formation were deposited in a brackish water environment and contain 14% inertinite.The data show that abundant inertinite equates to more unburned carbon in ESP fly ash, and to enhanced capture of mercury in cold-side ESP fly ash. This indicates that the inertinite content of a coal seam may be indicative of the percentage of unburned carbon and the percentage of mercury captured by a cold-side ESP.     

Effects of coal fly ash amended soils on trace element uptake in plants

Variations in As, Ba, Bi, Cd, Co, Cu, Hg, Mn, Mo, Ni, Pb, Sb, Se, Sn, Th, Tl, U, W, and Zn uptake were evaluated in young, middle-aged, and mature basil, tomato, zucchini, and sunflower plants grown in soils amended with 5, 10, and 20% by weight fly ash. Elements susceptible to uptake with increasing fly ash were As and Tl, with As exceeding potentially toxic levels in basil and zucchini. Temporal variations in element uptake included (1) increasing Ba and Cd concentrations in tomato and As, Ba, Cd, and Tl in zucchini, (2) decreasing Co concentrations in tomato, zucchini, and sunflower, Ni in zucchini, and Tl in basil, and (3) increasing As and Ni concentrations in basil and Pb in zucchini and sunflower during early growth followed by decreasing concentrations at maturity. Although most of the trace elements were below reported toxic levels, the elevated concentrations of As in plant tissue suggests that fly ash treatment programs can lead to potentially toxic accumulations of As, and thus, should be carefully monitored.     

Measuring reactive pools of Cd,Pb and Zn in coal fly ash from the UK using isotopic dilution assays

Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005 M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH < 11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH > 11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43 M HNO₃ and 0.05 M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.