Mode of occurrence of trace elements in the Pellana lignite (SE Peloponnese,Greece)

Mineralogical and geochemical analyses of the Pellana lignite (SE Peloponnese, Greece) were carried out in order to predict the mode of occurrence of trace elements and their mobility during lignite combustion for power generation. Lignite and ash samples (after combustion at 750 °C) of two cores from this deposit were examined. The mean ash content is 30% to 43% and C contents on dry, ash-free basis range from 45% to 60%, respectively. The mineral phases contained in the lignite are quartz, K-feldspars, mixed-layer clays (illite-rich), micas, gypsum and pyrite. Factor analysis on geochemical data shows that the elements As, Ba, Mn, Mo, Sb, Se, Sr, U and V have both organic and inorganic affiliation. To study the mobility of each element during combustion, the relative enrichment factor was calculated. The most depleted and hence the most mobile elements, proved to be Hf, Nb and Sb, while Se, Ba and Bi are moderately depleted. In case of the Pellana lignite utilization we should expect environmental problems associated with the elements As, Ba, Bi, Hf, Mn, Mo, Nb, Sb and Se. These elements may be either volatilized during combustion or leached from fly ash-disposal areas into underground waters, causing severe environmental and health impacts.     

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.     

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.     

A comparative evaluation of minerals and trace elements in the ashes from lignite, coal refuse, and biomass fired power plants

Coal being a limited source of energy, extraction of energy from other sources like lignite, coal-refuse, and biomass is being attempted worldwide. The minerals and inorganic elements present in fuel feeds pose different technological and environmental concerns. Lignite ash, refuse ash, and biomass ash collected from Indian power plants burning lignite, coal-refuse, and mustard stalk, respectively, were analyzed for physico-chemical characteristics and trace elements. The lignite ash has high SiO₂, CaO, MgO, Al₂O_3, and SO₃; the refuse ash has high SiO₂ and Fe₂O₃, but low SO₃; the biomass ash has high SiO₂ (but low Al₂O₃), and high CaO, MgO, K₂O, Na₂O, SO₃, and P₂O₅. A substantial presence of chloride (2.1%) was observed in the biomass ash. Quartz is the most abundant mineral species. Other minerals are mullite, hematite, gehlenite, anhydrite, and calcite in the lignite ash; orthoclase in the refuse ash; albite, sanidine, gehlenite, anhydrite, and calcite in the biomass ash. Ashes with high concentrations (> 100 mg/kg) of trace elements are: lignite ash (V < La < Mn < Cr < Ni < Nd < Ba < Ce, Zn < Sr); refuse ash (Cr < Ce < V < Rb < Mn < Sr, Zn < Ba); biomass ash (Cu < Zn < Ba, Sr). Based on Earth crust normalization, Co, Ni, As, Se, Mo, Zn, Pb, U, and REEs (except Pr and Er) are enriched in the lignite ash; molybdenum, Zn, Cs, Pb, Th, U, La, Ce, and Lu in the refuse ash; and Mo, Zn, Sr, Cs, Pb, and Lu in the biomass ash. Elements As, Zn, Mo, Ni, Pb, Rb, Cr, V, Ba, Sr, and REEs are correlated with Al, indicating the possibilities of their association with aluminum silicates minerals. Similarly, barium, Cs, Th, and U are correlated with iron oxides; molybdenum and Sr may also be associated with sulfates and chlorides. Due to the alkaline nature of these ashes, the high concentrations of As and Se in the lignite ash; molybdenum in the biomass ash; and Se in the refuse ash may pose environmental concerns.     

The studies of the sorption properties of soils at the base of the ash storage of the projected power station on Sakhalin Island

The soil sorption properties were determined for the base of ash storage at a proposed power station on Sakhalin Island. The analyses of aqueous extracts of the coal ashes that are intended for use at the station resulted in the identification of potential pollutant elements that might be transferred with the infiltrate of atmospheric precipitation. The composition of the infiltrate-modeling solution was selected based on the data. The sorption capacity of the covering soil by identified pollutants was evaluated at static and dynamic conditions, along with the degree of potential desorption of these pollutants.     

Leaching characteristics of a high-calcium fly ash as a function of pH: a potential source of selenium toxicity

Using a modified extraction procedure, the effect of pH on the leaching of selected elements from Ca-rich (Type C) power plant fly ash was studied. Continuous additions of acetic acid were used to maintain pH values of fly ash slurries at 4.0, 6.0 and 8.0 for 24 h and an additional set was leached at its natural pH (average 11.8) value. Analyses for Se, As, Ca, Cd, Cr, Fe, Na and Pb showed that the highest concentrations occur in the leachate at pH 4.0 and decline with increasing pH. Concentrations of Cr and Fe increased slightly between neutral and high pH. Arsenic, Cd, Cr, Pb and Se concentrations exceeded the Environmental Protection Agency's toxicity criteria at pH 4.0. Selenium was above its toxicity level at pH values near 7 but the other elements were below their respective toxicity levels near neutral pH. Because recent studies show adverse effects of Se on aquatic life at far lower concentrations than the current Environmental Protection Agency's standard, high-Ca, power plant fly ashes represent a potentially hazardous pollutant to surface and subsurface waters.     

Chemical and petrographical characterization of feed coal, fly ash and bottom ash from the Figueira Power Plant, Paraná, Brazil

The aim of the present study is the petrographic and chemical characterization of the coal at the Figueira Power Plant, Paraná, Brazil, prior and after the beneficiation process and the chemical characterization of fly and bottom ashes generated in the combustion process.Petrographic characterization was carried out through maceral analysis and vitrinite reflectance measurements. Chemical characterization included proximate analysis, determination of calorific value and sulphur content, ultimate analysis, X-ray diffraction, X-ray fluorescence, Inductively Coupled Plasma — Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma — Atomic Emission Spectrometry (ICP-AES) analysis, and determination of Total Organic Carbon (TOC) content.Vitrinite reflectance analyses indicate a high volatile B/C bituminous coal (0.61 to 0.73% Rrandom). Maceral analyses show predominance of the vitrinite maceral group (51.6 to 70.9 vol.%, m.m.f). Except of the Run of mine (ROM) coal sample, the average calorific value of the coals is 5205 kcal/kg and ash yields range from 21.4 to 38.1 wt.%. The mineralogical composition (X-ray diffraction) of coals includes kaolinite, quartz, plagioclase and pyrite, whereas fly and bottom ashes are composed by mullite, ettringite, quartz, magnetite, and hematite. Analyses of major elements from coal, fly and bottom ashes indicate a high SiO₂, Al₂O₃, and Fe₂O₃ content. Trace elements analysis of in-situ and ROM coals by ICP-MS and ICP-AES show highest concentration in Zn and As. Most of the toxic elements such as As, Cd, Cr, Mo, Ni, Pb, and Zn are significantly reduced by coal beneficiation. Considering the spatial distribution of trace elements in the beneficiated coal samples, which were collected over a period of three months, there appears to be little variation in Cd and Zn concentrations, whereas trace elements such as As, Mo, and Pb show a larger variation.In the fly and bottom ashes, the highest concentrations of trace elements were determined for Zn and As. When compared with trace element concentrations in the feed coal, fly ashes show a significant enrichment in most trace elements (As, B, Be, Cd, Co, Cr, Cu, Li, Mn, Mo, Ni, Pb, Sb, Tl, and Zn), suggesting a predominantly volatile nature for these elements. In contrast, Sn is distributed evenly within the different ash types, whereas U shows depleted concentration in both bottom and fly ash samples.According to the International Classification of in-seam coals the Cambuí coals are of para/ortho bituminous rank of low grade (except for the ROM sample), and are characterized by the predominance of vitrinite macerals.     

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…     

Impact of co-combustion of petroleum coke and coal on fly ash quality: Case study of a Western Kentucky power plant

Petroleum coke has been used as a supplement or replacement for coal in pulverized-fuel combustion. At a 444-MW western Kentucky power station, the combustion of nearly 60% petroleum coke with moderate- to high-sulfur Illinois Basin coal produces fly ash with nearly 50% uncombusted petroleum coke and large amounts of V and Ni when compared to fly ash from strictly pulverized coal burns. Partitioning of the V and Ni, known from other studies to be concentrated in petroleum coke, was noted. However, the distribution of V and Ni does not directly correspond to the amount of uncombusted petroleum coke in the fly ash. Vanadium and Ni are preferentially associated with the finer, higher surface area fly ash fractions captured at lower flue gas temperatures. The presence of uncombusted petroleum coke in the fly ash doubles the amount of ash to be disposed, makes the fly ash unmarketable because of the high C content, and would lead to higher than typical (compared to other fly ashes in the region) concentrations of V and Ni in the fly ash even if the petroleum coke C could be beneficiated from the fly ash. Further studies of co-combustion ashes are necessary in order to understand their behavior in disposal.     

Leachability of trace elements from two stabilized low lime Indian fly ashes

Fly ash is a waste by-product obtained from the burning of coal by thermal power plants for generating electricity. When bulk quantities are involved, in order to arrest the fugitive dust, it is stored wet rather than dry. Fly ash contains trace concentrations of heavy metals and other substances in sufficient quantities to be able to leach out over a period of time. In this study an attempt was made to study the leachabilities of a few selected trace metals: Cd, Cu, Cr, Mn, Pb and Zn from two different types of class F fly ashes. Emphasis is also laid on developing an alternative in order to arrest the relative leachabilities of heavy metals after amending them with suitable additives. A standard laboratory leaching test for combustion residues has been employed to study the leachabilities of these trace elements as a function of liquid to solid ratio and pH. The leachability tests were conducted on powdered fly ash samples before and after amending them suitably with the matrices lime and gypsum; they were compacted to their respective proctor densities and cured for periods of 28 and 180 days. A marked reduction in the relative leachabilities of the trace elements was observed to be present at the end of 28 days. These relative leachability values further reduced marginally when tests were performed at the end of 180 days.     

Risk assessment of bottom ash from fuel oil power plant of Italy: mineralogical,chemical and leaching characterization

The main aim of the present study is to contribute to the field of environmental research by providing new data on bottom ash samples derived from an oil power plant located in Southern Italy. To achieve this purpose, the mineralogical and chemical properties of representative bottom ash samples were investigated through the integrated employment of different analytical techniques, i.e., X-ray powder diffraction, scanning electron microscopy, X-ray fluorescence and atomic absorption spectrometry. The obtained experimental results show that quartz, alunogen, rhomboclase and potassium hydrogen silicate are the major crystalline phases of all the analyzed samples. Furthermore, the revealed main ash constituents are SiO₂ and SO₃, with low contents of Fe₂O₃ and Al₂O₃, and little amounts of CaO, Na₂O, K₂O, MgO, P₂O₅ and TiO₂. Among the trace elements, very high amounts of heavy metals, i.e., V, Cr, Ni, La, Pb and Mo, were detected. The comparison of the obtained heavy metal abundance data with those reported in the literature highlights significant differences. Leaching test evidenced V, Ni and Cr values that make these ashes a potential contamination source for groundwater quality and for soil, nearby the ash disposal landfills area. All the obtained findings show that these materials are highly harmful for the human health, with a greater extent for the heavy metal concentrations.     

Long-term brine impacted fly ash,Part II: Mobility of major species in the ash residues

The leaching of major species from fly ash is a function of the pH of the solution in contact with the fly ash. The aim of this study was to determine the effect of the pH of the leachant on the leaching of species from the ash residues recovered after the long-term fly ash–brine interactions. Acid neutralization capacity (ANC) tests using solutions of different pH values ranging from the initial pH of the ash residues (11–12) to pH 4 were employed in the leaching experiments. The ANC tests revealed that the release of major species from the ash residues depended on the pH of the leachants except for Na and Cl, where the significant concentrations leached were independent of the solution pH. The concentrations of Al and Si in the ANC leachates were very high at pH below 6 while Ca, K, Sr, Mg and B were immediately mobilized from the brine impacted fly ash when in contact with de-ionized water, and leaching increased as the pH decreased. The concentration of SO₄ leached from the brine impacted ash residues at high pH was high, and the leaching increased with decrease in the pH of the leachant. This study shows that most of the major elements captured in the ash residues could be mobilized when in contact with aqueous solutions of various pH. This reveals that the co-disposal of fly ash and brine may not be the best practice as the major elements captured in the ash residues could leach over time.     

煤及其燃烧产物飞灰和底灰中稀土元素地球化学特征及集散规律

采用ICP—MS法测试了褐煤、肥煤和无烟煤以及在不同燃烧条件下获取的飞灰、底灰等29个样品的稀土元素含量;分析了稀土元素地球化学特征。结果表明,不同煤种的稀土元素含量不同,相同煤种在不同燃烧条件下获取的飞灰、底灰中的稀土元素含量也不同;褐煤、肥煤、无烟煤及其燃煤产物飞灰、底灰的稀土元素分布模式呈左高右低的宽缓的“V”型曲线;Eu存在明显负异常。研究了燃煤过程中稀土元素的分布及集散规律,稀土元素在飞灰、底灰中的含量比原煤有明显提高,其增加幅度为几倍至20多倍不等,表明煤炭燃烧后稀土元素在飞灰、底灰中进一步聚集;飞灰和底灰中稀土元素含量、飞灰和底灰对煤的稀土元素含量比和富集因子以及飞灰对底灰的稀土元素含量比和富集因子等,不仅与原煤中稀土元素有直接关系,而且还受锅炉燃烧方式、燃烧温度(炉温)等人为因素的影响。     

Bottom ash of trees from Cameroon as fertilizer

Utilization of wood bottom ash as fertilizer additive contributes to the return of valuable nutrients to agricultural soils, especially when no artificial mineral fertilizer is being used. In general, wood combustion ash is enriched in calcium and potash, and may also contain elevated amounts of zinc, but the concentrations of these elements depend on tree species, part of the tree, harvest season and local soil type. In this study, bottom ash samples from eight different agricultural wood species from Cameroon, Africa were investigated by using X-ray diffraction and atomic absorption spectroscopy to determine the refractory components and the concentrations of selected heavy metals and arsenic. Results show calcite, potassium salts, periclase and quartz as major components. These phase contents were used to calculate major element concentrations, which were subsequently validated by X-ray-fluorescence analysis. The chemical compositions varied within the range of common compositions of wood ashes. Six of the ashes reached sufficient concentrations of calcium to be defined as a “calcium fertilizer”. Pb contents are most variable, ranging from 0.03 to 21.1 mg/kg. Concentrations of Ni, Cu, Zn, Cd, Pb, and As are all lower than the strictest limit concentrations required for wood ash fertilizers and therefore, the studied wood ashes can be used without environmental concern.     

高钙粉煤灰固化重金属污染土的工程性质试验研究

高钙粉煤灰是燃煤电厂排出的固体废物,其堆放不仅需占用大量土地,而且对周围环境存在严重威胁。通过系统的室内试验,着重研究了高钙粉煤灰固化铅与锌污染土的工程性质,揭示了其作用机制,探讨了利用高钙粉煤灰固化重金属污染土的可行性。试验结果表明,土体受到重金属离子污染后其无侧限抗压强度降低,掺入高钙粉煤灰可提高土体强度,并能抑制重金属离子的滤出;污染物浓度较低时,固化污染土中的Pb2+和Zn2+均能得到有效固化,污染物浓度较高时,Zn2+的固化效果优于Pb2+。干湿循环试验结果表明,高钙粉煤灰固化污染土的强度随干湿循环次数的增加,先增大后减小;固化土体中重金属离子浓度较低时,滤出液中金属离子浓度随干湿循环次数增加而增大;重金属离子浓度较高时,滤出液中金属离子浓度基本保持不变。     

Coal fly ash interaction with environmental fluids: Geochemical and strontium isotope results from combined column and batch leaching experiments

The major element and Sr isotope systematics and geochemistry of coal fly ash and its interactions with environmental waters were investigated using laboratory flow-through column leaching experiments (sodium carbonate, acetic acid, nitric acid) and sequential batch leaching experiments (water, acetic acid, hydrochloric acid). Column leaching of Class F fly ash samples shows rapid release of most major elements early in the leaching procedure, suggesting an association of these elements with soluble and surface bound phases. Delayed release of certain elements (e.g., Al, Fe, Si) signals gradual dissolution of more resistant silicate or glass phases as leaching continues. Strontium isotope results from both column and batch leaching experiments show a marked increase in ⁸⁷Sr/⁸⁶Sr ratio with continued leaching, yielding a total range of values from 0.7107 to 0.7138. For comparison, the isotopic composition of fluid output from a fly ash impoundment in West Virginia falls in a narrow range around 0.7124. The experimental data suggest the presence of a more resistant, highly radiogenic silicate phase that survives the combustion process and is leached after the more soluble minerals are removed. Strontium isotopic homogenization of minerals in coal does not always occur during the combustion process, despite the high temperatures encountered in the boiler. Early-released Sr tends to be isotopically uniform; thus the Sr isotopic composition of fly ash could be distinguishable from other sources and is a useful tool for quantifying the possible contribution of fly ash leaching to the total dissolved load in natural surface and ground waters.     

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.     

煤中铀的赋存分布及其在利用过程中的迁移特征

煤炭与铀两种资源在空间配置和成矿上有关联性,其合理开发利用及污染控制是我国国民经济和社会持续发展的重大需求。基于大量文献调研及前期研究成果,探讨了铀在煤中赋存分布及其在洗选、燃烧、淋滤过程中的迁移特征,取得一些认识:①煤中铀的富集成矿与成煤大地构造演化相关联,西南富铀煤主要与峨眉山玄武岩及断裂构造有关;西北富铀煤一般分布在拗陷和断拗陷盆地开阔地带一侧并与上覆砂岩型铀矿有关。②煤中铀主要与煤中有机质（主要是腐殖酸）结合,富铀煤中铀可以微细粒含铀矿物形式存在,并与有机硫、硫化物紧密共生,故在选煤过程中,无论重选还是浮选,其洗选脱除率均不高（最高为68.3%）,部分煤浮选时铀甚至富集到精煤中;在煤燃烧过程中,铀或多或少都会以气相形式挥发到大气中。③富铀煤一般也同时富集V、Mo、Se、Re、Cr等高价态变价元素,这与有机体深埋分解造成的强还原环境有关,对于那些不变价元素如Sc、Y、La等的沉淀富集主要与腐殖酸形成的酸化条件有关;这些共生组合元素,在富铀煤的分选及煤矸石的淋滤过程中表现出一致的迁移行为。④电厂燃煤过程中铀主要富集（呈数量级的增加）到飞灰和底灰中,粉煤灰中铀淋出浓度一般随淋滤液pH的增加呈降低趋势,其萃取率随灰化温度的升高呈现降低趋势。研究结果为铀资源利用和环境污染控制提供参考和依据。      

A preliminary study on the enrichment mechanism and occurrence of hazardous trace elements in the Tertiary lignite from the Shenbei coalfield, China

The Cr and Ni contents are high in the Eocene lignite of the Shenbei coalfield, which is a small intracontinental basin located in Liaoning Province, China. In this paper, we studied the distribution, origin and occurrence of Cr, Ni and other hazardous trace elements in the Shenbei lignite on the basis of coal petrology, and geochemistry of the lignite and combustion products. The following conclusions on the Shenbei lignite can be drawn: (1) The dominant maceral group in the Shenbei coal is huminite (humodetrinite), accounting for 96%–99% of the total maceral. Inertinite content is less than 1%. Liptinite content (sporinite and cutinite) is 0.2–1.6%. Common minerals in the Shenbei lignite include clay minerals (kaolinite), pyrite and quartz, and calcite and siderite. Chromite is not present in the lignite. (2) Potentially hazardous trace elements such as Co (22 μg/g), Cr (79 μg/g), Cu (63 μg/g), Zn (93 μg/g), V (88 μg/g) and Ni (75 μg/g) are strongly enriched in the Shenbei lignite compared with average concentration of trace elements in the Chinese coal and worldwide lignite. These elements are mainly associated with fulvic acid (FA) and/or coal organic macromolecular compounds in most of the studied lignite samples, indicating an organic association and enrichment of these elements in the Shenbei lignite. (3) Unusually high trace elements contents in the Shenbei lignite are derived mainly from the olivine basalt (country rock of coal basin) that consists of 52.7% plagioclase, 17.8% pyroxene, 14% olivine and 15.5% Ti–Fe oxide minerals. These olivine basalts have higher Cr, Ni, Pb and Zn contents than other types of rock and worldwide basalts do. (4) Fly ash of the Shenbei lignite, with 90% 1–50 μm amorphous particles and 8% 1–10 μm cenosphere, has high contents of Zn (23,707 μg/g), Be (12 μg/g), Sr (1574 μg/g), Pb (486 μg/g) and Cr (349 μg/g). In particular, the ferruginous micro-cenoshperes contain 1–12.79% Zn. Fine bottom ash (<0.031mm) of the Shenbei lignite has higher contents for most of the elements with the exception of Mo, Sn and Zn. Therefore, the potentially environmental and health impact of the fly ash and fine bottom ash should constitute a major concern.     

Leaching behavior of lignite fly ash with shake and column tests

The maximum concentration of the majority of the trace metals in the leachates from shake and column test of lignite fly ash (LFA) was within the prescribed limits; however, total dissolved solids, total hardness, cations and anions (except K⁺), being above the prescribed limits, may lead to the increase in the hardness and salinity in the soil on the disposal of LFA. Present generation of huge amount of fly ash from thermal power plants (TPPs) is a big challenge concerning contamination of soil, crop produce and surface and ground water bodies due to the presence of some of the toxic trace metals in it. The leaching behavior of alkaline LFA (pH, 10.94), from TPP of Neyveli Lignite Corporation (NLC), India, was investigated by shake and column tests using water and sodium acetate buffer. The leaching of trace metals from LFA was governed by their concentrations, association with the ash particles, leaching duration and pH of the leachate (most influencing parameter). The leaching of metals followed the order: buffer column > aqueous column > aqueous shake > buffer shake test.