Mobility of heavy metals from coal fly ash

The mobility of Cd, Co, Cu, Ni, Pb, Sb, and Zn from six different coal-fired power plant fly ashes that show a wide compositional range was examined using a sequential extraction procedure in order to assess their mobility when these wastes are ponded or landfilled. The extraction sequence was as follows: (1) water extractable, (2) cation exchangeable (CH₃COONH₄ at pH 7), (3) surface oxide-bound cations (CH₃COONH₄ at pH 5), (4) Fe oxide-bound cations (HONH₃Cl), and (5) residual (HF, HCl, HNO₃, 211). The heavy metal contents in the extraction solutions were determined by anodic (Cd, Cu, Pb, Sb, and Zn) and cathodic (Ni and Co) stripping voltammetry. The results reveal differences in the total contents of the selected trace elements among the fly ash samples, which must be related to differences in coal composition and combustion technology. The extractable fraction under natural conditions ranges from 1.5 to 36.4 percent of the total element content. Cadmium, Co, Cu, and Zn show the highest extractable fraction (10.8–18.9 percent on average). Cadmium is the most easily water-extractable element, while Co, Cu, and Zn increase their mobility as the severity of the extraction increases. Cobalt, Ni, Pb, and Zn are mainly associated with the surface oxide-bound and Fe oxide-bound fractions. Nickel, Pb, and Sb have low mobility potentials (5.3–6.6 percent as extractable fraction), but Sb presents a relatively high water-extractable fraction.     

Partitioning of major and trace inorganic contaminants in fly ash acid mine drainage derived solid residues

Acid mine drainage was reacted with coal fly ash over a 24 h reaction time and species removal trends evaluated. The evolving process water chemistry was modeled by the geochemical code PHREEQC using WATEQ4 database. Mineralogical analysis of the resulting solid residues was done by X-ray diffraction analysis. Selective sequential extraction was used to evaluate the transfer of species from both acid mine drainage and fly ash to less labile mineral phases that precipitated out. The quantity of fly ash, volume of acid mine drainage in the reaction mixture and reaction time dictated whether the final solution at a given contact time will have a dominant acidic or basic character. Inorganic species removal was dependent on the pH regime generated at a specific reaction time. Sulphate concentration was controlled by precipitation of gypsum, barite, celestite and adsorption on iron-oxy-hydroxides at pH > 5.5. Increase of pH in solution with contact time caused the removal of the metal ions mainly by precipitation, co-precipitation and adsorption. PHREEQC predicted precipitation of iron, aluminium, manganese-bearing phases at pH 5.53–9.12. An amorphous fraction was observed to be the most important in retention of the major and minor species at pH > 6.32. The carbonate fraction was observed to be an important retention pathway at pH 4–5 mainly due to initial local pockets of high alkalinity on surfaces of fly ash particles. Boron was observed to have a strong retention in the carbonate fraction.     

高铝粉煤灰中部分主微量元素的分布规律研究

本文旨在研究部分主微量元素在高铝粉煤灰中的分布规律,从而为其资源化利用提供科学依据。首先根据高铝粉煤灰的物相组成特点采用新的分离方法将之分离为三个相(或相组合):铁质微珠、莫来石-刚玉相以及玻璃相;然后分别用化学分析和ICP-MS测试主微量元素在高铝粉煤灰、铁质微珠以及莫来石-刚玉相中的含量,并结合相关数据计算出这些元素在玻璃相中的含量。结果表明,除Al、Mn外,其他元素均在玻璃相中有不同程度的富集;除Al外,其他元素则在莫来石-刚玉相中有不同程度的贫化;除Ti以外的铁族元素以及除Ga、Pb以外的金属成矿元素均在铁质微珠中富集,其他元素则在其中贫化。     

粉煤灰和二灰对桂林红黏土力学性质的影响

为了研究粉煤灰和二灰掺量及养护时间对桂林红黏土的改良效果,进行了直剪试验、固结试验以及电镜扫描试验。试验结果表明,粉煤灰的掺入提高了红黏土的抗剪强度,但超过一定量（18%粉煤灰掺量）反而会降低红黏土黏聚力,各掺量粉煤灰红黏土随养护龄期的延长,抗剪强度呈先增后缓趋势。二灰改良红黏土,在早期强度剧增,且强度随养护时间增长而大幅增加,一定龄期内,二灰红黏土黏聚力随二灰掺量呈先增后减趋势。粉煤灰和二灰的掺入均增大了红黏土的压缩模量,且随养护时间的延长而逐渐增大。红黏土中随粉煤灰、石灰的加入,发生一系列物理化学反应,从微观结构分析得知土中孔隙减少,结构性较素红黏土好。     

Effect of the alkaline industrial residues fly ash,green liquor dregs,and lime mud on mine tailings oxidation when used as covering material

The potential to use the alkaline residue products fly ash, green liquor dregs, and lime mud originating from paper mills as dry cover materials to seal tailings has been investigated. Metals concentration in lime mud and fly ash had the lowest and highest contents, respectively. The tailings (<1 % sulfur content, primarily pyrite) were disposed about 50 years ago and originated from the former Rönnskär mine site in Sweden. The results of chemical composition analysis show that the raw unoxidized tailings are active toward oxidation, while the components of the adjacent oxidized tailings are not. To quantify the release of metals from the tailings and to evaluate the effect of a sealing layer on oxidation and weathering of the tailings, batch leaching tests were conducted in which leachate from alkaline residue materials was fed to the tailings. The results show that a higher concentration of most trace elements is leached from the unoxidized tailings than from the oxidized tailings. Except As and Cr, the rest of analyzed metals (Cd, Cu, Ni, Pb) became immobilized in response to the increased pH as a consequence of the amendment. The three tested alkaline amendments show a similar potential for preventing the release of metals (with the exception of As and Cr) from the tailings. Under either aerobic or anaerobic conditions, microbial activity was found to be of minor importance. XRD analysis of the field samples revealed that it was feasible to use alkaline residue products in covering tailings, and that it was advantageous to use ash as a cover material more than dregs.     

Utilisation of fly ash in a geopolymeric material

Finding means of utilising waste products is a very important field of research at the moment. In this study, fly ash, a waste product of the electricity and petrochemical industries, was investigated as a basic ingredient of a new geopolymeric material. The similarity of fly ash to natural pozzolans has encouraged the use of this waste product in the synthesis of geopolymers, which, in turn, can best be viewed as consisting of a polymeric Si–O–Al framework. Manufacturing of the geopolymers was conducted by mixing fly ash, kaolinite, sodium silicate solution, NaOH and water. The samples were cured at 40, 50, 60 and 70 °C for different time intervals (6, 24, 48 and 72 h). The optimum condition was found to be at 60 °C for a period of 48 h. Compressive strength measurements show a maximum strength of almost 8 MPa after 28 days. Infrared spectroscopic measurements were obtained of the samples after 7 and 28 days. X-ray diffraction measurements show quartz as the main constituent with the largest part of the geopolymer structure being amorphous and glass-like.     

Mobility of potentially harmful metals in latosols impacted by the municipal solid waste deposit of Londrina,Brazil

The contamination of soils by metals issuing from municipal solid waste (MSW) disposal in tropical environments has hardly been studied with regard to the particular problems associated with them, i.e., generally a high permeability of soils despite the abundance of clay, and the role of reactive Fe compounds. From a previous geotechnical and chemical survey, three latosol profiles differently affected by MSW leachates in the region of Londrina (Paraná, Brazil) were selected. The aims were to evaluate the extent of their contamination, to better understand the fate of potentially harmful metals in tropical soils and rank the determining factors. Samples between 0.5 and 7 m depth were analyzed for their physical, mineralogical and chemical properties, and their micro-morphology was described by optical and transmission electron microscopy. Two steps of a sequential extraction procedure helped to assess the mobility of elements and to better discriminate between metals originating from pedogenesis and issued from MSW. These combined approaches showed that exposed soil profiles have been impacted at various depths, down to 7 m, through increased metal content, especially enhanced mobility of Zn, Co, Mn, Cu and Fe, and through increased salinity and organic matter. The mobility of potentially harmful metals should decrease with pH, which significantly increased in some impacted horizons, but other factors can reverse this trend.     

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.     

Magnetic stability of power-plant fly ash in different soil solutions

Temporal stability of magnetic parameters of anthropogenic ferrimagnetics in model soil conditions was studied. Fly ash from a power plant was used as original contaminant material, while soil reactive medium was modeled by different soil solutions. Changes in mass-specific magnetic susceptibility (χ), percentage frequency dependent magnetic susceptibility (χ_FD%), hysteresis parameters and thermomagnetic curves were measured for samples which underwent different leaching time periods. Virtually constant magnetic susceptibility values were obtained, independently on the soil medium (acid, neutral). On the other hand, the original highly non-stoichiometric maghemite phase rapidly transformed to stable magnetite. In some cases (model of free-draining soils) further decrease of Curie temperature (T_c) to 550–560°C is observed.     

粉煤灰灌浆材料在地质灾害防治工程中的应用

我国是地质灾害频发的国家。地质灾害的快速治理与应急抢险是减轻人民生命财产损失的主要手段和措施。地质灾害抢险救灾的工程实践表明，有效的灌浆和堆载是地质灾害防治工程的重要技术手段。因此，就灌浆而言，研究与之适应、性能可靠的灌浆材料是十分必要的。针对普通水泥在灌浆工程中的不足，提出了以工业废料粉煤灰为主要成分研制适应地质工程施工特点的新型灌浆材料。经过系统研究，提出了具有早强特点和可灌性好的复配方案。通过细化和均化等加工技术制成的灌浆材料具有浆液稳定，可灌性好，凝结时间可调，结石率高，强度高的特点。在静压注浆、高压旋喷注浆和帷幕灌浆等地质工程施工中的应用初步验证了这种粉煤灰灌浆材料的性能特点，能够在地质灾害防治工程中推广使用。     

Fluvial-aeolian interactions: Part II, ancient systems

An understanding of fluvial-aeolian deposition derived from modern case-examples in a previous study is applied to the Permian Cutler Formation and Cedar Mesa Sandstone on the Colorado Plateau. These formations supply an excellent three-dimensional exposure of intertonguing fluvial and aeolian strata. Four distinct facies associations form the bulk of the Cutler Formation and Cedar Mesa Sandstone: (1) aeolian dune deposits; (2) wet interdune deposits; (3) fluvial channel deposits; and (4) overbank-interdune deposits. In addition, two distinctive types of erosion surfaces are found within the Cutler Formation and Cedar Mesa Sandstone: pebble- to granule-rich erosion surfaces (aeolian deflation surfaces) and flood surfaces. Fluvial and aeolian intertonguing result in extensive tabular sheets of aeolian sandstone separated by flood surfaces and overbank-interdune deposits. Fluvial channels are associated with the deposits overlying flood surfaces and are incised into the underlying aeolian sandstones. Overbank-interdune deposits and wet interdune deposits cover flood surfaces and intertongue with overlying aeolian sandstones. The primary characteristics of ancient fluvial-aeolian deposition are overbank-interdune deposits and pronounced extensive erosion surfaces (flood surfaces), which are parallel to underlying fluvial sandstones and thus trend parallel to the palaeoslope and palaeohydrological gradient.     

Fine-grained barite in coal fly ash from the Upper Silesian Industrial Region

Barite nanocrystals are common and abundant in the troposphere over the Upper Silesian Industrial Region, Poland. The presence of barite nanocrystals is the result of burning Ba-enriched coals (up to 4,260 ppm Ba). ATEM, ASEM and EPMA analyses provided evidence of inefficient coal burning for domestic purposes at temperatures of 800-900 °C as the cause of emissions of barite, which survived unmelted. Much higher temperatures of coal burning for industrial purposes resulted in thermal decomposition of barite into BaO, which could react with airborne sulfuric acid to produce nanometre-sized secondary barite. Formation of both the secondary barite and gypsum in the troposphere contributes to the lowering of acidity of rain over Upper Silesia. Barite nanocrystals are often embedded in sheets of hydrocarbon materials with sizes in the range of respirable aerosols; therefore, they may enter the human respiratory system.     

The occurrence of gold in fly ash derived from high-Ge coal

We present the first data on the mode of occurrence of Au in fly ashes from the Wulantuga and Lincang power plants in China, which burn high-Ge coal. Gold occurs as fine-grained drop-like particles with a size of n*0.01–0.2 μm on the surface of the glass globules. These features of the Au particles are proof for Au condensation from the gas phase and deposition on the surface of fly ash in the cooler zone of the electrostatic precipitator and baghouse filter.     

Feasibility of using fly ash,lime, and bentonite to neutralize acidity of pore fluids

Acidic groundwater resulting from the poorly planned use of acid sulfate soils has become a major environmental issue in coastal Australia over the last several years. Use of permeable reactive barriers (PRBs) designed to generate alkalinity by promoting sulfate reduction has recently become popular as an alternative solution to this problem. However, recent studies have also revealed that the long-term performance of such PRBs can be significantly undermined by chemical precipitation and clogging of pore space, which would decrease the buffer capacity and hydraulic conductivity of the reactive material. This study seeks to explore the feasibility of using bentonite in addition to lime and fly ash to form mixtures with a high buffer capacity and permeability that would enable groundwater flow through PRBs over a substantial period of time. A series of laboratory experiments, including buffer capacity and leaching tests, were performed on different mixtures of fly ash with lime and bentonite using acidic fluids of low pH. It was found that the ability of such mixtures to neutralize acidic fluids was mostly controlled by the content of lime. Laboratory data also showed that an addition of bentonite to lime—fly ash mixtures could decrease the buffer capacity of soil. Compaction tests indicated that the presence of bentonite would increase the dry density of mixtures at the optimum moisture content. A series of hydraulic conductivity tests were carried out to study changes in the coefficient of permeability of lime—fly ash mixtures with different contents of bentonite permeated with acidic liquids. The obtained results revealed that the coefficient of permeability of the specimens tended to increase over a period of time, likely due to the changes in the diffuse double layer of bentonite particles.     

粉煤灰、粘土、膨润土等对Zn2+的吸附试验研究

研究了粉煤灰、粘土、膨润土等从溶液中去除有毒金属离子Zn2+的吸附过程。动态试验显示吸附过程是快速的。吸附试验结果表明,粉煤灰、膨润土对Zn2+的吸附能力相当,但远大于粘土、粉质粘土。平衡吸附模型充分说明,在高浓度下Zn2+在粉煤灰、粘土、粉质粘土上的吸附符合Langmuir等温线。试验结果亦表明,随着吸附剂中Zn2+含量的增加,粉煤灰等吸附剂对Zn2+吸附的百分率均呈减小的趋势。     

Particle size distribution and dissolution properties of metals in cyclone fly ash

The particles in the examined cyclone fly ash were all smaller than 0.25 mm. in diameter, and particles smaller than 0.075 mm. in diameter accounted for 88.4 % of the ash weight. This result indicates that cyclone fly ash consists of particles with a small diameter. The metals in the cyclone fly ash were enriched in small particles. The highest concentrations for zinc, copper, lead, cadmium and molybdenum in the cyclone fly ash were found in the smallest particle size fraction (< 0.075 mm.) and for Barium, chromium, nickel, Vanadium and Cobalt in the second to smallest particle size fraction (0.075-0.125 mm.). From an environmental and toxicological standpoint, the smallest particles are of the greatest concern when ash is handed at landfill disposal sites (transport and disposal especially in stormy weather conditions), and some studies have reported risks to workers from prolonged exposure to ash. The results of the comparison of various dissolution methods for metals showed that the digestion procedures with nitric acid alone (USEPA 3051) or with a mixture of nitric acid + hydrogen peroxide (USEPA 3050B) slightly underestimated the metal concentrations in the cyclone fly ash. Although the use of hydrofluoric acid is often necessary for the determination of a number of elements associated with siliceous minerals, its use can result in loss of trace elements during dissolution.     

Plerospheres and their role in reduction of emitted fine fly ash particles

Particles, less than PM10 in size, emitted from the stack of pulverized coal-fired power plants are of environmental concern since they can easily enter the human respiratory track. These fine particles are examined by Scanning Electron Microscope/Electron Dispersive Spectrometry （SEM/EDX）. Plerospheres are found in fly ash and are particles containing smaller particles formed during combustion of coal. The large plerospheres 〉50 μm mostly are present in ESP fly ash, indicating that they are effectively capturing fine particles and reducing their stack emission.     

利用高铝粉煤灰合成β-Sialon粉体的实验研究

在N2气氛中以粉煤灰为原料,采用碳热还原氮化工艺制备了β-Sialon粉体,研究了碳含量、合成反应温度、保温时间和氮气流量等因素对生成物物相的影响。在添加适量Al2O3、C含量23%、氮气流量2L/min、合成温度1450℃、保温时间为6h的条件下,可获得Z=3的纯晶相β-Sialon粉体,粒度均一,形态规则。β-Sialon粉体粒径在1～3μm之间,形态与结晶程度受合成条件影响。在不同的制备条件下,所合成的产物为β-Sialon和Al N、β-SiC、Si3N4、Al6Si2O13、O’-Sialon、α-Al2O3、Si O2等的混合物。并对高铝粉煤灰合成β-Sialon的反应过程进行了分析。     

Changes in mobility and speciation of heavy metals in clay-amended incinerator fly ash

The generation of municipal solid waste incinerator fly ash (MSWIF) has been increasing significantly over the recent past, and its disposal is problematic and costly due to high concentration of leachable heavy metals present in the material. This study explored a potential stabilization of MSWIF by blending with a natural sorbent material with low permeability, clay, and assessed the potential release of heavy metals from the stabilized mixtures under various simulated subsurface environments. The leachability of heavy metals such as Pb, Cd, Cr, Zn and Cu in the MSWIF-clay mixtures cured for 1 to 360 days was investigated by performing leaching tests and sequential chemical extractions (SCE). Leaching tests were performed at acidic, neutral and alkaline pH values. The leaching test results suggested that the natural clay could turn the MSWIF into non-hazardous material. All the MSWIF-clay mixtures demonstrated leaching behavior different from that of the original MSWIF. SCE results revealed that the acidic and reducing conditions were the most unfavorable to the immobilization of the heavy metals in the stabilized MSWIF-clay matrix. Conversely, the oxidizing and alkaline conditions were not critical to the stabilized MSWIF-clay mixtures. Apparently, clay in the mixtures could function as an adsorptive micro-barrier to retain the heavy metals within the MSWIF-clay matrices.