The leachability and chemical speciation of selected trace elements in fly ash from coal combustion and refuse incineration

A laboratory leaching test has been used to predict the potential mobility of As, Se, Pb and Cd in landfilled fly ash produced by coal combustion and refuse incineration. These waste residues also formed the basis of a speciation study in which the valency states of As and Se and the chemical forms of Pb and Cd have been determined. Selenium displayed the greatest leachability in each ash type, despite being present at relatively low concentrations in both materials. Substantial amounts of other trace elements were also leached, particularly Pb and Cd from refuse ash and As from coal ash. Chemical associations of Pb and Cd were examined by a sequential extraction procedure. In coal fly ash, both elements were mostly present in the residual fraction, while in refuse ash these elements were mainly associated with the exchangeable fraction. Water-soluble extracts of coal fly ash contained As exclusively as As(V); high background interference prevented the detection of water-soluble As in refuse ash. Selenium was present largely as Se(IV) in aqueous extracts of both ash types. The value of speciation techniques and leaching tests as predictors of environmental behaviour is discussed in conjunction with results of routine trace element determinations and plant uptake studies.     

Analysis of heavy metals in foliage near a modern refuse incinerator

Heavy metals such as cadmium and lead are typically found at high levels in fly ash from refuse incinerators. In two earlier studies it was found that such heavy metals on grass or tree foliage in the vicinity of old refuse incinerators with relatively low stacks and limited or no emission control devices showed a high degree of correlation between diminishing foliar concentration and the logarithm of sampling distance from the incinerator. In the study reported here of the concentration of cadmium and lead on foliage near a modern refuse incinerator with a high stack and efficient emission controls, the foliar concentrations of the metals showed no significant diminution with sampling distance from the incinerator. Factors affecting heavy metal emissions from refuse incinerators and contamination of nearby areas are discussed.     

Emissions of Chlorinated Organics from Two Municipal Incinerators in Ontario

In this paper the results of sampling for trace chlorinated organics at two municipal refuse incinerators in Ontario are presented. The information may be of Interest to individuals concerned with the assessment of PCDD/PCDF (polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran) emissions from incineration of refuse and their impact on the energyfrom- waste program. PCDDs, PCDFs, PCBs (polychlorinated biphenyls), CBs (chlorobenzenes) and CPs (chlorophenols) were quantified in all process streams including refuse, ash and stack emissions. Manual sorting of refuse and collection of ash samples were carried out simultaneously with three 24-hour continuous stack sampling tests at each plant. The results suggested that the total output of PCDDs and PCDFs varied proportionately with their input at both incinerators. However, the input of PCDDs/PCDFs could not account for their total output. The chemistry of PCDDs/PCDFs in the input and output streams were different in that only heptachlorinated and octachlorinated species were present in significant quantities in the refuse while lower chlorinated species were predominant in stack emissions and ash streams. There was no correspondence between the Input of PCBs/CBs/CPs and the output of PCDDs/PCDFs. The output of PCDDs/PCDFs, however, varied Inversely with the total output of PCBs/CBs/CPs, suggesting that the latter compounds could have been partially responsible for the formation of PCDDs and PCDFs. The PCDF emissions were also affected by combustion conditions; they were higher in magnitude and consisted of predominantly tetrachlorinated and pentachlorinated species at the plant where the combustion temperatures were lower.     

The Sulfur Balance of Incinerators

Municipal refuse usually contains only 0.10-0.15% sulfur. During combustion a minor fraction of the sulfur is released as SO₂, while the major fraction is fixed in the ash, which contains alkaline oxides. Contrasted with coal and heavy fuel oil, municipal refuse is a minor to negligible source of SO₂ air pollution.     

Ash from the combustion of wood treated with inorganic wood preservatives: Element composition and leaching

Wood samples impregnated with inorganic wood preservatives containing the elements arsenic, boron, chromium, copper, fluorine, and/or zinc were burned in a furnace. Three different kinds of ash were collected: furnace, boiler, and so-called fly ash. Analyses showed that the ash contained large amounts of elements originating from the inorganic wood preservatives. Further interest was focused on the leachability of the above-mentioned elements. For this purpose a laboratory batch leaching test according to the German Standard DIN 38 414 part 4 was chosen. The results indicate that the leachability is in a range where the release of these elements to the environment from deposited ash can be considered as detrimental.     

污泥焚烧底灰中重金属残留特性的实验研究

利用原子吸收分光光度计和程序控制温升炉研究了沈阳市污水处理厂污泥在不同焚烧工况下重金属Cu、Cr、Cd、Zn、Ni和Pb在焚烧底灰中的残留特性。考察了升温速率、焚烧温度、含水率以及停留时间等因素对重金属在污泥底灰中的残留特性的影响。实验表明 ,Pb、Cd和Cu在灰渣中的残留率随着温度和停留时间的增加而降低。大部分的重金属元素Zn、Cu和Cr残留在灰渣中 ,Cd、Pb和Ni部分残留在灰渣中     

不同粒度飞灰中16种微量元素的含量分布

研究了不同粒级的燃煤飞灰中的Ｂａ、Ｂｅ、Ｃｄ、Ｃｒ、Ｃｕ、Ｈｇ、Ｌｉ、Ｍｎ、Ｎｉ、Ｐｂ、Ｓｒ、Ｔｉ、Ｖ、Ｚｎ、Ｚｒ元素的含量分布,煤中元素的含量比及富集因子。     

Utilization of coal fly ash as a slow-release granular medium for soil improvement

This work proposes a new potential application of waste coal fly ash as a K fertilizer support. Fly ash was reacted with KOH to facilitate the impregnation of K as well as to enhance the bonding force. In particular, the applied process resulted in a significant slow-releasing characteristic of fertilizer elements. To examine the effect of K impregnation, a few detailed leaching tests were carried out in terms of process variables such as reaction time and temperature, sintering time and temperature, and KOH concentration. The current experiment presented an optimum preparation condition that is competitive with conventional commercial fertilizers. The manufactured ash fertilizers inhibited release of the K elements. It was also found through the continuous leaching test with pure water that the ash fertilizer had excellent moisture absorbability. However, the effects of some trace elements in fly ash on soil health and crop productivity as well as environmental considerations need to be established with long-term studies.     

Time-resolved leaching of cadmium and manganese from lignite and incinerator fly ash

Fly ashes from a lignite fired power plant and a municipal incinerator were leached for 3 hours using 0.1N HC1. Leachate was analyzed for Cd and Mn and plots of concentration versus time for these elements show Cd, a surface adsorbed element in the combustion process, to be rapidly removed from the ash particles in the initial four or five minutes of leaching. Manganese, a fly ash matrix element, is leached at a more constant rate as the ash praticles are dissolved. Total Cd and Mn concentrations in the incinerator fly ash are greater than total concentrations of these elements in the lignite fly ash.     

Trace Element Inputs from a Coal Burning Power Plant to Adjacent Terrestrial and Aquatic Environments

Inputs of trace elements derived from coal ash to terrestrial and aquatic environments were investigated near an 83 MW coal-burning power plant. Comparisons were made between terrestrial inputs of trace elements through aerial deposition during 23 years before installation of electrostatic precipitators and aquatic inputs from ash disposal basins after installation. A gaussian plume model was used to predict deposition patterns of 29 trace elements in coal ash about the power plant. Detectable increases of only Sr, As, Sb, and Be in surface soils within 3 km of the power plant were predicted. Concentrations measured in surface soils were largely consistent with these predictions. Measurements of aerial deposition of Cd, Pb, Cu, and Mn at a site 5.5 km distant were similar to those in other rural areas and indicated that little of the measured Cd, Cu, Mn, or Pb was derived from fly ash. Concentrations of 12 heavy metals in effluents from the basin receiving ash were comparable to those predicted in rainfall deposited nearest the plant. It is concluded that at other coal combustion facilities, basin disposal could be a more serious contamination threat to aquatic environments than aerial dispersal of ash.     

Pretreatment of automobile shredder residue (ASR) for fuel utilization

Automobile shredder residue (ASR) was pretreated to improve its quality for fuel utilization. Composition analysis revealed that ASR components could be classified into four groups: (1) urethane and textile-light fraction and combustibles containing low levels of ash and Cl; (2) plastics and rubber-light or heavy fraction and combustibles containing high levels of Cl; (3) metals and electrical wire-heavy fraction and incombustibles, and (4) particles smaller than 5.6mm with high ash contents. Based on these results, we successively performed sieving to remove particles smaller than 5.6mm, float and sink separations to reject the heavy fraction and plastics and rubber containing Cl, thermal treatment under an inert atmosphere to remove Cl derived from PVC, and char washing to remove soluble chlorides. This series of pretreatments enabled the removal of 78% of the ash and 91% of the Cl from ASR. Sieving using a 5.6-mm mesh removed a considerable amount of ash. Product quality was markedly improved after the float and sink method. Specifically, the sink process using a 1.1 g cm(-3) medium fluid rejected almost all rubber containing Cl and a large amount of PVC. The remaining Cl in char, after heating at 300 degrees C under an inert atmosphere and washing, was considered to be present as insoluble chlorides that volatilized at temperatures above 300 degrees C. Based on a tradeoff relationship between product quality and treatment cost, ASR may be utilized as a form of refuse plastic fuel or char.     

Trace metal emissions from co-combustion of refuse derived and packaging derived fuels in a circulating fluidized bed boiler

Energy recovery from refuse derived fuels (RDF) and packaging derived fuels (PDF) is one option in integrated waste management. Nine RDF and PDF co-combustion tests with peat and coal in a circulating fluidized bed boiler were carried out in this work. Heavy metal emissions in flue gas and fly ash were measured. Multivariate data analyses were used to find out the most important parameters affecting metal emissions in the flue gas.

The results showed that total heavy metal emissions were low. Although RDF and PDF had more heavy metals than peat and coal, the multivariate data analysis showed that an increase of the RDF or PDF share in the fuel mixture up to 20% did not correlate directly with the metal emissions in the flue gas. Distribution of Cd, Cu, Zn and Sn between flue gas and fly ash correlated with each other. Injection of limestone to bind sulphur and chlorine did not have a significant effect on heavy metal emissions in the flue gas. Heavy metals concentrated on the fly ash, but all fly ashes passed the EPA-TCLP tests.     

Aerosol composition and sources in Urban areas in India

The elemental composition of aerosols over four cities in India was determined by EDXRF over a 1-year period and the results are presented. The crustal element levels in air in all the cities are found to be similar to those reported for urban areas elsewhere in the world while that of anthropogenic elements are lower. The aerosol compositions show a seasonal variation. The levels of crustal elements are higher during summer and decrease with rainfall. The anthropogenic elements are generally higher during winter. The lead levels are essentially from non-auto exhaust sources such as refuse burning, smelter etc., and in three of the cities they are strongly correlated to zinc. The crustal elements are from local soils and no significant crust-air fractionation is seen. Factor analysis of the data suggests between four and six aerosol source types for the four cities. Soil dust accounts for the major fraction of the measured mass. About 68–80 % of the aerosol mass comprising the residuals seems to consist of C, O₂ and N, in particular, which were not measured.     

The national incinerator testing and evaluation program two-stage incinerator combustion tests

In this paper the summary results of tests conducted at the P.E.I. energy-from-waste facility, a two-stage incinerator, are presented. Extensive data on refuse feed, ash, emissions and operating conditions will provide the most significant body of information yet available for energy from waste facilities.     

Immobilization of heavy metals in polluted soils by the addition of zeolitic material synthesized from coal fly ash

The use of zeolitic material synthesized from coal fly ash for the immobilization of pollutants in contaminated soils was investigated in experimental plots in the Guadiamar Valley (SW Spain). This area was affected by a pyrite slurry spill in April 1998. Although reclamation activities were completed in a few months, residual pyrite slurry mixed with soil accounted for relatively high leachable levels of trace elements such as Zn, Pb, As, Cu, Sb, Co, Tl and Cd. Phytoremediation strategies were adopted for the final recovery of the polluted soils. The immobilization of metals had previously been undertaken to avoid leaching processes and the consequent groundwater pollution. To this end, 1100 kg of high NaP1 (Na6[(AlO2)6(SiO2)10] .15H2O) zeolitic material was synthesized using fly ash from the Teruel power plant (NE Spain), in a 10 m3 reactor. This zeolitic material was manually applied using different doses (10000-25000 kg per hectare), into the 25 cm topsoil. Another plot (control) was maintained without zeolite. Sampling was carried out 1 and 2 years after the zeolite addition. The results show that the zeolitic material considerably decreases the leaching of Cd, Co, Cu, Ni, and Zn. The sorption of metals in soil clay minerals (illite) proved to be the main cause contributing to the immobilization of these pollutants. This sorption could be a consequence of the rise in pH from 3.3 to 7.6 owing to the alkalinity of the zeolitic material added (caused by traces of free lime in the fly ash, or residual NaOH from synthesis).     

不同改性剂改善污泥土工性质的比较研究

选择了泥土、矿化垃圾、粉煤灰和建筑垃圾4种改性剂改性城市污水处理厂污泥(以下简称污泥)。结果表明:(1)随着4种改性剂与污泥的混合比增大,混合物含水率降低。(2)当混合比为0.7(质量比)时,各种混合物的抗压强度都达到50kPa的填埋要求;当混合比为0.3～1.0时,混合物的抗压强度随着混合比的增大呈指数形式增大;比较4种改性剂对抗压强度的增大能力,粉煤灰最强,建筑垃圾次之,泥土和矿化垃圾较弱。(3)在50kPa预压力下,混合物要达到不小于25kPa的抗剪强度,泥土与污泥最小混合比为1.0,矿化垃圾与污泥最小混合比为1.0,粉煤灰与污泥最小混合比为0.7,建筑垃圾与污泥最小混合比为0.7。(4)除加泥土的混合物外,混合物压缩系数随着混合比的增大呈总体下降趋势。(5)粉煤灰除臭效果最好,矿化垃圾次之,建筑垃圾较差,泥土最差。     

Effects of soil amendments at a heavy loading rate associated with cover crops as green manures on the leaching of nutrients and heavy metals from a calcareous soil

The potential risk of groundwater contamination by the excessive leaching of N, P and heavy metals from soils amended at heavy loading rates of biosolids, coal ash, N-viro soil (1:1 mixture of coal ash and biosolids), yard waste compost and co-compost (3:7 mixture of biosolids to yard wastes), and by soil incorporation of green manures of sunn hemp (Crotalaria juncea) and sorghum sudangrass (Sorghum bicolor x S. bicolor var. sudanense) was studied by collecting and analyzing leachates from pots of Krome very gravelly loam soil subjected to these treatments. The control consisted of Krome soil without any amendment. The loading rate was 205 g pot(-1) for each amendment (equivalent to 50 t ha(-1) of the dry weight), and the amounts of the cover crops incorporated into the soil in the pot were those that had been grown in it. A subtropical vegetable crop, okra (Abelmoschus esculentus L.), was grown after the soil amendments or cover crops had been incorporated into the soil. The results showed that the concentration of NO3-N in leachate from biosolids was significantly higher than in leachate from other treatments. The levels of heavy metals found in the leachates from all amended soils were so low, as to suggest these amendments may be used without risk of leaching dangerous amounts of these toxic elements. Nevertheless the level of heavy metals in leachate from coal ash amended soil was substantially greater than in leachates from the other treatments. The leguminous cover crop, sunn hemp, returned into the soil, increased the leachate NO3-N and inorganic P concentration significantly compared with the non-legume, sorghum sudangrass. The results suggest that at heavy loading rates of soil amendments, leaching of NO3- could be a significant concern by application of biosolids. Leaching of inorganic P can be increased significantly by both co-compost and biosolids, but decreased by coal ash and N-viro soil by virtue of improved adsorption. The leguminous cover crop, sunn hemp, when incorporated into the soil, can cause the concentration of NO3-N to increase by about 7 fold, and that of inorganic P by about 23% over the non-legume. Regarding the metals, biosolids, N-viro soil and coal ash significantly increased Ca and Mg concentrations in leachates. Copper concentration in leachate was increased by application of biosolids, while Fe concentration in leachates was increased by biosolids, coal ash and co-compost. The concentrations of Zn, Mo and Co in leachate were increased by application of coal ash. The concentrations of heavy metals in leachates were very low and unlikely to be harmful, although they were increased significantly by coal ash application.     

Environmental impact of a coal combustion-desulphurisation plant: abatement capacity of desulphurisation process and environmental characterisation of combustion by-products

The fate of trace elements in a combustion power plant equipped with a wet limestone flue gas desulphurisation (FGD) installation was studied in order to evaluate its emission abatement capacity. With this aim representative samples of feed coal, boiler slag, fly ash, limestone, FGD gypsum and FGD process water and wastewater were analysed for major and trace elements using the following techniques: inductively coupled plasma-mass spectrometry (ICP-MS), inductively coupled plasma-atomic emission spectrometry (ICP-AES), ion chromatography (IC), ion selective electrode (ISE) and atomic absorption spectroscopy (AAS). Mass balances were established allowing to determine the element partitioning behaviour. It was found that, together with S, Hg, Cl, F, Se and As were those elements entering in the FGD plant primarily as gaseous species. The abatement capacity of the FGD plant for such elements offered values ranged from 96% to 100% for As, Cl, F, S and Se, and about 60% for Hg. The environmental characterisation of combustion by-products (boiler slag, fly ash and FGD gypsum) were also established according to the Council Decision 2003/33/EC on waste disposal. To this end, water leaching tests (EN-12457-4) were performed, analysing the elements with environmental concern by means of the aforementioned techniques. According to the leaching behaviour of combustion by-products studied, these could be disposed of in landfills for non-hazardous wastes.     

基于集装化外运与综合型处理的上海城市生活垃圾管理对策

分析了上海市区生活垃圾收运处理现状与问题,借鉴国外特大城市生活垃圾收运处理管理经验和教训,提出了将现有垃圾水运系统升级改造为集装化水陆联运系统、将现有老港废弃物处置场扩建为生活垃圾分类、生化处理、焚烧发电、填埋等多种技术有机组合的综合型处理基地的方案,为改善上海市生活垃圾收运与处理处置系统提出可行的对策建议.     

Growth and metal accumulation in vetiver and two Sesbania species on lead/zinc mine tailings

The lead (Pb)/zinc (Zn) tailings contained high concentrations of heavy metals (total Pb, Zn, Cu and Cd concentrations 4164, 4377, 35 and 32 mg kg(-1), respectively), and low contents of major nutrient elements (N, P, and K) and organic matter. A field trial was conducted to compare growth performance, metal accumulation of Vetiver (Vetiveria zizanioides) and two legume species (Sesbania rostrata and Sesbania sesban) grown on the tailings amended with domestic refuse and/or fertilizer. It was revealed that domestic refuse alone and the combination of domestic refuse and artificial fertilizer significantly improved the survival rates and growth of V. zizanioides and two Sesbania species, especially the combination. However, artificial fertilizer alone did not improve both the survival rate and growth performance of the plants grown on tailings. Roots of these species accumulated similar levels of heavy metals, but the shoots of two Sesbania species accumulated higher (3-4 folds) concentrations of Pb, Zn, Cu and Cd than shoots of V. zizanioides. Most of the heavy metals in V. zizanioides were accumulated in roots, and the translocation of metals from roots to shoots was restricted. Intercropping of V. zizanioides and S. rostrata did not show any beneficial effect on individual plant species, in terms of height, biomass, survival rate, and metal accumulation, possibly due to the rather short experimental period of 5 months.