Removal of selected heavy metals from MSW fly ash by the electrodialytic process

This paper aims to assess the applicability of the electrodialytic remediation technique for the removal of zinc, lead, copper and cadmium from municipal solid waste (MSW) incinerator fly ash. A broad range of experimental conditions were studied including current densities, remediation times, use of assisting agents and cell design.

Several operational problems were identified during the electrodialytic experiments, among which are formation of precipitates, dryness of sample and partial dissolution of sample creating preferential pathways for the electric current. These problems may explain the low remediation efficiencies obtained.

Comparison between experiments showed that generally the use of Na-gluconate as assisting agent leads to better results than distilled water. Increasing the concentration of the assisting agent also results in higher removals.     

Evaluating the environmental risks associated with the use of chromated copper arsenate-treated wood products in aquatic environments

Chromated copper arsenate (CCA)-treated wood has been used worldwide since 1933. In properly fixed wood, the chromium, copper, and arsenic are tightly bound to the wood fibers. However, it has long been known that small amounts of these metals do leach from properly treated wood products. These metals, particularly the cupric ion (Cu²⁺), are known to be highly toxic to aquatic organisms at concentrations as low as 6 μg Cu l^?1. The United States Environmental Protection Agency has established a marine water quality standard of 2.9 μg Cu l^?1 total copper. Washington State has established a marine water quality standard of 2.5 μg Cu l^?1 and a marine sediment standard of 390 mg Cu g^?1 (dry sediment). Comparison of these standards with the results of bioassays suggests that these levels are sufficiently low to protect even the most sensitive organisms. Metal losses are an inverse function of time and decline to background levels within 60–90 d of treated wood immersion. Increasing use of CCA-treated wood to construct residential bulkheads in estuarine environments on the east coast of the United States has raised concerns regarding the near-term environmental risks associated with these uses. This paper reports the development of a spreadsheet-based computer model to predict water column and sediment concentrations of copper leached from bulkheads and piling. Model output is compared with data in Weis et al. (1991, 1993) and Weis and Weis (1992). The model predicts environmental levels of copper that are highly dependent on input parameters but below regulatory levels for most projects constructed in reasonably well-circulated bodies of water. The model does demonstrate the possibility of exceeding regulatory standards for up to 3 wk when bulkheads are installed in very poorly flushed aquatic environments or where the surface area of the CCA-treated wood structure is a significant proportion of the water body surface area.     

Test of experimental set-ups for electrodialytic removal of Cu, Zn, Pb and Cd from different contaminated harbour sediments

Electrodialytic removal of heavy metals from different harbour sediments was investigated. Electrodialytic remediation experiments in laboratory scale were made with calcareous and non-calcareous harbour sediments. Two different experimental set-ups were used for the study, one with stirring of the sediment slurry, the other without stirring. The removal of heavy metals was highest in the non-calcareous sediment, where 94% Cd, 91% Zn and 73% Cu were removed after 24 days. The highest removal obtained for the calcareous sediment was 81% Cd, 76% Zn, 75% Pb and 53% Cu after 21 days, with stirred sediment slurry. Electrodialytic experiments without stirring of calcareous sediment gave high removals (84% Zn, 58% Pb and 48% Cu), but there were problems with precipitations in the sediment, which limited the removal. The stirred experiments gave the highest removals of heavy metals and the voltage was the most stable in these experiments, and thus, the stirred set-up is the best choice for experimental set-up. The order in which the heavy metals were removed from the harbour sediments was Cd>Zn>Pb>Cu.     

Case study on the strategy and application of enhancement solutions to improve remediation of soils contaminated with Cu, Pb and Zn by means of electrodialysis

Numerous studies have been conducted with electrochemical removal of heavy metals from spiked kaolinite. Meanwhile, when moving from kaolinite to real soils, new factors must be taken into account—factors influencing, e.g., the buffering capacity of the soil against acidification and the adsorption/desorption processes of the heavy metals. The present study gives some examples where it is necessary to use an enhancement solution to aid desorption of Cu, Zn and Pb during electrodialytic treatment. Dependent on the composition of the pollution, different choices can be made. In the case of a Cu-polluted calcareous soil, ammonia may be used as enhancement solution, due to the formation of charged complexes between ammonia and Cu. Thus, Cu is mobile at high pH when ammonia is added and Cu can be removed without dissolving the calcareous parts. Zn is also mobilized by ammonia, but to a lesser extent than Cu. In the case of Cu, Zn and Pb at the same time, alkaline ammonium citrate may be a solution. It was shown that this enhancement solution could mobilize these three pollutants, but optimization of concentration and pH of the ammonium citrate is still needed. When choosing a remediation scheme for electrochemical treatment of an actual industrially polluted soil, this scheme must be chosen on basis of characterization of soil and pollution combination.     

Spatial variability of soils and stream sediments and the remediation effects in a Portuguese uranium mine area

The old Senhora das Fontes uranium mine, located in central Portugal, was closed down in 1971. The treatment of ores from this mine and other mines by heap-leach ended in 1982. Seven dumps partially covered by vegetation were left in the area. Soil and stream sediment samples were collected in December 2009. The remediation was carried out from May 2010 to January 2011. Stream sediment samples were collected again in October 2013. Before the remediation, soils from inside the mine influence area have higher Al, As, Co, Cr, Cu, Fe, Ni, Sr, Th, U and Zn concentrations than soils from outside this area, due to radionuclides, metals and metalloid released from the mine dumps. The principal component analysis (PCA) shows a distinction between soils from inside and outside the mine influence area. The U(VI), As(V) and metals from soils can be adsorbed to Fe-oxyhydroxides and the humic acid can increase the U uptake. Soils must not be used for public or private green and residential areas, because they are contaminated in U, As, Co, Cd and Ni. Before the remediation, downstream sediments have higher Al, As, Cu, Mn, Ni, Pb, U and Zn than upstream sediments, due to erosion and percolation of water through the mine dumps. The PCA shows a distinction between downstream and upstream sediments. The U(VI), Th and As(V) can be adsorbed to Fe-oxyhydroxides. The stream sediments are contaminated in As, Mn, Th and U. Downstream sediments are the most contaminated in U and As. After the remediation, upstream and downstream sediments have generally higher Al, Fe, As, Cr, Ni, Th, U and Zn concentrations than before the remediation, attributed to the relocation of dumps. Radionuclides, metals and metalloids were transported by surface water. Consequently downstream sediments have higher Al, As, Cu, Mn, Ni, Th, U and Zn concentrations than upstream sediments. The U(VI), Th and As(V) can be adsorbed to Fe-oxyhydroxides. Stream sediments became more contaminated in U, Th and As than before the remediation, but more intensively downstream.     

珠江口西部海域表层沉积物重金属元素多尺度空间变化特征

笔者应用因子克里格分析方法,研究了珠江口西部海域388个表层沉积物中7种重金属元素Cd, Ni,Cu,Zn,Pb,Cr和As的空间结构特征,识别并分离了重金属元素不同尺度的空间主成分及其分布特征,探讨了不同空间尺度重金属的物源及控制因素。结果显示,研究区7种重金属元素在空间上存在块金尺度、局部尺度(变程为60 km的球状结构)和区域尺度(变程为160 km的球状结构)3种尺度的空间变化。以迭代算法模拟了研究区重金属元素线性协同区域化模型。根据不同尺度上区域化因子的主成分得分分布特征可知:局部尺度上,F₁因子(Zn,Cr,Ni,Cu)和F₂因子(As)的高值区表现为"牛眼"状局部特征,并分布在陆地沿海的河口或者港湾区,指示了可能受人为污染成分影响的重金属区域。其中,雷州半岛东部沿海是最可能的重金属污染区,其空间分布主要受控于局部的地形、海流等因素。F₂因子不同于F₁的空间分布,主要在于As不同于Zn,Cr,Ni,Cu等的地球化学行为。区域尺度上,F₁(Zn,Cr,Ni)和F₂(As)因子主要反映了不同陆源母岩物质的影响。Zn,Cr,Ni等主要源于华南大陆陆源母岩物质,而As主要受到海南岛陆源母岩物质的控制。F₁和F₂因子得分高值区整体上表现为NNE向自陆地向较深海域延伸的"片状"分布特征,推测其主要受到海平面变化及NNE向区域性海洋环流的控制。     

湖南水口山多金属矿区废石堆重金属污染评价及赋存形态分析

湖南水口山及周边是湖南省重金属污染较为严重的地区之一,龙王山金矿床是该区中部的一个重要金矿床.为调查该矿床废石堆污染状况、是否为周边环境的污染源、污染途径、重金属迁移能力和潜在的危害,对矿区FS17废石堆进行了自然淋滤水和24 m浅钻系统取样,开展重金属元素总量分析,利用单因子指数法和内梅罗综合污染指数法对其重金属污染程度进行污染评价,采用四步改良BCR提取法分析废石堆中8种重（类）金属元素（Pb、Zn、Cd、Cu、Cr、Ni、As和Fe）的赋存形态,并利用迁移指数量化废石堆重金属元素迁移能力;发现废石堆中Cd、Cu、Pb、As、Zn、Ni重金属元素严重超标,且在垂向上分布极不均匀;其自然淋滤水样中重金属元素Cd、Ni、Zn、Cu也严重超标;废石堆浅层重金属元素潜在迁移能力顺序为:Cd＞Ni≈Zn＞Cu＞Pb＞As＞Cr＞Fe,深层重金属元素迁移能力顺序为:Cd＞Zn＞Cu＞Ni＞Cr＞Pb＞As＞Fe,浅层重金属元素的迁移性大于深层;说明该废石堆重金属元素含量高,是周围环境重要污染源,酸性废水排放为其释放污染元素的主要途径;Cd、Cu、Zn、Ni迁移能力强,是周围环境的主要污染元素;Pb、Ni、As的迁移性在深层明显降低,可以通过埋深来削弱其迁移性,而Cr不会对周边环境产生污染.      

Spatio-temporal trends of heavy metals and source apportionment in Tolo Harbour,Hong Kong

This study provided a picture of the spatial and temporal distributions of Cr, Co, Ni Cu, Zn, As, Cd and Pb in bottom sediments of Tolo Harbour. The concentrations of the eight heavy metals differed significantly between sites due to the poor tidal flushing in Tolo Harbour. The levels of Cu, Zn, Cd and Pb were generally enriched in sediments from inner Tolo Harbour, while sediments from outer Tolo Harbour (Tolo Channel) had higher levels of Cr, Co and Ni. The redox sensitive element arsenic showed no distinct spatial pattern in Tolo Harbour. The decreasing levels of Cu, Zn, Pb and Cd in sediments with increasing distance from land demonstrated a typical diffusion pattern from land to the direction of sea. Two hot spots of Cu, Zn, Pb and Cd in sediments were located near Tai Po and Sha Tin new town, indicating that Cu, Zn, Pb and Zn were from land-derived sources. The sites with relatively high levels of Cr, Co and Ni in sediments were located in areas close to waste spoil in sea floor. The natural and anthropogenic inputs from Sha Tin and Tai Po to Tolo Harbour were mostly responsible for Cu, Zn, Cd and Pb enrichment in sediments from inner Tolo Harbour. The waste spoil in sea floor was believed to contribute to the Cr, Co and Ni in outer Tolo Harbour. The results of correlation coefficient between the eight heavy metals showed that Cu, Zn, Cd and Pb were strongly positively correlated, and Cr, Co and Ni were also significantly correlated with each other. The best explanation of strong correlation was their similar source. As, however, is not well correlated with the other seven heavy metals. The average concentrations of Cu and Zn displayed general increasing trends from 1978 to 2006 in Tolo Harbour, while the mean levels of Cr and Pb displayed a substantial decrease from 1978 to 1987, then a slight increase after 1987. No distinct temporal trends of the concentrations of Ni and As were observed from 1978 due to the inconsecutive data. On the other hand, the increasing trends of Cr, Cu, Zn, Cd and Pb were observed since 1996.     

Spatial and temporal variability of surface water and groundwater before and after the remediation of a Portuguese uranium mine area

The old Senhora das Fontes uranium mine, in central Portugal, consists of quartz veins which penetrated along fracture shear zones at the contact between graphite schist and orthogneiss. The mine was exploited underground until a depth of 90 m and was closed down in 1971. The ores from this mine and two others were treated in the mine area by the heap-leach process which ended in 1982. Seven dumps containing a total of about 33,800 m³ of material and partially covered by natural vegetation were left in the mine area. A remediation process took place from May 2010 to January 2011. The material deposited in dumps was relocated and covered with erosion resisting covers. Surface water and groundwater were collected in the wet season just before the remediation, in the following season at the beginning of the remediation and also after the remediation in the following dry season. Before, at the beginning and after the remediation, surface water and groundwater have an acid-to-alkaline pH, which decreased with the remediation, whereas Eh increased. In general, before the remediation, uranium concentration was up to 83 μg/L in surface water and up to 116 μg/L in groundwater, whereas at the beginning of the remediation it increases up to 183 μg/L and 272 μg/L in the former and the latter, respectively, due to the remobilization of mine dumps and pyrite and chalcopyrite exposures, responsible for the pH decrease. In general, after the remediation, the U concentration decreased significantly in surface water and groundwater at the north part of the mine area, but increased in both, particularly in the latter up to 774 μg/L in the south and southwest parts of this area, attributed to the remobilization of sulphides that caused mobilization of metals and arsenic which migrated to the groundwater flow. Uranium is adsorbed in clay minerals, but also in goethite as indicated by the geochemical modelling. After the remediation, the saturation indices of oxyhydroxides decrease as pH decreases. The remediation also caused decrease in Cd, Co, Cr, Ni, Pb, Zn, Cu, As, Sr and Mn concentrations of surface water and groundwater, particularly in the north part of the mine area, which is supported by the speciation modelling that shows the decrease of most dissolved bivalent species. However, in general, after the remediation, Th, Cd, Al, Li, Pb, Sr and As concentrations increased in groundwater and surface water at south and southwest of the mine area. Before and after the remediation, surface water and groundwater are contaminated in U, Cd, Cr, Al, Mn, Ni, Pb, Cu and As. Remediation caused only some improvement at north of the mine area, because at south and southwest part, after the remediation, the groundwater is more contaminated than before the remediation.     

Heavy metal pollution and acid drainage from the abandoned Balya Pb-Zn sulfide Mine,NW Anatolia,Turkey

This study was conducted to determine the effects of the waste-rock dump (WRD) of the underground polymetallic Balya Mine on the Kocacay River and eventually on Lake Manyas in Turkey. Data presented in this paper include geochemical characteristics of various kinds of water (mine, surface and groundwater) and of suspended-particle samples in the vicinity of Balya. The more polluted mine waters have low pH and high conductivity, while high concentrations of Zn, Cd, Mn tend to be found in the dry and wet seasons. High concentrations of Pb, As, Cr, Cu and S appear only in the wet season. The sources of the heavy metal concentration within the Kocacay River are leached waste, surface run off, and overflow from the spillway of the WRD. To minimize the formation of acids and dissolved metal, and for the remediation of the harmful effects of extreme contamination conditions, it is recommended that lime or alkali materials and organic carbon be added to simulate the action of sulfate-reducing bacteria.     

Application of the Haug model for process design of petroleum hydrocarbon-contaminated soil bioremediation by composting process

The main scope of this work is applying an aerobic composting model for remediation of petroleum hydrocarbon-contaminated soil. For this purpose, the reaction kinetics was integrated with the mass and energy balances over the composting system. Literature pilot scale data for bioremediation of diesel oil-contaminated soil was used for model validation. Comparisons of simulation results with experimental data for diesel concentration and oxygen concentration showed good agreement during the remediation process. With validated model for bioremediation of diesel oil-contaminated soil, the influence of amendment type, bulking agent, amendment/soil ratio, bulking agent/soil ratio, moisture content and airflow rate were investigated on diesel biodegradation. The simulation results showed that maximum degradation of diesel occurred in the presence of yard waste as amendment. Furthermore, addition of bulking agent (wood chips) increased the diesel degradation about 6 %. In presence of yard waste as amendment and wood chips as bulking agent, the optimal values for maximum remediation were amendment/soil ratio (2.5 kg kg^?1), bulking agent/soil ratio (2.25 kg kg^?1), initial moisture content (62.5 %) and airflow (0.520 m³ day^?1 kgBVS^?1).     

AB-DTPA提取法在重金属污染土壤修复模拟试验中的应用可行性

将碳酸氢铵-二乙三胺五乙酸(AB-DTPA)提取重金属生物有效态的方法应用于重金属污染土壤修复的模拟试验中,该土壤的污染元素主要是铜、锌和镉,试验所用修复材料是钠化膨润土。研究表明,AB-DTPA提取法具有很好的稳定性,而且能准确指示铜、锌、镉元素在土壤中的有效态含量,同时AB-DTPA对土壤中铜、锌、镉元素的提取率也适用于模拟试验中修复效果的平行对比。AB-DTPA提取法在重金属污染土壤修复模拟试验中的应用是可行的。     

重金属污染的菊芋茎秆沼气化性能及蓄积重金属的归趋

利用菊芋(Helianthus tuberosus)进行重金属污染土壤修复会产生大量秸秆废弃物,通过厌氧消化将其转化为沼气,是其资源化利用途径之一。为了评估该处置技术的环境风险,实验以重金属污染土壤种植的菊芋茎秆为对象开展厌氧消化研究,对其产气性能、重金属形态变化、可迁移能力及生物有效性进行评估。结果表明,菊芋秸秆中茎主要重金属(Cu,Zn,Pb,Cr,Cd)含量为5.69×10^-6,19.19×10^-6,0.23×10^-6,0.33×10^-6,0.50×10^-6,叶中的含量分别为9.11×10^-6,23.83×10^-6,0.57×10^-6,0.43×10^-6,0.48×10^-6相对与根与块茎较较高;菊芋秸秆厌氧发酵总产气量为206.58 ml·g^-1 TS,显示产气潜力良好;厌氧消化后,Cu,Pb和Cr的重金属可迁徙因子值低,相对比较稳定,迁移能力较弱。Cr和Cd的生物可利用度减小,其中Cr大幅度减小了41.54%,Cd减小了12.30%,说明厌氧消化能有效降低Cr和Cd的生物可利用度,减小对环境的危害。但Pb的生物有效性大幅度上升,应在沼渣管控环节关注。     

Contaminant removal from acidic mine pit water via in situ hydrotalcite formation

Remediation of 56 ML of acidic, contaminant-laden Baal Gammon mine pit water was undertaken using in situ hydrotalcite formation. The pit water composition was modified via the addition of MgCl₂·6H₂O to form a 2.5:1 M²⁺:M³⁺ metal ion ratio followed by the addition of NaOH to increase the pH 10 to induce spontaneous hydrotalcite precipitation. As a result of the in situ hydrotalcite precipitation a broad spectrum of elements of environmental concern including Al, Cd, Co, Cr, Cu, Fe, In, Mn, Mo, Ni, V and Zn were removed from solution. Significantly, an ore grade hydrotalcite precipitate containing Cu (8.0 ± 1.0%) and Zn (3.9 ± 0.5%) was produced directly from the mine pit water column allowing for potential recovery of valuable metals to offset remediation costs. The final water quality produced after in situ remediation was of a simple Na–Cl–SO₄ type.     

Remediation of metal-contaminated soil in polar environments: Phosphate fixation at Casey Station,East Antarctica

Remediation of metal-contaminated soils by phosphate fixation is successful in temperate environments, whereas its efficacy in cold and freezing environments is understudied. Phosphate fixation is a low-cost technique and is potentially very useful in these remote environments where the logistics of remediation are difficult and expensive. Here we describe a field study at Casey Station, East Antarctica, where phosphate (triple superphosphate and phosphate rock) and a buffer, Emag (magnesium carbonate and magnesium oxide), were introduced to contaminated soil from nearby Thala Valley landfill. A pilot scale experiment was set up, sampled and monitored from December 2008 to February 2010. Relative to levels in the untreated landfill material, concentrations of Cd, Cu, Co, Fe, Mn, Pb and Zn in leachates were decreased by phosphate addition (fixation most effective for Mn and Zn), whereas the technique increased concentrations of As, Cr and Ni. The most successful fixation was found for the 3:2 ratio of triple superphosphate and Emag, and the least effective fixation occurred with the 2:1:1 ratio of triple superphosphate, Emag and phosphate rock. Although there was an undesirable initial flush of metals from the contaminated soil in the 24–48 h after treatment addition, concentrations in leachate were reduced and stabilised in the second summer. During a full-scale field implementation, complementary techniques would be required to contain and treat contaminated runoff until leachates have reduced to acceptable concentrations.     

Site-specific accentuation of heavy metals in groundwaters from Ankaleshwar industrial estate, India

The seasonal behavior of environmentally sensitive polymetallic contaminants in groundwaters from Ankaleshwar industrial estate (AIE) India was studied. The potentially toxic elements (Co, Cr, Cu, Mn, Fe, Mo and Ni) demonstrated accentuated enrichment signatures during post-monsoon, besides colossal spatial variability on temporal scale. GIS-based accrual factor raster mapping facilitated the spot-specific quantitative and comparative appraisal of metallic distensions during post-monsoon with a decreasing hierarchy of seasonal augmentation Ni > Cu > Mn > Fe > Co > Mo > Cr. High inconsistencies and spot (pixel) strict exceedingly high accrual factors over these maps concur with diverse land use and surface-polluting sources. Inter-annual adiabatic extension of heavy metals in groundwaters implies their widespread availability in soil and atmospheric backgrounds in the region. Dissimilar performance with contrasting accretion patterns of redox-sensitive metals (Fe and Mo) is revealed by three-component color composites. Heavy metal hyper-accrual realms warrant an immediate demand for upgrading the existing waste management methodologies and aquifer remediation, as the region is highly cultivated and groundwater is the sole source of water supply for drinking, agricultural and other purposes.     

Spatial distribution and source of heavy metals in reclaimed lands of Homebush Bay: The venue of the 2000 Olympic Games,Sydney, New South Wales

A large part of the Sydney 2000 Olympic Site at Homebush Bay was reclaimed over several decades using an estimated 9 Mt of domestic, commercial and industrial waste. Past activities, such as reclamation of wetlands, land clearing, shoreline remodelling and industrial practices, have caused an adverse environmental impact on the Homebush Bay site. Core samples (n = 4513) collected from the reclaimed lands of Homebush Bay show that, prior to remediation, soil contaminated by heavy metals (Cr, Cu, Pb, Zn) may have posed a threat to groundwater in the area. Mean Pb concentrations from the three land types at the Olympic site range from 65 to 374 μg/g in reclaimed areas, 78–167 μg/g in landfill areas and 44–52 μg/g in non‐infilled areas, respectively. Heavy‐metal concentrations in soils from non‐infilled areas indicate that these parts of the site were uncontaminated. The distribution of heavy metals in soil samples revealed a close association between elevated concentrations and the presence of fill materials at the site. Metal concentrations were frequently above Australian and New Zealand Guidelines for Fresh and Marine Water Quality. The Olympic Coordination Authority's remediation strategy to clean up the Homebush Bay site included consolidating contaminated waste into landscaped hills, which were capped with impermeable clay and thermal destruction of scheduled waste on site. The primary aims of the current study were to provide a scientific foundation for the remediation/rehabilitation of natural systems, and to make a contribution to the Olympic Coordination Authority's Development Plan and Environmental Management System for the site.     

An assessment of the utilization of waste resources for the immobilization of Pb and Cu in the soil from a Korean military shooting range

Military shooting range soils contaminated by heavy metals have been subjected to remediation efforts to alleviate the detrimental effects of exposure on humans and the surrounding environment. Waste materials can be used as cost-effective soil amendments to immobilize heavy metals in contaminated soils. In this study, naturally occurring lime-based waste materials including egg shells, oyster shells, and mussel shells were assessed for their effectiveness toward heavy metal immobilization in military shooting range soil in Korea. Soil was treated in batch leaching experiments with 0, 2.5, 5, 10, and 15% of each lime-based waste material. The results showed that the lime-based waste materials effectively reduced water-soluble Pb at an application rate of 2.5% by weight of the soil. Increase in soil pH from 6.6 to 8.0 was considered to be the main chemistry of Pb immobilization, which was supported by the formation of insoluble Pb species at high pH values as confirmed by the visual MINTEQ thermodynamic model. In contrary, water-soluble Cu was increased in the lime-based waste material-treated soils when compared to the untreated soil. This was likely attributed to the formation of soluble Cu?CDOC (dissolved organic carbon) complexes as all lime-based waste materials applied increased DOC contents in the soil. Therefore, care must be taken in selecting the appropriate amendment for immobilizing metals in shooting range soils.     

Temperature and pH Dependence of Some Metals Leaching from Fly Ash of Municipal Solid Waste

Abstract. Municipal solid waste combustion leads to concentration of various metals in the solid residue (fly ash) remaining after combustion. These metals pose serious environmental hazard and require proper handling and monitoring in order to control their harmful effects. Leachability of some metals from fly ash was examined in fly ash and Milli-Q water mixture (liquid-to-solid ratio, 100) under various temperature and pH conditions in the laboratory. The leaching experiments conducted for 24 hours showed that pH was generally more important than temperature in controlling the amount of metals leached out of the fly ash. However, at a given pH, rise in temperature led to different degree of (usually one to two fold) enhanced or reduced leaching of metals. Owing to amphoteric nature of oxides of Al, Cr, Pb and Zn, these metals often yielded typical pattern of increase and decrease in their concentrations with change in pH. The extent of leaching of Cr and Pb in our experiments suggests that decrease of pH to acidic range in the case of Pb and to neutral to acidic range for Cr over a long period of storage of fly ash at solid waste dumping site may facilitate leaching of these metals from fly ash, leading to contamination of groundwater to the level that exceeds beyond the level permitted by the environmental laws.     

北京市密云水库上游土壤重金属污染调查评价

2002年9月在密云水库周边及上游地区(北京境内)总共采集土样98个,以《土壤环境质量标准》GB15168-95Ⅰ级标准为评价标准,对密云水库上游地区土壤重金属Cd、Pb、As、Hg、Cr、Cu、Ni、Zn的污染状况作了初步评价。研究结果发现密云水库周边及上游地区重金属污染以Cr和Hg为主,牤牛河上游为污染最严重地区,清水河上游、潮河下游放马峪地区、德田沟--崎峰茶地区受Cr元素轻度污染。该地区土壤重金属污染,主要原因是金属矿山不合理排放的尾砂及废矿石等人为因素所致。