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1.
Improved methods are required to assess the risks posed by the uptake of potentially toxic elements such as selenium (Se), boron (B), and molybdenum (Mo) by vegetation on contaminated sites. In order to develop such methods and assess risk, vegetation was collected from two sites on a soil-capped coal fly ash landfill near Dunkirk, New York, during June of 1991 and June and August of 1992. The mean concentrations (μg g-1 dry weight) of Se and Mo in the shoots did not exceed, respectively, 0.12 and 18.7 in bird's-foot trefoil (Lotus corniculatus L.), 0.06 and 12.1 in red clover (Trifolium pratense L.), 0.07 and 5.3 in timothy (Phleum pratense L.), and 0.09 and 2.2 in a mixture of grasses. These concentrations were greater than those in the same species harvested concurrently from a non-landfill site. The mean concentrations of B at the landfill ranged from 29 to 53 μg g-1 in the legumes and from 2 to 11 μg g-1 in the grasses, less than those at one non-landfill site but greater than those at another. Within the landfill, the concentration of Se in grasses was not correlated with the concentration of Se in soil and fly ash. The concentration of Se in grasses on both landfill sites was double that of grasses on the non-landfill site despite higher mean concentrations of Se in the upper soil (0–15 cm) on the non-landfill site. Therefore grass roots seem to be accessing Se from the ash by means of mass flow or other mechanisms. Based on our findings of significant variation in trace element uptake among species, harvests, and locations within sites, we recommend that contemporaneous transect sampling of at least two species be used to assess uptake of potentially toxic trace elements on landfills or other sites where contamination may occur.  相似文献   

2.
Abstract

To assess the mineral composition of plants growing in pure fly ash, grasses growing on lysimeters filled with alkaline, neutral, or acid fly ash were sampled several times in a 6‐year period. The samples were analyzed for elements essential for plants and animals as well as non‐essential, but environmentally significant, trace elements. Grasses were also sampled from ash dumps that were 20 and 30 years old. Fly ash is not a proper source of plant macronutrients N, P, and K. Plant growth on the alkaline fly ash can be influenced for some time by the high salinity of that ash. Grasses growing on unweathered fly ash were found to be high in Al, B, Co, Fe, Mo, Ni, Pb, and Se. Concentrations of several elements declined in time but levels of B, Fe, Mo, and Ni were still elevated in grasses on both fly ash dumps. All concentrations, except Al, were lower than toxicity levels for plants as found in literature. In plants growing on fresh fly ash concentrations of Mo, Pb, and Se can exceed the maximum tolerable levels for domestic animals. On weathered fly ashes (ash dumps) the Mo, Pb, and Se concentrations in grasses were below the maximum tolerable levels. Effects on animals by Mo in weathered ash may not be excluded because Mo concentrations can be high enough to induce Cu deficiency. Animals that feed on plants grown on fly ash could suffer from Ca, Mg, Na, and P deficiency.  相似文献   

3.
An experiment was conducted for two years in northwest India to explore the feasibility of using coal fly ash for reclamation of waterlogged sodic soils and its resultant effects on plant growth in padi–wheat rotation. The initial pH, electrical conductivity, exchangeable sodium percentage and sodium adsorption ratio of the experimental soil were 9.07, 3.87 dS m−1, 26.0 and 4.77 (me l)−1/2, respectively. The fly ash obtained from electrostatic precipitators of thermal power plant had a pH of 5.89 and electrical conductivity of 0.88 dS m−1. The treatments comprised of fly ash levels of 0.0, 1.5, 3.0, 4.5, 6.0 and 7.5 per cent, used alone as well as in combination with 100, 80, 60, 40, 20 and 10 per cent gypsum requirement of the soil, respectively. There was a slight reduction in soil pH while electrical conductivity of the soil decreased significantly with fly ash as measured after padi and wheat crops. The sodium adsorption ratio of the soil decreased with increasing fly ash levels, while gypsum treatments considerably added to its favourable effects. Fly ash application increased the available elemental status of N, K, Ca, Mg, S, Fe, Mn, B, Mo, Al, Pb, Ni, Co, but decreased Na, P and Zn in the soil. An application of fly ash to the soil also increased the concentrations of above elements except Na, P and Zn in the seeds and straw of padi and wheat crops. The available as well as elemental concentrations in the plants was maximum in the 0 per cent fly ash + 100 per cent gypsum requirement treatment except Na and heavy elements like Ni, Co, Cr. The treatment effects were greater in the fly ash + gypsum requirement combinations as compared to fly ash alone. Saturated hydraulic conductivity and soil water retention generally improved with the addition of fly ash while bulk density decreased. Application of fly ash up to 4.5 per cent level increased the straw and grain yield of padi and wheat crops significantly in both years. The results indicated that for reclaiming sodic soils of the southwest Punjab, gypsum could possibly be substituted up to 40 per cent of the gypsum requirement with 3.0 per cent acidic fly ash. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

4.
Abstract

Rice is a plant that requires high levels of silica (Si). As a silicate (SiO2) source to rice, coal fly ash (hereafter, fly ash), which has an alkaline pH and high available silicate and boron (B) contents, was mixed with phosphor‐gypsum (hereafter, gypsum, 50%, wt wt?1), a by‐product from the production of phosphate fertilizer, to improve the fly ash limitation. Field experiments were carried out to evaluate the effect of the mixture on soil properties and rice (Oryza sativa) productivity in silt loam (SiL) and loamy sand (LS) soils to which 0 (FG 0), 20 (FG 20), 40 (FG 40), and 60 (FG 60) Mg ha?1 were added. The mixture increased the amount of available silicate and exchangeable calcium (Ca) contents in the soils and the uptake of silicate by rice plant. The mixture did not result in accumulation of heavy metals in soil and an excessive uptake of heavy metals by the rice grain. The available boron content in soil increased with the mixture application levels up to 1.42 mg kg?1 following the application of 60 Mg ha?1 but did not show toxicity. The mixture increased significantly rice yield and showed the highest yields following the addition of 30–40 Mg ha?1 in two soils. It is concluded that the fly ash and gypsum mixture could be a good source of inorganic soil amendments to restore the soil nutrient balance in rice paddy soil.  相似文献   

5.
Agronomic use of coal combustion by-products is often associated with boron (B) excess in amended soils and subsequently in plants. A greenhouse study with corn (Zea mays L.) as test plant was conducted to determine safe application rates of five fly ashes and one flue gas desulfurization gypsum (FDG). All by-products increased soil and corn tissue B concentration, in some cases above toxicity levels which are 5 mg hot water soluble B (hwsB) kg?1 soil and 100 mg B kg?1 in corn tissue. Acceptable application rates varied from 4 to 100 Mg ha? for different by-products. Leaching and weathering of a high B fly ash under ponding conditions decreased its B content and that of corn grown in fly ash amended soil, while leaching of the same fly ash under laboratory conditions increased fly ash B availability to corn in comparison to the fresh fly ash. Hot water soluble B in fly ash or FDG amended soil correlated very well with corn tissue B. Hot water soluble B in fly ash amended soil could be predicted based on soil pH and B solubility in ash at different pH values but not so in the case of FDG. Another greenhouse study was conducted to compare the influence of FDG and Ca(OH)2 on B concentration in spinach (Spinacia oleracea L.) leaves grown in soil amended with the high B fly ash. The Ca(OH)2 significantly decreased tissue B content, while FDG did not affect B uptake from fly ash amended soil.  相似文献   

6.
粉煤灰堆场附近农田土壤硒环境污染评价   总被引：3，自引：1，他引：2  
对贞观山煤灰库附近农田土壤、土壤剖面、灌溉水、母岩以及稻米,蔬菜等农作物中Se含量特征及污染现状进行了系统分析与评价.结果显示:煤灰库周围的农田土壤Se含量范围为0.15～6.12mg/kg,受到不同程度污染.土壤Se含量空间分布特征表明.离煤灰库越近的农田土壤Se污染越严重.农田土壤Se污染主要是由Se含量超标地表水灌溉以及煤灰库的长期处置所引起的,受母岩的影响不大.研究区稻米Se含量较高,为0.04～1.12mg/kg,部分稻米样品Se含量超标严重,并且受土壤Se污染影响明显.长期食用Se含量超标大米对人体健康会产生潜在危害.  相似文献   

7.
Rangeland management can affect plant diversity and plant functional groups of native grassland communities. To improve pasture for livestock grazing from the existing poisonous and ruderal vegetation in the ‘black soil land’ grassland in the headwaters of the Yangtze and the Yellow Rivers (HAYYR) of the Qinghai‐Tibetan Plateau, three treatments (fencing‐FT, artificial seeding with local grasses‐ST and abandonment‐AT) were applied during a 5‐year period (2000–2005). Plant diversity and groups (sedges, grasses and dwarf shrubs) in the treated plots were compared with non‐treated control plots. Results showed that (1) FT promoted an increase in forbs species, but there was no change in the other plant functional groups; (2) with ST, species richness of forbs decreased but grass species increased indicating that sowing local grasses could change plant composition of black soil land in the short‐term, and increase the proportion of grasses and, thus, forage for grazing and (3) AT, after plowing, was similar to CK plots, with forbs being the dominant plant functional group for the 5 years. In conclusion, the goal to alter black soil land cover from poisonous and ruderal plants to more useful plants for livestock grazing by either fencing, artificial seeding or abandonment was not successful in the long term. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

8.
Coal fly ash has physical and chemical characteristics that makeit useful as a soil amendment, one of the more important beingthe potential to permanently improve the soil water relations ofsandy, drought-prone soils. We axemined changes in theinfiltration rate and water holding capacity of a sandy soilafter application of high rates (up to 950 Mg ha-1) of aClass F fly ash. Fly ash was applied to large field plots byeither conventional tillage (CT; moldboard plow-disk) orintensive tillage (IT; chisel plow-rotovate-disk), and tomicroplots using a rototiller. Infiltration rate (i) wasmeasured in both studies with a disk permeameter on threeoccasions over a 12-month period. Ash effects on gravimetric water content (θg) at the 0–40 cm soil depth were measuredduring a 168 hr period following a 2.5 cm rainfall event andwater release curves (33 to 500 kPa) were constructed in thelaboratory using soils from the large plots. In both studiesi was decreased by ～80% one year after additionof fly ash and θgin ash-amended soil was higher than unamended soil throughoutthe 168 hr monitoring period. Soil water distribution variedwith tillage; the IT treatment had the highest θg increasesin the 0–20 cm depth while the CT treatment had θgincreases throughout the 0–40 cm depth. Soil water content anddistribution in ash-amended microplots were similar to ITtreatments. Fly ash amendment not only increased water holdingcapacity but also increased plant available water by 7–13% inthe 100–300 kPa range. These results suggest fly ash amendmentmay have the potential to improve crop production in excessivelydrained soils by decreasing i and increasing the amountof plant available water in the root zone.  相似文献   

9.
Application of fine-textured and Ca-rich fly ash may be helpful in enhancing soil carbon content via protecting soil organic C (SOC) by organo-mineral complexation and via reducing CO2 emission by carbonation (e.g. formation of CaCO3). However, very limited information is available on the effects of fly ash application on gases loss of C and soil C content. In this study, to estimate the potential use of fly ash as a soil amendment for SOC enhancement purposes, the effects of fly ash application (0, 5, and 10 w/w %) on microbial biomass C (MBC), CH4 and CO2 emissions, and on soil C content were investigated. A 60-days incubation experiment was conducted with an acidic soil in the presence of organic input (pig manure compost, PMC; hairy vetch, HV) with contrasting substrate quality under changing water regime from water-logged to unsaturated via a transition period. Fly ash application did not affect MBC under water-unsaturated conditions, but reduced (P < 0.01) microbial growth under water-logged conditions, probably due to the increased solubility of a certain toxic element such as arsenic under the anaerobic conditions. Across the 60 days of incubation, the CO2 emission was reduced by fly ash regardless of organic input by 20.5–41.3%; meanwhile, a decline of CH4 emission by fly ash application was significant (P < 0.05) only in the HV treatment. Overall, fly ash application slowed down gases C loss and increased soil C content, probably due to the retardation of CH4 and CO2 emission as well as the addition of C contained in the fly ash. Biochemical (inhibition of microbial activity), chemical (formation of CaCO3 via carbonation), and physical (restriction of gas diffusion) mechanisms were suggested for the fly ash effects.  相似文献   

10.
Decline of leafy spurge (Euphorbia esula) in the northern Great Plains of the US is generally viewed as a success story for biological control, but quality of the vegetation that survived the infestation is key to recovery of ecosystem function. In addition, effects of other invasive species, notably cool-season exotic grasses, must be taken into account. Objectives of this study were (1) to evaluate direction and significance of changes in biomass of native and exotic grasses, forbs, and leafy spurge and in plant species composition following control of leafy spurge by flea beetles and (2) to evaluate the relative effects of leafy spurge and exotic grasses on biomass of native grasses, biomass of forbs, and richness of native species. We monitored species composition (1998-2003 and 2008) and biomass (2000, 2002, 2003 and 2008) of these groups on spurge-infested and noninfested permanent plots at three sites with unbroken prairie sod in North Dakota, USA. We found little evidence, in terms of species richness or biomass of native grasses or forbs, that leafy spurge was being replaced by desirable native species, although desirable as well as weedy and exotic species were characteristic of 2008 vegetation at all three sites. Structural equation models revealed that leafy spurge had temporally intermittent negative effects on forb biomass and species richness, but no effects on native grasses. In contrast, exotic grass had consistently strong, negative effects on native grass biomass, as well as stronger negative effects than leafy spurge on native species richness. Although substantial native plant diversity remains at these sites, exotic grasses pose an important threat to these crucial building blocks of native prairie ecosystems.  相似文献   

11.
不同大豆品种积累硒的特性及基因型差异   总被引：12，自引：1，他引：11  
田间试验结果表明 ,在低硒土壤上 ,施硒极显著提高植株、子粒中的积硒量 ,增加幅度植株为夏大豆 秋大豆 春大豆 ,子粒为秋大豆 夏秋大豆 春大豆 ;并筛选出富集硒能力强的品种 10份。在富硒土壤上种植的不同春大豆品种 ,植株、子粒硒积累量也存在显著差异。在不同硒浓度条件下 ,同一大豆品种各生育阶段硒积累量存在差异 ,其大小顺序为成熟期 花期 苗期。施硒浓度以 1 0mg/L单株积累量最高  相似文献   

12.
The influences of fly ash and fly‐ash–quicklime‐treated‐sludge mixtures (with fly‐ash doses of 40%, 80%, and 120% on dry‐weight basis) on the microbial numbers in soil and leachate were investigated by using 60 cm soil columns. Heterotrophic bacteria and total coliform numbers were determined in soil and leachate samples following an artificial rainfall event. The results indicated that land application of untreated sludge and fly‐ash–sludge mixtures appear to introduce large numbers of bacteria to leachates and soil. Although the numbers in leachates and soils were found to decrease with increasing ash ratios, they were still all significantly above the control levels. Application of alkaline‐stabilized and pasteurized sludge did not increase bacterial numbers significantly in soil and leachate. Distribution of heterotrophic bacteria through soil profile clearly showed no increase in soils amended with alkaline‐stabilized and pasteurized sludges. Additionally, no significant inhibitory effect of lignite fly ash on soil microbial population was observed.  相似文献   

13.
The combustion of coal in power plants generates solids (e.g., fly ash, bottom ash) and flue gas (e.g., SO x , CO2). New Clean Air Act mandated reduction of SO x emissions from coal burning power plants. As a result, a variety of Clean Coal Technologies (CCT) are implemented to comply with these amendments. However, most of the CCT processes transfer environmentally sensitive elements (e.g., As, Cd, Pb, Se) from flue gas to CCT ash. The objective of this study was to determine the effect of a pressurized CO2 treatment on the chemistry of CCT ash. Three CCT ash samples, produced from lime injection, atmospheric fluidized bed combustion, and sodium carbonate injection processes were reacted under different CO2 pressure treatment conditions. Treated and untreated samples were subjected to various experiments including, X-ray diffraction (XRD) analysis, calcium carbonate solubility studies, and trace element extraction studies. Factors influencing the efficiency of a CO2 treatment for CCT ash samples include combustion process, moisture, CO2 concentration, and pressure. The CO2 pressure treatment resulted in the precipitation of calcite in CCT ash samples, and thus lowered the pH and the concentration of extractable trace elements (e.g., Cd, Pb, Cr, As, Se). Furthermore, we found that CO2 pressure treatment was more effective for lime injection and atmospheric fluidized bed combustion processed samples than for sodium carbonate injection processed samples.  相似文献   

14.

Purpose

Fly ash can reduce CO2 emission from soils via biochemical (i.e., inhibition of microbial activity) and physicochemical (i.e., carbonation) mechanisms. This study investigated the effects of fly ash amendment on biochemical and physicochemical reduction in CO2 emission from normal and saline soils.

Materials and methods

The physicochemical mechanisms of reduction in CO2 emission by fly ash were estimated in a batch experiment with carbonate solution as a CO2 source by the scanning electron microscope (SEM) and inductively coupled plasma analyses. Biochemical mechanisms of reduction in CO2 emission by fly ash were investigated in a 3-day laboratory incubation experiment with normal and saline soils in the absence and presence of fly ash. Finally, the effects of fly ash amendment at a variety rate from 2 to 15?% (w/w) on CO2 emission from normal and saline soils in the presence of additional organic carbon source (glucose) were investigated through a 15-day laboratory incubation study.

Results and discussion

In the batch experiment with carbonate solution, both the SEM image of fly ash and changes in soluble Ca and Mg concentrations during reaction with carbonate suggested that the formation of CaCO3 and MgCO3 via carbonation was the principal physicochemical mechanism of carbonate removal by fly ash. In the 3-day incubation study conducted to examine biochemical mechanisms of reduction in CO2 emission by fly ash, microbial respiration of saline soil was inhibited (P?<?0.05) by fly ash due to high pH, salinity, and boron concentration of fly ash; meanwhile, for normal soil, there was no inhibitory effect of fly ash on microbial respiration. In the 15-day incubation with glucose, fly ash application at a variety rates from 2 to 15?% (w/w) reduced CO2 emission by 3.6 to 21.4?% for normal and by 19.8 to 30.3?% for saline soil compared to the control without fly ash. For saline soil, the reduction in CO2 emission was attributed primarily to inhibition of microbial respiration by fly ash; however, for normal soil in which suppression of microbial respiration by fly ash was not apparent, carbonation was believed to play an important role in reduction of CO2 emission.

Conclusions

Therefore, fly ash may be helpful in reducing CO2 emission from normal soils via carbonation. For saline soil, however, fly ash needs to be carefully considered as a soil amendment to reduce CO2 emission as it can inhibit soil microbial activities and thus degrade soil quality.  相似文献   

15.
通过田间试验,研究了生物肥和粉煤灰、秸秆干馏液配合施用共4种不同调控措施对强酸性高硒茶园土壤上茶叶硒含量、土壤理化性质和土壤硒有效性的影响。结果表明,4种调控措施不同程度地提高了土壤中有效硒含量和茶叶硒含量,由高到低依次为：生物肥处理〉粉煤灰-秸秆干馏液-生物肥复合处理〉粉煤灰-生物肥复合处理〉秸秆干馏液-生物肥复合处理;对土壤pH值提高幅度的大小次序为：粉煤灰-秸秆干馏液-生物肥复合处理〉粉煤灰-生物肥复合处理〉生物肥处理〉秸秆干馏液-生物肥复合处理;另外,4种不同措施对改善酸化茶园土壤其他理化性质也呈现不同效果,其中秸秆干馏液-生物肥复合处理的综合效果较差。研究结果对于江苏高硒地区土壤中硒素的有效利用和加快发展富硒茶产业具有实际的参考价值和重要的指导意义。  相似文献   

16.
To quantify the growth and yield responses to CO2 enrichment in an open field setting, freeair CO2 enrichment (FACE) technology was used to expose a cotton (Gossypium hirsutum L.) crop to 550 γmol mol−2 CO2 throughout the growing seasons of 1989, 1990 and 1991 in fields near Maricopa, Arizona. In 1990 and 1991 a water stress treatment was also imposed. Response data for all years were consistent, and the data for 1991 were the least compromised by unusual weather or equipment failures. In that season the biomass was increased 37% by the 48% increase in CO2 concentration. Harvestable yield was increased 43%. The increase in biomass and yield was attributed to increased early leaf area, more profuse flowering and a longer period of fruit retention. The FACE treatment increased water-use efficiency (WUE) to the same amount in the well-irrigated plots as in the water-stressed plots. The increase in WUE was due to the increase in biomass production rather than a reduction of consumptive use.  相似文献   

17.
Fly ash‐enriched soils occur widely throughout the industrial regions of eastern Germany and in other heavily industrialized areas. A limited amount of research has suggested that fly ash enrichment alters the water repellency (WR) characteristics of soil. This study concentrates on the influence of fly ash enrichment on WR of forest soils with a focus on forest floor horizons (FFHs). The soils were a Technosol developed from pure lignite fly ash, FFHs with lignite fly ash, and FFHs without lignite fly ash enrichment. Three different methods (water drop penetration time, WDPT, test; water and ethanol sorptivity measurement and the derived contact angle, θR; and the Wilhelmy‐plate method contact angle, θwpm) were used to characterize soil WR. Additionally, carbon composition was determined using 13C‐NMR spectra to interpret the influence of the organic matter. This study showed that the actual WR characteristics of undisturbed, fly ash‐enriched soils can be explained in terms of the composition of soil organic matter, with the fly ash content playing only a minimal role. Regardless of the huge amounts of mainly mineral fly ash enrichment, all undisturbed FFHs were comparable in their WR characteristics and their carbon compositions, which were dominated by recently‐formed organic substances. The pure fly ash deposit was strongly influenced by lignite remains, with the topsoil having a greater content of recent plant residues. Thus, the undisturbed topsoil was more repellent than the subsoil. When homogenized samples were used, we found a distinct effect of fly ash enrichment and structure on WR. Water repellency of the pure fly ash horizons did not differ distinctly, while the fly ash enrichment in the FFHs caused a significant reduction in WR. The methods used (WDPT, θR and θwpm) identified these differences similarly. These results led to the assumption that water‐repellent structures of the topsoils were probably the result of hydrophobic coatings of recently formed organic substances, whereby the initially high wettability of the mainly mineral, hydrophilic fly ash particles was reduced.  相似文献   

18.
Abstract

Rice variety IR 36, grown under flooding, was studied in 1998 to determine the effects of fly ash, organic, and inorganic fertilizers on changes in pH and organic carbon, release of nutrients (NH4 +-N, Bray's P, and NH4OAc K), and dehydrogenase activity in an acid lateritic soil at 15-day intervals. Application of fly ash at 10?t?ha?1 alone did not improve the availability of NH4 +-N, or P, as well as the rice grain yield. Availability of NH4 +-N (35.3–36.9?mg?kg?1), and P (12.3–14.6?mg?kg?1) at 15 days after transplanting, and rice grain yields (48.0–51.7?g per pot) were similar under the various fertilization sources such as inorganic fertilizer alone, inorganic fertilizer?+?fly ash or inorganic fertilizer?+?green manure?+?fly ash. Mean dehydrogenase activity was the highest (8.47?µg triphenyl formazon g?1 24?h?1) under the mixed fertilization treatments with green manure. At the end of the cropping season (75 days after transplanting), pH, organic carbon, and dehydrogenase activity were higher under the mixed fertilization treatments involving green manure by 3, 15 and 154%, respectively, compared with the inorganic fertilizer alone.  相似文献   

19.
A bioassay technique was used to investigate heavy metals uptake by wheat seedlings grown in fly ash-amended soils. No negative effect of fly ash on the growth of wheat seedlings was found. The addition of the fly ash generally decreased the heavy metal concentration in the wheat seedlings. The total accumulation largely depended on the soil characteristics. The variation in the soil pH induced by the fly ash treatment could be considered the most important parameter that influenced heavy metals uptake. In the soil with a higher increase of pH (2 units) total accumulation of heavy metals decreased with increasing fly ash addition. In the other soils where the pH variation was lower (0.4 units), total accumulation of some heavy metals increased. These obtained data provide useful information which is required before the agronomic use of fly ash can be recommended in Italian soils.  相似文献   

20.
Arsenate Displacement from Fly Ash in Amended Soils   总被引：1，自引：0，他引：1  
Arsenic (As) is the biggest environment contaminant in most of the soils where fly ash is applied. Usually, it is not mobile and strongly adsorbed on to soil particles. However, in gypsum and phosphorus amended soils As may be much more mobile. A study in repacked columns was conducted to determine whether or not As becomes mobile when Ca(H2PO4)2and CaSO4are used as leaching solutions, and to compare the competitive interactions between PO4-AsO4and SO4-AsO4. Arsenic concentration in leachate was found to be approximately ten times greater when Ca(H2PO4)2was used to leach the columns as compared to CaSO4. A maximum concentration of 800 μg As L-1was found in the leachate in this case, which is much higher than the groundwater limit of 50 μg L-1for drinking water established by the United States Environmental Protection Agency. In fly ash, the portion of arsenate non-specifically adsorbed is believed to be much lower than that of specifically adsorbed. Sulfate anions were able to displace only non-specifically adsorbed arsenate. In this case the concentration of As in leachate was found to be within acceptable limits. On the other hand, phosphate can compete with arsenate for all available adsorption sites, non-specific and specific. Phosphate displacement of both forms of arsenates increases As mobility in both control and fly ash treatments.  相似文献   

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