Co-disposal of Heavy Metals Containing Waste Water and Medical Waste Incinerator Fly Ash by Hydrothermal Process with Addition of Sodium Carbonate: A Case Study on Cu(II) Removal

Fly ash generated from medical waste incinerator and wastewater produced from electroplating plants contains various hazardous contaminants such as heavy metals and chlorinated organic compounds. The primary goal of this research was to investigate the feasibility of removing heavy metals from wastewater using medical waste incinerator fly ash as the treatment reagent with addition of small amount of sodium carbonate (Na₂CO₃) in a hydrothermal process. Copper (Cu) was used as the model heavy metal contaminant in the process. The results revealed that medical waste incinerator fly ash could effectively stabilize Cu(II) ion from wastewater, the crystal phase and simple substance formed during the treatment played a significant role in the fixation of heavy metals in wastewater and fly ash. The heavy metal leachability of treated ash was also measured after removal process. The co-disposal of Cu-containing wastewater and heavy metals-bearing medical waste incinerator fly ash by hydrothermal treatment with addition of a small amount of Na₂SO₃ was found promising as an effective way of removing Cu from wastewater. The reutilization feasibility of fly ash and the formation mechanism of copper-containing substances were also discussed in this paper.     

Reduction in CO2 emission from normal and saline soils amended with coal fly ash

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.     

Oxidant effects on forest tree seedling growth in the Appalachian mountains

Long range transport of episodic concentrations of O₃ into the Appalachian Mountains of Virginia was recorded in the summer season of 1979 and 1980. Continuous monitoring of O₃ indicated monthly averages of ? 0.05 ppm O₃ and several periods averaged ? 0.08 ppm O₃. Open-top chambers were used to test the effect of ambient doses of the pollutant on the growth of 8 planted forest tree species native to the area. Height growth was suppressed for all species at the end of the second growing season when grown in open plots (no chamber) and ambient chambers compared to those grown in charcoal-filtered air supplied chambers. Height growth trends of open < ambient chamber < filtered air chamber were consistent. Virginia pine and green ash were significantly taller (p=0.10) when grown within filtered air chambers. Tulip poplar and green ash manifested purple stippling on the adaxial leaf surface and sweetgum developed purple coloration under open or ambient chamber conditions; other species exhibited no visible injury.     

A Comparison of Inorganic Solid Wastes as Adsorbents of Heavy Metal Cations in Aqueous Solution and Their Capacity for Desorption and Regeneration

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺ and Cr³⁺ was determined at two metal concentrations (10 and 100 mg?L^?1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr³⁺????Pb²⁺????Cu²⁺?>?Zn²⁺?=?Cd²⁺. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO₃ electrolyte were very small, but those removed with 0.01 M HNO₃, and more particularly 0.10 M HNO₃, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO₃ as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.     

Evaluation of industrial wastes as sources of fertilizer silicon using chemical extractions and plant uptake

Six inorganic industrial‐waste materials (coal fly ash, bauxite‐processing mud, steel slag, two samples of air‐cooled blast furnace [BF] slag, and one sample of water‐cooled BF slag), along with wollastonite, were evaluated as fertilizer‐Si sources. Evaluation was carried out by analyzing total and extractable Si fractions in the materials, by incubating them at two rates with a Si‐deficient soil and measuring potentially available extractable Si and by measuring yield and Si uptake by two successive rice crops grown in the fertilized soils. Of the waste materials used, fly ash had the highest total Si content (29%) but a negligible quantity was present in extractable forms. Steel slag and bauxite‐processing mud had only 5%–7% Si content while BF slags contained 14%–18% Si. All materials, other than fly ash, increased the amount of extractable Si present in the soil. Additions of steel slag and bauxite‐processing mud caused greater increases in Si extractability than the air‐cooled BF slags while water‐cooled BF slag–treated soils contained notably high acid‐extractable Si. Because of the alkaline nature of the materials, and their reaction products, there was a positive relationship between extractable soil Si and soil pH. However, an equilibration experiment using NaSiO₃ as the Si source confirmed that Si solubility in the soil decreased with increasing pH. Dry‐matter yields of rice, at the lower rate of Si addition, were increased by all treatments other than fly ash. The higher rates of steel slag and bauxite‐processing mud caused yield depressions. Total Si uptake by rice was increased by all treatments, other than fly ash, and was greater at the higher rate of Si addition. It was concluded that the BF slags are the most effective waste materials as fertilizer‐Si sources and that, in slag‐amended soils, CaCl₂ and NH₄ acetate are the most reliable soil‐test extractants.     

Nutrient dynamics,dehydrogenase activity,and response of the rice plant to fertilization sources in an acid lateritic soil

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.     

Leachability of Lead from Lead Tailings

Laboratory column studies were used to predict the effect on the leachability of lead when using fly ash or a fly ash/sludge mixture as a cover for a lead tailings site. A high pH fly ash cover produced a leachate with a pH 12. This was sufficiently high to allow for the formation of lead hydroxide complexes which are slightly soluble. Therefore, the leachate had an average lead concentration of about 5 mg L^-1, while the pH in the leachate from the column with only tailings was 7.8 and a lead concentration below the detection limit (≤0.1 mg L^-1). The fly ash cover changed the availability of the remaining lead, making it less available. Rainfall rate did not affect the fly ash cover, but did have an effect on the fly ash/sludge cover.     

Ash Leaching of Forest Species Treated with Phosphate Fire Retardants

The chemical, mineralogical, and leaching behavior of three dominant Greek forest species ashes (Pinus halepensis, Pistacia lentiscus, and Olea europaea), before and after treating forest species with diammonium phosphate (DAP) 5% and 10% weight to weight, have been studied using a new five-step shake leaching method at pH?=?6. For the analysis of ashes (prior and after leaching) and leachants, the following analytical techniques were used: atomic absorption spectroscopy, X-ray diffraction, and scanning electron microscopy with energy dispersive X-ray fluorescence analysis. The presence of DAP obstructs the extraction process of some metal ions (i.e., Na, K) contained in ashes by converting the soluble carbonate salts to the less soluble phosphates (i.e., Na₂CO₃ → Na₃PO₄). On the contrary, DAP enhances the mobility of some other metals (i.e., Ca) by forming more soluble compounds [i.e., CaCO₃ → Ca₃(PO₄)₂]. In addition, the presence of DAP lowers the pH of leachates, causing dissolution of some toxic elements (i.e., Mn, Pb, Zn). Unexpectedly, DAP prevents the leachability of Cr from ash. The above study concerns the environmental effects (soil and ground and underground water streams) caused by the use of chemical retardants on forest fires.     

Comparing chemical-enhanced washing and waste-based stabilisation approach for soil remediation

Purpose

This study aimed to compare the effectiveness of chemical-enhanced soil washing (with chelating agents, humic substances and inorganic acids) and soil stabilisation by inorganic industrial by-products (coal fly ash, acid mine drainage sludge and zero-valent iron) and organic resource (lignite) for timber treatment site remediation.

Materials and methods

Both remediation options were assessed in terms of extraction/leaching kinetics and residual leachability (toxicity characteristic leaching procedure, TCLP) of the major risk drivers, i.e. Cu and As.

Results and discussion

In chemical-enhanced soil washing, chelating agents only minimised the Cu leachability. Humic substances were ineffective while inorganic acids reduced the As leachability to the detriment of the soil quality. For the waste-stabilised soil, the short-term leaching potential (72 h) and long-term TCLP leachability (9 months) revealed that Fe-/Al-/Ca-rich AMD sludge and coal fly ash sequestered As through adsorption and (co-)precipitation, while carbonaceous lignite stabilised Cu with oxygen-containing functional groups. The short-term and long-term leaching of Cu and As into the soil solution was negligible in the presence of the waste materials. However, the waste-stabilised soil did not maintain sufficient Cu stability in the TCLP tests, in which acetate buffer induced significant mineral dissolution of the waste materials.

Conclusions

These results suggest that chelant-enhanced washing (significant reduction of Cu leachability) may be augmented with subsequent stabilisation with inorganic waste materials (effective control of As leachability), thus minimising the environmental risks of both Cu (heavy metal) and As (metalloid) while preserving the reuse value of the soil. Additional tests under field-relevant conditions are required to provide a holistic performance evaluation.     

Chromium Alters Iron Nutrition and Water Relations of Spinach

Spinach (Spinacea oleracea L. cv. ‘Banarasi’), known to be responsive to potentially toxic elements, was investigated for chromium (Cr^{6 +}) effect on iron metabolism and water relations. After 40 days growth in sand culture, a set of plants was supplied with 100 and 400 μM Cr^{6 +} (potassium dichromate, K₂Cr₂O₇), superimposed over the complete nutrient solution (control). Excess Cr^{6 +} produced visual symptoms of toxicity and increased accumulation of Cr, more in roots than in leaves. Decreased concentration of chlorophylls and the activities of heme enzymes, catalase and peroxidase in excess Cr^{6 +} may suggest interference of Cr in iron metabolism of plants. These changes associated with decrease in iron (Fe) accumulation in Cr^{6 +} treated plants, indicate that by reducing absorption of Fe, Cr^{6 +} impairs the Fe requiring steps of chlorophyll and heme biosynthesis. In spite of lower water saturation deficit, the leaves of Cr^{6 +} treated plants showed a decrease in leaf water potential, associated with increase in diffusive resistance and lowering of transpiration rate along with proline accumulation indicates water stress. The changes observed in water stress parameters in Cr^{6 +} treated plants indicate that excess supply of Cr^{6 +} reduces the physiological availability of water.     

The practice of leaching boron and soluble salts from fly ash-amended soils

The leachability of B and salts from two fly ash-amended soils was conducted in a column leaching experiment. Fly ash was applied to the surface 3 cm of a Baywood (acid) sand and an Arizo (calcareous) sandy, loam at 5% by weight; the columns were continously leached with Colorado River water at two different pH's. Boron from fly ash was solubilized more readily in the Baywood than in the Arizo soil. Addition of fly ash increased B levels in the leachates from 0.25 to 2.35 μg ml^?1 (Baywood) and 0.93 μg ml^?1 (Arizo). Acidified leaching water had no significant effect on B leaching patterns but resulted in leaching higher soluble salts. Approximately 348 and 161 cm of water for the Arizo and the Baywood soils respectively, would be required to reduce the B concentration below a critical limit for B sensitive crops. It is suggested that crops planted when fly ash is applied for disposal/recycling on land should be both salt and B tolerant.     

Fall exposure of beech saplings (Fagus sylvatica L.) to ozone and simulated acidic mist: Effects on gas exchange and leachability

Two yr old beech saplings (Fagus sylvatica L.) were exposed under an early autumn climate to four levels of O₃ (10, 40, 75, and 110 nL L O₃) with or without preceding simulated acidic mist (pH 3.5). As a first response in gas exchange to O₃, stomatal conductance was transiently increased followed by a decline in net photosynthesis. Thus, regarding exposure effects on stomatal behavior, both O₃ and acidic mist increased the pollutant flux into the leaf interior. The subsequent impairment of cell permeability consisted of dose-dependent increases in efflux rates of dichlorofluorescein, indicating greater membrane permeabilities. While the efflux rates of Mg and Ca correlated with those of the fluorescent dye, the leachability of K was increased only at the highest O₃ levels. Changes in compartmentation of K, Ca, Mg, and S was derived from selective cell wall extraction; thereafter, the exposure to O₃ and acidic mist resulted in increased extracellular fractions of these elements.     

In situ remediation of cadmium-polluted soil reusing four by-products individually and in combination

Purpose

The aim of this study was to evaluate the effectiveness of mining, industrial and agricultural solid by-products in the in situ immobilisation of soil cadmium (Cd) based on soybean plant Cd content, soil pH, Cd extractability, bioavailability, leachability and Cd distribution in soils.

Materials and methods

The experiment was conducted as a field experiment in Cd-polluted-soil, wherein four by-products, including fly ash, spent mushroom substrate, silkworm excrement and limestone, were tested individually and in combination. The total Cd in soybean and the soil/by-products samples were determined. The Cd contents in the contaminated soil were analysed by the diffusive gradients in thin-film technique, the toxicity characteristic leaching procedure and four chemical methods. Changes in the fractions of Cd were determined following the Tessier method.

Results and discussion

The results showed that all the additions of the by-products increased the soil pH significantly and simultaneously decreased Cd mobility, bioavailability and leachability, particularly weakened the rate of Cd²⁺ ion transport from soil to solution. The by-products caused 23.5–76.4% of the exchangeable (EX) fraction of Cd to immobilised Cd fractions which include carbonates bound (CA), Fe-Mn oxides bound (OX), organic matter bound and residual fractions. The mobile faction of Cd was reduced from 33.7 to 16.8–27.8% for the amendments addition, respectively. Limestone was the most effective in immobilising the soil Cd among all the treatments, followed by fly ash. Soil pH observed significantly negative correlations with the Cd concentration in extractability, bioavailability and leachability. Soil pH had positive correlations with the percentages of CA-Cd and OX-Cd, but negatively correlated with the percentages of EX-Cd and the sum of EX-Cd and CA-Cd.

Conclusions

By-products addition increased the soil pH and decreased Cd mobility, bioavailability and leachability. The addition of limestone and fly ash exhibited higher efficiency than the other five additions. The combined additions had better performance on Cd extractability and soil pH than the corresponding single treatment, which decreased more concentrations of mobile, bioavailable and leachable Cd. This study offered four potentially cost-effective amendments singly or jointly for Cd immobilisation, reducing the potential hazards associated with excess Cd and the waste-disposal pressure and promoting a resource-saving development strategy.     

Geochemical behavior assessment and apportionment of heavy metal contaminants in the bottom sediments of lower reach of Changjiang River

Heavy metal contamination of bottom sediments of the Changjiang River is widely reported, however, the potential source and methods of transportation of these heavy metals in the contaminated sediments is poorly defined. This paper examines the correlation between heavy metals and geochemical indices, including Fe₂O₃, Al₂O₃, total organic carbon (TOC) and black carbon (BC), as well as magnetic susceptibility (MS). Using these indices we investigate the contamination characteristics of heavy metals in the sediments by with Principal Component Analysis (PCA). Results from 83 sediment samples collected in the lower reach of Changjiang River (from Nanjing to Shanghai) show that the first principal component accounts for 52.23% of the total variance, corresponding to the heavy metals, Co, Cr, Cu, Ni and Zn, and conservative components of Fe₂O₃, Al₂O₃ and TOC. This result indicates that heavy metal distributions are controlled by the transportation and sedimentation of fine particles which is also confirmed by particle size analysis. The second principal component explains 24.81% of the variance and is dominated by Cd, Pb and MS, which, collectively, result chiefly from industrial and transportation activities and, for MS, fly ash production. The third principal component accounts for 7.91% of the variance and corresponds solely to Hg. Principal component analysis/multiple linear regression (PCA/MLR) was used to estimate the contribution of the three principal components to each heavy metal. PCA/MLR results suggest that more than 50% of Co, Cr, Cu, Ni and Zn were influenced by the particle size effect. Particle size effect and fly ash account for 37.1% and 27.7% of As. Cd and Pb were mainly explained by fly ash. 98.9% of Hg was related to PC3, which represented black carbon (BC). Our study indicates that the combination of geochemical and multivariable statistical methods clearly characterizes the geochemistry of heavy metals in sediment of the lower reaches of the Changjiang River and suggests that power plants are the main source of heavy metal pollution.     

Effect of Flue Gas Treatment on the Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Studies were conducted to examine the effect of flue gas carbon dioxide (CO₂) on solubility and availability of different metals in fly ash of Powder River Basin (PRB) coal, Wyoming, USA. Initial fly ash (control) was alkaline and contains large amounts of water-soluble and exchangeable metals. Reaction of flue gas CO₂ with alkaline fly ash resulted in the formation of carbonates which minimized the solubility of metals. Results for metal fractionation studies also supported this fact. The present study also suggested that most of the water-soluble and exchangeable metals present in the control (untreated) fly ash samples decreased in the flue gas-treated samples. This may be due to the transfer of the above two forms to more resistant forms like carbonate bound (CBD), oxide bound (OXD), and residual (RS). Geochemical modeling (Visual MINTEQ) of water solubility data suggested that the saturation index (SI) values of dolomite (CaMg(CO₃)₂) and calcite (CaCO₃) were oversaturated, which has potential to mineralize atmospheric CO₂ and thereby reduce leaching of toxic metals from fly ash. Results from this study also showed that the reaction of flue gas CO₂ with alkaline fly ash not only control the solubility of toxic metals but also form carbonate minerals which have the potential to fix CO₂.     

Formulation of Environmentally Sound Waste Mixtures for Land Application

Major impediments to the land application of coal combustion byproducts (fly ash) for crop fertilization have been the presence of heavy metals and their relatively low and imbalanced essential nutrient concentration. Although nutrient deficiencies, in particular N, P, and K, may be readily augmented by adding organic wastes such as sewage sludge and animal manure, the indiscriminate application of mixtures to crops can cause excessive soil alkalinity, imbalanced nutrition (P, Mg), phytotoxicities (B, Mn, ammonia, nitrite), and unspecified contamination of the food chain by elements such as As. In this study, nutrient availability data and linear programming (LP) were used to solve these problems by formulating fly ash-biosolid triple mixtures which complied with both plant and soil fertilization requirements, and met existing U.S.A. environmental regulations for total As application in sewage sludge (EPA-503). Thirteen different fly ash samples were LP-formulated with sewage sludge, poultry manure, CaCO₃, and KCl to yield 13 unique mixtures, which were then evaluated in greenhouse pot experiments. Results indicated that normal growth and balanced nutrition of sorghum (Sorghumbicolor L.) and soybean (Glycine max (L.) Merr.) crops were achieved in all mixtures, comparable to a balanced fertilizer reference treatment, and significantly better than the untreated control. Phytotoxic levels of B, NH₃, NO₂ ^-, overliming problems, and excessive As levels which were previously encountered from indiscriminate use of these waste materials, were all well controlled by LP-formulated mixtures. Most fly ash quantities in mixtures were limited by either available B (< 4 kg ha^-1) or total As (< 2 kg ha^-1) restrictions during formulation, while the most alkaline fly ash was limited by its high calcium carbonate equivalence (CCE = 53.9%). These results confirmed that fly ash land application should not be at arbitrary fixed rates, but should be variable, depending on the soil, crop, and particularly the fly ash chemistry.     

Speciation of Selected Minor and Major Elements in Oil Ash I. Operationally Defined Chemical Associations and Aqueous Speciation

This study is focused on the speciation of selected elements in oil ash. Our efforts were directed primarily to obtain information on the various forms of vanadium, chromium and nickel. One sample was characterized via its total composition and via its capacity for releasing various elements. The latter was estimated by hot water and nitric acid extractios. A rapid cold water extraction technique has been developed and utilized for sample preparation prior to aqueous speciation by high pressure ion chromatography (HPIC). Results of the HPIC measurements, in agreement with electron spin resonance (ESR) investigations performed on the solid sample, indicate that 38% of the vanadium is present as VOSO₄, 58% of the chromium is Cr₂(SO₄)₃ and 30% of the nickel is NiSO₄. The pH and the redox potential values of the cold water extract support the existence of these forms. Results of a generic study with successive fractionation extractions show the probable existence of oxides, associations with organic matter and aluminosilicate minerals.     

Solubility and Fractionation of Different Metals in Fly Ash of Powder River Basin Coal

Coal is one of the major sources of fuel for electricity production and will continue to be used for many more decades. Thus, it is important to study the effects of disposal of coal burning byproducts including fly ash into the environment. In this study, the solubility of cations and anions from the fly ash in water is discussed. Also, the fractionation of different metals from fly ash in water is studied to understand which fraction of the metals would likely be mobilized. The results from these studies suggested that the metals in the fly ash are bound mostly to carbonate, organic, and residual fractions. Also, when water solubility data are modeled with a geochemical model (Visual MINTEQ), the saturation index predictions suggested that brucite (Mg(OH)₂) and calcite (CaCO₃) could potentially precipitate and mineralize the atmospheric CO₂. Such mineralization process could potentially reduce the leaching of toxic metals from fly ash. Results from this study will be helpful in understanding the fate of different metals from fly ash land disposal environments.     

Changes in microbial biomass,CH4 and CO2 emissions,and soil carbon content by fly ash co-applied with organic inputs with contrasting substrate quality under changing water regimes

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.     

Reducing Bioavailability and Leachability of Copper in Soils using Coal Fly Ash,Apatite, and Bentonite

Soils treated with two concentrations of copper (Cu; 200 and 400 mg kg^?1) were amended with three amendments (coal fly ash, apatite, and bentonite) at the rates of 1.5% and 2.5%, respectively. The effects of amendment application on the bioavailability and leachability of Cu in the soil were evaluated using the wheat uptake, single extraction, and sequential extraction tests. The addition of coal fly ash, apatite, and bentonite at the rate of 2.5% increased wheat biomass by 50.5%, 41.1%, and 61.7%, respectively. The application of amendments significantly (P < 0.01) reduced the Cu contents extract that will buy DW (deionized water), TCLP (toxicity characteristics leaching procedure), and DTPA (diethylenetriaminepentaacetic acid) in the soil. The amendments also reduced the water-soluble/exchangeable, carbonate, iron (Fe)–manganese (Mn) oxide, and organically bound fraction contents of Cu but increased the amounts of residual Cu in soil. Our results demonstrated that these amendments were effective in reducing the bioavailability and leachability of Cu in soil.