Weathered Fly Ash Research Articles

Comparative assessment of P adsorption, release kinetics, enzymatic activities of weathered fly ash amended texturally different soils

Safe disposal of huge quantity of fly ash is compulsory to avoid environmental problems, and contents of significant amount of plant nutrients, particularly phosphorus (P), make it a potential amendment in agriculture. A comparative assessment of P adsorption, release kinetics and enzymatic activities of weathered fly ash amended texturally different soils is yet to be explored. This article explores the influence of fly ash with or without FYM on P adsorption parameters and indices, release kinetics, P activity coefficient (PAC) and enzymatic activities in Inceptisol and Vertisol with the treatments comprising graded doses of weathered fly ash and FYM. Increased fly ash doses amplified the P adsorption in soils, which further increased with FYM application. Binding energy, adsorption maxima and P sorption index also augmented by increased doses of fly ash. Gibb’s free energy of adsorption indicated that P adsorption was due to chemisorption. However, rate of P release was 6–10 times higher at initial stages and increased concentration of P through fly ash and FYM quantified higher P diffusion rate. PAC was negatively influenced by higher quantity of fly ash, but FYM positively influences PAC. Enzymatic activities decreased in Inceptisol beyond 200 t ha−1 fly ash; however, 50 t ha−1 FYM nullifies the negative impact of fly ash and increased enzymatic activities in both the soils. Increased maximum P buffering capacity, PAC, enzymatic activities and liming effects on acidic soils suggested better management options of fly ash as slow release P source in crop production along with FYM.

Mineral phases and carbon content in weathered fly ashes

Historically, fly ash generated in the United States was dry disposed on land or sluiced into ponds for solid/liquid separation, while freshly generated ash was sold for application in concrete. Recent seasonal shortages in the fly ash market have generated interest in beneficial application of the ponded ash as a supplementary cementitious material (SCM); however, exposure to water during disposal and permanent storage has impacted the morphology and geochemistry of the ponded coal fly ash. This study examines the mineral phases and carbon content of 27 samples of weathered fly ash, to determine how weathering changed the ash. Thermogravimetry analysis indicates that weathered fly ashes have hydrated phases that contribute to LOI values over 6% (the maximum limit for ash use as SCMs in concrete). Because these ashes have been exposed to water, a significant percentage of total mass loss is due to mineral volatilization and dehydration during thermal treatment. The general inorganic composition of weathered fly ashes is comparable to unweathered fly ashes, and all weathered ashes met the oxide and fineness requirements of Class F fly ashes. The differences between weathered and unweathered fly ashes are primarily related to differences in morphology and volatile behavior during thermal treatment.

Coal gasification ash and Weathered fly ash, as partial replacement of Portland cement – effect on selected durability properties of concrete

This study uses Sasol ashes as cement extenders to contribute to the technology of partially replacing Portland cement by mass. There are two types of Sasol ashes; coal gasification ash (CGA) and weathered fly ash (WFA) produced from low grade coal. These ashes are disposed of by Sasol with no specific utilisation. In this investigation, PC will be partially replaced by mass with WFA, CGA and FA at 10%, 15% and 30% proportions for each type of ash. The durability indices will be measured and compared for all blended specimen (PC/WFA, PC/CGA and PC/FA). A 100% Portland cement specimen will be used as a control. The durability properties will be used to determine the potential of Sasol ashes being used as a cement extender.

Effects of Surfactants on the Removal of Carbonaceous Matter and Dioxins from Weathered Incineration Fly Ash

ABSTRACTOur previous study demonstrated flotation to be effective in removing carbonaceous matter and dioxins from fresh fly ash in medical waste incinerators (MWIs). However, flotation of weathered fly ash seems to be difficult because of the oxidation of the ash surface and the presence of hydrophilic unburned carbon. Three types of surfactants namely nonionic Tween 80, anionic sodium dodecyl sulfate (SDS) and cationic CTAB were employed at different doses to improve flotation performance. Results indicated that Tween 80 exhibited superior decarburization performance compared with SDS and CTAB. The effect of surfactants on dioxin removal was found to correspond to the carbon removal from MWI fly ash. The optimal removal yields (90.6% of carbonaceous matter and 88.6% of dioxins) were obtained when 5% (w/w) Tween 80 was added. However, an excessive dose might cause the dissolution of dioxins.

Chemical and morphological changes of weathered Victorian brown coal fly ash and its leaching characteristic upon the leaching in ammonia chloride and hydrochloric acid

Abstract In this paper, the properties and leaching propensity of weathered Victorian brown coal fly ash have been investigated. This study was conducted to assess if the weathered ash could replace fresh fly ash in mineral carbonation process. Through the use of a variety of advanced instruments, the mineralogical properties of weathered fly ash have been investigated. In addition, the leaching of such a fly ash in the mixture of ammonium chloride and sole hydrochloric acid has been examined. As has been confirmed, the weathered fly ash is dominated by hydrates and carbonates which were formed in aqueous landfilling system. These species were mostly poorly crystallized, and even loosely agglomerated into clusters in the weathered fly ash. Irrespective of the leaching reagent, the target Ca and Mg in weathered fly ash were more easily extracted than in the fresh ash counterpart under the same leaching conditions. In addition, for the use of either leaching agent, the temperature and time played little or marginal role on the extraction of target Ca and Mg out of the weathered fly ash sample. Decreasing the pH of the leaching agent is beneficial in enhancing the extraction of Ca and Mg, at a cost of a gradually lowered selectivity due to the simultaneous elution of impure elements. The optimum pH value was found to be around 4 for the mixture of NH 4 Cl + HCl, which maximized the extraction yields of Ca and Mg close to ~ 70% at a minimal elution of the impurities. This is attributed to the buffering property of NH 3 and its complexing capability to prevent the dissolution of impure elements. Instead, the use of sole HCl even at the same pH value as the mixture of NH 4 Cl + HCl resulted in a deep penetration of protons into particle inside, the intense breakage of ash cluster, and hence, the simultaneous dissolution of plenty of impurities.

Low temperature alkaline activation of weathered fly ash: Influence of mineral admixtures on early age performance

In the field of alkali activated materials, weathered fly ash represents a scarcely explored edge, since most of the studies related to alkali activated fly ash use qualified/highly reactive samples. In this work, early-age behavior of several binary alkali activated binders was assessed in terms of workability, chemical shrinkage, strength development and ultrasonic pulse velocity. The mineral admixtures in the binary systems were blast furnace slag, silica fume and metakaolin. Curing temperature was fixed at 20°C, in opposition to most literature studies that focused on more energy-intensive curing conditions. An efficiency index was defined and calculated in order to synthesize all the results and compare the binders. Silica fume addition did not determine performance improvement even at significant mass percentages (up to 15%). Metakaolin improved significantly the mechanical performance but reduced excessively the paste flowability. Blast furnace slag revealed to be the most effective secondary component, since this system was able to develop a highly promising mechanical performance and exhibit a satisfactory flowability and low early age shrinkage.

Measuring reactive pools of Cd, Pb and Zn in coal fly ash from the UK using isotopic dilution assays

Large volumes of coal fly ash are continually being produced and stockpiled around the world and can be a source of environmentally sensitive trace elements. Whilst leaching tests are used for regulatory purposes, these provide little information about the true geochemical behaviour and ‘reactivity’ of trace elements in coal ash because they are poorly selective. Isotope dilution (ID) assays are frequently used in soil geochemistry as a means of measuring the reactive pools of trace metals that are in equilibrium with soil pore waters. This paper examines the applicability of multi-element ID assays in measuring the labile or reactive pool of Cd, Pb and Zn in a range of fresh and weathered fly ash, where pH is generally much more alkaline than in soils. The method generally worked well using 0.0005M EDTA as a background electrolyte as it provided robust analytical ICP-MS measurements as well as fulfilling the important principle of ID that non-labile metal should not be solubilised. Reactive pools were equivalent to 0.5–3% of the total Pb pool and 4–13% of the total Cd pool. For Zn, where samples had pH<11.5, the reactive Zn pool varied between 0.3% and 2%; when fresh ash samples with pH>11.5 were tested, the method failed as the spiked isotope appeared to be sorbed or precipitated. Ash weathering was found to exert little impact on the lability of Cd, Pb and Zn. Isotope dilution results were compared with 0.43M HNO3 and 0.05M EDTA extractions, these commonly being used as analogues of the ID assay, and concluded that these can be used as fast, cost-effective and simple proxies for the ID assays. Results suggest that ID methods can be used to enhance knowledge of trace element behaviour in fresh and weathered fly ash.

An Investigative Study on the Chemical, Morphological and Mineralogical Alterations of Dry Disposed Fly Ash During Sequential Chemical Extraction

The hazardous elements associated with various physicochemical forms in coal fly ash are of environmental concern due to their leaching potential and subsequent contamination of surface and groundwater in the vicinity of the ash dump. Selective sequential extraction was performed on dry disposed fly ash samples from a coal-fired power station in Mpumalanga province, South Africa. The alteration of the chemical, morphological and mineralogical species of weathered fly ash during the selective sequential extraction was investigated using X-ray fluorescence (XRF), Nano-scan electron microscopy (NANOSEM) and X-ray powder diffraction (XRD). Insoluble residue from the water-soluble fraction is composed of amorphous alumino-silicate. The residues from exchangeable carbonate and Fe and Mn fractions consisted mostly of amorphous alumino-silicate spheres with a lesser quantity of iron-rich spheres. The iron-rich spheres are surrounded by amorphous alumino-silicate spheres. The leaching behavior of trace metals (such as Ce, Y, Nb, Rb, U, and Tl) in weathered dry disposed fly ash was considered to have a dependency relationship with the components of SiO 2 , CaO, MgO, P 2 O 5 , and amount of unburned carbon. The decrease in the quantities of calcite with successive extraction could be considered as a marker of progress of sequential extraction technique. At the same time, the increase in the quantities of quartz could be also considered as an indicator of progress of the sequential extraction scheme. Trace elements bound to exchangeable or carbonate fraction during sequential chemical extraction were found associated with calcite. The elemental concentrations, as determined by electron dispersive x-ray spectroscopy (EDS), were consistent with XRF and XRD data. Therefore, the chemical extractant used in this study proved efficient for extraction of inorganic metals associated with various physicochemical forms in weathered fly ash. Key words: Coal fly ash; Selective sequential extraction; Major components; Trace elements; Morphology; Mineralogical composition

Chemical Weathering in a Hypersaline Effluent Irrigated Dry Ash Dump: An Insight from Physicochemical and Mineralogical Analysis of Drilled Cores

Accumulation of high ionic strength effluents (brines) that require disposal in inland industries where water recycling is necessary due to scarcity is a major challenge. A coal combustion power utility in South Africa utilizing a dry ash disposal system produces 1.765 Mt of fly ash per annum and also employs the zero liquid effluent discharge policy (ZLED) to manage its liquid effluents. Fly ash is conditioned for dust suppression before being conveyed to the ash dumps with the high saline effluent. The saline effluents results from various processes employed for maximum utilization, upgrading and re-use of various mine water and industrial effluents such as RO, EDR, softening and ion exchange in an effort to adhere to ZLED policy. In the ash dumps it is further conditioned by irrigation with the high saline effluents, therefore the ash acts as a repository for the salts. This study is an attempt to understand the chemical weathering of the effluent conditioned fly ash and species mobility in a dry disposal scenario. A combination of leaching tests was performed for fresh ash and drilled cores to estimate the highly leachable species. Results from DIN-S4 tests of the fresh and weathered ash reveal that Ca, K, Na, Mg, Ba, SO 4 2- , Se, Mo and Cr are highly leached. Leaching tests also revealed that major soluble components in the solution at equilibrium are Ca, Na, SO 4 2- and K. Weathering profiles of the ash dump cores were observed to follow a similar trend. The greatest weathering was observed to take place at the top layer (0.55-3 m depth) in the weathered ash cores (15 years and older), showing that infiltration of rain water over time has a profound effect on the decrease of the pore water pH. Analysis of the extracted pore water in each of the different weathered ash cores by depth indicated the mobility of several elements through the ash. Increased cation exchange capacity at 4-5 m depth suggests a transient mineralization zone. Key words : Weathered fly ash; Pore water; Ash dumps; Hypersaline effluents; X-ray diffraction analysis; DIN-S4 test; Cation exchange capacity

Comparative study on elemental composition and DNA damage in leaves of a weedy plant species, Cassia occidentalis, growing wild on weathered fly ash and soil

Open dumping of fly ash in fly ash basins has significant adverse environmental impacts due to its elevated trace element content. In situ biomonitoring of genotoxicity is of practical value in realistic hazard identification of fly ash. Genotoxicity of openly disposed fly ash to natural plant populations inhabiting fly ash basins has not been investigated. DNA damage, and concentrations of As, Co, Cr, Cu and Ni in the leaves of natural populations of Cassia occidentalis growing at two contrasting sites-one having weathered fly ash (fly ash basin) and the other having soil (reference site) as plant growth substrates-were assessed. The foliar concentrations of As, Ni and Cr were two to eight fold higher in plants growing on fly ash as compared to the plants growing on soil, whereas foliar concentrations of Cu and Co were similar. We report, for the first time, based upon comet assay results, higher levels of DNA damage in leaf tissues of Cassia occidentalis growing wild on fly ash basin compared to C. occidentalis growing on soil. Correlation analysis between foliar DNA damage and foliar concentrations of trace elements suggests that DNA damage may perhaps be associated with foliar concentrations of As and Ni. Our observations suggest that (1) fly ash triggers genotoxic responses in plants growing naturally on fly ash basins; and (2) plant comet assay is useful for in situ biomonitoring of genotoxicity of fly ash.

Weathered Fly Ash Does Not Affect Soil And Biosolid Carbon Mineralization

Fly ash and biosolid wastes can be mixed and applied to soil as a means of disposal. A significant decline in soil respiration following waste application indicates restricted activities of functional microbial populations. Weathering decreases salinity and neutralizes alkalinity in fly ash, but there is little information on the effects of unweathered fly ash and biosolid mixtures on soil carbon (C) mineralization. The objective of this study was to determine the effects of a weathered fly ash–limestone scrubber residue (LSR) mixed with an aerobically digested biosolid on soil respiration in a laboratory incubation study. Biosolids significantly increased carbon dioxide (CO2) production (p < 0.05), but up to 6.75% (w/w) fly ash did not. Mean total C mineralization was 770 mg CO2‐C kg−1 soil in the control and 3,810 mg CO2‐C kg−1 soil in the 6.75% (w/w) biosolid treatment. Fly ash with neutral pH and low salinity appears unlikely to affect soil and biosolid C mineralization.

Bioaccumulation and translocation of metals in the natural vegetation growing on fly ash lagoons: a field study from Santaldih thermal power plant, West Bengal, India

A field study was conducted in the fly ash lagoons of Santandih Thermal Power Plant located in West Bengal (India) to find out total, EDTA and DTPA extractable metals in fly ash and their bioaccumulation in root and shoot portion of the naturally growing vegetation. Fly ash sample has alkaline pH and low conductivity. The concentration of total Cu, Zn, Pb and Ni were found higher than weathered fly ash and natural soil, where as Co, Cd and Cr were found traces. Five dominant vegetation namely, Typha latifolia, Fimbristylis dichotoma, Amaranthus defluxes, Saccharum spontaenum and Cynodon dactylon were collected in the winter months (November-December). Bioaccumulation of metals in root and shoot portions were found varied significantly among the species, but all concentration were found within toxic limits. Correlation between total, DTPA and EDTA extractable metals viz. root and shoot metals concentration were studied. Translocation factor (TF) for Cu, Zn and Ni were found less than unity, indicates that these metals are immobilized in the root part of the plants. Metals like Mn have TF greater than unity. The study infers that natural vegetation removed Mn by phytoextraction mechanisms (TF > 1), while other metals like Zn, Cu, Pb and Ni were removed by rhizofiltration mechanisms (TF < 1). The field study revealed that T. latifolia and S. spontaenum plants could be used for bioremediation of fly ash lagoon.

Geochemistry of leachates from coal ash

Abstract The combustion of coal around the world for power generation produces huge volumes of fly ash. In Europe alone this amounted to about 40 Mt in 2000 of which less than 50% was utilized. The waste ends in lagoons, ash mounds, and landfill sites. Coal ashes have high concentrations of many trace elements, some of which are of environmental concern. Although the origin of elements in coals is not considered in this chapter, other aspects of the geochemistry are, and in particular the location of elements within the coal as this influences the behaviour of elements during combustion. During combustion many elements are volatile and are concentrated on the surfaces of the ash particles. Analyses of input coal and combustion residues from Eggborough power station (UK) demonstrate retention of the majority of elements in the solid combustion products, and analyses of size-fractionated fly ash have enabled the percentage surface association to be calculated, which for elements such as As and Mo is considerable. A consideration of the general leaching behaviour leads to the conclusion that it is the surface-associated elements that are most susceptible to leaching in the aqeous environment. The pH is an important control on trace element mobility in water, and in leachates from fly ash ranges from 3.3 to 12.3. High-sulphur coals generate acidic leachates, but not exclusively as the laboratory and field data demonstrate in case studies on UK coals. Batch and column leaching tests on fly ashes are reviewed and data presented for fresh fly ash and weathered fly ashes from two UK mounds dating back 17 and 40 years. The weathered ashes do have lower leachate concentrations than the fresh ash, but in spite of their ages they would not be considered to be inert. The batch leaching tests are of value in simulating high liquid-to-solid ratios encountered in ash lagoons, whereas the column leaching tests relate more closely to ash mounds. Finally, the results of field studies are reviewed and data presented for samples from boreholes in the two ash mounds. Analyses of the ash and extracted porewaters demonstrate depth-related changes due to reaction of the ash with the infiltrating water and whether or not equilibrium was established. Calculations demonstrate that the porewaters achieve saturation with respect to gypsum at depth in the boreholes. Infiltration over the years has led to detectable changes in the concentrations of some of the major elements in the bulk ash, such as Ca, and this enables realistic infiltration rates to be calculated. However, there are not comparable changes in the concentrations of the trace elements in the ash because the rate at which elements are being removed in solution is not sufficiently great.

Polychlorinated biphenyls removal from weathered municipal solid waste incineration fly ash by collector-assisted column flotation

Polychlorinated biphenyls (PCBs), polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) are highly toxic micropollutants emitted from municipal solid waste incineration (MSWI), in particular, concentrated in the unburned carbon (UC) of MSWI fly ash. Because of concerns over their adverse health effects, a number of countries have classified MSWI fly ash as hazardous material and required further treatment before its final disposal in landfills. The technologies for removing the toxic chlorinated micropollutants in the MSWI fly ash have been studied, however, until now no mature technique has been obtained in this purpose. In this research, we used a technique of collector-assisted column flotation to remove PCBs-enriched UC from MSWI fly ash. We found that 36.9% PCBs could be removed from fresh MSWI fly ash with 61.7% UC removal efficiency, whereas only 21.7% PCBs could be removed from weathered MSWI fly ash with a low UC removal efficiency of 33.7%. By adding a mixture of two kinds of surfactants: sorbitan mono-oleate and polyoxyethylene (20) sorbitan mono-oleate to the weathered fly ash slurry as the collector assistant, 39.3% PCBs was removed at the hydrophile–lipophile balance (HLB) value of 13.5, while the UC removal efficiency increased to 49.0%. The results showed that the collector assistant could enhance PCBs and UC removal efficiencies during the column flotation process, and the mechanism has been discussed in detail. Higher PCBs and UC removal efficiencies could be expected by further optimizing the conditions of collector-assisted column flotation.

Chlorobenzenes removal from municipal solid waste incineration fly ash by surfactant-assisted column flotation

The organic contaminants in municipal solid waste incineration (MSWI) fly ash, including chlorinated aromatic compounds and polycyclic aromatic hydrocarbons, have high toxicity and a potential negative impact on the environment. An effective and low energy consumption technique to remove the organic contaminants from MSWI fly ash is required urgently. Organic contaminants, such as chlorobenzenes (CBzs), in MSWI fly ash are known to become enriched in the unburnt carbon (UC) fraction. It is proposed that removal of UC from fly ash will result in the effective removal of most organic micropollutants. In this research, we use a technique of surfactant-assisted column flotation to decontaminate MSWI fly ash by removal of the CBzs-enriched UC from MSWI fly ash. We find that 39.8% of CBzs can be removed from fresh MSWI fly ash with 61.7% UC removal efficiency, whereas only 33.2% of CBzs can be removed from weathered MSWI fly ash with a low UC removal efficiency of 33.7%. By adding a mixture of two kinds of surfactants: sorbitan mono-oleate and polyoxyethylene (20) sorbitan mono-oleate to the weathered fly ash, 47.0% of CBzs were removed at the hydrophile lipophile balance value of 13.5, while the UC removal efficiency increased to 49.0%. The results show that surfactants can enhance CBzs and UC removal efficiencies during the column flotation process. Higher CBzs and UC removal efficiencies can be expected by further optimizing the conditions of surfactant-assisted column flotation.

Leaching characteristics of selected Korean fly ashes and its implications for the groundwater composition near the ash disposal mound

Currently only 20% of the fly ash produced in Korea is utilised for industry, and the remainder is disposed as waste in landfill sites. Both anthracite and sub-bituminous coals are burnt in Korea. Fly ash and coal samples were collected from five different coal-fired power stations in Korea and analysed for their chemistry and mineralogy. Batch leaching tests were also carried out to investigate the leaching behaviour of selected fly ashes. The fly ash leachate chemistry was compared with the groundwater taken directly from the monitoring well installed in one of the power stations. The anthracite coals contain illite, pyrophyllite and kaolinite whereas kaolinite is the representative clay mineral for the sub-bituminous coals. Anthracite coals were higher in Si, Al and K than the sub-bituminous coals, reflecting higher mineral matter contents in the anthracite coals. Mullite and quartz are the main mineral phases for two different types of the fly ashes, with some iron oxides. The chemical compositions of the anthracite and sub-bituminous fly ashes are comparable with each other, except for extraordinary high concentrations of Cr for one anthracite fly ash. Most of the trace elements in the ash were enriched in the finer fraction, indicating surface associations. Although, some elements including Na, K, Ca and Cu were released rapidly in the initial stage of leaching, measurable amounts of metals were still detectable in the fly ash leachate treated several times with distilled water. Such leaching behaviour indicates slow and long-term leaching of elements associated with the glass fractions of the ash particle. This was confirmed by leaching of weathered fly ash, which had been disposed of for several years. Comparison of the ash leachate, treated with 0.1N-HCl, fly ash slurry in the ash pond and the groundwater indicate the influence of the ash leachate from the ash disposal mound on the groundwater composition.

Reduced leaching of nitrate, ammonium, and phosphorus in a sandy soil by fly ash amendment

Low ionic sorption capacities and high hydraulic conductivities of sandy soils contribute to the potential for leaching of nutrients applied to these soils. Batch sorption experiments were used to examine NO3–, NH4+, and P sorption/desorption isotherms for Karrakatta sand and Kwinana fly ash. Column experiments assessed leaching of these nutrients from this sandy soil, when amended with 4 rates (0, 5, 10, and 20%, wt/wt) of fly ash. The sorption of NO3–, NH4+, and P was higher for fly ash than the sandy soil. Phosphorus sorption was greatest for unweathered fly ash, followed by weathered fly ash and then the soil; for example, sorption from a solution containing 20 mg/L P was 90%, 28%, and 14%, respectively. Desorption of P was much slower in the unweathered fly ash than weathered fly ash or the soil. Leachates collected from columns containing fly ash amended soil (5, 10, and 20%, wt/wt) generally had lower concentrations of NO3– and NH4+ than leachates from non-amended soil. Prior to adding fertiliser, the concentration of P was greater in leachate from fly ash amended soil than from the native soil, due to fly ash (weathered) itself containing 92.5 mg/kg of extractable P. However, from day 35 onwards, the concentration of P was lower in leachates from soil amended with 10% or 20% fly ash than from non-amended soil. Thus, fly ash amendment retarded NO3–, NH4+, and P leaching in the sandy soil and may therefore be a useful tool for improvement of nutrient management in sandy soils.

Vegetation Establishment on Soil-amended Weathered Fly Ash

A field study was conducted with the following objectives in mind: (1) to study the effect of soil addition to weathered fly ash on the establishment and survival of different grasses and legumes, (2) to identify suitable grasses and/or legume species for vegetation of fly ash, (3) to study the fertilizer N and P requirements for successful vegetation establishment on fly ash and ash-soil mixtures, (4) to examine the nutrient composition of the plant species tested, and (5) to study the plant availability of P from fly ash and ash-soil mixtures. Three rooting media were used: weathered fly ash, and 33% or 50% soil blended with the ash. Four experiments were established on each of these media to evaluate warm season grasses in pure stands, warm season grasses inter-seeded with legumes, cool season grasses, and cool season grasses inter-seeded with legumes. Soil used in this study was more acidic than the fly ash. Only the results from characterization of the rooting media, ground cover, and yield will be presented here.

Differential effects of weathered coal fly ash and fly ash leachate on the maize genome

Land application of coal fly ash is currently under consideration as a means of reducing the amount of industrial waste that must be landfilled. It has previously been reported that alterations occur in the maize genome when plants are grown in soil mixed with fly ash. This study was conducted to determine whether weathering coal fly ash by leaching it with water prior to mixing it with soil reduces its genotoxic effects. Fly ash leachate was produced by two leaching methods, a “one-day” and a “seven-day” method. Maize seedlings were treated with the two types of leachate and with one of the weathered fly ashes produced from the leaching experiments. Flow cytometry was used to determine whether nuclear alterations occurred in the seedlings as a result of treatment. Fly ash that had been weathered by leaching for one week did not cause changes in the mean DNA (deoxyribonuclei acid) amount (except for an increase in coefficient of variation—CV), plant height, or cell cycle. The leachate produced from this weathering process, however, caused changes in all these parameters. Leachate produced from a 24-h weathering process did not affect mean DNA amount, but did cause small changes in CV, plant height, and cell cycle. Weathering fly ash by leaching before applying it to the soil appears to reduce its potential hazard to the ecosystem. The leachate resulting from the weathering process is toxic to plants.

Trace element toxicity in va mycorrhizal cucumber grown on weathered coal fly ash

Mycorrhizal colonization is widely recognized as enhancing plant growth on severely disturbed sites. A greenhouse pot experiment was conducted to determine if inoculation with vesicular-arbuscular mycorrhizal (VAM) fungi will enhance vegetation establishment on abandoned coal fly ash basins. Spores of Glomus intraradices (Schenck and Smith) and Glomus etunicatum (Becker and Gerdemann) were added to weathered precipitator ash (EC = 0.91 dS m −1; pH 5.0) and to a pasteurized soil of the same pH (Grossarenic Paleudult, 92% sand, 1% organic matter). Some soil and ash were left unamended as non-mycorrhizal controls. Cucumber ( Cucumis sativus L. cv. Poinsette 76) seeds were sown, watered regularly, and fertilized periodically with macro-nutrient solution. By 8 weeks old, all ash-grown plants exhibited smaller leaves with leaf margin curl and necrosis, and plant biomass was significantly less (0.75 ×) than soil-grown plants. Based on analysis of 18 elements in plant tissues, toxicity to B, Mn or Zn could have caused growth suppression, confirming trace element problems for plant growth on fly ash. For plants grown on fly ash, G. etunicatum was the only fungus that colonized roots (20% of root length reduced from 67% on soil) and it suppressed plant growth to 0.80 × that of uninoculated ash-grown plants. Correspondingly, shoot Zn concentration in G. etunicatum -inoculated plants was 3.5 × higher than in uninoculated plants and at generally toxic levels (273 mg kg −1)- Glomus etunicatum had no other significant effects on elemental concentrations. These results indicate that VAM colonization in acid, weathered fly ash suppressed plant growth by facilitating uptake of Zn to toxic levels, and implies a limitation to successful use of VAM for vegetation establishment on abandoned coal fly ash basins.