Water Leaching Tests Research Articles

Effects of extraction methods and factors on leaching of metals from recycled concrete aggregates.

Leaching of metals (calcium (Ca), chromium (Cr), copper, (Cu), iron (Fe), and zinc (Zn)) of recycled concrete aggregates (RCAs) were investigated with four different leachate extraction methods (batch water leach tests (WLTs), toxicity leaching procedure test (TCLP), synthetic precipitation leaching procedure test (SPLP), and pH-dependent leach tests). WLTs were also used to perform a parametric study to evaluate factors including (i) effects of reaction time, (ii) atmosphere, (iii) liquid-to-solid (L/S) ratio, and (iv) particle size of RCA. The results from WLTs showed that reaction time and exposure to atmosphere had impact on leaching behavior of metals. An increase in L/S ratio decreased the effluent pH and all metal concentrations. Particle size of the RCA had impact on some metals but not all. Comparison of the leached concentrations of metals from select RCA samples with WLT method to leached concentrations from TCLP and SPLP methods revealed significant differences. For the same RCA samples, the highest metal concentrations were obtained with TCLP method, followed by WLT and SPLP methods. However, in all tests, the concentrations of all four (Cr, Cu, Fe, and Zn) metals were below the regulatory limits determined by EPA MCLs in all tests with few exceptions. pH-dependent batch water leach tests revealed that leaching pattern for Ca is more cationic whereas for other metals showed more amphoteric. The results obtained from the pH-dependent tests were evaluated with geochemical modeling (MINTEQA2) to estimate the governing leaching mechanisms for different metals. The results indicated that the releases of the elements were solubility-controlled except Cr.

Mechanical and Environmental Suitability of Recycled Concrete Aggregate as a Highway Base Material

The use of recycled concrete aggregate (RCA) materials in highway constructions is economically viable and reduces virgin natural resource demands on the environment. To evaluate their potential use in highway construction, two different RCA materials and four virgin granular aggregate base (GAB) materials and their select mixtures were tested in the laboratory for strength, resilient modulus, permanent deformation, and durability. Laboratory water leach tests and pH-dependent leaching tests were conducted to determine the environmental suitability of the RCA materials. The leaching behavior of Ca, Cr, Cu, Fe, and Zn and the effects of pH, curing time, liquid-to-solid (L∶S) ratio, and particle size on metal leaching from the RCAs were investigated. Summary resilient moduli (SMR) of the RCAs were up to 2.6 times higher than that of the GAB materials. Their stiffness also increased when subjected to freezing and thawing cycles. Consistent trends could not be observed with percent RCA addition and strength or SMR; however, the RCAs generally yielded higher permanent deformations compared with the GABs. Prolonged curing caused rehydration of cement particles and, in general, yielded a decrease in pH and leached metal concentrations. Increasing the L∶S ratio decreased leaching of elements significantly because of the dilution of leached elements in the aqueous solutions. pH excursions yielded cationic leaching patterns for Ca and amphoteric leaching patterns for Cr, Cu, Zn, and Fe.

Geotechnical and Leaching Properties of Municipal Solid Waste Incineration Fly Ash for Use as Embankment Fill Material

The beneficial use of municipal solid waste incineration (MSWI) fly ash promotes sustainability in highway construction. This study investigated the geotechnical and chemical leaching characteristics of fresh and aged MSWI fly ash samples for use of the material in highway construction applications. The results show that the geotechnical properties of MSWI fly ash resemble those of silty sands with poor drainage capacity. Compared with fresh ash (<10 days since placement), aged ash (3 to 6 months) has a higher California bearing ratio, higher unconfined compressive strength, and greater freeze–thaw durability. The concentrations of cadmium, chromium, selenium, silver, and sulfate from water leach tests are below the limits stipulated in Wisconsin NR 538. The concentrations of heavy metals in leachate from Synthetic Precipitation Leaching Procedure tests are below the U.S. Environmental Protection Agency’s standard maximum contaminant level, with the exception of arsenic. Cumulative mass release from column leach tests indicates that fresh ash will release more heavy metals than aged ash during long-term leaching processes. According to the geotechnical and environmental test results in this investigation, aged MSWI fly ash is identified as a viable material for potential use in roadway construction.

Treatment Methods for Mitigation of High Alkalinity in Leachates of Aged Steel Slag

AbstractSteel slag, a by-product of the steel-making industry, after it is aged, has a huge potential for use as a replacement of natural aggregates in highway construction. However, the high pH of leachates from aged steel slags is a major impediment for its beneficial use. This study hypothesized that minimizing hydration of CaO-containing mineral phases in slag can reduce leachate alkalinity. Treatment methods that include coating steel slag with bitumen, bathing steel slag in either Fe(III), Al(III), or PO4(-III), and mixing steel slag with an alum-based drinking water treatment residual (WTR) were designed and evaluated based on reduction in Ca release, pH, and alkalinity in the leachate of treated steel slag samples. According to batch-type 18-h water leach test results, bitumen coating (4% of dry weight) and Al2(SO4)3 passivation (0.05–0.10 M as Al) were able to reduce Ca release 50–70% and the levels of alkalinity mitigation were proportional to the reductions in Ca release. WTR addition provided ...

Effects of pH on the leaching mechanisms of elements from fly ash mixed soils

A laboratory pH-dependent batch water leach tests were conducted to investigate the leaching behavior of Al, Zn, Cr, Cu, Fe and Mn from soil–fly ash mixtures used in highway constructions under the influence of pH. Soil fly ash mixtures were prepared from six different soils (clayey and sand) and seven different fly ashes (C-type and high carbon fly ash) collected from Wisconsin, Minnesota and Maryland. Mn showed cationic leaching patterns where Mn concentrations decreased monotonically as pH increased, while Al, Cr, Cu, Fe, and Zn showed amphoteric leaching patterns where concentrations of these metals increased at acidic and alkaline pH. An increase in fly ash content increased the leached metal and mineral concentrations from soil–fly ash mixtures. Consistency in leaching behavior for many elements was observed between fly ash and soil–fly ash mixtures. High concentration of dissolved organic carbon in leachate was likely responsible for the increased leaching of Cu from the mixtures with soil having high organic matter. The Geochemical Model MINTEQA2 was used to determine the dominant oxidation states of leached metals and define their leaching controlling mechanisms. The results of geochemical modeling analyses indicated that releases of the elements were solubility-controlled. For a given element, the solubility-controlling solids were found to be very consistent. Oxide and hydroxide minerals control leaching of Al, Fe, Zn, and Cr, and leaching of Cu was controlled by oxide and/or carbonate minerals.

Preventing Swelling and Decreasing Alkalinity of Steel Slags Used in Highway Infrastructures

Steel slag is a byproduct of iron and steel production by the metallurgical industries. Annually, 21 million tons of steel slags are produced in the United States, and most of this slag is landfilled. Landfilling represents significant economic loss and uses valuable land space. Although steel slag has great potential for use in highway applications, especially as a granular highway base or subbase material, it has not been used extensively because of its high swelling potential and alkalinity. Swelling potential deteriorates the structural stability of highways, and high alkalinity poses an environmental challenge. This study seeks a methodology that promotes the use of steel slags in highway base and subbase layers by minimizing these two main disadvantages. Two treatment methods were used. In the first method, steel slag material was coated with bituminous material. In the second method, the slag was mixed with water treatment residuals at various percentages by weight. The mixtures prepared in this study were subjected to accelerated swelling tests and batch water leach tests. Results of the swelling tests indicated that the addition of both water treatment residuals and bituminous material into steel slag decreased the swelling rate significantly. Furthermore, bituminous-coated mixtures did not exhibit any swelling. These two methods also decreased the effluent pH of steel slag from 12.3 to 11.65 (bitumen-coated slag) and 9.8 (slag mixed with water treatment residuals). The batch test results did not satisfy the pH 8.5 limit regulated by the Maryland Department of Environment for placement of industrial byproducts in highways.

PH and fly ash type effect on trace metal leaching from embankment soils

A laboratory research program was initiated to assess the environmental suitability of highway embankment structures built with high carbon fly ash and C-type fly ashes. Two different laboratory leaching tests, water leach tests (WLTs) and column leach tests (CLTs), were conducted to study boron (B), manganese (Mn), molybdenum (Mo), and selenium (Se) leaching from the soil/fly ash mixtures. The results indicated that an increase in fly ash content increased the pH of the effluent solutions and generally increased the leached metal concentrations significantly. The mass of leached metals in WLTs was higher than those in CLTs with few exceptions. It was concluded that pH had great effects on the leaching of B, Mn, Mo, and Se metals and an increase in pH yielded an increase in the leached concentrations of B, Mo and Se while it caused a decrease in the Mn concentrations in the aqueous solutions. Fe2O3 and Al2O3 contents of the fly ashes decreased the leached Mn concentrations while no significant effect on leaching of Mo, Se and B metals was observed. Unburned carbon content of fly ashes did not have a direct effect on metal leaching.

Leaching of As, Cr, and Cu from High-Carbon Fly Ash–Soil Mixtures

Three coal fly ashes (FA) with different acid-base characteristics and unburned carbon contents, and their mixtures with a typical embankment soil, were analyzed for arsenic, copper, and chromium leaching as a function of pH using batch-type water leach tests. Final leachate pH of the samples was linearly correlated (R2=0.84) to their water-soluble Ca (a surrogate for soluble CaO) and oxalate-extractable Fe concentrations (a surrogate for amorphous iron hydroxides). The leaching behavior of Cu, Cr, and As appear to be primarily governed by leachate pH, and no significant difference in terms of leaching trends was observed among different fly ashes solely attributable to different unburned carbon content. At acidic pH, increased Cu and Cr (presumably in the form of CrIII) leaching were observed. CrVI was determined as the predominant species in leachates. As and CrVI were strongly retained below pH 7 and leached more at alkaline pH. According to CrVI sorption test results, CrVI retention capacity was higher for fly ashes with higher oxalate-extractable iron content. Thus, minimum metal release occurred from mixtures that produced leachates with pH values near neutral range. The leachate pH of acidic fly ash could be increased by adding soil or ash with neutral characteristics. The fly ash-to-soil ratio should be carefully adjusted because soil addition to ashes improved compactibility of the mixtures but also reduced the retention capacity for As and CrVI. Regardless, pH of naturally alkaline fly ash with high soluble CaO content could not be decreased to a neutral range and leached more metal, especially toxic CrVI.

Trace Metal Leaching from Embankment Soils Amended with High-Carbon Fly Ash

AbstractThe use of fly ash in highway applications as a stabilizing agent and soil amendment for embankments has become very common owing to its economical advantages. However, fly ash may contain toxic constituents that may pose environmental risk if they leach through the soil and reach groundwater. A series of water leach tests (WLTs), toxicity characteristic leaching procedure (TCLP) tests, and column leach tests (CLTs) were conducted to define the leaching of aluminum, arsenic, chromium, and zinc from a self-cementitious fly ash and four different off-spec high-carbon ashes. Laboratory results indicated that an increase in fly ash contents generally yields an increase in pH and leached metal concentrations regardless of the type of fly ash and metals. Furthermore, it was determined that there were significant differences in the leached metal concentrations measured in the three different laboratory tests, i.e., CCLT>CTCLP>CWLT. Analyses conducted using a numerical groundwater model indicated that pre...

Influence of soil mineralogy and chemistry on fungi and plants in a waste-rock dump from the Libiola mine (eastern Liguria, Italy)

This work illustrates the results of a multidisciplinary study aimed at understanding the relations among the mineralogy and chemistry of a sulphidic waste rock-dumps from the Libiola mine (eastern Liguria, Itlay) and the metal uptake by fungi and plants spontaneously growing in a flat part at the bottom of this dump. The soil of the studied dump is characterized by severe edaphic conditions, mainly represented by high concentration of several toxic metals (Cr, Cu, Co, Ni, and Zn), low pHs, paucity of nutrients (in particular P, Ca, and K) and presence of superficial Fe-rich hardpans. Despite these harsh environmental conditions, the studied waste rock dump has been progressively colonized by several plants of Pinus pinaster . We found that this species is able to cope with some of these limiting factors by completely avoiding toxic metals from its tissues. The success of Pinus pinaster colonization is mainly due to the presence of Telephora terrestris and Scleroderma polyrrhizum, ectomycorrhizic with pine. These fungi are also able to actively absorb in their basidiomata most of the potential toxic elements occurring in the mine spoil. The recognized absorption sequence Cu > Zn > Cr > Ni > Co obtained for these macrofungi well matches with the sequences resulted from water leaching tests and EDTA extractions. The results obtained in our work highlighted the importance of multidisciplinary studies to clarify the influence of mineralogical and chemical composition on metal accumulation or resistance by native plants and mycobiota in abandoned mining sites. This may also have important implications for fungi and plants potential use in future forestation programs on metal contaminated sites.

Soil-water interaction in soils of the Po River Plain (Ferrara, Northern Italy): insights on heavy-metal mobility and phytoavailability

The soils of the Po River plain, developed on the alluvial sediments, are often characterized by high concentration of heavy metals, in particular chromium and nickel. These geochemical anomalies are “geogenic”, i.e. related to the specific nature of the “mother rocks” outcropping in the basin that typically include mafic and ultramafic lithologies. The elevated heavy metal backgrounds of soils potentially represent an effective geochemical risk considering the toxicity of these elements. In order to delineate soil quality thresholds and to provide guidelines for human activities (e.g. agriculture) the current legislation takes into consideration the “pseudototal” metal content obtained with aqua regia extraction tests. However, only a fraction of this chemical budget is available for plant and human uptake. Soil leaching tests with deionized water plausibly provide a better analogue to simulate the natural soil-water interactions, in order to predict the behavior of metals in the environment. In particular, in this paper we investigate with water leaching tests soils sampled in the surrounding of Ferrara (eastern part of the Po plain) that were previously characterized by bulk XRF analyses and aqua regia extractions. The approach gives insights on the element-specific transport parameters, giving clues for a) the possible contamination of the natural water and b) the soil-to-plant uptake processes and phytoavailability. Results, expressed as solid-water partition coefficients, highlight that nickel is significantly more mobile and bioaccessible than chromium and should be monitored in the local agricultural products to avoid its possible transfer and bioaccumulation in the food chain.

Powder Injection Moulding of Alumina Using PEG/PVB Binder Systems

Powder injection moulding (PIM) is a process that is suitable for a fabrication of small and complex shape components. It consists of 4 main steps: feedstock preparation by mixing powder and binder, injection moulding of the prepared feedstock into the desired mould, removal of the binder and finally sintering to obtain materials with specific properties. In this study, powder injection moulding of alumina (Al2O3), using polyethylene glycol (PEG) based binder systems, was investigated. PEG is soluble in water; therefore, the use of organic solvents required for debinding of wax-based binder system can be avoided. PEG with a molecular weight of either 1500 or 4000 was used as a major constituent together with polyvinyl butyral (PVB) as a minor component. Stearic acid was also added during feedstock preparation to act as a lubricant. After mixing the powder with the binder, a variety of Al2O3 feedstocks were injected into the moulds. The mouldings were prepared by a laboratory-scaled plunger-typed machine. Debinding was carried out using a combination of solvent extraction and thermal debinding. Water leaching tests were performed at 30 and 50 °C to study PEGs removal rate. The pyrolysis of PVB was completed during ramping up of the mouldings to the sintering temperature. The mouldings were subjected to sintering at 1500 °C in air. It was found from the study that PEG/PVB binder systems can be used for the preparation of alumina powder injection moulding feedstocks. Specimens retained their shapes during and after leaching of the PEGs.

Lead Retention by Soils at Field Moisture Contents

The majority of studies pertaining to lead retention by clays and soils have examined the mechanisms, kinetics, and adsorption isotherms using the batch experiment technique that employs solid: water extracts of 1:10 and 1:20. Field soil deposits generally have much lower gravimetric water content ranging between 9 and 45%. Given the wide disparity in the solids: water ratio employed in the batch experiment technique and that prevailing in field deposits, this paper examines the lead retention characteristics of soils at field moisture contents (6%, 13%, and 25%) using artificially lead-contaminated soil specimens. A residually derived (i.e., formed by in-situ weathering of parent rock) red soil was used to prepare the artificially contaminated soil specimens. The impact of variations in clay content on lead retention was examined by diluting the residual soil with various amounts (0 to 60%) of river sand. Soil specimens remolded at 6 and 13% moisture contents produced very stiff to hard soils on compaction, while specimens remolded at 25% moisture content existed in the slurry state. The soil specimens were contaminated with low (30 mg/kg) to high (2500 mg/kg) concentrations of lead ions by remolding them with 160 ppm to 10,000 ppm ionic lead solutions. Lead retention by soils at field moisture contents was determined by extracting the lead from the soil using a water leach test. Experimental results showed that the bulk (71 to 99%) of the added lead was retained by the soil in insoluble form at the field moisture content. Correlations between the amount of lead retained and soil/solution parameters indicated that the amounts of Pb retained at field moisture content is a function of the initial Pb addition, total sand content, effective clay porosity, and soil pH.

Contaminants removal by bentonite amended slow sand filter

Earlier studies have indicated that variability in size, surface texture and charge greatly influence the contaminant removal process in granular media. Based on surface characteristics of montmorillonite, it is anticipated that small addition of this clay would increase adhesion sites for bacterial growth and extracellular polymer production in the slow sand filter and thereby enhance its contaminant removal ability. Experiments were performed by permeating groundwater contaminated with pathogens (total coliform and E. Coli) and inorganic contaminants through the bentonite amended slow sand filter (BASSF). Surprisingly, the BASSF retained inorganic contaminants besides pathogens. Water-leach tests (pH of water leachate ranged from 2 to 9) with spent BASSF specimen indicated that the inorganic contaminants are irreversibly adsorbed to a large extent. It is considered that the combined effects of enhanced-organic matter mediated adhesion sites and increased hydraulic retention time enables the BASSF specimen to retain inorganic contaminants. It is envisaged that BASSF filters could find use in treating contaminated groundwater for potable needs at household and community level.

Evaluation of Leaching Protocols for Testing of High-Carbon Coal Fly Ash–Soil Mixtures

Beneficial reuse of coal combustion byproducts, e.g., in highway construction, requires an evaluation of metal leaching potential. Metal leaching from high-carbon fly ash in soil mixes typical of highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Maximum CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might initially exceed regulatory limits, but only for a short time. A comparison of leaching results is discussed as a framework for the development of a flexible, integrated leaching protocol incorporating elements of batch and column leach tests to provide more accurate, site-specific leaching predictions given time and cost constraints. DOI: 10.1061/(ASCE)EE .1943-7870.0000668. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Chromium; Copper; Arsenic; Coal; Soils; Mixtures; Recycling. Author keywords: Leaching; Fly ash; Batch leach test; Column leach test; Chromium; Arsenic; Copper.

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM–fly ash–lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM–fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.

Leaching of Metals from Fly Ash–Amended Permeable Reactive Barriers

AbstractOne potential beneficial reuse of high-carbon-content (HCC) fly ashes is in reactive barrier applications for remediation of contaminated groundwater. However, leaching of metals from coal fly ashes into the environment is of concern. A series of column leach tests (CLTs) and batch water leach tests (WLTs) were performed to investigate the potential leaching of metals from HCC fly ashes during reactive barrier applications. Fly ash content and pH were two key factors affecting the amount leached in WLTs. Leaching of metals in CLTs exhibited a first flush, followed by a tailing elution pattern, for all fly ashes. Attempts to correlate the WLT and CLT data indicated that scale-up of the WLT results to the column experimental setup provided a better prediction of the leachable amount in CLTs compared with a direct comparison of concentrations. Nevertheless, caution should be exercised when building correlations because of the different testing conditions in the two test setups.

Arsenic and antimony contamination of waters, stream sediments and soils in the vicinity of abandoned antimony mines in the Western Carpathians, Slovakia

Abstract Environmental contamination with As and Sb caused by past mining activities at Sb mines is a significant problem in Slovakia. This study is focused on the environmental effects of the 5 abandoned Sb mines on water, stream sediment and soil since the mines are situated in the close vicinity of residential areas. Samples of mine wastes, various types of waters, stream sediments, soils, and leachates of the mine wastes, stream sediments and selected soils were analyzed for As and Sb to evaluate their geochemical dispersion from the mines. Mine wastes collected at the mine sites contained up to 5166 mg/kg As and 9861 mg/kg Sb. Arsenic in mine wastes was associated mostly with Fe oxides, whereas Sb was present frequently in the form of individual Sb, Sb(Fe) and Fe(Sb) oxides. Waters of different types such as groundwater, surface waters and mine waters, all contained elevated concentrations of As and Sb, reaching up to 2150 μg/L As and 9300 μg/L Sb, and had circum-neutral pH values because of the buffering capacity of abundant Ca- and Mg-carbonates. The concentrations of Sb in several household wells are a cause for concern, exceeding the Sb drinking water limit of 5 μg/L by as much as 25 times. Some attenuation of the As and Sb concentrations in mine and impoundment waters was expected because of the deposition of metalloids onto hydrous ferric oxides built up below adit entrances and impoundment discharges. These HFOs contained >20 wt.% As and 1.5 wt.% Sb. Stream sediments and soils have also been contaminated by As and Sb with the peak concentrations generally found near open adits and mine wastes. In addition to the discharged waters from open adits, the significant source of As and Sb contamination are waste-rock dumps and tailings impoundments. Leachates from mine wastes contained as much as 8400 μg/L As and 4060 μg/L Sb, suggesting that the mine wastes would have a great potential to contaminate the downstream environment. Moreover, the results of water leaching tests showed that Sb was released from the solids more efficiently than As under oxidizing conditions. This might partly explain the predominance of Sb over As in most water samples.

Leaching of trace metals from high carbon fly ash stabilized highway base layers

Fly ash produced by power plants in the United States occasionally contains significant amounts of unburned carbon due to the use of low nitrogen-oxide and sulphur-oxide burners in recent years. This ash cannot be reused in concrete production due to its reactivity with air entrainment admixtures and is largely placed in landfills. Roadways have high potential for large volume use of high carbon fly ash (HCFA). HCFA can be activated with lime kiln dust (LKD) and used as a base layer for newly paved roads. However, in such applications, the leaching of heavy metals from fly ash-stabilized base layers can be of concern. A series of batch water leach and column leach tests were conducted to investigate the leaching potential of six metals, Al, Cr, Fe, Mn, Sb and V, from the fly ash-lime kiln dust (LKD) stabilized soils. The results indicate that an increase in LKD amount, pH, and fly ash content have significant effects on leaching behavior of heavy metals from soil–fly ash–LKD mixtures. All six metals, except Al, exhibited a first flush pattern in column leach tests, and the measured concentrations quickly decreased to below EPA maximum concentration limits (MCLs) for drinking waters.

Trace Elements Leaching from Organic Soils Stabilized with High Carbon Fly Ash

AbstractLeaching of four trace elements [cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag)] from soft organic soils stabilized with high carbon fly ashes (HCFAs) was assessed using water leach tests (WLTs) and column leach tests (CLTs) on soil alone, fly ash alone, and soil-fly ash mixtures. Concentrations from the WLTs on soil-fly ash mixtures were lower than concentrations from the WLTs on fly ash alone, and were controlled more by the fly ash than the soil. However, dilution calculations based on tests on soil alone and fly ash alone were unreliable. Thus, leaching assessments should be conducted directly on soil-fly ash mixtures. Leaching patterns from the CLTs followed first-flush and lagged-response patterns with comparable frequency, although first-flush patterns were more common with fly ash with higher calcium oxide content. Cd and Cr exhibited first-flush leaching more frequently, Ag a lagged-response pattern more frequently, and Se exhibited first-flush or lagged-response patterns wit...