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Title: Leaching behavior of lime-fly ash mixtures

Abstract

As part of a larger investigation that included numerical and field-based components, the use of lime to reduce the leachability of a coal combustion fly ash was evaluated in the laboratory. The focus of this paper is on the experimental assessment of lime-fly ash leachability through sequential leach (SL), freeze-thaw (FT), and wet-dry (WD) leaching as well as multileachant sequential extraction (SE) tests. The results suggest that lime addition reduces the leachability for Cd, Se, and to some extent As. They also suggest that Cr is rendered more leachable with increasing lime content, for the conditions and low levels tested. It appears that there is a threshold lime content ({gt} 1.0%) that must be exceeded prior to reducing the leachability of As and Se. In particular, this threshold likely corresponds to the level at which appreciable cementitious reactions have developed. For example, in the case of As after the first cycle of leaching, the concentration was below the reporting limit (10 {mu} g/L) for 0% lime. However, at 0.5% lime amendment, the leached concentration increased to nearly 50 {mu} g/L. Subsequent lime additions reduced this concentration. No such threshold was observed for Cd leachability as was expected as a directmore » consequence of hydroxide precipitation, which is well established under the measured pH conditions. As such, Cd mobility is insensitive to the extent to which cementitious reactions are initiated. Overall, the results suggest that while lime stabilization may be effective for reducing leachability, sufficient amounts must be added; otherwise, the leachability of some constituents can actually be exacerbated.« less

Authors:
;  [1]
  1. University of North Carolina, Charlotte, NC (United States). Dept. of Civil Engineering
Publication Date:
OSTI Identifier:
20712183
Resource Type:
Journal Article
Resource Relation:
Journal Name: Environmental Engineering Science; Journal Volume: 23; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
01 COAL, LIGNITE, AND PEAT; FLY ASH; CALCIUM HYDROXIDES; LEACHING; INHIBITION; TRACE AMOUNTS; ELEMENTS; CADMIUM; SELENIUM; CHROMIUM; CONCENTRATION RATIO

Citation Formats

Daniels, J.L., and Das, G.P.. Leaching behavior of lime-fly ash mixtures. United States: N. p., 2006. Web. doi:10.1089/ees.2006.23.42.
Daniels, J.L., & Das, G.P.. Leaching behavior of lime-fly ash mixtures. United States. doi:10.1089/ees.2006.23.42.
Daniels, J.L., and Das, G.P.. Sun . "Leaching behavior of lime-fly ash mixtures". United States. doi:10.1089/ees.2006.23.42.
@article{osti_20712183,
title = {Leaching behavior of lime-fly ash mixtures},
author = {Daniels, J.L. and Das, G.P.},
abstractNote = {As part of a larger investigation that included numerical and field-based components, the use of lime to reduce the leachability of a coal combustion fly ash was evaluated in the laboratory. The focus of this paper is on the experimental assessment of lime-fly ash leachability through sequential leach (SL), freeze-thaw (FT), and wet-dry (WD) leaching as well as multileachant sequential extraction (SE) tests. The results suggest that lime addition reduces the leachability for Cd, Se, and to some extent As. They also suggest that Cr is rendered more leachable with increasing lime content, for the conditions and low levels tested. It appears that there is a threshold lime content ({gt} 1.0%) that must be exceeded prior to reducing the leachability of As and Se. In particular, this threshold likely corresponds to the level at which appreciable cementitious reactions have developed. For example, in the case of As after the first cycle of leaching, the concentration was below the reporting limit (10 {mu} g/L) for 0% lime. However, at 0.5% lime amendment, the leached concentration increased to nearly 50 {mu} g/L. Subsequent lime additions reduced this concentration. No such threshold was observed for Cd leachability as was expected as a direct consequence of hydroxide precipitation, which is well established under the measured pH conditions. As such, Cd mobility is insensitive to the extent to which cementitious reactions are initiated. Overall, the results suggest that while lime stabilization may be effective for reducing leachability, sufficient amounts must be added; otherwise, the leachability of some constituents can actually be exacerbated.},
doi = {10.1089/ees.2006.23.42},
journal = {Environmental Engineering Science},
number = 1,
volume = 23,
place = {United States},
year = {Sun Jan 15 00:00:00 EST 2006},
month = {Sun Jan 15 00:00:00 EST 2006}
}
  • The distribution of trace elements in coal combustion residues such as fly ash and bottom ash have received considerable attention. Several studies of fly ash have concentrated on relationships of trace elements to fly ash particle size. Studies related to etching, mineralogical transformation during combustion and leaching have also been reported. Dudas conducted long-term leachability studies. Grisafe et al. examined leachability of fly ash as a source of Se contamination. Femandez-Turiel et al. have looked at the mobility of heavy metals from coal fly ash. The objectives of these studies were primarily to understand potential problems associated with the storagemore » or disposal. To meet these objectives, the solvents used in these studies were chosen to emulate conditions in nature. This paper describes leaching data for Co, Cr, Ni, Sb, Th, and U.« less
  • The objectives of this work were the evaluation of sewage sludge stabilization by mixing with fly ash, the examination of the physicochemical properties of the produced materials and their leachates and the assessment of their environmental impact by the evaluation of the ecotoxic characteristics. Different ratios of fly ash and sewage sludge (1:1, 1:2, 1:3, 1:6, and 1:9) were mixed for 48 and 72 h. After mixing, the liquid phase of the produced materials was analyzed for total coliforms and Escherichia coli, while the solid residue was dried and tested for the leaching characteristics by the application of TCLP andmore » EN 12457-2 standard leaching methods. Furthermore, the produced leachates were analyzed for their content of specific metals, while their ecotoxicological characteristics were determined by the use of toxicity bioassays, using the marine photobacterium Vibrio fischeri and the crustacean Daphnia magna. The phytotoxicity of sewage sludge-fly ash mixtures was also determined by utilizing seeds of three higher plants (one monocotyl and two dicotyls). The mixtures exhibited low metal leaching in all cases, while the ecotoxic properties increased with the increase of fly ash/sewage sludge ratio. The phytotoxicity testing showed increased root length growth inhibition.« less
  • A mathematical model that accounts for simultaneous moisture movement and contaminant transport is developed to predict the leaching behavior from fly ash landfills with different age refuses. The approach is based on dividing the refuse layer into separate regions for each age refuse and solving model equations for each region. With the exception of boron in leachate of coal fly ash, good agreement between model simulation and experimental data of laboratory column-leaching tests was obtained. However, the simulated boron concentration profile can be improved by the addition of a retardation factor in the model equation. The important parameters were evaluatedmore » in a sensitivity analysis to see their respective effects. Four parameters were identified to influence strongly the model performance: dissolution rate constant (k{sub n}), exponential constant (n), ultimate mass of leachable contaminant (M{sub o}), and maximum contaminant concentration (C{sub max}).« less
  • The treatment of class C, I, and F fly ash (FA) with water, HNO{sub 3}, and aqueous CaCO{sub 3} has been investigated to develop a simple chemical route to change the morphology and surface chemistry of fly ash particles to enhance the setting properties of a cement/fly ash (C/FA) composite. The treatment of C-FA with an aqueous CaCO{sub 3} solution results in a dramatic improvement in the setting time and the setting profile on C-class FA; in contrast, the treatment has no effect on the set time for F-FA and reduces the set time and appears to result in anmore » even more nonideal induction setting curve as compared to the untreated C/I-FA. The enhancement observed for the treatment of C-FA with aqueous CaCO{sub 3} solution is not a consequence of the water solution since simply washing with water (i.e., C-FA(H{sub 2}O)) results in the extraction of Na and Ca with a concomitant increase in surface area and a performance similar to those observed for untreated I-FA and F-FA despite a much higher surface area. The acid (HNO{sub 3}) treatment of I-FA and F-FA results in the formation of an inert filler-like material, while acid treatment of C-FA results in a material with completely undesirable setting properties. Clearly, the enhancements observed for the aqueous CaCO{sub 3} treatment are not as a result of simply either the aqueous or acidic nature of the HCO{sub 3} containing CaCO{sub 3} solution. Based upon the forgoing, we propose that the efficacy of the aqueous CaCO{sub 3} treatment on C-FA is associated with the availability of 'reactive calcium'. Exposure of C-FA to dry CO{sub 2} does not affect the set time or set profile for C/C-FA mixture, but the retarding effect of the aqueous CaCO{sub 3} treatment on C-FA can be replicated by the exposure of the C-FA to a stepwise reaction with water and CO{sub 2}. Exposure of C-FA to wet CO{sub 2} results in the improvement of the setting induction profile without significantly affecting the set time.« less
  • A greenhouse study was conducted to evaluate the effect of fly ash (0, 10, 20, 30, and 40 g kg/sup -1/ of spoil) and agricultural lime (0, 10, 20, 40, and 80 g kg/sup -1/ of spoil) on ameliorating the low pH of acidic coal mine spoils. Topsoil depths of 0, 10, and 20 cm placed over the spoil were also evaluated. Two crops of barley (Hordeum vulgare L.) were grown to evaluate effects of the amendments and topsoil on aboveground plant biomass, root biomass and distribution, and element content of the vegetation. All levels of lime and fly ashmore » significantly increase the spoil pH, aboveground plant biomass, and root biomass. Topsoil placement over the spoil also generally increased plant biomass. Root growth in untreated spoil was limited to the depth of topsoil. However, when the spoil was amended with either fly ash or lime root growth occurred throughout the material. Fly ash and lime did not cause elemental toxicities to the plants, except for B. Although visual B toxicity symptoms and elevated levels of plant B were evident, no reduction in plant biomass occurred. The results indicate that fly ash is a feasible alternative to lime for treating acidic coal spoils in the region.« less