SREL Reprint #2586

 

 

 

Contaminant mobility in soils amended with fly ash and flue-gas gypsum: intact soil cores and repacked columns

C. F. Ishak1, J. C. Seaman2, W. P. Miller3, and M. Sumner3

1Soil Science Department, University Pertanian, Malaysia
2Advanced Analytical Center for Environmental Sciences, Savannah River Ecology Laboratory,
University of Georgia, Aiken, USA
3Department of Crop and Soil Sciences, University of Georgia, Athens, USA

Abstract: The impact of the land application of coal combustion by-products, fly ash (FA) and flue-gas desulfurization gypsum (FDG), to coarse-textured soils of the southeastern U.S.A. was investigated using batch and dynamic column techniques. Two FA samples, one an alkaline FA (Alk-FA) and the other an acidic FA (Acid-FA), were evaluated alone and in combination with FDG as soil amendments to an Appling loamy sand (Typic Hapludults). The effects of these waste products on clay dispersion, soil hydraulic conductivity (Ksat) and the migration of contaminants such as Arsenic (As) and Boron (B) were studied using intact soil cores and repacked soil columns. FA or combinations of FA + FDG were applied to the surface of intact soil cores (10 Mg ha-1) and repacked soil columns or incorporated within repacked soil columns. The columns were saturated and then leached for a prescribed number of pore volumes to simulate leaching conditions in the field. Effluent pH, electrical conductivity (EC), and turbidity were monitored and leachate fractions were collected for B, As, Ca, Mg, K and Na analysis. Both FA materials were ineffective at decreasing the inherent dispersibility of clay from the Ap horizon in batch tests. In fact, high application rates of the Alk-FA induced some clay dispersion in the well-flocculated Bt, soil materials, and column results suggest that incorporating the Alk-FA within the surface soil may actually reduce Ksat. In contrast, treatments with FDG were highly effective at inducing rapid clay flocculation in batch tests and eliminating effluent turbidity for intact and repacked soil columns. Boron was readily mobile from both intact and repacked soil columns, a majority of which leached from the columns within the first three pore volumes. Boron leaching was greater for combined treatments (FA + FDG), possibly indicative of enhanced solubilization in the presence of FDG or sulfate (SO42-) competition for sorption sites. Arsenic levels present in the leachates from FA and FDG columns were generally lower than control columns and roughly correlated with effluent turbidity. Combined treatments (FA + FDG) enhanced Mg and K leaching due to the added competition of Ca for cation exchange sites. Following leaching, the intact soil cores were sectioned at 5 cm intervals and the pH and EC of the soil, as well as the vertical distribution of As and B, were determined. Levels of residual As were only slightly higher in the upper section of the FA-amended columns, showing little downward movement, but no clear trend in residual B was observed due to its greater mobility.

Keywords: arsenic, boron, coal combustion byproducts, flue-gas desulfurization gypsum, fly ash, gypsum, water dispersible clay, water holding capacity

SREL Reprint #2586

Ishak, C. F., J. C. Seaman, W. P. Miller, and M. Sumner. 2002. Contaminant mobility in soils amended with fly ash and flue-gas gypsum: intact soil cores and repacked columns. Water, Air, and Soil Pollution 134: 287-305.

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