Abstract The objective of this study was to determine the effects of a CO2 treatment on the pH and soluble concentrations of inorganic contaminants in alkaline fly ash and spent shale solid wastes. A two-level (low and high), three-variable (moisture, time and pressure) statistical experiment was used to determine optimum CO2 treatment conditions. Treated and untreated samples were subjected to solubility and X-ray diffraction (XRD) studies. CO2 treatment conditions of 40 psi of pressure, 20% moisture and 120 h effectively precipitated calcite, and thus lowered the pH and leachable concentrations of certain inorganic contaminants (e.g. Cd, Pb, Zn, Mn, As and Se) in alkaline fly ash and spent shale samples. For instance, ~64-89% reduction in the leachable concentration of Mn was observed for CO2 treated samples. Our results suggest that reaction with CO2 under slightly elevated pressures is an effective means of reducing the soluble concentrations of certain inorganic contaminants in alkaline solid wastes, which should prevent their migration from disposal environments into groundwater.
Key words—alkaline solid wastes, contaminants, CO2 reaction, immobilization of contaminants
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