REACTION OF CO2 WITH ALKALINE SOLID-WASTES TO REDUCE CONTAMINANT MOBILITY

The objective of this study was to determine the effects of a CO2 trea tment on the pH and soluble concentrations of inorganic contaminants i n alkaline fly ash and spent shale solid wastes. A two-level (low and high), three-variable (moisture, time and pressure) statistical experi ment was used to determine optimum CO2 treatment conditions. Treated a nd untreated samples were subjected to solubility and X-ray diffractio n (XRD) studies. CO2 treatment conditions of 40 psi of pressure, 20% m oisture and 120 h effectively precipitated calcite, and thus lowered t he pH and leachable concentrations of certain inorganic contaminants ( e.g. Cd, Pb, Zn, Mn, As and Se) in alkaline fly ash and spent shale sa mples. For instance, approximate to 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 ino rganic contaminants in alkaline solid wastes, which should prevent the ir migration from disposal environments into groundwater.