Pressurized fluidized bed combustion ash 2. Soil and mine spoil amendment use options

Abstract

The commercial introduction of pressurized fluidized bed combustion (PFBC) has spurred evaluation of ash management options for this technology. ashes used in this study were produced in the Foster Wheeler Energia Oy's circulating PFBC pilot facility in Karhula, Finland and the American Electric Power Tidd PFBC facility in Ohio. The fly ashes contain numerous compounds, including calcite (CaCO 3), anhydrite (CaSO 4) and, in the Tidd fly ash, dolomite [CaMg(CO 3) 2], that have the potential to be a nutrient source and a soil amendment for the reclamation of acid and sodic soils (soils influenced by high levels of sodium). The objective of this research was to determine if the PFBC ash could be used as soil amendments for acid and sodic soils. The research effort consisted of three separate tests: (1) a laboratory equilibration study to determine the influence of fly ash amendments on pH and EC (electrical conductivity) of actively oxidizing, acid-forming, mine spoil material; (2) a greenhouse study to determine the influence of fly ash on plant growth; and (3) a hydraulic conductivity evaluation of sodic soils treated with the PFBC fly ash materials. The study showed that the PFBC fly ashes were effective acid spoil amendments. In a comparison with ag-lime, the fly ash reacted with the spoil at a slower rate and the final pH of the treated material was slightly lower (∼7 versus ∼8). In addition, the EC of the fly-ash-treated spoil was ∼1 mS cm −1 higher than that associated with the ag-lime-treated materials. The greenhouse study demonstrated that the fly ash was an effective amendment for the remediation of acid spoil materials. In fact, the soils amended with fly ash supported higher plant production than those amended with ag-lime. These findings are possibly due to pH and nutritional effects. The hydraulic conductivity study demonstrated that the application of fly ash to sodic soils resulted in enhanced permeability of the treated soil.