An evaluation of fluidized bed combustor ash as a source of alkalinity to treat toxic rock materials

The coal mining industry is in need of effective, locally available, low-cost ameliorants that can be used to treat the toxic materials generated by surface mining and coal cleaning plants. Ashes generated by fluidized bed combustors may locally fit these criteria. Samples of fly ash and bottom ash were acquired from facilities in West Virginia, Texas, and California and evaluated for their ability to generate alkalinity. The results show that FBC ash has the potential to produce solutions of high alkalinity depending on the CaO and CaCO₃ contents. The relative content of CaO, and to a lesser extent Ca(OH)₂, determines the rate at which alkalinity will be produced. The neutralization potential is the best parameter to evaluate the potential of an FBC ash to produce alkalinity. Because the composition of ashes from a facility vary over time and because no single parameter will accurately evaluate the rate at which alkalinity will be produced, the rate of alkaline production must be evaluated by controlled leach experiments.