Characterization of Fly Ash from the Gasification of Wood and Assessment for Its Application as a Soil Amendment

Fly ash was collected as a byproduct from the processing of southern pine wood chips in a pilot-scale biomass gasifier. General properties of the fly ash were determined to assess its applicability as a soil amendment. Its alkaline pH (9.5) and high concentrations of Ca, K, and Mg suggest that it could be used as both a liming agent and a fertilizer. The concentrations of most heavy metals in all ash samples in this study were lower than the ecological soil screening levels used as a guideline. A sequential extraction analysis was used to evaluate the bioavailability of selected nutrient elements and pollutant heavy metals in the fly ash. Most nutrient elements were present in exchangeable/acid extractable and easily reducible fractions. The heavy metals were generally less bioavailable, thus ameliorating concerns for land application of fly ash, with or without prior combustion. Comparison of sequential extraction test results for all of the ashes indicated that the conditions experienced during gasification, such as high processing temperatures, impacted both the total heavy metal concentrations and their potential bioavailabilities.