Comparative study of characterization and utilization of corncob ashes from gasification process and combustion process

•Basic properties of CCA from gasification and combustion process were investigated.•Gasification CCA has a higher content of nutrient elements than combustion ashes.•The agglomeration tendency of biomass ash could be enhanced at high temperatures.•Combustion CCA is more suitable for use as a pozzolan source than gasification CCA. In the present study, fly ashes were obtained as a byproduct respectively from the processing of corncob in a gasification plant and from the combustion of corncob in a muffle furnace. The aim of this study is to characterize the basic properties of the fly ashes from gasification process and combustion process whilst comparing the results between these two types of solid residues to evaluate their potential applications. The results indicate that the CCA from gasification is more suitable to be used as a raw material for activated carbon owing to its larger specific surface area and higher carbon content compared with the CCA from combustion. With higher concentrations of K, Ca, and P, the CCA from gasification process is more bioavailable than CCA from combustion to be soil amendment. SEM images show that these CCA particles are agglomerated and irregular in shapes. The external surface of agglomerated particles is covered with potassium chloride. The influence of ashing temperature on ash morphology and agglomeration behavior is obvious, and the agglomeration tendency and melting degree are enhanced at high temperatures. Thermal analysis reveals the stepwise mechanism of decomposition for CCA. Specifically, the combustion CCA is more suitable for use as a pozzolan in blended cement concrete compared with the gasification CCA. Also, all ash samples with high silica content are suitable for ceramics.