LAUSR

The effect of chemical speciation (H 2 O/NH 4 Ac/HCl-soluble and insoluble) of alkali and alkaline earth metallic species on the steam gasification of sawdust biochar was investigated in a lab-scale, fixed-bed reactor, with the method of chemical fractionation analysis. The changes in biochar structures and the evolution of biochar reactivity are discussed, with a focus on the contributions of the chemical speciation of alkali and alkaline earth metallic species (AAEMs) on the steam gasification of biochar. The results indicate that H 2 O/NH 4 Ac/HCl-soluble AAEMs have a significant effect on biochar gasification rates. The release of K occurs mainly in the form of inorganic salts and hydrated ions, while that of Ca occurs mainly as organic ones. The sp 3 -rich or sp 2 -sp 3 structures and different chemical-speciation AAEMs function together as the preferred active sites during steam gasification. H 2 O/HCl-soluble AAEMs could promote the transformation of biochar surface functional groups, from ether/alkene C-O-C to carboxylate COO − in biochar, while they may both be improved by NH 4 Ac-soluble AAEMs. H 2 O-soluble AAEMs play a crucial catalytic role in biochar reactivity. The effect of NH 4 Ac-soluble AAEMs is mainly concentrated in the high-conversion stage (biochar conversion >30%), while that of HCl-soluble AAEMs is reflected in the whole activity-testing stage.