Are the typical organic components in biomass pyrolyzed bio-oil available for leaching of alkali and alkaline earth metallic species (AAEMs) from biomass?

In this study, six dominant organic compounds in biomass pyrolyzed bio-oil, composed of acidic compound (acetic acid) and non-acidic compound (furfural, hydroxyacetone, ethylene glycol, phenol, and guaiacol) were used to remove AAEMs from different lignocellulosic biomass (rice husk, cotton stalk, and fir sawdust) by leaching pretreatment. Other four conventional solutions (deionized water, hydrochloric acid solution, aqueous phase bio-oil, and simulated bio-oil) were selected as control eluents. Results showed that the removal rate of AAEMs was highly affected by the types of immersion solutions, pH values, and the species of biomass. Majority of K in biomass could be removed by leaching of acetic acid. Ca was more difficult to be removed by leaching of water and acetic acid, but could be removed by leaching of HCl. In general, the removal rate of K was highest among the four species of AAMEs by using five non-acidic components, followed by Na, Mg, and Ca. The use of five non-acidic solutions was significantly benefit for the remove of K, Mg, and Na, but, was less useful in removal of Ca in rice husk and fir sawdust. However, the removal rates of Ca in cotton stalk by leaching of phenol, guaiacol, and hydroxyacetone were increased to nearly three times than water leaching. A synergistic effect for removing AAEMs occurred between acetic acid and non-acidic components in bio-oil, indicating that the non-acidic compounds also play an important role in leaching of AAEMs.