Removal of inorganic constituents from pine barks and switchgrass

The ash content of biomass has some negative impacts on the efficient utilization of biomass for the production of value-added products. In this paper, the techniques of ash removal from Mountain Pine Beetle (MPB) killed pine bark and switchgrass were examined systematically. Size fractionation was found to be effective for ash removal not only for the heterogeneous switchgrass but also for the homogeneous pine bark. Inorganic constituents of untreated samples and treated samples showed that leaching by water and four dilute acid solutions was effective in removing most of ash from both biomass samples. The inorganic element distributions in ash of pine bark samples before and after the acid leaching showed that substantial reductions were achieved in different main elements, Al (66%), Ca (90%), Fe (66%), K (92%), Mg (98%), Na (100%) and S (25%). For switchgrass, most of the element concentrations were reduced by water leaching because of its high content of water-soluble metals in the ash. For the purpose of practical applications of the two types of biomass, especially the underutilized pine barks, different leaching methods should be evaluated to identify the most suitable method for the removal of inorganic constituents.

Research Highlights
► Fractionation could remove up to 20% ash content from both heterogeneous switchgrass and homogeneous pine bark samples.
► Water leaching could remove up to 40% ash content for switchgrass because of its high content of water-soluble inorganic constituents.
► Water leaching was ineffective in reducing ash content from pine bark because of its low content of water-soluble inorganic constituents.
► Leaching by dilute acid solutions removed most organic constituents from both bark and switchgrass.