Insights into mineral removal, fusion, and evolution in biomass valorization through integrated pretreatment strategies from an ash chemistry perspective

Agricultural biomass thermochemical conversion represents an economical and environmentally-friendly approach to energy utilization, and it is innovative to explore the effect of leaching on biomass valorization from the ash chemistry perspective. Herein, we conducted a comprehensive investigation on the demineralization efficiency and kinetics, ash fusion prediction, and mineral evolution of wheat straw ash, aimed at identifying the critical factors affecting WS leaching valorization. The results indicated the significant demineralization occurred within a short schedule (<5 min), with up to 35 % of inorganic removal as particle size decreased, which was attributed to the diffusion gradient and solution accessibility. Leaching temperature was closely linked to the thermal motion and ionization potential of water molecules, resulting in lower demineralization efficiency at low temperatures (approximately 18 %). Meanwhile, pure acetic acid leaching significantly suppressed the demineralization efficiency, which underscored the crucial role of ionizable H + during leaching. The leaching process closely followed a second-order kinetic model ( R ² > 0.95), with the solution saturation concentrations of K, Mg, and Ca increasing by 7.04 g L⁻¹ , 0.68 g L⁻¹ , and 0.17 g L⁻¹ , respectively, over reducing particle size. Leaching further diminished the content of sinter-prone inorganics, promoted the formation of SiO 4 tetrahedral network, transformed ash slag system from K-Ca silicates to a SiO 2 -based fusion frame at high temperature, and further mitigated the ash sintering risk.