Carbon gasification enhancement and metal migration modulation in the thermochemical conversion mechanism of waste mushroom sticks treated with supercritical carbon dioxide

As an environmentally friendly and highly efficient waste valorization technology, biomass supercritical carbon dioxide (SC-CO₂) treatment provides an innovative solution for achieving high-value utilization of agricultural and forestry residues and carbon neutrality goals. This study focuses on waste mushroom sticks from edible fungus cultivation as a research object, which is characterized by high lignocellulosic content, low cost, and renewability, making it an ideal feedstock for biomass circular economy. Experimental results demonstrate that under CO₂ atmosphere at 600 °C, the carbon gasification efficiency and hydrogen conversion rate reach peak values of 25.94 % and 33.36 %, respectively. Phase transformation analysis of three-phase products (solid, liquid, gas) reveals that the low-temperature stage primarily involves solid-phase conversion into liquid and gaseous phases, while high-temperature conditions induce liquid-phase cracking into gaseous products. Compared to conventional pyrolysis under N₂ atmosphere, SC-CO₂ technology exhibits dual advantages: efficient carbon fixation at lower temperatures and significant tar suppression at elevated temperatures, coupled with enhanced metal-binding affinity. Notably, the introduction of H₂O into the SC-CO₂ system effectively improves the extraction efficiency of trace metal elements. This study establishes crucial theoretical foundations for optimizing supercritical fluid treatment processes for agricultural waste.