Steel slag-assisted hydrothermal liquefaction of hyperaccumulators for upgrading bio-oil and immobilization of arsenic

Hydrothermal liquefaction (HTL) effectively convert hyperaccumulators into valuable hydrochars and bio-oils. However, the treatment of high concentrations of heavy metals in the aqueous phase products of HTL is crucial for ensuring the sustainability of the phytoremediation industry. This study demonstrated the effects of steel slag (SS) on the immobilization, distribution, and environmental risk of heavy metals during the HTL of Pteris vittata L. (PVL). The introduction of SS in HTL resulted in maximum bio-oil yield and HHV of 25.35% and 30.27 MJ/kg, respectively, while promoting the deoxygenation of bio-oil. The steel slag-assisted HTL effectively immobilized arsenic from aqueous phase to solid phase in PVL, and the arsenic removal content reached 1584.62 mg/kg, with a maximum arsenic stabilization rate of 93.29%. Model compound experiments suggest that the mechanism of arsenic stabilization in SS involves the formation of co-precipitates by the reaction of metal oxides with arsenate and arsenite. Furthermore, the SS-assisted HTL effectively reduced the risk assessment value and bioavailability of heavy metals in PVL. Overall, this study presents a promising approach for immobilizing arsenic, increasing bio-oil production, and promoting environmentally safe treatment of As-enriched biomass and steel slag.