Modified steel slag/CaO2 enables magnetic separation and recovery of arsenic during hydrothermal liquefaction of hyperaccumulator

Heavy metal separation and recovery from hyperaccumulators are crucial to promote the industrialization of phytoremediation and prevent secondary heavy metal pollution. In this study, we developed an innovative modified steel slag/CaO 2 technology for arsenic recovery and separation via hydrothermal liquefaction (HTL) of As-enriched Pteris vittata L. (PVL). Arsenic migrated from the aqueous phase to the solid phase, with a recovery rate as high as 99.96 %, and the oxidation of arsenite was achieved with an impressive efficiency of 97.64 %. Experiments with model compounds revealed that the As in the PVL was immobilized by metal oxides (CaO, MgO, Fe 2 O 3 and SiO 2 ) in the modified steel slag and deposited in the solid phase. The coprecipitation of arsenic and heavy metals was verified via Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). As(III) was converted into As(V) via the strong oxidability of •OH and H 2 O 2 from CaO 2 . XPS confirmed that the interconversion of Fe 3+ and Fe 2+ significantly contributed to the oxidation and removal of arsenic. The concentration of As(III) in the system decreased to 1.96 % with this method. To investigate heavy metal recovery from the solid phase, magnetic experiments were subsequently conducted to investigate the arsenic distribution in the solid phase after magnetic separation. Notably, the As could be recovered in the magnetic solid phase, whereas 0.05 % of the As(III) and 18.46 % of the As(V) of the total arsenic were distributed in the non-magnetic solid phase. This study demonstrated that modified steel slag/CaO 2 has great potential for the detoxification and recovery of heavy metals in hyperaccumulators.