Recovery of arsenic and practical utilization of aqueous phase in hydrothermal liquefaction of hyperaccumulator

Abstract

Eco-friendly disposal and heavy metal recovery of hyperaccumulator are critical for the industrialization of phytoremediation. Hydrothermal liquefaction (HTL) is an effective method for treatment of hyperaccumulators. In this study, CaO/Ca(ClO)2 was used to assist arsenic recovery in hydrothermal liquefaction of As-enriched Pteris vittata L. (PVL). Arsenic was immobilized from aqueous phase to solid phase with a high recovery of 96.5%. Experiments with model compounds indicated that 11.3% of As(V) in feedstock was precipitously reduced to more toxic As(III) by electron transfer reaction in hydrochar, while 54.9% of As(III) could be converted into As(V) via the strong oxidability of ClO−. The concentration of As in the aqueous phase decreased by 89.9% with this method. To investigate practical application of the aqueous phase, pot planting experiments were conducted to investigate the dissolved organic matter (DOM) of the aqueous phase (after HTL for As recovery) for garlic growth promotion. Notably, the As content (stem-leaf, 0.31 mg/kg) of garlic treated with the aqueous phase of HTL-CaO-Ca(ClO)2 was below Food Safety Standard (GB 2762–2017). This work provides a potential route for the heavy metal recovery and practical utilization of the aqueous phase for environmentally sound disposal of hyperaccumulators.