Achieving on arsenic immobilization and reutilization of harvested Pteris vittata L. via red mud assisted hydrothermal processes: Mechanisms and practicality

Hydrothermal treatment (HTT) was a promising approach for the treatment of heavy metal hyperaccumulated plants, such as Pteris vittata L. (PVL), but the As distribution in solution hindered the further application. In this study, red mud (RM) was used to assist in the immobilization of arsenic (As) and reutilization of PVL organics within HTT. The results indicated that As was mainly concentrated in the solid phase (SP) instead of the liquid phase (LP), while some parts of As(III) were transformed into As(V) via electron transfers after RM adding. Further, most of As (70.14 %∼78.44 %) was shifted from the LP to SP, as immobilizing mechanisms of As were thoroughly investigated with characteristic techniques. To further explore the applied practicality of LP, pot experiments were used to assess the impact of dissolved organic matter (DOM) of LP on Brassica napus growth. Notably, the leaching concentration (0.36 mg/L) of LP after RM loading was below the integrated wastewater discharge standard (GB 8978–1996). Further, LP significantly improved soil physicochemical properties and promoted plant growth. In conclusion, this work provided a potential pathway for the reduction and safe utilization of heavy metal hyperaccumulator plants and practical utilization of this hazardous material. • RM assisted-HTT was firstly employed for the harvested PVL reutilization. • The RM addition realized As mainly immobilized in solid part (>70 %). • Mechanisms of RM assistance-HTT on As immobilization were proposed. • LP exhibited improvement on soil quality (TOC, TN, TP, and humic acid). • The practicality of LP was evaluated by pot and plant growth experiments.