Protonation stabilized high As/F mobility red mud for Pb/As polluted soil remediation.

The hazardous red mud (RM) with high As/F mobility and heavy metal contaminated soil have constituted severe environmental threats. This work demonstrates a "waste to eco-material" strategy through a reliable and low-cost protonation approach to eliminate the As/F leaching risk of RM, and then recycle it as heavy metal passivators for Pb/As polluted soil remediation. The As/F anions have been immobilized by the protonated Fe/Al (hydr)oxides within RM via the formation of stable As/F compounds during the protonation process, which satisfies the requirement by the World Health Organization (As leaching <0.01 mg/L; F leaching <0.8 mg/L). Moreover, in the oilseed rape pot experiments, by adding 30 g/kg stabilized RM into Pb/As polluted soils (100 ~ 300 ppm), benefited from its large adsorption capacity, approximately 40.9 ~ 49.7% Pb and 40.8 ~ 54.8% As concentrations in the plant are reduced without adverse effects. The whole process for RM treatment and soil remediation is cost-effective, straightforward and eco-friendly without secondary pollution or soil degradation. This research provides a green chemical strategy to address both RM recycling and heavy metal contaminated soil remediation problems, which shows high economic feasibility and ecological benefits.