The fate of Sb(V) and As(V) during the aging of ferrihydrite

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Iron (oxyhydr)oxides, especially ferrihydrite (Fh), abundant in the natural environment, are frequently applied in controlling the migration of heavy metals like antimony (Sb) and arsenic (As) in contaminated soils. However, little is known about the mobility and fate of Sb and As during the aging of Fh. In this study, we investigated the competitive adsorption between Sb(V) and As(V), the mineralogical transformation of Fh, and the redistribution of Sb(V)/ As(V) during the accelerated aging process of Fh. Our results showed that As(V) inhibited Sb(V) adsorption at the same concentration, but Sb(V) had no discernable influence on As(V) adsorption, suggesting As(V) had a stronger affinity to Fe minerals. XRD patterns showed that Fh was transformed into hematite or goethite in the presence of 25 mg/L Sb(V), but the transformation was inhibited in the presence of 25 mg/L As(V). Regarding the redistribution, the mobility of Sb(V) appeared to decrease probably via incorporation into Fe minerals during aging, and Fe minerals could host at least 20 % (w/w) Sb(V) in the low-mobility pool. As for As(V), the transformation of Fh was impeded resulting in high proportions of As(V) retained in high-mobility pool, with only 1.6 % (w/w) As(V) in the low-mobility pool. Our findings highlighted the differential behaviors of Sb(V) and As(V) during the adsorption and aging process on Fe oxide materials. These insights contributed to a deeper understanding of the mobility and fate of co-existing Sb(V) and As(V) in contaminated soils and offered practical guidance for their remediation using Fe oxide materials.