Antimony(V) removal from water within ferrihydrite transformation: Influence of humic acid

Antimony (Sb), a widely distributed heavy metal pollutant, poses a formidable threat to human health and the delicate ecological environment. Anthropogenic activities such as mining, industrial processes and the widespread use of Sb-containing products aggravate the toxicity and potential risks of Sb to the environment. The mobility and fate of Sb(V) in the water environment is affected by ferrihydrite (Fhy) transformation and humic acid (HA). However, the key role of HA on Sb(V) removal in the transformation of iron minerals remains unclear. In this study, the transformation of Fhy into goethite was significantly inhibited as a result of HA structural coating, while active functional groups of HA enhanced the combination with iron minerals and Sb(V) under acidic conditions. Residual Sb(V) concentration in water was less than 5 & mu;g/L, which meets the United States Environmental Protection Agency (USEPA) recommended Sb concentration of 6 & mu;g/L. Under alkaline conditions, the dissociation of HA provided more negative charges for the surface of transformed hematite and magnetite. Due to the stronger electrostatic repulsion and steric effects of HA, further removal of Sb(V) was limited. This work provided multiple secondary mineralization pathways of Fhy under the impact of HA and mechanistic insights into the removal process of Sb(V), which could contribute meaningful information regarding the interaction between Sb(V) and iron oxyhydroxides.