Release of antimony from Sb(V) incorporated iron oxides during oxalate-promoted recrystallization under aerobic conditions.

Iron oxides, which are ubiquitous in soils and sediments, can reduce the mobility of trace metals (i.e, antimony) by adsorption and structural incorporation. Researchers found that small organic acids, such as oxalate, can induce iron oxide recrystallization under aerobic conditions and simultaneously influence the immobility of structurally incorporated trace metals. In the present study, antimony transport during oxalate-promoted recrystallization of Sb(V)-substituted ferrihydrite and goethite was comprehensively investigated in acidic to alkalescent environments. Antimony release rate increased with oxalate concentrations (0.1, 1, and 10 mM), indicating that oxalate-promoted iron oxide dissolution was the main cause of antimony release. Another important factor affecting antimony release was pH. The release rate of antimony decreased with increasing pH, possibly due to the higher dissolution rate of iron oxides caused by oxalate under low pH conditions. However, the equilibrium release amount of antimony increased with rising pH in the Sb(V)-ferrihydrite system, probably because the adsorption capacity of Sb(V) decreased as pH increased. These results indicated that the release rate of structurally incorporated Sb(V) from iron oxides was significantly enhanced in the presence of oxalate. The findings also demonstrated a pathway of antimony release caused by iron oxide recrystallization under aerobic conditions, providing deeper insight into the fate of antimony in natural environments.