Immobilization of high-concentration antimony by schwertmannite: Structural incorporation and mineral stability

• Schwertmannite (Sch) exhibited similar adsorption behavior to ferrihydrite (Fh) toward Sb. • Sb(V) adsorption was favored at low pH, while Sb(III) was enhanced under alkaline condition. • Sch exhibited increased resistance to acidic dissolution after adsorption of Sb(III) or Sb(V). • Sb adsorption by Sch was primarily driven by structural incorporation and surface precipitation. Antimony (Sb) is a priority pollutant frequently co-occurring with arsenic (As) in mining-impacted environments. The speciation, mobility, and fate of Sb in the environment are intricately linked to its interactions with iron minerals at micro-interfaces. This study investigated the immobilization behavior and mechanisms of Sb(III) and Sb(V) at relatively high environmental concentrations onto schwertmannite (Sch), a common iron mineral prevalent in mining areas, with ferrihydrite (Fh) serving as a reference. Batch adsorption experiments demonstrated that Sb(V) adsorption was favored at low pH, whereas Sb(III) adsorption increased significantly at higher pH levels. The maximum adsorption capacities of Sch for Sb(V) and Sb(III) was determined to be 100.8 mg/g and 111.1 mg/g, respectively, at pH 7.0. Sequential extraction and spectroscopic analyses revealed that Sb immobilization on Sch occurred through hydroxyl complexation, structural incorporation, and surface precipitation mechanisms, with sulfate exchange also contributing to the immobilization of Sb(V). Additionally, Sb adsorption increased the mineral stability, enhancing the resistance to acidic dissolution. The co-existing As influenced Sb adsorption, with As(III) exerting a stronger inhibitory effect on Sb(III) adsorption. These findings reveal the immobilization behavior and mechanisms of high-concentration Sb by Sch, emphasizing the critical roles of structural incorporation and surface precipitation in Sb immobilization. This study offers new insights into the geochemical behavior of Sb and provides guidance for its remediation in contaminated environments.