Sorption of antimony(V) to naturally formed multicomponent secondary iron minerals: Sorption behavior and a comparison with synthetic analogs

Abstract

Antimony (Sb) pollution in water has attracted extensive attention due to the biotoxicity of Sb. Secondary iron minerals readily sorb heavy metal(loid)s and critically affect their cycling in terrestrial environments. However, compared with synthetic pure iron mineral phases, little is known about the Sb sorption behavior and mechanism on natural secondary iron minerals (nSIMs) composed of various mineral phases. In this study, sorption experiments were conducted to investigate the Sb(V) sorption properties of nSIMs from an acid mine drainage zone and corresponding single-component synthetic secondary mineral phases and to compare their sorption behaviors and mechanisms. Spectroscopic analyses indicated that the nSIMs structurally resembled a hybrid of schwertmannite, jarosite and goethite. Sb(V) sorption on nSIMs, schwertmannite, goethite and jarosite was controlled by chemisorption, with maximum Sb(V) sorption capacities of 217.39, 233.65, 32.17 and 35.61 mg/g, respectively. nSIMs demonstrated an excellent Sb(V) sorption capacity equivalent to or greater than that of the single-component phases. XRD, FTIR and Raman analyses indicated that Sb(V) was immobilized on nSIMs mainly through ion exchange with structural SO42− and complexation interactions with surface FeO and FeOH; then, an FeOSb surface phase formed during the dissolution and further transformation of schwertmannite and jarosite into goethite. SEM revealed that nSIMs had an advantage in surface microstructure over the single components. These results suggested that despite the similarities in Sb(V) binding mechanism between nSIMs and schwertmannite, nSIMs might be more reactive for Sb(V) sorption since the nSIM components could mutually influence each other and facilitate Sb(V) sorption. This research suggests that nSIMs have potential for Sb(V) removal and helps elucidate the environmental behavior of Sb(V) associated with nSIMs.