Influences of Particles and Aquatic Colloids on the Oxidation of Sb(III) in Natural Water

Antimony (Sb) is a hazardous metalloid that is ubiquitous in the environment. Its toxicity and mobility are strongly influenced by the valence state. Particles and aquatic colloids are abundant in natural water; however, there is little understanding of how Sb(III) is oxidized by these substances. In this study, crossflow ultrafiltration is used to separate the substances in natural water samples into macroparticles (>1 mu m), microparticles (1-0.1 mu m), colloids (<0.1 mu m, >1 kDa), and dissolved substances (<1 kDa). The effects of these different components on oxidation of Sb(III) were comprehensively investigated by kinetic measurements with the aid of quenchers under simulated sunlight irradiation and dark conditions. The results show that 95% of the Sb(III) oxidation process was done by the particles (macroparticles and microparticles) and aquatic colloids (colloids and dissolved substances). Macroparticles oxidized Sb(III) via active substances such as natural organic matter (NOM) and iron oxides, while colloids impacted the oxidation process via dissolved organic matter (DOM) with active groups such as amino acid-like organic matter. The dissolved substances oxidized Sb(III) via iron ions and some micromolecule organic matter. Common free ions in natural water had no effect on the oxidation of Sb(III). The reactive oxygen species (ROS) and excited triplet states of DOM ((DOM)-D-3*) produced by oxidants under photoirradiation can accelerate the oxidation of Sb(III). These results indicate that Sb(III) can be oxidized to Sb(V) rapidly with the help of sunlight in the presence of particles and colloids, and this oxidation process will greatly influence the fate of Sb(III) in natural water.