Effect of iron cyclic transformation on the natural purification of antimony in contaminated reservoirs of mines

To further understand the purification mechanism of antimony (Sb) in reservoirs, samples of stratified water and bottom interface sediment were collected in this study. The cross-flow ultrafiltration technique was used to separate the truly dissolved (<1 kDa) and colloidal (1 kDa–0.45 μm) phases of water, and two modified sequential extraction techniques were used to determine the Sb and Fe mineral forms in sediment, respectively. The results showed that the total Sb concentration could decrease from 142.2 μg/L in surface water to 98.6 μg/L at 16 m; this was contributed to by the removal of truly dissolved Sb. In comparison to particulate Sb (>0.45 μm), the formation of colloidal Sb played a greater role in the purification process. There was a positive correlation between Sb and Fe in the colloidal phase (r = 0.45, P < 0.05). The generation of colloidal Fe could be promoted by higher temperatures, pH values, DO, and DOC in the upper layer (0–5 m). However, the complexation of DOC with colloidal Fe inhibited the adsorption of truly dissolved Sb. After entering the sediment, the secondary release of Sb could not increase the Sb concentration in the lower layer obviously, while the supplementation of Fe(III) could further enhance Sb natural purification.