Effect of pH value and Fe(Ⅲ) on the oxidative dissolution of stibnite

The stibnite oxidative dissolution under the influence of mining activities is an important process affecting the mobilization of antimony in rock-soil-water environmental medium and its environmental effects. At present, the researches mainly focus on the kinetic characteristic of stibnite dissolution, and the understandings about important issues such as the pathway of stibnite oxidative dissolution, the influence of environmental factors, and the process of antimony release are not clear. In order to study the mechanism of antimony release into groundwater in mining area where the main lithology is carbonatite, important environmental factors pH value and Fe(Ⅲ) were selected. The batch experiment method under single-factor control condition was used to finely describe the oxidation dissolution rate of Sb₂S₃ and the composition characteristics of Sb and S oxidation products under dark conditions. The results show that Sb₂S₃ oxidative dissolution was a proton-producing process, and the Sb and S release rates, release pathways and reaction products characteristics were significantly affected by pH value and Fe (Ⅲ). Sb₂S₃ oxidative dissolution rate changed from rapid to slow and finally reached equilibrium. The magnitude of initial reaction rate was 10^-8 mol/(m²·s), and the magnitude of equilibrium reaction rate was 10^-10 mol/(m²·s). The release and oxidation rates of antimony increased with the increasing of pH value, and the strong alkali condition was the most favorable condition for the release and oxidation of Sb. Under strong acid condition, the escape of H₂S and SO₂ gas coupled with the precipitation of elemental sulfur promoted the dissolution of Sb₂S₃. Sb(Ⅲ) and S(0) were the dominate reaction products. Under neutral condition, dissolved HS^- was gradually oxidized to SO₄^2- and a small amount of S₂O₃^2-, meanwhile the concentration of Sb(Ⅲ) and Sb(Ⅴ) were similar. Under strong alkali conditions, the formation of SbS₃^3- and S_x^- significantly facilitated the Sb₂S₃ oxidative dissolution rate. Sb(Ⅴ) and S₂O₃^2- were the primary species. While Fe(Ⅲ) worked as the lone oxidant, Sb(Ⅴ) and S(0) were the main reaction products. However, the apparent rate of antimony release was not significantly increased, probably due to the precipitation of SbOCl and S(0). Studies have shown that O₂ can cooperate with Fe (Ⅲ) to oxidize Sb₂S₃, meanwhile Fe(Ⅲ) plays the major role in the reaction. This study characterizes the product composition characteristics of Sb₂S₃ oxidative dissolution under different pH values and oxidants, and proposes the Sb₂S₃ oxidative dissolution pathways are affected by different environmental factors. Carbonatite formation which can be a natural buffer is conducive to release and oxidation of antimony, and the environmental problem induced by antimony in karst groundwater will be more serious.