Recovery of bio‑sulfur and metal resources from mine wastewater by sulfide biological oxidation-alkali flocculation: A pilot-scale study

Abstract

Mine wastewater treatment using bio-sulfate reduction technology forms sulfur-containing wastewater that comprises sulfides (HS− and S2−) and metal ions. Bio‑sulfur generated by sulfur-oxidizing bacteria in such wastewater is usually negatively charged hydrocolloidal particles. However, bio‑sulfur and metal resource recovery are difficult using traditional methods. In this study, the sulfide biological oxidation-alkali flocculation (SBO-AF) method was investigated to recover the above resources, and to provide a technical reference for mine wastewater resource recovery and heavy metal pollution control. Specifically, the performance of SBO in forming bio‑sulfur and the key parameters of SBO-AF were explored and then applied in a pilot-scale process to recover resources from wastewater. Results show that partial sulfide oxidation was achieved under a sulfide loading rate of 5.08 ± 0.39 kg/m3·d, dissolved oxygen of 2.9–3.5 mg/L and temperature of 27–30 °C. The average sulfide oxidation rate and sulfur selectivity ratio were 92.86 % and 90.22 %, respectively. At pH 10, metal hydroxide and bio‑sulfur colloids co-precipitated through the precipitation catching and adsorption charge neutralization effect. The average manganese, magnesium and aluminum concentrations and turbidity in the wastewater were 53.93 mg/L, 522.97 mg/L, 34.20 mg/L and 505 NTU, respectively, and decreased to 0.49 mg/L, 80.65 mg/L, 1.00 mg/L and 23.33 NTU, respectively, after treatment. The recovered precipitate mainly contained sulfur, along with metal hydroxides. The average sulfur, manganese, magnesium and aluminum contents were 45.6 %, 29.5 %, 15.1 % and 6.5 %, respectively. Economic feasibility analysis and the above results show that SBO-AF has obvious technical and economic advantages in the recovery resources from mine wastewater.