Low temperature removal of inorganic sulfur compounds from mining process waters

Abstract

Process water and effluents from mining operations treating sulfide rich ores often contain considerable concentrations of metastable inorganic sulfur compounds such as thiosulfate and tetrathionate. These species may cause environmental problems if released to downstream recipients due to oxidation to sulfuric acid catalyzed by acidophilic microorganisms. Molecular phylogenic analysis of the tailings pond and recipient streams identified psychrotolerant and mesophilic inorganic sulfur compound oxidizing microorganisms. This suggested year round thiosalt oxidation occurs. Mining process waters may also contain inhibiting substances such as thiocyanate from cyanidation plants. However, toxicity experiments suggested their expected concentrations would not inhibit thiosalt oxidation by Acidithiobacillus ferrivorans SS3. A mixed culture from a permanently cold (4-6 °C) low pH environment was tested for thiosalt removal in a reactor design including a biogenerator and a main reactor containing a biofilm carrier. The biogenerator and main reactors were successively reduced in temperature to 5-6 °C when 43.8% of the chemical oxidation demand was removed. However, it was found that the oxidation of thiosulfate was not fully completed to sulfate since low residual concentrations of tetrathionate and trithionate were found in the discharge. This study has demonstrated the potential of using biotechnological solutions to remove inorganic sulfur compounds at 6°C and thus, reduce the impact of mining on the environment.

Gene Identification and Substrate Regulation Provide Insights into Sulfur Accumulation during Bioleaching with the Psychrotolerant Acidophile Acidithiobacillus ferrivorans

“…The ability to switch between substrates (Fe 2ϩ and ISC) is important for the ecological flexibility of A. ferrivorans SS3 and hence for its applications in biomining (28) and the bioremediation of wastewaters from mineral processing (8). Therefore, we investigated genetic determinants of Fe 2ϩ and ISC oxidation in A. ferrivorans SS3, its growth on different substrates, and the implications for bioleaching.…”

“…Acidithiobacillus ferrivorans SS3 (originally named Acidithiobacillus ferrooxidans SS3) is the only psychrotolerant acidophile characterized (5) and has been shown to oxidize Fe 2ϩ (6) and ISCs at low temperatures (7,8). It is also capable of catalyzing pyrite dissolution in stirred tank reactors (STRs) at 4°C.…”

Recent Developments in Microbiological Approaches for Securing Mine Wastes and for Recovering Metals from Mine Waters

“…), are produced by several mechanisms during the (bio)processing of sulfide ores, including reactions that occur during comminution and flotation, and also as intermediates during the microbial oxidation of pyrite [5,39]. When discharged into aerated waters, RISCs are susceptible to microbial oxidation, generating sulfuric acid (e.g., Equation (2)).…”

“…This has been demonstrated at 37 °C using a mixed culture of mesophilic and moderately thermophilic sulfur-oxidizing bacteria (described [40]) and at 4-10 °C using the cold-adapted bacterium At. ferrivorans [39].…”

Draft Genome of the Psychrotolerant Acidophile Acidithiobacillus ferrivorans SS3

“…Strains of A. ferrivorans catalyze low-temperature metal solubilization in the biotechnological process "bioleaching," and it is the dominant species during complex multi-metal sulfide mineral dissolution at 7°C (2). In addition, a mixed culture dominated by A. ferrivorans is being investigated for low-temperature ISC removal from mining process waters (9).…”