Abstract: In this study, two moderately thermophilic bacteria, includingL. ferrooxidans(Leptospirillum ferrooxidans) andA. caldus(Acidithiobacillus caldus), used in bioleaching processes of refractory gold ores were taken as the main research objects. The effects of valence of arsenic (As(Ⅲ) and As(Ⅴ)) on the bio-oxidation of two moderately thermophilic bacteria were investigated through studied by shake flask experiment. The results were compared with two mesophilic bacteria,A. ferrooxidans(Acidithiobacillus ferrooxidans) andT. thiooxidans(Thiobacillus thiooxidans). The results showed that the tolerance to As(Ⅲ) of moderately thermophilic bacteria was significantly weaker than that of mesophilic bacteria, but both of thermophilic and mesophilic bacteria showed similar tolerance to As(Ⅴ). At the same time, the effect of As(Ⅲ) on iron-oxidizing bacteria in growth was greater than that on sulfur-oxidizing bacteria. It was found that increasing the bacteria inoculation amount and domesticating bacteria was conducive to the adaptation of moderately thermophilic bacteria to arsenic toxicity. In the actual ore pulp system, increasing the inoculation amount could make moderately thermophilic bacteria finally to adapt to the high arsenic environment and obtain better ore bioleaching effect. The highest mass concentration can reach about 1.54 g/L, and the arsenic leaching rate can be up to 70% in only 10 days.

Key words: bio-oxidation, moderately thermophilic bacteria, valence of arsenic, domestication, bacteria inoculation amount