Bioleaching of chalcopyrite by mixed culture of moderately thermophilic microorganisms

A mixed culture of moderately thermophilic microorganisms was enriched from acid mine drainages(AMDs)samples collected from several sulphide mines in China,and the bioleaching of chalcopyrite was conducted both in shake flask and bioreactor.The results show that in the shake flask,the mixture can tolerate 50 g/L chalcopyrite after being acclimated to gradually increased concentrations of chalcopyrite.The copper extraction increases obviously in bioleaching of chalcopyrite with moderately thermophilic microorganisms supplemented with 0.4 g/L yeast extract at 180 r/min,74% copper can be extracted in the pulp of 50 g/L chalcopyrite after 20 d.Compared with copper extractions of mesophilic culture,unacclimated culture and acclimated culture without addition of yeast extract,that of accliniated culture with addition of yeast extract is increased by 53%,44% and 16%,respectively.In a completely stirred tank reactor,the mass fraction of copper and total iron extraction reach up to 81% and 56%,respectively.The results also indicate that it is necessary to add a large amount of acid to the pulp to extract copper from chalcopyrite effectively.

Effect of As(Ⅲ)on kinetics of Fe^(2+)bio-oxidation

Fe^(2+) bio-oxidation influenced by toxic metal ions released from the dissolution of arsenic-bearing gold ores was investigated.Fe^(2+) bio-oxidation by moderately thermophilic microorganisms was studied under different initial concentrations of Fe^(2+) and As(Ⅲ),and Monod equation was used to fit the Fe^(2+) bio-oxidation under different conditions.Results showed that the Fe^(2+) bio-oxidation rate increased as the initial Fe^(2+) concentration increased until it reached 12 g/L.As(Ⅲ)severely inhibited Fe^(2+) bio-oxidation.When the As(Ⅲ)concentration was 8 g/L,9 g/L Fe^(2+) was more than 200 h.The Monod equation fitted the Fe^(2+) bio-oxidation well.In the absence of As(Ⅲ),the maximum specific growth rate of the culture and the substrate affinity constant were 0.142 h^(−1) and 0.053 g/L,respectively.As(Ⅲ)inhibited Fe^(2+) bio-oxidation via competitive inhibition,and the inhibition constant was 0.0035 g/L.

Formation of passivation film during pyrrhotite bioleached by pure L. ferriphilum and mixed culture of L. ferriphilum and A. caldus

Bioleaching and electrochemical experiments were conducted to evaluate pyrrhotite dissolution in the presence of pure L.ferriphilum and mixed culture of L. ferriphilum and A. caldus. The results indicate that the pyrrhotite oxidation behavior is the preferential dissolution of iron accompanied with the massive formation of sulfur in the presence of L. ferriphilum, which significantly hinders the leaching efficiency. Comparatively, the leaching rate of pyrrhotite distinctly increases by 68% in the mixed culture of L. ferriphilum and A. caldus at the 3rd day. But, the accumulated ferric ions and high p H value produced by bioleaching process can give rise to the rapid formation of jarosite, which is the primary passivation film blocking continuous iron extraction during bioleaching by the mixed culture. The addition of A. caldus during leaching by L. ferriphilum can accelerate the oxidation rate of pyrrhotite, but not change the electrochemical oxidation mechanisms of pyrrhotite. XRD and SEM/EDS analyses as well as electrochemical study confirm the above conclusions.