Bioleaching And Electrochemical Behavior Of Pyrrhotite Bioleached By Moderately And Extremely Thermophilic Bacteria

Abstract:Pyrrhotite is a common sulfide associated with various useful components (such as gold, cobalt, nickel, copper ect.), fine-grained disseminated gold and other precious metals are difficult to be dissolved, and thus easily mixed in tailings. Meanwhile, the decomposition of pyrrhotite will consume a large amount of acid during the recovery of gold. Developing the deep research on oxidation mechanism of pyrrhotite and grasping its decomposition process have great significance to providing technical guidance for the comprehensive available recovery of valued metals.On the basis of leaching behaviors of pyrrhotite bioleached by moderately thermophilic iron-oxidizing L. ferriphilum, iron-and sulfur-oxidizing S. thermosulfidooxidans and extremely thermophilic A. manzaensis. Then using XRD、SEM and electrochemical testing method to reveal the microbial oxidation mechanism of pyrrhotite.The results of bioleaching tests showed that moderately thermophilic iron-oxidizing L. ferriphilum was not appropriate for leaching pyrrhotite solely, the leaching rate of total iron only reached31.11%, however, the leaching effect was significantly improved with the addition of sulfur-oxidizing A.caldus, the total iron extraction reached85.68%only after3days of bioleaching. Moderately thermophilic iron-and sulfur-oxidizing S.thermosulfidooxidans cultivated by different energy sources showed obviously disparate leaching performance in iron extraction. The total iron extraction of pyrrhotite leached by S. thermosulfidooxidans which was raised by ferrous ions reached28.05%after bioleaching for ten days, and was just9precent higher than that of abiotic system while65.28precent of total iron extraction was achieved during bioleached by S. thermosulfidooxidans grown on sulfur. Extremely thermophilic A.manzaensis could bring about the rapid increasement of pH value during the oxidation of pyrrhotite, and higher pH value would inhibit the growth of bacteria. The addition of A.manzaensis had no positive impact on pyrrhotite dissolution.Electrochemical testing results showed that bacteria did not change the oxidation mechanism of pyrrhotite. The results indicated that the surface passivation of pyrrhotite in leaching process was determined by its decomposition mechanism and leaching conditions together. Sulfur was the major factors which inhibited the oxidation of pyrrhotite during bioleached by iron-oxidizing bacteria, the elemental sulfur layer would result in the surface passivation and low leaching rate. However, jarosite was the major components of a passivation film blocking the reactions of the electrode surface during bioleached by iron-and sulfur-oxidizing bacteria at the late stage.