Limited role of sessile acidophiles in pyrite oxidation below redox potential of 650\u2009mV

Chang Liu,Xuekun Leng,Qiaoyi Tan,Yan Jia,Xiaopeng Niu,Heyun Sun,Renman Ruan

doi:10.1038/s41598-017-04420-2

Chang Liu, Xuekun Leng + Show 5 more

Open Access

https://doi.org/10.1038/s41598-017-04420-2

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Abstract

Pyrite oxidation by mixed mesophilic acidophiles was conducted under conditions of controlled and non-controlled redox potential to investigate the role of sessile microbes in pyrite oxidation. Microbes attached on pyrite surfaces by extracellular polymeric substances (EPS), and their high coverage rate was characterized by scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). The dissolution of pyrite was negligible if the redox potential was controlled below 650 mV (near the rest potential of pyrite), even though the bacteria were highly active and a high coverage rate was observed on pyrite surfaces. However, with un-controlled redox potential the rate of pyrite oxidation increased greatly with an increasing redox potential. This study demonstrates that sessile microbes play a limited role in pyrite oxidation at a redox potential below 650 mV, and highlight the importance of solution redox potential for pyrite oxidation. This has implications for acid mine drainage control and pyrite oxidation control in biometallurgy practice.

Highlights

Pyrite (FeS2) is the most abundant sulfide mineral on earth and is found in most mining environments
After eliminating the “non-contact chemical attack” present in solution, oxidation of pyrite was negligible more than 70% of the pyrite surface was covered by bacteria
These results suggest that sessile bacteria are of limited impact on pyrite dissolution, if the redox potential is kept below 650 mV

Summary

Introduction

Pyrite (FeS2) is the most abundant sulfide mineral on earth and is found in most mining environments. “Contact leaching” occurs if sessile cells are adhering to the pyrite surface, with the extracellular polymeric substances (EPS) serving as the reaction space for the oxidation of ferrous ions and dissolution of pyrite by ferric ions This process is not completely understood[30]. The EPS are thought to contain ferric glucuronic acid complexes, and in addition cell-sized pits are observed on the pyrite surface, which are considered as evidence of “contact leaching”[31,32,33] In these studies the solution redox potential is not reported, and the ferric concentration is high in the solution environment, which does not eliminate the effect of “non-contact leaching” on pyrite oxidation. The conclusions provide useful theoretical support for heap bio-oxidation of pyrite and control of acid mine drainage

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