Effects of dissolved oxygen and carbon dioxide under oxygen-rich conditions on the biooxidation process of refractory gold concentrate and the microbial community

Hong Wang, Xu Zhang, Minglong Zhu, Wensong Tan

State Key Laboratory of Bioreactor Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, PR China.

Abstract

Biomining microorganisms obtain energy from the oxidation of reduced sulfur and iron (II) by using dissolved oxygen (DO) as the electron acceptor. Carbon dioxide, the carbon source for biomining microorganisms, is essential for biooxidation. However, to date, no published reports exist regarding the effect of reactive oxygen species (ROS) and the CO₂ content in an oxygen-rich condition (when oxygen is sufficient) on the biooxidation process. In this study, a microbial community was used to oxidize refractory sulfide gold concentrate in a 1.5 L experimental stirred tank reactor. The effects of DO in a slurry and the CO₂ content in the intake gas on the biooxidation process, bacterial growth and microbial community were investigated. It was found that the biooxidation efficiency increased at first and then decreased as the DO level elevated, while the content of ROS significantly increased within the bacteria cells. Under an oxygen-rich condition, the biomass increased as the CO₂ content increased, while the biooxidation efficiency first increased and then decreased. These changes revealed that the oxidation activity of biomining microorganisms was inhibited by a high CO₂ content and that bacterial growth and energy utilization were decoupled. Leptospirillum ferriphilum-like bacteria andSulfobacillus thermosulfidooxidans were the dominate strains in the experiment. As the DO increased, the relative proportion of L. ferriphilum-like bacteria in the bacteria community first increased and then decreased, while S. thermosulfidooxidans showed the opposite trend. With an increasing CO₂ content in the intake gas, the relative proportion of S. thermosulfidooxidans increased, while that of L. ferriphilum-like bacteria decreased.

Keywords: Refractory sulfide gold concentrate; Dissolved oxygen; CO₂; Microbial community structure; Reactive oxygen species.