Investigation of cleaner sulfide mineral oxidation technology: Simulation and evaluation of stirred bioreactors for gold-bioleaching process

Bio-oxidation technology for leaching sulfide mineral of refractory gold concentrate is cleaner than conventional methods. Although liquid agitation can maintain cells and particles in suspension, thereby improving the mass transfer efficiency of oxygen, carbon dioxide, and nutrients, it also generates shear stress, which can reduce bio-oxidation reaction efficiency by destroying shear sensitive cells. In this study, a multiphase Eulerian model with the standard k-ε equation and auxiliary models were evaluated based on previously conducted experiments investigating two and three phase flows of gas-liquid, solid-liquid and gas-liquid-solid. The predicted shear stress on bacteria, gas holdup, bubble diameter and turbulence energy dissipation rate were then calculated by these models to reveal the key factors influencing bio-leaching efficiency and to analyze the primary region in which cell death occurs. The results showed that shear stress on bacteria in the impeller region is higher than in other regions. Based on the results of the study, an optimal operation condition was applied to bio-oxidation technology investigations. Comparing with classic roasting technology, bio-oxidation technology completely eliminates toxic gas emissions, reduces 4.3tons of wastewater per ton of refractory gold concentrate and reduces the leaching toxicity of total arsenic in the solid waste from 0.57 mg/L to 0.36 mg/L. It is demonstrated that bio-oxidation technology is cleaner and more eco-friendly than classic roasting technology. This work provides guidance for further study and designation of the stirred bioreactor scale-up in both biochemical and environmental engineering applications.