Toward Bioleaching Industrial Application of a Low-Shear Stirred Tank

When a stirred reactor is scaled up, a larger aspect ratio requires less land and is more energy-efficient. To promote the application of the low-shear reactor in the bioleaching industry, its aspect ratio is elongated to 1.78, and a dual-impeller configuration is adopted. Power consumption, particle suspension, and gas–liquid mass transfer characteristics therein are investigated systematically. It is found that such a configuration presents a good particle suspension and gas–liquid mass transfer performances. Meanwhile, one limit is found in which almost no bubbles can be recirculated in the annular gap. It can also be inferred that this problem will be further exacerbated when the reactor is further scaled up. Then the draft tube is cut into two sections (Hdd = 0.035 m), and many bubbles are observed in the annular gap. However, compared to a single-stage draft tube, there are significant decreases in power consumption, and consequently, kLa also decreases under the same impeller speed. This result is detrimental to biological processes. Further experiments are conducted to optimize the spacing between two-stage draft tubes. An optimized spacing (Hdd = 0.070 m) is found, and kLa per power consumption significantly increases compared to that with a single-stage draft tube. Under typical gassing rates and particle loads, two correlations regarding Pv and kLa are obtained to provide a reference for the design and scaling up of bioleaching reactors.