Froth separation of ferrihydrite slurry using microbubbles with ultrasonic irradiation

Here we show the newly developed process of microbubble froth separation enhanced by ultrasonic irradiation for colloidal slurry. In this study, microbubbles were applied to the froth separation of dilute ferrihydrite colloidal suspension. Furthermore, enhancement of the microbubbles froth separation by controlling the motion, aggregation and clustering of microbubbles using the "Bjerknes force" in ultrasonic acoustic fields was investigated. The rate of microbubble froth separation of ferrihydrite colloidal slurry was increased by the ultrasonic irradiation and was more efficient than settling separation. Adjustment of the ultrasonic frequency is important for the microbubble froth separation. With a frequency of 38 kHz producing stronger primary and secondary Bjerknes forces, the motion and clustering of microbubbles are too extreme; the microbubbles abruptly aggregated to form clusters and rose rapidly without carrying the ferrihydrite colloidal particles. However, with ultrasonic irradiation at a frequency of 430kHz, the motion of microbubbles was moderate and they aggregated widely. In this case, the clear froth separation of ferrihydrite colloidal slurry progressed rapidly, and its rate was increased with increasing output power of ultrasonic irradiation.