The Effect of Inorganic Salt on Multiphase Flow Characteristics in a Microbubble Column: A Focus on the Ionic Strength

With enormous interfacial area for particle collection, microbubbles exhibit great application prospect in the mineral flotation. Under certain ionic strength, microbubbles can be produced continuously in the microbubble column without extra reagent addition. In this work, multiphase flow characteristics (Sauter mean diameter, bubble size distribution, gas holdup & interfacial area) were studied systematically with variables including the salt type, salt concentration, and operating conditions. Based on mathematical model, critical coalescence concentration was determined for each investigated salt. According to experimental results, a mathematical correlation was established between the Sauter mean diameter and ionic strength. For the formation of microbubble system, the lowest ionic strength was approximately 0.5 mol/L. Multiphase flow characteristics in the microbubble column depended highly on the ionic strength. The interfacial area and gas holdup increased by 38 times and more than 3 times respectively, with the ionic strength of Al 2 (SO 4 ) 3 rising from 0 to 1.5 mol/L. The critical coalescence concentration ranged from 0.037 mol/L (Al 2 (SO 4 ) 3 ) to 0.517 mol/L (NaCl), which correlated with the ionic strength of each salt.