Effect of inorganic cation on dynamic characteristics of bubble generation.

• Bubble generation process was divided into Formation , Expansion and Contraction stages according to the contact angle between the bubble and the capillary as 90°. Na+, Mg2+, Ca2+ and Al3+ promoted the bubble growth during the Formation and Expansion stages while restrained the growth during the Contraction stage. Al3+ roughly presented the most obvious promotion on the bubble generation. • Bubble internal pressure increased as the bubble grew. Pressure difference inside and outside the bubble generally followed the order Na+ > Mg2+ > Ca2+ > Al3+. Na + presented the thickest hydration layer at the bubble surface and the highest bubble internal pressure. • Net force acting on the bubble first kept constant and then decreased with the concentrations of Na+, Mg2+ and Ca2+, while it first increased and decreased then in the presence of Al3+. Understanding the effect of inorganic cations on dynamic bubble generation is an important precursor for predicting the bubble characteristics in actual coal flotation. Using the high-speed motion acquisition system, we investigated the bubble growth in different inorganic salt solutions. The bubble generation process was divided into Formation , Expansion, and Contraction stages according to the contact angle between the bubble and the capillary as 90°. Na+, Mg2+, Ca2+, and Al3+ were found to promote bubble growth during the Formation and Expansion stages while restraining the growth during the Contraction stage. Al3+ roughly presented the most obvious promotion of the bubble generation. The dynamic bubble width and length during different bubble growth stages were analyzed to discuss the bubble pressure. The internal pressure increased as the bubble grew. The pressure difference inside and outside the bubble generally followed the order Na+ > Mg2+ > Ca2+ > Al3+. The forces acting on the bubble were attempted to be discussed. The net force acting on the bubble first kept constant and then decreased with the concentrations of Na+, Mg2+, and Ca2+, while it first decreased and then increased in the presence of Al3+. Our results can provide valuable insight into the development of the technology for mineral flotation. [ABSTRACT FROM AUTHOR]