A novel method for evaluating the hydrophobic interaction between coal particles and air bubbles and its role in flotation

Abstract

Among surface forces, the non-Derjaguin-Landau-Verwey-Overbeek hydrophobic force between hydrophobic surfaces is critical to bubble-particle attachment and, as a result, mineralization in flotation. However, it brings challenge to study the hydrophobic interaction between coal particles and air bubbles due to lack of the hydrophobic interaction constant. In this study, a novel method was proposed to evaluate the hydrophobic interaction between coal particles and air bubbles, which comprehensively combines the extended Derjaguin-Landau-Verwey-Overbeek theory, the Stefan-Reynolds model and the experimentally measured attachment time. It was found that the attachment time between coal particles and air/oily bubbles was respectively 246 and 50 ms. The decay length for hydrophobic interactions was about 25 nm. Then, according to the obtained attachment time and decay length, the derive Stefan-Reynolds model was solved and the hydrophobic interaction energy constant between air bubbles and coal particles was determined to be −4.19 mJ/m2, about 1/7 of that between oily bubbles and coal particles. These findings clearly demonstrated the significant difference between conventional and oily-bubble flotations, and the critical role of the hydrophobic interaction in coal flotation was confirmed.