Effect of natural organic matter on the stability of a liquid film between two colliding bubbles

The aim of this study was to investigate the effect of aquatic humic substances on froth stability. A novel experimental apparatus was built for conducting bubble coalescence experiments, specifically the study of liquid films formed between two bubbles of constant air volume that were pushed coaxially to each other. Two types of natural humic substances (HSs) were tested, along with two synthetic ones, and were found to affect both the coalescence frequency and the coalescence time. Humic substances appeared to reduce or inhibit the coalescence of bubbles and to increase the coalescence time, depending on their type and concentration in the solution. Furthermore, their effect was compared with that of electrolytes. In all cases, humic substances had a much higher effect on bubble coalescence than any electrolyte tested in this work.