Effect of frothers on bubble coalescence and foaming in electrolyte solutions and seawater

• A new concept was introduced in surface tension of frothers–NaCl solutions.
• The dynamic foamability index showed higher foamability of DF-250 than of MIBC.
• In NaCl solutions, MIBC and DF-250 do not decrease bubble size beyond NaCl alone.
• Bubble coalescence in seawater is better prevented than in NaCl solutions.

Inhibition of bubble coalescence is of fundamental importance in a flotation process because it determines the size of bubbles and foam stability. For this work commercial frothers have been selected, MIBC, DF-250, DF-400 and DF-1012; and NaCl as inorganic electrolyte. Surface tension measurements used to characterize the tested frothers revealed that these frothers have quite different properties. Polypropylene glycols are much more surface active than MIBC. The differences between these two are further augmented in concentrated NaCl electrolyte solutions. The concept of the surface tension switch point (s.t.s.p.) is introduced to characterize the effect of electrolyte concentration on frother properties. The s.t.s.p. values for MIBC and DF-250 were determined to be around 120 ppm and 1.2 ppm, respectively. The effect of MIBC and DF-250 frothers on bubble coalescence was not very different, although finer bubbles were generated in the presence of MIBC than of DF-250 in seawater. Only dynamics foamability measurements (DFI) confirmed the differences, the foams produced in the presence of DF-250 were much more stable, also in electrolyte solutions. This fact confirms the importance of dynamic effects in foam formation and stabilization.