Frothing behavior of aqueous solutions of oleic acid

Frothers are surface-active agents widely used in flotation to facilitate the generation of small bubbles by preventing coalescence and increasing the surface area flux, which is the driving factor in flotation. Flotation collectors also exhibit frothing capabilities but these have never been adequately quantified. In this paper the effect of two typical fatty acids, sodium oleate and tall oil, on the coalescence of air bubbles was determined by measuring the critical coalescence concentration (CCC), gas holdup, and foamability. The results revealed that the frothing behavior of fatty acids is qualitatively similar to the behavior of other frothers (e.g. MIBC), but the CCC value was considerably higher, e.g., for sodium oleate at natural pH the CCC was 70 mg/L compared to about 10 mg/L for MIBC. Alkaline pH conditions produced lower CCC and higher foamability. Since fatty acids are weak electrolytes, the effect of pH on the frothing behavior was discussed in terms of speciation. Alkaline solutions of fatty acids produced considerable foam compared to typical frothers. However, lower pH values (7–7.5) completely prevented any foam growth.

Graphical abstractFoamability of oleic acid solutions is a strong function of pH.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Oleic acid and tall oil were shown to be very weak frothers. ► Critical coalescence concentration was determined. ► Gas dispersion and frothing power were a strong function of pH. ► Prevention of coalescence in bulk solution enhanced foaming.