Dynamic surface tension of alkaline dodecylamine solutions

Abstract

Using a bubble pressure technique, the time dependent surface tension of dodecylamine solutions over a wide range of conditions (2 × 10 −5 to 8 × 10 −4 M and pH 7–13) was investigated. A pronounced pH dependence was observed, surface activity of the amine increasing with pH up to pH 10 then declining sharply. Hydrolysis of the amine ion to amine molecule is shown to be an incomplete explanation; ion-molecule complexes are proposed. The data presented is used to discuss the flotation of oxides using dodecylamine as collector. The importance of the “age” of the bubble in flotation is noted; the high surface tension exerted by fresh bubbles in comparison with aged bubbles is shown to be an advantage to flotation. A correlation between collector surface activity and flotation recovery is demonstrated and discussed; optimum flotation conditions (pH 8–11) are shown to correlate with the maximum surface activity observed. A combination of adsorption of amine ion-molecule complexes at the oxide surface and the high surface tension exerted by fresh bubbles is considered to be responsible for the successful flotation achieved at ∼pH 10.