A CRITICAL EXAMINATION OF THE ROLE OF INK SURFACE HYDROPHOBICITY IN FLOTATION DEINKING

J.J. Magda*, J.Y. Lee

University of Utah

EXECUTIVE SUMMARY

In the flotation deinking step of wastepaper recycle, various additives known as "collectors" and "dispersant/collectors" are believed to enhance flotation by increasing the hydrophobicity or contact angle of the ink surface. However, the surface hydrophobicity of a typical oil-based liquid ink particle has rarely been measured. We report here measurements of the surface hydrophobicity of commercial offset printing inks, and estimate the effects of sodium oleate (a dispersant), calcium oleate (a collector), and a nonionic surfactant. The inks studied are quite hydrophobic in their native states without additives. Sodium oleate addition reduces ink hydrophobicity; calcium oleate addition partially restores it. Hydrophobicity measurements alone cannot fully explain the ability of calcium oleate to enhance ink collection and flotation. The surface activity of oleate-containing solutions is a very complex function of pH, and cannot be predicted theoretically from bulk solution chemistry calculations. Therefore, aqueous phase surface tension measurements are recommended as an empirical guide to the choice of pH for flotation. For various minerals, the pH value of maximum flotation response (with oleate collector) is known to correlate with the minimum in the aqueous surface tension and a similar correlation may be valid for printing inks. Microphotographs show that the shape of collected ink aggregates can be changed from sphere-like to fiber-like by adjusting the collector concentration, a surprising result which might be useful for improving the kinetics of flotation.

( TAPPI Journal,Vol. 82:No. 3,pages 139-145,1999)