THE EFFECT OF SURFACE HETEROGENEITY ON PSEUDOLINE TENSION AND THE FLOTATION LIMIT OF FINE PARTICLES

The contact angles theta for water at methylated quartz surfaces were measured using the sessile-drop technique to determine the advancing contact angle, and using a captive-bubble technique to examine the effect of bubble size on contact angle. No linearity between cos theta and 1/r, where r is the drop base radius, was observed for these systems as would be expected for an ideal system. In fact the pseudo-line tension decreased with decreasing bubble size. Also, the degree of quartz methylation effected a change in the pseudo-line tension. The pseudo-line tension increased from 0.4 .10(-6) N to 3.3 . 10(-6) N with an increase in the fractional coverage of trimethylsilyl groups from 0.14 to 0.51 for large bubbles (bubble base diameter d > 0.34 mm), whereas the pseudo-line tension decreased from 2.2 .10(-7) N to 0.8 .10(-7) N with an increase in fractional coverage for small bubbles (bubble base diameter d = 0.06-0.2 mm). The flotation limit of fine particles has been re-examined based on the effect of bubble size on contact angle, and a new surface chemistry-limited relationship describing the minimum particle size which can be floated is proposed: [GRAPHICS] where r(c) is the critical bubble (drop) radius for which there is no effective attachment between solid surface and dispersed phase, gamma(LV) is the interfacial tension at the liquid-vapor interface, DELTArho is the density difference between the particle and the liquid and V is the bubble ascent velocity.