Particles size, hydrophobicity and flotation response

Quartz particles of various discrete particle size ranges have been methylated to varying known mounts using trimethylchlorosilane and their flotation behaviour has been assessed in a modification of the Hallimond tube. For each particle size there is a definite degree of. surface coverage below which the particles do not float. A 'flotation domain' is identified which shorvs that both coarse (-100pm) and fine (-10pm) particles require a greater degree of surface coverage to initiate flotation than do intermediate (-40pm) particles. Water contact angles have been measured on quartz plates and powders which have been methylated (under the same conditions) with trimethylchlorosilane. Both advancing and receding water contact angles measured on quartz plates as a function of degree of surface methylationare in good agreement with the angles predicted by the Cassie equation. Advancing water contact angles measured on quartz particles as a function of degree of surface methylation are also in good agreement with angles predicted by the Cassie equation up to surface coverages of'about 70%. The angles measured at higher surface coverages are less than those anticipated by the Cassie equation. The flotation behaviour of the particles has been compared with that predicted by existing flotation theories. It has been shown that coarse particle behaviour is predicted by the kinetic theory of flotation proposed by Schulze. Fine particle behaviour, however, only qualitatively agrees with Scheludko's theory of fine particle behaviour. Calculated induction times, in conjunction with observed flotation behaviour, indicate that the bubble-particle attachment process is most efficient for particles of about 38pm in diameter ander the set experimental conditions used in this study. Flotation rate trials were performed for three particle size ranges and rate constants were evaluated for the various degrees of surface coverage. It was found that the dependence of rate constant on particle size is essentially linear.