Correlation of Adsorption and Surface Hydrophobicity

The use of contact angle measurements to complement electrochemical techniques for the study of adsorption of thiols at metals and metal sulfides was first applied to the interaction of methyl, ethyl, and butyl 

Contact angle measurements were also correlated with voltammetry by Chander and Fuerstenau in their study of the interaction of diethyl dithiophosphate with copper and chalcocite surfaces. Finite angles were observed when the potential was in the region of stability of copper dithiophosphate, but detailed information on the wettability of chemisorbed dithiophosphate was not reported. Recent studies of this system established that the contact angle becomes finite when the chemisorbed species is present an angle of -60° was observed for a monolayer, and this is the characteristic value for the ethyl group. 

It has been demonstrated that the potential at which the contact angle measurements indicate that abraded mineral surfaces become hydrophobic in the presence of a thiol can be somewhat higher than the value at which chemisorption commences. It was considered that this reflects the presence of a significant induction time in establishing a captive bubble on such a surface. Energy barriers in particle-to-bubble attachment 

The determination of flotation recovery using particulate sulfide mineral bed electrodes under potential control was refined by Richardson and co-workers and applied to the study of the interaction of ethyl xanthate with a range of sulfide minerals. The approach introduced by these authors was to employ relatively large particles (590-840 //m) and to keep the bed under positive pressure during potential conditioning. With this technique, they were able to combine flotation recovery determinations with voltammetry and with UV-vis spectroscopy of the solution phase. 

A different method for the determination of flotation recovery as a function of potential was conceived by Trahar and co-workers. These authors applied a modified laboratory flotation cell in which flotation was carried out with nitrogen, and the potential, monitored with a platinum electrode inserted in the pulp, was adjusted by the controlled addition of oxidizing or reducing agents. This experimental technique had the disad- 

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