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Flotation collector action has been more thoroughly investigated than has any other phase of the flotation process. As a result, little doubt remains as to the “outward” orientation of the hydrocarbon portion of the collector molecule. However, the actual mechanism of collector attachment to the mineral particle is still a subject for debate and controversy.
The nature of the forces of attraction between the polar portion of the collector and the mineral surface has been discussed in a number of papers by M.A. Cook, A. M. Gaudin, H. Hagihara, A.F. Taggart, I.W. Wark, and many others. The theories proposed include the chemical or solubility theory, and also various adsorption theories involving attachment to the collector as an ion, a molecule, a monolayer, and/or a multilayer.
Recent investigations using radioactive tracers and electron diffraction techniques have provided additional information. However, no single theory is yet wholly acceptable.
The chemical or solubility theory postulates the formation of a metallo-organic compound on the mineral surface. It was recognized that when copper and lead sulfides are separated form zinc sulfides by xanthates flotation, very insoluble metal xanthates are formed on the surface of the copper and lead. Thus (it was believed) copper and lead sulfides are floated because the resultant copper and lead xanthates are more insoluble than the copper and lead minerals. The zinc sulfide, because of its more soluble xanthates, is not floatable. Figure 2 illustrates this theorized type of xanthates attachment.
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