TABLE OF CONTENTS Regulators, or modifiers, are used extensively in flotation to modify the action of the collector, either by intensifying or by reducing its water-repellent effect on the mineral surface. They thus make collector action more selective towards certain minerals. Regulators can be classed as activators, depressants, or pH modifiers.
These reagents alter the chemical nature of mineral surfaces so that they become hydrophobic due to the action of the collector. Activators are generally soluble salts which ionise in solution, the ions then reacting with the mineral surface.
A classical example is the activation of sphalerite by copper in solution. Sphalerite is not floated satisfactorily by a xanthate collector, since the collector products formed, such as zinc xanthate, are relatively soluble in water, and so do not provide a hydrophobic film around the mineral. Floatability can be improved by the use of large quantities of long-chain xanthates, but a more satisfactory method is to use copper sulphate as an activator, which is readily soluble and dissociates into copper ions in solution. Activation is due to the formation of molecules of copper sulphide at the mineral surface, due to the fact that copper is more electronegative than zinc and therefore ionises less readily:
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The copper sulphide deposited on the sphalerite surface reacts readily with xanthate to form insoluble copper xanthate, which renders the sphalerite surface hydrophobic. Recent work, however, suggests that this simple ion-exchange mechanism may be oversimplified, and Wang et al. (1989a,b) propose a model based on surface oxidation...
