Theories of Mineral-Collector Interaction

The 1930s saw the development of theories to elucidate collector-mineral interaction and to explain the selectivity for sulfide mineral flotation of thiol collectors such as the xanthates. Three propositions were put forward, and each was promoted and defended by its proponents with considerable vigor and intensity. 

For an explanation of adsorption we must await a fuller development of the theory of intermolecular attractions, but one simple generalization is useful in this field, namely that adsorption can usually be expected if a compound which is relatively insoluble is formed between the metal of the mineral and the anion of the collector this is the Paneth-Horowitz principle, enunciated in 1915. Taggart, who re-discovered the principle a decade later, proceeded to ascribe all adsorption to double decomposition, but this explanation is far too simple. 

In the concept promoted by Taggart, the formation of a hydrophobic surface is governed by the solubility of the metal thiol compounds. In order to overcome the difficulty that flotation occurs at collector concentrations that are orders of magnitude less than those at which one would expect a metal thiol compound to deposit from solubility considerations based on bulk species, Taggart and Hassialis considered that the concentration of the metal ion be taken as that in the lattice of the mineral. Sutherland and Wark pointed out the fallacy of this reasoning and reaffirmed the conviction that, to explain the floatability at low collector concentrations, an adsorption process must be operative. 

three theories had been developed and each had difficulties formation of metal thiols did not fit thermodynamics, adsorption of ions did not fit charge requirements, and adsorption of thiol acids did not fit stability criteria. 

Nixon also suggested that prominent theories of flotation could be reconciled by the electrochemical approach. This is illustrated in Fig. 1, in which the requirement of a neutral surface species in Cook and Nixon s model can be met in different ways. The anodic reaction can be adsorption as proposed by Wark and Cox (Fig. la). Also, it can be the formation of a metal thiol compound as proposed by Taggart and co-workers. The latter process can occur as a single step as in Fig. lb or through separate surface oxidation and ion-exchange processes as shown in Figs. Ic and Id. In addition, the anodic process can be the formation of the dithiolate as suggested by Nixon and illustrated in Fig. le. 

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