Electrochemical Equilibriums in Collectorless Flotation

Although the nature of the hydrophobic entity responsible for the self-induced flotation of sulphide minerals remains somewhat obscure, most reported results clearly show that it is only when the environment becomes slightly oxidizing that flotation is observed. The elemental sulphur and polysulphide-intermediates in the oxidation of sulphide to sulphur have ever been suggested to be of the hydrophobic species. Whatever it is, there is no doubt that sulphur can generate hydrophobicity and floatability. 

For chalcopyrite, the sulphur-producing reactions include in alkaline medium 

The formation of sulphur on chalcopyrite surface would be expected to occur at 0.15 V at pH = 6 by assuming [Fe ] = 10 mol/L according to reaction (2-8), 0.08 V at pH = 8 and -0.1 V at pH = 11 according to reaction (2-9). While flotation does begin very near these potential for the experimental conditions reported by some authors as shown in Table 2.1. 

For galena, the reactions producing elemental sulphm may include 

The reaction potential producing elemental sulphur are 0.24 V at pH = 6 based on the reaction (2-10), 0.28 V at pH =8 on the reaction (2-11), and 0.1 V at pH = 11 on die reaction (2-12) with lO mol/L concentration of dissolved species. The reported flotation initial potential (see Table 2.1) are very close to these theoretical calculation values. The theoretical and experimental values in Table 2.1 indicate that the elemental sulphur might be responsible for the hydrophobicity of sulphide surfaces. At different pH media the formation of elemental sulphur occurs and hence the flotation behavior undergoes different processes. 

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