interactions between electrode surfaces

The interactions between electrode surfaces are often called galvanic. They are due to the different electrochemical activity that the conducting solids present. The combination of a cathodic surface (electron acceptor) and an anodic one (electron donor) result in the creation of a galvanic cell. The existence of a convenient oxidant, such as dissolved oxygen, enhances the creation of a galvanic current, serving as the ultimate electron acceptor [2]. Such reactions can be hindered either by lowering the activity of oxygen in water or increasing the pH of solution. The electrochemical activity of minerals is characterized by means of their rest potential (i.e. the potential reached spontaneously by the mineral electrode in an aqueous solution). The mineral with the higher rest potential acts as a cathode, while the other one with the lower rest potential is the anode.

During the flotation process, the galvanic interactions have a significance influence as there is a mixing of solids with varying electrochemical activity, such as sulphide minerals and metals originated from the corrosion of grinding media (being iron alloys). The latter are more anodic than the sulphides, consequently, affect the selectivity of the process.

The next figure presents the mechanism of galvanic interactions and the possible reactions during the electrolytic contact of two sulphides or with grinding media (steel balls, rods). The hydroxyls that are produced on the cathodic mineral result in the depression of flotation, while the elemental sulphur that forms on the anodic sulphide can increase its hydrophobicity and even lead sometimes to collectorless flotation. The environment during grinding facilitates the above reactions [3,4].

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