Oxidation of Pyrite in Lime Medium

Further, the EIS of pyrite imder different polarization potential in the lime medium are measured and shown in Fig. 7.10. The relationship between polarization resistance and potential can be demonstrated in Fig. 7.11. It can be seen from Fig. 7.10 and Fig. 7.11 that when the anodic polarization potential is between 20 and 350 mV, all the curves appear as a single capacitive reactance loop. But surface process of pyrite electrode is controlled by a quite different 

Comparing EIS for p)oite in lime medium and different polarization potential (Figs. 7.10 and 7.11) with those in sodium hydroxide solution (Fig. 7.6 and Fig. 7.7), it can be seen that at a potential of about 50 mV the surface resistance in the NaOH solution (about 8700 Q) is lower than that in the lime medium (about 12000 fl). It means that besides the formation of hydroxyl precipitate on the surface of pyrite in lime media similar to that in NaOH media, there may be other surface products being formed, which may be due to the following reactions  

The formation of hydroxyl iron and calcixxm sulphate precipitates makes pyrite surface very hydrophilic and inhibits other electrochemistry reaction on pyrite like collector giving rise to the depression of pyrite. The depression effect of lime on pyrite may be stronger than that of NaOH. 

3 Corrosive Electrochemistry Study on Interactions between Collector and Pyrite 

Figtire 7.12 is the polarization curves of pyrite electrode in xanthate solution with different concentration for dipping for 48 hours. Electrochemistry parameters determined by the computer PARcal are listed in Table 7.2. Inhibiting efficiency can be calculated by Eq. (7-7), Rp- is the polarization resistance after adding collector, Rp is the polarization resistance without collector. It can be seen from Fig. 7.12 and Table 7.2 diat, with the increase of xanthate concentration, corrosive potential and corrosive current of the pyrite electrode decrease gradually while polarization resistance increases, indicating the formation of surface oxidation products. 

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