Oxygen mass transfer and electrochemical studies in flotation of complex nickel-copper sulphide ores

Complex sulphide ores containing pentlandite and chalcopyrite contain abundant amounts of pyrrhotite that is highly susceptible to oxidation. This has important consequences, e.g., its premature flotation when selectivity is crucial, or its low floatability when the middlings recovery is crucial. Pyrrhotite's behaviour is central to developing efficient processing strategies and it is often unpredictable. Therefore, some aspects of grinding and electrochemistry of these minerals were investigated under process related conditions. This involved evaluation of oxygen transfer into slurries and use of various electro-analytical methods.; The oxygen transfer coefficient decreased linearly from 8.69 min -1 to about 4.08 min-1 with increasing fineness from 24.7% -45 mum to 97.2% (2.13-fold) for the mild steel media. This effect was only 1.25 folds when the stainless steel media was used. Frother, lime and sodium chromate addition enhanced the oxygen transfer to a point of reversing the effect induced by mild steel material. As the sulphide content is increased, the slurry becomes more oxygen-deficient. The oxygen transfer into 30% Po slurry is about six times less than that into 30% Cp slurry.; The voltammograms obtained in the absence and presence of xanthate and dissolved oxygen provided no direct evidence for any peaks that can be associated with xanthate's adsorption or its transformation to dixanthogen. However, the current densities corresponding to the most prominent anodic potential for Po were lower in the presence of xanthate, suggesting its involvement in the formation of a partially passivating film. The rest potential measurements suggest that the formation of dixanthogen will be common to these minerals in oxygen-saturated solutions. However, under oxygen-deficient conditions in the presence of xanthate, Po develops rest potentials that are lower than the equilibrium potential for dixanthogen formation. This suggests that controlling the dissolved oxygen and potential at low levels will promote hydrophobicity of Pn in preference to Po, a point which was subsequently confirmed in this study.; Galvanostatic studies indicated that Fe(III) and Cu(II) ions facilitate formation of dixanthogen. If the availability of active metal ions is insufficient due to a high pH or presence of polyamines, the reaction for dixanthogen formation is severely limited.