One of the problems in the flotation of copper sulphide ores in moderately alkaline pH conditions is the misreporting of iron sulphide minerals into copper concentrates, which results in low copper grades. The relatively strong flotation of iron sulphides is caused by their copper activation from copper species dissolved from copper minerals present in the ore. In this study, several methods were used to reduce copper activation of pyrite during grinding or to minimise its effect on the flotation of pyrite at pH 9.0. Various surface analytical techniques were used to identify the mechanism of these methods and to optimise their performance. / First, it was confirmed that strong pyrite floatation at pH 9.0 in the presence of xanthate was caused by copper activation during grinding with copper sulphate or in the presence of chalcopyrite in single or mixed mineral flotation experiments, respectively. It was found that pyrite flotation is Eh dependent with low flotation for pulp oxidation potential, Eh, values lower than 7 mV (SHE), strong flotation between 7 and 50 mV, and flotation decreasing above 50 mV. The sharp increase in pyrite flotation around neutral Eh values was associated with high copper and xanthate adsorption while the decreased flotation at higher Eh values was caused by the formation of ferric hydroxide at the pyrite surface which in turn reduced copper adsorption but also reduced hydrophobicity. From the measurement by X-ray photoelectron spectroscopy (XPS) of the type and proportion of surface species, it was possible to calculated a hydrophobicity index at each step in the grinding discharge, during conditioning, in each flotation concentrate and finally in the tailing. A satisfactory agreement was obtained between this XPS hydophobicity index and the flotation recovery in each concentrate. / It was found that pyrite could be separated from chalcopyrite at pH 9.0 by controlling the pulp Eh value with maximum mineral separation and chalcopyrite flotation occurring at an Eh of 275 mV. This mineral separation could be further increased with the addition of zinc sulphate which selectively adsorbs or precipitates on the pyrite surface as zinc hydroxide via electrostatic interaction. The selectivity of this adsorption, and therefore larger pyrite depression, is the result of the larger amount of ferric hydroxide formed on the pyrite surface because of the more cathodic nature of this mineral. Thioglycolic acid (TGA) was also found to selectively depress pyrite flotation when added during grinding but, if added during conditioning, its effect on pyrite depression was only observed in the presence of citric acid (CA). This depression was related to the removal of copper hydroxide from the pyrite surface as both TGA and CA are strong complexants of cupric hydroxide (but also ferric hydroxide); as a result, fewer sites are available for xanthate adsorption. Citric acid is a weaker complexant than TGA, especially in the presence of xanthate; its role is to mop up the surface ferric hydroxide so that TGA is free to react with copper hydroxide. More importantly, in less oxidising conditions and with no Eh control, addition of zinc sulphate or TGA increased chalcopyrite flotation but had no effect on pyrite flotation. Pyrite flotation could also be reduced with addition of xanthate during grinding. In this case, the selective depression of pyrite flotation was attributed to the immobilisation of copper by xanthate at the chalcopyrite surface or its removal from solution, both mechanisms resulting in a reduced copper activation of pyrite. Pyrite depression and chalcopyrite flotation, and therefore mineral separation, were optimised with collector addition in both the grinding and conditioning stages. / Finally, the efficacy of these methods has been substantiated by comparing their effects on iron sulphide depression in two copper sulphide ores and with more common methods of iron sulphide depression. / Thesis (PhDAppliedScience)--University of South Australia, 2006
| Identifer | oai:union.ndltd.org:ADTP/267170 |
| Date | January 2006 |
| Creators | He, Shuhua |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | copyright under review |
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