The oxidation of pyrite was studied by thermal analysis and quenching of the phases formed at different stages of the reaction. The phases were characterized by optical microscopy, SEM, EDAX, XRD and microprobe analyses. The phases found were essentially those predicted assuming thermodynamic and pressure equilibria. The predictions were that (1) below 404 ~ hematite would form directly on the pyrite surface whereas at higher temperatures magnetite would intervene, (2) pyrrhotite would become a stable phase above 552 ~ (3) ferrous and ferric sulphates would form in the outer layers at temperatures below 583 and 644 ~ respectively. The ignition temperature of pyrite was found to correspond with the onset of pyrrhotite formation. An arrest in some of the TG traces was ascribed to the presence of sulphates, the presence or absence of the arrest depending upon the temperature rise sustained by the sample during oxidation.There is general agreement [1 -13] that the final product of the oxidation of pyrite in air is ferric oxide, usually hematite. Kopp and Kerr [8] mentioned the possible formation of y-ferric oxide and Banerjee [2] has identified this material in X-ray diffraction (XRD) patterns. Agreement as to the intermediate phases is not unanimous. Pyrrhotite was claimed to be present, or hinted at as a possibility, by many workers (3 -5, 7-9, 11, 12, 14] but it was searched for by Banerjee [2J using XRD and chemical means and Schorr and Everhart [6] using XRD alone, and reported absent. Similarly, although magnetite was claimed to be present by several workers [4,5,8,9,11], Schwab and Philinis [13] could not detect it by XRD. Wustite has not been identified, though its presence was alluded to by Blachere [7] and there were mentions of its formation during the oxidation of pyrrhotite, [13,15]. Sulphate has been claimed to be present, either as the ferrous [2, 4,5,[16][17] or ferric forms [2,13], but Schorr and Everhart [6] using high-temperature XRD found no evidence of sulphates. Similarly Niwa and Wada [12], who also used XRD techniques, were unable to find evidence of sulphates. Banerjee [2], claims to have identified a small amount of basic sulphate by chemical means.There is a need, therefore, to examine the phases formed during the oxidation of pyrite to resolve some of the controversy noted above. This was accomplished in the present study by a) using sensitive thermal analysis techniques to provide information on weight changes and heat effects accompanying the oxidation, 16

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To simulate the behavior of arsenic during the practical roasting of copper concentrate, a modified free-energy minimization method was developed. The calcine was assumed to be a pseudosolid solution in which the nonequilibrium arsenic species are contained as solutes, with a high activity (adjustment) coefficient. The validity of the method of calculation was checked by comparison to the results of conventional calculations. The validated procedure was then used to evaluate the effects of operating variables and to establish optimum roasting conditions. The change of the predominant gas and solid species during the course of oxidation and the effect on the volatility of arsenic are discussed. Arsenic removal from the concentrates was generally good, but it was affected by the extent of oxidation and the initial concentration in the concentrate. The extent of sulfur oxidation for optimum arsenic removal is around 70 pct. With the appropriate choice of an adjustment coefficient, the results simulated those obtained in practice.

The reaction shaft is the heart of a flash smelter. Current knowledge of the combustion of concentrate and ancillary fuels (coal, oil, and gas) in flash smelter shafts comes from laboratory studies, plant measurements, and physical and mathematical modeling. The latter is particularly useful when considering the complications of two-phase flow of particles and gas and chemical reactions; however, uncertainty as to effective particle size requires validation to establish confidence in the model outcomes. Those issues are addressed in the paper, together with the importance of the burner in achieving good mixing and dispersion. Simulations, which may be viewed on the web, show the consequences of poor mixing.