Metal—sulphur oxygen systems

Erom the phase stability diagram of a metal-sulphur-oxygen system, as shown in Eigure 7.6, it should be possible to predict which phase will be present in the scale, given the atmosphere composition. 

The method of construction of this type of diagram will be illustrated using the general case of the three component system metal-sulphur-oxygen (M-S-O) whose values of AG for the reactions between the various condensed phases are given in Talile 7.37 on page 7 191. 

Fig. 7.67 Phase stability diagram for a metal-sulphur-oxygen (M-S-O) system at I 000 K. (For the thermodynamic data AC 000 for the various across-boundary reactions, see Table 7.37)...

Ros] Rosenqvist, T., Hofseth, A., Phase Relations and Thermodynamies of tire Copper-Iron-Sulphur-Oxygen System at 700-1000°C , Scand. J. Metall., 9(3), 129—138 (1980) (Experimental, Phase Diagram, Phase Relations, Thermodyn., 21)... 

We saw in Chapter 12 that from the structural standpoint many transition metal-oxygen systems are surprisingly complex. This is also true of many metal-sulphur systems, as we shall show later for the sulphides of Cr, Ti, V, Nb, and Ta. Before doing this we shall note some of the simpler binary sulphide structures, taking them in the order M2S, MS, MS2, M2S3 and M3S4. The chapter concludes with a short account of thio-salts and complex sulphides. 

It is possible that Gottschalk and Buehler (1912) carried out the oxidation with an excess of oxygen which would not occur in nature at the oxidation interface of a mineral deposit. Granger and Warren (1969) conducted experiments to investigate the oxidation of iron sulphides by an aerobic aqueous phase in a sterile system. The objective was to study the formation of unstable intermediate ions during the oxidation process. The intermediate sulphur species detected were sulphite and thiosulphate. In general these products are more easily oxidised than the metallic sulphides and are stable only if removed from the oxidising environment. 

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