H2S-S8-H2O system

Since the sulfide/polysulfide couple is electroactive and the reaction at the surface of the platinum is rapid ( ], the potentials measured in the H2S-S8-H2O system must be characteristic of the equilibria between sulfide and polysulfide species. These equilibria correspond to the redox level within the environment since the reactions betweeh sulfide and polysulfide are rapid ( 5, 17]. In this instance, the redox potential can be directly interpreted in terms of chemical and electrochemical equilibria of the reduced sulfur species. Thus one can employ the notion of pe (pe = Eh/(2.3 xRx T X ] ] when in the presence of polysulfide ions. 

Figure 7. Eh-Es2- relation in H 18 and O 5 springs. The experimental points have been linked by a continuous curve. The dashed line equation is Eh = Eg2-+ 217 mV, i.e., the Eh-E< 2- relation in the H2S-S8-H2O system at 343 K. Eh and Es2- are given in mV/(HyH>). The symbols are the same as in Figure 6.

Figure 11. PE-pH diagram of brine PM2 sample PM2h, sample PM2c, The full line corresponds to the PE—pH stability diagram of the H2S-S8—H2O system for [S] = 1.5 X 10 g-atom/kg at 353 K and 1 bar (5). The dominant species in each domain is put in brackets.

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