Eh-pH Diagrams Including Chemisorbed States

A third limitation of conventional diagrams is that they portray only stable phases whereas, in the relatively short time scales operative in mineral processing, kinetic limitations may allow the development of metastable phases. This situation is particularly relevant to the reactions of sulfide minerals owing to the irreversibility of sulfate formation. Peters devised Eh-pH diagrams for sulfide mineral systems that took 

The Eh-pH diagrams shown in Fig. 29 portray the region of chemisorption as extending nearly 0.3 V below the stability zone of copper(I) xanthate. At high Eh values, chalcocite is oxidized to copper sulfides of progressively lower copper content. Chemisorbed xanthate will not coexist with these sulfides when CuO is formed since the oxide is expected to overlay the surface of the mineral. This implies that there is an upper potential limit to flotation of chalcocite with ethyl xanthate, and such behavior has been established for this system.  

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