Abstract:
Eh-pH diagrams (aka Pourbaix diagrams, electrochemical phase diagrams) are important to the development of hydrometallurgical and electrometallurgical processes. The diagrams present a roadmap to processes that separate one metal from another in an ore or concentrate, precipitate compounds from solution, purify wastewater, and generate metal by electrolytic processes. Engineers in several fields use Eh-pH diagrams, for numerous purposes.

The mysterious lines that comprise an Eh-pH diagram represent thermodynamic equilibria between adjacent species, and are derivable using three fundamental expressions — Faraday’s law, the Nernst equation, and the expression of equilibrium constants. The location of predominance regions for typical species in these diagrams can be predicted in advance, using fundamental chemical principles known to undergraduates.

This lecture describes the significance of Eh-pH diagrams, and how they are constructed. The extraction of three metals (cobalt, copper, and gold) is used to demonstrate the use of these variables, and the impact of assumptions made during their construction. The limitations of Eh-pH diagrams are described, along with their uses.

Citation: M. Schlesinger, "Eh-pH Diagrams," Missouri University of Science and Technology. MaterialsTechnology@TMS 2008.