Utility of mass-balanced EH-pH diagrams I — Applications of Gibbs’ Phase Rule
EH-pH diagrams are useful tools in understanding how mineral surfaces react in solution and particularly how aqueous conditions can be changed to enhance mineral leaching processes. Successful application of these diagrams, however, requires that several considerations be kept in mind to prevent what had been termed as “gross errors” in their calculation and use. In this paper, the aqueous Cu-S system is used as the basis for explaining the mass-balanced method of calculating EH-pH diagrams with the STABCAL thermodynamic equilibrium software. A breakdown of the Gibbs’ Phase Rule and how it is used in STABCAL to modify the diagrams is included. The methodology was applied to the aqueous Cu-As-S system, and resulting diagrams were compared against examples of those generated using the predominant-ion method. The complexity of such diagrams increases with every additional component, and competition between species becomes more apparent, as can be seen by curvature in the resulting mass-balanced diagrams. The complete diagram for enargite (Cu3AsS4) is shown. It compares well with spectroelectrochemical measurements from Raman spectroscopy and cyclic voltammetry studies.
Key wordsEnargite Arsenic Mass-balanced EH-pH diagrams Mass action equilibrium calculations STABCAL
Unable to display preview. Download preview PDF.
- Allison, J., Brown, D., and Novo-Gradac, K., 1990, “MINTEQA2/PRODEFA2 A Geochemical Assessment Model for Environmental System,” Version 3, Environmental Research Laboratory, U.S. Environmental Protection Agency.Google Scholar
- Chase, M.W., 1998, “NIST-JANAFThermochemicalTables, 4th Edition,” Journal of Physical and Chemical Reference Data, http://dx.doi.org/10.1063/L555992.
- Delfini, M., Ferrini, M., Manni, A., Massacci, P., and Piga, L., 2003, “Arsenic leaching by Na2S to decontaminate tailings coming from colemanite processing,” Min. Eng., Vol. 16, pp. 45–50, http://dx.doi.org/10.1016/s0892-6875(02)02100262-5.CrossRefGoogle Scholar
- Forssberg, K.S.E., Antti, B.M., and Palsson, B.I., 1984, “Computer-assisted calculations of thermodynamic equilibria in the chalcopyrite-ethyl xanthate system,” Reagents in the Minerals Industry, M.J. Jones and R. Oblatt, eds., The Institute of Materials, Minerals and Mining (IMM).Google Scholar
- Garrels R.M., and Christ, C.L., 1965, Solutions, Minerals, and Equilibria, Chapter 7: Eh-pH Diagrams, Harper & Row.Google Scholar
- Gibbs, J.W., 1875 and 1878, “On the equilibrium of heterogeneous substances,” Connecticut Academy, http://dx.doi.org/10.2475/ajs.s3-16.96.441.
- Gow, R., Young, C., and Huang, H., 2016, “Utility of mass-balanced EH-pH diagrams II: Cu-As-S-H2O system,” Minerals & Metallurgical Processing, Vol. 33, No. 3, in press.Google Scholar
- Gow, R., Young, C., Huang, H., Hope, G., and Takasaki, Y., 2014, “Spectroelec-trochemistry of Enargite II: Reactivity in Acidic Solutions,” Proceedings of Hydrometallurgy 2014, Victoria, British Columbia, Australia.Google Scholar
- Gow, R., Young, C., Huang, H., Hope, G., and Takasaki, Y., 2015a, “Spectro-electrochemistry of enargite I: Reactivity in alkaline solutions,” Minerals & Metallurgical Processing, Vol. 32, pp. 6–13.Google Scholar
- Gow, R., Young, C., Huang, H., and Hope, G., 2015b, “Spectroelectrochemistry of enargite III: Alkaline sulfide leaching,” Minerals & Metallurgical Processing, Vol. 32, pp. 14–21.Google Scholar
- Huang, H., 2013, “STABCAL,” Metallurgical & Materials Engineering, MontanaTech.Google Scholar
- Huang, H., Twidwell, L., and Young, C., 2005, “Speciation for aqueous systems — An equilibrium calculation approach,” Proceedings of COM 2005 and 35th Annual Hydrometallurgical Meeting, Calgary, Canada.Google Scholar
- Huang, H., and Young, C., 1996, “Mass-balanced calculation of EH-pH diagrams using STABCAL,” Electrochemistry in Mineral and Metal Processing IV, The Electrochemical Society Proceedings, R. Woods, F.M. Doyle and P. Richardson, eds., Vol. 96–6, pp. 227.Google Scholar
- Linkson, P., 1996, “Computer packages for chemical modelling of aqueous systems — Blind faith!” AusIMM Proceedings, pp. 23–28.Google Scholar
- Peters, E., 1986, “Leaching of sulfides” Advances in Mineral Processing, P. Somasundaran, ed., Society for Mining, Metallurgy & Exploration, Englewood, CO, pp. 445–462.Google Scholar
- Pourbaix, M., 1966, “Atlas of electrochemical equilibria in aqueous solutions,” National Association of Corrosion.Google Scholar
- Robie, R., Hemingway, B., and Fisher, J., 1984, “Thermodynamic Properties of Minerals and Related Substances at 298.15K and 1 Bar (105 Pascals) Pressure and at Higher Temperatures” U.S. Geological Survey Bulletin 1452.Google Scholar
- Robins, R., 1993, “Computer generated stability diagrams for the copper-sulfur-water system” Hydrometallurgy Fundamentals, Technology and Innovation, pp. 144–156.Google Scholar