Revised Pourbaix diagrams for chromium at 25-300 degrees C

The Pourbaix diagrams (potential-pH diagrams) for chromium at 25-300 degrees C have been revised. The diagrams were calculated for two concentrations: 10(-6) and 10(-8) molal. Extrapolation of thermochemical data to elevated temperatures has been performed with the revised model of Helgeson-Kirkham-Flowers, which also allows uncharged aqueous complexes, such as Cr(OH)(3)(aq), to be handled. The calculations show that the hydroxides Cr(OH)(2), Cr(OH)(3), and the oxides CrO2 and CrO3 are not stable at the investigated temperature and concentration interval. Cr2O3 is the only stable solid chromium compound in aqueous solution in the environment studied, with the exception of very diluted solutions such as 10(-8) molal at T > 150 degrees C, where no solid chromium compound is stable. The dichromate ion does not predominate anywhere within the calculated concentration range. Copyright (C) 1996 Elsevier Science Ltd