Pourbaix diagrams for chromium in concentrated aqueous lithium bromide solutions at 25 °C

Pourbaix diagrams (electrode potential-pH diagrams) for Cr–Br−–H2O system at 25 °C were developed in 400, 700, 850, and 992 g/L (4.61, 8.06, 9.79, and 11.42 M) LiBr solutions, common concentrations in different parts of absorption devices. The diagrams were compared with the simple Cr–H2O system at 25 °C. Equilibria for the Cr–Br−–H2O system at 25 °C were determined for bromide ion activities of 15.61, 194.77, 650.06, and 2042.65, which corresponded to the 400, 700, 850, and 992 g/L LiBr solutions, respectively. Activities of all the dissolved species containing chromium were plotted for 10−6, 10−4, 10−2, and 100. Comparison of the simple Cr–H2O system at 25 °C with the diagrams for Cr–Br−–H2O system at 25 °C showed that the dominant aqueous Cr(III) species in acid solutions was Cr+3 for Br− activities of 15.61, 194.77, and 650.06, whereas it was CrBr+2 for Br– activity of 2042.65. Aqueous CrBr+2 formed at a Br− activity higher than 943.05. The chromium solubility range in the acid area of the diagrams extended slightly to higher pH values with increasing Br− activity and decreasing water activity, as a result of destabilization of Cr2O3.