Thermodynamic study of K2CrO4-KAlO2-KOH-H2O and Na2CrO4-NaAlO2-NaOH-H2O systems

Phase diagrams of complex multi-component aqueous chromium salt system are the important theoretical bases for increasing the recovery ratio of chromium and reducing the poisonous waste in the chromate production process. Phase equilibrium of multi-component system has been calculated from the limited known data with thermodynamic models. The phase equilibriums of KOH-K2CrO4-H2O, KOH-KAlO2-H2O, NaOH-Na2CrO4-H2O and NaOH-NaAlO2-H2O systems were calculated with thermodynamic models. The solubilities of Cr and Al was measured in the systems at different temperatures. The results were compared with experimental data and they are consistent with each other. It shows that the lower concentration of KOH (or NaOH) is favorable for the crystallization of KAlO2 (or NaAlO2) and higher concentration of KOH (or NaOH) is favorable for the crystallization of K2CrO4 (or NaAlO2) with controlling the KOH concentration in (NaPOO. Therefore, K2CrO4 (or Na2CrO4) can be separated from KAlO2 ) solutions of KOH-K2CrO4-KAlO2-H2O or NaOH-Na2CrO4-NaAlO2-H2O systems.