Phase Diagram Modelling of a Multi-component Aqueous Solution of Katwe Salt Lake, Uganda

A methodology is developed to compute the phase diagram of a hexary system and to determine the mineral precipitation sequence upon removal of water. The methodology is applied to construct the phase diagram and precipitation sequence of the system (〖Na〗^+,K^+)(〖Cl〗^-,〖SO〗_4^(2-),〖CO〗_3^(2-) & 〖HCO〗_3^-) in water. The thermodynamic model chosen is the Extended UNIQUAC. A 3D grid is constructed in order to solve this model in MATLAB. On the basis of this grid, a 3D phase diagram is calculated and a Jänecke projection is obtained. The precipitation sequence due to evaporation is calculated thus obtaining the coordinates of the solution along this path as well as the order of precipitation. The numerical model is also able to calculate all these steps for temperatures 0-110°C. In addition, the number of ions and the composition of the system can be varied in order to model other elective systems. The obtained results are well suited to be used for designing salt extraction processes and understanding aqueous solutions in general.