The hydrochemistry of selected Tanzanian salt lakes and investigation of the potential for salt separation in such systems

This thesis presents the hydrochemistry of salt lakes (Eyasi, Kitangiri, Kindai, Mnangi, Singidani), inflows and upstream sources in the study area and a model for salt separation of brine constituents into pure and marketable form in such systems. The study has revealed that the concentration patterns in the lakes depend on location, depth and season. It has also been shown that in the catchment area. the following electrolyte concentration pattern is discernible: (i) Lake brines> upstream sources (including rivers, boreholes etc). The order of abundance of major ions is: Na+>>K+ >Ca2+ = Mg2+: CI->(CO32+HCO3 )> S042->PO43-> F The solubility equilibrium studies at temperatures 30 0C, 40 0C, 50 0C and 70 0C are presented in temps ofphase diagrams for the quatemaiy systems: (i) NaCI + NA2CO3 + NaHCO3 + H20 (ii) NaCI + NA2SO4 + NA2CO3 + H20 (iii) NaCI + NA2SO4, + NaHCO3+ H20 (iv) NA2CO3+ NA2CO4 + NaHCO3 + H20 The double salt trona is formed at all studied temperatures in the system NaCI + NA2CO3 + NaHCO3 + H20 while burkeite forms in the system NaCI + NA2SO4 + NA2CO3 + H20Both burkeite and trina are formed in the system NA2CO3+ NA2CO4 + NaHCO3 + H20The simulation and optimization of fractional crystallization processes employing the phase rule (phase diagrams) targeting the separation of pure salts from Lakes Balangida, Eyasi and Singidani have been demonstrated. It is found possible to recover all the three salts viz. sodium chloride, sodium sulphate and sodium carbonate in pure marketable forms.