Masters Dissertations

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Browsing Masters Dissertations by Author "Abdullah, Ally Makowa"

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    Comparative studies of the hydrochemistry of the rift valley salt lakes in Northern Tanzania.
    (University of Dar es Salaam, 1996) Abdullah, Ally Makowa
    The salt lakes of the northern part of the rift valley in Tanzania include the lakes Balangida, Manyara and Eyasi. Lakes Balangida and Eyasi represent typical saturated salt lake systems while Manyara is an example of an unsaturated salt lake. This research project include the results of the physical measurements, such as pH, conductivities and total dissolved solids (TDS) done on the lake brines. The results on pH, conductivities and TDS reveal that the lake brines are of very high electrolyte content. Chemical assays carried out on lake brines gave varying concentration of cations and anions for the three lakes. However, the results show similar ionic abundance patterns with Na+, K+ Mg2+ and Ca2+ being the major cations and Cl-, (CO32+ + HCO3-) and SO42- being the major anions in all the three lake systems. The action and anions are listed in descending order of concentrations. The concentrations of cations and anions were used to calculate the ionic strengths of the different salt lake brines. "Synthetic" brines of similar ionic strengths representing the salt lake environments were then re-constituted. These re-constituted synthetic brines were then used to evaluate the equilibria parameters, pKa, and activity coefficients in the lake-like environment. The Debye-Hückel limiting law was employed to determine the equilibria parameters for phosphate and carbonate, while the Vanderborgh theory was used to evaluate the pKa values for the fluoride equilibria. The results of this research project reveal that the pKa values for phosphate, carbonate and fluoride decrease with increasing ionic strength. A drastic decrease in activity coefficient with increasing ionic strength is observed in all cases. Graphical extrapolation of the results to zero ionic strength gives the pKa values and activity coefficient values at infinite dilution. The resulting equilibria parameters were then compared with the literature values. The pKa values for phosphate, carbonate and fluoride were found to be close to the literature values, and the activity coefficient at infinite dilution approaches unity for both the phosphate and carbonate. This has furnished as a good test for the validity of the results.