A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. May 2016. / The thermodynamic and equilibrium data for Na+/RH+ exchange reactions were generated using the batch method. The experimental data is unique in that the reactions were carried out at elevated temperatures (50oC–90oC), using low level counter ion solutions (0.001100–1.258 mg/l, Na+). The equilibrium data was modeled against the non-linear Langmuir and Freundlich isotherm models. The model parameters were determined by an iterative approach, using the ‗SOLVER‘ function of Microsoft Excel. The coefficient of determination, R2 was used to evaluate the goodness of fit. The R2 values for both models were satisfactory (R2 > 0.9) to a certain extent. From the experimental data, the equilibrium parameters; Selectivity coefficient, , and Corrected selectivity coefficient KI were computed. Irrespective of the initial solution concentration, the equilibrium parameters were found to decrease with increasing reaction temperature, indicating a poor uptake of Na+ from solution by candidate ion exchange resins. Thermodynamic parameters; enthalpy of reaction, ΔH (J/mol.K), and entropy, ΔS (J/mol.K) were calculated from the slope and intercept of the Van‘t Hoff plot respectively. The reaction‘s Gibbs free energy change, ΔG was calculated from the values of ΔH, and ΔS, and reaction temperature. Generally, ΔG was positive and increased with increasing reaction temperature, which proved that an elevated reaction temperature favours the reverse reaction. The reactions were found to be exothermic process with negative entropy. The effect of pH on the exchange reactions was also studied. There was a decrease in the equilibrium Na+ concentration in solution after pH conditioning, with a considerable difference when compared with that obtained from reactions without pH conditioning. The equilibrium quotient was used to define the selectivity coefficient for reactions carried out at varying pH. The equilibrium quotient increased across the initial solution concentration and was highest for reactions carried out at 1.258 mg/L. The equilibrium quotient decreased across the pH range, per initial solution concentration, indicating the pH effect. / GR 2016

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Ion chromatography (IC) as developed by Small et. al. in 1975 has become an efficient and reliable analytical technique for simultaneous analysis of multiple ions in solution. The principle requirement prior to use the IC for an analysis is sample preparation; these include sample decomposition, solvent extraction, and trapping in case the target element is in the gas phase, etc. Solvent extractions for fluoride, chloride, sodium, ammonium, and potassium ions which are soluble in soils are described. Sample decompositions include silicate rocks using hydrofluoric acid for the determination of phosphorus; organic pesticides using lithium fusion technique for the determination of halide and cyanide ions are also described. After these sample preparation techniques, the aqueous solutions obtained were analyzed on the ion chromatograph for the analyses of the anions and cations mentioned above. Recovery and reproducibility of each technique is in general quite good and the comparison between the results obtained from the IC method and other instrumentation are given.

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M.Sc. (Chemistry) / Please refer to full text to view abstract

Pineapple juice of low acid content was prepared by removal of acids by using weakly basic anion exchange resin, IRA-93. The changes in the contents of titratable acid, pH and total soluble solids of model solutions that contained the principal constituents of pineapple juice (citric acid, citrate salt and sucrose) were investigated. The adsorption of individual acids and changes in composition of juice after a de-acidification process were explored. The adsorbed acids were recovered as solutions by some eluants, and studies on colour development in the recovered solutions carried out. The solutions of adsorbed acids recovered by NaOH from the resin, which had been treated by model solutions, were brown in colour. The brown colour was also found immediately when NaOH was added to the resin treated with pineapple juice but it was not found in the treated juice during acid removal treatment when its pH rose to 10. A greater amount of the dark colour was observed in the desorbed solution from the resin that had been treated with pineapple juice. The use of sulphuric acid, sodium chloride, sodium sulphate, sodium bicarbonate and phosphate buffer solution to desorb the acids from pineapple juice-treated resins reduced the intensity of the colour, measured at pH 3.5, of desorbed acid solutions. The colours of the desorbed solutions were pH dependent. Either solution of sulphuric acid or sodium chloride has a comparable desorbing power to a solution of sodium hydroxide whereas the rest has a lower desorbing power / Master of Science (Hons) (Food Science)