>Magister Scientiae - MSc / A comparative study of electrolysers using different anodic materials for the electrolysis of brine (sodium chloride) for the production of sodium hypochlorite as a source of available chlorine for disinfection of rural water supplies has been undertaken. The electrolyser design used was tubular in form, having two chambers i.e. anode inside and cathode outside, separated by a tubular inorganic ceramic membrane. The anode was made of titanium rod coated with a thin layer of platinum and a further coat of metal oxide. The cathode was made of stainless steel wire. An assessment of these electrolysers was undertaken by studying the effects of some variable parameters i.e.current, voltage and sodium chloride concentration. The cobalt electrolyser has been shown to be superior as compared to the ruthenium dioxide and manganese dioxide electrolysers in terms of hypochlorite generation. Analysis of hydroxyl radicals was undertaken since there were claims that these are produced during brine electrolysis. Hydroxyl radical analysis was not successful, since sodium hypochlorite and hypochlorous acid interfere using the analytical method described in this study. / South Africa

Magister Scientiae - MSc / This study has shown that OHË radicals can be generated in an Fe/O2 cell from the electrode products via Fenton’s reaction and used for water disinfection. The cell system in which the experiments were carried out was open and undivided and contained two electrodes with iron (Fe) as the anode and oxygen (O2) gas diffusion electrode. Typically, 100 ml of Na2SO4.10H2O (0.5M) solution was used as a background electrolyte. OHË radicals were produced in-situ in an acidic solution aqueous by oxidation of iron (II), formed by dissolving of the anode, with hydrogen peroxide (H2O2). The H2O2 was electrogenerated by reduction of oxygen using porous reticulated vitreous carbon (RVC) as a catalyst. / South Africa

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This work has shown that nitrogen dioxide will selectively remove uranium hexafluoride from a mixture containing the hexafluorides of uranium, molybdenum and tungsten via the formation of nitrylium hexafluorouranate(V). The production of lower uranium fluorides and elemental sulphur or sulphur fluorides from many of the attempted preparations of uranium(VI) thiofluorides was predicted from a thermodynamic study of the stabilities of MC1nF6-n (M = U, Mo, W; n = 1-5), MOnF6-2n' MSnF6-2n (M = U, Mo, W; n = 1 or 2) with respect to decomposition and disproportionation. Sorption of the liquid hexafluorides on various potential sorbents was investigated. Encouraging results were obtained for cryolite. Salts such as ARuF6 (A = K, Rb, NH4) were synthesised by direct interactions between AF and RuF5 in AHF. These reactions were found to require the presence of a polar solvent. It was found that ruthenium pentafluoride in liquid uranium hexafluoride could be removed by the Introduction of trace quantities of water.

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Soil and grass filtration of a domestic sewage effluent for trace element removal was investigated by applying oxidation-pond-treated waste water to twelve 2.44-meter-long, 30.5-cm-diameter, lysimeter columns and to a half-acre plot planted to common bermudagrass. Bermudagrass was also planted on the soil columns to aid in the removal of accumulated metals, thus prolonging the filtering capacity of the soil system. Four irrigation patterns, continuous flooding, alternate day flooding, one day wet-three days dry cycles and two days wet-five days dry cycles, were employed during the eleven week lysimeter test. Water samples were extracted from the soil columns at eight sampling depths to determine the soil depth at which the various trace metals were removed from the filtrate by the processes of adsorption, absorption and biological assimilation. Atomic absorption spectrophotometric techniques were used to determine the concentrations of iron, manganese, hexavalent chromium, nickel, copper, zinc, lead, cadmium, cobalt and strontium in the applied effluent, filtrate, soil and grass clippings. Filtrate samples for trace metal analysis were also extracted at shallow depths and from two groundwater zones at 9.1 and 15.2 meters depth under the grass plot. In the lysimeter study, iron, manganese, nickel, copper, zinc, lead and cadmium were removed from the filtrate at, or near, the soil surface. Some copper, zinc and cobalt were found in the deeper filtrate samples during periods of high infiltration rates and in the presence of anaerobic conditions. Smaller amounts of manganese, nickel and lead were also found at the deeper sampling points. Strontium was not removed from the water percolating through the calcareous soil employed in this study. Chromium and cobalt were not present in measurable quantities in the applied effluent. Iron and manganese were removed from the soil system in the grass clippings in the greatest amounts. Traces of copper, zinc and cadmium were also detected in the grass clippings. Larger quantities of iron, manganese and copper were detected in the filtrate at the grass plot than at comparable depths of the lysimeter columns, probably due to effluent applications at the grass plot over a period of two years. Lower quantities of nickel and lead in the filtrate at the grass plot were attributed to leaching by effluent during grass filtration tests, prior to the trace metal experiments. The concentrations of trace metals in the filtrate at the bottom of the lysimeter columns and in the groundwater zones at the grass plot were irsignificant by United States Public Health Service drinking water standards (1962) and would meet most other water supply requirements. The total nitrogen and nitrate contents were successfully reduced when a combination of aerobic and anaerobic environments were present in the soil system. Total nitrogen and nitrate levels were not reduced by grass filtration through 304.8 meters of dense grass. Fewer total coliform organisms were detected in the aerobic lysimeter columns than in the continuously flooded columns. The majority of coliform organisms detected in the filtrate at the 61 cm depth were believed to be of non-fecal origin. The chemical oxygen demand of the applied effluent was reduced to as low as 105 mg/L by grass filtration. A substantial portion of the remaining COD was attributed to high algal concentrations. The most effective treatment employed in this study was the one day wet-three days dry irrigation cycles. This treatment provided the necessary aerobic environment for trace metal removal from the effluent, nitrification of reduced nitrogen compounds and coliform organism elimination. The flooding period provided the anaerobic conditions required for denitrification losses of nitrate.

The first order ternary interaction parameters of bismuth in molten copper containing either iron, arsenic or antimony have been evaluated using a pseudo equilibrium process at temperatures between 1398 K and 1473 K. The isopiestic distribution technique developed in this investigation yielded the following results: εFeBi=[(1.11x10⁶)/T]- 754 εAsBi=[(4.4x10⁴)/T]-24 εSbBi=-11 These results, coupled with other activity data, have been used to calculate the isoactivity curves for each constituent in the copper rich corner of each ternary system. The basis for the ternary interactions associated with εFeBi, εAsBi and εSbBi are also discussed.

In batch experiments at pH's 5 and 7, the partitioning of MS-2 between water and silica (unbonded) was compared with the partitioning between water and silica with 6.5 percent of the surface covered by hydrophobic C18 chains (bonded). The roles of double-layer and van der Waals forces in partitioning were explored by modeling the potential energies of interaction. MS-2 adsorption to unbonded silica was negligible at pH 7, but did occur at pH 5. Adsorption was independent of pH with the bonded silica and approximately 2.6 orders of magnitude greater than the unbonded at pH 5, suggesting the importance of hydrophobic partitioning. The total potential energies of interaction, which closely approach the pH-independent van der Waals potentials, are similar in magnitude for all pH's or silica types, and have no positive (repulsive) values. The insignificant contribution of the double-layer potentials suggests that these pH-dependent forces may not account for the pH-dependent adsorption observed with the unbonded silica.

No description available.

No description available.