The adsorption and desorption behavior of trace element contaminants was evaluated solids—goethite and ruthenium oxide. The importance of anion displacement as a mechanism responsible for arsenic release from iron oxides was investigated on goethite. The adsorption and polymerization of silicate on goethite was examined as a function of surface concentration determine the influence of adsorbed silicate monomers and polymers on arsenite adsorption desorption. A kinetic model was employed to describe arsenite adsorption and desorption absence and presence of silicate. The potential environmental impacts of the research discussed. Hydrous and crystalline ruthenium oxides were extensively characterized traditional colloidal surface characterization techniques, dissolution experiments, and macro- spectroscopic experiments. The two ruthenium oxide phases exhibited large specific areas, a high density of reactive surface functional groups and the presence of multiple oxidation states in both solids. Enhanced dissolution of hydrous ruthenium oxide occurred presence of oxalate and ascorbate. While enhanced dissolution of the crystalline phase only in the presence of oxalate at pH 3. Results from the dissolution experiments were develop possible mechanisms for the oxalate and ascorbate promoted dissolution of ruthenium oxides. Macroscopic adsorption studies of arsenate adsorption on both ruthenium oxides examined over a broad pH (3-10) and initial solution concentration range (0.01 to Results from the adsorption studies indicate arsenate forms a stable surface complex with ruthenium oxide phases. Extended x-ray absorption fine structure spectroscopy and Pressure-jump relaxation studies indicates arsenate is specifically adsorbed the ruthenium oxide Chromate adsorption on ruthenium oxides was investigated as a function of pH and chromate solution concentration. Macroscopic adsorption studies and zeta measurements suggest chromate forms an inner-sphere surface complex with both oxide X-ray absorption near edge spectroscopy data indicates chromate (Cr(VI)) is reduced chromium (Cr(III)) on the ruthenium oxide surface. Modeling of the first Cr shell indicated two oxygen backscattering distances similar to the Cr-O atomic distances reported for coordinated to Cr(VI) and Cr(III) providing additional evidence for Cr(VI) reduction. / Ph. D.

In South Africa, being the second largest global coal exporter, coal mining plays a pivotal role in the growth of our economy, as well as supplying our nation’s ever increasing electricity needs; while also accounting for more than 10% of the 20 x 109 m3 water used annually in the country. Coal mining may thus be classified as a large-scale water user; known to inevitably generate wastewater [acid mine drainage (AMD)] and other waste material, including fly ash (FA). Current and conventional AMD treatment technologies include precipitation–aggregation (coagulation/flocculation) – settling as hydroxides or insoluble salts. The process stream resulting from these precipitation processes is still highly saline, therefore has to undergo secondary treatment. The best available desalination techniques include reverse osmosis (RO), electro dialysis (ED), ion exchange and evaporation. All available treatment methods associated with raw AMD and its derived process stream fall prey to numerous drawbacks. The result is that treatment is just as costly as the actual coal extraction. In addition, remediation only slows the problem down, while also having a short lifespan. Research conducted into converting fly ash, an otherwise waste material, into a marketable commodity has shown that direct mixing of known ratios of FA with AMD to a pre-determined pH, erves a dual purpose: the two wastes (AMD and FA) could be neutralized and produced a much cleaner water (secondary co-disposal [FA/AMD]-process water), broadly comparable to the process water derived from precipitation-aggregation treated AMD. The collected post process solid residues on the other hand, could be used for production of high capacity ion exchange material (e.g. zeolite A, faujasite, zeolite P, etc.). The produced ion exchange material can subsequently be utilized for the attenuation of metal species in neutralized FA/AMDprocess waters. / Magister Scientiae - MSc