Browsing by Author "Ouma, Linda Immaculate A."

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    An Insight into the Adsorption Mechanism of Hexavalent Chromium onto Magnetic Pine Cone Powder
    (Springer, 2019-07-23) Ouma, Linda Immaculate A.; Naidoo, Eliazer B.; Ofomaja, Augustine E.
    The remediation of hexavalent chromium [Cr(VI)] contaminated water has been a challenge due to its high toxicity and mobility in the environment. Adsorption has so far been the most promising method for the treatment of chromium containing water due to the availability of low cost materials capable of chromium sequestration. The mechanism for hexavalent chromium removal has however not been fully understood with many studies pointing to a reduction-coupled mechanism. In this study, a composite material consisting of agricultural waste material (pine cone) and magnetite nanoparticles was used for the remediation of hexavalent chromium contaminated water with a focus on the removal mechanism and adsorbent regeneration studies. The mechanism was identified to be adsorption-coupled reduction where Cr(VI) was reduced on the adsorbent surface to the less toxic trivalent chromium [Cr(III)] before being adsorbed. The adsorbed chromium was successfully desorbed using NaOH allowing for concentration and chromium recovery. The adsorbent material was applied in three adsorption-desorption cycles without a significant loss in adsorption capacity.
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    Optimizing Cr(VI) adsorption parameters on magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles
    (Physical Sciences Review, 2023-07-23) Ouma, Linda Immaculate A.; Pholosi, Agnes; Onani, Martin
    Magnetite as an adsorbent is efficient since iron oxides have high affinities for heavy metal pollutants and are environmentally friendly. Manganese oxides provide catalytic properties which are desirable during the remediation of multi valent pollutants. Magnetite (Fe3O4) and manganese doped magnetite (MnxFe(3-x)O4) nanoparticles were synthesized and characterized to determine the manganese doping effects on magnetite’s crystal and surface properties. Fe3O4 and MnxFe(3-x)O4 showed similarities in crystal morphology indicating that manganese doping did not alter the nature of Fe3O4 nanoparticles. Manganese doping improved magnetite’s thermal properties as well as its surface area providing improved adsorption characteristics. The as-synthesized particles were applied in the optimization of hexavalent chromium adsorption. Adsorption proceeded under similar conditions for both adsorbents indicating their structural similarities. Higher efficiencies were observed on the doped adsorbent due to increased surface area and the presence of additional functional groups. Solution pH significantly affected the adsorption process aiding in the reduction of Cr(VI) ions to the less toxic Cr(III) species. The adsorption distribution coefficient KD indicated that manganese doping significantly improved magnetite’s affinity for hexavalent chromium. Adsorption and reduction were determined to responsible for pollutant reduction in solution at optimal conditions of pH 2, 5 g/L and 100 mg/L for adsorbent mass and solution concentration.