Browsing by Author "Hove, Mfandaidza"

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    The effect of different types of seeds on the oxidation and precipitation of iron.
    (Elsevier, 2009) Hove, Mfandaidza; Lewis, Alison E; Van Hille, Robert P
    The use of different types of seeding material to cause the layer deposition of desired iron phases is an attractive technique for the treatment of industrial waste waters, synthesis of iron products and the study of adsorption and dissolution reactions involving iron oxides. In this study, artificial solids (consisting of mainly ferrihydrite and lepidocrocite), natural goethite and natural haematite seeds were used during batch oxidation and precipitation of iron from a ferrous sulphate suspension. A 4 L standard stirred tank reactor was used. Air was used as the oxidising agent. High ferrous ion concentrations typical of acid mine drainage associated with South African coal and gold mining were used. All the three oxides of iron catalysed the oxidation reaction rate to almost the same extent. The products formed were mainly lepidocrocite for systems seeded with artificial solids and goethite for systems seeded with either goethite or haematite. The less stable ferrihydrite was not formed in the systems seeded with either goethite or haematite. Seeding resulted in reduced BET surface areas, improved settling rates and the formation of particles of bigger sizes.
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    The kinetics and mechanisms of the oxidation and precipitation of iron : the high density sludge (HDS) process
    (2008) Hove, Mfandaidza; Lewis, Alison Emslie; Van Hille, Rob
    The oxidation and precipitation of iron are key reactions in the treatment of hydrometallurgical waste water and acid mine drainage (AMD) by the high density sludge process (HDS). The removal of other pollutants by adsorption and coprecipitation using this technique depends on the nature and the process by which iron is removed. Although this technique is cheap and easy to operate and therefore the most common method by which hydrometallurgical waste water is treated, there are some problems inherent in this technique. Such problems include; the formation of gelatinous sludge which is difficult to dewater, the low solids density resulting in considerable water losses and a large land area for sludge disposal, the instability of the sludge thus requiring post neutralisation stabilisation and the formation of the solids as mixed sludge, thus diminishing chances for waste material recovery, reuse or recycle. In view of the above problems, the objectives of the present study were; to gain more understanding of the oxidation and precipitation reactions of iron through investigating the effect of pH on the oxidation rate and on the chemical and physical characteristics of the iron precipitates, to make an inference on the mechanisms by which iron precipitates are formed and finally to investigate the effect of seeding on the oxidation and precipitation of iron. To achieve the set objectives, experiments were carried out in a 4 L perspex batch reactor. The reactor was fitted with four equally spaced buffles and a draft tube to maximise mixing. Ferrous iron (Fe2+) was added as FeSO4.7H2O at initial concentrations of 200 mg/L and oxidised using air. pH control was achieved by titration with either 0.1 M NaOH or 0.1 M H2SO4 through a custom made Hitech Micro Systems controller. The reactions were carried out at pH levels 6.0, 8.0, 9.0 and 10.0. Three types of materials (recycled solids, natural haematite and natural goethite) at three concentration levels (Cs = 1.0, 0.5 and 0.1) were used as seed material in the seeded experiments.