Browsing by Author "Ojumu, Tunde V."

Now showing 1 - 6 of 6
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    Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach
    (Elsevier, 2011) Madzivire, Godfrey; Gitari, Wilson; Vadapalli, V.R. Kumar.; Ojumu, Tunde V.; Petrik, Leslie
    The treatment of acid mine drainage (AMD) and circumneutral mine water (CMW) with South African coal fly ash (FA) provides a low cost and alternative technique for treating mine wastes waters. The sulphate concentration in AMD can be reduced significantly when AMD was treated with the FA to pH 9. On the other hand an insignificant amount of sulphate was removed when CMW (containing a very low concentration of Fe and Al) was treated using FA to pH 9. The levels of Fe and Al, and the final solution pH in the AMD–fly ash mixture played a significant role on the level of sulphate removal in contrast to CMW–fly ash mixtures. In this study, a modelling approach using PHREEQC geochemical modelling software was combined with AMD–fly ash and/or CMW–fly ash neutralization experiments in order to predict the mineral phases involved in sulphate removal. The effects of solution pH and Fe and Al concentration in mine water on sulphate were also investigated. The results obtained showed that sulphate, Fe, Al, Mg and Mn removal from AMD and/or CMW with fly ash is a function of solution pH. The presence of Fe and Al in AMD exhibited buffering characteristic leading to more lime leaching from FA into mine water, hence increasing the concentration of Ca2+. This resulted in increased removal of sulphate as CaSO4·2H2O. In addition the sulphate removal was enhanced through the precipitation as Fe and Al oxyhydroxysulphates (as shown by geochemical modelling) in AMD–fly ash system. The low concentration of Fe and Al in CMW resulted in sulphate removal depending mainly on CaSO4·2H2O. The results of this study would have implications on the design of treatment methods relevant for different mine waters.
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    The production of hydrogen through the use of a 77 wt% Pd 23 wt% Ag membrane water gas shift reactor
    (Elsevier, 2016) Baloyi, Liberty N.; North, Brian C.; Langmi, Henrietta W.; Bladergroen, Bernard Jan; Ojumu, Tunde V.
    Hydrogen as an energy carrier has the potential to decarbonize the energy sector. This work presents the application of a palladium-silver (PdeAg) membrane-based reactor. The membrane reactor which is made from PdeAg film supported by porous stainless steel (PSS) is evaluated for the production of hydrogen and the potential replacement of the current two-stage Water-Gas Shift (WGS) reaction by a single stage reaction. The permeability of a 20 mmPdeAg membrane reactor was examined at 320° C, 380° C and 430° C. The effect of continuous hydrogen exposure on the PdeAg membrane at high temperature and low temperature was examined to investigate the thermal stability and durability of the membrane. During continuous operation to determine thermal stability, the membrane reactor exhibited stable hydrogen permeation at 320° C for 120 h and unstable hydrogen permeation at 430° C was observed. For the WGS reaction, the reactor was loaded with Ferrochrome catalyst. The membrane showed the ability to produce high purity hydrogen, with a CO conversion and an H2 recovery of 84% and 88%, respectively. The membrane suffered from hydrogen embrittlement due to desorption and adsorption of hydrogen on the membrane surface. SEM analysis revealed cracks that occurred on the surface of the membrane after hydrogen exposure. XRD analysis revealed lattice expansion after hydrogen loading which suggests the occurrence of phase change from a-phase to the more brittle b-phase.
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    The production of hydrogen through the use of a 77 wt% Pd 23 wt% Ag membrane water gas shift Reactor
    (Elsevier, 2016) Baloyi, Liberty N.; North, Brian C.; Langmi, Henrietta W.; Bladergroen, Bernard J.; Ojumu, Tunde V.
    Hydrogen as an energy carrier has the potential to decarbonize the energy sector. This work presents the application of a palladium-silver (PdeAg) membrane-based reactor. The membrane reactor which is made from PdeAg film supported by porous stainless steel (PSS) is evaluated for the production of hydrogen and the potential replacement of the current two stage Water-Gas Shift (WGS) reaction by a single stage reaction. The permeability of a 20 mm PdeAg membrane reactor was examined at 320 _C, 380 _C and 430 _C. The effect of continuous hydrogen exposure on the PdeAg membrane at high temperature and low temperature was examined to investigate the thermal stability and durability of the membrane. During continuous operation to determine thermal stability, the membrane reactor exhibited stable hydrogen permeation at 320 _C for 120 h and unstable hydrogen permeation at 430 _C was observed. For the WGS reaction, the reactor was loaded with Ferrochrome catalyst. The membrane showed the ability to produce high purity hydrogen, with a CO conversion and an H2 recovery of 84% and 88%, respectively. The membrane suffered from hydrogen embrittlement due to desorption and adsorption of hydrogen on the membrane surface. SEM analysis revealed cracks that occurred on the surface of the membrane after hydrogen exposure. XRD analysis revealed lattice expansion after hydrogen loading which suggests the occurrence of phase change from a-phase to the more brittle b phase.
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    Removal of sulphates from South African mine water using coal fly ash
    (University of the Western Cape, 2009) Madzivire, Godfrey; Petrik, Leslie F.; Ojumu, Tunde V.; Dept. of Chemistry; Faculty of Science
    This study evaluated SO4 2- removal from circumneutral mine water (CMW) collected from Middleburg coal mine using coal FA collected from Hendrina power station. The following parameters were investigated: the effect of the amount of FA, the effect of the final pH achieved during treatment, the effect of the initial pH of the mine water and the effect of Fe and Al on SO4 2- removal from mine water. The precipitation of ettringite at alkaline pH was evaluated to further reduce the SO4 2- concentration to below the DWAF limit for potable water. Removal of SO4 2- from mine water was found to be dependent on: the final pH achieved during treatment, the amount of FA used to treat the mine water and the presence of Fe and Al in the mine water. Treatment of CMW using different CMW:FA ratios; 5:1, 4:1, 3:1, and 2:1 resulted in 55, 60, 70 and 71 % SO4 2- removal respectively. Treatment of CMW to pH 8.98, 9.88, 10.21, 10.96, 11.77 and 12.35 resulted in 6, 19, 37, 45, 63 and 71 % SO4 2- removal respectively. When the CMW was modified by adding Fe and Al by mixing with Navigation coal mine AMD and treated to pH 10, 93 % SO4 2- removal was observed. Further studies were done to evaluate the effects of Fe and Al separately. Treatment of simulated Fe containing AMD (Fe-AMD) to pH 9.54, 10.2, 11.8, and 12.1 resulted in 47, 52, 65, and 68 % SO4 2- removal respectively. When Al containing AMD was treated to pH 9.46, 10.3, 11.5 and 12 percentage SO4 2- removal of 39, 51, 55 and 67 % was observed respectively.
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    Synthesis of zeolites Na-P1 from South African coal fly ash: effect of impeller design and agitation
    (MDPI, 2013) Mainganye, Dakalo; Ojumu, Tunde V.; Petrik, Leslie
    South African fly ash has been shown to be a useful feedstock for the synthesis of some zeolites. The present study focuses on the effect of impeller design and agitation rates on the synthesis of zeolite Na-P1 which are critical to the commercialization of this product. The effects of three impeller designs (4-flat blade, Anchor and Archimedes screw impellers) and three agitation speeds (150, 200 and 300 rpm) were investigated using a modified previously reported synthesis conditions; 48 hours of ageing at 47 °C and static hydrothermal treatment at 140 °C for 48 hours. The experimental results demonstrated that the phase purity of zeolite Na-P1 was strongly affected by the agitation rate and the type of impeller used during the ageing step of the synthesis process. Although zeolite Na-P1 was synthesized with a space time yield (STY) of 15 ± 0.4 kg d−1m−3and a product yield of 0.98±0.05 g zeolites/g fly ash for each impeller at different agitation speeds, zeolite formation was assessed to be fairly unsuccessful in some cases due the occurrence of undissolved mullite and/or the formation of impurities such as hydroxysodalite with the zeolitic product. This study also showed that a high crystalline zeolite Na-P1 can be synthesized from South African coal fly ash using a 4-flat blade impeller at an agitation rate of 200 rpm during the ageing step at 47 °C for 48 hours followed by static hydrothermal treatment at 140 °C for 48 hours.
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    Waste minimization protocols for the process of synthesizing zeolites from South African coal fly ash
    (MDPI, 2013) Du Plessis, Pieter W.; Ojumu, Tunde V.; Petrik, Leslie
    Production of a high value zeolite from fly ash has been shown to be an avenue for the utilization of South African fly ash which presently constitutes a huge disposal problem. The synthesis of zeolites Na-P1 and analcime on a micro-scale has been successful and preliminary investigation shows that scale-up synthesis is promising. However, the post-synthesis supernatant waste generated contains high levels of NaOH that may constitute a secondary disposal problem. A waste minimization protocol was developed to reduce the volume of waste generated with a view to enhancing the feasibility of the scale synthesis. Series of experiments were conducted in 100 mL jacketed batch reactors. Fly ash was reacted with 5 Mol NaOH on a 1:1 mass basis during the aging step, followed by hydrothermal treatment in which ultrapure water was added to the slurry. This study shows that by re-introducing the supernatant waste into the experiments in such a way that it supplies the required reagent (NaOH) for the zeolite synthesis, zeolite Na-P1 and analcime can be synthesized. It also shows that the synthesis process can be altered to allow up to 100% re-use of the supernatant waste to yield high value zeolitic products. This study effectively constructed two protocols for the minimization of waste generated during the synthesis of zeolites from South African coal fly ash. This result could be used to establish a basis for legal and environmental aspects involved in the commission of a full-scale plant synthesizing zeolites NaP1 and analcime.