Browsing by Author "Madzivire, Godfrey"

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    Chemistry and speciation of potentially toxic and radioactive elements during mine water treatment
    (University of the Western Cape, 2012) Madzivire, Godfrey; Petrik, Leslie; Gitari, W. M.; Vadapalli, Viswanath R. K.
    Mine water poses a serious environmental challenge and contains elements such as Fe, Al, and Mn in potentially toxic concentrations. The major anion in mine water is sulphate. The complexity and diversity of mine water composition makes its treatment very expensive, and there is no “one-fits-all” treatment option available for mine water. Active treatment of mine water produces water with good quality but the processes are not sustainable because of the costs. Previous studies have shown that acid mine drainage can be treated with coal FA to produce better quality water. The use of coal FA, a waste material from coal fired power station and mine water would go a long way in achievement of sustainable treatment of mine water as per previous studies. In this study mine water and coal FA were characterized to determine their physiochemical properties. This study linked the modelling results obtained by using the Geochemist’s workbench (GWB) software to the results obtained during the actual treatment of Matla mine water and Rand Uranium mine water using coal FA and lime. The chemistry involved when Matla mine water and Rand Uranium mine water were treated with flocculants was also investigated. Lastly the chemistry and kinetics involved was investigated when mine water was treated with various ameliorants such as Matla coal FA, lime and/or Al(OH)3 using jet loop mixing or overhead stirring. Mine water from Matla coal mine had a pH of 8 and therefore was classified as neutral mine drainage (NMD). Rand Uranium mine water had a pH of less than 3 and therefore was classified as acid mine drainage (AMD). The concentration of sulphate, Na, Ca, Mg, B, Hg, Se and Cd ions in Matla mine water was 1475, 956, 70, 40, 15, 2.43, 1.12 and 0.005 mg/L respectively. The concentration of sulphate, Fe, Ca, Mn, Mg, Al, B, Cr, Pb, U, Cd, Se and As ions in Rand Uranium mine water was 4126, 896, 376, 282, 155, 27, 5.43, 3.15, 0.51, 0.29, 0.007, 0.06 and 0.006 mg/L respectively . These concentrations were above the target water quality range (TWQR) for potable water set by the Department of Water Affairs (DWA) and World Health Organization (WHO). The gross alpha radioactivity was 6.01 Bq/L and gross beta radioactivity was 6.05 Bq/L in Rand Uranium mine water.
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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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    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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    Removal of sulphates from South African mine water using coal fly ash
    (University of the Western Cape, 2009) Madzivire, Godfrey; Petrik, Leslie. F
    South African power stations generate large amounts of highly alkaline fly ash (FA). This waste product has a serious impact on the environment. Acid mine drainage (AMD) is another environmental problem associated with mining. AMD has high heavy metal content in addition to high SO/- concentrations. Several studies have shown that 80-90 % of SO/- can be removed when FA is codisposed with AMD rich in Fe and AI. In South Africa, many sources of contaminated mine waters have circumneutral pH and much lower concentrations of Fe and Al (unlike AMD), but are rich in Ca, Mg and SO2-4. This study evaluated sol removal from circumneutral mme 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 SO/- removal from mine water. The precipitation of ettringite at alkaline pH was evaluated to further reduce the SO/- concentration to below the DWAF limit for potable water. Removal of sol 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 % SO/- 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 % SO/- 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 % SO/- 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 % SO/- removal respectively. When Al containing AMD was treated to pH 9.46, 10.3, 11.5 and 12 percentage SO/- removal of 39, 51,55 and 67 % was observed respectively. Ion chromatography (IC), inductively coupled plasma-mass spectrometry (ICPMS) and inductively coupled plasma-atomic emission (ICP-AES) analysis of the product water, x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectrometry analysis of FA and solid residues collected after treatment of mine water complemented with PHREEQC thermodynamic modelling have shown that the mechanism of S042 - removal from mine water depends on the composition of the mine water. The sol- removal mechanism from CMW was observed to depend on gypsum precipitation. On the other hand sol- removal from mine water containing Fe and Al was dependent on the precipitation of gypsum and Fe and Al oxyhydroxysulphates. The oxyhydroxysulphates predicted by PHREEQC as likely to precipitate were alunite, basaluminite, ettringite, jarosites and jurbanite. Treatment of CMW with FA to pH 12.35 removed sol- from 4655 ppm to approximately 1500 ppm. Addition of amorphous AI(OH)3 to CMW that was treated to pH greater than 12 with FA was found to further reduce the sol concentration to 500 ppm which was slightly above the threshold for potable water of 400 ppm. The further decrease of sol concentration from 1500 to 500 ppm was due to ettringite precipitation. Mine water treatment using FA was found to successfully remove all the major elements such as Fe, AI, Mn and Mg to below the DWAF limit for drinking water. The removal of the major elements was found to be pH dependent. Fe and Al were removed at pH 4-7, while Mn and Mg were removed at pH 9 and 11 respectively. The process water from FA treatment followed by gypsum seeding and addition of AI(OH)3 had high concentration of Ca, Cr, Mo and B and a pH of greater than 12. The pH of the process water from FA treatment followed by gypsum seeding and addition of AI(OH)3 was reduced by reacting the process water with CO2 to 7.06. The process water from the carbonation process contained trace elements such as Cr, Mo and B above the DWAF effluent limit for domestic use. Carbonation of the process water reduced the water hardness from 5553 ppm to 317 ppm due to CaC03 precipitation, thereby reducing the Ca concentration from 2224 ppm to 126 ppm.
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    A review of combined advanced oxidation technologies for the removal of organic pollutants from water
    (Springer Verlag, 2014) Tijani, Jimoh O.; Fatoba, Ojo O.; Madzivire, Godfrey; Petrik, Leslie
    Water pollution through natural and anthropogenic activities has become a global problem causing short-and long-term impact on human and ecosystems. Substantial quantity of individual or mixtures of organic pollutants enter the surface water via point and nonpoint sources and thus affect the quality of freshwater. These pollutants are known to be toxic and difficult to remove by mere biological treatment. To date, most researches on the removal of organic pollutants from wastewater were based on the exploitation of individual treatment process. This single-treatment technology has inherent challenges and shortcomings with respect to efficiency and economics. Thus, application of two advanced treatment technologies characterized with high efficiency with respect to removal of primary and disinfection by-products in wastewater is desirable. This review article focuses on the application of integrated technologies such as electrohydraulic discharge with heterogeneous photocatalysts or sonophotocatalysis to remove target pollutants. The information gathered from more than 100 published articles, mostly laboratories studies, shows that process integration effectively remove and degrade recalcitrant toxic contaminants in wastewater better than single-technology processing. This review recommends an improvement on this technology (integrated electrohydraulic discharge with heterogeneous photocatalysts) viz-a-vis cost reduction in order to make it accessible and available in the rural and semi-urban settlement. Further recommendation includes development of an economic model to establish the cost implications of the combined technology. Proper monitoring, enforcement of the existing environmental regulations, and upgrading of current wastewater treatment plants with additional treatment steps such as photocatalysis and ozonation will greatly assist in the removal of environmental toxicants.