Fate of sulphate removed during the treatment of circumneutral mine water and acid mine drainage with coal fly ash: Modelling and experimental approach |
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| Authors: | Godfrey Madzivire Wilson M. Gitari V.R. Kumar Vadapalli Tunde V. Ojumu Leslie F. Petrik |
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| Affiliation: | aEnvironmental & Nano Sciences Research Group, Chemistry Department, University of the Western Cape, Modderdam Road, Private Bag X17, Bellville, 7535 Cape Town, South Africa;bDepartment of Ecology and Resources Management, School of Environmental Studies, University of Venda, Private Bag X5050, Thohoyandou 0950, South Africa;cNatural Resources and Environment Department, Council for Scientific and Industrial Research, P.O. Box 395, Pretoria, South Africa;dDepartment of Chemical Engineering, Faculty of Engineering, Cape Peninsula University of Technology, Cape Town Campus, P.O. Box 652, Cape Town 8000, South Africa |
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| Abstract: | 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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| Keywords: | Fly ash Circumneutral mine water Acid mine drainage PHREEQC geochemical modelling and sulphates |
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