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Silverton, South Africa

Vadapalli V.R.K.,Environmental Geosciences | Fester V.,Cape Peninsula University of Technology | Petrik L.,University of the Western Cape | Slatter P.,RMIT University
Desalination and Water Treatment | Year: 2014

Abstract: Large quantities of fly ash (FA) are generated annually in South Africa and most of it is disposed in landfills and ash dams. Previous studies indicated that FA can be used to treat acid mine drainage (AMD), another waste stream commonly found in the minerals industry. Moreover, encouraging results were obtained from the studies carried out on the sludge (referred as solid residues (SR) hereafter) recovered from FA-AMD treatment as a suitable mine backfill material. Particle size distribution (PSD) of FA plays an important role in the AMD treatment quality and viscosity of the SR that can be used directly for backfill purposes. In this study, we have investigated the effect of PSD of FA on AMD neutralisation and metal removal. This work also looked at the effect of PSD on the rheology of the SR. Neutralisation experiments indicated that the higher fines fraction enhances the treatment of AMD by reducing the time taken to increase the pH to a minimum of 7. Moreover, FA with higher fines fraction has reduced the Mn and (Formula presented.) levels better than the normal and higher coarse fraction FA. X-ray fluorescence analysis on SR confirmed the metal removal trends observed during the neutralisation experiments. Laboratory scale studies were carried out on the rheology of SR using a rheometer. It was found that increasing the coarse fraction results in higher viscosity than by increasing the fines fraction. The observed behaviour is contrary to the notion that increase in fines fraction will increase the viscosity of the suspension. This study shows that there may be some truth in the controversial effect of coarse particles on the rheology of suspensions. © 2013, © 2013 Balaban Desalination Publications. All rights reserved. Source

Winter A.,University of Puerto Rico at Mayaguez | Zanchettin D.,Max Planck Institute for Meteorology | Zanchettin D.,University of Venice | Miller T.,University of Puerto Rico at Mayaguez | And 12 more authors.
Nature Communications | Year: 2015

Approximately half of the world's population lives in the tropics, and future changes in the hydrological cycle will impact not just the freshwater supplies but also energy production in areas dependent upon hydroelectric power. It is vital that we understand the mechanisms/processes that affect tropical precipitation and the eventual surface hydrological response to better assess projected future regional precipitation trends and variability. Paleo-climate proxies are well suited for this purpose as they provide long time series that pre-date and complement the present, often short instrumental observations. Here we present paleo-precipitation data from a speleothem located in Mesoamerica that reveal large multi-decadal declines in regional precipitation, whose onset coincides with clusters of large volcanic eruptions during the nineteenth and twentieth centuries. This reconstruction provides new independent evidence of long-lasting volcanic effects on climate and elucidates key aspects of the causal chain of physical processes determining the tropical climate response to global radiative forcing. © 2015 Macmillan Publishers Limited. Source

Madzivire G.,University of the Western Cape | Maleka P.P.,IThemba LABS | Vadapalli V.R.K.,Environmental Geosciences | Gitari W.M.,University of Venda | And 2 more authors.
Journal of Environmental Management | Year: 2014

Mining of coal is very extensive and coal is mainly used to produce electricity. Coal power stations generate huge amounts of coal fly ash of which a small amount is used in the construction industry. Mining exposes pyrite containing rocks to H2O and O2. This results in the oxidation of FeS2 to form H2SO4. The acidic water, often termed acid mine drainage (AMD), causes dissolution of potentially toxic elements such as, Fe, Al, Mn and naturally occurring radioactive materials such as U and Th from the associated bedrock. This results in an outflow of AMD with high concentrations of sulphate ions, Fe, Al, Mn and naturally occurring radioactive materials. Treatment of AMD with coal fly ash has shown that good quality water can be produced which is suitable for irrigation purposes. Most of the potentially toxic elements (Fe, Al, Mn, etc) and substantial amounts of sulphate ions are removed during treatment with coal fly ash. This research endeavours to establish the fate of the radioactive materials in mine water with coal fly ash containing radioactive materials. It was established that coal fly ash treatment method was capable of removing radioactive materials from mine water to within the target water quality range for drinking water standards. The alpha and beta radioactivity of the mine water was reduced by 88% and 75% respectively. The reduced radioactivity in the mine water was due to greater than 90% removal of U and Th radioactive materials from the mine water after treatment with coal fly ash as ThO2 and UO2. No radioisotopes were found to leach from the coal fly ash into the mine water. © 2013 Elsevier Ltd. Source

Madzivire G.,University of the Western Cape | Gitari W.M.,University of Venda | Vadapalli V.R.K.,Environmental Geosciences | Petrik L.F.,University of the Western Cape
International Journal of Environmental Science and Technology | Year: 2015

Recent studies have shown that a combination of coal fly ash (FA) and Al(OH)3 can be used to treat neutral mine drainage (NMD) and reduce sulphate concentration to within South African drinking water quality levels, Class II (400–600 mg/L). The shortcomings of this method were the large amounts of FA required to raise the pH to greater than 11 (3:1 liquid-to-solid ratio) so that Al(OH)3 can be added to facilitate removal of sulphate ions through ettringite precipitation. This requires large silos to store FA, making up-scaling of this treatment technology using normal mixing methods to be unrealistic. In the current study, a jet loop reactor was used to reduce the amount of FA needed to increase the pH to greater than 11. The pH was raised to greater than 11 by mixing 0.25 % of lime (w/v ratio) and 13 kg of coal FA with 80 L of NMD in a jet loop reactor. After the pH of the mixture was above 11, amorphous Al(OH)3 (83.2 g) was added to the mixture. This resulted in the sulphate concentration decreasing to less than 500 mg/L. Bench-scale studies using 0.25 % (w/v) of lime and 6:1 coal mine water to FA ratio could not reduce the sulphate concentration to below 500 mg/L. Therefore, the impingement and cavitation mixing techniques that happen in a jet loop reactor played an important role in enhancing sulphate removal. © 2013, Islamic Azad University (IAU). Source

Zvimba J.N.,South African Council for Scientific and Industrial Research | Mathye M.,South African Council for Scientific and Industrial Research | Vadapalli V.R.K.,Environmental Geosciences | Swanepoel H.,South African Council for Scientific and Industrial Research | Bologo L.,South African Council for Scientific and Industrial Research
Water Science and Technology | Year: 2013

This study investigated Fe(II) oxidation during acid mine drainage (AMD) neutralization using CaCO3 in a pilot-scale Sequencing Batch Reactor (SBR) of hydraulic retention time (HRT) of 90 min and sludge retention time (SRT) of 360 min in the presence of air. The removal kinetics of Fe(II), of initial concentration 1,033±0 mg/L, from AMD through oxidation to Fe(III) was observed to depend on both pH and suspended solids, resulting in Fe(II) levels of 679±32, 242 ±64, 46± 16 and 28±0 mg/L recorded after cycles 1, 2, 3 and 4 respectively, with complete Fe(II) oxidation only achieved after complete neutralization of AMD. Generally, it takes 30 min to completely oxidize Fe(II) during cycle 4, suggesting that further optimization of SBR operation based on both pH and suspended solids manipulation can result in significant reduction of the number of cycles required to achieve acceptable Fe(II) oxidation for removal as ferric hydroxide. Overall, complete removal of Fe(II) during AMD neutralization is attractive as it promotes recovery of better quality waste gypsum, key to downstream gypsum beneficiation for recovery of valuables, thereby enabling some treatment-cost recovery and prevention of environmental pollution from dumping of sludge into landfills. © IWA Publishing 2013. Source

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