Assessment of pollution potential of old tailings dam; a case study of the Idaupriem Gold Mine in Ghana

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Tailings Dams are found in many mining areas in Ghana. Various toxic substances are found in these tailings dams. This study was carried out to ascertain the pollution potential of these tailings dams. Augur drilled samples were taken from the old tailings dam at the Iduapriem Gold Mine and extensive laboratory investigation such as particle size analysis, XRD analysis, microscopic examination, AAS analysis of the solid phase and the mobile phase, physico-chemical analysis and micro biological analysis were conducted. It was found that the tailings material was silty sand having less than 10% fine materials and would therefore be permeable to liquids. There were sulphide materials present and most of these sulphides have been altered through weathering. The presence of these suiphides suggests that this dam has the potential of producing some level of ARD. The solid phase of the tailings material contained relatively high level of iron while Mn, Zn, Cu, and Pb were low. The liquid phase also contained these ions which concentration increases with increase in depth. The prevailing pH after pulping to 1:1 solid/liquid was between 6 and 8 while Total Dissolved Solids (TDS) and Electrical Conductivity (EC) values of the mobile phase were also found to be increasing with depth. (NB The insitu values would be much higher than the values reported due to dilution) The potential therefore exist of mobilizing these ions into the environment if the OTD is not lined. The laboratory investigation further revealed the presence of the following ions in the tailings: CN-, NH4+, HCO3 -, SO42-, NO3- and CO32- It was confirmed by the studies that cyanide has been extensively attenuated (i.e. from about 250ppm to less than 0.2ppm) producing NH4+ and CO3- and that these ions have also been transformed to NO3- and HCO3- respectively through microbial activity and chemical reaction. Consequently, the long term environmental impact of this tailings dam will be the production of bicarbonates and nitrates and decommissioning of this tailings dam may therefore concentrate on the mitigation of nitrates in particular as they are likely to cause infant Metamoglobinamia ( i.e. The blue baby disease).
A thesis submitted to the Department of Mineral Processing and Extractive Metallurgy in partial fulfilment of the requirements for the award of Master of Science degree in Environmental Resources Management, 2002