Browsing by Author "Nwagboso, Oluchi Esther"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Use of alkaline pre-treatment with cyanide and glycine to extract gold from tailings
    (Stellenbosch : Stellenbosch University, 2022-04) Nwagboso, Oluchi Esther; Tadie, Margreth; Akdogan, Guven; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.
    ENGLISH SUMMARY: In South Africa, particularly in the Witwatersrand area where mining has occurred since 1886, there has been a decrease in high–grade, free milling ores. Additionally, due to the long and lucrative history of mining there is an abundance of tailing dams. Several of these have caused environmental and social issues such as acid mine drainage and the occupation of land that has commercial potential. Therefore, the prospect of processing tailings has become of both environmental and economic interest as it may be less expensive to process the tailings that are already above ground. The possibility of recovering gold from a tailings heap was considered in this study. A mineralogical characterisation of the tailings was performed to comprehend the size, associations, and occurrence of the gold. Fire assay gave a gold grade of 0.208 g/t and 0.804 g/t for the low–grade and high–grade tailings, respectively. Whilst the X-ray diffraction and scanning electron microscopy displayed silicates were the most abundant mineral phase in the tailings. The outcome of the characterisation informed the selection of the methods of extraction of the gold from the tailings. Firstly, direct cyanidation as the most common method for the extraction of gold from most ores, was conducted on the two tailings groups. A 24-hour leach using 2 kg/t NaCN, 60% pulp density at pH of 11 resulted in an average of 40% and 67% gold dissolution for the low–grade and high–grade tailings respectively. Alkaline pre-treatment experiments were carried out using sodium hydroxide to break down the silicate matrices that encapsulating the microscopic gold. Leaching tests were performed to determine the rate and extent to which gold could be leached at different conditions. Following a six-hour leach period using 2 M sodium hydroxide at 80 °C, a 20% increase in gold recovery was observed. Further increase in sodium hydroxide concentration led to decrease in the gold dissolution. Secondly, tests were conducted to assess the use of glycine as a lixiviant for gold from tailings. Potassium permanganate was found to be effective as an oxidant in the gold-glycine leaching system. Gold was leached at ambient conditions, however, increased temperature proved to be essential for the process. Glycine concentration was found to be statistically significant to gold dissolution. At high glycine concentrations and elevated temperatures there was possible formation of polypeptides. Up to 52.3% gold dissolution was achieved using 0.05 M glycine solution at 60°C and 30% pulp density with 1 g/L KMnO4 as an oxidant. Preliminary techno-economic modelling and a sensitivity analysis showed that, in a brown stone field operation, using both an alkaline pre-treatment before cyanidation as well as glycine as an alternative lixiviant could be economically feasible and profitable endeavours.