Use of alkaline pre-treatment with cyanide and glycine to extract gold from tailings

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dc.contributor.advisorTadie, Margrethen_ZA
dc.contributor.advisorAkdogan, Guvenen_ZA
dc.contributor.authorNwagboso, Oluchi Estheren_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Process Engineering.en_ZA
dc.date.accessioned2022-03-09T09:20:28Zen_ZA
dc.date.accessioned2022-04-29T09:24:57Zen_ZA
dc.date.available2022-03-09T09:20:28Zen_ZA
dc.date.available2022-04-29T09:24:57Zen_ZA
dc.date.issued2022-04en_ZA
dc.descriptionThesis (MEng)--Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH 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.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: In Suid-Afrika, veral in die Witwatersrandarea waar mynbou plaasvind vanaf 1886, is daar ’n afname in hoë-graad, vrymallende erts. Addisioneel, as gevolg van die lang en winsgewende geskiedenis van mynbou is daar ’n oorvloed van uitskothope. Verskeie van hierdie het omgewings- en sosiale kwessies veroorsaak, soos suurmyndreinering en die beset van land wat kommersiële potensiaal het. Daarom, die vooruitsig van prosessering van uitskotdamme het beide ’n omgewings- en ekonomiese belang omdat dit goedkoper kan wees om die uitskot wat reeds bo die grond is, te prosesseer. Die moontlikheid om goud uit ’n uitskothoop te herwin is eers oorweeg in hierdie studie. ’n Mineralogiese karakterisering van die uitskot is uitgevoer om die grootte, assosiasies, en die voorkoms van die goud te verstaan. Vuurproef het ’n goudgraad van 0.208 g/t en 0.804 g/t vir die laer graad en hoë-graad uitskot, onderskeidelik gegee, terwyl die x-straaldiffraksie en skandeerelektronmikroskopie silikate as die mees oorvloedige mineraalfase in die oorskot getoon het. Die uitkoms van die karakterisering het die keuse van die metodes van ekstraksie van die goud uit die uitskot ingelig. Eerstens, direkte sianidering as die mees algemene metode vir die ekstraksie van goud uit meeste erts is uitgevoer op die twee uitskotgroepe. ’n 24-uur loog wat 2 kg/t NaCN, 60% soliede digtheid by pH 11 gebruik, het ’n gemiddeld van 40% en 67% goudoplossing vir die laer-graad en hoë-graad uitskotte tot gevolg gehad, onderskeidelik. Alkaliese voorbehandelingseksperimente is uitgevoer wat seepsoda gebruik om die silikaatmatrikse wat die mikroskopiese goud vasvang, te breek. Logingtoetse is uitgevoer om die tempo en omvang te bepaal waartoe goud geloog kan word by verskillende kondisies. Na ’n ses-uur-loogperiode waar 2 M seepsoda by 80 °C gebruik is, is ’n 20% verhoging in goudherwinning waargeneem. Verdere verhoging in seepsodakonsentrasie het tot afname in die goudoplossing gelei. Tweedens is toetse uitgevoer om die gebruik van glisien as ’n loogmiddel vir goud uit uitskot te assesseer. Kaliumpermanganaat is gevind as ’n effektiewe oksidant in die goud-glisien loogsisteem. Goud is geloog by omgewingskondisies, maar, verhoogde temperatuur was essensieel vir die proses. Glisienkonsentrasie is gevind om statisties beduidend te wees vir goudoplossing. By hoë glisienkonsentrasies en verhoogde temperature was daar moontlike vorming van polipeptiede. Tot en met 52.3% goudoplossing is bereik deur 0.05 M glisienoplossing by 60 °C en 30% soliede digtheid met 1 g.L KMnO4 as oksidant te gebruik.af_ZA
dc.description.versionMastersen_ZA
dc.format.extent172 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/124659en_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectGold tailings, Gold extraction, Glycine leaching, Cyanide leaching, Alkaline Pre-treatmenten_ZA
dc.subjectGold mines and miningen_ZA
dc.subjectLeachingen_ZA
dc.subjectTailings (Metallurgy)en_ZA
dc.subjectUCTDen_ZA
dc.titleUse of alkaline pre-treatment with cyanide and glycine to extract gold from tailingsen_ZA
dc.typeThesisen_ZA
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