Gold deportment and ore characterisation of the historical Witwatersrand tailings dams with emphasis placed on the sulphides

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dc.contributor.advisorVon der Heyden, Bjornen_ZA
dc.contributor.advisorTadie, Margrethen_ZA
dc.contributor.authorChingwaru, Steve Jasonen_ZA
dc.contributor.otherStellenbosch University. Faculty of Science. Dept. of Earth Sciences.en_ZA
dc.date.accessioned2024-02-28T18:27:21Z
dc.date.accessioned2024-04-26T14:35:38Z
dc.date.available2024-02-28T18:27:21Z
dc.date.available2024-04-26T14:35:38Z
dc.date.issued2024-03
dc.descriptionThesis (PhD)--Stellenbosch University, 2024.en_ZA
dc.description.abstractENGLISH ABSTRACT: The Witwatersrand Basin, discovered in 1881, has yielded over 53,000 tons of native gold hosted in quartz pebble conglomerates. Present gold extraction methods involve comminution and direct cyanidation, resulting in the retention of 5-10 % of residual gold in tailings. Re-mining primarily targets native gold recovery, achieving an average of 30-50 % gold recovery through direct cyanidation. This implies that the remaining 50-70 % of unrecovered gold, along with approximately 30 million tons of residual sulphide waste, is re-dumped to the tailing stream. The Witwatersrand tailings significantly contribute to South Africa's pollution, causing acid mine drainage and deleterious element effluent due to sulphide waste oxidation. The mineralogical distribution of unrecovered gold during tailings reprocessing is inadequately characterized and absent from existing literature. Furthermore, the current body of literature lacks a comprehensive environmental assessment specifically addressing the movement and dispersion of deleterious elements during sulphide oxidation within the Witwatersrand tailings. This PhD research focuses on the ore characterization and mineralogical deportment of unrecovered gold within the Witwatersrand tailings from Klerksdorp, Carletonville, Evander, and Central Rand goldfields. Simultaneously, an environmental assessment explores deleterious element behaviour, retention, and release mechanisms during sulphide oxidation in Witwatersrand tailings dumps. The methodology utilized employs the multi-element, high- resolution, and low-detection capabilities of laser ablation inductively coupled plasma mass spectrometry analysis, combined with an automated mineralogical technique to analyse bulk tailings samples and their operationally defined mineral fractions. Additional analytical methods include aqua regia digestion combined with ICP-MS analysis and fire assay. Mineralogical analysis using optical microscopy, electron microscopy, and X-ray diffraction analysis provides comprehensive insights into the composition and physical properties of minerals. Metallurgical test work, incorporating gravity separation, direct cyanidation, and diagnostic leaching, validates Witwatersrand tailings behaviour in processing scenarios. Results indicate cyanide amenable gold recovery at 14- 61 %, primarily in the form of micron to nano-sized native gold particles. Non-cyanide amenable phases contributing to the refractory behaviour of gold include sulphides (mainly pyrite) and silicates at 4-38 % and 11- 32 %, respectively. In situ pyrite analysis reveals 'invisible' gold within detrital pyrite and arsenian pyrite. These Archean detrital pyrites exhibit grades comparable to auriferous sulphides from surrounding Archean granite- greenstone gold ores on the Kaapvaal craton (up to 2700 ppm). Pyrite also hosts a substantial concentration of deleterious elements, with Co, Au, and Pb strongly leached during pyrite oxidation. However, a significant proportion of As, Ni, Cu, and Zn is retained in the iron oxyhydroxide alteration rims through incorporation and absorption. The study underscores the necessity of addressing 'invisible gold' during beneficiation, proposing tailored leaching parameters and a pretreatment strategy to potentially recover up to 420 tons of gold, thereby contributing to the local economy. Furthermore, the recovery of metals can not only reclaim valuable 'sweetener' by-product metals such as Cu, Co, and Ni but also directly mitigate issues related to deleterious element pollution and acid mine drainage associated with surface tailings dumps. The findings presented in this dissertation represent significant and original contributions to multiple scientific disciplines, notably including geometallurgy, geology, mineral processing, and environmental sciences.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Die Witwatersrand-bekken, wat in 1881 ontdek is, het al meer as 53,000 ton inheemse goud opgelewer wat gehuisves is in kwarts-kiesel-konglomeraat. Huidige goudonttrekkingsmetodes behels verkleining en direkte sianidasie, wat lei tot die retensie van 5-10% van residuele goud in die storting. Herwinning fokus hoofsaaklik op die herwinning van inheemse goud, met 'n gemiddelde van 30-50% herwinning deur direkte sianidasie. Dit impliseer dat die oorblywende 50-70% van onherwinde goud, saam met sowat 30 miljoen ton residuele sulfiedafval, na die stortvloeistroom hergelei word. Die Witwatersrand-storte dra beduidend by tot die besoedeling van Suid-Afrika, wat suurmyndreinering en nadelige element-effluente veroorsaak as gevolg van die oksidasie van sulfiedafval. Die mineralogiese verspreiding van onherwinde goud tydens die herprosessering van storte, is ontoereikend gekarakteriseer en afwesig in die bestaande literatuur. Verder ontbreek daar 'n omvattende omgewingsassessering in die huidige literatuur wat spesifiek daarop gemik is om die beweging en verspreiding van nadelige element tydens sulfiedoksidasie binne die Witwatersrand-storte aan te spreek. Hierdie doktorale navorsing fokus op die erts-karakterisering en mineralogiese gedrag van onherwinde goud binne die Witwatersrand-storte vanaf Klerksdorp, Carletonville, Evander, en die sentrale Rand-goudvelde. Gelyktydig ondersoek 'n omgewingsassessering die gedrag, retensie en vrylating van nadelige element tydens sulfiedoksidasie in Witwatersrand-storte. Die navorsingsmetodologie maak gebruik van die multi-element, hoë resolusie, en lae opsporingseienskappe van laser-ablasie gekoppel aan induktief gekoppelde plasma massaspektrometrie-analise, sowel as 'n outomatiese mineralogiese tegniek om bulkstortmonsters en hul operasioneel-gedefinieerde minerale te ontleed. Addisionele analitiese metodes sluit aqua regia vertering gekoppel aan ICP-MS-analise, vuurproef, en mineralogiese analise in met behulp van optiese mikroskopie, elektronmikroskopie, en X-straal diffraksie-analise. Metallurgiese toetswerk, wat gravitasieskeiding, direkte sianidasie, en diagnostiese uitloging insluit, bekragtig die gedrag van Witwatersrand-storte in proses-senario's. Resultate dui op sianied-gevoelige goudherwinning van 14- 61%, hoofsaaklik in die vorm van mikro- tot nanogrootte inheemse goudeeltjies. Nie-sianied-gevoelige fases wat bydra tot die refraktêre gedrag van goud, sluit sulfiede (hoofsaaklik piriet) en silikate in, teen onderskeidelik 4- 38% en 11-32%. In situ piriet-analise onthul 'onsigbare' goud binne detritiese piriet en arseniese piriet. Hierdie Argeense detritiese piriete het kwaliteite vergelykbaar met auriferous sulfiede van die omliggende Argeense graniet-groenstof gouderts op die Kaapvaal kraton (tot 2700 ppm). Piriet huisves ook 'n beduidende konsentrasie van nadelige element, waar Co, Au, en Pb sterk uitgeloog word tydens pirietoksidasie. 'n Beduidende proporsie van As, Ni, Cu, en Zn word egter in die ysteroksihidroksied alterasie-rande behou deur inkorporasie en absorpsie. Die studie beklemtoon die noodsaaklikheid om aandag te gee aan 'onsigbare goud' tydens die veredeling, deur op maatgemaakte loggingsparameters en 'n voorbehandelingsstrategie voor te stel om potensieel tot 420 ton goud te herwin, wat tot die plaaslike ekonomie kan bydra. Verder kan die herwinning van nadelige element nie net waardevolle 'versoeter' byproduk-metale soos Cu, Co, en Ni herwin nie, maar kan ook direk probleme met nadelige elementbesoedeling en suurmyndreiniging wat met oppervlakstortings verband hou, verminder. Die bevindinge wat in hierdie proefskrif aangebied word, verteenwoordig beduidende en oorspronklike bydraes tot verskeie wetenskaplike dissiplines, insluitend geometalurgie, geologie, minerale verwerking, en omgewingswetenskappe.af_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentxxi, 253 pages : illustrations (some color), mapsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/130355
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshMines and mineral resources -- South Africa -- Witwatersrand Areaen_ZA
dc.subject.lcshGold ores -- Metallurgyen_ZA
dc.subject.lcshGold ores -- South Africa -- Witwatersranden_ZA
dc.subject.lcshPyrites -- South Africa -- Witwatersranden_ZA
dc.subject.lcshTailings (Metallurgy)en_ZA
dc.subject.lcshMineral processingen_ZA
dc.subject.lcshOre-dressingen_ZA
dc.subject.nameUCTDen_ZA
dc.titleGold deportment and ore characterisation of the historical Witwatersrand tailings dams with emphasis placed on the sulphidesen_ZA
dc.typeThesisen_ZA
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