Thesis (PhD)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: In recent years acid mine drainage (AMD) has become the focus on many mine sites throughout the world.
The Witwatersrand gold mines have been the main focus of AMD in South Africa due to their extensive
impact on especially groundwater resources. The Witwatersrand Basin is a regional geological feature
containing the world-famous auriferous conglomerate horizons. It is divided into sub-basins and the East
Rand Basin is one of them. Due to the regional scale of the East Rand Basin AMD issues, a systems
approach is required to provide a useful tool to understand the pollution source term and fate and transport
dynamics and to aid in environmental decision making and to evaluate the geochemical impact of mitigation
measures and evaluate future scenarios.
The numeric geochemical models, using a systems perspective, show that the mine waste facilities,
specifically the tailings dams are significant contamination point sources in the East Rand Basin, specifically
for acidity (low pH), SO4, Fe, Mn, U, Ni, Co, Al and Zn. When the AMD solution enters the soil beneath the
tailings, ferrous and SO4 concentrations remain elevated, while Mn, U, Ni and Co and perhaps other metals
are adsorbed. After ~50 years the pollution plume starts to break through the base of the soil profile and the
concentration of the adsorbed metals increase in the discharging solution as the adsorption capacity of the
soil becomes saturated. The pollution pulse then starts to migrate to the shallow groundwater where
contamination of this resource occurs.
Toe seepage from the tailings either first reacts with carbonate, where acidity is neutralised to a degree and
some metals precipitated from solution, where after it reaches the surface water drainage, such as the
Blesbokspruit, where it is diluted. Some evaporation can occur, but evaporation only leads to concentration
of acidity and dissolved constituents, thereby effectively worsening the AMD solution quality. The mixing
models have shown that the dilution factor is sufficient to mitigate much of the AMD, although seasonal
variability in precipitation and evapotranspiration is expected to have some influence on the mixing ratio and
some variability in the initial solution will also be reflected in variation in surface water quality. From a sustainability perspective, a basic cost benefit analysis shows that the costs for the operating mine
and society in general is lower when mitigation measures are employed during operation. For a theoretical
mine in the ERB with an operating life of 100 years, the cost of operational mitigation measures is ~R 31
billion. This value is 4% of turnover and 19% of profits over the time period. Post closure remediation costs
are ~R 67 billion. This value is 8% of turnover and 41% of profit over the time period. Although the initial
capital investment in mitigation measures is substantial, although some measures will be implemented
during operation, it is a smaller percentage of profits than eventual post-closure mitigation. / AFRIKAANSE OPSOMMING: In die laaste paar jaar het suur mynwater loging (SML) die fokus geword by baie myn areas regoor die
wêreld. Die Witwatersrand goud myne het die hoof fokus van SML in Suid Afrika geword as gevolg van die
groot impak wat Witwatersrand SML op veral grondwater bronne het.
Die Witwatersrand Kom is ‘n regionale geologiese struktuur wat die wêreld beroemde goud-draende
konglomeraat horisonne bevat. Die Witwatersrand Kom word onderverdeel in sub-komme, waarvan die Oos-
Rand Kom een is. As gevolg van die regionale skaal van die Oos-Rand Kom SML probleem sal ‘n
sistemiese benadering ‘n bruikbare middel wees om besoedelingsbron migrasie en eindpunt dinamika te
verstaan asook om omgewingsbesluitneming en die geochemiese impakte en mitigerings metodieke asook
toekoms senarios te evalueer.
Die numeriese geochemiese modelle, wat vanuit ‘n sitemiese oogpunt beskou is, wys dat die myn afval
fasiliteite, veral die slikdamme in die Oos-Rand Kom, beduidende kontaminasie puntbronne is van veral suur
inhoud, SO4, Fe, Mn, U, Ni, Co, Al and Zn. Wanneer die SML oplossing die grond onder die slikdamme
binnedring, bly Fe2+ en SO4 konsentrasies hoog, terwyl Mn, U, Ni en Co asook ander metale geadsorbeer
word. Na ~50 jaar begin die besoedelingsoplossingspluim deur die basis van die grond profile breek. Die
konsentrasie van die geadsorbeerde metale neem dan toe in die oplossing wat deur die grondprofiel beweeg
het soos wat die adsorpsie kapasiteit van die grond versadig word. Die besoedelingspuls begin dan stadig
na die vlak grondwater akwifeer migreer waar dit dan besoedeling van die grondwater versoorsaak.
Water wat van die slikdam basis sypel reageer eers met karbonaat, waar suur tot so ‘n mate geneutraliseer
word, dat sommige metale uit die oplossing neerslaan, waarna dit die oppervlak water lope, soos die
Blesbokspruit, beryk en verdun word. Verdamping van die SML oplossing kan plaasvind, maar verdamping
veroorsaak die konsentrasie van suur en opgeloste stowwe, wat die SML probleem dus kan vererger. Meng
modelle het gewys dat die verdunning faktor genoegsaam is om baie van die SML te mitigeer, alhoewel
seisoenale fluktuasies in reënval en verdampings syfers kan verwag word om ‘n mate van invoed op die
meng verhouding tussen die SML oplossing en oppervlak water te hê wat dan in die oppervlak water
kwaliteit gereflekteer sal word. Vanuit ‘n volhoubaarheidsperspektief is ‘n basiese koste voordeels analise gedoen. Hierdie analise het
gewys dat die koste van ‘n operasionele myn en die samelewening as geheel laer is wanneer mitigasie
metodieke tydens operasie toegepas word. Vir ‘n teoretiese myn in die Oos-Rand Kom met ‘n operasionele
lewe van 100 jaar, is die operasionele mitigeringsmetodieke koste ~R31 miljard. Hierdie waarde is 4% van
die myn omset en 19% van winste oor die tyds periode. Na operasionele remdiasie kostes is ~R67 miljard.
Hierdie syfer is 8% van omset en 41% van winste oor die tydperk. Alhoewel die inisiële kapitaal uitleg van
mitigasie metodes groot is, alhoewel sekere metodes eers tydens operasie implimenteer sal word, is die
uitleg ‘n kleiner persentasie van winste as wanneer remediasie na operasie implimenteer word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95880 |
| Date | 12 1900 |
| Creators | Hansen, Robert Neill |
| Contributors | Roychoudhury, Alakendra, Stellenbosch University. Faculty of Science. Dept of Earth Sciences. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 196 p. : ill. maps |
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