negative impact of gold mining in south africa
This coal mining project is an open pit mine located in Nigeria, announced by mining company - Western Goldfields - that it has discovered 62,400,000 tonnes of proven reserves of coal deposits worth US$1.2 billion which could be used for the generation of electric power...
the impact of gold mining on the witwatersrand on the rivers and karst system of gauteng and north west province, south africa - sciencedirect
The Witwatersrand has been subjected to geological exploration, mining activities, parallel industrial development and associated settlement patterns over the past century. The gold mines brought with them not only development, employment and wealth, but also the most devastating war in the history of South Africa, civil unrest, economical inequality, social uprooting, pollution, negative health impacts and ecological destruction. One of the most consistent and pressing problems caused by mining has been its impact on the water bodies in and adjacent to the Witwatersrand. The dewatering and rewatering of the karstic aquifer overlying and adjacent to the Witwatersrand Supergroup and the pollution caused by Acid Mine Drainage (AMD) are some of the most serious consequences of gold mining in South Africa and will affect the lives of many South Africans.
The Witwatersrand, once occupied by a farming community, was transformed within a few years into the densest populated region in Southern Africa after the discovery of gold. Johannesburg was founded in 1886 after the discovery of the Main Reef. Other parts of the reef were discovered to the east and the west during the next few years and the towns of Germiston and Boksburg were established to the east of Johannesburg and Krugersdorp, Roodepoort, Randfontein and Klerksdorp were established to the west of Johannesburg. Over the next few decades further towns such as Nigel, Brakpan and Carletonville came into existence along the Witwatersrand. Black townships such as Orlando, Kliptown (the nuclei around which Soweto grew), Vosloorus, Katlehong and Thembisa were established on the outskirts of the major urban centres.
The settlements along the Witwatersrand initially started off to provide housing for miners. Shortly thereafter other supporting industries were established which attracted people of diverse occupations and an infrastructure was developed including roads, railway lines, telegraph, electricity, gas and water supply. Within a few months these settlements grew from mine camps to shanty towns and ultimately to municipalities where schools, hospitals and businesses opened their doors. Some of these towns grew into cities, in the case of Johannesburg, within a few decades.
The urban centres grew to such an extent that a continuous strip of habitation stretching over a hundred kilometres, from Nigel to Carletonville, was formed within a century. The residents consist of not only a cross-section of the ethnic groups of South Africa, but also people from other African countries such as Lesotho, Swaziland, Botswana, Zimbabwe, Mozambique, Malawi and Zambia.
Squatter camps sprung up in the open spaces between the towns as destitute people from rural areas and neighbouring countries flocked to the cities, and more particularly to the mines and other industries in the hope of finding work. This strip of mines and humanity is separated by farms between the mining region known as the Far West Rand which includes Carletonville and Khutsong southwest of Randfontein and the mining centre of Klerksdorp, Orkney and Stilfontein near Potchefstroom further to the west.
Avarice and opportunism rather than careful planning with an eye to long-term sustainability were the main motives behind the development of the mines and industries and the settlement patterns along the Witwatersrand. One of the first major problems that government and mining houses had to solve was the supply of water for drinking and sanitation purposes for the urban population and for the running of the industries and mines in the area. The water security situation in Gauteng and North West Province has taken a turn for the worse with the efflux over the past decade of mine effluent from the mine void on the Witwatersrand.
Johannesburg is one of the few major cities in the world that was not founded near a lake or a river. For the first few decades the small rivers and groundwater along the Witwatersrand were sufficient for the needs of the small but rapidly growing population, but after the Anglo-Boer War the need for additional water became more pressing. The Vaal Barrage Dam, which was an engineering feat at the time, was built in the Vaal River between 1916 and 1923 to supply the Witwatersrand, and especially
The term Witwatersrand Supergroup was derived from the discovery and description of the auriferous outcrop on the Witwatersrand. Subsequent exploration and research proved that this sequence of gold-bearing sedimentary rocks occurs in a wide arc surrounding the Vredefort Dome and is found in Gauteng, North West and the Free State Provinces. The layers that constitute the Witwatersrand Sequence were deposited as sediments when deltas, fed by large river systems, fed into an inland sea in the
Pieter Jacob Marais, the fist official gold prospector of the Transvaal Republic, discovered alluvial gold in 1853 in the Jukskei and Crocodile Rivers in the western Transvaal. Undoubtedly this gold originated from the Witwatersrand, Ventersdorp and Transvaal Supergroups. Marais, like many other prospectors at the time, focussed on the alluvial deposits in the rivers and although they crossed the Witwatersrand Supergroup often, the largest gold deposit in the world remained unknown.
It is noticeable that the names of many of the farms on the Central and West Rand have been derived from the word fontein, the Afrikaans word for fountain or spring eg. Vogelfontein, Elandsfontein, Driefontein, Doornfontein, Turffontein and Vogelstuisfontein, and then there is of course the town Springs. This is due to the proximity of the Witwatersrand Supergroup to the karstic dolomite-rich Transvaal Supergroup. Groundwater issues from the karst along the length of the Witwatersrand, from
The US Environmental Protection Agency recognised already in 1987 that ...problems related to mining waste may be rated as second only to global warming and stratospheric ozone depletion in terms of ecological risk. The release to the environment of mining waste can result in profound, generally irreversible destruction of ecosystems.
The salinity of river systems that receive mine effluent is greatly affected by the volumes of sulphates contained in the effluent. The mine effluent discharged from the Witwatersrand mines to the south of the watershed accounts for only 5% of the volume of water in the Vaal River but it accounts for 20% of the salts entering the system (DWAF, 2009).
Metals enter the river systems through the run-off from slimes dams and rock dumps and from the mine void via seeps and decanting. It also enters the groundwater by means of seepage of rainwater through mine dumps and the decanting of mine effluent from the slimes dams into the groundwater (Kleywegt, 1977, Jones et al., 1988a, Jones et al., 1988b, Naicker et al., 2003). AMD containing metals can also seep through swallow holes and cracks in the dolomites linking the surface run-off to the water
The Witwatersrand Supergroup contains more uranium than gold and the Witwatersrand gold mines are in fact also uranium mines. Uranium was originally mined as a by-product of the gold mining industry in Gauteng and the West Rand (Von Backstrm, 1976). South Africa also had one of the first uranium extraction plants in the world, which provided the uranium used in the making of the atom bombs dropped on Hiroshima and Nagasaki. As the strategic importance of uranium was realised, other countries
The cyanide process for the extraction of gold may have saved the mines a century ago, but simultaneously it posed a major environmental and health impact. The gold extraction process with cyanide involves the exposure of crushed gold-containing rock or sand to cyanide, treatment with active coal, heating, treatment with some more chemicals and lastly ore electrolysis (Korte and Coulston, 1998). During the Heap Leach treatment, a cyanide solution is percolated through large piles of low grade
The water quality of the river systems, wetlands and groundwater has deteriorated noticeably over the past decade due to mine effluent issuing from mines in Gauteng and the North West Province. Certain rivers are devoid of macroscopic organisms and the riparian vegetation has suffered a loss of biodiversity in affected areas (Fig. 17).
The efflux of AMD-contaminated water is the most costly environmental and socio-economic problem in South Africa (Oelofse et al., 2007). Attempts by government departments to involve the mining companies in the rehabilitation of the areas impacted by mining activities have been frustrated because of the mine companies refusal to accept responsibility for the situation (Funke et al., 2007). Mine companies usually claim that they inherited the situation which already existed before they took
Mine closure and especially the rehabilitation of the environment need to be addressed urgently. According to the Department of Mineral Resources there are over 8000 derelict and ownerless mines in South Africa which would take approximately 800years to rehabilitate at a cost of billions of Rands (Brown, 2007). If one adds the rehabilitation of the water bodies affected by AMD, the health impacts on humans, the disruption of societies and the destruction of the biodiversity, the cost becomes
Mining of gold in the Welkom and Virginia areas of the Free State Province in South Africa has produced numerous gold mine tailings, which contain a variety of contaminants. The extent of contamination of groundwater in the area was studied by measuring several water quality indicators at eight sampling sites, and within three zones. The overall contamination of groundwater was quantified by computing a Drinking Water Quality Index (WQI). The results revealed that majority of the groundwater in the Welkom and Virginia areas is unsuitable for drinking, as confirmed by high WQIs. At only three sites was the water samples suitable for drinking. One site revealed water to be of very poor quality, while the remainder 40% of the sites indicated water to be of poor quality. The high indicator microbiological counts also affirmed the poor quality of the groundwater. Faecal coliform bacterial counts were 100% non-compliant to drinking water quality limits when compared to the World Health Organization and South African National Standard on Drinking Water 241, while E. coli counts exceeded both the drinking water quality limits at 50% of the sampling sites. Of the potential harmful elements analysed, Pb and Fe were found to be at toxic levels. For Pb, 40% of the water samples exceeded the drinking water quality limits while 63% of water samples were non-compliant for Fe. This result exposes the poor quality of the groundwater in the Welkom and Virginia areas, which poses a serious threat to the health of the local people, as groundwater is their primary source of drinking water. This research highlights the urgent need for mitigation measures to be introduced by the local authorities to improve the quality of the groundwater in the study area.
The Odiel and Tinto rivers show singular characteristics due to the significant acid mine drainage (AMD) generated in the first section of their basins and the phosphogypsum (PG) stacks located on their common estuary. AMD leads to low pH and high redox potential, which keep high amounts of toxic elements and radionuclides in dissolution. The objective of this work was to analyse the seasonal evolution of U-Th isotopes and 210Po in these rivers and the estuarine mixing zone. Four sampling points were selected (a fluvial point and an estuarine one for each river) and water samples were collected monthly throughout a year. The concentrations of natural radionuclides in the dissolved and particulate phases were determined by alpha spectrometry. The Odiel and Tinto rivers show concentrations of U-Th isotopes and 210Po from one to three orders of magnitude higher than background continental waters due to the strong effect of AMD, and 234U/238U activity ratios up to 2.
The studied radionuclides show a clear seasonal behaviour in these rivers, with three different stages during the year: (1) concentration peaks observed during November and December due to the washing effect produced by the first rainfalls of the hydrological year, (2) a dilution effect by runoff in the rainy winter, and (3) a progressive concentration effect during the spring and summer. A non-conservative behaviour of the analysed radionuclides in the estuaries was demonstrated due to precipitation processes produced by the increase of pH. The polluted outflows from the PG stacks located in the Tinto estuary produce a significant radioactive impact, mainly during the rainiest months, increasing the concentration of U-isotopes and 210Po in the particulate phase.
The current work illustrates the use of Central Composite Design (CCD) and Response Surface Methodology (RSM) to gain insight into the effect of five process factors (i.e. pressure, MgSO4 concentration, Fe2(SO4)3 concentration, Al2(SO4)3 concentration and carbon nanotubes loading) on the treatment of synthetic Acid Mine Drainage (AMD) solution with a Thin Film Nanocomposite (TFN) membrane. Performances of polyamide TFN membranes with different multi-walled carbon nanotube (MWCNT) loading were tested to determine optimum loading under different operating conditions. The treatment efficiency was examined in terms of flux and rejection, and based on these results, the optimum region from RSM was selected. The five previously mentioned process variables were investigated, and regression models were built, while data on permeate flux behaviour, MgSO4 rejection, Fe2(SO4)3 rejection, and Al2(SO4)3 rejection as the response values were collected. Predicated models were in good agreement with experimental data and the results showed that pressure and carbon nanotubes (CNT) loading are the main effects that influence the process. The optimal conditions were a pressure of 20bars and a CNT loading of 0.3%. Under these conditions, a permeate flux of 83%, 94% MgSO4 rejection, 92% Fe2(SO4)3 rejection, and 89% Al2(SO4)3 rejection were observed. RSM models demonstrate the ability to overcome limitations of conventional experimental methods by accounting for interactions between the main factors which affect the process. RSM is applied as a novel method to optimise process conditions of CNT-infused TFN membranes in the removal of heavy metal ions from AMD.
Biological sulphate reduction and partial sulphide oxidation, occurring simultaneously within the hybrid linear flow channel reactor (LFCR) were evaluated, under controlled conditions at laboratory scale, as a function of hydraulic residence time (HRT) using a synthetic media containing 1g/L sulphate. The hybrid LFCR comprises a rectangular channel containing carbon microfibers as a support matrix for attachment of sulphate-reducing bacteria and an exposed air-liquid interface to facilitate the formation of a floating sulphur biofilm. Exposure to decreasing HRT, from 3 days to 12h, resulted in an increase in the volumetric sulphate reduction rate (0.14 to 0.63mmol/L.h), achieving levels typically associated with active reactors. Sulphate conversion was highest (97 %) at a 3 day HRT, decreasing to 73 % at 12h. The highest sulphide removal efficiency (82 %) and accompanying sulphur recovery through harvesting of the floating sulphur biofilm (FSB) was observed at a 2 day HRT. The sulphur fraction not recovered through the biofilm was predominantly released within the effluent as colloidal elemental sulphur and fragments of the sulphur-rich biofilm, with minimal re-oxidation to sulphate occurring in the reactor. The hybrid LFCR technology was able to achieve high rates of sulphate reduction and effective sulphide removal within a single, semi-passive reactor unit.
High concentrations of arsenic (As) occur in acid mine drainage (AMD), while the mechanisms governing its distribution along the flow of AMD are not fully understood. In this study, As species distribution was surveyed along the flow of an AMD in Jiaole coal mine in a typical kast area, in which length of creek is about 1100m. AMD from the discharging source contained 1754.2g/L As (1570.0g/L in As (III)) and 644.1mg/L Fe (all in Fe (II)) at pH3.45. Both As and Fe concentrations decreased drastically to trace levels along the flow in the creek. As(III) oxidation to As(V) and Fe(II) oxidation to Fe(III) were discovered in a short distance from the discharging source. Lab experiments were performed to unveil the mechanisms governing As and Fe species distribution. Biological mechanism governed As(III) and Fe(II) oxidation in the AMD phase without contact with solid matrix, while different mechanisms governed the oxidation in the presence of solid matrix at different stages of AMD flow. At the beginning of AMD discharge, its contact with the soil matrix in rich of carbonate minerals in the karst area facilitated Fe(II) oxidation by O2 due to pH rise, which generated reactive oxidants for As(III) oxidation and iron oxyhydroxides for As adsorption or co-precipitation. Along the AMD flow, bacteria in the underlying sediments profoundly accelerated the biological oxidation of As(III) and Fe(II) as well as the co-precipitation into the sediments. Findings of this study deepen the understanding of As transport and transformation along the AMD flow, particularly in karst areas.
Clay minerals are affordable, abundant, naturally occurring minerals found in many parts of the world that have been used effectively for remediation of many contaminants. This review article is aimed at studies involving the use of clay minerals for the remediation of soils and water contaminated with heavy metals. All relevant scientific literature using science direct online database from the year 2000 till 2019 were evaluated. The review highlighted the properties of clay minerals which make them good adsorbents and the processes necessary for adsorption to take place. It revealed that clay minerals are quite effective for remediation purposes, confirmed that clay minerals are very affordable, reliable, and environmentally friendly remediation materials for heavy metal contaminated media. Also, several methods are available for the modification of clay minerals in order to increase their adsorption capacity. However, in order to establish the use of clay minerals as heavy metal remediation materials compared to other established methods, more investigations are required, to determine the best modification type for clay minerals as well as the standard dosage of clay minerals required for the adsorption of heavy metals.
Wadi Queih basin records different continental settings that interacted with explosive volcanism. This paper discusses the contrasting aggradational mechanisms in fluvial systems strongly influenced by explosive volcanism which took place during sedimentation of the Queih basin. Six main facies associations composed of 12 lithofacies have been recognized in the Neoproterozoic succession filling the Queih basin: (1) lava flows and pedogenically modified pyroclastics facies association, (2) debris-flow-dominated alluvial fan facies association, (3) sheetflood-dominated alluvial fan facies association, (4) crevasse-splay facies association, (5) lacustrine facies association, and (6) loess facies association. These facies assemblages are typical of low-sinuosity rivers flowing through unsymmetrical half graben basin. Petrographical and geochemical data of the Queih sediments indicate a predominantly continental volcanic block provenance and stable craton to fault-bounded basement uplift. Low values of Chemical and Plagioclase Index of Alteration (CIA and PIA) are consistent with low intensity source rock weatherning under prevailing semi-arid to arid climate.
During deposition of the lower member of the Queih basin, common fall and flow tuff events occurred, indicating syn-eruptive conditions. In contrast, deposition of the upper member occurred in a fluvialaeolian setting without input of primary volcaniclastic detritus, indicating inter-eruptive conditions. The change in depositional mode from the lower to upper is considered to be due to a change in the balance between the sedimentation rate and the rate of lake-level rise. Lithofacies stacking and rapid lateral changes of lithological units in conjunction with interformational unconformities and basin margin faults suggest tectonically induced sedimentation. Volcanism can also influence basin evolution and the delicate balance between erosion, sedimentation, and prevalent transport processes is affected the Queih basin by volcanic input. Thus, the Queih basin records the response of fluvial system to large, volcanism-induced sediment loads.
The Interference between the northeast, EastWest, and northwest oriented faults imposed a complex structural setting of the northwestern margin of the Nile Delta, Northeast Africa. The pre-existing faults were reactivated during the evolution of the Nile Delta by two tectonic events. These events took place during the Late MioceneEarly Pliocene and Late PlioceneEarly Pleistocene times and were coeval with two falls in the sea level pattern. Some of these faults have continued to affect the bottom sea sediments and increased the northerly slope of the upper surface of the delta body. The thickness of the Pliocene-Recent sediments and the location of the pre-existing faults controlled these reactivations. The mechanical contrast of these sediments and fault displacements controlled the geometry of the reactivated faults. The rotated displacement on some of these faults is associated with growth units upward. The northwest sinking (bending) of the outer part of the African continental margin under the Eurasian plate at the Hellenic subduction Arc has induced a tangential northwest trending extension (an average of N37WS37E trend) in the outer zone of the northern African margin that is responsible mainly for the reactivations of the pre-existing faults.
The main objectives of this study were to evaluate uranium (U) toxicity in the crayfish Procambarus clarkii at a low dose of exposure and to discriminate between the chemotoxicity and radiotoxicity of U. We conducted two sets of experiments using either 30gL1 of depleted uranium (DU) or 233U, which differ from each other only in their specific activity (DU=1.7104Bqg1, 233U=3.57108Bqg1). The endpoints were oxidative stress responses and mitochondrial functioning in the gills and hepatopancreas, which were measured in terms of enzyme activities and gene expression levels. U accumulation levels were measured in different organs (gills, hepatopancreas, stomach, intestine, green gland, muscles, and carapace), and internal dose rates in the hepatopancreas were compared after DU and 233U exposures. Significant U accumulation occurred in the organs of P. clarkii, and mitochondrial damage and antioxidant responses were detected. Despite the huge difference (21,000) in the specific activities of DU and 233U, few significant differences in biological responses were detected in P. clarkii exposed to these two pollutants. This finding indicates that the radiotoxicity was low compared to the chemotoxicity under our exposure conditions. Finally, genes expression levels were more sensitive markers of U toxicity than enzyme activities.
The area considered in this study lies within the western section of the East African Rift System (EARS) and saline groundwater occurs in some parts of the valley plain. Hydrochemical groundwater types were classified into three groups (G1G3), indicating different stages of groundwater chemical evolution. An overall incongruent weathering of aluminosilicate minerals causes the groundwater solution to generally be in equilibrium with montmorillonite. Ca(Mg)HCO3 groundwater (G1), with relatively low TDS (average TDS=548mg/L), are mainly found in areas with Karoo basalt and Precambrian basement complex rocks. This water type is mainly governed by aluminosilicate weathering. Towards the middle of the valley, Na- and mixed cation-HCO3 groundwater (G2; average TDS=1061mg/L) predominates. This water type results from a combination of aluminosilicate mineral weathering, cation exchange and precipitation of clays and carbonates. The increase in ionic strength of G2 samples, in comparison with G1 samples, is attributed to mixing with high TDS groundwater in G3. Brackish and saline groundwaters (G3; average TDS=3457mg/L) are dominated by sodium, chloride and sulphate ions, which is attributable to dissolution of Cl and SO42- evaporative salts. These are found in clusters and in aquifers with low recharge capacity (low transmissivity) and are attributable to intrusion of mineralised groundwater probably through fault zones from mainly sedimentary Karoo and Cretaceous Lupata formations. Evaporation plays a role in brackish/saline groundwaters found in areas with shallow water table along the Shire River.
Uranium and gold-bearing pyrobitumen from the Carbon Leader Reef in the Witwatersrand Basin, South Africa, was investigated by high-resolution transmission electron microscopy. This study provides evidence for the in-situ growth of uraninite and anatase nanocrystals in the pyrobitumen, implying mobilization and concentration of uranium and titanium by formerly mobile liquid hydrocarbons. Individual nanocrystals of uraninite and anatase are pervasively distributed and locally isolated within the pyrobitumen matrix. Crystallization of uraninite and anatase led to the formation of complex nanocrystal aggregates by oriented attachment, in which anatase generally provided nuclei for the growth of uraninite. Single nanocrystals of curite occur locally in channel ways within masses of uraninite nanocrystals, consistent with later auto-oxidation of uraninite and limited release of water during hydrocarbon maturation. On the basis of evidence for the migration of liquid hydrocarbons in the Witwatersrand Basin and the presence of abundant uraninite and anatase nanoparticles in pyrobitumen, a new model is proposed for the transport and concentration of uranium (and titanium) in the Carbon Leader Reef. According to this model, liquid hydrocarbons that were circulating in the Witwatersrand Basin dissolved detrital UTi-bearing minerals and transported the uranium and titanium until thermal degradation immobilized the hydrocarbons by solidifying them as pyrobitumen. The latter process involved the release of volatiles and the destruction of bonds that may have held the uranium and titanium in solution, thereby inducing the growth of individual uraninite and anatase nanocrystals and the formation of complex nanocrystal aggregates within the pyrobitumen.
High-resolution scanning- and transmission-electron microscopy of pyrobitumen-hosted uraninite reveal that uraninite grains are highly porous aggregates of uniformly sized nanocrystals, and that many of their pores are filled by native gold. These texturally late gold grains, in turn, contain small pores occupied by former oil droplets that were converted to pyrobitumen during burial and metamorphism. The pyrobitumen in the pores of the gold grains contains in situ-formed uraninite nanocrystals. Galena also occupies the pores of the uraninite aggregates. In addition, this study reveals the first occurrence of rare lanarkite that engulfs the galena in the pores of the uraninite.
On the basis of the nature of the uraninite and the filling of some of its pores with native gold, we propose a mineralization model for the deposition of the uranium and gold in the Carbon Leader Reef that calls upon the interaction of oil and aqueous (hydrothermal) fluids to form micro-emulsions. According to this model, uraninite nanocrystals precipitated from uranium-bearing hydrocarbon liquids and flocculated to form porous, uraninite aggregates. These liquids interacted with auriferous hydrothermal fluids in the Carbon Leader Reef, leading to the formation of a micro-emulsion at the interface between the two fluids. Gold precipitated as native metal around droplets of the oil owing to a reduction in oxygen fugacity, which destabilized the bisulfide species responsible for gold dissolution. Commonly, this process went hand in hand with the flocculation of the uraninite nanocrystals, causing entrapment of the native gold in the pores of the uraninite aggregates. The hydrocarbon liquid, which occurs as droplets in the gold and is the host to the uraninite aggregates, was transformed to pyrobitumen. As a result of this process, a thin pyrobitumen seam containing uraninite nanocrystals formed along the inner walls of the pores in the native gold. Lead introduced by the hydrocarbon liquid precipitated as galena. Interaction of the uraninite with hydrothermal fluids or radiolysis of the pore water facilitated the development of local zones of oxidation between galena and uraninite, which led to the crystallization of rare lanarkite.