The Causes and Effects of Acid Mine Drainage on the Witwatersrand Basin

Introduction

For over 120 years, the economy of South Africa has largely dependent on mining. Formal mining started at Langlaagte near Johannesburg and spread through the whole of the Witwatersrand basin. Before the adaptation of environmental legislation, mines have been reckless with protecting the environment. The mining activities in the Witwatersrand Basins have resulted in Acid Mine Drainage which has adverse effects on the community and the environment. The motivation behind this research on Acid Mine Drainage is that it is major environmental challenge which threatens the scarce water resources in South. In this paper we shall focus on the causes and effects of AMD on the community located around the basins as well as South Africa. Literature What is Acid Mine Drainage?Acid mine drainage arises when sulphur containing orebodies such as pyrite come into contact with oxygenated water. The sulphur containing orebodies undergo a two staged oxidation process with the first reaction producing sulphuric acid and ferrous sulphate and the second reaction producing orange-red ferric hydroxide and sulphuric acid(McCarthy TS, 2011). The sulphuric acid produced dissolves heavy toxic metals such as zinc, copper and magnesium, radioactive metals such as palladium and radium are also dissolved. The water becomes not only acidic but toxic. Acid mine drainage then occurs when the toxic and acid water flows or seeps into the river channels. Although the process occurs naturally and rocks such as dolomite are able to neutralize the acid, in South Africa a vast number of coal and diamond mines exist in one central area, and the natural neutralization process becomes overwhelmed by the large quantities of acid produced. The reactions below, as stated by (N. F. Gray, 1997) shows the formation of acid from pyrite rock.

The causes of acid mine drainage in south Africa?

Mine Dumps

Ever since the discovery of gold in 1886 in the Central Basin, the Witwatersrand Basin has been responsible for 30 percent of the gold in the world. Mponeng and TauTona gold mines are one of the deepest mines in the world, all located in the Witwatersrand Basin. The gold in the Witwatersrand occurs in the conglomerate rock which forms part of the approximately 7000m thick sequence of sedimentary rocks(McCarthy TS, 2011). The process of mining the rock involves extracting the rock from underground and transporting it to the surface where it can be crushed and processed. However, after extraction of the gold, some conglomerate which contains 3% pyrite is dumped in heaps called mine dumps or tailings. There is an economic value of the gold that is contained in the tailings and some mines go as far as treating the tailings to extract more gold. The location of the tailings is controversial. (Durand, 2012) claims that mines built the slime and holding dams on dolomite because it would minimize the probability of it to collapse. However, (Oelofse, Hobbs, Rascher, & Cobbing, 2007) argue that the usage of heaps especially on dolomite, would result in the contamination of streams through indirect or direct methods. This raises the question whether a HAZOP Analysis was done during the planning and construction of the holding dams? If it were done, did the engineers choose to have a stable holding dam over environmental contamination? What happens inside the tailings is that, rainwater oxides the pyrite forming the toxic and acidic water, which then emerges from the base of the tailings to join the local groundwater as pollution plume. In a study conducted by 6, it was found that the streams draining around the dumps were very acidic, contained a high sulphate and heavy metal concentration, all confirming that the AMD is from the dumps.Decantation of Void

Another source of AMD is from the Witwatersrand void, during the mining process, miners created a void by extracting the gold-bearing rock and through continuous pumping out of water, they ensured that the void remained filled with air. Because of the interconnectedness of the shafts in the Basins, after shutdown of most the mines and only East Rand Propriety Mines Ltd. (ERPM), was left pumping out the water in the void. It later shutdown and in 2010. An interesting note is that, () reported that the water level is raising at 15m per month and in 36 months the water will start decanting. As stated before, when pyrite oxides the result is water with toxic metals as well as sulphuric acid. The water that will decant will be toxic and will discharge from the lower level into the nearby streams. To calculate the outflow of AMD from the void, the inflow of water to the void before it became filled amounted to about 40 million litres per day, and the volume of decanting water can be expected to be similar (probably slightly less)(). Critic of the issue.

In this paper, an attempt will be made to answer several questions and raise several issues to the readers. Since there is a nearby community located next to the basins, one would ask themselves the effects of AMD on the health and well-being of the community. Most of the community practice farming in their homes as a source of food, what are the effects of AMD on the vegetation as well as the community that digest the food on a daily basis? After the discovery of AMD, many mines were forced to shut down, what are the effects on this loss of job opportunities to the community? Also, should the mining managers that can be located be held accountable for not performing a HAZOP Analysis on the location of the slime dams? Lastly, why has AMD which was discovered by () not prevented or treated when it was still same scale and manageable? These are the issues that will be discussed in the rest of the paper.

Discussioncondition of the ground water at the Witwatersrand basinsSoil-Ground relation.

To understand the effects of AMD on the community and quality of the water, an analysis of the groundwater needs to be done. Although the ground water outside the mining area is sulphate dominated and has a neutral pH, (H. Tutu, T.S. McCarthy, & E. Cukrowska, 2008) stated that the ground water around the mining area is very acidic and has a high heavy metal concentration. They concluded that this is the result of oxidation of iron underground, which is the primary cause of AMD. Moreover, the site observed by (N. F. Gray, 1997) has never been covered by tailings but it still has a high metal concentration. The reason for this behavior is that, metal rich ground water is drawn upwards by capillarity and evaporates on the soil surface producing a gysum crust which is enriched in metal sulphate. From this, we can conclude that not only does AMD affect the groundwater directly near the surface but also, through evaporation and surface runoff, the heavy metals can move to the nearby groundwater resources.

The Effects of Acid Mine Drainage on the Witwatersrand Basin.

Effect of acid mine drainage on the environment.

The effect of Acid Mine Drainage differs because of the different metals and acidity found in the discharge. However, the effects can be generalized into chemical, physical, biological and ecological, as shown in Figure 4-1. The overall impact of Acid Mine Drainage is the elimination of species, simplification of the food chain which then reduces the ecological stability.

Figure 4:1: General effects of acid-mine drainage in the chemical, physical, biological and ecological systems (N. F. Gray, 1997).

Lowering the acidity of water.

One of the effects of acid mine drainage is lowering the pH of water where it is unsuitable for domestic or any other use. (H. Tutu et al., 2008) state that the pH of acid mine drainage entering steams in the Western Basin is found slightly lower than 3. Although the water is not corrosive but in the long term it will finally have an effect on the materials in constantly comes into contact with.Lowering the water quality

(H. Tutu et al., 2008) conducted a study on the quality of water near the tailings and further downstream. It was concluded that acid mine drainage adversely affects the quality of water because closer to the tailing the water quality was poor but further downstream the water quality showed an increase.

Damage to the scenery

With focus on the Witwatersrand Basins, one should look at the ecological damage of the Robinson Lake on the West Rand. The lake which was a recreational dam has become a radioactive site. Mine acid water was pumped into the dam as an emergency measure to contain the acid water from decanting. Soil pollution

Soil pollution arises due to surface runoff, contaminates are transported from the heaps to the surrounding soils which might be a residential area. (Oelofse et al., 2007) argue that through the practice of geophagy, which is the practice of eating earth, the heavy metal might be able to enter into the body systems of the community. Heavy metals inside the human body may result in cancer and mental retardation in kids. Geological Instability.

Dolomite and limestone are very soluble in an acidic medium. These rocks pose a threat of excessive karstification in the Witwatersrand basin which may result in subterranean cavities in the dolomite. When the water with AMD flows through the karstic aquifers in the dolomite, fissures widen and sinkholes may result when the surface collapses into the void(Durand, 2012)The effect of Acid Mine Drainage on the EconomyUneconomical mining activities.

Provided that acidic mine drainage remains uncontrolled in the Witwatersrand Basin, any mining company that would like to pursue the extraction of the remaining gold will run at a loss.

The effect of Acid Mine Drainage on the people of South Africa.Misuse of water resources.

South Africa is listed as the 28th most water stressed country in the world and therefore cannot afford to be negligent about its water usage(T.I Ewart, 2011). The unmanaged discharge of contaminated mining effluent has resulted in the hydrological transport of toxic metal and acidic water into streams, rivers and drainage basins thus polluting the primary element of South Africas water availability mix. Currently, the salinity of the AMD discharge from the Witwatersrand basin is only managed once it enters the Vaal River System where it is diluted with clean water from the Lesotho Highlands Project, which can be seen as a waste of clean water which could be used to supply the population of South Africa. Another example (Durand, 2012) stated is that, the slimes dams were built on dolomite which the AMD drained into the karst system in Gauteng and North West Province. However, the water from the karst could have provided the residences of the provinces with more water but instead, it was contaminated with AMD. Increased unemployment

Since the first decant of AMD, the relationship between the government and the mining companies has been under strain. Mines which provided employment to the nearby communities closed down and this resulted in the loss of job opportunities and increased unemployment(Oelofse et al., 2007). Although one can argue that subsistence farming can be used to sustain the families, but AMD leaves the soil and the water filled with heavy metals.

Threat to Health of the Users of Water.

One of the greatest effect of AMD is the threat to exposure of all living organisms to toxic metal and radionuclide contamination as a result of AMD(T.I Ewart, 2011). Although most living organisms require metallic elements in varying amounts, but other heavy metals pose no benefit to living organism. Continuous exposure to these heavy elements may cause ecological destruction, serious illness or even death to animals. Such metals include nickel, copper, cadmium, arsenic and lead. To name one of the illnesses that is speculated to be caused by heavy metals in autism. ( Carin Smit,2009), says that. When toxic metals enter the body, they attach themselves to the sulphr and hydrogen proteins, which exist in the enzymes and hormones of the body, disabling these catalytic elements randomly or purposely leaving neuro-immuno-endocrinological devastation. Children who are exposed to these heavy metals appear to have a missing mentally and are diagnosed as having autistic spectrum disorder. Uranium which is one of the radioelements found in the AMD discharge is very deadly to human life. It decays into radioactive substances such as thorium, radium, radon and palladium. Uranium is described as being neuro-toxic and can lead to seizures, mental retardation if children are exposed to it. Radon is an odorless gas if inhaled excessively can cause lung diseases which one of them is cancer. Focusing on the Witwatersrand Basins an informal settlement on the West Rand, which is between Roodeport and Krugersdorp had measured radioactivity levels between 10 000 and 100000 Becquerels per cubic meter(T.I Ewart, 2011). It was recommended that they should be relocated and genetic disease should be carried out to determine the impact of the communitys level of exposure.

Figure 4:2 Tudor shaft informal settlement. Source: (T.I Ewart, 2011)

Conclusion The realities of acid mine drainage are harsh, but sadly in South Africa we are yet to understand the importance of environmental integrity and a strong economy. As much as Acid Mine Drainage could have been prevented by the mine that extracted gold, even now the government is still dragging their feet to address this environmental crisis. Mines that have maximized their profits and left slime dams filled with AMD should be accountable for their actions. AMD is an environmental crisis that the government needs to address urgently.

ReferencesDurand, J. (2012). The impact of gold mining on the Witwatersrand on the rivers and karst system of Gauteng and North West Province, South Africa. Journal of African Earth Sciences, 68, 2443.H. Tutu, T.S. McCarthy, & E. Cukrowska. (2008). The chemical characteristics of acid mine drainage with particular reference to sources, distribution and remediation: The Witwatersrand Basin, South Africa as a case study. Applied Geochemistry, 23(23), 36663684.McCarthy TS. (2011). The impact of acid mine drainage in South Africa. S Afr J Sci, 107(5/6)(712), 7.N. F. Gray. (1997). Environmental impact and remediation of acid mine drainage: a management problem. Environmental Geology, 30.Nstenfedzeni Obed Novhe. (2012). Evaluation of the applicability of the passive treatment for the management of polluted mine water in the Witwatersrand Goldflieds. Council for Geosciences, Environmental Geosciences Uint.Oelofse, S., Hobbs, P., Rascher, J., & Cobbing, J. (2007). The Pollution and Destruction Threat of Gold Mining Waste on the Witwatersrand: A West Rand Case Study (pp. 1113). Presented at the 10th International Symposium on Environmental Issues and Waste management in Energy and Mineral Production (SWEMP, 2007), Bangkok.T.I Ewart. (2011, December). Acid Mine drainage in the Gauteng province of South Africa - A phenomenoloigca; study on the degree of alignment between stakeholders concerning a sustainable solution to acid mine drainage. University of Stellenbosch.

1 Acid mine drainage arising from gold mining activity in Johannesburg, South Africa and environs2 The decanting of acid mine water in the Gauteng city-region