Misconceptions around AMD remain a threat to the environment

23rd August 2019

By: Khutso Maphatsoe



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Acid mine drainage (AMD) has become one of South Africa’s largest environmental threats, as AMD has caused considerable damage to the natural environment and communities living near mining areas, says engineering consultants WSP Africa’s hydrology, environment and energy senior associate Karen King.

She explains that, while areas such as the Modderfontein spruit and the Robinson lake in the old Witwatersrand area, in Gauteng, have been affected the most, the effects of AMD are still being felt across a large geographical area.

While a large volume of AMD has been and will continue to be treated to increase its pH to neutralise it, King acknowledges that this will not solve the broader problem, as water of an acceptable quality is not produced from the treatment. Although the acid in the water is neutralised, the result is highly saline water.

King, therefore, emphasises the implementation of two treatment processes – ion exchange and reverse osmosis.

Ion exchange is the process during which metals are removed from water, while reverse osmosis is for desalination of the water.

King notes that government has tasked State-owned entity the Trans-Caledon Tunnel Authority (TCTA), with financing and implementing bulk raw water infrastructure projects in South Africa to treat AMD in the West, Central and Eastern basins.

King adds that government has been conducting various investigations to find a feasible solution to the treatment of AMD since about 2010.

TCTA is managing three operational AMD treatment plants, namely the Central Basin Plant in Germiston and the Western Basin Plant in Krugersdorp, which have been operational for a few years, as well as the Eastern Basin Plant, which is the largest of the three plants with the capacity to clean 110 mℓ of water a day and put the water back into the Vaal river system. All three plants use short-term neutralisation, which involves ion exchange and the high-density sludge processes.

While King advocates for the continuation of water treatment, she notes that “addressing the issue and treating AMD to standards that are acceptable will be an ongoing, very extensive, expensive and complex undertaking”.

She further declares that the effects of AMD, despite treatment to greater levels, cannot be entirely reversed.

Effects of AMD

King explains that AMD is a consequence of old mining methods and legislation that were not environmentally friendly. The mines responsible for AMD in the past stopped pumping the water out of their mines, which resulted in water levels rising and coming into contact with pyrite in the mine rock faces. The oxidation and reduction reactions between the pyrite, air and water leads to AMD.

Moreover, no one is willing to take responsibility for the AMD and its management. This lack of accountability has led to certain locational ecosystem losses.

Borehole water is also polluted, while in some areas, the soil also absorbs the water and becomes unarable.

“There have also been reports of high uranium levels found in water and soil and using this water for plants and agricultural purposes is not an option,” she says.

To educate mineworkers and communities in mining areas, King tells Mining Weekly that the larger local mines, which have to be health and safety conscious, host “toolbox talks” to explain water treatment processes and AMD to mine staff.

King suggests that the best way for communities who depend on water from rivers for their drinking water, whether polluted by AMD or other pollutants, is the old tried-and-tested method of boiling the water and adding a teaspoon of bleach to every litre of water.

“When people say AMD is being treated in South Africa, they are right. However, people tend to make the assumption that the water has been treated and returned back to its original water quality, which is not the case at all.”

The treatment process has taken out the most damaging elements – the high acidity and the metals and uranium – yet this neither makes the water drinkable for humans or livestock, nor can it always be used for irrigation purposes, she elaborates.

Further, King says that extensive and historical mining, paired with the geology of the Witwatersrand that has led to natural AMD occurrences, has resulted in an underestimation of the volume of AMD that needs to be treated.

Therefore, AMD must be understood and regarded as a serious issue that needs to be adequately addressed and with a sense of urgency, she advocates.

“There are solutions such as reverse osmosis desalination treatment processes that can be used that are being investigated, but we need to increase the pressure on government and the mining houses, as that can help to ensure that adequate responsibility, funding and support for AMD treatment are taken seriously,” she concludes.

Edited by Mia Breytenbach
Creamer Media Deputy Editor: Features



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