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Govt prioritises fight against acid mine water in Gauteng

AURORA MINE Legal issues which halted operations at the Aurora mine have resulted in a significant build-up of underground acid mine water

LONG-TERM PROBLEMShort-term treatment of acid mine drainage is falling short of removing a high content of salt in the treated water

Photo by Duane Daws

MINE DRAINAGE Acid mine water is generated when sulphide-bearing minerals, often in the form of pyrite, are exposed to oxygen and water

MARIETTE LIEFFERINKGreater public consultation is required to ensure overall treatment of acid mine drainage is undertaken in a transparent and inclusive manner

Photo by Duane Daws

DILUTION SOLUTION Dilution of treated acid mine water through the Lesotho Highlands Water Project is a possible solution to dealing with the high salt content of semitreated acid mine water

17th June 2016

By: Donna Slater

Features Deputy Editor and Chief Photographer

  

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Government’s acknowledgment of the severity of acid mine drainage (AMD) in the Witwatersrand, Gauteng, and the subsequent priority given to taking steps to alleviate the problem are of “significant importance”, states Federation for a Sustainable Environment (FSE) CEO Mariette Liefferink.

After years of numerous mines having decanted, or verged on the precipice of decanting acid mine water, the Department of Water and Sanitation (DWS) has taken strategic steps with the allocation of funds and plans to tackle the issue of acid mine water poisoning water courses throughout South Africa.

Acid mine water is commonly referred to as AMD.

AMD is generated when sulphide-bearing minerals, often in the form of pyrite (which is iron sulphide found in reefs mined for gold), are exposed to oxygen and water. This process, termed pyrite oxidation, is characterised by the generation of sulphuric acid and dissolved iron. The build-up of AMD has been taking place over several decades, but has seen its worst impact at abandoned mines, which no longer operate dewatering pumps and AMD treatment plants. Thus, nature has been allowed to set its course, with a high risk of poisoning above- and below-ground water resources.

AMD is generally characterised by a number of factors, including a low pH level (high acidity), a high salt content (mostly made up of sulphates) and high levels of metals – particularly iron – giving AMD a characteristic red-orange colour. In addition, where uranium is present, radiological risks may also be present in conjunction with the threats of AMD.

Water and Sanitation Minister Nomvula Mokonyane announced in May that a yearly allocation of R600-million will be committed to directly address the AMD issue. The budget will come from the National Treasury.

The announcement was made at the South West Vertical Shaft, in the Central basin, in Germiston, where the DWS hosted industry experts, together with the implementing agent, the Trans-Caledon Tunnel Authority.

Mokonyane says the solution “promises to simultaneously augment water supply to the nation’s economic hub of the Gauteng region”, adding that the long-term intervention will, therefore, turn the AMD problem into a long-term sustainable solution by producing fully treated water that will significantly increase water supply to the Vaal river system and defer the need for further costly augmentation beyond Phase 2 of the Lesotho Highlands Water Project (LHWP) for “at least another 30 years”.

The solution proposed by the DWS pivots on turning a polluted resource, which is “considered with contempt”, into a commodity that can assist in making more water resources from the Vaal river system available.

Further, with the support of the National Treasury, the DWS has decided to cap the contributions of water users at only 33% of the cost of the project to address the AMD issue. The intention of government is to recover the balance of 67% from the mines through a proposed environmental levy.

In the interim, however, prior to the implementation of the policy and associated consultations, government will cover the anticipated costs. Almost 1 000 short- and long-term jobs have been created through the solution, which started implementation in 2014.

AMD is a growing issue, stemming from underground mining operations as far back as when commercial-scale mining began in South Africa. In the Witwatersrand area of Gauteng, mining has taken place in the three underground mining basins of the East, Central and West Rand since the discovery of gold in 1886, subsequently catalysing economic growth and the development of Gauteng and making the province the backbone of South Africa’s economy for many years.

During this time, more than 120 mines were required to pump out water that had entered their operations to allow for safe mining conditions. However, as mining progressed, an increasing number of projects started reaching the end of their lives and were, therefore, abandoned. This, in turn, led to a growing number of mines conducting ongoing dewatering operations, resulting in a growing number of abandoned mines being filled with water, as dewatering operations were not implemented at these mines.

Besides the impact on above-ground water resources, AMD also poses the risk of increasing the likelihood of seismic activity around mines, owing to the high level of water in underground mines. In addition, AMD can contaminate shallow aquifers and, if the underground mine water reaches the near-surface environment, geotechnical impacts, such as sinkholes, may potentially be caused. The uncontrolled rising of the underground mine water levels may also result in negative socioeconomic consequences. For example, it has the potential to sterilise the remaining gold reserves as well as flood the mining museum of Gold Reef City, located in Johannesburg.

Cautious Approach
Liefferink tells Mining Weekly that AMD has been a well-known problem since 1903 and reached critical levels when it started decanting from the Western basin in 2002.

This decanting was subsequently halted in 2012 when the DWS intervened and deployed dewatering equipment to treat AMD decanting from within the mines and prevent further decanting as part of a short-term strategy.

“In July 2013, the feasibility studies for the long-term treatment of AMD . . . were finalised at a cost of R25-million,” she says, adding, however, that officials of the DWS were pressured into accelerating their efforts into concluding the findings of the study.

The study included determining the feasibility of available technologies and apportionment of liability.

At the moment, treatment of AMD is active in the Western and Central basins. The DWS issued a statement in April, claiming treatment works for AMD in the Eastern basin were ready to go into operation. Liefferink notes, however, that, pending environmental assessments on the sludge generated by this plant, the treatment works will only be fully operational in 2020.

In addition, the treatment of AMD at the plant in the Eastern basin only deals with the neutralisation of AMD and not further purification and the removal of salts, according to Liefferink.

She says government’s recent acknowledgement of the severity of the situation is heartening, adding that there are still many gaps in the available information and many uncertainties as to how to further treat AMD so that it can be released into water courses and potentially be used by the agriculture industry and also be converted into potable water for domestic consumption.

The first major issue, she says, concerns the reconciliation strategies for the integrated Vaal river system, as the system currently suffers from a growing number of deficiencies. Even with the introduction of more volumes of water from the LHWP’s Phase 1, Liefferink says, treated AMD will still be required to contribute to resolving deficiencies in the Vaal river system.

Further, she notes that, according to a recent statement by Mokonyane, there are plans to introduce desalination plants to treat AMD by 2020, thereby enabling fully- treated AMD to be fed into natural water courses and used downstream by the agri- culture industry or to be purified as a potable water supply by a municipal entity or water utility Rand Water.

However, any desalination of sulphate-rich AMD is being delayed, owing to the State’s failure to proactively and timeously conduct an environmental-impact assessment. This will be followed by the construction of another treatment plant, which Liefferink presumes will use reverse osmosis technology.

“During the period [leading up to the plant’s commissioning], it is hoped there will be no water restrictions, or poor water quality because of the continued discharge of highly saline water into the Vaal river system. These potential risks can only be mitigated by releasing water from the Vaal dam and a deficit in the upper regions of the Vaal river, which could have severe economic impacts,” she says.

Liefferink points out that, in the Eastern basin, as a result of the Aurora mine ceasing the pumping of water that accumulated in the mine, no water has been released into the Vaal river system. However, with the implementation of the short-term AMD solution in the Eastern basin, a significant volume of salt-rich water is expected to be added to the Vaal river system.

The salinity issue is significant, she points out. Treated AMD water released from mines, but without the removal of sulphates, has been recorded as having sulphate levels as high as 3 000 mg/ℓ, with more than 100 Mℓ of water a day to be pumped from the Eastern basin.

Such a salt-rich water resource could have drastic impacts on the agriculture industry. For example, water with a salinity of more than 250 mg/ℓ of sulphate has resulted in lower fertility rates in cattle, as it suppresses copper and selenium.

Irrigation of crops will also be affected by increased costs, owing to farmers having to use alternative methods for removing salts, which will increase the rate of corrosion of metal fittings in water distribution systems.

Further, Liefferink says that even State- owned power utility Eskom will be significantly affected, as the utility draws water from rivers and dams to use in the cooling towers at its power stations. “Eskom’s requirements for water are between 15 mg/ℓ and 40 mg/ℓ of sulphate.”

The international acceptable level of salt in drinking water is 200 mg/ℓ of sulphate, she says, adding that this will require Rand Water to desalinate a sulphate-rich water resource at an additional cost, thereby impacting on rate- payers’ pockets.

Besides treating AMD water in a desalination plant to remove salts, another possible solution is running treated AMD through a large body of water, such as the LHWP. However, Liefferink says it is the considered opinion of the FSE that pollution should be treated at its source. “It is unrealistic to use very expensive water of very good quality (referring to water of the LHWP) to simply dilute a water resource that is highly saline.”

She adds that greater public consultation is required to ensure overall treatment of AMD is undertaken in a transparent and inclusive manner.

Liefferink asserts that one of the biggest challenges with resolving the AMD issue is the apportionment of liability and holding guilty parties to account for remediation and rehabilitation activities. She suggests that, while it may be easy to point out responsible agents, such as mine owners, managers, executive directors and even shareholders, it is not always as easy to hold them all to account, as certain mines no longer formally exist after having been closed, liqui- dated or placed under business rescue.

Edited by Martin Zhuwakinyu
Creamer Media Senior Deputy Editor

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