Keep it in the ground

Coal mining has been a mainstay of the South African economy for well over a century, driving economic growth, generating export income, and providing a reliable, affordable source of energy. As conversations about responsible mining gain traction, innovations in responsible mine closure could be paramount.

“While coal mining generates valuable resources, it also produces substantial solid waste that can contribute to environmental pollution. Once mining operations cease, the mine site can still have a lasting impact on the environment if it has not been properly closed and rehabilitated,” explains Thashni Chetty, African mining lead for engineering professional services consulting firm WSP in Africa.

“The consequences of ineffective mine closure in South Africa are evident from the prevalence of abandoned mines and operations that remain in prolonged care and maintenance. The transfer of mines to companies with fewer resources for closure, along with the rise in illegal mining activities, further highlights this issue,” Chetty continues.

There are approximately 108 operational coal mines in SA, according to GlobalData’s mines and projects database (2023). Coal beneficiation (processing raw coal to meet certain quality standards) generates significant discard. Traditionally managed through surface disposal, this poses long-term environmental liabilities that remain even after mining operations cease. Thus, abandoned or ineffectively closed mines can continue to pose risks to the environment and surrounding communities.

As the mining industry grapples with environmental challenges, planning for responsible mine closure is key. Gloria Dube, a geoscientist at WSP in Africa, urges mine operators to start thinking about mine closure strategies in the initial planning stages, noting: “Ideally, plans for mine closure should form part of every mining stage to avoid the historic trend of mines being abandoned without adequate rehabilitation measures.”

In-pit disposal of coal discard is increasingly recognised as a viable solution for responsible mine closure in SA. A recent WSP study – presented by Dube at the South African Institute of Mining and Metallurgy (SAIMM) Mine Closure Conference in February – explored this method as an alternative to traditional surface disposal. The study highlights in-pit disposal’s potential to mitigate and/or minimise acid rock drainage (ARD) and metal leaching effects on the environment, while aligning with regulatory compliance. 

“In-pit disposal, where discard is placed into mined-out pits, offers a controlled environment that reduces oxygen exposure, a key driver of acid generation,” Dube explains. “The study evaluated the geochemical behaviour of old and fresh coal discard, and revealed that old discard is highly acid-generating, with minimal buffering capacity, while fresh discard initially maintains a neutral pH but risks acidification under extreme oxidation.” 

Overall, the risk assessment indicates that in-pit disposal of coal discard is a viable option if the discard is disposed of below the final pit water level – where no or little oxidation of pyrite will take place – minimising ARD generation. Compared to surface disposal, it significantly prevents secondary mineral formation such as gypsum and jarosite (acid-storing sulphate) and eliminates the need for additional land use, making it a more responsible alternative.

As approaches and technologies advance, Dube admits that plans may change. “Yet planning for and implementing in-pit disposal allows mine operators to mitigate their impacts as they go and keep future issues from becoming major obstacles at the closure stage,” she adds.

Integrating closure plans from the get-go is also better from a profitability point of view, as responsible solutions throughout the mine’s operation cycle reduce end-of-life remediation costs. “These costs can accumulate to millions of rands by the time a mine reaches closure, if impacts are left to accumulate over the years,” Dube says. “While mineral right holders await closure certificates, environmental impacts and legal liabilities remain their responsibilities.”

She goes on to emphasise that effective and responsible mine closure is a critical conversation for South Africa, no matter the size of the operation. “The studies we do now examine responsible practices that can be implemented during operations – helping our clients to meet changing regulatory requirements,” she notes. “It addresses environmental issues throughout the mine’s lifecycle to ensure proper rehabilitation and repurposing that is safe for the environment and the communities living in the area.” 

Chetty expands on this by pointing out: “As the industry shifts towards responsible mining practices, adopting in-pit disposal – selective placement – for coal discard offers a pragmatic solution to reducing environmental footprints while ensuring compliance with evolving regulatory frameworks. Our study underscores the importance of innovative discard and waste management solutions in shaping the future of responsible mining in South Africa.”