by Sarah Dyke of Venmyn Deloitte Environmental Services and Sabatha Mhlanga of Deloitte
Acid mine water drainage (AMD) has the potential not only to impact the future of South Africa’s mining industry, but also to become a major issue for local businesses across the supply chain as polluted water continues to make its way into the nation’s waterways.
As ground and surface water systems in South Africa are interconnected, acid mine drainage could pollute vast volumes of water with the result that all major industries could be impacted on. Mitigating the potential for substantial environmental, social and industrial impacts resulting from AMD will require solutions that will undoubtedly have major financial implications for business.
Acid mine water is characterised by a low pH, and a high salt and heavy metal content. The current situation in South Africa results predominantly from the disturbance of ore containing an abundance of sulphide minerals, particularly pyrite, which are associated with various base metal-containing ores.
After more than 120 years of deep level gold mining on the Witwatersrand, mining and dewatering has stopped in various areas, either due to the exhaustion of gold resources or due to the uneconomic nature of the remaining reserves.
This has resulted in the groundwater levels rising, and decanting of acid water into surrounding river catchments. Presently, it is probable that these discharges could impact on river systems in Mpumalanga, the Free State, Gauteng, Limpopo, and North West.
Besides affecting South Africa’s scarce water resources, associated risks include reducing levels of food security, pollution of cross-border water supplies, reduced water quality resulting from droughts or flooding, and less suitable water available to major industries.
Attending to the problem is therefore a national imperative and demands a shift from current solutions, such as pumping acid water using submersible pumps to maintain acid water levels below environmental critical levels and neutralising AMD, which provide temporary solutions at best.
The scale of the AMD throughput experienced in the Witwatersrand, and changes in chemical composition in AMD requires the development and implementation of solutions that are able to address the scale and variability in chemical composition of acid water . A commercially sustainable and cost-effective solution is required.
An example of what can be achieved is the use of the CSIR’s ABC water treatment process, which is designed to achieve neutralisation and metal and sulphate removal from AMD by the optimal (efficient) use of readily available and affordable chemicals. The water stage is integrated with a sludge processing stage to recover alkali, barium and calcium (A, B, C) from the chemical sludge produced in the water treatment part of the process.
Due to various challenges facing the resolution process, the implementation and commissioning of these AMD treatment plants has not yet been realised, however, feasible solutions have been researched.
The Emalahleni Water Reclamation Plant has been designed to recover potable water from acid mine drainage from several mines in the Emalahleni (Witbank) area by Anglo Coal and BHP Billiton Energy Coal South Africa (BECSA). The R300 million joint project by two competing global resource companies provides a sustainable solution that benefits the communities that surround their mining operations. Commissioned in 2007, the plant desalinates rising underground water from Anglo Thermal Coal’s Landau, Greenside and Kleinkopje collieries, as well as from BECSA’s defunct South Witbank Mine using the HI recovery Precipitating Reverse Osmosis (HiPRO) process.
It is imperative therefore that the needs and the potential for AMD in each region are understood and mitigated against by the application of insightful technological solutions and active engagement from all stakeholders.