Magnesite softening reverse osmosis and valorisation technology

The CSIR has developed a zero liquid discharge technology to minimise the ecological footprints of acid mine drainage (AMD). AMD has been a thorny issue in South Africa for many decades and continues to contaminate both freshwater sources and the environment.

Acid mine drainage is a direct result of the weathering of sulphide-bearing minerals during and after the mining of valuable minerals, such as coal and gold. These hazardous chemicals have a direct effect on living organisms and the host environment; hence the urgent need to contain and mitigate the risk of contamination.

Conventional technologies to treat AMD often relied on the use of a lime and filtration technology that generated toxic sludge. This has prompted the need to look for alternative technologies with a minimum or zero ecological footprint.

The CSIR’s quest to find an alternative cleaner technology to curtail the impact of AMD on the environment resulted in the development of a robust treatment technology called magnesite softening reverse osmosis.

The game-changing technology relies on a combination of activated magnesite, softeners and reverse osmosis to recover valuable minerals at different stages of the process. The technology has been tested and validated at a laboratory and a pilot plant with a 20 000 litre per day capacity, located at the CSIR in Pretoria. The plant’s robustness has been assessed against effluents that emanate from coal and gold mines.

The CSIR has designed and is at the advanced stage of constructing a modular pilot plant with a capacity of 0.5 million litres per day. This initiative will foster the concept of a circular economy, waste valorisation and beneficiation. Revenue generated from the re-sale of recovered minerals will offset the running costs of the system, making it self-sustainable.

The quality of effluent can be controlled through the installation of reverse osmosis membranes to produce high-grade water. The process has been patented and its efficiency as a means of converting waste streams into an environmentally friendly resource has been demonstrated over five years.

Research and development partners, to date, include Exxaro, one of the largest black-empowered diversified mining companies in South Africa; South32, a globally diversified mining and metals company and the Trans-Caledon Tunnel Authority.

Companies interested in discussing the use of the plant or licensing of the technology can contact the CSIR Water Resource Management Research Centre.