Processing chemical wastes for product benefits
Not only does South Africa experience significant environmental pollution from sulphur waste (liquid, solid and gas), but the solid waste that includes the slush that is produced when water is treated by the mines contain valuable deposits that are lost.
The Western, Central and Eastern Basins of the Witwatersrand produce 200-million litres of acid mine water.
During desalination of saline water, large brine streams are also produced. In addition, the fertiliser industry produces 15 000 tonnes per day of waste gypsum as sulphuric acid is used for the processing of phosphate rock into phosphoric acid.
Professor Jan Maree, Rand Water Chair in Water Utilisation and the team leader of the Treatment Group at the Tshwane University of Technology (TUT), in conjunction with its industrial partner on the project, Key Structure Holdings, focused on developing a cost-effective solution for the treatment of acid water and brines.
“Our focus was to minimise the cost of treatment of mine water. The team developed a process where limestone could be used for the removal of the most prominent components in mine water. In the case of the processing of the slush, we aimed to recover the value product inside it, such as sulphur and rare earth metals,” says Maree.
He says that through Key Structure Holdings, the university had an industrial partner who could provide it with the necessary assistance on the project. This has resulted in the development of a limestone neutralisation process that has already been implemented at several places in South Africa, Botswana and Australia with considerable cost savings when compared to other acid neutralisation processes.
“Current improvements allow a further saving in alkali cost of 50%. This is due to the fact that limestone, the cheapest alkali, can be used for removal of iron, the main component in acid mine water,” adds Maree.
Furthermore, a process has been developed for the processing of gypsum. During this, gypsum powder is thermally reduced in a kiln, using coal as reducing agent, to produce calcium sulphide as starting material for the production of calcium carbonate and sulphur.
“South Africa imports sulphur to the value of R6-billion a year. The proposed projects will result in huge opportunities for local and foreign investments. The processing of waste gypsum into sulphur will require large investments for the construction of full-scale plants,” he says.
Such investments will offer large benefits for the national balance of payments. Sulphur that is currently imported will be produced from processed mine-water and gypsum wastes. Also, less water will need to be imported through expensive pipelines and tunnels from the Lesotho Highland Scheme, for drinking water.
This supplement has been paid for by the Mail & Guardian’s advertisers. Contents and photographs were supplied and approved by the NSTF.