Mine water treatment plant under way

The wastewater treatment demonstration plant to be built at Anglo Coal’s operations in the Emalahleni municipality, using the GypSLiM process, is under way and product recovery and industrial waste recycling company Sulphide Tech process engineer Shaan Oosthuizen says that plant construction is progressing well, with one building already constructed.

In March last year, the Council for Scientific and Industrial Research (CSIR) and Sulphide Tech signed a R6-million contract with Anglo Coal to build a GypSLiM demonstration plant. The aims of building the demonstration plant was the recovery of products from waste gypsum gener- ated by the Emalahleni project, to create drinking water from acid mine water. Large volumes of mine water contain high levels of total dissolved salt, which is not suitable for human consumption or industrial use.

The Emalahleni water reclamation project will produce 20 Mℓ/d of clean water for the Emalahleni municipality, and 5-Mℓ will be supplied to neighbouring Anglo Coal. At present, only a small portion of the gypsum from the main plant will be used in the pilot plant. However, after successful completion of pilot tests, the large-scale plant will convert about 1 000 t/d of waste gypsum.

The demonstration plant is slightly behind schedule and the original budget has been adjusted owing to factors such as the inclusion of a new partner, and process advances enabling, for instance, the production of high-purity calcium carbonate. The core technologies of the demonstration plant will begin to run on a continuous basis from December 2008 for final evaluation.

The GypSLiM process converts waste to useful products, it provides the means for acid mine drainage treatment through the recycling of calcium carbonate produced in the process, and neutralises acid.

The GypSLiM process entails a number of steps. Oosthuizen explains that acid mine water contains sulphuric acid, which is neutralised with limestone, through a patented process to form gypsum, which precipitates out of the water. In the GypSLiM process, the gypsum is con- verted to produce limestone and sulphur, and in the event of any magnesium pollutants present in the water, magnesite is produced. The resultant limestone can be recycled to the point where acid is neutralised, or it can be sold as a purified product, along with sulphur and magnesite that are also produced. A secondary step can be added to the process to produce cement and lime. Recent adaptations to process design offer high-purity by-products, and related equipment is being delivered for the treatment plant over the next few weeks.

Oosthuizen expects that 1 t of gypsum will produce about 700 kg of limestone and 200 kg of sulphur. The quantity of magnesite extracted will vary, depending on the values of magnesium in the treated water.

The technology for the pilot plant was developed in-house by Sulphide Tech, with assistance from the CSIR and the National Research Foundation’s technology and human resources for industry programme, which aims to boost South African industry by supporting research and technology development. The core technologies have been captured by the CSIR in patents, and provisional patents are presently being filed for additional breakthroughs.

Sulphide Tech is finalising two new projects to treat polluted mine water. The company will supply core technologies for efforts that aim to clean the polluted mining water on the West Rand. The Integrated Process, developed alongside the CSIR, holds the promise of providing clean water to an area presently under threat of acid mine drainage decant, which contains high levels of radioactivity, says Oosthuizen. A pilot plant has been constructed in the area and the process is being evaluated for large-scale roll-out, as the decant poses a threat to the cradle of humankind.

Moreover, should a second pilot plant for treating effluent from gold mines on the West Rand prove viable, up to 70 Mℓ of polluted water, producing several thousand tons of waste gypsum a day, will be treated with Sulphide Tech’s pro- cess, he says.

With rapid price increases of sulphur and sulphuric acid, from $70/t to $600/t in less than a year, significant interest has been expressed in this environment-friendly method of converting waste gypsum to sulphur and sulphuric acid. A joint venture is also being negotiated with a multinational mining technology firm to recycle sulphuric acid at copper leaching operations, for example.

Locally, despite increased interest for the gypsum conversion process from South African fertiliser manufacturers, not all companies are equally responsive, says Oosthuizen, despite up to 11 000 t/d of waste gypsum being released in oceans in South Africa.