The business unit of water, environment and forestry technology, at the Council for Scientific and Industrial Research in Pretoria, is home to a key Technology and Human Resources for Industry Programme (Thrip) project that looks set to help solve the problem of what to do with waste mine water.
Under the leadership of Dr JP (Jannie) Maree, the project has developed landmark processes that use limestone to neutralise acids in waste mine water, and bacteria to remove sulphates from mine effluent.
The production of acid mine drainage (AMD) in the mining industry has always been a key pollution issue.
AMD is metal-rich, saline and usually acid water, formed from chemical and biological reactions between water and rocks containing sulphur-bearing minerals. Ore or coal-mining activities expose rocks containing sulphur-bearing pyrite (iron sulphide), which subsequently reacts with water and air, forming sulphuric acid and dissolved iron in a highly acid run-off.
This acid run-off dissolves heavy metals such as copper, lead and mercury into ground or surface water, contaminating drinking water, adversely affecting plant and animal life and corroding infrastructure such as pipes and bridges.
Maree’s project has made tremendous inroads into solving the AMD problem, and, in the process, has disproved the popular belief that it costs more to be environmentally friendly.
In fact, the research team has found that it can cut the cost of cleaning up the acid water by half.
They have achieved this with the use of waste calcium carbonate from the paper industry. This calcium carbonate is a substantially cheaper alternative to obtaining lime by the traditional method of heating limestone to 1 000°C, burning coal as an energy source. The waste calcium carbonate is also more environmentally friendly, as heating limestone by burning coal releases large amounts of carbon dioxide into the atmosphere, ultimately damaging the ozone layer.
The cheap calcium carbonate is converted to a slurry to enable a constant density to be achieved. Maree’s team has developed a density meter to control the concentration of the slurry as it is introduced to the neutralisation process.
This cheap calcium carbonate can also be used for partial sulphate removal at a cost of 10c a kilogram of sulphate removed. However, the sulphate values of the water after this initial neutralisation are not sufficiently low for safe release back into the environment and the water is treated further, this time with the more expensive lime treatment at a cost of 28c a kilogram of sulphate removed.
Finally, a third process is used for removal of the remaining sulphates in the water. This process is a biological one, using an organic material such as ethanol, sugar, hydrogen or carbon monoxide as an energy source. It costs R1,50 a kilogram of sulphate removed.
Because the majority of the neutralisation and sulphate removal are achieved by treatment with cheap calcium carbonate, the cost of the entire neutralisation process is considerably reduced. Indeed, the Navigation and Kromdraai coal mines near Witbank would have had to budget R8-million for acid water neutralisation each year. The project’s processes reduce that figure to R4-million.
These findings have made a huge impact on the project’s industry partners, among them Anglo Coal, BCL Botswana and Ticor Empangeni, all of which are set to benefit from the construction and testing of a full-scale treatment plants at the mentioned sites.
Maree has devoted the past 10 years to this project and is very proud of the leaps forward made over that decade. The Water Research Commission supported the work during the initial stages of development, while Coaltech supported the research to determine its suitability for the coal-mining industry. Thrip has been involved in the work since 1999 and Maree says the sponsorship provided by Thrip and his industry partners has enabled his 15-member team to advance quickly to the implementation stage of development.
‘Add to this the wonderful collaborations we have with the universities of Stellenbosch, Potchefstroom, Venda, Pretoria and Technikon Pretoria, and you can understand how we have come so far so quickly,” he said.
‘We already have a full-scale limestone/lime neutralisation process at Ticor in Empangeni, a pilot scale biological sulphate removal plant, limestone handling and dosing system, and a full-scale limestone neutralisation plant at Anglo Coal’s Navigation mine, and density meters in operation,” said Maree, adding that Kromdraai mine, Ticor and BCL Botswana also have limestone handling and dosing systems in operation.
‘These projects also have considerable commercial spin-offs. Thuthuka Project Managers was sub-contracted to be responsible for the construction of all our plants and all of our powder calcium carbonate is supplied by Aqualime, which operates under licence from Sappi. In addition, we have the likes of Golder and Associates Africa and Weir-Envig licensed to commercialise our processes,” said Maree.
‘All of this means that our research is benefiting a wide range of industries and commercial concerns, as well as ultimately helping sustain our environment and save money while doing so.”