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Turning ash into cash

Author: Alumni Relations Office Tel: 021 959 2143

The coal ash dumps of the Highveld and Mpumalanga pose a significant environmental threat.

Turning ash into cash

The coal ash dumps of the Highveld and Mpumalanga pose a significant environmental threat. This could soon be resolved thanks to groundbreaking research at UWC, in collaboration with the Cape Peninsula University of Technology (CPUT).

Professor Leslie Petrik of UWC’s Department of Chemistry is leading research to prove that fly ash, the residue from burning coal at power stations, can provide a cost-effective alternative to cement.

Fly ash constitutes about 40 percent of the low-grade coal burned in South Africa’s coal-fired power stations, as much as 35 million tons annually.

The ash is dumped near the power stations, much of it mixed in slurry dams with the brine (extremely salty water) condensed from spent steam that has to be removed from the power stations during the process of electricity generation. As new legislation will prohibit this practice, finding solutions has become imperative.

The ash consists of very fine particles which are corrosive and abrasive and contains many toxic pollutants such as mercury and chromium.

The UWC-CPUT team aims to prove fly ash can be turned into lower-cost roof tiles, bricks, paving stones, and building elements like lintels, fire-retardant panels and insulation material.

The building industry already used up to 6 percent fly ash in concrete and plaster, as a cement extender.

During the production of cement, the ingredients must be heated at very high temperatures to produce the rock-like substance, which is then ground into fine-powdered cement. This is hugely costly in terms of carbon dioxide generation. The UWC-CPUT research aims to show that cement can be entirely replaced with fly ash.

“Fly ash has already been mined in the form of coal, and has been through the combustion process during power generation. It is there lying on the ground. If you activate it chemically, it turns into the equivalent of concrete without using cement. This means that it’ll be cheaper and offer huge energy savings,” says Prof Petrik.

Fly ash is also fire-retardant, which could offer alternatives in low-cost housing to replace chipboard and gypsum board, both highly flammable.

“Our research began about seven years ago with Sasol. Once that funding ended we received funding from the National Research Foundation to carry on with our work,” says Prof Petrik.

The team has funding from the Technology Innovation Agency to develop prototype roof tiles, in collaboration with CPUT’s Professor Tunde Ojumu and his students, who are process engineers.

Commercial partners will be approached once the prototype work has been completed.​

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