THREE-SIXT-E | ALUMNI E-NEWSLETTER | ISSUE 14/SEPTEMBER 2015
ALUMNI E-NEWSLETTER | ISSUE 14/SEPTEMBER 2015
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Turning ash into cash In South Africa, coal-fueled power generation results in at least 36 million tonnes of solid waste called fly ash annually. Low-grade coal has up to 40% inorganic residue that turns into ash on combustion. Most fly ash is collected in huge dumps or ash dams. Older ash disposal sites are rehabilitated by covering the ash with soil and revegetating the sites. Fly ash contains many toxic metals and soluble salts which leach into the environment, polluting surface and ground water. The fine particles may harm humans if they are inhaled. Following extensive studies on fly ash disposal, management and re-use in South Africa, UWC researchers are developing ways to turn the huge dumps of fly ash at power stations into value-added products. “This has the twin benefits of creating new and useful products while also reducing its harmful environmental effects,” says Professor Leslie Petrik, leader of UWC’s Environmental and Nano Science Research Group, which conducted the study funded by Eskom and Sasol. “Fly ash can be used to neutralise and treat acid
Professor Leslie Petrik leads UWC’s Environmental and Nano Science Research Group.
mine drainage from coal or gold mines, reducing major inorganic contaminants in the water to within water quality specifications,” Petrik explains. According to Petrik, fly ash treatment systems involve vigorously mixing the contaminated water with fly ash or allowing gravity flows of the polluted water to run through a bed of fly ash. Studies show that fly ash neutralises the acidity and improves the quality of acid mine drainage, “by removing almost all sulphate and toxic metals in a one-step process.” Petrik adds that because it consists mainly of silica and aluminium oxide, fly ash can be converted into zeolites, a stable and porous mineral solid that can be used in everyday products such as washing powder, or for gas purification and separation. When converted into a geopolymer, it can be used as durable or lightweight concrete replacement material in construction (fly ash is currently used as a cement extender in brick and concrete manufacture). “These scientific breakthroughs provide further proof that there are multiple uses for fly ash and that, in the medium to long-term, discarding this waste in ash dumps can be abandoned,” Petrik says. PAGE ONE