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360º PERSPECTIVES | ISSUE 4 | 2015/2016
Breakthrough water-recovery technology In a 2010 report, an expert team reporting to an inter-ministerial committee on acid mine drainage (AMD) highlighted the “urgency of implementing intervention measures before problems become more critical”, listing many environmental and health threats. Professor Leslie Petrik.
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n 2014, the Department of Water Affairs warned that it would cost the country between nine and ten billion rand to purify AMD into potable water. AMD is a global problem, and is a particular concern in South Africa’s gold, coal and copper mining areas. It occurs when water and oxygen react with the sulphur contained in rocks. While this process occurs naturally, mining exposes more of the sulphur when rocks are broken up. During normal operations, water is pumped from the mines and treated. However, abandoned and disused mines are a concern as AMD can seep into groundwater, and eventually pollute streams and rivers surrounding mining areas. Apart from a range of very complex salts, acid mine drainage also holds high concentrations of metals and sulphates. “There’s a whole periodic table of chemicals and minerals in there,” says Professor Leslie Petrik, leader of the Environmental and NanoSciences (ENS) group in the Department of Chemistry at UWC. Prof Petrik’s team has developed a water recovery plant to clean the acid mine drainage. The system uses fly ash, a waste residue that remains after the burning of coal, as well as low-cost nano-materials known as zeolites – with structures so small they are invisible to the human eye and even standard
microscopes. Zeolites are minerals that occur naturally, but synthetic versions can also be produced, as Prof Petrik has done. Both natural and synthetic zeolites have a typical cage-like molecular structure that allows them to trap other molecules, including the toxic elements found in AMD. A pilot study has shown that the water recovery plant works better and cheaper than most other technologies. Studies have found that fly ash zeolites cost as little as one-fifth of commercially available zeolites. The plant has performed well in tests, removing the bulk of the pollutants in the AMD.