It might sound like fighting fire with fire, but geologist Chen Zhu proposes the application of another industrial waste to the Hungarian bauxite residue spill, with the aim of reducing toxicity via a technique called carbon sequestration. While he says it wouldn't render the residue completely harmless, it would at least minimize the environmental damage.
Bauxite residue is created as a by-product of the aluminum industry, and since there is currently no regulation or imposed company responsibility to neutralize the waste, the corrosive material is often left in container ponds. It is estimated that worldwide there are in excess of 200 million tonnes (220.46 million US tons) of “red sludge” in ponds like this.
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When the pond near Kolontar, Hungary burst on October 4th, it released between 598 and 697 million liters (158-184 million US gallons) of toxic waste – between 79-92 percent of the entire gulf spill that dominated the press this summer. Thirteen people have been killed, 150 injured and several communities destroyed and potentially abandoned. The immediate and long-term damage to the ecosystem is untold, covering an area of 40 square kilometers (15.4 square miles). The devastation spread as the spill reached the Danube, Europe's second-longest river, having already killed all the fish in the Marcal river.
It is ironic, then, that this could be addressed by the addition of another industrial waste – oil field brine – the by-product of oil and gas production. This approach has been proposed by Indiana University Bloomington geologist Chen Zhu, who submitted a U.S. Department of Energy patent application in 2007 describing the technique.
“Carbon sequestration” is the process by which carbon is removed and stored. In this case, the brine provides the medium in which the carbon dioxide can dissolve. Once dissolved, CO2 reacts with water to create carbonic acid which will reduce pH (currently between 11 and 13) and cause the precipitation of salts that would otherwise react with living matter.
It's important to realize, however, that this is both expensive and certainly not a cure-all solution. "By reducing the pH and causing the precipitation of problematic salts, what we're left with is not something that's non-toxic, but less toxic than what we started with," says Zhu.
"Every year millions of tons of bauxite residues are being generated by industry around the world. Disposal ponds are where most of it goes. There is a great need for research on how to improve disposal. Companies don't voluntarily spend money to neutralize waste unless someone tells them to do it, sadly," he adds. "Our technique could be quite expensive. When you have a disaster like the one we're seeing in Hungary, though, I think perhaps companies and governments may think twice about what 'too expensive' means."
Early environmental disaster reports have been revised as the Danube dilutes the sludge, reducing pH, and as salts react with the river's organic matter. There is still, however, the issue of long-lasting arsenic. Greenpeace claims that there are “twice the usual concentrations in red mud,” adding, “This toxic pollution causes an additional long-term risk to the ecosystems and drinking water."