Academic journal article Environmental Health Perspectives

Aluminum Floc Formation. (Metal Toxicity)

Academic journal article Environmental Health Perspectives

Aluminum Floc Formation. (Metal Toxicity)

Article excerpt

When aluminum-rich acidic runoff from mining sites travels through less acidic stream or river water, fluffy flocs of suspended solids form. These flocs carry toxic metals--which normally would have stayed in the streambed--downstream from the mine area, where they can poison aquatic animals and plants. Now scientists have gained further insight into how flocs form.

Gerhard Furrer, a geochemist at the Institute of Terrestrial Ecology in Zurich, and colleagues report in the 27 September 2002 issue of Science that aluminum flocs originate mainly from condensations of the aluminum complex Al[O.sub.4][Al.sub.12][(OH).sub.24][([H.sub.2]O).sub.12.sup.7+], or [Al.sub.13]. These condensations form rapidly and then aggregate as the pH of acidic effluent increases to more than 5. Aluminum-rich acidic solutions form [Al.sub.13] as an intermediate compound, then [Al.sub.13] molecules aggregate to form flocs, says coauthor William Casey, a geochemist at the University of California, Davis.

"Previously it was thought that [[Al.sub.13]] was quite rare and kind of a curiosity that you find in some solutions," says Casey. "We now think that it is very, very common--that is the real important finding of this paper," he says.

Paul Bertsch, director of the Savannah River Ecology Laboratory in Aiken, South Carolina, and colleagues had proposed in a chapter of the 1996 text The Environmental Chemistry of Aluminum that [Al. …

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