The Origin of Aluminum Flocs in Polluted Streams

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Abstract
About 240,000 square kilometers of Earth's surface is disrupted by mining, which creates watersheds that are polluted by acidity, aluminum, and heavy metals. Mixing of acidic effluent from old mines and acidic soils into waters with a higher pH causes precipitation of amorphous aluminum oxyhydroxide flocs that move in streams as suspended solids and transport adsorbed contaminants. On the basis of samples from nine streams, we show that these flocs probably form from aggregation of the ɛ -Keggin polyoxocation AlO 4 Al 12 (OH) 24 (H 2 O) 12 7+ (aq) (Al 13 ), because all of the flocs contain distinct Al(O) 4 centers similar to that of the Al 13 nanocluster.