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Chemicals for Re-use from Waste Water

Mining processes often cause severe water pollution. In one instance, mining operations near Prague in the Czech Republic produced acid-laden waste water that has accumulated in deep underground caverns threatening the aquifer that supplies drinking water to the city, about 70 miles south of the mine.

In 1995, a two-step site cleanup began, carried out by Resources Conservation Co. International (RCCI), a U.S. company. First, the acid water is pumped to the surface. Then the stream, which contains sulfuric acid and aluminum ammonium sulfate (ammonium alum), evaporated and crystallized to recover freshwater for reuse and the ammonium alum, a widely used water-treatment chemical.

To ensure that iron in the waste water does not precipitate in the ammonium alum crystals, spoiling the chemical's commercial value, RCCI enlisted the help of the Advanced Electrolytic Technologies (AET) group of the Electrode Corporation. AET designed 16 electrochemical cells, which reduce iron levels in the waste water. The plant, on-line since the end of 1995, is able to treat 600 gal/min of waste water.

Electrochemistry is cleaner and potentially more cost effective than traditional reducing methods, such as the use of reducing agents. For example, treating the 600 gal/min stream with sodium sulfite would require nearly 10,000 lb/d of the reducing agent. At US-Dollar 0.30/lb, this sodium sulfite would cost $3,000U.S./d. In addition, operators would face treatment, transportation and disposal costs for the 6 tons/d of sulfate sludge produced. The electrochemical approach produces no sludge, and electricity costs (which vary from region to region) are a fraction that of reducing agents. (From "Environmental Engineering World")

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