Influence of Sulfate Ions on the Rate of Cadmium Sulfide Precipitation during the Treatment of Cadmium-containing Wastewater with Pulverized Iron Sulfide.

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The treatment of wastewater containing heavy metals at a nearly neutral pH with pulverized iron sulfide was investigated. Cadmium-containing wastewater was treated to produce sulfide precipitates. In general, the solubilities of sulfides are lower than those of other salts, so it is preferable to remove heavy metals from the wastewater with sulfide ions and to fix the metals as sulfides. The overall reaction rate for the formation of cadmium sulfide was examined by the change in cadmium concentration observed during the formation process of cadmium sulfide. In particular, attention was paid to the coexisting sulfate ions which may influence the reaction rate.<BR>As a result, it was found that the dissolved sulfate ions came from the pulverized iron sulfide at a nearly neutral pH. Thus, the sulfate ions interfered with the formation of cadmium sulfide precipitates. It was also found that the overall reaction rate in this system was controlled by the rate of dissolution of cadmium sulfate rather than being due to the formation of cadmium sulfide.
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