ABSTRACT
Precipitation is the treatment process most often employed to remove heavy metals from metal-finishing wastestreams. This method is used by a vast majority of the electroplating facilities which treat aqueous metal bearing wastes. Precipitation techniques practiced on aqueous metal wastes include hydroxide, sulfide and carbonate precipitation processes. Sulfide precipitation is highly effective in the removal of cadmium, cobalt, copper, iron, mercury, manganese, nickel, silver, tin, and zinc. Carbonate precipitation is effective in removing cadmium, nickel, and lead at a slightly lower pH than either hydroxide or sulfide techniques. Hydroxide precipitation is used in treating aqueous metal wastestreams. This technology offers an effective alternative for removing heavy metals from spent process wastewaters. Cyanide plating rinse waters, resulting from high plating bath pH values, will acquire background carbonate from the uptake of atmospheric CO2. Optimum treatment efficiency for cadmium can be obtained at neutral pH in the presence of sufficient carbon.
