A study of the sulfide precipitation process for the removal of heavy metallic ions from aqueous system



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A new process for the removal of metallic ions in industrial waste waters has been developed using (1) the sulfide ion as a precipitation agent, (2) a cationic organic polyelectrolyte as a coagulant aid, and (3) sedimentation and two micron filtration operations for solids-liquid separation. On the basis of laboratory studies, potential effluent water quality would be four µg/l for chromium, four µg/l for iron and five µg/l for copper. On the basis of both laboratory and pilot plant studies, the effluent water quality was four µg/l for mercury. Maximum allowable, effluent concentrations for copper, chromium, and mercury in both inland and tidal waters of the State of Texas are 1000 µg/l, 5000 µg/l, and 5 µg/l respectively. Process design parameters for sulfide reaction with these metallic ions were evaluated. These parameters include the effect of pH, sulfide reaction time, rate of sedimentation of precipitants, reaction time for coagulant aid and filtration rates. Atomic absorption spectrophotometric techniques for the measurement of metallic ions were very accurate for the detection of these metals in the microgram per liter (µg/l) concentration range.