Using Acid Mine Drainage to Recover a Coagulant from Water Treatment Residuals

We evaluated the recovery of aluminum from water treatment residuals by acidification using acidic coal mine drainage as an extraction solution. The water treatment residuals had Al and total Fe concentrations of 1.2 and 1.3%, respectively, based on mass. The influence of contact time of the mine water with the water treatment residuals and the percent of excess sulfate were assessed. The results showed that 28 min of contact and 100% of excess sulfate allowed recovery of >90% of the Al. Color was reduced from 25.9 to 0.8 total color units (TCU) and turbidity was reduced from 6 to 0 nephelometric turbidity units (NTU). The recovered coagulant performed appropriately in water treatment tests, based on physical–chemical parameters. The only parameter that requires more attention is antimony, which was close to the maximum concentration limits for drinking water.