Treatment of High-Flow, Low-Iron Mine Drainage with A Semi-Passive System

Abstract

Mine drainage flowing at approximately 2600 L/min and containing 5 to 6 mg/L of iron was treated using the influent water to power a dry chemical feed system using lime. After lime addition, the water was directed into four wetland cells with a total area of 0.40 ha. Tracer tests, using a pulse input of potassium bromide, indicated that the four-cell wetland had a detention time of approximately 8 hours. Prior to the addition of lime, the wetland received iron concentrations between 5 and 10 mg/L at a pH of 4.0 to 6.5. As the water flowed through the four wetland cells, pH remained virtually unchanged and iron was not significantly removed with typical iron removal of about 1 mg/L or less. In the summer of 2003, pebble lime (CaO) was added to the influent water using an Aquafix™ system. The system used a split of the influent water to turn a water wheel that is geared to a screw feeder located at the bottom of a hopper containing the lime, which was added at a rate of about 75 kg/day. The pH of the mine water increased from approximately 5 to between 7 and 8. Total iron concentrations were lowered from 6 mg/L at the influent to less than 0.5 mg/L at the effluent. Iron removal rates within the first wetland cell were less than 1 gd -1 m -2 without lime addition and ranged between 6 and 11 gd -1 m -2 with lime addition.