REFINEMENT OF IRON OXIDE RECOVERY METHODS FOR AMD TREATMENT SYSTEMS

Abandoned Mine Drainage (AMD) from coal mines commonly contains elevated concentrations of iron. When this water is alkaline, naturally or through pretreatment with limestone, passive treatment is a highly effective treatment alternative. In passive systems with pH 6-8, Fe oxidizes to form iron oxide solids that precipitate in ponds and wetlands, creating a high quality effluent to the receiving stream. The long-term success of this approach relies largely on the retention time of the system which is eroded as the ponds fill with iron sludge. In order to sustain good treatment, the ponds must be periodically cleaned out. For the last 14 years, Iron Oxide Recovery, Inc. has been removing sludge from passive treatment ponds, dewatering the recovered solids, and processing them to marketable iron oxide products. Approximately 5 million gallons of slurry have been recovered and processed to 4,000 tons of iron oxide solids. The paper will detail various methods that have been tested for removing slurries from ponds and for dewatering the recovered slurries. Efficient removal of iron sludge requires appropriate pumps and water management. Dewatering is achievable by a variety of technologies including frame presses, belt presses, geotubes, and passive. The pros and cons of each technology will be discussed. The final processing of the dewatered iron oxide involves drying and screening. A passive drying approach will be highlighted. Advances in the recovery of iron slurries from ponds have resulted in increased appreciation regarding the design of ponds for efficient sludge removal. Passive systems are now being designed with features that facilitate iron sludge removal and assure continued water treatment during sludge removal activities. These advances in solids management are solidifying passive treatment as the most cost-effective and reliable technology for treating Fe contaminated coal mine drainages.