Mine Water Treatment with a Pilot Scale RAPS-System
In 1985, economic reasons caused the closure of the fluorspar mine “Hohe Warte” near Gernrode in the German Harz Mountains. Though remediation works were conducted in the preceding years, mine water is currently flowing out freely of the dewatering adit and is impacting the environment and the receiving brook. The mine water is characterised by low pH-values, high conductivities and contains considerable amounts of iron, manganese, and arsenic. Annually, the mine discharges 0.7 Mio m of mine water with 7.8 tons of iron, 3.8 tons of manganese and 13 kg of arsenic. Therefore, the discharging mine water has a great potential to affect the quality of the receiving streams and resulted in a decrease of biological diversity. Based on hydrogeological and hydrochemical investigations, a passive treatment system would be able to treat the mine water. In February 2003 a pilot system was installed near the dewatering adit consisting of a settlement pond, a RAPS system and a constructed wetland. It could be shown that this passive system was able to treat an aliquot of the mine water down to ecologically acceptable standards.
Passive Treatment Systems for Acid Mine Drainage
PASSIVE TREATMENT SYSTEMS provide an alternative method for removing metals from acid mine drainage. There are several types of passive treatment systems; they may be used on their own or in combination to treat difficult effluents. The type of system selected is dependent upon the chemistry of the acid mine drainage and the flow of the discharge, as well as State and Federal regulations. Passive treatment systems do not require power and are less expensive than active treatment systems. They also require less maintenance, which makes them advantageous in remote locations.
Zinc removal from hard, circum-neutral mine waters using a novel closed-bed limestone reactor
Abstract Zinc is an ecotoxic metal commonly associated with discharges from abandoned mines. Previous difficulties in removing zinc from circum-neutral mine waters with anaerobic wetlands have led to the development of a novel method to remove zinc from some mine waters of the North Pennine Orefield, UK. Geochemical modelling indicates that zinc carbonate (smithsonite, ZnCO3) should precipitate from these mine waters if pH can be raised from the ambient value of 7.5 to 8.2. It was postulated that this could be achieved through closed-system reaction with calcite, in a simple gravity-flow, sealed bed of limestone gravel (an “anoxic limestone drain” (ALD)). Previous applications of ALD technology have been for strongly acidic mine waters, with the intention of achieving wholesale alkalinity generation. In this new application, the ALD is meant to achieve a marginal increase in pH to encourage removal of zinc from the water by smithsonite precipitation. Testing of this concept by laboratory and field experiments has yielded encouraging results. The laboratory system gave an average of 50% reduction in zinc concentration over a 14 h retention period. The field system presently gives a 22% average reduction in zinc concentration over a similar retention time. With further development, it is hoped that ALDs could become a cheap and attractive unit process for treating drainage from abandoned mines, particularly in situations where conventional treatment is not feasible on economic or practical grounds.