Heavy metals are frequently found in streams affected by acid mine drainage (AMD) which continues to be an important water pollution problem in regions of the United States and around the world. Current treatment technologies are either inadequate or too expensive to be employed at numerous abandoned mine land sites which are sources of untreated AMD. For example, limestone used for pH adjustment becomes coated with iron oxyhydroxide, reducing its solubility; consructed wetlands have sometimes een successful, but create metal-contaminated soils and potentially contaminate groundwater. The treatment employed for acidic iron wastewaters from active mines and certain industrial processes involves rapid neutralization with lime or caustic soda followed by sedimentation. The iron sludge created requires dewatering and has a high cost for ultimate disposal, particularly if classified as a hazardous waste.
展开▼
