FACTS AND MYTHS ON THE EFFECTIVENESS OF WATER COVERS TO SUPPRESS SULFIDE OXIDATION AND METAL LEACHING - FIELD AND LABORATORY EVIDENCE

摘要

Largely due to the low diffusivity of dissolved oxygen in water, reactive tailings are often rendered harmless upon disposal underwater. However, both field observations and results of simulated weathering studies in the laboratory have shown that as long as a water cover remains oxygenated, sulfides exposed at the tailings/water interface are susceptible to oxidation. The two primary factors that determine whether or not net acid generation is to occur are the alkalinity balance in the water cover and the rate of deposition of a more efficient oxygen scavenger like organic matter to further isolate the submerged tailings. Even if net acid generation may not materialize, metal leaching can still occur as a result of galvanic interaction. Moreover, because of the changing redox conditions, many potentially deleterious trace elements with multiple oxidation states like arsenic and antimony are subject to remobilization from mine wastes disposed underwater. Thus, the choice of a proper management alternative for the long-term disposal of reactive mine wastes must duly consider the composition of the mine wastes as well as the environmental settings of the site after mine closure.