Abstract
Mill tailings collected from seven copper mine mill sites in the western United States were examined by researchers from the Bureau of Mines for metal dissolution properties using a column leaching procedure involving a formulated “western rain” leachant. Studies investigated effects of height of waste column, wet/dry cycle, and maximum leachability of waste tailings. Further studies on selected samples indicated that treatment of acid-producing tailings with chemical stabilizers such as phosphates and carbonates did not greatly affect mobilization of heavy metals leached from these samples. Increased metal mobilization from unsaturated columns was often associated with decreased leachate pH and increased sulfate production, but was not observed in all samples examined. Results from these and other studies suggest that the driving force for metal dissolution and/or acid formation in unsaturated mine tailings is the oxidation of metal sulfides by atmospheric oxygen. The maintenance of tailings at or near saturation or the exclusion of atmospheric oxygen appear to produce leachates of nearly constant to slowly decreasing metal concentrations with each subsequent leaching.
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