Chemical Interactions in Sulfide Mineral Tailings

This paper reviews some of the work that has attempted to identify species which exist, or are formed, in sulfide mineral tailings, indicating that the resultant chemical reactions, combined with physical properties of the tailings and their surrounds, can explain movement and attenuation of metal concentrations. Additionally, it introduces the consideration of the reactions and speciation which occur in the reduction zone of a sulfide tailings heap, which is a subject that has previously received little attention. As evidence for reductive dissolution of sulfides in tailings, an investigation of the Anaconda Tailings (in Montana, U.S.A.) is cited. The contention that chemical modeling provides an accurate basis for predicting tailings chemistry is refuted. Attempts to model the effects of chemical interactions in sulfide tailings have to date been distinctly inaccurate. The use of various computer codes to aid modeling of the chemical reactions in these tailings has become widely adopted, but the success of the computer techniques relies on the choice of appropriate chemical species that may be influencing the interactions. In many instances the particular species involved may not have been characterised thermodynamically or it may not even be known.