UBC Theses and Dissertations
The reclamation of Sullivan mine iron tailings Ames, Susan Eveline
The Sullivan Mine iron tailings pose serious problems to reclamation which result from their high acid producing potential, extreme saline conditions, relatively high concentrations of heavy metals and tendency to cement upon oxidation. Oxidation results in the formation of a hard impermeable layer referred to as a ferruginous cap. Standard techniques of reclamation oriented towards vegetation establishment on the tailings have been unsuccessful due to the adverse physical and chemical characteristics of the tailings. Covering the tailings with soil or overburden may be the only solution to this difficult reclamation problem. However, the question arises whether the acids, salts, and metals, resulting from continuous oxidation, would migrate upwards under evaporating conditions and Capillary movement. This may ultimately lead to the contamination of the overburden, making it ineffective as a cover. To test this, a laboratory column study was set up under accelerated conditions. The experiment had two main objectives: 1) to test whether overburden, placed on the surface of the oxidized iron tailings, would become contaminated, in time, by the acids, salts and metals from the tailings; and 2) to test whether a barrier of gravel between the overburden and tailings would effectively insulate the overburden from potential contamination from the tailings. The experiment was oriented towards examining the processes which would occur if either of the treatments were adopted in a field situation. Predictions of the processes were made from the analyses of solutions extracted at specific locations on a monthly basis and from the analyses of overburden samples obtained through destructive sampling of the columns at 3, 6 and 9 month intervals. Sampling at specific locations and at time intervals yielded the data required for a rate of migration estimation and an evaluation of the factor of time. The results of the study indicated that the barrier was effective. The overburden in the columns with the gravel was not contaminated. The overburden in the second treatment did become contaminated due to the direct contact with the tailings. In this treatment, calcium salts migrated rapidly to the surface in all of the columns within 1 month of the initiation of the experiment suggesting that in a field situation salinity effects may be the dominant factor initially, in' inhibiting vegetation establishment on an overburden cover placed in direct contact with the oxidized iron tailings. The overburden was secondarily contaminated, to roughly 20 cm (from the overburden tailings boundary), by iron, zinc, and copper salts. All of the metals migrated to roughly 20 cm, controlled by pH and most of the contamination occurred within the first 3 months of the experiment. Above 20 cm alkaline conditions caused the precipitation of the metals. These metals were not irreversibly precipitated however, as they were easily removed by acid extraction suggesting that they would be remobilized with the development of acid conditions sufficient to effect their solubility. Iron did not migrate to the same extent as the other metals. This metal became concentrated near the overburden-tailings boundary where it irreversibly precipitated into a hard pan. Aluminum and manganese, which contaminated the overburden, were derived from the overburden. This resulted from the destruction of the overburden minerals by migrating acids and the consequental release of aluminum and manganese into a soluble form. The overburden in the treatment with the gravel became highly desiccated as the connection, through similar particle size, between the water table, located in the tailings, and the overburden, was broken by the gravel. Therefore it is predicted that similar conditions would occur in the field. Consequently, drought resistant plant species or supplemental irrigation would be required if the barrier approach were adopted. The results indicate that the column study was an effective means of studying the kinds of processes which would occur if the reclamation of the tailings was approached by covering them with overburden (or soil). If the overburden is placed directly on the Sullivan Mine oxidized iron tailings it would become contaminated with time and iron pan formation would occur. Covering can be an effective approach to reclamation if a gravel barrier is used to separate the overburden from the tailings.
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