Marine Tailings Disposal Simulation

Abstract

The disposal of mine tailings in deep water body requires comprehensive assessment of the potential environmental impacts, and estimates of the effective storage capacity of the bottom bathymetry for accommodating the anticipated volume of disposed tailings over the life of a mine. A mathematical simulation model was developed for this purpose to predict the distribution and long-term deposition patterns of tailings in a fjord. The model describes the mechanics of the tailings slurry flow along the bottom of the receiving water body and the settling of suspended particles, as well as the redistribution of the deposited sediments due to slumping of unstable slopes. Specific processes simulated in the model also include entrainment at the top of the density current, entrainment associated with internal hydraulic jumps in areas of changing bottom slopes, hindered settling and coagulation of suspended particles, and sediment deposition and bathymetric changes resulting from the deposition of large quantities of tailings. Long-term tailings deposition patterns are predicted by analyzing the flow of the tailings slurry in a series of time increments, from a few months to a year. The bathymetry is assumed to remain unchanged within each time increment, and the model first simulates the steady-state flow field for the tailings slurry along the bottom and the resulting deposition rates for several sizes of suspended particles. Then the estimated tailings deposition rates are combined with slope stability considerations to predict the new bathymetry of the receiving water body. Data from several operating marine tailings disposal systems were reviewed to assess the applicability of specific relationships used in the model. The model was calibrated using data from one of the most extensively studied marine tailings disposal systems, the Island Copper mine in Rupert Inlet of Vancouver Island, British Columbia. Comparison of simulated tailings deposition patterns in Rupert Inlet with data from field observations and measurements suggests that calibration of the model is satisfactory and provides confidence in the capability of the model to predict deposition patterns and suspended sediment concentrations for proposed mines.