Dynamic Tailings Basin Study: Final Report

Abstract

The Hibbing Taconite Company operates an iron mine and mill in northern Minnesota, USA The tailings produced by the mine are disposed in a tailings basin. The point of feed is the upstream end of one of the sub-basins within the tailings pond, the West Area #1. The tailings deposit forms an aggrading alluvial fan within each sub-basin. Projections of tailings deposition rates within the West Area # 1 indicate an imminent over-filling at the upper end of the basin. This premature filling, which threatens to reduce the lifetime of the tailings pond below design expectations, is the result of slopes in the upper part of the deposit which are steeper than anticipated at the time of basin design. st. Anthony Falls Laboratory, University of Minnesota, under contract from Barr Engineering, has undertaken a combined field, experimental, and theoretical study of the dynamics of tailings-basin sedimentation, with a particular focus on the physical controls (i.e., water discharge, sediment load, and sediment size distribution) on upper fan slope. This study has provided the tools necessary to evaluate the relative effectiveness of several tailings management schemes intended to alleviate the problem. The tools were developed in two stages. In Stage 1, the analysis was restricted to West Area #1 due to the availability of specific data pertaining to that area. The results for Stage 1 were based on the assumption that all future tailings would be stored in West Area #1. The assumption was made for illustrative purposes only. The results of the calculation allow, however, for inferences concerning the performance of the entire pond. In Stage 2, a numerical model was developed to describe filling of the entire basin. The model allows for the testing of a variety of schemes for tailings management.