A Review of Scale Factors for Estimating Waste Rock Weathering from Laboratory Tests

摘要

Authorization to start or expand most hardrock mines now requires the proponents to estimate a priori the environmental impacts they may have on surface and groundwater water quality. These estimates are often based on the intrinsic environmental characteristics of mine waste measured in laboratory-scale tests, including total concentrations of major minerals and regulated metals, soluble metals liberated by aqueous leach tests, and rates of sulfide-mineral oxidation and solute release under standard weathering conditions. Waste-rock leach rates under full-scale weathering are then estimated by "scaling" from these laboratory rates to field conditions. This paper reviews laboratory- and field-scale studies of sulfidic waste rock weathering, then provides updated estimates of scale factors based on moisture content, fragment size, temperature, contact (i.e., the fraction of rock actually flushed by unsaturated flow), and oxygen concentration. The results provide a basis for making screening level estimates of mine-water impacts at proposed mines. Further, the ranges in scale factors provide a basis for conducting probabilistic estimates impacts. Ultimately, the goal is to improve mine permitting by identifying the ranges for these critical scale factors that will bracket reliably estimates of pollutant release from full-scale mine waste facilities.