A numerical modelling approach to assess long-term unsaturated flow and geochemical transport in a waste rock pile

Abstract

This article presents an approach to investigate unsaturated water flow and geochemical transport in sulphidic waste rock piles using numerical simulations with stochastically distributed material properties. The water retention curve and hydraulic conductivity function are used to represent spatial variability for water flow, while distributed geochemical parameters are used for reactive transport. The results illustrate how the spatial correlation of hydraulic properties affects the moisture distribution and flow within the pile, which in some cases creates local preferential flow paths. The numerical simulations also show how sulphide mineral oxidation rates can be influenced by the grain size, sulphide fraction and moisture content distribution, which may explain the large spatial variations observed in the composition of drainage water. Such simulations help to better understand the long-term response of a typical waste rock pile.