Modelling the impact of physical and chemical heterogeneity on solute leaching in pyritic overburden mine spoils

Spatial variability of physical and chemical properties may affect acidific ation and acid mine drainage in sulfide-bearing overburden mine spoils. Thi s study compares heterogeneous with vertically layered and horizontally ave raged spatial distributions of chemical components in a generic 2D-vertical spoil cross-section with heterogeneous distributions of water and air cont ents and of water flux densities. The initial spatial distributions of the fraction of sulfur and the pre-oxidized zones follow autocorrelated random functions. The initial background chemistry distribution is correlated to t he degree of pre-oxidation using five classes of differing initial chemical systems. Processes considered include variably saturated water flow, oxyge n diffusion, shrinking-core kinetics of pyrite oxidation, multicomponent re active solute transport, and geochemical equilibrium reactions between aque ous and mineral components. Spatial distributions were generated using the SGSIM-GSLIB geostatistical simulation algorithm and estimated parameters. R esults: show differences in vertical concentration profiles of chemical com ponents and in integrated breakthrough curves at 30 m depth between the het erogeneous and the layered case for both-high and low-sulfur content scenar ios. Differences are relatively large in the beginning and with respect to the distribution of solid phase components. A heterogeneous sulfide mineral distribution results in vertical spreading of the oxidation front while pr ecipitation and dissolution of the secondary minerals affects the acid mine drainage, by locally retarding and releasing the solutes. (C) 2001 Elsevie r Science B.V. All rights reserved.