Experimental and numerical evaluation of the potential reuse of waste rock as an evaporation barrier in engineered cover systems: effects of particle size

One of the key challenges for the mining industry is the development of effective and durable management, closure, and reclamation strategies for acid mine drainage (AMD) generating tailings storage facilities (TSF). The elevated water table technique is particularly effective in preventing AMD under humid and temperate climate, as it reduces oxygen fluxes by maintaining the tailings saturated. A protection layer made of coarse-grained material (capillary break) is often needed to enhance water infiltration and reduce evaporation by reducing capillaries upward flow. A sustainable approach therefore consists in reusing waste rock to build this layer, reducing surface-stored mine waste and the environmental impact of borrow pits. However, the heterogeneity and reactivity of waste rock have so far limited their large-scale valorization in cover systems. The objective of this research was to evaluate the potential reuse of different size fractions of waste rock in an evaporation barrier. Laboratory column tests were carried out to evaluate the effectiveness of the cover made of waste rock to control water balance. Results indicated that waste rock containing fine fractions were less efficient in reducing evaporation than coarser fractions without fines for shallow water table. Numerical simulations were also carried out successfully to reproduce the effect of particle size on evaporation fluxes. This study underlines the importance of optimizing the particle size distribution in the design of evaporation barriers.