Effects of less impermeable sealings for mine piles

Abstract

Saline contaminants from potash mining endanger aquatic ecosystems. Uncovered piles of potash tailings release high amounts of chloride and sodium. Conventional coverage systems with a transpiration-intensive vegetation on a soil layer reduce percolation water only to some extent and do not protect the surrounding environment sufficiently. Powerful sealings are used to cover other mining deposits but are still uncommon for potash tailings piles. Because clay for constructing a sealing is limited, an alternative coverage system is required. The aim of this study is to identify a coverage system that conserves resources but also effectively minimises the release of contaminants. Water balance components (evapotranspiration, runoff, storage) of 44 different coverage systems were modelled with BOWAHALD. 4 model settings describe common conventional coverage and 40 settings include an additional sealing. The chosen coverage systems differ in soil layer thickness (1.5 to 3 m), vegetation productivity as well as in the thickness (10 and 50 cm) and impermeability of the sealing (kf values range between 8 × 10−08 and 5 × 10−09 m/s). The most impermeable sealing is also common whereas the less impermeable sealings are new designed. The results show that an additional sealing always outperforms (max. 26% percolation rate) conventional coverage without an additional sealing (28.7% percolation rate). Furthermore, a coverage system with less impermeable sealing and lush vegetation can substitute a coverage system with a more impermeable sealing and sparse vegetation without changing the percolation rate. Site-specific examinations, considering geographical orientation and inclination, show that a more impermeable sealing works best on north-facing slopes, whereas lush vegetation performs better on south-facing slopes. A mixed coverage according to site-specific performance reduces the percolation rate more than uniform coverage and requires less sealing material. I conclude that a mixed and site-specific coverage system is the most effective one to improve water quality in post-mining landscapes.