A column study of the impact of layering the different Lac Tio mine waste rock lithologies on drainage water quality

Abstract

In the mining industry, the extraction of waste rocks (WR), without economic value, is needed to access ore deposits. The amount of WR are very large in the case of open pit mines. They are usually stored at the surface in waste rock piles. The presence of reactive minerals such as sulphides in waste rock can lead to the contamination of drainage water that come-out from these waste rock piles. In order to limit the production of contaminants and the volume of drainage water, an innovative method of construction of waste rock piles has been developed. In this context, an experimental waste rock pile was constructed at the Lac Tio mine near Havre-Saint-Pierre (Quebec, Canada) to evaluate the performance of this approach in field conditions. To understand the geochemical mixing between the leachate from the hemo-ilmenite and anorthosite waste rock layers constituting this experimental pile, tests using lab columns that were filled with layers of these two types of materials were run. The anorthosite and hemo-ilmenite waste rock subjected to column tests generated near-neutral drainage (pH ~7) containing up to 4.5 mg/l of nickel, and 1500 mg/l of sulphate. The nickel and sulphate release rates varied from one to two orders of magnitude depending on the type of waste rocks and their configuration (pure or mixed with each other). The drainage water quality was affected by changes in the volume of rinsing water, by the precipitation/dissolution of secondary minerals, and by Ni sorption within anorthosite waste rock. This study demonstrates that the storage of hemo-ilmenite waste rock over anorthosite waste rock is an effective way to reduce Ni levels in drainage waters from the Lac Tio mine materials.