Two pit lakes formed in mine pits in an arid region. To estimate potential future pit lake water quality composition, and given uncertainties and data gaps in the dataset, eight scenarios were modelled for each pit lake using end-member input for the most-sensitive and least-understood input parameters. Key inputs were the hydraulic conductivity of the aquifer, and the acidity of pit wall runoff. In all but one scenario, both pit lakes remained circumneutral, but water quality is unlikely to meet water quality standards in any scenario because arsenic exceeds the agricultural use standard. The estimates were used to prioritize field programs to reduce uncertainty.

Water is an important factor in the stability of large mine slopes. Groundwater pressure on a potential failure surface in a slope reduces the effective stress on that surface, which reduces frictional strength of that surface and the Factor of Safety of the slope by as much as 40%. This effect is normally considered in standard slope stability analyses. However, water pressure acting on the surface of a potential failure mass also exerts a lateral driving force, which in saturated slopes generally exceeds the gravitational driving force, and results in a further reduction of the Factor of Safety of more than 50%. This water-drive is rarely correctly considered in standard slope stability analyses. For slopes that can have positive groundwater pressure within them, ignoring water-drive leads to dangerously under-estimating the likelihood of failure. This paper presents the theoretical basis for including water-drive in slope stability analyses, quantifies the magnitude of the failure risk that is introduced by water drive, and provides stabilization strategies that manage those risks.

With the closure of several dams, tailings disposal in dry stacks has become a management challenge from both geotechnical and environmental perspectives. One key concern is the quality of the effluents generated by these new structures. It is crucial to predict the chemical composition of the drainage that will pass through the bottom drains and eventually be discharged into the environment. Leading global guidelines and best practices for effluent management in mining (e.g., MEND, AMIRA, INAP) recommend conducting predictive studies of chemical concentrations before constructing tailings containment structures, including dry stacks. Additionally, the Global Industry Standard on Tailings Management (GISTM) advises multidisciplinary studies encompassing geochemistry, water quality, hydrology, and geotechnics, among other fields.

In this context, the objective of this study is to assess potential changes in the chemical composition of effluents resulting from the mixing of iron ore tailings with lime. This mixture aims to reduce the moisture content of filtered tailings and improve the geotechnical stability of dry stacks. However, it is essential to evaluate the environmental and hydrogeochemical implications of this strategy.

The study was conducted during the conceptual phase of the project, aligning with best environmental practices. The methodology combined laboratory testing with hydrogeochemical numerical modeling to predict the long-term behavior of the tailings-lime mixture. Laboratory tests included static and kinetic drainage prediction, as well as chemical and mineralogical analyses of pure iron ore tailings and tailings mixed with lime in varying proportions. Hydrogeochemical modeling was performed using the PHREEQC software to simulate the deposition of the material in a dry stack, considering scaling factors, rainwater percolation, hydrogeology, and partial gas pressure. The laboratory results revealed that mixing iron ore tailings with lime generates an alkaline pH, which promotes silicate dissolution and the formation of neoformed minerals through pozzolanic reactions. Additionally, kinetic tests showed that the alkaline conditions favor the release of metals into solution, which would otherwise remain relatively inert under neutral pH.

The numerical modeling indicates that calcium carbonate precipitation may occur under atmospheric exposure, potentially creating low-permeability zones and preferential flow paths within the dry stack structure. These factors should be carefully considered in geotechnical designs. This study highlights key factors related to effluent quality and environmental impacts that must be addressed in projects involving the mixing of iron ore tailings with lime.