Mining Environment: Challenges and Solutions for a Sustainable Future

Pre-mining, intra-mining, and post-mining acid rock drainage (ARD) studies conducted at the Troilus mine (1996-2010) predicted ARD at the site. However, after more than 20 years of exposure to atmospheric conditions, no large-scale ARD has been detected. This suggests that the neutralization potential (NP) measured by the Sobek test (1978) and its modified versions may have been underestimated.

The Sobek test measures the NP primarily associated with carbonates. Acid neutralization by silicates has long been recognized, but is difficult to quantify. Neutralization by silicates is only possible if the rate of acid generation is relatively slow, allowing the fastest-neutralizing silicate minerals to act.

Several studies have been carried out to quantify the neutralization of silicates, including:

1- full-scale on-site kinetic tests;

2- large on-site kinetic tests of various rock units;

3- geochemical characterization of carefully selected core intervals based on sulphur geostatistics, dominant rock units, and 3D spatial distributions;

4- various laboratory kinetic tests;

5- mineralogy using XRD, SEM/EDX, petrographics, and Raman spectroscopy;

6- sulphide-oxidation rates; and

7- compilations of silicate mineral stoichiometry and reaction rates.

These integrated studies revealed several important aspects of Silicate NP at the Troilus Mine, inluding:

1- while silicate minerals make up a large percentage of Troilus rocks, only a small portion reacts sufficiently fast to allow neutralization;

2- calcium-rich plagioclase minerals, such as bytownite and labradorite, represent nearly all the Fast-Neutralizing Silicates found in major Troilus rock units under tested conditions;

3- at slower rates of acid generation, such as from coarser particles, additional silicate minerals can contribute significantly to effective NP;

4- at faster rates of acid generation, lower microscale pH levels are created and neutralization by other silicate minerals can accelerate and contribute significantly to effective NP.

General geochemical analyses like four-acid-digestion ICP-MS of samples can be mathematically adjusted to estimate Fast-Neutralizing Silicate NP. This allows the more than 150,000 drillcore assays at Troilus to become more accurate surrogate ABAs.

Most graphite deposits contain abundant pyrrhotite. Consequently, graphite mining projects are plagued with acid mining drainage from the pyrrhotite oxidation. Due to its stringent sensitive location, innovative solutions to mitigate AMD were proposed for the Lac Knife project. A review of the concept, fruition of a large team of scientists and engineers, that led to an elaborate dolomitic amending, including insights from the geometallurgical model as well as groundbreaking approaches to convert pyrrhotite from a costly liability to a revenue will be discussed.

The demand for lithium has increased exponentially in recent years, driven primarily by the surge in demand for lithium batteries essential to the production of low-carbon electric vehicles. In this context, Canada's Critical Minerals Strategy has identified lithium as a key material in the transition to renewable energy. Several lithium projects are currently under development in Canada, encompassing both traditional mining and less conventional sources such as oil-field brine and industrial waste water. Quebec is home to the largest lithium reserves in Canada, located within spodumene pegmatite deposits, and offers an existing infrastructure that is an asset for the extraction of this substance using conventional mining methods. Despite the history of lithium mining in Quebec dating back several decades, little is known about the geochemical behaviour of the mining materials generated by these operations (ore, waste rock and tailings). In light of the projected increase in lithium production in the province, it is essential to understand the environmental challenges and risks associated with the development and operation of these mining projects. Here we present a review and comparative assessment of geochemical characterization data obtained from three lithium deposits in Quebec at different stages of development. The geochemical data presented were obtained through mineralogical analyses, static tests and kinetic leaching tests conducted at varying scales (humidity cells, leach columns and field cells) on ore (spodumene pegmatite), tailings and waste rock. The objective of this work is to assess and compare the geochemical behaviour (e.g., acid generation and metal leaching potential) of these materials, identify the principal environmental risks and provide this information to current and future spodumene-based lithium mining projects.

Permafrost degradation is an important environmental issue that can significantly impact the chemical and physical properties of the water in Arctic and subarctic ecosystems. The apprehended impacts to watersheds related to permafrost degradation can affect all phases of a mining project, both operationally and economically. In this paper, we present a conceptual model to help understand the changes in water quality that occur in northern watersheds due to permafrost degradation. The model provides a framework for understanding the complex processes that drive changes in water quality caused by permafrost degradation and informs the development of monitoring programs to predict downstream water quality impacts under future climate change scenarios.

The conceptual model consists of five major components: climate, geology, permafrost, hydrology/hydrogeology, and geochemistry, which inform contemporary and future changes to permafrost and water quality within a particular watershed. Increasing air temperatures and precipitation are causing permafrost thaw and potential groundwater flow through the active layer, resulting in the expansion of suprapermafrost taliks that allow for geochemical reactions to progress in previously frozen soil and rock. The geochemistry of locally mineralized zones in the geological units within the thickening active layer and suprapermafrost taliks is anticipated to produce increased concentrations of total dissolved solids in groundwater and surface water through sulphide oxidation and potential biologically-mediated metals dissolution.

Recent measurements of water quality indicate variability in the degree of permafrost thaw and hydrology influences. Overall, this conceptual model contributes to our understanding of the impacts of permafrost degradation on water quality in northern watersheds and can inform the development of monitoring and management strategies to protect vulnerable ecosystems in the face of ongoing climate change.

These hydrologic and geochemical processes have the potential to produce a continuously evolving background water quality, which complicates compliance monitoring programs. Therefore, this conceptual model is applicable to environmental baseline studies for proposed mines, compliance monitoring programs for operating mines, and when establishing water quality objectives for mine closure in discontinuous and continuous permafrost environments.

Rare earth elements (REEs) are used in electronic devices, electric cars, medical imaging, and wind turbines. Several development projects are being studied in Canada, often on Indigenous lands. These elements must be better understood at the environmental and ecotoxicological level, and governments need information to establish criteria. In recent years, we have studied the main factors influencing their distribution in aquatic environments from southern Quebec to Nunavik. In the North, we helped develop a community-based monitoring plan in partnership with an Inuit community. At the water level, we have identified the main factors influencing concentrations in the aquatic environment. REEs were transported in waterways in association with aluminum, iron, titanium and humic dissolved organic matter, as well as thorium, a radionuclide of ecological concern. At the biological level, we have demonstrated that REEs do not transfer well between prey and predator, so animals at the top of terrestrial, marine and freshwater food webs are relatively uncontaminated, especially at the muscle level. This allows for a better estimate of human exposure from consuming country food. We also studied how REEs partition in animal cells to understand their potential for toxicity. We found that invertebrates accumulate REE in fractions of cells that are not very sensitive to a toxic effect, whereas fish accumulate REE less well but in sensitive fractions such as mitochondria. Following this research, we developed biomonitoring tools in the aquatic environment, studying the link between the speciation of REE in water and REE accumulation in sentinel animals, such as zooplankton. Our research is done in partnership with governments, Indigenous communities, and sometimes the industry. These results are useful for properly documenting the effect of developing mining operations, and we were also involved in evaluating the federal environmental quality guidelines for REEs.