Assessing and Reducing Risks from Mining of Technology Critical Elements

Abstract

In recent years, there has been a rapid increase in the global demand for many elements used in green energy and high-tech applications, including antimony (Sb), cobalt (Co), indium (In), lithium (Li), niobium (Nb) and the rare earth elements (REE). Canada has abundant resources of these critical elements, and many companies are working to bring new mines into production. However, we know very little about the potential environmental impacts of mining critical elements compared to mining other commodities such as gold or copper. Processing resources such as REEs has led to environmental degradation in some parts of the world, but there are few published studies of these environmental impacts and related risks to human health. This talk will summarize the key geoenvironmental characteristics of critical element deposits, including results from recent studies of the St. Lawrence Columbium Mine in Oka, Quebec. This mine operated from 1961 to 1976 and at the time was one of the largest Nb producers in the world. Samples of waste rock, tailings, slag, surface water, and groundwater were collected from 2015 to 2018. Mineralogical analyses show that in waste rock and tailings most uranium (U), thorium (Th) and REEs are hosted by low-solubility oxide and silicate minerals. However, some REEs and fluorine (F) are contained in minerals such as calcite and fluorapatite, which are relatively soluble under weathering conditions. Smelter slag at the mine contains concentrations of U, Th and radioactive isotopes that exceed Canadian guidelines for the disposal of radioactive waste. Measurements of U, Th, F, Nb, REEs, and radionuclides in tailings seepage and pit lake waters indicate that these elements are relatively immobile in oxic surface waters, but may be transported in deeper, anoxic groundwaters. The results of this research should help to improve environmental predictions for future Nb- and REE-mining projects and support the development of new environmental guidelines.