Temporally Explicit Life Cycle Assessment as an Environmental Performance Decision Making Tool in Rare Earth Project Development

Rare Earth Deposits & Mining

Pell, and 4 co-authors, reported in 2019 that a detailed life-cycle assessment (LCA) can be carried out for a proposed mining project as soon as Prefeasibility (PFS) data are available. The prefeasibility study is one of the key early steps in bringing a deposit towards production and results are often publicly available. This study applies the technique to a rare earth deposit because rare earth element (REE) consumption is increasing owing to their use in low-carbon technologies such as electric vehicles and wind turbines. It is therefore particularly important to understand the environmental impacts of the raw materials.

A number of REE deposits are under development to give additional supply and many possess novel mineral compositions and will require different processing methods than previously used. Assessing the environmental performance of the production of REE during the development of projects offers significant insights into how to improve the sustainability of a project. In this study the authors used life-cycle assessment (LCA) to quantify the environmental impacts for producing rare earth oxide (REO) from the Bear Lodge Project, United States. The Life Cycle Impact Assessment results were produced for each year over the life of the project, generating insight about the relationships between ore composition, grade, processing method and environmental impacts. The environmental impacts vary significantly during the life of a project and a temporally explicit LCA can highlight these.

The authors concluded that a predictive temporally explicit LCA at a project scale can be a useful tool in identifying environmental hotspots and advising on processing options that could improve the environmental performance of a rare earth project. Adding a temporal dimension provides a greater opportunity to explore the relationships between the properties of the deposit, the mining and mineral processing methods and the environmental impacts. The results indicate that there is a positive relationship between decreasing grade and global warming impact, but there are also patterns that exist between the ore composition and the global warming potential. The beneficiation approaches compared generated different environmental impacts over time.

The beatification process presented in the Pre-feasibility Study Report (2014), which included crushing, grinding, magnetic and gravity separation had a higher average impact over the life of mine for the acidification, eco-toxicity, human health, human toxicity, and smog, whilst the flotation approach presented by Cui and Anderson had a lower global warming impact. Applying the LCA methodology higher uncertainty in this stage of a project for both the geology of the deposit and the mining and mineral processing methods that will be used is offset by the fact that high impact areas can be explored and changes can be implemented as a project moves through development into the feasibility stage.