Life cycle assessment of rare earths and niobium concentrate co-recovery from phosphate flotation tailings: case of a Finnish fluorapatite deposit.

Critical metals, such as rare earth elements (REEs) and niobium, face significant supply risks stemming from highly concentrated production and geopolitical factors. In this regard, reprocessing of mine tailings as a secondary resource for mining critical metals provides an opportunity to secure access to these metals. In this study, a life cycle assessment (LCA) to quantify the environmental impacts for the co-recovery of two critical metals (REEs and niobium) from phosphate rock flotation tailings was presented, using the geology of the Sokli carbonatite-fluorapatite deposit in Finland. In addition to the upstream mining process, we also modelled the emissions associated with tailings disposal using time-resolved metal leaching data sourced from sequential extraction experiments. The results indicated that reprocessing tailings to recover REEs and niobium increases the climate change impact of the Sokli mine by 13.04 kg CO2 eq. Nevertheless, the total impacts of co-mining these metals from a single deposit were 79.1 kg CO2 eq. lower than separate mining from primary resources. The reprocessing of tailings to recover REEs and Nb was the highest contributing life cycle stage in climate change impacts, whereas the disposal of tailings was identified as a hotspot in the freshwater ecotoxicity and human toxicity impact categories. Normalization and weighting showed freshwater ecotoxicity and human toxicity from tailings disposal as the dominant environmental impact and thus underpins the need to reduce mining waste to mitigate these emissions.