Life Cycle Assessment in mineral processing – a review of the role of flotation

Purpose: The aim of this literature review is to investigate the role of the beneficiation stage in the Life Cycle Assessment (LCA) of metals and minerals with a focus on the flotation process. Methods: The systematic literature search included LCA studies comprising the beneficiation stage in their system boundaries and resulted in 29 studies that met the criteria requirements and were analysed. First, the system boundaries are investigated, along with the level of detail in the description of the sub-processes (e.g. flotation) and data granularity. Then, the life cycle inventories are scrutinised: data transparency and the relation between system granularity and data availability is commented. Of particular relevance, the way in which the functional unit is dealt with is examined. Finally, studies impact assessments are compared and discussed, and key parameters are highlighted. Results and discussion: For system boundaries, beneficiation is generally embedded into the mining stage. Even when described on its own, important sub-processes (e.g. flotation) are not considered, except for eight cases analysed. Functional unit definition is hindered by the output of the system being an intermediate product. Indeed, most studies use a declared functional unit but fail to provide its relevant characteristics, which is essential for a correct interpretation of results and for comparisons. Most studies rely on secondary data, not always presented transparently, to describe beneficiation. Results on the role of beneficiation in the metal value chain environmental impacts are conflicting, partly because of its site dependency. Site-dependent parameters found to be determining are ore grade, energy mix, mining technique, concentrate grade and ore mineralogy. Conclusions: The flotation process, and more generally the beneficiation stage, is typically overlooked in LCA studies despite its growing relevance. Beneficiation not being assessed as a standalone stage, detailed in its subprocess, the use of outdated and secondary data, along with a lack of transparency in the inventory and in the key parameters are all factors that affect the environmental assessment of the entire metal and mineral sector, and thus the LCA of many products. Recommendation: Greater efforts should be allocated to considering the sub-processes in the beneficiation stage, particularly flotation. Information on the identified key parameters should be available to the practitioners and sensitivity analyses to investigate their influence are recommended. Hotspots specific to flotation have been identified and should be used to orient data gathering when focusing on this process. Five options of functional unit and their application are recommended.