MO.1.A || Life Cycle Approaches in the Raw Materials Sector

Sonderegger, Thomas; Bourgault, Guillaume; Moreno Ruiz, Emilia; Wernet, Gregor

The use of mineral resources is of importance in LCA and Circular Economy. To account for the extraction of mineral resources, the activities from mining to production of mineral commodities are included in Life Cycle Inventory databases such as ecoinvent. Since mining of one often results in multiple commodities, allocation methods are applied to distribute resource inputs and emissions to the different products. Thereby, economic allocation attributes more of these environmental exchanges to those commodities that are more valuable. While this makes sense regarding losses, it also can result in distortions of mass balances to a degree where less than 1 kg of silver extraction may be attributed to 1 kg of silver product. This contradicts ISO allocation rules (allocation based on underlying physical relationships) as well as intuition. We present a hybrid allocation, in which physical flows of resources into products are maintained, whereas losses are attributed economically. This allows to “correct” for distortions of mass balances in the allocated version of the database for mineral commodities. The result is a more ISO-compliant and intuitive result: LCIs contain at least the same amount of metal present in the final product, in addition to some losses of other co-produced metals. This is also relevant for other areas, e.g., the carbon content of wood products, which is also “corrected” for in the ecoinvent database. A hybrid allocation as presented here for metals allows for an improved assessment of resource use in LCA and hence for better information on mineral resource intensity of products.