1 Introduction
2 Mineral resources, dissipation: defining the concepts in the context of LCA
2.1 Mineral resources: current concept in LCA
2.2 Abiotic resource dissipation: concept in life-cycle-based studies
2.3 Mineral resources: concept in LCA, adapted to account for dissipation
-
Regarding primary mineral resources: (i) “if the mineral or aggregate has a value as such (e.g., gypsum or sand), the mineral is considered the relevant elementary flow” (Berger et al. 2020), that is to say it is the resource; and instead (ii) if the value of a mineral ore is to host elements only, there are different views on what should be considered the resource(s) (as reflected by the definition of the “task force mineral resources”): either the mineral (e.g., chalcopyrite) and/or the totality (or some) of the elements contained therein (e.g., copper). In this study, the target elements in the ore are considered to be the resources (as in the ecoinvent 3 database; Weidema et al. 2013);
-
Regarding mineral resources in use in the technosphere, and potentially valuable as secondary resources: as long as the chemical elements, minerals and aggregates hold their original, or a significant, value in the product system under study, they are resources. This enables to account for secondary resources in the product system: not only primary resources can be dissipated, but more generally any chemical element, mineral or aggregate which provides its original or a significant function in a product-in-use;
-
Finally, as a basis, the list of mineral resource flows derives from the EF reference package (version 3.0; EC, 2019), considering all minerals classified as “resources from ground”.
3 Method
3.1 Rationale: dissipative flows at the unit process level
3.2 Temporal perspective considered in this study
3.3 Dissipative flows in this temporal perspective
3.3.1 Dissipation in products-in-use
Flows to | |||
---|---|---|---|
Environment | Final waste disposal facilities | Products-in-use | |
Dissipative | Copper emitted to air from a copper smelter | Any metal targeted through an extractive process-chain, ending in waste to final disposal (e.g., copper in copper tailings ponds) | Copper in slags from a copper smelter, used in construction (low function) Any metal non-functionally recycled (e.g., chromium and nickel in special steel recycled in ordinary steel) |
Non-dissipative | Copper emitted from coal combustion (copper in coal is not considered a resource) Argon emissions to air | Any metal non-targeted through an extractive process-chain, ending in waste to final disposal (e.g. cadmium in copper tailings ponds) | Quartz sand transferred to slags through copper smelting, and used in construction (significant function) |
3.3.2 Dissipation to the environment and to final waste disposal facilities
3.3.3 Occupation-in-use is not a form of dissipation
3.4 Resource flow analysis to quantify dissipative flows
3.5 Data requirements: potentialities of existing LCI datasets
-
Only resources can be dissipated (as in Table 1). Accordingly, one needs first to identify the resources inputs to the unit process under study before classifying the corresponding output emissions as dissipative;
-
Moreover, some resources are not emitted to the environment “as such.” For example, in the mining and metal industry, limestone (primarily calcium carbonate) may be dissipatively used as a reagent and partially emitted to the environment (e.g., as CO2 to air). In such a case, calcium carbonate is the resource dissipated to the environment. More generally, the dissipative resource flow should not be reported as the substance/compound emitted, but rather as the corresponding resource entering the unit process, whether emitted to the environment under the same form or not;
-
Finally, the nomenclature should specifically indicate that the corresponding flow is a “dissipative” flow of “resource,” i.e., the current approach for reporting emissions to the environment in LCIs should be complemented.
4 Application to a case study: cradle-to-gate production of copper cathodes
4.1 General description
4.2 System boundaries
-
Mining and concentration, which result in the production of copper concentrate (containing around 30% of copper) from sulfidic copper ore extraction and treatment. This activity additionally generates molybdenite, as a co-product whose subsequent life cycle is considered out of the scope of the system boundaries, and sulfidic tailings (waste). In this case study, tailings are considered to be disposed of in a tailings management facility (heaps or ponds), as common practice in the industry (Classen et al. 2009);
-
Pyrometallurgy, resulting in the production of copper cathodes from the treatment of copper concentrate. The process also generates iron silicate slags, considered to be used in construction, as common practice in the industry (Cusano et al. 2017).
4.3 Life cycle inventory
4.3.1 Resource flow analysis
4.3.2 Derivation of dissipative resource flows
-
Distinguishing the dissipative flows (copper and graphite) from the non-dissipative ones (quartz sand), among the flows of resources in slags used in construction (in that case slag is a “product-in-use” in the technosphere; Table 1).
-
Considering the resource flows to tailings disposal facilities as dissipative. The recovery of critical and other raw materials from extractive waste is not a widely diffused practice in the European Union yet, despite some notable examples (as e.g., reported in Sect. 3.3.2) which demonstrate the availability of technologies and the existence of a highly innovative sector (Blengini et al. 2019). It is therefore a reasonable assumption to consider that resources in tailings generated and disposed of along the cradle to gate production of 1 kg of copper cathodes will not be accessible to any future users in a 25-year timeframe, i.e. are dissipated. This assumption is moreover consistent with the modelling of tailings disposal in the ecoinvent database, which does not consider any potential future extraction of their resource content through reprocessing.
-
Allocating the dissipative resource flows directly generated by mining and concentration (to environment and tailings disposal facility) respectively to copper concentrate and to molybdenite. Economic allocation has been applied as in Classen et al. (2009). This implies that regarding the co-production of 1 kg of copper concentrate and 0.0041 kg of molybdenite, most (99%) of the dissipative resource flows are allocated to the output copper concentrate, while only a limited share (1%) is allocated to molybdenite. It is noteworthy that the allocation procedure could have been implemented in different ways, for example considering updated prices of copper concentrate and molybdenite, potentially completed with a physical allocation approach (e.g., considering the allocation of all primary copper resource dissipated to the copper concentrate). More generally, diverse allocation procedures may be applied to dissipative flows of mineral resources in LCI datasets, as is already the case for other elementary flows such as for example mineral resources extracted from the ecosphere (Berger et al. 2020).
Activity | Type of dissipative resource flow | Amount dissipated | Unit | Share of total mass |
---|---|---|---|---|
Mining and concentration | Dissipation to environment | |||
Chromium | 5.78E − 06 | kg | 0% | |
Copper | 4.23E − 06 | kg | 0% | |
Calcium carbonate | 1.98E − 01 | kg | 22% | |
Iron | 5.11E − 05 | kg | 0% | |
Nickel | 8.82E − 06 | kg | 0% | |
Sulfur | 2.84E − 02 | kg | 3% | |
Zinc | 2.41E − 05 | kg | 0% | |
Disposal of sulfidic tailings | Dissipation in tailings disposal facility | |||
Chromium | 1.65E − 02 | kg | 2% | |
Copper | 2.30E − 01 | kg | 26% | |
Iron | 6.79E − 02 | kg | 8% | |
Molybdenum | 1.92E − 02 | kg | 2% | |
Nickel | 7.34E − 03 | kg | 1% | |
Potassium | 5.69E − 03 | kg | 1% | |
Sodium | 2.04E − 03 | kg | 0% | |
Sulfur | 1.42E − 02 | kg | 2% | |
Zinc | 1.15E − 02 | kg | 1% | |
Pyrometallurgy | Dissipation to environment | |||
Copper | 2.75E − 03 | kg | 0% | |
Calcium carbonate | 2.49E − 01 | kg | 28% | |
Slags use in construction | Dissipation in slags used in construction | |||
Copper | 2.99E − 02 | kg | 3% | |
Carbon (graphite) | 1.00E − 03 | kg | 0% | |
Total | 8.84E − 01 | kg | 100% |
4.3.3 Inventory analysis
Total dissipative flows | Copper dissipative flows | |||
---|---|---|---|---|
Activities | Main approach: short-term perspective | Alternative approach: long-term perspective | Main approach: short-term perspective | Alternative approach: long-term perspective |
Mining and concentration | 26% | 47% | 0% | 0% |
Disposal of sulfidic tailings | 42% | 1% | 88% | 3% |
Pyrometallurgy | 29% | 52% | 1% | 95% |
Slags use in construction | 3% | 0% | 11% | 2% |