Multifunctionality is a recurring issue in the life cycle assessment (LCA) of primary metals production, as one metal is often co-produced with other metals. In this context, this study aims at i) reviewing the approaches actually implemented in the literature for solving multifunctionality in the context of the LCA of primary metals co-production; ii) comparing the currently existing multifunctionality-solving approaches as defined by the ISO hierarchy, considering the carbon footprint assessment (in a life-cycle perspective) of copper (Cu), zinc (Zn), lead (Pb) and silver (Ag) co-production through the implementation of on-site “mine-to-metal” technologies at pilot scale in a Spanish mine; iii) discussing the implications associated with the use of these different approaches in the context of primary metals co-production and the extent to which they may affect the assessment of the environmental performances of metals. Overall, the allocation approach stands for the first option for solving multifunctionality in the LCA of metals co-production based on the review of 27 studies; despite the ISO hierarchy recommends the use of allocation as last resort. Based on a representative set of primary data drawn from on-site trials at a pilot scale, the potential climate change impacts induced by the co-production of 1 ton Cu and 6 tons Zn cathodes along with 2.65 tons Pb and 0.045 ton Ag precipitates are calculated to amount to 90,324 kg CO₂-eq in a life cycle perspective. Depending on the multifunctionality-solving approach, the apportionment of these impacts to each co-product shows significant discrepancies. The implementation of partial subdivision combined with market prices allocation attributes most (80%) of the impacts to Zn and Ag. The use of allocation approaches attribute the largest share of impacts to Zn (62%) and Pb (27%) when considering a mass criterion; while the impacts are primarily attributed to Ag (respectively 48% and 45%) and Zn (respectively 30% and 33%) when considering economic criteria (respectively market prices and production costs). In terms of representativeness, the use of partial subdivision shall be considered as a more representative approach for solving multifunctionality than the mere application of allocation. Moreover, the results obtained through the application of economic allocation are considered more consistent than those obtained by mass allocation in this case study; while the use of production costs may be seen as an alternative for overcoming the limits associated with market prices. Finally, the use of system expansion shows that the recovery of Zn, Pb and Ag in addition to Cu potentially avoids 25% of the total climate change impacts. The approach implemented to solve multifunctionality largely influences the estimated impacts of each co-produced metal, subsequently with potential large implications for the footprints of products and sectors using these metals. The way multifunctionality is solved shall therefore be transparently reported in the scope of LCA studies, with privileging subdivision whenever possible.

多功能性是初级金属生产生命周期评估 (LCA) 中反复出现的问题，因为一种金属通常与其他金属共同生产。在此背景下，本研究旨在 i) 回顾文献中实际实施的解决初级金属联合生产 LCA 背景下的多功能性的方法；ii) 比较 ISO 层次结构定义的当前现有的多功能解决方法，考虑铜 (Cu)、锌 (Zn)、铅 (Pb) 和银 (Ag) 的碳足迹评估（从生命周期的角度）通过在西班牙矿山中试规模实施现场“矿山到金属”技术进行联合生产；iii) 讨论与在初级金属联合生产的背景下使用这些不同方法相关的影响以及它们可能影响金属环境性能评估的程度。总体而言，基于对 27 项研究的审查，分配方法是解决金属联产 LCA 中多功能性的首选方法；尽管 ISO 层次结构建议使用分配作为最后的手段。基于从中试规模现场试验中提取的一组代表性主要数据，由 1 吨铜和 6 吨锌阴极以及 2.65 吨铅和 0.045 吨银沉淀物共同生产引起的潜在气候变化影响是计算为 90,324 kg CO 基于对 27 项研究的审查，分配方法代表解决金属联产 LCA 中多功能性的第一个选项；尽管 ISO 层次结构建议使用分配作为最后的手段。基于从中试规模现场试验中提取的一组代表性主要数据，由 1 吨铜和 6 吨锌阴极以及 2.65 吨铅和 0.045 吨银沉淀物共同生产引起的潜在气候变化影响是计算为 90,324 kg CO 基于对 27 项研究的审查，分配方法代表解决金属联产 LCA 中多功能性的第一个选项；尽管 ISO 层次结构建议使用分配作为最后的手段。根据从中试规模的现场试验中获得的一组代表性主要数据，由 1 吨铜和 6 吨锌阴极以及 2.65 吨铅和 0.045 吨银沉淀物共同生产引起的潜在气候变化影响是计算为 90,324 kg CO₂-eq 在生命周期的角度。根据多功能性解决方法，这些影响对每个副产品的分配显示出显着差异。部分细分的实施结合市场价格分配将大部分 (80%) 的影响归因于锌和银。在考虑质量标准时，分配方法的使用将最大份额的影响归因于锌 (62%) 和铅 (27%)；而在考虑经济标准（分别为市场价格和生产成本）时，影响主要归因于银（分别为 48% 和 45%）和锌（分别为 30% 和 33%）。在代表性方面，部分细分的使用应该被认为是解决多功能性的一种比单纯应用分配更具有代表性的方法。而且，在本案例研究中，通过应用经济分配获得的结果被认为比通过大规模分配获得的结果更一致；而使用生产成本可能被视为克服与市场价格相关的限制的替代方法。最后，系统扩展的使用表明，除了铜之外，锌、铅和银的回收可能避免 25% 的总气候变化影响。为解决多功能性而实施的方法在很大程度上影响了每种联合生产金属的估计影响，随后对使用这些金属的产品和部门的足迹产生了潜在的重大影响。因此，解决多功能性的方式应在 LCA 研究范围内透明地报告，并在可能的情况下进行特权细分。