Life cycle assessment of metals: a scientific synthesis

• Published in: PloS one 2014-07, Vol.9 (7), p.e101298
• Main Authors: Nuss, Philip, Eckelman, Matthew J
• Format: Article
• Language: English
• Subjects: Alternative energy sources; Aluminum; Biology and Life Sciences; Carbon dioxide; Carbon Dioxide - analysis; Carbon Dioxide - chemistry; Chemical Sciences; Climate change; Computer simulation; Copper; Ecology and Environmental Sciences; Ecosystem; Emissions; Energy consumption; Engineering and Technology; Environmental impact; Environmental Monitoring; Global Warming; Gold; Greenhouse effect; Greenhouse gases; Heavy metals; Humans; Iron; Iron and steel making; Life cycle analysis; Life cycle assessment; Life cycle engineering; Life cycles; Manganese; Metals; Metals - analysis; Metals - chemistry; Minerals; Minerals - analysis; Minerals - chemistry; Mining; Monte Carlo method; Monte Carlo simulation; Organic chemistry; Physical Sciences; Platinum; Purification; Silver; Silver mines; Stability analysis; Tellurium; Thallium; Titanium
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0101298

We have assembled extensive information on the cradle-to-gate environmental burdens of 63 metals in their major use forms, and illustrated the interconnectedness of metal production systems. Related cumulative energy use, global warming potential, human health implications and ecosystem damage are estimated by metal life cycle stage (i.e., mining, purification, and refining). For some elements, these are the first life cycle estimates of environmental impacts reported in the literature. We show that, if compared on a per kilogram basis, the platinum group metals and gold display the highest environmental burdens, while many of the major industrial metals (e.g., iron, manganese, titanium) are found at the lower end of the environmental impacts scale. If compared on the basis of their global annual production in 2008, iron and aluminum display the largest impacts, and thallium and tellurium the lowest. With the exception of a few metals, environmental impacts of the majority of elements are dominated by the purification and refining stages in which metals are transformed from a concentrate into their metallic form. Out of the 63 metals investigated, 42 metals are obtained as co-products in multi output processes. We test the sensitivity of varying allocation rationales, in which the environmental burden are allocated to the various metal and mineral products, on the overall results. Monte-Carlo simulation is applied to further investigate the stability of our results. This analysis is the most comprehensive life cycle comparison of metals to date and allows for the first time a complete bottom-up estimate of life cycle impacts of the metals and mining sector globally. We estimate global direct and indirect greenhouse gas emissions in 2008 at 3.4 Gt CO2-eq per year and primary energy use at 49 EJ per year (9.5% of global use), and report the shares for all metals to both impact categories.