Mitigating Climate Change

Highly recycled nickel-containing stainless steels lower carbon emissions
By Viginia Heffernan

Nickel Magazine, September 2007 -- Fresh research out of Yale University concludes that the energy required to produce nickel-containing, austenitic stainless steel from scrap is less than a third of the energy used to produce stainless steel from virgin sources. As an additional environmental bonus, recycling produces just 30% of the CO₂ emissions.

Already one of the most recycled materials in the world, stainless steel could, theoretically, be made entirely from scrap if there weren't serious limitations on the availability of this material. Ironically, one of the main benefits of the material – its durability – limits its recycling potential: stainless steel structures and products tend to last a long, long time.

Meanwhile, demand for stainless steel has never been stronger as developing economies such as China and India accumulate the materials necessary to build infrastructure. Virgin production is growing to meet this demand, lowering the overall percentage of recycled content.

“Eventually, the demand curve has to flatten and the amount of in-use stainless steel that becomes available for recycling will grow as a percentage of total demand,” says Bruce McKean, director of sustainable development and product development for the Nickel Institute, which partly funded the Yale work upon which this study draws. “Therefore the percentage of secondary material in future stainless production will rise.”

McKean says there should be much more scrap available in 20 to 30 years than there is today as the current generation of products and structures that contain stainless steel are replaced, usually because of obsolescence. Currently, end users must rely on material that was produced in the 1960s and 1970s, when stainless steel use was significantly lower.

As Yale’s The Energy Benefit of Stainless Steel Recycling recently published in Energy Policy shows, a higher recycling rate would provide a significant environmental benefit. Under current operations (based on 2004 figures), the world produces about 17 million tonnes of austenitic stainless steel using 9.0 X 10¹⁷ Joules of primary energy and emitting about 61 million tonnes of CO₂ throughout the life cycle of production. Current recycling operations reduce primary energy use by about 33% and CO₂ by 32% compared with production from virgin sources alone. But if stainless steel were to be produced solely from scrap (a merely hypothetical scenario), about 67% of the energy could be saved and CO₂ emissions cut by 70%.

“It confirms common sense,” says Barbara Reck, a research associate at the School of Forestry and Environmental Studies at Yale and second author on the paper. “The biggest energy use is in the mining and smelting phase, and you don’t have to go through this phase using scrap. But now we have calculated this systematically and our hypothesis has been confirmed.”

The lead authors on the paper have each studied the main constituents of austenitic stainless steel separately: Reck focuses on nickel, Johnson, on chromium, and Wang, on iron. They combined their expertise and data to come up with an analysis of stainless steel and its environmental impact over three different scenarios: current global operations; 100% recycling; and use of only virgin materials.

“We had so far only worked quantitatively on the life cycles of the different metals,” says Reck. “The idea was to take this quantitative information and use it to try to understand the energy needed to produce virgin materials or reprocess scrap.”

The study is part of the Yale Stocks and Flows project, which uses flow analysis of material (from resource extraction to final disposal) to study how different metals move within different countries and around the planet as a whole. The project initially focused on copper and zinc, and then moved to other metals including nickel, silver, iron, chromium, tungsten, tin, and lead.

Virginia Heffernan is a Toronto-based freelance science writer.

Illustration: Mark Crozier.

"The Energy Benefit of Stainless Steel Recycling" by J. Johnson, B. Reck, T. Wang, and T. E. Graedel, Yale University. For a PDF of this paper, please contact the lead author Jeremiah Johnson

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