Finding the Most Efficient Way to Remove Residual Copper from Steel Scrap
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UCTION
THE amount of steel discarded yearly will triple from the present day to 2050, as predicted by Pauliuk et al.[1] using a global stock-saturation model. Milford et al.[2] have shown that much more steel must be produced from scrap to meet emissions targets, and utilizing this growing resource is a sound economic strategy.[3] However, the presence of contaminating elements restricts the applications in which end-of-life scrap can replace primary steel. Copper is the most pervasive contaminant for steel scrap, present as wiring in vehicles, appliances and equipment, and alloyed with steel in engine blocks and powder metallurgy products. During hammer shredding, copper wiring entangles with the fragmented steel scrap. Subsequent magnetic separation is not completely effective, and steel-encased motors often remain with the steel scrap. Copper is not currently extracted from the steel melt,[4] and it can lead to metallurgical problems during downstream
KATRIN E. DAEHN, ANDRE´ CABRERA SERRENHO, and JULIAN ALLWOOD are with the Department of Engineering, University of Cambridge, Trumpington Street, CB2 1PZ, Cambridge, UK. Contact e-mail: [email protected] Manuscript submitted September 7, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS B
thermo-mechanical processing, such as resistance to hot rolling and surface hot shortness, as reviewed by Rod et al.[5] Shredded end-of-life scrap typically has 0.4 wt pct copper, which can be tolerated in reinforcing bar, but many flat steel products require less than 0.1 wt pct copper.[6] As a result, today’s primary and secondary steelmakers generally serve different markets, but in the future this strategy will become impractical. Analysis of the global steel cycle estimates that the amount of copper in scrap will exceed the amount which can be tolerated across all products by 2050 unless methods for improved control are introduced.[7] Copper contamination could be managed by interventions at various points along the steel scrap supply chain. Figure 1 provides a representation of the stakeholders involved in the steel cycle, considering the steps each is responsible for and the incentives each has to control copper. The makers of cars, appliances, and equipment could use less copper (by challenging the trend of incorporating more electronic features,[8] or using aluminum wiring instead[9]), or modify designs for easy disassembly at end-of-life (such as using detachable wiring harnesses[10]). However, product re-designs must be motivated by consumer support or regulation. A compromise in performance or price for enhanced recyclability may be unacceptable. Additionally, steel
behind-the-scenes
visible
stakeholder phase
incentive for copper control
carmaker design manufacture
no incentive, at odds with other objectives
consumer use
disposal
unaware delay: product lifetime
determines product shape, type
scrap processor
steelmaker
collection shredding magnetic separation no incentive without adjusted composition measurement
batching
melting
casting
rolling
add diluents
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