Finding the Most Efficient Way to Remove Residual Copper from Steel Scrap

Abstract

The supply of end-of-life steel scrap is growing, but residual copper reduces its value. Once copper attaches during hammer shredding, no commercial process beyond hand-picking exists to extract it, yet high-value flat products require less than 0.1 wt pct copper to avoid metallurgical problems. Various techniques for copper separation have been explored in laboratory trials, but as yet no attempt has been made to provide an integrated assessment of all options. Therefore, for the first time, a framework is proposed to define the full range of separation routes and evaluate their potential to remove copper, while estimating their energy and material input requirements. The thermodynamic, kinetic, and technological constraints of the various techniques are analyzed to show that copper could be removed to below 0.1 wt pct with relatively low energy and material consumption. Higher-density shredding allows for greater physical separation, but requires proper incentivization. Vacuum distillation could be viable with a reactor that minimizes radiation heat losses. High-temperature solid scrap pre-treatments would be less energy intensive than melt treatments, but their efficacy with typical shredded scrap is yet unconfirmed. The framework developed here can be applied to other impurity-base metal systems to coordinate process innovation as the scrap supply expands.

The potential for material circularity and independence in the U.S. steel sector

“…Daehn et al. () provide an up‐to‐date and comprehensive review of the refining options. Government could support the development of EOL strategies through funding for research into economical scrap separation and refining methods and by creating programs, for example, tax breaks or interest‐free loans, for recyclers who invest in advanced recycling technologies.…”

“…EOL vehicles and appliances are typically shredded before remelting. Shredding embeds copper strands into the steel and makes magnetic separation ineffective (Daehn, Serrenho, & Allwood, 2019). Advanced design for recycling (e.g., product modularity that allows easy separation of copper containing electronics from the product's steel structure) could be motivated by extended producer responsibility policies (Ayres, Ferrer, & Leynseele, 1997;Nasr & Thurston, 2006).…”

“…Higher-density shredding causes greater separation and sulfide slagging and vacuum induction melting Savov et al, 2003) are two current technologies capable of removing copper from steel scrap but are expensive and have seen negligible commercial uptake. Daehn et al (2019) provide an up-to-date and comprehensive review of the refining options. Government could support the development of EOL strategies through funding for research into economical scrap separation and refining methods and by creating programs, for example, tax breaks or interest-free loans, for recyclers who invest in advanced recycling technologies.…”

Industrial Sustainability: Reviewing the Past and Envisioning the Future

“…Copper contamination from wiring is likely to constrain the global recycling rate of steel by midcentury [255] and is already limiting domestic U.S. and European steel recycling [256,257]. Options to increase the EoL recycling rate and the value of the scrap include improved design for recycling (e.g., designing easily detachable copper wiring harnesses for vehicles [258]), component disassembly before shredding at EoL [259], and the development and deployment of solid state scrap separation systems and liquid state scrap refining processes [260,261].…”

Preventing Wetting Between Liquid Copper and Solid Steel: A Simple Extraction Technique

“…[5] An extraction process could be developed to separate copper from steel. The possible separation routes were evaluated by their potential to remove copper, and their specific energy and material input requirements by Daehn et al [6] This analysis shows that techniques such as sulfide slagging [7] and vacuum distillation [8] have received considerable experimental investigation, but are difficult to implement in practice. However, premelt techniques, such as improved physical scrap preparation, appear to be particularly viable.…”