Copper contamination in end-of-life steel recycling, developing a new strategy from million-tonnes to milligrams

Increasing the share of scrap-based steel production is necessary to achieve CO2 emissions targets. However, the quality of recycled steel is compromised by contaminating elements, of which copper is the most pervasive. Copper from wiring and motors entangles with steel fragments during shredding and is not completely removed by magnetic separation. Beyond hand-picking, no commercial process exists for extraction, but copper in solution with steel segregates during hot rolling, causing surface cracking and defects that are unacceptable for high-quality flat products. This thesis characterizes copper in the global steel system, evaluates the energy requirements of possible extraction processes and presents experimental results to aid in the development of an efficient extraction technique. Copper contamination is currently managed by globally trading contaminated scrap to tolerant applications and by dilution with primary steel. An evaluation of copper in the global steel system is needed to develop long-term strategies, and this is presented in the first part of this thesis. The copper concentration of flows along the 2008 steel supply chain are estimated from a range of literature sources and compared with the maximum concentration that can be tolerated in all steel products. Quantities of final steel demand and scrap supply by sector from a global stock-saturation model are used to estimate the amount of copper in the future scrap supply, and the total amount tolerable. Assuming current scrap preparation continues, more copper will enter the steel cycle than can be tolerated by demanded products by 2050. This global constraint will set in sooner if primary production is cut to meet climate mitigation targets. Given the upcoming constraints, improved copper control is necessary. 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 these options. The second part of this thesis presents a framework 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 0.1wt% (enabling the production of high-value flat products) with 5-20% of the melting energy in the electric arc furnace route. The above analysis reveals a promising and under-explored process route: preferential melting of copper from solid steel scrap, which could be integrated into conventional scrap re-melting with little additional energy. Previous investigations show removal of liquid copper is limited by its adherence to solid scrap. In the third part of this thesis, the individual and combined effects of several parameters (steel carbon content, initial surface oxidation and applied coatings) on the wetting behavior of liquid copper are observed with a heating microscope to understand if a process window to enable separation exists. The most significant factor was carbon content. On medium carbon steel substrates, copper spread rapidly, likely due to reduction of the oxide layer by carbon. Non-wetting copper droplets were observed on low carbon substrates in an inert atmosphere. This indicates a possible process window, but further investigation considering diverse, fragmented end-of-life scrap is needed. The scrap supply of all metals is expanding. The multi-scale, interdisciplinary method developed in this thesis could be applied to other metal systems to understand the constraints caused by contamination and identify key areas to develop efficient extraction processes, necessary to conserve resources and reduce CO2 emissions.Cambridge Trust International Scholarshi

Finding the most efficient way to remove residual copper from steel scrap

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 0.1wt% 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 0.1wt% 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.EPSRC, Cambridge Trust

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

Abstract: Copper contamination of end-of-life steel scrap is the main barrier to high-quality recycling. Preferential melting of copper from solid steel scrap is a potential extraction technique, which could be integrated into conventional scrap re-melting with little additional energy. However, previous investigations show removal of liquid copper is limited by its adherence to solid scrap. Preventing wetting between liquid copper and steel is essential to enable separation. The carbon content of steel, initial surface oxidation, and applied coatings effect wetting behavior, but have not been systematically studied. In this study, the individual and combined effects of these parameters on wetting behavior in an inert gaseous environment are observed with a heating microscope. Carbon content appears to be the most significant factor: blistering of the oxide scale on medium-carbon steels causes liquid copper to flow rapidly between the oxide and steel substrate. Liquid copper exhibited a stable droplet on low-carbon steel, regardless of the initial level of oxidation. The tested coatings did not consistently improve nonwetting behavior, but impaired the connection between the scale and steel substrate. This study confirms the potential of the preferential melting technique, but further investigation is needed to determine the most robust process conditions to handle diverse, fragmented scrap at an industrial scale

How Will Copper Contamination Constrain Future Global Steel Recycling?

Copper in steel causes metallurgical problems, but is pervasive in end-of-life scrap and cannot currently be removed commercially once in the melt. Contamination can be managed to an extent by globally trading scrap for use in tolerant applications and dilution with primary iron sources. However, the viability of long-term strategies can only be evaluated with a complete characterization of copper in the global steel system and this is presented in this paper. The copper concentration of flows along the 2008 steel supply chain is estimated from a survey of literature data and compared with estimates of the maximum concentration that can be tolerated in steel products. Estimates of final steel demand and scrap supply by sector are taken from a global stock-saturation model to determine when the amount of copper in the steel cycle will exceed that which can be tolerated. Best estimates show that quantities of copper arising from conventional scrap preparation can be managed in the global steel system until 2050 assuming perfectly coordinated trade and extensive dilution, but this strategy will become increasingly impractical. Technical and policy interventions along the supply chain are presented to close product loops before this global constraint.K.D. is funded by a Cambridge Trust scholarship. A.S. and J.A. are funded by EPSRC, grant reference EP/N02351X/1

Electrolytic production of copper from chalcopyrite

The transition to renewable energy infrastructure necessitates rapid growth in copper production, averaging at least 3.5% annually to 2050. The current smelting–converting–electrorefining route must be revisited considering these future prospects as ore grades deplete and the costs to mitigate emissions to the environment increase. Here, we investigate electrolytic alternatives, reviewing the background and recent developments for four classes of electrolytes to directly decompose the most important industrial copper mineral, chalcopyrite: aqueous solutions, ionic liquids, molten salts, and molten sulfides. These electrolytes are discussed in the framework of electrochemical engineering, as applied to the electrolytic decomposition of chalcopyrite. A vision is proposed in which an electrolytic technique, integrated with low cost and sustainable power, enables the production of unprecedented annual tonnages of copper from low-grade chalcopyrite, with valuable by-products and enhanced selectivity for impurities

Environmentally Responsible Lightweight Passenger Vehicle Design and Manufacturing

Abstract The mass reduction of passenger vehicles has been a great focus of academic research and federal policy initiatives of the United States with coordinated funding efforts and even a focus of a Manufacturing USA Institute. The potential benefit of these programs can be described as modest from a societal point of view, for example reducing vehicle mass by up to 25% with modest cost implications (under $5 per pound saved) and the ability to implement with existing manufacturing methods. Much more aggressive reductions in greenhouse gas production are necessary and possible, while delivering the same service. This is demonstrated with a higher-level design thinking exercise on an environmentally responsible lightweight vehicle, leading to the following criteria: lightweight, low aerodynamic drag, long-lived (over 30 years and 2 million miles), adaptable, electric, and used in a shared manner on average over 8 h per day. With these specifications, passenger-mile demand may be met with around 1/10 of the current fleet. Such vehicles would likely have significantly different designs and construction than incumbent automobiles. It is likely future automotive production will be more analogous to current aircraft production with higher costs per pound and lower volumes, but with dramatically reduced financial and environmental cost per passenger mile, with less material per vehicle, and far less material required in the national or worldwide fleets. Subsidiary benefits of this vision include far fewer parking lots, greater accessibility to personal transportation, and improved pedestrian safety, while maintaining a vibrant and engaging economy. The systemic changes to the business models and research and development directions (including lightweight design and manufacturing) are discussed, which could bring forth far more sustainable personal transportation

Liquid Copper and Iron Production from Chalcopyrite, in the Absence of Oxygen

Clean energy infrastructure depends on chalcopyrite: the mineral that contains 70% of the world’s copper reserves, as well as a range of precious and critical metals. Smelting is the only commercially viable route to process chalcopyrite, where the oxygen-rich environment dictates the distribution of impurities and numerous upstream and downstream unit operations to manage noxious gases and by-products. However, unique opportunities to address urgent challenges faced by the copper industry arise by excluding oxygen and processing chalcopyrite in the native sulfide regime. Through electrochemical experiments and thermodynamic analysis, gaseous sulfur and electrochemical reduction in a molten sulfide electrolyte are shown to be effective levers to selectively extract the elements in chalcopyrite for the first time. We present a new process flow to supply the increasing demand for copper and byproduct metals using electricity and an inert anode, while decoupling metal production from fugitive gas emissions and oxidized by-products