Recycling of scrap is essential to the copper value chain
Copper can be infinitely recycled without losing its properties. As such, the entire economy of the copper and brass industry is dependent on the economic recycling of surplus products and material otherwise known as scrap. Using scrap as a low-cost feedstock to make new products contributes to a sustainable planet and keeps costs down for both producers and users of copper-based products.
The two main categories of scrap used to produce copper and copper alloy products are primary scrap and secondary scrap. Primary scrap is comprised of excess material produced during manufacturing which is typically returned to the mill that provided the raw material. Secondary scrap is comprised of products that have reached the end of service life (i.e. old products removed from buildings during demolition) and is typically aggregated and sold on the open market by scrap dealers.
Different types of copper-based scrap must be recycled separately
A variety of manufacturing processes are used to produce copper and alloy products which contain different levels of alloying and impurity elements depending on the process and application. The different chemical compositions of copper and alloy products can affect their subsequent use as feedstock in the form of scrap. Depending on the scenario, cross-contamination between different types of copper-based scrap can introduce deleterious impurities to melting operations that cause problems in upstream production, even at low concentrations (i.e. <10ppm). Impurities can also negatively impact material properties and contribute to product failures. As the copper and copper alloy scrap stream is a finite resource, the strict segregation of certain types of copper-based scrap is vital from both economic and sustainability perspectives.
Impact of impurities
Impurities can gradually concentrate in the metal stream over time, and in some cases, an additional refining step may be required to reduce impurities to acceptable levels. Importantly, some impurity elements are impossible to remove with current refining technology and can irreversibly contaminate the scrap stream. In many cases, dilution is the only solution. If the availability of “clean” scrap is diminished by the buildup of contaminants, producers of copper and alloy products would be forced to use more virgin metal as feedstock. This would increase the cost of the materials and reduce the sustainability of copper as a metals system.
Additionally, the frequency of rejected shipments from scrap dealers could increase if the presence of contaminants in the scrap stream continues to trend upwards. As a precautionary measure, some producers of copper and alloy products have upgraded equipment and internal controls to more accurately detect impurities in scrap before they are introduced to the melting furnace.
The following points provide key insights on several types of copper-based scrap and their compatibility as feedstock to produce new copper and alloy products.
- Several different types of “lead-free” brass alloys were developed and introduced in response to regulations restricting the use of lead in potable water components and other applications.
- Scrap from brass alloys containing lead should not be used to produce lead-free brass alloys which do not contain lead.
- Scrap from tertiary lead-free brass alloys, which contain copper, zinc and an element replacing lead (i.e. silicon, bismuth) should not be used to produce leaded brass alloys, or binary lead-free brass alloys which contain copper and zinc only.
- Scrap from different types of tertiary lead-free brass alloys should also be segregated from each other. For example, scrap from lead-free alloys containing bismuth should not be used to produce lead-free alloys containing silicon and vice versa.
- Scrap from binary lead-free brass alloys (copper and zinc only) can be used to produce leaded brass alloys and all types of lead-free brass alloys without issue.
- Products made from certain types of lead-free alloys were not widely used until the last 15-20 years. Brass products have long service lives, and accordingly, lead-free brass secondary scrap has not yet entered the recycling stream on a significant scale. Cross-contamination between incompatible brass scrap types could increase as more lead-free brass products are eventually recycled as secondary scrap.
- Proper segregation of primary brass scrap sourced from manufacturers is easier to manage in comparison to secondary brass scrap.
- Two different processes can be used to make copper rod that is drawn into wire and cable products that have slightly different chemical compositions respectively. The two products are Fire-Refined High Conductivity (FRHC) copper and Electrolytic Tough Pitch (ETP) copper.
- Scrap from FRHC copper wire and cable products (i.e. bare/insulated wire and wire chops) cannot be used to economically produce certain types of copper products including ETP copper rod.
- The FRHC copper rod production process can tolerate scrap feedstock with higher impurities which are removed via thermal refining.
Bimetallic copper scrap
- Scrap from copper-clad aluminum products (i.e. wire and cable, busbar, architectural flat products) should not be used to produce certain copper and alloy products.
- Aluminum impurities introduced to melting operations via copper-clad aluminum scrap readily oxidize and are difficult to detect in melt samples.
- Scrap from copper-clad steel products should not be used to produce certain copper and alloy products. Copper-clad steel can be removed from mixed scrap by magnetic separation, but still presents practical challenges.
A complex problem
- Many of the incompatible copper-based scrap types described above are visually indistinguishable which makes sorting difficult in practice.
- Segregation of copper-based scrap is further complicated by the international trade of scrap as a commodity. Global coordination across multiple value chain segments is required.
- The Institute of Scrap Recycling Industries (ISRI) publishes specifications for copper-based scrap. Scrap specifications with harmonized limits for known contaminants can help address the problem. Four new ISRI specifications were published in 2016 which set tolerance limits for certain impurities in leaded and lead-free brass scrap: Nascent, Niche, Ebulent and Ecstatic.
- Harmonized markings on brass components (i.e. water meters, valves, fittings) that identify the alloy family (i.e. lead, silicon, or bismuth-containing) could facilitate the sortation of secondary brass scrap. However, the cost and disruption to implement a marking system presents challenges.
- Portable instrumentation such as X-ray fluorescent spectrometers can facilitate sorting of certain types of copper and alloy scrap, but is not a cost-effective or efficient solution for large batches.
- Sensor-based sortation technology offers a promising solution to segregate some forms of mixed copper and alloy scrap. Cost, throughput, cleanliness, and sizing control are limiting factors.
Proper care must be deployed throughout the value chain to ensure that certain types of copper and alloy scrap are not mixed. The above insights can help avoid rejected scrap shipments, keep costs down for suppliers and users of copper products, and protect the viability of the copper and brass scrap stream.
For more information, please contact
Copper Development Association, Inc.
Adam Estelle is Director of the Copper Development Association’s Rod & Bar Council whose mission is to defend and grow the use brass rod for precision machined and forged products. In addition, Adam manages a market development initiative for copper alloys based on their inherent antimicrobial properties, and he also leads an industry working group formed to protect the viability of the copper and brass recycling stream.
The Copper Development Association Inc. is the market development, engineering and information services arm of the copper industry, chartered to enhance and expand markets for copper and its alloys in North America.