Assessing recycling strategies for critical raw materials in waste electrical and electronic equipment

The circular economy is a strategy for reducing risks that result from the criticality of commodities in our economic system. Therefore, anticipatory planning of recycling infrastructure must consider the historical and future use of metals as well as detailed product characterizations. For bulk materials like plastics, industrial base metals (IBMs) such as steel, aluminum, copper, and precious metals (PM), e.g. gold, silver, palladium, well-established methodologies and a profound knowledge base exist that enable a detailed process modeling. Similar information is missing for a selected set of critical raw materials (S-CRMs), which are applied to a large extent in modern electrical and electronic equipment (EEE). Although, being highly important for the producing industry and being related to potential future supply risks, a functional recycling from waste electrical and electronic equipment (WEEE) is currently not practiced. This doctoral thesis focuses on the provision of WEEE product-centric information with a special emphasis on S-CRMs via the consolidation and further development of available methods to support the derivation of recycling strategies. Research is needed explicitly for gallium in integrated circuits (ICs), indium applied as indium tin oxide (ITO) in liquid crystal displays (LCD), rare earth elements (REEs) used in NdFeB magnets applied in hard disk drives (HDDs), and tantalum in tantalum capacitors applied on printed circuit boards (PCBs). Following a consecutive methodology, in a first step, S-CRMs will be identified and localized in WEEE flows via material flow analysis (MFA), and single WEEE products via recycling-oriented product characterization. In a second step, theoretically available mass flows of these S-CRMs and by-applied materials are quantified for EEE put-on-market (worldwide/Germany) and WEEE collected (Germany) in 2013. Recyclability of S-CRMs in selected WEEE applications is assessed via customized recycling processes. Data are then collated in a recycling barrier analysis investigating the framework for a successful recovery of S-CRMs. WEEE flow results indicate a lower relevance of S-CRM recovery from WEEE, as significantly higher yields can be gained by reducing losses in the primary production of S-CRMs, in subsequent refining steps, and in the manufacture of semi-finished products. However, supply risks typically accompanying the primary production routes of S-CRMs indeed suggest considering S-CRMs recycling from WEEE. Current recycling strategies of WEEE are solely optimized for the recovery of bulk and valuable materials. Results on the general pre-processing of WEEE show that S-CRM recovery is not the core focus, which results in their dilution with other materials in mechanical treatment. A later S-CRM recovery from generated output fractions is hardly possible. Together with the loss of S-CRMs, other valuable materials, such as gold or copper, are lost within those output fractions as well, due to limited liberation and separation techniques in mechanical treatment. Results from WEEE product analyses confirm the earlier indicated lower relevance of S-CRM recovery, as the mass fractions in the WEEE devices is rather low. However, selected liberated components contain high S-CRM mass fractions of up to 30-50% and are worth further end-of-life treatment. The typical design of WEEE devices often impedes a feasible recycling of the S-CRMs. Also, the technical identification of smaller components (e.g. tantalum capacitors and in particular ICs), which contain SCRMs, is complex due to lacking well identifiable characteristics. Chemical analyses prove heavily fluctuating mass fractions of S-CRMs in WEEE components. Furthermore, they have a limited selectivity, as with the removal of materials carrying S-CRMs, other elements are unintentionally removed. This applies to valuable materials such as gold, copper in ICs and silver in tantalum capacitors. Also, contaminating elements are affected such as nickel in NdFeB magnets or even toxic heavy metals such as arsenic, chromium, lead, and antimony in LCD panels.