Final processing of fractions containing precious metals

On 25 and 26 September 2023, the members of the Swico/SENS TC met in Spiez, in the canton of Bern, for a two-day training course. In addition to the regular organisational and technical exchange, the topic of processing fractions containing precious metals was explored in depth. Christian Hagelüken was brought on board as an expert in (precious) metal recycling. He shared with us his extensive knowledge, built up through his many years of industry experience and through his involvement in various large-scale projects, expert groups and initiatives. In addition to technical input and open exchange, the programme also included a visit to Batrec in Wimmis, where the TC gained an in-depth insight into battery recycling processes and developments in the processing of lithium-ion batteries.

Multi-metal recycling

WEEE is a complex waste stream containing plastics, glass, ceramics, precious, base and special metals, halogens, pollutants, etc., in a close combination of materials. These materials are separated to the greatest extent possible in a partly manual, partly mechanical pre-processing stage, so they can be fed into the corresponding recycling process. The precious and special metals are concentrated in certain fractions, but these still consist of a mixture of materials. Clean separation of such metals is not possible at present. Fractions rich in precious and special metals are therefore fed into a multi-metal recycling process. After melting, masses rich in copper, nickel and lead are separated from one another. These metals serve as collectors and (chemically) take along precious metals with corresponding metallurgical and thermodynamic properties. When copper, nickel and lead are recovered using special processes, the ‘collected’ metals remain in the resulting residues, which they can be recovered from in subsequent processes¹ (see Figure 1). So high recycling rates are possible even if the target metals are only present as trace elements in the input.

^{1 The article describes the process that Umicore Hoboken uses. The processes at other smelting works may differ.}

Challenges

The process complexity is high because, in addition to the different melting and refining processes, there are also strict requirements regarding air pollution control and residue management. The required investment is correspondingly high. Since the processes also require a great deal of energy, high and sometimes volatile energy costs are incurred, not to mention investments in the decarbonisation of the processes. These costs arise in the face of decreasing precious metal content in electronic products and volatile metal prices. To ensure the economic viability of a multi-metal recycling plant for electronics, economies of scale are of central importance. There are therefore only a limited number of such plants worldwide.

Another challenge is taking representative samples for material analysis. This is required for each delivery to correctly remunerate for the purchased material based on the actual target metal contents, as well as any contaminant and pollutant contents. In addition, this information is essential to ensure optimum composition of the input material for the melting process.

Limits

Target metals that are fed into a corresponding multi-metal recycling process can be recovered with high quality. The process yield for precious metals is over 95%. However, this is the last step in the recycling chain. Waste electrical and electronic equipment must first be collected and sent for pre-processing. If waste electrical and electronic equipment is not collected in the first place or if it is disposed of inappropriately, the contained metals are lost. Further losses can also occur during pre-processing if precious and special metals are separated into fractions that they cannot be recovered from. The overall recycling efficiency is determined by the weakest link in the chain (see Figure 2).

Precious and special metals are only found in waste electrical and electronic equipment in small quantities. Due to the high investment and process costs, economical recycling is only possible if the process can be used to capacity with the necessary quantities and if the metal prices are correspondingly high. The latter can be assumed in the case of precious metals and copper, but not for many special metals. These can only be recovered economically because the corresponding synergies exist with copper and precious metal recycling. Metals without the metallurgical and thermodynamic properties for the applied processes move as oxides into the final slag, which they generally cannot be recovered from in an economically or ecologically sensible manner.

Lithium-ion battery recycling

Lithium-ion batteries have become pervasive in electronic products. Since these are specific components, they can and must be removed at an early stage and recycled separately. Not only do lithium-ion batteries represent a major risk potential² in the waste stream; the raw materials they contain can also be better recovered if the batteries are fed into targeted recycling as a separate stream. Since batteries are often fixed (glued, welded) in the equipment but need to remain as undamaged as possible when removed, this process itself presents an initial technical and economic challenge. There are also a variety of different designs and battery chemistries. Sorting is only possible if the waste stream is homogeneous, for example electric car batteries of the same type and design. Lithium-ion batteries from waste electrical equipment are not usually sorted, but are rather mixed in a special shredding process to obtain what is known as ‘black mass’ – a primary material for final processing. In addition to nickel and copper, black mass also contains cobalt, lithium and other metals. In the previously described process for recovering precious and special metals, only copper and nickel can be recovered. The other metals would be lost in the slag. To efficiently recover the raw materials contained in the black mass, other special processes are needed. Such processes are currently under development by various companies, including Umicore. Recovery rates of > 90% for cobalt, nickel and copper and > 50% for lithium are already achievable.

Visit to Batrec

Batrec also developed a process for metal recovery from lithium-ion batteries. The lithium-ion batteries, some of which arrive mixed with other battery types³, are separated manually and the pure lithium-ion battery fraction is then processed by means of a special shredding process. Among other things, black mass is obtained. It serves as a primary material for final processing by a customer.

Alongside the tour and insights into the recycling processes for ordinary household batteries, visitors had the chance to view the manual sorting and shredding process for lithium-ion batteries during the visit to Wimmis. In an open exchange with Batrec specialists, questions that often arise during auditing activities regarding the handling of lithium-ion and lithium metal batteries were answered.

^{2 Heat development in the event of a short circuit caused by damage can quickly lead to fires.
3 Nickel-cadmium, alkaline, nickel-metal hybrid (NiMH) batteries, etc.}

Source:
C. Hagelüken, «Recycling of Electronic Scrap at Umicore. Precious Metals Refining.» in Acta Metall, Waste – Secondary Raw Materials III, Strbske Pleso, Slovakia, 2006.