Shredded, ball shaped, sorted – recovering valuable metals from residues
Following a newly formed partnership announced earlier this year, CEMAC technologies will distribute German manufacturer BHS-Sonthofen equipment in Australia and New Zealand.
BHS-Sonthofen further optimizes innovative processes for the fine processing of metalliferous residues.
Whether pre-shredded end-of-life vehicles (ASR), waste from electrical and electronic equipment (WEEE) or incinerator bottom ash (waste incineration plant), they all have one thing in common: they contain valuable metals that are always worth recovering. Therefore, fine processing of the materials is of high importance. BHS-Sonthofen offers a well-established process which has recently been further refined. This standard process consists of pre-sorting as well as several shredding stages in the rotor impact mill, which accomplishes multiple challenging processing tasks at once. These steps are followed by sorting via screens as well as magnetic and eddy current separation. Each plant is individually adapted to the customer’s requirements due to the large variance of input material.
Electrical scrap, shredder residues from automobile recycling as well as incinerator bottom ash and other residual fractions all contain a wealth of valuable metals. However, recovering these metals individually is a real challenge. The composites and minerals also contained in the input material, as well as the structure of the individual components, make disaggregation and the subsequent sorting process more difficult. For instance, the copper from the shredded cables is still shielded by insulating material. Yet, freeing the cables from their sheathings is just one important aspect. In order to be able to sort the exposed wires and separate them from the rest of the metal fraction on the separating table, they must also be shaped into balls. This is the only way to recover pure copper.
Another challenge in processing these fractions is the wide variance in feed material. Even with seemingly identical input material, the differences are striking. For example, the material components in ASR vary significantly depending on the class of the shredded end-of-life vehicles and the year they were built as well as the proportion of additional WEEE they contain. When light and heavy shredder fractions or cable residues are recycled, the material still must be prepared in such a way that the metals are ready for sale at the end of the process.
BHS adapts standard processes for each customer
Such a wide variety of materials requires an innovative process that always ensures the highest yield of high-quality metals by continuously making further developments. BHS-Sonthofen invests a lot of time in research and development work to optimize the fine processing of residues containing metal especially regarding the fine fraction of 0-25 millimeters. The result of these successful endeavors is not only a wider range of possible input materials, but also higher throughput with lower costs for wear and operation.
BHS-Sonthoffen offers a standard process for recycling metal-containing residues that is now established. But as Jörg Ehrich from the Process Development department at BHS points out, “Here, ‘standard’ almost has to be put in quotation marks. The core components for our recycling process for ASR and other fractions containing metal are set. However, we adapt the process in great detail together with the customers according to their individual requirements and are able to modularly expand the process. This is a crucial step, because I have yet to experience two customers coming to us with a truly identical input material. Usually, the composition of the feed material varies depending on the application or country. We use our tests to make sure that the adjustments actually fit the input material’s characteristics.”
The tests with original feed material, which Jörg Ehrich and his colleagues run together with customers at the Sonthofen Test Center, form the basis for the optimized process recommended by BHS. Moreover, the tests and their results are used for further process optimization, as a foundation for detailed plant engineering and for an individual profitability calculation of the client’s project.
Repeated shredding with reduced wear
The first step in the process involves gathering the input material in a hopper, followed by initial pre-sorting, in which protective screens sort out impurities as well as pieces with a grain size of more than 25 millimeters. A zigzag sifter then removes dust and the largest part of the contained minerals. This specifically reduces wear on the equipment and makes the process run more smoothly.
The most important process step takes place after this initial presorting: using the rotor impact mill of type RPMX. Unique to its class, this high-performance shredder with a vertical shaft ensures that the input material is subjected to the optimum level of stress, thanks to its unique impeller rotor and special anvil ring. The high circumferential speed of the rotor generates centrifugal forces. At the same time, the shredding tools cause impact and shear forces, which result in a high energy input into the feed material. Thanks to a rotor cover plate, the material is additionally directed from above into a narrow gap between the ring armor and the impact hammers. This way, the entire height of the milling gap is used for the crushing process, which ensures a longer dwell time and higher stress on the input material. An intensive ball shaping effect is created between the horseshoe-shaped hammers and the ring armor, which sets the stage for subsequent efficient separation and sorting of non-ferrous metals and other materials. According to the desired result, the input material is processed in the rotor impact mill until it is small enough to exit the machine through the gap.
The RPMX works selectively: Mineral and brittle particles that were not removed from the feed material during presorting are crushed and pulverized by the machine. It reliably breaks down composite materials and metals. Rubber and plastic components also pass through the mill but remain largely intact – the machine merely detaches them from other materials. Cable sheathing and other substances attached to metals are thereby reliably removed.
In order to be able to sort valuable components, it is crucial that the rotor impact mill shapes ductile materials into balls: all pliable metals, such as copper or aluminum. This is the only way to cleanly separate the non-ferrous metals from the other materials afterwards. In the standard process, each batch that is fed in passes through the mill two to three times. Light material and dust are separated and discharged one more time before each round of shredding in the circulation process in order to avoid unnecessary stress on the machine.
Shredded and ball-shaped for sorting
The final shredding step is followed by the second part of the process: sorting the processed material. In this part, the processed material runs over a hopper onto a screening machine, which sorts it into different fractions. The type of fraction they are sorted into depends on how they are further processed. The individual fractions are separated on the separating table into the categories “heavy” (all metals and metal mixtures) and “light” (neutral material such as plastics and rubber). Magnet technologies, such as overbelt magnets, separate the heavy fractions, which contain the valuable metals, into magnetic and non-magnetic metal fractions. The latter undergo an additional separation step. An eddy current separator sorts the valuable fractions into heavy metals, such as copper, gold and silver, and light metals, such as aluminum. “The material can be perfectly sorted during eddy current separation due to the fact that the RPMX has already shaped all the soft metals into balls, and the hard metal parts are well separated,” explains Jörg Ehrich. All the sorted metal concentrates are then immediately ready for sale.
An efficient process that is as unique as the input material
Over time, BHS has developed numerous options for adapting the fine processing process in order to cater to all feed materials and meet customer requirements. The standard process is generally a circulation process, in which material passes through the rotor impact mill (RPMX) two to three times until it is optimally prepared for the second process step: sorting.
If more than one machine is used, the throughput in the first shredding stage can be significantly increased, explains Ivan Glamuzina, Senior Project Manager at BHS: “A more efficient alternative to the recirculation process – if sufficient space is available – makes use of a second rotor impact mill arranged in series, so that the material is continuously fed through the plant. Much higher tonnages can be processed with this process variant.” Whether recirculating or sequentially arranged rotor impact mills: Before each subsequent crushing stage in the RPMX, a zigzag classifier removes dust and light material of 0-8 millimeters.
Becoming more efficient thanks to further improvements
In recent years, BHS has continuously refined the process for waste and metal-containing residues to guarantee more effective and customized options for adaptation. Therefore, the company has also looked extensively at new options for optimizing the rotor impact mill of type RPMX and has made improvements to key process steps as a result. The focus was on how to further increase throughput while maintaining low replacement and maintenance costs as this machine forms the heart of the entire processing plant.
The answer was to redesign the hammers being used: “We have examined the RPMX’s impact hammers and looked at how we can make them even more effective and resilient,” reveals Jörg Ehrich. “Our goal is, on the one hand, to optimize the output quality and to reduce wear even further. On the other hand, we simplified the process for replacing and adjusting the hammers in case of wear to make maintenance more effective and easier for the workers. The improved maintenance concept allows customers to readjust the hammers on their own, in a quick and uncomplicated way. We also integrated a special tool for dislodging the hammers – known as a mandrel – into the design, as well as a load hook to aid the replacement process. The latter simply hooks into the hammer so that it is easy to lift out or set in place using a crane, which significantly reduces the physical strain on personnel.”
Using an alternative or additional crushing methods in combination with sensor-based sorting technology may lead to even more adaptation options in the future. “We are currently running tests to determine whether these technologies might be suitable for improving the output quality in the recycling of lithium-ion batteries. We are also testing whether an additional crusher might lead to an even better processing of input material with a high cable content,” adds Ivan Glamuzina. BHS offers the process with sorting technology from its own portfolio as well as with additional sorting technology from third-party suppliers (if necessary). The core components of the standard process – crushing technology, sifters and screens, sorting and separating tables and the entire plant control system – all come from BHS-Sonthofen.
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