New ways for metal recycling
REWAVE XRF 3-way-sorting in innovative “Free-Fall”-design
Recycling of metal and aluminium knows no limits because it can be remelted as scrap indefinitely. Metals, however have to be separated from non-metallic impurities, and different metals have to be sorted in pure fractions to be used as secondary raw materials substituting primary resources. Especially when it comes to aluminium a lot of energy can be saved when remelting scrap aluminium. By using secondary raw materials in the production of aluminium, the energy-intensive electrolyses process is eliminated, thereby reducing the total energy consumption to below 10 percent compared to primary production. Furthermore, mining of many ores for primary production occurs in politically unstable regions. On another note ore mining and the processes that follow can produce tailings and leave toxic residues such as “red mud” behind.
Global demand for ferrous and nonferrous metals is increasing each year. Industrial production in all areas of daily life devours an enormous quantity of aluminium and other nonferrous metals, including copper, brass, nickel, tin, zinc and lead. Zorba is a scrap metal grade that is defined by the Institute of Scrap Recycling Industries Inc. (ISRI), and consists predominantly of aluminium and also contains other non-ferrous metals such as copper, zinc, brass, stainless steel.
Zorba - a cheap resource
Nowadays, most of Zorba produced in Europe and USA is exported to China as separate mixed aluminium (defined by ISRI as Twitch) and mixed heavy metal fraction. However, more and more Zorba is expected to stay within Western countries as a result of rising labour costs in China and surplus of primary aluminium in China as well as improved sorting technologies. With the possibility to use sensor-based sorting, separating mixed heavy metals becomes possible as well as inexpensive. Also the mixed aluminium fraction can be further sorted with sensor-based sorting.
Let us, before we go into detail on sensor-based sorting technologies take a closer look at the aluminium (Twitch) fraction and especially its composition and origination. In Europe the average end-of-life vehicle contains approx. 140 kg aluminium (Ducker Worldwide), whereas in the North America it is around 115 kg (Ducker Worldwide). All this aluminium (except the wheels) can only be used to produce foundry alloys and this what has been done up to now. By using XRF-sensor-based sorting, however Zorba and Twitch can be further sorted.
Picture selection: Zorba Fraktion
An XRF-machine is capable of sorting aluminium alloys based on their zinc and/or copper content. Taking Zorba as example, it is possible to sort in 3 different aluminium categories: one low zinc low copper fraction compatible with semi prime foundry alloys such as 356.1, one high copper high zinc fraction compatible with regular die casting alloys such as Din 226 (or A380 in the USA) and one fraction with medium contents of zinc and copper compatible with piston alloys. REDWAVE calls this process 3-way-sorting.
By sorting Zorba with the 3-way-sorting strategy an aluminium stream (low copper low zinc) compatible with some wrought alloys can be obtained. This stream has a Zn and Cu level of around 0,10 % to 0,2 % with Si at around 1,0 to 1,5 %. It can be used in several 6xxx series alloys and would lower the cost for (automotive) sheet significantly. This would mean that automotive sheet, a product nowadays mostly made of primary aluminium, can be produced using scrap aluminium, resulting in enormous energy and money savings and a green footprint. This (Zorba-) scrap is already available at an extent of around 4 million tons (North-America and Europe combined) and will be increasing as the average aluminium content in cars constantly rose in the past 15 years and furthermore, will be rising even more in future cars (e.g. F 150 from Ford with 490 kg aluminium).
Picture: REDWAVE 3-way-sorting
X-ray Sorting Technology
X-ray machines are available for a few years on the market to sort pieces of scrap at high speed in an industrial environment. In general, two different x-ray based machines are available including XRT (x-ray transmission) and XRF (x-ray fluorescence). XRT sorts based on a density difference and can separate light scrap from heavy scrap. In practice this is very similar to what a flotation does with the advantage of a flotation to also separate magnesium from aluminium. XRT, flotation and XRF can separate aluminium from heavy metals.
XRF (X-ray fluorescence)
XRF is used for more than 2 decades for non-destructive testing in lab- or Handheld devices to test and sort individual pieces. XRF is a very precise analysis method, which performs a complete chemical analysis. REDWAVE has developed the first XRF-based sorting machine worldwide 10 years ago for glass sorting, more precisely to identify and remove so called heat resistant glass and lead crystal glass. The use of this technology is not limited to one material class or application and the need of an XRF-based sorter for metal scrap was soon realized. XRF machines offer several significant advantages compared to XRT machines. Like XRT, they can separate light from heavy such as heavy metals from aluminium in Zorba, however XRF can also further separate the aluminium stream into various fractions. This strategy is not limited to copper and zinc as explained in the 3-way-sorting. Also, other elements such as iron and manganese can be used. The same applies for the heavy metal fraction, which always makes up a certain percentage in Zorba. In contrary to XRT, XRF can also further separate heavy metals into pure packages of each copper, brass, stainless steel, zinc, etc. These fractions are of high quality and can be used directly in a smelters after only one sorting step. Furthermore, an XRT can only “see” the presence of heavy elements, however cannot distinguish between them. Heavy elements of similar density are always seen together, hence it is impossible to do any kind of sorting based on copper versus zinc in aluminium alloys or further sort heavy metals.
REDWAVE XRF- innovative free-fall design
As mentioned above the first machine using XRF was produced 10 years ago for glass sorting and developed as belt-type machine. The technology was then further developed to making it ideal for metal scrap and includes a new innovative free-fall design, a combination of XRF with Camera-recognition and an advanced software algorithm.
The compact free-fall design offers advantages compared to a belt-type machine, especially when it comes to heterogeneous and 3-dimensional material such as metal scrap. While with XRF or XRT belt-type machines the material needs to be screened in several streams (usually 5 fractions), the requirement with the free-fall design is only one screening step between 10 mm and 180 mm although having efficiencies and purities in the mid to high 90s. The capacity per meter sorting width is with up 10 t/h for Zorba and Twitch also significantly higher compared to XRT. The largest REDWAVE XRF is able to sort Zorba and Twitch with a capacity of 15 t/h. Low maintenance costs and efforts, no moving parts and the very compact design are some more advantages of the free-fall over the belt design. What makes the free-fall design unique worldwide is the combination of object recognition and chemical analysis together with the advanced software algorithm. It is not only possible to just qualify the material in terms of present elements, the software algorithm calculates a so-called “intensity per pixel ratio”, which is basically the content (percentage) of the element. This makes it possible to not only sort alloy groups from each other, but to also sort within the same alloy group by looking at the same element but at different concentrations.
Choice of Picutres: REDWAVE XRF sorting machine, Copyright REDWAVE
New possibilities in sorting metal scrap
Zorba and its separated Twitch and heavy metal fraction are not the only product an XRF-machine can handle. Old cast for instance, can also be sorted with the same strategy. In Europe, the amount of old cast is quite high as the engine is usually taken out before shredding the car and treated separately. As for heavy metals, in general, any heavy metal fraction can be sorted using XRF. The sorting effort is determined by the requirements in regards to quality and composition of the final product. This can be from a simple separation of copper and brass from heavy metals to separating individual brass and bronze or stainless steel types from each other. Furthermore, the non-ferrous fraction from IBA (incinerated bottom ash) can be sorted the same way and a sorting step to separate gold, silver, platinum and other precious metals makes the investment even more economic. A similar logic of sorting scrap before the smelter also applies to other industries. Let us use the copper industry as an example. Instead of buying the highest scrap grade, for instance Birch or Cliff (definitions by ISRI) can be purchased as (cheap) copper source and sorted with XRF for any contamination such as brass, nickel or silver.
What kind of scrap should be bought?
For scrap recyclers, being able to use one technology for multiple different applications and sort Zorba, Twitch, heavy metals, Zurik, IBA, etc. is a significant advantage of XRF over XRT, camera or flotation. If the quantity does not justify investing in multiple machines the very same machine could be used for various applications and theoretically for all above described applications. Owners of flotation or XRT have the option of installing an XRF-sorter to further sort the material stream and increase the revenue of each product.
During the same step when sorting metals, it can also be used to get the exact composition in pieces and percent of each alloy and metal type. If for example Zorba only contains 3% copper pieces rather than 4% as promised by the vendor, you will be able to document and claim.
Impact on Secondary Aluminium Recycler
Secondary alloy producer and recycler can take advantage of the possibilities of XRF. By having XRF-machines installed on their site, they can buy Zorba and adopt a sorting logic based on their production, material mix and needs. They can for instance optimize their own operation by either buying more Zorba and doing less sorting or by buying less Zorba and doing more (aluminium) sorting. The best strategy would be driven by marked conditions. By buying Zorba and processing it you can start with one of the cheapest sources of scrap in the market and this can replace some of the most expensive scrap grades you have to buy nowadays. The savings can easily be € 200 per tonne.
Sorting with LIBS
There have been quiet some efforts made recently to develop LIBS (Laser Induced Breakdown Spectroscopy) for sorting aluminum alloys. At the moment, LIBS is multiple times more expensive than XRF or XRT in terms of cost per tonnage and only a very few prototype installations exist worldwide only the future can answer to whether this technology will be cost effective. However, one is certain, any kind of sorting will start with cheaper technologies such as eddy current, camera, XRF or XRT machines. If the time is right for LIBS it will only be used after XRF or XRT in applications where further separation justifies the high investment cost.
Choice of pictures: Copyright REDWAVE
REDWAVE supplies ground-breaking and economic sorting plants for recyclables as well as turnkey waste treatment plants. Furthermore, it is a leading manufacturer of sensor-based sorting machines with a sturdy industrial design. They feature a high selectivity for several recycling materials. This results in a high yield of pure fractions. REDWAVE is operating worldwide and headquartered in Austria. It maintains branch offices in Germany, Asia and the USA.
BT-Wolfgang Binder GmbH:
BT-Wolfgang Binder GmbH is operating worldwide as general contractor for the execution of facilities since 20 years. The company is divided into two divisions: Recycling & Waste Treatment is managed under the trade name REDWAVE, Mineral Processing & Materials Handling Systems under the trade name BTW Plant Solutions.