19. 10. 2022

Separation of aluminum from mixed waste (case study)

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1. Separation of aluminum cans from plastic and other non-metallic mixed waste. The material processed by the client has already passed through magnetic separation and does not contain iron tramp. However, in order to make use of the the non-ferrous metal, the client needs to separate it from the remaining municipal waste (paper, wood, plastics, etc.).
2. Separation of aseptic beverage cartons (tetra pack type) from the mixed waste which does not contain ferrous particles..Aseptic beverage cartons consist of six layers, only one of which is made of aluminum (four are polyethylene and one is paper. Aluminum protects the contents of the carton from light, the paper gives strength to the packaging and polyethylene ensures packaging impermeability). Complete and separated recycling of all three components is still rather rare. Usually the paper fibers are recovered in paper mills (where beverage packaging is mixed in a water bath and the paper fibers are subsequently used in the production of recycled paper). Relatively widespread (and simple) is using whole cartons for the production of construction and insulation boards (having then similar properties to plasterboards). Polyethylene is sometimes also obtained from cartons to produce recycled plastics. The aluminium component is the least used so far, in spite of the fact that its economic potential is very significant. Especially, if we take into account the current price of aluminum and if we multiply it by the huge amount of aseptic beverage packaging in the mixed waste... A fundamental condition for using aluminum from aseptic beverage packaging is the quality separation of the packaging waste. This material is then crushed and aluminum is separated from plastic and paper by the application of electrostatic separators (making it possible to recycle up to 99 % of the aluminum contained in the aseptic beverage cartons!).
3. Simultaneous separation of aluminium cans and aseptic beverage cartons from the mixed waste (that does not contain iron tramp).. 

 Operational principle of the non-ferrous metal separator

 The eddy current separator is equipped with a short conveyor belt. In its driven roller with non-metallic shell there is (centrically or eccentrically) embedded a high-speed magnetic rotor. The separation of a metal non-magnetic particle occurs at the moment when this particle transported on the conveyor belt enters the magnetic field of the rotating rotor. The magnetic field will magnetize it for a limited time and its polarity will be the same as that of the rotor's magnetic field - therefore the materials magnetized in this way are repelled and automatically ejected from the conveyor belt of the non-ferrous metal separator. The condition for achieving the best possible results of sorting non-magnetic metal waste is a uniform flow and (if possible) a monolayer of the material transported on the belt conveyor - therefore it is always suitable to place a vibrating feeder in front of the non-ferrous metal separator. It should also be kept in mind that before sorting non-ferrous metals, it is necessary to remove ferrous particles from the material to be cleaned (e. g.  by the application of a magnetic drum, pulley or overband magnet).

Problem

The eddy current separator is used to separate non magnetic metals from other non-magnetic materials. Aluminum belongs to the well-conducting light non-ferrous metals, so its separation using an eddy current separator is mostly problem-free. Besides the type of material itself, electrical conductivity is also affected by its shape and volume, therefore, e. g. aluminium sheets or cans are separated more easily than short and thin wires. As to the electrical conductivity, for example the very thin layer of aluminum in aseptic beverage containers is also problematic. Besides, the electrical conductivity of aluminium cans is very different. That is why the separation of both material types by the same kind of an eddy current separator may be difficult - which also had to be verified during the test.

 Solution

Using the four-pole centric ECS-C separator of non-ferrous metals we first tested the separation of individual aluminium cans at a belt speed of 1.5 m/s. The result of the test proved 100 % reliability of the rejection of this material type when using ECS-C (the eddy current separator threw away all the cans considerably beyond the splitting axis). That is why we proceeded to test the separation of aluminium cans from the mixed waste - and the result was the separation of all aluminium cans from the tested material. Subsequently, we also performed the same test with tetra pack packaging - firstly without admixture of other materials, then we tested the separation of these packagings from the mixed waste. Both tests showed that although ECS-C can also separate tetra pack with the aluminum coating for the most part, however, the very thin aluminum layer does not allow a 100 % reliable separation to be achieved with the four-pole centric variant of the eddy current separator.

Then we tested the separability of both aluminium cans and tetra pack, using the twelve-pole eccentric eddy current separator ECS-E. At first glance, it was obvious that the kinetic energy imparted by the magnetic field of the separator to both the cans and the tetra pack packaging is much greater than that which the four-pole centric separator could impart to them during sorting. Thus, 100 % capture of aluminium cans and aluminium-plated tetra packs was achieved. In addition, because both material types were thrown to a greater distance than required, the opening in the sorting box for the non-magnetic material could be enlarged. This fundamentally increased the total capacity of the separation line, which had a significantly positive effect on the overall economic results of the mixed waste sorting.

Evaluation of the possible technical solutions

If there is a need to separate Al cans, e. g. from a mixture of other non-magnetic waste, the application of an eddy current separator with centrically mounted few magnetic pole system appears to be the best solution, for the following reasons:

• Very fast investment return (in case of a higher percentage of aluminium particles and larger processed quantities, the return can be in the order of a few weeks)
• Reliable separation of aluminium cans
• In the given case, it is an absolutely tantamount equivalent of more expensive multi-pole eccentric separators = attractive price/performance ratio
• Separator with automatic cleaning without the interruption of the material flow (24/7) = fluent processing operation
• High efficiency even at higher speeds
• Working width up to 2,000 mm = high processing capacity

If the client needs to separate less electrically conductive aseptic beverage cartons from mixed non-magnetic waste or capture aseptic beverage cartons and aluminium cans at the same time, then the best solution is to use a multi-pole non-ferrous metal separator with an eccentrically mounted rotor, offering the following advantages in particular:

• Reliable separation of aseptic beverage cartons (despite the only very thin aluminum layer)
• A universal solution in the case of separation of non-magnetic metallic materials even with substantially different properties
• Separator with automatic cleaning without interrupting the material flow (24/7) = fluent processing operation
• High efficiency even at higher speeds
• Working width of up to 2,000 mm + throwing aluminium objects to a great distance = high operating capacity

Benefits of our solution for the client

• Utilization of a valuable secondary raw material
• Reduction of the ecological burden caused by the production of primary aluminum from bauxite
• Significant increase in work productivity, profit ratio and profitability in the field of the mixed waste sorting