New industrial sorting systems based on laser spectroscopy (LIBS), magnetic induction, and machine vision for recycling of non-ferrous metals.
SMEs and research organisations in the EU-funded SHREDDERSORT project have developed and demonstrated a new industrial sorting system to separate non-ferrous shredder scrap into cast aluminium (Al), wrought Al, and non-Al categories. Compared to the unsorted material, the sorted categories are better suited for recycling into secondary metals, have a higher market value, and will reduce the use of raw materials.
New products and technologies
End-of-life vehicles (ELV) generate around 10 million tonnes of waste per year in the EU. Around 75% of this waste is currently recycled or recovered, but this level still falls short of the 95% target set by the European ELV Directive - 2000/53/EC.
The initial processing is of ELV metal scrap is carried out in shredder plants which chop the dismantled and depolluted vehicles into pieces around 5-20 cm in size to facilitate sorting and separation. Magnetic separators are used to separate out the ferrous metals (iron and steel), and eddy current separators are then used to separate the non-ferrous metals - aluminium (Al), copper (Cu), magnesium (Mg) etc. - from residual non-metals such as plastic and glass.
The non-ferrous metal fraction is dominated by cast and wrought Al alloys. Cast Al alloys are used in cast components such as engine blocks, pistons and cylinder heads. Wrought Al alloys are used in stamped, extruded and forged vehicle components. Most Al scrap, both cast and wrought, is currently recycled to produce secondary cast Al, which tolerates higher levels of contaminating elements, notably Silicon (Si). However, for the automotive industry, from as early as 2018, the supply of scrap aluminium will begin to exceed that required to produce secondary cast aluminium, and there will be an increasing shortage of sorted wrought aluminium scrap to meet the demand for the production of secondary wrought aluminium alloys. Around 50 million tonnes of Al products are currently produced worldwide, and this is expected to increase by a factor of four by 2050.
Other high value metals in ELV scrap include copper and copper alloys, such as bronze, and a small quantity of Mg alloy. Mg is listed as a critical metal, essential for high-technology, green and defence applications, but vulnerable to politically or economically driven fluctuations in supply.
To improve the recycling of the high value metals present in ELV shredder scrap, for use in the production of secondary metals, and to reduce the demand on raw materials the SHREDDERSORT consortium is developing three sorting systems for use in shredder plants:
1) One which uses Laser Induced Breakdown Spectroscopy (LIBS) systems to distinguish and separate cast and wrought Al alloys.
2) One which uses LIBS to distinguish and separate Mg and individual Al alloys series.
3) One which uses magnetic induction and machine vision methods to identify and separate Cu alloys, Al alloys, and stainless steels.
The first LIBS sorting line became operational in April 2016. In that system, cast Al, wrought Al and non-Al metal fragments travel on a 1 m wide conveyor at a speed of 2 meters per second, with a target throughput of 1 tonne per hour. In LIBS, a short, high power laser pulse is focussed onto the each of the metal fragments as they pass by, which ablates a small mass from the surface of the fragment and generates a plasma plume with temperatures in excess of 100,000 °C. As the plasma cools, the characteristic emission lines of elements in the ablated material are measured using a high speed spectrometer, to distinguish between the different Al alloys prior to separation into 3 classes by air ejectors.
The remaining two sorting systems, are under construction, and will be operational by September 2016, prior to the validation of all three systems in commercial shredder plants from Oct-Dec 2016.
The SME partners and end-users in the project aim to commercialize and use the systems in ELV and other recycling applications including demolition and construction waste, industrial scrap, and waste electronic and electrical equipment (WEEE).
For more information about the project and the participating partners, please refer to the project website: www.shreddersort.eu
Recycling, non-ferrous metals, scrap sorting, end of life vehicle, ELV, shredder, secondary metals, cast aluminium, wrought aluminium, critical metals, laser, laser induced breakdown spectroscopy, LIBS, machine vision, image processing