Combining laser cleaning and LIBS: fast and precise recycling of metal alloys

In respect of a limited amount of raw material, costs, CO2 and waste reduction, high precision metal recycling is getting more and more important these days. Contaminations of the melt with unwanted or outright detrimental elements (e.g. C, S, P, Cu or Pb in steel, Cr or Ni in low-alloy steels, Li in aluminium and so forth) are a huge liability toward the ‘‘alloy-to-alloy’’ recycling goal and essentially the only option in this case, is either costly dilution with clean raw materials, downgrading or worst case scenario discarding.

by Chao, Madlen; Günther, Jens-Uwe; Ashan, Amit; and Bohling, Christian

The usage of secondary materials in metal production enables a significant saving of required energy and emitted CO2, However, to produce high-quality metal alloys the purity of the recycled fractions is very important. Any contamination with unwanted elements can spoil the melt and in worst case it must be discarded. The high demands on the purity of the secondary materials require precise methods for analysing the composition of waste materials (scrap metals, mixed alloys). Based on the analysis results this material can be sorted into fractions with tight composition specifications. Laser-induced breakdown spectroscopy (LIBS) provides a fast, multi-element analysis with no sample preparation and is ideal for sorting applications [4,5]. However, LIBS is a surface sensitive analysis method. Any contaminations (e.g. paintings, dirt, rust) can influence the analysis accuracy. With the combination of laser cleaning (pre-ablation) and LIBS all alloying elements (e.g. Si, Mg, Mn, Fe, Cu, etc. in aluminium and Cr, Ni, Cu, Si, Mn, Mo etc. in steel) are analysed quantitatively even at conveyor belt speeds up to 2 m/s. With a new modified system Secopta has achieved enhanced pre-ablation capabilities allowing the removal of thicker contamination layers. With this system it is possible to get precise LIBS analysis results even for scraps with thick coatings, rust or oxide layers. The paper will be focused on the comparison of the standard pre-ablation and the deeper pre-ablation and their analysis quality in dependency of the layer thickness of different coated materials.

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published: Recy & DepoTech, 11|2020
Keywords: Material Recovery, Metals, Germany