Limited resources and increasing energy prices are helping promote the usage of secondary raw materials. In the field of material recycling in particular, there is a need to characterize secondary raw material streams in terms of their basic elements prior to the melt process, and particularly to sort these various materials. Laser-induced breakdown spectroscopy (LIBS) offers a flexible, viable process for this application that provides contactless multi-element analysis of various metallic materials, such as stainless steel, aluminum or titanium.

Method

The laser direct analysis uses a pulsed Nd:YAG laser, which exposes moving objects on a conveyor belt (3 m/s) to a laser pulse using a galvanometric scanner mirror system. The laser-induced plasma of each individual object is analyzed spectroscopically and a sorting decision taken. In conjunction with a sorting and recycling plant manufacturer, the LIBS system developed at the Fraunhofer ILT has been integrated into a sorting system, see figure 2. The entire system will be tested in terms of its robustness for industrial usage with high mass throughputs of > 4 t/h.

Result

Initial measurements with defined sample rates demonstrate that aluminum cast and wrought alloys can be correctly identified and separated with up to 95 percent accuracy. To this end, silicon - the characteristic element for both analyzed alloys - was used as a sorting criterion.

Applications

Applications of this technology can be found especially in the recycling industry to identify individual particles, as well as to characterize material flows. Laser excitation of the measuring radiation means this method of optical LIBS is not limited to metallic materials, but can also be used for minerals, such as limestone, dolomite, coal, etc.