The Fraunhofer Institute for Laser Technology ILT playing a leading role.
The recycling industry is increasingly relying on laser-induced breakdown spectroscopy (LIBS) to identify reusable raw materials in waste streams. The Fraunhofer Institute for Laser Technology ILT in Aachen, Germany is playing a leading role in developing this highly precise technology for element analysis and is continuously expanding its range of applications.
The transformation to a circular economy is in full swing. Recycling rates for raw materials such as paper or aluminium from packaging are already above 90 per cent. In order to close further material cycles, however, the recycling industry needs sensor-based processes that can identify a great deal of different recyclable materials in waste streams not only reliably, but also fully automatically and at high-speed.
Real recycling rates still too low
A fundamental goal of the circular economy is to reuse valuable raw materials – if at all possible – without downcycling. The most important prerequisite for this is separation by type. However, this is precisely where there are still technological gaps in many cases. For example, Germany is considered exemplary when it comes to implementing the EU End-of-Life Vehicles Directive and complies with the specified recycling rate of 95% for end-of-life vehicles; in the current reporting year (2021), it was 97.5%.
However, in addition to material recycling, this rate also includes energy recycling, i.e. incinerating materials that are not recyclable or for which the recovery processes through to reuse are not worthwhile. When recycled for energy, these materials are at least used to generate electricity and heat.
Of this 97.5 per cent of end-of-life vehicles, 86.6 per cent of the material was recently recycled according to the German Federal Environment Agency (UBA). However, there is also room for improvement here. The UBA criticises the fact that material recycling all too often leads to downcycling: Recovered secondary materials are used in applications that do not correspond to their original value. For example, high-quality automotive steel from cars is often reused as construction steel.
Valuable car glass often ends up as insulation material or filling material for landfills since coatings on the glass are difficult to remove, making them easier to downcycle. For non-metallic materials, value-preserving recycling is the exception rather than the rule: According to the UBA, only 13.5 per cent of plastics and 8.3 percent of glass are recycled at all.
Laser-based sensor technology helps to close material cycles
Fraunhofer ILT has a solution that can significantly improve recycling and minimise high-loss downcycling through highly efficient, reliable and differentiated analyses of the valuable materials contained in waste streams: Laser-induced breakdown spectroscopy (LIBS) is one of the key technologies for an economy based on actual material cycles. This is because the highly accurate, real-time spectroscopic determination of which chemical elements materials contain enables differentiated separation by type.
For spectroscopy, a high-energy laser pulse excites the surface of the material. This creates a plasma in which the chemical bonds between the elements of the material are broken up. The atomic fingerprint is different for each material and can be read spectroscopically at the moment when the atoms return to their stable state: They emit light in specific wavelengths, from which the respective element can be deduced. LIBS, therefore, reveals the exact chemical composition of the laser-excited material in fractions of a second. The non-contact method can be applied to all materials, regardless of whether they are solids, liquids or gases.
Dr. Cord Fricke-Begemann’s materials analysis working group at Fraunhofer ILT is driving forward the development of inline processes based on LIBS technology to pave the way for the unmixed recovery of metals from mountains of waste and scrap.
“Using a scanner-based selection of measuring points and around 100 LIBS measurements per second, we can very quickly create two-dimensional representations of the element distribution. Based on these spatially resolved analyses, we are able to detect technology metals in electronic waste and thus, for example, return valuable tantalum from capacitors to the material cycle,” explains the Fraunhofer ILT scientist.
Aluminium recycling: laser ensures higher purity
Particularly for complex material compositions, as in electronic waste or end-of-life vehicles, one-to one recycling depends crucially on the accurate, spatially resolved determination and separation of the individual material fractions. Only if recycling companies are able to determine exact chemical compositions in real time and sort waste on this basis will efficient reuse without downcycling be feasible. And this is what LIBS lays the foundation for: the automated, unmixed separation of a wide range of metal alloys using non-contact, laser-based, quasi-real-time analysis of materials.
The process helps users determines how the materials can be used based on product, and, thus, identifies their full value. This applies to high-quality metals in electronic scrap as well as special alloys in toolmaking or the wrought aluminium alloys widely used in automotive engineering.
However, the differentiated analysis of recyclable materials using LIBS is not only the basis for truly closed material flows without downcycling. It also paves the way for accelerated sorting processes and, in conjunction with automated sorting technology, contributes to their cost-effectiveness.
“We can process much more scrap in a shorter time than with traditional manual sorting and also achieve genuine sorting purity,” says Fricke-Begemann, summarising the advantages.
