Recycling is a hugely significant activity. According to a study by UN Environment’s International Resource Panel, global demand for raw materials has increased tenfold over the past century and now totals around 85 billion tons a year. Demand is expected to double again by 2030. The resources of finite raw materials are at threat of being completely exhausted in the medium term. That’s why it will become increasingly important to recycle raw materials in the future.
Dual energy methods
To be able to sort and identify raw materials in a reliable fashion, Fraunhofer EZRT is researching dual energy methods. These methods employ the fact that different materials exhibit different attenuation coefficients. This means that the input data for a quantitative determination of material properties can be obtained from energy-resolved “spectral” measurements. The material to be examined travels on a material chute or conveyor belt either past or through the detection unit, consisting of an X-ray tube and a special X-ray detector and is “X-rayed” as it passes.
This method can be used for a wide variety of separation tasks, especially in the recycling sector. A prerequisite is that the material is “radiolucent,” i.e. a significant proportion of the radiation hitting the sample will actually pass through it and can be registered by a detector located behind it.
Wide range of application areas
Furthermore, there needs to be a significant difference between the atomic numbers of the materials to be separated. While this means the method won’t work in every conceivable application, it does leave a very broad range of possible applications. It’s always important to take the specific task at hand into account.
For instance, the method can in principle even be used to distinguish between cast and wrought aluminum alloys, even though both have an atomic number very close to that of aluminum.
X-ray methods are used for separating and detecting diamonds, but it has not yet been possible to detect enclosed diamonds. The X-ray luminescence method used to date has a high error rate. Dual energy methods also addresses this issue.