In this report, we consider the suitability of the XRT and XRF technologies in aluminum sorting and the differences between the two X-ray based sorting technologies, namely XRF (X-Ray Fluorescence) and XRT (X-Ray Transmission). These technologies do not have high resolutions. To calculate the dimensions of a particle, i.e. shape and size, an additional sensor is often required with XRF.
XRT (X-Ray Transmission) is based on the detection of different materials by means of the atomic particle density. Heavy metals are shown dark and light metals or organic materials are shown brighter or indistinct in the original images from the XRT sensor.
To use XRT technology for sorting recycle enabled aluminum, the machine software is created according to the findings of the processor so that certain material is displayed in specific colors. For example, choose light gray or white for aluminum, red for copper, yellow for brass, blue for zinc, green for stainless steel, and black for the lead. In this way, recognition and display for sorting are easily possible. But what’s the catch?
The density of the material affects the permeability of the X-ray beam. It requires a greater force of radiation to penetrate dense material than soft material. The number of molecules per volume unit is decisive for the density of a material. Penetrating wood takes much less force than penetrating the heavy metal. It is easier to penetrate plastic than aluminum or magnesium. The volume also plays an important role in the penetration of a material and the associated image that the software displays on the monitor. A large piece of plastic is represented identically to a smaller piece of aluminum. Or: a large piece of aluminum is represented identically as a thin piece of zinc with the same surface.
Solutions to this challenge have been found over the course of time and with further developments in technology. However, it remains difficult and even mostly impossible to effectively sort aluminum production waste with XRT.
Sorting sometimes also means compromising quality
With XRT many materials can be recognized through the density of the material and consequently separated. The differences between heavy metals (higher molecular density) and light metals can be recognized and sorted in a well-fractionated material flow. Therefore, the use of XRT is well suited for a Zorba product, for example.
But what about the production waste in the aluminum sector? Using XRT, slight differences between aluminum alloys can be recognized by recognizing denser molecules of elements such as Cu, Zn, Ni, Mn, etc. The quality of the recognition is not sufficient for a clean separation and compromises have to be accepted very often. XRF is the more suitable form of technology for sorting aluminum alloys.
To put it simply: XRF (X-Ray Fluorescence) is based on the spectroscopic analysis of existing elements from the periodic system. Based on the spectrum of the material sample is the composition of the elements determined qualitatively. This principle is used in X-ray fluorescence analysis and energy dispersion, among other things. Energy-dispersive X-ray analysis is a measurement method of material analysis belonging to X-ray spectroscopy. The atoms in the sample are excited by an electron beam of a certain energy. These then emit X-rays with energy specific to the respective element, the characteristic X-rays. This radiation provides information about the elemental composition of the sample.
In contrast to the XRT method, the X-rays are reflected and collected and analyzed by the sensors. From the information obtained, we learn the composition of the particle and then use this information for sorting.
Not all elements with XRF are detected, however. If we look at the periodic system, we see the so-called ordinal numbers of the elements. With the XRF-EDX process, reliable calculations can only be made from ordinal number 18. This means that a detection of Mg, Al and Si, for example, is not really possible and therefore no reliable data can be collected. Elements such as Cr, Mn, Fe, Co, Ni, Cu, Zn, Br, Au, Ag, on the other hand, are recognized very well and a meaningful sorting of metals can be achieved here very precisely and with high throughputs. The information obtained is decisive for the sorting quality.
XRT and XRF in use. A comparison:
- Belt sorting machine
- high conveying speed (3-4 m/s)
- high throughput
- Narrow & precise grain grid necessary
- well suited for Zorba sorting
- less suitable for production waste
- Light-heavy (high density / low density) sorting
- High energy consumption
- High spare part costs
- Large design
Conclusion: XRT is well suited for sorting heavy (high density) from light metals (low density). Example Zorba: easy and accurate separation of heavy metals such as Cu, Zn, brass, lead, and stainless steel from light metals such as Al, Mg.
- belt or slide machine
- Lower conveying speed (2-3 m s)
- Lower throughput per working meter
- Independent of the grain grid
- Exact material analysis
- Versatile, for mixed shredder fractions as well as for production waste
- Lower energy consumption
- Low spare parts costs
- Compact design
Conclusion: When using XRF, the individual elements can be sorted very precisely into the light and heavy metals based on the sorting criteria set in the sorting software, regardless of grain size and grain grid. In addition, XRF enables the detection of metal alloys. In this way, differences between individual heavy metals such as copper, brass, bronze or zinc, for example, can be recognized, which can be important for the quality of a Zurik fraction. Let us take zinc as an example: In addition to free zinc particles, you can also see the zinc content in an aluminum alloy. For the actual sorting, alloys can also be included in the sorting decision.
When sorting Zorba material, we see that XRT can sort heavy metals very well and with high throughput. The XRF technology can be used equally well for this sorting task and can also be used to further process Zorba or Zurik heavy metals in a second sorting step, depending on the requirements for the end product. With the help of XRF technology, nuanced sorting can be carried out, whereby an increase in the value of the material flows can be achieved. This can make sense for companies and better cover today’s sales strategy and those in the future.
In fact, there are no suppliers of both technologies, and the manufacturers understandably always recommend their own technology. The customer is left to his own choice and should make the right purchase decision based on their sorting task and corporate strategy.
The best solution for your aluminum sorting is the one that best covers both your technical and economic requirements.