EP-4493331-B1 - X-RAY SEPARATOR FOR SORTING METALS FROM RECYCLED MATERIAL

Inventors

• DANESI, Stefano
• OLIAN FANNIO, Francesco
• TURINI, GABRIELE

Dates

Publication Date

20260506

Application Date

20230310

Claims (6)

1. Metal separator comprising: - an X-ray source (1) configured to produce a radiation beam (2) capable of passing through a ground material (M) containing scrap metal; - at least one array of transmission sensors (4) arranged transverse to the feed direction of said ground material (M) and aligned with said radiation beam (2), said array being positioned on the side of the stream of ground material (M) opposite with respect to said X-ray source (1); and - a control unit configured to receive reading data from said array of transmission sensors (4) and to control a valve for emitting an air jet; characterized in that it further comprises an array of fluorescence sensors (5) positioned adjacent to the radiation beam (2) and arranged transverse to said feed direction, said array being positioned on the same side of the stream of ground material (M) as the X-ray source (1) and being operatively connected to said control unit for transmitting its reading data to it; and in that the control unit is configured to analyse and compare the reading data from both the transmission sensors (4) and the fluorescence sensors (5) relating to the same piece of ground material (M); and in that the X-ray source (1) has the following characteristics - the anode-cathode voltage is between 100 kV and 130 kV, preferably between 100 kV and 110 kV; - the current intensity is at least 20 mA; - its distance (H) from the array of transmission sensors (4) is between 300 mm and 700 mm, preferably between 350 mm and 550 mm.
2. Metal separator according to claim 1, characterized in that the distance of the array of fluorescence sensors (5) from the base of the stream of ground material (M) is between 50 mm and 150 mm, preferably between 100 mm and 120 mm.
3. Metal separator according to claim 1 or 2, characterized in that it comprises two arrays of transmission sensors (4) identical in size and pitch but having different energy sensitivities, said two arrays being overlapped so that the upstream array, with respect to the direction of origin of the radiation beam (2), generates a signal integrating absorption at low energies emitted by the X-ray source (1), while the downstream array integrates absorption at high energies.
4. Metal separator according to claim 3, characterized in that in the presence of a band of overlapping energies in which both arrays give a signal, the control unit is configured to filter them out and eliminate them when processing the readout data.
5. Metal separator according to any of the preceding claims, characterized in that the X-ray source (1) has a tungsten target inclined at 20°, a beryllium window and an aluminum filter, preferably having a thickness of 0.4 mm.
6. Metal separator according to any of the preceding claims, characterized in that the control unit is configured to synchronize the two signals acquired from the fluorescence sensors (5) and transmission sensors (4) via an external trigger signal.

Description

The present invention concerns the recovery of metals from scrap, and in particular an X-ray separator for sorting nonferrous metals. As is well known, at the end of their lives, cars, and also other large industrial and household products of essentially metallic composition, are ground with large hammer mills (so-called car shredders) that reduce them into pieces less than 150 mm in size so as to obtain scrap metal. On leaving these mills, the mixed ground material undergoes a deferrization action using large electromagnetic drums for the purpose of recovering and cleaning up the ferromagnetic steel. What is discarded by such electromagnetic drums consists mainly of plastics, rubbers, polyurethane foams, glass, aluminum, copper, zinc, zamac, lead, stainless steel, electrical wires, stone residues, iron oxides, and some ferromagnetic steel parts lost during the deferrization action. Next, Foucault current and inductive sensors separators are employed to produce mixed metal concentrates. Further wet or dry densimetric separation processes allow the separation of light non-ferrous metals, such as aluminum and magnesium, from heavy metals such as copper, brass, stainless steel, and lead. The present invention finds application in the subsequent step focusing on the separation of metals of different natures. A special feature of this application is that the separation process, to achieve the throughput of at least 1 ton/h typically considered as a minimum for the recycling industry, requires working on high numbers of pieces/hour since the weight of the pieces varies from a few grams (3-4g) to over 1000g with an average weight typically ranging from 10 to 50g. This implies that the separator has a time in the order of milliseconds, typically 5 to 50 ms, to identify the chemical composition of each piece that makes up the material stream. Separators that are capable of performing this task use an X-ray technique that can be of two types, fluorescence technique (X-Ray Fluorescence = XRF) or transmission technique (X-Ray Transmission = XRT). The XRF fluorescence technique makes it possible to gather information about the chemical nature of a material through a purely superficial investigation, since the signal comes from a few hundred micrometers deep from the surface, so it says nothing about the internal composition of the piece (called the "sample") being analyzed and is reliable only under the assumption of absolute homogeneity of sample composition. In other words, if the interior of the sample, called the "bulk," has a different chemical composition from the surface layer, for example because the sample is made from a piece of a certain metal with an insert composed of another metal, fluorescence will not be able to establish this. This is a frequent situation when considering the material obtained from a car shredder as the material from which to sort metals, since the metal pieces to be sorted may be composed of a mixture of metals or inserts of metals with different chemical nature, or metals with a coating of other metals (e.g., galvanized pieces). Another frequent case is tubes and wires covered with a plastic sheath, which can prevent the fluorescence signal of the underlying metal from being detected if it is sufficiently thick, so that XRF analysis leads to the conclusion that there is no metal in the sample. In addition, the material can be dirty, and the surface layer of dirt, usually metal powders, can also alter the result of the XRF analysis. Additional drawbacks of the XRF technique are limitations on the metals to be sorted and poor spatial resolution. In the former case, due to the speed of analysis that the application under consideration imposes (a few milliseconds per piece), the fluorescence phenomenon is very weak for lighter elements such as Al or Mg, while it is definitely more intense for heavier chemical elements (e.g., from Ti on up). In terms of spatial resolution, a typical XRF separator comprises a source producing a polychromatic X-ray beam that is projected onto the material stream to be analyzed, with an adjacent array of fluorescence sensors (called SDDs=Silicon Drift Detectors) arranged equidistant from each other along a linear array transverse to the direction of the stream. Ideally, the longitudinal resolution in the flow direction is limited by the sample speed and acquisition time of the SDDs, which typically ranges from 5 ms to 50 ms, while the transverse resolution is limited by the number of SDDs and the pitch with which they are arranged along the array (typically 15 mm to 60 mm). For example, with SDDs having a pitch of 50 mm, which corresponds to the width of the field of view of each SDD, an acquisition time of 15 ms, and a material passage time of 2.5 mm/ms, we obtain a readout "surface" of 1875 square mm (=50 mm x 15 ms x 2.5 mm/ms), which is comparable with the average surface area of the parts being processed. In view of the low spatial resolution of the XRF