Laser sorting of aluminum scrap


Laser induced breakdown spectroscopy (LIBS) is a method of atomic emission spectroscopy, which is able to provide a rapid chemical analysis of various materials, including, all metals. The advent of more compact, including, hand, systems, It enables the use of laser spectroscopy directly in processes.

Details about the sorting and processing of aluminum scrap:

Handbook of aluminium recycling /Ch. Schmitz – 2014

Aluminium recycling /M. Schlesinger – 2017

The method of laser emission spectroscopy

The main advantage of laser spectroscopy is, that it is capable of performing rapid and remote chemical analysis of the material without sample preparation.

The method of laser emission spectroscopy is based on focusing the short laser pulses, which cause the formation of plasma from a small amount of vaporized material (figure 1).

Figure 1 – A schematic shows the components of a typical LIBS setup [1]

Very high temperature plasma material inside makes vaporized decomposed into ions and excited atoms. When the plasma cools, then it emits characteristic atomic emission lines, which can be easily recovered by the spectrograph. This method allows rapid and sensitive chemical analysis of almost any type of substance – solid, liquid and gaseous state.

The threshold of detection of various chemical elements are typically a few millionths of heavy metal elements. For light elements above the sensitivity of this method, than tezhelo.

Sample preparation is usually not required, so this method in many cases, can be considered to be non-destructive, It has been removed from the surface of a very small amount of material. In such applications, as sorting aluminum scrap, this feature does not matter. Another advantage of laser microscopy method is its ability to operate through contamination on the surface of the material, that is very important to sort aluminum scrap.

Laser analyzers for aluminum scrap

Compactness and ability to work "in the field" makes laser spectroscopy is very convenient for sorting of scrap aluminum.

Most of the aluminum scrap market secondary aluminum It comes after the processing of metal scrap on the so-called "shredders" — huge machines, grinders , where cars and other industrial machines and household products are broken up into small pieces, no longer than 100 mm, and not always of aluminum.

Really, this milled material is very heterogeneous and comprises not only pieces of different aluminum alloys, but also from various other metals, as well as plastics and other organic materials. At present, such aluminum scrap is sorted virtually by hand, mainly in China and other developing countries, or using a very rough and not quite reliable aluminum scrap sorting methods.

Chemical analysis of aluminum scrap

The uncertainty of the chemical composition of materials, which make up the aluminum scrap, It limits the ability to use recycled aluminum alloys, who are strict and precise limits on the chemical composition, for example, such impurities, like iron, copper or zinc.

Due to the lack of effective aluminum scrap sorting methods, At first, of metal species, and, Secondly, of aluminum alloys, Only a limited amount of recycled aluminum can be employed in the manufacture of aluminum products. Almost all the secondary aluminum is used to produce cast aluminum alloys and aluminum castings. This is because, most cast aluminum alloys are extremely tolerant to high content of impurities, for example, gland. Moreover, casting in permanent molds under high pressure is required just high iron content in order, to molten aluminum "did not stick" to the steel casting molds.

However, to expand application possibilities of secondary aluminum foundries, as well as other sectors of the aluminum industry, need more thorough and rapid classification and sorting of aluminum scrap flows. It promises great benefits for aluminum producers, both from an economic point of view, and from the point of view of reducing the negative impact on the environment.

Industrial aluminum sorting house

laser sorting systems aluminum scrap has successfully worked in the laboratory and is already quite widely used in industrial environments. They demonstrate the ability to rapidly "recognition" of various metals and even different aluminum alloys, which gives them advantages for use in sorting aluminum scrap. EXAMPLE pilot laser spectroscopic system sorting scrap aluminum is shown in Figure 2.


Figure 2 – A prototype of LIBS system for automatic scrap metal sorting is field-tested [1]

Moreover, laboratory and industrial test equipment for laser sorting of scrap aluminum, demonstrate the ability of this method to work with contaminated aluminum scrap directly in the field of aluminum scrap storage places. Laser spectroscopy has proven ability to clearly distinguish between the chemical composition of even highly contaminated metal components, including, of different aluminum alloys.

To all appearances, that the laser emission spectroscopy technique has great potential for use in industrial control devices for chemical analysis for sorting scrap aluminum. More accurate and careful sorting scrap aluminum to enhance its processing and expand the possibility of using recycled aluminum in various industries.