Method For Recycling Waste Electrical And Electronic Equipment

Abstract

The method for separation of metals from electronic cards includes a step of processing the electronic cards in an aqueous medium under supercritical conditions. The method also a later step of crushing solid materials coming from the treatment under supercritical conditions.

Claims

1. A process for separating metals from electronic boards, characterized in that it comprises: a) a step of treating electronic boards in an aqueous medium under supercritical conditions of said medium and b) a subsequent step of crushing the materials in the solid state that are derived from the step of treating under supercritical conditions.

2. The separation process as claimed in claim 1, wherein, in step a), the electronic boards are not fragmented.

3. The separation process as claimed in claim 1, wherein the electronic boards are subjected to a fragmentation step prior to the treatment under supercritical conditions and are reduced to fragments having a size greater than or equal to 1 cm and less than or equal to 5 cm.

4. The separation process as claimed in claim 1, wherein said medium contains oxygen or one or more oxygen-generating species.

5. The separation process as claimed in claim 1, wherein the temperature and pressure conditions applied to the medium range from 374° C. to 600° C. and from 22.1 MPa to 30 MPa.

6. The separation process as claimed in claim 1, wherein said supercritical conditions of the aqueous medium are maintained for a duration greater than or equal to 30 minutes.

7. The separation process as claimed in claim 1, wherein, for the step of treating under supercritical conditions, the temperature is above 500° C.

8. The separation process as claimed in claim 1, wherein the crushed materials are treated so as to separate the fragments having a size of less than 2 mm.

9. The separation process as claimed in claim 1, wherein step a) is carried out in an autoclave and the supercritical conditions are achieved by increasing the temperature.

10. The separation process as claimed in claim 1, wherein the crushed materials are subjected to a low-intensity magnetic separation.

11. (canceled)

12. The separation process as claimed in claim 4, wherein said medium contains hydrogen peroxide.

13. The separation process as claimed in claim 6, wherein said supercritical conditions of the aqueous medium are maintained for a duration ranging from 60 minutes to 180 minutes.

14. The separation process as claimed in claim 7, wherein, for the step of treating under supercritical conditions, the temperature is about 600 ° C.

15. The separation process as claimed in claim 10, wherein the crushed materials are subjected to a low-intensity magnetic separation under a magnetic field of 400 gauss.

16. An electronic board prepared by the process of claim 1.

17. A process for separating metals from electronic boards, characterized in that it comprises: a) fragmenting an electronic board into fragments having a size less than or equal to 5 cm; b) treating the fragmented boards in an aqueous medium under supercritical conditions of said medium to a temperature of 374° C. to 600° C. and from 22.1 MPa to 30 MPa in an autoclave; c) crushing in the solid state the treated materials derived from the step of treating under supercritical conditions; and d) subjecting the crushed material to a low-intensity magnetic separation.

18. The process of claim 17, wherein the crushed materials are separated into fragments having a size of less than 2 mm.

19. The process of claim 17, wherein the fragments obtained in the step of fragmenting have a size greater than or equal to 1 cm.

20. The process of claim 17, wherein said aqueous medium contains oxygen or one or more oxygen-generating species.

21. The process of claim 17, wherein said low-intensity magnetic separation involves subjecting the crushed material to a magnetic field of 400 gauss.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0042] FIG. 1 depicts the steps of one embodiment of the process for recycling electronic boards according to the invention exemplified in examples 1 to 3.

[0043] FIG. 2 presents the crusher used to crush the electronic boards in the implementation examples 1 to 3.

[0044] FIG. 3 is a photograph taken with a scanning electron microscope (SEM) representing the morphological appearance of the solid portion obtained after fragmentation according to example 3.

[0045] FIGS. 4 to 6 bring together the local qualitative chemical analyses by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) carried out on the solid portion obtained at the end of the fragmentation according to example 3, during the SEM visualization thereof.

[0046] FIG. 7 is a SEM photograph representing the appearance of the fines obtained at the end of the crushing according to example 3.

[0047] FIG. 8 presents a local qualitative chemical analysis carried out by SEM-EDS at a point of the fraction of the fines obtained at the end of the crushing according to example 3.

[0048] FIG. 9 presents a table bringing together the images of the products obtained in examples 1 and 2 after attack with supercritical water in the presence of hydrogen peroxide.

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLES 1 AND 2

[0049] In a first example, laptop computer electronic boards were subjected to a fragmentation using a knife mill equipped with a screen having a 5 cm mesh. This is the (“shredding”) step 1 of the process depicted in FIG. 1. In this example, the objective of the fragmentation was to obtain fragments having a size generally greater than 1 cm and smaller than 5 cm. At the end of the fragmentation, the fragments are subjected to a grading (step 2 of the process depicted in FIG. 1). The fragments having a size greater than 5 cm are again subjected to the shredding step 1. The fragments having a smaller size are subjected to step 3 of the process depicted in FIG. 1. More specifically, 30 g of fragments thus obtained were then introduced into an autoclave having a volume of 300 ml in which they were bought into contact with 30 g of an aqueous solution of hydrogen peroxide having a concentration of 33% by weight. The temperature in the autoclave was raised to 600° C. which made it possible to achieve a pressure of 250 bar. These pressure and temperature conditions were achieved in around 30 minutes. The fragments were then maintained under these conditions for 30 minutes, then the autoclave was depressurized.

[0050] The solid phase was then separated from the liquid phase by filtration on filter paper having a porosity of 2.5 μm, so as to recover all of the solid phase (step 4 of the process depicted in FIG. 1).

[0051] The solid phase was then passed through a crusher represented in FIG. 2, which is an example of the crusher indicated in step 5 of the process depicted in FIG. 1.

[0052] FIG. 2 represents a crusher 7 which is a drum screen with heavy elements, also used in examples 1 to 3 as a grader. Solid residues 8 resulting from the attack under supercritical conditions (step 3 of the process) are placed in a rotary screen 9 which has a 2 mm mesh and contains two heavy bars 10 and 11. The heavy bars 10 and 11 are cylinders, each with a length of 15 cm, a diameter of 4 cm and a weight of 1.9 kg. The device is closed and positioned on two bars 12 and 13 positioned outside the screen 9. These bars are rotated, which drives the rotation of the screen, thus ensuring the movement of the heavy bars 10 and 11 and the crushing of the solid residues 8. This crushing releases friable portions 14 of the initial resin which again stick to the solid residues 8. These crumbled portions 14, referred to as “fines”, pass through the openings of the screen and are recovered at the bottom, having a mean particle size of less than 2 mm, in dedicated trays 15. The crushing time was around 3 minutes, at the end of which time there were no longer, visually, any fine particles exiting the screen. The material remaining in the screen is referred to as “solids” and is recovered. The “fines” and the “solids” are then weighed.

[0053] The metals thus separated from the resin may then be subjected to a low-intensity magnetic separation, under a magnetic field of 400 gauss. The non-ferrous metals, including the precious metals, were thus separated from the scrap iron.

[0054] The process described in example 1 was repeated in another example, example 2, but the duration during which the fragments of electronic boards were maintained under supercritical conditions is 2 hours once the pressure and temperature rise is achieved, and not 30 minutes as in example 1. The crushing time was around 1 minute 30 seconds, at the end of which time there were no longer, visually, any particles exiting the screen.

[0055] FIG. 9 brings together the images of the products obtained after attack with supercritical water in the presence of hydrogen peroxide of examples 1 and 2.

[0056] Table 3 indicates the weights of fines and solids obtained respectively in examples 1 and 2.

TABLE-US-00002 TABLE 3 Supercritical oxidation 2 h Supercritical oxidation 30 min Fines 3.91 g 43.9%  5.95 g 51.0% Solids 5.00 g 56.1%  5.72 g 49.0% TOTAL 8.91 g  100% 11.67 g  100%

[0057] The appearance of the products before they pass through the bar crusher suggests a better degradation of the resin after two hours of treatment. The smaller percentage of fines for the product obtained after a supercritical oxidation of two hours confirms this observation. Furthermore, the duration of the crushing is also two times shorter.

EXAMPLE 3

[0058] In a third example, a laptop computer electronic board was subjected, as in examples 1 and 2, to shredding using a knife mill equipped with a screen having a 5 cm mesh. The fragments obtained have a mean size of 5 cm.

[0059] 30 g of the fragments thus prepared were then introduced into an autoclave having a volume of 300 ml in which they were bought into contact with 30 g of water. The temperature in the autoclave was raised to 600° C. which made it possible to achieve a pressure of 250 bar. These pressure and temperature conditions were achieved in around 30 minutes. The fragments were then maintained under these conditions for 60 minutes, then the autoclave was depressurized.

[0060] The solid phase was then separated from the liquid phase by filtration on filter paper having a porosity of 2.5 μm, so as to recover all of the solid phase.

[0061] The solid phase was then passed through the crusher described in FIG. 2 for a duration of around 1 to 3 minutes, until there were no longer, visually, any particles exiting the screen. The portions thus crumbled were recovered and have a particle size of less than 2 mm.

[0062] The metals thus separated from the resin may be subjected to a low-intensity magnetic separation, under a magnetic field of 400 gauss. The non-ferrous metals, including the precious metals, were thus separated from the scrap iron.

[0063] FIG. 3 presents an electron microscope image of the solid portion obtained after passing through the crusher represented in FIG. 2. The solid has a light surface (16) of homogeneous appearance and dark deposits (17) on this surface.

[0064] A determination of the local chemical composition was carried out by SEM-EDS in different zones of the board seen in FIG. 3. More specifically, an analysis was carried out on the light zone (16) of the board, and two analyses were carried out on two of the darker zones (17). The results are presented in FIGS. 4 (analysis of the light zone) and 5 and 6 (analysis of the dark zones).

[0065] In the SEM-EDS analysis, a stream of electrons bombards the sample and gives rise to an emission of x-ray photons, the energy spectrum of which characterizes the constituent elements of the material to be analyzed. This spectrum is analyzed by a semiconductor detector which produces voltage peaks proportional to the energy of the photons received (principle of Energy Dispersive Spectroscopy, EDS). The voltage peaks obtained make it possible to quantify the elements emitting at a given energy, expressed in kiloelectron volts (keV). By way of example, FIG. 6 shows in particular the emission peak of yttrium, level L (Y L), at around 1.9 keV.

[0066] Thus, FIG. 4 shows a zone composed of virtually pure copper metal. Conversely, FIG. 5 and FIG. 6 show little copper but a lot of calcium, tin, europium and yttrium oxides.

[0067] A similar characterization to that carried out for the pure solids was performed on the fines recovered after crushing and constituted of the fibers of the reinforcement of the board. The SEM image (FIG. 7) presents an assembly of acicular particles, that is to say in the form of needles and of homogeneous appearance. Due to the fact that the initial fibers have a needle shape and that the resin has no particular shape, it appears that the fines mainly contain fibers. The supercritical water has therefore mainly attacked the resin of the electronic board and not the fibers.

[0068] This is confirmed by the results of analysis of the local chemical composition by SEM-EDS (FIG. 8). This analysis makes it possible to identify the glass fibers of the board (silicon, calcium and aluminum oxides, traces of barium). The analysis reveals copper, but in the form of ultra-trace amounts.

[0069] Table 4 presents the chemical composition data of the liquid phase at the outlet of the step of attack by supercritical water, after the filtration (step 4 of FIG. 1) of the products of example 1.

TABLE-US-00003 TABLE 4 Elements Ag Al As Ba Be Cd Co Cr Content 0.44 0.22 0.07 420.95 0.00 0.22 0.01 0.00 ppm Elements Cu Li Mn Ni Pb Sn Sr Zn Content 81.55 1.49 1.40 2.34 0.32 0.00 13.69 0.27 ppm

[0070] It appears that the liquid phase contains very few metal elements, in particular very little Ag and Cu. Almost all of the metals are thus recovered in the solid phase of the treatment by supercritical water. The chemical analysis of the fraction of fines obtained after crushing (FIG. 8) also reveals an absence of copper. The process presented therefore makes it possible to recover almost all of the copper in a solid phase, which may subsequently be treated by hydrometallurgy. Advantageously, the solid phase may, prior to the hydrometallurgical treatment, be subjected to magnetic separation in order to eliminate the ferrous particles