Method for extracting one or more rare and precious metals from substrates containing said metals

Abstract

A further method for extracting RPM from recyclable materials is provided. The present disclosure relates to a method for extracting rare and precious metals (RPMs) from substrates, particularly from recyclable materials such as e-waste and exhaust catalysts, based on exposing a region of interest of the substrate containing the RPMs to focused high-intensity ultrasound.

Description

[Technical Field]

[0001] The present disclosure relates to a method for extracting rare and precious metals (RPM) from substrates, in particular from recyclable materials such as e-waste and exhaust catalytic converters, in particular the extraction is based on the removal of RPM from the recyclable material using ultrasound. [Background technology]

[0002] In recent years, the significant demand for rare and precious metals (RPMs) by modern industry has led to growing interest in exploring new sources of these metals. Traditional mining, i.e., the extraction of minerals and metals from the Earth's crust, is becoming increasingly difficult as resource nodes are depleted. To address this, urban mining from e-waste, such as discarded printed circuit boards (PCBs), is an expanding field. Because e-waste contains high concentrations of RPMs, e-waste can be used to enrich RPMs back into usable forms.

[0003] Current technologies for recycling RPM through extraction from e-waste consume large amounts of energy and produce harmful contamination from chemical processing. This process typically involves three steps: mechanical pretreatment, pyrometallurgy, and hydrometallurgy. Mechanical pretreatment, for example, consists of manual PCB decomposition and / or PCB crushing. In the pyrometallurgical step, the pretreated PCBs are incinerated to separate the metals from other materials. This process generates harmful emissions and toxic waste. The final hydrometallurgical step involves leaching the metals. The substances used in leaching either produce toxic fumes or are themselves highly toxic or corrosive, such as cyanides and acids. Bioleaching, which uses microorganisms or their metabolic products for leaching, is an emerging environmentally friendly field. Unfortunately, leaching rates are low, and microorganisms are easily poisoned by toxic by-products, which halts the leaching process. Therefore, bioleaching is currently only performed on a laboratory scale.

[0004] Therefore, there is a need for additional methods for extracting RPM from recyclable materials. Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure is based on the discovery that RPMs can be extracted from a substrate, such as a recyclable material containing one or more RPMs, by generating controlled, focused cavitation at a predetermined location within the substrate immersed in a fluid.

[0006] An object of the present invention is therefore a method for extracting one or more rare and precious metals (RPM) from a substrate containing said metals, comprising the steps of: i) providing a substrate; ii) immersing the substrate in a fluid; iii) scanning at least a portion of the surface of the substrate with ultrasonic waves, wherein the intensity of the ultrasonic waves at at least a portion of the surface of the substrate is 1 W / cm 2 and iv) recording ultrasound echoes; v) constructing an amplitude map of at least a portion of the surface of the substrate based on the recorded echoes; vi) selecting one or more regions of interest of at least a portion of the substrate comprising one or more RPMs based on the amplitude map; vii) exposing one or more regions of interest to focused ultrasound, wherein the intensity of the ultrasound at the one or more regions of interest is at least 1 W / cm 2 , preferably at least 10 W / cm 2 whereby extracting one or more RPM from the substrate into a fluid; The object of the present invention is to provide a method comprising the steps of:

[0007] Further objects of the invention are set out in the attached dependent claims.

[0008] The illustrative, non-limiting embodiments of the present invention, both as to structure and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific exemplary embodiments when considered in conjunction with the accompanying drawings.

[0009] The verbs "comprise" and "to include" are used in this specification as open limitations which neither exclude nor require the presence of unrecited features. Features recited in the accompanying dependent claims may be freely combined with each other, unless expressly stated otherwise. Furthermore, throughout this specification, it is to be understood that the use of "a" or "an", i.e., the singular, does not exclude the plural. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is an exemplary schematic diagram of a HIFU setup suitable for the methods of the present disclosure. [Figure 2] FIG. 1 is another exemplary schematic diagram of a HIFU setup suitable for the methods of the present disclosure. [Figure 3] A) shows a photograph of a gold pad on a PCB, and B) shows an amplitude map of the PCB imaged with a HIFU transducer. [Figure 4] Figure 1 shows coded excitation scanning acoustic microscopy topography maps of one extraction area: A) top view showing the cavitation extraction geometry, and B) depth profile showing extraction depth into gold and nickel. DETAILED DESCRIPTION OF THE INVENTION

[0011] According to one aspect, the present disclosure provides a method for extracting one or more rare and precious metals (RPM) from a substrate containing said metals, the method comprising: i) providing a substrate; ii) immersing the substrate in a fluid; iii) scanning at least a portion of the surface of the substrate with ultrasonic waves, wherein the intensity of the ultrasonic waves at at least a portion of the surface of the substrate is 1 W / cm 2 and iv) recording ultrasound echoes; v) constructing an amplitude map of at least a portion of the surface of the substrate based on the recorded echoes; vi) selecting one or more regions of interest of at least a portion of the substrate comprising one or more RPMs based on the amplitude map; vii) exposing one or more regions of interest to focused ultrasound, wherein the intensity of the ultrasound at the one or more regions of interest is at least 1 W / cm 2 , preferably at least 10 W / cm 2 whereby one or more RPMs are extracted from the substrate into a fluid, and preferably further viii) separating the one or more RPMs from the fluid; The present invention relates to a method comprising:

[0012] The RPMs are typically selected from rhodium, platinum, gold, ruthenium, iridium, osmium, palladium, rhenium, nickel, and silver. Preferred RPMs are gold and platinum, more preferably gold.

[0013] The substrate is preferably a recyclable material containing one or more RPMs, such as e-waste or vehicle exhaust catalytic converters. A particular e-waste is a printed circuit board (PCB) containing significant amounts of gold. The fluid preferably comprises water. A particular fluid is water.

[0014] According to this method, at least a portion of the surface of the substrate is scanned using ultrasonic waves generated by an ultrasonic transducer, and the echo of the ultrasonic signal is recorded, for example, using an oscilloscope. Then, an amplitude map is constructed from the recorded echo using a computer. Next, at least one region of interest containing the desired RPM is selected from the amplitude map, and the selected region is exposed to high-intensity focused ultrasound (HIFU) generated by the transducer. The generated cavitation extracts the RPM into a fluid. One or more RPM can be separated from the fluid using methods known in the art. Exemplary methods include evaporation of the fluid, filtration, and exposure to a magnetic field.

[0015] An exemplary system 100 suitable for use in the present method is shown in Figure 1. The system includes: a housing 101 for a substrate 102 and a fluid 103 for immersing the substrate; - calculation means 104, - Arbitrary Waveform Generator 105, - power amplifier 106, - ultrasonic transducer 107, - oscilloscope 108, and - Attenuation Probe 109 Equipped with.

[0016] According to one exemplary and non-limiting embodiment, the signal from the computing means 104 is sent to an arbitrary waveform generator 105 and then to a transducer 107 via a low-setting power amplifier 106. The ultrasound intensity at the surface is 1 W / cm 2 Depending on the surface, the intensity of the ultrasound may be significantly lower, e.g., less than 1 mW / cm 2 may be less than, or even than 1 μW / cm 2 An example of an intensity range is 1 μW / cm 2 ~1mW / cm 2The transmitted signal is reflected from the substrate 102 and the echoes are recorded on an oscilloscope 108 using an attenuated probe 109 (e.g., 100x) and stored in the computing means 104. An amplitude map is constructed from the echoes, which shows relatively high reflected amplitudes from the region of interest, thereby distinguishing it from background regions. To obtain an image of the substrate, a three-axis motorized translation stage can be used to scan over the sample.

[0017] According to one exemplary embodiment, parameters used for ultrasonic imaging, which involves scanning the surface of a substrate with ultrasound, include a transducer center frequency of 12 MHz, 20 cycles / burst, one transmit burst per imaging point, a 10 μm step size, and a pressure amplitude low enough to avoid damaging the surface of the substrate. Generally, it is preferable to use low amplitudes for imaging so as not to damage the surface of the substrate. Therefore, for imaging, the amplitude is kept as low as possible while still allowing discernible echoes. For gold, pressure amplitudes of up to 7 MPa are applicable.

[0018] With regard to cycles / bursts in imaging, it is preferable to use as few cycles as possible, typically 3 to 20, for example 10.

[0019] According to a preferred embodiment, imaging is performed by coded excitation, which improves the signal-to-noise ratio by transmitting chirps instead of sinusoidal pulses, thereby significantly improving imaging capabilities.

[0020] The optimal imaging step size is transducer dependent, as the step size is determined by the transducer's center frequency and focusing. An example step size is 100 μm for a 12 MHz transducer.

[0021] Ultrasonic scanning can be performed on the entire surface of a substrate. However, it is highly likely that only certain parts of a substrate, such as a PCB, are expected to contain RPM. To avoid unnecessary scanning of the entire surface, a preliminary surface inspection can be performed using a machine vision system, and according to the generated image, an amplitude map is generated only from the RPM-rich surface area. According to this embodiment, the method includes, prior to the scanning in step iii), generating an image of the surface of the substrate using a machine vision system, and selecting at least a portion of the surface for ultrasonic scanning based on the image. Typically, the substrate is moved, for example on a conveyor belt, during the generation of the image.

[0022] According to another embodiment, the method includes extracting one or more rare and precious metals (RPM) from a plurality of substrates. An example of a system suitable for this embodiment is shown in Figure 2. System 200 includes: a housing 201 for a plurality of substrates 202a-202c and a fluid 203 for immersing the plurality of substrates; - calculation means 204, - Arbitrary Waveform Generator 205, - power amplifier 206, - ultrasonic transducer 207, - Oscilloscope 208, and - Attenuation probe 209, - conveyor belt 210, and - Machine Vision System 211 Equipped with.

[0023] The arrows in Figure 2 show an example of the direction in which the conveyor belt moves. According to this embodiment, a machine vision system is used to identify when the substrate is under the ultrasonic transducer, and the ultrasonic transducer is used to scan the surface when the substrate is under the ultrasonic transducer. This avoids unnecessary scanning of the conveyor belt. According to this embodiment, the method uses the exemplary system 200 to: i) providing a plurality of substrates 202a-202c; ii) placing a plurality of substrates on a conveyor belt 210 immersed in a fluid 203; iii) moving the conveyor belt; iv) generating an image by imaging a conveyor belt containing a plurality of substrates using a machine vision system 211; v) determining when one of the plurality of substrates is scannable using the ultrasonic transducer 207 based on the image, and if so, a) scanning at least a portion of a surface of one of the plurality of substrates with ultrasonic waves, wherein the ultrasonic wave intensity at the surface is 1 W / cm 2 shall be less than b) recording ultrasound echoes; c) constructing an amplitude map of at least a portion of the surface based on the recorded echoes; d) selecting one or more regions of interest in at least a portion of one of the plurality of substrates based on the amplitude map; e) exposing one or more regions of interest to focused ultrasound, wherein the intensity of the ultrasound at the one or more regions of interest is at least 1 W / cm 2 , preferably at least 10 W / cm 2 whereby extracting one or more RPM from the substrate into a fluid; Includes.

[0024] For extraction, the transducer is configured to emit focused ultrasound waves toward the interface between the region of interest on the substrate and the fluid. An example of a transducer suitable for this method is a focused piezoelectric transducer. An example of an operating frequency is 12 MHz. The intensity of the ultrasound waves at the target is at least 1 W / cm. 2 , which can remove material from the substrate. HIFU-induced cavitation erosion removes material from the substrate. According to one exemplary embodiment, a 500 W continuous wave power amplifier 105 is utilized to transmit high pressure waves, which create inertial cavitation at a focal point.

[0025] The transducer emits 1 W / cm at the focus. 2 Higher, preferably 10 W / cm 2 The transducer must operate at an intensity of at least 20 kHz, preferably 1 MHz to 15 MHz. An example frequency is 12 MHz. Higher frequencies provide a smaller focus for more localized extraction. For example, for a 12 MHz transducer with a 0.85 numerical aperture, the cavitation erosion pit radius ranges from 20 μm to 200 μm, depending on the sample and ultrasonic parameters. Because increasing frequency increases the cavitation pressure threshold, higher frequencies require a higher degree of focusing and / or a higher piezo drive voltage.

[0026] Cohesive failure of a sample, e.g., a gold surface, requires a higher acoustic pressure amplitude and higher total energy than adhesive failure of a sample, e.g., a thin film on a hard substrate. For gold in water, the pressure amplitude at the focal point should be greater than 30 MPa, preferably higher, e.g., 40-50 MPa. Because the probability of cavitation increases with increasing amplitude, higher amplitudes result in higher erosion / extraction efficiency. As amplitude increases, the area above the cavitation threshold increases, thereby increasing the erosion region. Therefore, the spatial resolution of this method is amplitude-dependent. The cavitation threshold is frequency-dependent; i.e., the higher the frequency, the higher the cavitation threshold. A pressure of 15 MPa is sufficient for adhesive failure, and the extraction region can be adjusted by adjusting the amplitude. The number of cycles in the ultrasonic burst is preferably 20-80 or more to provide a sufficiently high probability of cavitation. The pulse repetition frequency (PRF) should be adjusted to avoid overheating the transducer. For example, in the case of a water-immersion type 12MHz single element piezoelectric ceramic, a maximum forward power of 1W to 50W is suitable.

[0027] Exemplary parameters used for the extraction of material from a substrate are: f = 12 MHz (transducer center frequency), 30 cycles / burst, 250,000 bursts, pulse repetition frequency = 1 kHz, peak positive pressure = 40 MPa. These are the parameters for each sonication spot. An example extraction region consists of a 5 x 5 grid of sonication spots with 20 μm spacing.

[0028] Exemplary parameters for step vii) of the method are listed below: The HIFU intensity at the focus is 1W / cm 2 Higher, preferably 10 W / cm 2 That's all. The transducer frequency should be at least 20 kHz, preferably at least 1 MHz, preferably between 1 MHz and 15 MHz. Even higher frequencies can be used. The pressure amplitude at the focus is preferably greater than 30 MPa, for example 40-50 MPa. The number of cycles in the ultrasonic burst is 20 to 80 or more. The pulse repetition frequency (PRF) is adjusted to prevent the transducer from overheating. For example, for a water-immersed 12MHz single-element piezoelectric ceramic, a maximum average power of 1W to 50W forward power is appropriate.

[0029] Experimental setup and samples The HIFU setup is shown in Figure 1. The 12 MHz HIFU transducer was equipped with a custom-made piezoelectric bowl (F5265018, Meggit A / S, Qvistgård, Denmark) (bandwidth = 2 MHz, element diameter 1.9 cm, focal length 1.5 cm, focal width = 140 µm). Signals were generated using an arbitrary waveform generator (FG31052 SERIES, Tektronix, Oregon, USA) and transmitted to a power amplifier (500A 100A, Amplifier Research, Pennsylvania, USA, bandwidth 10 kHz–100 MHz) at either a low (imaging) or high (material extraction) setting. Echoes were recorded using an oscilloscope (PicoScope 5442D, Pico Technology, Cambridgeshire, UK) through a 100x attenuated voltage probe (TT-HV250, TESTEC Elektronik GmbH, Hesse, Germany) and stored on a computer. A 3D translation stage (Techno Isel router table, Isel Germany AG, Hesse, Germany) was used to scan the sample for imaging. Both imaging and extraction were performed in reverse osmosis purified water (RiOs Essential Water Purification Systems, Milli-Q, Hesse, Germany) that had been degassed for 20 min. This was done to remove contaminants and control dissolved gas concentrations, since both particulate matter and gas bubbles act as nucleation sites for cavitation.

[0030] The sample was an old PCB containing gold pads (Fig. 3A). The gold pads consisted of a copper base coated with 6 μm of nickel and then covered with gold. Because the thickness of the gold layer on the gold pads varies depending on the manufacturing method, the gold layer was analyzed by Rutherford backscattering spectroscopy ( 7 Measurements using a Li beam (beam energy 5MeV) revealed a value of (870±20) nm.

[0031] Identifying the region of interest A 6 × 8 mm area of ​​the gold pad was scanned with a HIFU transducer (f = 12 MHz, 20-cycle burst, 100 μm step size). An amplitude map was constructed from the echoes (Figure 3B). This amplitude map shows a relatively high reflection amplitude from the gold pad, distinguishing it from the substrate.

[0032] Gold extraction For gold extraction, one gold pad was selected. Three separate extraction regions, 520 μm apart, were sonicated. Each region consisted of a 5 x 5 grid of sonication spots (80 μm x 80 μm area) with 20 μm spacing. The following acoustic parameters were used for each sonication: f = 12 MHz, 30 cycles / burst, 250 k bursts, PRF = 1 kHz, PPPP = 40 MPa. Extraction was quantified using a coded excitation scanning acoustic microscope (CESAM) equipped with a 375 MHz transducer (140 MHz bandwidth, 2.5 μm beamwidth, 1 μm scan step size). The Tx signal was a 300-500 MHz linear chirp with a 1 μs burst length (Gaussian envelope). The measured topography maps were used to calculate the amount of material removed from each extraction region.

[0033] result The topography map and depth profile of one extraction area are shown in Figure 4A and Figure 4B as an example. For each extraction area, an ROI mask was manually created that included only the cavitation extraction area (including small cavitation pits). The surface zero level was determined, and the depth profile was used to calculate the gold and nickel removal amounts. To examine the reproducibility of the extraction, the average extraction area, volume, and gold and nickel removal amounts were calculated (mean ± standard deviation): A = (12.2 ± 0.5) × 10. 3 μm 2 , V = (18 ± 2) × 10 3 μm 3 , m Au = (190 ± 20) ng, and m Ni= (150 ± 30) ng. As shown in Figure 4B, the volume variation was larger than the area variation because the bottom of the extraction area was not flat. The uncertainty in the gold and nickel masses is due to the uncertainty in the gold layer thickness (± 20 nm). The uncertainty caused by the standard deviation of the calculated mass and the volume uncertainty was several orders of magnitude smaller than the contribution of the layer thickness uncertainty. Finally, the total amount of material removed from all three extraction areas was calculated to be m Au,tot = (570 ± 20) ng, and m Ni,tot =(440±30)ng.

[0034] To quantify material removal, an in-house coded excitation scanning acoustic microscope (CESAM; imaging parameter transducer: f C = 375 MHz, BW = 140 MHz; Tx coded excitation: linear chirp 300-500 MHz, 1 μs burst length (Gaussian envelope). The coded excitation was a linear chirp of 300-500 MHz with a 1 μs duration. As can be seen from the topography map, the selected extraction area (5 × 5 grid of sonication spots (20 μm spacing); actuation parameters for each sonication spot: f = 12 MHz, 30 cycles, 250 k bursts, PRF = 1 kHz, pressure amplitude p PPP = 40 MPa) is clearly visible. Depth profiles were then used to quantify the material removal.

[0035] The extracted particulates can be filtered from the water to collect the gold particles. Nickel is ferromagnetic and therefore can be easily separated from gold. A method for separating gold particles from complex aqueous solutions, such as metal-organic framework / polymer composites, is disclosed by Sun, DT et al., Journal of the American Chemical Society, vol. 140, no. 48, pp. 16697-16703, 2018.

[0036] The specific examples provided in the above description should not be construed as limiting the scope and / or applicability of the appended claims.

Claims

1. 1. A method for extracting one or more rare and precious metals (RPM) from a substrate containing said metals, comprising: i) providing the substrate; ii) immersing the substrate in a fluid; iii) scanning at least a portion of the surface of the substrate with ultrasonic waves, wherein the ultrasonic wave intensity at the surface is 1 W / cm ２ and iv) recording echoes of said ultrasound; v) constructing an amplitude map of said at least part of said surface of said substrate based on said recorded echoes; vi) selecting one or more regions of interest of the at least a portion of the surface of the substrate based on the amplitude map; vii) exposing the one or more regions of interest to focused ultrasound, wherein the intensity of the ultrasound at the one or more regions of interest is at least 1 W / cm ２ , preferably at least 10 W / cm ２ whereby said one or more RPMs are extracted from said substrate into said fluid; A method comprising:

2. 10. The method of claim 1, further comprising, prior to step iii), generating an image of the surface of the substrate using a machine vision system, and selecting the at least a portion of the surface of the substrate for scanning based on the image.

3. The method of claim 1 or 2, comprising the step of moving the substrate.

4. 4. The method according to any one of claims 1 to 3, wherein the ultrasound in step iii) produces a pressure amplitude at the surface of up to 7 MPa and comprises 3 to 20 cycles / burst, preferably 3 to 5 cycles / burst.

5. 5. The method according to any one of claims 1 to 4, wherein the ultrasound in step vii) comprises one or more of the following: a central frequency of 2 to 30 MHz, preferably 1 to 15 MHz; 30 to 80 cycles per burst; a pulse repetition frequency of at least 1 kHz.

6. below: viii) separating one of the plurality of RPMs from the fluid. The method according to any one of claims 1 to 5, comprising:

7. The method of claim 6 , wherein the separating step comprises one or more of evaporating, filtering, and exposing the fluid to a magnetic field.

8. 8. The method of any one of claims 1 to 7, wherein the RPM is selected from the group consisting of rhodium, platinum, gold, ruthenium, iridium, osmium, palladium, rhenium, nickel, and silver, preferably gold and platinum, most preferably gold.

9. The method according to any one of claims 1 to 8, wherein the substrate is a recyclable material.

10. 10. The method of claim 9, wherein the recyclable material is selected from electronic waste and exhaust catalytic converters.

11. The method of claim 10, wherein the electronic waste is a printed circuit board.

12. The method of any one of claims 1 to 11, wherein the fluid comprises water.

13. The method according to any one of claims 1 to 11, wherein the fluid is water.

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