Ultrasonic-assisted photocatalytic precious metal leaching method

Abstract

The invention discloses an ultrasonic-assisted photocatalytic precious metal leaching method, and belongs to the technical field of precious metal recovery. The method comprises the following steps: (1) material pretreatment: treating electronic waste powder containing gold, silver and copper into electronic waste powder capable of being leached by a proper method; (2) preparing a reaction system: adding electronic waste powder containing gold, silver and copper into a leaching solvent, then sequentially adding FeCl3 and a photocatalyst, and uniformly stirring; (3) photocatalytic leaching: carrying out ultrasonic-assisted leaching reaction on the suspension reaction system under ultraviolet irradiation; and (4) solid-liquid separation is conducted, and leaching liquid containing precious metal and leaching residues are obtained. According to the method, the synergistic effect of FeCl3 and the photocatalyst is combined, efficient leaching of precious metal is achieved under ultraviolet irradiation, and the method has the advantages of being environmentally friendly, efficient, good in cyclicity, mild in condition, easy to operate and the like, is suitable for large-scale recovery of precious metal from electronic waste containing gold, silver and copper and has important economic and environmental significance.

Description

Technical Field

[0001] This invention belongs to the field of precious metal recycling technology, specifically relating to an ultrasound-assisted photocatalytic leaching method for precious metals, which is particularly suitable for leaching and recovering precious metals from electronic waste containing gold, silver, and copper. Background Technology

[0002] With the rapid development of the electronics industry, the amount of electronic waste generated has increased dramatically. Electronic waste contains various precious metals such as gold, silver, and copper, with a content far exceeding that of natural ores, giving it extremely high recycling value. Therefore, the efficient recovery of precious metals from electronic waste can not only alleviate resource shortages but also reduce environmental pollution, holding significant economic and environmental importance.

[0003] Currently, methods for leaching precious metals from electronic waste mainly fall into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy suffers from drawbacks such as high energy consumption, generation of toxic and harmful gases, and low precious metal recovery rates; hydrometallurgy, on the other hand, is widely used due to its advantages of low energy consumption and good selectivity. Traditional hydrometallurgical leaching agents mainly include cyanide, thiourea, and thiosulfate, but cyanide is highly toxic and poses significant risks to the environment and human health; thiourea and thiosulfate leaching agents suffer from low leaching efficiency and poor stability. Photocatalysis, as a green and environmentally friendly advanced oxidation technology, has attracted attention in the field of precious metal leaching in recent years. Photocatalysts can generate active species with strong redox properties under light irradiation, which can promote the oxidative dissolution of precious metals. Existing photocatalytic leaching technologies mostly use aqueous solutions, which suffer from poor leaching selectivity and the need to improve the precious metal leaching rate. Therefore, developing an environmentally friendly, efficient, and highly selective ultrasound-assisted photocatalytic leaching method for precious metals is of significant practical importance.

[0004] Patent CN114807613A discloses a method for recovering precious metals from solid waste using a polar aprotic solvent, achieving efficient gold recovery. However, this system has certain drawbacks: after multiple cycles, the leaching efficiency of precious metals tends to decrease significantly due to the inevitable introduction of water. Bian et al. (Nat.Sustain., 2021, 14, 618-626.) proposed a photocatalytic recovery method for precious metals using MeCN / DCN as a solvent. This method can selectively leach gold, silver, and other precious metals from electronic waste, spent automotive three-way catalysts, and ores, achieving high leaching rates. However, this system still has limitations: conventional electronic waste materials often contain large amounts of copper, and the preferential leaching of copper during leaching leads to excessively long reaction times required for precious metal recovery, increasing energy consumption.

[0005] To address the above problems, this invention provides an ultrasound-assisted photocatalytic leaching method for precious metals. It uses acetonitrile or an acetonitrile-water mixed solvent as the leaching solvent, combining the synergistic effect of FeCl3 and a photocatalyst with ultrasound assistance to achieve highly efficient leaching of precious metals under ultraviolet light irradiation. This method is environmentally friendly, efficient, and has excellent recyclability, effectively overcoming the shortcomings of existing technologies. Summary of the Invention

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An ultrasound-assisted photocatalytic leaching method for noble metals includes the following steps: (1) Material pretreatment: Electronic waste powder containing gold, silver and copper is subjected to primary screening, air roasting, ball milling and thermal reduction to obtain electronic waste powder that can be leached; (2) Preparation of reaction system: The pretreated electronic waste powder was added to the leaching solvent, and FeCl3 and photocatalyst were added in sequence. The mixture was then ultrasonically dispersed to obtain a suspension reaction system. (3) Photocatalytic leaching: The suspension reaction system obtained in step (1) is placed under ultraviolet light irradiation to carry out photocatalytic leaching reaction. Stirring is maintained during the reaction, and ultrasound can be added. (4) Solid-liquid separation: After the leaching reaction is completed, the reaction system is subjected to solid-liquid separation to obtain a leachate containing precious metals and a leaching residue;

[0008] Furthermore, in step (1), the air roasting temperature of the electronic waste powder is 700-800℃;

[0009] Further, in step (1), the ball milling speed of the electronic waste powder is 400-800 r / min;

[0010] Further, in step (1), the thermal reduction atmosphere of the electronic waste powder is an Ar / H2 atmosphere, and the thermal reduction temperature is 450-600℃;

[0011] Furthermore, in step (2), the particle size of the electronic waste powder is 100-500 mesh;

[0012] Further, in step (2), the solid-liquid ratio of the electronic waste powder to the leaching solvent is 1:10 to 1:50 g / mL, and the photocatalyst is TiO2 or commercial mixed-phase catalyst P25;

[0013] Further, in step (2), the amount of FeCl3 added is 0.05-0.5 mol / L, and the amount of photocatalyst added is 0.5-5 g / L;

[0014] Furthermore, in step (3), the wavelength of the ultraviolet light is 200–400 nm, the power is 50–300 W, and the irradiation time is 1–36 h;

[0015] Furthermore, in step (3), the stirring rate is 300-800 r / min, the reaction temperature is 10-80℃, and the ultrasonic power is 50-300 W;

[0016] Furthermore, the leaching solvent is pure acetonitrile or an acetonitrile-water mixed solvent, wherein the volume ratio of acetonitrile to water in the acetonitrile-water mixed solvent is 1:99 to 99:1;

[0017] Furthermore, in step (4), the solid-liquid separation method is centrifugal separation or filtration separation, the centrifugation speed is 3000-8000 r / min, and the filtration uses a 0.22-0.45 μm filter membrane;

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] This invention combines the synergistic effect of FeCl3 and P25 photocatalysts. Under ultraviolet light irradiation, the active species generated by P25 can enhance the oxidation capacity of FeCl3, promote the accelerated leaching of copper and the oxidative dissolution of precious metals such as gold and silver, and improve the leaching efficiency of precious metals. The addition of ultrasound can also further improve the leaching efficiency.

[0020] The present invention has excellent cycle performance and can achieve efficient leaching under different water contents in the solvent. It does not need to consider the impact of a small amount of water introduced during solvent circulation on the leaching efficiency, and the performance is stable after multiple cycles.

[0021] The leaching process of this invention is mild, can be carried out at room temperature, has low energy consumption, is simple to operate, and is easy to apply industrially. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0023] Figure 1 XRD pattern of pretreated electronic waste powder;

[0024] Figure 2 The image shows the leaching effect of gold, silver, and copper at room temperature.

[0025] Figure 3 The leaching efficiency curves of the three metals under different solvent water contents are shown.

[0026] Figure 4The curves show the leaching rate of precious metals under the same leaching time and for different number of cycles. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 The XRD pattern of gold and silver-containing electronic waste powder is shown. The figure reveals that the main phase in the pretreated material is metallic copper. Because copper is easily oxidized in air, it also contains some characteristic peaks that match those of cuprous oxide.

[0030] Example 1

[0031] An ultrasound-assisted photocatalytic leaching method for noble metals includes the following steps: (1) Preparation of reaction system: 50 mg of pretreated electronic waste powder containing gold, silver and copper was added to 50 mL of pure acetonitrile, 1 g of FeCl3 and 50 mg of commercial mixed-phase P25 photocatalyst were added, and the mixture was sonicated to obtain a suspension reaction system; (2) Photocatalytic leaching: The suspension reaction system obtained in step (1) was placed under ultraviolet light with a wavelength of 365 nm and a power of 100 W, and stirred at a rate of 300 r / min for 8 h at room temperature, with 50 W sonication throughout the process; (3) Solid-liquid separation: After the leaching reaction was completed, the mixture was centrifuged at 6000 r / min to obtain the leachate containing precious metals and the leaching residue. The leaching rates of gold, silver and copper were all 100%.

[0032] Figure 2 The leaching effect diagrams of gold, silver and copper at room temperature in Example 1 are shown. It can be seen from the diagrams that copper was leached earlier than silver and gold.

[0033] Example 2

[0034] Same as Example 1, except that the leaching solvent was changed from 50 mL of pure acetonitrile to a mixed solvent of 40 mL of acetonitrile and 10 mL of deionized water. The leaching rates of gold, silver and copper were all 100% after testing.

[0035] Example 3

[0036] Same as Example 1, except that the leaching solvent was changed from 50 mL of pure acetonitrile to a mixed solvent of 10 mL of acetonitrile and 40 mL of deionized water, and the reaction time was changed from 8 h to 12 h. The leaching rates of gold, silver and copper were all 100% after testing.

[0037] Figure 3 The leaching efficiency of metallic gold under different solvent water contents in Examples 2 and 3 is shown. As can be seen from the figure, the solvent water content has no significant effect on the final leaching effect of the present invention over a large range, and the leaching efficiency is relatively stable under different solvent water contents.

[0038] Example 4

[0039] Same as Example 1, except that the reaction temperature was adjusted from room temperature to 10°C, the ultrasonic power was adjusted to 100 W, and the solid-liquid separation method was changed from centrifugation at 6000 r / min to filtration through a 0.22 μm filter membrane. Testing showed that the leaching rates of gold, silver, and copper were all 100%.

[0040] Example 5

[0041] Same as Example 1, except that the reaction temperature was adjusted from room temperature to 60°C, the ultrasonic power was adjusted to 100 W, the reaction time was adjusted from 8 hours to 4 hours, and the solid-liquid separation method was changed from centrifugation at 6000 r / min to filtration through a 0.22 μm filter membrane. Testing showed that the leaching rates of gold, silver, and copper were all 100%.

[0042] Example 6

[0043] Same as Example 1, except that the volume of acetonitrile was adjusted from 50 mL to 100 mL, the mass of FeCl3 was adjusted from 1 g to 2 g, and the mass of P25 was adjusted from 50 mg to 100 mg. The leaching rates of gold, silver, and copper were all 100% as tested.

[0044] Example 7

[0045] Same as Example 1, except that the mass of electronic waste powder was adjusted from 50 mg to 25 mg, the volume of acetonitrile was adjusted from 50 mL to 100 mL, the mass of FeCl3 was adjusted from 1 g to 2 g, the mass of P25 was adjusted from 50 mg to 100 mg, and the reaction time was adjusted from 8 h to 4 h. After testing, the leaching rates of gold, silver and copper were all 100%.

[0046] Example 8

[0047] An ultrasound-assisted photocatalytic leaching method for noble metals includes the following steps: (1) First leaching: 50 mg of pretreated electronic waste powder containing gold, silver and copper was added to 50 mL of pure acetonitrile, 1 g of FeCl3 and 50 mg of commercial mixed-phase P25 photocatalyst were added, and the mixture was sonicated to obtain a suspension reaction system; the suspension reaction system was placed under ultraviolet light with a wavelength of 365 nm and a power of 100 W, and stirred at a rate of 300 r / min for 8 h at room temperature, with an additional 50 W of sonication during the process, and the volatile solvent was condensed and recovered; after the reaction was completed, the mixture was filtered and separated using a 0.22 μm filter membrane to obtain the leachate containing precious metals and the leachate residue, and the solvent recovered by condensation was collected; (2) Solvent recycling: The above-mentioned leachate containing precious metals is placed in a rotary evaporator for rotary evaporation and the solvent is collected. The leaching operation in step (1) is repeated using the recycled solvent for a total of 10 times. Tests showed that after the initial leaching and 10 cycles of recycling, the leaching rates of gold, silver, and copper remained at 95%-100% within the same time period, indicating good solvent cycle stability.

[0048] Figure 4 The results show the changes in the leaching rates of gold, silver, and copper over the same time period as the number of cycles increases, indicating that the leaching efficiency of the metals decreases with increasing cycle number, but remains at a high level.

[0049] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for ultrasonic-assisted photocatalytic leaching of noble metals, characterized in that, Includes the following steps: (1) Material pretreatment: Electronic waste powder containing gold, silver and copper is subjected to primary screening, roasting, ball milling and thermal reduction to obtain electronic waste powder that can be leached; (2) Preparation of reaction system: The pretreated electronic waste powder was added to the leaching solvent, and FeCl3 and photocatalyst were added in sequence. The mixture was then ultrasonically dispersed to obtain a suspension reaction system. (3) Photocatalytic leaching: The suspension reaction system obtained in step (1) is placed under ultraviolet light irradiation to carry out photocatalytic leaching reaction, and stirring and sonication are maintained during the reaction; (4) Solid-liquid separation: After the leaching reaction is completed, the reaction system is subjected to solid-liquid separation to obtain a leachate containing precious metals and a leaching residue; The leaching solvent is pure acetonitrile or an acetonitrile-water mixture, wherein the volume percentage of water in the acetonitrile-water mixture is 0.1%-90%.

2. The method according to claim 1, characterized in that, In step (1), the air roasting temperature of the electronic waste powder is 700-800℃.

3. The method according to claim 1, characterized in that, In step (1), the ball milling speed of the electronic waste powder is 400-800 r / min.

4. The method according to claim 1, characterized in that, In step (1), the thermal reduction atmosphere of the electronic waste powder is an Ar / H2 atmosphere, and the thermal reduction temperature is 450-600℃.

5. The method according to claim 1, characterized in that, In step (2), the particle size of the electronic waste powder is 100 to 500 mesh.

6. The method according to claim 1, characterized in that, In step (2), the solid-liquid ratio of the electronic waste powder to the leaching solvent is 1:1 to 1:5 mg / mL, and the photocatalyst is TiO2 or commercial mixed-phase catalyst P25.

7. The method according to claim 1, characterized in that, In step (2), the amount of FeCl3 added is 0.05 to 0.5 g / L, and the amount of photocatalyst added is 0.5 to 5 g / L.

8. The method according to claim 1, characterized in that, In step (3), the wavelength of the ultraviolet light is 200-400nm, the power is 50-300W, the irradiation time is 1-36h, the stirring rate is 300-800 r / min, the reaction temperature is 10-80℃, the ultrasonic power is 50-300W, and the volume ratio of water in the acetonitrile-water mixed solvent is 0.1%-90%.

9. The method according to claim 1, characterized in that, In step (4), the solid-liquid separation method is centrifugal separation or filtration separation, the centrifugation speed is 3000-8000 r / min, and the filtration uses a 0.22-0.45 μm filter membrane.

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