Method for selectively recovering gold in solid waste through eutectic system

Abstract

The invention relates to the field of metal recovery and solid waste recycling, in particular to a method for selectively recovering gold in solid waste through a eutectic system. The eutectic system comprises a hydrogen bond acceptor, a hydrogen bond donor and an oxidizing agent. The gold-containing solid waste is immersed into the eutectic system to be leached, after leaching is finished, a leaching agent is subjected to electro-deposition, gold elementary substances are obtained, and gold in the solid waste is selectively recycled through the eutectic system. According to the method, the environment-friendly deep eutectic solvent-iodine system serves as a reaction medium, traditional strong acid / alkali and other corrosive leaching agents are replaced, the precious metal gold in the gold-containing solid waste is selectively extracted, the technological process and operation are simple and efficient, the leachate can be recycled, and a new way is provided for green and efficient recovery of the gold in the solid waste.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of metal recovery and solid waste resource utilization, in particular to a method for selectively recovering gold in solid waste by using a eutectic system. BACKGROUND

[0002] Gold is a highly sought-after resource worldwide due to its rarity, corrosion resistance, and unique aesthetic value. It is widely used in smart phones, computer chips, and medical sensors. Waste circuit boards are an important component of electronic waste and also one of the key sources for gold recovery. According to statistics, the gold content in one ton of waste circuit boards can reach up to 300 grams, far exceeding the average content of traditional gold mines (about 5 grams per ton). This high concentration of gold distribution makes waste circuit boards known as "urban mines", and the recovery of gold from waste circuit boards has important significance for alleviating the contradiction between supply and demand of global precious metal resources.

[0003] CPU is the core component of electronic devices, containing a high proportion of precious and rare metals, and its resource value far exceeds that of ordinary electronic components. Through scientific and efficient recycling, not only can the demand for primary mineral resources be greatly reduced, but also the environmental problems such as soil pollution and water resource destruction caused by mining can be reduced. According to statistics, about 1000-1500 grams of gold can be extracted from one ton of waste CPU, and a large number of silver, palladium, copper and other metals can also be recovered. The resource recovery efficiency of CPU is hundreds of times that of natural ore. In addition, this process can also avoid the release of harmful substances due to random disposal, effectively curb the erosion of electronic waste on the ecological environment, and has both economic and ecological benefits. It is an important measure to promote the resource utilization of electronic waste and contribute to global green and sustainable development.

[0004] Currently, the mainstream technologies for recovering gold from solid waste mainly include pyrometallurgy, hydrometallurgy, and bioleaching. Although pyrometallurgical technology has high metal enrichment capacity, it still has environmental bottlenecks such as the risk of secondary pollutant generation. Typical problems include the release of dioxin-containing, heavy metal vapor gaseous pollutants at high-temperature smelting stage; and the disposal pressure of toxic metals remaining in the molten by-products. Traditional hydrometallurgical processes rely on strong acids (such as nitric acid, aqua regia) or cyanide as leaching agents, generating a large amount of wastewater and waste gas containing heavy metals and toxic substances. Although microbial leaching is cleaner than traditional cyanide heap leaching, it usually has a slower processing speed and requires a longer processing period to achieve satisfactory metal recovery rate. At the same time, the biological activity is significantly affected by environmental factors such as pH, temperature, and oxygen concentration, which need to be strictly controlled, increasing the complexity and difficulty of the process. In summary, existing gold recovery technologies have different degrees of environmental pollution, high recovery cost, and poor selectivity.

[0005] To solve the above problems, the application provides a method for selectively recovering gold in solid waste by using a eutectic system. SUMMARY

[0006] To solve the problems of the prior art, the application aims to provide a method for selectively extracting precious metal gold in solid waste by using a eutectic solution plus iodine system. The method is based on a eutectic solvent, which has the advantages of non-flammability, environmental friendliness, low melting point, etc., and is suitable for establishing a high-efficiency resource recovery process route for precious metals in a mild reaction system.

[0007] To achieve the above-mentioned purpose, the application provides the following solutions.

[0008] In one of the technical solutions of the application, a eutectic system for selectively recovering gold in solid waste comprises a hydrogen bond acceptor, a hydrogen bond donor and an oxidizing agent.

[0009] In a preferred embodiment of the application, the hydrogen bond acceptor is choline chloride; the hydrogen bond donor is one of malonic acid, ethylene glycol, citric acid, levulinic acid, succinic acid, xylitol, trifluoroacetamide and acetic acid; and the oxidizing agent is iodine.

[0010] In a preferred embodiment of the application, the molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1 or 1:2.

[0011] In a preferred embodiment of the application, the concentration of the oxidizing agent in the eutectic system is 0.1-0.3 mol / L.

[0012] In a preferred embodiment of the application, the pH of the eutectic system is 6-8.

[0013] In another technical solution of the application, a method for selectively recovering gold in solid waste by using a eutectic system comprises the following steps:

[0014] The gold-containing solid waste is immersed in the eutectic system described above for leaching, and then the leaching agent is subjected to electrodeposition to obtain gold.

[0015] In a preferred embodiment of the application, the hydrogen bond acceptor and the hydrogen bond donor are heated to 60-100 DEG C until a uniform and transparent liquid is formed, and then iodine is added to completely dissolve, thereby obtaining the eutectic system.

[0016] In a preferred embodiment of the application, the gold-containing solid waste is a gold-containing circuit board and / or CPU.

[0017] In a preferred embodiment of the application, the leaching temperature is 60-100 DEG C, and the leaching time is 60-240 min.

[0018] The stirring is also carried out in the leaching process, and the stirring speed is the stirring speed commonly used by those skilled in the art, such as 300 rpm.

[0019] In the preferred embodiment of the present application, the electrodeposition is carried out in a constant potential mode, the voltage of the electrodeposition is-0.6 to-0.9 V, the maximum current of the electrodeposition is-0.9 to-1.3 mA, and the time of the electrodeposition is 60 to 300 min.

[0020] In the preferred embodiment of the present application, the liquid-solid ratio of the eutectic system to gold in the gold-containing solid waste is 500 to 5000 ml: 1 g.

[0021] The present application carries out a pure gold gold leaching experiment, which proves that the liquid-solid ratio of 500 ml: 1 g is feasible; the amount of the eutectic system can be further increased, and the technical effects of the present application can also be achieved. Considering the cost and technical effects, the present application preferably limits the liquid-solid ratio of the eutectic system to gold in the gold-containing solid waste to the above range.

[0022] The leaching agent left after the electrodeposition of gold can be recycled.

[0023] The present application discloses the following technical effects:

[0024] The process of the present application is simple, low-toxicity, environmentally friendly, convenient to operate, and low in cost. The eutectic solvent plus iodine system is used to replace the traditional strong acid, strong base oxidant system, which has the characteristics of high stability, good solvation effect, and simple synthesis. In the selective recovery of gold from solid waste, other metals in the solid waste are avoided to be reduced, and the difficulty of recovering high-purity gold is reduced, which provides a thought and practical basis for the recovery of gold from solid waste. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0026] Figure 1 The process flow diagram for the present application to selectively recover gold from solid waste using a eutectic system;

[0027] Figure 2 The SEM picture and EDS spectrum of the gold deposit in Example 1;

[0028] Figure 3 The XRD spectrum analysis of the gold deposit in Example 1;

[0029] Figure 4 Figure 2 is a comparison chart of waste CPU before and after leaching in Example 1.

[0030] Figure 5 Figure 3 is a comparison chart of waste circuit board before and after leaching in Example 2, wherein the left chart is before leaching and the right chart is after leaching. DETAILED DESCRIPTION

[0031] The various illustrative embodiments of the present application will now be described in detail in connection with the accompanying drawings. This description is made for illustrative purposes only and is not intended to limit the application.

[0032] It should be understood that the terms used herein are merely for describing particular embodiments and are not intended to limit the application. In addition, for numerical ranges in the present application, it should be understood that every intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value between any stated value or stated range, as well as any other stated value or intermediate value in the stated range, is also included in the present application. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present application, the preferred methods and materials are described herein. Unless otherwise stated, the following terms are intended to have the meanings presented here.

[0034] Many modifications and variations of the present application described in the specification are possible without departing from the scope or spirit of the application. Other implementations of the application will be apparent to those skilled in the art from consideration of the specification and practice of the application. The specification and examples are illustrative only.

[0035] As used herein, the terms "comprise", "comprising", "include", "including", "have", "having" and the like are open-ended terms that are intended to mean "including but not limited to".

[0036] The "%" described in the present application means mass percentage unless otherwise specified.

[0037] The present application uses gold-containing solid waste as raw material and leaches it in a eutectic solvent-iodine system. After the reaction, the residue is filtered, and the obtained leaching solution is directly subjected to electrodeposition. The noble metal gold can be obtained after the electrodeposition. The present application uses the environmentally friendly eutectic solvent-iodine system as the reaction medium, instead of the traditional strong acid / alkali and other corrosive leaching agents, to selectively extract the noble metal gold in the gold-containing solid waste. The process flow and operation are simple and efficient, the leaching solution can be recycled, and a new way is provided for the green and efficient recovery of gold from solid waste.

[0038] The technical solutions described in the present application are conventional solutions in the art if not specifically stated, and the reagents or raw materials used are purchased from commercial channels or are publicly disclosed if not specifically stated.

[0039] The technical solutions provided by the present application will be described in detail below in conjunction with examples, but they should not be understood as limiting the scope of protection of the present application.

[0040] Example 1 (waste CPU)

[0041] The ICP-OES measurement showed that the waste CPU contained 0.047% of gold, 0.009% of silver, and 0.002% of palladium. 20.58 g of waste CPU was taken in 50 mL of choline chloride-malonate solvent containing 0.1 mol / L I2 (iodine element), and the molar ratio of choline chloride to malonic acid was 1:1. The mixture was heated and leached under magnetic stirring (300 rpm) at 80°C for 120 min. After the leaching was completed, the leaching agent was subjected to electrodeposition, and the voltage was set to -0.7 V, the maximum current was -0.9 mA, and the deposition was performed for 4 h (the reference electrode was a silver chloride electrode, the counter electrode was a titanium electrode, and the working electrode was a carbon nanotube film, and the electrodeposition was performed in a constant potential mode). After the deposition was completed, the precipitate was washed with deionized water, and then dried to obtain the Au product. The product was analyzed by SEM-EDS and XRD, and the SEM image and EDS spectrum of the precipitate are shown in Figure 2 , and the XRD spectrum is shown in Figure 3 . Figure 4 The figure is a comparison before and after the leaching of the waste CPU in Example 1. The surface of the waste CPU pin before leaching is gold, and the surface layer disappears after leaching, confirming that the gold has been effectively leached out.

[0042] The SEM-EDS results show that the product is mainly gold element, and the XRD spectrum is consistent with the standard spectrum of gold. The calculated gold leaching rate can reach 99.9%, indicating that the method described in the present application can efficiently recover gold from solid waste.

[0043] Example 2 (waste circuit board)

[0044] The content of Au in waste circuit board is 0.038% and the content of Ag is 0.163% and the content of Pd is 0.012% measured by ICP-OES, 19.63g of waste circuit board is taken in 50mL of choline chloride-xylitol solvent containing 0.1mol / L of I2 (the molar ratio of choline chloride and xylitol is 1:1), and heated and leached under the condition of magnetic stirring (300rpm) at 80℃ for 120min; after the leaching is completed, electrodeposition is carried out on the leaching agent, the voltage is set to-0.8V, the maximum current is-1mA, and the deposition is carried out for 4h (the reference electrode is a silver chloride electrode, the counter electrode is a titanium electrode, and the working electrode is a carbon nanotube film, and the electrodeposition is carried out in a constant potential mode), and the Au product is obtained after the deposition is completed. Figure 5 It is a comparison chart of waste circuit board before and after leaching of Example 2. The surface of the waste circuit board before leaching is gold, and the surface layer disappears after leaching, which proves that the gold is effectively leached.

[0045] In this embodiment, the leaching rate of gold can reach 99.8%.

[0046] Comparative Example 1

[0047] The only difference between Example 1 and this comparative example is that the choline chloride-malonic acid solvent does not contain I2.

[0048] Result: In this comparative example, there is no obvious change in the waste CPU before and after leaching, and the gold is not effectively leached.

[0049] Comparative Example 2

[0050] The only difference between Example 1 and this comparative example is that 2g of reducing agent sodium sulfite is added to reduce gold after the leaching is completed, and the step of electrodeposition is omitted.

[0051] Result: In this comparative example, there is no obvious change in the leaching solution after the reducing agent is added, and the gold is not effectively extracted.

[0052] Comparative Example 3

[0053] The only difference between Example 2 and this comparative example is that the choline chloride-xylitol solvent does not contain I2.

[0054] Result: In this comparative example, there is no obvious change in the surface of the waste circuit board before and after leaching, and the gold is not effectively leached.

[0055] Comparative Example 4

[0056] The only difference between Example 1 and this comparative example is that 0.1mol / L of I2 in the choline chloride-malonic acid solvent is replaced by 0.1mol / L of FeCl3.

[0057] Result: In this comparative example, there is no obvious change in the waste CPU before and after leaching, and the gold is not effectively leached.

[0058] Comparative Example 5

[0059] The difference from Example 1 is that the concentration of I2 in the choline chloride-malonate solvent is 0.5 mol / L.

[0060] Result: In this comparative example, the leaching time of the waste CPU is prolonged, and the excessive amount of iodine increases the viscosity of the solution, the cost and the difficulty of subsequent processing, and reduces the leaching efficiency.

[0061] Comparative Example 6

[0062] The difference from Example 1 is that the concentration of I2 in the choline chloride-malonate solvent is 0.05 mol / L.

[0063] Result: In this comparative example, a small part of the surface layer of the waste CPU disappears after leaching, confirming that the gold is not completely leached out.

[0064] The above-described examples are only used to describe the preferred modes of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by those skilled in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A eutectic system for selectively recovering gold from solid waste, characterized in that, The hydrogen bond acceptor, the hydrogen bond donor and the oxidant.

2. The eutectic system for selectively recovering gold from solid waste according to claim 1, characterized in that, The hydrogen bond acceptor is choline chloride; the hydrogen bond donor is one of malonic acid, ethylene glycol, citric acid, levulinic acid, succinic acid, xylitol, trifluoroacetamide and acetic acid; and the oxidant is iodine.

3. The eutectic system for selectively recovering gold from solid waste according to claim 1, characterized in that, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:1 or 1:

2.

4. The eutectic system for selectively recovering gold from solid waste according to claim 1, wherein The concentration of the oxidant in the eutectic system is 0.1-0.3 mol / L.

5. The eutectic system for selectively recovering gold from solid waste according to claim 1, wherein The pH of the eutectic system is 6-8.

6. A method for selectively recovering gold from solid waste in a deep eutectic solvent system, characterized by, The method comprises the following steps: The gold-containing solid waste is immersed in the eutectic system of any one of claims 1-5 to leach out, and then the leaching agent is electrodeposited to obtain elemental gold.

7. The method of claim 6, wherein, The gold-containing solid waste is a circuit board and / or CPU containing gold.

8. The method of claim 6, wherein, The leaching temperature is 60-100℃, and the leaching time is 60-240 min.

9. The method of claim 6, wherein, The electrodeposition is performed in a constant potential mode, the voltage is -0.6 to -0.9 V, the maximum current is -0.9 to -1.3 mA, and the time is 60-300 min.

10. The method of claim 6, wherein, The liquid-solid ratio of the eutectic system to gold in the gold-containing solid waste is 500-5000 ml:1 g.

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