Method for selectively recovering precious metal in waste chip by utilizing persulfate-metal chloride system

Abstract

The invention provides a method for selectively recycling precious metal in a waste chip by utilizing a persulfate-metal chloride system, and belongs to the technical field of waste electronic resource recycling. The method provided by the invention comprises the following steps: mixing the waste chips with a leaching solution, leaching under a heating condition, then carrying out solid-liquid separation, and collecting a solution containing Pd (II) and Au (III); introducing reducing gas into the solution containing Pd (II) and Au (III) to carry out reduction reaction, then carrying out solid-liquid separation, and collecting solid product gold precipitate and the solution containing Pd (II); adding iron powder into the solution containing Pd (II) to carry out replacement reaction, and then carrying out solid-liquid separation to obtain palladium precipitate; the solutes in the leachate are persulfate and metal chloride. According to the method, ammonium persulfate is catalyzed by metal chloride to generate free radicals, and efficient and selective leaching and separation of the precious metal are achieved in cooperation with the coordination effect of chloride ions.

Description

Technical Field

[0001] This invention relates to the field of waste electronic resource recycling technology, and in particular to a method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system. Background Technology

[0002] Palladium and gold, as key strategic precious metals, play an irreplaceable role in high-end electronic devices, semiconductor manufacturing, and other fields. With the increasingly tight supply of strategic metal resources and the rapid iteration of electronic products, the efficient recovery of palladium and gold from electronic waste such as discarded chips has become an important way to alleviate resource constraints and promote the development of a resource-based circular economy, offering multiple benefits including environmental, economic, and social advantages. However, existing precious metal recycling technologies still face severe challenges such as significant environmental pollution, complex processes, and limited selectivity.

[0003] Traditional pyrometallurgical recovery processes are energy-intensive and prone to producing toxic gases. Mainstream hydrometallurgical processes rely heavily on highly corrosive or toxic reagents such as aqua regia and cyanide. While these processes offer good leaching results, they also present significant problems including severe environmental pollution, high operational risks, and rapid equipment corrosion. Chinese invention patent CN105907976A discloses a method for recovering palladium from waste electronic components. Although it avoids the use of aqua regia and cyanide, it still operates in a highly acidic and oxidizing chemical environment, and the fundamental problems remain unresolved.

[0004] In recent years, some catalytic oxidation methods have been attempted for precious metal recovery, but these often require the introduction of additional catalysts, complex energy inputs (such as ultraviolet light), or the generation of large amounts of iron / copper sludge, resulting in complex processes, high energy consumption, or secondary pollution. Persulfate advanced oxidation technology, due to its ability to generate highly oxidizing sulfate radicals (SO4), offers a solution. - SO4 has received considerable attention in the field of environmental remediation. - It possesses an oxidation potential comparable to that of hydroxyl radicals (approximately 2.5-3.1 V), along with a longer half-life and a wider pH adaptability range. If applied to precious metal recovery, it holds promise for achieving green and efficient recovery of precious metals under milder conditions. However, the energy consumption of simply thermally activating persulfate remains high, and its selective dissolution mechanism for precious metals in complex matrices is unclear, limiting its application.

[0005] Therefore, developing a new technology for recycling precious metals from waste chips that is efficient, highly selective, environmentally friendly, and simple in process is of great practical significance and application value. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies, such as high environmental pollution, poor selectivity, and complex processes, and to provide a method for the selective recovery of palladium and gold from waste chips based on a persulfate-metal chloride synergistic activation system. This method utilizes metal chloride to catalyze the generation of free radicals from ammonium persulfate, and synergistically coordinates with chloride ions to achieve efficient and selective leaching and separation of precious metals.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system includes the following steps: S1. After mixing the waste chip with the leaching solution, leach it under heating conditions, then separate the solid and liquid components and collect the solution containing Pd(II) and Au(III); S2. A reducing gas is introduced into the solution containing Pd(II) and Au(III) to carry out a reduction reaction, followed by solid-liquid separation, and the solid product gold precipitate and the solution containing Pd(II) are collected. S3. Add iron powder to the solution containing Pd(II) to carry out a displacement reaction, followed by solid-liquid separation to obtain palladium precipitate; The solutes in the leachate are persulfate and metal chloride.

[0008] The mechanism of this invention is as follows: This invention combines the persulfate advanced oxidation system with chlorine coordination chemistry. Metal ions (such as Cu) 2+ / Fe 2+ Catalytic activation of ammonium persulfate to produce strongly oxidizing SO4. - Free radicals attack and oxidize noble metals; simultaneously, Cl in the system... - With oxidized noble metal ions (Pd) 2+ Au 3+ This forms stable chloride anions (such as [PdCl4]). 2- [AuCl4] - The copper, iron, aluminum, and other base metals in the waste chips have a very low solubility tendency under this mild oxidation-coordination system, thus achieving highly selective leaching of precious metals.

[0009] The present invention discloses the following technical effects: 1. Green and environmentally friendly, with mild conditions: This invention eliminates traditional high-risk reagents such as aqua regia and cyanide. Persulfate and the selected metal chloride are stable and environmentally friendly. The reaction is carried out in near-neutral or weakly acidic aqueous solutions, requiring no strong acid environment and producing no toxic or harmful gases, greatly reducing the environmental burden and safety risks.

[0010] 2. Simple process and high efficiency: The subsequent separation utilizes the difference in reduction potential between gold and palladium. Gold is preferentially reduced by simply passing SO2 gas, and then palladium is replaced by iron powder, which can achieve efficient separation and recovery of the two. The leaching rate of gold and palladium is >95%, the recovery rate is >90%, the process is short and the operation is simple.

[0011] 3. Low cost and broad prospects: The reagents used are inexpensive and readily available, the reaction conditions are easy to achieve, and the recovery rate and purity of precious metals are high, providing an economical and feasible new technology path for the resource utilization of electronic waste such as waste chips. Attached Figure Description

[0012] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 This is a schematic diagram of the process flow for selectively recovering precious metals from waste chips using a persulfate-metal chloride system, as per the present invention. Detailed Implementation

[0014] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0015] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0016] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0017] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0018] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0019] This invention provides a method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system, comprising the following steps: S1. After mixing the waste chip with the leaching solution, leach it under heating conditions, then separate the solid and liquid components and collect the solution containing Pd(II) and Au(III); S2. A reducing gas is introduced into the solution containing Pd(II) and Au(III) to carry out a reduction reaction, followed by solid-liquid separation, and the solid product gold precipitate and the solution containing Pd(II) are collected. S3. Add iron powder to the solution containing Pd(II) to carry out a displacement reaction, followed by solid-liquid separation to obtain palladium precipitate; The solutes in the leachate are persulfate and metal chloride.

[0020] In a preferred embodiment of the present invention, the persulfate is ammonium persulfate; the metal chloride is selected from copper chloride dihydrate, ferrous chloride tetrahydrate, magnesium chloride, or manganese chloride tetrahydrate; and the solvent of the leachate is water.

[0021] In a preferred embodiment of the present invention, the mass ratio of persulfate to metal chloride is (0.5~3):1; and the mass ratio of solute to solvent in the leachate is 1:(4~10).

[0022] More preferably, the mass ratio of persulfate to metal chloride is 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, or 3:1.

[0023] In this invention, further increasing the proportion of persulfate will lead to a gradual decrease in the leaching rates of the precious metals Pd and Au.

[0024] In a preferred embodiment of the present invention, the waste chip is a waste chip containing palladium and / or gold; before mixing the waste chip with the leachate, the method further includes a step of crushing the waste chip to a particle size of 0.3~0.5 mm.

[0025] In a preferred embodiment of the present invention, the leaching temperature is 60-90 °C, and the leaching time is 40-120 min. The leaching process also includes a stirring step to ensure more thorough leaching. The present invention does not have special requirements for the stirring rate; it can be set according to conventional parameters known to those skilled in the art, for example, a stirring rate of 300-800 rpm.

[0026] In a preferred embodiment of the present invention, the reducing gas is SO2; the SO2 is introduced at a rate of 2-5 mL / s for 10-20 min.

[0027] In a preferred embodiment of the present invention, the amount of iron powder used is 1.1 to 1.5 times the theoretical molar amount of palladium.

[0028] In a preferred embodiment of the present invention, the method further includes washing and drying the gold and palladium precipitates.

[0029] To further improve the purity of recovered precious metals and meet the stringent quality requirements of high-purity gold and palladium for high-end electronic devices, the solution containing Pd(II) and Au(III) collected after leaching the waste chips using the aforementioned leaching solution can be used to separate elemental gold and palladium using the following method: The collected solutions containing Pd(II) and Au(III) were combined with a dual-mode extraction and stepwise back-extraction technique based on the ionic liquid Cyphos 101 to deeply purify Au(III) and Pd(II) in the leachate: co-extraction and enrichment of Au(III) and Pd(II) were achieved in the extraction stage, while separation and purification of the two were completed through selective stripping in the back-extraction stage. Specifically, a toluene solution of Cyphos 101 was first used as the extractant to perform liquid-liquid extraction on Au(III) and Pd(II) in the leachate, achieving extraction rates of over 99% for Au and Pd. Subsequently, in the back-extraction stage, a low-concentration thiourea hydrochloric acid solution (e.g., 0.1 mol / L) is used to preferentially back-extract Pd(II) from the supported organic phase, achieving a back-extraction rate of over 96%, while Au(III) remains in the organic phase. Then, a higher concentration thiourea solution (e.g., 1.0 mol / L) or a reducing back-extraction agent (e.g., sodium thiosulfate, oxalic acid) is used to completely strip Au(III). Through multiple extraction-step back-extraction cycles, impurity ions can be gradually removed, ultimately yielding gold and palladium products with a purity of ≥99.99%. This optimized process avoids the use of highly toxic reagents such as cyanide throughout, offering advantages such as ease of operation, high selectivity, and environmental friendliness, significantly enhancing the added value and market competitiveness of the product.

[0030] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0031] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0032] The main metal components of the waste chips used in the examples and comparative examples are shown in Table 1.

[0033] Table 1. Analysis of valuable metal composition of the waste chips used.

[0034] Example 1 1. Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. Ammonium persulfate and copper chloride dihydrate (CuCl2·2H2O) were weighed at a molar ratio of 0.5:1, with a total mass of 5 g, and added to the Erlenmeyer flask, followed by 20 g of deionized water. The mixture was stirred at 80 ℃ and 600 rpm for 100 min. After the reaction was completed, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 97.2%, the leaching rate of Au was 96.1%, while the leaching rates of Cu, Fe, and Al were all less than 2%, and the leaching rate of Ag was less than 0.5%.

[0035] 2. Gold Extraction: The clarified leachate was cooled to 30°C, and 10% SO2 gas was introduced into it at a rate of 4 mL / s for 15 min. Brownish-black gold powder gradually precipitated from the solution. After stopping the gas flow, the solution was filtered, the precipitate was washed with deionized water and ethanol, and then dried under vacuum at 65°C for 4 h to obtain 13.67 mg of high-purity gold powder. The calculated recovery rate of Au was 91.1%.

[0036] 3. Extraction of palladium: Excess iron powder (1.2 times the theoretical molar amount of palladium in the filtrate) was added to the filtrate after gold precipitation, and the mixture was stirred at room temperature for 30 min. The mixture was filtered, and the black palladium powder was washed with dilute hydrochloric acid and water. The powder was then dried under vacuum at 65℃ for 4 h to obtain 5.54 mg of metallic palladium. The recovery rate of Pd was 92.3%. The purity of both the purified gold and palladium was ≥99.99%.

[0037] Example 2 1. Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. Ammonium persulfate and ferrous chloride tetrahydrate (FeCl2·4H2O) were weighed at a molar ratio of 1:1, with a total mass of 5 g, and added to the Erlenmeyer flask, followed by 25 g of deionized water. The mixture was stirred at 70 ℃ and 600 rpm for 120 min. After the reaction was completed, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 94.7%, the leaching rate of Au was 93.5%, while the leaching rates of Cu, Fe, and Al were all less than 2%, and the leaching rate of Ag was less than 0.5%.

[0038] 2. Gold Extraction: The clarified leachate was cooled to 30°C, and 10% (w / v) SO2 gas was introduced into it at a rate of 3 mL / s for 18 min. Brownish-black gold powder gradually precipitated from the solution. After stopping the gas flow, the solution was filtered, the precipitate was washed with deionized water and ethanol, and then dried under vacuum at 65°C for 4 h to obtain 14.36 mg of high-purity gold powder. The calculated Au recovery rate was 95.7%.

[0039] 3. Extraction of palladium: Excess iron powder (1.2 times the theoretical molar amount of palladium in the filtrate) was added to the filtrate after gold precipitation, and the mixture was stirred at room temperature for 30 min. The mixture was filtered, and the black palladium powder was washed with dilute hydrochloric acid and water. The powder was then dried under vacuum at 65℃ for 4 h to obtain 5.79 mg of metallic palladium. The recovery rate of Pd was 96.5%. The purity of both the purified gold and palladium was ≥99.99%.

[0040] Example 3 1. Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. Ammonium persulfate and magnesium chloride (MgCl2) were weighed at a molar ratio of 2:1, with a total mass of 5 g, and added to the Erlenmeyer flask, followed by 30 g of deionized water. The mixture was stirred at 85 ℃ and 600 rpm for 90 min. After the reaction was completed, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 95.9%, the leaching rate of Au was 95.1%, while the leaching rates of Cu, Fe, and Al were all less than 2%, and the leaching rate of Ag was less than 0.5%.

[0041] 2. Gold Extraction: The clarified leachate was cooled to 30°C, and 10% SO2 gas was introduced into it at a rate of 3 mL / s for 18 min. Brownish-black gold powder gradually precipitated from the solution. After stopping the gas flow, the solution was filtered, the precipitate was washed with deionized water and ethanol, and then dried under vacuum at 65°C for 4 h to obtain 13.77 mg of high-purity gold powder. The calculated recovery rate of Au was 91.8%.

[0042] 3. Extraction of palladium: Excess iron powder (1.2 times the theoretical molar amount of palladium in the filtrate) was added to the filtrate after gold precipitation, and the mixture was stirred at room temperature for 30 min. The mixture was filtered, and the black palladium powder was washed with dilute hydrochloric acid and water. The powder was then vacuum dried at 65℃ for 4 h to obtain 5.43 mg of metallic palladium. The recovery rate of Pd was 90.5%. The purity of both the purified gold and palladium was ≥99.99%.

[0043] Comparative Example 1 Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. 5 g of ammonium persulfate was added to the flask, followed by 20 g of deionized water. The mixture was stirred at 80 ℃ and 600 rpm for 100 min. After the reaction, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 5.1%, and the leaching rate of Au was 3.7%. The results indicate that, without the catalytic activation of metal chlorides, ammonium persulfate itself is insufficient to effectively oxidize and dissolve precious metals under the aforementioned conditions.

[0044] Comparative Example 2 Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. 5 g of copper chloride (CuCl2·2H2O) was added to the flask, followed by 20 g of deionized water. The mixture was stirred at 80 ℃ and 600 rpm for 100 min. After the reaction, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 2.6%, and the leaching rate of Au was 3.2%. The results indicate that, without the catalytic activation of ammonium persulfate, the metal chlorides themselves are insufficient to effectively oxidize and dissolve the precious metals under the given conditions.

[0045] Comparative Example 3 Leaching of precious metals from waste chips: Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. Ammonium persulfate and cobalt chloride (CoCl2·6H2O) were weighed into the Erlenmeyer flask at a molar ratio of 1:1, followed by the addition of 20 g of deionized water. The mixture was stirred at 80 ℃ and 600 rpm for 100 min. After the reaction was complete, the mixture was filtered to obtain a clear leachate. ICP-OES analysis showed that the leaching rate of Pd was 3.4%, and the leaching rate of Au was 1.9%. The results indicate that cobalt chloride is difficult to effectively oxidize and dissolve precious metals under the described conditions.

[0046] Comparative Example 4 Waste chips were crushed, and 100 mg of powder sample with a particle size of approximately 0.4 mm was weighed into an Erlenmeyer flask. Then, 10 mL of freshly prepared aqua regia (concentrated nitric acid to concentrated hydrochloric acid, volume ratio 1:3) was added, and the mixture was stirred at 85 °C for 2 h. After the reaction, the mixture was filtered, and the leaching rate of metal elements in the leachate was determined by ICP-OES: the leaching rates of Pd and Au were both greater than 99%, but the leaching rates of Cu, Fe, and Al were also as high as 85%, 78%, and 65%, respectively. This indicates that although the aqua regia system has strong leaching capacity, its selectivity is extremely poor, leading to exceptionally complex subsequent separation and purification steps and the generation of a large amount of acidic waste liquid containing impurities.

[0047] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system, characterized in that, Includes the following steps: S1. After mixing the waste chip with the leaching solution, leach it under heating conditions, then separate the solid and liquid components and collect the solution containing Pd(II) and Au(III); S2. A reducing gas is introduced into the solution containing Pd(II) and Au(III) to carry out a reduction reaction, followed by solid-liquid separation, and the solid product gold precipitate and the solution containing Pd(II) are collected. S3. Add iron powder to the solution containing Pd(II) to carry out a displacement reaction, followed by solid-liquid separation to obtain palladium precipitate; The solutes in the leachate are persulfate and metal chloride.

2. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, The persulfate is ammonium persulfate; the metal chloride is selected from copper chloride dihydrate, ferrous chloride tetrahydrate, magnesium chloride, or manganese chloride tetrahydrate; the solvent of the leachate is water.

3. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1 or 2, characterized in that, The mass ratio of persulfate to metal chloride is (0.5~3):1; the mass ratio of solute to solvent in the leachate is 1:(4~10).

4. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, The waste chip is a waste chip containing palladium and / or gold; before mixing the waste chip with the leachate, the process further includes a step of crushing the waste chip to a particle size of 0.3~0.5 mm.

5. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, The leaching temperature is 60~90 ℃ and the time is 40~120 min.

6. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, The reducing gas is SO2; the SO2 is introduced at a rate of 2–5 mL / s for 10–20 min.

7. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, The amount of iron powder used is 1.1 to 1.5 times the theoretical molar amount of palladium.

8. The method for selectively recovering precious metals from waste chips using a persulfate-metal chloride system according to claim 1, characterized in that, It also includes the steps of washing and drying the gold and palladium precipitates.

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