A method for recovering valuable metals from waste circuit boards

Abstract

This invention discloses a method for recovering valuable metals from waste circuit boards, including pretreatment, low-temperature enhanced leaching, selective adsorption separation, purification preparation, and residue treatment. Pretreatment involves pulverizing the waste circuit boards into a mixed powder, magnetically separating iron powder to obtain a mixed powder of non-metallic and valuable metals. Low-temperature enhanced leaching involves adding the mixed powder to a leaching system to obtain a leachate and leaching residue. Selective adsorption separation involves passing the leachate through an adsorption column filled with coconut shell-based aminophosphonic acid modified biochar, using a gradient elution with an eluent. This invention utilizes coconut shell-based aminophosphonic acid modified biochar as its core component. Using natural coconut shell biochar as a substrate, it is activated with hydrochloric acid and incorporating aminotrimethylene phosphonic acid groups. The surface is rich in amino and phosphonic acid groups, which can form stable complexes with valuable metal ions, providing both leaching aid and adsorption functions. This eliminates the need for additional leaching aids and adsorbents, simplifying the process and reducing reagent waste.

Description

Technical Field

[0001] This invention relates to the field of valuable metal recycling technology, specifically a method for recycling valuable metals from waste circuit boards. Background Technology

[0002] With the rapid pace of electronic device upgrades, the amount of waste circuit boards generated has increased significantly. These boards contain valuable metals such as copper, gold, silver, and palladium, making them highly valuable for recycling. Current recycling technologies suffer from the following technical challenges: 1. Single acid leaching is often used, which involves highly corrosive reagents and large quantities, easily causing equipment damage and environmental pollution; 2. Adsorbents are mostly traditional materials, lacking targeted modification, and cannot achieve selective adsorption of valuable metals. Multiple reagents need to be added to assist separation, which makes the process complex and results in serious reagent waste. 3. At the same time, most existing adsorbents are non-renewable, have low resource utilization rates, and are difficult to balance environmental protection and recycling effects.

[0003] To address the above problems, a method for recycling valuable metals from waste circuit boards is proposed. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for recycling valuable metals from waste circuit boards, thus overcoming the deficiencies of existing technologies.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The technical solution provided by this invention is: a method for recycling valuable metals from waste circuit boards, comprising the following steps: S1. Pretreatment: Remove surface impurities and packaging shells from waste circuit boards, crush them into mixed powder with a particle size of 40-150μm, separate iron powder by magnetic separation, and obtain a mixed powder of non-metallic and valuable metals. S2. Low-temperature enhanced leaching: The mixed powder obtained in step S1 is added to the leaching system, which consists of a low-concentration mixed acid, a leaching aid, and deionized water. The leaching temperature is controlled at 35-55℃, the liquid-to-solid ratio at 8-15mL / g, and the stirring rate at 180-220r / min. Leaching is carried out for 1.5-3 hours to obtain leachate and leaching residue. The leaching aid is coconut shell-based aminophosphonic acid modified biochar, and its addition amount is 3-8% of the mass of the mixed powder. S3. Selective adsorption separation: The leachate obtained in step S2 is passed into an adsorption column filled with coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature is controlled at 25-35℃ and the flow rate is 1-3mL / min. After adsorption is completed, gradient elution is performed using eluents to obtain copper ion eluent, gold ion eluent, silver ion eluent and palladium ion eluent in sequence. S4. Purification and preparation: The eluents of each valuable metal obtained in step S3 are purified and reduced to obtain high-purity copper powder, gold powder, silver powder and palladium powder. S5. Residue treatment: The leaching residue obtained in step S2 is washed and dried, and then used to prepare building filler; the coconut shell-based aminophosphonic acid modified biochar is desorbed and regenerated, and then reused in steps S2 and S3.

[0006] Furthermore, in step S1, the pulverization is carried out under inert gas protection, and the inert gas is nitrogen, with a nitrogen flow rate of 50-80 sccm during the pulverization process.

[0007] Furthermore, in step S1, the non-metallic and valuable metal mixed powder obtained after magnetic separation needs to be subjected to vibrating sieving with a screen aperture of 20-30μm to remove non-metallic impurities with excessively large particle sizes.

[0008] Further, in step S2, the low-concentration mixed acid is composed of sulfuric acid and citric acid in a volume ratio of 2-3:1, with a sulfuric acid concentration of 0.8-1.5 mol / L and a citric acid concentration of 0.5-1.0 mol / L. The preparation method of the coconut shell-based aminophosphonic acid modified biochar is as follows: the coconut shell biochar is pulverized to 80-100 mesh, soaked and activated with 1-2 mol / L hydrochloric acid for 2-3 hours, washed until neutral and dried, and then added to an aqueous solution of aminotrimethylene phosphonic acid (ATMP) with a mass fraction of 10%-20% and a solid-liquid mass ratio of 1:5-1:10. The pH is adjusted to 3-5, and the mixture is refluxed at 100-120℃ for 4-6 hours, or reacted in a hydrothermal reactor at 120-150℃ for 4-6 hours. After cooling, the mixture is filtered, washed with deionized water until no phosphorus is detected, dried, and pulverized to 100-120 mesh to obtain the coconut shell-based aminophosphonic acid modified biochar.

[0009] Furthermore, in step S2, an leaching aid is added every 30 minutes during the leaching process, in 2-3 additions, to ensure that the leaching aid is in full contact with the mixed powder.

[0010] Furthermore, in step S3, the eluent is a gradient elution system, which sequentially uses 0.5-0.8 mol / L sulfuric acid solution, 1.0-1.5 mol / L thiourea-hydrochloric acid mixed solution, 0.3-0.6 mol / L ammonia solution, and 1.2-1.8 mol / L nitric acid solution as eluents, with each elution time being 30-60 min.

[0011] Furthermore, in step S3, during the gradient elution process, ultrasonic-assisted elution is used for each elution stage, with an ultrasonic power of 100-150W and an ultrasonic frequency of 20-40kHz.

[0012] Furthermore, in step S4, the purification process employs solvent extraction, with LIX84 as the extractant for the copper ion eluent and trioctylphosphine oxide as the extractant for the gold, silver, and palladium ion eluents; in the reduction process, copper ions are reduced using iron powder, and gold, silver, and palladium ions are reduced using hydrazine hydrate, with a reduction temperature of 40-60℃ and a reduction time of 40-80 min.

[0013] Furthermore, in step S5, the desorption and regeneration method of the coconut shell-based aminophosphonic acid modified biochar is as follows: soak the adsorbed biochar in a 2-3 mol / L sodium hydroxide solution for 2-3 hours, wash until neutral, and dry before regeneration. The number of regenerations is not less than 5 times.

[0014] The beneficial effects of this technical solution are: (1) The present invention uses coconut shell-based aminophosphonic acid modified biochar as the core component. Natural coconut shell biochar is used as the base material. After activation with hydrochloric acid, aminotrimethylene phosphonic acid groups are added. The surface is rich in amino and phosphonic acid groups, which can form stable complexes with valuable metal ions. It has both leaching aid and adsorption functions. No additional leaching aid and adsorbent are needed, which simplifies the process and reduces reagent waste.

[0015] (2) The low-concentration sulfuric acid-citric acid mixed acid system is the core leaching component. Sulfuric acid provides an acidic leaching environment to promote the dissolution of valuable metals, while citric acid, as a complexing agent, can stabilize metal ions in the leaching solution and prevent their precipitation. The two work together to achieve efficient leaching at low concentrations, reducing corrosion of equipment and environmental pollution. Compared with a single acid leaching system, this mixed acid system can achieve efficient leaching at low temperatures and with a lower concentration, which can reduce corrosion of equipment, reduce production costs, and avoid environmental pollution caused by high-concentration acids.

[0016] (3) The components work together to form a complete recycling system. The modified biochar’s leaching and adsorption functions, the mixed acid’s leaching and complexing functions, the eluent’s gradient elution function, and the extractant and reducing agent’s purification functions work together. Without the need for complex high-end equipment, the efficient separation and purification of valuable metals such as copper, gold, silver, and palladium can be achieved. The leaching residue can be used as building filler, and the modified biochar can be desorbed, regenerated, and reused, realizing the recycling of components and taking into account both environmental protection and resource recovery efficiency. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the preparation process of a method for recycling valuable metals from waste circuit boards proposed in this invention. Detailed Implementation

[0018] 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.

[0019] Example 1:

[0020] S1. Pretreatment: Take 100 parts by weight of waste circuit board, manually remove surface dust, plastic packaging shell and other impurities, put it into an inert gas protected pulverizer, introduce nitrogen (flow rate 50 sccm), and pulverize it into a mixed powder with a particle size of 40~80μm; put the mixed powder into a magnetic separator, and magnetically separate 8 parts by weight of iron powder to obtain 92 parts by weight of non-metallic and valuable metal mixed powder; perform vibratory sieving on the mixed powder, using a 20μm sieve to remove non-metallic impurities with excessive particle size, to obtain 88 parts by weight of sieved mixed powder (the valuable metals are mainly copper, gold, silver and palladium, of which copper content is 18 parts by weight, gold 0.05 parts by weight, silver 0.3 parts by weight and palladium 0.02 parts by weight).

[0021] S2. Preparation of coconut shell-based aminophosphonic acid modified biochar: Take 50 parts by weight of coconut shell biochar, pulverize it to 80 mesh, add 200 parts by weight of 1 mol / L hydrochloric acid solution, soak and activate for 2 hours, stirring once every 30 minutes during the process. After soaking, wash repeatedly with deionized water until the washing solution is neutral, and dry in an oven at 105℃ for 2 hours. Take 45 parts by weight of the dried coconut shell biochar, add 225 parts by weight of 10% aminotrimethylenephosphonic acid (ATMP) aqueous solution, with a solid-liquid mass ratio of 1:5, adjust the pH to 3 with 0.1 mol / L hydrochloric acid, place in a reflux apparatus, and reflux at 100℃ for 4 hours, maintaining uniform stirring during the reaction. After the reaction, cool to room temperature, filter to obtain solid product, wash with deionized water until no phosphorus is detected in the washing solution (detected by ammonium molybdate spectrophotometry), dry at 105℃ for 3 hours, pulverize to 100 mesh, and obtain 42 parts by weight of coconut shell-based aminophosphonic acid modified biochar for later use.

[0022] S3. Low-temperature enhanced leaching: Take 88 parts by weight of the sieved mixed powder and add it to the leaching container to prepare the leaching system: take 30 parts by weight of 0.8 mol / L sulfuric acid solution, 15 parts by weight of 0.5 mol / L citric acid solution (sulfuric acid to citric acid volume ratio 2:1), 3.52 parts by weight of the prepared coconut shell-based aminophosphonic acid modified biochar (4% of the mass of the mixed powder), and 352 parts by weight of deionized water. Add the leaching system to the leaching container, control the leaching temperature at 35℃, the liquid-to-solid ratio at 8 mL / g, and the stirring speed at 180 r / min. During the leaching process, add the leaching aid every 30 min, in two additions (1.76 parts by weight each time), and leach for 1.5 h. After leaching, filter to obtain 386 parts by weight of leachate and 42 parts by weight of leaching residue.

[0023] S4. Selective adsorption separation: 386 parts by weight of the leachate were passed into an adsorption column filled with 20 parts by weight of prepared coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature was controlled at 25℃ and the flow rate at 1 mL / min. After adsorption, a gradient elution system was used for elution. 80 parts by weight of 0.5 mol / L sulfuric acid solution (elution time 30 min), 80 parts by weight of 1.0 mol / L thiourea-hydrochloric acid mixed solution (thiourea to hydrochloric acid volume ratio 1:1), 80 parts by weight of 0.3 mol / L ammonia solution, and 80 parts by weight of 1.2 mol / L nitric acid solution were used as eluents in sequence. Ultrasonic assisted elution was used during each elution stage (ultrasonic power 100W, frequency 20kHz) to obtain 85 parts by weight of copper ion eluent, 82 parts by weight of gold ion eluent, 81 parts by weight of silver ion eluent, and 83 parts by weight of palladium ion eluent in sequence.

[0024] S5. Purification and Preparation: The eluents of each valuable metal were purified and reduced: 4 parts by weight of LIX84 extractant were added to the copper ion eluent, and the mixture was stirred and extracted for 30 min. After standing and separating into layers, the organic phase was taken, and 2 parts by weight of iron powder were added for reduction. The reduction temperature was controlled at 40℃ and the reduction time was controlled at 40 min. After filtration, washing, and drying, 17.2 parts by weight of copper powder were obtained. 3 parts by weight of trioctylphosphine oxide extractant were added to the gold ion, silver ion, and palladium ion eluents, respectively, and the mixture was stirred and extracted for 30 min. After standing and separating into layers, the organic phase was taken, and 1 part by weight of hydrazine hydrate was added for reduction. The reduction temperature was controlled at 40℃ and the reduction time was controlled at 40 min. After filtration, washing, and drying, 0.048 parts by weight of gold powder, 0.28 parts by weight of silver powder, and 0.019 parts by weight of palladium powder were obtained.

[0025] S6. Residue treatment: 42 parts by weight of leaching residue were washed three times with deionized water, with 80 parts by weight of deionized water added each time. After washing, the residue was dried at 105℃ for 2 hours to obtain 38 parts by weight of dried residue, which was used to prepare building filler. The adsorbed coconut shell-based aminophosphonic acid modified biochar was taken out, and 100 parts by weight of 2 mol / L sodium hydroxide solution was added. The biochar was soaked for 2 hours, washed with deionized water until neutral, and dried at 105℃ for 2 hours to complete desorption and regeneration. The biochar was then ready for use.

[0026] Table 1

[0027] As shown in Table 1, the recovery method employed in Example 1 achieved the required purity for all valuable metals, with copper powder purity reaching 99.6% and gold, silver, and palladium powder purity all exceeding 99.9%. The recovery rates for all valuable metals were above 93%, with gold achieving the highest recovery rate of 96%, indicating that this method is highly effective in recovering valuable metals. The leaching time was 1.5 hours and the total elution time was 2 hours, resulting in high process efficiency. The modified biochar had an adsorption capacity of 12.3 mg / g, demonstrating good adsorption performance and effectively adsorbing valuable metal ions from the leachate. The leaching residue had a moisture content of 8.2%, and after drying, it could be directly used to prepare building fillers, achieving rational utilization of the residue and stably realizing the efficient recovery of valuable metals from waste circuit boards.

[0028] The pretreatment stage utilizes inert gas-protected pulverization, magnetic separation, and vibrating sieving to effectively remove impurities and enrich valuable metals. Coconut shell-based aminophosphonic acid-modified biochar is prepared using hydrochloric acid activation and ATMP reflux reaction. The preparation process parameters are well-defined and repeatable. The modified biochar exhibits excellent metal ion adsorption performance, serving as a leaching aid to enhance leaching efficiency and enabling selective separation of valuable metals through adsorption separation. The use of a low-concentration mixed acid (sulfuric acid to citric acid volume ratio of 2:1) ensures leaching efficiency while reducing equipment corrosion. Ultrasonic-assisted elution shortens elution time and improves elution efficiency. The purification stage employs specified extractants and reducing agents to ensure the purity of valuable metals meets standards. The residue treatment and modified biochar regeneration steps achieve resource recycling. The entire process is coherent, highly operable, and reproducible.

[0029] Example 2

[0030] S1. Pretreatment: Take 100 parts by weight of waste circuit board, manually remove surface dust, plastic packaging shell and other impurities, put it into an inert gas protected pulverizer, introduce nitrogen (flow rate 65 sccm), and pulverize it into a mixed powder with a particle size of 80~120μm; put the mixed powder into a magnetic separator, and magnetically separate 8.5 parts by weight of iron powder to obtain 91.5 parts by weight of non-metallic and valuable metal mixed powder; perform vibratory sieving on the mixed powder using a 25μm sieve to remove non-metallic impurities with excessive particle size, to obtain 86 parts by weight of sieved mixed powder (the valuable metals are mainly copper, gold, silver and palladium, of which copper content is 17 parts by weight, gold 0.045 parts by weight, silver 0.28 parts by weight and palladium 0.018 parts by weight).

[0031] S2. Preparation of coconut shell-based aminophosphonic acid modified biochar: Take 50 parts by weight of coconut shell biochar, pulverize to 90 mesh, add 200 parts by weight of 1.5 mol / L hydrochloric acid solution, soak and activate for 2.5 h, stirring once every 30 min during the process. After soaking, wash repeatedly with deionized water until the washing solution is neutral, and dry in an oven at 105℃ for 2 h; Take 44 parts by weight of the dried coconut shell biochar, add 308 parts by weight of 15% aminotrimethylenephosphonic acid (ATMP) aqueous solution, with a solid-liquid mass ratio of 1:7, adjust the pH to 4 with 0.1 mol / L hydrochloric acid, and place in a hydrothermal reactor, react at 135℃ for 5 h; After the reaction, cool to room temperature, filter to obtain solid product, wash with deionized water until no phosphorus is detected in the washing solution (detected by ammonium molybdate spectrophotometry), dry at 105℃ for 3 h, pulverize to 110 mesh, and obtain 40 parts by weight of coconut shell-based aminophosphonic acid modified biochar for later use.

[0032] S3. Low-temperature enhanced leaching: Take 86 parts by weight of the sieved mixed powder and add it to the leaching container to prepare the leaching system: take 43 parts by weight of 1.2 mol / L sulfuric acid solution, 17.2 parts by weight of 0.8 mol / L citric acid solution (sulfuric acid to citric acid volume ratio 2.5:1), 5.16 parts by weight of the prepared coconut shell-based aminophosphonic acid modified biochar (6% of the mass of the mixed powder), and 688 parts by weight of deionized water. Add the leaching system to the leaching container, control the leaching temperature at 45℃, the liquid-to-solid ratio at 12 mL / g, and the stirring speed at 200 r / min. During the leaching process, add the leaching aid every 30 min, in 3 additions (1.72 parts by weight each time), and leach for 2.2 h. After leaching, filter to obtain 712 parts by weight of leachate and 40 parts by weight of leaching residue.

[0033] S4. Selective Adsorption Separation: 712 parts by weight of the leachate were passed into an adsorption column filled with 25 parts by weight of prepared coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature was controlled at 30℃ and the flow rate at 2 mL / min. After adsorption, a gradient elution system was used for elution. 100 parts by weight of 0.65 mol / L sulfuric acid solution (elution time 45 min), 100 parts by weight of 1.25 mol / L thiourea-hydrochloric acid mixed solution (thiourea to hydrochloric acid volume ratio 1:1), 100 parts by weight of 0.45 mol / L ammonia solution, and 100 parts by weight of 1.5 mol / L nitric acid solution were used as eluents in sequence. Ultrasonic assisted elution was used during each elution stage (ultrasonic power 125 W, frequency 30 kHz) to obtain 108 parts by weight of copper ion eluent, 105 parts by weight of gold ion eluent, 103 parts by weight of silver ion eluent, and 106 parts by weight of palladium ion eluent in sequence.

[0034] S5. Purification and Preparation: The eluents of each valuable metal were purified and reduced: 5 parts by weight of LIX84 extractant were added to the copper ion eluent, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 2.5 parts by weight of iron powder were added for reduction. The reduction temperature was controlled at 50℃ and the reduction time was 60 min. The mixture was filtered, washed, and dried to obtain 16.5 parts by weight of copper powder. 3.5 parts by weight of trioctylphosphine oxide extractant were added to the gold ion, silver ion, and palladium ion eluents, respectively, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 1.2 parts by weight of hydrazine hydrate was added for reduction. The reduction temperature was controlled at 50℃ and the reduction time was 60 min. The mixture was filtered, washed, and dried to obtain 0.043 parts by weight of gold powder, 0.265 parts by weight of silver powder, and 0.017 parts by weight of palladium powder.

[0035] S6. Residue treatment: Wash 40 parts by weight of the leaching residue three times with deionized water, adding 80 parts by weight of deionized water each time. After washing, dry at 105℃ for 2 hours to obtain 36.5 parts by weight of dried residue, which is used to prepare building filler. Take out the adsorbed coconut shell-based aminophosphonic acid modified biochar, add 120 parts by weight of 2.5 mol / L sodium hydroxide solution, soak for 2.5 hours, wash with deionized water until neutral, and dry at 105℃ for 2 hours to complete desorption and regeneration, and set aside for later use.

[0036] Table 2

[0037] As shown in Table 2, the purity of each valuable metal was further improved in the recovery method of Example 2. The purity of copper powder was 99.7%, and the purity of gold, silver, and palladium powders was around 99.92%. The recovery rate of each valuable metal was above 94%, with the highest copper recovery rate reaching 97.06%, indicating that the recovery effect was better after optimizing the process parameters. The leaching time was 2.2 h and the total elution time was 3 h, and the process efficiency was stable. The adsorption capacity of the modified biochar was increased to 13.1 mg / g, and the adsorption performance was better than that of Example 1, indicating that the modified biochar prepared by hydrothermal reaction had a better adsorption effect. The leaching residue had a water content of 7.8%, and its performance was stable after drying. It can be directly used for the preparation of building fillers, and can achieve efficient recovery of valuable metals.

[0038] Based on Example 1, this embodiment optimizes the process parameters. In the pretreatment stage, the particle size, nitrogen flow rate, and sieve aperture were adjusted to further enhance the enrichment effect of valuable metals. The coconut shell-based aminophosphonic acid modified biochar was prepared using 1.5 mol / L hydrochloric acid activation, a 15% ATMP aqueous solution, and a hydrothermal reaction. Compared to reflux reaction, the hydrothermal reaction allows ATMP to be more fully grafted onto the surface of the coconut shell biochar, improving the adsorption performance of the modified biochar. The low-concentration mixed acid was adjusted to a sulfuric acid to citric acid volume ratio of 2.5:1, and the concentration was also increased accordingly, further strengthening the leaching effect. The leaching aid was added in three stages to ensure sufficient contact with the mixed powder, improving leaching efficiency. The power and frequency of the ultrasonic-assisted elution were appropriately increased to further optimize the elution effect. In the purification stage, the dosage and reaction parameters of the extractant and reducing agent were adjusted to ensure improved purity and recovery rate of valuable metals.

[0039] Example 3

[0040] S1. Pretreatment: Take 100 parts by weight of waste circuit board, manually remove surface dust, plastic packaging shell and other impurities, put it into an inert gas protected pulverizer, introduce nitrogen (flow rate 80 sccm), and pulverize it into a mixed powder with a particle size of 100~150μm; put the mixed powder into a magnetic separator, and magnetically separate 9 parts by weight of iron powder to obtain 91 parts by weight of non-metallic and valuable metal mixed powder; perform vibratory sieving on the mixed powder, using a 30μm sieve to remove non-metallic impurities with excessive particle size, to obtain 85 parts by weight of sieved mixed powder (the valuable metals are mainly copper, gold, silver and palladium, of which copper content is 16.5 parts by weight, gold 0.04 parts by weight, silver 0.26 parts by weight and palladium 0.017 parts by weight).

[0041] S2. Preparation of coconut shell-based aminophosphonic acid modified biochar: Take 50 parts by weight of coconut shell biochar, pulverize to 100 mesh, add 200 parts by weight of 2 mol / L hydrochloric acid solution, soak and activate for 3 hours, stirring once every 30 minutes during the process. After soaking, wash repeatedly with deionized water until the washing solution is neutral, and dry in an oven at 105℃ for 2 hours. Take 43 parts by weight of the dried coconut shell biochar, add 430 parts by weight of 20% aminotrimethylene phosphonic acid (ATMP) aqueous solution, with a solid-liquid mass ratio of 1:10, adjust the pH to 5 with 0.1 mol / L hydrochloric acid, place in a reflux apparatus, and reflux at 120℃ for 6 hours, maintaining uniform stirring during the reaction. After the reaction, cool to room temperature, filter to obtain solid product, wash with deionized water until no phosphorus is detected in the washing solution (detected by ammonium molybdate spectrophotometry), dry at 105℃ for 3 hours, pulverize to 120 mesh, and obtain 39 parts by weight of coconut shell-based aminophosphonic acid modified biochar for later use.

[0042] S3. Low-temperature enhanced leaching: Take 85 parts by weight of the sieved mixed powder and add it to the leaching container to prepare the leaching system: take 51 parts by weight of 1.5 mol / L sulfuric acid solution, 17 parts by weight of 1.0 mol / L citric acid solution (sulfuric acid to citric acid volume ratio 3:1), 6.8 parts by weight of the prepared coconut shell-based aminophosphonic acid modified biochar (8% of the mass of the mixed powder), and 1275 parts by weight of deionized water. Add the leaching system to the leaching container, control the leaching temperature at 55℃, the liquid-to-solid ratio at 15 mL / g, and the stirring speed at 220 r / min. During the leaching process, add the leaching aid every 30 min, in two batches (3.4 parts by weight each time). Leach for 3 h. After leaching, filter to obtain 1320 parts by weight of leachate and 39 parts by weight of leaching residue.

[0043] S4. Selective Adsorption Separation: 1320 parts by weight of the leachate were passed into an adsorption column filled with 30 parts by weight of prepared coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature was controlled at 35℃ and the flow rate at 3mL / min. After adsorption, a gradient elution system was used for elution. 120 parts by weight of 0.8mol / L sulfuric acid solution (elution time 60min), 120 parts by weight of 1.5mol / L thiourea-hydrochloric acid mixed solution (thiourea to hydrochloric acid volume ratio 1:1), 120 parts by weight of 0.6mol / L ammonia solution, and 120 parts by weight of 1.8mol / L nitric acid solution were used as eluents in sequence. Ultrasonic assisted elution was used during each elution stage (ultrasonic power 150W, frequency 40kHz) to obtain 135 parts by weight of copper ion eluent, 132 parts by weight of gold ion eluent, 130 parts by weight of silver ion eluent, and 133 parts by weight of palladium ion eluent in sequence.

[0044] S5. Purification and Preparation: The eluents of each valuable metal were purified and reduced: 6 parts by weight of LIX84 extractant were added to the copper ion eluent, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 3 parts by weight of iron powder were added for reduction. The reduction temperature was controlled at 60℃ and the reduction time was controlled at 80 min. After filtration, washing, and drying, 16.1 parts by weight of copper powder were obtained. 4 parts by weight of trioctylphosphine oxide extractant were added to the gold ion, silver ion, and palladium ion eluents, respectively, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 1.5 parts by weight of hydrazine hydrate was added for reduction. The reduction temperature was controlled at 60℃ and the reduction time was controlled at 80 min. After filtration, washing, and drying, 0.038 parts by weight of gold powder, 0.25 parts by weight of silver powder, and 0.016 parts by weight of palladium powder were obtained.

[0045] S6. Residue treatment: Wash 39 parts by weight of leaching residue with deionized water 3 times, adding 80 parts by weight of deionized water each time. After washing, dry at 105℃ for 2 hours to obtain 35.8 parts by weight of dried residue, which is used to prepare building filler. Take out the adsorbed coconut shell-based aminophosphonic acid modified biochar, add 150 parts by weight of 3mol / L sodium hydroxide solution, soak for 3 hours, wash with deionized water until neutral, and dry at 105℃ for 2 hours to complete desorption and regeneration, and set aside for later use.

[0046] Table 3

[0047] As shown in Table 3, in the recovery method of Example 3, the purity of each valuable metal remained at a high level. The purity of copper powder was 99.6%, and the purity of gold, silver, and palladium powders were all above 99.92%, with gold powder reaching the highest purity of 99.94%. The recovery rates of each valuable metal were all above 94%, with copper reaching 97.58% and silver reaching 96.15%, demonstrating excellent recovery effects. The leaching time was 3 hours and the total elution time was 4 hours, meeting the process requirements of low-temperature leaching, and the leaching and elution were more thorough. The adsorption capacity of the modified biochar increased to 13.5 mg / g, exhibiting the best adsorption performance, indicating that the modified biochar prepared by high-concentration ATMP and long-term reflux reaction has a stronger adsorption capacity for metal ions. The leaching residue had a moisture content of 7.5%, and its performance was stable after drying, making it suitable for direct use as building filler.

[0048] In this embodiment, the pretreatment stage uses the maximum nitrogen flow rate and the maximum screen aperture to ensure stable pulverization and thorough impurity removal. The coconut shell-based aminophosphonic acid modified biochar is prepared by activation with 2 mol / L hydrochloric acid, a 20% ATMP aqueous solution, and a long-term reflux reaction at 120°C. Increasing the hydrochloric acid concentration, ATMP concentration, and reaction time ensures more complete activation of the coconut shell biochar and a higher ATMP grafting rate, thereby improving the adsorption performance of the modified biochar. The low-concentration mixed acid uses the upper limit ratio of sulfuric acid to citric acid (3:1 volume ratio), and the concentration also reaches the maximum value, further enhancing the leaching effect of valuable metals. The leaching aid is added at the upper limit of 8%, in two stages, ensuring full contact with the mixed powder and improving leaching efficiency. Ultrasonic assisted elution uses the maximum power and frequency to further shorten elution time and improve elution effect. The purification stage uses the maximum amount of extractant and reducing agent, as well as the highest reduction temperature and time, to ensure sufficient purification of valuable metals, achieving high levels of purity and recovery rate.

[0049] Example 4

[0050] S1. Pretreatment: Take 100 parts by weight of waste circuit board, manually remove surface dust, plastic packaging shell and other impurities, put it into an inert gas protected pulverizer, introduce nitrogen (flow rate 70 sccm), and pulverize it into a mixed powder with a particle size of 60~100μm; put the mixed powder into a magnetic separator, and magnetically separate 8.2 parts by weight of iron powder to obtain 91.8 parts by weight of non-metallic and valuable metal mixed powder; perform vibratory sieving on the mixed powder using a 22μm sieve to remove non-metallic impurities with excessive particle size, to obtain 87 parts by weight of sieved mixed powder (the valuable metals are mainly copper, gold, silver and palladium, of which copper content is 17.5 parts by weight, gold 0.048 parts by weight, silver 0.29 parts by weight and palladium 0.019 parts by weight).

[0051] S2. Preparation of coconut shell-based aminophosphonic acid modified biochar: Take 50 parts by weight of coconut shell biochar, pulverize to 90 mesh, add 200 parts by weight of 1.2 mol / L hydrochloric acid solution, soak and activate for 2.2 h, stirring once every 30 min during the process. After soaking, wash repeatedly with deionized water until the washing solution is neutral, and dry in an oven at 105℃ for 2 h; Take 44.5 parts by weight of the dried coconut shell biochar, add 267 parts by weight of 12% aminotrimethylene phosphonic acid (ATMP) aqueous solution, with a solid-liquid mass ratio of 1:6, adjust the pH to 3.5 with 0.1 mol / L hydrochloric acid, and place in a hydrothermal reactor, react at 120℃ for 4.5 h; After the reaction, cool to room temperature, filter to obtain solid product, wash with deionized water until no phosphorus is detected in the washing solution (detected by ammonium molybdate spectrophotometry), dry at 105℃ for 3 h, pulverize to 105 mesh, and obtain 41 parts by weight of coconut shell-based aminophosphonic acid modified biochar for later use.

[0052] S3. Low-temperature enhanced leaching: Take 87 parts by weight of the sieved mixed powder and add it to the leaching container to prepare the leaching system: take 38.28 parts by weight of 1.0 mol / L sulfuric acid solution, 15.31 parts by weight of 0.6 mol / L citric acid solution (sulfuric acid to citric acid volume ratio 2.5:1), 4.35 parts by weight of the prepared coconut shell-based aminophosphonic acid modified biochar (5% of the mass of the mixed powder), and 783 parts by weight of deionized water. Add the leaching system to the leaching container, control the leaching temperature at 40℃, the liquid-to-solid ratio at 9 mL / g, and the stirring speed at 190 r / min. During the leaching process, add the leaching aid every 30 min, in two batches (2.175 parts by weight each time). Leach for 2 h. After leaching, filter to obtain 815 parts by weight of leachate and 41 parts by weight of leaching residue.

[0053] S4. Selective Adsorption Separation: 815 parts by weight of the leachate were passed into an adsorption column filled with 22 parts by weight of prepared coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature was controlled at 28℃ and the flow rate at 1.5 mL / min. After adsorption, a gradient elution system was used for elution. 90 parts by weight of 0.6 mol / L sulfuric acid solution (elution time 40 min), 90 parts by weight of 1.1 mol / L thiourea-hydrochloric acid mixed solution (thiourea to hydrochloric acid volume ratio 1:1), 90 parts by weight of 0.4 mol / L ammonia solution, and 90 parts by weight of 1.3 mol / L nitric acid solution were used as eluents in sequence. Ultrasonic assisted elution was used during each elution stage (ultrasonic power 110 W, frequency 25 kHz) to obtain 95 parts by weight of copper ion eluent, 92 parts by weight of gold ion eluent, 91 parts by weight of silver ion eluent, and 93 parts by weight of palladium ion eluent in sequence.

[0054] S5. Purification and Preparation: The eluents of various valuable metals were purified and reduced: 4.5 parts by weight of LIX84 extractant were added to the copper ion eluent, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 2.2 parts by weight of iron powder were added for reduction. The reduction temperature was controlled at 45℃ and the reduction time was controlled at 50 min. After filtration, washing, and drying, 16.9 parts by weight of copper powder were obtained. 3.2 parts by weight of trioctylphosphine oxide extractant were added to the gold ion, silver ion, and palladium ion eluents, respectively, and the mixture was stirred and extracted for 30 min. After standing and separating the layers, the organic phase was taken, and 1.1 parts by weight of hydrazine hydrate was added for reduction. The reduction temperature was controlled at 45℃ and the reduction time was controlled at 50 min. After filtration, washing, and drying, 0.046 parts by weight of gold powder, 0.27 parts by weight of silver powder, and 0.018 parts by weight of palladium powder were obtained.

[0055] S6. Residue treatment: 41 parts by weight of leaching residue were washed three times with deionized water, with 80 parts by weight of deionized water added each time. After washing, the residue was dried at 105℃ for 2 hours to obtain 37.2 parts by weight of dried residue, which was used to prepare building filler. The adsorbed coconut shell-based aminophosphonic acid modified biochar was taken out, and 110 parts by weight of 2.2 mol / L sodium hydroxide solution was added. The biochar was soaked for 2.2 hours, washed with deionized water until neutral, and dried at 105℃ for 2 hours to complete desorption and regeneration. The biochar was then ready for use.

[0056] Table 4

[0057] As shown in Table 4, Example 4, using the intermediate process parameters defined in the claims, achieved high purity levels for all valuable metals: copper powder purity was 99.7%, and gold, silver, and palladium powder purity was all above 99.91%. The recovery rates for all valuable metals were above 93%, with gold recovery at 95.83% and palladium recovery at 94.74%, demonstrating stable recovery performance. The leaching time was 2 hours, and the total elution time was 2.67 hours, resulting in high process efficiency, balancing sufficient leaching with production efficiency. The modified biochar had an adsorption capacity of 12.8 mg / g, exhibiting good adsorption performance and effectively adsorbing valuable metal ions in the leachate. The leaching residue had a moisture content of 8.0%, and after drying, it could be directly used as building filler.

[0058] In this embodiment, the nitrogen flow rate, particle size, and sieve aperture within the middle range were selected in the pretreatment stage to ensure the stability and versatility of the process. Coconut shell-based aminophosphonic acid modified biochar was prepared by activation with 1.2 mol / L hydrochloric acid, 12% ATMP aqueous solution, and hydrothermal reaction at 120℃ for 4.5 h. The parameters were selected at the middle value, which ensured the modification effect while reducing production costs, making it suitable for industrial production. The low-concentration mixed acid used a sulfuric acid to citric acid volume ratio of 2.5:1, balancing leaching efficiency and equipment corrosivity. The leaching aid was added at a rate of 5% in two stages to ensure full contact with the mixed powder. The ultrasonic-assisted elution parameters were moderate, balancing elution efficiency and energy consumption. The purification stage parameters were mild and the operation was simple, enabling stable and efficient recovery of valuable metals.

[0059] Comparative Example 1 The difference between this comparative example and Example 1 is that coconut shell-based aminophosphonic acid modified biochar is not used; instead, an equal weight of unmodified coconut shell biochar is used. All other process steps, parameters, and raw material weights are completely consistent with Example 1.

[0060] Table 5

[0061] As shown in Table 5, after Comparative Example 1 was replaced with unmodified coconut shell biochar, the purity of all valuable metals decreased. The purity of copper powder dropped to 98.2%, and the purity of gold, silver, and palladium powders were all below 99.5%. The recovery rate of all valuable metals dropped to between 80% and 88%, a decrease of 7-12 percentage points compared to Example 1. The adsorption capacity of biochar was only 5.7 mg / g, far lower than the 12.3 mg / g of Example 1. Furthermore, the unmodified biochar could not be desorbed, regenerated, or reused. This indicates that the unmodified coconut shell biochar lacks amino and phosphonic acid groups, and cannot form stable complexes with valuable metal ions. Therefore, it cannot effectively enhance the leaching effect, nor can it achieve selective adsorption of valuable metal ions.

[0062] This comparative example, by replacing the core component (unmodified coconut shell biochar instead of coconut shell-based aminophosphonic acid modified biochar), clarifies the key role of modified biochar in this technical solution. Unmodified coconut shell biochar only has basic adsorption capacity, lacks leaching aid function, and has low adsorption capacity and cannot be regenerated, resulting in a significant decrease in leaching efficiency and adsorption separation effect. The purity and recovery rate of valuable metals did not meet expectations. Compared with Example 1, it can be seen that the amino and phosphonic acid groups of coconut shell-based aminophosphonic acid modified biochar are the core for achieving efficient leaching, selective adsorption, and resource recycling of valuable metals.

[0063] Comparative Example 2 The difference between this comparative example and Example 1 is that the sulfuric acid-citric acid mixture is not used; instead, an equal volume of single sulfuric acid solution is used (the concentration is adjusted to 1.0 mol / L to ensure that the acidity is consistent with the mixed acid in Example 1). All other process steps, parameters, and raw material weight parts are completely consistent with Example 1.

[0064] Table 6

[0065] Data Description: As shown in Table 6 of the experimental data, after Comparative Example 2 was replaced with a single sulfuric acid solution, the purity of each valuable metal decreased. The purity of copper powder decreased to 98.5%, and the purity of gold, silver, and palladium powders was all below 99.5%. The recovery rate of each valuable metal decreased to between 83% and 89%, a decrease of 4-11 percentage points compared to Example 1. The adsorption capacity of modified biochar decreased to 9.8 mg / g, lower than 12.3 mg / g in Example 1. This indicates that the single sulfuric acid solution lacks complexation, and the leached metal ions are prone to precipitate, reducing the stability of metal ions in the leachate, thereby affecting the adsorption and purification effect. This highlights the synergistic advantage of the sulfuric acid-citric acid mixed acid system in this technical solution.

[0066] This comparative example, by replacing the leaching system (using single sulfuric acid instead of the sulfuric acid-citric acid mixture), verifies the importance of the mixed acid system. Single sulfuric acid can only provide an acidic environment and cannot prevent metal ion precipitation, leading to a decrease in leaching efficiency, which in turn affects the subsequent adsorption separation and purification effects. The purity and recovery rate of valuable metals are significantly lower than in Example 1. Compared with Example 1, it can be seen that sulfuric acid provides an acidic leaching environment, and citric acid plays a complexing and stabilizing role. The synergistic effect of the two is necessary to achieve efficient leaching of valuable metals under low temperature conditions, which confirms the rationality of the leaching system design of this technical solution.

[0067] Comparative Example 3 The difference between this comparative example and Example 1 is that in the preparation of coconut shell-based aminophosphonic acid modified biochar, aminotrimethylenephosphonic acid (ATMP) is not used, but is replaced with an equal mass fraction of phosphoric acid. The remaining process steps, parameters and raw material weight parts are completely consistent with Example 1.

[0068] Table 7

[0069] As shown in Table 7, after replacing ATMP with phosphoric acid to prepare modified biochar in Comparative Example 3, the purity of each valuable metal decreased, with copper powder purity dropping to 98.4%, and gold, silver, and palladium powder purity all below 99.5%. The recovery rate of each valuable metal decreased to between 88% and 92%, a decrease of 0-8 percentage points compared to Example 1. The adsorption capacity of the modified biochar decreased to 8.9 mg / g, far lower than the 12.3 mg / g in Example 3, and the adsorption performance decreased significantly after desorption and regeneration, making it unstable and reusable. This indicates that phosphoric acid can only introduce phosphonic acid groups, not amino groups, and cannot form stable complexes with valuable metal ions, resulting in a significant decrease in adsorption and leaching effects. This highlights the core advantage of ATMP modification in this technical solution.

[0070] This comparative example, by replacing the modifier (phosphoric acid instead of ATMP), verifies the key role of ATMP in the preparation of modified biochar. ATMP can simultaneously introduce amino and phosphonic acid groups, and the two work synergistically to improve the adsorption and leaching performance of biochar. In contrast, phosphoric acid can only introduce phosphonic acid groups and lacks the complexation effect of amino groups, resulting in a decrease in the adsorption capacity and leaching effect of the modified biochar, a reduction in the purity and recovery rate of valuable metals, and a deterioration in regeneration performance. Compared with Example 1, it can be seen that ATMP modification is the key to achieving efficient adsorption, leaching, and regeneration of coconut shell-based biochar, confirming the rationality and superiority of the modifier selection in this technical solution.

[0071] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific technical solutions or characteristics is not elaborated upon here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for recycling valuable metals from waste circuit boards, characterized in that, Includes the following steps: S1. Pretreatment: Remove surface impurities and packaging shells from waste circuit boards, crush them into mixed powder with a particle size of 40-150μm, separate iron powder by magnetic separation, and obtain a mixed powder of non-metallic and valuable metals. S2. Low-temperature enhanced leaching: The mixed powder obtained in step S1 is added to the leaching system, which consists of a low-concentration mixed acid, a leaching aid, and deionized water. The leaching temperature is controlled at 35-55℃, the liquid-to-solid ratio at 8-15mL / g, and the stirring rate at 180-220r / min. Leaching is carried out for 1.5-3 hours to obtain leachate and leaching residue. The leaching aid is coconut shell-based aminophosphonic acid modified biochar, and its addition amount is 3-8% of the mass of the mixed powder. S3. Selective adsorption separation: The leachate obtained in step S2 is passed into an adsorption column filled with coconut shell-based aminophosphonic acid modified biochar. The adsorption temperature is controlled at 25-35℃ and the flow rate is 1-3mL / min. After adsorption is completed, gradient elution is performed using eluents to obtain copper ion eluent, gold ion eluent, silver ion eluent and palladium ion eluent in sequence. S4. Purification and preparation: The eluents of each valuable metal obtained in step S3 are purified and reduced to obtain high-purity copper powder, gold powder, silver powder and palladium powder. S5. Residue treatment: The leaching residue obtained in step S2 is washed and dried, and then used to prepare building filler; the coconut shell-based aminophosphonic acid modified biochar is desorbed and regenerated, and then reused in steps S2 and S3.

2. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S1, the pulverization is carried out under inert gas protection, and the inert gas is nitrogen. The nitrogen flow rate during the pulverization process is 50-80 sccm.

3. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S1, the non-metallic and valuable metal mixed powder obtained after magnetic separation needs to be subjected to vibrating sieving with a screen aperture of 20-30μm.

4. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S2, the low-concentration mixed acid is composed of sulfuric acid and citric acid in a volume ratio of 2-3:1, with a sulfuric acid concentration of 0.8-1.5 mol / L and a citric acid concentration of 0.5-1.0 mol / L. The preparation method of the coconut shell-based aminophosphonic acid modified biochar is as follows: the coconut shell biochar is pulverized to 80-100 mesh, activated by soaking in 1-2 mol / L hydrochloric acid for 2-3 hours, washed until neutral, dried, and then added to an aqueous solution of aminotrimethylene phosphonic acid (ATMP) with a mass fraction of 10%-20% at a solid-liquid mass ratio of 1:5-1:

10. The pH is adjusted to 3-5, and the reaction is refluxed at 100-120℃ for 4-6 hours, or reacted in a hydrothermal reactor at 120-150℃ for 4-6 hours. After cooling, the mixture is filtered, washed with deionized water until no phosphorus is detected, dried, and pulverized to 100-120 mesh to obtain the coconut shell-based aminophosphonic acid modified biochar.

5. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S2, an leaching aid is added every 30 minutes during the leaching process, in 2-3 additions.

6. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S3, the eluent is a gradient elution system, which sequentially uses 0.5-0.8 mol / L sulfuric acid solution, 1.0-1.5 mol / L thiourea-hydrochloric acid mixed solution, 0.3-0.6 mol / L ammonia solution, and 1.2-1.8 mol / L nitric acid solution as eluents, with each elution time being 30-60 min.

7. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S3, during the gradient elution process, ultrasonic-assisted elution is used in each elution stage, with an ultrasonic power of 100-150W and an ultrasonic frequency of 20-40kHz.

8. The method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S4, the purification process uses solvent extraction. The extractant for the copper ion eluent is LIX84, and the extractant for the gold, silver, and palladium ion eluents is trioctylphosphine oxide. In the reduction process, copper ions are reduced with iron powder, and gold, silver, and palladium ions are reduced with hydrazine hydrate. The reduction temperature is 40-60℃, and the reduction time is 40-80 min.

9. A method for recycling valuable metals from waste circuit boards according to claim 1, characterized in that, In step S5, the desorption and regeneration method of the coconut shell-based aminophosphonic acid modified biochar is as follows: soak the adsorbed biochar in a 2-3 mol / L sodium hydroxide solution for 2-3 hours, wash until neutral, and dry before regeneration. The number of regenerations shall not be less than 5.

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