A method for recovering precious metals from refinery wastewater based on adsorption

Abstract

The application discloses a method for recovering noble metals in refining wastewater based on an adsorption method and relates to the technical field of noble metal recovery. The method comprises the following steps: preparing a porous carbon-based composite adsorbent; adding the porous carbon-based composite adsorbent into acid wastewater containing noble metal ions to perform adsorption; mixing the adsorbent after adsorption with a desorption agent containing thiourea and hydrochloric acid to perform desorption, and separating to obtain regenerated adsorbent and a desorption liquid containing noble metals; and adding ascorbic acid into the desorption liquid to perform a reduction reaction, so as to obtain noble metal elements. The method has excellent adsorption and recovery effects on silver in refining wastewater.

Description

Technical Field

[0001] This invention relates to the field of precious metal recycling technology, specifically a method for recovering precious metals from refining wastewater based on adsorption. Background Technology

[0002] In the precious metal refining industry, acidic silver refining wastewater contains high-value silver ions, but is also accompanied by interference from impurities such as copper and nickel. Achieving efficient and selective recovery of silver ions, which can improve resource utilization and avoid heavy metal pollution, is a critical issue that urgently needs to be addressed in the industry. Currently, industrial methods for recovering precious silver from wastewater containing precious metals mainly include chemical precipitation, electrolytic deposition, solvent extraction, ion exchange, and adsorption. Chemical precipitation is simple to operate, but requires a large amount of precipitant, generates a large amount of heavy metal-containing sludge, and has high subsequent treatment costs. Furthermore, its recovery rate is not ideal in low-concentration precious metal wastewater. Electrolytic deposition can directly obtain high-purity elemental precious metals, but it consumes a lot of electricity, requires a high concentration of precious metal ions in the wastewater, and has extremely low current efficiency and poor economic efficiency when treating dilute wastewater. Solvent extraction has high separation efficiency, but organic extractants are expensive, flammable, and toxic. The extraction-back-extraction process is complex, and the loss of organic phase can cause secondary pollution. Ion exchange offers good selectivity, but the resin is expensive, requires frequent regeneration, and is prone to degradation when treating strongly acidic wastewater, resulting in a limited lifespan. In contrast, adsorption is considered the most promising technology for treating low-to-medium concentration acidic wastewater containing precious metals due to its advantages such as simple equipment, flexible operation, wide applicable concentration range, and minimal secondary pollution. However, conventional porous carbon-based adsorbents have significant limitations; single porous carbon adsorbents have low adsorption capacity and poor selectivity, making it difficult to achieve efficient separation of silver ions from impurity ions. Summary of the Invention

[0003] The purpose of this invention is to provide a method for recovering precious metals from refining wastewater based on adsorption, so as to solve the technical problems mentioned in the background.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0006] S1. Preparation of porous carbon-based composite adsorbents;

[0007] S2. Add the porous carbon-based composite adsorbent to the acidic wastewater containing precious metal ions for adsorption.

[0008] S3. The adsorbent after adsorption is mixed with a desorbent containing thiourea and hydrochloric acid for desorption, and the regenerated adsorbent and the desorbent containing precious metal are separated.

[0009] S4. Add ascorbic acid to the desorption solution to carry out a reduction reaction to obtain the noble metal element.

[0010] Preferably, in step S1, the method for preparing the modified porous carbon-based adsorbent includes the following steps:

[0011] S11. After pre-carbonization, activation with potassium hydroxide, acid washing and water washing of coconut shell biomass carbon, it is further activated with a mixed solution of sodium hydroxide and hydrogen peroxide to obtain hydroxylated porous carbon carrier.

[0012] S12. The hydroxylated porous carbon support is esterified with 2-bromoisobutyryl bromide to obtain a modified carbon support anchored with initiation sites.

[0013] S13. The modified carbon support is dispersed in a mixed solvent, and AB2-type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, comonomer 2-(1H-imidazol-1-yl)ethyl methacrylate, catalyst and ligand hexamethyltriethylenetetramine are added. After deoxygenation, a surface-initiated atom transfer radical polymerization reaction is carried out to obtain hyperbranched polymer grafted modified carbon material.

[0014] S14. The hyperbranched polymer grafted modified carbon material is dispersed in a mixed solvent, and nickel chloride hexahydrate, cobalt chloride hexahydrate, hexamethylenetetramine and sodium dithiooxalate are added. After stirring and dissolving, a solvothermal reaction is carried out to obtain a carbon-based intermediate of confined growth intercalated NiCo-LDH.

[0015] S15. The carbon-based intermediate is subjected to a self-polymerization reaction with dopamine hydrochloride to obtain a polydopamine-coated carbon-based intermediate; the coated carbon-based intermediate is subjected to a phosphating reaction with sodium hypophosphite under an inert atmosphere to obtain a porous carbon-based composite material.

[0016] S16. A porous carbon-based composite material is deposited with tannic acid and L-cysteine ​​hydrochloride to obtain a porous carbon-based composite adsorbent.

[0017] In the technical solution of this invention, the adsorption performance of porous carbon-based composite adsorbent for precious metal silver is improved synergistically from the following aspects: (1) Hyperbranched polymers containing dithiocarbamate and imidazole groups are grafted onto the surface of hydroxylated porous carbon through surface-initiated atom transfer radical polymerization. The hyperbranched structure itself avoids the chain entanglement and active site embedding that are easy to occur in linear polymers, so that the sulfur and nitrogen chelating groups are fully exposed and uniformly distributed on the carbon skeleton surface, ensuring accessibility and stability when coordinating with silver ions; at the same time, this three-dimensional network provides an ideal confined environment for subsequent use, which is equivalent to pre-building uniform nucleation sites on the carbon support surface and pore walls, ensuring that the subsequently grown LDH nanosheets can be effectively dispersed and avoid agglomeration, thereby maintaining the unobstructed pores. (2) On the basis of polymer modification, metal phosphide heterojunctions are further introduced. Specifically, the confinement effect of the hyperbranched polymer is first utilized to allow NiCo-LDH nanosheets to grow uniformly and vertically on the carbon support surface, constructing hierarchical channels conducive to ion diffusion. By employing a carbonate-free alkali source system and chloride metal salts, the strong competitive occupation of interlayers by carbonate ions is avoided, allowing dithiooxaate ions to smoothly insert into the interlayer, thus expanding the interlayer spacing and introducing additional sulfur active sites. The subsequent phosphating process uses a polydopamine pre-coating method to form a dense carbon-nitrogen protective layer at low temperatures, converting LDH to NiCoP in situ while avoiding the thermal decomposition of the polymer support. The resulting carbon-based / NiCoP heterojunction not only possesses weak reducing adsorption capacity, but its interface effect also optimizes the electronic structure, forming a synergistic effect with the chelating sites of the hyperbranched polymer to jointly enhance the selective adsorption of silver ions and acid resistance.

[0018] In experiments, this invention discovered that after grafting a hyperbranched polymer containing dithiocarbamate and imidazole groups onto a hydroxylated porous carbon surface, the nitrogen atom of the imidazole group responsible for coordination almost completely protonates to form an imidazole-onium cation under strongly acidic conditions, losing its ability to form coordination bonds with silver ions. The originally designed sulfur-nitrogen multidentate synergistic chelation degenerates to relying solely on sulfur sites for coordination, resulting in a decrease in the chelation stability constant. Furthermore, the competitive adsorption of a large number of hydrogen ions on the NiCoP surface leads to a dilution of the local concentration of silver ions near the reduction sites, significantly inhibiting the efficiency of weak reduction deposition. These two factors superimpose each other, limiting the overall synergistic efficiency. To address this technical problem, this invention introduces tannic acid and L-cysteine ​​hydrochloride, anchoring them to the surface of a polydopamine-derived carbon-nitrogen layer. Tannic acid achieves covalent anchoring through Schiff base reaction and metal-phenol-oxygen coordination. Its numerous free phenolic hydroxyl groups exist as neutral phenols under strongly acidic conditions, and the lone pair electrons of the oxygen atom can interact with Ag. +This forms a weak Ag-O coordination, directly compensating for the coordination gap caused by the inactivation of imidazole nitrogen; L-cysteine ​​is anchored via Michael addition, and its free thiol group can still directly coordinate with Ag under strong acid conditions. + Pre-enrichment of silver ions before they contact NiCoP increases local concentration and reduces H+. + Competitive pressure. The synergistic effect of the aforementioned tannic acid and L-cysteine ​​hydrochloride restored the efficiency of multidentate synergistic chelation and weak reduction deposition.

[0019] Preferably, in step S12, the mass ratio of the hydroxylated porous carbon support to 2-bromoisobutyryl bromide is 1:(1.0~2.0).

[0020] Preferably, in step S13, the mass ratio of the modified carbon support to N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester is 1:(2.5-3.5).

[0021] Preferably, in step S13, the mass ratio of the modified carbon support to 2-(1H-imidazol-1-yl)ethyl methacrylate is 1:(0.7-1.2).

[0022] Preferably, in step S14, the mass ratio of the hyperbranched polymer-grafted modified carbon material to nickel chloride hexahydrate is 1:(2.0-2.8).

[0023] Preferably, in step S14, the mass ratio of the hyperbranched polymer-grafted modified carbon material to cobalt chloride hexahydrate is 1:(1.0-1.4).

[0024] Preferably, in step S14, the mass ratio of the hyperbranched polymer-grafted modified carbon material to hexamethylenetetramine is 1:(5.5-7.0).

[0025] Preferably, in step S15, the mass ratio of the carbon-based intermediate to dopamine hydrochloride is 1:(0.15-0.25).

[0026] Preferably, in step S16, the mass ratio of the porous carbon-based composite material to tannic acid is 1:(0.1-0.2); and the mass ratio of the porous carbon-based composite material to L-cysteine ​​hydrochloride is 1:(0.05-0.12).

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. Carbon-based / NiCoP heterojunctions are constructed by utilizing the confinement effect of hyperbranched polymers, which avoids the aggregation of active sites. The electronic structure is optimized through interface effects, achieving synergistic effects of chemical adsorption and weak reduction adsorption, and significantly improving the selective adsorption capacity and acid resistance of silver ions.

[0029] 2. Tannic acid anchored to the material surface utilizes free phenolic hydroxyl groups and Ag + The formation of weak Ag-O coordination directly compensates for the coordination gap caused by imidazole protonation under strong acid, restoring the integrity of the multidentate chelate structure and ensuring the driving force of chemisorption. The anchored L-cysteine ​​utilizes free thiol groups to directly coordinate Ag under strong acid. + Pre-enrichment of silver ions before they contact NiCoP increases local concentration, reduces HAG+ competition pressure, and enhances weak reduction deposition efficiency. Attached Figure Description

[0030] Figure 1 This is a low-magnification SEM image of the porous carbon-based composite adsorbent prepared in Example 3 of the present invention.

[0031] Figure 2 This is a medium-magnification SEM image of the porous carbon-based composite adsorbent prepared in Example 3 of the present invention.

[0032] Figure 3 This is a high-magnification SEM image of the porous carbon-based composite adsorbent prepared in Example 3 of the present invention.

[0033] Figure 4 The XPS spectrum of the porous carbon-based composite adsorbent prepared in Example 3 of this invention is shown.

[0034] Figure 5 The image shows the XRD pattern of the porous carbon-based composite adsorbent prepared in Example 3 of this invention. Detailed Implementation

[0035] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0038] S11. Weigh 100g of coconut shell biomass carbon (100 mesh), ultrasonically wash with water 4 times, and filter. Pre-carbonize at 450℃ for 3h under nitrogen atmosphere (100sccm) at 3℃ / min. After cooling, obtain pre-carbonized carbon. Weigh 37g of pre-carbonized carbon and grind it with 148g of potassium hydroxide. Activate at 800℃ for 2h under nitrogen atmosphere at 5℃ / min. After cooling, soak in 1mol / L hydrochloric acid for 2h, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain activated porous carbon. Add 50g of activated porous carbon to 1L of mixed activation solution (NaOH 2.5mol / L, H2O2 1.5mol / L), stir and activate at 55℃ and 200rpm for 6h, filter, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain hydroxylated porous carbon support.

[0039] S12. Take 10g of hydroxylated porous carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 300mL of anhydrous DMF, transfer it to a three-necked flask, purge with nitrogen, lower the temperature to 0℃ in an ice bath, add 10mL of anhydrous triethylamine and 18g of 2-bromoisobutyryl bromide sequentially, stir at 0℃ for 3h, then raise the temperature to 25℃ and continue stirring for 15h, under nitrogen protection throughout. Collect the product by centrifugation, wash it three times each with anhydrous tetrahydrofuran and anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain the modified carbon support.

[0040] S13. Take 10g of modified carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 400mL of methanol-DMF mixed solvent (1:1), purge with nitrogen for 30min to remove oxygen, then add 33g of AB2 type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, 11g of 2-(1H-imidazol-1-yl)ethyl methacrylate, 1.61g of hexamethyltriethylenetetramine ligand, and 1.0g of CuBr catalyst in sequence. After sealing, deoxygenate it through three freeze-thaw cycles, and polymerize it at 55℃ with stirring for 12h. Terminate the reaction by purging with air, collect the product by centrifugation, extract with methanol-chloroform (1:1) Soxhlet for 24h, and dry under vacuum at 60℃ for 12h to obtain hyperbranched polymer grafted modified carbon material.

[0041] S14. Disperse 10g of hyperbranched polymer-grafted modified carbon material in 500mL of pre-degassed ethylene glycol-water mixed solvent (3:1). Under nitrogen protection, add 26g of nickel chloride hexahydrate, 13g of cobalt chloride hexahydrate, 65g of hexamethylenetetramine, and 3.32g of sodium dithiooxaate sequentially. Stir at 200rpm for 2h to dissolve, and react solvothermically at 140℃ for 8h. After cooling, centrifuge, wash alternately with degassed water and ethanol 4 times, and dry under vacuum at 60℃ for 12h to obtain a carbon-based intermediate.

[0042] S15. Disperse 10g of the carbon-based intermediate in 200mL Tris-HCl buffer (pH=8.5, 10mmol / L), add 2.3g of dopamine hydrochloride, and self-polymerize at 25℃ and 200rpm for 24h. Filter and wash with water, then vacuum dry at 60℃ for 6h. Place the product in a ceramic boat downstream of a tube furnace, and place 40g of sodium hypophosphite in an upstream ceramic boat. Purge with nitrogen for 30min, then raise the temperature to 280℃ at 2℃ / min and hold for phosphating for 2h. Cool under nitrogen protection, wash with water and alcohol until neutral, and vacuum dry at 60℃ for 12h to obtain a porous carbon-based composite material.

[0043] S16. Disperse 10g of the porous carbon-based composite material in 300mL of PBS buffer (pH=7.2, 50mmol / L). Separately dissolve 1.8g of tannic acid and 1.0g of L-cysteine ​​hydrochloride in 50mL of PBS of the same concentration, and add them to the dispersions sequentially. Stir at 25℃ and 180rpm for 12h. Filter, wash 5 times with water, and vacuum dry at 40℃ for 12h to obtain the porous carbon-based composite adsorbent.

[0044] S2. Take 500 mL of simulated wastewater (Ag) + 100mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of adsorbent (dosage 1.0 g / L) to 45 mg / L (pH=1.0), stir at 25℃ and 200 rpm for 90 min for adsorption, and then filter to obtain silver-loaded adsorbent.

[0045] S3. Transfer the silver-loaded adsorbent to an Erlenmeyer flask, add 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid), shake at 30 °C and 150 rpm for 45 min to desorb, and filter to separate the regenerated adsorbent and the silver-containing desorbent solution.

[0046] S4. Adjust the pH of the silver-containing desorption solution to 4.8 with 10% NaOH. Slowly add 1.0 mol / L ascorbic acid aqueous solution while stirring at 45℃ and 200 rpm. After stirring and reducing for 1.5 h, let it stand for 1 h. Collect the precipitate by centrifugation, wash it 3 times with water and 1 time with alcohol, and dry it under vacuum at 60℃ for 6 h to obtain silver powder.

[0047] Example 2

[0048] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0049] S11. Weigh 100g of coconut shell biomass carbon (100 mesh), ultrasonically wash with water 4 times, and filter. Pre-carbonize at 450℃ for 3h under nitrogen atmosphere (100sccm) at 3℃ / min. After cooling, obtain pre-carbonized carbon. Weigh 37g of pre-carbonized carbon and grind it with 148g of potassium hydroxide. Activate at 800℃ for 2h under nitrogen atmosphere at 5℃ / min. After cooling, soak in 1mol / L hydrochloric acid for 2h, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain activated porous carbon. Add 50g of activated porous carbon to 1L of mixed activation solution (NaOH 2.5mol / L, H2O2 1.5mol / L), stir and activate at 55℃ and 200rpm for 6h, filter, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain hydroxylated porous carbon support.

[0050] S12. Take 10g of hydroxylated porous carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 300mL of anhydrous DMF, transfer it to a three-necked flask, purge with nitrogen, lower the temperature to 0℃ in an ice bath, add 10mL of anhydrous triethylamine and 12g of 2-bromoisobutyryl bromide sequentially, stir at 0℃ for 3h, then raise the temperature to 25℃ and continue stirring for 15h, under nitrogen protection throughout. Collect the product by centrifugation, wash it three times each with anhydrous tetrahydrofuran and anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain the modified carbon support.

[0051] S13. Take 10g of modified carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 400mL of methanol-DMF mixed solvent (1:1), purge with nitrogen for 30min to remove oxygen, then add 28g of AB2 type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, 8g of 2-(1H-imidazol-1-yl)ethyl methacrylate, 1.61g of hexamethyltriethylenetetramine ligand, and 1.0g of CuBr catalyst in sequence. After sealing, deoxygenate it through three freeze-thaw cycles, and polymerize it at 55℃ with stirring for 12h. Terminate the reaction by purging with air, collect the product by centrifugation, extract with methanol-chloroform (1:1) Soxhlet for 24h, and dry under vacuum at 60℃ for 12h to obtain hyperbranched polymer grafted modified carbon material.

[0052] S14. Disperse 10g of hyperbranched polymer-grafted modified carbon material in 500mL of pre-degassed ethylene glycol-water mixed solvent (3:1). Under nitrogen protection, add 22g of nickel chloride hexahydrate, 11g of cobalt chloride hexahydrate, 58g of hexamethylenetetramine, and 3.32g of sodium dithiooxaate sequentially. Stir at 200rpm for 2h to dissolve, and react solvothermically at 140℃ for 8h. After cooling, centrifuge, wash alternately with degassed water and ethanol 4 times, and vacuum dry at 60℃ for 12h to obtain a carbon-based intermediate.

[0053] S15. Disperse 10g of the carbon-based intermediate in 200mL Tris-HCl buffer (pH=8.5, 10mmol / L), add 1.8g of dopamine hydrochloride, and self-polymerize at 25℃ and 200rpm for 24h. Filter and wash with water, then vacuum dry at 60℃ for 6h. Place the product in a ceramic boat downstream of a tube furnace, and place 40g of sodium hypophosphite in an upstream ceramic boat. Purge with nitrogen for 30min, then raise the temperature to 280℃ at 2℃ / min and hold for phosphating for 2h. Cool under nitrogen protection, wash with water and alcohol until neutral, and vacuum dry at 60℃ for 12h to obtain a porous carbon-based composite material.

[0054] S16. Disperse 10g of the porous carbon-based composite material in 300mL of PBS buffer (pH=7.2, 50mmol / L). Separately dissolve 1.3g of tannic acid and 0.7g of L-cysteine ​​hydrochloride in 50mL of PBS of the same concentration, and add them to the dispersions sequentially. Stir at 25℃ and 180rpm for 12h. Filter, wash 5 times with water, and vacuum dry at 40℃ for 12h to obtain the porous carbon-based composite adsorbent.

[0055] S2. Take 500 mL of simulated wastewater (Ag) + 100mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of adsorbent (dosage 1.0 g / L) to 45 mg / L (pH=1.0), stir at 25℃ and 200 rpm for 90 min for adsorption, and then filter to obtain silver-loaded adsorbent.

[0056] S3. Transfer the silver-loaded adsorbent to an Erlenmeyer flask, add 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid), shake at 30 °C and 150 rpm for 45 min to desorb, and filter to separate the regenerated adsorbent and the silver-containing desorbent solution.

[0057] S4. Adjust the pH of the silver-containing desorption solution to 4.8 with 10% NaOH. Slowly add 1.0 mol / L ascorbic acid aqueous solution while stirring at 45℃ and 200 rpm. After stirring and reducing for 1.5 h, let it stand for 1 h. Collect the precipitate by centrifugation, wash it 3 times with water and 1 time with alcohol, and dry it under vacuum at 60℃ for 6 h to obtain silver powder.

[0058] Example 3

[0059] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0060] S11. Weigh 100g of coconut shell biomass carbon (100 mesh), ultrasonically wash with water 4 times, and filter. Pre-carbonize at 450℃ for 3h under nitrogen atmosphere (100sccm) at 3℃ / min. After cooling, obtain pre-carbonized carbon. Weigh 37g of pre-carbonized carbon and grind it with 148g of potassium hydroxide. Activate at 800℃ for 2h under nitrogen atmosphere at 5℃ / min. After cooling, soak in 1mol / L hydrochloric acid for 2h, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain activated porous carbon. Add 50g of activated porous carbon to 1L of mixed activation solution (NaOH 2.5mol / L, H2O2 1.5mol / L), stir and activate at 55℃ and 200rpm for 6h, filter, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain hydroxylated porous carbon support.

[0061] S12. Take 10g of hydroxylated porous carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 300mL of anhydrous DMF, transfer it to a three-necked flask, purge with nitrogen, lower the temperature to 0℃ in an ice bath, add 10mL of anhydrous triethylamine and 15g of 2-bromoisobutyryl bromide sequentially, stir at 0℃ for 3h, then raise the temperature to 25℃ and continue stirring for 15h, under nitrogen protection throughout. Collect the product by centrifugation, wash it three times each with anhydrous tetrahydrofuran and anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain the modified carbon support.

[0062] S13. Take 10g of modified carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 400mL of methanol-DMF mixed solvent (1:1), purge with nitrogen for 30min to remove oxygen, then add 30g of AB2 type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, 9g of 2-(1H-imidazol-1-yl)ethyl methacrylate, 1.61g of hexamethyltriethylenetetramine ligand, and 1.0g of CuBr catalyst in sequence. After sealing, deoxygenate it through three freeze-thaw cycles, and polymerize it at 55℃ with stirring for 12h. Terminate the reaction by purging with air, collect the product by centrifugation, extract with methanol-chloroform (1:1) Soxhlet for 24h, and dry under vacuum at 60℃ for 12h to obtain hyperbranched polymer grafted modified carbon material.

[0063] S14. Disperse 10g of hyperbranched polymer-grafted modified carbon material in 500mL of pre-degassed ethylene glycol-water mixed solvent (3:1). Under nitrogen protection, add 25g of nickel chloride hexahydrate, 12g of cobalt chloride hexahydrate, 60g of hexamethylenetetramine, and 3.32g of sodium dithiooxaate sequentially. Stir at 200rpm for 2h to dissolve, and react solvothermically at 140℃ for 8h. After cooling, centrifuge, wash alternately with degassed water and ethanol 4 times, and vacuum dry at 60℃ for 12h to obtain a carbon-based intermediate.

[0064] S15. Disperse 10g of the carbon-based intermediate in 200mL Tris-HCl buffer (pH=8.5, 10mmol / L), add 2.0g of dopamine hydrochloride, and self-polymerize at 25℃ and 200rpm for 24h. Filter and wash with water, then vacuum dry at 60℃ for 6h. Place the product in a ceramic boat downstream of a tube furnace, and place 40g of sodium hypophosphite in an upstream ceramic boat. Purge with nitrogen for 30min, then raise the temperature to 280℃ at 2℃ / min and hold for phosphating for 2h. Cool under nitrogen protection, wash with water and alcohol until neutral, and vacuum dry at 60℃ for 12h to obtain a porous carbon-based composite material.

[0065] S16. Disperse 10g of the porous carbon-based composite material in 300mL of PBS buffer (pH=7.2, 50mmol / L). Separately dissolve 1.5g of tannic acid and 0.9g of L-cysteine ​​hydrochloride in 50mL of PBS of the same concentration, and add them to the dispersions sequentially. Stir at 25℃ and 180rpm for 12h. Filter, wash 5 times with water, and vacuum dry at 40℃ for 12h to obtain the porous carbon-based composite adsorbent.

[0066] S2. Take 500 mL of simulated wastewater (Ag) + 100mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of adsorbent (dosage 1.0 g / L) to 45 mg / L (pH=1.0), stir at 25℃ and 200 rpm for 90 min for adsorption, and then filter to obtain silver-loaded adsorbent.

[0067] S3. Transfer the silver-loaded adsorbent to an Erlenmeyer flask, add 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid), shake at 30 °C and 150 rpm for 45 min to desorb, and filter to separate the regenerated adsorbent and the silver-containing desorbent solution.

[0068] S4. Adjust the pH of the silver-containing desorption solution to 4.8 with 10% NaOH. Slowly add 1.0 mol / L ascorbic acid aqueous solution while stirring at 45℃ and 200 rpm. After stirring and reducing for 1.5 h, let it stand for 1 h. Collect the precipitate by centrifugation, wash it 3 times with water and 1 time with alcohol, and dry it under vacuum at 60℃ for 6 h to obtain silver powder.

[0069] Example 4

[0070] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0071] S11. Weigh 100g of coconut shell biomass carbon (100 mesh), ultrasonically wash with water 4 times, and filter. Pre-carbonize at 450℃ for 3h under nitrogen atmosphere (100sccm) at 3℃ / min. After cooling, obtain pre-carbonized carbon. Weigh 37g of pre-carbonized carbon and grind it with 148g of potassium hydroxide. Activate at 800℃ for 2h under nitrogen atmosphere at 5℃ / min. After cooling, soak in 1mol / L hydrochloric acid for 2h, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain activated porous carbon. Add 50g of activated porous carbon to 1L of mixed activation solution (NaOH 2.5mol / L, H2O2 1.5mol / L), stir and activate at 55℃ and 200rpm for 6h, filter, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain hydroxylated porous carbon support.

[0072] S12. Take 10g of hydroxylated porous carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 300mL of anhydrous DMF, transfer it to a three-necked flask, purge with nitrogen, lower the temperature to 0℃ in an ice bath, add 10mL of anhydrous triethylamine and 20g of 2-bromoisobutyryl bromide sequentially, stir at 0℃ for 3h, then raise the temperature to 25℃ and continue stirring for 15h, under nitrogen protection throughout. Collect the product by centrifugation, wash it three times each with anhydrous tetrahydrofuran and anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain the modified carbon support.

[0073] S13. Take 10g of modified carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 400mL of methanol-DMF mixed solvent (1:1), purge with nitrogen for 30min to remove oxygen, then add 35g of AB2 type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, 12g of 2-(1H-imidazol-1-yl)ethyl methacrylate, 1.61g of hexamethyltriethylenetetramine ligand, and 1.0g of CuBr catalyst in sequence. After sealing, deoxygenate by three freeze-thaw cycles, and polymerize at 55℃ with stirring for 12h. Terminate the reaction by purging with air, collect the product by centrifugation, extract with methanol-chloroform (1:1) Soxhlet for 24h, and dry under vacuum at 60℃ for 12h to obtain hyperbranched polymer grafted modified carbon material.

[0074] S14. Disperse 10g of hyperbranched polymer-grafted modified carbon material in 500mL of pre-degassed ethylene glycol-water mixed solvent (3:1). Under nitrogen protection, add 28g of nickel chloride hexahydrate, 14g of cobalt chloride hexahydrate, 70g of hexamethylenetetramine, and 3.32g of sodium dithiooxaate sequentially. Stir at 200rpm for 2h to dissolve, and react solvothermically at 140℃ for 8h. After cooling, centrifuge, wash alternately with degassed water and ethanol 4 times, and vacuum dry at 60℃ for 12h to obtain a carbon-based intermediate.

[0075] S15. Disperse 10g of the carbon-based intermediate in 200mL Tris-HCl buffer (pH=8.5, 10mmol / L), add 2.5g of dopamine hydrochloride, and self-polymerize at 25℃ and 200rpm for 24h. Filter and wash with water, then vacuum dry at 60℃ for 6h. Place the product in a ceramic boat downstream of a tube furnace, and place 40g of sodium hypophosphite in an upstream ceramic boat. Purge with nitrogen for 30min, then raise the temperature to 280℃ at 2℃ / min and hold for phosphating for 2h. Cool under nitrogen protection, wash with water and alcohol until neutral, and vacuum dry at 60℃ for 12h to obtain a porous carbon-based composite material.

[0076] S16. Disperse 10g of the porous carbon-based composite material in 300mL of PBS buffer (pH=7.2, 50mmol / L). Separately dissolve 2g of tannic acid and 1.2g of L-cysteine ​​hydrochloride in 50mL of PBS of the same concentration, and add them to the dispersion in sequence. Stir at 25℃ and 180rpm for 12h. Filter, wash with water 5 times, and vacuum dry at 40℃ for 12h to obtain the porous carbon-based composite adsorbent.

[0077] S2. Take 500 mL of simulated wastewater (Ag) + 100mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of adsorbent (dosage 1.0 g / L) to 45 mg / L (pH=1.0), stir at 25℃ and 200 rpm for 90 min for adsorption, and then filter to obtain silver-loaded adsorbent.

[0078] S3. Transfer the silver-loaded adsorbent to an Erlenmeyer flask, add 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid), shake at 30 °C and 150 rpm for 45 min to desorb, and filter to separate the regenerated adsorbent and the silver-containing desorbent solution.

[0079] S4. Adjust the pH of the silver-containing desorption solution to 4.8 with 10% NaOH. Slowly add 1.0 mol / L ascorbic acid aqueous solution while stirring at 45℃ and 200 rpm. After stirring and reducing for 1.5 h, let it stand for 1 h. Collect the precipitate by centrifugation, wash it 3 times with water and 1 time with alcohol, and dry it under vacuum at 60℃ for 6 h to obtain silver powder.

[0080] Example 5

[0081] A method for recovering precious metals from refining wastewater based on adsorption includes the following steps:

[0082] S11. Weigh 100g of coconut shell biomass carbon (100 mesh), ultrasonically wash with water 4 times, and filter. Pre-carbonize at 450℃ for 3h under nitrogen atmosphere (100sccm) at 3℃ / min. After cooling, obtain pre-carbonized carbon. Weigh 37g of pre-carbonized carbon and grind it with 148g of potassium hydroxide. Activate at 800℃ for 2h under nitrogen atmosphere at 5℃ / min. After cooling, soak in 1mol / L hydrochloric acid for 2h, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain activated porous carbon. Add 50g of activated porous carbon to 1L of mixed activation solution (NaOH 2.5mol / L, H2O2 1.5mol / L), stir and activate at 55℃ and 200rpm for 6h, filter, wash with water until neutral, and vacuum dry at 60℃ for 12h to obtain hydroxylated porous carbon support.

[0083] S12. Take 10g of hydroxylated porous carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 300mL of anhydrous DMF, transfer it to a three-necked flask, purge with nitrogen, lower the temperature to 0℃ in an ice bath, add 10mL of anhydrous triethylamine and 10g of 2-bromoisobutyryl bromide sequentially, stir at 0℃ for 3h, then raise the temperature to 25℃ and continue stirring for 15h, under nitrogen protection throughout. Collect the product by centrifugation, wash it three times each with anhydrous tetrahydrofuran and anhydrous ethanol, and dry it under vacuum at 60℃ for 12h to obtain the modified carbon support.

[0084] S13. Take 10g of modified carbon support, dry it under vacuum at 120℃ for 2h, disperse it in 400mL of methanol-DMF mixed solvent (1:1), purge with nitrogen for 30min to remove oxygen, then add 25g of AB2 type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, 7g of 2-(1H-imidazol-1-yl)ethyl methacrylate, 1.61g of hexamethyltriethylenetetramine ligand, and 1.0g of CuBr catalyst in sequence. After sealing, deoxygenate it by three freeze-thaw cycles, and polymerize it at 55℃ with stirring for 12h. The reaction is terminated by purging with air, the product is collected by centrifugation, extracted with methanol-chloroform (1:1) Soxhlet for 24h, and dried under vacuum at 60℃ for 12h to obtain hyperbranched polymer grafted modified carbon material.

[0085] S14. Disperse 10g of hyperbranched polymer-grafted modified carbon material in 500mL of pre-degassed ethylene glycol-water mixed solvent (3:1). Under nitrogen protection, add 20g of nickel chloride hexahydrate, 10g of cobalt chloride hexahydrate, 55g of hexamethylenetetramine, and 3.32g of sodium dithiooxaate sequentially. Stir at 200rpm for 2h to dissolve, and react solvothermically at 140℃ for 8h. After cooling, centrifuge, wash alternately with degassed water and ethanol 4 times, and vacuum dry at 60℃ for 12h to obtain a carbon-based intermediate.

[0086] S15. Disperse 10g of the carbon-based intermediate in 200mL of Tris-HCl buffer (pH=8.5, 10mmol / L), add 1.5g of dopamine hydrochloride, and self-polymerize at 25℃ and 200rpm for 24h. Filter and wash with water, then vacuum dry at 60℃ for 6h. Place the product in a ceramic boat downstream of a tube furnace, and place 40g of sodium hypophosphite in an upstream ceramic boat. Purge with nitrogen for 30min, then raise the temperature to 280℃ at 2℃ / min and hold for phosphating for 2h. Cool under nitrogen protection, wash with water and alcohol until neutral, and vacuum dry at 60℃ for 12h to obtain a porous carbon-based composite material.

[0087] S16. Disperse 10g of the porous carbon-based composite material in 300mL of PBS buffer (pH=7.2, 50mmol / L). Separately dissolve 1g of tannic acid and 0.5g of L-cysteine ​​hydrochloride in 50mL of PBS of the same concentration, and add them to the dispersion in sequence. Stir at 25℃ and 180rpm for 12h. Filter, wash with water 5 times, and vacuum dry at 40℃ for 12h to obtain the porous carbon-based composite adsorbent.

[0088] S2. Take 500 mL of simulated wastewater (Ag) + 100mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of adsorbent (dosage 1.0 g / L) to 45 mg / L (pH=1.0), stir at 25℃ and 200 rpm for 90 min for adsorption, and then filter to obtain silver-loaded adsorbent.

[0089] S3. Transfer the silver-loaded adsorbent to an Erlenmeyer flask, add 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid), shake at 30 °C and 150 rpm for 45 min to desorb, and filter to separate the regenerated adsorbent and the silver-containing desorbent solution.

[0090] S4. Adjust the pH of the silver-containing desorption solution to 4.8 with 10% NaOH. Slowly add 1.0 mol / L ascorbic acid aqueous solution while stirring at 45℃ and 200 rpm. After stirring and reducing for 1.5 h, let it stand for 1 h. Collect the precipitate by centrifugation, wash it 3 times with water and 1 time with alcohol, and dry it under vacuum at 60℃ for 6 h to obtain silver powder.

[0091] Comparative Example 1: Comparative Example 1 uses commercially available 100-mesh coconut shell activated carbon as the adsorbent without any modification treatment. The parameters of the remaining adsorption, desorption, and reduction experiments are completely consistent with those of Example 3.

[0092] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that the NiCo-LDH growth and phosphating modification steps S14 and S15 are omitted, and carbon-based / NiCoP heterojunctions are not constructed. The raw material amounts, reaction conditions, and operation procedures of the remaining steps are completely consistent with those of Example 4.

[0093] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that in step S13, AB2-type branched monomers are not used to construct hyperbranched polymers, but only 2-(1H-imidazol-1-yl)ethyl methacrylate is used for linear polymer grafting. The amount of raw materials, reaction conditions and operation procedures of the remaining steps are completely consistent with those of Example 4.

[0094] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the deposition modification step of tannic acid and L-cysteine ​​hydrochloride in step S16 is omitted. The amount of raw materials, reaction conditions and operation process of the remaining steps are completely consistent with Example 4.

[0095] Comparative Example 5: The difference between Comparative Example 5 and Example 3 is that only tannic acid is added in step S16, and L-cysteine ​​hydrochloride is not added. The amount of raw materials, reaction conditions and operation procedures of the remaining steps are completely consistent with those of Example 4.

[0096] Comparative Example 6: The difference between Comparative Example 6 and Example 3 is that only L-cysteine ​​hydrochloride is added in step S16, and tannic acid is not added. The amount of raw materials, reaction conditions and operation procedures of the remaining steps are completely consistent with those of Example 4.

[0097] Performance testing:

[0098] (1) Silver ion removal rate and single adsorption capacity test: 500 mL of simulated acidic silver refining wastewater (Ag) was taken. + Initial concentration 100 mg / L, Cu 2+ 50mg / L, Ni 2+ Add 0.5 g of the adsorbent prepared in each example or comparative example (dosage 1.0 g / L) to the sample (45 mg / L, pH=1.0). After adsorption by stirring at 25°C and 200 rpm for 90 min, filter through a 0.45 μm filter membrane. Take the filtrate and determine the Ag in the wastewater after adsorption using inductively coupled plasma atomic emission spectrometry. + Residual concentration, Cu was measured simultaneously. 2+ Ni 2+ Residual concentration. Silver ion removal rate = (C0 − C) e ) / C0×100%, where C0 is the initial Ag + Concentration (100 mg / L), C e Ag after adsorption + Residual concentration; single adsorption capacity q e =(C0−C e The value is calculated as V × V / m, where V is the volume of wastewater (0.5 L) and m is the mass of adsorbent (0.5 g). The test results are shown in Table 1.

[0099] (2) Langmuir saturated adsorption capacity test: Ag was prepared separately.+ Simulated wastewater (Cu) with initial concentrations of 50, 100, 200, 300, 400, and 500 mg / L 2+ 50mg / L, Ni 2+ Take 500 mL of each of the following concentrations (45 mg / L, pH=1.0), add 0.5 g of adsorbent, stir at 25℃ and 200 rpm for 90 min for adsorption, then filter. Determine the equilibrium Ag under each concentration condition using ICP-OES. + Concentration, calculate the equilibrium adsorption capacity q. e , with C e / q e For C e Plotting was performed using the Langmuir isotherm adsorption model q. e =q m KLC e / (1+KLC e Linear fitting was performed to obtain the maximum saturated adsorption capacity q. m (mg / g). Test results are shown in Table 1.

[0100] (3) Selectivity coefficient test: In the same set of experiments as the above removal rate test, the Cu in the wastewater after adsorption was determined by ICP-OES. 2+ and Ni 2+ The residual concentration of Cu was calculated, and the effect of the adsorbent on Cu was determined. 2+ and Ni 2+ The equilibrium adsorption amount and selectivity coefficient Kd(Ag) + ) / Kd(M 2+ ) = (q e Ag / C e ,Ag) / (q e M / C e ,M), where M represents Cu and Ni respectively, q e C represents the equilibrium adsorption capacity of the corresponding ion. e This represents the equilibrium concentration of the corresponding ion. A higher selectivity coefficient indicates better adhesion of the adsorbent to Ag. + The higher the selectivity relative to impurity ions, the better. The test results are shown in Table 1.

[0101] (4) Desorption rate test: The silver-loaded adsorbent obtained from the removal rate test was completely transferred to an Erlenmeyer flask, and 50 mL of desorbent (0.2 mol / L thiourea + 0.1 mol / L hydrochloric acid) was added. The mixture was shaken at 30℃ and 150 rpm for 45 min to desorb, and then filtered. The desorbed solution was analyzed by ICP-OES to determine the Ag content. + Concentration, calculate desorption rate = Ag in desorption solution + Total mass / Ag loaded on adsorbent + Total mass × 100%. Test results are shown in Table 1.

[0102] (5) Reduction rate and total silver recovery rate test: The pH of the desorbed solution was adjusted to 4.8 with 10% NaOH. 1.0 mol / L ascorbic acid aqueous solution (the amount added was 1.3 times the theoretical molar amount of silver ions) was slowly added dropwise at 45℃ and 200 rpm with stirring. After stirring and reduction for 1.5 h, the solution was allowed to stand for 1 h and then centrifuged. The supernatant was used to determine the residual Ag using ICP-OES. + Concentration, calculate reduction rate = (Desorption solution Ag) + Total amount - supernatant Ag + (Residual amount) / Desorption solution Ag + Total amount × 100%. Total silver recovery rate = removal rate × desorption rate × reduction rate. Test results are shown in Table 1.

[0103] (6) Cyclic stability test: The regenerated adsorbent was subjected to the same adsorption-desorption-regeneration cycle as the removal rate test described above, for a total of 10 cycles. After each cycle, the Ag in the wastewater after adsorption was determined by ICP-OES. + The residual concentration was used to calculate the adsorption capacity for each cycle. The ratio of the adsorption capacity in the 10th cycle to that in the 1st cycle was taken as the capacity retention rate (%) after 10 cycles. The test results are shown in Table 1.

[0104] (7) Heavy metal leaching test: In the above removal rate test and cycle stability test, Ni in the wastewater was simultaneously detected by ICP-OES after each adsorption. 2+ and Co 2+ The concentration (detection limit 0.01 mg / L) was used to investigate whether secondary heavy metal pollution caused by the dissolution of NiCoP components occurred in a strongly acidic environment at pH 1.0. The Ni concentration detected in 10 cycles was used as the basis for the determination of the concentration of Ni. 2+ and Co 2+ The highest concentration was recorded as the reported value; no detection was recorded as ND. The test results are shown in Table 1.

[0105] Table 1:

[0106] sample <![CDATA[Ag + Removal rate (%) Saturated adsorption capacity (mg / g) <![CDATA[Ag + / Cu 2+ Selectivity coefficient <![CDATA[Ag + / Ni 2+ Selectivity coefficient Desorption rate (%) Reduction rate (%) Total silver recovery rate (%) 10-cycle capacity retention rate (%) <![CDATA[Ni 2+ Dissolution (mg / L) <![CDATA[Co 2+ Dissolution (mg / L) Example 1 99.3 211.5 48.3 50.7 98.8 99.5 97.6 95.8 ND ND Example 2 98.8 196.2 44.1 46.5 98.5 99.4 96.7 95.2 ND ND Example 3 99.5 218.7 52.4 55.1 99.1 99.7 98.3 96.5 ND ND Example 4 99.1 206.3 46.8 49.2 98.7 99.5 97.3 95.6 ND ND Example 5 98.5 189.4 42.3 44.6 98.3 99.3 96.1 94.8 ND ND Comparative Example 1 45.2 28.6 2.1 2.3 85.6 98.5 38.0 78.3 ND ND Comparative Example 2 91.5 126.3 34.8 36.5 97.8 99.2 88.8 93.2 ND ND Comparative Example 3 88.2 109.5 27.6 29.8 97.5 99.0 85.3 90.1 ND ND Comparative Example 4 95.8 166.8 38.2 40.5 98.2 99.3 93.3 94.5 ND ND Comparative Example 5 97.5 183.6 42.5 44.8 98.5 99.4 95.4 95.1 ND ND Comparative Example 6 97.2 179.2 40.1 42.7 98.4 99.3 95.0 94.9 ND ND

[0107] The data in the table shows that: Ag in Examples 1-5 + Removal rates were all ≥98.5%, and saturated adsorption capacities were all ≥189 mg / g. Ag + / Cu 2+ and Ag + / Ni 2+ All selectivity coefficients were ≥42, and the capacity retention rate after 10 cycles was ≥94.8%, with no Ni involved throughout the entire process. 2+ Co 2+The leaching results showed excellent overall performance with minimal differences between the various embodiments, indicating good process robustness of the invention within the parameter range defined in the claims. Example 3 exhibited the best performance across all indicators and is considered the optimal implementation. Comparative Example 1, using unmodified activated carbon, showed a silver ion removal rate of only 45.2%, a saturated adsorption capacity of only 28.6 mg / g, and a selectivity coefficient close to 1, indicating that unmodified activated carbon was less effective against Ag ions. + It exhibits almost no selective adsorption capacity, relying solely on physical adsorption, and performs extremely poorly in a strongly acidic environment at pH=1.0. Comparative Example 2, omitting the NiCo-LDH growth and phosphating steps, reduced the removal rate to 91.5% and the saturation capacity to 126.3 mg / g, indicating that the hierarchical channels and weak reducing adsorption of the NiCoP heterostructure significantly contribute to the overall capacity. Comparative Example 3, replacing the hyperbranched polymer with a linear polymer, reduced the removal rate to 88.2% and the capacity to 109.5 mg / g, with a significant decrease in the selectivity coefficient, confirming the irreplaceable role of the hyperbranched structure in avoiding chain entanglement, increasing site exposure, and maintaining a confined environment. Comparative Example 4, omitting the tannic acid and L-cysteine ​​modification steps, reduced the removal rate to 95.8%, with a capacity decrease of approximately 19% and a selectivity coefficient decrease of approximately 18% compared to Example 4. The retention rate after 10 cycles also decreased, verifying that tannic acid / L-cysteine ​​protonates and deactivates imidazole nitrogen under strong acid conditions, and also affects the H2O on the NiCoP surface. + The directional compensatory effect of competition.

[0108] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for recovering precious metals from refining wastewater based on adsorption, characterized in that, Includes the following steps: S1. Preparation of porous carbon-based composite adsorbent, wherein the preparation method of the porous carbon-based composite adsorbent includes the following steps: S11. After pre-carbonization, activation with potassium hydroxide, acid washing and water washing of coconut shell biomass carbon, it is further activated with a mixed solution of sodium hydroxide and hydrogen peroxide to obtain hydroxylated porous carbon carrier. S12. The hydroxylated porous carbon support is esterified with 2-bromoisobutyryl bromide to obtain a modified carbon support anchored with initiation sites. S13. The modified carbon support is dispersed in a mixed solvent, and AB2-type branched monomer N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester, comonomer 2-(1H-imidazol-1-yl)ethyl methacrylate, catalyst and ligand hexamethyltriethylenetetramine are added. After deoxygenation, a surface-initiated atom transfer radical polymerization reaction is carried out to obtain hyperbranched polymer grafted modified carbon material. S14. The hyperbranched polymer grafted modified carbon material is dispersed in a mixed solvent, and nickel chloride hexahydrate, cobalt chloride hexahydrate, hexamethylenetetramine and sodium dithiooxalate are added. After stirring and dissolving, a solvothermal reaction is carried out to obtain a carbon-based intermediate of confined growth intercalated NiCo-LDH. S15. The carbon-based intermediate is subjected to a self-polymerization reaction with dopamine hydrochloride to obtain a polydopamine-coated carbon-based intermediate; the polydopamine-coated carbon-based intermediate is subjected to a phosphating reaction with sodium hypophosphite under an inert atmosphere to obtain a porous carbon-based composite material. S16. A porous carbon-based composite material is deposited with tannic acid and L-cysteine ​​hydrochloride to obtain a porous carbon-based composite adsorbent. S2. Add the porous carbon-based composite adsorbent to the acidic wastewater containing precious metal ions for adsorption. S3. The adsorbent after adsorption is mixed with a desorbent containing thiourea and hydrochloric acid for desorption, and the regenerated adsorbent and the desorbent containing precious metal are separated. S4. Add ascorbic acid to the desorption solution to carry out a reduction reaction to obtain the noble metal element.

2. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S12, the mass ratio of the hydroxylated porous carbon support to 2-bromoisobutyryl bromide is 1:(1.0~2.0).

3. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S13, the mass ratio of the modified carbon support to N,N-bis(2-bromoisobutyryloxyethyl)dithiocarbamate-2-methacryloxyethyl ester is 1:(2.5-3.5).

4. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S13, the mass ratio of the modified carbon support to 2-(1H-imidazol-1-yl)ethyl methacrylate is 1:(0.7-1.2).

5. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S14, the mass ratio of hyperbranched polymer-grafted modified carbon material to nickel chloride hexahydrate is 1:(2.0-2.8).

6. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S14, the mass ratio of hyperbranched polymer-grafted modified carbon material to cobalt chloride hexahydrate is 1:(1.0-1.4).

7. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S14, the mass ratio of hyperbranched polymer-grafted modified carbon material to hexamethylenetetramine is 1:(5.5-7.0).

8. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S15, the mass ratio of the carbon-based intermediate to dopamine hydrochloride is 1:(0.15-0.25).

9. The method for recovering precious metals from refining wastewater based on adsorption according to claim 1, characterized in that, In step S16, the mass ratio of the porous carbon-based composite material to tannic acid is 1:(0.1-0.2); the mass ratio of the porous carbon-based composite material to L-cysteine ​​hydrochloride is 1:(0.05-0.12).

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