Adsorbent for recovering precious metals in refining wastewater and preparation method thereof

Abstract

The invention discloses an adsorbent for recovering precious metals in refining wastewater and a preparation method thereof, and relates to the technical field of recycling of precious metal materials. The method comprises the following steps: preparing a composite carbon source by taking lignin and coffee grounds as raw materials, and carbonizing and etching the composite carbon source and a heteroatom precursor containing Co, N, P, S and Se under the assistance of a template to obtain a hierarchical porous carbon substrate; the preparation method comprises the following steps: preparing a UiO-66-NH2 core-shell structure adsorbent, performing amination and sulfydryl functional modification on the UiO-66-NH2 core-shell structure adsorbent, constructing an interface bridging layer through MXene-phytic acid interpenetration, and finally inducing to grow a UiO-66-NH2 shell layer, thereby obtaining the core-shell structure adsorbent. The adsorbent prepared by the invention has high specific surface area, abundant heteroatom active sites and specific chelating groups, high selectivity, high adsorption capacity and excellent cycle stability for noble metal ions such as Au and the like, and is suitable for efficient recovery of noble metals in complex refining wastewater.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precious metal material recycling, in particular to a kind of precious metal adsorbent in recovery refining wastewater and preparation method thereof. BACKGROUND

[0002] Precious metals (gold, silver, platinum, palladium, ruthenium, etc.) are widely used in high-end fields such as electronics manufacturing, chemical catalysis, jewelry, aerospace, etc. due to their excellent electrical conductivity, catalytic activity, chemical stability and ductility, and are indispensable strategic resources for modern industry. However, the natural reserves of precious metals are scarce, difficult to mine, and high in production cost. With the continuous growth of global industrial demand, the problem of resource shortage is becoming increasingly prominent. At the same time, a large amount of refining wastewater is generated in non-ferrous metal refining, electronic component electroplating, and precious metal smelting industries. This kind of wastewater is complex in composition, containing not only acid, alkali, salt, and impurity ions such as copper, iron, and lead, but also low-concentration (usually ppm level) but highly valuable precious metal ions. Some precious metals also exist in stable forms such as sulfide sulfate complex and chloride complex. If this kind of wastewater is directly discharged, not only will it waste valuable precious metal resources, but it will also cause serious environmental pollution. Achieving efficient recovery of precious metals from refining wastewater can not only alleviate the pressure of resource shortage, but also reduce environmental governance costs, with significant economic value and environmental protection significance.

[0003] Currently, the methods for recovering precious metals from refining wastewater mainly include chemical precipitation, electrolysis, ion exchange, and adsorption. Among them, the chemical precipitation method separates by adding a precipitant to form a difficultly soluble compound with the precious metal ions, but has the defects of large amount of precipitant, large amount of heavy metal sludge, high difficulty of subsequent treatment, and low recovery efficiency for low-concentration precious metals. The electrolysis method can directly recover metal elements, but has high energy consumption, large equipment investment, and is seriously affected by the acidity and alkalinity of the wastewater and impurity ions, making it suitable for high-concentration precious metal wastewater treatment and difficult to meet the recovery needs of low-concentration refining wastewater. The ion exchange method separates precious metals by ion exchange of ion exchange resin, but has high resin synthesis cost, complex regeneration process, and short service life due to swelling and degradation in strong acid and alkali environment of refining wastewater, limiting its large-scale application.

[0004] In contrast, the adsorption method has the advantages of simple operation, controllable cost, less pollution, and wide applicable concentration range, and has become a research hotspot in the field of precious metal recovery from refinery wastewater. The existing adsorbents mainly include carbon materials (activated carbon, biomass carbon, porous carbon, etc.), chelating resins, metal organic framework (MOF) materials, and mesoporous materials. Among them, carbon materials are widely concerned due to their wide sources, acid and alkali corrosion resistance, and strong stability. However, the traditional carbon materials have obvious shortcomings: the pore structure is single (mostly microporous or disordered macroporous), the specific surface area is limited, which leads to large mass transfer resistance of precious metal ions and low adsorption capacity; the simple mixing and calcination process is used for heteroatom doping (such as N and S doping), which has the problems of single type of heteroatom, uneven distribution, and weak combination with carbon skeleton, and the interaction between the heteroatom and the precious metal ions (especially the complexed precious metal) in the refinery wastewater is weak, the adsorption selectivity is poor, and the adsorbent is easily interfered by impurity ions. The chelating resin adsorbent forms a stable chelate with the precious metal ions through the surface chelating group, and has relatively good selectivity, but has the problems of low mechanical strength, easy swelling and falling off under long-term immersion in refinery wastewater, poor regeneration performance, and difficulty in adapting to complex working conditions. Although the MOF material has ultra-high specific surface area and rich coordination active sites, the theoretical adsorption capacity is high, but when used alone, it has the defects of low mass transfer efficiency, easy aggregation, and insufficient stability in aqueous solution; and the existing composite technology of carbon materials and MOFs is mainly simple physical mixing or in-situ growth process, and the adsorption performance of the prepared composite adsorbent has not been effectively improved. SUMMARY

[0005] The present application aims to provide a kind of recovery refinery wastewater precious metal adsorbent and its preparation method to solve the technical problems raised in the above background art.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A preparation method of a precious metal adsorbent for recovering refinery wastewater, comprising the following steps:

[0008] (1) mixing lignin and coffee grounds, and acetylating under the action of a catalyst to obtain acetylated lignin, and then compounding the acetylated lignin with carbonized coffee grounds powder to obtain a composite carbon source;

[0009] (2) mixing a phytic acid solution and a cobalt chloride solution, then adding thiourea and selenourea, adjusting the pH to alkaline, and then adding dopamine monomer to react to obtain a heteroatom coordination precursor;

[0010] (3) dispersing mesoporous silica in anhydrous ethanol, adding the composite carbon source and the heteroatom coordination precursor, stirring and mixing, then evaporating the solvent under reduced pressure and drying;

[0011] carrying out temperature rising carbonization under inert atmosphere to obtain a carbon / silica composite;

[0012] treating the carbon / silica composite with an alkaline solution to obtain a multi-element heteroatom doped hierarchical porous carbon substrate;

[0013] (4) performing acid soaking and amination treatment on the carbon substrate, and then performing reaction with thiosalicylic acid to obtain a carbon material modified with mercapto on the surface;

[0014] (5) performing reaction of the carbon material with Ti3C2T x performing reaction of MXene nanosheets and phytic acid to form a carbon material modified by interpenetration of MXene-phytic acid interfaces;

[0015] (6) dispersing the carbon material modified by interpenetration of MXene-phytic acid interfaces in an organic solvent, adding zirconium salt, organic acid regulator and 2-amino terephthalic acid, performing reaction, and performing vacuum heat treatment to obtain a noble metal adsorbent.

[0016] In the technical scheme of the present application, the adsorption performance of the adsorbent for noble metals is improved from the following aspects: on the one hand, the carbon substrate is improved from the aspects of structure and active sites, the catalytic acetylation modification of the composite carbon source optimizes the compatibility and structural stability of lignin and coffee residue carbonized powder, forming a composite carbon carrier with high carbon content and good dispersity, providing reliable support for subsequent heteroatom doping and pore construction; the synthesis of the organic phosphorus chelate stabilized precursor realizes the uniform dispersion and stable immobilization of N, S, P and Se multi-element heteroatoms, avoiding agglomeration or loss of the heteroatoms; mesoporous silica impregnation and structure compounding precisely construct ordered mesoporous structures through a single hard template, eliminating steric hindrance between templates and ensuring that the carbon source and the precursor are fully filled in the pores, laying a foundation for subsequent formation of high specific surface area structures; anaerobic carbonization and selenium retention treatment maximizes the retention of multi-element heteroatom active sites through an inert atmosphere and a mild heating program, avoiding the loss of active elements by volatilization; these heteroatoms can form strong interactions with noble metal ions, strengthening the chemical adsorption capacity; template mild removal and purification completely remove the template while avoiding damage to the pore structure and erosion of the heteroatom sites, and finally form a multi-element heteroatom doped hierarchical porous carbon substrate, which greatly increases the specific surface area through ordered hierarchical pores, reduces the mass transfer resistance of noble metal ions, provides sufficient physical space for adsorption, and additionally enhances the chemical capture capacity of noble metal ions through uniformly distributed multi-element heteroatom active sites, thereby solving the problems of low adsorption capacity and poor mass transfer efficiency of traditional carbon materials and significantly improving the basic adsorption performance.

[0017] On the other hand, the selectivity, capacity and stability of adsorption are further optimized by the grafting of specific chelating groups and the core-shell effect of high-stability MOF. Specifically, the surface mild activation treatment introduces a small amount of hydroxyl and carboxyl groups on the surface of the carbon material under the premise of avoiding the oxidation and shedding of internal heteroatoms, achieving a balance between the preservation of original internal heteroatom sites and the construction of new active sites on the surface; the non-aqueous grafting of silane coupling agents eliminates solvent competition reactions, ensuring the high-density covalent combination of amino groups on the carbon surface, providing sufficient and stable anchoring sites for subsequent chelating group grafting; the non-aqueous phase system chelating group grafting enables the stable mounting of sulfur-containing and oxygen-containing specific chelating groups on the surface of the carbon skeleton through a high-efficiency catalytic condensation reaction, which greatly improves the adsorption selectivity and resists the interference of impurity ions in the refining wastewater; the heteronucleation growth of the regulator-assisted UiO-66-NH2 forms a high-crystallinity core-shell structure, and the ultra-high specific surface area and rich coordination sites of the MOF material itself provide additional high-capacity adsorption space for noble metal adsorption, and the core-shell structure further optimizes the mass transfer path; the gradient vacuum activation and drying empty the solvent molecules in the MOF channels, while enhancing the bonding force between the MOF shell and the carbon substrate, thereby improving the overall stability of the material. The second aspect improves the adsorption selectivity through specific chelating groups, increases the adsorption capacity through the MOF core-shell structure, and optimizes the mass transfer efficiency through the stable composite structure, which, in cooperation with the carbon substrate in the first aspect, significantly improves the capture efficiency, selectivity and adsorption capacity of the adsorbent for noble metal ions, while enhancing the stability of the material in complex wastewater environments.

[0018] Preferably, in step (1), the acetylation modification is carried out in an ice acetic acid solvent, using 4-dimethylaminopyridine as a catalyst, adding acetic anhydride, and refluxing at 85-95°C for 4-8h.

[0019] Preferably, in step (2), the molar ratio of phytic acid, cobalt chloride, thiourea and selenourea is 3:(2-3):5:2.

[0020] Preferably, in step (3), the mass ratio of mesoporous silica, composite carbon source and heteroatom coordination precursor is 1.5:(0.8-1.2):(0.6-1.0).

[0021] Preferably, in step (3), argon gas is continuously introduced during the entire carbonization process, and the temperature rising program is as follows: heating at 1-2°C / min to 200-220°C for 2h, and then heating at 2-3°C / min to 600-650°C for 3-5h.

[0022] Preferably, in step (3), the alkali solution is sodium hydroxide solution.

[0023] The concentration of the sodium hydroxide solution is 1-2mol / L.

[0024] As preferred, in the step (4), the mass ratio of the carbon base after the amination treatment to the thiosalicylic acid is 5:(2-4).

[0025] As preferred, in the step (5), the carbon material, Ti3C2T x The mass ratio of the MXene nanosheet to the phytic acid is 3:(0.5-1.0):(1.0-2.0).

[0026] The present application found in experiments that the in-situ growth of the UiO-66-NH2 MOF shell layer performs indiscriminate coating, which is easy to form a dense crystal film at the pore opening of the carbon base, seriously hindering the mass transfer of noble metal ions to the internal active sites (such as Se, S doped sites); at the same time, the interface electron transfer resistance between the carbon base and the insulating MOF shell layer is large, which limits the rate of redox-assisted adsorption. To further solve this technical problem, MXene nanosheets and phytic acid are introduced before the growth of the MOF, the two-dimensional MXene nanosheet is used as a space spacing support to insert into the pore of the carbon material, combined with the guiding effect of the phosphate group of the phytic acid molecule, the MOF crystal is guided to heterogeneously nucleate in a point-like and discontinuous manner, thereby forming a penetrating fluid channel, effectively preventing the pore from being blocked; secondly, the MXene penetrates the MOF shell layer by virtue of its metal-like conductivity, and builds an electron fast transfer bridge between the carbon base and the surface, significantly accelerating the reduction and adsorption process of noble metal ions such as AuCl4 - ; at the same time, the phosphate gradient formed by the phytic acid at the interface has the function of "ion reservoir" for pre-capturing metal ions, improving the mass transfer kinetics; in addition, through the multiple coordination of the phytic acid with the MXene, the carbon surface and Zr 4+ , a strong chemical bonding chain of "carbon-amino-phytic acid-Zr-MOF" is formed, which greatly enhances the structural stability of the core-shell interface. It realizes the leap from simple physical compounding to functional gradient interface, and through the synergy of multi-scale space regulation and electrochemical assisted adsorption, the internal high specific surface area active site and the external high specificity MOF shell layer are deeply coupled, further improving the adsorption performance of the adsorbent.

[0027] As preferred, in the step (6), ZrCl4 is selected as the zirconium salt.

[0028] A noble metal adsorbent for recycling and refining wastewater is prepared by the method described above.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] 1. By accurately constructing a multi-level pore carbon base doped with multiple heteroatoms, high specific surface area and a large number of chemical adsorption sites are provided, and at the same time, the ordered pore structure is ensured, thereby realizing high adsorption capacity and fast ion mass transfer.

[0031] 2. By grafting specific chelating groups onto the carbon substrate surface, the material is endowed with the ability to accurately identify noble metal ions. At the same time, by constructing a robust MOF core-shell structure, not only is the adsorption space increased, but the structural stability and cycle life of the material in complex wastewater environments are also significantly improved.

[0032] 3. The introduction of MXene and phytic acid for interface modification effectively prevents the MOF shell from blocking the internal pores and establishes a rapid dual channel for electron / ion transport, thereby significantly improving adsorption kinetics and redox adsorption efficiency. Attached Figure Description

[0033] Figure 1 This is a SEM image of the noble metal adsorbent prepared in Example 3 of the present invention.

[0034] Figure 2 The above is the XPS spectrum of the noble metal 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 preparing an adsorbent for recovering precious metals from refining wastewater includes the following steps:

[0038] Step 1: Mix 30g of lignin with a number-average molecular weight of 6000 Da with 20g of waste coffee grounds with a particle size of 50-100μm. Add 200mL of glacial acetic acid as a solvent, then add 50mL of acetic anhydride and 0.5g of 4-dimethylaminopyridine (DMAP) catalyst. Reflux at 90℃ for 7h to perform acetylation modification. After the reaction, precipitate the product with deionized water, wash until neutral, and dry to obtain acetylated lignin. Separately, place 20g of coffee grounds into a tube furnace and carbonize at 500℃ for 3h under nitrogen protection at a heating rate of 5℃ / min. Pulverize the carbonized coffee grounds through a 200-mesh sieve to obtain coffee grounds carbon powder. Mix 20g of acetylated lignin with 10g of coffee grounds carbon powder at a mass ratio of 2:1, add 150mL of anhydrous ethanol, ultrasonically disperse for 40min, remove the ethanol by rotary evaporation, and dry to obtain a composite carbon source.

[0039] Step 2: Accurately weigh 3 mmol of phytic acid and dissolve it in 60 mL of deionized water. Slowly add cobalt chloride solution (containing 2.8 mmol CoCl2) while stirring to form a stable organophosphorus-cobalt chelate system. Then add 5 mmol of thiourea and 2 mmol of selenourea to the system, stir to dissolve, and adjust the pH of the system to 8.5 using Tris buffer solution. Add 2 g of dopamine monomer and react at room temperature (25°C) in the dark for 6 h to obtain a multi-component heteroatom coordination precursor through the self-polymerization reaction of dopamine.

[0040] Step 3: Weigh 15g of mesoporous silica SBA-15 with a pore size of 8nm and disperse it in 150mL of anhydrous ethanol. Sonicate the mixture for 30min. Add 11g of composite carbon source and 9g of heteroatom coordination precursor, stir and mix for 24h, then evaporate the solvent under reduced pressure at 40℃ and dry under vacuum at 60℃. Place the dried solid into a quartz boat in a tube furnace, and maintain the furnace under high-purity argon gas. Heat the furnace to 210℃ at a rate of 1.5℃ / min and hold for 2h, then heat to 630℃ at a rate of 2.5℃ / min and hold for 4h to obtain a carbon / silica composite. After cooling, place the solid in 200mL of 1.5mol / L sodium hydroxide solution and stir at 90℃ for 8h to remove the hard template. After washing and drying, obtain a multi-component heteroatom-doped hierarchical porous carbon substrate.

[0041] Step 4: Place 5g of the above carbon substrate into 150mL of 1mol / L nitric acid solution and soak for 12h at room temperature (25℃) for surface activation. After washing and drying, disperse the activated carbon material in 150mL of anhydrous toluene, add 2g of 3-aminopropyltriethoxysilane (APTES), and reflux under nitrogen protection at 110℃ for 12h to complete the amination treatment. After washing, disperse 5g of the amination carbon material in 100mL of anhydrous DMF, add 3.5g of thiosalicylic acid, 2.5g of EDCI, and 1.5g of NHS condensing agent, and react at room temperature in the dark for 24h to obtain carbon material with mercapto (-SH) modified surface.

[0042] Step 5: Take 3g of surface-modified thiol-modified carbon material, disperse it in 80mL of deionized water, and then add 0.9g of exfoliated Ti3C2T sequentially. x MXene nanosheets and 1.8 g of phytic acid were reacted with magnetic stirring at room temperature for 4 h. Two-dimensional MXene sheets were intercalated into the pores of carbon materials using electrostatic attraction and coordination, with abundant phosphate sites provided by phytic acid molecules, forming an intermediate material with MXene-phytic acid interface intercalation modification.

[0043] Step 6: The above intermediate material was dispersed in 80 mL of DMF organic solvent, 1.2 mmol ZrCl4 was added as a zirconium salt, and 36 mmol glacial acetic acid was added as an organic acid regulator. The mixture was ultrasonically treated for 30 min. Then, 1.2 mmol 2-aminoterephthalic acid was added to the system, and the mixture was transferred to a polytetrafluoroethylene-lined pressure vessel and heat-treated at 120 °C for 24 h. After washing with DMF and soaking in methanol for 3 days, the reaction product was placed in a vacuum drying oven, pre-dried at 60 °C, and then heated to 150 °C at a rate of 0.5 °C / min. It was then activated at an ultimate vacuum of -0.098 MPa for 12 h to finally obtain the adsorbent for recovering precious metals from refining wastewater.

[0044] Example 2

[0045] A method for preparing an adsorbent for recovering precious metals from refining wastewater includes the following steps:

[0046] Step 1: Mix 30g of lignin with a number-average molecular weight of 6000 Da with 20g of waste coffee grounds with a particle size of 50-100μm. Add 200mL of glacial acetic acid as a solvent, then add 50mL of acetic anhydride and 0.5g of 4-dimethylaminopyridine (DMAP) catalyst. Reflux at 90℃ for 5h to perform acetylation modification. After the reaction, precipitate the product with deionized water, wash until neutral, and dry to obtain acetylated lignin. Separately, place 20g of coffee grounds into a tube furnace and carbonize at 500℃ for 3h under nitrogen protection at a heating rate of 5℃ / min. Pulverize the carbonized coffee grounds through a 200-mesh sieve to obtain coffee grounds carbonized powder. Mix 20g of acetylated lignin with 10g of coffee grounds carbonized powder at a mass ratio of 2:1, add 150mL of anhydrous ethanol, ultrasonically disperse for 40min, remove the ethanol by rotary evaporation, and dry to obtain a composite carbon source.

[0047] Step 2: Accurately weigh 3 mmol of phytic acid and dissolve it in 60 mL of deionized water. Slowly add cobalt chloride solution (containing 2.3 mmol CoCl2) while stirring to form a stable organophosphorus-cobalt chelate system. Then add 5 mmol of thiourea and 2 mmol of selenourea to the system, stir to dissolve, and adjust the pH of the system to 8.5 using Tris buffer solution. Add 2 g of dopamine monomer and react at room temperature (25°C) in the dark for 6 h to obtain a multi-component heteroatom coordination precursor through the self-polymerization reaction of dopamine.

[0048] Step 3: Weigh 15g of mesoporous silica SBA-15 with a pore size of 8nm and disperse it in 150mL of anhydrous ethanol. Sonicate the mixture for 30min. Add 9g of composite carbon source and 7g of heteroatom coordination precursor, stir and mix for 24h, then evaporate the solvent under reduced pressure at 40℃ and dry under vacuum at 60℃. Place the dried solid into a quartz boat in a tube furnace, and purge it with high-purity argon gas throughout. Heat the furnace to 210℃ at a rate of 1.5℃ / min and hold for 2h, then heat it to 630℃ at a rate of 2.5℃ / min and hold for 4h to obtain a carbon / silica composite. After cooling, place the solid in 200mL of 1.5mol / L sodium hydroxide solution and stir at 90℃ for 8h to remove the hard template. After washing and drying, obtain a multi-component heteroatom-doped hierarchical porous carbon substrate.

[0049] Step 4: Place 5g of the above carbon substrate into 150mL of 1mol / L nitric acid solution and soak for 12h at room temperature (25℃) for surface activation. After washing and drying, disperse the activated carbon material in 150mL of anhydrous toluene, add 2g of 3-aminopropyltriethoxysilane (APTES), and reflux under nitrogen protection at 110℃ for 12h to complete the amination treatment. After washing, disperse 5g of the amination carbon material in 100mL of anhydrous DMF, add 2.5g of thiosalicylic acid, 2.5g of EDCI, and 1.5g of NHS condensing agent, and react at room temperature in the dark for 24h to obtain carbon material with mercapto (-SH) modified surface.

[0050] Step 5: Take 3g of surface-modified thiol-containing carbon material, disperse it in 80mL of deionized water, and then add 0.6g of exfoliated Ti3C2T sequentially. x MXene nanosheets and 1.2 g of phytic acid were reacted with magnetic stirring at room temperature for 4 h. Two-dimensional MXene sheets were intercalated into the pores of carbon materials using electrostatic attraction and coordination, with abundant phosphate sites provided by phytic acid molecules, forming an intermediate material with MXene-phytic acid interface intercalation modification.

[0051] Step 6: The above intermediate material was dispersed in 80 mL of DMF organic solvent, 1.2 mmol ZrCl4 was added as a zirconium salt, and 36 mmol glacial acetic acid was added as an organic acid regulator. The mixture was ultrasonically treated for 30 min. Then, 1.2 mmol 2-aminoterephthalic acid was added to the system, and the mixture was transferred to a polytetrafluoroethylene-lined pressure vessel and heat-treated at 120 °C for 24 h. After washing with DMF and soaking in methanol for 3 days, the reaction product was placed in a vacuum drying oven, pre-dried at 60 °C, and then heated to 150 °C at a rate of 0.5 °C / min. It was then activated at an ultimate vacuum of -0.098 MPa for 12 h to finally obtain the adsorbent for recovering precious metals from refining wastewater.

[0052] Example 3

[0053] A method for preparing an adsorbent for recovering precious metals from refining wastewater includes the following steps:

[0054] Step 1: Mix 30g of lignin with a number-average molecular weight of 6000 Da with 20g of waste coffee grounds with a particle size of 50-100μm. Add 200mL of glacial acetic acid as a solvent, then add 50mL of acetic anhydride and 0.5g of 4-dimethylaminopyridine (DMAP) catalyst. Reflux at 90℃ for 6h to perform acetylation modification. After the reaction, precipitate the product with deionized water, wash until neutral, and dry to obtain acetylated lignin. Separately, place 20g of coffee grounds into a tube furnace and carbonize at 500℃ for 3h under nitrogen protection at a heating rate of 5℃ / min. Pulverize the carbonized coffee grounds through a 200-mesh sieve to obtain coffee grounds carbon powder. Mix 20g of acetylated lignin with 10g of coffee grounds carbon powder at a mass ratio of 2:1, add 150mL of anhydrous ethanol, ultrasonically disperse for 40min, remove the ethanol by rotary evaporation, and dry to obtain a composite carbon source.

[0055] Step 2: Accurately weigh 3 mmol of phytic acid and dissolve it in 60 mL of deionized water. Slowly add cobalt chloride solution (containing 2.5 mmol CoCl2) while stirring to form a stable organophosphorus-cobalt chelate system. Then add 5 mmol of thiourea and 2 mmol of selenourea to the system, stir to dissolve, and adjust the pH of the system to 8.5 using Tris buffer solution. Add 2 g of dopamine monomer and react at room temperature (25°C) in the dark for 6 h to obtain a multi-component heteroatom coordination precursor through the self-polymerization reaction of dopamine.

[0056] Step 3: Weigh 15g of mesoporous silica SBA-15 with a pore size of 8nm and disperse it in 150mL of anhydrous ethanol. Sonicate the mixture for 30min. Add 10g of composite carbon source and 8g of heteroatom coordination precursor, stir and mix for 24h, then evaporate the solvent under reduced pressure at 40℃ and dry under vacuum at 60℃. Place the dried solid into a quartz boat in a tube furnace, and purge it with high-purity argon gas throughout. Heat the furnace to 210℃ at a rate of 1.5℃ / min and hold for 2h, then heat it to 630℃ at a rate of 2.5℃ / min and hold for 4h to obtain a carbon / silica composite. After cooling, place the solid in 200mL of 1.5mol / L sodium hydroxide solution and stir at 90℃ for 8h to remove the hard template. After washing and drying, obtain a multi-component heteroatom-doped hierarchical porous carbon substrate.

[0057] Step 4: Place 5g of the above carbon substrate into 150mL of 1mol / L nitric acid solution and soak for 12h at room temperature (25℃) for surface activation. After washing and drying, disperse the activated carbon material in 150mL of anhydrous toluene, add 2g of 3-aminopropyltriethoxysilane (APTES), and reflux under nitrogen protection at 110℃ for 12h to complete the amination treatment. After washing, disperse 5g of the amination carbon material in 100mL of anhydrous DMF, add 3g of thiosalicylic acid, 2.5g of EDCI and 1.5g of NHS condensing agent, and react at room temperature in the dark for 24h to obtain carbon material with thiol (-SH) modified on the surface.

[0058] Step 5: Take 3g of surface-modified thiol-modified carbon material, disperse it in 80mL of deionized water, and then add 0.7g of exfoliated Ti3C2T sequentially. x MXene nanosheets and 1.5 g of phytic acid were reacted with magnetic stirring at room temperature for 4 h. Two-dimensional MXene sheets were intercalated into the pores of carbon materials using electrostatic attraction and coordination, with abundant phosphate sites provided by phytic acid molecules, forming an intermediate material with MXene-phytic acid interface intercalation modification.

[0059] Step 6: The above intermediate material was dispersed in 80 mL of DMF organic solvent, 1.2 mmol ZrCl4 was added as a zirconium salt, and 36 mmol glacial acetic acid was added as an organic acid regulator. The mixture was ultrasonically treated for 30 min. Then, 1.2 mmol 2-aminoterephthalic acid was added to the system, and the mixture was transferred to a polytetrafluoroethylene-lined pressure vessel and heat-treated at 120 °C for 24 h. After washing with DMF and soaking in methanol for 3 days, the reaction product was placed in a vacuum drying oven, pre-dried at 60 °C, and then heated to 150 °C at a rate of 0.5 °C / min. It was then activated at an ultimate vacuum of -0.098 MPa for 12 h to finally obtain the adsorbent for recovering precious metals from refining wastewater.

[0060] Example 4

[0061] A method for preparing an adsorbent for recovering precious metals from refining wastewater includes the following steps:

[0062] Step 1: Mix 30g of lignin with a number-average molecular weight of 6000 Da with 20g of waste coffee grounds with a particle size of 50-100μm. Add 200mL of glacial acetic acid as a solvent, then add 50mL of acetic anhydride and 0.5g of 4-dimethylaminopyridine (DMAP) catalyst. Reflux at 95℃ for 8h to perform acetylation modification. After the reaction, precipitate the product with deionized water, wash until neutral, and dry to obtain acetylated lignin. Separately, place 20g of coffee grounds into a tube furnace and carbonize at 500℃ for 3h under nitrogen protection at a heating rate of 5℃ / min. Pulverize the carbonized coffee grounds through a 200-mesh sieve to obtain coffee grounds carbon powder. Mix 20g of acetylated lignin with 10g of coffee grounds carbon powder at a mass ratio of 2:1, add 150mL of anhydrous ethanol, ultrasonically disperse for 40min, remove the ethanol by rotary evaporation, and dry to obtain a composite carbon source.

[0063] Step 2: Accurately weigh 3 mmol of phytic acid and dissolve it in 60 mL of deionized water. Slowly add cobalt chloride solution (containing 3 mmol CoCl2) while stirring to form a stable organophosphorus-cobalt chelate system. Then add 5 mmol of thiourea and 2 mmol of selenourea to the system, stir to dissolve, and adjust the pH of the system to 8.5 using Tris buffer solution. Add 2 g of dopamine monomer and react at room temperature (25°C) in the dark for 6 h to obtain a multi-component heteroatom coordination precursor through the self-polymerization reaction of dopamine.

[0064] Step 3: Weigh 15g of mesoporous silica SBA-15 with a pore size of 8nm and disperse it in 150mL of anhydrous ethanol. Sonicate the mixture for 30min. Add 12g of composite carbon source and 10g of heteroatom coordination precursor, stir and mix for 24h, then evaporate the solvent under reduced pressure at 40℃ and dry under vacuum at 60℃. Place the dried solid into a quartz boat in a tube furnace, and purge it with high-purity argon gas throughout. Heat the furnace to 220℃ at a rate of 2℃ / min and hold for 2h, then heat it to 650℃ at a rate of 3℃ / min and hold for 5h to obtain a carbon / silica composite. After cooling, place the solid in 200mL of 2mol / L sodium hydroxide solution and stir at 90℃ for 8h to remove the hard template. After washing and drying, obtain a multi-component heteroatom-doped hierarchical porous carbon substrate.

[0065] Step 4: Place 5g of the above carbon substrate into 150mL of 1mol / L nitric acid solution and soak for 12h at room temperature (25℃) for surface activation. After washing and drying, disperse the activated carbon material in 150mL of anhydrous toluene, add 2g of 3-aminopropyltriethoxysilane (APTES), and reflux under nitrogen protection at 110℃ for 12h to complete the amination treatment. After washing, disperse 5g of the amination carbon material in 100mL of anhydrous DMF, add 4g of thiosalicylic acid, 2.5g of EDCI and 1.5g of NHS condensing agent, and react at room temperature in the dark for 24h to obtain carbon material with mercapto (-SH) modified surface.

[0066] Step 5: Take 3g of surface-modified thiol-modified carbon material, disperse it in 80mL of deionized water, and add 1.0g of exfoliated Ti3C2T sequentially. x MXene nanosheets and 2g of phytic acid were reacted with magnetic stirring at room temperature for 4h. Electrostatic attraction and coordination enabled the two-dimensional MXene sheets to interpenetrate within the pores of the carbon material, with abundant phosphate sites provided by phytic acid molecules, forming an intermediate material with MXene-phytic acid interface interpenetration modification.

[0067] Step 6: The above intermediate material was dispersed in 80 mL of DMF organic solvent, 1.2 mmol ZrCl4 was added as a zirconium salt, and 36 mmol glacial acetic acid was added as an organic acid regulator. The mixture was ultrasonically treated for 30 min. Then, 1.2 mmol 2-aminoterephthalic acid was added to the system, and the mixture was transferred to a polytetrafluoroethylene-lined pressure vessel and heat-treated at 120 °C for 24 h. After washing with DMF and soaking in methanol for 3 days, the reaction product was placed in a vacuum drying oven, pre-dried at 60 °C, and then heated to 150 °C at a rate of 0.5 °C / min. It was then activated at an ultimate vacuum of -0.098 MPa for 12 h to finally obtain the adsorbent for recovering precious metals from refining wastewater.

[0068] Example 5

[0069] A method for preparing an adsorbent for recovering precious metals from refining wastewater includes the following steps:

[0070] Step 1: Mix 30g of lignin with a number-average molecular weight of 6000 Da with 20g of waste coffee grounds with a particle size of 50-100μm. Add 200mL of glacial acetic acid as a solvent, then add 50mL of acetic anhydride and 0.5g of 4-dimethylaminopyridine (DMAP) catalyst. Reflux at 85℃ for 4h to perform acetylation modification. After the reaction, precipitate the product with deionized water, wash until neutral, and dry to obtain acetylated lignin. Separately, place 20g of coffee grounds into a tube furnace and carbonize at 500℃ for 3h under nitrogen protection at a heating rate of 5℃ / min. Pulverize the carbonized coffee grounds through a 200-mesh sieve to obtain coffee grounds carbonized powder. Mix 20g of acetylated lignin with 10g of coffee grounds carbonized powder at a mass ratio of 2:1, add 150mL of anhydrous ethanol, ultrasonically disperse for 40min, remove the ethanol by rotary evaporation, and dry to obtain a composite carbon source.

[0071] Step 2: Accurately weigh 3 mmol of phytic acid and dissolve it in 60 mL of deionized water. Slowly add cobalt chloride solution (containing 2 mmol CoCl2) while stirring to form a stable organophosphorus-cobalt chelate system. Then add 5 mmol of thiourea and 2 mmol of selenourea to the system, stir to dissolve, and adjust the pH of the system to 8.5 using Tris buffer solution. Add 2 g of dopamine monomer and react at room temperature (25°C) in the dark for 6 h to obtain a multi-component heteroatom coordination precursor through the self-polymerization reaction of dopamine.

[0072] Step 3: Weigh 15g of mesoporous silica SBA-15 with a pore size of 8nm and disperse it in 150mL of anhydrous ethanol, then sonicate for 30min. Add 8g of composite carbon source and 6g of heteroatom coordination precursor, stir and mix for 24h, then evaporate the solvent under reduced pressure at 40℃ and dry under vacuum at 60℃. Place the dried solid into a quartz boat in a tube furnace, and purge it with high-purity argon gas throughout the process. Heat the furnace to 200℃ at a rate of 1℃ / min and hold for 2h, then heat it to 600℃ at a rate of 2℃ / min and hold for 3h to obtain a carbon / silica composite. After cooling, place the solid in 200mL of 1mol / L sodium hydroxide solution and stir at 90℃ for 8h to remove the hard template. After washing and drying, obtain a multi-component heteroatom-doped hierarchical porous carbon substrate.

[0073] Step 4: Place 5g of the above carbon substrate into 150mL of 1mol / L nitric acid solution and soak for 12h at room temperature (25℃) for surface activation. After washing and drying, disperse the activated carbon material in 150mL of anhydrous toluene, add 2g of 3-aminopropyltriethoxysilane (APTES), and reflux under nitrogen protection at 110℃ for 12h to complete the amination treatment. After washing, disperse 5g of the amination carbon material in 100mL of anhydrous DMF, add 2g of thiosalicylic acid, 2.5g of EDCI and 1.5g of NHS condensing agent, and react at room temperature in the dark for 24h to obtain carbon material with mercapto (-SH) modified surface.

[0074] Step 5: Take 3g of surface-modified thiol-containing carbon material, disperse it in 80mL of deionized water, and then add 0.5g of exfoliated Ti3C2T sequentially. x MXene nanosheets and 1g of phytic acid were reacted with magnetic stirring at room temperature for 4h. Two-dimensional MXene sheets were intercalated into the pores of carbon materials using electrostatic attraction and coordination, with abundant phosphate sites provided by phytic acid molecules, forming an intermediate material with MXene-phytic acid interface intercalation modification.

[0075] Step 6: The above intermediate material was dispersed in 80 mL of DMF organic solvent, 1.2 mmol ZrCl4 was added as a zirconium salt, and 36 mmol glacial acetic acid was added as an organic acid regulator. The mixture was ultrasonically treated for 30 min. Then, 1.2 mmol 2-aminoterephthalic acid was added to the system, and the mixture was transferred to a polytetrafluoroethylene-lined pressure vessel and heat-treated at 120 °C for 24 h. After washing with DMF and soaking in methanol for 3 days, the reaction product was placed in a vacuum drying oven, pre-dried at 60 °C, and then heated to 150 °C at a rate of 0.5 °C / min. It was then activated at an ultimate vacuum of -0.098 MPa for 12 h to finally obtain the adsorbent for recovering precious metals from refining wastewater.

[0076] Comparative Example 1: The difference between Comparative Example 1 and Example 3 is that commercially available conventional coffee grounds activated carbon were directly added to a DMF solution containing zirconium salt, ligand and regulator, and MOF was grown according to the method in step 6.

[0077] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that only phytic acid, cobalt chloride and thiourea are added in step 2, and selenourea is not added.

[0078] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that thiosalicylic acid is not grafted in step 4. The carbon substrate after amination treatment in step 4 is directly introduced into step 5 for MXene-phytic acid modification, and then MOF is grown according to step 6. That is, the surface of the obtained product has amino and MOF layers, but lacks thiol chelation sites.

[0079] Comparative Example 4: The difference between Comparative Example 4 and Example 3 is that the carbon material with thiol-modified surface obtained in step 4 is directly dispersed in DMF without MXene and phytic acid treatment, and the shell of UiO-66-NH2 is grown, washed and activated according to the method in step 6.

[0080] Performance testing:

[0081] 1. Saturated Adsorption Capacity Test: Simulated refining wastewater with different initial concentrations was prepared (HAuCl4 dissolved in 0.1 mol / L HCl solution, with initial gold ion concentrations set at 50-2000 mg / L). 10 mg of each of the adsorbents prepared in Examples 1-5 and Comparative Examples 1-4 were weighed and placed in 50 mL centrifuge tubes, and 20 mL of simulated wastewater of different concentrations were added. The tubes were shaken at 25℃ and 200 rpm for 24 h to reach adsorption equilibrium. The gold ion concentrations before and after adsorption were measured using inductively coupled plasma optical emission spectrometry (ICP-OES). The equilibrium adsorption capacity of each sample was calculated according to the mass balance equation, and the maximum adsorption capacity was obtained by fitting the Langmuir adsorption isotherm model. The test results are shown in Table 1.

[0082] 2. Adsorption Kinetics Test: The initial concentration of gold ions in the simulated refining wastewater was set at 500 mg / L, and the pH value was 2.0. 50 mg of adsorbent was weighed and added to 100 mL of the solution. Samples were taken at regular intervals of 5 min, 10 min, 20 min, 30 min, 60 min, 120 min, 240 min, and 480 min with continuous stirring. After filtration through a 0.22 μm filter membrane, the residual gold ion concentration in the filtrate was measured. Adsorption time was plotted against adsorption capacity to observe the time required for adsorption equilibrium. The test results are shown in Table 1.

[0083] 3. Adsorption selectivity test: Prepare a competitive mixed solution containing multiple metal ions, including Au. 3+ Cu 2+ Ni 2+ Zn 2+ Fe 3+ Pb 2+ The initial concentration of each ion was 100 mg / L. 10 mg of adsorbent was weighed and added to 20 mL of the above mixed solution, and the mixture was shaken for 2 h for adsorption. The concentration changes of each ion in the solution before and after adsorption were measured by ICP-OES, and the selectivity coefficient (Au / Cu) was calculated to evaluate the specific recognition and capture ability of the adsorbent in a complex ionic environment. The test results are shown in Table 1.

[0084] 4. Cyclic Regeneration Stability Test: The adsorbent after adsorbing gold ions was collected and eluted with a mixed solution of 0.5 mol / L thiourea and 0.1 mol / L HCl at 40°C for 4 hours. The eluted material was washed with deionized water until neutral and then reactivated and dried. The above "adsorption-elution" process was repeated, and the amount of gold ions adsorbed after each cycle was recorded. The chemical stability and structural robustness of the material under the complex conditions of refining wastewater were evaluated by calculating the ratio of the adsorption capacity of the 10th cycle to that of the 1st cycle. The test results are shown in Table 1.

[0085] Table 1:

[0086] Maximum adsorption capacity (mg / g) Adsorption equilibrium time (min) Selectivity coefficient (Au / Cu) Capacity retention rate after 10 cycles (%) Example 1 1186 45 683 97.2 Example 2 1143 52 650 96.5 Example 3 1210 40 715 98.1 Example 4 1168 48 667 96.8 Example 5 1095 58 621 95.4 Comparative Example 1 282 181 75 42.5 Comparative Example 2 913 65 420 94.0 Comparative Example 3 627 76 42 91.6 Comparative Example 4 715 212 386 86.3

[0087] The performance of Examples 1-5 is significantly superior to that of the comparative examples, especially Example 3, which achieved an adsorption capacity of 1210 mg / g and reached adsorption equilibrium within 40 min, demonstrating the superiority of the integrated structure of hierarchical porous carbon substrate, specific chelating groups, MXene conductive bridge, and MOF shell. Comparative Example 4, lacking the MXene-phytic acid interface layer, experienced a significant increase in adsorption equilibrium time from 40 min to 210 min, and its adsorption capacity also decreased significantly. This confirms that in-situ MOF growth does indeed cause pore blockage, while the introduction of the MXene intercalation structure effectively establishes a permeable fluid channel. Comparative Example 3, lacking thiol sites, saw its selectivity coefficient plummet from 715 to 42, indicating that the grafting of thiosalicylic acid is crucial for eliminating interference from high-concentration impurity metal ions in refining wastewater.

[0088] 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 preparing an adsorbent for recovering precious metals from refining wastewater, characterized in that, Includes the following steps: (1) Mix lignin with coffee grounds and acetylate them under the action of a catalyst to obtain acetylated lignin, which is then compounded with coffee grounds carbonized powder to obtain a composite carbon source. (2) Mix phytic acid solution with cobalt chloride solution, then add thiourea and selenourea, adjust the pH to alkaline, add dopamine monomer, and react to obtain heteroatom coordination precursor; (3) Disperse mesoporous silica in anhydrous ethanol, add composite carbon source and heteroatom coordination precursor, stir and mix, evaporate solvent under reduced pressure and dry; Carbonization was carried out under an inert atmosphere to obtain a carbon / silica composite. A multi-component heteroatom-doped hierarchical porous carbon substrate was obtained by treating the carbon / silica composite with an alkaline solution. (4) The carbon substrate is subjected to acid soaking and amination treatment, and then reacted with thiosalicylic acid to obtain carbon material with thiol groups on the surface. (5) Combine carbon materials with Ti3C2T x MXene nanosheets and phytic acid are mixed and reacted to form carbon materials with MXene-phytic acid interface interpenetration modification; (6) The carbon material with MXene-phytic acid interface interpenetration modification is dispersed in an organic solvent, and zirconium salt, organic acid regulator and 2-aminoterephthalic acid are added to react and then subjected to vacuum heat treatment to obtain a noble metal adsorbent.

2. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (1), the acetylation modification is carried out in glacial acetic acid solvent, with 4-dimethylaminopyridine as catalyst, acetic anhydride is added and refluxed at 85-95°C for 4-8 hours.

3. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (2), the molar ratio of phytic acid, cobalt chloride, thiourea, and selenourea is 3:(2-3):5:

2.

4. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (3), the mass ratio of mesoporous silica, composite carbon source, and heteroatom coordination precursor is 1.5:(0.8-1.2):(0.6-1.0).

5. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (3), argon gas is introduced for protection throughout the carbonization process. The heating program is as follows: heat up to 200-220℃ at 1-2℃ / min and hold for 2 hours, then heat up to 600-650℃ at 2-3℃ / min and hold for 3-5 hours.

6. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (3), the alkaline solution is sodium hydroxide solution; The concentration of the sodium hydroxide solution is 1–2 mol / L.

7. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (4), the mass ratio of the amination-treated carbon substrate to thiosalicylic acid is 5:(2-4).

8. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (5), carbon materials, Ti3C2T x The mass ratio of MXene nanosheets to phytic acid is 3:(0.5~1.0):(1.0~2.0).

9. The method for preparing an adsorbent for recovering precious metals from refining wastewater according to claim 1, characterized in that, In step (6), the zirconium salt is ZrCl4.

10. An adsorbent for recovering precious metals from refining wastewater, characterized in that, It is prepared by the method described in any one of claims 1 to 9 above.

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