Preparation method and application of sulfur-nitrogen gradient channel biomass adsorbent
Patent Information
- Application Number
- CN202610929144.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-06-25
- Publication Date
- 2026-09-25
AI Technical Summary
由于金、铂、钯浓度极低（mg/L级）且酸度极高，传统沉淀法、萃取法难以有效回收，造成稀贵金属流失
[0030]本发明提供了一种硫-氮梯度孔道生物质吸附剂的制备方法，核心构思在于：采用生物质材料作为基体，通过以下特定时序的步骤构建梯度孔道结构：包括先在内层（纤维素无定形区）引入-SH/-S-S-软配位域，再通过碱处理扩孔使硫位点内嵌，最后仅在孔道表面及入口接枝PEI形成-NH3+静电筛分层。由此形成“外层静电排斥贱金属阳离子、内层软配位捕获贵金属氯配阴离子”的梯度孔道结构，其功能类似于分子筛。
Abstract
Description
Technical Field
[0001] This invention belongs to the field of hydrometallurgical functional materials technology, specifically relating to a method for preparing and applying a sulfur-nitrogen gradient porous biomass adsorbent. Background Technology
[0002] Copper anode slime is a secondary enrichment resource generated during copper electrolytic refining, rich in rare and precious metals such as gold, platinum, and palladium. In the all-wet process, after copper anode slime undergoes sulfation roasting followed by acid leaching or oxygen pressure leaching to separate copper, the resulting copper-separated slag needs further chlorination leaching (hydrochloric acid + sodium chlorate or chlorine gas) to release gold, platinum, and palladium in chloride anionic form (AuCl4). - PtCl6 2- PdCl4 2- The gold ions are introduced into the solution. Subsequently, under controlled potential conditions, sodium bisulfite is added or SO2 gas is introduced to reduce the large number of gold ions in the solution to elemental gold precipitate and separate them. This process is called "gold precipitation".
[0003] After gold immersion treatment, the remaining solution is the gold immersion solution. Typical characteristics of this solution include: high acidity (containing 2-4M HCl) and high chloride ion concentration (Cl...). - The metals present include approximately 3-6 mg / L, trace amounts of precious metals (Au 0.5-10 mg / L, Pt 1-5 mg / L, Pd 1-10 mg / L), residual oxidizing properties (containing unreacted sodium chlorate or dissolved chlorine, ORP 400-600 mV), and small amounts of base metals (Cu 0.5-3 g / L, Fe 0.1-1 g / L) and rare elements such as selenium and tellurium. Due to the extremely low concentrations (mg / L level) and extremely high acidity of gold, platinum, and palladium, traditional precipitation and extraction methods are difficult to effectively recover them, resulting in the loss of rare and precious metals.
[0004] If the precious metals in the solution after the above gold precipitation treatment are to be recovered, the existing technology has obvious shortcomings, specifically: 1) Commercial ion exchange resins (such as D201) are expensive and are easily oxidized and degraded in high acid and high oxidizing environments, and have extremely low adsorption capacity for trace Pt and Pd; 2) Ordinary biomass adsorbents have not been deeply modified, and their structure collapses in high acid and high salt environments, and they lack the ability to specifically recognize Pt and Pd; 3) Single functional group materials (containing only amino groups or only thiol groups) are difficult to cope with electrostatic competition and complex ion interference under high acidity, and have low capture efficiency for trace precious metals. Summary of the Invention
[0005] To address the problems of the existing technologies, there is an urgent need to develop a biomass adsorption material that is resistant to extreme acid and chlorine environments, contains multiple synergistic coordination functional groups, and has specific recognition capabilities for Au / Pt / Pd, for the deep recovery of trace precious metals from gold precipitation solutions.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows:
[0007] This invention provides a method for preparing a sulfur-nitrogen gradient porous biomass adsorbent, comprising the following steps:
[0008] (1) Hydrothermal ammonium thiocyanate pre-modification: Biomass powder is mixed with thiourea aqueous solution, the pH value is adjusted to 8-11, and hydrothermal reaction is carried out at 120-180℃ for 1-4 h to form sulfur-modified matrix;
[0009] (2) Alkali treatment for directional pore expansion and sulfur site embedding: The sulfur-modified matrix obtained in step (1) is mixed with sodium hydroxide solution and stirred at 50-70℃ for 2-5 h. The reaction product is washed until neutral and dried to obtain a porous sulfur embedded matrix.
[0010] (3) PEI surface grafting and double crosslinking: The porous sulfur embedded matrix obtained in step (2) is mixed with a polyethyleneimine (PEI) aqueous solution, glutaraldehyde (GA) is added for primary crosslinking, and then epichlorohydrin (ECH) is added for secondary crosslinking;
[0011] (4) Protic acid activation: The product obtained in step (3) is activated with hydrochloric acid and then dried under vacuum to obtain the biomass adsorbent with sulfur-nitrogen gradient pore structure.
[0012] Preferably, in step (1), the biomass powder is garlic peel, garlic stalks or rice straw, with a particle size of 40-80 mesh; the concentration of the ammonia thiocyanate aqueous solution is 30-60% (w / v), and the solid-liquid ratio is 1:1-1:5 g / mL; preferably, the hydrothermal temperature is 170℃, and the reaction time is 2 h.
[0013] In the above process, ammonium thiocyanate decomposes under alkaline hydrothermal conditions to produce HS. - S 2- The active sulfur radicals undergo nucleophilic substitution with the C-6 hydroxyl groups in cellulose, introducing thiol groups (-SH) and disulfide bonds (-SS-) into the amorphous region of the biomass skeleton. Controlling the pH to be weakly alkaline rather than strongly alkaline is to inhibit further oxidation of -SH to sulfonic acid groups, while simultaneously promoting disulfide bond formation to enhance stability.
[0014] Preferably, in step (2), the concentration of the sodium hydroxide solution is 0.5-2 M, and the solid-liquid ratio is 1:10-1:30 g / mL; preferably, the reaction temperature is 60℃, and the reaction time is 3-4 h; the specific surface area of the obtained porous sulfur embedded matrix is 5-15 m². 2 / g, with an average pore size of 5-20 nm.
[0015] In the above process, NaOH selectively swells the amorphous regions of cellulose, embedding the sulfur sites formed in step (1) deep within the secondary channels, while the crystalline regions of cellulose remain intact as a framework. This directional pore-expanding process transfers the sulfur sites from the surface of the biomass matrix into the inner layer, leaving space for subsequent surface grafting of PEI.
[0016] Preferably, in step (3), the concentration of the PEI aqueous solution is 5-15% (w / v), and the solid-liquid ratio is 1:5-1:20 g / mL; the amount of glutaraldehyde added is 1-5% of the volume of the PEI solution, and the preferred primary crosslinking temperature is 40-60℃, and the time is 4-8 h; the amount of epichlorohydrin added is 2-10% of the volume of the PEI solution, and the preferred secondary crosslinking temperature is 50-70℃, and the time is 1-3 h.
[0017] In the above process, glutaraldehyde (GA) is added for primary cross-linking. GA forms Schiff bases with the amino groups of PEI, which makes PEI form an amino-rich cross-linked network on the pore surface and inlet region. Subsequently, epichlorohydrin (ECH) is added for secondary cross-linking. ECH reacts with the residual amino groups of PEI and the hydroxyl groups on the surface of cellulose to form CNC and COC cross-links, constructing a dense three-dimensional surface sieve layer to prevent PEI from dissolving and falling off in strong acid.
[0018] Preferably, in step (4), the hydrochloric acid concentration is 0.05-0.2 M. The HCl atmosphere protects the embedded -SH groups from oxidation, causing the amino groups on the pore surface to be protonated into ammonium groups (-NH3). + This stabilizes the activity of the embedded thiol groups. In the examples, the resulting sulfur-nitrogen gradient adsorbent is designated G-SN-GP.
[0019] The present invention also provides a sulfur-nitrogen gradient porous biomass adsorbent prepared by the method, wherein the adsorbent has a core-shell gradient structure, comprising a core and an outer layer, wherein the core is a sulfur coordination domain rich in thiol groups and disulfide bonds, and the outer layer is an electrostatic sieve layer rich in protonated ammonium groups.
[0020] Preferably, the adsorbent has a sulfur content of 0.5-3.0 wt% and a nitrogen content of 2.0-8.0 wt%, and the mass loss rate after soaking in 3 M HCl for 72 h is less than 5%.
[0021] The present invention also provides the application of the sulfur-nitrogen gradient porous biomass adsorbent, including its addition to a gold precipitation solution to selectively enrich trace amounts of gold, platinum and / or palladium.
[0022] Preferably, the application includes the following steps:
[0023] 1) Add the adsorbent to the gold precipitate solution at a dosage of 0.5-5 g / L, and shake to adsorb at room temperature for 1-4 h;
[0024] 2) Filter and separate the adsorbent loaded with precious metals from the raffinate to achieve selective enrichment of gold, platinum and palladium.
[0025] Preferably, in step 1), the gold immersion solution is the residual solution after copper anode mud has undergone copper separation, chlorination leaching, and controlled potential reduction gold immersion, containing HCl 2-4 M, trace amounts of Au 0.5-10 mg / L, Pt 1-5 mg / L, Pd 1-10 mg / L, and small amounts of Cu 0.5-3 g / L, Se 30-300 mg / L, Te 1-3 g / L, and Fe 0.1-1 g / L.
[0026] Preferably, in step 2), the adsorbent has an adsorption rate of over 99% for Au, Pt, and Pd in the gold immersion solution, while the adsorption rate for Cu, Fe, and Ni is less than 5%.
[0027] Preferably, the application further includes step 3) adsorbent regeneration and desorption liquid closed-loop circulation step: the adsorbent loaded with precious metals and the desorbent are mixed at a solid-liquid ratio of 1:5-1:20, shaken and desorbed for 0.5-2 h, and filtered to obtain desorption liquid and regenerated adsorbent; the desorbent is a 0.5-2 M hydrochloric acid solution containing 0.1-3 M thiourea; the desorption liquid directly recovers the cathode precious metal through electrolysis, and the thiourea mother liquor after electrolysis is returned to the desorption process for recycling after replenishing losses, so as to achieve zero emission of thiourea.
[0028] Preferably, after the regenerated adsorbent is recycled 5 times, the adsorption performance of Au, Pt and Pd decreases by less than 10%.
[0029] The beneficial effects of the technical solution provided by this invention include at least the following:
[0030] This invention provides a method for preparing a sulfur-nitrogen gradient pore biomass adsorbent. The core concept is to use biomass materials as a matrix and construct a gradient pore structure through the following specific time sequence steps: firstly, introducing -SH / -SS- soft coordination domains into the inner layer (amorphous cellulose region); secondly, enlarging the pores through alkali treatment to embed sulfur sites; and finally, grafting PEI only on the pore surface and at the inlet to form -NH3. + Electrostatic sieve stratification. This forms a gradient pore structure in which "the outer layer electrostatically repels base metal cations and the inner layer softly coordinates and captures noble metal chloride anions", which functions similarly to a molecular sieve.
[0031] Among them, the outer layer -NH3 + Protonation of Cu in a strongly acidic medium after gold immersion solution 2+ Fe 3+ Ni 2+Base metal cations exhibit electrostatic repulsion; simultaneously, AuCl4 is enriched through the Donnan effect. - PtCl6 2- PdCl4 2- Plasmon anions;
[0032] Inner layer -SH / -SS-: Specific soft coordination (S→Au, S→Pt, S→Pd) occurs for noble metal ions (soft acids) crossing the electrostatic layer, forming stable covalent coordination bonds;
[0033] The key to the aforementioned timing control is that if PEI is grafted first and then thiourea is modified, PEI will block the pores, preventing thiourea from entering the inner layer; if the modification is simultaneous, the two groups will compete disorderly, making it impossible to form a gradient. Therefore, the specific timing of this invention is a necessary condition for forming a gradient structure. Detailed Implementation
[0034] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with specific embodiments.
[0035] Example 1
[0036] Preparation of G-SN-GP
[0037] (1) 100 g of garlic peel powder (60 mesh) was mixed with 0.1 L of 20% (w / v) ammonium thiocyanate solution, and the pH was adjusted to 10 with ammonia water. The mixture was placed in a hydrothermal reactor and reacted at 170℃ for 2 h. After the reaction was completed, the mixture was cooled, repeatedly filtered and washed with deionized water until the filtrate was neutral, and dried at 80℃ to obtain the sulfur-modified matrix. XPS showed that S 2p had peaks at 162.3 eV and 163.5 eV, corresponding to -SH and -SS-, with a sulfur content of 1.8 wt%.
[0038] (2) Mix 50 g of sulfur-modified matrix with 1 L of 1 M NaOH solution and stir at 60 °C for 4 h. After the reaction is complete, wash until neutral and dry at 80 °C to obtain a porous sulfur-embedded matrix.
[0039] (3) Mix 30 g of porous sulfur-embedded matrix with 300 mL of 10% (w / v) PEI solution, add 15 mL of glutaraldehyde (GA, 50% by mass) aqueous solution, and stir at 50 °C for 6 h. Add 30 mL of epichlorohydrin (ECH) to the reaction system, raise the temperature to 60 °C, and continue stirring for 2 h.
[0040] (4) After the reaction is complete, the product is thoroughly washed with deionized water until no impurities remain, then activated by soaking in 0.1 M HCl for 1 h, and finally washed with deionized water until neutral. The product is then dried in a vacuum drying oven at 50 °C until constant weight to obtain G-SN-GP.
[0041] XPS displays N 1s at 401.5 eV (-NH3). + S 2p at 162.5 eV (intercalated -SH retained); SEM-EDS line scan showed that the N / S atomic ratio on the particle surface was about 8:1 and the N / S ratio at the cross-section center was about 1:5, confirming the gradient structure.
[0042] Example 2
[0043] Selective adsorption in post-gold immersion solution (GRRS)
[0044] The solution after gold leaching was taken from a copper anode mud wet processing production line. It is the residual solution after copper slag has been chlorinated and leached (HCl + NaClO3), and sodium bisulfite was added at a controlled potential to reduce the gold leaching. Typical components and concentrations are: HCl 3 M, Cu 1.85 g / L, Se 185 mg / L, Te 2.45 g / L, Au 4.2 mg / L, Pt 3.8 mg / L, Pd 8.5 mg / L, Fe 0.65 g / L, ORP 520 mV (vs SCE).
[0045] Take 100 mL of the gold-precipitated solution and place it in a 250 mL Erlenmeyer flask. Add 0.3 g of the G-SN-GP adsorbent prepared in Example 1 (3 g / L). Shake and adsorb for 2 h at 25 °C and 150 r / min. After adsorption, filter and determine the concentration of each element in the filtrate.
[0046] Results: The adsorption rates of precious metals were: Au 99.6%, Pt 99.3%, and Pd 99.5%; the adsorption rates of impurity metal elements were: Cu 1.0%, Fe 0.6%, and Ni 0.5%. This indicates that the adsorbent has extremely high selectivity for trace precious metals in the gold precipitation solution containing 3 M HCl, which is highly oxidizing and contains multiple elements.
[0047] Example 3
[0048] Antioxidant stability and cycling performance
[0049] G-SN-GP was subjected to adsorption-desorption cycling experiments in the above-mentioned gold precipitation solution (ORP 520 mV). The desorbent was 0.5 M thiourea / 1 M HCl, with a solid-liquid ratio of 1:10, and desorption was performed by shaking for 1 h. After each desorption, XPS analysis showed that the intensity of the S 2p: 162.5 eV peak (-SH / -SS-) decreased by only 8%, demonstrating that the -SS- crosslinking structure effectively protected the embedded thiol groups. After 5 cycles, the adsorption rates of Au, Pt, and Pd remained above 98.8%, 98.5%, and 98.2%, respectively, with a performance degradation of less than 10%.
[0050] Example 4
[0051] Desorption liquid closed-loop circulation
[0052] G-SN-GP loaded with noble metals was desorbed using 0.5 M thiourea / 1 M HCl. The eluent composition was: Au 150 mg / L, Pt 120 mg / L, Pd 250 mg / L, 0.5 M thiourea, and 1 M HCl. This eluent was placed in a stainless steel cathode / graphite anode electrolytic cell at a current density of 50 A / m². 2 Electrolysis was performed for 4 hours. >98% of the precious metals were recovered by cathode deposition. After electrolysis, the thiourea concentration in the solution decreased to 1.85 M. After adding 0.15 M thiourea, the solution was returned to the desorption process. After three cycles, the desorption efficiency showed no significant decrease.
[0053] Example 5
[0054] Column-type continuous adsorption experiment
[0055] 1.5 g of G-SN-GP adsorbent was packed into a glass column with an inner diameter of 1.0 cm and a height of 25 cm. The gold-precipitated solution (Au 4.2 mg / L, Pt 3.8 mg / L, Pd 8.5 mg / L, HCl 3 M) was continuously passed through the column at a flow rate of 1.0 mL / min. After 200 min of operation, the concentrations of Au, Pt, and Pd in the effluent remained close to the detection limits, indicating that the adsorbent maintained a high efficiency in capturing trace precious metals in continuous flow mode.
[0056] Comparative Example 1
[0057] SN-GP without thiourea pre-modification
[0058] Prepared according to steps (2)-(4) of Example 1, omitting the hydrothermal thiourea pre-modification in step (1). Tested in the same gold immersion solution: Au adsorption rate 92%, Pt adsorption rate 68%, Pd adsorption rate 55%, Cu adsorption rate 12%. This demonstrates that in the absence of intercalated sulfide domains, Pt / Pd adsorption is severely suppressed, and base metal co-adsorption increases.
[0059] Comparative Example 2
[0060] S-GP without PEI grafting
[0061] Only steps (1)-(2) of Example 1 were performed, without the PEI grafting and crosslinking of steps (3)-(4). Tests were conducted in the gold immersion solution: Au adsorption rate 85%, Pt adsorption rate 45%, Pd adsorption rate 38%, and Cu adsorption rate 25%. This demonstrates that in the absence of surface electrostatic sieve stratification, base metals are largely co-adsorbed, and the adsorption rate of Au decreases due to the lack of electrostatic enrichment.
[0062] Comparative Example 3
[0063] Synchronous modification (non-timing control)
[0064] Thiourea and PEI were simultaneously added to biomass powder for hydrothermal reaction and cross-linking. The product, in the post-gold precipitation solution, showed the following adsorption rates: Au 78%, Pt 52%, Pd 48%, and Cu 35%. This demonstrates that the randomly distributed sulfur / nitrogen groups cannot form a gradient sieve, resulting in extremely poor selectivity.
[0065] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.
Claims
1. A method for preparing a sulfur-nitrogen gradient porous biomass adsorbent, characterized in that, Includes the following steps: (1) Hydrothermal ammonium thiocyanate pre-modification: Biomass powder is mixed with thiourea aqueous solution, the pH value is adjusted to 8-11, and the mixture is hydrothermally reacted at 120-180℃ for 1-4 h to form a sulfur-modified matrix; (2) Alkali treatment for directional pore expansion and sulfur site embedding: The sulfur-modified matrix obtained in step (1) is mixed with sodium hydroxide solution and stirred at 50-70℃ for 2-5 h. The reaction product is washed until neutral and dried to obtain a porous sulfur embedded matrix. (3) PEI surface grafting and double crosslinking: The porous sulfur embedded matrix obtained in step (2) is mixed with a polyethyleneimine (PEI) aqueous solution, glutaraldehyde (GA) is added for primary crosslinking, and then epichlorohydrin (ECH) is added for secondary crosslinking; (4) Protic acid activation: The product obtained in step (3) is activated with hydrochloric acid and then dried under vacuum to obtain the biomass adsorbent with sulfur-nitrogen gradient pore structure.
2. The method for preparing the sulfur-nitrogen gradient porous biomass adsorbent according to claim 1, characterized in that, In step (1), the biomass powder is garlic peel, garlic stalks or rice straw, with a particle size of 40-80 mesh; the concentration of the ammonia thiocyanate aqueous solution is 30-60% (w / v), and the solid-liquid ratio is 1:1-1:5 g / mL.
3. The method for preparing the sulfur-nitrogen gradient porous biomass adsorbent according to claim 1, characterized in that, In step (2), the concentration of the sodium hydroxide solution is 0.5-2 M, and the solid-liquid ratio is 1:10-1:30 g / mL; the specific surface area of the obtained porous sulfur embedded matrix is 5-15 m². 2 / g, with an average pore size of 5-20 nm.
4. The method for preparing the sulfur-nitrogen gradient porous biomass adsorbent according to claim 1, characterized in that, In step (3), the concentration of the PEI aqueous solution is 5-15% (w / v), and the solid-liquid ratio is 1:5-1:20 g / mL; the amount of glutaraldehyde added is 1-5% of the volume of the PEI solution, preferably the primary crosslinking temperature is 40-60℃, and the time is 4-8 h; the amount of epichlorohydrin added is 2-10% of the volume of the PEI solution, preferably the secondary crosslinking temperature is 50-70℃, and the time is 1-3 h.
5. The method for preparing the sulfur-nitrogen gradient porous biomass adsorbent according to claim 1, characterized in that, In step (4), the concentration of hydrochloric acid is 0.05-0.2 M.
6. The sulfur-nitrogen gradient porous biomass adsorbent prepared by the method according to any one of claims 1 to 5, characterized in that, The adsorbent has a core-shell gradient structure, comprising a core and an outer layer, wherein the core is a sulfur coordination domain rich in thiol groups and disulfide bonds, and the outer layer is an electrostatic sieve layer rich in protonated ammonium groups.
7. The sulfur-nitrogen gradient porous biomass adsorbent according to claim 6, characterized in that, The adsorbent has a sulfur content of 0.5-3.0 wt% and a nitrogen content of 2.0-8.0 wt%, and its mass loss rate after soaking in 3 M HCl for 72 h is less than 5%.
8. The application of the sulfur-nitrogen gradient porous biomass adsorbent prepared by the method according to any one of claims 1 to 5, or the sulfur-nitrogen gradient porous biomass adsorbent according to claim 6 or 7, characterized in that, This includes adding it to the gold immersion solution to selectively enrich trace amounts of gold, platinum, and / or palladium.
9. The application according to claim 8, characterized in that, The application includes the following steps: 1) Add the adsorbent to the gold precipitate solution at a dosage of 0.5-5 g / L, and shake to adsorb at room temperature for 1-4 h; 2) Filter and separate the adsorbent loaded with precious metals from the raffinate to achieve selective enrichment of gold, platinum and palladium.
10. The application according to claim 8, characterized in that, In step 1), the gold immersion solution is the residual solution after copper anode mud has undergone copper separation, chlorination leaching, and controlled potential reduction gold immersion. It contains HCl 2-4 M, trace amounts of Au 0.5-10 mg / L, Pt 1-5 mg / L, Pd 1-10 mg / L, and small amounts of Cu 0.5-3 g / L, Se 30-300 mg / L, Te 1-3 g / L, and Fe 0.1-1 g / L. And / or, the application further includes step 3) adsorbent regeneration and desorption liquid closed-loop circulation step: the adsorbent loaded with precious metals is mixed with the desorbent at a solid-liquid ratio of 1:5-1:20, shaken and desorbed for 0.5-2 h, and filtered to obtain the desorption liquid and regenerated adsorbent; the desorbent is a 0.5-2 M hydrochloric acid solution containing 0.1-3 M thiourea; the desorption liquid directly recovers the cathode precious metal through electrolysis, and the thiourea mother liquor after electrolysis is returned to the desorption process for recycling after replenishing losses, so as to achieve zero emission of thiourea.