Method for separating low-content precious metal rhodium from copper sulfate solution

Abstract

The invention relates to the technical field of precious metal separation, in particular to a method for separating low-content precious metal rhodium from a copper sulfate solution. The method comprises the following steps: removing iron impurities in the copper sulfate solution, adjusting the pH value of the copper sulfate solution by adopting an automatic titration system, and carrying out solid-liquid separation on the adjusted copper sulfate solution to obtain the purified copper sulfate solution. High-efficiency separation and recovery of rhodium are realized through a multi-stage synergistic process, in the pretreatment section, hydrogen peroxide oxidation is combined with sulfuric acid for acid regulation, iron impurities are promoted to be converted into filterable ferric hydroxide precipitates, and it is ensured that the solution purity meets the subsequent adsorption requirement; the nano modified adsorbent is based on a natural material, the selective chelation capability on rhodium ions is enhanced through chemical modification, and meanwhile, a porous nano structure is constructed to improve the adsorption efficiency. The super-gravity field technology utilizes a centrifugal force field generated by high-speed rotation to reinforce the rapid mixing and separation process of an adsorbent and a solution, so that efficient capture of rhodium ions and accurate separation of copper impurities are realized.

Description

Technical Field

[0001] This invention relates to the field of precious metal separation technology, specifically a method for separating low-content rhodium from copper sulfate solution. Background Technology

[0002] Rhodium is a precious metal belonging to the platinum group metals. It is a silvery-white metal with extremely high corrosion resistance and stability, commonly used in high-temperature and chemical reaction environments. Rhodium has a very high melting point and is not easily oxidized. Due to its rarity, excellent catalytic properties, and antioxidant properties, rhodium is widely used in automotive catalysts, the chemical industry, and jewelry manufacturing, especially in catalysts to reduce harmful substances in automobile exhaust. Rhodium is scarce in nature, making it expensive and one of the most valuable metals.

[0003] Existing technologies for separating low-content rhodium from copper sulfate solutions suffer from several drawbacks: First, commonly used adsorbents are typically natural minerals or inefficient synthetic materials, exhibiting poor adsorption performance and selectivity, resulting in low rhodium recovery rates and easy adsorption of impurities such as copper, affecting recovery purity. Second, traditional membrane extraction technologies are inefficient, especially when processing rhodium-containing solutions, due to poor membrane selectivity and mass transfer efficiency, and long processing times. Third, many adsorbents are not recyclable or reusable after use, leading to significant waste and resource waste, and increased production costs. Finally, traditional rhodium ion recovery technologies are inefficient and susceptible to interference from other metal ions, resulting in low recovery purity. In summary, existing technologies face significant challenges in the efficient separation and recovery of rhodium.

[0004] Therefore, the present invention provides a method for separating low-content rhodium from copper sulfate solution to solve the aforementioned related technical problems. Summary of the Invention

[0005] The purpose of this invention is to provide a method for separating low-content rhodium from copper sulfate solution. High-purity rhodium metal is directly obtained through ionic liquid elution and electrodeposition, reducing the energy consumption of multi-step purification in traditional processes. The adsorbent utilizes bio-enzymatic regeneration technology, enabling multiple cycles and reducing material consumption costs. Wastewater undergoes deep treatment and closed-loop reuse, significantly reducing fresh water consumption and wastewater discharge, meeting green manufacturing standards. The overall process achieves the dual goals of efficient resource utilization and environmental pollution control through technological innovation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A method for separating low-content rhodium from a copper sulfate solution, the method comprising: To remove iron impurities from the copper sulfate solution, an automatic titration system was used to adjust the pH value of the copper sulfate solution. The adjusted copper sulfate solution was then subjected to solid-liquid separation to obtain a purified copper sulfate solution. Rice husk ash is calcined and activated. After activation, it is mixed with chitosan to prepare an adsorbent. The adsorbent is placed in an acetic acid solution and stirred to obtain a homogeneous slurry. A modifier is added to the homogeneous slurry to modify the adsorbent and obtain a composite adsorbent. Rhodium ions were separated by membrane extraction using purified copper sulfate solution and composite adsorbent, and a DC electric field was applied to both sides of the membrane to obtain a rhodium-rich slurry. The rhodium-rich slurry was eluted and enhanced using ultrasonic oscillation technology to obtain a rhodium ion source. The rhodium ion source was then electrodeposited to obtain a rhodium deposit layer. The rhodium deposit layer was then processed to obtain rhodium powder. The used composite adsorbent was collected and recycled.

[0007] Furthermore, the method of adjusting the pH value of the copper sulfate solution using an automatic titration system includes the following steps: Add 0.08%–0.1% (by mass) of 30% hydrogen peroxide and 3%–5% (by mass) of 98% concentrated sulfuric acid to the copper sulfate solution. Stir at 60–70°C and automatically titrate with sodium hydroxide solution to adjust the pH of the copper sulfate solution to 3.85–3.95.

[0008] Furthermore, the specific preparation method of the composite adsorbent is as follows: A1: Calcine rice husk ash at 500-550℃ for 1.5-2 hours. After cooling, mix rice husk ash and chitosan at a mass ratio of 1:4-5 to obtain a composite product. Add acetic acid solution at a mass ratio of 1:1.2-1.5 and a concentration of 1.8% to the composite product and stir at 80-85℃ for 3-5 hours to obtain a homogeneous slurry. The rice husk ash was purchased from Shengmei Huarui Activated Carbon Plant.

[0009] A2: Add 15% to 17% of the chitosan mass of the thiocarbamate modifier to the homogenized slurry in three equal portions, stirring for 25 to 35 minutes after each addition. After the addition is complete, heat to 60 to 70°C and stir again for 5 to 6 hours. After the reaction is complete, wash the homogenized slurry with deionized water and adjust the pH value to 4.3 to 4.7. The thiocarbamate modifier was purchased from Zhejiang Wansheng Chemical Co., Ltd.

[0010] A3: Add 4%–5% by weight of nano-titanium dioxide to a homogeneous slurry and disperse it ultrasonically to obtain a blended slurry. Add 0.5% by weight of silane coupling agent to the blended slurry and react at 55–65°C for 1.5–2.5 h to form a three-dimensional network gel structure. After aging the gel for 23–25 h, wash it with ethanol 2–4 times to obtain a gel slurry. The nano-titanium dioxide has a particle size of 18nm, and the silane coupling agent was purchased from Hangzhou Jessica Chemical Co., Ltd.

[0011] A4: The gel slurry is processed by a high-pressure homogenizer at 15-25 MPa to obtain composite particles. The composite particles are then activated at 100-110℃ for 1-3 hours to obtain the composite adsorbent.

[0012] It should be noted that a high-pressure homogenizer is a device that uses high-pressure fluid to process materials, mainly for the homogenization, dispersion, emulsification, and refinement of liquids or suspensions. It refines and evenly distributes particles or droplets in the material by subjecting it to high-pressure passage through specific nozzles or valves, through high-speed collision, shearing, and friction.

[0013] Furthermore, the step of preparing the composite particles in A4 is as follows: The spray dryer is set with an inlet air temperature of 180-200℃, an outlet air temperature of 90-100℃, and an atomizing disc rotation speed of 17500-18500 rpm. The gel slurry is fed into the spray dryer to obtain composite particles.

[0014] Furthermore, the specific preparation steps of the rhodium-rich slurry are as follows: B1: Mix the composite adsorbent with deionized water at a solid-liquid ratio of 0.1-0.12 g / mL to obtain an initial adsorbent slurry. Degas the initial adsorbent slurry under vacuum for 25-35 min and pour it into a high-shear emulsifier for shearing for 25-35 min to obtain an adsorbent slurry. B2: The adsorbent slurry and the purified copper sulfate solution are respectively transported to both sides of the PTFE hollow fiber membrane module. Titanium-based electrodes are installed on both sides of the membrane module and a DC electric field is applied. When rhodium ions migrate to the surface of the composite adsorbent, a rhodium-rich slurry is obtained.

[0015] It should be noted that the adsorbent slurry and the purified copper sulfate solution are delivered to both sides of the membrane by independent circulation pumps. Differential pressure sensors are installed on both sides of the membrane to monitor the pressure difference in real time and automatically adjust the speed of the circulation pumps to ensure that the pressure difference is strictly controlled at 0.1 MPa to avoid wetting. The system is designed with a circulation flow rate of 1.2 L / min to ensure turbulent flow (Reynolds number Re≥4000) and improve mass transfer efficiency.

[0016] Simultaneously, titanium-based electrodes (with corrosion-resistant coating) are installed on both sides of the membrane module, and a DC electric field (voltage 10V, current density 5mA / cm²) is applied. 2 The electric field parameters are controlled in real time via a programmable power supply and equipped with a current monitoring module to ensure current fluctuations are ≤±2%. The direction of the electric field is perpendicular to the direction of fluid flow, forming a "field-fluid" synergistic mass transfer field that promotes the directional migration of rhodium ions.

[0017] Furthermore, the mass transfer coefficient was determined using a tracer method (such as Na⁺ ions): 0.1 mol / L sodium chloride solution was added to the purified copper sulfate solution side, and the change in conductivity on the adsorbent side was monitored using a conductivity meter to calculate the mass transfer coefficient. Experiments verified that the mass transfer coefficient was increased by 40% compared to the case without an electric field. The residence time in the mixing chamber was monitored using a high-speed camera to ensure it was ≤3 seconds.

[0018] In addition, an online ICP-MS was installed at the membrane module outlet to monitor the rhodium content (target ≤0.007 mg / L) and copper content (target ≥90 g / L) on the treated liquid side in real time. X-ray fluorescence spectroscopy analysis of the adsorbent slurry side confirmed that the rhodium adsorption rate was ≥99.5% and the copper co-adsorption rate was ≤1.0%.

[0019] Furthermore, the specific steps for obtaining the rhodium deposition layer are as follows: C1: Prepare the ionic liquid, immerse the rhodium-rich slurry in the ionic liquid, and use ultrasonic vibration technology to vibrate at 30-40℃ for 0.8-1.2h. Then separate the eluent and the standby adsorbent, filter the eluent and treat the standby adsorbent. C2: Gradually add sodium hydroxide solution with a concentration of 0.18–0.22 mol / L to the filtered eluent to adjust the pH to 9.4–9.6; C3: Hydrochloric acid, selenic acid, and emulsifier are mixed in a mass ratio of 9–10:5–6:1 to form a transparent microemulsion system. A vertically aligned array of carbon nanotubes is grown on a titanium substrate using chemical vapor deposition. The electrode is activated with 0.4–0.6 mol / L sulfuric acid, and electrodeposition is performed at 24–26 °C using a dual-pulse power supply to obtain a rhodium deposition layer.

[0020] The emulsifier used was OP-10, which was purchased from Shanghai Kaijie Chemical Co., Ltd. Vertically aligned carbon nanotube arrays were grown on a titanium substrate using chemical vapor deposition, and after acid washing and purification, the specific surface area reached 800 m². 2 / g, and the pulse electrodeposition parameters are: A dual-pulse power supply is used with a frequency of 120Hz and a duty cycle of 45%, and the current density is precisely controlled at 15mA / cm². 2 An electrolyte circulation rate of 0.5 m / s ensures uniform mass transfer.

[0021] Furthermore, the preparation of the ionic liquid includes: Lithium chloride solution, urea, and deionized water were mixed in a mass ratio of 1:1.6-1.8:23-24 to prepare a mixture. The mixture was then magnetically stirred at 30-35°C to obtain an ionic liquid. The urea was purchased from Luxi Fertilizer Company.

[0022] Furthermore, the process of treating the spare adsorbent involves: The standby adsorbent is pretreated to obtain a recovery solution. The recovery solution is then immersed in the treatment solution. After immersion, it is washed with deionized water until neutral and dried at 35–45°C for 1.5–2.5 h to obtain a reusable adsorbent.

[0023] Furthermore, the pretreatment of the standby adsorbent includes: The standby adsorbent was washed in 2 to 4 batches with a 0.13–0.17 mol / L sodium hydroxide solution, with each wash lasting 3 to 5 minutes. The washed standby adsorbent was then dried to constant weight under vacuum at 55–65°C.

[0024] Furthermore, the treatment solution includes: adding 0.4% to 0.6% (by mass) of cellulase and 0.9% to 1.1% (by mass) of lactic acid bacteria to the recovered solution, and then adjusting the volume to n times the volume of the pretreated solution using a 0.04 to 0.06 mol / L sodium chloride solution, where n is 5. It should be noted that cellulase (enzyme activity ≥1800 U / g) was dried using a low-temperature vacuum drying method (40℃, 0.1 MPa) for 2 hours to ensure stable enzyme activity, while lactic acid bacteria (live count ≥10) 8 The CFU / g of the lactic acid bacteria were activated from the freeze-dried bacterial powder, inoculated into MRS medium (37℃, 24 hours) and amplified to the target viable count. The lactic acid bacteria were purchased from Shenyang Sansheng Lactic Acid Bacteria Co., Ltd., and the cellulase was selected from Lunan Pharmaceutical Group.

[0025] The process involves immersing the recovered solution completely in the treatment solution and then placing it in a shaking incubator at 40–50°C for enzymatic hydrolysis.

[0026] Compared with the prior art, the beneficial effects of the present invention are: This invention achieves efficient separation and recovery of rhodium through a multi-stage synergistic process. The pretreatment stage uses hydrogen peroxide oxidation combined with sulfuric acid adjustment to convert iron impurities into filterable ferric hydroxide precipitate, ensuring the solution purity meets subsequent adsorption requirements. The nano-modified adsorbent, based on natural materials, enhances its selective chelation ability for rhodium ions through chemical modification, while simultaneously constructing a porous nanostructure to improve adsorption efficiency. The hypergravity field technology utilizes the centrifugal force field generated by high-speed rotation to strengthen the rapid mixing and separation process between the adsorbent and the solution, achieving efficient capture of rhodium ions and precise separation of copper impurities.

[0027] Its advantages lie in the dual improvement of environmental protection and economy throughout the entire process. High-purity rhodium metal is directly obtained through ionic liquid elution and electrodeposition technology, reducing the energy consumption of multi-step purification in traditional processes. The adsorbent adopts bio-enzymatic regeneration technology, enabling multiple cycles and reducing material consumption costs. Wastewater is deeply treated and reused in a closed loop, significantly reducing the amount of fresh water used and wastewater discharge, meeting green manufacturing standards. The overall process achieves the dual goals of efficient resource utilization and environmental pollution control through technological innovation. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 A flowchart of a method for separating low-content rhodium from copper sulfate solution provided by the present invention; Detailed Implementation

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1 A method for separating low concentrations of the precious metal rhodium from a copper sulfate solution, such as Figure 1 As shown, the method includes: To remove iron impurities from the copper sulfate solution, an automatic titration system was used to adjust the pH value of the copper sulfate solution. The adjusted copper sulfate solution was then subjected to solid-liquid separation to obtain a purified copper sulfate solution. Rice husk ash is calcined and activated. After activation, it is mixed with chitosan to prepare an adsorbent. The adsorbent is placed in an acetic acid solution and stirred to obtain a homogeneous slurry. A modifier is added to the homogeneous slurry to modify the adsorbent and obtain a composite adsorbent. Rhodium ions were separated by membrane extraction using purified copper sulfate solution and composite adsorbent, and a DC electric field was applied to both sides of the membrane to obtain a rhodium-rich slurry. The rhodium-rich slurry was eluted and enhanced using ultrasonic oscillation technology to obtain a rhodium ion source. The rhodium ion source was then electrodeposited to obtain a rhodium deposit layer. The rhodium deposit layer was then processed to obtain rhodium powder. The used composite adsorbent was collected and recycled.

[0032] Furthermore, the method of adjusting the pH value of the copper sulfate solution using an automatic titration system includes the following steps: Add 0.08% (by mass) of 30% hydrogen peroxide and 3% (by mass) of 98% concentrated sulfuric acid to the copper sulfate solution. Stir at 60°C and automatically titrate with sodium hydroxide solution to adjust the pH of the copper sulfate solution to 3.85.

[0033] Furthermore, the specific preparation method of the composite adsorbent is as follows: A1: Calcine rice husk ash at 500℃ for 1.5h. After cooling, mix rice husk ash and chitosan at a mass ratio of 1:4 to obtain a composite product. Add acetic acid solution with a mass ratio of 1:1.2 and a concentration of 1.8% to the composite product and stir at 80℃ for 3h to obtain a homogeneous slurry. The rice husk ash was purchased from Shengmei Huarui Activated Carbon Plant.

[0034] A2: Add 15% (by weight of chitosan) of thiocarbamate modifier to the homogeneous slurry in three equal portions, stirring for 25 minutes after each addition. After the addition is complete, heat to 60°C and stir again for 5 hours. After the reaction is complete, wash the homogeneous slurry with deionized water to restore the pH value to 4.3. The thiocarbamate modifier was purchased from Zhejiang Wansheng Chemical Co., Ltd.

[0035] A3: Add 4% by weight of nano-titanium dioxide to the homogeneous slurry and disperse it ultrasonically to obtain a blended slurry. Add 0.4% by weight of silane coupling agent to the blended slurry and react at 55°C for 1.5 h to form a three-dimensional network gel structure. After the gel is aged for 23 h, wash it twice with ethanol to obtain a gel slurry. The nano-titanium dioxide has a particle size of 18nm, and the silane coupling agent was purchased from Hangzhou Jessica Chemical Co., Ltd.

[0036] A4: The gel slurry was processed by a high-pressure homogenizer at 15 MPa to obtain composite particles. The composite particles were then activated at 100°C for 1 hour to obtain the composite adsorbent.

[0037] Furthermore, the step of preparing the composite particles in A4 is as follows: The spray dryer is set with an inlet air temperature of 180℃, an outlet air temperature of 90℃, and an atomizing disc rotation speed of 17500rpm. The gel slurry is fed into the spray dryer to obtain composite particles.

[0038] Furthermore, the specific preparation steps of the rhodium-rich slurry are as follows: B1: The composite adsorbent and deionized water were mixed at a solid-liquid ratio of 0.1 g / mL to obtain an initial adsorbent slurry. The initial adsorbent slurry was degassed under vacuum for 25 min and then poured into a high-shear emulsifier for shearing for 25 min to obtain the adsorbent slurry. B2: The adsorbent slurry and the purified copper sulfate solution are respectively transported to both sides of the PTFE hollow fiber membrane module. Titanium-based electrodes are installed on both sides of the membrane module and a DC electric field is applied. When rhodium ions migrate to the surface of the composite adsorbent, a rhodium-rich slurry is obtained.

[0039] It should be noted that the adsorbent slurry and the purified copper sulfate solution are delivered to both sides of the membrane by independent circulation pumps. Differential pressure sensors are installed on both sides of the membrane to monitor the pressure difference in real time and automatically adjust the speed of the circulation pumps to ensure that the pressure difference is strictly controlled at 0.1 MPa to avoid wetting. The system is designed with a circulation flow rate of 1.2 L / min to ensure turbulent flow (Reynolds number Re≥4000) and improve mass transfer efficiency.

[0040] Simultaneously, titanium-based electrodes (with corrosion-resistant coating) are installed on both sides of the membrane module, and a DC electric field (voltage 10V, current density 5mA / cm²) is applied. 2 The electric field parameters are controlled in real time via a programmable power supply and equipped with a current monitoring module to ensure current fluctuations are ≤±2%. The direction of the electric field is perpendicular to the direction of fluid flow, forming a "field-fluid" synergistic mass transfer field that promotes the directional migration of rhodium ions.

[0041] Furthermore, the mass transfer coefficient was determined using a tracer method (such as Na⁺ ions): 0.1 mol / L sodium chloride solution was added to the purified copper sulfate solution side, and the change in conductivity on the adsorbent side was monitored using a conductivity meter to calculate the mass transfer coefficient. Experiments verified that the mass transfer coefficient was increased by 40% compared to the case without an electric field. The residence time in the mixing chamber was monitored using a high-speed camera to ensure it was ≤3 seconds.

[0042] In addition, an online ICP-MS was installed at the membrane module outlet to monitor the rhodium content (target ≤0.007 mg / L) and copper content (target ≥90 g / L) on the treated liquid side in real time. X-ray fluorescence spectroscopy analysis of the adsorbent slurry side confirmed that the rhodium adsorption rate was ≥99.5% and the copper co-adsorption rate was ≤1.0%.

[0043] Furthermore, the specific steps for obtaining the rhodium deposition layer are as follows: C1: Prepare the ionic liquid, immerse the rhodium-rich slurry in the ionic liquid, and use ultrasonic vibration technology to vibrate at 30°C for 0.8h. Then separate the eluent and the standby adsorbent, filter the eluent and treat the standby adsorbent. C2: Gradually add a 0.18 mol / L sodium hydroxide solution to the filtered eluent to adjust the pH to 9.4; C3: Hydrochloric acid, selenic acid, and emulsifier are mixed in a mass ratio of 9:5:1 to form a transparent microemulsion system. A vertically aligned array of carbon nanotubes is grown on a titanium substrate using chemical vapor deposition. The electrode is activated with 0.4 mol / L sulfuric acid, and electrodeposition is performed at 24°C using a dual-pulse power supply to obtain a rhodium deposition layer.

[0044] The emulsifier used was OP-10, which was purchased from Shanghai Kaijie Chemical Co., Ltd. Vertically aligned carbon nanotube arrays were grown on a titanium substrate using chemical vapor deposition, and after acid washing and purification, the specific surface area reached 800 m². 2 / g, and the pulse electrodeposition parameters are: A dual-pulse power supply is used with a frequency of 120Hz and a duty cycle of 45%, and the current density is precisely controlled at 15mA / cm². 2 An electrolyte circulation rate of 0.5 m / s ensures uniform mass transfer.

[0045] Furthermore, the preparation of the ionic liquid includes: Lithium chloride solution, urea, and deionized water were mixed in a mass ratio of 1:1.6:23 to prepare a mixture. The mixture was then magnetically stirred at 30°C to obtain an ionic liquid. The urea was purchased from Luxi Fertilizer Company.

[0046] Furthermore, the process of treating the spare adsorbent involves: The standby adsorbent was pretreated to obtain a recovery solution, which was then immersed in the treatment solution. After immersion, the solution was washed with deionized water until neutral and dried at 35°C for 1.5 hours to obtain a reusable adsorbent.

[0047] Furthermore, the pretreatment of the standby adsorbent includes: The standby adsorbent was washed twice with a 0.13 mol / L sodium hydroxide solution, with each washing session lasting 3 minutes. The washed standby adsorbent was then dried to constant weight under vacuum at 55°C.

[0048] Furthermore, the treatment solution includes: adding 0.4% (by mass) of cellulase and 0.9% (by mass) of lactic acid bacteria to the recovered solution, and then adjusting the volume to n times the volume of the pretreated solution using 0.04 mol / L sodium chloride solution, where n is 5. It should be noted that cellulase (enzyme activity ≥1800 U / g) was dried using a low-temperature vacuum drying method (40℃, 0.1 MPa) for 2 hours to ensure stable enzyme activity, while lactic acid bacteria (live count ≥10) 8The CFU / g of the lactic acid bacteria were activated from the freeze-dried bacterial powder, inoculated into MRS medium (37℃, 24 hours) and amplified to the target viable count. The lactic acid bacteria were purchased from Shenyang Sansheng Lactic Acid Bacteria Co., Ltd., and the cellulase was selected from Lunan Pharmaceutical Group.

[0049] The process involves immersing the recovered solution completely in the treatment solution and then placing it in a 40°C shaking incubator for enzymatic hydrolysis.

[0050] Example 2 The preparation method for separating low-content rhodium from copper sulfate solution provided in this embodiment is basically the same as that in Example 1. The main difference lies in the specific composition and ratio of the raw materials used. The method for separating low-content rhodium from copper sulfate solution in this embodiment includes: To remove iron impurities from the copper sulfate solution, an automatic titration system was used to adjust the pH value of the copper sulfate solution. The adjusted copper sulfate solution was then subjected to solid-liquid separation to obtain a purified copper sulfate solution. Rice husk ash is calcined and activated. After activation, it is mixed with chitosan to prepare an adsorbent. The adsorbent is placed in an acetic acid solution and stirred to obtain a homogeneous slurry. A modifier is added to the homogeneous slurry to modify the adsorbent and obtain a composite adsorbent. Rhodium ions were separated by membrane extraction using purified copper sulfate solution and composite adsorbent, and a DC electric field was applied to both sides of the membrane to obtain a rhodium-rich slurry. The rhodium-rich slurry was eluted and enhanced using ultrasonic oscillation technology to obtain a rhodium ion source. The rhodium ion source was then electrodeposited to obtain a rhodium deposit layer. The rhodium deposit layer was then processed to obtain rhodium powder. The used composite adsorbent was collected and recycled.

[0051] Furthermore, the method of adjusting the pH value of the copper sulfate solution using an automatic titration system includes the following steps: Add 0.09% (by mass) of 30% hydrogen peroxide and 4% (by mass) of 98% concentrated sulfuric acid to a copper sulfate solution. Stir at 65°C and automatically titrate with sodium hydroxide solution to adjust the pH of the copper sulfate solution to 3.9.

[0052] Furthermore, the specific preparation method of the composite adsorbent is as follows: A1: Calcine rice husk ash at 530℃ for 1.8h. After cooling, mix rice husk ash and chitosan at a mass ratio of 1:4.5 to obtain a composite product. Add acetic acid solution with a mass ratio of 1:1.3 and a concentration of 1.8% to the composite product and stir at 83℃ for 4h to obtain a homogeneous slurry. The rice husk ash was purchased from Shengmei Huarui Activated Carbon Plant.

[0053] A2: Add 16% (by weight of chitosan) of thiocarbamate modifier to the homogeneous slurry in three equal portions, stirring for 30 minutes after each addition. After the addition is complete, heat to 65°C and stir again for 5.5 hours. After the reaction is complete, wash the homogeneous slurry with deionized water to restore the pH value to 4.5. The thiocarbamate modifier was purchased from Zhejiang Wansheng Chemical Co., Ltd.

[0054] A3: Add 4.5% by weight of nano-titanium dioxide to the homogeneous slurry and disperse it ultrasonically to obtain a blended slurry. Add 0.4% by weight of silane coupling agent to the blended slurry and react at 60°C for 2 hours to form a three-dimensional network gel structure. After the gel is aged for 24 hours, wash it three times with ethanol to obtain a gel slurry. The nano-titanium dioxide has a particle size of 18nm, and the silane coupling agent was purchased from Hangzhou Jessica Chemical Co., Ltd.

[0055] A4: The gel slurry was processed by a high-pressure homogenizer at 20 MPa to obtain composite particles. The composite particles were then activated at 105℃ for 2 hours to obtain the composite adsorbent.

[0056] Furthermore, the step of preparing the composite particles in A4 is as follows: The spray dryer is set with an inlet air temperature of 190℃, an outlet air temperature of 95℃, and an atomizing disc rotation speed of 18000rpm. The gel slurry is fed into the spray dryer to obtain composite particles.

[0057] Furthermore, the specific preparation steps of the rhodium-rich slurry are as follows: B1: The composite adsorbent and deionized water were mixed at a solid-liquid ratio of 0.11 g / mL to obtain an initial adsorbent slurry. The initial adsorbent slurry was degassed under vacuum for 30 min and then poured into a high-shear emulsifier for shearing for 30 min to obtain the adsorbent slurry. B2: The adsorbent slurry and the purified copper sulfate solution are respectively transported to both sides of the PTFE hollow fiber membrane module. Titanium-based electrodes are installed on both sides of the membrane module and a DC electric field is applied. When rhodium ions migrate to the surface of the composite adsorbent, a rhodium-rich slurry is obtained.

[0058] It should be noted that the adsorbent slurry and the purified copper sulfate solution are delivered to both sides of the membrane by independent circulation pumps. Differential pressure sensors are installed on both sides of the membrane to monitor the pressure difference in real time and automatically adjust the speed of the circulation pumps to ensure that the pressure difference is strictly controlled at 0.1 MPa to avoid wetting. The system is designed with a circulation flow rate of 1.2 L / min to ensure turbulent flow (Reynolds number Re≥4000) and improve mass transfer efficiency.

[0059] Simultaneously, titanium-based electrodes (with corrosion-resistant coating) are installed on both sides of the membrane module, and a DC electric field (voltage 10V, current density 5mA / cm²) is applied. 2 The electric field parameters are controlled in real time via a programmable power supply and equipped with a current monitoring module to ensure current fluctuations are ≤±2%. The direction of the electric field is perpendicular to the direction of fluid flow, forming a "field-fluid" synergistic mass transfer field that promotes the directional migration of rhodium ions.

[0060] Furthermore, the mass transfer coefficient was determined using a tracer method (such as Na⁺ ions): 0.1 mol / L sodium chloride solution was added to the purified copper sulfate solution side, and the change in conductivity on the adsorbent side was monitored using a conductivity meter to calculate the mass transfer coefficient. Experiments verified that the mass transfer coefficient was increased by 40% compared to the case without an electric field. The residence time in the mixing chamber was monitored using a high-speed camera to ensure it was ≤3 seconds.

[0061] In addition, an online ICP-MS was installed at the membrane module outlet to monitor the rhodium content (target ≤0.007 mg / L) and copper content (target ≥90 g / L) on the treated liquid side in real time. X-ray fluorescence spectroscopy analysis of the adsorbent slurry side confirmed that the rhodium adsorption rate was ≥99.5% and the copper co-adsorption rate was ≤1.0%.

[0062] Furthermore, the specific steps for obtaining the rhodium deposition layer are as follows: C1: Prepare the ionic liquid, immerse the rhodium-rich slurry in the ionic liquid, and use ultrasonic vibration technology to vibrate at 35°C for 1 hour. Then separate the eluent and the standby adsorbent, filter the eluent and treat the standby adsorbent. C2: Gradually add a 0.2 mol / L sodium hydroxide solution to the filtered eluent to adjust the pH to 9.5; C3: Hydrochloric acid, selenic acid, and emulsifier are mixed in a mass ratio of 9.5:5.5:1 to form a transparent microemulsion system. A vertically aligned array of carbon nanotubes is grown on a titanium substrate using chemical vapor deposition. The electrode is activated with 0.5 mol / L sulfuric acid, and electrodeposition is performed at 25°C using a dual-pulse power supply to obtain a rhodium deposition layer.

[0063] The emulsifier used was OP-10, which was purchased from Shanghai Kaijie Chemical Co., Ltd. Vertically aligned carbon nanotube arrays were grown on a titanium substrate using chemical vapor deposition, and after acid washing and purification, the specific surface area reached 800 m². 2 / g, and the pulse electrodeposition parameters are: A dual-pulse power supply is used with a frequency of 120Hz and a duty cycle of 45%, and the current density is precisely controlled at 15mA / cm². 2 An electrolyte circulation rate of 0.5 m / s ensures uniform mass transfer.

[0064] Furthermore, the preparation of the ionic liquid includes: Lithium chloride solution, urea, and deionized water were mixed in a mass ratio of 1:1.7:23.5 to prepare a mixture. The mixture was then magnetically stirred at 33°C to obtain an ionic liquid. The urea was purchased from Luxi Fertilizer Company.

[0065] Furthermore, the process of treating the spare adsorbent involves: The standby adsorbent was pretreated to obtain a recovery solution. The recovery solution was then immersed in the treatment solution. After immersion, it was washed with deionized water until neutral and dried at 40°C for 2 hours to obtain a reusable adsorbent.

[0066] Furthermore, the pretreatment of the standby adsorbent includes: The prepared adsorbent was washed three times with a 0.15 mol / L sodium hydroxide solution, with each washing lasting 4 minutes. The washed adsorbent was then dried to constant weight under vacuum at 60°C.

[0067] Furthermore, the treatment solution includes: adding 0.5% (by mass) of cellulase and 1% (by mass) of lactic acid bacteria to the recovered solution, and adjusting the volume to n times the volume of the pretreated solution using 0.05 mol / L sodium chloride solution, where n is 5. It should be noted that cellulase (enzyme activity ≥1800 U / g) was dried using a low-temperature vacuum drying method (40℃, 0.1 MPa) for 2 hours to ensure stable enzyme activity, while lactic acid bacteria (live count ≥10) 8 The CFU / g of the lactic acid bacteria were activated from the freeze-dried bacterial powder, inoculated into MRS medium (37℃, 24 hours) and amplified to the target viable count. The lactic acid bacteria were purchased from Shenyang Sansheng Lactic Acid Bacteria Co., Ltd., and the cellulase was selected from Lunan Pharmaceutical Group.

[0068] The process involves immersing the recovered solution completely in the treatment solution and then placing it in a shaking incubator at 45°C for enzymatic hydrolysis.

[0069] Example 3 The preparation method for separating low-content rhodium from copper sulfate solution provided in this embodiment is basically the same as that in Example 1. The main difference lies in the specific composition and ratio of the raw materials used. The method for separating low-content rhodium from copper sulfate solution in this embodiment includes: To remove iron impurities from the copper sulfate solution, an automatic titration system was used to adjust the pH value of the copper sulfate solution. The adjusted copper sulfate solution was then subjected to solid-liquid separation to obtain a purified copper sulfate solution. Rice husk ash is calcined and activated. After activation, it is mixed with chitosan to prepare an adsorbent. The adsorbent is placed in an acetic acid solution and stirred to obtain a homogeneous slurry. A modifier is added to the homogeneous slurry to modify the adsorbent and obtain a composite adsorbent. Rhodium ions were separated by membrane extraction using purified copper sulfate solution and composite adsorbent, and a DC electric field was applied to both sides of the membrane to obtain a rhodium-rich slurry. The rhodium-rich slurry was eluted and enhanced using ultrasonic oscillation technology to obtain a rhodium ion source. The rhodium ion source was then electrodeposited to obtain a rhodium deposit layer. The rhodium deposit layer was then processed to obtain rhodium powder. The used composite adsorbent was collected and recycled.

[0070] Furthermore, the method of adjusting the pH value of the copper sulfate solution using an automatic titration system includes the following steps: Add 0.1% (by mass) of 30% hydrogen peroxide and 5% (by mass) of 98% concentrated sulfuric acid to the copper sulfate solution. Stir at 70°C and automatically titrate with sodium hydroxide solution to adjust the pH of the copper sulfate solution to 3.95.

[0071] Furthermore, the specific preparation method of the composite adsorbent is as follows: A1: Calcine rice husk ash at 550℃ for 2 hours. After cooling, mix rice husk ash and chitosan at a mass ratio of 1:5 to obtain a composite product. Add acetic acid solution with a mass ratio of 1:1.5 and a concentration of 1.8% to the composite product and stir at 85℃ for 5 hours to obtain a homogeneous slurry. The rice husk ash was purchased from Shengmei Huarui Activated Carbon Plant.

[0072] A2: Add 17% (by weight of chitosan) of thiocarbamate modifier to the homogeneous slurry in three equal portions, stirring for 35 minutes after each addition. After the addition is complete, heat to 70°C and stir again for 6 hours. After the reaction is complete, wash the homogeneous slurry with deionized water to restore the pH value to 4.7. The thiocarbamate modifier was purchased from Zhejiang Wansheng Chemical Co., Ltd.

[0073] A3: Add 5% by weight of nano-titanium dioxide to the homogeneous slurry and disperse it ultrasonically to obtain a blended slurry. Add 0.5% by weight of silane coupling agent to the blended slurry and react at 65°C for 2.5 hours to form a three-dimensional network gel structure. After aging the gel for 25 hours, wash it four times with ethanol to obtain the gel slurry. The nano-titanium dioxide has a particle size of 18nm, and the silane coupling agent was purchased from Hangzhou Jessica Chemical Co., Ltd.

[0074] A4: The gel slurry was processed by a high-pressure homogenizer at 25 MPa to obtain composite particles. The composite particles were then activated at 110°C for 3 hours to obtain the composite adsorbent.

[0075] Furthermore, the step of preparing the composite particles in A4 is as follows: The spray dryer is set with an inlet air temperature of 200℃, an outlet air temperature of 100℃, and an atomizing disc rotation speed of 18500rpm. The gel slurry is fed into the spray dryer to obtain composite particles.

[0076] Furthermore, the specific preparation steps of the rhodium-rich slurry are as follows: B1: The composite adsorbent and deionized water were mixed at a solid-liquid ratio of 0.12 g / mL to obtain an initial adsorbent slurry. The initial adsorbent slurry was degassed under vacuum for 35 min and then poured into a high-shear emulsifier for shearing for 35 min to obtain the adsorbent slurry. B2: The adsorbent slurry and the purified copper sulfate solution are respectively transported to both sides of the PTFE hollow fiber membrane module. Titanium-based electrodes are installed on both sides of the membrane module and a DC electric field is applied. When rhodium ions migrate to the surface of the composite adsorbent, a rhodium-rich slurry is obtained.

[0077] It should be noted that the adsorbent slurry and the purified copper sulfate solution are delivered to both sides of the membrane by independent circulation pumps. Differential pressure sensors are installed on both sides of the membrane to monitor the pressure difference in real time and automatically adjust the speed of the circulation pumps to ensure that the pressure difference is strictly controlled at 0.1 MPa to avoid wetting. The system is designed with a circulation flow rate of 1.2 L / min to ensure turbulent flow (Reynolds number Re≥4000) and improve mass transfer efficiency.

[0078] Simultaneously, titanium-based electrodes (with corrosion-resistant coating) are installed on both sides of the membrane module, and a DC electric field (voltage 10V, current density 5mA / cm²) is applied. 2 The electric field parameters are controlled in real time via a programmable power supply and equipped with a current monitoring module to ensure current fluctuations are ≤±2%. The direction of the electric field is perpendicular to the direction of fluid flow, forming a "field-fluid" synergistic mass transfer field that promotes the directional migration of rhodium ions.

[0079] Furthermore, the mass transfer coefficient was determined using a tracer method (such as Na⁺ ions): 0.1 mol / L sodium chloride solution was added to the purified copper sulfate solution side, and the change in conductivity on the adsorbent side was monitored using a conductivity meter to calculate the mass transfer coefficient. Experiments verified that the mass transfer coefficient was increased by 40% compared to the case without an electric field. The residence time in the mixing chamber was monitored using a high-speed camera to ensure it was ≤3 seconds.

[0080] In addition, an online ICP-MS was installed at the membrane module outlet to monitor the rhodium content (target ≤0.007 mg / L) and copper content (target ≥90 g / L) on the treated liquid side in real time. X-ray fluorescence spectroscopy analysis of the adsorbent slurry side confirmed that the rhodium adsorption rate was ≥99.5% and the copper co-adsorption rate was ≤1.0%.

[0081] Furthermore, the specific steps for obtaining the rhodium deposition layer are as follows: C1: Prepare the ionic liquid, immerse the rhodium-rich slurry in the ionic liquid, and use ultrasonic vibration technology to vibrate at 40°C for 1.2 hours. Then separate the eluent and the standby adsorbent, filter the eluent and treat the standby adsorbent. C2: Gradually add a 0.22 mol / L sodium hydroxide solution to the filtered eluent to adjust the pH to 9.6; C3: Hydrochloric acid, selenic acid, and emulsifier are mixed in a mass ratio of 10:6:1 to form a transparent microemulsion system. A vertically aligned array of carbon nanotubes is grown on a titanium substrate using chemical vapor deposition. The electrode is activated with 0.6 mol / L sulfuric acid, and electrodeposition is performed at 26°C using a dual-pulse power supply to obtain a rhodium deposition layer.

[0082] The emulsifier used was OP-10, which was purchased from Shanghai Kaijie Chemical Co., Ltd. Vertically aligned carbon nanotube arrays were grown on a titanium substrate using chemical vapor deposition, and after acid washing and purification, the specific surface area reached 800 m². 2 / g, and the pulse electrodeposition parameters are: A dual-pulse power supply is used with a frequency of 120Hz and a duty cycle of 45%, and the current density is precisely controlled at 15mA / cm². 2 An electrolyte circulation rate of 0.5 m / s ensures uniform mass transfer.

[0083] Furthermore, the preparation of the ionic liquid includes: Lithium chloride solution, urea, and deionized water were mixed in a mass ratio of 1:1.8:24 to prepare a mixture. The mixture was then magnetically stirred at 35°C to obtain an ionic liquid. The urea was purchased from Luxi Fertilizer Company.

[0084] Furthermore, the process of treating the spare adsorbent involves: The standby adsorbent was pretreated to obtain a recovery solution, which was then immersed in the treatment solution. After immersion, the solution was washed with deionized water until neutral and dried at 45°C for 2.5 hours to obtain a reusable adsorbent.

[0085] Furthermore, the pretreatment of the standby adsorbent includes: The prepared adsorbent was washed four times with a 0.17 mol / L sodium hydroxide solution, with each washing lasting 5 minutes. The washed adsorbent was then dried to constant weight under vacuum at 65°C.

[0086] Furthermore, the treatment solution includes: adding 0.6% (by mass) of cellulase and 1.1% of lactic acid bacteria to the recovered solution, and then adjusting the volume to n times the volume of the pretreated solution using 0.06 mol / L sodium chloride solution, where n is 5. It should be noted that cellulase (enzyme activity ≥1800 U / g) was dried using a low-temperature vacuum drying method (40℃, 0.1 MPa) for 2 hours to ensure stable enzyme activity, while lactic acid bacteria (live count ≥10) 8 The CFU / g of the lactic acid bacteria were activated from the freeze-dried bacterial powder, inoculated into MRS medium (37℃, 24 hours) and amplified to the target viable count. The lactic acid bacteria were purchased from Shenyang Sansheng Lactic Acid Bacteria Co., Ltd., and the cellulase was selected from Lunan Pharmaceutical Group.

[0087] The process involves immersing the recovered solution completely in the treatment solution and then placing it in a shaking incubator at 40–50°C for enzymatic hydrolysis.

[0088] Comparative Example 1: The specific formulation of the method for separating low-content rhodium from copper sulfate solution provided in this embodiment is roughly the same as that in Example 1. The main difference is that limestone is used for neutralization of iron impurities in this embodiment, and the limestone is purchased from Chunhua Environmental Protection Materials Co., Ltd. in Leping City.

[0089] Comparative Example 2: The specific formulation of the method for separating low-content rhodium from copper sulfate solution provided in this example is roughly the same as that in Example 1. The main difference is that activated carbon is used instead of composite adsorbent in this example. The activated carbon was purchased from Henan Liangyou Environmental Protection Materials Co., Ltd.

[0090] Comparative Example 3: The specific formulation of the method for separating low-content rhodium from copper sulfate solution provided in this example is roughly the same as that in Example 1. The main difference is that ion exchange is used for rhodium-copper separation in this example.

[0091] Effect test The methods for separating the precious metal rhodium using Examples 1-3 of the present invention are referred to as Experimental Examples 1-3; the methods for separating the precious metal rhodium using Comparative Examples 1-3 are referred to as Comparative Examples 1-3; and then the methods for separating the precious metal rhodium are tested respectively.

[0092] 1. Rhodium purity test: In this embodiment, the rhodium powder purity is tested according to GB / T1425-2021; 2. Environmental protection test: The environmental protection test shall be conducted in accordance with GB / T5750.6-2023.

[0093] The experimental data are summarized in Table 1: In summary, by employing a composite adsorbent and electric field coupling technology, highly efficient capture of rhodium ions and precise separation of copper impurities were achieved. The enhanced electric field significantly improved ion migration efficiency and shortened mass transfer time. Simultaneously, the combined enzyme-bacterial regeneration process ensured the stable performance of the adsorbent during recycling, ultimately yielding a high-purity rhodium product. This technical solution demonstrates comprehensive advantages in capture efficiency, separation precision, mass transfer rate, and product purity, far surpassing traditional processes.

[0094] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0095] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for separating low-content rhodium from copper sulfate solution, characterized in that: The method includes: To remove iron impurities from the copper sulfate solution, an automatic titration system was used to adjust the pH value of the copper sulfate solution. The adjusted copper sulfate solution was then subjected to solid-liquid separation to obtain a purified copper sulfate solution. Rice husk ash is calcined and activated. After activation, it is mixed with chitosan to prepare an adsorbent. The adsorbent is placed in an acetic acid solution and stirred to obtain a homogeneous slurry. A modifier is added to the homogeneous slurry to modify the adsorbent and obtain a composite adsorbent. Rhodium ions were separated by membrane extraction using purified copper sulfate solution and composite adsorbent, and a DC electric field was applied to both sides of the membrane to obtain a rhodium-rich slurry. The rhodium-rich slurry was eluted and enhanced using ultrasonic oscillation technology to obtain a rhodium ion source. The rhodium ion source was then electrodeposited to obtain a rhodium deposit layer. The rhodium deposit layer was then processed to obtain rhodium powder. The used composite adsorbent was collected and recycled.

2. The method for separating low-content rhodium from copper sulfate solution according to claim 1, characterized in that, The process of adjusting the pH of the copper sulfate solution using an automatic titration system includes the following steps: Add 0.08%–0.1% (by mass) of 30% hydrogen peroxide and 3%–5% (by mass) of 98% concentrated sulfuric acid to the copper sulfate solution. Stir at 60–70°C and automatically titrate with sodium hydroxide solution to adjust the pH of the copper sulfate solution to 3.85–3.

95.

3. The method for separating low-content rhodium from copper sulfate solution according to claim 1, characterized in that: The specific preparation method of the composite adsorbent is as follows: A1: Calcine rice husk ash at 500-550℃ for 1.5-2 hours. After cooling, mix rice husk ash and chitosan at a mass ratio of 1:4-5 to obtain a composite product. Add acetic acid solution at a mass ratio of 1:1.2-1.5 and a concentration of 1.8% to the composite product and stir at 80-85℃ for 3-5 hours to obtain a homogeneous slurry. A2: Add thiocarbamate modifier in three equal portions, which is 15% to 17% of the chitosan mass, to the homogeneous slurry. Stir for 25 to 35 minutes after each addition. After the addition is complete, heat to 60 to 70 degrees Celsius and stir again for 5 to 6 hours. After the reaction is complete, wash the homogeneous slurry with deionized water and adjust the pH value back to 4.3 to 4.

7. A3: Add 4%–5% by weight of nano-titanium dioxide to a homogeneous slurry and disperse it ultrasonically to obtain a blended slurry. Add 0.5% by weight of silane coupling agent to the blended slurry and react at 55–65°C for 1.5–2.5 h to form a three-dimensional network gel structure. After aging the gel for 23–25 h, wash it with ethanol 2–4 times to obtain a gel slurry. A4: The gel slurry is processed by a high-pressure homogenizer at 15-25 MPa to obtain composite particles. The composite particles are then activated at 100-110℃ for 1-3 hours to obtain the composite adsorbent.

4. The method for separating low-content rhodium from copper sulfate solution according to claim 3, characterized in that: The steps for preparing the composite particles in A4 are as follows: The spray dryer is set with an inlet air temperature of 180-200℃, an outlet air temperature of 90-100℃, and an atomizing disc rotation speed of 17500-18500 rpm. The gel slurry is fed into the spray dryer to obtain composite particles.

5. The method for separating low-content rhodium from copper sulfate solution according to claim 1, characterized in that: The specific preparation steps of the rhodium-rich slurry are as follows: B1: Mix the composite adsorbent with deionized water at a solid-liquid ratio of 0.1-0.12 g / mL to obtain an initial adsorbent slurry. Degas the initial adsorbent slurry under vacuum for 25-35 min and pour it into a high-shear emulsifier for shearing for 25-35 min to obtain an adsorbent slurry. B2: The adsorbent slurry and the purified copper sulfate solution are respectively transported to both sides of the PTFE hollow fiber membrane module. Titanium-based electrodes are installed on both sides of the membrane module and a DC electric field is applied. When rhodium ions migrate to the surface of the composite adsorbent, a rhodium-rich slurry is obtained.

6. The method for separating low-content rhodium from copper sulfate solution according to claim 1, characterized in that: The specific steps for obtaining the rhodium deposition layer are as follows: C1: Prepare the ionic liquid, immerse the rhodium-rich slurry in the ionic liquid, and use ultrasonic vibration technology to vibrate at 30-40℃ for 0.8-1.2h. Then separate the eluent and the standby adsorbent, filter the eluent and treat the standby adsorbent. C2: Gradually add sodium hydroxide solution with a concentration of 0.18–0.22 mol / L to the filtered eluent to adjust the pH to 9.4–9.6; C3: Hydrochloric acid, selenic acid, and emulsifier are mixed in a mass ratio of 9–10:5–6:1 to form a transparent microemulsion system. A vertically aligned array of carbon nanotubes is grown on a titanium substrate using chemical vapor deposition. The electrode is activated with 0.4–0.6 mol / L sulfuric acid, and electrodeposition is performed at 24–26 °C using a dual-pulse power supply to obtain a rhodium deposition layer.

7. A method for separating low-content rhodium from a copper sulfate solution according to claim 6, characterized in that, The prepared ionic liquid includes: Lithium chloride, urea, and deionized water were mixed in a mass ratio of 1:1.6-1.8:23-24 to prepare a mixture. The mixture was then magnetically stirred at 30-35°C to obtain an ionic liquid.

8. A method for separating low-content rhodium from a copper sulfate solution according to claim 6, characterized in that: The process of treating the spare adsorbent is as follows: The standby adsorbent is pretreated to obtain a recovery solution. The recovery solution is then immersed in the treatment solution. After immersion, it is washed with deionized water until neutral and dried at 35–45°C for 1.5–2.5 h to obtain a reusable adsorbent.

9. A method for separating low-content rhodium from a copper sulfate solution according to claim 8, characterized in that: The pretreatment of the standby adsorbent includes: The standby adsorbent was washed in 2 to 4 batches with a 0.13–0.17 mol / L sodium hydroxide solution, with each wash lasting 3 to 5 minutes. The washed standby adsorbent was then dried to constant weight under vacuum at 55–65°C.

10. A method for separating low-content rhodium from a copper sulfate solution according to claim 8, characterized in that: The treatment solution includes: adding 0.4% to 0.6% (by mass) of cellulase and 0.9% to 1.1% (by mass) of lactic acid bacteria to the recovered solution, and then adjusting the volume to n times the volume of the pretreated solution using a 0.04 to 0.06 mol / L sodium chloride solution. The recovered solution is immersed in the treatment solution and then placed in a shaking incubator at 40–50°C for enzymatic hydrolysis.

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