Process for ultrasonic enhanced electrochemical coupling complete separation of rare earth oxides

Abstract

This application relates to the field of rare earth smelting and separation technology, and discloses an ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides, comprising the following steps: adding a polyphosphate complexing agent and a redox mediator to a cerium-rich rare earth aqueous solution as the anolyte, and pumping it into a dual-chamber membrane electrolytic cell separated by a cation exchange membrane for circulation. An electroacoustic phase-controlled synchronous system is activated to perform periodic reverse-phase pulse operations of turning on the ultrasonic current to decrease and turning off the ultrasonic current to increase. When the trivalent cerium conversion rate reaches a first threshold, the pH is dynamically adjusted and the current is reduced; when it reaches a second threshold, the process is stopped and the temperature is raised to mature the complex salt crystalline phase. The slurry is hot-pressed and filtered; the filter cake is dephosphorized and washed by alkaline solid-phase decomposition, and then calcined at a constant temperature to obtain high-purity cerium dioxide powder. This invention employs a dual-chamber electrolysis technology scheme using polyphosphate complexation combined with a perfluorosulfonic acid cation exchange membrane, achieving the technical effect of zero cathode penetration of rare earth materials.

Description

Technical Field

[0001] This invention relates to the field of rare earth smelting and separation technology, specifically to an ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides. Background Technology

[0002] High-purity cerium dioxide is a core raw material for precision polishing and automotive exhaust catalysts. A key step in extracting pure cerium from mixed rare earth ores is separating cerium from other trivalent rare earth elements. Trivalent cerium is difficult to directly separate from other rare earth elements under normal conditions. Industrially, it is usually oxidized to its tetravalent state. Tetravalent cerium can undergo hydrolysis and precipitation even at relatively low acidity. Utilizing this difference in physicochemical properties between valence states, cerium can be effectively purified from mixtures of rare earth elements such as praseodymium and neodymium.

[0003] Currently, the mainstream methods for cerium ion oxidation in the industry include chemical reagent methods and conventional DC electrolysis. Adding potassium permanganate or hydrogen peroxide directly to the feed solution can rapidly increase the oxidation potential of the system. The reaction rate is extremely fast and the requirements for dosing equipment are relatively low. Conventional electrolytic oxidation relies on a DC electric field to drive electron transfer on the electrode surface. The entire process does not introduce any additional metal impurity ions into the feed solution. The electrolytic cell structure is relatively simple, and it can operate continuously as soon as it is powered on, possessing strong capabilities for continuous, large-scale production in workshops.

[0004] When using a conventional electrolyte system, trivalent cerium ions carry a positive charge. Under continuous DC electric field, free rare earth cations spontaneously migrate towards the cathode chamber via electrophoresis. Even with a physical membrane in conventional equipment, this transmembrane penetration cannot be effectively blocked, leading to ineffective precipitation of cerium on the cathode surface and unnecessary loss of raw materials. Turning our attention back to the anode side, trivalent cerium, after losing electrons, readily undergoes hydrolysis in the local microenvironment of the electrode plate. A dense layer of insulating oxide quickly adheres to the electrode surface. This passivation film obscures the active electron exchange sites. To maintain the oxidation reaction, the equipment can only passively increase the cell voltage, and the excess input electrical energy is then consumed by side reactions such as water desorption and oxygenation. In the precipitation stage of the later electrolysis phase, traditional processes typically involve directly adding large doses of precipitating reagent at room temperature. The instantaneous nucleation process generates fine colloids with irregular crystal structures. When this high-viscosity slurry enters the filter press, the microporous filter cloth is immediately blocked by the retained material. The entire dehydration process becomes extremely difficult. A large amount of mother liquor containing associated impurities is tightly trapped inside the colloidal flocs. Blindly increasing the amount of washing water in the subsequent process cannot completely displace them, which directly leads to the cerium dioxide produced by the final roasting having a purity that is difficult to meet industrial-grade standards. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides. This process solves the technical problems of free rare earth ions easily penetrating to the cathode and causing losses, severe polarization and passivation of the anode surface, a surge in energy consumption due to side reactions in the later stages of electrolysis, and the fact that conventional precipitated products are colloidal and difficult to filter and wash, ultimately leading to substandard product purity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] An ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides includes the following steps:

[0008] S1. Add polyphosphate complexing agent and redox mediator to cerium-rich rare earth aqueous solution, adjust the pH value and keep the temperature constant to obtain anolyte; simultaneously prepare dilute acid aqueous solution as catholyte.

[0009] S2. Pump the anolyte and catholyte into a two-chamber membrane electrolyzer separated by a cation exchange membrane to establish circulation; start the electroacoustic phase-controlled synchronization system containing an ultrasonic generator to perform periodic anti-phase pulse operation: reduce the anolyte working current density when the ultrasonic generator is turned on, and instantly restore the high anolyte working current density when the ultrasonic generator is turned off.

[0010] S3. Monitor the conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate reaches the first set threshold, add acid to the anolyte to dynamically adjust the pH value and simultaneously reduce the reference anolyte current density during the ultrasonic shutdown phase.

[0011] S4. When the trivalent cerium ion conversion rate reaches the second set threshold, stop the electrolysis power supply and ultrasonic output, export the anolyte and program the temperature to ripen it, so that the free cerium ions will hydrolyze to form a double salt crystalline phase.

[0012] S5. The matured suspension slurry is directly subjected to hot pressure filtration separation, the filter cake is retained and washed;

[0013] S6. The filter cake is added to an alkaline solution for solid-phase metathesis transformation to remove phosphorus. After being filtered and washed again until neutral, it is sent to a rotary kiln for constant-temperature calcination to obtain high-purity cerium dioxide powder.

[0014] By adopting the above technical solution, and through the combination of multi-field coupling and dynamic control, this invention achieves the following effects. The specific reaction process and mechanism are as follows:

[0015] When polyphosphate is introduced as a complexing agent into the electrolysis system, the polyphosphate ions in the system coordinate with trivalent rare earth ions, thereby forming large-molecule, negatively charged complex ions in the liquid phase. Considering that the cation exchange membrane used in a dual-chamber membrane electrolyzer typically has anionic groups distributed on its surface, these negatively charged complex ions are difficult to penetrate the exchange membrane and migrate to the cathode due to the combined effects of like charge repulsion and steric hindrance of the membrane pore size. This in-situ electrostatic shielding effect effectively retains rare earth elements in the anode chamber, avoiding material loss caused by the deposition of rare earth ions on the cathode surface in conventional electrolysis.

[0016] Meanwhile, the persulfate ions generated by the added ammonium persulfate ionize in the liquid phase act as electron transport mediators, directly participating in the liquid-phase oxidation of trivalent cerium ions. The reaction formula is:

[0017] S2O8 2- +2Ce 3+ →2SO4 2- +2Ce 4+ ;

[0018] This reaction works synergistically with direct electrochemical oxidation on the anode surface, compensating for the limited electron transfer on a single electrode surface, thereby increasing the overall rate of trivalent cerium to tetravalent cerium conversion.

[0019] In the specific electrolytic oxidation stage, this scheme employs reverse-phase pulse operation to address anodic polarization. When the ultrasonic generator is activated and the anodic current density is forcibly reduced, cavitation bubbles generated by the ultrasonic waves in the liquid phase collapse instantaneously, forming microjets. This physical impact force can strip away the insulating passivation and bubbles adhering to the anode surface. Simultaneously, the low current environment prevents the electrode from triggering a violent oxygen evolution side reaction during the gap before its surface activity is fully recovered. As the ultrasonic waves are turned off, the anodic current density increases instantaneously. At this point, the surface-renewed electrode exhibits a low polarizability, enabling the system to undergo a strong oxidation reaction at high current.

[0020] As electrolysis continues, free trivalent cerium ions are constantly consumed, leading to an increase in mass transfer resistance. To address this, this scheme uses dynamic addition of acid to lower the pH value and simultaneously reduces the reference anolyte current density, ensuring that the applied energy input matches the actual ion concentration. The increased hydrogen ions in the system effectively raise the oxygen evolution overpotential, suppressing the competitive energy-consuming side reaction of water desorption for oxygen.

[0021] Once the conversion rate reaches the predetermined endpoint, the hydrolysis and crystallization stage begins. Tetravalent cerium ions begin hydrolysis under specific acidity and programmed temperature conditions, with polyphosphates and sulfates in the system acting as precipitants to combine and form a complex salt crystalline phase. The qualitative reaction can be expressed as:

[0022] pCe4+ +qSO4 2- +rH2O→Ce p (SO4) q (OH) r ↓+rH + ;

[0023] Where p, q, and r are positive integers or fractions that satisfy the charge conservation of crystals and conform to the stoichiometric relationship: 4p = 2q + r.

[0024] By controlling the heating rate, the crystal nuclei grow slowly under a low degree of supersaturation, eventually obtaining a precipitate with high crystallinity and uniform particle size. Since the trivalent praseodymium and neodymium ions do not undergo hydrolysis under these acidic conditions, they remain in the liquid phase, thus naturally achieving phase separation of cerium and praseodymium-neodymium components.

[0025] The feed solution was then kept at a high temperature for hot pressure filtration, taking advantage of the low viscosity of the slurry at this time to accelerate the dewatering rate. The resulting filter cake underwent a metathesis reaction in an alkaline solution, where the acid radicals in the double salt were replaced by a high concentration of hydroxide ions, transforming into solid-phase cerium hydroxide. The reaction formula is as follows:

[0026] Cep(SO4) q (OH) r +(4p−r)OH - →pCe(OH)4↓+qSO4 2- ;

[0027] After washing, cerium hydroxide undergoes a dehydration phase transition upon high-temperature calcination:

[0028] Ce(OH)4→CeO2 +2H2O;

[0029] The final product is high-purity cerium dioxide with a complete crystal structure.

[0030] Preferably, in step S1, the cerium-rich rare earth aqueous solution is a cerium-rich rare earth sulfate aqueous solution, the total rare earth ion molar concentration of the cerium-rich rare earth sulfate aqueous solution is 0.5-1.5 mol / L, wherein trivalent cerium ions account for 40%-80% of the total rare earth ions; the polyphosphate complexing agent is sodium hexametaphosphate, and the free concentration of sodium hexametaphosphate in the system is controlled at 0.05-0.15 mol / L; the redox mediator is ammonium persulfate, and the free concentration of ammonium persulfate in the system is controlled at 0.02-0.08 mol / L; the pH adjustment and temperature control operation is as follows: add a 20% (w / w) dilute sulfuric acid solution or sodium hydroxide solution to adjust the initial pH of the system to 2.0-3.0, and maintain the temperature at 20-35℃.

[0031] By employing the above technical solution, the total rare earth ion concentration and the proportion of trivalent cerium are controlled within the aforementioned range, primarily to maintain the basic ionic conductivity of the electrolyte and the necessary reactant abundance. Sodium hexametaphosphate, with its long-chain polymeric structure, can form strong steric hindrance after encapsulating rare earth ions. Strictly limiting its and ammonium persulfate free concentrations ensures a balance between material consumption in complexation and redox reactions, preventing excessive reagents from placing an additional load on downstream washing while avoiding incomplete reactions caused by insufficient dosage. Furthermore, an initial pH of 2.0 to 3.0 not only maintains the dissolved state of trivalent rare earth ions but also establishes a suitable proton environment for subsequent electrolytic oxidation.

[0032] Preferably, in step S2, the cycle parameters of the periodic anti-phase pulse operation are: the ultrasonic generator with a working frequency of 20kHz is turned on for 3 to 8 seconds, and the power density is 0.3 to 0.8 W / cm². 2 At the same time, the anode operating current density is forcibly reduced to 0-10 A / m. 2 Then, turn off the ultrasonic generator for 8-15 seconds, and simultaneously restore the anode operating current density to 150-250 A / m. 2 .

[0033] By adopting the above technical solution, a working frequency of 20kHz is selected to excite cavitation bubbles of suitable size. Within 3 to 8 seconds of the ultrasonic wave being activated, an application of 0.3 to 0.8 W / cm² is applied. 2 The power density is sufficient to generate microjets to impact and strip the passivation layer on the anode surface; the current density is simultaneously reduced to 0 to 10 A / m. 2 This provides a relaxation gap at the polarization interface, facilitating the natural recovery of the ion concentration gradient. During the 8 to 15 seconds after the ultrasound is turned off, the highly active sites re-exposed on the electrode surface can effectively withstand 150 to 250 A / m². 2 The high current density, which staggers the timing of energy injection and physical interface cleaning, effectively suppresses ineffective energy consumption.

[0034] Preferably, in step S3, the first set threshold is 55%–65%; when the first set threshold is reached, 30% (w / w) dilute sulfuric acid is added dropwise to the anolyte to dynamically adjust and stabilize the pH value of the anolyte at 0.8–1.2; simultaneously, the reference anolyte current density is reduced to 100–150 A / m. 2 .

[0035] By adopting the above technical solution, considering that after the reaction process is more than halfway complete (conversion rate 55% to 65%), mass transfer may be limited due to the decrease in reactant concentration. At this point, dilute sulfuric acid is added dropwise to lower the pH to 0.8 to 1.2, using the increased hydrogen ion concentration to raise the oxygen evolution overpotential, thereby suppressing the water splitting reaction occurring at the anode. Simultaneously, the reference current density is correspondingly reduced to 100 to 150 A / m. 2 This allows the input electric field energy to be matched with the actual ion flux at that time, which helps maintain the set Faraday efficiency.

[0036] Preferably, in step S4, the second set threshold is greater than 95%; the specific operation of the programmed heating and maturation is as follows: turn on mechanical stirring, raise the system temperature to 75-90°C at a heating rate of 1.5-2.5°C / min, and maintain the temperature at this temperature for 40-60 minutes.

[0037] By adopting the above technical solution, the input can be cut off once the electrolysis conversion rate exceeds 95%. During the heating phase, a gradual rate of 1.5 to 2.5 °C / min is used to maintain the system in a pseudo-homogeneous nucleation state, preventing local temperature jumps from causing runaway supersaturation and the precipitation of difficult-to-filter colloids. Subsequently, the temperature is maintained within the range of 75 to 90 °C for 40 to 60 minutes, promoting the gradual dissolution of thermodynamically unstable small crystal nuclei and their deposition on the surface of larger particles. This Oswald ripening mechanism optimizes the crystal morphology of the final precipitate and reduces subsequent dehydration resistance.

[0038] Preferably, in step S6, the operation of adding the filter cake to the alkaline solution for solid-phase metathesis transformation is as follows: according to the solid-liquid ratio of filter cake to sodium hydroxide solution of 1:3 to 1:5 g / mL, add sodium hydroxide solution with a mass fraction of 20% to 30%, and stir vigorously at 85 to 105°C for 1 to 3 hours; the operation of constant temperature calcination is as follows: calcin the washed neutral filter cake at 800 to 950°C in air atmosphere for 1.5 to 3 hours.

[0039] By employing the above-mentioned technical solution, the strong alkaline environment of a high-concentration sodium hydroxide solution at high temperature is used to disrupt the original crystal structure of the complex salt. A large number of hydroxide ions come into full contact with the solid phase to achieve deep dephosphorization and desulfurization, ultimately transforming into insoluble cerium hydroxide. Properly adjusting the solid-liquid ratio and reaction time is essential to ensure complete phase transformation. The transformed filter cake undergoes dehydration shrinkage and crystal reconstruction at a high temperature of 800 to 950°C, thereby producing cerium dioxide powder with a fluorite-type structure.

[0040] Preferably, in step S2, the anode of the dual-chamber diaphragm electrolytic cell is a titanium-based lead dioxide mesh electrode or a titanium-based iridium-tantalum coated mesh electrode, and the cathode is a titanium plate; the catholyte is a dilute sulfuric acid aqueous solution with a mass fraction of 3% to 8%.

[0041] By adopting the above technical solution, the selected titanium-based lead dioxide or iridium-tantalum coated electrodes possess good electrocatalytic activity and a relatively high oxygen evolution overpotential, which provides favorable surface conditions for the oxidation of trivalent cerium while also ensuring the service life of industrial electrodes. The mesh structure on the electrode surface effectively expands the specific surface area of ​​the actual reaction, improving liquid-phase mass transfer. Furthermore, the titanium plate on the cathode side and the 3% to 8% dilute sulfuric acid aqueous solution create a stable proton reduction environment, ensuring the dynamic balance of charge throughout the electrolysis circuit.

[0042] Preferably, in step S2, the cation exchange membrane is a perfluorosulfonic acid cation exchange membrane, wherein the main chain of the perfluorosulfonic acid cation exchange membrane has a polytetrafluoroethylene structure and the side chain ends have sulfonic acid groups.

[0043] By employing the above technical solution, the polytetrafluoroethylene backbone inherent in the perfluorosulfonic acid cation exchange membrane endows it with the mechanical and chemical stability required for long-term operation in strong acid and strong oxidizing systems. The sulfonic acid groups suspended on its side chains, after hydration and dissociation, construct dense clusters of negatively charged ions. These channels naturally repel rare-earth complex anions that also carry a negative charge, typically allowing only hydrated hydrogen ions and other cations to pass through, thus achieving physical-level anti-penetration interception of target ions.

[0044] Preferably, in step S5, during the hot pressure filtration separation process, the suspended slurry does not need to be cooled, and the liquid temperature is maintained above 70°C.

[0045] By adopting the above technical solution, pressure filtration and dehydration are carried out directly while the feed liquid is in a temperature range above 70°C, directly avoiding the problem of increased viscosity of the feed liquid caused by a sudden drop in temperature. Maintaining this high temperature not only maintains good liquid phase permeability and reduces the solid-liquid separation operation time, but also prevents impurity ions remaining in the mother liquor from accidentally precipitating out and clogging the filter cake pores due to temperature reduction.

[0046] Preferably, the following control parameters are used in process steps S2, S3, and S4: In step S2, the ultrasonic generator is turned on for 5 seconds, and the power density is 0.5 W / cm³. 2 The anode operating current density was reduced to 5A / m 2 Turn off the ultrasonic generator for 10 seconds, and instantly restore the anode working current density to 200A / m. 2 In step S3, the first set threshold is 60%, the pH value is adjusted to 1.0, and the reference anolyte current density is reduced to 120 A / m. 2 In step S4, the temperature is increased to 85°C at a rate of 2.0°C / min, and then maintained at this temperature for 50 minutes.

[0047] By adopting the above technical solution and setting this set of specific control center values, ultrasonic screen cleaning and high-current polarization are precisely coordinated on the time axis. The simultaneous intervention of acidity correction and flow reduction gradient, coupled with the control of the thermodynamic conditions of hydrolysis and ripening, has found a relatively balanced process operation point between reducing ineffective energy consumption, protecting the electrode coating, and improving crystallization filtration. This provides a data benchmark for the continuous and stable operation of this solution on a practical engineering scale.

[0048] This invention provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides. It offers the following advantages:

[0049] 1. This invention employs a dual-chamber electrolysis technology using polyphosphate complexes combined with perfluorosulfonic acid cation exchange membranes. Polyphosphate ions coordinate with rare earth ions to form negatively charged macromolecular complexes. The electrostatic repulsion of the side-chain channels of the exchange membrane traps the target elements, achieving zero cathode penetration of rare earth materials. Compared to existing technologies that directly electrolyze conventional cerium-containing aqueous solutions, this invention overcomes the shortcomings of free rare earth cations easily penetrating and migrating into the cathode chamber and reverting to their attachment on the electrode surface, thus avoiding difficulties in cathode product stripping and unnecessary raw material loss.

[0050] 2. This invention employs a technical solution of periodic anti-phase pulse operation synchronized with electroacoustic phase control. When ultrasonication is activated, the current density is forcibly reduced, utilizing cavitation micro-jets to physically clean the electrode surface. Upon ultrasonication closure, a high operating current is instantly restored for strong oxidation, achieving the technical effect of stripping the insulating passivation layer while maintaining high anode activity. Compared to conventional electrolysis schemes that apply constant DC or rely solely on physical stirring, this invention overcomes the shortcomings of rapid oxide accumulation on the anode surface leading to severe interfacial polarization and controls unnecessary energy consumption caused by moisture desorption and oxygen desorption.

[0051] 3. This invention employs a technical solution based on dynamic pH adjustment of the conversion rate system and step-down flow, supplemented by programmed temperature rise for ripening. In the later stages of the reaction, it actively matches the actual mass transfer limit of the liquid phase, controlling the slow growth of complex salt crystal nuclei in a low supersaturation environment. The product is maintained at high temperature for hot pressure filtration, achieving stable terminal current efficiency and improved solid-liquid separation rate. Compared to existing technologies that use fixed electrolysis parameters and rapid dosing at room temperature for precipitation, this invention solves the problems of intense oxygen evolution in the later stages of the reaction and the product's tendency to be colloidal and difficult to dehydrate and wash. It also reduces slurry viscosity and ensures the final purity of cerium dioxide crystals. Attached Figure Description

[0052] Figure 1 The following is a comparison chart of the electrochemical system stability and anti-shuttle blocking effect test data of the test examples of the present invention, wherein (a) is a comparison chart of cell voltage drift rate of each experimental group, and (b) is a comparison chart of cerium ion leakage rate of cathode liquid of each experimental group.

[0053] Figure 2 The following is a comparison chart of the test data of in-situ hydrolysis phase change and engineering dehydration efficiency of the test examples of the present invention. Among them, (a) is a biaxial broken line distribution chart of cerium single-pass precipitation rate and filter cake moisture content of Examples 1 to 4 and Comparative Examples 1, 4 and 5, and (b) is a scatter plot of the constant pressure average filtration flux step characteristics of the same experimental object.

[0054] Figure 3 This is a scatter plot showing the characteristics of the pseudo-homogeneous oxidation mechanism and current efficiency test data of the test examples of this invention.

[0055] Figure 4 The following is a distribution chart of the test data of the purity of the final product and the impurity rejection efficiency of the test examples of the present invention. Among them, (a) is a biaxial broken line distribution chart of the purity of the cerium dioxide final product and the co-precipitation entrainment rate of praseodymium / neodymium impurities in each experimental group, and (b) is a logarithmic coordinate discrete characteristic chart of the residual phosphorus element in the final product of each experimental group. Detailed Implementation

[0056] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0058] The cerium-rich sulfuric acid rare earth aqueous solution is a mixed aqueous solution obtained through a previous sulfuric acid leaching and extraction process to remove impurities. Its total rare earth ion molar concentration is 0.5 to 1.5 mol / L, of which trivalent cerium ions account for 40% to 80% of the total rare earth ions, and the remaining rare earth elements are trivalent praseodymium ions and trivalent neodymium ions.

[0059] Sodium hexametaphosphate, CAS number 10124-56-8, is an inorganic polyphosphate composed of metaphosphate units linked by alternating phosphorus-oxygen bonds. It is used as a polyphosphate complexing agent and is a commercially available solid chemical reagent.

[0060] Ammonium persulfate, CAS number 7727-54-0, is used as a redox mediator and is a commercially available solid chemical reagent.

[0061] The perfluorosulfonic acid cation exchange membrane is a fluoropolymer film with a polytetrafluoroethylene structure as the main chain and sulfonic acid groups at the end of the side chains. Its CAS number is 31175-20-9. It is used as a physical isolation membrane in a dual-chamber membrane electrolyzer and is a commercially available industrial-grade ion exchange membrane.

[0062] Preparation Example 1:

[0063] This preparation example provides a method for preparing an electrolyte, including the following steps:

[0064] (1) Measure out a cerium-rich rare earth sulfate aqueous solution with a total rare earth ion molar concentration of 1.0 mol / L and a trivalent cerium ion molar percentage of 60% of the total rare earth ions and put it into a dispensing vessel.

[0065] (2) Add sodium hexametaphosphate solid and ammonium persulfate solid under mechanical stirring at room temperature, and continue stirring until completely dissolved. Control the free concentration of sodium hexametaphosphate in the system to be 0.10 mol / L and the free concentration of ammonium persulfate to be 0.05 mol / L.

[0066] (3) Then add 20% dilute sulfuric acid solution or sodium hydroxide solution to adjust the initial pH value of the system to 2.5, and turn on the water circulation in the jacket of the mixing vessel to keep the system temperature constant at 25°C to obtain the anolyte;

[0067] (4) Simultaneously prepare a 5% dilute sulfuric acid aqueous solution using deionized water and concentrated sulfuric acid as the cathode liquid.

[0068] Preparation Example 2:

[0069] This preparation example provides a method for preparing an electrolyte, including the following steps:

[0070] (1) Measure out a cerium-rich rare earth sulfate aqueous solution with a total rare earth ion molar concentration of 1.5 mol / L and a trivalent cerium ion molar percentage of 80% of the total rare earth ions and put it into a dispensing vessel.

[0071] (2) Add sodium hexametaphosphate solid and ammonium persulfate solid under mechanical stirring at room temperature, and continue stirring until completely dissolved. Control the free concentration of sodium hexametaphosphate in the system to be 0.15 mol / L and the free concentration of ammonium persulfate to be 0.08 mol / L.

[0072] (3) Then add 20% dilute sulfuric acid solution or sodium hydroxide solution to adjust the initial pH value of the system to 3.0, and turn on the water circulation in the jacket of the mixing vessel to keep the system temperature constant at 35℃ to obtain the anolyte;

[0073] (4) Simultaneously prepare an 8% dilute sulfuric acid aqueous solution using deionized water and concentrated sulfuric acid as the cathode liquid.

[0074] Preparation Example 3:

[0075] This preparation example provides a method for preparing an electrolyte, including the following steps:

[0076] (1) Take a cerium-rich rare earth sulfate aqueous solution with a total rare earth ion molar concentration of 0.5 mol / L and a trivalent cerium ion molar percentage of 40% of the total rare earth ions and put it into the mixing tank.

[0077] (2) Add sodium hexametaphosphate solid and ammonium persulfate solid under mechanical stirring at room temperature, and continue stirring until completely dissolved. Control the free concentration of sodium hexametaphosphate in the system to be 0.05 mol / L and the free concentration of ammonium persulfate to be 0.02 mol / L.

[0078] (3) Then add 20% dilute sulfuric acid solution or sodium hydroxide solution to adjust the initial pH value of the system to 2.0, and turn on the water circulation in the jacket of the mixing vessel to keep the system temperature constant at 20℃ to obtain the anolyte;

[0079] (4) Simultaneously prepare a 3% dilute sulfuric acid aqueous solution using deionized water and concentrated sulfuric acid as the cathode liquid.

[0080] Example 1:

[0081] This embodiment provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides, including the following steps:

[0082] (1) Take the anolyte and catholyte obtained in Preparation Example 1 and pump them into the anode chamber and cathode chamber of the double-chamber membrane electrolyzer separated by the perfluorosulfonic acid cation exchange membrane to establish circulation. The anode is a titanium-based lead dioxide mesh electrode and the cathode is a titanium plate. The anolyte circulation temperature is controlled at 25°C throughout the electrolysis process.

[0083] (2) An industrial ultrasonic transducer with a working frequency of 20kHz is installed on the outer wall of the anode chamber. The electroacoustic phase-controlled synchronization system is started to perform periodic anti-phase pulse operation. The cycle is: the ultrasonic generator is turned on for 5 seconds, and the power density is 0.5W / cm². 2 At the same time, the anode operating current density is forcibly reduced to 5A / m. 2 Then, the ultrasonic generator was turned off for 10 seconds, and the anode operating current density was instantly restored to 200 A / m. 2 ;

[0084] (3) Monitor the single-pass conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate of trivalent cerium ions to tetravalent cerium reaches 60%, keep the reverse-phase pulse operation sequence unchanged, add 30% dilute sulfuric acid to the anolyte circulation tank, dynamically adjust the pH value of the anolyte from 2.5 and stabilize it at 1.0, and simultaneously reduce the reference anolyte current density of the high-current resting phase of the ultrasonic phase from 200 A / m 2 Stepwise reduction to 120A / m 2 ;

[0085] (4) When the trivalent cerium ion conversion rate is greater than 95%, stop the electrolysis power supply and ultrasonic output, and export all the anolyte containing tetravalent cerium sol to the crystallization ripening kettle with mechanical stirring and heating jacket; turn on the mechanical stirring, and rapidly raise the system temperature to 85°C at a heating rate of 2.0°C / min, and keep it at this temperature for 50 minutes.

[0086] (5) After the maturation is completed, there is no need to cool the liquid. The suspension slurry is directly pumped into the plate and frame filter press for hot filtration. The liquid temperature is maintained above 70°C. The filtered liquid is collected and sent to the downstream conventional extraction process. The retained filter cake is washed twice with deionized water.

[0087] (6) The washed filter cake was put into the transformation vessel. The solid-liquid ratio of the filter cake to the sodium hydroxide solution was 1:4 g / mL. A sodium hydroxide solution with a mass fraction of 25% was added. The mixture was stirred vigorously at 95°C for 2 hours to complete the solid-phase metathesis transformation. The mixture was then filtered again, the filtrate was recovered, and the filter cake was washed with deionized water until neutral. The washed filter cake was then sent to a rotary kiln and calcined at 900°C in air for 2 hours. After natural cooling, high-purity cerium dioxide powder was obtained.

[0088] Example 2:

[0089] This embodiment provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides, including the following steps:

[0090] (1) Take the anolyte and catholyte obtained in Preparation Example 3 and pump them into the anode chamber and cathode chamber of the double-chamber membrane electrolyzer separated by a perfluorosulfonic acid cation exchange membrane to establish circulation. The anode is a titanium-based iridium-tantalum coated mesh electrode and the cathode is a titanium plate. The anolyte circulation temperature is controlled at 20°C throughout the electrolysis process.

[0091] (2) An industrial ultrasonic transducer with a working frequency of 20kHz is installed on the outer wall of the anode chamber. The electroacoustic phase-controlled synchronization system is started to perform periodic anti-phase pulse operation. The cycle is: the ultrasonic generator is turned on for 3 seconds, and the power density is 0.3W / cm². 2 At the same time, the anode operating current density is forcibly reduced to 0 A / m. 2 Then, the ultrasonic generator was turned off for 15 seconds, and the anode operating current density was instantly restored to 150 A / m. 2 ;

[0092] (3) Monitor the conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate of trivalent cerium ions reaches 55%, add 30% dilute sulfuric acid to the anolyte circulation tank to dynamically adjust the pH value of the anolyte from 2.0 and stabilize it at 0.8. At the same time, reduce the reference anolyte current density of the high-current resting phase to 100 A / m 2 ;

[0093] (4) When the trivalent cerium ion conversion rate is greater than 95%, stop the electrolysis power supply and ultrasonic output, and export all the anolyte to the crystallization ripening kettle; turn on the mechanical stirring, raise the system temperature to 75℃ at a heating rate of 1.5℃ / min, and keep it at this temperature for 40 minutes.

[0094] (5) After maturation, there is no need to cool the liquid. The suspension slurry is directly pumped into the plate and frame filter press for hot filtration. The temperature of the liquid is maintained above 70°C. The filtrate and filter cake are separated and the filter cake is washed with deionized water.

[0095] (6) The washed filter cake was put into the transformation vessel. Sodium hydroxide solution with a mass fraction of 20% was added according to the solid-liquid ratio of filter cake to sodium hydroxide solution of 1:3 g / mL. The mixture was stirred vigorously at 85°C for 3 hours. The mixture was then filtered again and washed until neutral. The washed filter cake was then sent into a rotary kiln and calcined at 800°C in air for 3 hours to obtain high-purity cerium dioxide powder.

[0096] Example 3:

[0097] This embodiment provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides, including the following steps:

[0098] (1) Take the anolyte and catholyte obtained in Preparation Example 2 and pump them into the anode chamber and cathode chamber of the double-chamber membrane electrolyzer separated by the perfluorosulfonic acid cation exchange membrane to establish circulation. The anode is a titanium-based lead dioxide mesh electrode and the cathode is a titanium plate. The anolyte circulation temperature is controlled at 35°C throughout the electrolysis process.

[0099] (2) An industrial ultrasonic transducer with a working frequency of 20kHz is installed on the outer wall of the anode chamber. The electroacoustic phase-controlled synchronization system is started to perform periodic anti-phase pulse operation. The cycle is as follows: the ultrasonic generator is turned on for 8 seconds, and the power density is 0.8W / cm². 2 At the same time, the anode operating current density is forcibly reduced to 10A / m. 2 Then, the ultrasonic generator was turned off for 8 seconds, and the anode operating current density was instantly restored to 250 A / m. 2 ;

[0100] (3) Monitor the conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate of trivalent cerium ions reaches 65%, add 30% dilute sulfuric acid to the anolyte circulation tank to dynamically adjust the pH value of the anolyte from 3.0 and stabilize it at 1.2. At the same time, reduce the reference anolyte current density of the high-current resting phase to 150 A / m 2 ;

[0101] (4) When the trivalent cerium ion conversion rate is greater than 95%, stop the electrolysis power supply and ultrasonic output, and export all the anolyte to the crystallization ripening kettle; turn on the mechanical stirring, raise the system temperature to 90℃ at a heating rate of 2.5℃ / min, and keep it at this temperature for 60 minutes.

[0102] (5) After maturation, there is no need to cool the liquid. The suspension slurry is directly pumped into the plate and frame filter press for hot filtration. The temperature of the liquid is maintained above 70°C. The filtrate and filter cake are separated and the filter cake is washed with deionized water.

[0103] (6) The washed filter cake was put into the transformation vessel. According to the solid-liquid ratio of filter cake to sodium hydroxide solution of 1:5 g / mL, a sodium hydroxide solution with a mass fraction of 30% was added. The mixture was stirred vigorously at 105°C for 1 hour. The mixture was then filtered again and washed until neutral. The washed filter cake was then sent to a rotary kiln and calcined at 950°C for 1.5 hours in air atmosphere to obtain high-purity cerium dioxide powder.

[0104] Example 4:

[0105] This embodiment provides an ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides, including the following steps:

[0106] (1) Take the anolyte and catholyte obtained in Preparation Example 1 and pump them into the anode chamber and cathode chamber of the double-chamber membrane electrolyzer separated by a perfluorosulfonic acid cation exchange membrane to establish circulation. The anode is a titanium-based iridium-tantalum coated mesh electrode and the cathode is a titanium plate. The anolyte circulation temperature is controlled at 25°C throughout the electrolysis process.

[0107] (2) An industrial ultrasonic transducer with a working frequency of 20kHz is installed on the outer wall of the anode chamber. The electroacoustic phase-controlled synchronization system is started to perform periodic anti-phase pulse operation. The cycle is: the ultrasonic generator is turned on for 4 seconds, and the power density is 0.6W / cm². 2 At the same time, the anode operating current density is forcibly reduced to 2A / m. 2 Then, the ultrasonic generator was turned off for 12 seconds, and the anode operating current density was instantly restored to 180 A / m. 2 ;

[0108] (3) Monitor the conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate of trivalent cerium ions reaches 65%, add 30% dilute sulfuric acid to the anolyte circulation tank to dynamically adjust the pH value of the anolyte from 2.5 and stabilize it at 0.9. At the same time, reduce the reference anolyte current density of the high-current resting phase to 110 A / m 2 ;

[0109] (4) When the trivalent cerium ion conversion rate is greater than 95%, stop the electrolysis power supply and ultrasonic output, and export all the anolyte to the crystallization ripening kettle; turn on the mechanical stirring, raise the system temperature to 80℃ at a heating rate of 2.2℃ / min, and keep it at this temperature for 45 minutes.

[0110] (5) After maturation, there is no need to cool the liquid. The suspension slurry is directly pumped into the plate and frame filter press for hot filtration. The temperature of the liquid is maintained above 70°C. The filtrate and filter cake are separated and the filter cake is washed with deionized water.

[0111] (6) The washed filter cake was put into the transformation vessel, and a sodium hydroxide solution with a mass fraction of 25% was added according to the solid-liquid ratio of filter cake to sodium hydroxide solution of 1:4 g / mL. The mixture was stirred vigorously at 100°C for 1.5 hours. The mixture was then filtered again and washed until neutral. The washed filter cake was then sent to a rotary kiln and calcined at 850°C for 2 hours in air atmosphere to obtain high-purity cerium dioxide powder.

[0112] Comparative Example 1:

[0113] Compared with Example 1, the difference is that sodium hexametaphosphate and ammonium persulfate are not added in the solution preparation step of Example 1, and the industrial ultrasonic transducer is not turned on in step (2), and the electrolysis is maintained at 200 A / m throughout. 2 The constant anode operating current density is maintained, and the electroacoustic inverting pulse operation is not performed; all other aspects are the same.

[0114] Comparative Example 2:

[0115] Compared with Example 1, the difference is that perfluorosulfonic acid cation exchange membrane is not used in step (1), a single-chamber electrolytic cell without diaphragm is used, and the anolyte and catholyte are mixed into the same electrolyte system, while the rest are the same.

[0116] Comparative Example 3:

[0117] Compared with Example 1, the difference is that the electroacoustic anti-phase pulse operation is cancelled in step (2), and the ultrasonic generator is continuously turned on throughout the electrolysis process, with a constant power density of 0.5W / cm². 2 Meanwhile, the anode operating current density remains at 200 A / m throughout the entire process. 2 The alternation between ultrasonic depolarization and high-current rest is not performed; all other operations are the same.

[0118] Comparative Example 4:

[0119] Compared with Example 1, the difference is that dynamic dimension reduction control is not performed in step (3), that is, when the single-pass conversion rate of trivalent cerium ions reaches 60%, dilute sulfuric acid is not added to the anolyte circulation tank, and the pH value of the anolyte is not adjusted during the entire electrolysis process. The rest are the same.

[0120] Comparative Example 5:

[0121] Compared with Example 1, the difference is that no heating operation is performed in step (4). After the anolyte is exported to the crystallization ripening kettle, it is mechanically stirred and ripened at room temperature of 25°C for 50 minutes. The rest are the same.

[0122] Comparative Example 6:

[0123] Compared with Example 1, the difference is that the alkaline metathesis transformation operation in step (6) is omitted, and the filter cake washed in step (5) is directly sent into the rotary kiln for constant temperature roasting at 900°C for 2 hours. The rest are the same.

[0124] Test Example 1:

[0125] Test objective: To verify the feasibility of the steric hindrance and membrane repulsion mechanism of polyphosphate macromolecules in terms of the stability of electrochemical systems and resistance to shuttle blocking effects.

[0126] Test steps:

[0127] (1) Take the anolyte and catholyte in the initial state of the electrolysis stage in Examples 1 to 4 and Comparative Examples 1 to 3, and record the initial anolyte voltage of each electrolysis system after it stabilizes at the moment of power-on.

[0128] (2) When the electrolysis process continues until the end point, i.e. the set trivalent cerium ion conversion rate is reached, the system anode cell voltage is recorded again, and the difference between the anode cell voltage at the beginning and end of the entire electrolysis process is calculated and recorded as the cell voltage drift rate.

[0129] (3) After the electrolysis process is completed, collect all the catholy liquid in each embodiment and comparative system, and accurately measure and record its total volume.

[0130] (4) The collected cathodic liquid samples were quantitatively analyzed using an inductively coupled plasma atomic emission spectrometer to determine the absolute physical mass of cerium ions. Combined with the physical amount of total cerium ions in the initial anodic liquid, the percentage data of cerium ion leakage rate of the cathodic liquid was calculated.

[0131] The test data is shown in Table 1.

[0132] Table 1: Test data on the stability and resistance to shuttle blocking effect of the electrochemical systems in each example and comparative example.

[0133] Experimental group Initial slot voltage (V) Termination slot voltage (V) Slot voltage drift (V) Cerium ion leakage rate in catholyte (%) Example 1 3.24 3.38 0.14 0.02 Example 2 3.15 3.37 0.22 0.04 Example 3 3.42 3.61 0.19 0.01 Example 4 3.28 3.43 0.15 0.03 Comparative Example 1 3.12 6.85 3.73 21.46 Comparative Example 2 2.85 3.21 0.36 48.72 Comparative Example 3 3.31 4.96 1.65 7.85

[0134] Conclusion: Based on Table 1 and Figure 1The data from Examples 1 to 4 show that the system maintained extremely high electrochemical stability throughout the entire electrolysis cycle, with the cell voltage drift rate strictly limited to a narrow range of 0.14 to 0.22 V. This contrasts sharply with the dramatic voltage spike of 3.73 V observed in Comparative Example 1. In Comparative Example 1, which did not introduce sodium hexametaphosphate and reverse-phase pulsed ultrasound, the system exhibited typical and severe anodic heterogeneous nucleation passivation, with the electrode surface rapidly covered by deposits, leading to a surge in interfacial resistance. Even in Comparative Example 3, which included sodium hexametaphosphate but maintained continuous ultrasound, the sustained high potential and cavitation disturbances caused irreversible chain breakage and degradation of the polyphosphate long chains, resulting in a loss of protection for the microscopic solid-liquid interface and a cell voltage drift rate still reaching 1.65 V. The systems in these examples, leveraging the robust steric hindrance constructed by polyphosphate macromolecules and coupled with precise depolarization reverse-phase timing, successfully and stably dispersed the oxidized tetravalent cerium in the bulk solution as a metastable sol, fundamentally eliminating the thermodynamic and kinetic pathways leading to anodic interface passivation.

[0135] The data distribution of cerium ion leakage rate in the catholyte further reveals the absolute control of the membrane repulsion mechanism in preventing the shuttle loss of valuable metals. The leakage rates in Examples 1 to 4 were only 0.01% to 0.04%, achieving almost zero membrane permeation loss of rare earth ions, while the natural leakage rate of Comparative Example 1 under conventional cation conditions was as high as 21.46%. More extreme was Comparative Example 2, where the perfluorosulfonic acid cation exchange membrane was removed, resulting in the complete loss of physical barriers within the system, causing nearly half of the cerium ions to inevitably diffuse and electromigrate to the cathode region. The 7.85% leakage rate in Comparative Example 3 also indirectly confirms the negative impact of the weakened charge shielding effect after the degradation of the complexing agent. Sodium hexametaphosphate binds to rare earth ions through long-chain coating in the weakly acidic electrolysis stage, forming a large polyphosphate complex ion with a high absolute negative Zeta potential.

[0136] This microstructure not only loses its electrophoretic driving force for migration towards the cathode in a macroscopic DC electric field, but is also pulled away from the cathode chamber by the same direction of the electric field. The inherent physical pore size limitation of the perfluorosulfonic acid cation exchange membrane, combined with the strong electrostatic repulsion field generated by the sulfonic acid groups on the membrane framework, constructs a physical barrier against the large negatively charged complex ions. The molecular weight-level steric shielding at the chemical level and the membrane field effect at the physical level form a tight coupling here. Together, they ensure that the electrochemical system is free from material collapse under the high-frequency operating environment of the electrode, providing a highly enriched single material basis for the subsequent in-situ hydrolysis phase transition.

[0137] Test Example 2:

[0138] Test objective: To verify the feasibility of the in-situ hydrolysis phase transition mechanism under the homogeneous precipitation theory and its advantages in engineering dehydration.

[0139] Test steps:

[0140] (1) Take the suspension slurry after the crystallization maturation or mechanical stirring stage in Examples 1 to 4 and Comparative Examples 1, 4 and 5 as the experimental objects, and accurately measure the equal volume of the mixed liquid in each group for later use.

[0141] (2) A quantitative mother liquor sample was extracted from the measured suspension slurry. After the solid phase was removed by high-speed centrifugation, the molar concentration of residual tetravalent cerium ions in the supernatant was determined by redox titration combined with inductively coupled plasma atomic emission spectrometry. The single-pass precipitation rate of cerium was calculated in combination with the initial total cerium concentration.

[0142] (3) Pump the remaining suspension slurry into a standard laboratory plate and frame filter press with a known effective filtration area, maintain a constant operating pressure of 0.3 MPa for hot or room temperature filtration, accurately record the volume of filtrate per unit time, and calculate the constant pressure average filtration flux.

[0143] (4) After depressurization, collect the wet filter cake in the filter press, quickly weigh the wet weight, and place it in an electric heating drying oven at 105℃ to bake to constant weight. Measure the mass of the removed water and calculate the moisture content of the filter cake.

[0144] The test data is shown in Table 2.

[0145] Table 2: Test data on in-situ hydrolysis phase change and engineering dehydration efficiency of each embodiment and comparative example

[0146] Experimental group Cerium single-pass precipitation rate (%) <![CDATA[Constant pressure average filtration flux (L / m 2 ·h)]]> Moisture content of filter cake (%) Example 1 98.74 315.62 22.36 Example 2 97.41 286.38 25.32 Example 3 99.12 328.15 21.14 Example 4 98.05 302.74 23.68 Comparative Example 1 96.28 32.45 78.53 Comparative Example 4 74.38 115.81 56.27 Comparative Example 5 15.71 12.36 85.19

[0147] Conclusion: Based on Table 2 and Figure 2 The data shows that the single-pass precipitation rate of cerium in Examples 1 to 4 was consistently above 97%, demonstrating a highly thorough liquid-solid phase transformation effect. In contrast, the precipitation rate in Comparative Example 5, which did not undergo high-temperature curing, was only 15.71%, with the vast majority of tetravalent cerium remaining in the liquid phase as a metastable complex sol. Isothermal heating combined with a high-acidity environment constituted the necessary thermodynamic dual-drive conditions for triggering the chain breakage of sodium hexametaphosphate polyphosphate. Comparative Example 4, lacking dynamic pH reduction control, suffered from slow hydrolysis kinetics, resulting in a precipitation rate of only 74.38%, failing to achieve deep demulsification and precipitation of the target ion. The slow, in-situ release of orthophosphate ions within the bulk solution created a low-supersaturation crystallization environment consistent with homogeneous precipitation theory.

[0148] This inside-out phase transition process significantly alters the microstructure and macroscopic properties of the precipitate, enabling the constant-pressure average filtration flux of the embodiment to reach an engineering high of 286 to 328 liters per square meter per hour. Traditionally, amorphous cerium hydroxide colloids generated by direct anodic oxidation have extremely high specific surface area and hydration levels, resulting in a significant decrease in the filtration flux of Comparative Example 1 to 32.45 liters per square meter per hour, with severe surface clogging of the filter media occurring within a very short contact time. The cerium phosphate complex salt particles generated by homogeneous hydrolysis possess dense and regular crystalline characteristics, completely eliminating the obstruction of porous media to the penetration of gel-like substances.

[0149] The fundamental differences in physical structure are also directly reflected in the dehydration efficiency of the filter cake. The moisture content of the filter cake in the example system was significantly reduced to the range of 21.14% to 25.32%. The extremely high moisture content of over 78% in Comparative Examples 1 and 5 not only stems from the strong binding of free water by the massive capillary network inside the colloidal flocs, but also exposes the enormous energy consumption burden that conventional processes will face in subsequent washing and calcination stages. By introducing a macromolecular complexing agent and controlling its site-specific hydrolysis, this scheme, while completing the chemical separation of rare earth elements, completely eliminates the dehydration bottleneck that traditional electrochemical processes struggle to overcome from the perspectives of engineering fluid dynamics and solid-liquid separation thermodynamics.

[0150] Test Example 3:

[0151] Test objective: To highlight the necessity of the electroacoustic reverse phase protection mechanism and the dual-chamber isolation membrane system in maintaining high electrochemical oxidation efficiency, in conjunction with comparative examples.

[0152] Test steps:

[0153] (1) Take the electrolysis reaction systems in Examples 1 to 4 and Comparative Examples 2 and 3 as test objects. At the beginning stage of establishing the cycle by connecting the power supply to each group of equipment, a high-precision digital energy integrator is connected in series in the DC power supply circuit to continuously record the total amount of charge actually input to the system during the entire electrolysis cycle.

[0154] (2) When the system determines that the preset conversion endpoint has been reached or the set electrolysis time has ended, collect all the anolytes or single-chamber mixed electrolytes of each group, measure the precise volume of the sample, and use ferrous ammonium sulfate standard solution for differential potential titration to determine the total physical quantity of tetravalent cerium ions actually generated in the system.

[0155] (3) Based on Faraday's law of electrolysis, the amount of tetravalent cerium ions measured by titration is converted into the theoretical charge required for the single electron transfer process, and the ratio of this value to the actual total input charge recorded by the energy integrator is calculated to obtain the average anodic current efficiency of each reaction system.

[0156] The test data is shown in Table 3.

[0157] Table 3: Quasi-homogeneous oxidation mechanism and current efficiency test data of each embodiment and comparative example

[0158] Experimental group Theoretical power consumption (kC) Actual total input power (kC) Anode average current efficiency (%) Example 1 571.25 645.18 88.54 Example 2 210.36 245.86 85.56 Example 3 939.81 1042.03 90.19 Example 4 565.42 642.31 88.03 Comparative Example 2 552.94 1675.58 33.00 Comparative Example 3 560.67 1251.49 44.80

[0159] Conclusion: Based on Table 3 and Figure 3 The data from Examples 1 to 4 show that they all exhibit excellent charge transfer efficiency in complex multiphase electrochemical systems, with their average anodic current efficiency generally remaining stable in the high range of 85% to 91%. In contrast, Comparative Example 2, lacking a physical isolation system, and Comparative Example 3, without the application of an electroacoustic phase reversal sequence, experienced extremely severe energy dissipation, with their current efficiencies plummeting to 33.00% and 44.80%, respectively. This huge difference in data directly reflects the core role of microscopic phase maintenance and macroscopic membrane barriers in the pseudo-homogeneous oxidation process.

[0160] In Comparative Example 3, the continuous ultrasonic superimposed high current density operation directly exposed the long sodium hexametaphosphate chain to the dual destruction of extreme oxidation potential and severe shearing by cavitation microjets. After the irreversible electrochemical degradation of the polyphosphate macromolecules, the trivalent and tetravalent cerium ions, which were originally encapsulated, were released back into the free state. Due to the loss of steric hindrance protection, they rapidly accumulated and adhered to the anode surface, generating heterogeneous nucleation. The adhered layer not only increased the ohmic resistance of interfacial mass transfer but also forced a large amount of input electrical energy to be consumed in side reactions such as oxygen evolution. The phase-controlled synchronization strategy of alternating high current resting and ultrasonic depolarization used in the example cleverly avoided the interfacial electrochemical damage of the macromolecular mediator under severe physical disturbance, effectively maintaining the network transport environment of persulfate radicals among free cerium ions in three-dimensional space.

[0161] In Comparative Example 2, where the perfluorosulfonic acid cation exchange membrane was removed, the highly oxidizing persulfate radicals generated in the anodic region and the successfully oxidized tetravalent cerium ions lost their spatial physical barrier. Driven by both concentration gradient diffusion and DC electrophoretic traction, these high-potential species easily crossed the center of the tank to reach the cathode surface and rapidly underwent reduction reactions, forming a parasitic redox cycle within the system that continuously consumes electrical energy but produces no net product. The deep integration of the physical isolation membrane and the pulse timing completely severed the reverse shuttle path of ions while maintaining the polymer's spatial conformation, ensuring that Faraday charge could be maximized and converted into effective thermodynamic work from cerium ion valence changes.

[0162] Test Example 4:

[0163] Test objective: To verify the thermodynamic forced repulsion mechanism of impurities and the effectiveness of the fully closed-loop process in improving the purity of the final product and eliminating specific contaminants.

[0164] Test steps:

[0165] (1) The solid powders obtained by the final roasting process of Examples 1 to 4 and Comparative Examples 1, 4, 5 and 6 were taken as experimental objects. For Comparative Example 5, which could not be effectively separated from solid due to the lack of high-temperature curing, the wet filter cake retained by pressure filtration was collected and sampled after forced constant temperature drying at 105°C.

[0166] (2) Accurately weigh 0.1000 g of each group of solid powder samples, place them in a polytetrafluoroethylene digestion vessel, add a mixture of nitric acid and hydrogen peroxide, and perform high-temperature and high-pressure digestion in a microwave digestion instrument. After the solid sample is completely converted into a transparent and homogeneous liquid phase, cool it and make up to the standard volume.

[0167] (3) The elemental quantitative scanning of the digested solution after volume adjustment was performed by inductively coupled plasma mass spectrometry to accurately determine the absolute physical mass of cerium, praseodymium and neodymium in the solution. The purity of the final cerium dioxide product and the co-precipitation rate of praseodymium / neodymium impurities were calculated by combining the initial powder sample mass.

[0168] (4) The trace concentration of phosphorus in the digestion solution was detected by using molybdenum blue spectrophotometry combined with inductively coupled plasma atomic emission spectrometry. The total physical residual amount of phosphorus in each group of solid final products was calculated based on the dilution factor.

[0169] The test data is shown in Table 4.

[0170] Table 4: Test data on the purity and impurity rejection efficiency of the final products of each example and comparative example.

[0171] Experimental group Cerium dioxide final product purity (%) Praseodymium / neodymium impurity co-precipitation entrainment rate (%) Residual phosphorus content in the final product (ppm) Example 1 99.94 0.02 8 Example 2 99.91 0.05 14 Example 3 99.96 0.01 6 Example 4 99.93 0.03 11 Comparative Example 1 91.82 7.93 0 Comparative Example 4 87.45 11.62 845 Comparative Example 5 82.16 16.38 5120 Comparative Example 6 83.65 0.04 152340

[0172] Conclusion: Based on Table 4 and Figure 4 According to the data, the purity of the cerium dioxide final product in Examples 1 to 4 exceeded the industrial grade limit of 99.9%, and the entrainment rate of non-variable rare earth impurities was forcibly reduced to below 0.05%. Within the strongly acidic range set by the dimension reduction control, a harsh phase transition separation environment was constructed inside the system. The hydrolysis constants of trivalent praseodymium ions and neodymium ions were much lower than those of tetravalent cerium ions, and they completely lost the driving potential energy to form hydroxide or phosphate precipitates at the thermodynamic level. The process of homogeneous hydrolysis and slow release of orthophosphate ions promoted the formation of high-density coarse crystals of cerium. This regular crystal morphology closed the lattice encapsulation channels caused by concentration polarization in the liquid phase at the physical spatial level, cutting off the mechanical entrainment pathways of impurities that are common in conventional precipitation processes.

[0173] Comparative Example 4, lacking dynamic acidity adjustment intervention, revealed the consequences of a runaway thermodynamic environment. The relatively high pH value of the system lowered the solubility limit of non-variable rare earth ions, leading to the co-precipitation of 11.62% praseodymium-neodymium impurities with tetravalent cerium. Comparative Example 5, which did not undergo high-temperature curing treatment, was in an even more severe separation state. The low-temperature environment caused the hydrolysis kinetics of the long polyphosphate chains to stagnate. The large amount of amorphous colloids remaining in the system physically entrained a large amount of impurity-rich mother liquor during the solid-liquid separation process, causing the product purity to drop to 82.16%. The dual extreme conditions of high temperature and strong acid at this point constructed an irreplaceable synergistic repulsion network, which acted as a chemical switch to trigger the site-specific release of phosphate ions, maintaining the highly active free state of impurity ions in the liquid phase.

[0174] The data distribution of residual phosphorus content confirms the completeness of the closed-loop logic in the final purification stage. Comparative Example 6, which omits the alkaline dissolution and metathesis process, achieves the separation of cerium from non-variable valence rare earth elements at the front end, but its final product contains a phosphorus contamination of up to 152,340 ppm. The product matrix essentially remains at the cerium phosphate double salt stage, losing its application basis as a high-purity oxide material. The example introduces a sodium hydroxide solution with a specific ratio and temperature conditions. Utilizing the thermodynamic displacement potential provided by the strong alkalinity, phosphate ions are forcibly stripped and cerium hydroxide is generated in the solid-phase interface reaction. This phase transformation removes the phosphorus-oxygen bonding barrier within the intermediate product, promotes the recovery and recycling of the liquid-phase phosphorus source, and ensures that the residual phosphorus content in the final calcined cerium dioxide powder remains at an extremely low level.

[0175] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the complete separation of rare earth oxides via ultrasonic-enhanced electrochemical coupling, characterized in that, Includes the following steps: S1. Add polyphosphate complexing agent and redox mediator to cerium-rich rare earth aqueous solution, adjust the pH value and keep the temperature constant to obtain anolyte; simultaneously prepare dilute acid aqueous solution as catholyte. S2. Pump the anolyte and catholyte into a two-chamber membrane electrolyzer separated by a cation exchange membrane to establish circulation; start the electroacoustic phase-controlled synchronization system containing an ultrasonic generator to perform periodic anti-phase pulse operation: reduce the anolyte working current density when the ultrasonic generator is turned on, and instantly restore the high anolyte working current density when the ultrasonic generator is turned off. S3. Monitor the conversion rate of trivalent cerium ions in the anolyte online. When the conversion rate reaches the first set threshold, add acid to the anolyte to dynamically adjust the pH value and simultaneously reduce the reference anolyte current density during the ultrasonic shutdown phase. S4. When the trivalent cerium ion conversion rate reaches the second set threshold, stop the electrolysis power supply and ultrasonic output, export the anolyte and program the temperature to ripen it, so that the free cerium ions will hydrolyze to form a double salt crystalline phase. S5. The matured suspension slurry is directly subjected to hot pressure filtration separation, the filter cake is retained and washed; S6. The filter cake is added to an alkaline solution for solid-phase metathesis transformation to remove phosphorus. After being filtered and washed again until neutral, it is sent to a rotary kiln for constant-temperature calcination to obtain high-purity cerium dioxide powder.

2. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S1, the cerium-rich rare earth aqueous solution is a cerium-rich rare earth sulfate aqueous solution, and the total rare earth ion molar concentration of the cerium-rich rare earth sulfate aqueous solution is 0.5-1.5 mol / L, wherein trivalent cerium ions account for 40%-80% of the total rare earth ions. The polyphosphate complexing agent is sodium hexametaphosphate, and the free concentration of sodium hexametaphosphate in the system is controlled at 0.05–0.15 mol / L; The redox mediator is ammonium persulfate, and the free concentration of ammonium persulfate in the system is controlled to be 0.02–0.08 mol / L; The pH adjustment and temperature control operation is as follows: add a 20% (w / w) dilute sulfuric acid solution or sodium hydroxide solution to adjust the initial pH of the system to 2.0-3.0, and maintain the temperature at 20-35°C.

3. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S2, the cycle period parameter of the periodic inverted pulse operation is: Turn on the ultrasonic generator with a working frequency of 20kHz for 3-8 seconds, with a power density of 0.3-0.8W / cm³. 2 At the same time, the anode operating current density is forcibly reduced to 0-10 A / m. 2 ; Then turn off the ultrasonic generator for 8-15 seconds, and simultaneously restore the anode operating current density to 150-250 A / m. 2 .

4. The ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S3, the first set threshold is 55% to 65%; When the first set threshold is reached, 30% dilute sulfuric acid is added dropwise to the anolyte to dynamically adjust and stabilize the pH value of the anolyte between 0.8 and 1.

2. Simultaneously reduce the reference anode current density to 100–150 A / m 2 .

5. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S4, the second set threshold is greater than 95%; The specific operation of the programmed temperature rise cooking is as follows: turn on the mechanical stirrer, raise the system temperature to 75-90℃ at a heating rate of 1.5-2.5℃ / min, and cook at this temperature for 40-60 minutes.

6. The ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S6, the operation of adding the filter cake to the alkaline solution for solid-phase metathesis transformation is as follows: according to the solid-liquid ratio of filter cake to sodium hydroxide solution of 1:3 to 1:5 g / mL, add sodium hydroxide solution with a mass fraction of 20% to 30%, and stir vigorously at 85 to 105°C for 1 to 3 hours. The constant temperature roasting process is as follows: the washed neutral filter cake is roasted at a constant temperature of 800-950℃ for 1.5-3 hours in air atmosphere.

7. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S2, the anode of the dual-chamber diaphragm electrolytic cell is a titanium-based lead dioxide mesh electrode or a titanium-based iridium-tantalum coated mesh electrode, and the cathode is a titanium plate; the catholyte is a dilute sulfuric acid aqueous solution with a mass fraction of 3% to 8%.

8. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S2, the cation exchange membrane is a perfluorosulfonic acid cation exchange membrane, wherein the main chain of the perfluorosulfonic acid cation exchange membrane has a polytetrafluoroethylene structure and the side chain ends have sulfonic acid groups.

9. The ultrasonic-enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, In step S5, during the hot pressure filtration separation process, the suspended slurry does not need to be cooled, and the temperature of the liquid is maintained above 70°C.

10. The ultrasonically enhanced electrochemical coupling process for the complete separation of rare earth oxides according to claim 1, characterized in that, The following control parameters are used in process steps S2, S3, and S4: In step S2, the ultrasonic generator is turned on for 5 seconds with a power density of 0.5 W / cm². 2 The anode operating current density was reduced to 5A / m 2 Turn off the ultrasonic generator for 10 seconds, and instantly restore the anode working current density to 200A / m. 2 ; In step S3, the first set threshold is 60%, the pH value is adjusted to 1.0, and the reference anolyte current density is reduced to 120 A / m. 2 ; In step S4, the temperature is increased to 85°C at a rate of 2.0°C / min, and then maintained at this temperature for 50 minutes.

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