A process for deep purification and refining of rare earth nitrates from complex chloride salt systems.

Abstract

This invention relates to the field of rare earth refining technology and discloses a process for deep purification and refining of rare earth nitrates from a complex chloride salt system. The process includes: adjusting the absolute pressure of the treatment environment to 35 kPa to 45 kPa; distributing the rare earth chloride solution into a falling film and counter-currently mass-transferring it with nitric acid vapor; utilizing the latent heat of nitric acid vapor condensation to drive the vaporization phase change of the falling film water, maintaining the gas-liquid interface temperature at 80°C to 85°C to inhibit irreversible hydrolysis of rare earth ions; and allowing hydrogen chloride to escape through interfacial anion replacement to obtain a rare earth nitrate enriched solution. This invention resolves the physical antagonism between dechlorination requirements and hydrolysis limitations through a latent heat self-balancing mechanism, achieving deep anion stripping in a continuous fluid production environment without the need for external solid precipitants, avoiding material loss and wastewater treatment pressure, and improving the purity and space-time yield of rare earth nitrates.

Description

Technical Field

[0001] This invention belongs to the field of rare earth refining technology, and in particular relates to a process for deep purification and refining of rare earth nitrates from complex chloride salt systems. Background Technology

[0002] Currently, rare earth hydrometallurgical refining processes typically utilize anion exchange to convert rare earth chlorides into high-purity rare earth nitrates. The industry generally employs a precipitation-resolution process, using ammonium bicarbonate or oxalic acid as precipitants to generate a solid precipitate of rare earth ions in the liquid phase. After multi-stage water washing to remove chloride ions adsorbed on the solid surface, the solid precipitate is dissolved in nitric acid to obtain a rare earth nitrate solution. However, the precipitation-resolution process faces significant physical constraints and environmental burdens in practical engineering applications. The introduction of exogenous precipitants generates large amounts of industrial wastewater containing high concentrations of ammonia nitrogen and chloride ions. The repeated conversion of rare earth materials between the solid and liquid phases leads to interfacial entrainment losses, reducing the overall rare earth yield. Furthermore, the rare earth chloride aqueous solution system exhibits an inherent antagonism between the dechlorination kinetic requirements and the thermodynamic limitations of metal ion hydrolysis.

[0003] Dissociation of rare earth ions and chloride ions requires high proton concentration and energy input. However, rare earth ions exhibit a strong tendency to hydrolyze in high-temperature aqueous environments. Interfacial temperature rise triggers irreversible hydrolysis side reactions in the intrinsic liquid system, generating insoluble and inactive rare earth chloride oxides. This physical conflict means that traditional processes rely on solid-liquid physical isolation, making in-situ anion replacement impossible in a continuous fluid production environment. Existing technologies drive anion replacement by increasing the stripping temperature or acid concentration, but due to the lack of effective enthalpy decoupling methods, the hydrolysis problem caused by interfacial overheating remains unresolved. Besides the physical limitations caused by solid-liquid phase transitions, existing process logic architectures are inadequate, making it difficult to simultaneously achieve material continuity and extremely low chloride residue. For example, publication number CN111874936... Chinese invention patent A discloses a method for preparing raw materials for preparing nano-rare earth oxides. It replaces the traditional precipitation process by using a multi-stage countercurrent washing combined with nitric acid back-extraction solvent extraction path. When dealing with complex high-concentration chloride salt systems, the technical premise is that rare earth ions migrate to the organic phase in advance. The rare earth chloride salt path in the aqueous system is forcibly introduced into a huge organic solvent circulation system, which faces the risk of organic phase entrainment loss. Moreover, it is completely dependent on the diffusion equilibrium of the liquid-liquid interface, which limits the deep chloride ion stripping ability inside the hydrated coordination sphere. The washing water consumption is huge and high-salt washing water that is difficult to dispose of is generated. This kind of solution does not address the essential contradiction between the dechlorination kinetic requirements of the aqueous system and the thermodynamic instability of rare earth cations. When dealing with complex variable operating conditions, it is impossible to accurately match the energy field to balance the anion stripping rate and product yield.

[0004] Therefore, the technical problem to be solved by this invention is how to simultaneously suppress the hydrolysis of rare earth ions during the stripping of chloride ions in a continuous fluid production environment without introducing exogenous solid precipitants, through the decoupling control of energy field and pressure field. Summary of the Invention

[0005] This invention aims to solve the problem of deep chloride ion stripping in situ in a liquid environment due to the contradiction between the dechlorination kinetic requirements in aqueous solutions and the thermodynamic limitations of rare earth hydrolysis.

[0006] In this technical solution, a process for deep purification and refining of rare earth nitrates from a complex chloride salt system includes the following steps:

[0007] Step 101: Provide a rare earth chloride solution, and control the mass percentage concentration of rare earth ions in the rare earth chloride solution to be 15% to 25%;

[0008] Step 102: Adjust the absolute pressure of the treatment environment to 35 kPa to 45 kPa by decompression to establish physical conditions suitable for low-temperature vaporization of water molecules.

[0009] Step 103: The rare earth chloride solution is distributed into a falling film of uniform thickness through the distributor at the top of the column, while nitric acid vapor with a temperature of 110°C to 115°C and a mass concentration of 65% to 68% is continuously introduced into the bottom of the column to countercurrent mass transfer with the falling film.

[0010] Step 104: Nitric acid vapor condenses and releases heat on the surface of the falling film, driving the moisture inside the falling film to absorb the heat and generate a vaporization phase change, forming a phase change interface on the surface of the falling film. The temperature of the phase change interface is maintained at 80°C to 85°C through latent heat exchange to suppress the irreversible hydrolysis side reaction of rare earth ions.

[0011] Step 105: Taking advantage of the concentration of nitrate ions at the phase transition interface, chloride ions coordinated with rare earth ions inside the falling film diffuse to the interface and undergo anion replacement. The generated hydrogen chloride molecules escape to the gas phase side with water vapor. As the falling film flows from the top to the bottom of the tower, the chloride ion concentration continuously decreases, and finally a high-purity rare earth nitrate enriched solution with a chloride ion mass percentage of less than 0.005% is obtained at the bottom of the tower.

[0012] Preferably, step 103 further includes: controlling the thickness of the falling film to be 0.2 mm to 0.8 mm, and adjusting the Reynolds number of the falling film to be 1200 to 2500, so as to generate a surface eddy current that enhances mass transfer and increases the dynamic contact area at the phase change interface formed by the falling film and nitric acid vapor.

[0013] Preferably, the method further includes: performing gradient cooling crystallization on the rare earth nitrate enrichment solution, thereby limiting the critical supersaturation of the rare earth nitrate enrichment solution during the cooling process, so that the rare earth nitrate crystals preferentially precipitate from the substrate rich in impurity ions, thus achieving phase separation of rare earth nitrate and impurity ions.

[0014] Preferably, in step 104, the gaseous mixture is introduced into the condensation unit. By adjusting the temperature of the condenser wall of the condensation unit to the range of 95°C to 105°C, the nitric acid component in the mixture is converted into a liquid phase and guided back to step 103 by gravity, while keeping the hydrogen chloride molecules in the gaseous phase.

[0015] Preferably, the mass percentage of metal impurity ions in the rare earth chloride solution is not higher than 2%; in step 105, the free nitric acid mass concentration inside the falling film is maintained at 35% to 45% by adjusting the flux of nitric acid vapor, so as to reduce the adsorption activity of metal impurity ions on the surface of rare earth nitrate crystal nuclei.

[0016] Preferably, in step 101, the pH value of the rare earth chloride solution is adjusted to 1.5 to 3.0 to pre-inhibit the hydrolysis of rare earth cations by utilizing the acidic environment, and the initial density of the rare earth chloride solution is adjusted to 1.2 g / cm³ to 1.4 g / cm³ according to the type of rare earth ions.

[0017] Preferably, the top distributor includes a ring with a serrated overflow edge, the tooth tip spacing of which is 3 mm to 6 mm. The rare earth chloride solution is converted into a falling film evenly distributed along the inner wall of the tower by the capillary force formed by the tooth tip spacing under gravity.

[0018] Preferably, after gradient cooling crystallization is completed, the obtained material is centrifuged to separate solid and liquid to obtain high-purity rare earth nitrate crystals, and the separated mother liquor is returned to step 101 as a solvent for recycling, so as to reintroduce the residual rare earth ions in the mother liquor into the negative pressure environment.

[0019] Preferably, in step 103, the mass ratio of the incoming nitric acid vapor flow rate to the input rare earth chloride solution flow rate is controlled to be 3:1 to 5:1. By limiting the mass flow rate ratio of the gas and liquid phases, it is ensured that all chloride ions are replaced and removed within the contact time before the falling film flows to the bottom of the tower.

[0020] Compared with existing technologies, the process for deep purification and extraction of rare earth nitrates from complex chloride salt systems of the present invention has the following advantages:

[0021] 1. In the process of deep purification and refining of rare earth nitrates, an isothermal transformation zone is constructed at the gas-liquid phase change interface by coupling a deep negative pressure environment with specific enthalpy parameters. This is achieved by offsetting the latent heat of condensation of nitric acid vapor with the latent heat of vaporization of water molecules. This energy transfer method utilizes the endogenous heat transfer of the phase change process to offset the sensible heat shock brought by external steam injection, thus clamping the actual temperature of the reaction interface below the metal ion hydrolysis temperature limit. This ensures that rare earth ions can withstand high-concentration proton chemical stripping while avoiding the formation of insoluble chlorine oxide precipitation. This mechanism solves the physical antagonism between the dechlorination kinetic requirements and the thermodynamic limitations of hydrolysis in rare earth wet refining, and achieves the non-destructive reconstruction of the chemical form of the target product in a continuous fluid environment.

[0022] 2. The falling film liquid phase distribution and countercurrent gas stripping process form a large-area dynamic mass transfer interface. Combined with the immediate extraction of gas phase products, the chemical equilibrium in the system shifts unidirectionally towards the formation of rare earth nitrates. Since hydrogen chloride has low solubility and high relative volatility in the high-temperature, high-acidity liquid phase, the generated hydrogen chloride rapidly penetrates the liquid film and enters the gas phase under negative pressure driven by water vapor, achieving in-situ stripping and deep removal of chloride ions. This dechlorination method based on the difference in physical phase equilibrium eliminates the dependence of traditional precipitation processes on reagents such as oxalic acid or ammonium carbonate, eradicates the source of a large amount of ammonia nitrogen wastewater in the precipitation mother liquor, and reduces the environmental load of the subsequent tail gas treatment system.

[0023] 3. Utilizing the physical reality that the substrate is in a high-concentration, critically supersaturated state after gas stripping conversion, gradient cooling crystallization is performed by limiting the cooling rate. Taking advantage of the significant difference in the solubility decay curves of rare earth nitrates and associated impurity nitrates, high-purity rare earth nitrate crystals are preferentially precipitated. This step directly utilizes the residual heat field left over from the conversion process, without the need to introduce additional external crystallization control additives. This avoids material entrainment losses caused by multi-stage washing in traditional precipitation and resolution processes. The entire process highly folds anion replacement, solvent concentration, and impurity ion separation within a closed-loop fluid operation, improving the space-time yield of the refining process while ensuring a high rare earth yield. Attached Figure Description

[0024] Figure 1 This is a flow chart of the rare earth nitrate deep purification and refining process of the present invention;

[0025] Figure 2 This is the hardware architecture and feedback logic diagram of the purification system of this invention. Detailed Implementation

[0026] The technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application are within the scope of protection of this application.

[0027] It should be noted that all directional and positional terms used in this invention, such as: up, down, left, right, front, back, vertical, horizontal, inner, outer, top, bottom, transverse, longitudinal, center, etc., are only used to explain the relative positional relationship and connection between components in a specific state (as shown in the accompanying drawings). They are only for the convenience of describing this invention and do not require that this invention be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention. In addition, the descriptions of "first," "second," etc., in this invention are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0028] In the description of this invention, unless otherwise explicitly specified and limited, the terms installation, connection, and linking should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections; they can refer to direct connections or indirect connections through an intermediate medium; they can refer to the internal connection of two components. For those skilled in the art, the specific meaning of the above terms in this invention can be understood in conjunction with the specific circumstances.

[0029] In the description of this specification, references to the terms "an embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples," 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 present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example, and the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0030] A process for deep purification and refining of rare earth nitrates from complex chloride salt systems includes the following steps:

[0031] Step 101: Provide a rare earth chloride solution, and control the mass percentage concentration of rare earth ions in the rare earth chloride solution to be 15% to 25%;

[0032] Step 102: Adjust the absolute pressure of the treatment environment to 35 kPa to 45 kPa by decompression to establish physical conditions suitable for low-temperature vaporization of water molecules.

[0033] Step 103: The rare earth chloride solution is distributed into a falling film of uniform thickness through the distributor at the top of the column, while nitric acid vapor with a temperature of 110°C to 115°C and a mass concentration of 65% to 68% is continuously introduced into the bottom of the column to countercurrent mass transfer with the falling film.

[0034] Step 104: Nitric acid vapor condenses and releases heat on the surface of the falling film, driving the moisture inside the falling film to absorb the heat and generate a vaporization phase change, forming a phase change interface on the surface of the falling film. The temperature of the phase change interface is maintained at 80°C to 85°C through latent heat exchange to suppress the irreversible hydrolysis side reaction of rare earth ions.

[0035] Step 105: Taking advantage of the concentration of nitrate ions at the phase transition interface, chloride ions coordinated with rare earth ions inside the falling film diffuse to the interface and undergo anion replacement. The generated hydrogen chloride molecules escape to the gas phase side with water vapor. As the falling film flows from the top to the bottom of the tower, the chloride ion concentration continuously decreases, and finally a high-purity rare earth nitrate enriched solution with a chloride ion mass percentage of less than 0.005% is obtained at the bottom of the tower.

[0036] Preferably, step 103 further includes: controlling the thickness of the falling film to be 0.2 mm to 0.8 mm, and adjusting the Reynolds number of the falling film to be 1200 to 2500, so as to generate a surface eddy current that enhances mass transfer and increases the dynamic contact area at the phase change interface formed by the falling film and nitric acid vapor.

[0037] Preferably, the method further includes: performing gradient cooling crystallization on the rare earth nitrate enrichment solution, thereby limiting the critical supersaturation of the rare earth nitrate enrichment solution during the cooling process, so that the rare earth nitrate crystals preferentially precipitate from the substrate rich in impurity ions, thus achieving phase separation of rare earth nitrate and impurity ions.

[0038] Preferably, in step 104, the gaseous mixture is introduced into the condensation unit. By adjusting the temperature of the condenser wall of the condensation unit to the range of 95°C to 105°C, the nitric acid component in the mixture is converted into a liquid phase and guided back to step 103 by gravity, while keeping the hydrogen chloride molecules in the gaseous phase.

[0039] Preferably, the mass percentage of metal impurity ions in the rare earth chloride solution is not higher than 2%; in step 105, the free nitric acid mass concentration inside the falling film is maintained at 35% to 45% by adjusting the flux of nitric acid vapor, so as to reduce the adsorption activity of metal impurity ions on the surface of rare earth nitrate crystal nuclei.

[0040] Preferably, in step 101, the pH value of the rare earth chloride solution is adjusted to 1.5 to 3.0 to pre-inhibit the hydrolysis of rare earth cations by utilizing the acidic environment, and the initial density of the rare earth chloride solution is adjusted to 1.2 g / cm³ to 1.4 g / cm³ according to the type of rare earth ions.

[0041] Preferably, the top distributor includes a ring with a serrated overflow edge, the tooth tip spacing of which is 3 mm to 6 mm. The rare earth chloride solution is converted into a falling film evenly distributed along the inner wall of the tower by the capillary force formed by the tooth tip spacing under gravity.

[0042] Preferably, after gradient cooling crystallization is completed, the obtained material is centrifuged to separate solid and liquid to obtain high-purity rare earth nitrate crystals, and the separated mother liquor is returned to step 101 as a solvent for recycling, so as to reintroduce the residual rare earth ions in the mother liquor into the negative pressure environment.

[0043] Preferably, in step 103, the mass ratio of the incoming nitric acid vapor flow rate to the input rare earth chloride solution flow rate is controlled to be 3:1 to 5:1. By limiting the mass flow rate ratio of the gas and liquid phases, it is ensured that all chloride ions are replaced and removed within the contact time before the falling film flows to the bottom of the tower.

[0044] Example 1: In an industrial rare earth extraction and separation line with a high chloride ion background and rich in non-rare earth metal impurities such as iron, aluminum, calcium, and magnesium, a mixed rare earth chloride solution of lanthanum chloride and cerium chloride is used as the starting material. The initial mass percentage concentration of rare earth ions is controlled between 15% and 25%. At this time, rare earth ions and chloride ions in the system form stable hydrated coordination spheres. ,in, Referring to rare earth elements, Refers to the coordination number of water molecules. The coordination number of chloride ions is used. This coordination structure is thermodynamically stable under normal atmospheric pressure, making it difficult to achieve anion replacement without inducing rare earth hydrolysis by simply heating.

[0045] The absolute pressure inside the gas-liquid contact equipment is regulated and maintained at 35 kPa to 45 kPa using a vacuum pump unit, causing the boiling point of water in the system to drop below 80°C. A rare earth chloride solution preheated to 75°C to 80°C is then passed through a distributor at the top of the tower to form a falling film with a thickness of 0.2 mm to 0.8 mm, which flows along the inner wall of the tower. Simultaneously, nitric acid vapor at a temperature of 110°C to 115°C and a mass concentration of 65% to 68% is continuously injected from the bottom of the tower. Under negative pressure, the superheated nitric acid vapor condenses in situ upon contact with the falling film surface, releasing latent heat of condensation. This energy directly drives the water molecules on the surface of the liquid film to boil and vaporize, absorbing the latent heat of vaporization. The flow rate of the nitric acid vapor is adjusted by regulating the mass ratio of the input nitric acid vapor flow rate to the rare earth chloride solution flow rate. The ratios ranged from 3:1 to 5:1, among which To achieve a balance in enthalpy at the gas-liquid interface through a specific mass ratio, the temperature of the interface is clamped between 80°C and 85°C. This control mechanism based on overall mass ratio essentially relies on a high-speed turbulent liquid film with a thickness of only 0.2mm to 0.8mm and a Reynolds number of 1200 to 2500 as a mesoscopic physical conduction bridge. The micron-sized geometry and intense internal fluid turbulence break down the normal heat transfer resistance of the liquid phase. This allows the condensation heat released by nitric acid vapor molecules colliding with the liquid surface to be instantly absorbed and dissipated by the violent boiling and vaporization of the lower water molecules before causing a destructive local temperature rise. This, in turn, allows the external temperature to gradually decrease. The valve power supply logic is mapped across scales to seamlessly counteract and suppress transient hot spots on the interface surface. Since the phase change interface is maintained within the safe temperature range for hydrolysis, the proton flow dissociated from the condensed nitric acid continuously breaks the rare earth-chlorine hydrate coordination network. The displaced chloride ions are converted into hydrogen chloride molecules, and the accompanying vapor escapes to the gas phase side under negative pressure. The mass percentage of chloride ions in the rare earth nitrate enriched solution obtained at the bottom of the tower is less than 0.005%. The enriched solution is introduced into a gradient cooling crystallizer, and high-purity rare earth nitrate crystals are precipitated by utilizing the solubility difference between rare earth nitrates and impurity metal nitrates such as iron and aluminum.

[0046] Example 2: On an experimental platform equipped with a liquid ring vacuum pump group, a steam generator, and an online ion monitor, a mixed solution of lanthanum chloride and cerium chloride with an initial rare earth ion mass percentage concentration of 20.2% and a chloride ion mass percentage concentration of 8.5% was selected as the starting material. The ion monitor's acquisition accuracy was better than 0.001%, and the original acquisition link was superimposed with Gaussian white noise with a signal-to-noise ratio of 25dB to simulate a non-ideal sensing environment. Under this sensing condition rich in strong acid corrosion, the probe of the online ion monitor was not directly exposed to the main reaction field, but was equipped with a polytetrafluoroethylene high-temperature resistant and corrosion-resistant sampling bypass. A high-flux microporous hydrophobic permeable membrane was deployed in the bypass. This physical water-blocking layer only allows gaseous hydrogen chloride molecules to directionally permeate into the controlled isothermal electrochemical buffer pool inside the sensor. While shielding against overheated acid mist and droplet scouring above 110°C, it achieves accurate and non-destructive continuous monitoring of the potential of the gas-phase dechlorination products. The mass ratio of nitric acid vapor to rare earth chloride solution was... It is used to balance the vaporization driving force provided by the latent heat of nitric acid vapor condensation with the risk of thermal runaway caused by sensible heat. Its value is based on the instantaneous partial pressure of hydrogen chloride in the escape phase at the top of the column. It is confirmed that, among them, For mass ratio, For the partial pressure of hydrogen chloride, when The absolute value of the rate of change is lower than the equilibrium threshold. Time increases Given values, where To balance the threshold, the test selected typical operating conditions. The value is 4.2:1.

[0047] Three comparative systems were set up to verify the synergistic effect. Comparative system one used an absolute pressure of 101.3 kPa and was heated to 110°C. Comparative system two used only heat transfer through the tower wall at an absolute pressure of 40.5 kPa without introducing nitric acid vapor. The experimental system used an absolute pressure of 40.5 kPa and was set to... The ratio was 4.2:1. In control group one, a white flocculent precipitate formed in the liquid phase after 45 min of reaction, which was characterized by X-ray diffraction as lanthanum oxychloride. In control group two, the solvent vaporization rate decreased by 78.5% compared to the experimental group, and insufficient interfacial proton concentration led to stagnation of anion replacement. The experimental group maintained the temperature of the gas-liquid phase transition interface at 82.3℃ to 83.1℃ under an absolute pressure of 40.5 kPa, avoiding the sensitive region of hydrolysis side reactions and obtaining a enriched solution with a chloride ion mass percentage of 0.0032%. This enriched solution was cooled at a rate of 5℃ / h, and rare earth nitrate crystals with a purity of not less than 99.995% precipitated at 25.4℃. The response characteristics of the parameter boundaries were examined. When the absolute pressure increased to 50.5 kPa, the equilibrium temperature of the phase transition interface increased to 88.5℃, and insoluble chloride oxide with a mass percentage of 0.05% was detected in the liquid phase. When the chloride ion removal rate increases to 6.5:1, the system reaches a plateau and the total energy consumption increases by 32.4%. These data confirm the effects of pressures between 35 kPa and 45 kPa and the mass ratio. A ratio of 3:1 to 5:1 represents the working window for hydrolysis and anionic stripping.

[0048] Example 3: This example combines Figures 1 to 2 A process description for the deep purification and extraction of rare earth nitrates from a complex chloride salt system, such as... Figure 1 As shown, in step 101, a rare earth chloride solution is provided and the concentration is controlled to be 15 to 25%. Then, the flow proceeds to step 102, where the pressure is reduced to adjust the absolute pressure to 35 to 45 kPa. The flow proceeds to step 103, where the solution forms a falling film and is countercurrently mass-transferred with nitric acid vapor. In step 104, the latent heat of condensation of nitric acid vapor is used to maintain the phase transition interface temperature at 80°C to 85°C. In step 105, anion exchange is performed to obtain a rare earth nitrate enriched solution.

[0049] like Figure 2As shown, the overall hardware environment consists of multiple core layers. The vacuum and steam system at the top is equipped with a vacuum pump group and a nitric acid vapor generator, which outputs a 35-45 kPa pressure field to the core of the falling film mass transfer tower. The monitoring feedback control cluster located on the side is equipped with an infrared thermal imaging sensor and an online ion monitor, which continuously sends enthalpy compensation commands to the core of the falling film mass transfer tower. The main body of the core of the falling film mass transfer tower contains, from top to bottom, a tower top distributor, a falling film phase change interface, and a gas phase escape flow unit. The rare earth nitrate enriched liquid exported from the bottom enters the refining and recovery system at the lower end. The refining and recovery system integrates a condensation interception unit and a gradient cooling crystallizer. The condensation interception unit guides the acquired nitric acid components back to the tower top distributor of the core of the falling film mass transfer tower.

[0050] Example 4: In a continuous purification production line where the mass percentage concentration of rare earth ions fluctuates by up to 15% due to upstream extraction, to maintain the stability of the falling film flow field, the falling film distributor at the top of the gas-liquid contact device is equipped with an annular distribution slit, the width of which is... Based on the kinematic viscosity of rare earth chloride solutions With the preset liquid film thickness Based on the Navier-Stokes equations, a simplified boundary layer model in a gravity-driven falling film flow field is established, and quantitative constraints on structural parameters and fluid viscous drag are constructed. The formula is then used. Establish a mapping relationship. In the mathematical expression sequence, besides the parameter to be solved and the known input parameters, This represents the mass overflow rate per unit circumference of the annular slit distribution. This represents the measured density of the solution. Represents the gravitational acceleration constant. The dimensionless geometric correction factor, with values ​​between 1.05 and 1.15, compensates for liquid film boundary layer deviation caused by slit edge roughness. The width of the slit. For liquid film thickness, Kinematic viscosity is the viscosity of the raw material liquid. exist to When the range changes, adjust the slit width. Increase the thickness of the liquid film The thickness is stabilized at 0.5 mm to avoid mass transfer efficiency degradation caused by thickness fluctuations. Here, the numerical limit of the dimensionless geometric correction coefficient k is derived from the measured comparison matrix data of the influence of the surface features of machined parts on the fluid boundary layer. The surface roughness of the overflow metal inner wall of the distributor, which is based on industrial-grade standard polishing, will cause the fluid to expand along the wall when it actually flows out. Its apparent thickness deviates from the calculated value of the theoretical inviscid flow field equation by an inherent increment of 5% to 15%. The tolerance compensation limit of 1.05 to 1.15 extracted from this directly ensures the dimensional accuracy of the fluid dynamics theory derivation into the image of the engineering physical equipment.

[0051] To eliminate the thermodynamic uncertainties in the anion replacement process, the system utilizes infrared thermal imaging sensors deployed at different heights within the tower to collect the temperature field distribution at the gas-liquid phase transition interface in real time and calculate the measured interface temperature. The deviation from the upper limit of the safe hydrolysis temperature of 85℃, of which To measure the interface temperature, under these conditions, the infrared thermal imaging sensor integrates a heated, temperature-controlled transmission window to forcibly prevent surface droplet fogging. Simultaneously, its internal photoelectric detection components are confined to a specific atmospheric window infrared detection band of 8 to 14 micrometers. Utilizing the physical penetration characteristics of high-temperature water vapor and nitric acid molecules—which have extremely low absorption rates of infrared radiation in this band—it avoids the scattering and shielding interference of dense mixed airflow on thermal radiation. This ensures that the sensor can overcome the vapor barrier, non-destructively acquire and reconstruct the true radiation energy field of the falling film liquid phase surface, and balance the threshold. The settings are based on the following: under a negative pressure environment of 35 kPa to 45 kPa, the partial pressure of hydrogen chloride is continuously collected for 50 sampling cycles. And calculate its partial pressure standard deviation. ,Will Determined as The quantitative judgment benchmark; the dynamic adjustment path of the enthalpy offset method includes: the sensor reading the current absolute pressure. Calculate the theoretical boiling point of water in the liquid phase under this pressure. Calculate the latent heat flow released by the condensation of superheated nitric acid vapor. Latent heat flow absorbed by moisture vaporization ,determination and Whether the ratio is within the energy balance range of 0.95 to 1.05; when the ratio is less than 0.95 and The absolute value of the rate of change is less than At this time, the given value of nitric acid vapor flow rate is increased step by step, with each adjustment increment being 2% of the rated flow rate, until the ratio returns to the energy balance range.

[0052] Under this control, when the feed flow rate undergoes a 10% positive abrupt change, the system detects an increase in the enthalpy absorption rate at the gas-liquid phase change interface, leading to... and If the balance state deviates, the controller retrieves the energy balance deviation and drives the steam regulating valve to increase its opening, thus adjusting the mass ratio. The compensation ratio was increased from 4.2:1 to 4.8:1, where... To maintain the mass ratio, the interface temperature was re-clamped at 83.5℃, ensuring that the anion exchange did not result in rare earth hydrolysis loss due to material load fluctuations. Ultimately, under fluctuating material load conditions, the chloride ion mass percentage in the enriched liquid produced at the bottom of the tower remained constant below 0.004%. Compared to a constant ratio method lacking enthalpy self-balancing feedback, this maintained a rare earth recovery rate of over 99.8%, verifying the stability of the control logic in dynamic environments. By deterministically mapping the interface physicochemical state to input variables, the purification process was controlled.

[0053] Example 5: In the production preparation condition of changing rare earth raw material batches or adjusting the lanthanum-cerium component ratio, the offline benchmark calibration procedure is initiated, and the rare earth chloride solution to be treated is introduced into the test unit and absolute pressure is maintained. The critical vaporization enthalpy of the system at the upper limit of hydrolysis temperature (85℃) was determined by adjusting the amount of nitric acid vapor injected, with a pressure of 40 kPa. During this period, an online ion monitoring instrument collected 100 sets of data at a sampling period of 1 second, and the partial pressure of hydrogen chloride of this batch of raw materials under the temperature gradient was fitted to generate the partial pressure of hydrogen chloride. Baseline curve, calculate the standard deviation of partial pressures and will Determined as the balance threshold This ensures that the sensor feedback parameters match the thermodynamic properties of the material.

[0054] When the system encounters a condition where the thermal conductivity coefficient drifts, the energy deviation correction program is activated. When the falling film flows to the middle position, the infrared thermal imaging sensor acquires the measured temperature at the interface. ,in The measured temperature at the interface is in °C. The feed flow rate and nitric acid vapor mass flow rate are read, and the real-time mass ratio is calculated. By comparing the latent heat flux of condensation released by condensed nitric acid The latent heat of vaporization absorbed by the vaporization of moisture The residual distribution at the phase transition interface is used to correct the enthalpy compensation operator, when and When the ratio deviates from 1.0 by more than 5%, the feedback loop gain coefficient is automatically corrected. Based on the classical proportional-integral control principle, the nonlinear thermal load disturbance of the system is addressed, and the continuous-cycle energy balance residual is extracted to perform active system state compensation. The formula is used. Update the proportional gain at the current execution moment, where, This represents the updated proportional gain coefficient. Both represent the historical baseline gain coefficient of the previous control cycle and are dimensionless quantities with absolute values ​​greater than zero. Represents the sliding time window for integration. Represents the current execution time. Representing the dimensionless residual, obtain and The absolute difference between the ratio and the benchmark stationary value of 1.0. This represents the proportional adjustment constant, with a value limited to the range of 0.15 to 0.25. This represents the integral adjustment constant, with a value limited to the range of 0.05 to 0.10, obtained from system calculations. The initial steam regulation step size is then directly multiplied, and the output is converted into a frequency-modulated valve stepper motor opening pulse command. This matches the nitric acid steam step regulation amplitude with the fluctuation of the liquid phase vaporization rate, and the temperature of the gas-liquid phase change interface is maintained at the theoretical boiling point of the liquid phase water under disturbance. The nearby preset safety zone, for which the closed-loop gain parameter boundary is located, was pre-calibrated through experiments on the anti-disturbance step response characteristics of this equipment under negative pressure environment. When the parameter value drops below 0.15, the temperature rise peak caused by feedback hysteresis can easily penetrate the hydrolysis defense line; if it exceeds 0.25, it will induce oscillations in the gas phase efflux flow. If the parameter shrinks to below 0.05, the long-term accumulated heat residual at steady state cannot be eliminated; if it exceeds 0.10, it will cause excessive integration and lead to the phase change interface going out of control. This definition anchors the stable base of dynamic optimization from an engineering perspective.

[0055] Example 6: When the gas-liquid contact equipment is first deployed on the production site, the system initiates the calibration procedure for the physical geometric parameters of the falling film distributor, using a test fluid with a preset kinematic viscosity as the input source under a gradient temperature environment. To adjust the kinematic viscosity, the system adjusts the width of the annular slit at the bottom of the distributor. Sampling points were set within the range of 0.2 mm to 1.0 mm, and the liquid film thickness was measured and recorded at different mass flow rates. The correlation matrix, where, The width of the slit. The liquid film thickness is determined by the Reynolds number of the flow field when the sensor detects localized flow interruption or localized dry wall phenomena in the falling film. Correct slit width The lower limit value of , where The Reynolds number ensures that the liquid film completely covers the inner wall of the tower under absolute pressure conditions of 35 kPa to 45 kPa, providing a physical carrier for the in-situ condensation of nitric acid vapor at the gas-liquid interface.

[0056] When the system performs startup or shutdown cleaning operations, the water hydrolysis self-test logic is activated. Before the rare earth chloride solution is injected, the vacuum pump unit continues to run to maintain the absolute pressure inside the equipment. Reaching 35 kPa, of which The pressure is absolute, expressed in kPa. Steam is introduced into the inner wall of the pure water steam preheating equipment until the temperature collected by the infrared thermal imaging sensor reaches the theoretical boiling point of liquid water at the corresponding pressure. Furthermore, when the temperature deviation is less than 2℃, the rare earth raw material liquid enters the equipment through the distributor. In the initial stage of material injection, the controller adjusts the mass ratio of nitric acid vapor to rare earth chloride solution. The ratio is locked at an upper limit of 5:1. Proton flow is used to suppress rare earth ion hydrolysis caused by residual moisture on the inner wall, waiting for the partial pressure of hydrogen chloride in the gas phase to reach the upper limit. When the rate of increase stabilizes above 0.05 kPa / s, the enthalpy offsetting mode switches from open-loop mode to closed-loop regulation mode based on energy balance residual. The replacement process remains in a safe state before the equipment achieves thermal balance.

[0057] The embodiments of this application have been described above with reference to the accompanying drawings. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. This application is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of this application without departing from the spirit of this application and the scope of protection of this invention, and all of these forms are within the protection scope of this application.

Claims

1. A process for deep purification and refining of rare earth nitrates from complex chloride salt systems, characterized in that, Includes the following steps: Step 101: Provide a rare earth chloride solution, and control the mass percentage concentration of rare earth ions in the rare earth chloride solution to be 15% to 25%; Step 102: Adjust the absolute pressure of the treatment environment to 35 kPa to 45 kPa by decompression to establish physical conditions suitable for low-temperature vaporization of water molecules. Step 103: The rare earth chloride solution is distributed into a falling film of uniform thickness through the distributor at the top of the column, while nitric acid vapor with a temperature of 110°C to 115°C and a mass concentration of 65% to 68% is continuously introduced into the bottom of the column to countercurrent mass transfer with the falling film. Step 104: Nitric acid vapor condenses and releases heat on the surface of the falling film, driving the moisture inside the falling film to absorb heat and generate a vaporization phase change, forming a phase change interface on the surface of the falling film. The temperature of the phase change interface is maintained at 80°C to 85°C through latent heat exchange to suppress irreversible hydrolysis side reactions of rare earth ions. Step 105: Taking advantage of the concentration of nitrate ions at the phase transition interface, chloride ions coordinated with rare earth ions inside the falling film diffuse to the interface and undergo anion replacement. The generated hydrogen chloride molecules escape to the gas phase side with water vapor. As the falling film flows from the top to the bottom of the tower, the chloride ion concentration continuously decreases, and finally a high-purity rare earth nitrate enriched solution with a chloride ion mass percentage of less than 0.005% is obtained at the bottom of the tower.

2. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, Step 103 further includes: controlling the thickness of the falling film to be 0.2 mm to 0.8 mm, and adjusting the Reynolds number of the falling film to be 1200 to 2500, so as to generate a surface eddy current that enhances mass transfer and increases the dynamic contact area at the phase change interface formed by the falling film and nitric acid vapor.

3. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, It also includes: gradient cooling crystallization of rare earth nitrate enrichment solution, by limiting the critical supersaturation of rare earth nitrate enrichment solution during the cooling process, so that rare earth nitrate crystals preferentially precipitate from the substrate rich in impurity ions, thereby achieving phase separation of rare earth nitrate and impurity ions.

4. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, In step 104, the gaseous mixture is introduced into the condensation unit. By adjusting the temperature of the condenser wall of the condensation unit to the range of 95°C to 105°C, the nitric acid component in the mixture is converted into a liquid phase and guided back to step 103 by gravity, while keeping the hydrogen chloride molecules in the gaseous phase.

5. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, The mass percentage of metal impurity ions in the rare earth chloride solution is no higher than 2%; in step 105, the free nitric acid mass concentration inside the falling film is maintained at 35% to 45% by adjusting the flux of nitric acid vapor, so as to reduce the adsorption activity of metal impurity ions on the surface of rare earth nitrate crystal nuclei.

6. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, In step 101, the pH value of the rare earth chloride solution is adjusted to 1.5 to 3.0 to pre-inhibit the hydrolysis of rare earth cations by utilizing the acidic environment, and the initial density of the rare earth chloride solution is adjusted to 1.2 g / cm³ to 1.4 g / cm³ according to the type of rare earth ions.

7. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, The top distributor includes a ring with a serrated overflow edge, the tooth tip spacing of which is 3 mm to 6 mm. The rare earth chloride solution is converted into a falling film evenly distributed along the inner wall of the tower by the capillary force formed by the tooth tip spacing under gravity.

8. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 3, characterized in that, After gradient cooling crystallization is completed, the obtained material is centrifuged to separate solid and liquid to obtain high-purity rare earth nitrate crystals. The separated mother liquor is then returned to step 101 as a solvent for recycling, so as to reintroduce the residual rare earth ions in the mother liquor into the negative pressure environment.

9. The process for deep purification and refining of rare earth nitrates from a complex chloride salt system according to claim 1, characterized in that, In step 103, the mass ratio of the incoming nitric acid vapor flow rate to the input rare earth chloride solution flow rate is controlled to be 3:1 to 5:

1. By limiting the mass flow rate ratio of the gas and liquid phases, it is ensured that all chloride ions are replaced and removed within the contact time before the falling film flows to the bottom of the tower.

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