A praseodymium-neodymium oxide separation and purification process and regeneration system

Abstract

The present invention relates to the technical field of rare earth metal separation, and specifically discloses a praseodymium-neodymium oxide separation and purification process and a regeneration system. The process comprises: after H2S impurity removal and filtration, P507 / TRPO is used to collaboratively extract the organic phase for multi-stage countercurrent extraction, HCl is graded to strip praseodymium, and HNO3 is stripped to strip neodymium; the regeneration system comprises a wastewater treatment unit and an organic phase regeneration unit, the wastewater is recycled through neutralization precipitation, precision filtration and reverse osmosis, and the organic phase is recycled through alkali washing, acid activation and 4A molecular sieve dehydration. The collaborative extraction makes the praseodymium-neodymium separation coefficient reach 2.0-2.2, and the number of stages is reduced by 40%; the dual regeneration system reduces the organic phase loss to ≤2%, and the wastewater reuse rate is ≥92%; the obtained neodymium oxide has a purity of ≥99.99% and Fe ≤10ppm. The extraction efficiency of the present invention is significantly improved, the life of the organic phase is doubled, the product purity exceeds the limit, the wastewater discharge is closed-loop near-zero, the stability of the whole process is guaranteed, and the resource utilization is maximized.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare earth metal separation, and in particular relates to a praseodymium-neodymium oxide separation and purification process and a regeneration system. Background Art

[0002] In the rare earth industry, the efficient and precise separation of the rare earth elements praseodymium (Pr) and neodymium (Nd) remains a core and extremely challenging problem. Currently, solvent extraction, the mainstream process, often employs acidic phosphonate extractants such as 2-ethylhexylphosphonate (P507) to treat mixed Pr and Nd solutions. However, this process has numerous significant drawbacks, severely limiting the efficiency, cost, and product quality of rare earth production.

[0003] 1. Separation Efficiency: The traditional P507 system has an extremely limited β separation coefficient for praseodymium and neodymium, ranging only from 1.4 to 1.6. To obtain high-purity praseodymium and neodymium products, a massive extraction system must be constructed, typically requiring more than 20 extraction tanks. This not only significantly increases the equipment footprint but also increases the organic phase input by over 30% compared to the ideal scenario. From an economic perspective, the combined equipment, space, and organic phase costs associated with multi-stage operation significantly increase overall production costs and reduce production efficiency.

[0004] 2. Organic phase stability: During long-term continuous operation, the extractant faces numerous chemical challenges. On the one hand, hydrolysis is prone to occur, and under highly acidic stripping conditions, the risk of oxidative degradation increases significantly, leading to frequent emulsification. This emulsification issue results in an organic phase loss rate as high as 5-8%, resulting in wasted resources and increased costs. On the other hand, the continuous accumulation of degradation products in the system further reduces the extractant's selectivity for praseodymium and neodymium, gradually deteriorating the separation effect and ultimately forcing companies to frequently replace the organic phase, increasing production complexity and costs.

[0005] 3. Product purity control challenges: During the stripping process, the co-extraction of impurity ions is difficult to completely resolve. Non-rare earth ions such as iron and aluminum gradually accumulate in the organic phase with increasing cycles. This directly results in iron impurity levels in neodymium oxide products often exceeding 30 ppm, making it impossible to consistently maintain the high purity standard of 99.95%, affecting the product's suitability for high-end applications.

[0006] 4. Wastewater treatment cost dilemma: The stripping process generates a large amount of acidic wastewater, primarily a mixture of HCl and HNO₃. While traditional lime neutralization can treat acidic wastewater, it produces sludge containing heavy metals. This sludge is considered hazardous waste and its disposal costs are high, accounting for over 15% of operating costs. Furthermore, the wastewater contains a significant amount of residual organic matter, with a chemical oxygen demand (COD) exceeding 5000 mg / L. This significantly increases the burden on subsequent biochemical treatment, resulting in a wastewater reuse rate of less than 50%, further exacerbating water resource waste and increasing production costs.

[0007] 5. Regeneration system design flaws: Existing technologies often overly focus on the separation process itself, while neglecting the integrated design of organic phase regeneration and wastewater recycling. For example, in the alkaline wash regeneration process, the lack of precise control of temperature and stirring conditions often leads to saponification failure of the extractant, making it impossible to effectively restore its extraction performance. In the dehydration process, the selection of molecular sieve types lacks scientific standards and operating parameters are unclear, resulting in fluctuations in the water content of the organic phase after regeneration exceeding 200ppm, seriously affecting the balance and stability of the extraction process.

[0008] 6. Insufficient process control precision: Currently, there is a lack of standardized, precise monitoring methods for key extraction process parameters, such as mixing time and clarification rate, and adjustments often rely on manual experience. This crude control approach results in poor process stability. For example, in H2S impurity removal, its concentration is not effectively linked to online monitoring, resulting in heavy metal removal rates fluctuating by as much as ±15%, which in turn affects the stability of the subsequent extraction process and product quality.

[0009] In summary, the existing rare earth element praseodymium and neodymium separation process has many shortcomings, and innovative technologies are urgently needed to improve separation efficiency, optimize product quality, and reduce production costs and environmental impact. Summary of the Invention

[0010] The purpose of the present invention is to provide a praseodymium-neodymium oxide separation and purification process and a regeneration system.

[0011] In order to achieve the above object, the present invention provides the following technical solutions:

[0012] A process for separating and purifying praseodymium-neodymium oxide comprises the following steps:

[0013] (a) A praseodymium-neodymium chloride solution with a concentration of 200-250 g / L of REO is introduced into H2S to a concentration of 0.08-0.12 mol / L, and then filtered through a ≤0.5 μm precision filter to remove impurities;

[0014] (b) mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (P507), trialkylphosphine oxide (TRPO) and sulfonated kerosene according to volume percentage, wherein 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester accounts for 35-40%, trialkylphosphine oxide accounts for 8-12%, and sulfonated kerosene is supplemented to 100%, to form a synergistic extraction organic phase;

[0015] (c) Under the control of pH=4.0-4.5, the pretreated liquid and the co-extraction organic phase were subjected to 8-10 stages of countercurrent extraction, with the flow ratio O / A=(2.5-3.5):1, the mixing time was 2.5-3.5 min, the stirring speed was 300±50 rpm, and the clarification rate was measured at 25°C at 14-16 L / (m 2 min), separating the organic phase loaded with praseodymium / neodymium; the synergistic extraction organic phases were mixed in the order of sulfonated kerosene → P507 → TRPO;

[0016] (d) stripping the praseodymium-loaded organic phase with 1.4-1.6 mol / L HCl at a flow ratio of O / A = (4.5-5.5):1, a temperature of 60-80°C, a contact time of 10-20 min, to obtain a praseodymium chloride solution;

[0017] (e) Stripping the organic phase loaded with neodymium with 3.8-4.2 mol / L HNO3 at a flow ratio of O / A = (2.8-3.2):1 at a temperature of 60-80°C for a contact time of 10-20 min to obtain a neodymium nitrate solution.

[0018] A regeneration system for a praseodymium-neodymium oxide separation and purification process, comprising:

[0019] (f) Wastewater treatment unit: a neutralization tank, a sedimentation tank, a 0.1 μm precision filter, and a reverse osmosis device connected in sequence by pipelines;

[0020] The neutralization tank adds Ca(OH)2 to 1-3 g / L to adjust the pH to 6.0-7.0, the sedimentation tank adds 5-10 wt% Na2CO3, and the reverse osmosis permeate water is reused in the stripping process;

[0021] (g) Organic phase regeneration unit: an alkaline washing tank, an acid activation tank and a dehydration tower connected in sequence;

[0022] The alkaline washing tank is washed with 4.5-5.5wt% NaOH solution at 45-55°C, and the acid activation tank is activated with 0.4-0.6mol / L HCl under stirring at room temperature for 20-30 minutes.

[0023] Furthermore, the clarification rate in step (c) is measured at 25° C. and normal pressure.

[0024] Furthermore, the pH value of step (c) is regulated by automatically adding 10 wt % ammonia water.

[0025] Furthermore, in step (b), the order of mixing the organic phase is to first add sulfonated kerosene, then add 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, and finally add trialkylphosphine oxide, and stir at 200-400 rpm for ≥30 min until the transmittance is ≥95% and λ=650 nm.

[0026] Furthermore, the dehydration tower is filled with 4A molecular sieve, with a filling height of 1-2m and an operating temperature of 80-100°C. 3 The organic phase is regenerated once after 30 days of continuous operation. The regeneration conditions of the dehydration tower are: nitrogen purge at 250℃ for 4h.

[0027] Furthermore, the concentrated water outlet of the reverse osmosis device is connected to an evaporative crystallizer to recover NaCl crystals. The operating temperature of the evaporative crystallizer is 100-120°C, the crystallization time is 2-4 hours, and industrial first-grade NaCl crystals are recovered with a purity of ≥99%.

[0028] Furthermore, a pH online monitor is installed between the neutralization tank and the sedimentation tank, and a turbidity sensor is installed at the outlet of the sedimentation tank with a monitoring range of 0-100NTU.

[0029] A praseodymium oxide product, Pr6O 11 / TREO≥99.5% and Fe≤10ppm.

[0030] A neodymium oxide product having Nd2O3 / TREO ≥ 99.99% and a total non-rare earth impurity content ≤ 100 ppm.

[0031] The beneficial effects of the present invention are:

[0032] 1. Significantly Improved Extraction Efficiency: The specific volume ratio of P507 / TRPO (35-40%:8-12%) in the synergistic extractant achieves a praseodymium-neodymium separation coefficient of 2.0-2.2. Combined with 8-10 countercurrent extraction stages and precise pH control (±0.1), the number of stages is reduced by 40%, achieving a single-stage extraction efficiency exceeding 98% at a flow ratio of O / A (2.5-3.5):1, significantly reducing equipment investment and operating energy consumption.

[0033] 2. Doubled organic phase life: The three-stage regeneration system of alkaline washing, acid activation, and dehydration works synergistically with process parameters: alkaline washing at 45-55°C removes degradation products, activation with 0.4-0.6 mol / L HCl restores extraction activity, and dehydration with 4A molecular sieve at 80-100°C stabilizes the water content to ≤50 ppm. This reduces organic phase loss to less than 2%, extending the regeneration cycle to 6 months.

[0034] 3. Product purity breaks through the limit: graded stripping conditions (HCl concentration 1.4-1.6 mol / L for stripping praseodymium, HNO3 concentration 3.8-4.2 mol / L for stripping neodymium) and temperature / time coordinated control (60-80℃, 10-20min) completely inhibit Fe 3+ Co-extraction. The purity of neodymium oxide reaches 99.99% and Fe ≤ 10ppm, and the purity of praseodymium oxide is above 99.5%, meeting the magnetic material grade standards.

[0035] 4. A near-zero wastewater discharge closed loop: The neutralization-sedimentation-filtration-reverse osmosis system integrates Ca(OH)2 / Na2CO3 dual-stage impurity removal, combined with 0.1μm precision filtration and RO membrane concentration, achieving a wastewater reuse rate of ≥92%. Concentrated water is evaporated and crystallized to recover >95% of industrial salt, with a COD residual of ≤80mg / L and a heavy metal retention rate of 99.9%.

[0036] 5. Ensure stability throughout the entire process: A mixing sequence (kerosene → P507 → TRPO) and stirring for ≥30 minutes ensures full complexation of the extractant. A transmittance of ≥95% (λ=650nm) quantifies mixing uniformity. An online pH meter and turbidity sensor (0-100 NTU) provide real-time feedback and control, minimizing process fluctuations to ±5%.

[0037] 6. Maximizing resource utilization: The regeneration system is deeply coupled with the separation process: The molecular sieve in the dehydration tower is regenerated every 100 cycles, and the reuse of stripping wastewater reduces acid consumption by 30%. The NaCl crystallization rate reaches industrial-grade standards. The overall rare earth recovery rate exceeds 99.2%, and the cost of auxiliary materials is reduced by 40%. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the process flow for separation and purification of praseodymium-neodymium oxide.

[0039] Figure 2 Schematic diagram of the centrifugal extraction and regeneration cycle system. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] Example 1: Raw material pretreatment: Prepare a praseodymium-neodymium chloride solution (Pr6O 1126.5% and Nd2O3 accounted for 73.5%), H2S gas was continuously introduced, and the H2S concentration was controlled at 0.09 mol / L by an online sulfur ion concentration meter (model: ThermoOrion 290A+). The filtrate was filtered through a 0.45 μm polytetrafluoroethylene precision filter. 2+ , Pb 2+ Content ≤0.3ppm.

[0042] Preparation of synergistic extractant: Sulfonated kerosene was first added to a 2000 L stirred tank. 2-Ethylhexylphosphonic acid mono-2-ethylhexyl ester was slowly injected while stirring at 250 rpm to a total volume of 36%. Finally, trialkylphosphine oxide was added to a total volume of 11%. The speed was adjusted to 380 rpm and stirring was continued for 40 minutes. The transmittance was measured at a wavelength of 650 nm using a spectrophotometer (Shimadzu UV-2600) to achieve a value of 97.5%.

[0043] Countercurrent extraction and separation: The pretreated liquid and the organic phase of the synergistic extraction were fed into a 9-stage mixing and clarification tank, and the flow ratio of the organic phase to the aqueous phase was controlled to be 3.2:1. 10 wt% ammonia water was added dropwise by an automatic metering pump to maintain the pH at 4.2 ± 0.1. The stirring time in the mixing chamber was 2.8 min. The clarification rate was measured at a constant temperature of 25 °C at 14.8 L / (m 2 ·min); and separation yielded a praseodymium-loaded organic phase (Pr / Nd molar ratio of 21.7:1) and a neodymium-loaded organic phase (Nd / Pr molar ratio of 96.3:1).

[0044] Graded stripping and purification: The organic phase loaded with praseodymium was stripped with 1.55 mol / L HCl solution (flow ratio O / A=4.8:1), and the reaction was carried out at a constant temperature of 65°C for 18 min to obtain a PrCl3 solution; the organic phase loaded with neodymium was stripped with 3.95 mol / L HNO3 solution (flow ratio O / A=3.1:1), and the reaction was carried out at a constant temperature of 78°C for 13 min to obtain a Nd(NO3)3 solution.

[0045] Regeneration system operation:

[0046] 1. Wastewater regeneration cycle: The stripping wastewater is pumped into the neutralization tank, and analytical pure Ca(OH)2 powder is added to the concentration of 2.3g / L, and the pH is adjusted to 6.8 (pH online meter: Mettler Toledo InPro 3250); after entering the sedimentation tank, 9wt% Na2CO3 solution is added and filtered through a 0.1μm ceramic membrane filter (Pall Membralox ® ) to remove suspended solids; the filtrate is treated by a reverse osmosis device (Dow SW30XHR-400), and the permeate COD value is 76 mg / L and is returned to the stripping process. The concentrated water is evaporated and crystallized to produce industrial grade 1 NaCl (purity 99.35%). The evaporation temperature is 100-120℃ and the crystallization time is 2-4h.

[0047] The outlet of the sedimentation tank is connected to a low-background α / β radioactivity measuring instrument (according to GB / T43358-2023) for detecting the total α / β activity, controlling the radionuclide retention rate to ≥99.9%, and ensuring that the total α activity of the concentrated water crystallized salt is ≤1.0Bq / g.

[0048] 2. Organic phase regeneration:

[0049] Alkaline washing tank: 4.8% NaOH solution at 48 ° C with mechanical stirring (paddle stirrer 200 rpm) for 30 minutes;

[0050] Acid activation tank: 0.52 mol / L HCl solution stirred at room temperature for 28 min;

[0051] Dehydration tower: 4A molecular sieve filling height 1.8m, dehydration at 88℃ for 2.5h, the water content of the organic phase after regeneration is 42ppm.

[0052] Preparation of high-purity products: PrCl3 solution was calcined at 850℃ for 6h to obtain praseodymium oxide product (Pr6O 11 / TREO=99.58%, Fe content 7.9ppm);

[0053] The Nd(NO3)3 solution was calcined at 900℃ for 5h to obtain neodymium oxide product (Nd2O3 / TREO=99.995%, total non-rare earth impurities 78ppm).

[0054] Example 2: Synergistic extractant extreme ratio: 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester 40% + trialkylphosphine oxide 8% + sulfonated kerosene 52%, countercurrent extraction 10 stages, O / A = 3.5:1, Nd / Pr ratio of the aqueous phase of the neodymium tank = 95.1:1; molecular sieve long cycle operation: the dehydration tower is continuously operated for 100 cycles (each cycle processes 5m3 of organic phase) 3 After dehydration at 100°C, the molecular sieve was regenerated by purging with nitrogen at 250°C (flow rate 10L / min) for 4 hours; the organic phase extraction efficiency decayed by 2.7% after regeneration. The cycle is defined as the volume basis of the organic phase processed in a single cycle (e.g., 5m3 / cycle is processed per cycle). 3 organic phase) or the time period of continuous operation (measured in units of 30 days).

[0055] Example 3: Cyclic stability verification of molecular sieve 500:

[0056] The dehydration tower runs continuously for 500 cycles (accumulatively processing 2500m3 of organic phase). 3 ), each processing 100m 3 The organic phase is regenerated once after 30 days of continuous operation;

[0057] After 500 cycles, the molecular sieve adsorption capacity decay rate was 4.8%, and the water content of the organic phase after regeneration was ≤55ppm (still meeting the process tolerance of ≤50ppm±10%).

[0058] The purity of the corresponding neodymium oxide product is maintained at 99.992%, and the Fe content is ≤11ppm.

[0059] Comparative Example 1: Trialkylphosphine oxide was omitted, and only 40% mono-2-ethylhexylphosphonate and 60% sulfonated kerosene were used as the organic phase. Under the same extraction conditions, the separation coefficient β dropped to 1.48, requiring 16 countercurrent extraction stages to achieve a 90:1 Nd / Pr ratio in the aqueous phase of the neodymium cell. After stripping, the Fe content in the neodymium oxide rose to 28 ppm.

[0060] Comparative Example 2: The neodymium stripping temperature was lowered to 50°C (other conditions were the same as in Example 1). The stripping contact time was extended to 25 minutes. The resulting Nd(NO3)3 solution, after calcination, had a neodymium oxide purity of 99.91% and an Fe impurity of 32 ppm.

[0061] Comparative Example 3: Omitting the organic phase regeneration unit and directly recycling the extractant. After eight cycles, the organic phase viscosity increased by 47%, the extraction rate decreased by 31%, and the total amount of non-rare earth impurities in the neodymium oxide product increased to 215 ppm.

[0062] See the schematic diagram of the process flow for separation and purification of praseodymium and neodymium oxide. Figure 1 Schematic diagram of centrifugal extraction and regeneration cycle system is shown in Figure 2 .

[0063] Table 1: Final performance comparison table

[0064]

[0065] The above description is merely a preferred embodiment of the present invention; however, the scope of protection of the present invention is not limited thereto. Any person skilled in the art who, within the technical scope disclosed by the present invention, makes equivalent substitutions or modifications based on the technical solutions and improved concepts of the present invention shall be covered by the scope of protection of the present invention.

Claims

1. A process for separating and purifying praseodymium-neodymium oxide, characterized in that: The following steps are involved: (a) A praseodymium-neodymium chloride solution containing 200-250 g / L of REO was introduced into H2S to a concentration of 0.08-0.12 mol / L, and the solution was filtered through a 0.5 μm precision filter to remove impurities; (b) mixing 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, trialkylphosphine oxide and sulfonated kerosene according to volume percentage, wherein 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester accounts for 35-40%, trialkylphosphine oxide accounts for 8-12%, and sulfonated kerosene is supplemented to 100%, to form a synergistic extraction organic phase; (c) Under the control condition of pH=4.0-4.5, the pretreated liquid and the co-extraction organic phase were subjected to 8-10 stages of countercurrent extraction, the flow ratio O / A was controlled to be (2.5-3.5):1, the mixing time was 2.5-3.5 min, the stirring speed was 300±50 rpm, and the clarification rate was measured at 25°C at 14-16 L / (m 2 min), separating the organic phase loaded with praseodymium / neodymium; the synergistic extraction organic phases were mixed in the order of sulfonated kerosene → P507 → TRPO; (d) stripping the praseodymium-loaded organic phase with 1.4-1.6 mol / L HCl at a flow ratio of O / A = (4.5-5.5):1, a temperature of 60-80° C., a contact time of 10-20 min, to obtain a praseodymium chloride solution; (e) stripping the organic phase loaded with neodymium using 3.8-4.2 mol / L HNO3 at a flow ratio of O / A = (2.8-3.2):1, a temperature of 60-80°C, a contact time of 10-20 min, to obtain a neodymium nitrate solution; The regeneration system of the praseodymium-neodymium oxide separation and purification process comprises: (f) Wastewater treatment unit: a neutralization tank, a sedimentation tank, a 0.1 μm precision filter, and a reverse osmosis device connected in sequence by pipelines; The neutralization tank adds Ca(OH)2 to 1-3 g / L to adjust the pH to 6.0-7.0, the sedimentation tank adds 5-10 wt% Na2CO3, and the reverse osmosis permeate water is reused in the stripping process; (g) organic phase regeneration unit: an alkaline washing tank, an acid activation tank and a dehydration tower connected in sequence; The alkaline washing tank is washed with 4.5-5.5wt% NaOH solution at 45-55°C, and the acid activation tank is activated with 0.4-0.6mol / L HCl under stirring at room temperature for 20-30min.

2. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: The clarification rate in the step (c) is measured at 25° C. and normal pressure.

3. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: The pH value of step (c) is regulated by automatically adding 10 wt % ammonia water.

4. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: In step (b), the organic phase is mixed in the following order: first add sulfonated kerosene, then add 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester, and finally add trialkylphosphine oxide, and stir at 200-400 rpm for ≥30 min until the transmittance is ≥95% and λ=650 nm.

5. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: The dehydration tower is filled with 4A molecular sieve, with a filling height of 1-2m and an operating temperature of 80-100℃. 3 The organic phase is regenerated once after 30 days of continuous operation. The regeneration conditions of the dehydration tower are: nitrogen purge at 250℃ for 4h.

6. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: The concentrated water outlet of the reverse osmosis device is connected to an evaporation crystallizer to recover NaCl crystals. The operating temperature of the evaporation crystallizer is 100-120° C., the crystallization time is 2-4 hours, and industrial first-grade NaCl crystals are recovered with a purity of ≥99%.

7. The process for separating and purifying praseodymium-neodymium oxide according to claim 1, wherein: A pH online monitor is installed between the neutralization tank and the sedimentation tank, and a turbidity sensor is installed at the outlet of the sedimentation tank with a monitoring range of 0-100NTU.

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