A method for extracting and recovering thorium from Baiyunebo rare earth tailing acid leaching solution

Abstract

This invention discloses a method for extracting thorium from acidic leachate of Bayan Obo rare earth tailings, belonging to the fields of hydrometallurgy and nuclear fuel cycle technology. The invention provides a method for preparing an organic phase using 10% (v / v) Cyanex 272 as the extractant and sulfonated kerosene as the diluent. In a nitric acid or hydrochloric acid system with an initial acidity of 2.0–3.0 mol / L, a three-stage cross-flow extraction is performed with a ratio (O / A) of 1:2. The total extraction rate of Th(IV) is not less than 94% in the nitric acid medium and not less than 89% in the hydrochloric acid medium. Under the same acidity conditions, using a 30% (v / v) P350 extractant as a control extractant, the three-stage cross-flow extraction rate of Th(IV) in the nitric acid medium is only 49.6%, and in the hydrochloric acid medium it is only 21.9%, indicating that the present invention has significantly better extraction performance than P350 in both media systems. This invention can directly process strongly acidic leachate solutions and is compatible with both nitric acid and hydrochloric acid media systems, providing a clear and feasible technical solution for the selective recovery of thorium from complex acidic leachates.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy and nuclear fuel cycle technology, and relates to a method for extracting radioactive thorium from acidic leachate of Bayan Obo rare earth tailings. Specifically, it relates to a method for selectively extracting thorium under conditions of coexistence of multiple ions such as calcium, iron, aluminum, magnesium, manganese, and phosphate. It is suitable for the extraction and enrichment of radioactive thorium associated with rare earth ores and can be used in conjunction with mainstream rare earth leaching processes such as nitric acid and hydrochloric acid. Background Technology

[0002] In compound-type rare earth mineral resources (such as monazite and bastnaesite), the radioactive element thorium often coexists with rare earth elements. Achieving effective separation of thorium from rare earth elements in the acidic leachate of these minerals is a key research direction in hydrometallurgy and radioactive waste disposal. Because thorium... 4+ With light rare earth ions (such as Pr) 3+ 、Nd 3+ The properties of thorium are similar, and the alkaline earth metal ions (such as Ca²⁺, Mg²⁺, etc.) and other coexisting metal ions present in large quantities in the feed solution also constitute competitive interference to the extraction process. The key to achieving selective extraction of thorium in a complex feed solution with strong acidity and multiple components lies in the selection of the extractant and the matching of process conditions.

[0003] Liquid-liquid extraction is one of the main techniques for separating thorium and rare earth elements, and the choice of extractant is a core factor determining the separation effect. Among extractant categories, organophosphonic acid extractants (such as P204, P507, P350, etc.) are the most widely studied class of extractants in this field due to their strong coordination ability with both rare earth and actinide elements and their mature industrial applications. Specifically, Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphonic acid) can selectively extract thorium under strongly acidic conditions. 4+ However, its extraction ability for light rare earth ions is relatively weak, which is beneficial for the separation of thorium from light rare earth elements. In existing technologies, Cyanex 272 shows good extraction performance for thorium in both hydrochloric acid and nitric acid systems. 4+ It has a certain extraction capacity, at higher H2O levels. + Th can be achieved under conditions of reduced concentration. 4+ Selective extraction. However, existing technologies mostly employ single-stage extraction or synthetic feed systems. For the complex composition (containing various impurity ions such as Fe, Ca, Si, and Al) of the acidic leachate from the Bayan Obo rare earth tailings, a multi-stage cross-flow liquid-liquid extraction method using Cyanex 272 as the extractant achieves Th extraction in different acidity ranges. 4+ No systematic studies on selective extraction have been reported in the existing literature.

[0004] To address the highly soluble residue generated during the monazite process, patent CN106381406A proposes using P350 as an extractant in a hydrochloric acid system for separation. This patent indicates that when operating at a hydrochloric acid concentration of approximately 2.0 mol / L, titanium in the feed solution readily hydrolyzes to form titanium hydroxyl complexes and titanium oxide, easily forming a three-phase mixture during extraction. Therefore, pretreatment of the feed solution is necessary, including hydrolysis to remove titanium, pH adjustment, and multiple filtrations. Simultaneously, under these conditions, P350 exhibits a low separation coefficient for rare earth elements and thorium, necessitating an increased number of extraction and washing stages. To address this, the patent increases the feed solution acidity to 4.8-5.5 mol / L, which avoids titanium hydrolysis and improves the separation coefficient. This process requires operation at a hydrochloric acid concentration of 4.8-5.5 mol / L, compared to an O / A ratio of 4-8:1, and achieves 15-20 extraction stages. Unlike the high-acidity route of P350, carboxylic acid extractants (such as CA-12) utilize a low-pH route. The extraction system described in patent CN112458320A, which uses unsaponified CA-12 as an extractant, needs to be operated within the pH range of 2 to 3 and is difficult to apply directly to strongly acidic leachates.

[0005] In addition to the acidic extractants mentioned above, the combination of neutral extractants TBP and N235 has also been used for the deep purification of thorium. Although the combined process using TBP and N235 as extractants (CN121538477A) can achieve thorium extraction, it involves more steps and requires operation at a higher nitrate concentration.

[0006] In recent years, eutectic solvents have been introduced into the field of thorium extraction and separation as alternatives to traditional organic solvents. A system using eutectic solvent (DES) as the extraction medium (CN113667843A) can extract thorium under weakly acidic conditions of pH=2-5. However, this pH range does not match the original acidity of the strongly acidic leachate of rare earth tailings ([H⁺] approximately 0.5-3 mol / L), and pre-alkali adjustment is required.

[0007] Besides liquid-liquid extraction, precipitation is another method for thorium separation. Precipitation (CN119506624A) uses pyrophosphoric acid or phosphate to precipitate thorium from wastewater, but the precipitation process is relatively lengthy (2-3 days) and the precipitated product requires further acid dissolution treatment.

[0008] Therefore, developing a thorium extraction method that can directly process the strongly acidic leachate from Bayan Obo rare earth tailings, is compatible with both nitric acid and hydrochloric acid media, requires no pre-adjustment of alkali or acid, has a short process, and has high extraction efficiency is of great practical significance. Summary of the Invention

[0009] The acidic leachate from the Bayan Obo rare earth tailings contains a large number of coexisting ions such as calcium and iron (with concentrations reaching 10). 2 ~10 4The concentrations of Th(IV) are typically on the order of 10 mg / L, while the concentrations of Th(IV) are usually on the order of 10 mg / L, a difference of 1 to 3 orders of magnitude. To address the difficulty in selectively separating Th(IV) due to the coexistence of multiple ions in highly acidic systems, this invention provides a method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings.

[0010] To achieve the above objectives, the present invention adopts the following technical solution: S1: Using Cyanex 272 as the extractant and sulfonated kerosene as the diluent, an organic phase with a volume concentration of 5%-15% was prepared; S2: The organic phase is mixed and contacted with a nitric acid leaching solution or hydrochloric acid leaching solution containing Th(IV) (hydrogen ion concentration of 0.4-3.0 mol / L) at a single-stage ratio of O / A=1:2-1:2.3, and three-stage cross-flow extraction is performed. The shaking time for each stage is 3-5 min. After standing and phase separation, the organic phase loaded with Th(IV) is separated. S3: After each stage of extraction and phase separation, the loaded organic phase is separated, and the raffinate aqueous phase is retained. The second and third stages of extraction are then performed sequentially using the fresh organic phase. S4: Collect the final raffinate phase, which is the raffinate phase with reduced thorium concentration.

[0011] Preferably, when the acidic leachate is a nitric acid medium, the hydrogen ion concentration is 2-3 mol / L.

[0012] Preferably, when the acidic leachate is hydrochloric acid medium, the hydrogen ion concentration is 1.5-2 mol / L.

[0013] Preferably, the volume concentration of Cyanex 272 in the organic phase is 10%.

[0014] Preferably, in the three-stage cross-flow extraction, the single-stage ratio O / A is 1:2.

[0015] Preferably, the acidic leachate includes, but is not limited to, the following coexisting ions: Ca 2+ 13000-14000 mg / L, Fe 2+ / Fe 3+ 8000-9000 mg / L, Mg 2+ 4000-4600 mg / L, Mn 2+ 2500-2700 mg / L, Al 3+ 1000-1500 mg / L, PO4 3- 1300-1500 mg / L, Nd 3+ 450-500 mg / L, Pr 3+ 95-135 mg / L.

[0016] Preferably, the oscillation time for each stage in step S3 is 3-5 minutes.

[0017] Preferably, the mixing contact in step S3 is achieved by manual oscillation or mechanical stirring for 4 minutes.

[0018] The beneficial effects of this invention are: (1) The extraction target of this invention is the actual acidic leachate of Bayan Obo rare earth tailings. This raw material system has not been systematically reported in the Cyanex 272 extraction research. Although existing studies know that Cyanex 272 has the ability to extract Th(IV), most of them are based on simulated synthetic feed solutions without high concentrations of calcium, iron, magnesium, manganese and phosphate. This invention targets the actual acidic leachate of Bayan Obo rare earth tailings, screens and obtains a complete set of three-stage cross-flow process parameters, achieves high-efficiency thorium extraction under high impurity coexistence conditions, and is compatible with nitric acid and hydrochloric acid leachates, achieving unexpected technical effects.

[0019] (2) The present invention does not require pre-adjustment of alkali and can directly treat the original solution under strongly acidic conditions.

[0020] (3) The present invention adopts a three-stage cross-flow liquid-liquid extraction method, which takes into account both extraction efficiency and feasibility of industrial continuous production. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0022] This invention employs a separatory funnel oscillation extraction method. For industrial continuous production, a stirred reactor, a mixing and clarifying tank, or a centrifugal extractor can be used. Multi-stage countercurrent extraction is employed, with the volume ratio of organic phase to aqueous phase maintained at 0.43:1-0.57:1 in each stage. The contact time between the two phases in a single stage is 3-5 min, the stirring speed in the mixing chamber is 300-800 r / min, and the clarification chamber is used for static stratification. After the organic phase is loaded with thorium, it is uniformly transported to the back-extraction process.

[0023] This method involves the enrichment and recovery of radioactive thorium. In actual industrial implementation, it must strictly comply with relevant regulations such as the "Radioactive Pollution Prevention and Control Law" and be equipped with supporting facilities such as radioactive safety protection, waste disposal, and environmental monitoring.

[0024] Specifically: (1) Preparation of organic phase The organic phase is obtained by mixing industrial-grade Cyanex 272 (used directly without further purification) with sulfonated kerosene at the required volume ratio.

[0025] (2) Source of liquid feed The acidic leachate from the Bayan Obo rare earth tailings of this invention can be prepared using acid leaching methods known in the art. For example, hydrothermal leaching with hydrochloric acid or nitric acid can be used: a liquid-to-solid ratio of 6:1 mL / g, a temperature of 90°C, and a leaching time of 4 h. The resulting leachate, after solid-liquid separation, can be used as the raw material for the method of this invention. This leaching method has been disclosed in the inventors' previous research (Li Guanghui, et al. Hydrothermal leaching behavior and interfacial reaction mechanism of surface sites in Bayan Obo rare earth tailings [J]. Metal Mines, 2026, 55, 185-193.). However, it should be noted that the core technical contribution of this invention lies in the extraction and recovery method of thorium in the leachate, rather than the leaching process itself. Therefore, the acidic leachate described in this invention can also be obtained by other acid leaching methods, as long as it meets the ionic composition and concentration range described in this invention.

[0026] The leaching solutions used in Examples 1-7 are actual acidic leachates from the Bayan Obo rare earth tailings, wherein the nitric acid system leachate Th 4+ The concentration range was 1.26-22.57 mg / L (Examples 1-4), and the hydrochloric acid system leachate Th 4+ The concentration range was 7.526-20.85 mg / L (Examples 5-7). The comparative experiments used leachates from the same source. 4+ The initial concentration range was 20.85-22.57 mg / L.

[0027] (3) Acidity of aqueous phase This invention utilizes naturally obtained nitric acid and hydrochloric acid leachates under different leaching conditions, with initial hydrogen ion concentrations [H⁺] of 3 mol / L and 0.4 mol / L for the nitric acid system, and 2 mol / L and 0.5 mol / L for the hydrochloric acid system. All solutions remain clear, without precipitation or emulsification, and can be used directly for extraction without pre-adjusting the alkali.

[0028] (4) Extraction operation The acidic leachate was mixed with the organic phase at a single-stage ratio O / A = 1:2–1:2.3, and a three-stage cross-flow extraction was performed. After extraction, the mixture was allowed to stand and separate into layers, and the loaded Th phases were collected separately. 4+ Organic phase and raffinate aqueous phase.

[0029] This invention investigates the effect of Cyanex 272 on Th in acidic rare earth tailings leaching solution. 4+ To assess the extraction effect, all experimental groups used the same process conditions: the organic phase was composed of 10% by volume of industrial-grade Cyanex 272 and 90% sulfonated kerosene. The single-stage extraction ratio O / A≈0.48:1 (i.e., 33 mL of organic phase was used in each 70 mL aqueous phase). The mixture was manually shaken for 3-5 min at room temperature (20-25℃), allowed to stand, the loaded organic phase was separated, and the raffinate aqueous phase was retained for the next stage of extraction.

[0030] (5) Analysis and testing methods This invention investigates the effect of Cyanex 272 on Th in the acidic leaching solution of Bayan Obo rare earth tailings. 4+ The extraction effect is negligible. The volume change of the aqueous phase before and after extraction is negligible; therefore, the extraction rate (E) is calculated using the following formula: E = (C0 – C3) / C0 × 100% In the formula: E is the three-stage cross-flow extraction rate (%); C0 is the Th content in the leachate. 4+ The initial mass concentration (mg / L); C3 is the Th content in the raffinate phase after three-stage cross-flow extraction. 4+ The mass concentration (mg / L).

[0031] Ion concentrations were measured using inductively coupled plasma optical emission spectrometry (ICP-OES).

[0032] Example 1 The leachate from the Bayan Obo rare earth tailings, obtained by hydrothermal leaching with nitric acid as the medium, contains NO3. - ,Th 4+ Ca 2+ Fe 2+ / Fe 3+ Mg 2+ Mn 2+ SO4 2- PO4 3- Al 3+ Ce 3+ K + Pr 3+ and Nd 3+ Coexisting ions, their hydrogen ion concentration [H + The concentration is 3 mol / L, Th 4+ The initial mass concentration was 22.57 mg / L.

[0033] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0034] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0035] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0036] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0037] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 1.26 mg / L, and the extraction rate was 94.4%.

[0038] Example 2 Take 70 mL of rare earth tailings leachate obtained by hydrothermal leaching with nitric acid as the medium, and determine the hydrogen ion concentration [H]. + The concentration is 3 mol / L, Th 4+ The initial mass concentration was 11.38 mg / L.

[0039] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0040] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0041] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0042] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0043] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The concentration was 0.54 mg / L, and the extraction rate was 95.2%.

[0044] Example 3 Take 70 mL of the final raffinate aqueous phase obtained after three-stage cross-flow extraction in Example 1 (of which Th 4+ The mass concentration is 1.26 mg / L, [H + The sample solution was 3 mol / L, which was used as the starting solution in this embodiment to examine the deep extraction effect on low concentrations of thorium.

[0045] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0046] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0047] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0048] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0049] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The concentration was 0.045 mg / L, and the extraction rate was 96.4%.

[0050] Example 4 Take 70 mL of rare earth tailings leachate obtained by hydrothermal leaching with nitric acid as the medium, and determine the hydrogen ion concentration [H]. + The concentration is 0.4 mol / L, Th 4+ The initial mass concentration was 9.86 mg / L.

[0051] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0052] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0053] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0054] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0055] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The concentration was 3.99 mg / L, and the extraction rate was 59.5%.

[0056] Example 5 The leachate from the Bayan Obo rare earth tailings, obtained by hydrothermal leaching with hydrochloric acid as the medium, contains Cl. - ,Th 4 + Ca 2+ Fe 2+ / Fe 3+ Mg 2+ Mn 2+ SO4 2- PO4 3- Al 3+ Ce 3+ K + Pr 3+ and Nd 3+ Coexisting ions, their hydrogen ion concentration [H + The concentration is 2 mol / L, Th 4+ The initial mass concentration was 20.85 mg / L.

[0057] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0058] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0059] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0060] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0061] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 2.12 mg / L, and the extraction rate was 89.8%.

[0062] Example 6 Take 70 mL of rare earth tailings leachate obtained by hydrothermal leaching with hydrochloric acid as the medium, and the hydrogen ion concentration [H]+ The concentration is 2 mol / L, Th 4+ The initial mass concentration was 16.29 mg / L.

[0063] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0064] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0065] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0066] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0067] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 1.12 mg / L, and the extraction rate was 93.1%.

[0068] Example 7 Take 70 mL of rare earth tailings leachate obtained by hydrothermal leaching with hydrochloric acid as the medium, and the hydrogen ion concentration [H] + The concentration is 0.5 mol / L, Th 4+ The initial mass concentration was 7.53 mg / L.

[0069] To prepare an organic phase with a Cyanex 272 volume percentage of 10%, measure 10 mL of Cyanex 272 and mix it with 90 mL of sulfonated kerosene, shake well, and the mixture is ready.

[0070] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0071] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0072] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0073] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 3.98 mg / L, and the extraction rate was 47.1%.

[0074] The experimental results of Examples 1-7 show that: In nitric acid systems, NO3 - With Th 4+ The weak coordination competition of H partially inhibited the chelation extraction of Cyanex 272, therefore, with H + Concentration decreases ([H) + The extraction rate decreased significantly (from 94.4%-96.4% to 59.5%) as the concentration of the solvent decreased from 3 mol / L to 0.4 mol / L.

[0075] In the hydrochloric acid system, Cl - To Th 4+ Its coordination ability is weaker than NO3. - Interference from anion coordination competition is relatively small. With H + Concentration decreases ([H) + As the concentration of Cyanex 272 decreased from 2 mol / L to 0.5 mol / L, the degree of deprotonation increased, weakening the coordination ability of the extractant and thus significantly reducing the extraction rate (from 89.8%-93.1% to 47.1%). This differential behavior indicates that the present invention is compatible with two types of media and can select the corresponding acidity range according to the feed system.

[0076] Example 8: Calculation of theoretical stages in simulated countercurrent extraction (nitric acid medium) (1) Theoretical series derivation In Example 1, in the leaching solution of Bayan Obo rare earth tailings using nitric acid as the medium, Th 4+ The initial mass concentration was 22.57 mg / L, and the hydrogen ion concentration [H] was... + The concentration of Th in the final raffinate was 3 mol / L after three-stage cross-flow extraction. 4+ With a mass concentration of 1.26 mg / L, the total extraction efficiency of the three-stage cross-flow system is 94.4%. Assuming that the residual rate of each stage in the three-stage cross-flow system is equal, the residual rate of each stage, f, is: f = (1.26 / 22.57) 1 / 3 ≈0.382. This means the single-stage extraction residue is approximately 38.2%, corresponding to a single-stage extraction rate E of approximately 61.8%. Under the condition of O / A = 33:70 ≈ 0.471, the single-stage distribution ratio D is: D = E / (1-E) × (V A / V O =0.618 / 0.382×(70 / 33)≈3.43.

[0077] For multi-stage countercurrent extraction, under the ideal condition of a constant distribution ratio D, the Kremsell equation is used to describe the theoretical residual rate of N-stage countercurrent extraction: ; Extraction factor E ext = .

[0078] When the target extraction rate is ≥94.4%, the theoretical residual rate at N=2 stages is about 2.3%, corresponding to an extraction rate of about 97.7%, which is higher than the target requirement of 94.4%.

[0079] (2) Estimated conclusions Under the same conditions as in Example 1, including the same comparison and extraction time, in nitric acid medium, two-stage countercurrent extraction can theoretically increase the Th... 4+ The extraction rate reached 97.7%, meeting the requirements of Th. 4+ The target requirement is an extraction rate of ≥94.4%.

[0080] This embodiment demonstrates that, based on the results of the three-stage countercurrent extraction in Example 1, under the same phase ratio and extraction time conditions, when using two-stage countercurrent extraction in nitric acid medium, Th 4+ The theoretical extraction rate can reach 97.7%, higher than the 94.4% of three-stage cross-current extraction; at the same time, the number of extraction stages is reduced from 3 to 2, and the amount of organic phase used is reduced to 66 mL. Therefore, under the premise of unchanged extraction time and ratio, changing three-stage cross-current extraction to two-stage countercurrent extraction not only reduces the number of extraction stages and organic phase consumption, but also achieves a higher Th... 4+ Extraction rate. Because the organic phase can be recycled during countercurrent extraction, this method is more suitable for industrial continuous production applications.

[0081] Example 9: Calculation of theoretical stages in simulated countercurrent extraction (hydrochloric acid medium) (1) Theoretical series derivation In Example 5, in the leaching solution of Bayan Obo rare earth tailings using hydrochloric acid as the medium, Th 4+ The initial mass concentration was 20.85 mg / L, and the hydrogen ion concentration [H] was... + The concentration of Th in the final raffinate was 2 mol / L. After three-stage cross-flow extraction, the Th concentration in the raffinate was... 4+ With a mass concentration of 2.12 mg / L, the total extraction efficiency of the three-stage cross-flow system is 89.8%. Assuming that the residual rate of each stage in the three-stage cross-flow system is equal, the residual rate of each stage, f, is: f = (2.12 / 20.85) 1 / 3≈0.467. This means the single-stage extraction residue is approximately 46.7%, corresponding to a single-stage extraction rate E of approximately 53.3%. Under the condition of O / A = 33:70 ≈ 0.471, the single-stage distribution ratio D is: D = E / (1-E) × (V A / V O =0.533 / 0.467×(70 / 33)≈2.42.

[0082] For multi-stage countercurrent extraction, under the ideal condition of a constant distribution ratio D, the Kremsell equation is used to describe the theoretical residual rate of N-stage countercurrent extraction: ; Extraction factor E ext = When the target extraction rate is ≥94.4%, the theoretical residual rate is about 5.6% when N=3 stages, corresponding to an extraction rate of about 94.4%, which meets the target requirement.

[0083] (2) Estimated conclusions Under the same conditions as in Example 5, including the same comparison and extraction time, in hydrochloric acid medium, three-stage countercurrent extraction can theoretically enable Th... 4+ The extraction rate reached 94.4%, achieving the target extraction rate requirement.

[0084] This embodiment demonstrates that, based on the results of the three-stage countercurrent extraction in Example 5, under the same phase ratio and extraction time conditions, the Th... 4+ The theoretical extraction rate reached 94.4%, achieving the target extraction rate and improving upon the three-stage cross-current extraction (89.8%) by 4.6 percentage points. This demonstrates that, under the premise of unchanged extraction time and volume, replacing the three-stage cross-current extraction with three-stage countercurrent extraction can significantly improve the extraction efficiency (Th) at the same number of stages. 4+ The extraction rate is improved, and the organic phase is recycled instead of being added fresh at each stage, which can significantly reduce the consumption of organic phase and the amount of waste liquid generated, making it more suitable for industrial continuous production.

[0085] A comparison of the calculation results from Examples 8 and 9 shows that Cyanex 272 in nitric acid medium has a significant effect on Th... 4+The single-stage distribution ratio (D≈3.43) is higher in nitric acid medium than in hydrochloric acid medium (D≈2.42), therefore the number of countercurrent stages required to achieve the same extraction rate target (≥94.4%) differs—only two-stage countercurrent extraction is needed in nitric acid medium (theoretical extraction rate 97.7%), while three-stage countercurrent extraction is required in hydrochloric acid medium (theoretical extraction rate 94.4%). This difference reflects the influence of different acid media on extraction equilibrium, but does not affect the universality of the method of this invention in both media systems: under the same conditions of O / A=33:70 and extraction time of 4 min, countercurrent extraction with the corresponding number of stages can meet the Th... 4+ The extraction rate is ≥94.4%, which is better than the corresponding three-stage cross-flow extraction scheme (from 94.4% to 97.7% in nitric acid medium and from 89.8% to 94.4% in hydrochloric acid medium). At the same time, the organic phase can be recycled, which is suitable for industrial continuous production applications.

[0086] Experimental Example 1 To further verify the superiority of the technical solution of this invention compared with the prior art, the following comparative experiment was conducted: (1) Using P350 (a typical extractant in the prior art) as a control, the effects of Cyanex 272 and P350 on Th under the same extraction conditions were investigated. 4+ The difference in extraction performance was investigated. The comparative experiment used Bayan Obo rare earth tailings from the same source as in Examples 1-7, and different concentrations of nitric acid or hydrochloric acid were used to prepare corresponding acidic leachates during the leaching reaction. The extraction conditions were kept consistent with those in the examples.

[0087] (2) Comparison of nitric acid system experimental group ([H) + [3 mol / L, three-stage cross-flow extraction] Take 70 mL of rare earth tailings leachate from the same source as in Example 1, using nitric acid as the medium. + The concentration is 3 mol / L, Th 4+ The initial mass concentration was 22.57 mg / L. Prepare a 30% volume concentration P350-sulfonated kerosene organic phase (30 mL P350 + 70 mL sulfonated kerosene, total volume 100 mL).

[0088] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0089] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0090] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0091] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 11.38 mg / L, and the extraction rate was 49.6%.

[0092] (3) Comparison of hydrochloric acid system with experimental group (hydrogen ion concentration [H+]) + [2 mol / L, three-stage cross-flow extraction] Take 70 mL of rare earth tailings leachate from the same source as in Example 5, using hydrochloric acid as the medium. + The concentration is 2 mol / L, Th 4+ The initial mass concentration was 20.85 mg / L. Prepare a 30% volume concentration P350-sulfonated kerosene organic phase (30 mL P350 + 70 mL sulfonated kerosene, total volume 100 mL).

[0093] Three-level cross-flow extraction: First-stage extraction: Take 70 mL of the above leachate, place it in a separatory funnel, add 33 mL of the above organic phase (comparative O / A≈33:70), shake manually for 4 min, let stand, separate the loaded organic phase, and retain the raffinate aqueous phase.

[0094] Second-stage extraction: Add 33 mL of fresh organic phase to the aqueous phase obtained from the first stage, and repeat the above operations of shaking, standing, separating the loaded organic phase, and retaining the aqueous phase.

[0095] Third-stage extraction: Add 33 mL of fresh organic phase to the aqueous raffinate obtained in the second stage, and repeat the above operation of shaking, standing, separating the loaded organic phase, and retaining the final aqueous raffinate.

[0096] After the three-stage cross-flow extraction is completed, the final raffinate phase is collected, and the Th content is measured. 4+ The mass concentration was 16.29 mg / L, and the extraction rate was 21.9%.

[0097] Analysis of experimental results: The above comparative data show that, under the same nitric acid system and three-stage cross-flow extraction conditions, 10% Cyanex 272 (volume concentration) has a significant effect on Th... 4+ The total extraction efficiency of the three-stage cross-flow extraction method reached 94.4%, while that of P350 at a volume concentration of 30% was only 49.6%. Under the same hydrochloric acid system and three-stage cross-flow extraction conditions, Cyanex 272 at a volume concentration of 10% achieved a significantly higher extraction efficiency for Th... 4+The total extraction efficiency of the three-stage cross-flow system can reach 89.8%, while the total extraction efficiency of the P350 with a volume concentration of 30% is only 21.9%.

[0098] In terms of media adaptability, Cyanex 272 exhibits stability in both hydrochloric acid and nitric acid systems, making it compatible with both mainstream leaching processes for rare earth tailings. P350, while retaining some extraction capability in nitric acid systems, shows a significant decrease in extraction rate when switched to hydrochloric acid systems, with noticeable performance fluctuations during media switching.

[0099] Taking into account extraction efficiency, media versatility, and reagent consumption, under the same source of Bayan Obo rare earth tailings leachate and the same extraction conditions, the three-stage cross-flow extraction rate of 10% Cyanex 272 (94.4% in nitric acid system, 89.8%~93.1% in hydrochloric acid system) is significantly better than that of 30% P350 (49.6% in nitric acid system, 21.9% in hydrochloric acid system). Furthermore, the volume of pure Cyanex 272 reagent in the organic phase of this invention is only 1 / 3 of the volume of pure P350 reagent in the control experiment, yet it achieves a thorium extraction efficiency far exceeding that of P350, demonstrating its advantage in reagent consumption.

[0100] This invention has the following advantages: (1) Good extraction selectivity: This invention uses Cyanex 272 as the extractant, which has good selectivity for Th in a wide range of strongly acidic conditions ([H⁺] 0.4-3 mol / L). 4+ It exhibits selective extraction capabilities, enabling efficient extraction and enrichment of thorium. It demonstrates excellent extraction performance in both nitric acid and hydrochloric acid media.

[0101] (2) Strong process adaptability: This invention exhibits extraction efficiency in both nitric acid and hydrochloric acid leaching systems, and can adapt to the complex composition of the Bayan Obo rare earth tailings leachate. The nitric acid system can achieve efficient thorium extraction (three-stage extraction rate 94.4%-96.4%) under [H⁺]≈3 mol / L conditions, and the hydrochloric acid system can achieve efficient thorium extraction (three-stage extraction rate 89.8%-93.1%) under [H⁺]≈2 mol / L conditions. Operating parameters can be flexibly selected according to different leaching processes. The above acidity range is the original acidity of the leachate, which does not require pre-adjustment of alkali or acid, and can be directly connected with the original solution, adapting to actual industrial production conditions.

[0102] (3) Short and economical process: This invention adopts a conventional liquid-liquid extraction process, using Cyanex 272 as a single extractant. Only three stages of cross-flow extraction are required to achieve efficient thorium extraction, resulting in a short and easy-to-operate process. Compared with existing technologies: it eliminates the need for deep alkali adjustment of the leachate to pH ≥ 2 as in the CA-12 system; it eliminates the need to increase the acidity to an ultra-high concentration of 4.8-5.5 mol / L as in the P350 system; it eliminates the need for a six-step process as in the TBP / N235 system; and it eliminates the need for pre-synthesis and the energy consumption of heating at 40-80℃ as in the DES system. The extractant can be recycled and reused, resulting in lower industrial implementation costs.

[0103] (4) High resource utilization rate: The raffinate phase of this invention can be returned to the rare earth leaching / recovery process for recycling, reducing waste liquid discharge; Loaded with Th 4+ The organic phase can be processed by conventional back-extraction (such as back-extraction with 4 mol / L sulfuric acid solution) to obtain a thorium-rich solution, which can be used for subsequent preparation of products such as thorium nitrate and thorium hydroxide.

[0104] Industrial application prospects of this invention: The method of this invention can be directly integrated with the hydrothermal leaching process of rare earth tailings from Bayan Obo using hydrochloric acid or nitric acid. The acidic leachate obtained after solid-liquid separation of the leaching reaction mixture directly enters the extraction process. The thorium concentration in the raffinate aqueous phase can be reduced to below 0.05 mg / L, allowing it to be recycled back into the rare earth leaching / recovery process. The supported organic phase, after back-extraction, yields a thorium-rich solution for subsequent preparation of thorium nitrate, thorium hydroxide, and other products. This invention features a simple process, easy operation, and recyclable extractant, demonstrating promising prospects for industrial application.

[0105] The foregoing has shown and described the basic principles and main features of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the basic features of the present invention.

[0106] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings, characterized in that, Includes the following steps: S1: Using Cyanex 272 as the extractant, it is mixed with sulfonated kerosene to prepare an organic phase with a volume concentration of 5%-15%; S2: Perform three-stage cross-flow extraction, oscillating for 3-5 minutes per stage, and then allowing the loaded organic phase to separate after standing and phase separation. S3: After each stage of extraction and phase separation, the loaded organic phase is separated, and the raffinate aqueous phase is retained. The second and third stages of extraction are then performed sequentially using the fresh organic phase. S4: Collect the final raffinate phase, which is the raffinate phase with reduced thorium concentration.

2. The method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings according to claim 1, characterized in that, The hydrogen ion concentration of the acidic leachate is 0.4-3 mol / L.

3. The method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings according to claim 2, characterized in that, When the acidic leachate is in nitric acid medium, the hydrogen ion concentration is 2-3 mol / L.

4. The method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings according to claim 3, characterized in that, When the acidic leachate is in hydrochloric acid medium, the hydrogen ion concentration is 1.5-2 mol / L.

5. The method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings according to claim 1, wherein the volume concentration of Cyanex 272 in the organic phase is 10%.

6. The method for extracting and recovering thorium from acidic leachate of Bayan Obo rare earth tailings according to claim 1, characterized in that, The acidic leachate includes, but is not limited to, the following coexisting ions: Ca 2+ 13000-14000 mg / L、Fe 2+ / Fe 3+ 8000-9000 mg / L、Mg 2+ 4000-4600 mg / L、Mn 2+ 2500-2700 mg / L、Al 3+ 1000-1500 mg / L、PO4 3- 1300-1500 mg / L、Nd 3+ 450-500 mg / L、Pr 3+ 95-135mg / L。 7. The method according to claim 1, characterized in that, The oscillation time for each stage in step S3 is 3-5 minutes.