Method for extracting and separating rare earth, iron and uranium in monazite excellent dissolving slag leaching solution

Abstract

The invention discloses a method for extracting and separating rare earth, iron and uranium in monazite excellent molten slag, which comprises the following steps: step 1, a hydrochloric acid complete dissolution step: realizing preliminary release of valuable elements in the monazite excellent molten slag; 2, oxalic acid precipitation, wherein specific separation and solution purification of thorium are achieved; 3, primary uranium extraction is conducted, and preliminary separation of rare earth elements and uranium iron is achieved; step 4, a rare earth recovery step; 5, back extraction is carried out, and preliminary enrichment of uranium and iron is achieved; 6, secondary extraction of uranium to realize uranium-iron separation; step 7, iron precipitation; step 8, uranium back extraction; and 9, uranium product forming. The method aims at achieving step-by-step extraction and separation of rare earth, iron and uranium in the leaching solution of the optimal dissolving slag, the problem that uranium and iron are difficult to separate in the existing extraction process is solved, and the recovery rate of valuable elements of rare earth and uranium is increased.

Description

Technical Field

[0001] This invention relates to the field of monazite leaching technology, and in particular to a method for extracting and separating rare earth elements, iron and uranium from monazite leaching leachate. Background Technology

[0002] Monazite dissolution residue is a solid waste generated after the dissolution treatment of monazite. This residue contains valuable components such as rare earth elements, thorium, uranium, and iron, making its recycling and treatment significant for resource utilization and environmental protection.

[0003] Existing patent CN111004920A discloses a method for smelting and separating uranium, thorium, and rare earth elements from monazite slag. Using monazite slag as raw material, the method includes the following steps: complete dissolution with hydrochloric acid, aging of the solution, liquid-solid separation, extraction and enrichment of uranium with an amine extractant, extraction of thorium with an acidic phosphorus-containing extractant, and wastewater treatment. The raffinate obtained after thorium extraction is returned to the monazite hydrochloric acid dissolution process to recover a mixture of rare earth chlorides. After extraction and separation, precipitation yields single uranium and thorium products. The resource recovery rate of uranium, thorium, and rare earth elements is greater than 95%. Most of the process water is directly returned to the system for recycling, and a small amount of wastewater is comprehensively treated before being returned to the system, achieving zero wastewater discharge. Although this method has advantages in resource recovery rate and environmental protection, its operation is complex and costly, thus limiting its widespread application. Summary of the Invention

[0004] The main objective of this invention is to provide a method for extracting and separating rare earth elements, iron, and uranium from the leachate of monazite slag, aiming to solve the problem of low cost-effectiveness in the recovery and treatment of valuable components in monazite slag.

[0005] To achieve the above objectives, the present invention provides a method for extracting and separating rare earth elements, iron, and uranium from monazite slag, the method comprising the following steps:

[0006] Step 1: Mix the monazite slag with water at a mass-to-volume ratio of 1t:(1.0~1.2)m³. 3 The mixture is stirred and pulped to obtain a mixed slurry A. Then, concentrated hydrochloric acid is added to the mixed slurry A, and the mass-to-volume ratio of monazite slag to concentrated hydrochloric acid is controlled at 1t:(0.38~0.6)m. 3 Stirring and reacting for 1-2 hours yields a high-quality leaching slurry with a residual acid concentration of 2.3-2.7 mol / L.

[0007] Step 2: Add oxalic acid to the leachate slurry of the soluble residue, stir and react for 1-2 hours, heat to 70-80℃, and then filter to obtain leachate B containing thorium oxalate and filter residue C. The volume-to-mass ratio of the leachate slurry to oxalic acid is 1 m³ / s. 3(12~15) kg, the residual acid concentration in the leachate B of the superior slag is 2.3~2.7 mol / L, and the leachate B of the superior slag includes iron, uranium and rare earth oxides;

[0008] Step 3: Add a first mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene to the leachate B of the soluble residue for a single uranium extraction treatment to separate rare earth elements from uranium iron, obtaining an extract D loaded with an organic phase and a raffinate E containing rare earth elements. The volume ratio of trioctyldecyl tertiary amine to sec-octanol is 1:1, and trioctyldecyl tertiary amine accounts for 15-20% of the total volume of the first mixed extractant. The flow rate ratio of the leachate B of the soluble residue to the first mixed extractant is (1.0-1.5):1.

[0009] Step 4: Stir the rare earth-containing raffinate E with monazite cake to form a slurry, then add hydrochloric acid and mix, and filter to obtain rare earth chloride solution and monazite residue.

[0010] Step 5: Add hydrochloric acid solution to the extract D loaded with organic phase for back-extraction to obtain uranium-iron back-extraction solution F and the first lean organic phase. The concentration of hydrochloric acid is 0.05~0.1 mol / L, and the flow rate ratio of extract D to hydrochloric acid solution is 3:1.

[0011] Step 6: Add sodium acetate or ammonium acetate to the back-extraction solution F, then add a second mixed extractant consisting of trioctyldecyl tertiary amine, 2-octanol, and sulfonated kerosene for secondary uranium extraction to separate uranium and iron, obtaining an extractant G loaded with an organic phase and an iron-containing raffinate H. The volume ratio of trioctyldecyl tertiary amine to 2-octanol is 1:1, and trioctyldecyl tertiary amine accounts for 15-20% of the total volume of the second mixed extractant. The flow rate ratio of back-extraction solution F to the second mixed extractant is (1.0-1.5):1, and the volume-to-mass ratio of back-extraction solution F to sodium acetate or ammonium acetate is 1 m³ / min. 3 (8~10) kg;

[0012] Step 7: Add sodium hydroxide solution to the iron-containing raffinate H, control the pH value of the raffinate to 3-4, and obtain ferric hydroxide after filtration.

[0013] Step 8: Add hydrochloric acid solution to the extract G loaded with organic phase for back-extraction to obtain uranium-containing back-extraction solution I and second lean organic phase. The concentration of hydrochloric acid is 0.05~0.1 mol / L, and the flow rate ratio of extract G to hydrochloric acid solution is 3:1.

[0014] Step 9: Add sodium hydroxide solid to uranium-containing back-extraction solution I, control the pH value of the slurry to 7-8, and obtain sodium diuranate precipitate after filtration.

[0015] Optionally, step 4 specifically includes mixing the rare earth-containing raffinate E with monazite cake at a volume-to-mass ratio of 1 m³ / g. 3 1.2t of alkali slurry was stirred and mixed to form an alkali slurry. Then, concentrated hydrochloric acid was added to part of the alkali slurry to carry out a preferential solubility reaction. The pH value of the slurry was controlled at 1.2~1.5. After stirring and reacting for 2 hours, the remaining alkali slurry was added to adjust the pH value of the slurry back to 3.5~4.0. The mixture was then heated to 70~80℃ and kept at that temperature for 2 hours before being filtered to obtain a preferential solubility residue of rare earth chloride and monazite.

[0016] Optionally, step 5 further includes: adding 2.5 mol / L hydrochloric acid solution to the first lean organic phase, and recycling the first lean organic phase and hydrochloric acid solution to the uranium primary extraction process in step 3, wherein the volume ratio of the first lean organic phase to the added hydrochloric acid solution is 8:1.

[0017] Optionally, step 8 further includes: adding 2.5 mol / L hydrochloric acid solution to the second lean organic phase, and recycling the second lean organic phase and hydrochloric acid solution to the uranium secondary extraction process in step 6, wherein the volume ratio of the second lean organic phase to the added hydrochloric acid solution is 8:1.

[0018] Optionally, in step 3, the first mixed extractant consists of 15% by volume of trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene.

[0019] Optionally, in step 6, the second mixed extractant consists of 20% by volume of trioctyldecyl tertiary amine N235, 20% sec-octanol, and 60% sulfonated kerosene.

[0020] Optionally, in step 1, the monazite slag and water are mixed at a mass-to-volume ratio of 1t:1.2m. 3 Stir and mix.

[0021] Optionally, in step 2, the volume-to-mass ratio of the leaching slurry to oxalic acid is 1 m³ / s. 3 14kg.

[0022] Optionally, in step 6, the volume-to-mass ratio of the back-extraction solution F to sodium acetate or ammonium acetate is 1 m³ / g. 3 10kg.

[0023] Optionally, the monazite slag contains 38-46% water by mass, and the monazite slag contains 0.7-1.2% uranium by mass, 9-14% rare earth oxides by mass, 0.3-0.8% iron by mass, and 11-16% thorium by mass.

[0024] Beneficial effects:

[0025] This invention employs a process of leaching a high-quality solvent residue slurry with concentrated hydrochloric acid, controlling residual acidity in the material to obtain a high-quality solvent residue leaching slurry. Oxalic acid is added to precipitate thorium. The filtered high-quality solvent residue leaching solution undergoes a first-stage uranium extraction treatment using a first mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene, separating rare earth elements to obtain an extract D loaded with an organic phase. Extract D is then back-extracted using hydrochloric acid solution to obtain a back-extract F. Sodium acetate or ammonium acetate is added to back-extract F, followed by a second-stage uranium extraction treatment using a second mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene, resulting in the separation of uranium and iron to obtain an extract G loaded with an organic phase. Extract G is then back-extracted using hydrochloric acid solution to obtain a back-extract I. Uranium products are precipitated from back-extract I. Therefore, this method can achieve stepwise extraction and separation of rare earth elements, iron, and uranium in the high-quality solvent residue leaching solution, solving the problem of difficult separation of uranium and iron in existing extraction processes and improving the recovery rate of valuable rare earth elements and uranium. The entire process is simple to operate and low in cost, making it easy to promote and apply effectively. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0027] Figure 1 This is a schematic flowchart of an embodiment of the method for extracting and separating rare earth elements, iron, and uranium from the leachate of monazite slag according to the present invention.

[0028] Figure 2 for Figure 1 A logic block diagram corresponding to the embodiment.

[0029] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0030] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0031] See Figure 1-2 This invention provides a schematic flowchart of an embodiment of a method for extracting and separating rare earth elements, iron, and uranium from monazite leaching residue. The method includes the following steps:

[0032] Step 1: Mix the monazite leaching residue with a predetermined amount of water to form a slurry, resulting in slurry A. Then, add a predetermined volume of concentrated hydrochloric acid to slurry A and stir for a predetermined time to obtain a leaching slurry with a residual acid concentration of 2.3~2.7 mol / L. The monazite leaching residue contains 38~46% water, 0.7~1.2% uranium, 9~14% rare earth oxides, 0.3~0.8% iron, and 11~16% thorium. The mass-to-volume ratio of the monazite leaching residue to water is 1t:(1.0~1.2)m³. 3 The mass-to-volume ratio of monazite slag to concentrated hydrochloric acid is 1t:(0.38~0.5)m. 3 The stirring reaction is preset for 1-2 hours. This step achieves the preliminary leaching and activation of valuable elements in the solid raw material. Specifically, through the chemical reaction between hydrochloric acid and the optimal solvent residue, valuable elements such as uranium, rare earth elements, and iron are transferred from the solid phase to the liquid phase. The residual acid concentration is controlled to provide a suitable acidic environment for the subsequent precipitation reaction. The optimized solid-liquid ratio balances the reaction efficiency and reagent consumption, creating the necessary chemical conditions for the subsequent oxalic acid precipitation step.

[0033] Step 2: Add oxalic acid to the leachate slurry of the soluble residue, stir and react for 1-2 hours, then heat the slurry to 70-80℃ and filter to obtain leachate B of the soluble residue and filter residue C containing thorium oxalate. The volume-to-mass ratio of the leachate slurry to oxalic acid is 1 m³ / s. 3 (12~15) kg. This step utilizes the significant difference in Ksp between thorium oxalate and rare earth oxalate to precipitate thorium while preventing rare earth precipitation in the leachate slurry of the superior leaching residue, thereby improving the filtration effect of the leachate slurry. Among them, the H of the leachate B of the superior leaching residue... + The concentration is 2.3~2.7 mol / L. The iron content in the leachate B of the superior leaching residue is 1.2~2.5 g / L, the uranium content is 1.8~3.5 g / L, and the rare earth oxide concentration is 31~45 g / L. This step is an oxalic acid precipitation step, which achieves specific separation and solution purification of thorium. Utilizing the property that oxalic acid reacts with thorium to form insoluble thorium oxalate, selective precipitation of thorium is achieved, avoiding thorium interference and improving the purity of rare earth elements. Specifically, the slurry is heated to 70-80℃ to promote the growth of precipitate particles and improve filtration performance; the separated thorium oxalate-containing filter residue can be used as raw material for thorium products or further processed; the purified leachate B provides a clean raw material for subsequent extraction processes.

[0034] Step 3: Add a mixed extractant consisting of trioctyldecyl amine, sec-octanol, and sulfonated kerosene to the leachate B of the uranium leaching residue for primary uranium extraction. This allows for the separation of rare earth elements from uranium iron, yielding an extract D containing an organic phase and a raffinate E containing rare earth elements. The volume ratio of trioctyldecyl amine to sec-octanol is 1:1, with trioctyldecyl amine comprising 15-20% of the total volume of the mixed extractant. The flow rate ratio of the leachate B to the mixed extractant is (1.0-1.5):1. A three-stage countercurrent extraction operation is used in the primary uranium extraction. This step is the primary uranium extraction step, achieving the initial separation of rare earth elements from uranium iron. Specifically, the amine extractant (trioctyldecyl amine) selectively complexes uranyl ions and iron ions under acidic conditions. The specific reaction formula is as follows:

[0035] ;

[0036] ;

[0037] 2-Octanol is used as a phase regulator to prevent the formation of a third phase and improve phase separation performance; the flow rate ratio (1.0-1.5:1) optimizes mass transfer efficiency and ensures extraction rate >99%; and the initial separation of rare earth elements (remaining in the aqueous phase) and uranium iron (entering the organic phase) is achieved.

[0038] Step 4: The rare earth-containing raffinate E is stirred with monazite cake to form a slurry, and then hydrochloric acid is added to dissolve it to prepare a rare earth chloride solution and a monazite dissolving residue. Specifically, the rare earth-containing raffinate E and monazite cake are mixed at a volume-to-mass ratio of 1 m³ / g. 3 1.2t of alkali slurry is stirred and mixed to form an alkaline slurry. Concentrated hydrochloric acid is then added to the alkali slurry for a preferential solubility reaction. The pH of the slurry is controlled at 1.2-1.5. After stirring for 2 hours, more alkali slurry is added to adjust the pH back to 3.5-4.0, and the mixture is heated to 70-80℃ and kept at this temperature for 2 hours. The mixture is then filtered, and the filter residue is the monazite preferential solubility residue. The filtrate is the rare earth chloride solution. After desulfurization, concentration, and crystallization, the rare earth chloride product is obtained. This step is the rare earth recovery step, where the rare earth in the raffinate E is further purified by optimizing the pH (1.2-4.0) to obtain the rare earth chloride product.

[0039] Step 5 involves adding hydrochloric acid solution to the extract D containing the organic phase for back-extraction, yielding a back-extract F containing uranium and iron and a lean organic phase. The hydrochloric acid concentration is 0.05–0.1 mol / L, and the flow rate ratio of extract D to hydrochloric acid solution is 3:1. The back-extraction process employs a 6–8 stage countercurrent extraction operation, adding 2.5 mol / L hydrochloric acid solution to the lean organic phase, and then returning both the lean organic phase and hydrochloric acid solution to step 3. The volume ratio of the lean organic phase to the added hydrochloric acid solution is 8:1. This step is the first back-extraction step, using dilute hydrochloric acid (0.05–0.1 mol / L) to back-extract uranium and iron from the organic phase to the aqueous phase, achieving preliminary enrichment of uranium and iron. This provides a suitable feed solution for subsequent uranium and iron separation. Furthermore, the lean organic phase is regenerated and recycled, reducing operating costs.

[0040] Step 6: Add sodium acetate or ammonium acetate to the back-extraction solution F, then add a mixed extractant consisting of trioctyldecyl tertiary amine, 2-octanol, and sulfonated kerosene for secondary uranium extraction, resulting in uranium-iron extraction separation, yielding an extractant G loaded with an organic phase and an iron-containing raffinate H. The volume ratio of trioctyldecyl tertiary amine to 2-octanol is 1:1, and trioctyldecyl tertiary amine accounts for 15-20% of the total volume of the mixed extractant. The flow rate ratio of back-extraction solution F to the mixed extractant is (1.0-1.5):1. Specifically, the volume-to-mass ratio of back-extraction solution F to sodium acetate or ammonium acetate is 1 m³ / min. 3 (8~10) kg, the uranium secondary extraction process employs a 3-stage countercurrent extraction operation. This step is the uranium secondary extraction step, achieving deep separation of uranium and iron; specifically, the addition of sodium acetate / ammonium effectively masks iron ions to form soluble ferric acetate, and uranium combines with the ammonium extractant to achieve preferential uranium extraction, significantly improving the uranium-iron separation coefficient (β>100). The specific reaction formula is as follows:

[0041] Acetate masking effect: Fe 3+ +3CH3COO - →Fe(CH3COO)3 (soluble);

[0042] Uranium preferential extraction: UO2 2+ It preferentially binds to amine extractants.

[0043] The secondary extraction further enriches uranium and improves product quality; the optimized flow rate ratio ensures uranium recovery rate >99.5% and iron removal rate >98%; laying the foundation for the preparation of high-purity uranium products.

[0044] Step 7: Add the iron-containing raffinate H to a sodium hydroxide solution, control the pH value of the raffinate to 3-4, and filter to obtain ferric hydroxide; wherein, the mass fraction of the added sodium hydroxide solution is 35%, and this step controls the pH to 3-4 to ensure that the iron is completely precipitated in the form of ferric hydroxide.

[0045] Step 8 involves adding hydrochloric acid solution to the extract G containing the organic phase for back-extraction, yielding a uranium-containing back-extract I and a lean organic phase. Specifically, the hydrochloric acid concentration is 0.05–0.1 mol / L, and the flow rate ratio of extract G to hydrochloric acid solution is 3:1. The back-extraction process employs 6–8 stages of countercurrent back-extraction, and 2.5 mol / L hydrochloric acid solution is added to the lean organic phase. The lean organic phase and hydrochloric acid solution are then returned to step 6. The volume ratio of the lean organic phase to the added hydrochloric acid solution is 8:1. This step is a uranium back-extraction sub-step, effectively purifying the uranium product, removing trace impurities, and ensuring that the final uranium product meets nuclear-grade purity requirements.

[0046] Step 9: Add solid sodium hydroxide to the uranium-containing back-extraction solution I, control the pH of the slurry to 7-8, and filter to obtain sodium diuranate product. This step precipitates sodium diuranate by adding sodium hydroxide to back-extraction solution I, and controls the pH to (7-8) to ensure complete uranium precipitation (residual <0.1mg / L). The product meets nuclear industry standards (U>50%, impurity content meets standards), realizing the final resource utilization of valuable elements.

[0047] This invention employs a process of leaching a high-quality solvent residue slurry with concentrated hydrochloric acid, controlling residual acidity in the material to obtain a high-quality solvent residue leaching slurry. Oxalic acid is added to precipitate thorium. The filtered high-quality solvent residue leaching solution undergoes a first-stage uranium extraction treatment using a first mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene, separating rare earth elements to obtain an extract D loaded with an organic phase. Extract D is then back-extracted using hydrochloric acid solution to obtain a back-extract F. Sodium acetate or ammonium acetate is added to back-extract F, followed by a second-stage uranium extraction treatment using a second mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol, and sulfonated kerosene, resulting in the separation of uranium and iron to obtain an extract G loaded with an organic phase. Extract G is then back-extracted using hydrochloric acid solution to obtain a back-extract I. Uranium products are precipitated from back-extract I. Therefore, this method can achieve stepwise extraction and separation of rare earth elements, iron, and uranium in the high-quality solvent residue leaching solution, solving the problem of difficult separation of uranium and iron in existing extraction processes and improving the recovery rate of valuable rare earth elements and uranium.

[0048] Furthermore, to better illustrate the process and effects of a method for extracting and separating rare earth elements, iron, and uranium from monazite slag leachate, specific examples are provided below for detailed explanation:

[0049] Example 1

[0050] The monazite slag, by mass percentage, has a moisture content of 42.27%, a uranium content of 1.07%, an iron content of 0.54%, rare earth oxides of 12.22%, and a thorium content of 13.78%.

[0051] Step 1: Mix the monazite slag with water at a mass-to-volume ratio of 1t:1.2m³.3 The mixture was stirred and combined to obtain mixed slurry A. Then, concentrated industrial hydrochloric acid was added to mixed slurry A, and the mixture was stirred and reacted for 2 hours to obtain a high-quality leaching slurry. The mass-to-volume ratio of high-quality leaching slurry to concentrated industrial hydrochloric acid was 1 t: 0.46 m³ / t. 3 Controlling residual acid H in leaching pulp from high-quality solvent residue + The concentration is 2.5 mol / L.

[0052] Step 2: Add oxalic acid to the leachate from the leaching residue. The dosage of oxalic acid is 14 kg / m³. 3 After stirring and reacting for 1 hour, the slurry was heated to 75°C and filtered to obtain a high-quality leaching solution B and a filter residue C containing thorium oxalate. The high-quality leaching solution B contains H... + The concentration is 2.52 mol / L. The iron content in the leachate B of the superior slag is 1.78 g / L, the uranium content is 2.59 g / L, and the rare earth oxide concentration is 38.46 g / L.

[0053] Step 3: The leachate B from the soluble residue undergoes a three-stage countercurrent extraction in a mixing and clarifier. The extractant consists of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene to separate rare earth elements. The oil-water flow rate ratio is 1:1, yielding extract D with an organic phase and raffinate E containing rare earth elements. Raffinate E contains 0.03 g / L of uranium, 0.02 g / L of iron, and 38.38 g / L of rare earth oxides. Extract D with an organic phase contains 2.53 g / L of uranium and 1.70 g / L of iron.

[0054] Step 4: The extract D containing the organic phase is subjected to a 6-stage countercurrent back-extraction with 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1, yielding a back-extraction solution F containing uranium and iron and the first lean organic phase; the raffinate E containing rare earth elements is then mixed with monazite cake at a volume-to-mass ratio of 1 m³ / L. 3 1.2t of alkali slurry was stirred and mixed to form an alkaline slurry. Concentrated hydrochloric acid was then added to a portion of the slurry for a preferential solubility reaction. The pH of the slurry was controlled at 1.5. After stirring for 2 hours, the remaining alkali slurry was added to adjust the pH back to 4.0. The mixture was then heated to 73℃ and held at that temperature for 2 hours before filtration. The resulting filter residue was the monazite preferential solubility residue, and the resulting filtrate was the rare earth chloride solution. After desulfurization, concentration, and crystallization, the rare earth chloride product was obtained. The back-extraction solution F contained 7.57 g / L of uranium and 5.18 g / L of iron. The rare earth chloride product contained 45.27% REO, 0.01% Fe2O3, and 0.01% ThO2, meeting the requirements of the standard GB / T4148-2015 "Mixed Rare Earth Chloride Products".

[0055] Step 5: Mix the uranium-containing iron back-extraction solution F with sodium acetate at a volume-to-mass ratio of 1 m³ / L. 3The mixture was stirred and mixed with 8 kg of water, and then subjected to three-stage countercurrent extraction in a mixer-clarifier. The extractant consisted of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene, with an oil-to-water flow rate ratio of 1:1. This process separated uranium and iron, yielding an organically loaded extract G and an iron-containing raffinate H. Raffinate H contained 0.02 g / L of uranium and 5.16 g / L of iron, while extract G contained 7.54 g / L of uranium.

[0056] Step 6: Add the iron-containing raffinate H to a 35% sodium hydroxide solution, control the pH of the raffinate to 4.0, and filter to obtain ferric hydroxide filter residue. Perform a 6-stage countercurrent back-extraction of the organic-loaded extract G using 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1 to obtain uranium-containing back-extraction solution I and a second lean organic phase. The uranium content in back-extraction solution I is 22.61 g / L.

[0057] Step 7: Add solid sodium hydroxide to the uranium-containing back-extraction solution I, control the final pH value of the slurry to 8.0, stir and react for 10 hours, and filter to obtain sodium diuranate product. The sodium diuranate product has a uranium dry basis content of 58.76%, an iron content of 0.16%, a rare earth oxide content of 0.13%, and a thorium content of 0.21%, which meets the technical requirements of the diuranate industry standard (EJ / T803-1993).

[0058] The first organic-lean phase obtained in step 4 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 3. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0059] The second organic-lean phase obtained in step 6 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 5. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0060] Example 2

[0061] The monazite slag, by mass percentage, has a moisture content of 41.26%, a uranium content of 0.93%, an iron content of 0.57%, rare earth oxides of 11.57%, and a thorium content of 14.22%.

[0062] Step 1: Mix the monazite slag with water at a mass-to-volume ratio of 1t:1.2m³. 3 The mixture is stirred and mixed to obtain slurry A. Then, concentrated industrial hydrochloric acid is added to slurry A to control the residual acid H in the slurry. + The concentration was 2.4 mol / L, and the reaction was stirred for 2 hours to obtain a high-quality leaching slurry. The mass-to-volume ratio of the high-quality leaching slurry to industrial concentrated hydrochloric acid was 1 t: 0.42 m³ / L. 3 .

[0063] Step 2: Add oxalic acid to the leachate from the leaching residue. The dosage of oxalic acid is 13 kg / m³. 3 After stirring and reacting for 1 hour, the slurry was heated to 78°C and filtered to obtain a high-quality leaching solution B and a filter residue C containing thorium oxalate. The H content of the high-quality leaching solution B is... + The concentration is 2.41 mol / L. The iron content in the leachate B of the superior slag is 1.97 g / L, the uranium content is 2.73 g / L, and the rare earth oxide concentration is 36.45 g / L.

[0064] Step 3: The leachate B from the soluble residue undergoes a three-stage countercurrent extraction in a mixing and clarifier. The extractant consists of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene to separate rare earth elements. The oil-water flow rate ratio is 1:1, yielding extract D with an organic phase and raffinate E containing rare earth elements. Raffinate E contains 0.02 g / L of uranium and 0.02 g / L of iron, with a rare earth oxide concentration of 35.24 g / L. Extract D with an organic phase contains 2.57 g / L of uranium and 1.89 g / L of iron.

[0065] Step 4: The extract D containing the organic phase is subjected to a 6-stage countercurrent back-extraction with 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1, yielding a back-extraction solution F containing uranium and iron and the first lean organic phase; the raffinate E containing rare earth elements is then mixed with monazite cake at a volume-to-mass ratio of 1 m³ / L. 3 1.2t of alkali slurry was formed by stirring and mixing. Concentrated hydrochloric acid was then added to the alkali slurry for a preferential solubility reaction. The pH of the slurry was controlled at 1.5. After stirring for 2 hours, more alkali slurry was added to adjust the pH back to 4.0, and the mixture was heated to 75℃ and kept at that temperature for 2 hours. The mixture was then filtered, and the resulting filter residue was the monazite preferential solubility residue. The resulting filtrate was the rare earth chloride solution. After desulfurization, concentration, and crystallization, the rare earth chloride product was obtained. The back-extraction solution F contained 7.62 g / L of uranium and 5.35 g / L of iron. The rare earth chloride product contained 45.42% REO, 0.003% Fe2O3, and 0.008% ThO2, meeting the requirements of the standard GB / T4148-2015 "Mixed Rare Earth Chloride Products".

[0066] Step 5: Mix the uranium-containing iron back-extraction solution F with sodium acetate at a volume-to-mass ratio of 1 m³ / L. 3 The mixture was stirred and mixed with 9 kg of water, and then subjected to three-stage countercurrent extraction in a mixer-clarifier. The extractant consisted of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene, with an oil-to-water flow rate ratio of 1:1. This process separated uranium and iron, yielding an organically loaded extract G and an iron-containing raffinate H. Raffinate H contained 0.03 g / L of uranium and 5.26 g / L of iron, while extract G contained 7.45 g / L of uranium.

[0067] Step 6: Add the iron-containing raffinate H to a 35% sodium hydroxide solution, control the pH of the raffinate to 4.0, and filter to obtain ferric hydroxide filter residue. Perform a 6-stage countercurrent back-extraction of the organic-loaded extract G using 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1 to obtain uranium-containing back-extraction solution I and a second lean organic phase. The uranium content in back-extraction solution I is 22.26 g / L.

[0068] Step 7: Add solid sodium hydroxide to the uranium-containing back-extraction solution I, control the final pH value of the slurry to 8.0, stir and react for 10 hours, and filter to obtain sodium diuranate product. The sodium diuranate product has a uranium dry basis content of 60.19%, an iron content of 0.28%, a rare earth oxide content of 0.23%, and a thorium content of 0.35%, which meets the technical requirements of the diuranate industry standard (EJ / T803-1993).

[0069] The first organic-lean phase obtained in step 4 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 3. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0070] The second organic-lean phase obtained in step 6 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 5. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0071] Example 3

[0072] The monazite slag, by mass percentage, has a moisture content of 43.59%, a uranium content of 0.85%, an iron content of 0.62%, a rare earth oxide content of 12.49%, and a thorium content of 13.82%.

[0073] Step 1: Mix the monazite slag with water at a mass-to-volume ratio of 1t:1.2m³. 3 The mixture is stirred and mixed to obtain slurry A. Then, concentrated industrial hydrochloric acid is added to slurry A to control the residual acid H in the slurry. + The concentration was 2.6 mol / L, and the reaction was stirred for 2 hours to obtain a high-quality leaching slurry. The mass-to-volume ratio of the high-quality leaching slurry to industrial concentrated hydrochloric acid was 1 t: 0.47 m³ / L. 3 .

[0074] Step 2: Oxalic acid is added to the leachate slurry of the thorium oxalate at a dosage of 13 kg / m³. After stirring and reacting for 1 hour, the slurry is heated to 76°C and filtered to obtain leachate B containing thorium oxalate and filter residue C containing thorium oxalate. The thorium oxalate leachate B contains H... +The concentration is 2.60 mol / L. The iron content in the leachate B of the superior slag is 2.01 g / L, the uranium content is 2.59 g / L, and the rare earth oxide concentration is 32.87 g / L.

[0075] Step 3: The leachate B from the soluble residue undergoes a three-stage countercurrent extraction in a mixing and clarifier. The extractant consists of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene to separate rare earth elements. The oil-water flow rate ratio is 1:1, yielding extract D with an organic phase and raffinate E containing rare earth elements. Raffinate E contains 0.03 g / L of uranium, 0.01 g / L of iron, and 33.13 g / L of rare earth oxides. Extract D with an organic phase contains 2.72 g / L of uranium and 2.11 g / L of iron.

[0076] Step 4: The extract D containing the organic phase is subjected to a 6-stage countercurrent back-extraction with 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1, yielding a back-extraction solution F containing uranium and iron and the first lean organic phase; the raffinate E containing rare earth elements is then mixed with monazite cake at a volume-to-mass ratio of 1 m³ / L. 3 1.2t of alkali slurry was formed by stirring and mixing. Concentrated hydrochloric acid was then added to the alkali slurry for a preferential solubility reaction. The pH of the slurry was controlled at 1.5. After stirring for 2 hours, more alkali slurry was added to adjust the pH back to 4.0, and the mixture was heated to 72℃ and kept at that temperature for 2 hours. The mixture was then filtered, and the resulting filter residue was the monazite preferential solubility residue. The resulting filtrate was the rare earth chloride solution. After desulfurization, concentration, and crystallization, the rare earth chloride product was obtained. The back-extraction solution F contained 7.93 g / L of uranium and 5.96 g / L of iron. The rare earth chloride product contained 45.64% REO, 0.012% Fe2O3, and 0.016% ThO2, meeting the requirements of the standard GB / T4148-2015 "Mixed Rare Earth Chloride Products".

[0077] Step 5: Mix the uranium-containing iron back-extraction solution F with ammonium acetate at a volume-to-mass ratio of 1 m³ / L. 3 The mixture was stirred and mixed with 8 kg of water, and then subjected to three-stage countercurrent extraction in a mixer-clarifier. The extractant consisted of 15% (v / v) trioctyldecyl tertiary amine N235, 15% sec-octanol, and 70% sulfonated kerosene, with an oil-to-water flow rate ratio of 1:1. This process separated uranium and iron, yielding an organically loaded extract G and an iron-containing raffinate H. Raffinate H contained 0.02 g / L of uranium and 5.88 g / L of iron, while extract G contained 7.79 g / L of uranium.

[0078] Step 6: Add the iron-containing raffinate H to a 35% sodium hydroxide solution, control the pH of the raffinate to 4.0, and filter to obtain ferric hydroxide filter residue. Perform a 6-stage countercurrent back-extraction of the organic-loaded extract G using 0.1 mol / L hydrochloric acid solution at an oil-to-water flow rate ratio of 3:1 to obtain uranium-containing back-extraction solution I and a second lean organic phase. The uranium content in back-extraction solution I is 23.41 g / L.

[0079] Step 7: Add solid sodium hydroxide to the uranium-containing back-extraction solution I, control the final pH value of the slurry to 8.0, stir and react for 10 hours, and filter to obtain sodium diuranate product. The sodium diuranate product has a uranium dry basis content of 62.18%, an iron content of 0.24%, a rare earth oxide content of 0.13%, and a thorium content of 0.27%, which meets the technical requirements of the diuranate industry standard (EJ / T803-1993).

[0080] The first organic-lean phase obtained in step 4 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 3. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0081] The second organic-lean phase obtained in step 6 above is added with 2.5 mol / L hydrochloric acid solution, and the entire organic-lean phase and hydrochloric acid solution are returned to step 5. The volume ratio of the organic-lean phase to the added hydrochloric acid solution is 8:1.

[0082] As can be seen from Examples 1-3 above, the final uranium / iron separation coefficient is improved from 10-20 in the traditional method to over 100; the recovery rate is optimized: rare earth recovery rate > 95%, uranium recovery rate > 96%; uranium products meet nuclear grade standards, and rare earth products meet GB / T4148.

[0083] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for extracting and separating rare earth elements, iron, and uranium from monazite slag, characterized in that, The method includes the following steps: Step 1: Mix the monazite slag with water to make a slurry, and then add concentrated hydrochloric acid to the slurry A. After stirring and reacting, the monazite slag leachate is obtained. Step 2: Add oxalic acid to the leachate slurry of the soluble residue, heat to 70-80℃ and filter to obtain leachate B of the soluble residue and filter residue C containing thorium oxalate. The residual acid concentration in leachate B of the soluble residue is 2.3~2.7 mol / L. Leachate B of the soluble residue includes iron, uranium and rare earth oxides. Step 3: Add a first mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol and sulfonated kerosene to the leachate B of the soluble residue for a primary uranium extraction treatment, so as to separate rare earth from uranium iron extraction and obtain extract D with organic phase and raffinate E containing rare earth. Step 4: Stir the rare earth-containing raffinate E with monazite cake to form a slurry, then add hydrochloric acid and mix, and filter to obtain rare earth chloride solution and monazite residue. Step 5: Add hydrochloric acid solution to the extract D loaded with organic phase for back-extraction to obtain uranium-iron back-extraction solution F and the first lean organic phase, wherein the flow rate ratio of extract D to hydrochloric acid solution is 3:

1. Step 6: Add sodium acetate or ammonium acetate to the back-extraction solution F, and then add a second mixed extractant consisting of trioctyldecyl tertiary amine, sec-octanol and sulfonated kerosene for secondary uranium extraction treatment to separate uranium and iron, and obtain extract solution G loaded with organic phase and raffinate H containing iron. Step 7: Add sodium hydroxide solution to the iron-containing raffinate H, control the pH value of the raffinate to 3-4, and obtain ferric hydroxide after filtration. Step 8: Add hydrochloric acid solution to the extract G loaded with organic phase for back-extraction to obtain uranium-containing back-extraction solution I and a second lean organic phase, wherein the flow rate ratio of extract G to hydrochloric acid solution is 3:

1. Step 9: Add sodium hydroxide solid to the uranium-containing back-extraction solution I, control the pH value of the slurry to 7-8, and obtain sodium diuranate precipitate after filtration.

2. The method as described in claim 1, characterized in that, Step 4 specifically includes mixing the rare earth-containing raffinate E with monazite cake at a volume-to-mass ratio of 1 m³ / g. 3 1.2t of alkali slurry was stirred and mixed to form an alkali slurry. Then, concentrated hydrochloric acid was added to part of the alkali slurry to carry out a preferential solubility reaction. The pH value of the slurry was controlled at 1.2~1.

5. After stirring and reacting for 2 hours, the remaining alkali slurry was added to adjust the pH value of the slurry back to 3.5~4.

0. The mixture was then heated to 70~80℃ and kept at that temperature for 2 hours before being filtered to obtain a preferential solubility residue of rare earth chloride and monazite.

3. The method as described in claim 1, characterized in that, Step 5 further includes: adding 2.5 mol / L hydrochloric acid solution to the first lean organic phase, and returning the first lean organic phase and hydrochloric acid solution to the uranium primary extraction process in step 3 for recycling, wherein the volume ratio of the first lean organic phase to the added hydrochloric acid solution is 8:

1.

4. The method as described in claim 1, characterized in that, Step 8 further includes: adding 2.5 mol / L hydrochloric acid solution to the second lean organic phase, and returning the second lean organic phase and hydrochloric acid solution to the uranium secondary extraction process in step 6 for recycling, wherein the volume ratio of the second lean organic phase to the added hydrochloric acid solution is 8:

1.

5. The method as described in claim 1, characterized in that, In step 3, the volume ratio of trioctyldecyl tertiary amine to 2-octanol is 1:1, and the trioctyldecyl tertiary amine accounts for 15-20% of the total volume of the first mixed extractant; the flow rate ratio of the superior slag leachate B to the first mixed extractant is (1.0-1.5):

1.

6. The method as described in claim 1, characterized in that, In step 6, the volume ratio of trioctyldecyl tertiary amine to 2-octanol is 1:1, and the trioctyldecyl tertiary amine accounts for 15-20% of the total volume of the second mixed extractant; the flow rate ratio of back-extraction liquid F to the second mixed extractant is (1.0-1.5):

1.

7. The method as described in claim 1, characterized in that, In step 1, the monazite slag and water are mixed at a mass-to-volume ratio of 1t:(1.0~1.2)m³. 3 The mass-to-volume ratio of monazite slag to concentrated hydrochloric acid is 1 t : (0.38~0.6) m. 3 .

8. The method as described in claim 1, characterized in that, In step 2, the volume-to-mass ratio of the leaching slurry to oxalic acid is 1 m³ / s. 3 : (12~15) kg.

9. The method as described in claim 1, characterized in that, In step 6, the volume-to-mass ratio of the back-extraction solution F to sodium acetate or ammonium acetate is 1 m. 3 : (8~10) kg.

10. The method according to any one of claims 1 to 9, characterized in that, The monazite slag contains 38-46% water by mass, and the monazite slag contains 0.7-1.2% uranium by mass, 9-14% rare earth oxides by mass, 0.3-0.8% iron by mass, and 11-16% thorium by mass.

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