High-temperature oxidation-reduction monazite smelting integrated comprehensive recovery technology

Abstract

The invention discloses a high-temperature oxidation-reduction monazite smelting integrated comprehensive recovery technology, which comprises the following steps: pressing monazite and carbon powder with proper particle size into balls, performing three-section temperature control reduction, namely an inert atmosphere preheating section, an oxygen-enriched atmosphere high-temperature main reduction section and an oxygen-enriched air oxidation section, and washing tail gas to prepare phosphoric acid for recovery. And after ball crushing and acid dissolution, respectively treating filter residues, removing iron from the solution, extracting uranium, precipitating thorium and concentrating according to the temperature of a high-temperature main reduction section in an oxygen-enriched atmosphere. The recovery rate of rare earth elements such as yttrium and radioactive element uranium in the technology is high, the potential safety hazard problem of white phosphorus is solved, waste liquid is little, and radioactive waste residues are greatly reduced.

Description

Technical Field

[0001] This invention relates to the field of environmental protection technology, specifically to a high-temperature oxidation-reduction monazite smelting integrated recycling technology. Background Technology

[0002] Monazite is a typical associated radioactive mineral rich in rare earth elements, uranium, and thorium. On the one hand, monazite contains 15 of the 10 rare earth elements, exhibiting characteristics of both light and heavy rare earth elements, with a rare earth content of approximately 55%, making it one of the important rare earth minerals. On the other hand, monazite contains radioactive elements uranium (approximately 0.3%–0.5%) and thorium (approximately 4%–12%). The uranium content is one order of magnitude higher than that of uranium ore mined in most uranium mines in China, making it a typical associated uranium resource. Due to the high activity concentration of naturally occurring uranium and thorium nuclides in monazite, the transportation, storage, smelting, and waste disposal of monazite require close attention to radiation protection for workers and the radiation risks to the surrounding environment.

[0003] Currently, the main production process for extracting rare earth elements from monazite ore is the alkaline process. During the reaction of monazite ore with liquid alkali, rare earth elements are converted into water-insoluble rare earth hydroxide, phosphorus reacts to form trisodium phosphate, and the rare earth hydroxide is then dissolved in hydrochloric acid to obtain rare earth chloride. The main problems with this process are: large wastewater volume, complex process, low resource recovery rate, failure to recover uranium and thorium resources, and high cost of compliant disposal of the generated radioactive waste.

[0004] Research has begun on using integrated recycling technologies to recover uranium and thorium resources. For example, Hunan CNNC Jinyuan New Materials Co., Ltd. uses alkali conversion, acid dissolution, extraction, or resin adsorption to extract uranium, adjust pH to precipitate thorium hydroxide, remove radioactive and impurities, and concentrate to produce mixed rare earth chlorides; or alkali conversion, acid dissolution, acid dissolution to pH 4 to recover mixed rare earth chlorides, followed by further acid dissolution to pH 2 to dissolve uranium and thorium, recovering uranium and precipitating thorium. This process has the following problems: the alkali dissolution process generates a large amount of radioactive wastewater, making treatment difficult, the process complex, and the resource recovery rate low (the overall rare earth recovery rate is approximately 94%). Uranium / thorium is not recovered, and the disposal cost of radioactive waste is high. The main reason is that the alkali conversion process produces acid-insoluble slag, which leads to a large amount of unrecoverable Y (yttrium) resources, and the crystals always contain 0.3% unrecoverable uranium resources.

[0005] Some studies have employed pyrometallurgical pretreatment of monazite, such as the patent application CN2022110249918, which proposes high-temperature treatment of monazite to recover phosphorus and rare earth products. The problems with this approach are: high pretreatment temperatures (above 1300 degrees Celsius), high energy consumption, and failure to achieve comprehensive utilization of uranium and thorium resources during the recovery process; furthermore, despite the high reaction temperatures, phosphate crystals of important rare earth elements such as Dy are not fully opened, leading to significant economic losses due to the inability to recover them through acid dissolution; additionally, the inability to precisely control the phosphate reduction endpoint results in a large amount of phosphate being reduced to white phosphorus, which is prone to spontaneous combustion and can easily produce highly toxic chemicals such as phosphorus chloride in acidic environments, posing significant safety hazards during the production process.

[0006] As mentioned above, there is a need to develop an integrated recycling technology for monazite smelting, which results in low wastewater volume, high rare earth recovery rate, and high safety. Summary of the Invention

[0007] To address the aforementioned problems, the inventors discovered that by pressing monazite and carbon powder of suitable particle size into spheres, followed by a three-stage temperature-controlled reduction process—namely, an inert atmosphere preheating stage, an oxygen-enriched atmosphere high-temperature main reduction stage, and an oxygen-enriched air oxidation stage—and by washing the tail gas with water to recover phosphoric acid, the spheres are crushed and acid-dissolved, and the filter residue is treated according to the temperature of the oxygen-enriched atmosphere high-temperature main reduction stage. The solution is then used for iron removal, uranium extraction, thorium precipitation, and concentration. This method achieves high recovery rates of rare earth elements such as yttrium and radioactive elements such as uranium, solves the safety hazard of white phosphorus, produces less waste liquid, and significantly reduces radioactive waste residue, thus completing this invention.

[0008] The purpose of this invention is to provide an integrated high-temperature oxidation-reduction monazite smelting and recycling technology. This technology involves pressing monazite and carbon powder of suitable particle size into spheres, which are then subjected to three-stage temperature-controlled reduction: an inert atmosphere preheating stage, an oxygen-enriched atmosphere high-temperature main reduction stage, and an oxygen-enriched air oxidation stage. The tail gas is washed with water to recover phosphoric acid. After the spheres are crushed and acid-dissolved, the filter residue is treated according to the temperature of the oxygen-enriched atmosphere high-temperature main reduction stage. The solution is then subjected to iron removal, uranium extraction, thorium precipitation, and concentration.

[0009] In this invention, monazite mainly has an apatite-type structure with alternating PO4 tetrahedra and REO9 polyhedra, exhibiting high stability and being difficult to be directly destroyed by acids or alkalis.

[0010] The inventors have creatively proposed a three-stage temperature-controlled reduction process: an inert atmosphere preheating stage, an oxygen-enriched atmosphere high-temperature main reduction stage, and an oxygen-enriched air oxidation stage. This process effectively opens up the acid-insoluble crystal structure in monazite while avoiding the formation of white phosphorus, ensuring that rare earth elements can be highly recovered.

[0011] In a preferred embodiment of the present invention, the inert atmosphere preheating section is a low-temperature reaction section with a temperature not lower than 300°C, preferably 300-450°C, and more preferably 300-350°C. The preheating time is preferably not less than 20 minutes, and more preferably not less than 25 minutes. Under an inert atmosphere, preheating can effectively remove volatiles, which helps monazite to fully react and open the acid-insoluble crystal structure in the subsequent oxygen-enriched high-temperature main reduction section, and promotes the full oxidation of phosphorus in the oxygen-enriched air oxidation section to avoid the formation of white phosphorus.

[0012] For an inert atmosphere, non-reactive gases such as nitrogen, helium, neon, and argon can be used.

[0013] In a preferred embodiment of the present invention, the oxygen-enriched atmosphere high-temperature main reduction section is a high-temperature reduction reaction section, with a preferred temperature of 850-2000℃, more preferably 900-1650℃, and even more preferably 1400-1600℃. The reduction reaction time is preferably not less than 20 minutes, more preferably not less than 25 minutes, and particularly preferably not less than 35 minutes. Under this oxygen-enriched atmosphere, the high-temperature main reduction reaction can fully disrupt the bond energy of the monazite structure, open up the insoluble structures, especially the phosphate structures of elements such as Y and Dy, as well as uranium-thorium oxide, thereby improving the rare earth recovery rate and the recovery rate of radioactive elements uranium and thorium, achieving more efficient resource utilization.

[0014] In particular, the inventors discovered that when the temperature of the high-temperature main reduction section in an oxygen-enriched atmosphere is above 1650°C, the acid-insoluble structure can be almost completely opened, and it dissolves almost completely during subsequent acid dissolution, leaving no insoluble matter, which is beneficial for subsequent processing. However, such a high temperature naturally results in high energy consumption, so in practice, the temperature of the high-temperature main reduction section in an oxygen-enriched atmosphere needs to be selected specifically according to the situation.

[0015] For the oxygen-rich atmosphere here, air with an oxygen content of not less than 25% can be used, especially air with an oxygen content of 28-30%.

[0016] In a preferred embodiment of the present invention, the oxygen-enriched air oxidation section is a low-temperature reaction section, with the reaction temperature preferably below 200°C, preferably 120-160°C, and more preferably 140-160°C, which can safely and fully oxidize residual carbon, white phosphorus, etc., ensuring safety.

[0017] For the oxygen-rich atmosphere here, air with an oxygen content of not less than 25% can be used, especially air with an oxygen content of 28-30%.

[0018] The reaction time in the oxygen-enriched air oxidation section is preferably not less than 5 minutes, and more preferably 5-10 minutes.

[0019] In this invention, the flue gas in the three-stage temperature-controlled reduction process contains phosphorus (P2O5), and phosphoric acid is recovered by water washing. The tail gas is preferably discharged after being adsorbed by activated carbon to remove radioactivity.

[0020] Through extensive experiments, the inventors discovered that, in order to promote the full reaction of monazite in the three-stage temperature-controlled reduction process, it is more advantageous to pelletize monazite powder with reducing carbon powder.

[0021] In a preferred embodiment of the present invention, the monazite powder is ground to a particle size of less than 45 μm, with the fraction exceeding 95 wt%; the reducing carbon powder is ground to a particle size of 0.05-0.1 mm, wherein the carbon powder with a particle size of less than 0.08 mm accounts for more than 50%, in order to facilitate the effective mixing of the monazite powder and the reducing carbon powder, and to ensure sufficient reaction in the subsequent three-stage temperature-controlled reduction stage.

[0022] In this invention, reducing carbon powder with a high fixed carbon content can be used, such as carbon powder, coke powder, coal, coke, semi-coke, etc., with semi-coke being preferred. This is because semi-coke not only has a high fixed carbon content, but also has well-developed pores, which can promote the decomposition reaction, prevent the local enrichment and explosion of phosphorus vapor, and has low volatile matter, low ash content, and low sulfur content, effectively inhibiting the occurrence of side reactions and avoiding the formation of harmful or insoluble impurities.

[0023] In a preferred embodiment of the present invention, the semi-coke preferably has a fixed carbon content of 85% or more, a volatile matter content of 8% or less, and an ash content of 6% or less.

[0024] In this invention, the ratio of reducing toner to monazite is by mass, preferably monazite:toner = 1:0.35-0.5, more preferably monazite:toner = 1:0.38-0.47, and even more preferably monazite:toner = 1:0.42-0.46.

[0025] To briquette monazite powder and carbon powder, a binder can be used to mix them before briquetting.

[0026] As a binder, organic binders, inorganic binders, composite binders, etc. can be used, with organic binders, such as modified starch and modified cellulose binders, being preferred, because organic binders will volatilize and release in subsequent reactions, without affecting the reaction of rare earth elements and radioactive elements.

[0027] The inventors have discovered that the preferred amount of binder is 3%-11.8% of the total mass of monazite and carbon powder, more preferably 7%-10%.

[0028] For briquetting equipment, no special briquetting equipment is needed. Commonly used briquetting equipment in this field can be used to press the mixed powder of binder, monazite powder, and carbon powder into spherical or irregularly shaped granules. The maximum geometric length of the pressed shape should not exceed 20 mm. To facilitate the transportation and filling of the pressed material, the packing porosity of the pressed granules is preferably not less than 25%, with a compressive strength of 50 N / granule, preferably greater than 100 N / granule, a pulverization rate of less than 1.5% when the number of stacked layers is greater than 50, and a bursting rate of less than 12% when baked at 300℃.

[0029] After the compressed particles undergo three stages of temperature-controlled reduction, the rare earth elements and radioactive elements have fully reacted to form acid-soluble substances, and the phosphorus element has formed oxides that are absorbed by water. Therefore, they can be crushed and acid-dissolved, and then the radioactive elements and rare earth elements can be separated and recovered.

[0030] Based on the temperature of the high-temperature main reduction section in an oxygen-rich atmosphere, if it is above 1650℃, there are almost no acid-insoluble substances, and iron can be directly removed, uranium extracted, thorium precipitated, and rare earth elements concentrated after acid dissolution. If it is below 1650℃, there may still be trace amounts of acid-insoluble substances. The residue after acid dissolution is then subjected to alkali dissolution, followed by iron removal, uranium extraction, thorium precipitation, and rare earth element concentration to promote the full recovery of rare earth elements and radioactive elements.

[0031] In a preferred embodiment of the present invention, the crushing is carried out at a low temperature, preferably below 40°C, and the particle size of the crushed powder is preferably below 46 μm.

[0032] In a preferred embodiment of the present invention, acid dissolution is preferably carried out using hydrochloric acid, and the hydrochloric acid is preferably concentrated hydrochloric acid, such as a concentration of 1 mol / L or more, preferably 3 mol / L or more, and more preferably 5 mol / L or more.

[0033] It is preferred to use excess hydrochloric acid for dissolution, and more preferably to stir and filter under pH less than 2 to obtain a mixed rare earth chloride solution and filter residue.

[0034] In a preferred embodiment of the present invention, the filtrate after acid dissolution and the filtrate after alkali dissolution can be used to remove iron, extract uranium, precipitate thorium, and then remove impurities and concentrate rare earth elements.

[0035] For iron removal, common iron removal methods can be used, such as the sodium ferrous sulfate method and the P507 extraction method.

[0036] For uranium extraction, resin adsorption is the preferred method.

[0037] Regarding thorium precipitation, thorium hydroxide can be precipitated by adjusting and increasing the pH. Thorium oxide can be recovered as thorium nitrate by dissolving it in nitric acid, and the filter residue can be disposed of as radioactive waste.

[0038] Regarding impurity removal, non-rare earth element plating / heavy metal ions can be removed through extraction. Commonly used extraction methods in this field can be employed, with no particular limitations.

[0039] Regarding concentrated rare earth elements, the solution after impurity removal can be concentrated by methods such as evaporation to crystallize rare earth chloride.

[0040] Preferably, to improve the quality of rare earth elements, hydrogen rare earth elements can be appropriately proportioned according to the different heavy rare earth element contents in the concentrated rare earth chloride. In practice, this proportion should be flexibly determined based on the heavy rare earth element content.

[0041] The present invention has the following beneficial effects: (1) By pressing monazite and reducing carbon powder into particles with a certain mechanical strength, the reduction-oxidation reaction can be fully carried out, and side reactions can be avoided. (2) After three-stage temperature-controlled reduction, the rare earth elements and radioactive elements in monazite have fully reacted to form acid-soluble substances, namely, the petrothermal reduction reaction and the oxygen-enriched oxidation reaction reduce phosphate. Moreover, due to the full oxidation of white phosphorus and red phosphorus produced by over-reduction, the generated phosphorus pentoxide is recovered from the flue gas to obtain phosphoric acid products, thereby improving the utilization rate of phosphorus resources and avoiding the occurrence of elemental phosphorus toxicity. (3) By using a petrothermal reaction, the yttrium / dysprosium elements in the monazite crystals that cannot be recovered by conventional hydrometallurgy and the uranium / thorium elements in the acid-insoluble slag are opened up, and subsequent hydrometallurgical recovery is realized, which improves the recovery rate of rare earth resources and uranium resources and improves economic benefits. (4) Reduce the reaction conditions of traditional alkaline decomposition and acid dissolution processes, reduce acid and alkali consumption and equipment load, reduce the generation and use of hazardous chemicals in the system, reduce the amount of wastewater generated, reduce the radioactivity level and generation of radioactive waste residue, and save the cost of wastewater treatment and radioactive waste residue disposal. Detailed Implementation

[0042] The present invention will now be described in detail through specific embodiments, and the features and advantages of the present invention will become clearer and more explicit with these descriptions.

[0043] Example 1 Raw material: 25 kg of monazite concentrate (rare earth oxides REO 55.2%, U 0.48%, Th 8.1%, P2O5 25.5%, the remainder being silicon, calcium and other trace impurities) Step 1-1: Grinding and Mixing Monazite concentrate was ground to D using a Raymond mill. 95 <45μm, specific surface area ≥450 m² 2 / kg.

[0044] Semi-coke (88% fixed carbon, 5.5% ash) used as reducing carbon powder was pulverized into D using an air jet mill. 50 =0.075mm, of which powder particles with a diameter less than 0.08mm account for ≥60%.

[0045] Monazite powder and carbon powder were mixed evenly using a twin-screw mixer at a mass ratio of 1:0.42 (monazite:carbon powder). The coefficient of variation (CV) was <5%.

[0046] Steps 1-2: Pressing and Molding Hydroxypropyl methylcellulose (viscosity 4000 mPa·s), used as a binder, was pregelatinized and sprayed into the mixture powder obtained in step 1-1 at 8.5% of the total mass of monazite powder and toner.

[0047] The spheres are then formed into Φ15mm ellipsoids using a roller briquetting machine. The compressive strength of a single sphere is ≥120N, and the packing porosity is 28%~32%. Drying process: 280℃×40min, with a bursting rate ≤10%.

[0048] Step 2: Three-stage temperature control restoration The three sections utilize the following equipment: a multi-hearth furnace (6 layers) + an oxygen-enriched combustion system + a tail gas quench tower. stage Temperature control Atmosphere / medium Key Operations Inert atmosphere preheating 300~350℃ <![CDATA[N2 protection (O2 < 0.5%)]]> Let it stand for 25 minutes to remove volatile components. High-temperature primary reduction in an oxygen-rich atmosphere 1450±50℃ <![CDATA[Oxygen-enriched air (O2 28~30%)]]> Natural gas assisted heating, reduction time 35 minutes Oxygen-enriched air oxidation 150±10℃ <![CDATA[Oxygen-enriched air (O2 28%)]]> Ventilate for 8 minutes to remove residual carbon. The tail gas is used to recover phosphoric acid using a three-stage water washing tower (circulating liquid pH=1.5~2.0), with a P2O5 capture rate of ≥95%, yielding 20% ​​dilute phosphoric acid.

[0049] Furthermore, the exhaust gas undergoes radioactive protection after being washed and recovered with water, that is, it is adsorbed by activated carbon before being emitted.

[0050] Step 3: Crushing and Grinding The pellets, after being reduced in three stages of temperature control in step 2, are spray-cooled to below 40°C, and then subjected to jaw crusher + ball milling to D. 100 <46μm, where quality control includes reduction rate detection (TREO recovery rate of total rare earth oxides ≥97.5%).

[0051] Step 4: Acid dissolution and solid-liquid separation The powder obtained in step 3 was dissolved in hydrochloric acid under the following conditions: hydrochloric acid concentration 6 mol / L, liquid-to-solid ratio 4:1 (mass ratio), stirred at 80℃ for 2 h, with an endpoint pH of 0.8. The mixture was then filtered to obtain filtrate and filter residue.

[0052] Step 5: Separate treatment of filter residue The filter residue was subjected to alkali melting at 145℃ and 0.4 MPa (alkali-to-ore ratio (mass ratio) 0.7) in an alkali melting tank. The filtrate was filtered to recover trace amounts of trisodium phosphate. The alkali-melted filter residue was dissolved in 6 mol / L hydrochloric acid at a liquid-to-solid ratio of 4:1 to obtain a solution.

[0053] Step 6: Extract uranium and deposit thorium Iron removal: The solution obtained in step 4 and the filtrate obtained in step 5 are subjected to the sodium ferrous sulfate method (pH=3.5~4.0) to remove Fe. 3+ .

[0054] Uranium extraction: The filtrate used for iron removal was adsorbed by a 201×7 strong basic anion exchange resin with an adsorption capacity of 120 mg U / g resin. It was desorbed by 5% Na2CO3 solution with a desorption rate of ≥99%, and 166g of uranium octoxide was recovered, with a uranium recovery rate of 90.1%.

[0055] Thorium precipitation: The pH of the filtrate after uranium extraction was adjusted to 4.2~4.5 to obtain Th(OH)4 precipitate. The precipitate was collected by filtration and dissolved with 7mol / L nitric acid to obtain 4340g of nuclear-grade thorium nitrate (ThO2≥99.9%).

[0056] Step 7-1: Deep Impurity Removal The filtrate obtained in step 6 was extracted using the following extraction system: P507 (2-ethylhexylphosphonic acid mono-2-ethylhexyl ester)-HCl system, using three-stage countercurrent extraction to remove Pb, Ca, and Mg. A total of 3.075 kg of radioactive residue was obtained, which was collected and disposed of in a landfill facility that meets the requirements of HJ1114.

[0057] Step 7-2: Concentration The aqueous phase obtained in step 7-1 was evaporated and crystallized, and concentrated to 46.5% rare earth oxide (REO) using an MVR evaporator. Rare earth chloride (H2O≤3%) was crystallized, yielding 13.2 kg of heavy rare earth chlorides enriched with gadolinium, terbium, and dysprosium. The total rare earth recovery rate was 96.2%, the yttrium recovery rate was 96%, and the Dy recovery rate was 95.5%.

[0058] Mix light rare earth oxide (LREO) and heavy rare earth oxide (HREO) in a mass ratio of 7:3, and package in a sealed, moisture-proof container.

[0059] Example 2 Raw material: 50 kg of monazite concentrate (rare earth oxides REO 55.2%, U 0.48%, Th 8.1%, P2O5 25.5%, the remainder being silicon, calcium and other trace impurities) Step 1-1: Grinding and Mixing Monazite ore was ground to a particle size of <45μm, accounting for 98% (by air jet mill classification control).

[0060] Semi-coke (86% fixed carbon, 5.8% ash) used as reducing carbon powder is ground to a particle size of 0.05-0.1 mm, of which powder with a particle size of less than 0.08 mm accounts for 65%.

[0061] The monazite powder and toner powder were mixed using a twin-screw mixer according to the mass ratio of monazite to toner powder: 1: 0.44.

[0062] Steps 1-2: Pressing and Molding Hydroxypropyl methylcellulose (HPMC) organic binder is added to the mixed powder of monazite powder and carbon powder at 8% of the total mass of monazite powder and carbon powder, and pressed into pellets with a diameter of 15 mm. The compressive strength is 120 N / pellet, the packing porosity is 28%, and the bursting rate after baking at 300℃ is 9.5%.

[0063] Step 2: Three-stage temperature control restoration: Inert atmosphere preheating section: Under the protection of nitrogen atmosphere, the pellets are preheated to 350℃.

[0064] High-temperature main reduction section with oxygen-enriched atmosphere: temperature 1550℃±50℃, oxygen-enriched air (oxygen concentration 28%) for combustion support, residence time 45 minutes, during which rare earth phosphates decompose into oxides, and most phosphorus is released in the form of P2O5.

[0065] Oxygen-enriched air oxidation section: Cool down to 140℃, introduce 28% oxygen-enriched air, and ventilate for 8 minutes to oxidize residual carbon and white phosphorus.

[0066] In this process, the high-temperature / low-temperature exhaust gas from each section absorbs P2O5 in a water washing tower to generate dilute phosphoric acid (concentration 20%), with a P2O5 recovery rate of 92%, and is then discharged after being adsorbed by activated carbon.

[0067] Step 3: Crushing and Grinding After the pellets obtained in step 2 were reduced to 40°C, they were crushed and ball-milled to a particle size of <40μm (accounting for 98%) to obtain "reduced monazite powder".

[0068] Step 4: Acid extraction of rare earth elements Dissolve the reduced monazite powder obtained in step 3 in hydrochloric acid, add excess 6 mol / L HCl to the powder, pH≤1.5, and stir at 80℃ for 2 hours.

[0069] The mixture of rare earth chloride solution (REO concentration 250 g / L, rare earth solubility rate, i.e., initial rare earth recovery rate: 98.3%) and filter residue (containing uranium, thorium and undissolved impurities) were obtained by filtration.

[0070] Step 5: Filter residue grading treatment The filter residue is further recovered by alkali melting in an alkali melting tank: the alkali melting tank is pressurized at 0.4 MPa, the alkali-to-ore ratio (mass ratio) is 0.7, stirred at 145℃, and held for 14 hours. After alkali melting, the residue is filtered, and the filtrate is used to recover and concentrate trace amounts of trisodium phosphate. The alkali-melted filter residue is dissolved in 6 mol / L HCl.

[0071] Step 6: Extract uranium and deposit thorium The solution obtained in step 4 and the filtrate obtained in step 5 were extracted together with P507 extractant to remove Fe. 3+ Pb 2+ wait.

[0072] Uranium extraction: The pH of the extract was adjusted to 3.0, and uranium was adsorbed through an anion exchange resin (201×7). After saturation, it was desorbed with Na2CO3, and 274g of uranium oxide (UO3) was recovered, of which 232.35g was uranium. The uranium recovery rate was 89.2%.

[0073] Thorium precipitation: Adjust the pH to 4.0, add hydrogen peroxide to precipitate Th(OH)4, and dissolve in nitric acid to obtain 8565g of thorium nitrate product, with a thorium recovery rate of 90%.

[0074] Step 7-1: Deep purification. Add barium sulfate solution to the filtrate obtained in step 6 to remove radium.

[0075] Step 7-2: Rare Earth Concentration and Blending The solution obtained in step 7-1 was evaporated and crystallized to obtain 26.5 kg of heavy rare earth chlorides enriched with samarium, europium, and gadolinium. The total rare earth recovery rate was 96.2%, the yttrium recovery rate was 96.5%, and the Dy recovery rate was 95%.

[0076] A total of 6.24 kg of radioactive waste was generated, which was collected, centrally disposed of, and landfilled in a landfill facility that meets the requirements of HJ1114.

[0077] Example 3 The procedure was carried out in the same manner as in Example 1, except that the mixing ratio of monazite ore to carbon powder was 1:0.46, and the temperature of the high-temperature main reduction section in an oxygen-rich atmosphere was 900°C. The results showed a total rare earth recovery rate of 95.7%, a uranium recovery rate of 89.5%, a phosphorus pentoxide recovery rate of 93.2%, a thorium recovery rate of 89.3%, a yttrium recovery rate of 95.1%, and a Dy recovery rate of 94.7%.

[0078] Example 4 The procedure was carried out in the same manner as in Example 2, except that the mixing ratio of monazite ore to carbon powder was 1:0.44, and the temperature of the high-temperature main reduction section in an oxygen-rich atmosphere was 1000°C. The results showed a total rare earth recovery rate of 96.1%, a uranium recovery rate of 89.6%, a phosphorus pentoxide recovery rate of 93.3%, a thorium recovery rate of 89.2%, a yttrium recovery rate of 95.3%, and a Dy recovery rate of 95.2%.

[0079] The present invention has been described in detail above with reference to specific embodiments and / or exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A high-temperature oxidation-reduction integrated monazite smelting and recycling technology, which involves pressing monazite and carbon powder of suitable particle size into balls, and then reducing them in three stages with controlled temperature: an inert atmosphere preheating stage, an oxygen-enriched atmosphere high-temperature main reduction stage, and an oxygen-enriched air oxidation stage. The tail gas is washed with water to recover phosphoric acid. After the balls are crushed and acid-dissolved, the filter residue is treated according to the temperature of the oxygen-enriched atmosphere high-temperature main reduction stage. The solution is then subjected to iron removal, uranium extraction, thorium precipitation, and concentration.

2. The technology according to claim 1, wherein, The inert atmosphere preheating section is a low-temperature reaction section with a temperature of not less than 300°C, preferably 300-450°C, and more preferably 300-350°C; the preheating time is not less than 20 minutes, preferably not less than 25 minutes.

3. The technology according to claim 1, wherein, The oxygen-enriched atmosphere high-temperature main reduction section is a high-temperature reduction reaction section with a temperature of 850-2000℃, preferably 900-1650℃, more preferably 1400-1600℃, and a reduction reaction time of not less than 20 minutes, preferably not less than 25 minutes, and particularly preferably not less than 35 minutes.

4. The technology according to claim 1, wherein, The oxygen-enriched air oxidation section is a low-temperature reaction section, with a reaction temperature below 200℃, preferably 120-160℃, more preferably 140-160℃, and a reaction time of not less than 5 minutes, preferably 5-10 minutes.

5. The technology according to claim 1, wherein, The oxygen-enriched atmosphere uses air with an oxygen content of not less than 25%, especially air with an oxygen content of 28-30%.

6. The technology according to claim 1, wherein, Monazite is pulverized and ground to a particle size of less than 45 μm, with the fraction exceeding 95 wt%. The reducing toner is ground to a particle size of 0.05-0.1 mm, of which toner particles smaller than 0.08 mm account for more than 50%. The ratio of reducing toner to monazite by mass is monazite:toner = 1:0.35-0.5, more preferably monazite:toner = 1:0.38-0.47, and even more preferably monazite:toner = 1:0.42-0.

46.

7. The technology according to claim 1, wherein, Monazite and carbon powder of suitable particle size are pressed into balls using a binder. Organic adhesives are used as binders.

8. The technology according to claim 7, wherein, The amount of binder is 3%-11.8% of the total mass of monazite and carbon powder, preferably 7-10%.

9. The technology according to claim 1, wherein, As a reducing toner, a reducing toner with a fixed carbon content is used, such as toner, coke powder, coal, coke, semi-coke, etc. Semi-coke is preferred, and semi-coke with a carbon content of more than 85%, volatile matter of less than 8%, and ash content of less than 6% is even more preferred.

10. The technology according to claim 1, wherein, If the temperature of the high-temperature main reduction section in an oxygen-rich atmosphere exceeds 1650℃, iron removal, uranium extraction, thorium precipitation, and rare earth concentration can be directly achieved after acid dissolution. If the temperature of the high-temperature main reduction section in an oxygen atmosphere is below 1650℃, the residue after acid dissolution is subjected to alkali dissolution, followed by iron removal, uranium extraction, thorium precipitation, and rare earth concentration.