Method for recycling rare earth, thorium and iron from iron-thorium slag resources

Abstract

This invention relates to a method for the resource recovery of rare earth, thorium, and iron from iron-thorium slag. The method includes the following steps: (1) finely grinding the iron-thorium slag; (2) uniformly mixing the finely ground iron-thorium slag with reducing carbon powder, and then roasting them together in a muffle furnace to obtain roasted slag; (3) mixing the roasted slag with alkaline solution and then placing it in a sealed container for high-temperature alkaline conversion reaction to obtain alkaline conversion slag; (4) washing the alkaline conversion slag with water to remove fluoride and aluminum, and then filtering and drying it to obtain water-washed slag; (5) subjecting the water-washed slag to acid dissolution reaction, and after separation, obtaining a thorium-containing rare earth solution and an acid-leached slag respectively; (6) after deep impurity removal, transferring the thorium-containing rare earth solution to an extraction system to separate and purify rare earth and thorium elements. This invention solidifies most of the iron in the iron-thorium slag in the form of goethite through high-temperature roasting, avoiding the loss of rare earth caused by the subsequent leaching process, and has the advantages of high rare earth recovery rate, low slag rate, and low auxiliary material consumption.

Description

Technical Field

[0001] This invention belongs to the field of rare earth hydrometallurgical technology, specifically a method for the resource recovery of rare earth, thorium and iron from iron thorium slag. Background Technology

[0002] Rare earth elements are widely used in high-tech fields such as national defense, military, electronics, and new functional materials due to their unique physicochemical properties. my country is a major rare earth resource country, characterized by large reserves, wide distribution, diverse types of mineable minerals, and high content of associated metal elements. Taking the rare earth mines in the Panxi region of Sichuan Province as an example, the rare earth mines in this region are mainly light rare earth fluorocarbon cerium ore. After beneficiation and enrichment, the rare earth concentrate obtained has a REO content of about 60% to 70%, of which the high-value rare earth elements praseodymium and neodymium account for as much as 14%, the iron content is about 2%, and the radioactive element ThO2 content is about 0.2%.

[0003] Currently, in the Panzhihua-Xichang region of Sichuan, the mainstream smelting process for fluorocarbon cerium concentrate is oxidative roasting—hydrochloric acid leaching—alkali conversion of the leached residue—hydrochloric acid dissolution. This hydrometallurgical process inevitably generates iron-thorium radioactive waste slag. According to smelter production data, typically, processing 1 ton of concentrate (calculated with a 70% REO content) produces approximately 0.12–0.16 tons of iron-thorium slag, with typical component contents shown in Table 1.

[0004] Table 1 Composition of Iron Thorium Slag

[0005]

[0006] The data above shows that the iron-thorium slag produced by the current smelting process is characterized by large slag volume, high rare earth content, significant loss of valuable elements such as praseodymium and neodymium, and high content of impurities such as fluorine and aluminum. Currently, the sulfuric acid double salt precipitation method is a relatively mature process for iron-thorium slag resource recovery. This process mainly involves dissolving the iron-thorium slag with sulfuric acid, then using sodium salt double salts to precipitate rare earth elements, obtaining rare earth double salt slag and iron-containing supernatant. However, this process has many drawbacks, including severe equipment corrosion, long process time, frequent solid-liquid conversion, low rare earth recovery rate, and poor process stability, and is gradually being phased out by the market. Chinese patent CN102534269A proposes that after sulfuric acid roasting and defluorination of iron-thorium slag, a rare earth sulfuric acid solution is obtained through water leaching, and then iron and rare earth elements are separated using an extraction method. However, due to the significant impact of high iron concentration in the solution on the service life of the extractant and the quality of the final product, it currently has no industrial application prospects. Chinese patent CN106916975A proposes a method to leach iron-thorium slag with hydrochloric acid to obtain a supernatant. Sodium sulfate is then added to the supernatant to generate rare earth double salts. The slag is then converted to rare earth fluoride salts by alkali, and hydrochloric acid is used to dissolve the alkali-converted slag to obtain a rare earth chloride solution, thereby achieving the purpose of rare earth recovery. However, this method is limited to iron-thorium slag that does not contain fluorine or has a low fluorine content. It has strict requirements for raw materials and also suffers from drawbacks such as a long process, frequent solid-liquid conversion, low rare earth recovery rate, and inability to recover radioactive thorium resources.

[0007] In summary, there is an urgent need for a simple and adaptable method that can efficiently recover rare earth and thorium elements from iron thorium slag, while simultaneously reducing the volume of waste slag, alleviating the pressure on enterprises to stockpile radioactive waste, and reducing the environmental burden. Summary of the Invention

[0008] The purpose of this invention is to address the problems existing in the prior art by providing a method for the resource-based recovery of rare earth elements, thorium, and iron from iron-thorium slag. This method, for the first time, describes a process for treating iron-thorium slag using carbothermal reduction to remove iron—alkali-to-fluorine conversion—acid leaching—extraction to separate rare earth elements and thorium. Its main principle is that under high-temperature conditions, carbon powder interacts with water vapor to form CO and H2, which, under the action of various reducing agents, reduce Fe(OH)3 to Fe. 2+ Fe 2+ Under high-temperature conditions, the iron is oxidized by air to form insoluble goethite, thus solidifying most of the iron. The calcined slag is then reacted with an alkaline solution to remove fluorine, yielding an alkaline leaching residue mainly composed of goethite, RE(OH)3, and Th(OH)4. This residue is dissolved in hydrochloric acid to obtain a mixed solution of rare earth chloride and thorium, as well as an iron-containing acid leaching residue. Rare earth and thorium are then separated and recovered through extraction, while the iron-containing acid leaching residue is utilized as a resource. This method features a short process flow, low auxiliary material consumption, high rare earth recovery rate, strong raw material adaptability, and low slag rate. It effectively separates and recovers rare earth, iron, and thorium resources, greatly alleviating the pressure of radioactive waste storage for enterprises, and demonstrating significant social and economic benefits.

[0009] To achieve the above-mentioned objectives, the specific technical solution of this invention is as follows:

[0010] A method for resource recovery of rare earth, thorium and iron from iron-thorium slag. The method generates insoluble goethite through the carbothermic reduction-air oxidation of iron, thereby solidifying most of the iron; then, alkali-to-fluoride conversion and acid-dissolution-alkali-to-slag conversion are used to obtain a thorium-containing rare earth solution and acid leaching slag; rare earth and thorium are recovered from the acid leaching solution by extraction.

[0011] The method specifically includes the following steps:

[0012] (1) Grind the iron thorium slag into fine powder;

[0013] (2) The finely ground iron thorium slag and reduced carbon powder are mixed evenly and then placed together in a muffle furnace for roasting to obtain roasted slag;

[0014] (3) After mixing the roasting residue obtained in step (2) with the alkaline solution, place it in a sealed container for high-temperature alkaline conversion reaction to obtain crude alkaline conversion residue.

[0015] (4) The crude alkali residue obtained in step (3) is washed with water to remove fluorine and aluminum, and then filtered and dried to obtain the washed residue.

[0016] (5) The water washing residue obtained in step (4) is subjected to acid dissolution reaction, and after separation, thorium rare earth solution and acid leaching residue are obtained respectively;

[0017] (6) After deep purification, the thorium-containing rare earth solution obtained in step (5) is transferred to the extraction system to separate and purify rare earth and thorium elements.

[0018] As a preferred embodiment of this application, the particle size of the iron thorium slag after fine grinding in step (1) is less than 170 mesh (specifically, it can be 200 mesh, 250 mesh, etc.).

[0019] In a preferred embodiment of this application, the amount of reducing carbon powder used in step (2) is 1.0% to 15.0% of the weight of iron thorium slag; the calcination temperature is controlled between 450 and 550°C (specifically, it can be 450°C, 460°C, 470°C, 480°C, 490°C, 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, etc.), and the calcination time is 0.2 to 2.0 h (specifically, it can be 0.2 h, 0.5 h, 1.0 h, 1.5 h, 2.0 h, etc.).

[0020] As a preferred embodiment of this application, the alkaline solution in step (3) is any one or a mixture of two of NaOH and KOH; the mass ratio of alkaline solution to roasting residue is 0.15:1 to 1.4:1; and the liquid-solid ratio in the alkaline conversion reaction is 2:1 to 4:1.

[0021] As a preferred embodiment of this application, the high-temperature alkali conversion reaction temperature in step (3) is greater than 90°C, and the reaction time is 2 to 8 hours.

[0022] As a preferred embodiment of this application, the pH value of the water washing endpoint solution in step (4) is controlled between 7 and 8 (specifically, it can be between 7.0, 7.2, 7.4, 7.6, 7.8, 8.0, etc.).

[0023] In a preferred embodiment of this application, in step (5), the water-washed residue undergoes an acid dissolution reaction, and the pH value at the endpoint of the acid dissolution reaction is controlled between 1.5 and 3.5 (specifically, it can be 1.5, 2.0, 2.5, 3.0, 3.5, etc.); the liquid-solid mass ratio in the acid dissolution reaction is 2:1 to 4:1.

[0024] In a preferred embodiment of this application, the temperature of the acid dissolution reaction in step (5) is 50-80°C (specifically, it can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.), and the time is 0.5-3h (specifically, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc.); the acid used in the acid dissolution reaction is one or a mixture of several inorganic acids.

[0025] In a preferred embodiment of this application, the inorganic acid includes hydrochloric acid and sulfuric acid.

[0026] As a preferred embodiment of this application, the method for resource recovery of rare earth, thorium and iron from iron thorium slag described in any one of the above methods is adopted. Through this method, the rare earth leaching rate is 96%, of which the high-value elements praseodymium and neodymium leaching rate is 98%, and the acid leaching residue rate is 30-40%; and it can also be used for iron resource recovery.

[0027] Compared with the prior art, the positive effects of the present invention are reflected in:

[0028] (1) The method used in this invention has the advantages of short process flow, low consumption of auxiliary materials, high rare earth recovery rate, strong adaptability of raw materials and low slag rate. It has achieved the separation and recovery of rare earth, iron and thorium resources, greatly alleviated the pressure of enterprise radioactive waste storage, and has significant social and economic benefits.

[0029] (2) This method controls the redox atmosphere of the roasting furnace to generate goethite, which is insoluble in acid, thus solidifying most of the iron and avoiding the waste of auxiliary materials caused by secondary leaching of iron. At the same time, it greatly reduces the burden of subsequent solution purification and impurity removal processes. The rare earth elements combined with fluorine are released through the alkali conversion process, ensuring a high recovery rate of rare earth elements in the acid leaching process. The process treats iron thorium slag with a rare earth leaching rate of 96%, of which the high-value elements praseodymium and neodymium have a leaching rate of up to 98%. The main component of the acid leaching residue is Fe, and the slag rate is about 30-40%. As an iron resource recovery process, the process is simple to operate, has low operating costs, and has a significant waste reduction effect. It reduces the pressure of radioactive waste storage for enterprises, is easy to industrialize, and has significant social and economic benefits. Detailed Implementation

[0030] All features disclosed in this specification, or all steps in all disclosed methods or processes, may be combined in any way, except for mutually exclusive features and / or steps.

[0031] Any feature disclosed in this specification (including the claims and abstract) may be replaced by other equivalent or similar features, unless specifically stated otherwise. That is, unless specifically stated otherwise, each feature is merely one example of a series of equivalent or similar features.

[0032] In this application, unless otherwise specified, the liquid-to-solid ratio refers to the ratio of liquid volume (ml) to solid mass (g).

[0033] In this application, any percentage not explicitly stated refers to a mass percentage, i.e., wt%.

[0034] Example 1:

[0035] Take 100g of iron-thorium slag, crush and grind it to -170 mesh. Its composition is shown in Table 2. Mix the reduced carbon powder with the crushed iron-thorium slag evenly, place it in a muffle furnace for roasting, the amount of reduced carbon powder is 1.0% of the mass of iron-thorium slag, the roasting temperature is controlled at 500℃, and the roasting time is 1.5h. After roasting, place the roasted slag and NaOH solution in a sealed alkali transfer container at the same time. The amount of NaOH is 0.50 times the mass of roasted slag, the liquid-solid ratio of the alkali transfer reaction is 3:1, the alkali transfer temperature is 100℃, and the reaction time is 6h. Wash the alkali transfer slag with water to remove fluoride until the pH value of the supernatant is between 7 and 8, filter and dry the alkali transfer slag. After alkali-to-slag conversion and slurry preparation, HCl was added dropwise to control the final solution pH at 2.0. The acid leaching liquor-to-solid ratio was 4:1, the reaction temperature was 80℃, and the reaction time was 30 min. Solid-liquid separation was achieved by filtration. The acid leaching residue was dried and weighed to approximately 39.6 g. Samples were taken for rare earth element content analysis. Based on the analysis results, the REO leaching rate reached 96.5%, with the high-value elements praseodymium and neodymium leaching rates at approximately 98.4%. The Fe content in the acid leaching liquor was 0.001 g / L. After impurity removal, the acid leaching liquor entered an extraction system to separate and recover thorium and REO. The iron-thorium slag after this process had a residue rate of only 39.6% of the original, making it suitable for iron resource recovery. The acid leaching liquor underwent extraction to separate and purify rare earth elements and thorium, achieving efficient recovery of REO, iron, thorium, and waste volume reduction.

[0036] Table 2. Analysis of Main Components of Iron-Thorium Slag

[0037]

[0038] Example 2:

[0039] Take 100g of iron-thorium slag, crush and grind it to -200 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 15.0% of the mass of the iron-thorium slag. Mix the reducing carbon powder and the crushed iron-thorium slag evenly, and place it in a muffle furnace for roasting. The roasting temperature is controlled at 550℃, and the roasting time is 2 hours. After roasting, place the roasted slag and NaOH solution in a sealed alkali transfer container at the same time. The amount of NaOH is 0.15 times the mass of the roasted slag. The liquid-solid ratio of the alkali transfer reaction is 2:1, the alkali transfer temperature is 90℃, and the reaction time is 2 hours. Wash the alkali transfer container with water. The residue was leached until the pH of the supernatant was between 7 and 8. The residue was then filtered and dried. After slurry preparation, HCl was added dropwise to control the final pH at 3.5. The acid leaching solution-to-solid ratio was 3:1, the reaction temperature was 60℃, and the reaction time was 1 hour. The residue was then filtered to separate solids and liquids. The dried residue weighed approximately 38.1g, and samples were taken for analysis of rare earth elements and impurities. Based on the analysis results, the REO leaching rate reached 96.0%, with the high-value elements praseodymium and neodymium leaching rate at approximately 98.0%. The Fe content in the acid leaching solution was 0.007g / L. After this process, the iron-thorium slag ratio was only 38.1% of the original, making it suitable for iron resource recovery. The acid leaching solution was purified by an extraction system to separate and purify rare earth elements and thorium, achieving efficient recovery of REO, iron, thorium, and waste volume reduction.

[0040] Example 3:

[0041] Take 100g of iron thorium slag, crush and grind it to -200 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 10.0% of the iron thorium slag mass. Mix the reducing carbon powder and the crushed iron thorium slag evenly, and place it in a muffle furnace for roasting. The roasting temperature is controlled at 450℃, and the roasting time is 0.2h. After roasting, place the roasted slag and KOH solution in a sealed alkali transfer container at the same time. The amount of KOH is 1.4 times the mass of the roasted slag. The alkali transfer reaction liquid-solid ratio is 3:1, the alkali transfer temperature is 100℃, and the reaction time is 8h. Wash the alkali transfer slag with water until the pH value of the supernatant is between 7 and 8. Filter and dry the alkali transfer slag. After the alkali transfer slurry is prepared, add HC dropwise. The process involved controlling the final pH value to 1.5, the acid leaching solution to solid ratio to 4:1, the reaction temperature to 50℃, and the reaction time to 0.5h. After filtration to separate the solid and liquid components, the acid leaching residue was dried and weighed to approximately 39.8g. Samples were taken for analysis of rare earth elements and impurities. Based on the analysis results of the acid leaching residue, the REO leaching rate was calculated to be 97.15%, with the high-value elements praseodymium and neodymium leaching rates at approximately 98.9%. Fe was not detected in the acid leaching solution. The iron-thorium slag rate after this process was only 39.8% of the original, making it suitable for iron resource recovery. The acid leaching solution was further purified by an extraction system to separate and purify rare earth elements and thorium, achieving the goal of efficient recovery of REO, iron, thorium, and waste volume reduction.

[0042] Example 4:

[0043] Take 100g of iron-thorium slag, crush and grind it to -170 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 5.0% of the iron-thorium slag mass. Mix the reducing carbon powder and the crushed iron-thorium slag evenly, place it in a muffle furnace for roasting, control the roasting temperature at 480℃, and roast for 0.5h. After roasting, place the roasted slag and KOH solution in a sealed alkali transfer container. The amount of KOH is 0.8 times the mass of the roasted slag. The alkali transfer reaction liquid-solid ratio is 3:1, the alkali transfer temperature is 100℃, and the reaction time is 8h. Wash the alkali transfer slag with water until the pH value of the supernatant is between 7 and 8. Filter and dry the alkali transfer slag. After the alkali transfer slurry is prepared, add H2SO4 dropwise, controlling the final concentration. The pH value was 3.5, the acid leaching solution to solid ratio was 2:1, the reaction temperature was 80℃, and the reaction time was 1.0 h. After solid-liquid separation by filtration, the acid leaching residue was dried and weighed to approximately 38.7 g. Samples were taken for analysis of rare earth elements and impurity content. Based on the analysis results of the acid leaching residue, the REO leaching rate was calculated to be 96.84%, of which the high-value elements praseodymium and neodymium leaching rate was approximately 99.51%. The Fe concentration in the acid leaching solution was 0.012 g / L. The iron-thorium slag rate after this process was only 38.7% of the original, and it can be used for iron resource recovery. The acid leaching solution was separated and purified by an extraction system to remove rare earth elements and thorium, achieving the goal of efficient recovery of REO, iron, thorium, and waste volume reduction.

[0044] Example 5:

[0045] Take 100g of iron-thorium slag, crush and grind it to -230 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 5.0% of the mass of the iron-thorium slag. Mix the reducing carbon powder and the crushed iron-thorium slag evenly, and place it in a muffle furnace for roasting. The roasting temperature is controlled at 450℃, and the roasting time is 1.0h. After roasting, place the roasted slag and NaOH solution in a sealed alkali transfer container. The amount of NaOH is 0.4 times the mass of the roasted slag. The liquid-solid ratio of the alkali transfer reaction is 3:1, the alkali transfer temperature is 100℃, and the reaction time is 6h. Water The alkali-leaching residue was washed until the pH of the supernatant was between 7 and 8. The residue was then filtered and dried. After slurry preparation, H₂SO₄ was added dropwise to control the final acidity at pH 2.5. The acid leaching solution-to-solid ratio was 3:1, the reaction temperature was 80℃, and the reaction time was 3 hours. After filtration and solid-liquid separation, the dried residue weighed approximately 37.1g. Samples were taken for analysis of rare earth elements and impurities. Based on the analysis results, the REO leaching rate reached 97.8%, with the high-value elements praseodymium and neodymium leaching rates at approximately 99.5%. Fe was not detected in the acid leaching solution. The iron-thorium slag after this process had a residue rate of only 37.1% of the original, making it suitable for iron resource recovery. The acid leaching solution was purified by an extraction system to separate and refine rare earth elements and thorium, achieving efficient recovery of REO, iron, thorium, and waste volume reduction.

[0046] Comparative Example 1:

[0047] Take 100g of iron-thorium slag, crush and grind it to -150 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 5.0% of the mass of the iron-thorium slag. Mix the reducing carbon powder and the crushed iron-thorium slag evenly, place it in a muffle furnace for roasting, control the roasting temperature at 400℃, and roast for 1.5h. After roasting, place the roasted slag and NaOH solution in a sealed alkali transfer container. The amount of NaOH is 1.0 times the mass of the roasted slag. The liquid-to-solid ratio of the alkali transfer reaction is 3:1, the alkali transfer temperature is 100℃, and the reaction time is 8h. Wash the alkali transfer slag with water until the pH value of the supernatant is between 7 and 8. Filter and dry the alkali transfer slag. After the slag was transferred and the slurry was prepared, H2SO4 was added dropwise to control the final acidity at pH 3.5, the acid leaching solution to solid ratio of 3:1, the reaction temperature at 80℃, and the reaction time at 3h. After filtration to separate the solid and liquid, the acid leaching residue was dried and weighed to approximately 31.6g. Samples were taken for analysis of rare earth elements and impurity content. Based on the analysis results of the acid leaching residue, the REO leaching rate was calculated to be 94.9%, of which the high-value elements praseodymium and neodymium leaching rate was approximately 95.7%, and the Fe concentration in the acid leaching solution was 0.422g / L. Subsequent impurity removal operations are required for the Fe in the acid leaching solution. Iron removal is usually achieved by adjusting the solution acidity and extraction, which inevitably results in the loss of rare earth elements.

[0048] Comparative Example 2:

[0049] Take 100g of iron thorium slag, crush and grind it to -150 mesh. Its composition is the same as in Example 1. The amount of reducing carbon powder is 10.0% of the mass of the iron thorium slag. Mix the reducing carbon powder and the crushed iron thorium slag evenly, and place it in a muffle furnace for roasting. The roasting temperature is controlled at 450℃, and the roasting time is 1.0h. After roasting, place the roasted slag and NaOH solution in a sealed alkali transfer container at the same time. The amount of NaOH is 0.8 times the mass of the roasted slag. The liquid-solid ratio of the alkali transfer reaction is 3:1, the alkali transfer temperature is 98℃, and the reaction time is 6h. Wash the alkali transfer slag with water until the pH value of the supernatant is between 7 and 8. Filter and dry the alkali transfer slag. After the alkali transfer slurry is prepared, add HCl dropwise to control the final pH value. The concentration of the acid leaching solution was 0.5, the solid-to-acid ratio was 2:1, the reaction temperature was 80℃, and the reaction time was 2.5h. After solid-liquid separation by filtration, the acid leaching residue was dried and weighed to approximately 29.4g. Samples were taken for analysis of rare earth elements and impurity content. Based on the analysis results of the acid leaching residue, the REO leaching rate was calculated to be 96.7%, of which the leaching rate of high-value elements praseodymium and neodymium was approximately 97.1%. Due to the high acidity of the acid leaching solution, the Fe concentration in the acid leaching solution reached 1.82g / L. Subsequent impurity removal operations were required for the Fe in the acid leaching solution. Iron removal is usually achieved by adjusting the solution acidity and extraction, which inevitably leads to the loss of rare earth elements.

[0050] The examples described above are merely preferred embodiments of this patent, but the scope of protection of this patent is not limited thereto. It should be noted that, for those skilled in the art, without departing from the principles of this patent, based on the technical solution and patent concept of this patent, several improvements and modifications can be made, and these improvements and modifications should also be considered within the scope of protection of this patent.

Claims

1. A method for the resource recovery of rare earth elements, thorium, and iron from iron thorium slag, characterized in that... Includes the following steps: (1) Grind the iron thorium slag into fine powder; (2) The finely ground iron thorium slag and reduced carbon powder are mixed evenly and then placed together in a muffle furnace for roasting to obtain roasted slag; (3) The roasted residue obtained in step (2) is mixed with the alkaline solution and placed in a sealed container for high-temperature alkaline conversion reaction to obtain crude alkaline conversion residue; the alkaline solution is any one or a mixture of two of NaOH and KOH; the high-temperature alkaline conversion reaction temperature is 90~100℃ and the reaction time is 2~8h; (4) The crude alkali slag obtained in step (3) is washed with water to remove fluorine and aluminum, and then filtered and dried to obtain the washed slag; (5) The water-washed residue obtained in step (4) is subjected to acid dissolution reaction, and after separation, a thorium-containing rare earth solution and an acid-leached residue are obtained respectively; the acid dissolution reaction temperature is 50~80℃ and the time is 0.5~3h; (6) After deep purification, the thorium-containing rare earth solution obtained in step (5) is transferred to an extraction system to separate and purify rare earth and thorium elements; In step (2), the amount of reducing carbon powder used is 1.0% to 15.0% of the weight of iron thorium slag; the roasting temperature is controlled between 450 and 550℃, and the roasting time is 0.2 to 2.0 h; In step (5), the water-washed residue undergoes an acid dissolution reaction, and the pH value at the end of the acid dissolution reaction is controlled between 1.5 and 3.5; the ratio of liquid volume (mL) to solid mass (g) in the acid dissolution reaction is 2:1 to 4:

1.

2. The method for resource recovery of rare earth elements, thorium, and iron from iron thorium slag as described in claim 1, characterized in that: In step (1), the particle size of the iron thorium slag after fine grinding is less than 170 mesh.

3. The method for resource recovery of rare earth elements, thorium, and iron from iron thorium slag as described in claim 1, characterized in that: The mass ratio of alkali solution to roasting residue in step (3) is 0.15:1 to 1.4:1; the ratio of liquid volume (mL) to solid mass (g) in the alkali conversion reaction is 2:1 to 4:

1.

4. The method for resource recovery of rare earth elements, thorium, and iron from iron thorium slag as described in claim 1, characterized in that: In step (4), the pH value of the final water washing solution is controlled between 7 and 8.

5. The method for resource recovery of rare earth elements, thorium, and iron from iron thorium slag as described in claim 1, characterized in that: The acid used in the acid dissolution reaction in step (5) is one or a mixture of several inorganic acids.

6. The method for resource recovery of rare earth elements, thorium, and iron from iron thorium slag as described in claim 5, characterized in that: The inorganic acids mentioned include hydrochloric acid and sulfuric acid.

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