A system and method for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas.

Abstract

This invention belongs to the field of resource recycling technology, specifically relating to a system and method for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas. The invention employs a self-developed system to treat polluted water bodies in ion-adsorption rare earth mining areas, promoting the aggregation of colloidal rare earth elements in the water into suspended particles that settle into the bottom sediment, resulting in bottom sediment with a high concentration of rare earth elements. This facilitates recycling and reuse, achieving the removal of colloidal rare earth elements from polluted water bodies surrounding ion-adsorption rare earth mining areas and the sustainable utilization of secondary rare earth resources. Furthermore, the recovery method is simple, with high rare earth leaching recovery rates and good selectivity. It also allows for the recycling of leaching agents, resulting in low cost and minimal secondary pollution, demonstrating good economic and environmental benefits.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology. More specifically, it relates to a system and method for recovering colloidal rare earth elements from polluted water bodies in ion-type rare earth mining areas. Background Technology

[0002] Rare earth elements (REEs) comprise 16 elements, including the 15 lanthanides and yttrium (Y) in the periodic table. Their unique physicochemical properties make them widely used in metallurgy, petrochemicals, glass, ceramics, catalysis, permanent magnet materials, superconducting materials, and novel optoelectronic and magnetic materials. They are essential raw materials for high-end manufacturing and are often referred to as "industrial MSG" and "industrial vitamins." my country possesses abundant and diverse rare earth resources. Among them, the ion-adsorption type rare earth deposits unique to southern China, also known as weathering crust leaching type rare earth deposits, are rich in medium and heavy rare earth elements and are important strategic resources for my country, playing a crucial role in high-tech fields.

[0003] Over-mining of ion-adsorption rare earth minerals can cause serious pollution to the surrounding atmosphere, soil, and water environment. Existing research indicates that high concentrations of rare earth elements can be toxic to animals, plants, and microorganisms in the ecosystem, inhibiting their growth, development, and reproduction, thereby disrupting the balance of the ecosystem. They can even enter the human body through the food chain, accumulate metabolically, and potentially induce toxic effects, posing a threat to human health.

[0004] With the large-scale development of rare earth mines, frequent mining activities can lead to a scarcity of rare earth resources. Therefore, it is necessary to comprehensively recycle and utilize rare earth from other secondary resources. Currently, most industrial activities focus on recovering rare earth elements from end products such as waste rare earth magnetic materials, rare earth catalytic materials, and rare earth hydrogen storage materials. In addition, the recycling of residual rare earth from natural resources has become an important supplement to the rare earth supply, such as rare earth-rich metallurgical tailings, marine sediments, and rare earth resources in polluted waters surrounding some mining areas. If these residual rare earth resources from natural resources can be recycled and utilized, it can effectively alleviate the supply and demand imbalance in the rare earth industry, bring certain economic value, and solve the environmental pollution problems induced by rare earths.

[0005] Rare earth resources in polluted water bodies are mainly divided into soluble rare earths and colloidal rare earths. The recovery of colloidal rare earths is particularly difficult. Firstly, enriching colloidal rare earths in the early stages is challenging. Secondly, the leaching conditions for these precipitates rich in colloidal rare earths are more complex than those for soluble rare earths, making leaching and recovery difficult using conventional chemical leaching methods. Currently, many scholars have developed effective treatment schemes for the recovery of rare earth-containing wastewater sediment. For example, Chinese patent application CN106636689A directly uses the sediment from rare earth wastewater ponds as the initial treatment target. It first pre-calcines the sediment, then uses mineral acid to leach the calcined product to obtain a rare earth-containing leachate. Ammonium sulfate and oxalic acid are then added sequentially to the leachate, causing the rare earths to separate from soluble impurities in the form of solid-phase precipitation, thus efficiently recovering rare earths from the sediment in rare earth wastewater ponds. However, the key first step of the above treatment method is to obtain rare earth-rich wastewater sediment. Existing methods for obtaining rare earth-rich wastewater sediment often require adding a large amount of coagulant to the wastewater containing rare earth metals to promote its precipitation. However, the addition of too much coagulant will cause chemical pollution and increase the treatment cost. Furthermore, before using leaching treatment, the patented method also requires high-temperature (800-900℃) roasting of the obtained rare earth wastewater sediment, which further increases energy consumption and treatment cost.

[0006] Therefore, there is an urgent need to find a method for the efficient, highly selective, low-secondary-pollution, and low-cost recovery of colloidal rare earth resources from polluted water bodies in ion-type rare earth mining areas. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the defects and shortcomings of the prior art, which requires a large amount of chemical agents to promote the precipitation of colloidal rare earth metals in water to obtain the enriched colloidal rare earth metal precipitate, and the difficulty of leaching and recovering the rich colloidal rare earth precipitate by conventional methods. The present invention provides a pretreatment system for recovering colloidal rare earths from polluted water bodies in ion-type rare earth mining areas.

[0008] Another object of the present invention is to provide a system for recovering colloidal rare earths from polluted water bodies in ion-type rare earth mining areas.

[0009] Another object of the present invention is to provide a method for recovering colloidal rare earth elements from polluted water bodies in ion-type rare earth mining areas using the system described above.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution:

[0011] This invention protects a pretreatment system for recovering colloidal rare earth from polluted water in ion-type rare earth mining areas, comprising a slow-flow chamber, a grid chamber, a sedimentation chamber, and a sludge collection chamber, wherein the slow-flow chamber, the grid chamber, the sedimentation chamber, and the sludge collection chamber are connected in sequence.

[0012] The top and bottom of the slow-flow chamber are staggered with baffles, which form an S-shaped curved water flow channel in the slow-flow chamber;

[0013] A coarse grille is fixedly installed inside the grille chamber;

[0014] The sedimentation chamber is equipped with a radial flow sedimentation tank device, which includes inlet and outlet water pipes, a drive system, a water distributor, a vertical flow energy dissipation pipe, a rotating shaft, a sludge scraper support, a truss, and a sludge scraper. One end of the inlet and outlet water pipes is connected to the bar screen chamber, and the other end is connected to the vertical flow energy dissipation pipe. A water distributor is installed at the top of the vertical flow energy dissipation pipe, and a drive system is installed at the top of the water distributor. There are at least two rotating shafts, which are symmetrically arranged about the vertical flow energy dissipation pipe about an axis of symmetry. One end of each rotating shaft is movably connected to the vertical flow energy dissipation pipe, and the other end is fixedly connected to the sludge scraper support. There are at least two trusses, which are symmetrically arranged about the vertical flow energy dissipation pipe about an axis of symmetry, and the trusses are fixedly connected to the sludge scraper support. The sludge scraper is fixedly connected to the bottom side wall of the sludge scraper support.

[0015] The bottom of the sludge collection chamber is connected to the bottom of the sedimentation chamber.

[0016] Preferably, the length of the partition is 1 / 2 to 2 / 3 of the internal height of the slow-flow chamber.

[0017] Preferably, there are at least two partitions.

[0018] More preferably, the partition consists of 5 pieces.

[0019] Preferably, the coarse grid consists of 6 to 9 bars, and the gap between the bars is 16 to 40 mm.

[0020] Preferably, the angle between the coarse screen and the bottom of the screen chamber is 40° to 60°, which is beneficial for removing larger suspended solids, floating solids and solid particulate matter from wastewater.

[0021] Furthermore, the coarse grid is fixed by a metal bracket.

[0022] Furthermore, the radial flow sedimentation tank has a circular bottom with a diameter of 20–50 m and a water depth of 1.5–3.0 m around the perimeter. The bottom slope should not be less than 0.05. When polluted water enters the tank through the distributor, it flows slowly towards the perimeter along the radial direction. Colloidal rare earth elements agglomerate into suspended particles during the flow and settle in the bottom sediment. They then enter the center of the tank bottom along the slope and are discharged through the sludge discharge pipe. The resulting clarified water overflows from the perimeter of the tank and is discharged through the effluent pipe.

[0023] The polluted water from the ion-adsorption rare earth mining area is diverted into the pretreatment system. After passing through a slow-flow chamber and a coarse screen, the water is further treated by energy dissipation through a vertical flow energy dissipation pipe and rectification by a water distributor. This reduces the water flow velocity and removes larger suspended solids, floating matter, and solid particulate matter from the polluted water, which facilitates the rapid settling of colloidal rare earths into the sediment. The sediment is then collected for extraction and recovery of the colloidal rare earths.

[0024] Furthermore, the driving system provides power to the rotating shaft, which in turn drives the sludge scraper bracket. The scraper plate, connected to the bottom side wall of the sludge scraper bracket, rotates to scrape the sludge, collecting the fallen bottom sludge at the center of the bottom of the sedimentation tank, and then discharges it through the sludge discharge pipe.

[0025] Furthermore, the truss serves to support and fix the sludge scraper support, thereby enhancing the structural stability of the support.

[0026] Preferably, one end of the rotating shaft is connected to the vertical flow energy dissipation pipe via a movable knob.

[0027] This invention also protects a system for recovering colloidal rare earths from polluted water bodies in ion-type rare earth mining areas. The system includes a pretreatment system, a leaching chamber, a pH adjustment tank, a reagent treatment tank, and a calcination chamber, which are connected in sequence.

[0028] This invention also protects a method for recovering colloidal rare earth elements from polluted water bodies in ion-type rare earth mining areas, specifically comprising the following steps:

[0029] S1. The polluted water from the ion-type rare earth mining area is diverted into the system to obtain colloidal rare earth sediment. The colloidal rare earth sediment is pretreated and then leached with a leaching agent. The sediment is then filtered to obtain rare earth leachate.

[0030] S2. Adjust the pH of the rare earth leachate obtained in step S1 to 1-2, and filter to recover the rare earth mother liquor.

[0031] S3. Continue to add precipitant and impurity remover to the rare earth mother liquor obtained in step S2, and filter to obtain rare earth precipitate;

[0032] S4. After thoroughly drying the rare earth precipitate obtained in step S3, calcine it thoroughly to obtain the rare earth oxide product.

[0033] Specifically, in step S1, the process of diverting polluted water from the ion-adsorption rare earth mining area into the system to obtain colloidal rare earth sediment is as follows: The polluted water from the ion-adsorption rare earth mining area first enters the slow-flow chamber through the inlet pipe. The baffles in the slow-flow chamber cause the polluted water to form an S-shaped curved water flow channel within the chamber, thereby reducing the water flow velocity. The polluted water then enters the screen chamber through the first inlet / outlet pipe. The coarse screen removes larger suspended solids, floating matter, and solid particles from the polluted water to ensure the normal operation of the subsequent sedimentation chamber and prevent blockage of the sludge discharge pipe. After passing through the screen, the polluted water flows out from the second inlet / outlet pipe at the bottom and enters the vertical flow energy dissipation pipe. The water flow is further reduced in velocity after passing through the energy dissipation and water distributor, and then flows out in all directions. At this time, the colloidal rare earth elements will settle and accumulate in the bottom mud of the sedimentation tank due to gravity settling in the polluted water. Since the bottom of the tank itself has a certain slope, which is high around the edges and low in the middle, it is conducive to the polluted water flowing from the bottom slope to the middle of the tank. In addition, the drive system drives the rotating shaft, which in turn drives the sludge scraper support, causing the scraper plate on the bottom side wall of the sludge scraper support to rotate and accelerate the collection of the bottom mud in the tank. The fallen bottom mud is collected in the center of the bottom of the sedimentation tank and enters the mud collection chamber through the mud discharge pipe. The clarified water obtained after the bottom mud is collected overflows from the perimeter of the tank and is discharged from the outlet pipe.

[0034] Preferably, in step S1, the flow velocity of the polluted water in the ion-type rare earth mining area is reduced to ≤0.9m / s after passing through the slow-flow chamber; the flow velocity of the polluted water in the ion-type rare earth mining area is reduced to ≤0.2m / s after passing through the radial flow sedimentation tank device for rectification.

[0035] Preferably, in step S1, the leaching agent is one or more of EDTA-Na2, malic acid, and citric acid.

[0036] Preferably, in step S1, the leaching agent is EDTA-Na2. When the added leaching agent is EDTA-Na2, EDTA can be precipitated by adjusting the pH, thereby achieving the purpose of recycling.

[0037] Preferably, in step S1, the solid-liquid ratio of the pretreated colloidal rare earth sediment to the leaching agent is 1:2 to 1:5.

[0038] Preferably, in step S1, the leaching treatment time is ≥12h.

[0039] Preferably, in step S1, the concentration of the leaching agent is 0.04–0.1 mol / L.

[0040] Preferably, in step S1, the polluted water from the ion-type rare earth mining area remains in the sedimentation chamber for >12 hours.

[0041] Furthermore, in step S1, the pretreatment includes drying, grinding, and sieving.

[0042] Preferably, the particle size of the sediment sample obtained after pretreatment in step S1 is 20 mesh.

[0043] Preferably, in step S3, the precipitant is oxalic acid.

[0044] Preferably, in step S3, the impurity removal agent is ammonium sulfate.

[0045] Preferably, the temperature for thorough roasting is 850–1000°C.

[0046] Specifically, in step S1, the leaching process is an oscillating leaching at a speed of 180 r / min under room temperature conditions.

[0047] Furthermore, in step S3, in actual processing, when the precipitant is oxalic acid and the impurity remover is ammonium sulfate, the amount of impurity remover added is twice the theoretical amount, and the amount of precipitant added is three times the theoretical amount. The theoretical amount is specifically calculated using the following chemical reaction equation; when other impurity removers and precipitants are used, their amounts are adjusted according to the corresponding chemical reaction equations.

[0048] Specifically, oxalic acid is used as a precipitant and ammonium sulfate as a remover. Oxalic acid precipitates rare earth elements. In the leachate system obtained in step S3, calcium oxalate also has low solubility at pH 2; therefore, Ca is the key impurity that precipitates along with the rare earth elements. Co-precipitation of Ca is avoided by adding ammonium sulfate to generate soluble (NH4)2[Ca(SO4)2], thus achieving selective leaching of rare earth elements. The chemical reactions occurring in the process can be represented by the following chemical reaction equation:

[0049] 2REE 3+ + 3C2O4 2- = REE2(C2O4)3 (1)

[0050] 2Ca 2+ + 3C2O4 2- = Ca2(C2O4)3 (2)

[0051] Ca 2+ + 2SO4 2- + 2NH4 + = (NH4)2[Ca(SO4)2] (3)

[0052] Among them, REE 3+ This represents rare earth ions.

[0053] Preferably, in step S4, the time for full roasting is at least 1 hour.

[0054] Preferably, the rare earth oxide is a rare earth oxide with a purity >95%.

[0055] The present invention has the following beneficial effects: The present invention uses a self-made sedimentation system to treat polluted water bodies in ion-adsorption rare earth mining areas, which promotes the agglomeration of colloidal rare earth in the water body to form suspended particles that settle into the bottom sediment, thereby obtaining bottom sediment with a high concentration of rare earth, which is easy to recycle and reuse. This realizes the removal of colloidal rare earth in polluted water bodies around ion-adsorption rare earth mining areas and the sustainable utilization of secondary rare earth resources. In addition, the recycling method is simple, the rare earth leaching recovery rate is high, the selectivity is good, and the leaching agent can be recycled and reused. It is low in cost and has little secondary pollution, thus having good economic and environmental benefits. Attached Figure Description

[0056] Figure 1 This is a structural diagram of a pretreatment system for recovering colloidal rare earths from polluted water in an ionic rare earth mining area, as shown in Example 1.

[0057] Figure 2 This is a flowchart of a method for recovering colloidal rare earth elements from polluted water bodies in ion-type rare earth mining areas.

[0058] Figure 3 (a) A statistical chart showing the rare earth leaching efficiency of the eight leaching agents provided in Example 2 on the bottom sediment of the polluted water body;

[0059] Figure 3 (b) is a graph showing the relationship between the leaching efficiency of rare earth elements in the sediment of the polluted water body and the leaching time of the leaching agent EDTA-Na2 provided in Example 2.

[0060] Figure 3 (c) is a graph showing the relationship between the leaching efficiency of rare earth elements in the sediment of the polluted water body and the concentration of the leaching agent EDTA-Na2 provided in Example 2.

[0061] Figure 3 (d) is a graph showing the relationship between the leaching efficiency of rare earth elements in the sediment of the polluted water body and the solid-liquid ratio of the leaching agent EDTA-Na2 provided in Example 2.

[0062] Figure 3 (e) is a graph showing the relationship between the rare earth content and the solid-liquid ratio in the leachate obtained by leaching the sediment of the polluted water body with the leaching agent EDTA-Na2 provided in Example 2.

[0063] Figure 3 (f) is a graph showing the relationship between the content of coexisting impurities (Al, Fe, Ca) and the solid-liquid ratio in the leachate obtained by leaching the bottom sediment of the polluted water body with the leaching agent EDTA-Na2 provided in Example 2.

[0064] Figure 4Statistical graph (a) showing the rare earth precipitation rate for different amounts of ammonium sulfate and graph (b) showing the relationship between the content of coexisting impurities (Al, Fe, Ca) in the leachate obtained from the leaching of sediment from the polluted water body and different amounts of ammonium sulfate.

[0065] The following are the labels in the diagram: 1 is the inlet pipe; 2 is the baffle plate; 3 is the slow-flow chamber; 4 is the first inlet / outlet pipe; 5 is the screen chamber; 6 is the coarse screen; 7 is the second inlet / outlet pipe; 8 is the drive system; 9 is the water distributor; 10 is the vertical flow energy dissipation pipe; 11 is the sedimentation chamber; 12 is the rotating shaft; 13 is the sludge scraper support; 14 is the truss; 15 is the sludge scraper; 16 is the outlet pipe; 17 is the sludge discharge pipe; 18 is the sludge collection chamber. Detailed Implementation

[0066] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in this technical field.

[0067] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0068] Example 1: A pretreatment system for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas.

[0069] like Figure 1 As shown, Figure 1 This invention relates to a pretreatment system for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas. The pretreatment system includes a slow-flow chamber 3, a bar screen chamber 5, a sedimentation chamber 11, and a sludge collection chamber 18. The slow-flow chamber 3, bar screen chamber 5, and sedimentation chamber 11 are arranged sequentially along a transverse path, with the sludge collection chamber 18 positioned below the sedimentation chamber 11. The slow-flow chamber 3 and bar screen chamber 5 are connected via an inlet / outlet water pipe 4; the sedimentation chamber 11 is connected to the bar screen chamber 5 via an inlet / outlet water pipe 7, and the sedimentation chamber 11 is connected to the sludge collection chamber 18 via a sludge discharge pipe 17.

[0070] The slow-flow chamber 3 is equipped with 5 baffles 2, which are staggered at the top and bottom of the slow-flow chamber 3. The polluted water first enters the slow-flow chamber 3 through the inlet pipe 1. The 5 baffles 2 in the slow-flow chamber 3 make the polluted water form an S-shaped curved water flow channel in the slow-flow chamber 3, thereby reducing the water flow velocity (to 0.9m / s).

[0071] A coarse screen 6 is installed inside the screen chamber 5. The coarse screen 6 consists of 9 bars with a spacing of 50 mm. The coarse screen 6 is fixed by a bottom support, and the angle formed between the coarse screen 6 and the bottom of the screen chamber 5 is 60°. After the polluted water body passes through the slow flow chamber 3 to reduce the flow velocity to about 0.9 m / s, it enters the screen chamber 5 through the inlet and outlet pipes 4. The coarse screen 6 removes larger suspended solids, floating objects, and solid particulate matter from the polluted water body to ensure the normal operation of the subsequent sedimentation chamber 11 and prevent blockage of the sludge discharge pipe.

[0072] The sedimentation chamber 11 is equipped with an outlet pipe 16 and a sludge discharge pipe 17. The main equipment inside the sedimentation chamber 11 is similar to a radial flow sedimentation tank system in sewage treatment processes. It mainly consists of inlet and outlet pipes 7, a drive system 8, a water distributor 9, a vertical flow energy dissipation pipe 10, a rotating shaft 12, a sludge scraper support 13, a truss 14, and a sludge scraper 15. One end of the inlet and outlet pipe 7 is connected to the screen chamber 5, and the other end is connected to the vertical flow energy dissipation pipe 10. The top of the vertical flow energy dissipation pipe 10 is equipped with a water distributor 9, and the top of the water distributor 9 is equipped with a drive system 8. One end of the two symmetrical rotating shafts 12 is connected to the vertical flow energy dissipation pipe 10 through a movable knob, and the other end is fixed to the sludge scraper support 13 by welding. There are six trusses 14, which are symmetrically arranged about the axis of symmetry of the vertical flow energy dissipation pipe 10, and the trusses 14 are fixed to the sludge scraper support 13 by welding. The sludge scraper 15 is fixed to the bottom side wall of the sludge scraper support 13 by welding.

[0073] The radial flow sedimentation tank is circular with a diameter of 35m, a water depth of 2m around the tank, and a slope of 0.1.

[0074] After passing through the screen, the polluted water flows out from the bottom inlet / outlet pipe 7 and enters the vertical flow energy dissipation pipe 10. The water flow is rectified by the vertical flow energy dissipation pipe 10 and the water distributor 9, reducing the flow velocity to ≤0.2m. Then it flows out in all directions. At this time, the colloidal rare earth will settle at the bottom of the pool due to gravity. Since the bottom of the pool itself has a certain slope, which is high at the edges and low in the middle, it is conducive to the polluted water flowing from the bottom slope to the middle of the pool. In addition, the drive system drives the rotating shaft, which in turn drives the sludge scraper support. This causes the scraper plate on the bottom side wall of the sludge scraper support to rotate and collect the bottom sludge in the pool. The fallen bottom sludge is collected in the center of the sedimentation tank and enters the sludge collection chamber 18 through the sludge discharge pipe 17. The clarified water obtained after the bottom sludge is collected overflows from the pool and is discharged from the outlet pipe 16.

[0075] Example 2: A method for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas.

[0076] like Figure 2As shown, a method for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas is disclosed. The physicochemical properties of the polluted water bodies in these areas are shown in Table 1. The water bodies have a temperature of 11.3℃, a pH of 7.63, an organic matter content of 1.11 mg / L, and a rare earth content of 15.31 μmol / L. Among these, the colloidal rare earth content is 15.11 μmol / L, accounting for 99%, and colloidal rare earth elements are the main form of rare earth elements in the polluted water bodies.

[0077] Table 1 Physicochemical properties of polluted water bodies in ion-adsorption rare earth mining areas

[0078]

[0079] The specific operation includes the following steps:

[0080] (1) The polluted water from the ion-adsorption rare earth mining area was introduced into the pretreatment system in Example 1 from one side. After treatment by the pretreatment system, the flow velocity of the polluted water was reduced from 1.5 m / s to <0.2 m / s, so as to achieve a better sedimentation effect of colloidal rare earth in the polluted water. The rare earth content in the polluted water decreased from 15.31 μmol / L to 1.47 μmol / L, of which the colloidal rare earth content decreased from 15.11 μmol / L to 0.06 μmol / L.

[0081] (2) The bottom sediment in the sediment collection chamber 18 after the polluted water in step (1) was pretreated by the system was collected and recovered. The rare earth content of the bottom sediment was determined by ICP-MS, and the rare earth content reached 2580 ppm. The specific elemental composition of the bottom sediment and the occurrence form and content of each rare earth element are shown in Table 2. The rare earth elements in the bottom sediment are mainly in the reduced state (Fe-Mn oxidized state, 75%), followed by the acid-soluble state (exchange state, 10%), oxidized state and residual state.

[0082] Table 2. Specific elemental composition of sediment and the occurrence forms and content percentages of each rare earth element.

[0083]

[0084] (3) Formic acid, acetic acid, malic acid, citric acid, oxalic acid, EDTA-Na2, ascorbic acid, and ammonium sulfate were selected as leaching agents. The concentration of ammonium sulfate was set to 2.5%, and the concentrations of the other leaching agents were all set to 0.1 mol / L. The solid-liquid ratio was 1:20. The mixture was shaken at 180 r / min for 24 hours at room temperature. The rare earth leaching rates of the bottom sediment of the polluted water body were compared using different leaching agents. The experimental results are as follows: Figure 3 As shown in (a), the screening and comparison show that EDTA-Na2 has the best rare earth leaching effect on the bottom sediment of the polluted water body, with a rare earth leaching rate of >80%, followed by citric acid and malic acid, with a rare earth leaching rate of >40%.

[0085] (4) Based on the selection of the best-performing leaching agent EDTA-Na2 in step (3), further optimization of leaching conditions (leaching time, leaching agent concentration, and solid-liquid ratio) was conducted. By controlling single-factor variables, the rare earth leaching rate of EDTA-Na2 on the bottom sediment of the polluted water body was compared under different leaching times, leaching agent concentrations, and solid-liquid ratios. Furthermore, the content of rare earth elements and other coexisting impurity ions (such as Al, Fe, and Ca) in the leachate under different liquid-to-solid ratios was also compared. The experimental results are as follows: Figure 3 As shown in (b)-(f), considering the above factors, the optimal leaching conditions for the EDTA-Na2 leaching agent are: leaching time ≥ 12 hours; leaching agent concentration 0.04–0.1 mol / L; solid-liquid ratio 1:2–1:5 (the selection of the solid-liquid ratio prioritizes the rare earth content, followed by other factors). Within this optimal leaching condition range, the rare earth content in the leachate is > 300 mg / L, and the main coexisting impurities are Al < 200 mg / L; Fe < 1200 mg / L; and Ca < 400 mg / L.

[0086] Note: Figure 3 In the graphs (d) to (f), the number 2 on the horizontal axis (solid-liquid ratio) indicates a solid-liquid ratio of 1:2, 5 indicates a solid-liquid ratio of 1:5, and so on.

[0087] (5) Adjust the pH of the above leachate to 2, filter and recover some EDTA precipitate, about 30% of the EDTA precipitate can be recovered.

[0088] (6) Ammonium sulfate and oxalic acid were added to the filtrate after filtration in step (5) to obtain rare earth oxalate precipitate. The effects of the amount of ammonium sulfate added (0.5 to 4 times the theoretical amount) and the amount of oxalic acid added (3 times the theoretical amount) on the selective precipitation of rare earth elements were studied and compared. The experimental results are as follows: Figure 4 As shown, the results indicate that when the amount of ammonium sulfate added is 0.5 to 4 times the theoretical amount, the rare earth precipitation rate is above 84%; when the amount of ammonium sulfate added is 2 times the theoretical amount, the rare earth precipitation rate is as high as about 87%, and at the same time, almost 90% of the coexisting impurity Ca is retained in the filtrate without precipitation.

[0089] (7) The rare earth oxalate precipitate obtained in step (6) is first dried at 60°C for 24 hours, and then placed in a muffle furnace at 900°C for 1 hour to obtain a mixed rare earth oxide with a purity of >95%.

[0090] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for recovering colloidal rare earth elements from polluted water bodies in ion-adsorption rare earth mining areas, characterized in that, Specifically, the steps include the following: S1. The polluted water body of the ion-type rare earth mining area is diverted into the pretreatment system for recovering colloidal rare earth from the polluted water body of the ion-type rare earth mining area to obtain colloidal rare earth bottom mud. After pretreatment, the colloidal rare earth bottom mud is added with leaching agent for leaching treatment and filtered to obtain rare earth leachate. S2. Adjust the pH of the rare earth leachate obtained in step S1 to 1-2, and filter and recover the rare earth mother liquor. S3. Continue to add precipitant and impurity remover to the rare earth mother liquor obtained in step S2, and filter to obtain rare earth precipitate; S4. After thoroughly drying the rare earth precipitate obtained in step S3, calcine it thoroughly to obtain rare earth oxide products. The solid-liquid ratio of the colloidal rare earth sediment to the leaching agent is 1:2 to 1:5; The concentration of the leaching agent is 0.04~0.1 mol / L; The flow velocity of the polluted water in the ion-adsorption rare earth mining area is reduced to ≤0.9 m / s after passing through the slow-flow chamber; the flow velocity of the polluted water in the ion-adsorption rare earth mining area is reduced to ≤0.2 m / s after passing through the radial flow sedimentation tank device for rectification. The leaching agent is selected from EDTA-Na2; The pretreatment system for recovering colloidal rare earth from polluted water in ion-type rare earth mining areas includes a slow-flow chamber (3), a grid chamber (5), a sedimentation chamber (11), and a sludge collection chamber (18), which are connected in sequence. The top and bottom of the slow-flow chamber (3) are staggered with partitions (2), which form an S-shaped curved water flow channel in the slow-flow chamber (3); A coarse grid (6) is fixedly installed inside the grid chamber (5); The sedimentation chamber (11) is equipped with a radial flow sedimentation tank device, which includes an inlet / outlet water pipe (7), a drive system (8), a water distributor (9), a vertical flow energy dissipation pipe (10), a rotating shaft (12), a sludge scraper support (13), a truss (14), and a sludge scraper (15). One end of the inlet / outlet water pipe (7) is connected to the grate chamber (5), and the other end is connected to the vertical flow energy dissipation pipe (10). A water distributor (9) is installed at the top of the vertical flow energy dissipation pipe (10). (9) A drive system (8) is provided at the top; the rotating shaft (12) is symmetrically arranged about the vertical flow energy dissipation pipe (10) with respect to the axis of symmetry, and one end of the rotating shaft (12) is movably connected to the vertical flow energy dissipation pipe (10), and the other end is fixedly connected to the sludge scraper (13); there are at least two trusses (14), which are symmetrically arranged about the vertical flow energy dissipation pipe (10) with respect to the axis of symmetry, and the trusses (14) are fixedly connected to the sludge scraper (13); the sludge scraper (15) is fixedly connected to the bottom side wall of the sludge scraper (13); The bottom of the sludge collection chamber (18) is connected to the bottom of the sedimentation chamber (11); The coarse grid (6) consists of 6 to 9 grid bars, with a spacing of 16 to 40 mm between the grid bars; The angle formed between the coarse grid (6) and the bottom of the grid chamber (5) is 40°~60°; The pretreatment system, leaching chamber, pH adjustment tank, reagent treatment tank, and calcination chamber are connected in sequence.

2. The method according to claim 1, characterized in that, In step S1, the leaching treatment time is ≥12 h.

3. The method according to claim 1, characterized in that, The pretreatment includes drying, grinding, and sieving.

4. The method according to claim 1, characterized in that, The precipitant is oxalic acid.

5. The method according to claim 1, characterized in that, The impurity remover is ammonium sulfate.

6. The method according to claim 1, characterized in that, The temperature for thorough roasting is 850–1000°C.

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