Method for removing phosphorus from a rare earth sulfate solution

Abstract

The present application belongs to the field of rare earth hydrometallurgy, and relates to a clean and efficient method for removing phosphorus from a rare earth sulfate solution. First, a ferrous salt is added to the rare earth sulfate solution to adjust the iron-phosphorus ratio, obtaining a ferrous-containing solution; then, an oxidizing agent is added to the ferrous-containing solution to obtain an iron-containing solution; finally, a pH adjusting agent is added to the iron-containing solution to adjust the pH value of the solution, and after a period of reaction, the solution is cooled and filtered to obtain a low-phosphorus rare earth sulfate solution and a phosphorus removal residue; wherein the low-phosphorus rare earth sulfate solution can be used as an extraction raw material, and the phosphorus removal residue can be used as a secondary raw material for recovering Fe and P. The present application mainly utilizes the characteristic that iron ions in the rare earth sulfate solution will combine with phosphate ions to form iron phosphate precipitate within a certain pH value range, thereby achieving the removal of phosphate ions. The present application not only has a high recovery rate, but also has less waste residue, and is simple in process, low in cost, and suitable for promotion and application. 2+ , Ca 2+ and other impurities while recovering phosphorus, and has a high recovery rate, less waste residue, a simple process, low cost, and is suitable for promotion and application.

Description

Technical Field

[0001] This invention belongs to the field of rare earth hydrometallurgical methods and relates to a new method for removing phosphate ions from rare earth sulfate solutions. Specifically, it discloses a clean and efficient method for removing phosphorus from rare earth sulfate solutions. Background Technology

[0002] Rare earth elements are widely used in various industries, making the efficient recovery of high-purity rare earth elements crucial. The Bayan Obo mine is a typical polymetallic associated light rare earth deposit, primarily composed of bastnaesite and monazite with vastly different chemical properties. Currently, concentrated sulfuric acid roasting has become the mainstream process for processing Bayan Obo rare earth concentrate due to its simplicity, adaptability, and ease of operation, making a significant contribution to the development of my country's rare earth industry. However, due to the presence of monazite, the rare earth sulfate solution obtained through concentrated sulfuric acid roasting inevitably contains phosphate impurities. If phosphate ions remain in the system for an extended period, they will react with rare earth elements to form insoluble phosphate precipitates, thus affecting the recovery rate of rare earth elements. Therefore, researching and developing efficient methods for removing phosphate ions from rare earth sulfate solutions is of great significance to the development of my country's rare earth metallurgical industry.

[0003] The traditional phosphorus removal process in rare earth sulfuric acid solutions can be broadly classified into the following two types:

[0004] The first method involves adding a certain amount of iron-containing minerals (CN201910424015.3) to the mixed rare earth concentrate beforehand. During the roasting process with concentrated H2SO4, the iron-containing minerals will decompose to form Fe2(SO4)3, and then Fe2(SO4)3 will be extracted during the water leaching process. 3+ and The combination forms FePO4 precipitate, thereby achieving PO 3 4 - Separation from rare earth ions is possible, but iron-containing minerals consume concentrated H2SO4, increasing waste gas treatment costs; simultaneously, due to Fe... 3+ With PO 3 4- Incomplete reaction; to achieve phosphorus removal, Fe is often... 3+ It is higher than the theoretical value, so the excess Fe 3+ It is still necessary to use alkaline oxides such as magnesium oxide and calcium oxide to adjust the pH of the solution and remove excess Fe. 3+ The precipitation of Mg as Fe(OH)3 not only increases the amount of waste residue, introduces impurities, and increases costs, but also... 2+ Ca 2+ Introducing it into wastewater increases the difficulty of wastewater treatment.

[0005] Another method is to directly add Fe-containing substances such as polyferric sulfate to the rare earth sulfate solution. 3+The chemical reagent (CN202111614293.9), through the regulation of reaction conditions, promotes the reaction of Fe. 3+ and The phosphorus is removed by combining and forming FePO4 precipitate, but due to Fe... 3+ With PO4 3- Incomplete reaction, residual Fe 3+ It is still necessary to use alkaline oxides such as magnesium oxide and calcium oxide to adjust the pH of the solution and remove excess Fe. 3+ The precipitate forms as Fe(OH)3. Although this process does not increase the amount of concentrated H2SO4 used, the amount of waste residue is still relatively large, and Mg... 2+ Ca 2+ Inevitably, it will be introduced into rare earth sulfate solutions and wastewater, increasing the difficulty of wastewater treatment and thus increasing production costs. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a clean and efficient method for removing phosphorus from rare earth sulfate solutions, which does not introduce Mg. 2+ Ca 2+ While removing impurities, it can also efficiently recover phosphorus. Moreover, this removal method produces little waste, is simple in process, and has low cost, making it suitable for promotion and application.

[0007] It should be noted that a key aspect of this invention is the use of freshly oxidized Fe. 3+ Its chemical properties are active, Fe 3+ and The reaction is more thorough, and Fe is also removed during the phosphorus removal process. 3+ The removal of these substances reduces the need for subsequent steps to adjust the pH of the solution using alkaline oxides such as magnesium oxide and calcium oxide, thereby reducing the amount of waste pollution, lowering costs, and providing a new approach for the treatment of mixed rare earth minerals in Bayan Obo and other phosphorus-containing minerals.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A clean and efficient method for removing phosphorus from rare earth sulfate solutions, specifically comprising the following steps:

[0010] (1) Adjusting the iron-phosphorus ratio: Add ferrous salt to the rare earth sulfate solution to adjust the iron-phosphorus ratio and obtain a ferrous solution for later use;

[0011] This step mainly involves adding an appropriate amount of Fe to the solution. 2+ Adjust the iron-to-phosphorus ratio in the solution so that after adjusting the pH value later, Fe 3+ It combines with all phosphate ions to form ferric phosphate precipitate, thus achieving the purpose of removing phosphate ions.

[0012] (2) Oxidation: Add an oxidizing agent to the ferrous solution obtained in step (1), stir and react to obtain an iron-containing solution;

[0013] Because the Fe that has just been oxidized 3+ Compared to the original Fe in the solution 3+ It has higher activity, so the main purpose of this step is to remove the Fe from the ferrous solution obtained in step (1). 2+ All oxidized into more reactive Fe 3+ (Equation 1), thereby enhancing its ability to bind with phosphate.

[0014] 2Fe 2+ +H₂O₂ + 2H₂ + →2Fe 3+ +2H₂O (Equation 1)

[0015] (3) Phosphorus removal: Add pH adjuster to the iron-containing solution obtained in step (2) to adjust the pH to 2-2.5, heat, stir and react fully to obtain the reaction solution;

[0016] This step mainly utilizes the strong binding affinity between newly generated iron ions and phosphate ions, as well as the fact that phosphate ions readily bind with Fe at a pH of around 2. 3+ By combining the characteristic of generating phosphate precipitates (Equation 2), the purpose of removing phosphate ions from rare earth sulfate solutions is achieved without introducing new impurities.

[0017]

[0018] (4) Cooling: The reaction solution obtained in step (3) is placed in an environment of 20℃~25℃ for cooling to obtain a cooling liquid;

[0019] This step is mainly to reduce the loss of rare earth elements. The principle is that the solubility of rare earth sulfate decreases as the temperature increases, so the solubility of rare earth sulfate solution is greatest at 20℃~25℃.

[0020] (5) Filtration: The coolant obtained in step (4) is filtered to separate solids and liquids, resulting in phosphorus-removed slag and low-phosphorus rare earth sulfate solution.

[0021] This step is mainly to separate the generated iron phosphate precipitate from the rare earth sulfate solution, thereby making the rare earth sulfate solution purer in terms of impurities.

[0022] It is worth noting that this invention employs a novel approach, first adding Fe to the rare earth sulfate solution. 2+ The iron-phosphorus molar ratio of the ions was adjusted to 1:1 to 1.5:1, and then, with the help of an oxidizing agent, the Fe... 2+ Oxidized to Fe 3+ Utilizing Fe formed in situ3+ It has a strong affinity for ligand phosphates, achieving a higher phosphorus removal efficiency than traditional methods.

[0023] Then, utilizing the property of rare earth carbonates combining with hydrogen ions, the pH of the solution is adjusted to 2–2.5. This not only effectively removes phosphate ions, but also allows the Fe obtained through oxidation with the oxidant to be further processed. 3+ The reaction with phosphate is more complete, and Mg can be avoided. 2+ Ca 2+ Impurities such as rare earth carbonate can reduce the burden of rare earth purification and wastewater treatment in the later stages, and rare earth carbonate can increase the rare earth concentration of rare earth sulfate solution.

[0024] In summary, the removal process disclosed in this invention is mature in each step and the equipment is simple. It can not only achieve clean and efficient removal of phosphate ions from rare earth sulfate, but also effectively reduce the introduction of various impurity ions. It has obvious environmental advantages, simple procedures, and is in line with my country's high-quality and sustainable development strategy, making it more suitable for promotion and application.

[0025] Optionally, in step (1), the rare earth concentration in the rare earth sulfate solution is 10 g / L to 25 g / L, and the amount of ferrous salt added depends on the phosphorus content in the rare earth sulfate solution, adjusting the iron-phosphorus molar ratio to 1:1 to 1.5:1.

[0026] Furthermore, the ferrous salt is at least one of ferrous sulfate, ferrous chloride, ferrous carbonate, and ferrous chloride.

[0027] Optionally, in step (2), the oxidant is at least one of hydrogen peroxide solution, ozone, and chlorine water; and the molar ratio of the oxidant to the ferrous salt is 1.2 to 2:1, and it is advisable to add a slightly excessive amount.

[0028] It should be noted that the oxidation process should be rapid and complete, and the resulting iron-containing solution should be immediately processed in step (3).

[0029] Optionally, in step (3), the pH adjuster is rare earth carbonate, rare earth carbonate containing crystal water, or mixed rare earth carbonate, to adjust the pH to 2 to 2.5.

[0030] It should be noted that when using rare earth carbonate to adjust the pH, the pH should not exceed 2.5 to reduce the loss of rare earth. Furthermore, if the concentration of rare earth in the original rare earth sulfate solution is too high, it is not recommended to use rare earth carbonate to adjust the pH. Instead, alkaline oxides such as magnesium oxide, magnesium hydroxide, magnesium carbonate, and calcium oxide should be used to prevent excessive loss of rare earth due to saturation of the solution.

[0031] Furthermore, in step (3), the reaction temperature is 25℃~50℃, the reaction time is 55min~95min, and the stirring speed is 250rpm~350rpm.

[0032] It should be noted that since the solubility of some rare earth sulfates is negatively correlated with temperature, that is, the higher the temperature, the lower the solubility of rare earth sulfates, the reaction should not be filtered immediately after the reaction. Instead, step (4) should be carried out and step (5) should be carried out when the reaction solution is cooled to 20℃~25℃ (20℃ is the best). This operation can effectively reduce the loss of rare earths.

[0033] As can be seen from the above technical solution, compared with the prior art, the method for removing phosphorus from rare earth sulfate solution provided by the present invention has the following superior effects:

[0034] 1) This invention uses only rare earth carbonates to adjust the pH of rare earth sulfate solutions, unlike traditional chemical reagents for adjusting pH (alkaline oxides such as magnesium oxide and calcium oxide), and does not introduce Mg. 2+ Ca 2+ Impurities such as these are eliminated, reducing processing costs and improving production efficiency;

[0035] Furthermore, the present invention uses rare earth carbonate to adjust the pH value of rare earth sulfate solution, which can increase the concentration of rare earth sulfate solution on the one hand, and can be recycled within the system on the other hand, and will not release polluting gases, resulting in significant environmental and economic benefits.

[0036] 2) This invention uses Fe 2+ Oxidative phosphorus removal can enhance Fe 3+ and The bonding process for Fe 3+ , This also provides convenience for removal.

[0037] 3) The present invention has a significant phosphorus removal effect, with an optimal phosphorus removal efficiency of 99.71%, and the iron retention rate is only 1.12%, while the rare earth loss rate is 1.61%, resulting in significant economic benefits.

[0038] 4) The removal process disclosed in this invention has a simple overall route and mature equipment, which can facilitate the industrial transformation and upgrading of relevant enterprises. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0040] Figure 1 This is a process flow diagram of a clean and efficient method for removing phosphorus from a rare earth sulfate solution according to the present invention. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] This invention discloses a clean and efficient method for removing phosphorus from rare earth sulfuric acid solutions, comprising the following steps:

[0043] (1) Add ferrous salt to rare earth sulfate solution, adjust the iron-phosphorus ratio to obtain ferrous solution for later use;

[0044] (2) Add an oxidizing agent to the ferrous solution obtained in step (1), stir and react to obtain an iron-containing solution;

[0045] (3) Add rare earth carbonate to the iron-containing solution obtained in step (2), adjust the pH to 2-2.5, heat and stir, and after the reaction is complete, obtain the reaction solution;

[0046] (4) The reaction solution obtained in step (3) is placed in an environment of 20°C for cooling to obtain a cooling liquid;

[0047] (5) The coolant obtained in step (4) is filtered to separate the solid and liquid, and phosphorus-removing slag and rare earth sulfate solution are obtained.

[0048] In the embodiments of the present invention, the rare earth sulfate solutions used were all industrially produced, with REO content of 14.88 g / L, P content of 2450.75 μg / mL (calculated as P2O5), and Fe content of 20.46 μg / mL (calculated as Fe2O3). The ferrous salt added in step (1) was selected as solid ferrous sulfate heptahydrate, with addition amounts of 0.48 g and 0.68 g, corresponding to iron-phosphorus molar ratios of 1:1 and 1.4:1, respectively. The oxidant added in step (2) was fixed at 3 ml of 30% hydrogen peroxide solution.

[0049] To better understand the present invention, the following embodiments and comparative examples further illustrate the present invention in detail, but should not be construed as limiting the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above-described invention are also considered to fall within the protection scope of the present invention.

[0050] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0051] The testing method is described below:

[0052] (1) Determination of phosphorus content:

[0053] The test shall be conducted in accordance with the test methods specified in GB / T 18114.9-2010.

[0054] (2) Determination of REO content:

[0055] The test shall be conducted in accordance with the test methods specified in GB / T 18114.1-2010.

[0056] (3) Determination of iron content:

[0057] The test shall be conducted in accordance with the test methods specified in GB / T 18114.7-2010.

[0058] Detailed process parameters are shown in Table 1. The REO content, phosphorus content, and iron content in the rare earth sulfate solution were measured, and the phosphorus removal rate and rare earth loss rate were calculated. The results are shown in Table 2.

[0059] Table 1 Detailed Process Parameters

[0060]

[0061] Comparative Example 1

[0062] The iron-phosphorus molar ratio in step (1) was adjusted to 1.7:1, and the other conditions were the same as in Example 4. The phosphorus removal rate, iron retention rate, and rare earth loss rate are shown in Table 2.

[0063] Comparative Example 2

[0064] The iron-phosphorus molar ratio in step (1) was adjusted to 1:0.8, and the other conditions were the same as in Example 4. The phosphorus removal rate, iron retention rate, and rare earth loss rate are shown in Table 2.

[0065] Comparative Example 3

[0066] In step (3), the pH was adjusted to 2.7, and the other conditions were the same as in Example 4. The phosphorus removal rate, iron retention rate, and rare earth loss rate are shown in Table 2.

[0067] Comparative Example 4

[0068] In step (3), the pH was adjusted to 1.5, and the remaining conditions were the same as in Example 4. The experimental results showed that solid-liquid separation could not be performed because a stable solid sample was not formed.

[0069] Comparative Example 5

[0070] Step (4) is omitted, and the remaining conditions are the same as in Example 4. The removal rate of phosphorus, the retention rate of iron, and the loss rate of rare earth are shown in Table 2.

[0071] Table 2

[0072]

[0073]

[0074] As can be seen from the results of Comparative Examples 1 and 2 and Example 4 in Table 2, the iron content in the solution affects the removal efficiency of phosphate. As the iron content increases, the removal efficiency of phosphate also increases. However, as the iron content increases, the retention rate of iron ions after the reaction also increases, making it impossible to achieve a perfect removal effect. Therefore, the iron content should not be increased indiscriminately to improve the phosphorus removal efficiency, so as to prevent the introduction of too much iron impurity after phosphorus removal.

[0075] The results of Comparative Examples 3 and 4 and Example 4 show that solution pH is a key factor in ensuring phosphate removal. As the pH increases, the phosphate removal rate also increases. However, since rare earth ions will also precipitate due to the increase in pH, the pH should be controlled below 2.5 in order not to increase the loss of rare earth elements. Also, since iron ions and phosphate cannot form a solid precipitate when the pH is too low, the pH should be controlled above 2 to ensure that steps (4) and (5) can be carried out.

[0076] The results of Comparative Example 5 and Example 4 show that if the cooling treatment in step (4) is not performed, the removal rate of phosphate and the retention rate of iron will not be significantly affected, but the loss rate of rare earth will be increased. Therefore, step (4) must be performed for economic benefits.

[0077] In summary, the above analysis shows that this invention not only achieves a high phosphate removal rate, but also keeps the rare earth loss rate within an acceptable range. At an iron-to-phosphorus molar ratio of 1:1, a reaction temperature of 25°C, and a reaction time of 58 minutes, a phosphate removal rate of 87.43% can be achieved, with the rare earth loss rate controlled at 0.26%. Furthermore, if a rare earth loss of 1.61% is acceptable, the phosphate ion removal rate of this invention can reach 99.71%, almost completely removing phosphate from the feed solution. Therefore, both theoretically and in laboratory results, this invention exhibits a low rare earth loss rate and high phosphate removal efficiency.

[0078] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, based on the general principles defined herein. Other embodiments may be implemented without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A clean and efficient method for removing phosphorus from rare earth sulfate solution, characterized in that, Specifically, the steps include the following: (1) Adjusting the iron-phosphorus ratio: Add ferrous salt to the rare earth sulfate solution and adjust the iron-phosphorus molar ratio to 1~1.5:1 to obtain a ferrous solution for later use; (2) Oxidation: Add an oxidizing agent to the ferrous solution obtained in step (1), stir and react to obtain an iron-containing solution; (3) Phosphorus removal: Add a pH adjuster to the iron-containing solution obtained in step (2) to adjust the pH to 2~2.5, heat and stir, and after the reaction is complete, obtain the reaction solution; the pH adjuster is rare earth carbonate, rare earth carbonate containing crystal water or mixed rare earth carbonate; (4) Cooling: After cooling the reaction solution obtained in step (3), filter it to separate the solid and liquid, and obtain phosphorus-removed slag and low-phosphorus sulfuric acid rare earth solution.

2. The method for removing phosphorus from a clean and efficient rare earth sulfate solution according to claim 1, characterized in that, In step (1), the rare earth concentration in the rare earth sulfate solution is 10 g / L to 25 g / L.

3. The method for removing phosphorus from a clean and efficient rare earth sulfate solution according to claim 1, characterized in that, In step (1), the ferrous salt is at least one of ferrous sulfate, ferrous chloride, and ferrous carbonate.

4. The method for removing phosphorus from a clean and efficient rare earth sulfate solution according to claim 1, characterized in that, In step (2), the oxidant is at least one of hydrogen peroxide solution, ozone, and chlorine water; and the molar ratio of the oxidant to the ferrous salt is 1.2 to 2:

1.

5. The method for removing phosphorus from a clean and efficient rare earth sulfate solution according to claim 1, characterized in that, The reaction temperature in step (3) is 25 ℃~50 ℃, and the reaction time is 55 min~95 min.

6. The method for removing phosphorus from a clean and efficient rare earth sulfate solution according to claim 1, characterized in that, The cooling temperature in step (4) is 20 ℃~25 ℃.

7. A method for removing phosphorus from a clean and efficient rare earth sulfate solution according to any one of claims 1 to 6, characterized in that, The phosphorus removal rate in the rare earth sulfate solution is ≥85%, the iron retention rate is ≤14%, and the rare earth loss rate is ≤2%.

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