A method for preparing high-purity rare earth carbonates and oxides

Abstract

The application provides a preparation method of high-purity rare earth carbonate and oxide, and relates to the technical field of rare earth wet separation. The method comprises the following steps: adding an organic acid or an organic acid salt as a purifying agent into a rare earth feed liquid, stirring and mixing, adding a precipitant, filtering, and obtaining a purified feed liquid; continuously adding a carbonate precipitant into the purified feed liquid under stirring, so that the rare earth is precipitated in the form of carbonate, and the rare earth carbonate precipitant is obtained through aging and crystallization at 20-80 DEG C, filtration, washing, and drying; and the high-purity rare earth oxide is prepared by calcining the rare earth carbonate precipitant at 900-1000 DEG C. The application utilizes the coordination of the organic acid or the organic acid salt to separate the rare earth and aluminum-iron from the rare earth feed liquid, utilizes the stability difference of the complexes of the organic acid or the organic acid salt with the rare earth and the aluminum-iron impurities to improve the separation efficiency, reduces the rare earth loss caused by the coprecipitation, and can obtain the high-purity rare earth oxide product with high yield.

Description

Technical Field

[0001] This invention relates to the field of rare earth hydrometallurgy and separation technology, and in particular to a method for preparing high-purity rare earth carbonates and oxides. Background Technology

[0002] Rare earth elements, as typical metallic elements, are widely used in traditional markets such as metallurgy, petrochemicals, glass and ceramics, and agriculture due to their unique optical, electrical, and other chemical properties. With the rapid development of technology, high-purity and ultra-high-purity rare earth elements are also finding increasing applications due to their unique properties, and high-purity rare earth metals are the foundation for the application of high-performance rare earth elements in magnetic, optical, and electrical functional materials.

[0003] Rare earth elements are difficult to separate due to their similar chemical properties, making the preparation of high-purity rare earths quite challenging. my country's advanced extraction and separation technology has solved the problem of separating rare earth elements. However, the precipitation separation of rare earths from some non-rare earth elements with similar properties remains difficult because these impurity ions have similar precipitation conditions to rare earths, such as iron, aluminum, calcium, and magnesium. During permanent precipitation for impurity removal, significant rare earth losses can occur due to co-precipitation. Therefore, pre-precipitating and removing impurity ions before precipitating rare earths is a common method used in both laboratory and industrial production. For example, in recovering rare earths from ion-type rare earth leachates using precipitation, a 1986 patent proposed adjusting the pH to between 5.0 and 5.6 using ammonium bicarbonate or ammonia to allow iron and aluminum impurities to precipitate as hydroxides first. The filtered purified solution is then further precipitated with ammonium bicarbonate to obtain a qualified rare earth oxide product.

[0004] Rare earth carbonate precipitation crystallization is a classic method for precipitating rare earth elements from solution and separating them from a large number of associated ions. Chinese invention patent CN113830817A discloses a method for preparing cerium-based oxide materials and their precursors, comprising the following steps: preparing a rare earth solution mainly composed of cerium; mixing a precipitant solution with the rare earth solution to form a rare earth precipitate; aging and crystallizing the rare earth precipitate to obtain a rare earth precursor compound; and calcining the precursor compound to obtain cerium-based oxides. The precipitant solution is either ammonium bicarbonate or ammonium carbonate.

[0005] Chinese invention patent CN112126977A discloses a method for producing high-purity flaky single crystals and densely aggregated cerium carbonates. This method involves pre-adding ammonium citrate to regulate the crystallization process during the precipitation of cerium using ammonium carbonate / ammonium bicarbonate. This invention utilizes triammonium citrate to regulate the crystallization process in existing carbonate precipitation systems, primarily by reducing the crystallization rate of rare earth carbonates to decrease chloride content and reduce the entrainment and co-precipitation of impurities during the precipitation process.

[0006] Precipitation is the most widely used technique in scientific research and industrial production, offering advantages such as low raw material costs, minimal equipment requirements, and simple operation. Ammonium bicarbonate precipitant is inexpensive, but its precipitation method suffers from poor selectivity. Another method utilizes the property that iron and aluminum ions hydrolyze to precipitate hydroxides more readily than rare earth ions. By controlling the pH of the solution, iron and aluminum are preferentially precipitated and removed beforehand. This method has been used industrially for decades and can remove most iron and aluminum. However, due to co-precipitation with rare earth elements, the rare earth elements are lost along with the iron and aluminum hydroxides. Furthermore, for optimal iron and aluminum removal, it is best to remove them in two steps: first, hydrolyze to remove iron, then filter or perform liquid-solid separation, and finally add alkali to raise the pH to allow aluminum to precipitate. While a one-step method to directly adjust the pH to the level required for aluminum hydrolysis to simultaneously remove iron and aluminum is theoretically feasible, its practical effectiveness is poor. If the aluminum concentration is reduced to the desired level, the loss of rare earth elements will be even greater, proving that the co-hydrolysis and precipitation of iron and aluminum increases the co-precipitation tendency of rare earth elements, leading to a greater loss. This is because during the precipitation of rare earth elements using ammonium bicarbonate, Al... 3+ Fe 3+ Impurity ions readily precipitate with rare earth elements, significantly impacting the purity and quality of the final rare earth product. Therefore, a solution is urgently needed to address this issue and obtain a method capable of producing rare earth products in Al... 3+ Fe 3+ A new method for precipitating rare earth elements in rare earth feed solutions with a wide range of impurity content and separating them from impurities.

[0007] Coordination precipitation is used for the purification and removal of impurities from rare earth solutions. It often utilizes the difference in stability between the complexes formed by the coordinating reagent and the impurity ions and rare earth ions, allowing the more stable ions to delay precipitation and thus achieve purification. For example, the aforementioned invention patent CN112126977A describes a method for preparing highly crystalline and pure flake-shaped rare earth carbonate crystals by adding citrate to reduce the precipitation and crystallization rate of rare earth carbonates. This invention proposes a new method to effectively improve the removal rate of aluminum and iron impurities and reduce rare earth co-precipitation losses by adding organic acids and their salts. This method utilizes the strong coordination ability of a small amount of coordinating reagent with iron and aluminum, allowing iron and aluminum to precipitate under lower pH conditions, thus reducing rare earth co-precipitation. It can remove iron and aluminum in one step through hydrolysis and reduce rare earth co-precipitation losses. This ensures that when rare earth carbonates are finally precipitated, the amount of impurity ions entering the product is greatly reduced, resulting in high-purity rare earth carbonates and their oxides. Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing high-purity rare earth carbonates and oxides, which can pre-remove aluminum and iron from rare earth feed solutions with a wide range of impurity contents and reduce rare earth co-precipitation losses. This ensures reduced binding and adsorption of impurity ions during the rare earth precipitation and crystallization process, thereby obtaining high-purity rare earth carbonate and oxide products.

[0009] This invention provides a method for preparing high-purity rare earth carbonates and oxides from rare earth feed solutions by citric acid-assisted iron-aluminum co-precipitation purification, comprising the following steps:

[0010] Organic acids or organic acid salts are added to the rare earth feed solution to enhance the separation effect between rare earths and impurities using a coordination method. A precipitant is added while stirring to pre-remove impurities containing aluminum and iron from the feed solution. After filtration, the precipitant is added to the filtrate and stirring continues. The precipitated rare earth carbonates are aged and crystallized within a certain temperature range to obtain high-purity rare earth carbonates. Calcination yields the corresponding rare earth oxides. The purifying agent is an organic acid or organic acid salt, represented by citric acid and its salts, whose iron-aluminum complexes are more stable than their rare earth complexes. The precipitant includes at least one of the carbonates.

[0011] The purified liquid is continuously added with carbonate precipitant while stirring, so that rare earths are precipitated as carbonates. The precipitate is then aged and crystallized at 20-80℃, filtered, washed, and dried to obtain rare earth carbonate precipitate.

[0012] High-purity rare earth oxides are obtained by calcining rare earth carbonate precipitates at 900-1000℃.

[0013] The beneficial effect of the method for preparing high-purity rare earth carbonates and oxides provided by this invention lies in the fact that by adding organic acids or organic acid salts as purifying agents, the method first coordinates with aluminum and iron ions, thereby lowering the pH required for aluminum and iron ion precipitation. This reduces the co-precipitation loss of rare earths while removing aluminum and iron. The rare earth solution after filtration or liquid-solid separation is further precipitated with carbonates and then aged and crystallized to obtain high-purity rare earth carbonates with low impurity content. Calcination of rare earth carbonates yields high-purity rare earth oxides.

[0014] Optionally, when the precipitant is a carbonate, the pH adjusted during the pre-removal process is 3.3-4.6, which is lower than the pH required for general pre-treatment and removal of impurities, thus greatly reducing the amount of rare earth co-precipitate.

[0015] Optionally, when the precipitant is a carbonate, the pH of the rare earth carbonate preparation process is controlled between 5.6 and 7.3, and the mixture is aged and crystallized to obtain high-purity rare earth carbonate.

[0016] Optionally, organic acids or organic acid salts are added to the rare earth solution to remove impurities using a coordination method. After stirring and mixing, a precipitant is added to pre-remove impurities from the rare earth solution containing a wide concentration range of aluminum and iron. After filtration, a precipitant is added to the filtrate and stirring is continued to produce rare earth carbonate crystals, including:

[0017] Organic acids or organic acid salts are added as purifying agents to rare earth feed containing iron and aluminum impurities, and the mixture is stirred and dissolved to obtain a mixed feed solution.

[0018] Optionally, during the process of adding organic acids or organic acid salts to the rare earth feed solution as a purifying agent, the molar ratio of the purifying agent to aluminum and iron in the rare earth feed solution is 0%-2.8%.

[0019] Optionally, during the process of adding organic acids or organic acid salts to the rare earth feed solution as purification agents, the rare earth feed solution includes at least one of rare earth chloride solution and rare earth nitrate solution.

[0020] The mixture is stirred with a precipitant, and the pH of the solution is controlled between 3.6 and 4.6. The solution is then filtered. The filtrate is then stirred and mixed with the precipitant again, and the pH of the solution is controlled between 5.6 and 7.3 to produce rare earth carbonate.

[0021] Optionally, the rare earth carbonates produced by the reaction are aged and crystallized at 20-80°C for 0.5-8 hours. Attached Figure Description

[0022] Figure 1 A flowchart illustrating a high-purity rare earth carbonate and oxide process provided in an embodiment of the present invention;

[0023] Figure 2 Ion content of each component in the pre-removed impurity and iron-removed supernatant;

[0024] Figure 3 Precipitation rates of various ions in the pre-removed and iron-removed supernatant;

[0025] Figure 4 Ion content of each component in the pre-removal and aluminum-removal supernatant;

[0026] Figure 5 Precipitation rates of various ions in the pre-removed impurities and aluminum-removed supernatant;

[0027] Figure 6 The percentage of each ion in ammonium bicarbonate precipitate after different aging times;

[0028] Figure 7 After pre-removal of impurities, triammonium citrate and ammonium bicarbonate are added to precipitate the supernatant, resulting in a high precipitation rate.

[0029] Figure 8 After pre-removal of impurities, triammonium citrate and ammonium bicarbonate are added to precipitate the substance.

[0030] Figure 9 The effect of different amounts of triammonium citrate added on the aluminum ion concentration in the supernatant during the pre-purification process;

[0031] Figure 10 The effect of different amounts of triammonium citrate added on the aluminum removal rate in the pre-purification process;

[0032] Figure 11 The effect of different amounts of triammonium citrate on the loss rate of rare earth elements before impurity removal;

[0033] Figure 12 The effect of different amounts of triammonium citrate on the iron removal rate in the pre-removal process;

[0034] Figure 13 The optimal amount of triammonium citrate added during the pre-purification process and the percentage of each ion in the precipitate at different aging times;

[0035] Figure 14 The effect of different additives and their dosages on the aluminum ion concentration in the supernatant during the pre-purification process;

[0036] Figure 15 The effect of different additives and their dosages on the rare earth ion concentration in the supernatant during the pre-purification process;

[0037] Figure 16 The effect of different additives and their dosages on the aluminum removal rate in the pre-removal process;

[0038] Figure 17 The effect of different additives and their dosages on the loss rate of rare earth elements before impurity removal;

[0039] Figure 18 Effect of different amounts of triammonium citrate added at 0.07 mol / L Al on the aluminum removal rate during pre-purification;

[0040] Figure 19 Effect of different amounts of triammonium citrate added at 0.07 mol / L Al on the iron removal rate in the pre-removal process;

[0041] Figure 20 Effect of different amounts of triammonium citrate added at 0.07 mol / L Al on the loss rate of rare earth elements during pre-removal;

[0042] Figure 21 Effect of different amounts of triammonium citrate at 0.105 mol / L Al on the aluminum removal rate during pre-purification;

[0043] Figure 22 Effect of different amounts of triammonium citrate at 0.105 mol / L Al on the pre-removal rate of iron;

[0044] Figure 23Effect of different amounts of triammonium citrate at 0.105 mol / L Al on the loss rate of rare earth elements during pre-removal;

[0045] Figure 24 Effect of different amounts of triammonium citrate at 0.14 mol / L Al on aluminum removal rate during pre-purification;

[0046] Figure 25 Effect of different amounts of triammonium citrate at 0.14 mol / L Al on the iron removal rate in the pre-removal process;

[0047] Figure 26 Effect of different amounts of triammonium citrate at 0.14 mol / L Al on the loss rate of rare earth elements during pre-removal;

[0048] Figure 27 Effect of different amounts of triammonium citrate added at 0.035 mol / L Al on the aluminum removal rate during pre-purification;

[0049] Figure 28 Effect of different amounts of triammonium citrate at 0.035 mol / L Al on the iron removal rate in the pre-removal process;

[0050] Figure 29 Effect of different amounts of triammonium citrate added at 0.035 mol / L Al on the loss rate of rare earth elements during pre-removal;

[0051] Figure 30 Effect of different amounts of triammonium citrate added at 0.0175 mol / L Al on the aluminum removal rate during pre-purification;

[0052] Figure 31 Effect of different amounts of triammonium citrate at 0.0175 mol / L Al on the pre-removal rate of iron;

[0053] Figure 32 Effect of different amounts of triammonium citrate added at 0.0175 mol / L Al on the loss rate of rare earth elements during pre-removal;

[0054] Figure 33 Relationship between different aluminum-iron molar ratios and the optimal amount of triammonium citrate added. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, 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. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0056] See Figure 1 This invention provides a method for preparing high-purity rare earth carbonates and oxides, comprising the following steps:

[0057] S1. Add organic acid or organic acid salt as a purifying agent to the rare earth solution. After stirring and mixing, add a precipitant to pre-remove impurities from the rare earth solution containing a wide range of aluminum and iron concentrations. Filter the solution. Continue to add precipitant to the filtrate while stirring to obtain rare earth carbonate precipitate.

[0058] S2. The rare earth carbonate precipitate is aged and crystallized at 20-80℃, filtered, washed and dried to obtain high-purity rare earth carbonate.

[0059] S3. High-purity rare earth oxides are obtained by calcining high-purity rare earth carbonates at 900-1000℃.

[0060] In fact, during the process of adding organic acids or organic acid salts as purifying agents to rare earth slurry and stirring, the purifying agents used include at least one of triammonium citrate, citric acid, ammonium salicylate, tartaric acid, malic acid, and ammonium tartrate.

[0061] In some embodiments, during the mixing process of adding organic acids or organic acid salts as purification agents to the rare earth feed solution, the rare earth feed solution used can be at least one of rare earth chloride and rare earth nitrate. Specifically, it can be purchased from a rare earth separation company, or prepared by dissolving the corresponding high-purity rare earth chloride or rare earth nitrate in high-purity water. Specifically, the molar concentration of rare earth in the rare earth feed solution can be 0.1-1.5 mol / L. In fact, there is no special limitation on the molar concentration of rare earth in the rare earth feed solution, and the relative purity of rare earth in the rare earth feed solution can be 30%-99.9%.

[0062] In some embodiments, organic acids or organic acid salts are added to the rare earth feed solution as purifying agents. After stirring and mixing, a precipitant is added to pre-remove impurities from the rare earth feed solution containing a wide range of aluminum and iron concentrations. The solution is then filtered, and the filtrate is added to the precipitant and stirred continuously to obtain rare earth carbonate. The process includes:

[0063] Organic acids or organic acid salts are added to rare earth slurry as purification agents, and the mixture is stirred and dissolved to obtain a mixed slurry.

[0064] The mixed liquid is stirred and mixed with a precipitant, and then filtered or separated into solid and liquid components to obtain a purified rare earth liquid.

[0065] In fact, during the process of mixing the mixture with the precipitant, the precipitant used includes at least one of carbonates. Specifically, the precipitant used can be at least one of ammonium bicarbonate and ammonium carbonate.

[0066] In practice, the mixing of the precipitant and the mixture can be done by simultaneous addition or sequential addition, and the mixing is carried out under continuous stirring. Specifically, the precipitant is slowly added to the mixture while stirring.

[0067] In some embodiments, when ammonium bicarbonate is used as the precipitant, the pH of the purified feed solution reacting with the precipitant to produce rare earth carbonate is 5.6-7.3, which is sufficient to precipitate the rare earths in the mixed feed solution. In practice, when the mixed feed solution and precipitant are stirred and mixed, the pH value at which the rare earths in the mixed feed solution are completely precipitated needs to be adjusted adaptively according to the rare earth content in the supernatant of the reaction feed solution. Specifically, complete precipitation of rare earths refers to the complete addition of the precipitant without the generation of obvious reaction bubbles.

[0068] In some embodiments, during the process of adding organic acids or organic acid salts to the rare earth solution as purifying agents, the molar ratio of the purifying agent to aluminum and iron in the rare earth solution is 0%-2.8%.

[0069] In some embodiments, the reaction solution is placed in an aging and crystallization process at 20-80°C for a duration of 0.5-8 hours.

[0070] In some embodiments, during the process of obtaining rare earth-containing precipitate by filtration, washing and drying, the filtration and washing method can be one of the existing conventional processes such as belt continuous vacuum filtration and washing or vacuum box filtration. Furthermore, the washing liquid can be detected during the washing of the precipitate after filtration. When no chloride ions and ammonium ions are detected in the washing liquid, the washing process is completed.

[0071] In fact, during the process of obtaining rare earth-containing precipitates through filtration, washing, and drying, it is best not to completely dry the filter cake layer before detecting the absence of chloride and ammonium ions in the washing liquid. It is also necessary to ensure that there are sufficient gaps within the filter cake layer to ensure washing efficiency.

[0072] Exploration Example 1

[0073] Take 100 mL of a rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0039 mol / L, and Al concentration of 0.085 mol / L (the proportions of each impurity are shown in Table 1) in a beaker. Slowly add 2% ammonium bicarbonate solution to the beaker to adjust the pH, stirring continuously during the addition of the ammonium bicarbonate solution. Take a small amount of the supernatant at different pH values, and use ICP-MS to determine the concentration of each ion in the supernatant, plotting the results as shown in the figure. Figure 2 Calculate the precipitation rate of each ion as follows: Figure 3 ;

[0074] Take 100 ml of the filtered liquid (pH 4.12) into a beaker, and slowly add 2% ammonium bicarbonate solution to adjust the pH while continuously stirring. Collect small amounts of supernatant at different pH values ​​and determine the concentrations of each ion in the supernatant using ICP-MS. Figure 4 Calculate the precipitation rate of each ion as follows: Figure 5 .

[0075] Exploration and Analysis: From Figure 2 , 3 As shown in Figures 4 and 5, the precipitation rate of iron and aluminum increases significantly with increasing pH. At pH 4.12, iron has completely precipitated, and more than 60% of aluminum has precipitated. Further increasing the pH does not improve the removal of aluminum and results in a significant loss of rare earth elements. This indicates that the presence of ferric hydroxide in the pre-removal process hinders the efflux of aluminum hydrolysate, and the co-precipitation of aluminum and iron leads to even greater rare earth losses. Therefore, for the purification of rare earth solutions containing aluminum and iron impurities, it is proposed to first remove iron (i.e., at pH 4.12), then adjust the pH of the filtered filtrate to further remove aluminum. At pH 4.6, the aluminum content in the supernatant is 0.18 g / L, the aluminum precipitation rate reaches 84%, and the rare earth loss rate is around 6%.

[0076] Table 1: Proportion of each ion in the initial feed solution

[0077] Na Mg Al Ca Rare earth Fe other 1.53％ 1.61％ 2.87％ 2.51％ 90.28％ 0.28％ 0.90％

[0078] Exploration Example 2

[0079] Example 2 of this study investigated the effect of using ammonium bicarbonate as a precipitant on the content of rare earth and impurity ions in the final rare earth oxide product, including the following steps:

[0080] Y1. Take 150 mL of the filtered solution after the stepwise removal of aluminum and iron in Example 1 (pH 4.6) and place it in a beaker. Slowly add 10% ammonium bicarbonate solution to the beaker until the pH of the mixed solution in the beaker is 6.43. Stir continuously during the addition of ammonium bicarbonate solution. A white precipitate appears in the beaker and bubbles are generated. Continue stirring to ensure that the precipitation reaction is complete.

[0081] Y2. After stopping stirring, the precipitate in the beaker is evenly distributed into five beakers. The five beakers are sealed and placed in a room temperature environment for 0.5h, 2h, 4h, 6h and 8h respectively. The precipitate is then filtered and washed until the washing liquid is free of chloride ions (it should not make the silver nitrate solution acidified by nitric acid cloudy). The precipitate is then dried at 80℃ to obtain rare earth carbonate precipitate.

[0082] Y3. Five groups of rare earth carbonate precipitates were placed in a muffle furnace and calcined at 950℃ to obtain rare earth oxide products. The rare earth oxide products were dissolved in a mixed solution of nitric acid and hydrogen peroxide, and the content of rare earth elements and impurities such as sodium, magnesium, and aluminum in the solution was determined by ICP-MS. Three parallel tests were performed for each sample, and the average value was taken. The results are as follows: Figure 6 As shown.

[0083] Exploration and Analysis: From Figure 6 It can be seen that: if the aging time is too long, more impurities will enter the precipitate; after 6 hours, there are relatively fewer impurities precipitated and the rare earth content is relatively high. The purity of rare earth oxide after 6 hours is 98.09%, of which Al accounts for 1.12%. Appropriate aging is beneficial for Na and Mg to remain in the supernatant, thus improving the product purity. However, after pre-removal of impurities, 0.18 g / L of the feed solution will still enter the precipitate, affecting the product purity.

[0084] Exploration Example 3

[0085] Example 3 of this study investigated the effect of adding triammonium citrate during the precipitation process using ammonium bicarbonate as a precipitant on the content of rare earth and impurity ions in rare earth oxide products, including the following steps:

[0086] Y1. Take 30 mL of the filtered solution from Example 1 (aluminum and iron removed stepwise, pH 4.6) and place it in 6 beakers. Add ammonium citrate to each beaker at molar ratios of 0, 0.6, 0.8, 1, 1.2, and 1.4 with aluminum respectively. Stir to dissolve and then slowly add 10% ammonium bicarbonate solution until the pH of the mixed solution in the beaker is 6.43. Stir continuously during the addition of ammonium bicarbonate solution. A white precipitate appears in the beaker and bubbles are generated. Continue stirring to ensure the precipitation reaction is complete.

[0087] Y2. After stopping stirring, the precipitate in the beaker is evenly distributed into five beakers. The five beakers are sealed and placed in a room temperature environment for 0.5h, 2h, 4h, 6h and 8h respectively. The precipitate is then filtered and washed until the washing liquid is free of chloride ions (it should not make the silver nitrate solution acidified by nitric acid cloudy). The precipitate is then dried at 80℃ to obtain rare earth carbonate precipitate.

[0088] Y3. Five groups of rare earth carbonate precipitates were placed in a muffle furnace and calcined at 950℃ to obtain rare earth oxide products. The rare earth oxide products were dissolved in a mixed solution of nitric acid and hydrogen peroxide, and the content of rare earth elements and impurities such as sodium, magnesium, and aluminum in the solution was determined by ICP-MS. Three parallel tests were performed for each sample, and the average value was taken. The results are as follows: Figure 7 , 8 As shown.

[0089] Exploration and Analysis: From Figure 7 , 8 The results show that adding an appropriate amount of triammonium citrate can reduce the precipitation rate of aluminum, and also slightly reduce the precipitation rate of sodium and magnesium. The highest precipitation purity, 98.60%, is achieved when the molar ratio of citric acid is 1. Aluminum accounts for 0.8% of this. After pre-removal of impurities, adding triammonium citrate and precipitating with ammonium bicarbonate can complex some of the aluminum, improving the product purity. However, since the stability constants of aluminum citrate and rare earth citrate are quite similar, adding triammonium citrate cannot completely complex the aluminum, resulting in an excessively high aluminum content in the product and affecting its purity.

[0090] Exploration Example 4

[0091] Take 100 mL of the rare earth solution from Example 1 and add it to eight beakers. Add triammonium citrate at molar ratios of 0, 0.6, 1, 1.4, 1.87, 2.2, 2.6, and 3 to the iron solution, respectively. After stirring to dissolve, add 2% ammonium bicarbonate solution to the beakers to adjust the pH. Stir continuously during the addition of ammonium bicarbonate solution. Collect small amounts of the supernatant at each pH level and determine the aluminum ion concentration in the supernatant using ICP-MS. Figure 9 Aluminum ion precipitation rate, such as Figure 10 Rare earth ion loss rate, such as Figure 11 Iron ion precipitation rate as Figure 12 .

[0092] Exploration and Analysis: From Figure 9 , 10Figures 11 and 12 show that adding triammonium citrate at a molar ratio of 1.8 to aluminum and iron during the ammonium bicarbonate pre-purification process removes more aluminum at the same pH with minimal loss of rare earth elements. At pH 4.15, the aluminum removal rate can reach over 93%, and the aluminum ion content is reduced to 0.05 g / L. Triammonium citrate has a stronger complexing ability with iron than with rare earth elements and aluminum. Adding a small amount of triammonium citrate to complex iron can cause aluminum to precipitate earlier at a lower pH and reduce the co-precipitation loss of rare earth elements.

[0093] Exploration Example 5

[0094] Example 5 of this study investigated the effect of adding triammonium citrate on the content of rare earth and impurity ions in rare earth oxide products during the pre-purification process using ammonium bicarbonate as a precipitant. The study included the following steps:

[0095] Y1. Take 150 mL of the initial solution from Example 1 and place it in a beaker. Add triammonium citrate with a molar ratio of 1.8 to iron. After stirring and dissolving, add 2% ammonium bicarbonate solution to the beaker to adjust the pH to 4.15. Place the filtered solution in a beaker and slowly add 10% ammonium bicarbonate solution to the beaker until the pH of the mixed solution in the beaker is 6.43. Stir continuously during the addition of ammonium bicarbonate solution. A white precipitate appears in the beaker and bubbles are generated. Continue stirring to ensure that the precipitation reaction is complete.

[0096] Y2. After stopping stirring, the precipitate in the beaker is evenly distributed into five beakers. The five beakers are sealed and placed in a room temperature environment for 0.5h, 2h, 4h, 6h and 8h respectively. The precipitate is then filtered and washed until the washing liquid is free of chloride ions (it should not make the silver nitrate solution acidified by nitric acid cloudy). The precipitate is then dried at 80℃ to obtain rare earth carbonate precipitate.

[0097] Y3. Five groups of rare earth carbonate precipitates were placed in a muffle furnace and calcined at 950℃ to obtain rare earth oxide products. The rare earth oxide products were dissolved in a mixed solution of nitric acid and hydrogen peroxide, and the content of rare earth elements and impurities such as sodium, magnesium, and aluminum in the solution was determined by ICP-MS. Three parallel tests were performed for each sample, and the average value was taken. The results are as follows: Figure 13 As shown.

[0098] Exploration and Analysis: From Figure 13 The results show that the aging time affects the purity of the final rare earth oxide product, and a shorter aging time is beneficial for the separation of rare earth from other impurity ions. When the aging time is 0.5 hours, the purity of the cerium oxide product reaches 99.55%, with Al accounting for 0.35%. For feed solutions with high iron and aluminum impurities, adding an appropriate amount of triammonium citrate during the pre-impurity removal process can better remove iron and aluminum, thereby improving the purity of the final product.

[0099] Exploration Example 6

[0100] Take 100 mL of the rare earth solution from Example 1 and add it to ten beakers. Add triammonium citrate to the first five beakers at molar ratios of 0, 0.12, 0.6, 1.2, and 1.8 with iron, respectively. Add ammonium salicylate to the last five beakers at molar ratios of 0, 0.12, 0.6, 1.2, and 1.8 with iron, respectively. After stirring to dissolve, add 2% ammonium bicarbonate solution to the beakers to adjust the pH, stirring continuously during the addition of ammonium bicarbonate solution. Filter the solution when the pH reaches 4.15. Analyze the aluminum ion concentration in the supernatant of the filtrate using ICP-MS. Figure 14 Rare earth ion concentration such as Figure 15 Calculate the aluminum ion precipitation rate as follows: Figure 16 Rare earth ion precipitation rate, such as Figure 17 ;

[0101] Exploration and Analysis: From Figure 14 , 15 As can be seen from 16 and 17, adding appropriate amounts of triammonium citrate or ammonium salicylate during the ammonium bicarbonate pre-purification process results in better aluminum removal under the same pH conditions, with minimal loss of rare earth elements. The aluminum removal rate can reach over 90% at pH 4.15, with triammonium citrate showing the best aluminum removal effect.

[0102] Exploration Example 7

[0103] Take 100 mL of rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0035 mol / L, and Al concentration of 0.07 mol / L and add it to six beakers respectively. The Al:Fe molar ratio is 20:1. Add triammonium citrate with aluminum-iron molar ratios of 0, 1, 1.4, 1.8, 2.2, and 2.6 respectively. After stirring to dissolve, add 2% ammonium bicarbonate solution to the beakers to adjust the pH, stirring continuously during the addition of ammonium bicarbonate solution. Collect a small amount of supernatant at each pH. Use ICP-MS to determine the aluminum ion content in the supernatant and calculate the precipitation rate. Figure 18 Iron ion precipitation rate as Figure 19 Rare earth ion precipitation rate, such as Figure 20 .

[0104] 100 mL of a rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0035 mol / L, and Al concentration of 0.105 mol / L was added to six beakers, with an Al:Fe molar ratio of 30:1. Triammonium citrate was added to each beaker at molar ratios of 0, 1, 1.4, 1.8, 2.2, and 2.6 with respect to iron, respectively. After stirring to dissolve, 2% ammonium bicarbonate solution was added to the beakers to adjust the pH, while continuously stirring during the addition of the ammonium bicarbonate solution. Small amounts of supernatant were collected at different pH values, and the ion concentration of the supernatant was determined using ICP-MS. The aluminum ion precipitation rate was calculated as follows: Figure 21 Iron ion precipitation rate as Figure 22Rare earth ion precipitation rate, such as Figure 23 .

[0105] 100 mL of a rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0035 mol / L, and Al concentration of 0.14 mol / L was added to six beakers, with an Al:Fe molar ratio of 40:1. Triammonium citrate was added to each beaker at molar ratios of 0, 1, 1.4, 1.8, 2.2, and 2.6 with respect to iron, respectively. After stirring to dissolve, a 2% ammonium bicarbonate solution was added to the beakers to adjust the pH, while continuously stirring during the addition of the ammonium bicarbonate solution. Small amounts of supernatant were collected at different pH values, and the ion concentrations of the supernatants were determined using ICP-MS. The aluminum ion precipitation rate was calculated as follows: Figure 24 Iron ion precipitation rate as Figure 25 Rare earth ion precipitation rate, such as Figure 26 .

[0106] 100 mL of rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0035 mol / L, and Al concentration of 0.035 mol / L was added to six beakers, with an Al:Fe molar ratio of 10:1. Triammonium citrate was added to each beaker at molar ratios of 0, 1, 1.4, 1.8, 2.2, and 2.6 with iron, respectively. After stirring to dissolve, 2% ammonium bicarbonate solution was added to the beakers to adjust the pH, while continuously stirring during the addition of ammonium bicarbonate solution. Small amounts of supernatant were collected at different pH values, and the ion concentration in the supernatant was determined using ICP-MS. The aluminum ion precipitation rate was calculated as follows: Figure 27 Iron ion precipitation rate as Figure 28 Rare earth ion precipitation rate, such as Figure 29 .

[0107] 100 mL of a rare earth solution with a concentration of 0.5 mol / L, Fe concentration of 0.0035 mol / L, and Al concentration of 0.0175 mol / L was added to six beakers, with an Al:Fe molar ratio of 5:1. Triammonium citrate was added to each beaker at molar ratios of 0, 1, 1.4, 1.8, 2.2, and 2.6 with iron, respectively. After stirring to dissolve, 2% ammonium bicarbonate solution was added to the beakers to adjust the pH, while continuously stirring during the addition of ammonium bicarbonate solution. Small amounts of supernatant were collected at different pH values, and the ion concentration in the supernatant was determined using ICP-MS. The aluminum ion precipitation rate was calculated as follows: Figure 30 Iron ion precipitation rate as Figure 31 Rare earth ion precipitation rate, such as Figure 32 .

[0108] Exploration and Analysis: From Figure 18-32It can be seen that adding an appropriate amount of triammonium citrate results in a higher aluminum removal rate at the same pH, while iron is completely removed, and rare earth elements are not significantly lost. By changing the iron-aluminum molar ratio of the solution, the optimal triammonium citrate dosage is determined by achieving the highest aluminum precipitation rate at the same pH with different triammonium citrate dosages, showing a linear relationship with the iron-aluminum molar ratio. Figure 33 .

[0109] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A method for producing high-purity rare earth carbonates and oxides, characterized by, The method comprises the following steps: The purified solution is obtained by adding a purifying agent into the rare earth solution, stirring, adding a precipitant to adjust the pH to 4.15, and then filtering; the purifying agent is citric acid or citrate, the molar ratio of the purifying agent to iron in the rare earth solution is 1.8, and the precipitant is carbonate; the rare earth solution comprises at least one of a chlorinated rare earth solution and a nitric rare earth solution; The purified solution continues to be added with the carbonate precipitant under stirring, and the reaction is stirred until the pH of the slurry is 5.6-7.3, so that the rare earth is precipitated in the form of carbonate; the slurry is aged and crystallized at 20-80℃ for 0.5h, and then is filtered and washed, and dried to obtain the rare earth carbonate precipitate; The high-purity rare earth oxide is obtained by calcining the rare earth carbonate precipitate at 900-1000℃.

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