A method for separating rare earths from iron and aluminum boron in a leaching solution of neodymium iron boron calcined material

Abstract

The application provides a method for separating rare earth and iron aluminum boron from neodymium iron boron calcined material leaching solution. The method provided by the application comprises the following steps: obtaining neodymium iron boron calcined material leaching solution containing rare earth, aluminum, iron and boron based on hydrochloric acid preferential dissolution method, adding an oxidizing agent after adjusting the pH of the leaching solution to 3-5, stirring and reacting, and separating to obtain an iron-containing precipitate and an iron-removed solution; using an organic extractant to extract boron from the iron-removed solution to obtain a boron-containing organic phase and a boron-removed solution; adjusting the pH of the boron-removed solution to 4-5, and then performing deep hydrolysis to remove aluminum, and filtering and separating to obtain an aluminum-containing precipitate and a purified rare earth solution for extracting and separating rare earth; using deionized water or an alkaline solution to back-extract boron from the boron-containing organic phase, recycling the organic phase, and concentrating the back-extraction solution to obtain a boron-containing crystalline product. The method provided by the application can recover boron in the neodymium iron boron calcined material leaching solution, is conducive to the removal of aluminum by hydrolysis and reduces the loss of rare earth, and greatly reduces the environmental pressure and the subsequent wastewater treatment pressure.

Description

Technical Field

[0001] This invention relates to the fields of smelting separation and environmental protection technology, and in particular to a method for separating rare earth elements and iron-aluminum-boron from the leachate of NdFeB calcined feedstock. Background Technology

[0002] Neodymium iron boron (NdFeB) magnets are an important rare-earth functional material with advantages such as high coercivity and large magnetic energy product. They are widely used in fields such as electronics, new energy, medical devices, and aerospace. Therefore, with the rapid development of these fields, the demand for NdFeB is also increasing rapidly. However, NdFeB waste is inevitably generated in the entire process from raw material pretreatment to final product testing. In addition, over time, a large number of devices using NdFeB magnets will be scrapped due to the end of their service life, generating a large amount of NdFeB waste. This waste contains approximately 20-35% rare earth elements by mass, making it a valuable secondary rare earth resource.

[0003] Currently, the main industrial method for recovering valuable metals from NdFeB waste is the calcination + hydrochloric acid selective leaching method. This includes processes such as oxidative roasting, dilute acid dissolution, decomposition and impurity removal, extraction and separation, and precipitation roasting. The principle is to convert all rare earth elements and iron in the NdFeB waste into their highest valence oxides through oxidative roasting. Taking advantage of the fact that iron oxide is less soluble in acid than rare earth oxides and that ferric ions are easily hydrolyzed, hydrochloric acid is used to selectively leach rare earth elements. The insoluble matter is separated into solid and liquid phases to obtain iron-boron slag. The leachate is then subjected to staged impurity removal, extraction and separation, and precipitation roasting to obtain rare earth oxides. However, because the iron in the leachate hydrolyzes, the solution still contains high levels of impurities such as boron and aluminum. When using conventional hydrolysis precipitation and extraction methods to remove aluminum, the high boron concentration in the solution not only severely affects the aluminum hydrolysis removal efficiency but also increases the loss of rare earth elements. In industry, naphthenic acid extraction is often used to remove aluminum. However, when the aluminum content is high, it can easily cause emulsification of the organic phase. When the aluminum content is low, the extraction rate decreases, the loss rate of rare earth elements is high, and the boron in the leachate remains in the solution and eventually enters the high-salt wastewater, making it difficult to meet the discharge requirements.

[0004] Existing technology provides a method for recycling NdFeB magnet waste, which mainly involves removing oil from the NdFeB waste through vacuum dry distillation, followed by organic acid leaching, purification, and pyrolysis to obtain mixed rare earth oxides. This method is simple and avoids the large consumption of inorganic acids in the acid dissolution and extraction processes, as well as the consumption of expensive precipitants in the precipitation process, thus reducing energy consumption and production costs.

[0005] Existing technology also provides a method for recovering rare earth oxides and ferrous chloride from NdFeB magnet waste. This method mainly involves adding a reducing agent to a hydrochloric acid solution containing NdFeB, then extracting rare earths using a saponification P507 system. This yields an organic phase containing rare earths and a raffinate containing FeCl2. The organic phase containing rare earths is then back-extracted to obtain the rare earths, while the raffinate containing FeCl2 is added to hydrochloric acid, concentrated under negative pressure, cooled, crystallized, and centrifuged to obtain ferrous chloride tetrahydrate. This method reduces the need for oxidative roasting and iron removal processes, resulting in a shorter process flow, lower auxiliary material consumption, higher recovery rates of rare earths and iron, higher comparative value of the produced ferrous chloride tetrahydrate, wider applications, no iron-containing waste discharge, and less wastewater discharge.

[0006] Existing technology also provides a method for separating and recovering rare earth elements and iron from NdFeB waste. This method involves reacting an additive with iron oxide within the NdFeB calcined sand at high temperature to generate water-soluble ferrites. The water-soluble ferrites are then leached with water to obtain a leachate. Since rare earth oxides are insoluble in water and remain in a solid state, this achieves efficient rare earth recovery and selective separation of rare earth and iron. Simultaneously, an oxidant is used to oxidize the ferrites in the leachate to generate ferrates. These ferrates are then reacted with potassium hydroxide to form crystals, which are then filtered to obtain high-value potassium ferrate, thus achieving iron recovery. This method is low-cost, has good rare earth and iron separation effects, high rare earth and iron recovery rates, and a high resource utilization rate.

[0007] Existing technology also provides a method for preparing iron oxide red from the sludge generated during NdFeB waste recycling. The sludge is soaked in 10-35% hydrochloric acid with continuous stirring and temperature control to maintain a final pH of 1-7. Potassium chlorate is used to oxidize ferrous iron to ferric iron, and the mixture is rapidly heated. Ammonium bicarbonate is used for precipitation, and finally, the resulting ferric carbonate is calcined. This method not only achieves complete recovery and utilization of valuable elements, conserving mineral resources and protecting the ecological environment, but more importantly, it can recover highly pure iron oxide red from waste sludge.

[0008] As can be seen from the separation and recovery solutions provided in the existing technologies, most of them rely on different methods to improve the leaching rate of rare earth elements and recover the iron element as a byproduct. However, this ignores the impact of boron and aluminum elements contained in the feed solution on the subsequent rare earth extraction and separation and the quality of rare earth products. To eliminate the influence of aluminum, extraction methods are often used to remove aluminum, or suitable precipitants are selected during rare earth precipitation to reduce the impact of aluminum on the quality of rare earth products. However, boron is often left in the wastewater and discharged, increasing environmental pressure and the pressure on subsequent wastewater treatment, while also wasting boron, affecting economic value, and hindering the recycling of materials in NdFeB waste. Therefore, there is an urgent need to provide a solution to improve these problems. Summary of the Invention

[0009] The purpose of this invention is to provide a method for separating rare earth elements and iron, aluminum, and boron from the leachate of NdFeB calcined feedstock. This method can pre-separate and recover boron from the NdFeB calcined leachate, which not only facilitates the hydrolysis and removal of aluminum but also avoids the loss of rare earth elements, improves the purity and yield of subsequent rare earth extraction and separation, achieves full recovery of inorganic salts in wastewater, and significantly reduces environmental pressure and the pressure of subsequent wastewater treatment.

[0010] This invention provides a method for separating rare earth elements and iron, aluminum, and boron from the leachate of calcined neodymium iron boron feedstock, comprising the following steps:

[0011] (1) Based on the hydrochloric acid preferential solubility method, the leachate of NdFeB calcined material containing rare earth, aluminum, iron and boron is obtained. After adjusting the pH of the leachate to 3-5 under stirring, an oxidant is added to carry out an oxidation precipitation reaction. The solid and liquid are separated to obtain iron-containing precipitate and iron-removed material solution.

[0012] (2) Boron is extracted from the iron removal solution using an organic extractant to obtain a boron-containing organic phase and a boron removal solution; wherein the organic extractant includes at least 2-ethyl-1,3-hexanediol and a diluent, the diluent including kerosene;

[0013] (3) Boron is back-extracted from the boron-containing organic phase using deionized water or alkaline solution, concentrated and crystallized to obtain a boron-containing crystalline product, and the organic extractant is recovered and recycled.

[0014] (4) After adjusting the pH of the boron removal solution to 4-5, perform deep hydrolysis to remove aluminum, filter and separate aluminum-containing precipitate and purified rare earth solution, and use the purified rare earth solution for extraction and precipitation separation to obtain a single rare earth product.

[0015] The method provided by this invention involves adjusting the pH value of the leachate, oxidizing it with an oxidant to remove iron, and then using an organic extractant containing a mixture of 2-ethyl-1,3-hexanediol (EHD) and a diluent to extract boron from the iron-removed leachate. This not only facilitates the recovery of boron resources but also promotes the subsequent hydrolysis and precipitation of aluminum, thereby improving the purity of rare earth elements in the final rare earth solution.

[0016] Optionally, step (1) includes: adjusting the pH to 3-5 by adding a pH adjuster to the leachate under stirring conditions, then adding an oxidant and iron oxide seed crystals, and allowing it to stand for crystallization; wherein the oxidant includes at least one of sodium chlorate and hydrogen peroxide. Adding iron oxide seed crystals to the leachate facilitates the crystallization and precipitation of iron-containing precipitates, accelerates the filtration speed of solid-liquid separation, improves the overall separation efficiency, and saves energy.

[0017] Optionally, in step (1), when filtering and separating the iron-containing precipitate and the iron-removing solution, it is necessary to wash the iron-containing precipitate with deionized water and combine the washing solution and the iron-removing solution. By washing the iron-containing precipitate, the rare earth elements attached to the iron-containing precipitate can be washed out, thereby improving the final rare earth yield.

[0018] Optionally, the organic extractant in step (2) further includes at least one of isoamyl alcohol, isooctanol, 1,3-propanediol, 2,3-naphthol, 1,2-octanediol, 1,2-cyclopentanediol, and 2-ethyl-2-butyl-1,3-propanediol. Combining EHD with monohydric alcohols and dihydric alcohols is beneficial for improving the extraction efficiency of boron in the iron removal solution.

[0019] Optionally, during the extraction of boron from the iron removal solution using an organic extractant, the ratio of the organic extractant to the oil and water content of the iron removal solution is 0.1-5, and the extraction stage is 1-20.

[0020] Optionally, the process of back-extracting boron from the boron-containing organic phase in step (3) includes two stages: first, using water and alkaline solution to back-extract the boron-containing organic phase in a single stage to obtain a first boron-containing back-extract; second, using water and alkaline solution to back-extract the boron-containing organic phase in a series to obtain a second boron-containing back-extract; the first and second boron-containing back-extracts can be used to recover boron separately or by combining them. Attached Figure Description

[0021] Figure 1 This is a schematic flowchart illustrating a method for separating rare earth elements and neodymium iron boron from the leachate of calcined neodymium iron boron feedstock, provided as an embodiment of the present invention.

[0022] Figure 2 This is a graph showing the change in loading amount when boron in boric acid solution is loaded multiple times using an organic extractant in Example 2 of this invention.

[0023] Figure 3 This is a graph showing the change in loading of boron in boric acid solution when contact extraction is performed using an organic extractant at different pH levels in Example 3 of this invention.

[0024] Figure 4 Example 4 of this invention uses water to back-extract a saturated boron-containing organic phase. The graph shows the changes in boron content in the boron-containing back-extraction solutions obtained under different oil-water ratios.

[0025] Figure 5 The graph shows the change in boron content in the boron-containing back-extraction solution obtained when contact extraction of the first saturated extractable organic phase is performed using ammonia water of different concentrations in Example 5 of this invention.

[0026] Figure 6The graph shows the change in boron content in the boron-containing back-extraction solution obtained when contact extraction of the second saturated extraction organic phase is performed using ammonia water of different concentrations in Example 5 of this invention.

[0027] Figure 7 The graph shows the change in boron content in the boron-containing back-extraction solution obtained when contact extraction of the third saturated extraction organic phase is performed using ammonia water of different concentrations in Example 5 of this invention.

[0028] Figure 8 The graph shows the backwash rate variation of the saturated boron-containing organic phase back-extracted using sodium hydroxide solutions of different concentrations, as shown in Example 6 of this invention.

[0029] Figure 9 The graph shows the backwash rate variation of back-extraction of a saturated boron-containing organic phase using a 0.15 mol / L sodium hydroxide solution in Example 7 of this invention.

[0030] Figure 10 Example 8 of this invention shows the change in boric acid content in the boron-containing extraction solution after back-extraction of a saturated boron-containing organic phase using lime water of different pH values.

[0031] Figure 11 The graph shows the changes in boron extraction rate and the changes in backwash rate when using deionized water for back-extraction after extracting the iron removal solution with different organic extractants to obtain a boron-containing organic phase in Example 10 of this invention.

[0032] Figure 12 Example 12 of this invention illustrates the change in boron content in the organic phase after each backwash when deionized water is used to backwash a saturated boron-containing organic phase multiple times.

[0033] Figure 13 Example 12 of this invention illustrates the change in boron content in the organic phase after each backwash when a saturated boron-containing organic phase is backwashed multiple times using a 0.15 mol / L sodium hydroxide solution.

[0034] Figure 14 Example 12 of this invention shows the change in boron content in the organic phase after each backwash when using 0.2 mol / L ammonia solution to backwash a saturated boron-containing organic phase.

[0035] Figure 15 XRD characterization of ammonium borate crystals precipitated during backwashing of a saturated boron-containing organic phase using 0.2 mol / L ammonia water, as shown in Example 12 of this invention, is compared with the XRD pattern of an ammonium borate standard sample.

[0036] Figure 16 SEM characterization images of ammonium borate crystals precipitated during backwashing of a saturated boron-containing organic phase using 0.2 mol / L ammonia water, before and after drying, for Exploratory Example 12 of this invention; Figure 16The left image is a SEM image before drying, and the right image is a SEM image after drying.

[0037] Figure 17 Example 14 of this invention shows the variation of boron extraction rate of iron removal solution under the same phase when the organic phase after mixing EHD with kerosene at different concentrations is used as an organic extractant.

[0038] Figure 18 Example 15 of this invention uses a cascade countercurrent extraction tank to back-extract boron from iron removal solution using a boron extractant, and the graph shows the change in boron content in the aqueous phase of each organic phase agent during the process.

[0039] Figure 19 Example 16 of this invention shows the variation of boron extraction rate when an organic extractant consisting of a mixture of EHD and kerosene is used to extract iron removal solution at different oil-to-water ratios. Detailed Implementation

[0040] 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 to which this invention pertains.

[0041] See Figure 1 This invention provides a method for separating rare earth elements and iron, aluminum, and boron from the leachate of neodymium iron boron calcined feedstock, comprising the following steps:

[0042] (1) Based on the hydrochloric acid preferential solubility method, the leachate of NdFeB calcined material containing rare earth, aluminum, iron and boron is obtained. After adjusting the pH of the leachate to 3-5 under stirring, an oxidant is added to carry out an oxidation precipitation reaction. The solid and liquid are separated to obtain iron-containing precipitate and iron-removed material solution.

[0043] (2) Boron is extracted from the iron removal solution using an organic extractant to obtain a boron-containing organic phase and a boron removal solution; wherein the organic extractant includes at least 2-ethyl-1,3-hexanediol and a diluent, the diluent including kerosene;

[0044] (3) Boron is back-extracted from the boron-containing organic phase using deionized water or alkaline solution, concentrated and crystallized to obtain a boron-containing crystalline product, and the organic extractant is recovered and recycled.

[0045] (4) After adjusting the pH of the boron removal solution to 4-5, perform deep hydrolysis to remove aluminum, filter and separate aluminum-containing precipitate and purified rare earth solution, and use the purified rare earth solution for extraction and precipitation separation to obtain a single rare earth product.

[0046] In some embodiments, step (1) includes: adding a pH adjuster to adjust the pH to 3-5 to the leachate under stirring conditions, then adding an oxidant and iron oxide seed crystals, and allowing it to stand to crystallize; wherein the oxidant includes at least one of sodium chlorate and hydrogen peroxide.

[0047] In some embodiments, when filtering and separating the iron-containing precipitate and the iron removal solution in step (1), it is necessary to wash the iron-containing precipitate with deionized water and combine the washing solution and the iron removal solution.

[0048] In some embodiments, the organic extractant in step (2) further includes at least one of isoamyl alcohol, isooctanol, 1,3-propanediol, 2,3-naphthol, 1,2-octanediol, 1,2-cyclopentanediol, and 2-ethyl-2-butyl-1,3-propanediol.

[0049] In some embodiments, the ratio of the organic extractant to the oil and water in the iron removal solution in step (2) is 0.1-5:1, and the number of extraction stages during countercurrent extraction is 1-20.

[0050] In some embodiments, the process of back-extracting boron from the boron-containing organic phase in step (3) includes two stages: first, using water and alkaline solution to back-extract the boron-containing organic phase in a single stage to obtain a first boron-containing back-extract; second, using water and alkaline solution to back-extract the boron-containing organic phase in a series to obtain a second boron-containing back-extract; the first and second boron-containing back-extracts can be used to recover boron separately or by combining them.

[0051] Exploration Example 1

[0052] Example 1 of this study investigated the extraction performance of different organic extractants on boric acid in boric acid solution, including the following steps:

[0053] T1. Prepare a boron-containing solution: Dissolve 10.54g of boric acid in 1000mL of deionized water to prepare a boric acid solution with a concentration of 0.17mol / L, and adjust the pH of the boric acid solution to 5.

[0054] T2. Preparation of organic extractants: Mix isooctanol and kerosene at a volume ratio of 1:1 as the first extractant; mix isooctanol, isoamyl alcohol, and kerosene at a volume ratio of 1:1:2 as the second extractant; and mix 2-ethyl-1,3-hexanediol (EHD), isooctanol, and kerosene at a volume ratio of 2:3:5 as the third extractant.

[0055] T3. Extraction Experiment: The first, second, and third extractants were respectively subjected to contact extraction with boric acid solution at a 1:1 oil-water ratio. The boron-containing organic phase and the boron-removed feed solution were then separated. The residual boron concentration in the boron-removed feed solution was measured and the boron extraction rate was calculated. The results are shown in Table 1 below.

[0056] Table 1 Comparison of extraction performance of different organic extractants for boric acid

[0057]

[0058] Exploration Example 2

[0059] Example 2 of this exploration investigated the saturated extraction capacity of different organic extractants for boric acid in boric acid solution, including the following steps:

[0060] T1. Prepare a boron-containing solution: Same as in Investigation Example 1;

[0061] T2. Preparation of organic extractant: Same as in Exploratory Example 1;

[0062] T3. Extraction Experiment: The first, second, and third extractants were respectively subjected to contact extraction with boric acid solution at a 1:1 oil-to-water ratio to separate the boron-containing organic phase and the deboronized solution. The boric acid concentration in the boron-containing organic phase was measured. The boron-containing organic phase was then used as the organic extractant to extract the boric acid solution. The extraction was repeated 7 times to obtain the corresponding first, second, and third saturated extractable organic phases. The results are as follows: Figure 2 As shown.

[0063] Exploration Example 3

[0064] Example 3 of this exploration investigated the extraction performance of organic extractants on boron in boric acid solutions at different pH values, including the following steps:

[0065] T1. Preparation of boron-containing solutions: Dissolve 10.54g of boric acid in 1000mL of deionized water to prepare a boric acid solution with a concentration of 0.17mol / L. Adjust the pH of the boric acid solution to 1, 2, 3, 4, and 5 respectively as the first, second, third, fourth, and fifth boric acid test solutions.

[0066] T2. Preparation of organic extractant: Same as in Exploratory Example 1;

[0067] T3. Extraction Experiment: The first, second, and third extractants were combined with the first, second, third, fourth, and fifth boric acid test solutions, respectively, and contact extraction was performed at a 1:1 oil-water ratio. The boron-containing organic phase and the boron-removing solution were then separated. The residual boron concentration in the boron-removing solution was measured, and the boron extraction rate was calculated. The results are as follows: Figure 3 As shown.

[0068] Exploratory Analysis: Table 1 shows that when the third extractant is a mixture of EHD and isooctanol at a volume ratio of 2:3, it exhibits a higher extraction rate for boric acid in a single extraction process. Simultaneously, from... Figure 2 It can be seen that the saturated loading of the third extractant is significantly higher than that of the first and second extractants, reaching 1.06 mol / L; from Figure 3 As can be seen, the pH of the boric acid solution has varying degrees of influence on the extraction of organic extractants. For example, the pH of the boric acid solution has a relatively small effect on the third extractant, with a single-stage extraction rate greater than 85% when the pH is between 1 and 5. However, it has a greater impact on the extraction of the first and second extractants. As the boric acid solution approaches neutrality, the extraction effect of the first and second extractants becomes worse. This is because the increase in the pH of the boric acid solution affects the ionization balance of boric acid, which leads to a decrease in the extraction effect of monohydric alcohols (isooctanol and isoamyl alcohol). EHD, when mixed with isooctanol, can form a relatively stable six-membered ring complex with boric acid. Therefore, the extraction rate of the third extractant is less affected by the initial pH of the boric acid solution.

[0069] In summary, when using organic extractants to extract boron from iron removal solutions, a mixture of 2-ethyl-1,3-hexanediol and isooctyl alcohol provides better extraction results and exhibits more stable extraction performance under different pH conditions.

[0070] Exploration Example 4

[0071] Example 4 of this study investigated the changes in boron content in the boron-containing extraction solutions obtained under different oil-water ratios when using water to back-extract a saturated boron-containing organic phase. The steps included:

[0072] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0073] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0074] T3. Extraction experiment: Same as Exploratory Example 2;

[0075] T4. Backwashing Experiment: Water was backwashed with the first, second, and third saturated extraction organic phases, respectively, with oil-water ratios controlled at 5:1, 2:1, 1:1, 1:2, and 1:4. After the combined experiment, the boron concentration in the boron-containing backwash solution was measured, and the results are as follows: Figure 4 As shown.

[0076] Exploration and Analysis: From Figure 4 As can be seen, the boron content in the boron-containing back-extraction solution decreases as the oil-water ratio decreases. At the same ratio, the boron concentration in the boron-containing back-extraction solution obtained from the third saturated extractant is the highest, because the third extractant has a higher saturated extraction capacity for boron.

[0077] Exploration Example 5

[0078] Example 5 of this study investigated the changes in boron content in the obtained boron-containing extraction solution when ammonia water with different volume ratios was used for back-extraction of a saturated boron-containing organic phase. The steps included:

[0079] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0080] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0081] T3. Extraction experiment: Same as Exploratory Example 2;

[0082] T4. Backwashing Experiment: Saturated ammonia and deionized water were prepared at different volume ratios and used to backwash the first, second, and third saturated extraction organic phases, respectively, while maintaining an oil-to-water ratio of 1:1. The boron content in the boron-containing backwash solution was then determined after the combined experiment. The results are shown below. Figure 5 , Figure 6 , Figure 7 As shown, the single-stage back-extraction rate of the organic extractant is calculated based on the following formula: Single-stage back-extraction rate = Total boron ions in the boron-containing back-extraction solution / Total boron ions in the saturated extraction organic phase × 100%.

[0083] Exploration and Analysis: From Figures 5 to 7 It can be seen that as the volume ratio of ammonia to deionized water gradually decreases, the concentration of boric acid extracted remains basically unchanged. The single-stage extraction rates of the first and second extractants are both above 70%, and the single-stage extraction rate of the third extractant is above 80%. Furthermore, the concentration of boron in the extraction solution does not increase with the increase of ammonia concentration.

[0084] Exploration Example 6

[0085] Example 6 of this study investigated the changes in boron backwashing rate when using sodium hydroxide solutions of different concentrations for back-extraction of a saturated boron-containing organic phase, including the following steps:

[0086] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0087] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0088] T3. Extraction experiment: Same as Exploratory Example 2;

[0089] T4. Backwashing Experiment: Sodium hydroxide solutions of different concentrations were prepared and used to backwash the first, second, and third saturated extraction organic phases, respectively, maintaining an oil-to-water ratio of 1:1. The backwashing rate for boron was measured after a combined experiment. The results are shown below. Figure 8 As shown.

[0090] Exploration and Analysis: From Figure 8It can be seen that as the concentration of sodium hydroxide solution increases, the stripping rates of the second and third stripping agents gradually increase, while the stripping rate of the first stripping agent does not show an obvious increasing trend.

[0091] Exploration Example 7

[0092] Example 7 of this study investigated the change in boron backwashing rate during back-extraction of a saturated boron-containing organic phase using a 0.15 mol / L sodium hydroxide solution at different oil-to-water ratios, including the following steps:

[0093] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0094] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0095] T3, Extraction Experiment: Same as Exploratory Example 2;

[0096] T4. Backwashing Experiment: A 0.15 mol / L sodium hydroxide solution was used to backwash the first, second, and third saturated extraction organic phases at different oil-to-water ratios. After a combined experiment, the backwashing rate for boron was measured. The results are as follows: Figure 9 As shown.

[0097] Exploration and Analysis: From Figure 9 It can be seen that when using 0.15 mol / L sodium hydroxide solution to back-extract saturated boron-containing organic phases with different oil-water ratios, the back-extraction rate of boron increases as the oil-water ratio decreases. However, the overall concentration of boron back-extracted into the aqueous phase decreases, which greatly increases the difficulty of subsequent purification.

[0098] Exploration Example 8

[0099] Example 8 of this study investigated the changes in boric acid content in the boron-containing extraction solution obtained when a saturated boron-containing organic phase was back-extracted using limewater of different pH values. The steps included:

[0100] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0101] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0102] T3. Extraction experiment: Same as Exploratory Example 2;

[0103] T4. Backwashing Experiment: Lime water solutions with pH values ​​of 8, 10, 11, and 12 were prepared and used to backwash the first, second, and third saturated extraction organic phases, respectively, while maintaining an oil-to-water ratio of 1:1. After the combined experiment, the boric acid content in the boron-containing backwash solution was determined. The results are as follows: Figure 10 As shown.

[0104] Exploration and Analysis: From Figure 10 As can be seen from the data, as the pH of the limewater increases, the back-extraction rate of the first and second saturated extract organic phases shows a trend of first decreasing and then increasing. However, a higher pH is required for back-extraction of the third saturated extract organic phase, and the overall back-extraction rate is relatively low. This is because EHD forms a more stable six-membered ring complex structure with boric acid, and a stronger alkalinity is required for the boric acid ester to hydrolyze during limewater back-extraction.

[0105] Exploration Example 9

[0106] Example 9 of this study investigated the changes in rare earth content and impurity content after adjusting the pH of the NdFeB leaching solution to different values ​​using lime, including the following steps:

[0107] Y1. The NdFeB waste calcined material was directly dissolved in hydrochloric acid and then filtered to obtain the NdFeB calcined material leachate. The rare earth content and impurity content in the leachate were determined by ICP-Mass, as shown in Table 2. Lime was added to the leachate to adjust the pH to 3, and hydrogen peroxide was added as an oxidant. After stirring and reacting, the iron-containing precipitate and the iron-removing solution were separated by filtration. The iron-containing precipitate was washed with deionized water until no rare earth elements were detected in the washing solution. The washing solution and the iron-removing solution were combined to obtain the iron-removing solution. The rare earth content and impurity content in the iron-removing solution were determined, as shown in Table 2.

[0108] Y2. Take 10 mL of iron removal solution and place it in a flask. Add lime water to adjust the pH to 4, 5, 5.5, and 6. At each pH point, measure the volume, rare earth content, and impurity content of the iron removal solution. The measurement results are shown in Table 3 below. The removal rates of boron, iron, and aluminum impurities at different pH levels are calculated and shown in Table 4 below.

[0109] Table 2. Rare earth content and impurity content (g / L) when pH is adjusted to 3 with lime.

[0110]

[0111] Table 3. Rare earth content and impurity content (g / L) when lime is used to adjust the pH at different levels.

[0112]

[0113] Table 4. Removal rates of boron, iron, and aluminum impurities by lime at different pH levels.

[0114]

[0115] Analysis: Table 2 shows that the leachate from the NdFeB calcined feedstock contains high levels of impurities such as aluminum, iron, and calcium, as well as some cobalt and nickel. Furthermore, the overall acidity of the leachate is low due to the direct dissolution with hydrochloric acid. Adjusting the pH of the leachate to 3 with lime and then adding an oxidant removes most of the iron. After washing away the iron precipitate and combining the washing liquid with the iron removal liquid, the concentrations of rare earth ions, aluminum, iron, cobalt, and nickel impurities in the iron removal liquid decrease due to dilution, while the calcium content increases. The changes in content before and after pH adjustment show that the volume of the iron removal liquid is approximately twice that of the leachate.

[0116] As shown in Tables 3 and 4, the removal rates of rare earth ions, aluminum ions, iron ions, and boron ions in the iron removal solution varied depending on the pH of the solution. Furthermore, since most of the iron ions were removed by the preceding oxidation hydrolysis, the overall iron content of the iron removal solution was low. As the pH of the iron removal solution increased, the loss of rare earth ions also gradually increased, and the removal rates of aluminum and boron impurities were low, making it difficult to separate rare earth, aluminum, and boron and failing to achieve the expected results.

[0117] Exploration Example 10

[0118] Example 10 of this study investigated the effects of different organic extractants on the extraction rate of boron in the iron removal solution after pH adjustment with lime water and the backwashing rate during the back-extraction process when deionized water was used for back-extraction. The study included the following steps:

[0119] Y1. After directly dissolving the NdFeB waste calcined material with hydrochloric acid and filtering it to obtain the NdFeB calcined material leachate, lime water was added to the leachate to adjust the pH to 3, and sodium chlorate was added as an oxidant to stir the reaction. The iron-containing precipitate and the iron-removing solution were separated by filtration. The iron-containing precipitate was washed with deionized water until no rare earth elements were detected in the washing solution. The washing solutions were then combined to obtain the iron-removing solution.

[0120] Y2, the same as step T2 in Exploration Example 1;

[0121] Y3. After contact extraction with the first, second, and third extractants and the iron removal solution at a 1:1 oil-to-water ratio, the boron-containing organic phase and the boron removal solution were separated. The residual boron concentration in the boron removal solution was measured, and the extraction rate of boron by different organic extractants was calculated. Figure 11 As shown;

[0122] Y4. Backwash the first, second, and third extraction organic phases with water, respectively, maintaining an oil-to-water ratio of 1:1. After backwashing, measure the boron concentration in the boron-containing backwash solution and calculate the backwash rate of water on each extraction organic phase. Figure 11 As shown.

[0123] Exploration and Analysis: From Figure 11 The results show that the third extractant (EHD, isooctanol, kerosene) can extract 98.9% of the boron in the iron removal solution to the organic phase after a single extraction, while the first and second extractants (isooctanol, isoamyl alcohol, kerosene) can only extract 50-60% of the boron in a single extraction. This indicates that the third extractant has a higher extraction capacity for boron in the iron removal solution. However, from... Figure 10 It can also be seen that the effect of back-extraction using deionized water on the third extraction organic phase (the boron-containing organic phase obtained by the third extractant) is poor, and only 4.77% of the boron in the third extraction organic phase can be backwashed to the aqueous phase. The backwashing rates of the first extraction organic phase (the boron-containing organic phase obtained by the first extractant) and the second extraction organic phase (the boron-containing organic phase obtained by the second extractant) using deionized water are higher than those of the third extraction organic phase.

[0124] Exploration Example 11

[0125] Example 11 of this study investigated the changes in volume and elemental content of the iron-removing solution when the pH of the iron-removing solution was adjusted to different values ​​using lime water, including the following steps:

[0126] Y1, the same as step Y1 in Exploring Example 10;

[0127] Y2, the same as step Y2 in Exploring Example 10;

[0128] Y3, the same as step Y3 in Exploring Example 10;

[0129] Y4. Lime was added to the boron removal solution to adjust the pH to 4, 5, 5.5, and 6. The volume, rare earth content, and impurity content of the boron removal solution were measured at each pH point. The measurement results are shown in Table 5 below. The removal rates of boron, iron, and aluminum impurities at different pH levels were calculated and are shown in Table 6 below.

[0130] Table 5. Rare earth content and impurity content of the boron removal solution at different pH values.

[0131]

[0132]

[0133] Table 6. Removal rates of boron, iron, and aluminum impurities by the boron removal solution at different pH values.

[0134]

[0135] Analysis: Tables 5 and 6 show that the boron content in the extract after organic extraction of the iron removal solution is over 99% higher than before boron removal. Furthermore, as the pH of the extract solution is continuously increased, the aluminum removal rate also continuously increases, reaching over 90%. Combining Tables 3 and 4 with Tables 5 and 6, it can be seen that removing boron first and then aluminum results in a higher and more stable aluminum removal rate. This indicates that removing boron from the leachate is beneficial for hydrolysis and aluminum removal, helps control the amount of impurity ions in the decomposition and separation of NdFeB calcined feed leachate, and improves subsequent separation efficiency and product quality.

[0136] Exploration Example 12

[0137] Example 12 of this study investigated the changes in boron content in a boron-loaded saturated organic phase after each backwash following multiple backwashes, including the following steps:

[0138] T1. Prepare a boron-containing solution: Same as Exploratory Example 1;

[0139] T2. Preparation of organic extractant: Same as Exploratory Example 1;

[0140] T3. Extraction experiment: Same as Exploratory Example 2;

[0141] T4. Backwashing Experiment: Deionized water was repeatedly backwashed with the first, second, and third saturated extraction organic phases, maintaining an oil-to-water ratio of 2:1. The boron content in the organic phase was measured after each backwash. Figure 12 As shown; a 0.15 mol / L sodium hydroxide solution was used to continuously backwash the first, second, and third saturated extraction organic phases multiple times, controlling the oil-water ratio at 2:1. The boron content in the organic phase was measured after each backwash. Figure 13 As shown; 0.2 mol / L ammonia solution was used to continuously backwash the first, second, and third saturated extraction organic phases, respectively, maintaining an oil-to-water ratio of 1:1. The boron content in the organic phase was measured after each backwash. Figure 14 As shown;

[0142] T5. Crystallization Characterization: The boron-containing back-extraction solution obtained after backwashing with 0.2 mol / L ammonia was concentrated and crystallized to obtain ammonium borate crystals. X-ray diffraction analysis was performed on the precipitated ammonium borate crystals, and the XRD pattern of the ammonium borate crystals was compared with that of the ammonium borate standard sample. Figure 15 As shown; the precipitated ammonium borate crystals were characterized by SEM and then dried. The dried ammonium borate crystals were then characterized by SEM again, as shown. Figure 16 As shown.

[0143] Exploration and Analysis: From Figure 12 As can be seen, with the increase of the number of backwashes with deionized water, the boron concentration in the aqueous phase backwashed by deionized water gradually decreases. However, because the third saturated extractable organic phase (saturated third extractable organic phase) has a higher boron loading, although the single backwash rate of deionized water on the third saturated extractable organic phase is lower, its extraction concentration is still higher than that on the first saturated extractable organic phase (saturated third extractable organic phase) and the second saturated extractable organic phase (saturated second extractable organic phase). Therefore, when using the first and second extractants as organic extractants, deionized water can be used for boron back-extraction.

[0144] from Figure 13 It can be seen that the 0.15 mol / L sodium hydroxide solution has a good back-extraction effect on the first, second, and third saturated extraction organic phases, and the number of backwashes is much less than that of backwashing with deionized water. This is beneficial to accelerate the backwashing efficiency and enable the organic phase to be recycled more quickly.

[0145] from Figure 14 It can be seen that using 0.2 mol / L ammonia water has a good back-extraction effect on the first, second, and third saturated extraction organic phases. Furthermore, when the concentration of ammonium borate in the boron-containing back-extraction solution is too high, ammonium borate will directly precipitate as a solid. Figure 15 It can be seen from this that the removed ammonium borate solid has a high purity, and from... Figure 16 It can be seen that the morphology of the precipitated ammonium borate solid changed before and after drying, because the drying process accelerated the release of ammonia gas.

[0146] Exploration Example 13

[0147] Example 13 of this study investigated the effects of different stirring speeds and stirring times on the extraction rate and efficiency when using a third extractant as an organic extractant for contact extraction of iron removal solution (NdFeB iron removal solution). The steps included:

[0148] T1. Preparation of organic extractant: Mix 2-ethyl-1,3-hexanediol (EHD), isooctyl alcohol and kerosene in a volume ratio of 2:3:5 and use it as the third extractant.

[0149] T2. Extraction Experiment: The third extractant was mixed with the iron removal solution at an oil-to-water ratio of 1:5. After contact extraction with the mechanical speed and stirring time shown in Table 7, the boron-containing organic phase and the boron removal solution were separated. The residual boron content in the boron removal solution was measured and the boron extraction rate was calculated. The results are shown in Table 7.

[0150] Table 7. Effects of different stirring speeds and durations on boron extraction performance.

[0151]

[0152] Analysis: Table 7 shows that the higher the rotation speed after mixing, the higher the extraction rate of boron in the same time period. This is because the higher the rotation speed, the more uniform the third extractant and the iron removal liquid are mixed. When the rotation speed reaches 400 rpm and is stirred for 3 minutes, the extraction rate of boron remains stable.

[0153] Exploration Example 14

[0154] Example 14 of this study investigated the effect of using organic phases of EHD mixed with kerosene at different concentrations as organic extractants on iron removal solutions (NdFeB iron removal solutions) under the same phase ratio, including the following steps:

[0155] T1. Preparation of organic extractant: Kerosene and EHD are mixed in different volume ratios to prepare organic extractants with EHD contents of 20%, 30%, 40%, and 50% respectively.

[0156] T2. Extraction Experiment: The five organic extractants prepared in T1 were subjected to contact extraction with boric acid solution at an oil-to-water ratio of 1:5. The boron-containing organic phase and the boron-removed solution were separated. The boron content in the boron-removed solution was determined and the boron extraction rate was calculated. Figure 17 As shown.

[0157] Exploration and Analysis: From Figure 17 It can be seen that as the EHD content in the organic phase gradually increases, the boron extraction rate of the iron removal solution (NdFeB iron removal solution) gradually increases.

[0158] Exploration Example 15

[0159] Example 15 of this study investigated the boron extraction and back-extraction process of iron removal solution (NdFeB iron removal solution) using a cascade countercurrent extraction tank. In the first five stages, the third extractant (EHD, isooctanol, kerosene) was used as the organic extractant to extract boron from the iron removal solution. In the last four stages, a 0.15 mol / L sodium hydroxide solution was used for backwashing of the boron-containing organic phase. The changes in boron content in the aqueous and organic phases at each stage were measured as follows: Figure 18 As shown.

[0160] Exploration and Analysis: From Figure 18 It can be seen that cascade countercurrent extraction can introduce more than 90% of the boron in the iron removal solution into the organic phase. At the same time, the boron in the boron-containing organic phase can be back-extracted using sodium hydroxide solution, thus allowing the third extractant to be recycled.

[0161] Exploration Example 16

[0162] Example 16 of this study investigated the changes in boron extraction rate when using a third extractant (EHD, isooctanol, kerosene) as an organic extractant for single-stage extraction of an iron removal solution (NdFeB iron removal solution) with different oil-to-water ratios, as shown in the figure. Figure 19 As shown.

[0163] Exploration and Analysis: From Figure 19 It can be seen that as the volume of the iron removal liquid increases, the boron content in the boron removal liquid increases, and the boron extraction rate of the boron-containing organic phase decreases. When the single-stage extraction ratio is controlled at 1:1-2.25, the boron extraction rate of the organic phase is greater than 90%, but the single-stage loading of the boron-containing organic phase is low.

[0164] Exploration Example 17

[0165] Example 17 of this study investigated the mixing of a boron-containing organic phase with a boron loading of 5.764 g / L with concentrated ammonia, followed by separation after standing. After the solid precipitated, it was filtered out and dissolved in deionized water. The solid was then combined with the boron-containing back-extraction solution (the solution after back-extraction with concentrated ammonia). The dilute ammonia was then back-extracted with the boron-containing organic phase three times. The back-extraction rate of boron after each back-extraction is shown in Table 8.

[0166] Table 8. Changes in boron content during ammonia back-extraction.

[0167] Number of back-extractions Mass of boron extracted (mg) Total back-extraction rate of boron (%) 1 127.67 22.17％ 2 178.89 53.22％ 3 142.00 77.88％ 4 80.96 91.93％

[0168] Analysis: As can be seen from Table 8, solid ammonium borate can be precipitated after the first back-extraction with concentrated ammonia. However, the total back-extraction rate of boron is low in this case. After multiple back-extractions with dilute ammonia, the total back-extraction rate of boron can be greater than 90%.

[0169] Exploration Example 18

[0170] Example 18 of this study investigated the contact extraction of a boron-containing organic phase with concentrated ammonia. After the first precipitation of solid (solid ammonium borate), the mixture was allowed to stand and separate. The boron-containing organic phase was then added to the boron-containing back-extraction solution, and after the second precipitation of solid, the mixture was allowed to stand and separate. The boron loading of the boron-containing organic phase before the two back-extractions and the boron content of the aqueous phase after the back-extractions were measured. The results are shown in Table 9 below.

[0171] The reaction of a boron-loaded organic phase with concentrated ammonia was investigated. After the first solid precipitation, the mixture was allowed to stand and separate. The boron-loaded organic phase was then added to the back-extraction solution, resulting in a second solid precipitation, followed by further separation. The organic phase loading and boron content in the aqueous phases for both reactions are shown in Table 9. The results indicate that concentrated ammonia can be used for subsequent organic phase back-extraction crystallization, but the boron content in the aqueous phase gradually increases, which is detrimental to improving the efficiency of boron back-extraction with concentrated ammonia.

[0172] Table 9. Changes in boron content in the organic and aqueous phases after solid precipitation.

[0173] Boron content in the organic phase (g / L) Aqueous phase (g / L) 1 2.8 0.7676 2 3.64 1.377

[0174] Analysis: As can be seen from Table 9, concentrated ammonia can be used for subsequent back-extraction and crystallization of boron-containing organic phases after one back-extraction. However, the boron content in the aqueous phase will gradually increase, which is not conducive to improving the back-extraction efficiency of concentrated ammonia for boron.

[0175] Example 1

[0176] This embodiment 1 provides a method for separating rare earth elements and iron, aluminum, and boron from the leachate of neodymium iron boron calcined feedstock, including the following steps:

[0177] S1. The NdFeB waste calcined material is directly dissolved in hydrochloric acid and then filtered to obtain NdFeB calcined material leachate. Ammonia water is added to the leachate to adjust the pH to 5.0. Then, 15% hydrogen peroxide is added to adjust the pH of the overall solution back to 3.0 and the reaction is stirred. After filtration, iron-containing precipitate and iron-removing solution are obtained. The iron-containing precipitate is washed with deionized water until no rare earth elements are detected in the washing solution. The washing solution and iron-removing solution are combined to obtain iron-removing solution.

[0178] S2. 2-Ethyl-1,3-hexanediol (EHD), isooctyl alcohol, and kerosene are uniformly mixed at a volume ratio of 2:3:5 and used as organic extractant. Boron in the iron removal solution is extracted and back-extracted using a cascade countercurrent extraction tank. In the first five stages, the boron in the iron removal solution is extracted with organic extractant at an oil-water ratio of 1:5 to obtain a boron-containing organic phase and a boron-removed solution. In the last four stages, the boron in the boron-containing organic phase is back-extracted with a 0.15 mol / L sodium hydroxide solution to obtain a boron-containing back-extracted solution, which is then concentrated and crystallized to obtain a solid boron enrichment.

[0179] S3. Add ammonia to the boron-removed feed solution after iron and boron removal to adjust the pH to 5.0 and stir to react. Let it stand to allow the aluminum to hydrolyze completely, then filter to obtain a rare earth feed solution after iron, boron and aluminum removal. Add p507 extractant to the rare earth feed solution for saponification extraction and then separate to obtain rare earth concentrate.

[0180] 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 separating rare earth elements and iron-aluminum-boron from the leachate of NdFeB calcined feedstock, characterized in that, Includes the following steps: (1) Based on the hydrochloric acid preferential solubility method, the leachate of NdFeB calcined material containing rare earth, aluminum, iron and boron is obtained. After adjusting the pH of the leachate to 3-5 under stirring, an oxidant is added to carry out an oxidation precipitation reaction. The solid and liquid are separated to obtain iron-containing precipitate and iron-removed material solution. (2) Boron is extracted from the iron removal solution using an organic extractant to obtain a boron-containing organic phase and a boron removal solution; wherein the organic extractant includes at least 2-ethyl-1,3-hexanediol and a diluent, the diluent including kerosene; (3) Boron is back-extracted from the boron-containing organic phase using deionized water or alkaline solution, concentrated and crystallized to obtain a boron-containing crystalline product, and the organic extractant is recovered and recycled. (4) After adjusting the pH of the boron removal solution to 4-5, perform deep hydrolysis to remove aluminum, filter and separate aluminum-containing precipitate and purified rare earth solution, and use the purified rare earth solution for extraction and precipitation separation to obtain a single rare earth product.

2. The method according to claim 1, characterized in that, Step (1) includes: adding a pH adjuster to adjust the pH to 3-5 to the leachate under stirring conditions, then adding an oxidant and iron oxide seed crystals, and allowing it to stand to crystallize; wherein the oxidant includes at least one of sodium chlorate and hydrogen peroxide.

3. The method according to claim 1 or 2, characterized in that, In step (1), when filtering and separating the iron-containing precipitate and the iron-removing liquid, the iron-containing precipitate needs to be washed with deionized water, and the washing liquid and the iron-removing liquid are combined.

4. The method according to claim 1, characterized in that, The organic extractant in step (2) also includes at least one of isoamyl alcohol, isooctanol, 1,3-propanediol, 2,3-naphthol, 1,2-octanediol, 1,2-cyclopentanediol, and 2-ethyl-2-butyl-1,3-propanediol.

5. The method according to claim 1 or 4, characterized in that, The ratio of the organic extractant to the oil and water in the iron removal solution in step (2) is 0.1-5:1, and the number of extraction stages during countercurrent extraction is 1-20.

6. The method according to claim 1, characterized in that, The process of back-extracting boron from the boron-containing organic phase in step (3) includes two stages: first, using water and alkaline solution to back-extract the boron-containing organic phase in a single stage to obtain a first boron-containing back-extract; second, using water and alkaline solution to back-extract the boron-containing organic phase in a series to obtain a second boron-containing back-extract. The first and second boron-containing back-extracts can be used to recover boron separately or by combining them.

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