A method for recovering rare earth elements from rare earth molten salt electrolysis slag

Abstract

The present invention belongs to the technical field of mineral recovery and relates to a method for recovering rare earth elements from electrolytic slag. The steps are as follows: Add aluminum particles and aluminum chloride particles to the electrolytic slag, and conduct high-temperature sealed calcination; perform crushing treatment, mix with an inorganic strong acid solution, control the mixing temperature and stir for reaction, and then filter to obtain a primary acid leaching residue and a primary rare earth acid leaching solution; Add the primary acid leaching residue to an inorganic strong acid solution for secondary mixing, control the mixing temperature and stir for reaction, and then filter to obtain a secondary acid leaching residue and a secondary rare earth leaching solution. The method provided by the present invention can achieve a leaching rate of rare earth elements as high as 98%, realizing the efficient recovery of rare earth elements. The leaching rate is relatively high, the calcination product is easy to crush, and fluorine is fixed in the solid phase, reducing environmental pollution, lowering costs, and improving the comprehensive utilization rate of resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of mineral recovery, and relates to a method for recovering rare earth elements from rare earth molten salt electrolysis slag. Background Art

[0002] Rare earth elements have many unique physical and chemical properties and are widely used in various high-tech fields such as permanent magnets, catalysis, and special materials. The molten salt electrolysis method for producing rare earth metals has the advantages of low cost and high yield, so it has become the mainstream process for actual rare earth production. However, there are relatively many rare earth elements in the waste slag produced by this process. Due to the continuous increase in the demand for rare earths in magnetic materials in China at present, the output of materials such as neodymium iron boron has also increased year by year, and the amount of molten salt electrolysis slag produced therefrom has also increased greatly. Considering the current tight supply of rare earth mining and its continuously strong price, the recovery of rare earth elements from rare earth solid waste has received more and more attention in recent years. The rare earth elements in rare earth molten salt electrolysis slag generally exist in the form of rare earth fluorides, rare earth oxyfluorides, etc., and the rare earth content is about between 20% and 80%. In addition, there are some other complex non-rare earth impurities (such as silicon dioxide, iron oxide, etc.). However, these components are basically substances with stable properties and cannot be separated from rare earth elements by simple acid leaching and filtration methods. Therefore, researchers have tried various strategies for the problem that rare earth fluorides (oxyfluorides) are insoluble in acid and it is difficult to dissolve rare earths into the liquid phase. The most important and effective idea among them is to make rare earth fluorides (oxyfluorides) react with other substances to form substances that are easily soluble in aqueous solutions. For example, the concentrated sulfuric acid roasting method can react rare earth fluorides (oxyfluorides) with concentrated sulfuric acid to convert them into rare earth sulfate salts, and then the rare earth elements can be dissolved into the aqueous solution. Toxic gases such as hydrogen fluoride will be generated during the roasting process of this process, which seriously corrodes production equipment and will cause certain harm to the environment. In addition, there is also the alkali conversion roasting method. Under high temperature conditions, alkaline substances such as sodium hydroxide, sodium carbonate, and borax react with rare earth fluorides (oxyfluorides) to form rare earth oxides that are soluble in acid solution. At the same time, fluorine will become substances such as sodium fluoride. Finally, after entering the aqueous solution, it will form fluorine-containing wastewater, causing environmental pollution. In addition, some scholars have tried to mix Ca(OH)2, CaO, calcium chloride, etc. with rare earth molten salt slag and then roast it. Not only can rare earths be converted into oxides, but also fluorine can remain in the solid phase in the form of calcium fluoride, becoming solid waste, reducing the harmful impact on the environment. However, these roasting processes often require relatively high temperatures (generally greater than 700 °C) and long times, resulting in large energy consumption during the roasting process. Moreover, the products after most of the above roasting processes are seriously agglomerated, dense and hard, and are not easy to break, so repeated crushing is required, increasing the energy consumption. To sum up, aiming at the problems existing in the current rare earth electrolysis slag recovery rare earth process, it is urgent to develop an economical, efficient and environmentally friendly recovery and extraction process. Summary of the Invention

[0003] The present invention provides a technology for efficiently converting rare earth molten salt electrolysis slag into soluble rare earth compounds, with the calcined product being easily broken and fluorine being stably fixed in the solid phase. The main component of the solid waste formed is aluminum fluoride, which can be used as a flux for aluminum metal smelting after impurity removal and purification. This technology solves the problems of poor rare earth leaching effect, large reagent input, and pollution of fluorine-containing waste gas and wastewater in the existing process.

[0004] To achieve the above object, the present invention is implemented by the following technical solutions:

[0005] A method for recovering rare earth elements from rare earth molten salt electrolysis slag, the steps are as follows:

[0006] (1) Add aluminum particles and aluminum chloride particles to the electrolysis slag and mix evenly to obtain a solid mixture;

[0007] (2) Carry out high-temperature sealed calcination on the solid mixture;

[0008] (3) Crush the calcined solid mixture to obtain substance A;

[0009] (4) Mix substance A with an inorganic strong acid solution, control the mixing temperature and stir to react, then filter to obtain a primary acid leaching residue and a primary rare earth acid leaching solution;

[0010] (5) Add the primary acid leaching residue to an inorganic strong acid solution for secondary mixing, control the mixing temperature and stir to react, then filter to obtain a secondary acid leaching residue and a secondary rare earth leaching solution.

[0011] Preferably, in step (1), the mass ratio of electrolysis slag: aluminum particles: aluminum chloride particles is (2 - 8):1:(2 - 4), and the particle size of the aluminum particles is 80 - 200 mesh.

[0012] Preferably, in step (2), the calcination temperature is 500 - 700 °C, the calcination time is 1.5 - 3 h, and the calcination atmosphere is air containing a trace amount of hydrogen, where the volume fraction of hydrogen in the total calcination atmosphere is 0.05 - 0.2%.

[0013] Preferably, in steps (4) and (5), the inorganic strong acid solution is a hydrochloric acid solution with a concentration of 2.5 - 4 M, and the stirring reaction temperature is 85 - 95 °C.

[0014] Preferably, the secondary rare earth leaching solution obtained in step (5) is recycled and reused.

[0015] Principle: Aluminum can displace rare earth elements in the electrolysis slag, while forming aluminum fluoride that is insoluble in water itself, thus stabilizing fluorine elements in the solid phase.

[0016] Aluminum chloride can not only react with rare earth fluoride to form rare earth chloride that is easily soluble in water, but most importantly, it is easy to sublimate at high temperatures and can play a role in loosening the calcined slag during the roasting process. However, without aluminum particles, the sublimation effect of aluminum chloride is too obvious, and a large excess is required to achieve the conversion of rare earth salts. Therefore, the raw material input cost will be relatively high. In addition, experiments have shown that adding a small amount of hydrogen during the calcination process can not only increase the rare earth recovery rate but also make the calcined solid more porous, facilitating further crushing treatment in the later stage.

[0017] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0018] The method provided by the present invention can achieve a leaching rate of rare earth elements as high as 98%, realizing the efficient recovery of rare earth elements. Compared with the traditional rare earth electrolytic slag rare earth recovery process, this method has a higher rare earth leaching rate, the calcined product is easy to crush, fixes fluorine into a solid phase, reduces environmental pollution, reduces the reagent input cost, and improves the comprehensive utilization rate of resources. Detailed implementation manners

[0019] In order to more clearly understand the above objects, features, and advantages of the present invention, the following specific embodiments are used to further illustrate the present invention. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

[0020] Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Therefore, the present invention is not limited by the specific embodiments disclosed in the following specification.

[0021] Example 1

[0022] Take 10 g of rare earth molten salt electrolysis slag (source: Zhongxi Tianma New Materials Technology Co., Ltd.), 15 g of aluminum chloride hexahydrate, and 5 g of aluminum particles (average particle size 100 mesh), mix them evenly, place them in a tube furnace, seal and heat up. The heating rate is 10 °C / min. When the temperature rises above 400 °C, according to the volume of the tube furnace, introduce hydrogen with a total volume of 0.1%. Then continue to heat up to 700 °C at high temperature and keep roasting for 1.8 h. After the roasting is completed, cool naturally to room temperature, and then take out the solid substance. Grind and crush it through a 100-mesh sieve, and then add it to 740 mL of fresh or recycled hydrochloric acid solution with a concentration of 3 M. Heat it in a water bath at 90 °C and continuously stir and react for 2 h. The stirring rate is 200 - 800 rpm. After the reaction is completed, filter by suction to obtain the primary acid leaching solution and the primary acid leaching residue. Then add the primary acid leaching residue to 370 mL of fresh hydrochloric acid solution with a concentration of 3 M, and repeat the secondary reaction under the same conditions. That is, heat it in a water bath at 90 °C and continuously stir for 2 h. The stirring rate is 200 - 800 rpm. After the secondary reaction is completed, cool naturally to room temperature, filter by suction to obtain the secondary acid leaching residue and the secondary acid leaching solution. This secondary acid leaching solution can be added to the acid solution for primary treatment of the roasted product for use. The secondary acid leaching residue is naturally air-dried for more than 10 h to obtain the final waste residue.

[0023] The rare earth molten salt electrolysis slag used in this example was analyzed by XRF (X-ray fluorescence spectrometry), and the main element contents (%) were obtained as follows: F element 56.438, Nd element 28.551, Pr element 7.711, Fe element 4.654.

[0024] The final waste residue was analyzed by XRF, and the main elements (%) were obtained as follows: F element 62.182, Al element 30.031, Nd element 0.323, Pr element 0.021, Fe element 2.357.

[0025] Example 2

[0026] Take 10 g of rare earth molten salt electrolysis slag (source: Zhongxi Tianma New Materials Technology Co., Ltd.), 15 g of aluminum chloride hexahydrate, and 5 g of aluminum particles (average particle size 100 mesh), mix them evenly, place them in a tubular furnace, close it and heat up. The heating rate is 10 °C / min. When the temperature rises above 300 °C, according to the volume of the tubular furnace, introduce hydrogen with a total volume of 0.2%, continue to heat up to 500 °C, and keep roasting at a constant temperature for 2 h. After the roasting is completed, cool it naturally to room temperature, and then take out the solid substance. Grind and crush it through a 200-mesh sieve, and then add it to 740 mL of fresh or recycled hydrochloric acid solution with a concentration of 3 M. Heat it in a water bath at 85 °C and continuously stir and react for 2.2 h. The stirring rate is 300 rpm. After the reaction is completed, filter it by suction to obtain the primary acid leaching solution and the primary acid leaching residue. Then add the primary acid leaching residue to 370 mL of fresh hydrochloric acid solution with a concentration of 3 M, and repeat the secondary reaction under the same conditions. That is, heat it in a water bath at 85 °C and continuously stir for 2.2 h. The stirring rate is 300 rpm. After the secondary reaction is completed, cool it naturally to room temperature, filter it by suction to obtain the secondary acid leaching residue and the secondary acid leaching solution. This secondary acid leaching solution can be added to the acid solution for primary treatment of the roasted product for use. Dry the secondary acid leaching residue at 50 °C for 2 h to obtain the final waste residue.

[0027] The composition of the rare earth molten salt electrolysis slag used in this example is the same as that in Example 1. The final waste residue was analyzed by XRF, and the main elements obtained were (%) : F element 61.976, Al element 30.248, Nd element 0.365, Pr element 0.019, Fe element 2.541.

[0028] Example 3

[0029] Take 10 g of rare earth molten salt electrolysis slag (source: Zhongxi Tianma New Materials Technology Co., Ltd.), 15 g of aluminum chloride hexahydrate, and 5 g of aluminum particles (average particle size 100 mesh), mix them evenly, place them in a tubular furnace, close it and heat up. The heating rate is 10 °C / min. When the temperature rises above 300 °C, according to the volume of the tubular furnace, introduce hydrogen with a total volume of 0.15%. Continue to heat up to 600 °C and keep roasting at a constant temperature for 2.5 h. After the roasting is completed, cool it naturally to room temperature, and then take out the solid substance. Grind and crush it through a 150-mesh sieve, and then add it to 740 mL of fresh or recycled hydrochloric acid solution with a concentration of 3 M. Heat it in a water bath at 90 °C and continuously stir and react for 2 h. The stirring rate is 200 rpm. After the reaction is completed, filter it by suction to obtain the primary acid leaching solution and the primary acid leaching residue. Then add the primary acid leaching residue to 370 mL of fresh hydrochloric acid solution with a concentration of 3 M and repeat the secondary reaction under the same conditions. That is, heat it in a water bath at 90 °C and continuously stir for 2 h. The stirring rate is 200 rpm. After the secondary reaction is completed, cool it naturally to room temperature and filter it by suction to obtain the secondary acid leaching residue and the secondary acid leaching solution. This secondary acid leaching solution can be added to the acid solution for the initial treatment of the roasted product for use. Dry the secondary acid leaching residue at 50 °C for 2 h to obtain the final waste residue.

[0030] The composition of the rare earth molten salt electrolysis slag used in this example is the same as that in Example 1. The final waste residue was analyzed by XRF, and the main elements obtained were (%): F element 62.087, Al element 30.915, Nd element 0.417, Pr element 0.020, Fe element 2.493.

[0031] Comparative Example 1

[0032] The difference between this comparative example and Example 1 is that the calcination atmosphere is air and no hydrogen is added. The remaining conditions and operation processes are the same as those in Example 1. It was found that the solid obtained after the calcination showed a caking phenomenon, some of the solids had a high hardness, it was difficult to break them later, and the overall recovery rate of rare earth elements decreased.

[0033] Comparative Example 2

[0034] The difference between this comparative example and Example 1 is that the addition amount of aluminum chloride hexahydrate is 25 g. As a result, the roasted slag after calcination is powdery, and the particles can meet the 100-mesh requirement after simple vibration screening. However, the leaching rate of the later obtained product has decreased, and the reagent cost has increased. The main element content (%) obtained by XRF detection is: F element 59.182, Al element 28.031, Nd element 1.024, Pr element 0.186, Fe element 2.357.

[0035] Comparative Example 3

[0036] The difference between this comparative example and Example 1 is that the mass of the added aluminum particles is 15 g, and the rest of the preparation process and process conditions are the same as those in Example 1. As a result, the leaching rate of the finally obtained product is slightly improved, but the hardness of the solid obtained by roasting is significantly increased, making it difficult to crush.

[0037] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention in other forms. Any person skilled in the art may use the technical content disclosed above to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, as long as they do not depart from the technical solution content of the present invention, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for recovering rare earth elements from rare earth molten salt electrolytic slag, characterized in that: Here are the steps: (1) adding aluminum particles and aluminum chloride particles to the electrolytic slag and mixing them uniformly to obtain a solid compound; (2) calcining the solid compound in a closed environment at high temperature; (3) crushing the calcined solid to obtain substance A; (4) mixing the substance A with an inorganic strong acid solution, controlling the mixing temperature and stirring the mixture to react, and filtering the mixture to obtain a primary acid leaching residue and a primary rare earth acid leaching solution; (5) adding the primary acid leaching residue to an inorganic strong acid solution for secondary mixing, controlling the mixing temperature and stirring the reaction, filtering, and obtaining secondary acid leaching residue and secondary rare earth leaching solution; In step (1), the mass ratio of electrolytic slag: aluminum particles: aluminum chloride particles is (2-8): 1: (2-4); The calcination atmosphere is air containing trace amounts of hydrogen, with the hydrogen volume fraction being 0.05-0.2%; The calcination temperature in step (2) is 500-700°C; The stirring reaction temperature in steps (4) and (5) is 85-95°C.

2. The method for recovering rare earth elements from rare earth molten salt electrolytic slag according to claim 1, characterized in that: The aluminum particle size is 80-200 mesh.

3. The method for recovering rare earth elements from rare earth molten salt electrolytic slag according to claim 1, characterized in that: The calcination time is 1.5-3h.

4. The method for recovering rare earth elements from rare earth molten salt electrolytic slag according to claim 1, characterized in that: In step (4) and step (5), the inorganic strong acid solution is a hydrochloric acid solution with a concentration of 2.5-4M.

5. The method for recovering rare earth elements from rare earth molten salt electrolytic slag according to claim 1, characterized in that: The secondary rare earth leaching solution obtained in step (5) is recovered and reused.