Treatment method of mixed rare earth concentrate

Abstract

The present invention discloses a method for treating mixed rare earth concentrate, comprising the following steps: (1) mixing the mixed rare earth concentrate with sulfuric acid solution I and reacting at 100-140 °C; performing solid-liquid separation to obtain a first mother liquor and a first solid; wherein, the concentration of sulfuric acid solution I is 45-65 wt%; in the mixed rare earth concentrate, the CaO content is less than or equal to 2 wt%; (2) washing the first solid and then leaching with water to obtain a first rare earth sulfate solution and a first water leaching residue; (3) mixing the first water leaching residue with sulfuric acid solution II and reacting at 100-130 °C; performing solid-liquid separation to obtain a second mother liquor and a second solid; wherein, the concentration of sulfuric acid solution II is 90-98 wt%; the solid-liquid ratio of the first water leaching residue to sulfuric acid solution II is 1 g:2-4 ml; (4) washing the second solid and then leaching with water to obtain a second rare earth sulfate solution and a second water leaching residue. The treatment method of the present invention can further reduce the decomposition temperature of the mixed rare earth concentrate.

Description

Technical Field

[0001] The invention relates to a method for processing mixed rare earth concentrate. Background Art

[0002] Mixed rare earth concentrate is the main source of rare earths in the world, among which the most famous one in my country is the Bayan Obo mine in Baotou. Mixed rare earth ores mainly include fluorocarbon cerium and monazite.

[0003] Monazite has a high density and stable chemical properties. Compared with bastnaesite, it often requires more stringent conditions to decompose more thoroughly. Due to the complexity of the composition of mixed rare earth concentrates, there are also many studies on the decomposition of mixed rare earth concentrates.

[0004] CN109988903A discloses a method for decomposing high-grade mixed rare earth concentrate by two-stage roasting with concentrated sulfuric acid. First, the rare earth concentrate and concentrated sulfuric acid are mixed at a weight ratio of 1:1.3-1.55 for pre-reaction at room temperature; then, low-temperature roasting is performed at 180-380°C to obtain a low-temperature roasted ore; the low-temperature roasted ore is directly subjected to high-temperature roasting at 380-900°C to obtain a high-temperature roasted ore. The low-temperature roasting and high-temperature roasting temperatures of this method are both high, and the concentrated sulfuric acid decomposes severely. CN108950188A discloses a method for extracting phosphorus and rare earths from phosphorus-containing rare earth concentrate by low-temperature roasting with concentrated sulfuric acid. The phosphorus-containing rare earth concentrate and concentrated sulfuric acid are uniformly mixed at a weight ratio of 1:1.2-1.8, roasted and decomposed at 200-350°C to obtain a roasted ore; and then phosphorus and rare earth resources are extracted by leaching in steps. In this method, the roasting temperature is still high, and the concentrated sulfuric acid decomposes severely. In addition, this method uses a small amount of concentrated sulfuric acid and is basically a solid-phase reaction, which easily causes a large amount of solids to solidify on the inner wall of the equipment, which is not conducive to industrial production.

[0005] CN109097559B discloses a method for preparing mixed rare earth chloride from Baiyunebo rare earth concentrate. The rare earth concentrate is mixed with concentrated sulfuric acid in a weight ratio of 1:0.7-1.5 and roasted in three stages, the first stage is roasted at 100-150°C for 0.5-1h, the second stage is roasted at 150-200°C for 1-2h, and the third stage is roasted at 400-500°C for 1-2h. Although this method uses multi-stage temperature roasting of mixed rare earth concentrate, the main rare earth concentrate decomposition is still in the medium temperature stage, which is still a traditional sulfuric acid roasting process, and there are many steps and the process is relatively cumbersome.

[0006] CN111270092A discloses a method for decomposing mixed rare earth ores. A 35-85% sulfuric acid solution is used to decompose bastnasite in mixed rare earth concentrates at 100-140 °C according to a ore-acid ratio of 1:1.5-1.6 (weight ratio). After the decomposition is completed, solid-liquid separation is carried out. The acid leaching residue I is reacted with a 65-85% sulfuric acid solution at 150-300 °C according to a ore-acid ratio of 1:1.5-5 (weight ratio). This method decomposes mixed rare earth concentrates in two stages. However, in this method, monazite fails to decompose at 100-140 °C. And a 65-80% sulfuric acid solution has high requirements for equipment corrosion and high temperature resistance above 150 °C, which is not conducive to industrial application. Moreover, the phosphorus element content of the acid leaching residue I is not limited in this method. CN1113346622B discloses a method for decomposing rare earth concentrates. The rare earth concentrates are mixed with a 65-85 wt% concentrated sulfuric acid in a reaction vessel and then reacted at 150-185 °C to obtain a reaction product; wherein, the dosage ratio of the rare earth concentrates to the concentrated sulfuric acid is 1 kg:(7.8-9) L; the reaction product is subjected to solid-liquid separation to obtain a first filter residue and a first filtrate; the first filter residue is washed with water and then solid-liquid separated to obtain a second filter residue and a second filtrate. Although it is a liquid-solid reaction, the reaction temperature is relatively high, the liquid-solid ratio is relatively large, the requirements for equipment are relatively high, and the sulfuric acid dosage is relatively large.

[0007] Generally speaking, the decomposition reaction temperatures in the above studies are still relatively high, the requirements for equipment are relatively high, which is not conducive to industrial application.

[0008] CN109536746A discloses a method for cyclic slurry decomposition of low-calcium high-grade mixed rare earth concentrates, including: using an absolutely excessive lower-concentration sulfuric acid solution to rapidly decompose bastnasite in low-calcium high-grade mixed concentrates through a slurry reaction under heating conditions. After the reaction, the solid is subjected to water leaching to obtain a water leaching residue and a water leaching solution. The water leaching residue is decomposed with a strong alkali solution. In this method, the alkali solution cannot be directly recycled, and it is necessary to crystallize and recover sodium phosphate from the alkali wastewater before recycling. Moreover, the post-treatment of the alkali decomposition step is relatively cumbersome. In addition, the first-step acid decomposition in this method obtains a rare earth sulfate solution, and the second-step alkali decomposition treatment obtains a rare earth chloride solution, which is not conducive to combined treatment. Summary of the Invention

[0009] In view of this, the purpose of the present invention is to provide a method for treating mixed rare earth concentrates, which can further reduce the decomposition temperature of mixed rare earth concentrates. In addition, in this method, only sulfuric acid is used for decomposition, and the recycling rate of sulfuric acid is relatively high.

[0010] The present invention achieves the above purpose through the following technical solutions.

[0011] The present invention provides a method for treating mixed rare earth concentrates, including the following steps:

[0012] (1) Mix the mixed rare earth concentrate with sulfuric acid solution I and react at 100 - 140 °C; perform solid-liquid separation to obtain the first mother liquor and the first solid; wherein, the concentration of sulfuric acid solution I is 45 - 65 wt%; in the mixed rare earth concentrate, the CaO content is less than or equal to 2 wt%.

[0013] (2) Wash the first solid and then leach it with water to obtain the first rare earth sulfate solution and the first water leaching residue.

[0014] (3) Mix the first water leaching residue with sulfuric acid solution II and react at 100 - 130 °C; perform solid-liquid separation to obtain the second mother liquor and the second solid; wherein, the concentration of sulfuric acid solution II is 90 - 98 wt%; the solid-liquid ratio of the first water leaching residue to sulfuric acid solution II is 1 g: 2 - 4 ml.

[0015] (4) Wash the second solid and then leach it with water to obtain the second rare earth sulfate solution and the second water leaching residue.

[0016] According to the treatment method of the present invention, preferably, in step (1), the solid-liquid ratio of the mixed rare earth concentrate to sulfuric acid solution I is 1 g: 2 - 5 ml.

[0017] According to the treatment method of the present invention, preferably, in step (1), the reaction time is 90 - 150 min.

[0018] According to the treatment method of the present invention, preferably, in step (2), the P2O5 content in the obtained first water leaching residue is greater than or equal to 20 wt% and less than or equal to 24 wt%.

[0019] According to the treatment method of the present invention, preferably, in step (3), the reaction time is 65 - 120 min.

[0020] According to the treatment method of the present invention, preferably, it further includes the following steps:

[0021] Adjust the first mother liquor to a sulfuric acid concentration of 45 - 65 wt% for decomposing the next batch of mixed rare earth concentrate.

[0022] According to the treatment method of the present invention, preferably, in step (2), it includes the following specific steps: Wash the first solid with water to obtain filter cake I and washing liquid I; leach filter cake I with water, perform solid-liquid separation to obtain the first rare earth sulfate solution and the first water leaching residue.

[0023] According to the treatment method of the present invention, preferably, in step (4), it includes the following specific steps: Wash the second solid with water to obtain filter cake II and washing liquid II; leach filter cake II with water, perform solid-liquid separation to obtain the second rare earth sulfate solution and the second water leaching residue.

[0024] According to the processing method of the present invention, preferably, the following steps are further included:

[0025] Adjust the second mother liquor to a sulfuric acid concentration of 90-98 wt% for decomposing the next batch of first water-leached residues;

[0026] After the second mother liquor is recycled and decomposed for 3-6 batches of first water-leached residues, the second mother liquor is used to adjust the sulfuric acid concentration of the first mother liquor to 45-65 wt% for decomposing the mixed rare earth concentrate.

[0027] According to the processing method of the present invention, preferably, the mixed rare earth concentrate mainly consists of bastnasite and monazite; the mass ratio of bastnasite to monazite is greater than or equal to 2:1.

[0028] The present invention uses sulfuric acid solutions with different mass concentrations to treat the mixed rare earth concentrate in stages, and the overall treatment temperature is relatively low. Especially in the second-stage treatment, the present invention uses a higher concentration of sulfuric acid and completes the decomposition of the first water-leached residues (mainly monazite) at a lower temperature (100-130 °C), and the P2O5 decomposition rate is relatively high. The processing method of the present invention further reduces the decomposition temperature, thereby reducing energy consumption, reducing the decomposition of sulfuric acid, reducing the generation amount of sulfur dioxide and sulfur trioxide, and reducing acid consumption. In addition, the processing method of the present invention has a relatively high recycling rate of sulfuric acid. Not only can the mother liquor in each stage be recycled in the corresponding stage, but also the second mother liquor in the second-stage treatment can be used to adjust the sulfuric acid concentration of the first mother liquor in the first stage. Specific Embodiments

[0029] The present invention will be further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0030] In the present invention, examples of the mixed rare earth concentrate include, but are not limited to, a mixed ore mainly formed by bastnaesite and monazite. Monazite is a rare earth phosphate and is more stable and difficult to decompose than bastnaesite. In the prior art (such as CN111270092A, CN1113346622B), usually a relatively high reaction temperature (such as higher than 150 °C) is required to decompose monazite. The present invention finds that if a lower concentration of sulfuric acid is used, a higher decomposition temperature (such as above 150 °C) is required. At such a temperature, sulfuric acid corrodes the equipment more severely, and the high temperature resistance requirement for the equipment is higher, which is not conducive to industrial application. If a higher concentration of sulfuric acid is used, it is easily decomposed into sulfur dioxide and sulfur trioxide gases at a higher temperature. The present invention unexpectedly finds that by increasing the sulfuric acid concentration (to 90 - 98 wt%) and further reducing the decomposition temperature (100 - 130 °C), more thorough decomposition of monazite can be achieved, and at this temperature, the decomposition of sulfuric acid is less, and the acid consumption is also lower. The requirements for equipment are reduced, which is conducive to industrial application. In addition, the recycling rate of sulfuric acid is also relatively high.

[0031] The method for treating the mixed rare earth concentrate of the present invention comprises the following steps: (1) the first-stage reaction step; (2) the treatment step of the first mother liquor and the first solid; (3) the second-stage reaction step; (4) the treatment step of the second solid and the second mother liquor. The following is a detailed description.

[0032] <The first-stage reaction step>

[0033] Mix the mixed rare earth concentrate with sulfuric acid solution I and react at 100 - 140 °C; perform solid-liquid separation to obtain the first mother liquor and the first solid. This is conducive to reducing the reaction temperature, reducing the decomposition of the sulfuric acid solution, and greatly reducing the generation amounts of sulfur dioxide, sulfur trioxide, and sulfuric acid mist.

[0034] In the present invention, the mixed rare earth concentrate mainly consists of bastnaesite and monazite. The CaO content of the mixed rare earth concentrate of the present invention is less than or equal to 2 wt%; the mass ratio of bastnaesite to monazite is greater than or equal to 2:1; the REO content is greater than or equal to 55 wt%. This is conducive to reducing the consumption of sulfuric acid, enabling the consumption of concentrate and sulfuric acid to be balanced in the overall process flow, and improving the recycling rate of sulfuric acid.

[0035] In the present invention, the concentration of sulfuric acid solution I can be 45 - 65 wt%, preferably 50 - 65 wt%, and more preferably 55 - 60 wt%. On the one hand, this can make the decomposition of rare earth fluoride more thorough, and on the other hand, it can greatly reduce the generation amounts of sulfur dioxide, sulfur trioxide, and sulfuric acid mist during the reaction.

[0036] The solid-liquid ratio of the mixed rare earth concentrate to sulfuric acid solution I is 1 g: 2-5 ml, preferably 1 g: 3-5 ml, more preferably 1 g: 3.5-4.5 ml. This helps to form a slurry of sulfuric acid solution I and the mixed rare earth concentrate, which is beneficial to the decomposition of rare earth fluorides at a lower temperature. In addition, this is conducive to uniform mixing of the materials and more uniform reaction, and will not cause a large amount of solids to form on the inner wall of the equipment. In the present invention, when mixing the mixed rare earth concentrate with sulfuric acid solution I, stirring can be carried out.

[0037] The reaction temperature can be 100-140 °C, preferably 105-135 °C, more preferably 110-135 °C. The reaction time can be 90-150 min, preferably 100-150 min, more preferably 110-140 min. This is conducive to more thorough decomposition of the rare earth fluorides in the mixed rare earth concentrate and can also avoid the decomposition of the sulfuric acid solution due to too high a temperature (in the present invention, sulfuric acid solution I hardly decomposes). In the present invention, during the reaction, the steam generated by the reaction can be condensed and absorbed, so that a by-product containing hydrofluoric acid can be obtained.

[0038] After the reaction is completed, solid-liquid separation is carried out to obtain the first mother liquor and the first solid. In the present invention, the solid-liquid separation can be centrifugation or filtration. Filtration is preferred.

[0039] <Treatment steps of the first mother liquor and the first solid>

[0040] The first mother liquor is adjusted to a sulfuric acid concentration of 45-65 wt% for decomposing the next batch of mixed rare earth concentrate. It is preferably adjusted to a sulfuric acid concentration of 50-65 wt%, more preferably adjusted to a sulfuric acid concentration of 55-60 wt%.

[0041] In some embodiments, the first mother liquor is adjusted to a sulfuric acid concentration of 45-65 wt% with concentrated sulfuric acid (the concentration of concentrated sulfuric acid is not less than 90 wt%).

[0042] In some other embodiments, when the second mother liquor is recycled to decompose 3-6 batches of the first water-leached residue, the second mother liquor is used to adjust the sulfuric acid concentration of the first mother liquor to 45-65 wt% for decomposing the mixed rare earth concentrate. The present invention finds that since the decomposition rate of rare earth phosphate decreases after the second mother liquor is recycled to decompose 3-6 batches of the first water-leached residue, at this time, the second mother liquor is not suitable for continued recycling in the second-stage reaction, but it can be used to adjust the sulfuric acid concentration in the first mother liquor, so as to better realize the recycling of sulfuric acid and improve the recycling rate of sulfuric acid.

[0043] In still some other embodiments, the sulfuric acid concentration of the first mother liquor can also be adjusted to the use concentration by washing liquid I or washing liquid II.

[0044] In still other embodiments, after the concentration of P2O5 in the first mother liquor is greater than 80 g / L, the first mother liquor is subjected to extraction separation to obtain phosphoric acid and sulfuric acid solution. The concentration of the sulfuric acid solution obtained by extraction is adjusted to 45-65 wt% and used to decompose the mixed rare earth concentrate.

[0045] The first solid is washed and then leached with water to obtain a first rare earth sulfate solution and a first water leaching residue. In this way, rare earth sulfate can be obtained, and a first water leaching residue containing rare earth phosphate can be obtained. According to a specific embodiment of the present invention, the first solid is washed with water to obtain filter cake I and washing liquid I; the filter cake I is leached with water, and solid-liquid separation is performed to obtain a first rare earth sulfate solution and a first water leaching residue.

[0046] The first water leaching residue is used as a raw material for the second-stage reaction. In the present invention, the first water leaching residue is basically a monazite ore with a relatively high purity. The content of P2O5 in the obtained first water leaching residue is greater than or equal to 20 wt% and less than or equal to 24 wt%, preferably greater than or equal to 20 wt% and less than or equal to 23 wt%, and more preferably greater than or equal to 20.2 wt% and less than or equal to 22.5 wt%. Before this application, no one had realized that the phosphorus element content in monazite had any influence on its decomposition temperature. This application discovers that at a lower temperature, using sulfuric acid with a specific concentration and a specific dosage can decompose the first water leaching residue mainly composed of monazite, obtaining a higher P2O5 decomposition rate.

[0047] <Second-stage reaction step>

[0048] The first water leaching residue is mixed with sulfuric acid solution II and reacted at 100-130 °C; solid-liquid separation is performed to obtain a second mother liquor and a second solid. This is beneficial to further reduce the reaction decomposition temperature, reduce acid consumption, and reduce the decomposition of sulfuric acid.

[0049] In the present invention, the mass concentration of sulfuric acid solution II can be 90-98 wt%, preferably 92-98 wt%, and more preferably 92-95 wt%. This is beneficial to further reduce the decomposition temperature of monazite and reduce the requirements for equipment, which is beneficial to industrial application.

[0050] The solid-liquid ratio of the first water leaching residue to sulfuric acid solution II is 1 g:2-4 ml, preferably 1 g:2.5-4 ml, and more preferably 1 g:3-4 ml. This helps to reduce the decomposition reaction temperature and facilitate subsequent solid-liquid separation. In the present invention, the mass of the solid in the solid-liquid ratio refers to the dry weight of the first water leaching residue.

[0051] The reaction temperature can be 100 - 130°C, preferably 110 - 130°C, more preferably 110 - 120°C. The reaction time can be 65 - 120 min, preferably 75 - 120 min, more preferably 85 - 115 min. This is beneficial for more thoroughly decomposing monazite, reducing the reaction energy consumption, decreasing the decomposition of sulfuric acid, and hardly generating sulfur dioxide, sulfur trioxide, and sulfuric acid mist. In this step, the effective separation of phosphate radicals and rare earth elements is achieved, such that the phosphate radicals are basically present in the second mother liquor and the rare earth elements are basically present in the second solid.

[0052] In the present invention, the solid-liquid separation can be centrifugation or filtration. Filtration is preferred. This can separate the phosphate radicals from the rare earth elements and enable the phosphate radicals to dissolve in the second mother liquor while the rare earth elements are present in the second solid. The content of P2O5 in the second mother liquor is greater than that in the first mother liquor.

[0053] <Treatment steps for the second solid and the second mother liquor>

[0054] Adjust the second mother liquor to a sulfuric acid concentration of 90 - 98 wt% for decomposing the next batch of first water-leached residues. Oleum can be used to adjust the second mother liquor to a sulfuric acid concentration of 90 - 98 wt%, preferably adjusted to a sulfuric acid concentration of 92 - 98 wt%, more preferably a sulfuric acid concentration of 92 - 95 wt%. This can achieve the recycling of sulfuric acid.

[0055] In some embodiments, as described above, after the second mother liquor is recycled to decompose 3 - 6 batches of first water-leached residues, the second mother liquor is used to adjust the sulfuric acid concentration of the first mother liquor to 45 - 65 wt% for decomposing the mixed rare earth concentrate. This can improve the recycling rate of the sulfuric acid solution.

[0056] Wash the second solid and then leach it with water to obtain a second rare earth sulfate solution and a second water-leached residue. In this way, rare earth sulfates can be obtained. According to a specific embodiment of the present invention, the second solid is washed with water to obtain filter cake II and washing liquid II; filter cake II is leached with water, and after solid-liquid separation, a second rare earth sulfate solution and a second water-leached residue are obtained.

[0057] P2O5 decomposition rate = (P2O5 content in the first water-leached residue - P2O5 content in the second water-leached residue) / (P2O5 content in the first water-leached residue) × 100%.

[0058] The lower the P2O5 content in the second water-leached residue, the higher the P2O5 decomposition rate. In the present invention, the P2O5 decomposition rate is greater than 99.5%.

[0059] In the present invention, the first rare earth sulfate solution and the second rare earth sulfate solution can be combined for treatment. Conventional methods in the art can be used to neutralize and remove impurities from the first rare earth sulfate solution and the second rare earth sulfate solution to obtain a purer rare earth sulfate aqueous solution, which will not be elaborated here.

[0060] <Analysis method>

[0061] REO content: Analyzed by the gravimetric method.

[0062] P2O5 content: Analyzed by the phosphomolybdic bismuth blue spectrophotometric method.

[0063] F content: Analyzed by the distillation method.

[0064] CaO content: Analyzed by the EDTA titration method.

[0065] Example 1

[0066] In the mixed rare earth concentrate of this example, the REO content is 65.46 wt%, the P2O5 content is 10.14 wt%, the F content is 8.48 wt%, and the CaO content is 1.85 wt%; the mass ratio of bastnasite to monazite is 3:1.

[0067] Mix 100 g of the mixed rare earth concentrate with sulfuric acid solution I at 55 wt% (solid-liquid ratio of 1 g:5 mL), and react at 110 °C for 120 min. After the reaction, solid-liquid separation is carried out to obtain the first mother liquor and the first solid.

[0068] Adjust the first mother liquor to a sulfuric acid concentration of 55 wt%, and continue to be used for cyclic decomposition of the next batch of mixed rare earth concentrate. After washing the first solid, it is leached with water to obtain the second rare earth sulfate solution and the first water leaching residue. In the first water leaching residue, the REO content is 63.89 wt%, the F content is 0.39 wt%, the P2O5 content is 20.04 wt%, and the CaO content is 2.67%.

[0069] Mix the first water leaching residue with sulfuric acid solution II at 92 wt% (solid-liquid ratio of 1 g:3 ml), and react at 120 °C for 100 min; carry out solid-liquid separation to obtain the second mother liquor and the second solid.

[0070] After washing the second solid, it is leached with water to obtain the second rare earth sulfate solution and the second water leaching residue. The P2O5 content in the second water leaching residue is 0.05%, and the P2O5 decomposition rate is 99.86%.

[0071] Example 2

[0072] In the mixed rare earth concentrate of this embodiment, the REO content is 63.89 wt%, the P2O5 content is 10.22 wt%, the F content is 8.49 wt%, and the CaO content is 1.98 wt%; the mass ratio of bastnasite to monazite is 3:1.

[0073] Mix 100 g of the mixed rare earth concentrate with 65 wt% sulfuric acid solution I (solid-liquid ratio is 1 g: 2 mL), and react at 100 °C for 150 min. After the reaction, perform solid-liquid separation to obtain the first mother liquor and the first solid.

[0074] Adjust the first mother liquor to a sulfuric acid concentration of 65 wt%, and continue to be used for cyclic decomposition of the next batch of mixed rare earth concentrate. Wash the first solid and then leach it with water to obtain the second rare earth sulfate solution and the first water leaching residue. In the first water leaching residue, the REO content is 64.25 wt%, the F content is 0.49 wt%, the P2O5 content is 21.34 wt%, and the CaO content is 2.78 wt%.

[0075] Mix the first water leaching residue with 98 wt% sulfuric acid solution II (solid-liquid ratio is 1 g: 3 ml), and react at 110 °C for 65 min; perform solid-liquid separation to obtain the second mother liquor and the second solid.

[0076] Wash the second solid and then leach it with water to obtain the second rare earth sulfate solution and the second water leaching residue. The P2O5 content in the second water leaching residue is 0.08%, and the P2O5 decomposition rate is 99.58%.

[0077] Example 3

[0078] In the mixed rare earth concentrate of this embodiment, the REO content is 64.78 wt%, the P2O5 content is 10.12 wt%, the F content is 8.57 wt%, and the CaO content is 1.88 wt%; the mass ratio of bastnasite to monazite is 5:1.

[0079] Mix 100 g of the mixed rare earth concentrate with 65 wt% sulfuric acid solution I (solid-liquid ratio is 1 g: 2 mL), and react at 130 °C for 120 min. After the reaction, perform solid-liquid separation to obtain the first mother liquor and the first solid.

[0080] Adjust the first mother liquor to a sulfuric acid concentration of 65 wt%, and continue to be used for cyclic decomposition of the next batch of mixed rare earth concentrate. Wash the first solid and then leach it with water to obtain the second rare earth sulfate solution and the first water leaching residue. In the first water leaching residue, the REO content is 63.78 wt%, the F content is 0.49 wt%, the P2O5 content is 20.76 wt%, and the CaO content is 2.71 wt%.

[0081] Mix the first water leaching residue with 95 wt% sulfuric acid solution II (solid-liquid ratio is 1 g:4 ml), and react at 110 °C for 90 min; perform solid-liquid separation to obtain the second mother liquor and the second solid.

[0082] Wash the second solid and then leach it with water to obtain the second rare earth sulfate solution and the second water leaching residue. The P2O5 content in the second water leaching residue is 0.06%, and the P2O5 decomposition rate is 99.71%.

[0083] Comparative Example 1

[0084] In the mixed rare earth concentrate of this example, the REO content is 65.46 wt%, the P2O5 content is 10.14 wt%, the F content is 8.48 wt%, and the CaO content is 1.85 wt%; the mass ratio of bastnasite to monazite is 3:1.

[0085] Mix 100 g of the mixed rare earth concentrate with 55 wt% sulfuric acid solution I (solid-liquid ratio is 1 g:5 mL), and react at 110 °C for 120 min. After the reaction, perform solid-liquid separation to obtain the first mother liquor and the first solid.

[0086] Adjust the first mother liquor to a sulfuric acid concentration of 55 wt% and continue to be used for cyclic decomposition of the next batch of mixed rare earth concentrate. Wash the first solid and then leach it with water to obtain the second rare earth sulfate solution and the first water leaching residue. In the first water leaching residue, the REO content is 63.89 wt%, the F content is 0.39 wt%, the P2O5 content is 20.04 wt%, and the Cao content is 2.67 wt%.

[0087] Mix the first water leaching residue with 80 wt% sulfuric acid solution II (solid-liquid ratio is 1 g:3 ml), and react at 120 °C for 100 min; perform solid-liquid separation to obtain the second mother liquor and the second solid.

[0088] Wash the second solid and then leach it with water to obtain the second rare earth sulfate solution and the second water leaching residue. The P2O5 content in the second water leaching residue is 17.37%, and the P2O5 decomposition rate is 26.54%.

[0089] Comparative Example 2

[0090] In the mixed rare earth concentrate of this example, the REO content is 65.46 wt%, the P2O5 content is 10.14 wt%, the F content is 8.48 wt%, and the CaO content is 1.85 wt%; the mass ratio of bastnasite to monazite is 3:1.

[0091] Mix 100 g of the mixed rare earth concentrate with 55 wt% sulfuric acid solution I (solid-liquid ratio is 1 g:5 mL), and react at 110 °C for 120 min. After the reaction, perform solid-liquid separation to obtain the first mother liquor and the first solid.

[0092] The first mother liquor is adjusted to a sulfuric acid concentration of 55wt%, and is continuously used for recycling and decomposing the next batch of mixed rare earth concentrate. The first solid is washed and leached with water to obtain a second rare earth sulfate solution and a first water leaching residue. In the first water leaching residue, the REO content is 63.89wt%, the F content is 0.39wt%, the P2O5 content is 20.04wt%, and the Cao content is 2.67wt%.

[0093] The first water-leached residue was mixed with 92 wt % sulfuric acid solution II (solid-liquid ratio of 1 g:1.5 ml), and reacted at 120° C. for 100 min; the solid-liquid was separated to obtain a second mother liquor and a second solid.

[0094] The second solid is washed and then leached with water to obtain a second rare earth sulfate solution and a second water-leached residue. The second water-leached residue has a P2O5 content of 5.89% and a P2O5 decomposition rate of 75.44%.

[0095] Table 1

[0096]

[0097] The present invention is not limited to the above-mentioned embodiments. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be thought of by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method for treating mixed rare earth concentrates, characterized in that, It includes the following steps: (1) Mix the mixed rare earth concentrate with sulfuric acid solution I and react at 100 - 140 °C for 110 - 150 min; perform solid-liquid separation to obtain the first mother liquor and the first solid; wherein, the concentration of sulfuric acid solution I is 45 - 65 wt%; in the mixed rare earth concentrate, the CaO content is less than or equal to 2 wt%; the solid-liquid ratio of the mixed rare earth concentrate to sulfuric acid solution I is 1 g: 2 - 5 ml; (2) Wash the first solid with water to obtain filter cake I and washing liquid I; leach filter cake I with water and perform solid-liquid separation to obtain the first rare earth sulfate solution and the first water leaching residue; wherein, the P2O5 content in the obtained first water leaching residue is greater than or equal to 20 wt% and less than or equal to 24 wt%; (3) Mix the first water leaching residue with sulfuric acid solution II and react at 100 - 130 °C for 65 - 120 min; perform solid-liquid separation to obtain the second mother liquor and the second solid; wherein, the concentration of sulfuric acid solution II is 90 - 98 wt%; the solid-liquid ratio of the first water leaching residue to sulfuric acid solution II is 1 g: 2 - 4 ml; (4) Wash the second solid with water to obtain filter cake II and washing liquid II; leach filter cake II with water and perform solid-liquid separation to obtain the second rare earth sulfate solution and the second water leaching residue; Wherein, the P2O5 decomposition rate is greater than 99.5%; P2O5 decomposition rate = (P2O5 content of the first water leaching residue - P2O5 content of the second water leaching residue) / (P2O5 content of the first water leaching residue) × 100%; 2. The processing method according to claim 1, wherein It further includes the following steps: Adjust the first mother liquor to a sulfuric acid concentration of 45 - 65 wt% for decomposing the next batch of mixed rare earth concentrate.

3. The processing method according to claim 1, wherein It further includes the following steps: Adjust the second mother liquor to a sulfuric acid concentration of 90 - 98 wt% for decomposing the next batch of the first water leaching residue; After the second mother liquor is recycled to decompose 3 - 6 batches of the first water leaching residue, use the second mother liquor to adjust the sulfuric acid concentration of the first mother liquor to 45 - 65 wt% so as to be used for decomposing the mixed rare earth concentrate.

4. The processing method according to any one of claims 1 to 3, characterized in that, The mixed rare earth concentrate mainly consists of bastnasite and monazite; the mass ratio of bastnasite to monazite is greater than or equal to 2:1.

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