A method for reducing aluminum impurities in mixed rare earth chloride solution

Abstract

The present invention discloses a method for reducing aluminum impurities in a mixed rare earth chloride solution, comprising the following steps: A, using the mixed rare earth chloride solution as a mother liquor, adding sodium fluoride and heating to above 90°C, stirring the reaction for 1-3 hours; B, after the reaction is completed, standing and filtering, the filter residue is the cryolite product, the filtrate is tempered until the pH value of the filtrate is 4-4.5, then clarifying and filtering, the filter residue is the iron-thorium slag, and the filtrate is the mixed rare earth chloride solution after aluminum removal. The method of the present invention can reduce the Al2O3 content in the mixed rare earth chloride solution from about 0.1% to less than 0.01% to meet production needs, thereby eliminating the need to set an aluminum removal process in the extraction section, avoiding the problem of praseodymium and neodymium chloride loss caused by aluminum removal by mixed organic saponification of "naphthenic acid + kerosene + sec-octanol" in the extraction section.

Description

Technical Field

[0001] The invention relates to the technical field of rare earth hydrometallurgy, and in particular to a method for reducing aluminum impurities in a mixed rare earth chloride solution. Background Art

[0002] Aluminum exists mainly in the form of bauxite in rare earth ore. After the rare earth ore is enriched, rare earth concentrate is obtained. It is inevitable that some non-rare earth impurities containing aluminum are also present in the rare earth concentrate. The rare earth concentrate is treated by acid-base combined method to obtain mixed rare earth chloride. The content of mixed rare earth chloride is about 0.1% in terms of Al2O3 (the concentration of mixed rare earth chloride REO is about 250g / L). The aluminum impurities are enriched into the praseodymium-neodymium chloride solution by the cerium-praseodymium line in the extraction section, and its content can reach 0.35 % (the concentration of praseodymium-neodymium chloride is about 220g / L), and for the praseodymium-neodymium precipitation process, the aluminum content is required to be below 500ppm to meet the bottom sedimentation requirements. Therefore, the mainstream is to use extraction to remove aluminum, that is, to add a "naphthenic acid + kerosene + sec-octanol" mixed organic saponification section to the extraction section, and obtain a low-aluminum praseodymium-neodymium chloride material (aluminum content below 500ppm) and a high-aluminum praseodymium-neodymium chloride solution enriched with aluminum. The high-aluminum can meet production requirements by conventional precipitation. For example, reference can be made to Chinese patents CN101979680A and CN103146921A. These two patents both disclose a method for removing aluminum from rare earth feed liquid, which uses a mixed organic system composed of naphthenic acid + alcohol + kerosene to achieve the purpose of removing aluminum after a series of extraction and precipitation. Other traditional aluminum removal methods such as alkali method, acid method and hydrolysis method are rarely used due to their respective major technical defects.

[0003] In the extraction process for aluminum removal, the resulting high-aluminum praseodymium-neodymium chloride solution must be precipitated with oxalic acid at high temperatures to produce a praseodymium-neodymium oxalate product that meets production requirements. During the mixed organic saponification process for impurity removal, cyclohexane acid and sec-octanol (or isooctanol) are easily volatile, and the mixture can lose effectiveness after prolonged use. This results in inconsistent quality of the low-aluminum praseodymium-neodymium chloride solution during production, and unstable product quality in the precipitation process. Furthermore, this production process not only lengthens the processing steps but also reduces the yield of praseodymium-neodymium oxide, increasing production costs. Summary of the Invention

[0004] The object of the present invention is to provide a method for reducing aluminum impurities in a mixed rare earth chloride solution in order to solve the deficiencies of the prior art.

[0005] The technical solution adopted by the present invention is as follows: a method for reducing aluminum impurities in a mixed rare earth chloride solution, comprising the following steps:

[0006] A. Use the mixed rare earth chloride solution produced by the acid-base combined method as the mother liquor, first heat the mother liquor to 60-80°C, then add sodium fluoride, and then heat to above 90°C, stirring and reacting for 1-3 hours;

[0007] B. After the reaction is completed, the product is allowed to stand and filtered. The filter residue is the cryolite product. The filtrate is tempered until the pH value of the filtrate is 4-4.5. Then it is clarified and filtered. The filter residue is the iron-thorium slag. The filtrate is the mixed rare earth chloride solution after aluminum removal.

[0008] Furthermore, the concentration of the mixed rare earth chloride is 130±20g / L, and 500±10g of sodium fluoride is added to every 1000L of the mixed rare earth chloride solution. The amount of sodium fluoride added should not be too high or too low. If it is too high, rare earth fluoride precipitation will be easily generated, thereby reducing the rare earth yield. If it is too low, Al 3+ The removal is not thorough and the aluminum removal effect is poor.

[0009] Furthermore, the sodium fluoride is added in a speed of 10-30 minutes. The addition speed of sodium fluoride should not be too fast, as it will easily generate rare earth fluoride, resulting in a waste of sodium fluoride and incomplete removal of aluminum ions.

[0010] Furthermore, during the tempering process, sodium carbonate is added for tempering.

[0011] Furthermore, during the conditioning process, when the pH value of the filtrate reaches 4-4.5, the reaction is stirred for more than 0.5 h until the pH value does not change, the stirring is stopped, and the filtrate is clarified and filtered.

[0012] Furthermore, in step B, the filtrate after the conditioning treatment is subjected to lead and barium removal treatment to obtain a mixed rare earth chloride solution for the rare earth extraction section.

[0013] Furthermore, the filtrate is treated with sodium sulfide and sulfuric acid to remove lead and barium respectively.

[0014] Furthermore, in the mixed rare earth chloride solution after aluminum removal, the content of Al2O3 is below 0.01% in terms of Al2O3.

[0015] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0016] 1. After treatment by the method of the present invention, the Al2O3 content in the cerium-deficient solution is reduced from about 0.1% to below 0.01% to meet production requirements. Therefore, there is no need to set up an aluminum removal process in the extraction section, avoiding the problem of praseodymium and neodymium chloride loss caused by aluminum removal by organic saponification with a mixture of "naphthenic acid + kerosene + sec-octanol" in the extraction section;

[0017] 2. The present invention advances the original aluminum removal step, changing the original step of first tempering the low-cerium solution and then removing fluorine to first removing aluminum and fluorine and then tempering. The aluminum and fluorine removal effects are significantly better than the original process;

[0018] 3. The present invention adopts reverse thinking to add harmful impurity fluorine to the cerium solution to remove the harmful impurity aluminum and fluorine in the cerium solution. That is, the content of some harmful impurities is increased and the two harmful impurities are removed together by co-precipitation, which effectively saves production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the process flow of producing low-cerium solution using the existing acid-base combined method;

[0020] Figure 2 This is a process flow chart of removing aluminum and other impurities from a low-cerium solution of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described in detail below with reference to the accompanying drawings.

[0022] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0023] After oxidation roasting, the fluorocarbon cerium concentrate (rare earth concentrate) with REO=65% or more is leached once with hydrochloric acid. The leachate is called the first leachate. The leached residue is washed with water after alkali conversion and then leached with hydrochloric acid. The leachate is called the second leachate. The mixture of the first leachate and the second leachate is called the low-cerium solution. Generally, the REO concentration of this low-cerium solution is 140g / L during the production process. The specific process flow can be referred to. Figure 1 After oxidative roasting of fluorocarbon cerium concentrate (roasting temperature 430-520℃), hydrochloric acid (H + ≤0.2mol / L) once leaching to obtain a leaching solution and a leaching residue, and the leaching residue is then converted to (OH - ≥1.5mol / L), washed with water and dissolved in acid (pH=1.0-1.5) to obtain the second leaching solution and the second leaching residue. The mixture of the first leaching solution and the second leaching solution is called the cerium-poor solution, and the second leaching residue is the cerium-rich slag.

[0024] The acidity of the cerium solution should be controlled below 0.2 mol / L, and the concentration of Al2O3 should be around 2000ppm. 3+ The fluorine in the cerium-poor solution exists in the form of fluorine, while the fluorine in the cerium-poor solution mainly exists in the form of suspended matter, so the fluorine in the cerium-poor solution exceeds the quality standard of the cerium-poor solution entering the extraction tank (less than 0.1g / L). The present invention innovatively removes aluminum from the cerium-poor solution, and the main steps are:

[0025] Transfer the unremoved cerium-rich solution to a reaction tank, start stirring, and then heat it to above 60°C. Slowly add solid sodium fluoride (addition should take 10-30 minutes), and continue to heat it to above 90°C (the two-stage heating process is mainly to save reaction time. When the temperature is raised to 60°C and sodium fluoride is added, a small amount of cryolite will be produced. After the addition is completed, heating it to 90°C will accelerate the reaction and quickly form cryolite). React for 2 hours. The reaction equation is:

[0026] Al 3+ +F - +H + =H3AlF6

[0027] H3AlF6+3Na + =Na3AlF6↓

[0028] After 2 hours of reaction, aluminum and fluorine form cryolite, and the aluminum impurities in the cerium solution are removed to reach the standard Al2O3 of less than 100ppm before entering the extraction tank. The fluorine suspended matter, fluoride ions and fluoride ions in the unreacted sodium fluoride in the cerium solution originally exist in the cerium solution, resulting in the fluorine content in the cerium solution exceeding the quality standard of the cerium solution entering the extraction tank (less than 0.1g / L). Therefore, it is necessary to perform a conditioning treatment, that is, slowly add sodium carbonate solid to the cerium solution reaction tank after 2 hours of reaction until the pH of the cerium solution system reaches 4-4.5, and then react for 0.5 hours. If the pH value does not change, stop stirring, clarify and filter. The reaction equation is:

[0029] F - +RE 3+ +CO3 2- =REFCO3↓

[0030] Fe 3+ +3H2O=Fe(OH)3↓+3H +

[0031] Th 4+ +4H2O=Th(OH)4↓+4H +

[0032] 2RE 3+ +3CO3 2- =RE2(CO3)3↓

[0033] CO3 2- +2H + =H2O+CO2↑

[0034] According to the above reactions, during the tempering treatment, iron ions and thorium ions are mainly hydrolyzed to form hydroxide precipitates, of which the precipitation is basically complete at a pH of 4-4.5. Rare earth fluorocarbonate removes free fluoride ions, and suspended fluoride adheres to rare earth carbonate, rare earth fluorocarbonate and settleable hydroxide with better sedimentation effect to form filter residue (iron-thorium residue), which can be temporarily stored in hazardous waste storage or used to recover valuable rare earths. There is no need to worry about the problem of excessive addition of sodium fluoride.

[0035] Furthermore, according to the existing production operating procedures, the cerium-deficient liquid is concentrated, lead- and barium-removed, and then aged for 48 hours to obtain a mixed rare earth chloride solution that can be directly used for extraction. Since the aluminum content in the mixed rare earth chloride solution is controlled within an extremely low range, there is no need to use extraction to remove aluminum in the extraction section, which not only stabilizes the product quality of the precipitation process, but also reduces the process flow, saving production cycle and auxiliary material costs.

[0036] In order to better illustrate the present invention, some embodiments are listed below:

[0037] Example 1

[0038] S1, measure 10 cubic meters of mixed cerium solution with a concentration of 143.5g / L, the content of Al2O3 in the mixed cerium solution is 2500ppm, F - The content is 0.35g / L, the acidity is 0.19mol / L, and it is placed in a reactor. The mixed cerium solution is heated to 60°C, stirred, and then 5kg of sodium fluoride is slowly added to the cerium solution (addition is completed in 30 minutes);

[0039] S2, continue to heat to 90 ° C, react for 2 hours, then clarify, siphon the supernatant into a spare reactor, and then filter the mixture of residue and liquid at the bottom; transfer the filtrate to the spare reactor;

[0040] S3, heating up again and stirring, when the temperature rises to 80 ° C, slowly adding sodium carbonate to perform tempering operation until the pH value of the cerium solution is at least 4-4.5 without change, then stopping stirring after the reaction for 0.5 h, extracting the supernatant after clarification, filtering the slag-water mixture, the slag is the iron-thorium slag, and the filtrate is the tempered liquid after tempering;

[0041] S4. The tempering liquid was taken for testing, and the Al2O3 content was 75 ppm, the fluorine content was 0.085 g / L, the REO content in the iron-thorium slag was 11.67%, and the REO content in the cryolite was 0.17%.

[0042] Example 2

[0043] S1. Measure 5 cubic meters of the mixed cerium solution of the same batch as in Example 1, wherein the Al2O3 content is 2500 ppm; F- The content is 0.35 g / L, the acidity is 0.19 mol / L, and it is transferred to the reactor. The mixed cerium solution is first heated to 60 ° C, stirred, and then 2.7 kg of sodium fluoride is slowly added to the cerium solution (addition is completed in 30 minutes);

[0044] S2. Continue heating to 95°C and react for 2 hours, then clarify, siphon the supernatant into a spare reactor, and then filter the mixture of residue and liquid at the bottom; transfer the filtrate to the spare reactor;

[0045] S3. Heat up again and start stirring. When the temperature reaches 80°C, slowly add sodium carbonate for tempering until the pH value of the cerium liquid is at least 4-4.5 without any change. Then stop stirring after reacting for 0.5h. After clarification, extract the supernatant. After filtering the slag-water mixture, the slag is iron-thorium slag and the filtrate is the tempered liquid after tempering.

[0046] S4. The tempering liquid was taken for testing, and the Al2O3 content was 60 ppm, the fluorine content was 0.055 g / L, the REO content in the iron-thorium slag was 11.81%, and the REO content in the cryolite was 0.25%.

[0047] Example 3

[0048] S1. Measure 10 cubic meters of the mixed cerium solution from the same batch as in Example 1 and transfer it to a reactor. First, heat the mixed cerium solution to 65° C., start stirring, and then slowly add 4.5 kg of sodium fluoride to the cerium solution (addition takes 30 minutes);

[0049] S2. Continue heating to 95°C and react for 2 hours, then clarify, siphon the supernatant into a spare reactor, and then filter the mixture of residue and liquid at the bottom; transfer the filtrate to the spare reactor;

[0050] S3. Heat up again and start stirring. When the temperature reaches 80°C, slowly add sodium carbonate for tempering until the pH value of the cerium liquid is at least 4-4.5 without any change. Then stop stirring after reacting for 0.5h. After clarification, extract the supernatant. After filtering the slag-water mixture, the slag is iron-thorium slag and the filtrate is the tempered liquid after tempering.

[0051] S4. The tempering liquid was taken for testing, and the Al2O3 content was 85 ppm, the fluorine content was 0.070 g / L, the REO content in the iron-thorium slag was 11.60%, and the REO content in the cryolite was 0.12%.

[0052] Comparative Example 1

[0053] Comparative Example 1 was the same as Example 1, except that the sodium fluoride was added over a 5-minute period. Testing of the tempering solution revealed an Al₂O₃ content of 650 ppm and a fluorine content of 0.021 g / L. The REO content in the ferrothorium slag was 11.74%, and the REO content in the cryolite was 0.45%.

[0054] It can be seen that when the addition rate of sodium fluoride is too fast, a certain amount of rare earth fluoride is generated at the same time as cryolite, resulting in a significant increase in the REO content in cryolite and a reduction in the yield of rare earths; at the same time, the Al2O3 content in the conditioning solution also increases significantly, which not only causes a waste of sodium fluoride, but also causes the problem of incomplete removal of aluminum ions.

[0055] Comparative Example 2

[0056] Comparative Example 2 was the same as Example 1, except that 6.5 kg of sodium fluoride was added. Testing of the tempering solution revealed an Al₂O₃ content of 70 ppm and a fluorine content of 0.125 g / L. The REO content in the ferrothorium slag was 11.88%, and the REO content in the cryolite was 0.67%.

[0057] It can be seen that the excessive addition of sodium fluoride leads to a significant increase in the REO content in cryolite (a certain amount of rare earth fluoride is generated while cryolite is generated), which reduces the rare earth yield.

[0058] Comparative Example 3

[0059] Comparative Example 3 was the same as Example 1, except that 5 kg of sodium fluoride was slowly added directly to the cerium-deficient solution (addition was complete over 30 minutes), the temperature was not raised, and the reaction was allowed to proceed for 2 hours. Testing of the tempering solution revealed an Al2O3 content of 1250 ppm and a fluorine content of 0.225 g / L. The REO content in the thorium slag was 12.35%, and the REO content in the cryolite was 0.47%.

[0060] It can be seen that directly mixing the cerium-rich solution without heating it will affect the cryolite production reaction at the same reaction time. 3+ If it is not completely removed, the fluorine content in the conditioning solution will exceed the standard and the rare earth yield will be significantly reduced.

[0061] Comparative Example 4

[0062] Comparative Example 4 is the same as Example 1, except that the tempering treatment is performed first and then the aluminum is removed, specifically:

[0063] S1. 10 cubic meters of the same mixed cerium solution as in Example 1 were measured and placed in a reactor. The mixture was then heated to 80° C., stirred, and sodium carbonate was added for conditioning. During the conditioning process, sodium carbonate was slowly added according to the operation of Example 1 until the pH value of the cerium solution reached 4-4.5 without any change, at which time the addition of sodium carbonate was stopped. Stirring was then continued for 0.5 h, and stirring was stopped for clarification. The supernatant was extracted into a spare reactor, filtered, and the filtrate was transferred to a spare tank and combined with the supernatant to obtain a conditioning solution. The filter residue was an iron-thorium slag, and the REO in the iron-thorium slag was detected to be 11.78%.

[0064] S2. Heat the conditioning solution to 60°C, start stirring, then slowly add 5kg of sodium fluoride (addition takes 0.5h), continue heating to 90°C, continue to react for 2h, stop stirring, clarify, and take the supernatant for analysis. The content of Al2O3 is 64ppm, and F - The content of fluorine is 0.49g / L. According to the test results, tempering first and then removing Al did not achieve the effect of removing aluminum and fluorine at the same time.

[0065] Comparative Example 5

[0066] The low-cerium solution of Example 1 without impurity removal treatment was directly heated to 90° C. and stirred for 2 hours. The supernatant was clarified and sampled for analysis. The test results showed that except for the increase in the concentration of the low-cerium solution and the concentration of fluoride ions, the other indicators did not change.

[0067] The effects of the embodiments and comparative examples on fluorine and aluminum removal are shown in Table 1:

[0068] Table 1 Main impurity contents in the cerium-poor solution after treatment in the examples and comparative examples

[0069]

[0070] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for reducing aluminum impurities in a mixed rare earth chloride solution, characterized in that: The steps include: A. Using a mixed rare earth chloride solution produced by an acid-base combined method as a mother liquor, first heating the mother liquor to 60-80° C., then adding sodium fluoride, and then heating to above 90° C., stirring and reacting for 1-3 hours; the mixed rare earth chloride concentration is 130±20 g / L, and 500±10 g of sodium fluoride is added to every 1000 L of the mixed rare earth chloride solution; the sodium fluoride is added over 10-30 minutes; and in the mixed rare earth chloride solution after aluminum removal, the Al2O3 content is less than 0.01% in terms of Al2O3; B. After the reaction is completed, the product is allowed to stand and filtered. The filter residue is the cryolite product. The filtrate is tempered until the pH value of the filtrate is 4-4.

5. Then it is clarified and filtered. The filter residue is the iron-thorium slag. The filtrate is the mixed rare earth chloride solution after aluminum removal.

2. The method for reducing aluminum impurities in a mixed rare earth chloride solution according to claim 1, wherein: During the tempering process, sodium carbonate is added for tempering.

3. The method for reducing aluminum impurities in a mixed rare earth chloride solution according to claim 1, wherein: During the conditioning process, when the pH value of the filtrate reaches 4-4.5, stir the reaction for more than 0.5h until the pH value does not change, stop stirring, and clarify and filter.

4. The method for reducing aluminum impurities in a mixed rare earth chloride solution according to claim 1, wherein: In step B, the filtrate after the conditioning treatment is subjected to lead and barium removal treatment to obtain a mixed rare earth chloride solution for the rare earth extraction stage.

5. The method for reducing aluminum impurities in a mixed rare earth chloride solution according to claim 1, wherein: The filtrate was treated with sodium sulfide and sulfuric acid to remove lead and barium respectively.

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