CN115323199B - Rare earth element recovery method - Google Patents
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B59/00—Obtaining rare earth metals
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- C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
- C01F17/00—Compounds of rare earth metals
- C01F17/20—Compounds containing only rare earth metals as the metal element
- C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22B—PRODUCTION AND REFINING OF METALS; PRETREATMENT OF RAW MATERIALS
- C22B7/00—Working up raw materials other than ores, e.g. scrap, to produce non-ferrous metals and compounds thereof; Methods of a general interest or applied to the winning of more than two metals
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- C22B7/007—Wet processes by acid leaching
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- C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
- C25C3/34—Electrolytic production, recovery or refining of metals by electrolysis of melts of metals not provided for in groups C25C3/02 - C25C3/32
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Abstract
The invention provides a method for recovering rare earth elements, which comprises the following steps: step one, leaching rare earth waste with acid to obtain a rare earth-containing solution; adding a precipitant into the rare earth-containing solution to obtain a rare earth compound; third, firing the rare earth compound to obtain a first rare earth oxide or a second rare earth oxide; the method further comprises a first calcium removal step and/or a second calcium removal step; the first step of removing calcium comprises the following steps: mixing the first rare earth oxide with a calcium dissolving agent solution to obtain a second rare earth oxide, or mixing rare earth waste with the calcium dissolving agent or the calcium fixing agent solution before the first step and separating liquid; the second step of decalcification is that the second precipitant is alkaline solution. The recovery method of the rare earth element effectively reduces the calcium in the rare earth waste material from entering the rare earth oxide, and ensures that the rare earth raw material is electrolyzed and stabilized, thereby ensuring that the electrolysis production process is easy to control, the yield is high, the power consumption is low, the quality is good, and the current efficiency is improved.
Description
Technical Field
The invention relates to a method for recovering rare earth elements, in particular to a method for recovering rare earth elements from rare earth alloy scraps. Belonging to the technical field of comprehensive utilization of rare earth resources.
Background
The production and use processes of neodymium-iron-boron alloy and magnetic material, samarium-cobalt alloy and magnetic material, rare earth hydrogen storage alloy and material produce a large amount of waste containing rare earth elements, and calcium elements with different quality are easily mixed in the waste in the production, storage and transportation processes and the like. The waste is usually prepared by dissolving rare earth elements and other elements with acid, extracting and separating the rare earth elements, and preparing rare earth compounds or rare earth metals, alloys and the like according to the requirements. The method comprises the steps of adopting a high-temperature roasting degreasing and oxidation and hydrochloric acid optimal dissolution method to realize preliminary separation of rare earth and a large amount of non-rare earth elements, obtaining low-concentration rare earth chloride feed liquid, extracting by P507 and the like to realize deep separation of rare earth and non-rare earth impurities, obtaining high-concentration single rare earth element feed liquid, precipitating, high-temperature burning to obtain rare earth oxide, obtaining high-purity single rare earth oxide, preparing rare earth metal or alloy by electrolysis, and further preparing neodymium-iron-boron alloy, magnetic material, samarium-cobalt alloy, magnetic material, rare earth hydrogen storage alloy, material and other various rare earth materials.
The Chinese patent application with publication No. CN104451151A, 25 of 2015, discloses a preparation method of a high-value element-containing ferric hydroxide-based raw material, which adopts the steps of preparing iron-based waste into a high-value element-containing ferric hydroxide-based raw material comprising iron hydroxide, high-value element compounds and combustible organic matters through the steps of proportioning, reacting, drying and the like, wherein the iron and the high-value elements are mainly hydroxide, and the prepared product is powdery or easily crushed, does not self-ignite at the temperature of less than or equal to 200 ℃, and has the advantages of uniform texture, difficult self-ignition, convenience in use, safety, low consumption of chemical raw materials, high dissolution rate of the high-value elements and the like. The fire hazard of the iron-based waste in the transportation, loading, unloading, storage and production processes is eliminated. The preparation method and equipment of the invention are simple, easy to control, fully utilize the reaction heat, have high reaction speed, high safety and stability, large processing capacity and low production cost, greatly save the consumption of power, manpower and energy and are suitable for the technical effect of industrial production.
The Chinese patent application with publication number CN103540756A, publication number 2014, 01 and 29 discloses a method for treating rare earth dissolved out from waste neodymium-iron-boron material, which comprises the steps of crushing the material into powder, wetting and dispersing the powder by electrolyte solution, and pulping; then adding an oxidant to control the potential to +400- +800mV, and adding inorganic acid to control the pH to 2.5-4.5; leaching for 30-80 min at 50-90 ℃; after leaching, carrying out solid-liquid separation and filter residue washing; purifying, enriching and separating rare earth from the leaching solution after separating the solid leaching slag, and washing filter residues to be used as a raw material for producing iron products, so that the invention adopts weak acid oxidation leaching, improves the rare earth extraction rate, and is convenient for the subsequent extraction of rare earth by adopting various methods; but also reduces the dosage of acid, alkali and other chemicals; the high-temperature oxidation method is not adopted, and the energy consumption is reduced.
The prior art has the problems that a large amount of acid and alkali are consumed, the production flow is long, and the production cost is high because the rare earth elements and the impurity elements are separated by adopting an extraction separation method. The obtained product is a single rare earth oxide, and materials such as different rare earth elements are required to be added when the rare earth metal or alloy is prepared and applied to the production of neodymium-iron-boron alloy and the like, so that the production cost is increased, and various rare earth elements and the like cannot be fully and uniformly mixed. After the extraction process is abandoned, the acid and alkali consumed in the extraction process are saved, the production flow is shortened, and the production cost is reduced, but the defect that the production of rare earth metal or alloy by subsequent electrolysis is seriously influenced because the waste containing rare earth elements carries excessive calcium element and the quality of rare earth oxide is reduced is generated.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention provides a method for recycling rare earth elements from rare earth alloy scraps, which adopts the following technical scheme:
a method for recovering rare earth elements, comprising the steps of:
step one, leaching rare earth waste with acid to obtain a rare earth-containing solution;
adding a precipitant into the rare earth-containing solution to obtain a rare earth compound;
third, firing the rare earth compound to obtain a first rare earth oxide or a second rare earth oxide;
the method further comprises a first calcium removal step and/or a second calcium removal step;
the first calcium removal step comprises the following steps: mixing the first rare earth oxide with a calcium dissolving agent solution to obtain a second rare earth oxide, or mixing rare earth waste with the calcium dissolving agent or the calcium fixing agent solution before the first step and separating liquid;
the second decalcification step is that the precipitant is alkaline solution.
According to one of the preferred technical schemes of the invention, the rare earth compound is insoluble rare earth salt or rare earth hydroxide.
According to one preferable embodiment of the invention, the content of calcium element in the first rare earth oxide is 0.05 percent (calculated as oxide) and less than or equal to 0.3 percent (calculated as CaO) of CaO, and the content of calcium element in the second rare earth oxide is less than or equal to 0.05 percent (calculated as CaO).
According to one of the preferred technical schemes of the invention, the second decalcification step controls the pH of the end point to be more than 9.
According to still another preferred embodiment of the present invention, the content of calcium element in the first rare earth oxide is 0.1% < CaO > <0.3% by weight in terms of oxide.
According to a further preferred technical scheme of the invention, the rare earth compound comprises rare earth hydroxide, and a third decalcification step is further included between the second step and the third step: mixing rare earth hydroxide with a transforming agent solution to obtain insoluble rare earth salt.
According to a further preferred technical scheme of the invention, the transforming agent is at least one of oxalic acid solution, oxalate solution, potassium carbonate solution, potassium bicarbonate solution, sodium carbonate solution, sodium bicarbonate solution and ammonium bicarbonate solution.
According to a further preferred embodiment of the present invention, the acid is hydrochloric acid or nitric acid.
In a further preferred embodiment of the present invention, the method further comprises a step of roasting the rare earth waste material before the first decalcification step or after the first decalcification step.
According to a further preferred technical scheme of the invention, the roasting temperature of the roasting step is less than or equal to 1000 ℃.
According to a further preferred technical scheme of the invention, the roasting temperature of the roasting step is 200-900 ℃.
According to a further preferred technical scheme of the invention, the roasting temperature is 200-700 ℃.
According to a further preferred technical scheme of the invention, the oxidation rate of the rare earth waste after roasting is more than or equal to 70%.
According to a further preferred technical scheme of the invention, the oxidation rate of the rare earth waste after roasting is more than or equal to 95%.
In a further preferred embodiment of the present invention, the method further comprises a pulverizing step of pulverizing the calcined rare earth waste to pass through a 250 mesh sieve.
In a further preferred embodiment of the present invention, the method further comprises, before the second step, a step of adjusting the rare earth-containing solution to about ph3.5 and filtering to remove ferric hydroxide.
According to a further preferred technical scheme, the calcium dissolving agent is at least one of soluble chloride, nitrate and acetate, and the calcium fixing agent is at least one of soluble oxalate, sulfate, fluoride and phosphate.
According to still another preferred technical scheme of the invention, the chloride is at least one of sodium chloride, potassium chloride, lithium chloride, barium chloride and ammonium chloride, the nitrate is at least one of sodium nitrate, potassium nitrate, lithium nitrate, barium nitrate and ammonium nitrate, the acetate is at least one of sodium acetate, potassium acetate and ammonium acetate, the oxalate is at least one of sodium oxalate, potassium oxalate and ammonium oxalate, the sulfate is at least one of sodium sulfate, potassium sulfate, ammonium sulfate, sodium bisulfate, potassium bisulfate and ammonium bisulfate, the phosphate is at least one of sodium phosphate, potassium phosphate, ammonium phosphate, disodium phosphate, dipotassium phosphate, diammonium phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate and ammonium dihydrogen phosphate, and the fluoride is at least one of sodium fluoride, potassium fluoride, ammonium fluoride, sodium bifluoride and ammonium bifluoride.
According to a further preferred technical scheme of the invention, the calcium dissolving agent also contains a proper amount of acid.
According to a further preferred technical scheme of the invention, the rare earth waste is at least one of neodymium iron boron waste, samarium cobalt waste and hydrogen storage alloy waste.
Still another preferred embodiment of the present invention further includes: carrying out molten salt electrolysis on the electrolysis raw material to obtain rare earth metal or rare earth alloy and rare earth element and non-rare earth element alloy, wherein the rare earth alloy is an alloy of different rare earth elements; the electrolytic feed includes a second rare earth oxide.
According to a further preferred technical scheme of the invention, the electrolytic raw material further comprises rare earth fluoride, wherein the rare earth fluoride is prepared from the rare earth compound obtained in the second step, or at least one of the first rare earth oxide and the second rare earth oxide obtained in the third step.
According to a further preferred embodiment of the present invention, the alkaline solution includes at least one of sodium hydroxide and ammonia water.
According to a further preferred embodiment of the present invention, the alkaline solution further comprises ammonium bicarbonate.
According to a further preferred technical scheme of the invention, the rare earth metal or the rare earth alloy is prepared into an alloy of rare earth elements and non-rare earth elements. The rare earth alloy is an alloy between different rare earth elements, such as praseodymium neodymium alloy.
According to a further preferred technical scheme of the invention, the rare earth alloy is praseodymium neodymium terbium dysprosium alloy.
According to a further preferred technical scheme, rare earth metal or rare earth alloy and rare earth element and non-rare earth element alloy are prepared into neodymium-iron-boron alloy or samarium-cobalt alloy and hydrogen storage alloy.
According to a further preferred technical scheme, the neodymium-iron-boron alloy is prepared into a neodymium-iron-boron magnet.
The technical scheme of the invention has the following advantages:
the preparation process of the rare earth oxide omits the traditional extraction and separation process, so that the extraction cost including 5000kg of about 31% industrial hydrochloric acid, 5000kg of 30% liquid alkali, extractant and the like is saved by about 16000 yuan according to 1000kg of recovered second rare earth oxide; reducing the extraction wastewater by about 50M3 and the corresponding treatment cost; the production cycle is shortened by at least 50%. And the process is stable, the control difficulty is obviously reduced, and the automation is easy to realize. The rare earth impurities and non-rare earth impurities are controllable, the product quality is ensured, and the recycling is facilitated. The process equipment is simple, and is beneficial to industrialization. The process has strong adaptability, can process various raw materials and is beneficial to popularization.
Compared with the traditional process, the rare earth electrolysis process omits the processes of proportioning and mixing rare earth oxides, reducing terbium and dysprosium inclined compounds into terbium, dysprosium metal, praseodymium and neodymium metal, smelting and the like, omits auxiliary materials such as metal calcium for reducing terbium and dysprosium metal, reduces three wastes and treatment processes thereof, and improves the yield of terbium and dysprosium by about 1.5 percent relative to the reduction process. The invention effectively reduces the calcium in the rare earth waste from entering the rare earth oxide, stabilizes the electrolysis system under the conditions of not changing the existing equipment and electrolysis system for producing rare earth metal or alloy, the control method thereof and the like, and obtains the advantages of easy control of the electrolysis production process, high yield, low power consumption, good quality and the like of the electrolysis of the rare earth raw material, thereby improving the current efficiency. The obtained rare earth oxide, rare earth metal or alloy and raw materials are distributed together. The electrolytic product has good consistency, the terbium and dysprosium of high value elements are uniform, the production cost is greatly reduced, and the neodymium iron boron material produced by the process has good quality and strong performance, and the production cost is reduced. The carbon emission is reduced by about 25% from separation of rare earth elements to electrolysis to obtain rare earth alloys.
Detailed Description
The rare earth scrap is exemplified by neodymium iron boron scrap and the like.
The calcium dissolving agent is used for helping the calcium element to be dissolved in the liquid from rare earth waste or rare earth oxide, and a substance which has high solubility after anions and calcium ions form molecules and is weaker in alkalinity than calcium hydroxide generated by cations is generally selected as the calcium dissolving agent. The calcium fixing agent is used for preventing calcium element from entering the rare earth-containing solution in the acid leaching process.
The transforming agent transforms the rare earth hydroxide into insoluble rare earth salt, which can further reduce the content of calcium.
Comparative example one
Roasting neodymium iron boron waste (hereinafter referred to as waste I, the components are shown in Table I, the contained related elements are calculated by oxides, and the same is used for the following) at 200-900 ℃, wherein the oxidation rate is about 70%, crushing until all the waste passes through a 250-mesh sieve (crushed material), leaching by hydrochloric acid to obtain a rare earth solution, adjusting the pH value of the rare earth solution to about 3.5, and filtering to remove ferric hydroxide and acid insoluble residues to obtain the rare earth solution; oxalic acid is added into the rare earth-containing solution to obtain rare earth oxalate, and the rare earth oxalate is burned to obtain a first rare earth oxide (CaO content is 0.33%, and GB/T31965-2015 prescribes CaO less than or equal to 0.05%). And electrolyzing the rare earth oxide by adopting a fluoride molten salt electrolysis process to prepare the mixed rare earth metal. The power consumption of the mixed rare earth metal is gradually increased from 7.3kwh/kg to 8.7kwh/kg. The calcium content (calculated by elements) in the fused salt in the electrolytic furnace for producing about 4100kg of rare earth alloy in total is 3.25 percent, which is far higher than that in the fused salt for producing the same amount of similar products by taking the rare earth oxide obtained by the extraction process as the raw material, and the slag amount in the electrolytic furnace is increased. It is explained that calcium element accumulates in the molten salt and has a significant adverse effect on the electrolysis process.
Example 1
This example is essentially the same as comparative example one except that the crushed material is washed with an ammonium chloride solution under agitation prior to leaching with hydrochloric acid. The remainder being identical. The CaO content in the first rare earth oxide was obtained to be 0.27%. The related parameters are shown in a column. Indicating that some of the calcium element was removed but most of the calcium element was not removed in the ground material.
Example two
The first rare earth oxide obtained in the first embodiment was added to an ammonium acetate solution, and the CaO content in the first rare earth oxide obtained after stirring and washing was 0.25%. The relevant parameters are shown in Table I. Most of the calcium element in the first rare earth oxide still fails to be removed.
Example III
Adding a proper amount of ammonia water into the rare earth-containing solution obtained in the first embodiment, and controlling the final pH value to 9-10 to obtain rare earth hydroxide. Firing the rare earth hydroxide to obtain a first rare earth oxide (CaO content of 0.076%). The relevant parameters are detailed in the following table one. It can be seen that most of the calcium element in the neodymium iron boron waste has been removed.
Example IV
Adding an appropriate amount of oxalic acid solution into the rare earth hydroxide in the third embodiment to obtain rare earth oxalate. Firing the rare earth oxalate to obtain a first rare earth oxide (CaO content of 0.067%). The relevant parameters are detailed in the following table one.
Example five
The first rare earth oxide obtained in example four was washed with an ammonium nitrate solution to obtain a second rare earth oxide (CaO content of 0.050%). The relevant parameters are detailed in the following table one.
According to the fifth embodiment, 1kg of rare earth oxide is recovered and prepared, the extraction production cost is saved by about 16 yuan (about 5kg of 31% industrial hydrochloric acid, about 5kg of 30% liquid alkali, extractant and the like); about 50L of extraction wastewater and corresponding treatment cost are reduced; the production cycle is shortened by at least 50% and the carbon emissions of the separation process is reduced by about 30%. And the process is stable, the control difficulty is obviously reduced relative to extraction and separation, and automation is easy to realize. The rare earth impurity is controllable, which is beneficial to recycling. The process equipment is simple, and is beneficial to industrialization. The process has strong adaptability, can process various raw materials and is beneficial to popularization. Although the extraction and separation process is omitted, the non-rare earth impurities are still controllable, and the product quality is ensured.
Example six
And (3) adding acid to dissolve the rare earth hydroxide in the third embodiment, and adding a proper amount of ammonium bicarbonate solution to obtain rare earth carbonate. Firing the rare earth carbonate to obtain a second rare earth oxide (CaO content 0.042%). The relevant parameters are shown in the table I.
Example seven
The second rare earth oxide of example six was washed with an ammonium acetate solution to obtain a second rare earth oxide (CaO content 0.037%). The relevant parameters are shown in the table I.
Example eight
The rare earth hydroxide described in example three was added with an appropriate amount of hydrofluoric acid to obtain rare earth fluoride (CaO content 0.10%). The relevant parameters are shown in the table I.
Example nine
The second rare earth oxide obtained in the fifth example and the rare earth fluoride obtained in the eighth example are used as raw materials, about 4000kg of rare earth alloy is prepared according to the electrolysis process described in the first comparative example, the average power consumption of the obtained rare earth alloy is about 7.4kwh/kg, and the calcium content in the molten salt is measured to be 0.46%. The operation is stable in the electrolysis process, and the slag amount in the electrolysis furnace is small. The relevant parameters are shown in the table I.
Compared with the traditional process, the rare earth electrolysis process omits the processes of proportioning and mixing rare earth oxides, smelting and mixing terbium, dysprosium metal and praseodymium neodymium metal, and the like, omits auxiliary materials such as calcium and the like for reducing terbium and dysprosium metal, reduces three wastes, and improves the electrolysis yield of terbium and dysprosium by about 1.5 percent compared with the reduction process. The invention effectively reduces the calcium in the rare earth waste from entering the rare earth oxide, stabilizes the electrolysis system under the conditions of not changing the existing equipment and electrolysis system for producing rare earth metal or alloy, the control method thereof and the like, and obtains the advantages of easy control of the electrolysis production process, high yield, low power consumption, good quality and the like of the electrolysis of the rare earth raw material, thereby improving the current efficiency. The obtained rare earth oxide, rare earth metal or alloy and raw materials are distributed together. The electrolytic product has good consistency, the terbium and dysprosium of high value element are uniform, the production cost is reduced by about 20%, the neodymium iron boron material produced by the process has good quality and strong performance, and the carbon emission of the electrolytic process is reduced by about 20%. Terbium is a valence element and is not suitable for electrolysis alone. The terbium yield of the invention is improved by about 1.5 percent relative to the reduction process. The carbon emission is reduced by about 25% from separation of rare earth elements to electrolysis to obtain rare earth alloys.
The rare earth electrolysis process saves about 16% of electricity consumption compared with the comparative example. The invention effectively reduces the calcium in the rare earth waste from entering the rare earth oxide, stabilizes the electrolysis system under the conditions of not changing the existing equipment and electrolysis system for producing rare earth metal or alloy, the control method thereof and the like, and obtains the advantages of easy control of the electrolysis production process, high yield, low power consumption, good quality and the like of the electrolysis of the rare earth raw material, thereby improving the current efficiency. The neodymium iron boron material produced by the process has good quality and strong performance, and reduces the production cost.
Examples ten
The neodymium iron boron waste (the components are shown in Table I) is roasted at 500-700 ℃, the oxidation rate of the roasting material is about 95%, a second rare earth oxide (CaO content is 0.033%) and a rare earth fluoride (CaO content is 0.030%) are prepared according to the fifth embodiment and the eighth embodiment respectively, the rare earth alloy is prepared according to the electrolysis process described in the first comparative embodiment, the average power consumption of the obtained rare earth alloy is 7.5kwh/kg, and the calcium content in molten salt in an electrolysis furnace for producing about 4000kg of rare earth metal in total reaches 0.34%. The molten salt can be continuously used for producing rare earth alloy, slag amount in an electrolytic furnace is not increased, raw material, fluoride, oxide and rare earth alloy detection data and electrolytic yield of each rare earth element are shown in Table I.
Example eleven
This example is substantially the same as comparative example one except that the crushed material of example ten was added to an ammonium phosphate solution as a calcium-fixing agent, stirred, filtered and washed, and then leached with hydrochloric acid to obtain a rare earth-containing solution. The remainder being identical. The CaO content of the obtained first rare earth oxide was 0.30%. The related parameters are shown in a column. Indicating that some of the elemental calcium in the ground material was not leached by the hydrochloric acid.
Example twelve
Leaching neodymium iron boron waste materials with nitric acid to obtain rare earth feed liquid, adjusting the pH value of the rare earth-containing solution to be more than or equal to 3.2 by ammonia water, filtering to remove ferric hydroxide and acid insoluble residues, washing, combining filtrate and washing liquid to obtain rare earth-containing solution, continuously adding a proper amount of ammonia water, and controlling the final pH value to be 9-10 to obtain rare earth hydroxide. Firing the rare earth hydroxide to obtain a second rare earth oxide (CaO content of 0.034%). The relevant parameters are detailed in the following table one. It can be seen that most of the calcium element in the neodymium iron boron waste has been removed.
Example thirteen
And (3) regulating the rare earth feed liquid in the twelfth embodiment to be about pH3.5 or more by using ammonia water, filtering to remove ferric hydroxide and acid insoluble residues, combining filtrate and washing liquid to obtain the rare earth solution, adding sodium hydroxide solution to prepare rare earth hydroxide, and controlling the end point pH to be about 9. The remainder being identical. The CaO content of the obtained first rare earth oxide was 0.056%. The related parameters are shown in a column. It is shown that other alkaline solutions can also remove most of the calcium element in the presence of ammonium ions.
Examples fourteen
This example is basically the same as the twelve example except that the ammonia water is replaced with a mixed solution of ammonium chloride and sodium hydroxide. The remainder being identical. The CaO content of the obtained second rare earth oxide was 0.046%. The related parameters are shown in a column.
Example fifteen
The first rare earth oxide of example thirteen was washed with an ammonium nitrate solution to obtain a second rare earth oxide (CaO content 0.044%). The relevant parameters are detailed in the following table one.
Examples sixteen
And (3) after the rare earth hydroxide in the twelve-stage embodiment is acid-dissolved, adding a proper amount of sodium bicarbonate solution to obtain rare earth carbonate. Firing the rare earth carbonate to obtain a second rare earth oxide (CaO content of 0.025%). The relevant parameters are respectively detailed in the sequence number columns of the following table. The second rare earth oxide obtained by the secondary acid dissolution of the rare earth hydroxide has lower CaO content.
Example seventeen
And adding a proper amount of mixed solution of potassium oxalate and ammonium oxalate into the rare earth hydroxide in the twelve-stage reaction to obtain rare earth oxalate. Firing the rare earth oxalate to obtain a second rare earth oxide (CaO content of 0.015%). The proper amount refers to a little more oxalic acid radical than chemical dosage so as to ensure the yield of rare earth elements. The relevant parameters are respectively detailed in the sequence number columns of the following table.
Example eighteen
And (3) adding acid to dissolve the rare earth hydroxide in the twelve-stage embodiment, and adding a proper amount of ammonium oxalate solution to obtain rare earth oxalate. Firing the rare earth oxalate to obtain a second rare earth oxide (CaO content is less than 0.010%). The relevant parameters are detailed in the following table one.
Examples nineteenth
Will contain CaO1.8wt% and Sm on dry basis 2 O 3 26.72％、Co 2 O 3 Roasting 42.17% samarium cobalt waste material at 1050 ℃ to reach an oxidation rate of 68%, and completely passing through a 300-mesh sieve after grinding. Leaching with acid, adjusting pH to 5.0-5.5, and filtering to remove residue to obtain feed liquid containing rare earth and cobalt. Adding proper ammonia water, controlling the pH value of the end point to 9-10, and obtaining the mixed hydroxide of rare earth and cobalt. Dissolving mixed hydroxide of rare earth and cobalt by acid, and obtaining metallic cobalt by adopting a wet method cobalt electrowinning technology. And (3) carrying out oxalic acid precipitation on the residual solution to obtain samarium oxalate, and burning to obtain samarium oxide (CaO content is less than 0.01%). And then the metal samarium is prepared by a thermal reduction process. Can be further prepared into samarium cobalt alloy and samarium cobalt magnetic material.
Example twenty
Rare earth scrap (see Table I for details) was calcined at 500-700℃ with an oxidation rate of about 80% for the calcined material, and a second rare earth oxide (CaO content of 0.047%) and a rare earth fluoride (CaO content of 0.038%) were prepared according to example five and example eight, respectively, and a rare earth alloy was prepared according to the electrolytic process described in comparative example one. Raw materials, rare earth alloy detection data and the electrolysis yield of each rare earth element are shown in the table I.
Example twenty-one
The rare earth waste (see table one for details) is roasted at 200-500 ℃ and the oxidation rate is about 85%. Adding ammonium chloride solution, pulverizing to obtain powder, sieving with 400 mesh sieve, and solid-liquid separating to obtain residue. Leaching the filter residue with hydrochloric acid, adjusting the pH value to 3.5, and carrying out solid-liquid separation to obtain rare earth feed liquid. Ammonium bicarbonate is added to obtain rare earth carbonate, and then the rare earth carbonate is burnt to obtain a second rare earth oxide (CaO content is 0.049%).
Examples twenty two
The rare earth carbonate in the twenty-first embodiment is dissolved by adding acid, a proper amount of mixed solution of potassium oxalate and ammonium oxalate is added to obtain rare earth oxalate, and then the rare earth oxalate is burnt to obtain a second rare earth oxide (CaO content is 0.021%). The appropriate amount generally refers to an amount of oxalate slightly above stoichiometry to ensure rare earth yields.
Examples twenty-three
This example is basically the same as the twelve examples except that 10% potassium hydroxide solution is used instead of the whole ammonia water, and the final pH is controlled to 9-10 to obtain the rare earth hydroxide. Firing the rare earth hydroxide to obtain a second rare earth oxide (CaO content of 0.036%). The relevant parameters are detailed in the following table one. It can be seen that most of the calcium element in the neodymium iron boron waste has been removed.
List one
From the first table, the different calcium removing means have obvious effects; along with the reduction of the calcium content in the rare earth oxide, the calcium content in the fused salt is obviously reduced. Meanwhile, the yield of terbium and dysprosium produced by electrolysis is higher than that of a thermal reduction method.
The above are only a few preferred modes of the invention, and it will be appreciated by those skilled in the art that the embodiments of the invention are not limited to the above (e.g. rare earth elements may be leached with acetic acid), and any equivalent modifications made on the basis of the present invention shall fall within the scope of the protection of the invention.
Claims (23)
1. A method for recovering rare earth elements, comprising the steps of:
step one, leaching rare earth waste with acid to obtain a rare earth-containing solution;
adding a precipitant into the rare earth-containing solution to obtain a rare earth compound;
third, firing the rare earth compound to obtain a first rare earth oxide or a second rare earth oxide; the content of calcium element in the first rare earth oxide is 0.05 percent (calculated by oxide) and CaO is less than 0.3 percent (weight), and the content of calcium element in the second rare earth oxide is less than or equal to 0.05 percent (calculated by CaO);
the method also comprises a first calcium removal step, wherein the first calcium removal step is as follows: mixing the rare earth waste with a calcium dissolving agent or calcium fixing agent solution before the first step, and separating liquid;
the calcium dissolving agent is at least one of soluble chloride, nitrate and acetate;
the calcium fixing agent is at least one of soluble oxalate, sulfate and fluoride;
the method also comprises a second decalcification step;
the second decalcification step is that the precipitant is alkaline solution, and the second decalcification step controls the end point pH to be more than 9;
the rare earth waste is at least one of neodymium iron boron waste, samarium cobalt waste and hydrogen storage alloy waste.
2. The method for recovering rare earth elements according to claim 1, wherein the first rare earth oxide is mixed with a calcium-dissolving agent solution to obtain the second rare earth oxide.
3. The method for recovering rare earth element according to claim 1, further comprising a third decalcification step between the second and third steps: mixing rare earth hydroxide with a transforming agent solution to obtain insoluble rare earth salt.
4. The method for recovering rare earth element according to claim 3, wherein the transformation agent is at least one of oxalic acid solution, oxalate solution, potassium carbonate solution, potassium bicarbonate solution, sodium carbonate solution, sodium bicarbonate solution, and ammonium bicarbonate solution.
5. The method for recovering a rare earth element according to claim 1, wherein the acid is hydrochloric acid or nitric acid.
6. The method for recovering rare earth elements according to claim 1, further comprising a step of roasting rare earth waste before the first decalcification step or after the first decalcification step.
7. The method for recovering rare earth element according to claim 6, wherein a firing temperature in the firing step is 1000 ℃ or less.
8. The method for recovering rare earth element according to claim 7, wherein the firing temperature in the firing step is 200 ℃ to 900 ℃.
9. The method for recovering rare earth element according to claim 8, wherein the firing temperature is 200 ℃ to 700 ℃.
10. The method for recovering rare earth elements according to claim 9, wherein the oxidation rate of the rare earth waste after roasting is not less than 70%.
11. The method for recovering rare earth elements according to claim 10, wherein the oxidation rate of the rare earth waste after roasting is not less than 95%.
12. The method for recovering rare earth elements according to claim 6, further comprising a pulverizing step of pulverizing the calcined rare earth waste to pass through a 250 mesh sieve in its entirety.
13. The method for recovering rare earth elements according to claim 1, further comprising the step of adjusting the pH of the rare earth-containing solution to 3.5 and filtering to remove iron hydroxide before the second step.
14. The method according to claim 1, wherein the chloride is at least one of sodium chloride, potassium chloride, lithium chloride, barium chloride, and ammonium chloride, the nitrate is at least one of sodium nitrate, potassium nitrate, lithium nitrate, barium nitrate, and ammonium nitrate, the acetate is at least one of sodium acetate, potassium acetate, and ammonium acetate, the oxalate is at least one of sodium oxalate, potassium oxalate, and ammonium oxalate, the sulfate is at least one of sodium sulfate, potassium sulfate, ammonium sulfate, sodium bisulfate, potassium bisulfate, and ammonium bisulfate, and the fluoride is at least one of sodium fluoride, potassium fluoride, ammonium fluoride, sodium bifluoride, and ammonium bifluoride.
15. The method for recovering rare earth elements according to claim 1, wherein the calcium-dissolving agent further contains an appropriate amount of an acid.
16. The method for recovering a rare earth element according to any one of claims 1 to 15, further comprising: carrying out molten salt electrolysis on the electrolysis raw material to obtain rare earth metal or rare earth alloy and rare earth element and non-rare earth element alloy, wherein the rare earth alloy is an alloy of different rare earth elements; the electrolytic feed includes a second rare earth oxide.
17. The method of claim 16, wherein the electrolytic feed further comprises a rare earth fluoride, the rare earth fluoride being produced from the rare earth compound obtained in step two, or from step three to obtain a first rare earth oxide, or from at least one of the second rare earth oxides.
18. The method for recovering rare earth elements according to claim 16, wherein the rare earth metal is prepared as a rare earth alloy.
19. The method for recovering a rare earth element according to claim 18, wherein the rare earth alloy is praseodymium neodymium terbium dysprosium alloy.
20. The method for recovering rare earth elements according to claim 16, wherein the rare earth metal or rare earth alloy, and the alloy of rare earth element and non-rare earth element are prepared as neodymium-iron-boron alloy or samarium-cobalt alloy, or hydrogen storage alloy.
21. The method of claim 20, wherein the neodymium-iron-boron alloy is prepared as a neodymium-iron-boron magnet.
22. The method for recovering rare earth elements according to claim 1, wherein the alkaline solution comprises at least one of sodium hydroxide and aqueous ammonia.
23. The method for recovering a rare earth element according to claim 22, wherein the alkaline solution further comprises ammonium bicarbonate.
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