Method for short-process recovery of rare earth in rare earth molten salt slag

Abstract

The invention belongs to the technical field of rare earth secondary resource recycling and reusing, and particularly relates to a short-process method for recycling rare earth in rare earth molten salt slag. According to the method, the rare earth molten salt slag is firstly subjected to crushing and wet grinding treatment, the treated rare earth molten salt slag is roasted to remove fluorine, 99% of fluorine in the rare earth molten salt slag in the roasting process can be recycled to become hydrofluoric acid after being removed, meanwhile, the fluorine-removed rare earth molten salt slag is obtained, and then the rare earth oxide is obtained through the procedures of acid leaching, precipitation and firing. And the rare earth recovery rate is greater than 98%. According to the method provided by the invention, the rare earth and the fluorine in the rare earth molten salt slag can be separated through a simple roasting process under the condition that other materials are not added, the purpose of separating the rare earth from the fluorine is achieved, resource recycling of the rare earth and the fluorine is realized, the technological process is simple, and industrial production is easy.

Description

Technical Field

[0001] The invention belongs to the technical field of rare earth secondary resource recovery and reuse, and specifically relates to a method for recovering rare earths from rare earth molten salt slag in a short process, while fluorine element can also be recovered. Background Art

[0002] In the current industrial production of rare earth metals, molten salt electrolysis and calcium thermal reduction are mainly used. Molten salt electrolysis can produce rare earth metals and alloys without reducing agents, and has the advantages of simple process flow, easy operation, and low production and operation costs. It is used in industrial continuous production. However, the production of rare earth metals by rare earth molten salt electrolysis will inevitably produce rare earth molten salt slag. In recent years, the rare earth industry has attracted much attention due to its strategic position. Therefore, the recovery and utilization of rare earth resources from rare earth molten salt slag has increasingly attracted the attention of the rare earth industry. Since the rare earths in rare earth molten salt slag mainly exist as acid-insoluble rare earth fluorides and rare earth fluoride oxides, the key issue in recovering rare earths from rare earth molten salt slag is how to reconstruct the physical phases of rare earth fluorides and rare earth fluoride oxides to achieve a complete separation of rare earths and fluorine, so as to achieve the purpose of recovering rare earths.

[0003] The current research mainly recovers the rare earth elements by adding different substances such as acid, alkali, and salt combined with high-temperature roasting. Ma Ying et al. (Study on the decomposition of Baotou Rare Earth concentrate) used high-temperature enhanced concentrated sulfuric acid roasting to realize the conversion of rare earth fluoride into hydrogen fluoride and rare earth sulfate, thereby achieving the purpose of separating rare earth from fluorine. The sodium hydroxide roasting-acid leaching method proposed by Lu Yingbing (CN105256156A) et al. uses sodium hydroxide as a fluorine-fixing agent, and the rare earth fluoride is roasted to rare earth hydroxide, and then the difference in solubility between sodium fluoride and rare earth hydroxide is used to achieve the separation of rare earth and fluorine. Tong Zhifang (CN114457238 B) et al. used aluminum sulfate and calcium oxide complexing to roast rare earth molten salt slag, converting rare earth fluoride into rare earth oxide, and fluorine into calcium fluoride, and the separation of rare earth and fluorine was achieved by acid leaching. Summary of the invention

[0004] To this end, the present invention provides a method for recovering rare earths from rare earth molten salt slag in a short process. After the rare earth molten salt slag is crushed and wet-milled, it is simply roasted without adding other materials, and 99% of the fluorine in the rare earth molten salt slag can be removed in the form of hydrogen fluoride and then absorbed by an aqueous solution to become hydrofluoric acid, thereby realizing the separation of rare earth and fluorine, and achieving the purpose of separating rare earth and fluorine. The rare earth molten salt slag after fluorine removal is then acid-leached, precipitated, and calcined to obtain rare earth oxides. The present invention can recycle fluorine and rare earth elements in the rare earth molten salt slag, reducing resource waste and production costs.

[0005] The present invention provides a method for recovering rare earths from rare earth molten salt slag by a short process, comprising:

[0006] Step 1: The lump of rare earth molten salt slag is crushed into powder;

[0007] Step 2: Mix the powder obtained in step 1 with pure water, and then ball-mill in a ball mill. After ball milling, the rare earth molten salt slag is screened and filtered to obtain an oversize and an undersize. The oversize is returned to step 1 for further crushing. The undersize is allowed to stand and filtered to obtain a supernatant and water-leached residue. The water-leached residue is dried to obtain the treated rare earth molten salt slag, and the supernatant is returned to the ball mill for recycling;

[0008] Step 3: The treated rare earth molten salt obtained in step 2 is placed in a crucible and put into a tubular furnace for calcination reaction under high temperature conditions. Air is introduced into one end of the tubular furnace and the other end is connected to an aqueous solution that absorbs hydrogen fluoride gas. After the reaction, defluorinated rare earth molten salt slag and hydrofluoric acid solution are obtained.

[0009] Step 4: The rare earth molten salt slag obtained in step 3 after defluorination is subjected to acid leaching to obtain a rare earth-containing liquid, a precipitant is added to the rare earth liquid for precipitation, rare earth salt precipitate is obtained by filtration, and rare earth oxide is obtained after calcination at 850-1050° C.;

[0010] Step 5: The hydrofluoric acid solution obtained in step 3 can be further treated and recycled.

[0011] Preferably, the rare earth molten salt slag in step one includes one or more of praseodymium-neodymium molten salt slag, gadolinium-iron slag, holmium-iron slag, terbium-calcium slag and dysprosium-calcium slag.

[0012] Preferably, the composition of the rare earth molten salt slag in step 1 includes Fe: 0.1-40%, F: 5%-50%, RE: 1%-60%.

[0013] Preferably, in step 2, the mass ratio of rare earth molten salt slag powder to pure water is 1:1-10, and the ball milling speed is 100-500 r / min.

[0014] Preferably, in step 2, the temperature for drying the water-soaked residue is preferably 100-120° C.; and the drying time is preferably 180-480 min.

[0015] Preferably, in step three, the rare earth molten salt slag is calcined at a reaction temperature of 700 to 1200° C., and the calcination reaction time is 60 to 360 min.

[0016] Preferably, in step 4, the ratio of the rare earth molten salt slag after defluorination to the acid leaching solution is 1g:1-20mL, the concentration of the acid leaching solution is 4-12mol / L, and the acid leaching solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

[0017] Preferably, in step 4, the temperature of acid leaching of the rare earth molten salt slag after defluorination is 80-180°C, the acid leaching time is 60-360min, and the stirring speed is 100-400r / min; the rare earth concentration in the rare earth liquid is 20-200g / L.

[0018] Preferably, in step 4, the mass ratio of rare earth to precipitant in the feed solution is 1:1-3; the precipitant is one or more of oxalic acid solution, sodium carbonate solution, and ammonium carbonate solution.

[0019] Preferably, in step 4, the burning time is 0.5 to 3 hours.

[0020] The beneficial effects achieved by the present invention are as follows:

[0021] (1) The present invention utilizes the components of rare earth molten salt slag through a simple roasting process without adding other materials. 99% of the fluorine in the rare earth molten salt slag is removed in the form of hydrogen fluoride and can be recovered through an aqueous solution, thereby realizing the separation of rare earth and fluorine in the rare earth molten salt slag. The process is simple and easy to operate. Compared with the conventional method of adding acid, alkali, and salt combined with high-temperature roasting to recover rare earth from rare earth molten salt slag, the present invention significantly reduces the material input cost.

[0022] (2) The present invention realizes the recovery of rare earth and fluorine resources in rare earth molten salt slag, and the rare earth recovery rate can reach more than 98%, and 99% of fluorine can be recovered as resources. The process technology route of the present invention is short, and no fluorine-containing wastewater is generated, so as to realize the green and efficient recovery of rare earth molten salt slag, and provide a new method for the recovery of rare earth elements and fluorine in rare earth molten salt slag. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The present invention provides a process flow chart for a method for recovering rare earths from rare earth molten salt slag in a short process. DETAILED DESCRIPTION

[0024] The present invention provides a method for recovering rare earths from rare earth molten salt slag in a short process, comprising the following steps:

[0025] Step 1: The lump of rare earth molten salt slag is crushed into powder;

[0026] Step 2: Mix the powder obtained in step 1 with pure water, and then ball-mill in a ball mill. After ball milling, the rare earth molten salt slag is screened and filtered to obtain an oversize and an undersize. The oversize is returned to step 1 for further crushing. The undersize is allowed to stand and filtered to obtain a supernatant and water-leached residue. The water-leached residue is dried to obtain the treated rare earth molten salt slag, and the supernatant is returned to the ball mill for recycling;

[0027] Step 3: The treated rare earth molten salt obtained in step 2 is placed in a crucible and put into a tubular furnace for calcination reaction under high temperature conditions. Air is introduced into one end of the tubular furnace and the other end is connected to an aqueous solution that absorbs hydrogen fluoride gas. After the reaction, defluorinated rare earth molten salt slag and hydrofluoric acid solution are obtained.

[0028] Step 4: The rare earth molten salt slag obtained in step 3 after defluorination is subjected to acid leaching to obtain a rare earth-containing liquid, a precipitant is added to the rare earth liquid for precipitation, rare earth salt precipitate is obtained by filtration, and rare earth oxide is obtained after calcination at 850-1050° C.;

[0029] Step 5: The hydrofluoric acid solution obtained in step 3 can be further treated and recycled.

[0030] In the present invention, the mass percentage of iron in the rare earth molten salt slag is preferably 0.1-39%; the mass percentage of fluorine in the rare earth molten salt slag is preferably 5-48%; the mass percentage of rare earth in the rare earth molten salt slag is preferably 1-59%.

[0031] In the present invention, the blocky rare earth molten salt slag is crushed by a jaw crusher, and the ball milling is performed by a wet rolling ball mill.

[0032] In the present invention, the mass ratio of the rare earth molten salt slag to pure water is preferably 1:1 to 8. In the present invention, the mixing is preferably performed under stirring, and the stirring speed is preferably 200 to 400 r / min.

[0033] After ball milling, a rare earth molten salt slag aqueous solution is obtained. The present invention screens and filters the rare earth molten salt slag aqueous solution to obtain an oversize and an undersize. The oversize is returned to step one for further crushing. The undersize is allowed to stand and filtered to obtain a supernatant and water-leached residue. The water-leached residue is then dried to obtain treated rare earth molten salt slag. The supernatant is returned to the ball mill for further use, thereby realizing the recycling of water.

[0034] In the present invention, the drying temperature is preferably 100 to 105° C., and the drying time is preferably 240 to 420 min.

[0035] In the present invention, the calcination reaction temperature of the rare earth molten salt slag is preferably 800-1000° C., and the calcination reaction time is preferably 60-180 min.

[0036] In the present invention, the ratio of the rare earth molten salt slag after defluorination to the acid leaching solution is preferably 1g:1.5-18.5mL, the concentration of the acid leaching solution is preferably 6-12mol / L, and the acid leaching solution is hydrochloric acid.

[0037] In the present invention, the temperature of acid leaching of the rare earth molten salt slag after defluorination is 80-160°C, the acid leaching time is preferably 60-180min, and the stirring speed is preferably 100-400r / min; the rare earth concentration in the rare earth liquid is preferably 20-100g / L.

[0038] In the present invention, the mass ratio of rare earth to precipitant in the feed solution is 1:1-2; and the precipitant is oxalic acid.

[0039] In the present invention, the burning time is preferably 0.5 to 2 hours.

[0040] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0041] Example 1

[0042] A method for recovering rare earths from rare earth molten salt slag in a short process. Figure 1 As shown, the following steps are included:

[0043] S1. Take 100g of a rare earth molten salt slag and crush it with a jaw crusher. After crushing, put it in the ball mill of a ball mill, then add 100mL of water, set the ball mill speed to 200r / min, and the ball milling time to 6h. After ball milling, sieve it, crush the sieve material and continue to ball mill it until it passes the sieve. Let the sieve material stand and then filter it to obtain supernatant and water-leached residue. Dry the water-leached residue at 105℃ for 240min. After drying, there are 98.6g of water-leached residue, and the supernatant is returned to the next ball milling for continued use.

[0044] S2. Weigh 50 g of the rare earth molten salt slag obtained in S1, which contains 38.23% rare earth oxides, 0.12% iron and 10.94% fluorine. Place the above rare earth molten salt slag in a tubular furnace and roast it at 1000°C for 3 hours. After roasting, the mass of the rare earth molten salt slag is 23.1 g, the rare earth oxide content is 82.56%, the fluorine content is 3.14%, and the fluorine removal rate is 86.74%.

[0045] S3, weigh 10g of the rare earth molten salt slag obtained in S2, add 10mol / L hydrochloric acid solution for acid leaching, the solid-liquid ratio of the rare earth molten salt slag to the hydrochloric acid solution is 1g:1.8mL, the reaction temperature is 90°C, the reaction time is 3h, and the stirring speed is 300r / min. After the reaction is completed, the leachate and acid leaching residue are obtained by filtering, the acid leaching residue is 1.6g, and the rare earth leaching rate is 95.59%;

[0046] S4. Add oxalic acid solution to the leaching solution obtained in S3, maintain the precipitation temperature at 60° C., and filter to obtain rare earth oxalate; calcine the obtained rare earth oxalate at 950° C. for 3 h to obtain rare earth oxide.

[0047] Example 2

[0048] A method for recovering rare earths from rare earth molten salt slag in a short process. Figure 1 As shown, the following steps are included:

[0049] S1. Take 500g of a rare earth molten salt slag and crush it with a jaw crusher. After crushing, put it in the ball mill of a ball mill, then add 1000mL of water, set the ball mill speed to 200r / min, and the ball milling time to 6h. After ball milling, sieve it, crush the sieve material and continue to ball mill it until it passes the sieve. Let the sieve material stand and then filter it to obtain supernatant and water-leached residue. Dry the water-leached residue at 105℃ for 240min. After drying, there are 496.8g in the water-leached residue, and the supernatant is returned to the next ball milling for continued use.

[0050] S2. Weigh 100 g of the rare earth molten salt slag obtained in S1, which contains 38.18% rare earth oxides, 6.60% iron and 12.54% fluorine. Place the above rare earth molten salt slag in a tubular furnace and roast it at 1000°C for 3 hours. After roasting, the mass of the rare earth molten salt slag is 57.0 g, the rare earth oxide content is 66.76%, the fluorine content is 0.16%, and the fluorine removal rate is 99.27%.

[0051] S3, weigh 10g of the rare earth molten salt slag obtained in S2, add 12mol / L hydrochloric acid solution for acid leaching, the solid-liquid ratio of the rare earth molten salt slag to the hydrochloric acid solution is 1g:2mL, the reaction temperature is 120°C, the reaction time is 3h, and the stirring speed is 300r / min. After the reaction is completed, the leachate and acid leaching residue are obtained by filtering, the acid leaching residue is 1.1g, and the rare earth leaching rate is 97.67%;

[0052] S4. Add oxalic acid solution to the leaching solution obtained in S3, maintain the precipitation temperature at 60° C., and filter to obtain rare earth oxalate; calcine the obtained rare earth oxalate at 950° C. for 3 h to obtain rare earth oxide.

[0053] Example 3

[0054] A method for recovering rare earths from rare earth molten salt slag in a short process. Figure 1 As shown, the following steps are included:

[0055] S1. Take 100g of a rare earth molten salt slag and crush it with a jaw crusher. After crushing, put it in the ball mill of a ball mill, then add 100mL of water, set the ball mill speed to 200r / min, and the ball milling time to 6h. After ball milling, sieve it, crush the sieve material and continue to ball mill it until it passes the sieve. Let the sieve material stand and then filter it to obtain supernatant and water-leached residue. Dry the water-leached residue at 105℃ for 240min. After drying, there is 98.4g in the water-leached residue, and the supernatant is returned to the next ball milling for continued use.

[0056] S2. Weigh 50 g of the rare earth molten salt slag obtained in S1, which contains 38.18% rare earth oxides, 6.60% iron and 12.54% fluorine. Place the above rare earth molten salt slag in a tubular furnace and roast it at 800°C for 3 hours. After roasting, the mass of the rare earth molten salt slag is 29 g, the rare earth oxide content is 65.64%, the fluorine content is 2.14%, and the fluorine removal rate is 90.1%.

[0057] S3, weigh 10g of the rare earth molten salt slag obtained in S2, add 12mol / L hydrochloric acid solution for acid leaching, the solid-liquid ratio of the rare earth molten salt slag to the hydrochloric acid solution is 1g:3mL, the reaction temperature is 120°C, the reaction time is 3h, and the stirring speed is 300r / min. After the reaction is completed, the leachate and acid leaching residue are obtained by filtering, the acid leaching residue is 1.5g, and the rare earth leaching rate is 97.87%;

[0058] S4. Add oxalic acid solution to the leaching solution obtained in S3, maintain the precipitation temperature at 60° C., and filter to obtain rare earth oxalate; calcine the obtained rare earth oxalate at 950° C. for 3 h to obtain rare earth oxide.

[0059] Example 4

[0060] A method for recovering rare earths from rare earth molten salt slag in a short process. Figure 1 As shown, the following steps are included:

[0061] S1. Take 1500g of a rare earth molten salt slag and crush it with a jaw crusher. After crushing, put it in the ball mill of a ball mill, then add 4000mL of water, set the ball mill speed to 200r / min, and the ball milling time to 6h. After ball milling, sieve it, crush the sieve material and continue to ball mill it until it passes the sieve. Let the sieve material stand and then filter it to obtain supernatant and water-leached residue. Dry the water-leached residue at 105℃ for 240min. After drying, there are 1495.2g of water-leached residue, and the supernatant is returned to the next ball milling for continued use.

[0062] S2. Weigh 500 g of the rare earth molten salt slag obtained in S1, which contains 43.96% rare earth oxides, 16.44% iron and 13.42% fluorine. Place the above rare earth molten salt slag in a tubular furnace and roast it at 1000°C for 3 hours. After roasting, the mass of the rare earth molten salt slag is 415 g, the rare earth oxide content is 52.78%, the fluorine content is 0.034%, and the fluorine removal rate is 99.79%.

[0063] S3, weigh 100g of the rare earth molten salt slag obtained in S2, add 12mol / L hydrochloric acid solution for acid leaching, the solid-liquid ratio of the rare earth molten salt slag to the hydrochloric acid solution is 1g:3mL, the reaction temperature is 180°C, the reaction time is 3h, and the stirring speed is 300r / min. After the reaction is completed, the leachate and acid leaching residue are obtained by filtering, the acid leaching residue is 8g, and the rare earth leaching rate is 99.96%;

[0064] S4. Add oxalic acid solution to the leaching solution obtained in S3, maintain the precipitation temperature at 60° C., and filter to obtain rare earth oxalate; calcine the obtained rare earth oxalate at 950° C. for 3 h to obtain rare earth oxide.

[0065] Example 5

[0066] A method for recovering rare earths from rare earth molten salt slag in a short process. Figure 1 As shown, the following steps are included:

[0067] S1. Take 1000g of a rare earth molten salt slag and crush it with a jaw crusher. After crushing, put it in the ball mill of a ball mill, then add 2000mL of water, set the ball mill speed to 200r / min, and the ball milling time to 6h. After ball milling, sieve it, crush the sieve material and continue to ball mill it until it passes the sieve. Let the sieve material stand and then filter it to obtain supernatant and water-leached residue. Dry the water-leached residue at 105℃ for 240min. After drying, there are 995.4g in the water-leached residue, and the supernatant is returned to the next ball milling for continued use.

[0068] S2. Weigh 100 g of the rare earth molten salt slag obtained in S1, which contains 37.34% rare earth oxides, 10.43% iron and 10.48% fluorine. Place the above rare earth molten salt slag in a tubular furnace and roast it at 1000°C for 3 hours. After roasting, the mass of the rare earth molten salt slag is 63.7 g, the rare earth oxide content is 58.36%, the fluorine content is 0.09%, and the fluorine removal rate is 99.45%.

[0069] S3, weigh 50g of the rare earth molten salt slag obtained in S2, add 10mol / L hydrochloric acid solution for acid leaching, the solid-liquid ratio of the rare earth molten salt slag to the hydrochloric acid solution is 1g:2mL, the reaction temperature is 120°C, the reaction time is 3h, and the stirring speed is 300r / min. After the reaction is completed, the leachate and acid leaching residue are obtained by filtering, the acid leaching residue is 9.2g, and the rare earth leaching rate is 98.06%;

[0070] S4. Add oxalic acid solution to the leaching solution obtained in S3, maintain the precipitation temperature at 60° C., and filter to obtain rare earth oxalate; calcine the obtained rare earth oxalate at 950° C. for 3 h to obtain rare earth oxide.

[0071] It can be seen from the above embodiments that by controlling the parameters of the roasting process, the fluorine removal rate can reach more than 99%, and by controlling the parameters of the acid leaching process, the rare earth leaching rate can reach more than 98%.

Claims

1. A method for recovering rare earths from rare earth molten salt slag by a short process, characterized in that: include: Step 1: The lump of rare earth molten salt slag is crushed into powder; Step 2: Mix the powder obtained in step 1 with pure water, and then ball-mill in a ball mill. After ball milling, the rare earth molten salt slag is screened and filtered to obtain an oversize and an undersize. The oversize is returned to step 1 for further crushing. The undersize is allowed to stand and filtered to obtain a supernatant and water-leached residue. The water-leached residue is dried to obtain the treated rare earth molten salt slag, and the supernatant is returned to the ball mill for recycling; Step 3: The rare earth molten salt obtained in step 2 is placed in a crucible and put into a tubular furnace for roasting and defluorination reaction under high temperature conditions. Air is introduced into one end of the tubular furnace, and an aqueous solution for absorbing hydrogen fluoride gas is connected to the other end. After the reaction, rare earth molten salt slag and hydrofluoric acid aqueous solution after defluorination are obtained; Step 4: The rare earth molten salt slag obtained in step 3 after defluorination is subjected to acid leaching to obtain a rare earth-containing liquid, a precipitant is added to the rare earth liquid for precipitation, rare earth salt precipitate is obtained by filtration, and rare earth oxide is obtained after calcination at 850-1050° C.; Step 5: The hydrofluoric acid aqueous solution obtained in step 3 is further treated and recycled.

2. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: The rare earth molten salt slag in step 1 includes one or more of praseodymium-neodymium molten salt slag, gadolinium-iron slag, holmium-iron slag, terbium-calcium slag, and dysprosium-calcium slag.

3. A method for recovering rare earths from rare earth molten salt slag by a short process according to claim 1 or 2, characterized in that: The composition of the rare earth molten salt slag in the step 1 includes Fe: 0.1-40%, F: 5%-50%, RE: 1%-60%.

4. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 2, the mass ratio of rare earth molten salt slag powder to pure water is 1:1-10, and the ball milling speed is 100-500 r / min.

5. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 2, the temperature of drying the water-soaked residue is 100-120° C. and the drying time is 180-480 min.

6. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step three, the rare earth molten salt slag is calcined at a temperature of 700 to 1200° C. and for a time of 60 to 360 minutes.

7. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 4, the ratio of the rare earth molten salt slag after defluorination to the acid leaching solution is 1g:1-20mL, the concentration of the acid leaching solution is 4-12mol / L, and the acid leaching solution is one or more of hydrochloric acid, sulfuric acid, and nitric acid.

8. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 4, the temperature of acid leaching of the rare earth molten salt slag after defluorination is 80-180°C, the acid leaching time is 60-360min, and the stirring speed is 100-400r / min; the rare earth concentration in the rare earth liquid is 20-200g / L.

9. The method for recovering rare earth from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 4, the mass ratio of rare earth to precipitant in the feed solution is 1:1-3; the precipitant is one or more of oxalic acid solution, sodium carbonate solution, and ammonium carbonate solution.

10. The method for recovering rare earths from rare earth molten salt slag by a short process according to claim 1, characterized in that: In step 4, the burning time is 0.5 to 3 hours.

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