A method for recovering gallium from waste neodymium-iron-boron magnets

Abstract

The application provides a method for recovering gallium from waste neodymium-iron-boron magnets, comprising the following steps: S1, adding waste neodymium-iron-boron magnet powder into a sodium hydroxide solution and fully reacting in a high-pressure reaction kettle; S2, placing a gallium-containing solution obtained after the reaction into a resin adsorption tower for adsorption; S3, washing and resolving the resin adsorbed with gallium, then performing falling-film high-efficiency evaporation concentration on the obtained gallium-containing solution, and then freezing and crystallizing the obtained concentrated solution and filtering to obtain a gallium-rich solution; and S4, performing oxidation impurity removal and purification on the gallium-rich solution, and finally sending the purified gallium-rich solution into an electrolytic cell for electrolysis and recovering metal gallium. The preparation process is simple and easy to operate, and the comprehensive recovery rate of gallium is above 85%.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste recycling, and particularly relates to a method for recovering gallium from waste neodymium-iron-boron magnets. BACKGROUND

[0002] Gallium is a metal element with different uses. For example, due to the low melting point (302.98 K) of gallium, it is used as part of a low melting alloy. Gallium forms semiconductor compounds with some elements, such as gallium nitride and gallium arsenide. Gallium nitride is used as a single crystal in electronic components. Studies have also shown that compounds of gallium have potential therapeutic activity against certain cancers and infectious microorganisms. The concentration of gallium in the earth's crust is between 5-15 mg / kg. It has some common properties with iron (III), such as ionic radius, ionization potential and electron affinity, so gallium is also applied in magnet materials.

[0003] Most of the gallium is a by-product recovered from bauxite and produced from zinc smelting slag, in addition, some Ga also comes from coal fly ash. In terms of current technical trends, gallium is irreplaceable for other materials and metals, and the unique performance, limited natural resources and growing consumer demand will lead to a substantial increase in the demand for gallium, bringing great challenges to the supply of gallium from primary or associated ores. In order to ensure stable supply, the recovery of gallium from waste magnets, waste LEDs and waste electronic and electrical equipment (WEEE) and other waste products has become the focus of attention.

[0004] Nd2Fe 14 Nd-Fe-B permanent magnets usually contain about 1% boron, 60% iron and about 30% rare earth elements, and a small amount of cobalt, aluminum, copper, gallium and other elements according to the intended application field. While 20%-30% of the alloy of Nd-Fe-B permanent magnets becomes waste during processing and disposal. In addition, a large amount and increasing amount of NdFeB magnet waste is generated every year due to the end of service life of permanent magnets. At present, the recovery of neodymium iron boron waste mainly focuses on rare earth metals, iron and other metal elements. However, in addition to containing rare earth metals, iron and other valuable metals, neodymium iron boron waste also contains a small amount of gallium. Although gallium is added as a trace element in neodymium iron boron waste, the current large increase in the production of neodymium iron boron waste makes the recovery and utilization of rare and heavy metal gallium in neodymium iron boron waste have great significance in the development of circular economy, resource utilization and environmental protection. SUMMARY

[0005] The purpose of the present application is to selectively recover gallium from waste neodymium-iron-boron magnets, and further prepare metal gallium by enrichment and electrolysis.

[0006] Specifically, the present application provides a method for recovering gallium from waste neodymium-iron-boron magnets (gallium content of 0.05wt%-0.1wt%), comprising:

[0007] Step S1, the waste Nd-Fe-B magnet powder is added into sodium hydroxide solution and fully reacted in a high-pressure reaction kettle. Through such a reaction, gallium enters the solution as soluble gallate, while iron and rare earths do not react with the alkali and enter the slag, realizing selective extraction of gallium.

[0008] Step S2, the gallium-containing solution obtained after the reaction is put into a resin adsorption tower for adsorption;

[0009] Step S3, after the resin adsorbed with gallium is washed and desorbed, the obtained gallium-containing solution is concentrated by falling film high-efficiency evaporation, then the obtained concentrated solution is frozen crystallized and filtered to obtain a gallium-rich solution;

[0010] Step S4, the gallium-rich solution is subjected to oxidation and impurity removal purification, and finally the purified gallium-rich solution is sent to an electrolytic cell for electrolysis and recovery of metallic gallium.

[0011] Preferably, in step S1, the particle size of the waste Nd-Fe-B magnet powder is below 100 mesh; the solubility of sodium hydroxide is 1-8 mol / L; the liquid-solid ratio of the waste Nd-Fe-B magnet powder to sodium hydroxide is 3-15 mL / g.

[0012] Preferably, the reaction temperature in the high-pressure reaction kettle is 80-180 ℃, the reaction pressure is 0.1 MPa-1 MPa, and the reaction time is 1 h-4 h.

[0013] Preferably, in step S2, the adsorption resin is selected from one or more of LSC600, LSC700, LSC900, and ACD800. By selecting the above resin, strong selective adsorption of gallium can be achieved, avoiding interference with other impurity ions.

[0014] Preferably, in step S2, the flow rate of the gallium-containing solution into the resin adsorption tower is 0.5 m 3 / h-5 m 3 / h, the adsorption temperature of the adsorption tower is 25-80 ℃, and the adsorption time is 2 h-10 h.

[0015] Preferably, in step S3, the washing solution in the resin washing process is a sodium hydroxide solution with a concentration of 1-5 mol / L. Through the washing operation, residual NaAlO2 solution can be removed.

[0016] Preferably, in step S3, the desorbent used in the desorption process is a mixture of sodium hydroxide and sodium sulfide.

[0017] Preferably, in step S3, the concentration of sodium hydroxide used in the desorbent is 1 mol / L-5 mol / L, and the concentration of sodium sulfide is 0.5 mol / L-4 mol / L.

[0018] Preferably, in step S3, the gallium-containing solution is concentrated at least 1 times in the evaporation concentration process, the freezing crystallization temperature is 0-10 DEG C, and the crystallization time is 1-20 h.

[0019] Preferably, in step S4, the oxidant in the impurity removal and purification process by oxidation is hydrogen peroxide.

[0020] Preferably, in step S4, the electrolysis temperature is 25-60 DEG C, the electrolysis voltage is 2-10 V, the electrolysis current density is 300-600 A / m 2 , and the electrolysis time is 2-7 h.

[0021] The technical scheme provided by the embodiment of the present application has at least the following beneficial effects:

[0022] The technical scheme of the present application uses waste Nd-Fe-B magnets as raw materials, and creatively transfers the gallium with low content and difficult to separate in the magnetic powder to the liquid phase by reacting the magnetic powder with sodium hydroxide in an autoclave, and obtains high-purity metal gallium through subsequent purification, enrichment and electrolysis steps. The method is simple, green and environmentally friendly, and can effectively recover the gallium with extremely low content in waste Nd-Fe-B magnets, realizing effective recycling of resources. DETAILED DESCRIPTION

[0023] The technical scheme in the present application will be described below.

[0024] In the embodiments of the present application, the words such as "example", "for example" are used to represent as an example, illustration or description. Any embodiment or design scheme described as "example" in the present application should not be interpreted as more preferred or more advantageous than other embodiments or design schemes. In fact, the word "example" is intended to present the concept in a specific way. In addition, in the embodiments of the present application, the meaning expressed by "and / or" can be both, or can be one of the two.

[0025] In the embodiments of the present application, "image" and "picture" can be used interchangeably at times. It should be pointed out that when the distinction is not emphasized, the meanings expressed are consistent. "The", "corresponding" and "corresponding" can be used interchangeably at times. It should be pointed out that when the distinction is not emphasized, the meanings expressed are consistent.

[0026] In the embodiments of the present application, sometimes the subscript such as W1 may be mistakenly used in the form of non-subscript such as W1. When the distinction is not emphasized, the meanings expressed are consistent.

[0027] The specific embodiments are listed below for detailed description.

[0028] Embodiment 1:

[0029] Take 10 kg of waste Nd-Fe-B magnets, with a gallium content of 0.09% in the magnets.

[0030] First, the waste Nd-Fe-B magnets are crushed and sieved to ensure that the particle size is below 100 mesh.

[0031] Gallium extraction: the concentration of sodium hydroxide is 4.5 mol / L. The liquid-solid ratio of the waste magnetic powder and sodium hydroxide is 5 mL / g. The reaction temperature in the autoclave is 140 ℃, the reaction pressure is 0.2 Mpa, and the reaction time is 2 h. Take 10 kg of magnetic powder and add it to a 250 L autoclave, then add 50 L of sodium hydroxide solution with a concentration of 4.5 mol / L. Heat to 130 ℃, react at a pressure of 0.3 Mpa for 2 h, and then separate the solid and liquid to obtain a gallium-containing solution. The gallium extraction is 86.5%.

[0032] Gallium enrichment: the flow rate of the gallium-containing solution into the adsorption tower is 1 m 3 / h. The adsorption temperature of the adsorption tower is 45℃, and the adsorption time is 10 h. The gallium-containing filtrate is passed through the adsorption tower filled with adsorbent LSC700 at a flow rate of 1 m 3 / h, and adsorbed at 45℃ for 10 h.

[0033] Washing and elution: the washing liquid is a sodium hydroxide solution with a concentration of 2.5 mol / L. The eluent is a mixture of Na2S and NaOH, with a selected Na2S concentration of 1 mol / L and a NaOH concentration of 2 mol / L. After adsorption saturation, the resin is washed with 2.5 mol / L NaOH solution to remove residual aluminate. Then the resin is eluted with a mixture of Na2S and NaOH, and after the end of the elution, a high-purity gallium-rich solution is obtained.

[0034] Secondary gallium enrichment: the high-purity gallium solution is added to a falling film evaporator and concentrated at least 1 times. After natural cooling and freezing crystallization, sodium sulfide crystals are obtained, with a crystallization temperature of 10 ℃ and a crystallization time of 12 h. After filtration, the sodium sulfide crystals are returned to the elution step. Then the residual sodium sulfide in the enriched solution is oxidized with industrial H2O2 to make the gallium-rich solution meet the electrolysis requirements.

[0035] Gallium electrolysis: the electrolysis temperature is 40 ℃. The electrolysis voltage is 3 V. The electrolysis current density is 300 A / m 2 . The electrolysis time is 4 h. The gallium solution is transferred to the electrolysis tank and heated to 40 ℃. Then it is electrolyzed at a voltage of 3 V and a current density of 300 A / m 2 for 4 h, resulting in 7.75 g of metallic gallium, with a comprehensive gallium recovery rate of 86.1%.

[0036] Example 2:

[0037] Take 10 kg of waste Nd-Fe-B magnets, with a gallium content of 0.09% in the magnets.

[0038] First, the waste Nd-Fe-B magnets are crushed and sieved to ensure that the particle size is below 100 mesh.

[0039] Gallium extraction: the concentration of sodium hydroxide is 5 mol / L. The liquid-solid ratio of the waste magnetic powder and sodium hydroxide is 6 mL / g. The reaction temperature in the autoclave is 150 ℃, the reaction pressure is 0.3 MPa, and the reaction time is 2 h. Take 10 kg of magnetic powder and add it to a 250 L autoclave, then add 60 L of 5 mol / L sodium hydroxide solution. Heat to 150 ℃, react at a pressure of 0.3 MPa for 3 h, and then separate the solid and liquid to obtain a gallium-containing solution. The gallium extraction is 88.7%.

[0040] Gallium enrichment: the flow rate of the gallium-containing solution into the adsorption tower is 0.8 m 3 / h. The adsorption temperature of the adsorption tower is 50 ℃, and the adsorption time is 12 h. The gallium-containing filtrate is passed through the adsorption tower filled with adsorbent LSC700 at a flow rate of 0.8 m 3 / h, and adsorbed at 50 ℃ for 12 h.

[0041] Washing and elution: the washing liquid is a 2 mol / L sodium hydroxide solution. The eluent is a mixture of Na2S and NaOH, with a selected Na2S concentration of 1.5 mol / L and a NaOH concentration of 2 mol / L. After adsorption saturation, the resin is washed with a 2 mol / L NaOH solution to remove residual aluminate. Then the resin is eluted with a mixture of Na2S and NaOH, and after the elution is complete, a high-purity gallium-rich solution is obtained.

[0042] Secondary gallium enrichment: the high-purity gallium solution is added to a falling film evaporator and concentrated at least 1 times, then naturally cooled and frozen crystallized, with a crystallization temperature of 5 ℃ and a crystallization time of 12 h. After filtration, the sodium sulfide crystals are returned to the elution step. Then the residual sodium sulfide in the enriched solution is oxidized with industrial H2O2 to make the gallium-rich solution meet the electrolysis requirements.

[0043] Gallium electrolysis: the electrolysis temperature is 45 ℃. The electrolysis voltage is 3.5 V. The electrolysis current density is 400 A / m 2 . The electrolysis time is 5 h. The gallium solution is transferred to the electrolysis tank and heated to 45 ℃. Then electrolysis is carried out at a voltage of 4 V and a current density of 400 A / m 2 for 5 h, resulting in 7.86 g of metallic gallium, with a comprehensive gallium recovery rate of 87.3%.

[0044] Example 3:

[0045] Take 10 kg of waste Nd-Fe-B magnets, and the gallium content in the magnets is 0.09%.

[0046] First, the waste Nd-Fe-B magnets are crushed and sieved to ensure that the particle size is below 100 mesh.

[0047] Gallium extraction: the concentration of sodium hydroxide is 5 mol / L. The liquid-solid ratio of the waste magnetic powder and sodium hydroxide is 8 mL / g. The reaction temperature in the autoclave is 160 ℃, the reaction pressure is 0.4 MPa, and the reaction time is 4 h. Take 10 kg of magnetic powder and add it to a 250 L autoclave, then add 80 L of 5 mol / L sodium hydroxide solution. Heat to 160 ℃, and react at a pressure of 0.4 Mpa for 4 h. After solid-liquid separation, a gallium-containing solution is obtained, and the gallium extraction is 90.4%.

[0048] Gallium enrichment: the flow rate of the gallium-containing solution into the adsorption tower is 0.8 m 3 / h. The adsorption temperature of the adsorption tower is 50 ℃, and the adsorption time is 12 h. The gallium-containing filtrate is passed through the adsorption tower filled with adsorbent LSC700 at a flow rate of 0.8 m 3 / h, and adsorbed at 50 ℃ for 12 h.

[0049] Washing and elution: the washing liquid is a 2 mol / L sodium hydroxide solution. The eluent is a mixture of Na2S and NaOH, with a selected Na2S concentration of 2 mol / L and a NaOH concentration of 2 mol / L. After adsorption saturation, the resin is washed with a 2 mol / L NaOH solution to remove residual aluminate. Then the resin is eluted with a mixture of Na2S and NaOH, and after the end of the elution, a high-purity gallium-rich solution is obtained.

[0050] Secondary gallium enrichment: the high-purity gallium solution is added to a falling film evaporator and concentrated at least 1 times, naturally cooled and frozen crystallized, with a crystallization temperature of preferably 5 ℃ and a crystallization time of preferably 20 h. After filtration, the sodium sulfide crystals are returned to the elution step. Then the residual sodium sulfide in the enriched solution is oxidized with industrial H2O2 to make the gallium-rich solution meet the electrolysis requirements.

[0051] Gallium electrolysis: the electrolysis temperature is 50 ℃. The electrolysis voltage is 4.5 V. The electrolysis current density is 500 A / m 2 . The electrolysis time is 5 h. The gallium solution is transferred to the electrolysis tank and heated to 50 ℃. Then electrolysis is carried out at a voltage of 4.5 V and a current density of 500 A / m 2 for 5 h, and 7.98 g of metallic gallium is obtained, with a comprehensive gallium recovery rate of 88.7%.

[0052] The above merely illustrates the specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of the changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for recovering gallium from scrap neodymium-iron-boron magnets, characterized in that, The application relates to a method for recycling gallium from waste neodymium-iron-boron magnets. Step S1: adding waste neodymium-iron-boron magnet powder into a sodium hydroxide solution and fully reacting in a high-pressure reaction kettle; Step S2: placing the obtained gallium-containing solution after reaction into a resin adsorption tower for adsorption, wherein the adsorption resin is selected from one or more of LSC600, LSC700, LSC900 and ACD800; Step S3: after the gallium-adsorbed resin is washed and desorbed, the obtained gallium-containing solution is concentrated by falling film high-efficiency evaporation, then the obtained concentrated solution is frozen crystallized and filtered to obtain a gallium-rich solution, wherein the desorbing agent used in the desorption process is a mixed solution of sodium hydroxide and sodium sulfide; the concentration of the sodium hydroxide used in the desorbing agent is 1-5 mol / L, and the concentration of the sodium sulfide is 0.5-4 mol / L; Step S4: the gallium-rich solution is purified by oxidation and impurity removal, and finally the purified gallium-rich solution is sent into an electrolytic cell for electrolysis and recovery of metallic gallium.

2. The method of claim 1, wherein, In step S1, the particle size of the waste neodymium-iron-boron magnet powder is below 100 meshes; the solubility of the sodium hydroxide is 1-8 mol / L; and the liquid-solid ratio of the waste neodymium-iron-boron magnet powder to the sodium hydroxide is 3-15 mL / g.

3. The method of claim 1, wherein, The reaction temperature in the high-pressure reaction kettle is 80-180 DEG C, the reaction pressure is 0.1-1 MPa, and the reaction time is 1-4 h.

4. The method of claim 1, wherein, The flow rate of the gallium-containing solution into the resin adsorption tower in step S2 is 0.5 m 3 / h~ 5 m 3 / h, and the adsorption temperature of the adsorption tower is 25~80 ℃, and the adsorption time is 2 h~10 h.

5. The method of claim 1, wherein, In step S3, the washing liquid in the resin washing process is a sodium hydroxide solution with a concentration of 1-5 mol / L.

6. The method of claim 1, wherein, In step S3, the gallium-containing solution is concentrated by at least 1 times in the evaporation and concentration process, the freezing crystallization temperature is 0-10 DEG C, and the crystallization time is 1-20 h.

7. The method of claim 1, wherein, In step S4, the oxidant in the oxidation and impurity removal process is hydrogen peroxide.

8. The method of claim 1, wherein, In step S4, the electrolysis temperature is 25 ~ 60 ℃, the electrolysis voltage is 2-10 V, the electrolysis current density is 300 ~ 600 A / m 2 , and the electrolysis time is 2 ~ 7 h.