Neodymium-iron-boron waste slurry spraying synergistic boiling oxidation roasting method

Abstract

The invention relates to the field of neodymium-iron-boron waste recovery, in particular to a neodymium-iron-boron waste slurry spraying and boiling oxidation synergistic roasting method. The neodymium-iron-boron waste is crushed, ground and stirred after being mixed with water, and air or oxygen-enriched air are atomized and sprayed into the fluidized bed furnace through a spray gun to be oxidized and roasted. The problem that a traditional wet material containing oil and water is prone to blocking a hood of a fluidized bed furnace is solved, roasting can be conducted through a fluidized bed roaster of a common structure, the neodymium iron boron waste is treated through the synergistic effect of atomization and boiling, and the oxidation rate of rare earth and iron metal in the waste can be increased; the amount of residual rare earth in the iron trioxide slag in the subsequent acid dissolution process of the roasted product is reduced, and the rare earth recovery rate is increased; in addition, oily substances in the waste materials are also completely combusted, and the temperature of the flue gas is increased, so that waste heat is utilized to produce steam, carbon emission is reduced, and the production cost for purchasing the steam can be reduced.

Description

Technical Field

[0001] The invention relates to the field of NdFeB waste recovery, and in particular to a NdFeB waste slurry spraying coordinated boiling oxidation roasting method. Background Art

[0002] NdFeB magnets have the advantages of high coercivity, high remanence, and high magnetic energy product. They are known as the "King of Magnets" and are the rare earth permanent magnet materials with the highest output and the most extensive application in current industrial production. NdFeB magnets are widely used in new energy, high-end CNC machines, wind power generation, electronic information and other fields. In 2022, China's output of NdFeB permanent magnet materials exceeded 200,000 tons, and it is expected that in 2027, the annual output of NdFeB permanent magnet materials will exceed 270,000 tons.

[0003] However, in the production and processing of sintered NdFeB magnets, about 30% of the total weight of the raw materials will be produced as NdFeB waste due to cutting, grinding, drilling, oxidation and waste. With the high fluctuation of NdFeB metal prices in recent years and the demand for resource protection and sustainable development, the recycling of NdFeB waste has extremely high economic value and social benefits.

[0004] The hydrochloric acid superior dissolution method is the mainstream process in the current NdFeB waste recycling industry due to its strong adaptability to raw materials, convenient operation and high purity of rare earth products. The process flow of the hydrochloric acid superior dissolution method includes oxidative roasting, dilute acid dissolution, decomposition and impurity removal, extraction and separation, precipitation and roasting and other processes. The principle is to convert the metals in the NdFeB waste into high-valent oxides of rare earth and iron through oxidative roasting, control the precipitation conditions of iron oxide and rare earth oxide under different pH conditions, and realize the selective leaching of rare earth by dilute hydrochloric acid. The leachate is subjected to decomposition and impurity removal, extraction and separation, precipitation and calcination to obtain rare earth oxides. Therefore, oxidative roasting is a key step in the recycling of NdFeB waste, which directly affects the yield of rare earth products and the separation of rare earth and iron in subsequent recovery steps.

[0005] At present, NdFeB waste is often oxidized and roasted in a rotary kiln. The principle is that a "material curtain" can be formed in the rotary kiln during the material rotation process, so that the NdFeB waste will come into contact with the air during roasting to undergo an oxidation reaction, thereby laying a good foundation for the next step of hydrochloric acid dissolution to recover rare earths. However, since the oxidation reaction in the rotary kiln belongs to a "gas-solid" moving bed reaction, it often takes 6 to 8 hours to reach a high oxidation rate. In addition, since the rotary kiln mostly adopts a two-stage reaction, it also has the disadvantages of being large in size, occupying a large area, and having a large external heat dissipation area. At the same time, there are cold and hot alternation links and high energy consumption.

[0006] In order to solve the technical problems such as slow oxidation speed and long reaction time of rotary kiln, most NdFeB waste recycling enterprises and research institutions improve the oxidation rate of waste by deoiling the primary roasted material and then performing secondary roasting; or adjust the kiln temperature by controlling the proportion of raw materials and reducing the proportion of oil and sludge to avoid particle adhesion, thereby improving oxidation efficiency; or even add a large amount of oxidant in the hydrochloric acid solution process.

[0007] CN113652538A discloses a method for separating and recovering rare earth and iron from NdFeB sludge. In the technical scheme, detergent is used to wash and remove the sludge in the NdFeB sludge, and then the washed and oil-removed NdFeB is subjected to oxidative roasting to obtain NdFeB roasted sand, and then the NdFeB roasted sand is leached. In addition, solvent extraction is used to separate rare earth and iron, and rare earth is recovered in the form of rare earth oxide, and iron is recovered in the form of ferrous oxalate. The invention has the characteristics of low pretreatment cost and simultaneous recovery of rare earth and iron. However, the sludge is removed in the technical scheme, and the heat generated by the sludge itself is not fully utilized, which increases the energy consumption of oxidative roasting.

[0008] CN109504851A discloses a method for flash oxygen-enriched roasting of NdFeB waste, which is to spray the NdFeB waste into a high-temperature reaction tower space together with oxygen-enriched air through a dispersion nozzle after drying the NdFeB waste, so that the NdFeB oil sludge waste is highly dispersed, and in the process of descending from the upper end of the reaction tower to the lower end, the oil in the material is fully burned, and the rare earth and iron are quickly and fully oxidized by the oxygen-enriched air, and the product falls on the collector below the reaction tower, and the flue gas is emptied after dust collection. The invention uses flash oxygen-enriched roasting to quickly and fully oxidize the iron and rare earth in the waste, and overcomes the defects of slow rotary kiln roasting reaction, long process, and high energy consumption to a certain extent. However, this method requires drying the NdFeB waste, which increases the production cost and process operation difficulty to a certain extent.

[0009] Similarly, if the oily and water-containing NdFeB waste is directly fed into a fluidized bed furnace for oxidation roasting, it will easily stick to the hood of the fluidized bed furnace. There is no report on the direct industrial application of NdFeB waste using traditional fluidized bed oxidation roasting.

[0010] The present invention is proposed in view of the deficiencies in the prior art. Summary of the invention

[0011] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a method for spraying and boiling oxidation roasting of NdFeB waste slurry which is easy to operate, safe and environmentally friendly.

[0012] The present invention can be implemented by the following technical solutions:

[0013] Step 1. Crushing: crush and roughly grind the coarse NdFeB waste;

[0014] Step 2. Slurrying: Mix the crushed NdFeB waste with a certain amount of water, and then grind and stir to make NdFeB waste slurry;

[0015] Step 3. Spraying: The slurry prepared in step 3 is discharged into the spray gun through a hose pump, and is mixed with the atomizing medium in the spray gun and atomized, and then sprayed into the boiling furnace;

[0016] Step 4. Fluidized bed calcination: After the NdFeB waste atomized in step 3 is oxidized and roasted in a fluidized bed furnace for a certain period of time, the roasted sand collected from the overflow port on one side of the fluidized bed furnace is the solid oxide particles containing the NdFeB waste after roasting.

[0017] Preferably, in the NdFeB waste slurry spraying and boiling oxidation roasting method, in step 1, the coarser NdFeB waste solid particles are crushed and roughly ground into 150-200 meshes.

[0018] Preferably, in the NdFeB waste slurry spraying and boiling oxidation roasting method, the NdFeB waste (mass percentage of dry amount) in the NdFeB waste slurry in step 2 is 45% to 60%, and the water content (mass percentage) is 55% to 40%.

[0019] Preferably, in the method for spraying and boiling oxidation roasting of NdFeB waste slurry, the NdFeB waste slurry in step 2 is slurried by grinding and stirring with a stirred mill.

[0020] Preferably, in the method for spraying and boiling oxidation roasting of NdFeB waste slurry, in step 2, the solid particle size of the NdFeB waste slurry after grinding is 250-350 mesh.

[0021] Preferably, in the NdFeB waste slurry spraying and boiling oxidation roasting method, in step 3, the spray gun is a slurry-atomizing medium double-channel (or double-channel) spray gun, wherein the inner channel is the slurry channel, the outer channel is the atomizing medium channel, and the outer channel has a plurality of small inclined holes leading to the inner channel.

[0022] Preferably, in the method for spraying and boiling oxidation roasting of NdFeB waste slurry, in step 3, the atomizing medium is one of air or oxygen-enriched air.

[0023] Preferably, in the NdFeB waste slurry spraying and boiling oxidation roasting method, in step 3, the atomizing medium is pressurized by an air compressor and mixed with the slurry and then atomized and sprayed out by a spray gun, and the working pressure range of the air compressor is 0.5Mpa to 2Mpa.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The spray gun used in the present invention is a slurry-atomizing medium double-channel spray gun, such asFigure 3 As shown, the inner channel of the spray gun is a slurry channel so that the slurry can pass directly without being easily blocked; the outer channel is an atomizing medium channel, but there are multiple small inclined holes at the nozzle of the outer channel leading to the inner channel, that is, part of the atomizing medium can be directly sprayed to the outside of the spray gun to "externally mix" with the slurry, and part of the atomizing medium can be sprayed through the inclined holes at the nozzle into the inner channel to "internally mix" with the slurry, so that it has both the advantages of a dual-channel "straight-through low-pressure" spray gun and a mixing effect comparable to that of a "three-channel".

[0026] 2. The NdFeB waste slurry of the present invention adopts "stirring mill" grinding and stirring slurry. Since the stirring mill drives the ball to "ball mill" and "stir" by rapidly rotating the stirring rod, the slurry effect is better than that of the ordinary horizontal ball mill plus mechanical stirring, which makes the NdFeB waste slurrying process simple and the slurry atomization effect after slurrying is good.

[0027] 3. The present invention uses a spray gun to spray the NdFeB waste slurry and compressed air or oxygen-enriched air into the boiling layer of the high-temperature boiling furnace at the same time, so that the NdFeB waste slurry is in a "mist" state and surrounded by air or oxygen-enriched air. The solid particles of the NdFeB waste quickly undergo a "self-thermal oxidation" reaction and are in a "boiling" state, which will not block the hood of the boiling furnace. Therefore, the structure and process similar to the classic boiling roasting furnace can be adopted, which is easy to apply the present invention in industry; the "synergistic effect" of "atomization" and "boiling" makes the oxidation of NdFeB waste have Excellent reaction kinetic conditions; the iron and rare earth in the material are quickly and fully oxidized, with an oxidation rate of more than 98%, which is more than 5 percentage points higher than the traditional rotary kiln oxidation roasting, and the rare earth recovery rate can be increased by about 0.75 percentage points. The reaction time can be shortened to more than 50% of that of the rotary kiln, and the furnace temperature and atmosphere are easy to accurately control; the oil in the material is fully burned to avoid black smoke, and the operating environment is good, which is conducive to the use of flue gas waste heat and by-product steam for subsequent acid dissolution processes, reducing "carbon" emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein:

[0029] Figure 1 It is a process flow chart of the present invention;

[0030] Figure 2 This is a schematic diagram of the structure of the equipment system used in the present invention;

[0031] Figure 3 This is a schematic diagram of the structure of the atomizing spray gun used in the present invention;

[0032] In the figure: 1. ball mill; 2. feed inlet; 3. discharge outlet; 4. storage tank; 5. hose pump; 6. wet stirring mill; 7. front tank of furnace; 8. spray gun; 9. air compressor; 10. pressure regulating tank; 11. boiling furnace; 12. roasted sand overflow port; 13. air inlet; 14. smoke exhaust port; 15. blower. DETAILED DESCRIPTION

[0033] The embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0034] The NdFeB waste and water are discharged into the ball mill 1 through the feed port 2 of the ball mill 1, and the NdFeB waste is crushed and coarsely ground by the ball mill 1. After the waste particles pass through a 150-mesh screen, the ground solid particles are discharged into the discharge trough 4 for collection.

[0035] The slurry in the discharge trough 4 is discharged into the wet stirring mill 6 through the hose pump 5, and the corresponding weight of water is added to the wet stirring mill 6 according to the weight ratio of waste weight to water of 45:55, and the slurry inside the wet stirring mill 6 is ground and stirred to grind the solid particles of the waste to 250 mesh.

[0036] After the NdFeB waste is made into slurry, the slurry is discharged into the high-position furnace front tank 7 through the hose pump 5, and the slurry in the furnace front tank 7 is discharged into the slurry-air double-channel spray gun 8 through the hose pump 5. The air is pressurized to 0.5Mpa by the air compressor 9 and discharged into the pressure-stabilizing tank 10. The air in the pressure-stabilizing tank 10 is discharged into the spray gun 8 and then atomized and sprayed into the boiling furnace 11 together with the slurry in the spray gun 8. The air is blown into the boiling furnace 11 through the air inlet 13 by the blower 15. The temperature of the secondary hot air blown into the bottom of the boiling furnace 11 is 700°C, the blast pressure at the bottom of the furnace is 1000Pa, and the boiling roasting temperature in the furnace is controlled at 850°C. The waste particles are dispersed in the boiling furnace 11 and roasted for 1.5 hours. The roasted sand is discharged and collected through the overflow port 12. Part of the smoke is discharged through the smoke exhaust port 14, and part of it is returned to the boiling furnace as "secondary hot air" to be recycled as hot air at the bottom of the furnace.

[0037] The calcined sand after atomization synergistic boiling oxidation roasting was chemically analyzed, and the results showed that: 1) the rare earth oxides and ferric oxide in the calcined sand accounted for 98.1% of the total weight of the calcined sand, that is, under the "synergistic effect" of "atomization" and "boiling", the oxidation rate of the NdFeB waste reached more than 98%, which was more than 6 percentage points higher than the oxidation rate of the same material oxidized in a traditional rotary kiln. The reaction of Example 1 was shortened to 1.5 hours compared with 4.5 hours of the comparative example; 2) Due to the increase in the oxidation rate of the calcined material in Example 1, Under the same subsequent hydrochloric acid dissolution conditions, it is easily dissolved preferentially by dilute hydrochloric acid and separated from the solid ferric oxide slag, and the amount of residual rare earth oxides in the iron slag is reduced from 0.4% in the comparative example to 0.25%, that is, the rare earth recovery rate can be increased by about 0.75 percentage points; 3) The flue gas temperature in the comparative example is about 400-500°C, while the flue gas temperature in Example 1 is above 700°C, which makes it easy for the flue gas to pass through the waste heat boiler to produce steam for subsequent acid dissolution, which not only reduces "carbon" emissions, but also reduces the production cost of purchasing steam.

[0038] Embodiment 2:

[0039] The NdFeB waste and water are discharged into the ball mill 1 through the feed port 2 of the ball mill 1, and the NdFeB waste is crushed and coarsely ground by the ball mill 1. After the solid particles of the waste pass through a 200-mesh screen, the ground solid particles are discharged into the storage tank 4 for collection.

[0040] The slurry in the storage tank 4 is discharged into the wet stirring mill 6 through the hose pump 5, and the corresponding weight of water is added to the wet stirring mill 6 according to the weight ratio of waste material to water of 50:50, and the slurry inside the wet stirring mill 6 is ground and stirred to grind the waste material to 300 mesh.

[0041] After the NdFeB waste is ground and slurried, the dispersed slurry is discharged into the high-position furnace front tank 7 through the hose pump 5, and the slurry in the furnace front tank 7 is discharged into the slurry-air double-channel spray gun 8 through the hose pump 5. The air is pressurized to 1Mpa by the air compressor 9 and discharged into the pressure-stabilizing tank 10. After the air in the pressure-stabilizing tank 10 is discharged into the spray gun 8, it is atomized and sprayed into the boiling furnace 11 together with the slurry in the spray gun 8. The oxygen-enriched air with an oxygen content of 25% is blown into the boiling furnace 11 through the air inlet 13 by the blower 15. The temperature of the secondary hot air blown into the bottom of the fluidized bed furnace 11 is 750°C, the blast pressure of the bottom of the furnace is 1500Pa, the boiling roasting temperature in the furnace is controlled at 1000°C, the waste particles are dispersed in the fluidized bed furnace 11 and roasted for 100 minutes, the roasted sand is discharged and collected through the overflow port 12, the smoke is partially discharged through the exhaust port 14, and partly returned to the fluidized bed furnace as the secondary hot air recycling at the bottom of the furnace. The roasted sand is taken for chemical analysis, and the results show that the rare earth oxides and ferric oxide in the roasted sand account for 99.0% of the total weight of the roasted sand, that is, the oxidation rate of the NdFeB waste is as high as 99%.

[0042] Embodiment 3:

[0043] The NdFeB waste and water are discharged into the ball mill 1 through the feed port 2 of the ball mill 1, and the NdFeB waste is crushed and coarsely ground by the ball mill 1. After the waste particles pass through a 150-mesh screen, the crushed and coarsely ground solid particles are discharged into the storage tank 4 for collection.

[0044] The slurry in the discharge trough 4 is discharged into the wet stirring mill 6 through the hose pump 5, and the corresponding weight of water is added to the wet stirring mill 6 according to the weight ratio of waste weight to water of 60:40, and the slurry inside the wet stirring mill 6 is finely ground and stirred to grind the waste particles to 350 mesh.

[0045] After the NdFeB waste is slurried, the dispersed slurry is discharged into the high-position furnace front tank 7 through the hose pump 5, and the slurry in the furnace front tank 7 is discharged into the slurry-air double-channel spray gun 8 through the hose pump 5. The air is pressurized to 2Mpa by the air compressor 9 and discharged into the pressure-suppressing tank 10. After the air in the pressure-suppressing tank 10 is discharged into the spray gun 8, it is atomized and sprayed into the boiling furnace 11 together with the slurry in the spray gun 8. The air is blown into the boiling furnace 11 through the air inlet 13 by the blower 15. The hot air temperature blown into the bottom of the boiling furnace 11 is 800℃, the furnace bottom blast pressure is 2000Pa, and the boiling roasting temperature in the furnace is controlled at 1100℃. The waste particles are dispersed in the boiling furnace 11 and roasted for 120 minutes. The roasted sand after roasting is discharged and collected through the overflow port 12, and the smoke is discharged through the exhaust port 14 and returned to the boiling furnace to be recycled as the hot air at the bottom of the furnace. The roasted sand was taken for chemical analysis, and the results showed that the rare earth oxides and iron oxides in the roasted sand accounted for 99.4% of the total weight of the roasted sand.

[0046] The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, various changes, modifications, substitutions and variations can be made to these embodiments without departing from the technical principles of the present invention. These changes, modifications, substitutions and variations should also be regarded as the scope of protection of the present invention.

Claims

1. A method for spraying and boiling oxidation roasting of NdFeB waste slurry, characterized in that: The following steps are involved: Step 1. Crushing: crush and roughly grind the coarse NdFeB waste; Step 2. Slurrying: Mix the crushed NdFeB waste with a certain amount of water, and then grind and stir to make NdFeB waste slurry; Step 3. Spraying: The slurry prepared in step 3 is discharged into the spray gun through a hose pump, and is mixed with the atomizing medium in the spray gun and atomized, and then sprayed into the boiling furnace; Step 4. Fluidized bed calcination: After the NdFeB waste atomized in step 3 is oxidized and calcined in a fluidized bed furnace for a certain period of time, the roasted sand collected from the overflow port on one side of the fluidized bed furnace is the solid oxide particles after the NdFeB waste is calcined.

2. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1 is characterized in that: In step 1, the solid particles of NdFeB waste are crushed and coarsely ground to 150-200 meshes.

3. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1 is characterized in that: The NdFeB waste (mass percentage of dry mass) in the NdFeB waste slurry in step 2 is 45% to 60%, or the water content (mass percentage) is 55% to 40%.

4. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1, characterized in that: The NdFeB waste material pulping in step 2 is prepared by grinding and stirring the pulp by a stirred mill.

5. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1, characterized in that: In step 2, the solid particle size of the NdFeB waste slurry after grinding and stirring is 250-350 meshes.

6. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1, characterized in that: In step 3, the spray gun is a slurry-atomizing medium double-channel (or double-channel) spray gun, wherein the inner channel is the slurry channel, the outer channel is the atomizing medium channel, and at the same time, there are several small inclined holes connecting to the inner channel at the nozzle of the outer channel.

7. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1, characterized in that: In step 3, the atomizing medium is one of air or oxygen-enriched air.

8. The method for spraying and boiling oxidation roasting of NdFeB waste slurry according to claim 1, characterized in that: The atomizing medium is pressurized by an air compressor and mixed with the slurry before being atomized and sprayed out through a spray gun. The working pressure range of the air compressor is 0.5Mpa to 2Mpa.

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