A method for spray oxidation of NdFeB oil sludge waste based on rotary kiln

Abstract

The present invention discloses a method for spray oxidation of NdFeB oil sludge waste based on a rotary kiln, which involves the field of rare earth waste recycling, and in particular, NdFeB oil sludge waste is mixed with water, ground and stirred to form a slurry, and the slurry is sprayed into a rotary kiln for oxidation roasting through a three-channel spray gun together with one or more of high-pressure air or water vapor. The method can be used alone or in combination with the traditional spiral feeding method, which can simplify the process of "pre-treatment and de-oiling" when the oil sludge in NdFeB waste is too high, shorten the oxidation roasting reaction time, and improve the oxidation rate and the steam production rate of flue gas waste heat.

Description

[Technical field]

[0001] The invention relates to the field of rare earth recovery, and in particular to a rotary kiln-based NdFeB oil sludge waste spray oxidation method. [Background technology]

[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 process of sintered NdFeB magnets, due to cutting, grinding, oxidation and other reasons, about 30% of the total weight of the raw materials will be produced. In addition, the number of NdFeB magnets scrapped in NdFeB devices is increasing year by year. 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] Rotary kiln oxidation roasting of NdFeB waste is a common method in industry. The rotary kiln can form a "material curtain" during the material rotation process, so that the NdFeB waste is fully exposed to air during roasting to undergo oxidation reaction, thereby laying a good foundation for the next step of hydrochloric acid dissolution to recover rare earths. Therefore, improving the oxidation rate of NdFeB waste through rotary kiln oxidation 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 neodymium and iron oxides in subsequent recycling steps.

[0005] NdFeB waste can be roughly divided into three types according to their form: dry powder, water-based powder and sludge waste. Among them, sludge waste accounts for a large proportion and is the most difficult to handle. In the process of oxidative roasting of waste sludge in a rotary kiln, due to the flammability and high density of sludge waste, the sludge is very easy to burn violently in the rotary kiln, resulting in excessive temperature near the feed port in the first half of the rotary kiln, causing the sludge waste to melt and sinter into blocks, and the rare earth and iron inside the blocks are not completely oxidized, and then the lumped NdFeB waste further melts and agglomerates, similar to a "snowball" that gets bigger and bigger, eventually resulting in a high proportion of NdFeB sludge waste, which seriously reduces the efficiency of oxidative roasting of NdFeB waste, and often the NdFeB sludge is not completely oxidized, producing black smoke that pollutes the environment. For this reason, NdFeB waste comprehensive utilization enterprises often extract a part of NdFeB oil sludge waste and burn the organic matter in the oil sludge in a small rotary kiln for "pretreatment", and then put it into a large rotary kiln with the remaining oil sludge, water-based and dry powder NdFeB waste for "normal" oxidation roasting. Obviously, this method increases the process, and the oily smoke and black smoke generated by the combustion of oil sludge are not easy to handle.

[0006] CN114317974A discloses a pretreatment method for NdFeB oil sludge waste, firstly, the NdFeB oil sludge waste is subjected to solid-liquid separation to obtain liquid and solid NdFeB oil sludge; then, an organic solvent is added to the solid NdFeB oil sludge for leaching under stirring conditions, and after filtering, the NdFeB waste is vacuum dried to obtain NdFeB powder. Although the invention obtains clean NdFeB powder through simple centrifugation, leaching, drying and sieving, it still needs to be roasted in a rotary kiln, which occupies more equipment and has a longer process flow.

[0007] CN113357907A discloses a rotary kiln device and method for strengthening oxidation roasting of NdFeB alloy to process oil-containing waste. At least one strengthening aeration pipe is provided inside the rotary kiln furnace body, and the front opening of the strengthening aeration pipe is connected to the blower; the lower surface of the strengthening aeration pipe is provided with a plurality of aeration holes, and the strengthening aeration pipe is provided with temperature measuring thermocouples on the pipe wall in the dense area, transition area and sparse area respectively; each temperature measuring thermocouple is connected to the temperature aeration volume control system arranged outside the rotary kiln furnace body, and the temperature aeration volume control system controls the output air flow of the blower according to the temperature of different areas in the rotary kiln furnace body. The technical solution can optimize the oxidation roasting of waste, speed up the waste disposal speed, and alleviate the problems of particle agglomeration and insufficient roasting caused by excessive temperature in the kiln to a certain extent, but the equipment and control system are too complicated. Secondly, when the temperature drops, reducing the aeration flow may also cause problems such as insufficient oxidation.

[0008] The present invention is proposed in view of the deficiencies in the prior art. [Summary of the invention]

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for spray oxidation of NdFeB oil sludge waste based on a rotary kiln.

[0010] The present invention can be implemented by the following technical solutions:

[0011] The invention discloses a method for spray oxidation of NdFeB oil sludge waste based on a rotary kiln, comprising the following steps:

[0012] Step 1. Grinding: Add NdFeB oil sludge waste and water into a grinder and grind the solid particles in the NdFeB oil sludge waste to less than 0.28 mm;

[0013] Step 2. Pulping: Add the ground material in step 1 into a blender, add water, mix and stir to form a slurry;

[0014] Step 3. Spraying: The slurry prepared in step 2 is discharged into the spray gun through a hose pump, and mixed with the atomizing medium in the spray gun and sprayed into the rotary kiln;

[0015] Step 4. Rotary kiln oxidation roasting: After the NdFeB oil sludge waste atomized in step 3 is oxidized and roasted in a rotary kiln for a certain period of time, the solid particles collected from the discharge port on one side of the rotary kiln are the roasted sand products after oxidation of the NdFeB oil sludge waste.

[0016] Preferably, the slurry in step 2 is composed of NdFeB oil sludge waste and water, wherein the content of NdFeB oil sludge waste is 40% to 60%, or the total weight of water added in step 1 and step 2 is 60% to 40%.

[0017] Preferably, the stirring speed of the stirring in step 2 is 100 r / min to 300 r / min, and the stirring time is not less than 30 min.

[0018] Preferably, the atomizing medium in step 3 is one or both of air and water vapor.

[0019] Preferably, the spray gun described in step 3 is a three-channel (or three-channel) spray gun for slurry and atomizing medium, wherein the inner channel is the slurry channel, the outer and central channels are both atomizing medium channels, and there are several connecting small holes at the central channel nozzle leading to the inner channel.

[0020] Preferably, the atomizing spraying in step 3 is to pressurize the atomizing medium to 0.5 MPa to 1 MPa, mix it with the slurry and then spray it with a spray gun.

[0021] Preferably, the temperature of the rotary kiln oxidation roasting in step 4 is 800-1000° C., and the roasting time is 1-2 hours.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The spray gun used in the present invention is a three-channel spray gun, such as Figures 3 to 5 As shown, the inner flow channel of the spray gun is a slurry channel so that the slurry can pass directly without being easily blocked; the central flow channel and the outer flow channel are both atomizing medium channels, but there are multiple connecting holes at the nozzle of the central flow channel that lead to the inner flow channel, that is, the atomizing medium of the outer flow channel can be directly sprayed to the outside of the spray gun to "externally mix" with the slurry, and the atomizing medium of the central flow channel can be sprayed into the inner flow channel through the "connecting holes" at the nozzle to "internally mix" with the slurry, so that it has both the advantages of the "dual-flow channel" slurry "straight-through low-pressure" spray gun, and the excellent effect of the classic "three-flow channel" atomization of "first atomizing medium on the outside - slurry in the center - second atomizing medium on the inside".

[0024] 2. The present invention realizes the rapid oxidation reaction of NdFeB oil sludge waste by an external spray gun on the basis of a rotary kiln. The spray gun atomization feeding can be used alone or simultaneously with the original rotary kiln's spiral feeding, that is, part of the oil sludge is atomized and sprayed into the original rotary kiln for oxidation roasting through the spray gun, while the remaining oil sludge, aqueous or dry powder waste enters the same rotary kiln for oxidation roasting through the original spiral feeding. This is conducive to simplifying the "pretreatment deoiling" process required when the oil sludge is too high, shortening the oxidation roasting time of NdFeB waste, and improving the oxidation rate of NdFeB waste and the steam production rate of high-temperature flue gas waste heat utilization.

Brief Description of the Drawings

[0025] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein:

[0026] Figure 1 is a process flow chart of the present invention;

[0027] Figure 2 A schematic diagram of the structure of the device used in the present invention;

[0028] Figure 3 It is a schematic diagram of the spray gun structure;

[0029] Figure 4 It is a top view of the spray gun structure;

[0030] Figure 5 for Figure 4 Sectional view at AA;

[0031] In the figure: 1. grinder; 2. feed inlet; 3. pipeline; 4. mixer; 5. discharge port; 6. ground storage tank; 7. hose pump; 8. high-position furnace front tank; 9. spray gun; 10. pump; 11. air compressor; 12. pressure regulating tank; 13. screw feeder; 14. rotary kiln; 15. smoke exhaust port; 16. roasted sand discharge port; 17. inner slurry flow channel pipe; 18. central atomizing medium flow channel pipe; 19. outer atomizing medium flow channel pipe; 20. connecting small hole; 21. central atomizing medium inlet pipe; 22. outer atomizing medium inlet pipe. [Specific implementation method]

[0032] The embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0033] Embodiment 1:

[0034] The NdFeB sludge and water are discharged into the grinder 1 through the feed port 2 of the grinder 1 and are preliminarily ground until the solid particles therein are smaller than 0.28 mm (50 mesh).

[0035] The preliminary grinding material enters the mixer 4 through the pipeline 3 for further mixing and slurrying, wherein the total water added in the grinder and the mixer is 50:50 by weight to the sludge, the stirring speed of the mixer is set to 100r / min, and the stirring time is 60min. The prepared NdFeB sludge waste slurry is discharged into the ground storage tank 6 through the discharge port 5.

[0036] The slurry in the ground storage tank is discharged into the high furnace front tank 8 through the hose pump 7, and then the slurry in the furnace front tank 8 is discharged into the inner flow channel of the three-channel spray gun 9 through the hose pump. The 0.5Mpa steam is discharged into the central flow channel of the spray gun 9 through the connecting small hole and "internal mixing" with the slurry in the inner flow channel; the air compressor 11 pressurizes the air to 0.5Mpa and discharges it into the pressure-stabilizing tank 12. The air in the pressure-stabilizing tank 12 is discharged into the outer flow channel of the spray gun 9, mixed with the slurry in the spray gun 9, and sprayed into the rotary kiln 14 in an atomized form.

[0037] The temperature in the furnace chamber of the rotary kiln 14 is controlled at 800°C. After the spray gun atomizes and sprays into the rotary kiln, it is quickly "self-heated oxidized roasted". The roasting time is 1.5 hours. The roasted sand after oxidation roasting is discharged and collected through the roasted sand discharge port 16. Through chemical analysis, the rare earth oxides and iron oxides in the roasted sand account for 98.7% of the total weight of the roasted sand, indicating that the oxidation rate of rare earth and iron metal in the NdFeB sludge waste is as high as more than 98%. The high-temperature flue gas is discharged through the exhaust port 15 into the waste heat boiler to utilize the waste heat to produce steam, and then discharged after bag dust collection, spray dust collection, and electric demisting.

[0038] Embodiment 2:

[0039] The NdFeB sludge and water are discharged into the grinder 1 through the feed port 2 of the grinder 1 and are initially ground until the solid particles therein are less than 0.28 mm.

[0040] The preliminary grinding material enters the mixer 4 through the pipeline 3 for further mixing and slurrying, wherein the total water added in the grinder and the mixer is 40:60 by weight to the sludge, the stirring speed of the mixer is set to 200r / min, and the stirring time is 45min. The prepared NdFeB sludge waste slurry is discharged into the ground storage tank 6 through the discharge port 5.

[0041] The slurry in the ground storage tank is discharged into the high-position furnace front tank 8 through the hose pump 7, and then the slurry in the furnace front tank 8 is discharged into the inner flow channel pipe of the three-channel spray gun 9 through the hose pump; the air compressor 11 pressurizes the air to 1Mpa and discharges it into the pressure-stabilizing tank 12, and the air in the pressure-stabilizing tank 12 is discharged into the outer flow channel and the central flow channel of the spray gun 9 respectively, and then the high-pressure air in the outer flow channel and the central flow channel is mixed with the slurry in the spray gun 9 respectively, and then atomized and sprayed into the rotary kiln 14.

[0042] The temperature in the furnace chamber of the rotary kiln 14 is controlled at 900°C. After the spray gun atomizes and sprays into the rotary kiln, it is quickly "self-heated oxidized roasted". The roasting time is 1 hour. The roasted sand after oxidation roasting is discharged and collected through the roasted sand discharge port 16. Through chemical analysis, the rare earth oxides and iron oxides in the roasted sand account for 99.1% of the total weight of the roasted sand, indicating that the oxidation rate of rare earth and iron metal in the NdFeB sludge waste is as high as more than 99%. The high-temperature flue gas is discharged through the exhaust port 15 into the waste heat boiler to utilize the waste heat to produce steam, and then discharged after bag dust collection, spray dust collection, and electric demisting.

[0043] Embodiment 3:

[0044] The dry powder, aqueous waste and 1 / 3 of the sludge waste in the NdFeB waste are mixed and discharged into the rotary kiln 14 through the screw feeder 13 .

[0045] The remaining 2 / 3 of the sludge and water of the NdFeB waste are discharged into the grinder 1 through the feed port 2 of the grinder 1, and preliminary grinding is performed until the solid particles therein are less than 0.28mm (50 mesh). The preliminary grinding material enters the mixer 4 through the pipeline 3 for further mixing and slurrying, wherein the total water added to the grinder and the mixer is 60:40 in weight ratio to the sludge, the stirring speed of the mixer is set to 300r / min, and the stirring time is 30min. The prepared NdFeB sludge waste slurry is discharged into the ground storage tank 6 through the discharge port 5. The slurry in the ground storage tank is discharged into the high-position furnace front tank 8 through the hose pump 7, and then the slurry in the furnace front tank 8 is discharged into the inner flow channel pipe of the three-channel spray gun 9 through the hose pump; the air compressor 11 pressurizes the air to 0.75Mpa and discharges it into the pressure-stabilizing tank 12, and the air in the pressure-stabilizing tank 12 is discharged into the outer flow channel and the central flow channel of the spray gun 9 respectively, and then the high-pressure air in the outer flow channel and the central flow channel is mixed with the slurry in the spray gun 9 respectively, and then atomized and sprayed into the rotary kiln 14.

[0046] The temperature in the furnace of the rotary kiln 14 is controlled at 1000°C. The NdFeB waste material injected into the rotary kiln by spiral feeding and spray gun atomization is rapidly "self-heated oxidative roasted". The roasting time is 2 hours. The roasted sand after oxidative roasting is discharged and collected through the roasted sand discharge port 16. According to chemical analysis, the rare earth oxides and iron oxides in the roasted sand account for 97.5% of the total weight of the roasted sand, indicating that the oxidation rate of rare earth and iron metal in the NdFeB waste material is as high as more than 97%. The high-temperature flue gas is discharged through the exhaust port 15 and enters the waste heat boiler to produce steam by waste heat utilization, and then emptied after bag dust collection, spray dust collection, and electric demisting. About 1.2 tons of steam can be produced by waste heat utilization per ton of NdFeB waste material.

[0047] Comparative Example:

[0048] First, 2 / 3 of the sludge in the NdFeB waste is passed through a small rotary kiln for oxidation roasting at about 600-700°C to remove organic matter in the sludge.

[0049] The above-mentioned "de-oiled" sludge is then mixed with the remaining sludge, dry powder, and aqueous NdFeB waste, ground, and stirred, and then discharged into the rotary kiln 14 through a scraper conveyor and a screw feeder 13 for oxidation roasting for 4 hours. The high-temperature flue gas is discharged through the exhaust port 15 and enters the waste heat boiler to produce steam for waste heat utilization, and then emptied after bag dust collection, spray dust collection, and electric demisting. The results show that the oxidation rate of NdFeB waste is 95.0%, and each ton of NdFeB waste can produce about 1 ton of steam by waste heat utilization.

[0050] The oxidation roasting time of Example 3 is obviously shorter than that of the conventional method comparative example, while the oxidation rate and the waste heat utilization steam production rate are both improved.

[0051] 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 spray oxidation of NdFeB oil sludge waste based on a rotary kiln, characterized in that: The following steps are involved: Step 1. Grinding: Add NdFeB oil sludge waste and water into a grinder and grind the solid particles in the NdFeB oil sludge waste to less than 0.28 mm; Step 2. Pulping: Add the ground material in step 1 into a blender, add water, mix and stir to form a slurry; Step 3. Spraying: The slurry prepared in step 2 is discharged into the spray gun through a hose pump, and mixed with the atomizing medium in the spray gun and sprayed into the rotary kiln; Step 4. Rotary kiln oxidation roasting: After the NdFeB oil sludge waste atomized in step 3 is oxidized and roasted in a rotary kiln for a certain period of time, the solid particles collected from the discharge port on one side of the rotary kiln are the roasted sand products after oxidation of the NdFeB oil sludge waste.

2. The NdFeB oil sludge waste spray oxidation method based on a rotary kiln according to claim 1, characterized in that: The slurry in step 2 is composed of NdFeB oil sludge waste and water, wherein the content of NdFeB oil sludge waste is 40% to 60%, or the total weight of water added in step 1 and step 2 is 60% to 40%.

3. The method for spray oxidation of NdFeB oil sludge waste based on a rotary kiln according to claim 1, characterized in that: In step 2, the stirring speed is 100 r / min to 300 r / min, and the stirring time is not less than 30 min.

4. The NdFeB oil sludge waste spray oxidation method based on a rotary kiln according to claim 1, characterized in that: The atomizing medium in step 3 is one or both of air and water vapor.

5. The NdFeB oil sludge waste spray oxidation method based on a rotary kiln according to claim 1, characterized in that: The spray gun in step 3 is a three-channel (or three-channel) spray gun for slurry and atomizing medium, in which the inner channel is the slurry channel, the outer and central channels are both atomizing medium channels, and there are several small inclined holes at the central channel nozzle leading to the inner channel.

6. The NdFeB oil sludge waste spray oxidation method based on a rotary kiln according to claim 1, characterized in that: The atomizing spraying described in step 3 is to pressurize the atomizing medium to 0.5Mpa-1Mpa, mix it with the slurry, and then spray it through a spray gun.

7. The NdFeB oil sludge waste spray oxidation method based on a rotary kiln according to claim 1, characterized in that: The temperature of the rotary kiln oxidation roasting in step 4 is 800-1000° C., and the roasting time is 1-2 hours.

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