Device and method for recycling rare earth wastewater and co-producing ammonium chloride

Abstract

The present invention discloses an apparatus and method for recycling rare earth wastewater and co-producing ammonium chloride. The apparatus comprises a flotation tank, an inclined plate sedimentation tank, a filtration device, a disc-tube reverse osmosis device, a high-density sedimentation tank, a first sand filter, an MVR evaporator, a triple-effect evaporator, and a reverse osmosis device. The method for recycling rare earth wastewater and co-producing ammonium chloride utilizes the aforementioned apparatus. The present invention can produce two ammonium chloride products at low cost and low energy consumption, and achieves the recycling of rare earth wastewater.

Description

Technical Field

[0001] The invention relates to a device and method for recycling rare earth wastewater and co-producing ammonium chloride. Background Art

[0002] During rare earth ore production, the rare earth extraction, carbon precipitation, and desalination steps all generate large amounts of rare earth wastewater. Evaporation and crystallization are the conventional treatment methods for this wastewater. After pretreatment to remove impurities, the wastewater is evaporated and crystallized to recover solid ammonium chloride and fresh water. Some low-concentration wastewater is directly evaporated in the evaporation system, resulting in high energy consumption. Furthermore, the solid ammonium chloride product recovered during the evaporation process does not meet the standards for industrial-grade and agricultural-grade ammonium chloride products, and the condensed water produced cannot be directly reused. Those skilled in the art have been developing and improving rare earth wastewater treatment methods to reduce pollutant emissions and improve ammonium chloride recovery efficiency.

[0003] CN104140174A discloses a combined treatment method for rare earth extraction and separation of ammonium chloride wastewater. The method primarily involves a series of desalination and concentration processes, including oil separation, homogenization, aeration, electrocoagulation and demulsification, flotation oil removal, precipitation of calcium, magnesium, and heavy metal ions with chemical addition, microfiltration and ultrafiltration, nanofiltration, reverse osmosis, electrodialysis, and evaporation concentration, to produce recyclable desalinated purified water and an ammonium chloride product that meets agricultural standards. This method only treats rare earth extraction and separation of ammonium chloride wastewater and recovers only one ammonium chloride product.

[0004] CN103553257A discloses a recycling process for treating rare earth wastewater. The wastewater undergoes flotation treatment, electrolytic oxidation, primary composite separation, primary concentration, secondary composite separation, secondary concentration, reverse osmosis treatment, and evaporation crystallization, yielding recyclable solid salts and product water. CN104609627A discloses a method for treating rare earth production wastewater. The method comprises the following steps: performing reverse osmosis filtration on the precipitation mother liquor to obtain a first concentrated phase water and a first dilute phase water; mixing the first dilute phase water with precipitation wash water to obtain a first mixed liquid; performing reverse osmosis filtration on the first mixed liquid to obtain a second concentrated phase water and a second dilute phase water; mixing the first concentrated phase water with saponification wastewater to obtain a second mixed liquid; performing evaporation and concentration of the second mixed liquid using an MVR evaporator to obtain condensed water and sodium chloride or ammonium chloride; mixing the condensed water with the second dilute phase water to obtain a third mixed liquid; performing reverse osmosis filtration on the third mixed liquid to obtain a third concentrated phase water and a third dilute phase water. Neither of these two methods carries out chemical impurity removal treatment on rare earth wastewater, and the recycled water produced still fails to meet the standards. In addition, both methods only produce one type of ammonium chloride.

[0005] CN110282799A discloses a method for resource-recycling rare earth carbon precipitation wastewater and raffinate. This method targets high-ammonia nitrogen wastewater generated during the rare earth separation process using the P507-hydrochloric acid system and ammonia saponification, specifically wastewater containing heavy metal ions and high-concentration ammonium chloride, and raffinate containing oil and high-concentration ammonium chloride. The raffinate is filtered and concentrated using a ceramic membrane filtration system to recover the extractant, and the deoiled raffinate is evaporated. The rare earth carbon precipitation wastewater is first treated using pretreatment equipment to adjust pH, flocculate, react, and concentrate to remove suspended matter and heavy metal ions. Ultrahigh-pressure reverse osmosis equipment is then used for purification and concentration. Finally, an MVR evaporation and crystallization unit is used to produce an ammonium chloride product with a purity of 99%. This method is designed for rare earth wastewater with low calcium and magnesium concentrations and is not suitable for treating wastewater with high calcium and magnesium concentrations. Furthermore, this method only produces one type of ammonium chloride and does not reprocess the mother liquor. Summary of the Invention

[0006] In view of this, one object of the present invention is to provide an apparatus for recycling rare earth wastewater and co-producing ammonium chloride. Another object of the present invention is to provide a method for recycling rare earth wastewater and co-producing ammonium chloride. The present invention treats rare earth wastewater containing high concentrations of calcium and magnesium, achieving wastewater recycling with low energy consumption, and simultaneously producing two ammonium chloride products.

[0007] The present invention adopts the following technical solutions to achieve the above-mentioned purpose.

[0008] In one aspect, the present invention provides a device for recycling rare earth wastewater and co-producing ammonium chloride, the device comprising an air flotation tank, an inclined plate sedimentation tank, a filtration device, a disc-tube reverse osmosis device, a high-density sedimentation tank, a first sand filter, an MVR evaporator, a triple-effect evaporator, and a reverse osmosis device;

[0009] The flotation tank is used to float mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and to precipitate zinc ions, aluminum ions and iron ions in the mixed wastewater to obtain flotation slag and wastewater containing precipitates; the liquid outlet of the flotation tank is located at the bottom of the flotation tank, and the liquid outlet is connected to the feed port of the inclined plate sedimentation tank through a pipeline;

[0010] The inclined plate sedimentation tank is used to reprecipitate the wastewater containing sediment to obtain reprecipitate; the discharge port of the inclined plate sedimentation tank is connected to the feed port of the filtering device through a pipeline;

[0011] The filtering device is used to filter the reprecipitate to obtain a first filtrate; the liquid outlet of the filtering device is connected to the liquid inlet of the disc tube reverse osmosis device through a pipeline;

[0012] The disc-tube reverse osmosis device is used to perform disc-tube reverse osmosis treatment on the first filtrate to obtain concentrated water and fresh water; the concentrated water outlet of the disc-tube reverse osmosis device is connected to the liquid inlet of the high-density sedimentation tank through a pipeline, and the fresh water outlet of the disc-tube reverse osmosis device is connected to the liquid inlet of the reverse osmosis device through a pipeline;

[0013] The high-density sedimentation tank is used to precipitate calcium ions and magnesium ions in a mixture of rare earth extraction wastewater, rare earth carbon precipitation wastewater, and concentrated water obtained by disc tube reverse osmosis treatment; the discharge port of the high-density sedimentation tank is connected to the feed port of the first sand filter through a pipeline;

[0014] The first sand filter is used to filter the sediment generated in the high-density sedimentation tank; the filtrate outlet of the first sand filter is connected to the feed inlet of the MVR evaporator through a pipeline;

[0015] The MVR evaporator is used to evaporate and crystallize the filtrate from the first sand filter to obtain first ammonium chloride crystals, MVR evaporation mother liquor and MVR secondary steam condensate; the mother liquor outlet of the MVR evaporator is connected to the liquid inlet of the triple-effect evaporator through a pipeline, and the secondary steam condensate outlet of the MVR evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline;

[0016] The triple-effect evaporator is used to evaporate the crystallization MVR evaporation mother liquor to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor and triple-effect secondary steam condensate; the secondary condensate outlet of the triple-effect evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline;

[0017] The reverse osmosis equipment is used to perform reverse osmosis treatment on MVR secondary steam condensate, triple-effect secondary steam condensate and fresh water obtained by disc tube reverse osmosis treatment to obtain treated wastewater.

[0018] According to the device of the present invention, preferably, the device further comprises a negative pressure dryer, which is used to dry the mother liquor of the triple-effect evaporation to produce salt; the mother liquor outlet of the triple-effect evaporator is connected to the liquid inlet of the negative pressure dryer through a first pipeline; the mother liquor outlet of the triple-effect evaporator is also connected to the liquid inlet of the high-density precipitation tank through a second pipeline.

[0019] According to the device of the present invention, preferably, the filtration equipment includes a second sand filter and an ultrafiltration equipment, the feed port of the second sand filter is connected to the discharge port of the inclined plate sedimentation tank through a pipeline, and the filtrate outlet of the second sand filter is connected to the liquid inlet of the ultrafiltration equipment through a pipeline; the filtrate outlet of the ultrafiltration equipment is connected to the liquid inlet of the disc tube reverse osmosis equipment through a pipeline.

[0020] On the other hand, the present invention also provides a method for recycling rare earth wastewater and producing ammonium chloride using the above-mentioned device, comprising the following steps:

[0021] 1) Flotation and sedimentation: adding ammonia water to the mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater in the flotation tank to adjust the pH value to 5-8, and then adding PAC solution and PAM solution for flotation to obtain flotation slag and wastewater containing sediment;

[0022] 2) reprecipitation: adding the PAC solution and the PAM solution to the wastewater containing the precipitate in step 1) again for precipitation to obtain a reprecipitate;

[0023] 3) Filtration and disc-tube reverse osmosis: filtering the reprecipitate obtained in step 2) through the filtration device to obtain a first filtrate, passing the first filtrate through the disc-tube reverse osmosis device for disc-tube reverse osmosis treatment to obtain concentrated water and fresh water; passing the concentrated water into the high-density sedimentation tank for treatment, and passing the fresh water into the reverse osmosis device for reverse osmosis treatment;

[0024] 4) High-density precipitation: In the high-density precipitation tank, ammonia water is added to a mixture of the rare earth extraction wastewater, the rare earth carbon precipitation wastewater, and the concentrated water obtained in step 3) to adjust the pH to 7-9, and oxalic acid, diammonium hydrogen phosphate, PAC solution, and PAM solution are sequentially added to obtain a precipitate;

[0025] 5) Filtration and MVR evaporation crystallization: filtering the precipitate obtained in step 4) through the first sand filter to obtain a second filtrate, and passing the second filtrate into the MVR evaporator for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate; wherein the ammonium chloride mass fraction of the first ammonium chloride crystals is at least 99.0 wt%;

[0026] 6) triple-effect evaporation crystallization: passing the MVR evaporation mother liquor obtained in step 5) into the triple-effect evaporator for triple-effect evaporation crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate; wherein the ammonium chloride mass fraction of the second ammonium chloride crystals is 91-95 wt%;

[0027] 7) Reverse osmosis: The MVR secondary steam condensate and the triple-effect secondary steam condensate obtained in step 5) are subjected to reverse osmosis treatment together with the fresh water obtained in step 3) through a reverse osmosis device to obtain treated wastewater.

[0028] According to the method of the present invention, preferably, in step 3), the reprecipitate obtained in step 2) is filtered through a second sand filter, and then the filtrate of the second sand filter is ultrafiltered by an ultrafiltration device to obtain a first filtrate;

[0029] Step 3) further includes adjusting the pH value of the first filtrate to 2-6 before subjecting the first filtrate to disc tube reverse osmosis treatment.

[0030] According to the method of the present invention, preferably, in step 5), before the second filtrate is subjected to evaporation and crystallization, the pH value of the second filtrate is adjusted to 5-8.

[0031] According to the method of the present invention, preferably, during the MVR evaporation crystallization process in step 5):

[0032] The material concentration in the first-effect falling film circulation separator is 5-14wt%, the saturation temperature difference is 1-5°C, and the material liquid temperature in the first-effect falling film circulation separator is 90-105°C;

[0033] The material concentration in the second-effect falling film circulation separator is 10-22 wt%, the saturation temperature difference is 1-6°C, and the material liquid temperature in the second-effect falling film circulation separator is 90-96°C;

[0034] The material concentration in the forced circulation separator is 10-44 wt%, the saturation temperature difference is 5-15° C., and the material liquid temperature in the forced circulation separator is 90-102° C.

[0035] According to the method of the present invention, preferably, in the triple-effect evaporation crystallization process of step 6):

[0036] The material concentration in the first-effect separator is 10-44 wt%, the saturation temperature difference is 20-32°C, and the material liquid temperature in the separator is 90-112°C;

[0037] The material concentration in the second-effect separator is 10-44wt%, the saturation temperature difference is 1-10°C, and the material liquid temperature in the separator is 90-92°C;

[0038] The material concentration in the triple-effect separator is 10-40 wt%, the saturation temperature difference is 1-10°C, and the material liquid temperature in the separator is 60-66°C.

[0039] According to the method of the present invention, preferably, the triple-effect evaporation mother liquor obtained in step 6) is returned to step 4) for high-density precipitation, or is dried to form salt.

[0040] According to the method of the present invention, preferably, in step 1), step 2) and step 4), the mass concentration of the PAC solution is 2 to 30 wt%; based on each ton of wastewater, the amount of the PAC solution is 100 to 1000 g; the mass concentration of the PAM solution is 0.01 to 0.5 wt%; based on each ton of wastewater, the amount of the PAM solution is 1 to 50 g.

[0041] The present invention's apparatus and method for recycling rare earth wastewater and co-producing ammonium chloride combines MVR evaporation and crystallization with triple-effect evaporation and crystallization to treat multiple rare earth wastewaters, producing two ammonium chloride products at low cost and low energy consumption: industrial-grade ammonium chloride and agricultural-grade ammonium chloride. Furthermore, the concentrated water and fresh water obtained from rare earth wastewater treatment can be reused in the rare earth production system, achieving wastewater recycling and reducing energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic diagram of a device for recycling rare earth wastewater and co-producing ammonium chloride according to the present invention;

[0043] Figure 2 The present invention is a process flow chart of the method for recycling rare earth wastewater and co-producing ammonium chloride.

[0044] Reference numerals

[0045] 1- Flotation tank; 2- Inclined plate sedimentation tank; 3- Filtration equipment, 31- Second sand filter, 32- Ultrafiltration equipment; 4- Disc tube reverse osmosis equipment; 5- High density sedimentation tank; 6- First sand filter; 7- MVR evaporator; 8- Triple effect evaporator; 9- Reverse osmosis equipment; 10- Negative pressure dryer.

[0046] The present invention will be further described below with reference to specific embodiments, but the protection scope of the present invention is not limited thereto.

[0047] The "conductivity" mentioned in the present invention is the reciprocal of resistivity, which refers to the ability of a substance to transmit electric current. It is usually represented by σ and the unit is μs / cm.

[0048] The TDS mentioned in the present invention is total dissolved solids, which refers to the total amount of solids dissolved in water, including inorganic and organic matter, and the unit is mg / L.

[0049] <Device for recycling rare earth wastewater and co-producing ammonium chloride>

[0050] The apparatus for recycling rare earth wastewater and co-producing ammonium chloride of the present invention comprises an air flotation tank, an inclined plate sedimentation tank, a filtration device, a disc-tube reverse osmosis device, a high-density sedimentation tank, a first sand filter, an MVR evaporator, a triple-effect evaporator, and a reverse osmosis device. A detailed description is provided below.

[0051] flotation tank

[0052] The flotation tank is used to float mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and to precipitate zinc ions, aluminum ions and iron ions in the mixed wastewater to obtain flotation slag and wastewater containing precipitation; the liquid outlet of the flotation tank is located at the bottom of the flotation tank, and the liquid outlet is connected to the feed port of the inclined plate sedimentation tank through a pipeline.

[0053] According to one embodiment of the present invention, the flotation tank is a device known in the art. The present invention may utilize any type of flotation tank known in the art, without particular limitation. For example, it may be at least one of a horizontal flow flotation tank, a vertical flow flotation tank, an integrated flotation-reaction flotation tank, an integrated flotation-sedimentation flotation tank, or an integrated flotation-filtration flotation tank; preferably, it may be at least one of an integrated flotation-reaction flotation tank, an integrated flotation-sedimentation flotation tank, or an integrated flotation-filtration flotation tank; more preferably, it may be an integrated flotation-reaction flotation tank or an integrated flotation-sedimentation flotation tank.

[0054] Inclined plate sedimentation tank

[0055] The inclined plate sedimentation tank is used to reprecipitate wastewater containing sediment to obtain reprecipitate; the discharge port of the inclined plate sedimentation tank is connected to the feed port of the filtering equipment through a pipeline.

[0056] According to one embodiment of the present invention, the inclined plate sedimentation tank is a device known in the art. The present invention may utilize any type of inclined plate sedimentation tank known in the art, without particular limitation. For example, it may be at least one of a co-current inclined plate sedimentation tank, a counter-current inclined plate sedimentation tank, and a lateral flow inclined plate sedimentation tank; preferably, a co-current inclined plate sedimentation tank or a counter-current inclined plate sedimentation tank; more preferably, a counter-current inclined plate sedimentation tank.

[0057] Filtration equipment

[0058] The filtering device is used for filtering the reprecipitate to obtain the first filtrate; the liquid outlet of the filtering device is connected to the liquid inlet of the disc tube reverse osmosis device through a pipeline.

[0059] According to one embodiment of the present invention, the filtration equipment includes a second sand filter and an ultrafiltration equipment, the feed port of the second sand filter is connected to the discharge port of the inclined plate sedimentation tank through a pipeline, and the filtrate outlet of the second sand filter is connected to the liquid inlet of the ultrafiltration equipment through a pipeline; the filtrate outlet of the ultrafiltration equipment is connected to the liquid inlet of the disc tube reverse osmosis equipment through a pipeline.

[0060] According to one embodiment of the present invention, the filter material of the second sand filter can be at least one of quartz sand, anthracite, activated carbon, and diatomaceous earth, preferably at least one of quartz sand, anthracite, and activated carbon, and more preferably quartz sand or activated carbon.

[0061] According to another embodiment of the present invention, the particle size of the filter material of the first sand filter may be 0.5 to 2 mm, preferably 0.6 to 1.5 mm, and more preferably 0.8 to 1.2 mm.

[0062] Reasonable sand filter media and filter media particle size can ensure better filtration effect.

[0063] According to one embodiment of the present invention, the ultrafiltration (UF) device can be any ultrafiltration device known in the art. The ultrafiltration membrane used by the ultrafiltration device can be any ultrafiltration membrane known in the art that can be used for treating industrial wastewater. The structure of the ultrafiltration membrane can be tubular or flat, preferably tubular. The ultrafiltration membrane material can be at least one of cellulose acetate, aromatic polyamide, polyethersulfone, polyvinylidene fluoride, and polyacrylonitrile, preferably at least one of cellulose acetate, polyethersulfone, and polyvinylidene fluoride, more preferably a composite membrane of cellulose acetate, polyethersulfone and polyvinylidene fluoride. Reasonable ultrafiltration membrane is more conducive to ultrafiltration filtration of the reprecipitate and achieves effective separation.

[0064] Disc tube reverse osmosis equipment

[0065] The disc tube reverse osmosis equipment is used to perform disc tube reverse osmosis treatment on the first filtrate to obtain concentrated water and fresh water; the concentrated water outlet of the disc tube reverse osmosis equipment is connected to the liquid inlet of the high-density sedimentation tank through a pipeline, and the fresh water outlet of the disc tube reverse osmosis equipment is connected to the liquid inlet of the reverse osmosis equipment through a pipeline.

[0066] According to one embodiment of the present invention, the disc-tube reverse osmosis (DTRO) equipment can be any DTRO equipment known in the art. The dense layer material of the DTRO membrane used in the disc-tube reverse osmosis equipment can be at least one of polysulfone, polyethersulfone, polypropylene, and polytetrafluoroethylene, preferably at least one of polysulfone and polyethersulfone, and more preferably polysulfone or polyethersulfone. A suitable DTRO membrane is more conducive to disc-tube reverse osmosis of the first filtrate, achieving effective separation.

[0067] High-density sedimentation tank

[0068] The high-density sedimentation tank is used to precipitate calcium ions and magnesium ions in a mixture of rare earth extraction wastewater, rare earth carbon precipitation wastewater and concentrated water obtained by disc tube reverse osmosis treatment; the high-density sedimentation tank is connected to the first sand filter through a pipeline.

[0069] High-density sedimentation tanks are well-known in the art. The present invention can utilize any type of high-density sedimentation tank known in the art, without particular limitation. For example, it can be at least one of a dispersed high-density sedimentation tank, an integrated high-density sedimentation tank, and a multi-combination high-density sedimentation tank, preferably an integrated high-density sedimentation tank or a multi-combination high-density sedimentation tank.

[0070] First sand filter

[0071] The first sand filter is used to filter the sediment produced in the high-density sedimentation tank; the filtrate outlet of the first sand filter is connected to the feed inlet of the MVR evaporator through a pipeline.

[0072] According to one embodiment of the present invention, the filter material of the first sand filter can be at least one of quartz sand, anthracite, activated carbon, and diatomaceous earth, preferably at least one of quartz sand, anthracite, and activated carbon, and more preferably quartz sand or activated carbon.

[0073] According to another embodiment of the present invention, the particle size of the filter material of the first sand filter may be 0.5 to 2 mm, preferably 0.6 to 1.5 mm, and more preferably 0.8 to 1.2 mm.

[0074] Reasonable sand filter media and filter media particle size can ensure better filtration effect.

[0075] MVR evaporator

[0076] The MVR evaporator is used to evaporate and crystallize the filtrate from the first sand filter to obtain first ammonium chloride crystals, MVR evaporation mother liquor and MVR secondary steam condensate; the mother liquor outlet of the MVR evaporator is connected to the liquid inlet of the triple-effect evaporator through a pipeline, and the secondary steam condensate outlet of the MVR evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline.

[0077] According to one embodiment of the present invention, the MVR evaporator is a device known in the art. The present invention can utilize any type of MVR evaporator known in the art, without particular limitation. For example, it can be at least one of an MVR rising film evaporator, an MVR falling film evaporator, or an MVR forced circulation evaporator; preferably, it can be at least one of an MVR falling film evaporator and an MVR forced circulation evaporator; more preferably, it can be a combination of an MVR bipolar falling film evaporator and an MVR forced circulation evaporator. A suitable MVR evaporator further facilitates MVR evaporation and crystallization, thereby improving the production efficiency of the first ammonium chloride crystals.

[0078] According to a specific embodiment of the present invention, the MVR evaporator includes a first-effect falling film circulation separator, a second-effect falling film circulation separator, and a forced circulation separator.

[0079] Three-effect evaporator

[0080] The triple-effect evaporator is used to evaporate the crystallization MVR evaporation mother liquor to obtain the second ammonium chloride crystals, triple-effect evaporation mother liquor and triple-effect secondary steam condensate; the secondary condensate outlet of the triple-effect evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline.

[0081] According to one embodiment of the present invention, the triple-effect evaporator of the present invention is a device well known in the art. The present invention can use any type of triple-effect evaporator well known in the art, without being particularly limited herein. For example, it can be a flow-type triple-effect evaporator or a triple-effect parallel-flow evaporator, preferably a flow-type triple-effect evaporator. A reasonable triple-effect evaporator is more conducive to the triple-effect evaporation crystallization and improves the production efficiency of the second ammonium chloride crystals.

[0082] According to a specific embodiment of the present invention, the triple-effect evaporator includes a first-effect separator, a second-effect separator and a third-effect separator.

[0083] According to one embodiment of the present invention, the device for recycling rare earth wastewater and co-producing ammonium chloride may further include a negative pressure dryer for drying the mother liquor of the triple-effect evaporation to produce salt; the mother liquor outlet of the triple-effect evaporator is connected to the liquid inlet of the negative pressure dryer through a first pipeline; the mother liquor outlet of the triple-effect evaporator is also connected to the liquid inlet of the high-density sedimentation tank through a second pipeline.

[0084] Reverse osmosis equipment

[0085] The reverse osmosis equipment is used to perform reverse osmosis treatment on the MVR secondary steam condensate, triple-effect secondary steam condensate and fresh water obtained by disc tube reverse osmosis treatment to obtain treated wastewater.

[0086] According to one embodiment of the present invention, the reverse osmosis (RO) equipment can be any RO equipment known in the art and is not particularly limited herein. The RO membrane used in the reverse osmosis equipment can be any RO membrane known in the art that can be used to treat steam condensate. The RO membrane can be in a roll-type or flat-plate structure, preferably a roll-type structure. The RO membrane material can be at least one of cellulose acetate, aliphatic polyamide, and aromatic polyamide, preferably at least one of cellulose acetate and aromatic polyamide, and more preferably a composite membrane of cellulose acetate and aromatic polyamide.

[0087] Choosing a reasonable RO membrane is more conducive to reverse osmosis filtration of steam condensate and achieves effective separation.

[0088] <Method for recycling rare earth wastewater and producing ammonium chloride>

[0089] The present invention also provides a method for recycling rare earth wastewater and co-producing ammonium chloride using the above-mentioned apparatus, comprising a flotation and precipitation step, a reprecipitation step, a disc-tube reverse osmosis step, a high-density precipitation step, an MVR evaporation and crystallization step, a triple-effect evaporation and crystallization step, and a reverse osmosis step. Optionally, a drying step is also included. This is described in detail below.

[0090] Flotation and sedimentation steps

[0091] Ammonia water is added to the mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater in the flotation tank to adjust the pH value, precipitate zinc ions, aluminum ions and iron ions, and PAC solution and PAM solution are added for flotation to obtain flotation slag and wastewater containing precipitation.

[0092] According to one embodiment of the present invention, aqueous ammonia can be added to adjust the pH value to 5 to 8, preferably 5.5 to 7.5, more preferably 6 to 7. A reasonable pH value is more conducive to the precipitation of zinc ions, aluminum ions and iron ions.

[0093] According to another embodiment of the present invention, the mass concentration of the added ammonia water may be 5 to 28 wt %, preferably 10 to 26 wt %, and more preferably 20 to 25 wt %.

[0094] The rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater treated by the present invention are all wastewaters well known in the art and are produced by further removing impurities (zinc removal, aluminum removal or iron removal) in the process of obtaining water-soluble rare earth salts.

[0095] The rare earth zinc removal wastewater of the present invention contains: ZnO 0.1-1.0 g / L, acidity 0.01-1 mol / L; rare earth aluminum removal wastewater: Al2O3 1-20 g / L, pH value 1-6; rare earth iron removal wastewater: Fe2O3 1-20 g / L, acidity 0.01-1 mol / L.

[0096] Preferably, the rare earth zinc removal wastewater contains: ZnO 0.15-0.85 g / L, acidity 0.05-0.5 mol / L; the rare earth aluminum removal wastewater contains: Al2O3 5-15 g / L, pH 2-5; the rare earth iron removal wastewater contains: Fe2O3 5-15 g / L, acidity 0.1-0.9 mol / L.

[0097] More preferably, the rare earth zinc removal wastewater contains: ZnO 0.2-0.8 g / L, acidity 0.1-0.3 mol / L; the rare earth aluminum removal wastewater contains: Al2O3 6-10 g / L, pH 4-5; the rare earth iron removal wastewater contains: Fe2O3 6-10 g / L, acidity 0.5-0.8 mol / L.

[0098] The method of the present invention jointly treats the rare earth zinc removal wastewater, rare earth aluminum removal wastewater, rare earth iron removal wastewater, rare earth extraction wastewater and rare earth carbon precipitation wastewater, which can not only jointly produce two types of ammonium chloride, but also reduce the energy consumption of separately treating the rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater.

[0099] According to one embodiment of the present invention, the mass concentration of the PAC solution can be 2-30 wt%, preferably 5-25 wt%, and more preferably 8-20 wt%. The amount of PAC solution used per ton of wastewater is 100-1000 g, preferably 200-800 g, and more preferably 300-600 g. A too low amount of PAC solution will not achieve a coagulation effect; a too high amount of PAC solution will be detrimental to cost control.

[0100] According to another embodiment of the present invention, the mass concentration of the PAM solution can be 0.01-0.5 wt%, preferably 0.01-0.5 wt%, and more preferably 0.01-0.5 wt%. Based on each ton of wastewater, the amount of PAM solution used is 1-50 g, preferably 200-800 g, and more preferably 300-600 g. If the amount of PAM solution used is too low, the flocculation effect cannot be achieved; if the amount of PAM solution used is too high, it is not conducive to cost control.

[0101] Reprecipitation

[0102] The obtained wastewater containing precipitates is passed into an inclined plate sedimentation tank, and PAC solution and PAM solution are added again for precipitation to obtain reprecipitates.

[0103] According to one embodiment of the present invention, the mass concentration of the PAC solution can be 2-30 wt%, preferably 5-25 wt%, and more preferably 8-20 wt%. The amount of PAC solution used per ton of wastewater can be 100-1000 g, preferably 200-800 g, and more preferably 300-600 g. If the amount of PAC solution used is too low, the coagulation effect cannot be achieved; if the amount of PAC solution used is too high, it is not conducive to cost control.

[0104] According to another embodiment of the present invention, the mass concentration of the PAM solution can be 0.01-0.5 wt%, preferably 0.01-0.5 wt%, and more preferably 0.01-0.5 wt%. Based on each ton of wastewater, the amount of PAM solution used can be 1-50 g, preferably 200-800 g, and more preferably 300-600 g. If the amount of PAM solution used is too low, the flocculation effect cannot be achieved; if the amount of PAM solution used is too high, it is not conducive to cost control.

[0105] Filtration and disc-tube reverse osmosis

[0106] The obtained reprecipitate is filtered through a filtering device to obtain a first filtrate, and the first filtrate is subjected to a disc-tube reverse osmosis treatment through a disc-tube reverse osmosis device to obtain concentrated water and fresh water.

[0107] According to one embodiment of the present invention, the precipitate may be first filtered through a second sand filter, and then the filtrate of the sand filtration may be ultrafiltered through an ultrafiltration device to obtain a first filtrate.

[0108] According to one embodiment of the present invention, before the first filtrate is subjected to disc tube reverse osmosis (DTRO) filtration, the pH of the first filtrate can be adjusted to 2 to 6, preferably 2.5 to 5.5, and more preferably 3 to 4. A reasonable pH value can ensure the osmotic effect of disc tube reverse osmosis and is not likely to damage the DTRO membrane.

[0109] According to another embodiment of the present invention, a hydrochloric acid solution may be used to adjust the pH value of the first filtrate to 2 to 6. The concentration of the hydrochloric acid solution may be 0.1 to 10 mol / L, preferably 0.2 to 5 mol / L, and more preferably 0.5 to 3 mol / L.

[0110] According to one embodiment of the present invention, the water inlet pressure of the disc-tube reverse osmosis can be 75 to 160 bar, preferably 80 to 130 bar, and more preferably 90 to 120 bar. A reasonable water inlet pressure can improve the efficiency of the disc-tube reverse osmosis and is less likely to damage the DTRO membrane.

[0111] In the present invention, the wastewater obtained after the disc tube reverse osmosis treatment is divided into concentrated water (DTRO concentrated water) and fresh water (DTRO fresh water). The TDS of the DTRO concentrated water is ≥10000 mg / L, and the σ of the DTRO fresh water is ≤2000 μs / cm.

[0112] According to one embodiment of the present invention, the DTRO concentrated water can be passed through a high-density precipitation step, where it undergoes high-density precipitation along with rare earth extraction wastewater and rare earth carbon precipitation wastewater. Alternatively, the DTRO fresh water can be passed through a reverse osmosis step, where it undergoes reverse osmosis treatment along with MVR secondary steam condensate and triple-effect secondary steam condensate. This allows for wastewater recycling.

[0113] High-density precipitation step

[0114] In the high-density sedimentation tank, ammonia water is added to the mixture of the rare earth extraction wastewater, the rare earth carbon precipitation wastewater and the concentrated water obtained in step 3) to adjust the pH value, oxalic acid is added in sequence to precipitate calcium ions, diammonium hydrogen phosphate is added to precipitate magnesium ions, and PAC solution and PAM solution are added for treatment to obtain a precipitate;

[0115] According to one embodiment of the present invention, the pH value adjusted by adding ammonia water may be 7 to 9, preferably 7.2 to 8.5, and more preferably 7.5 to 8. A reasonable pH value in wastewater is more conducive to the precipitation of calcium ions by oxalic acid.

[0116] According to another embodiment of the present invention, the mass concentration of the added ammonia water may be 5 to 28 wt %, preferably 10 to 26 wt %, and more preferably 20 to 25 wt %.

[0117] According to one embodiment of the present invention, the amount of oxalic acid added is determined based on the theoretical amount of calcium ions in the precipitated mixed wastewater, and can be 1 to 10 wt% above the theoretical amount, preferably 2 to 8 wt% above the theoretical amount, and more preferably 3 to 6 wt% above the theoretical amount. If the amount of oxalic acid added is too low, the calcium ion precipitation is incomplete; if the amount of oxalic acid added is too high, it is not conducive to cost control.

[0118] According to one embodiment of the present invention, the amount of diammonium hydrogen phosphate added is determined based on the theoretical amount of magnesium ions in the precipitated mixed wastewater, and can be 1 to 10 wt% above the theoretical amount, preferably 2 to 8 wt% above the theoretical amount, and more preferably 3 to 6 wt% above the theoretical amount. If the amount of diammonium hydrogen phosphate added is too low, the magnesium ion precipitation is incomplete; if the amount of diammonium hydrogen phosphate added is too high, it is not conducive to cost control.

[0119] The rare earth extraction wastewater treated by the present invention is wastewater generated by extracting rare earth elements during rare earth production, which is well known in the art. The rare earth carbon precipitation wastewater treated by the present invention is wastewater generated by carbon precipitation of rare earth elements during rare earth production, which is well known in the art.

[0120] The rare earth extraction wastewater of the present invention comprises: a total dissolved solids (TDS) of 60,000 to 150,000 mg / L, CaO of 10 to 150 mg / L, MgO of 5 to 100 mg / L, and NH4Cl of 80 to 120 g / L; and the rare earth carbon precipitation wastewater of the present invention comprises: a TDS of 100,000 to 200,000 mg / L, CaO of 100 to 800 mg / L, MgO of 100 to 500 mg / L, and NH4Cl of 100 to 150 g / L.

[0121] Preferably, in the rare earth extraction wastewater of the present invention, the total dissolved solids (TDS) is 60,000-150,000 mg / L, CaO is 15-120 mg / L, MgO is 10-80 mg / L, and NH4Cl is 85-115 g / L; in the rare earth carbon precipitation wastewater, the TDS is 130,000-180,000 mg / L, CaO is 150-750 mg / L, MgO is 150-450 mg / L, and NH4Cl is 105-145 g / L.

[0122] More preferably, in the rare earth extraction wastewater of the present invention, the total dissolved solids (TDS) is 80,000-120,000 mg / L, CaO is 20-100 mg / L, MgO is 10-50 mg / L, and NH4Cl is 90-110 g / L; in the rare earth carbon precipitation wastewater, the TDS is 120,000-150,000 mg / L, CaO is 200-500 mg / L, MgO is 150-350 mg / L, and NH4Cl is 110-140 g / L.

[0123] The method of the present invention has better treatment effect on the rare earth extraction wastewater and rare earth carbon precipitation wastewater.

[0124] In the present invention, PAC (polyaluminium chloride) is used as a coagulant to promote the aggregation of suspended matter and colloids in wastewater to form larger particles; PAM (polyacrylamide) is used as a flocculant to promote the aggregation and precipitation of larger particles after coagulation.

[0125] According to one embodiment of the present invention, in this step, the mass concentration of the PAC solution can be 2-30 wt%, preferably 5-25 wt%, and more preferably 8-20 wt%. Based on each ton of wastewater, the amount of PAC solution used can be 100-1000 g, preferably 200-800 g, and more preferably 300-600 g. If the amount of PAC solution used is too low, the coagulation effect cannot be achieved; if the amount of PAC solution used is too high, it is not conducive to cost control.

[0126] According to another embodiment of the present invention, in this step, the mass concentration of the PAM solution can be 0.01 to 0.5 wt%, preferably 0.05 to 0.4 wt%, and more preferably 0.1 to 0.3 wt%. Based on each ton of wastewater, the amount of PAM solution used can be 1 to 50 g, preferably 3 to 30 g, and more preferably 5 to 20 g. Using too little PAM solution will not achieve a flocculation effect; using too much PAM solution will be detrimental to cost control.

[0127] Filtration and MVR evaporation crystallization steps

[0128] The precipitate obtained above is filtered through the first sand filter to obtain a second filtrate, and the second filtrate is passed into the MVR evaporator for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor and MVR secondary steam condensate.

[0129] According to one embodiment of the present invention, before the second filtrate is placed in the MVR evaporator for evaporation and crystallization, the pH of the filtrate can be adjusted to 5-8, preferably 5.5-7.5, and more preferably 6-7. The pH of the filtrate can be adjusted using a hydrochloric acid solution, the concentration of which can be 0.1-10 mol / L, preferably 0.2-5 mol / L, and more preferably 0.5-3 mol / L. A reasonable pH range can ensure stable operation of the MVR evaporator. A pH that is too low can corrode the MVR evaporator, while a pH that is too high is not conducive to the recovery of ammonium chloride.

[0130] According to one embodiment of the present invention, in the MVR evaporation crystallization:

[0131] The material concentration in the single-effect falling film circulation separator can be 5-14 wt%, preferably 6-12 wt%, more preferably 8-10 wt%; the saturation temperature difference can be 1-5°C, preferably 1.5-4.5°C, more preferably 2-4°C; the material liquid temperature in the single-effect falling film circulation separator can be 90-110°C, preferably 95-108°C, more preferably 100-105°C;

[0132] The material concentration in the second-effect falling film circulation separator can be 10-22 wt%, preferably 12-20 wt%, more preferably 15-18 wt%; the saturation temperature difference can be 1-10°C, preferably 3-10°C, more preferably 5-9°C; the material liquid temperature in the second-effect falling film circulation separator can be 90-96°C, preferably 91-95°C, more preferably 92-94°C;

[0133] The material concentration in the forced circulation separator can be 10-44wt%, preferably 15-40wt%, more preferably 20-30wt%; the saturation temperature difference can be 5-20°C, preferably 8-18°C, more preferably 10-16°C; the material liquid temperature in the forced circulation separator can be 90-105°C, preferably 92-103°C, more preferably 95-102°C.

[0134] Reasonable MVR evaporation and crystallization parameters can ensure the stable operation of the MVR evaporator while more efficiently obtaining the first ammonium chloride crystals. Parameters that are too low will affect production efficiency, while parameters that are too high will be detrimental to the stable operation of the MVR evaporator.

[0135] According to one embodiment of the present invention, the ammonium chloride mass fraction of the first ammonium chloride crystal obtained can be at least 99.0wt%, preferably at least 99.2wt%, more preferably at least 99.3wt%.The first ammonium chloride crystal obtained can be directly used in the production of industrial-grade ammonium chloride product (ammonium chloride content 99wt% or more).

[0136] Three-effect evaporation crystallization steps

[0137] The MVR evaporation mother liquor is passed into a triple-effect evaporator for triple-effect evaporation and crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor and triple-effect secondary steam condensate;

[0138] According to one embodiment of the present invention, in the triple-effect evaporation crystallization:

[0139] The material concentration in the first-effect separator can be 10-44 wt%, preferably 15-40 wt%, more preferably 20-30 wt%; the saturation temperature difference can be 20-32°C, preferably 22-30°C, more preferably 25-28°C; the material liquid temperature in the first-effect separator can be 90-115°C, preferably 95-112°C, more preferably 100-110°C;

[0140] The material concentration in the second-effect separator can be 10-44wt%, preferably 15-40wt%, more preferably 20-30wt%; the saturation temperature difference can be 1-10°C, preferably 2-8°C, more preferably 3-6°C; the material liquid temperature in the separator is 85-95°C, preferably 88-93°C, more preferably 90-92°C;

[0141] The material concentration in the triple-effect separator can be 10-40wt%, preferably 15-35wt%, more preferably 20-30wt%; the saturation temperature difference can be 1-10°C, preferably 2-8°C, more preferably 3-6°C; the material liquid temperature in the triple-effect separator can be 60-70°C, preferably 62-68°C, more preferably 63-66°C.

[0142] Reasonable triple-effect evaporation crystallization parameters can ensure the stable operation of the triple-effect evaporator while more efficiently obtaining the second ammonium chloride crystals. Parameters that are too low will affect production efficiency, while parameters that are too high will be detrimental to the stable operation of the triple-effect evaporator.

[0143] According to one embodiment of the present invention, the triple-effect evaporation mother liquor can be returned to the high-density precipitation step and subjected to high-density precipitation together with the mixed wastewater of rare earth extraction wastewater and rare earth carbon precipitation wastewater to achieve wastewater recycling.

[0144] According to another embodiment of the present invention, if the salt content in the triple-effect evaporation mother liquor reaches a set value, the triple-effect evaporation mother liquor can also be dried to produce salt, thereby realizing waste utilization. The drying process of the present invention can be carried out under negative pressure, preferably 50 to 200 Pa, and more preferably 100 to 150 Pa.

[0145] According to one embodiment of the present invention, the ammonium chloride mass fraction of the second ammonium chloride crystals is 91-95 wt %. Preferably, it is 91.5-94.5 wt %, and more preferably at least 91-93 wt %. The obtained second ammonium chloride crystals can be directly used in the production of agricultural-grade ammonium chloride products (ammonium chloride content 91.7-95 wt %).

[0146] Reverse osmosis steps

[0147] The MVR secondary steam condensate, the triple-effect secondary steam condensate and the fresh water obtained by the disc-tube reverse osmosis treatment are subjected to reverse osmosis treatment by a reverse osmosis device to obtain treated wastewater.

[0148] According to one embodiment of the present invention, the water inlet pressure for reverse osmosis treatment can be 10 to 60 bar, preferably 15 to 55 bar, and more preferably 20 to 50 bar. Reasonable water inlet pressure can improve reverse osmosis efficiency and is less likely to damage the RO membrane.

[0149] In the present invention, the wastewater obtained after reverse osmosis treatment is divided into concentrated water (RO concentrated water) and fresh water (RO fresh water). The TDS of RO concentrated water is ≥800 mg / L, and the TDS of RO fresh water is ≤100 mg / L.

[0150] According to one embodiment of the present invention, both the RO concentrated water and the RO fresh water can be reused in rare earth production. The specific application can be carried out according to the water requirements of each step in rare earth production.

[0151] <Test method>

[0152] In the wastewater treatment process of the present invention, the TDS, acidity, pH value and conductivity are all detected using an Extech EC500 conductivity tester.

[0153] Metal ion detection is carried out in accordance with the "Technical Specifications for Wastewater Monitoring HJ 91.1-2019".

[0154] <Ingredients>

[0155] The raw materials used in the following examples and comparative examples are described below:

[0156] The rare earth extraction wastewater, rare earth carbon precipitation wastewater, rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater used in the following examples are all wastewaters generated by corresponding treatment procedures in the rare earth production process.

[0157] Unless otherwise specified, other raw materials in the following examples are commercially available products.

[0158] The following is an explanation of the terms:

[0159] PAC: polyaluminium chloride;

[0160] PAM: polyacrylamide;

[0161] MVR: Mechanical vapor recompression;

[0162] DTRO: Disc-tube reverse osmosis.

[0163] Example 1

[0164] like Figure 1 As shown, the device for recycling rare earth wastewater and co-producing ammonium chloride described in this embodiment includes: a flotation tank 1, an inclined plate sedimentation tank 2, a filtration device 3, a disc tube reverse osmosis device 4, a high-density sedimentation tank 5, a first sand filter 6, an MVR evaporator 7, a triple-effect evaporator 8, a reverse osmosis device 9 and a negative pressure dryer 10.

[0165] The flotation tank 1 is used to float mixed wastewater formed by rare earth zinc removal wastewater, rare earth aluminum removal wastewater, and rare earth iron removal wastewater, and to precipitate zinc, aluminum, and iron ions in the wastewater to obtain flotation slag and wastewater containing precipitate. The flotation tank 1 of this embodiment is an integrated flotation and precipitation flotation tank.

[0166] The liquid outlet of the flotation tank 1 of this embodiment is located at the bottom of the flotation tank 1 , and the liquid outlet is connected to the feed port of the inclined plate sedimentation tank 2 through a pipeline.

[0167] The inclined plate sedimentation tank 2 is used to reprecipitate the wastewater containing the precipitate to obtain the reprecipitate (including the stratified precipitate and the wastewater). The inclined plate sedimentation tank 2 of this embodiment adopts a counter-current inclined plate sedimentation tank. The discharge port of the inclined plate sedimentation tank 2 is connected to the feed port of the filter device 3 through a pipeline.

[0168] Filtration equipment 3 is used to filter the reprecipitate to obtain a first filtrate. Filtration equipment 3 includes a second sand filter 31 and an ultrafiltration equipment 32. The feed inlet of the second sand filter 31 is connected to the discharge outlet of the inclined plate sedimentation tank 2 via a pipeline. The filtrate outlet of the second sand filter 31 is connected to the inlet of the ultrafiltration equipment 32 via a pipeline. The filtrate outlet of the ultrafiltration equipment 32 is also connected to the inlet of the disc-tube reverse osmosis equipment 4 via a pipeline.

[0169] In this embodiment, the filter material of the second sand filter 31 is quartz sand with a particle size of 1 mm. The ultrafiltration membrane of the ultrafiltration device 32 is a tubular composite membrane formed of cellulose acetate, polyethersulfone and polyvinylidene fluoride.

[0170] The disc-tube reverse osmosis unit 4 is used to perform disc-tube reverse osmosis treatment on the first filtrate to produce concentrated water and fresh water. The concentrated water outlet of the disc-tube reverse osmosis unit 4 is connected to the liquid inlet of the high-density sedimentation tank 5 via a pipeline, while the fresh water outlet of the disc-tube reverse osmosis unit is connected to the liquid inlet of the reverse osmosis unit 9 via a pipeline. In this embodiment, the dense layer of the DTRO membrane of the disc-tube reverse osmosis unit 4 is formed of polyethersulfone.

[0171] High-density sedimentation tank 5 is used to precipitate calcium and magnesium ions from a mixture of rare earth extraction wastewater, rare earth carbon precipitation wastewater, and concentrated water from disc-tube reverse osmosis. In this embodiment, high-density sedimentation tank 5 utilizes a multi-combination high-density sedimentation tank. The discharge port of high-density sedimentation tank 5 is connected to the feed port of the first sand filter 6 via a pipeline.

[0172] The first sand filter 6 is used to filter the sediment generated in the high-density sedimentation tank 5. In this embodiment, the filter material of the first sand filter 6 is quartz sand with a particle size of 1 mm. The filtrate outlet of the first sand filter 6 is connected to the feed inlet of the MVR evaporator 7 via a pipeline.

[0173] The MVR evaporator 7 is used to evaporate and crystallize the filtrate from the first sand filter 6 to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate. The MVR evaporator 7 of this embodiment is a composite MVR evaporator consisting of an MVR bipolar falling film evaporator and an MVR forced circulation evaporator. The MVR bipolar falling film evaporator includes a first-effect falling film circulation separator and a second-effect falling film circulation separator. The MVR forced circulation evaporator is also known as a forced circulation separator. The mother liquor outlet of the MVR evaporator 7 is connected to the liquid inlet of the triple-effect evaporator 8 via a pipeline, and the secondary steam condensate outlet of the MVR evaporator 7 is connected to the liquid inlet of the reverse osmosis device 9 via a pipeline.

[0174] The triple-effect evaporator 8 is used to evaporate the crystallization MVR evaporation mother liquor to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate. The triple-effect evaporator 4 of this embodiment adopts a flow-type triple-effect evaporator. The triple-effect evaporator 8 specifically includes a primary separator, a secondary separator, and a triple-effect separator. The secondary condensate outlet of the triple-effect evaporator 8 is connected to the liquid inlet of the reverse osmosis equipment 9 via a pipeline. The mother liquor outlet of the triple-effect evaporator 8 is connected to the liquid inlet of the negative pressure dryer 10 via a first pipeline and to the liquid inlet of the high-density precipitation tank 5 via a second pipeline.

[0175] Reverse osmosis equipment 9 is used to perform reverse osmosis filtration on the MVR secondary steam condensate, triple-effect secondary steam condensate, and fresh water obtained from disc-tube reverse osmosis treatment to obtain treated wastewater. In this embodiment, reverse osmosis equipment 9 utilizes a spiral RO membrane. This RO membrane is a composite membrane formed from cellulose acetate and aromatic polyamide.

[0176] Example 2

[0177] A method for recycling rare earth wastewater and co-producing ammonium chloride using the device for recycling rare earth wastewater and co-producing ammonium chloride described in Example 1 comprises the following steps:

[0178] 5 tons of rare earth zinc removal wastewater (ZnO: 0.8 g / L, acidity 0.2 mol / L), 5 tons of rare earth aluminum removal wastewater (Al2O3: 10 g / L, pH: 4), and 5 tons of rare earth iron removal wastewater (Fe2O3: 10 g / L, acidity 0.6 mol / L) were mixed to form a first mixed wastewater. The first mixed wastewater was passed into a flotation tank 1, where 24 wt% ammonia was added to adjust the pH to 6 to precipitate zinc, aluminum, and iron ions. After precipitation, 500 g of a 10 wt% PAC solution per ton of wastewater was added for coagulation. 500 g of a 0.2 wt% PAM solution per ton of wastewater was added for flocculation. After flotation, flotation residue and wastewater containing precipitate were obtained.

[0179] The wastewater containing the precipitate is passed into the inclined plate sedimentation tank 2, and 500 g of 10 wt% PAC solution is added per ton of wastewater for coagulation again, and 500 g of 0.2 wt% PAM solution is added per ton of wastewater for flocculation again to obtain a reprecipitate.

[0180] The reprecipitate is filtered through the second sand filter 31 of the filtration device 3 to obtain a sand filtration filtrate. The sand filtration filtrate is ultrafiltered through the ultrafiltration device 32 to obtain a first filtrate.

[0181] The pH of the first filtrate was adjusted to 3 using a 1 mol / L hydrochloric acid solution. The first filtrate was then passed through disc-tube reverse osmosis equipment 4 for disc-tube reverse osmosis treatment at an inlet pressure of 100 bar. The resulting DTRO fresh water (conductivity σ = 2000 μs / cm) was passed through reverse osmosis equipment 9 for reverse osmosis desalination. The resulting DTRO concentrate (TDS = 10,000 mg / L) was passed through a high-density sedimentation tank 5 for treatment, achieving wastewater recycling.

[0182] 5 tons of rare earth extraction wastewater (TDS: 100,000 mg / L, CaO: 20 mg / L, MgO: 10 mg / L, NH4Cl 100 g / L), 5 tons of rare earth carbon precipitation wastewater (TDS: 120,000 mg / L, CaO: 200 mg / L, MgO: 150 mg / L, NH4Cl 120 g / L), and DTRO concentrated water were mixed to form a second mixed wastewater. The second mixed wastewater was passed into a high-density sedimentation tank 5, where 24 wt% ammonia water was added to adjust the pH to 7.5. Oxalic acid was added at 5 wt% excess of the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate was added at 5 wt% excess of the theoretical amount to precipitate magnesium ions. After precipitation, 500 g of 10 wt% PAC solution per ton of wastewater was added for coagulation, and 500 g of 0.2 wt% PAM solution per ton of wastewater was added for flocculation to obtain a precipitate.

[0183] The precipitate is filtered through a first sand filter 6 to obtain a second filtrate. A 1 mol / L hydrochloric acid solution is used to adjust the pH of the second filtrate to 6, and then the second filtrate is passed into an MVR evaporator 7 for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate. The operating parameters of the MVR evaporator 7 are as follows: the material concentration in the first-effect falling film circulation separator is 8wt%, the saturation temperature difference is 4°C, and the material liquid temperature in the first-effect falling film circulation separator is 103°C; the material concentration in the second-effect falling film circulation separator is 15wt%, the saturation temperature difference is controlled at 7.5°C, and the material liquid temperature in the second-effect falling film circulation separator is 93°C; the material concentration in the forced circulation separator is 20wt%, the saturation temperature difference is controlled at 15°C, and the material liquid temperature in the forced circulation separator is 101°C. The first ammonium chloride crystals (ammonium chloride content of 99.5wt%) account for 90wt% of the total salt content (total ammonium chloride content in rare earth extraction wastewater and rare earth carbon precipitation wastewater) and can be directly used to produce industrial-grade ammonium chloride products.

[0184] The MVR evaporation mother liquor is passed into a triple-effect evaporator 8 for triple-effect evaporation and crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are as follows: the material concentration in the first-effect separator is 20wt%, the saturation temperature difference is 28°C, and the material liquid temperature in the first-effect separator is 110°C; the material concentration in the second-effect separator is 20wt%, the saturation temperature difference is 3°C, and the material liquid temperature in the second-effect separator is 90°C; and the material concentration in the third-effect separator is 20wt%, the saturation temperature difference is 3°C, and the material liquid temperature in the third-effect separator is 65°C. The second ammonium chloride crystals (ammonium chloride content is 92wt%) account for 9.8wt% of the total salt content (the total ammonium chloride content in the rare earth extraction wastewater and the rare earth carbon precipitation wastewater) and can be directly used to produce agricultural-grade ammonium chloride products. Part of the mother liquor produced by the triple-effect evaporation crystallization is returned to the high-density precipitation tank 5 for recycling, and part is dried under negative pressure at 100 Pa in the negative pressure dryer 10 to produce mixed salts. The mixed salts produced account for 0.2 wt% of the total salt amount.

[0185] The MVR secondary steam condensate, triple-effect secondary steam condensate, and DTRO fresh water are subjected to reverse osmosis treatment in reverse osmosis equipment 9 at an inlet pressure of 30 bar. The resulting RO concentrate (TDS = 1000 mg / L) and RO fresh water (TDS = 100 mg / L) are respectively recycled back into the rare earth production system, achieving wastewater recycling.

[0186] After calculation, the energy consumption cost of treating unit wastewater in this embodiment is as follows:

[0187] Each ton of wastewater consumes 0.046 tons of steam and 30 kW·h of electricity. Assuming a steam price of 200 yuan per ton and an electricity price of 0.6 yuan per kW·h, the energy cost of treating one ton of wastewater is 27.2 yuan.

[0188] The present invention realizes the recycling and reuse of wastewater and the high-quality recovery of valuable elements in the wastewater at a low treatment cost.

[0189] Example 3

[0190] A method for recycling rare earth wastewater and co-producing ammonium chloride using the device for recycling rare earth wastewater and co-producing ammonium chloride described in Example 1 comprises the following steps:

[0191] 5 tons of rare earth zinc removal wastewater (ZnO: 0.2 g / L, acidity 0.2 mol / L), 5 tons of rare earth aluminum removal wastewater (Al2O3: 6 g / L, pH: 5), and 5 tons of rare earth iron removal wastewater (Fe2O3: 6 g / L, acidity 0.6 mol / L) were mixed to form a first mixed wastewater. The first mixed wastewater was passed into a flotation tank 1, where 24 wt% ammonia was added to adjust the pH to 7 to precipitate zinc, aluminum, and iron ions. After precipitation, 500 g of a 10 wt% PAC solution per ton of wastewater was added for coagulation, and 500 g of a 0.2 wt% PAM solution per ton of wastewater was added for flocculation. After flotation, flotation residue and wastewater containing precipitate were obtained.

[0192] The wastewater containing the precipitate is passed into the inclined plate sedimentation tank 2, and a PAC solution is added at a concentration of 10 wt% by weight per ton of wastewater, and coagulation is performed again. A PAM solution is added at a concentration of 0.2 wt% by weight per ton of wastewater, and flocculation is performed again to obtain a reprecipitate.

[0193] The reprecipitate is filtered through the second sand filter 31 of the filtration device 3 to obtain a sand filtration filtrate. The sand filtration filtrate is ultrafiltered through the ultrafiltration device 32 to obtain a first filtrate.

[0194] The pH of the first filtrate was adjusted to 4 using a 1 mol / L hydrochloric acid solution. The first filtrate was then passed through disc-tube reverse osmosis equipment 4 for disc-tube reverse osmosis at an inlet pressure of 120 bar. The resulting DTRO fresh water (conductivity σ = 1500 μs / cm) was passed through reverse osmosis equipment 9 for reverse osmosis desalination. The resulting DTRO concentrate (TDS = 15,000 mg / L) was returned to high-density sedimentation tank 5 for treatment, achieving wastewater recycling.

[0195] 5 tons of rare earth extraction wastewater (TDS: 80,000 mg / L, CaO: 50 mg / L, MgO: 30 mg / L, NH4Cl 95 g / L), 5 tons of rare earth carbon precipitation wastewater (TDS: 120,000 mg / L, CaO: 200 mg / L, MgO: 150 mg / L, NH4Cl 130 g / L), and DTRO concentrated water were mixed to form a second mixed wastewater. The second mixed wastewater was passed into a high-density sedimentation tank 5, where 24 wt% ammonia was added to adjust the pH to 7.5. Oxalic acid was added at a 5 wt% excess of the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate was added at a 5 wt% excess of the theoretical amount to precipitate magnesium ions. After precipitation, 500 g of a 10 wt% PAC solution was added per ton of wastewater for coagulation, and 500 g of a 0.2 wt% PAM solution was added per ton of wastewater for flocculation to obtain a precipitate.

[0196] The precipitate is filtered through a first sand filter 6 to obtain a second filtrate. A 1 mol / L hydrochloric acid solution is used to adjust the pH value of the second filtrate to 7, and then the second filtrate is passed into an MVR evaporator 7 for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate. The operating parameters of the MVR evaporator 7 are as follows: the material concentration in the first-effect falling film circulation separator is 10wt%, the saturation temperature difference is 3.5°C, and the material liquid temperature in the first-effect falling film circulation separator is 102°C; the material concentration in the second-effect falling film circulation separator is 18wt%, the saturation temperature difference is controlled to 6°C, and the material liquid temperature in the second-effect falling film circulation separator is 92°C; the material concentration in the forced circulation separator is 30wt%, the saturation temperature difference is 15°C, and the material liquid temperature in the forced circulation separator is 101°C. The first ammonium chloride crystals (ammonium chloride content of 99.3 wt%) account for 85 wt% of the total salt content (total ammonium chloride content in rare earth extraction wastewater and rare earth carbon precipitation wastewater) and can be directly used to produce industrial-grade ammonium chloride products.

[0197] The MVR evaporation mother liquor is passed into a triple-effect evaporator 8 for triple-effect evaporation and crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are as follows: the material concentration in the first-effect separator is 30wt%, the saturation temperature difference is 28°C, and the material liquid temperature in the first-effect separator is 110°C; the material concentration in the second-effect separator is 30wt%, the saturation temperature difference is 10°C, and the material liquid temperature in the second-effect separator is 90°C; and the material concentration in the third-effect separator is 30wt%, the saturation temperature difference is 6°C, and the material liquid temperature in the third-effect separator is 65°C. The second ammonium chloride crystals (ammonium chloride content is 91.7wt%) account for 14.7wt% of the total salt content (the total ammonium chloride content in the rare earth extraction wastewater and the rare earth carbon precipitation wastewater) and can be directly used to produce agricultural-grade ammonium chloride products. Part of the mother liquor produced by the triple-effect evaporation crystallization is returned to the high-density sedimentation tank 5 for recycling, and part is dried under negative pressure at 150 Pa in the negative pressure dryer 10 to produce mixed salts. The mixed salts produced account for 0.2wt% of the total salt content.

[0198] The MVR secondary steam condensate, triple-effect secondary steam condensate, and DTRO fresh water are subjected to reverse osmosis treatment in reverse osmosis equipment 9 at an inlet pressure of 50 bar. The resulting RO concentrate (TDS = 800 mg / L) and RO fresh water (TDS = 100 mg / L) are respectively recycled back into the rare earth production system, achieving wastewater recycling.

[0199] After calculation, the energy consumption cost of treating unit wastewater in this embodiment is as follows:

[0200] Each ton of wastewater consumes 0.045 tons of steam and 30 kW·h of electricity. Assuming a steam price of 200 yuan per ton and an electricity price of 0.6 yuan per kW·h, the energy cost of treating one ton of wastewater is 27 yuan.

[0201] The present invention realizes the recycling and reuse of wastewater and the high-quality recovery of valuable elements in the wastewater at a low treatment cost.

[0202] Example 4

[0203] A method for recycling rare earth wastewater and co-producing ammonium chloride using the device for recycling rare earth wastewater and co-producing ammonium chloride described in Example 1 comprises the following steps:

[0204] 5 tons of rare earth zinc removal wastewater (ZnO: 0.5 g / L, acidity 0.2 mol / L), 5 tons of rare earth aluminum removal wastewater (Al2O3: 8 g / L, pH: 4), and 5 tons of rare earth iron removal wastewater (Fe2O3: 8 g / L, acidity 0.6 mol / L) were mixed to form a first mixed wastewater. The first mixed wastewater was passed into a flotation tank 1, where 24 wt% ammonia was added to adjust the pH to 6 to precipitate zinc, aluminum, and iron ions. After precipitation, 500 g of a 10 wt% PAC solution per ton of wastewater was added for coagulation, and 500 g of a 0.2 wt% PAM solution per ton of wastewater was added for flocculation. After flotation, flotation residue and wastewater containing precipitate were obtained.

[0205] The wastewater containing the precipitate is passed into the inclined plate sedimentation tank 2, and a PAC solution is added at a concentration of 10 wt% per ton of wastewater at a rate of 500 g, and coagulation is performed again. A PAM solution is added at a concentration of 0.2 wt% per ton of wastewater at a rate of 500 g, and flocculation is performed again to obtain a reprecipitate.

[0206] The reprecipitate is filtered through the second sand filter 31 of the filtration device 3 to obtain a sand filtration filtrate. The sand filtration filtrate is ultrafiltered through the ultrafiltration device 32 to obtain a first filtrate.

[0207] The pH of the first filtrate was adjusted to 3 using a 1 mol / L hydrochloric acid solution. The first filtrate was then passed through disc-tube reverse osmosis equipment 4 for disc-tube reverse osmosis treatment at an inlet pressure of 90 bar. The resulting DTRO fresh water (conductivity σ = 1800 μs / cm) was passed through reverse osmosis equipment 9 for reverse osmosis desalination. The resulting DTRO concentrate (TDS = 13000 mg / L) was passed through a high-density sedimentation tank 5 for treatment, achieving wastewater recycling.

[0208] 5 tons of rare earth extraction wastewater (TDS: 120,000 mg / L, CaO: 100 mg / L, MgO: 50 mg / L, NH4Cl 90 g / L), 5 tons of rare earth carbon precipitation wastewater (TDS: 150,000 mg / L, CaO: 500 mg / L, MgO: 350 mg / L, NH4Cl 125 g / L), and DTRO concentrated water were mixed to form a second mixed wastewater. The second mixed wastewater was passed into a high-density sedimentation tank 5, where 24 wt% ammonia was added to adjust the pH to 7.5. Oxalic acid was added at a 5 wt% excess of the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate was added at a 5 wt% excess of the theoretical amount to precipitate magnesium ions. After precipitation, 500 g of 10 wt% PAC solution per ton of wastewater was added for coagulation, and 500 g of 0.2 wt% PAM solution per ton of wastewater was added for flocculation to obtain a precipitate.

[0209] The precipitate is filtered through a first sand filter 6 to obtain a second filtrate. A 1 mol / L hydrochloric acid solution is used to adjust the pH of the second filtrate to 6, and then the second filtrate is passed into an MVR evaporator 7 for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate. The operating parameters of the MVR evaporator 7 are as follows: the material concentration in the first-effect falling film circulation separator is 9wt%, the saturation temperature difference is 3°C, and the material liquid temperature in the first-effect falling film circulation separator is 102°C; the material concentration in the second-effect falling film circulation separator is 16wt%, the saturation temperature difference is 8.5°C, and the material liquid temperature in the second-effect falling film circulation separator is 93.5°C; the material concentration in the forced circulation separator is 25wt%, the saturation temperature difference is 15°C, and the material liquid temperature in the forced circulation separator is 101°C. The first ammonium chloride crystals (ammonium chloride content of 99.5wt%) account for 80wt% of the total salt content (total ammonium chloride content in rare earth extraction wastewater and rare earth carbon precipitation wastewater) and can be directly used to produce industrial-grade ammonium chloride products.

[0210] The MVR evaporation mother liquor is passed into a triple-effect evaporator 8 for triple-effect evaporation and crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are as follows: the material concentration in the first-effect separator is 25%, the saturation temperature difference is 26°C, and the material liquid temperature in the first-effect separator is 105°C; the material concentration in the second-effect separator is 25wt%, the saturation temperature difference is 5°C, and the material liquid temperature in the second-effect separator is 91°C; and the material concentration in the third-effect separator is 25wt%, the saturation temperature difference is 5°C, and the material liquid temperature in the third-effect separator is 65°C. The second ammonium chloride crystals (ammonium chloride content is 93wt%) account for 19.5wt% of the total salt content (the total ammonium chloride content in the rare earth extraction wastewater and the rare earth carbon precipitation wastewater) and can be directly used to produce agricultural-grade ammonium chloride products. Part of the mother liquor produced by the triple-effect evaporation crystallization is returned to the high-density precipitation tank 5 for recycling, and part is dried under negative pressure at 120 Pa in the negative pressure dryer 10 to produce mixed salts. The mixed salts produced account for 0.2wt% of the total salt amount.

[0211] The MVR secondary steam condensate, triple-effect secondary steam condensate, and DTRO fresh water are subjected to reverse osmosis treatment in reverse osmosis equipment 9 at an inlet pressure of 20 bar. The resulting RO concentrate (TDS = 1200 mg / L) and RO fresh water (TDS = 100 mg / L) are respectively recycled back into the rare earth production system, achieving wastewater recycling.

[0212] After calculation, the energy consumption cost of treating unit wastewater in this embodiment is as follows:

[0213] Each ton of wastewater consumes 0.042 tons of steam and 30 kW·h of electricity. Assuming a steam price of 200 yuan per ton and an electricity price of 0.6 yuan per kW·h, the energy cost of treating one ton of wastewater is 26.6 yuan.

[0214] The present invention realizes the recycling and reuse of wastewater and the high-quality recovery of valuable elements in the wastewater at a low treatment cost.

[0215] Comparative Example

[0216] The device for recycling rare earth wastewater and co-producing ammonium chloride described in Example 1 is used to treat only the rare earth zinc removal wastewater, rare earth aluminum removal wastewater, and rare earth iron removal wastewater in Example 2, without treating the rare earth extraction wastewater and rare earth carbon precipitation wastewater. The remaining conditions are the same as those in Example 2. The energy consumption cost per unit wastewater is calculated as follows:

[0217] Each ton of wastewater consumes 0.024 tons of steam and 22 kW·h of electricity. Assuming a steam price of 200 yuan per ton and an electricity price of 0.6 yuan per kW·h, the energy cost of treating one ton of wastewater is 18 yuan.

[0218] The device for recycling rare earth wastewater and producing ammonium chloride described in Example 1 is used to treat only the rare earth extraction wastewater and rare earth carbon precipitation wastewater in Example 2, without treating the rare earth zinc removal wastewater, rare earth aluminum removal wastewater, and rare earth iron removal wastewater. The remaining conditions are the same as those in Example 2. The energy consumption cost per unit wastewater is calculated as follows:

[0219] Each ton of wastewater consumes 0.08 tons of steam and 50 kW·h of electricity. Assuming a steam price of 200 yuan per ton and an electricity price of 0.6 yuan per kW·h, the energy cost of treating one ton of wastewater is 46 yuan.

[0220] The energy consumption per unit wastewater for separate treatment of rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and for separate treatment of rare earth extraction wastewater and rare earth carbon precipitation wastewater is:

[0221] The energy consumption cost for treating 1 ton of wastewater is (18+46) / 2=32 yuan.

[0222] By comparing the data of the examples of the present application, it can be seen that the method of recycling rare earth wastewater and co-producing ammonium chloride in the present application can simultaneously treat rare earth zinc removal wastewater, rare earth aluminum removal wastewater, rare earth iron removal wastewater, rare earth extraction wastewater and rare earth carbon precipitation wastewater, while significantly reducing energy consumption costs.

[0223] The present invention is not limited to the above-mentioned embodiments. Any modification, improvement, or substitution that can be conceived by those skilled in the art without departing from the essential content of the present invention shall fall within the scope of the present invention.

Claims

1. A device for recycling rare earth wastewater and co-producing ammonium chloride, characterized in that: The device includes an air flotation tank, an inclined plate sedimentation tank, a filtration device, a disc tube reverse osmosis device, a high-density sedimentation tank, a first sand filter, an MVR evaporator, a triple-effect evaporator and a reverse osmosis device; The flotation tank is used to float mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and to precipitate zinc ions, aluminum ions and iron ions in the mixed wastewater to obtain flotation slag and wastewater containing precipitates; the liquid outlet of the flotation tank is located at the bottom of the flotation tank, and the liquid outlet is connected to the feed port of the inclined plate sedimentation tank through a pipeline; The inclined plate sedimentation tank is used to reprecipitate the wastewater containing sediment to obtain reprecipitate; the discharge port of the inclined plate sedimentation tank is connected to the feed port of the filtering device through a pipeline; The filtering device is used to filter the reprecipitate to obtain a first filtrate; the liquid outlet of the filtering device is connected to the liquid inlet of the disc-tube reverse osmosis device through a pipeline; The disc-tube reverse osmosis device is used to perform disc-tube reverse osmosis treatment on the first filtrate to obtain concentrated water and fresh water; the concentrated water outlet of the disc-tube reverse osmosis device is connected to the liquid inlet of the high-density sedimentation tank through a pipeline, and the fresh water outlet of the disc-tube reverse osmosis device is connected to the liquid inlet of the reverse osmosis device through a pipeline; The high-density sedimentation tank is used to precipitate calcium ions and magnesium ions in a mixture of rare earth extraction wastewater, rare earth carbon precipitation wastewater, and concentrated water obtained by disc tube reverse osmosis treatment; the discharge port of the high-density sedimentation tank is connected to the feed port of the first sand filter through a pipeline; The first sand filter is used to filter the precipitate generated in the high-density sedimentation tank; the filtrate outlet of the first sand filter is connected to the feed inlet of the MVR evaporator through a pipeline; The MVR evaporator is used to evaporate and crystallize the filtrate from the first sand filter to obtain first ammonium chloride crystals, MVR evaporation mother liquor and MVR secondary steam condensate; the mother liquor outlet of the MVR evaporator is connected to the liquid inlet of the triple-effect evaporator through a pipeline, and the secondary steam condensate outlet of the MVR evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline; The triple-effect evaporator is used to evaporate the crystallization MVR evaporation mother liquor to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor and triple-effect secondary steam condensate; the secondary condensate outlet of the triple-effect evaporator is connected to the liquid inlet of the reverse osmosis equipment through a pipeline; The reverse osmosis equipment is used to perform reverse osmosis treatment on MVR secondary steam condensate, triple-effect secondary steam condensate and fresh water obtained by disc tube reverse osmosis treatment to obtain treated wastewater.

2. The device according to claim 1, characterized in that The device also includes a negative pressure dryer, which is used to dry the mother liquor of the triple-effect evaporation to produce salt; the mother liquor outlet of the triple-effect evaporator is connected to the liquid inlet of the negative pressure dryer through a first pipeline; the mother liquor outlet of the triple-effect evaporator is also connected to the liquid inlet of the high-density precipitation tank through a second pipeline.

3. The device according to claim 1, characterized in that The filtration equipment includes a second sand filter and an ultrafiltration equipment. The feed port of the second sand filter is connected to the discharge port of the inclined plate sedimentation tank through a pipeline, and the filtrate outlet of the second sand filter is connected to the liquid inlet of the ultrafiltration equipment through a pipeline; the filtrate outlet of the ultrafiltration equipment is connected to the liquid inlet of the disc tube reverse osmosis equipment through a pipeline.

4. A method for recycling rare earth wastewater and co-producing ammonium chloride using the device according to claim 1, comprising the following steps: 1) Flotation and sedimentation: adding ammonia water to the mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater in the flotation tank to adjust the pH value to 5-8, and then adding PAC solution and PAM solution for flotation to obtain flotation slag and wastewater containing sediment; 2) reprecipitation: passing the wastewater containing precipitate obtained in step 1) into the inclined plate sedimentation tank, adding the PAC solution and the PAM solution again for precipitation to obtain a reprecipitate; 3) Filtration and disc-tube reverse osmosis: filtering the reprecipitate obtained in step 2) through the filtration device to obtain a first filtrate, passing the first filtrate through the disc-tube reverse osmosis device for disc-tube reverse osmosis treatment to obtain concentrated water and fresh water; passing the concentrated water into the high-density sedimentation tank for treatment, and passing the fresh water into the reverse osmosis device for reverse osmosis treatment; 4) High-density precipitation: In the high-density precipitation tank, ammonia water is added to the mixture of the rare earth extraction wastewater, the rare earth carbon precipitation wastewater, and the concentrated water obtained in step 3) to adjust the pH value to 7-9, and oxalic acid, diammonium hydrogen phosphate, PAC solution, and PAM solution are added in sequence to obtain a precipitate; 5) Filtration and MVR evaporation crystallization: filtering the precipitate obtained in step 4) through the first sand filter to obtain a second filtrate, and passing the second filtrate into the MVR evaporator for evaporation and crystallization to obtain first ammonium chloride crystals, MVR evaporation mother liquor, and MVR secondary steam condensate; wherein the ammonium chloride mass fraction of the first ammonium chloride crystals is at least 99.0 wt%; 6) triple-effect evaporation crystallization: passing the MVR evaporation mother liquor obtained in step 5) into the triple-effect evaporator for triple-effect evaporation crystallization to obtain second ammonium chloride crystals, triple-effect evaporation mother liquor, and triple-effect secondary steam condensate; wherein the ammonium chloride mass fraction of the second ammonium chloride crystals is 91-95 wt%; 7) Reverse osmosis: The MVR secondary steam condensate obtained in step 5), the triple-effect secondary steam condensate obtained in step 6), and the fresh water obtained in step 3) are subjected to reverse osmosis treatment through the reverse osmosis equipment to obtain treated wastewater.

5. The method according to claim 4, characterized in that: In step 3), the reprecipitate obtained in step 2) is filtered through a second sand filter, and then the filtrate of the second sand filter is ultrafiltered by an ultrafiltration device to obtain a first filtrate; Step 3) further includes adjusting the pH value of the first filtrate to 2-6 before subjecting the first filtrate to disc tube reverse osmosis treatment.

6. The method according to claim 4, characterized in that In step 5), before evaporating and crystallizing the second filtrate, the pH value of the second filtrate is adjusted to 5-8.

7. The method according to claim 4, characterized in that During the MVR evaporation crystallization process of step 5): The material concentration in the first-effect falling film circulation separator is 5-14wt%, the saturation temperature difference is 1-5°C, and the material liquid temperature in the first-effect falling film circulation separator is 90-105°C; The material concentration in the second-effect falling film circulation separator is 10-22 wt%, the saturation temperature difference is 1-6°C, and the material liquid temperature in the second-effect falling film circulation separator is 90-96°C; The material concentration in the forced circulation separator is 10-44 wt%, the saturation temperature difference is 5-15° C., and the material liquid temperature in the forced circulation separator is 90-102° C.

8. The method according to claim 4, characterized in that In the triple-effect evaporation crystallization process of step 6): The material concentration in the first-effect separator is 10-44 wt%, the saturation temperature difference is 20-32°C, and the material liquid temperature in the separator is 90-112°C; The material concentration in the second-effect separator is 10-44wt%, the saturation temperature difference is 1-10°C, and the liquid temperature of the material in the separator is 90-92°C; The material concentration in the triple-effect separator is 10-40 wt%, the saturation temperature difference is 1-10°C, and the liquid temperature of the material in the triple-effect separator is 60-66°C.

9. The method according to claim 4, characterized in that The triple-effect evaporation mother liquor obtained in step 6) is returned to step 4) for high-density precipitation, or dried to prepare salt.

10. The method according to claim 4, characterized in that In step 1), step 2) and step 4), the mass concentration of the PAC solution is 2 to 30 wt%; based on each ton of wastewater, the amount of the PAC solution is 100 to 1000 g; the mass concentration of the PAM solution is 0.01 to 0.5 wt%; Based on each ton of wastewater, the usage of the PAM solution is 1 to 50 g.

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