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

Abstract

The invention discloses a device and a method for co-producing ammonium chloride by recycling rare earth wastewater. The device for co-producing ammonium chloride by recycling rare earth wastewater comprises an air floatation tank, an inclined plate sedimentation tank, filtering equipment, disc tube type reverse osmosis equipment, a high-density sedimentation tank, a first sand filter, an MVR (mechanical vapor recompression) evaporator, a triple-effect evaporator and reverse osmosis equipment. The method for recycling the rare earth wastewater and co-producing the ammonium chloride is carried out by adopting the device. According to the method, two ammonium chloride products can be produced at low cost and low energy consumption, and cyclic utilization of the rare earth wastewater is realized.

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] In the rare earth ore production process, rare earth extraction, carbon precipitation and desalination steps will produce a large amount of rare earth wastewater. In the treatment process of these rare earth wastewaters, the conventional method is evaporation and crystallization. After pre-treatment and impurity removal, the rare earth wastewater is evaporated and crystallized to recover solid ammonium chloride and fresh water. Some low-concentration wastewater is directly evaporated in the evaporation system, which consumes high energy for treatment. The solid ammonium chloride product recovered in the evaporation process does not meet the product indicators of industrial-grade ammonium chloride and agricultural-grade ammonium chloride, and the condensed water produced cannot be directly reused. Those skilled in the art have been developing and improving the treatment method of rare earth wastewater to reduce pollutant emissions and improve the recovery efficiency of ammonium chloride.

[0003] CN104140174A discloses a combined treatment method for rare earth extraction and separation of ammonium chloride wastewater, which mainly uses oil separation, homogenization, aeration, electric flocculation demulsification, flotation machine oil removal, dosing precipitation of calcium, magnesium and heavy metal ions, microfiltration ultrafiltration, nanofiltration, reverse osmosis, electrodialysis, evaporation concentration and other processes to perform serial desalination and concentration treatment on the wastewater to obtain recyclable desalinated purified water and ammonium chloride products that meet agricultural standards. The method only treats rare earth extraction and separation of ammonium chloride wastewater and only recovers one ammonium chloride product.

[0004] CN103553257A discloses a recycling treatment process for rare earth wastewater, wherein the wastewater is subjected to flotation treatment, electrolytic oxidation, primary composite separation, primary concentration, secondary composite separation, secondary concentration, reverse osmosis treatment, evaporation crystallization and other steps in sequence to obtain recyclable solid salts and produced water. CN104609627A discloses a method for treating wastewater from rare earth production. The method for treating wastewater from rare earth production 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 the precipitation washing 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 the saponified wastewater to obtain a second mixed liquid, performing evaporation and concentration on 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. Both methods do not carry out chemical impurity removal treatment on rare earth wastewater, and the recycled water produced still fails to meet the standards. At the same time, both methods only produce one type of ammonium chloride.

[0005] CN110282799A discloses a method for resource treatment of rare earth carbon precipitation wastewater and raffinate, which is aimed at high ammonia nitrogen wastewater generated in the rare earth separation process of P507-hydrochloric acid system and ammonia saponification, that is, rare earth carbon precipitation wastewater containing heavy metal ions and high concentration of ammonium chloride, and raffinate containing oil and high concentration of ammonium chloride. For the raffinate, the ceramic membrane filtration equipment is used for circulation filtration and concentration, the extractant is recovered, and the raffinate after oil removal is evaporated; for the rare earth carbon precipitation wastewater, the pretreatment equipment is first used to adjust the pH, flocculate, react, and concentrate to remove the suspended matter and heavy metal ions in the rare earth carbon precipitation wastewater; secondly, the ultra-high pressure reverse osmosis equipment is used for purification and concentration; finally, the MVR evaporation crystallization device is used to produce an ammonium chloride product with a purity of 99%. This method is aimed at rare earth wastewater with low calcium and magnesium concentrations, and is not suitable for the treatment of rare earth wastewater with high calcium and magnesium concentrations. At the same time, this method only produces one kind 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 a device for recycling rare earth wastewater and producing ammonium chloride. Another object of the present invention is to provide a method for recycling rare earth wastewater and producing ammonium chloride. The present invention treats rare earth wastewater containing high concentrations of calcium and magnesium, realizes wastewater recycling under low energy consumption conditions, and simultaneously produces two types of ammonium chloride products by classification.

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

[0008] On the one hand, 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 filtering 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 flotate 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;

[0010] 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 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 mixed solution including 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 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;

[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 device through a pipeline;

[0016] The triple-effect evaporator is used to evaporate the crystallization MVR evaporation mother liquor to obtain the second ammonium chloride crystals, the triple-effect evaporation mother liquor and the 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 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.

[0019] According to the device described in the present invention, preferably, the filtering equipment includes a second sand filter and an ultrafiltration equipment, the feed inlet 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 precipitation: 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 precipitation;

[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 the mixed solution including rare earth extraction wastewater, rare earth carbon precipitation wastewater and 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;

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

[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 mass fraction of ammonium chloride in the second ammonium chloride crystals is 91-95wt%;

[0027] 7) Reverse osmosis: The MVR secondary steam condensate obtained in step 5), the triple-effect secondary steam condensate and the fresh water obtained in step 3) are subjected to reverse osmosis treatment 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 sand filtration of the second sand filter is ultrafiltered by an ultrafiltration device to obtain a first filtrate;

[0029] Step 3) also 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 evaporating and crystallizing the second filtrate, 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 of 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 10-22wt%, 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 10-44wt%, 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 10-44wt%, 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 10-40wt%, 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 2-30wt%; based on each ton of wastewater, the amount of the PAC solution is 100-1000g; the mass concentration of the PAM solution is 0.01-0.5wt%; based on each ton of wastewater, the amount of the PAM solution is 1-50g.

[0041] The device and method for recycling rare earth wastewater and producing ammonium chloride of the present invention couples MVR evaporation crystallization and triple-effect evaporation crystallization processes to treat various rare earth wastewaters, and produces two ammonium chloride products at low cost and low energy consumption, which can be used as industrial-grade ammonium chloride and agricultural-grade ammonium chloride respectively. In addition, the concentrated water and fresh water obtained after the rare earth wastewater is treated by the present invention can be reused in the rare earth production system, realizing the recycling of wastewater and saving energy and reducing consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a schematic diagram of the 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 is further described below in conjunction with 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, and is usually represented by σ, with a unit of 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 producing ammonium chloride>

[0050] The device for recycling rare earth wastewater and producing ammonium chloride comprises a flotation tank, an inclined plate sedimentation tank, a filtering 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, which is described in detail below.

[0051] Flotation Tank

[0052] The flotation tank is used for flotation of mixed wastewater including rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and precipitation of 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 can use any type of flotation tank known in the art, and is not particularly limited herein. For example, it can be at least one of a horizontal flow flotation tank, a vertical flow flotation tank, an air flotation-reaction integrated flotation tank, an air flotation-sedimentation integrated flotation tank, and an air flotation-filtration integrated flotation tank; preferably at least one of an air flotation-reaction integrated flotation tank, an air flotation-sedimentation integrated flotation tank, and an air flotation-filtration integrated flotation tank; more preferably, an air flotation-reaction integrated flotation tank or an air flotation-sedimentation integrated flotation tank.

[0054] Inclined plate sedimentation tank

[0055] The inclined plate sedimentation tank is used to re-precipitate wastewater containing sediment to obtain re-precipitate; 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 can use any type of inclined plate sedimentation tank known in the art, without particular limitation herein. For example, it can 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, it is a co-current inclined plate sedimentation tank or a counter-current inclined plate sedimentation tank; more preferably, it is a counter-current inclined plate sedimentation tank.

[0057] Filtration equipment

[0058] The filtering device is used to filter 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 filtering 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 in the ultrafiltration device can be any ultrafiltration membrane known in the art that can be used to treat 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, polyether sulfone, polyvinylidene fluoride, and polyacrylonitrile, preferably at least one of cellulose acetate, polyether sulfone, and polyvinylidene fluoride, more preferably a composite membrane of cellulose acetate, polyether sulfone and polyvinylidene fluoride. Reasonable ultrafiltration membrane is more conducive to ultrafiltration filtration of reprecipitates 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) device can be any DTRO device known in the art. The dense layer material of the DTRO membrane used in the disc-tube reverse osmosis device 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 reasonable DTRO membrane is more conducive to the disc-tube reverse osmosis of the first filtrate and realizes effective separation.

[0067] High density sedimentation tank

[0068] The high-density sedimentation tank is used to precipitate calcium ions and magnesium ions in a mixed solution including 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] The high-density sedimentation tank is a well-known device in the art. The present invention can use any type of high-density sedimentation tank known in the art, and is not particularly limited here. 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 filtering effect.

[0075] MVR Evaporator

[0076] The MVR evaporator is used to evaporate and crystallize the filtrate from the first sand filter to obtain the 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 of the present invention is a device known in the art. The present invention can use any type of MVR evaporator known in the art, and is not particularly limited here. For example, it can be at least one of an MVR rising film evaporator, an MVR falling film evaporator, and 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 composite MVR evaporator of an MVR bipolar falling film evaporator and an MVR forced circulation evaporator. A reasonable MVR evaporator is more conducive to the MVR evaporation crystallization and improves 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, which is not 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 crystal.

[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 also include a negative pressure dryer for drying the mother liquor of triple-effect evaporation to form 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, the triple-effect secondary steam condensate and the fresh water obtained by the disc-tube reverse osmosis treatment to obtain the treated wastewater.

[0086] According to one embodiment of the present invention, the reverse osmosis (RO) device may be any RO device known in the art, and is not particularly limited herein. The RO membrane used in the reverse osmosis device may be any RO membrane known in the art that can be used to treat steam condensate. The structure of the RO membrane may be a roll or a flat plate, preferably a roll. The RO membrane material may 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 device, comprising a flotation and precipitation step, a reprecipitation step, a disc-tube reverse osmosis step, a high-density precipitation step, an MVR evaporation crystallization step, a triple-effect evaporation crystallization step, and a reverse osmosis step. Optionally, a drying step is also included. The following is a detailed description.

[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, and 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; the rare earth aluminum removal wastewater contains: Al2O3 1-20 g / L, pH value 1-6; the rare earth iron removal wastewater contains: 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 co-produce two kinds 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 2-30wt%, preferably 5-25wt%, and more preferably 8-20wt%; based on each ton of wastewater, the amount of the PAC solution is 100-1000g, preferably 200-800g, and more preferably 300-600g. If the amount of the PAC solution is too low, the coagulation effect cannot be achieved; if the amount of the PAC solution is too high, it is not conducive to cost control.

[0100] According to another embodiment of the present invention, the mass concentration of the PAM solution can be 0.01-0.5wt%, preferably 0.01-0.5wt%, more preferably 0.01-0.5wt%; based on each ton of wastewater, the amount of the PAM solution is 1-50g, preferably 200-800g, more preferably 300-600g. If the amount of the PAM solution is too low, the flocculation effect cannot be achieved; if the amount of the PAM solution 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 2-30wt%, preferably 5-25wt%, and more preferably 8-20wt%; based on each ton of wastewater, the amount of the PAC solution can be 100-1000g, preferably 200-800g, and more preferably 300-600g. If the amount of the PAC solution is too low, the coagulation effect cannot be achieved; if the amount of the PAC solution 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 0.01-0.5wt%, preferably 0.01-0.5wt%, more preferably 0.01-0.5wt%; based on each ton of wastewater, the amount of the PAM solution can be 1-50g, preferably 200-800g, more preferably 300-600g. If the amount of the PAM solution is too low, the flocculation effect cannot be achieved; if the amount of the PAM solution 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 value 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 easy 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. Reasonable water inlet pressure can improve the efficiency of the disc tube reverse osmosis and is not easy 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 present invention can pass the DTRO concentrated water into the high-density precipitation step, and carry out high-density precipitation together with the rare earth extraction wastewater and the rare earth carbon precipitation wastewater; the present invention can also pass the DTRO fresh water into the reverse osmosis step, and carry out reverse osmosis treatment together with the MVR secondary steam condensate and the triple-effect secondary steam condensate. In this way, the recycling of wastewater can be achieved.

[0113] High density precipitation step

[0114] In the high-density sedimentation tank, ammonia water is added to the mixed solution including rare earth extraction wastewater, rare earth carbon precipitation wastewater and 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 % more than the theoretical amount, preferably 2 to 8 wt % more than the theoretical amount, and more preferably 3 to 6 wt % more than 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 % more than the theoretical amount, preferably 2 to 8 wt % more than the theoretical amount, and more preferably 3 to 6 wt % more than 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 produced by extracting rare earth elements in the rare earth production process, which is well known in the art. The rare earth carbon precipitation wastewater treated by the present invention is wastewater produced by carbon precipitation of rare earth elements in the rare earth production process, which is well known in the art.

[0120] The rare earth extraction wastewater of the present invention comprises: a total dissolved solid (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; the rare earth carbon precipitation wastewater of the present invention comprises: 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 60000-150000 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 130000-180000 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 80000-120000 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 120000-150000 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 the 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 2-30wt%, preferably 5-25wt%, and more preferably 8-20wt%; based on each ton of wastewater, the amount of the PAC solution can be 100-1000g, preferably 200-800g, and more preferably 300-600g. If the amount of the PAC solution is too low, the coagulation effect cannot be achieved; if the amount of the PAC solution 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 0.01-0.5wt%, preferably 0.05-0.4wt%, more preferably 0.1-0.3wt%; based on each ton of wastewater, the amount of the PAM solution can be 1-50g, preferably 3-30g, more preferably 5-20g. If the amount of the PAM solution is too low, the flocculation effect cannot be achieved; if the amount of the PAM solution is too high, it is not conducive to cost control.

[0127] Filtration and MVR evaporation crystallization steps

[0128] The precipitate obtained as 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 placing the second filtrate in the MVR evaporator for evaporation and crystallization, the pH value of the filtrate can be adjusted to 5 to 8, preferably 5.5 to 7.5, and more preferably 6 to 7. The pH value of the filtrate can be adjusted using a hydrochloric acid solution, and the concentration of the hydrochloric acid solution can be 0.1 to 10 mol / L, preferably 0.2 to 5 mol / L, and more preferably 0.5 to 3 mol / L. A reasonable pH range can ensure the stable operation of the MVR evaporator. Too low a pH value will corrode the MVR evaporator, and too high a pH value 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 first-effect falling film circulation separator can be 5-14wt%, preferably 6-12wt%, more preferably 8-10wt%; 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 first-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 10-22wt%, preferably 12-20wt%, more preferably 15-18wt%; 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%, and more preferably 20-30wt%; the saturation temperature difference can be 5-20°C, preferably 8-18°C, and more preferably 10-16°C; the material liquid temperature in the forced circulation separator can be 90-105°C, preferably 92-103°C, and more preferably 95-102°C.

[0134] Reasonable MVR evaporation crystallization parameters can ensure the stable operation of the MVR evaporator while obtaining the first ammonium chloride crystal more efficiently. If the parameters are too low, the production efficiency will be affected, and if the parameters are too high, it will be unfavorable for the stable operation of the MVR evaporator.

[0135] According to one embodiment of the present invention, the mass fraction of ammonium chloride in the first ammonium chloride crystals obtained can be at least 99.0wt%, preferably at least 99.2wt%, and more preferably at least 99.3wt%. The first ammonium chloride crystals obtained can be directly used in the production of industrial-grade ammonium chloride products (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 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 10-44wt%, preferably 15-40wt%, more preferably 20-30wt%; 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 obtaining the second ammonium chloride crystal more efficiently. If the parameters are too low, the production efficiency will be affected, and if the parameters are too high, it will be unfavorable for 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 form salt to achieve waste utilization. The drying of the present invention can be carried out under negative pressure, preferably 50 to 200 Pa, more preferably 100 to 150 Pa.

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

[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 through a reverse osmosis device to obtain treated wastewater.

[0148] According to one embodiment of the present invention, the water inlet pressure of the 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 the reverse osmosis efficiency and is not easy 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 of the present invention can be reused in rare earth production, and 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 detection of TDS, acidity, pH value and conductivity are all carried out using an Extech EC500 conductivity tester.

[0153] The detection of metal ions 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] The other raw materials in the following examples are all commercially available products unless otherwise specified.

[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 filtering 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 flotate mixed wastewater formed by 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 wastewater to obtain flotation slag and wastewater containing precipitation. The flotation tank 1 of this embodiment adopts an integrated flotation-precipitation flotation tank.

[0166] The liquid outlet of the air flotation tank 1 of this embodiment is located at the bottom of the air 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 countercurrent inclined plate sedimentation tank. The discharge port of the inclined plate sedimentation tank 2 is connected to the feed port of the filtering device 3 through a pipeline.

[0168] The filter device 3 is used to filter the reprecipitate to obtain the first filtrate. The filter device 3 includes a second sand filter 31 and an ultrafiltration device 32. The feed port of the second sand filter 31 is connected to the discharge port of the inclined plate sedimentation tank 2 through a pipeline, and the filtrate outlet of the second sand filter 31 is connected to the liquid inlet of the ultrafiltration device 32 through a pipeline; the filtrate outlet of the ultrafiltration device 32 is connected to the liquid inlet of the disc-tube reverse osmosis device 4 through 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 composite membrane with a tubular structure; the composite membrane is formed of cellulose acetate, polyethersulfone and polyvinylidene fluoride.

[0170] The disc-tube reverse osmosis device 4 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 4 is connected to the liquid inlet of the high-density sedimentation tank 5 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 9 through a pipeline. In this embodiment, the dense layer of the DTRO membrane of the disc-tube reverse osmosis device 4 is formed by polyethersulfone.

[0171] The high-density sedimentation tank 5 is used to precipitate calcium ions and magnesium ions in a mixed solution formed by rare earth extraction wastewater, rare earth carbon precipitation wastewater and concentrated water obtained by disc tube reverse osmosis. The high-density sedimentation tank 5 of this embodiment adopts a multi-combination high-density sedimentation tank. The discharge port of the high-density sedimentation tank 5 is connected to the feed port of the first sand filter 6 through 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 port of the MVR evaporator 7 through a pipeline.

[0173] The MVR evaporator 7 is used to evaporate and crystallize the filtrate from the first sand filter 6 to obtain the first ammonium chloride crystals, MVR evaporation mother liquor and MVR secondary steam condensate. The MVR evaporator 7 of this embodiment adopts a composite MVR evaporator 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 called 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 through 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 through a pipeline.

[0174] The triple-effect evaporator 8 is used to evaporate the crystallization MVR evaporation mother liquor to obtain the second ammonium chloride crystal, the triple-effect evaporation mother liquor and the 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 device 9 through a pipeline. The mother liquor outlet of the triple-effect evaporator 8 is connected to the liquid inlet of the negative pressure dryer 10 through a first pipeline and to the liquid inlet of the high-density precipitation tank 5 through a second pipeline.

[0175] The reverse osmosis device 9 is used to perform reverse osmosis filtration on the MVR secondary steam condensate, the triple-effect secondary steam condensate and the fresh water obtained by the disc-tube reverse osmosis treatment to obtain treated wastewater. The reverse osmosis device 9 of this embodiment uses a roll-type RO membrane. The RO membrane is a composite membrane formed by 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] 5t of rare earth zinc removal wastewater (ZnO: 0.8g / L, acidity 0.2mol / L), 5t of rare earth aluminum removal wastewater (Al2O3: 10g / L, pH value: 4) and 5t of rare earth iron removal wastewater (Fe2O3: 10g / L, acidity 0.6mol / L) are mixed to form the first mixed wastewater. The first mixed wastewater is passed into the flotation tank 1, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 6 to precipitate zinc ions, aluminum ions and iron ions. After precipitation, a PAC solution with a concentration of 10wt% of 500g per ton of wastewater is added to coagulate, and a PAM solution with a concentration of 0.2wt% per ton of wastewater is added to flocculate, and after flotation, a flotation slag and wastewater containing precipitation are 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 filtering device 3 to obtain a sand filtrate. The sand filtrate is ultrafiltered through the ultrafiltration device 32 to obtain a first filtrate.

[0181] The pH value of the first filtrate is adjusted to 3 using a hydrochloric acid solution with a concentration of 1 mol / L, and then the first filtrate is subjected to disc-tube reverse osmosis treatment by a disc-tube reverse osmosis device 4, with an inlet pressure of 100 bar. The DTRO fresh water (conductivity σ=2000μs / cm) produced by the disc-tube reverse osmosis is passed into a reverse osmosis device 9 for reverse osmosis desalination, and the produced DTRO concentrated water (TDS=10000mg / L) is passed into a high-density sedimentation tank 5 for treatment, thereby realizing the recycling of wastewater.

[0182] 5t of rare earth extraction wastewater (TDS: 100000mg / L, CaO: 20mg / L, MgO: 10mg / L, NH4Cl 100g / L), 5t of rare earth carbon precipitation wastewater (TDS: 120000mg / L, CaO: 200mg / L, MgO: 150mg / L, NH4Cl 120g / L) and DTRO concentrated water are mixed to form a second mixed wastewater. The second mixed wastewater is passed into a high-density sedimentation tank 5, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 7.5. Oxalic acid is added at 5wt% exceeding the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate is added at 5wt% exceeding 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 by the first sand filter 6 to obtain a second filtrate. A hydrochloric acid solution with a concentration of 1 mol / L is used to adjust the pH value of the second filtrate to 6, and then the second filtrate is passed into the MVR evaporator 7 for evaporation and crystallization to obtain the first ammonium chloride crystal, the MVR evaporation mother liquor and the MVR secondary steam condensate. The operating parameters of the MVR evaporator 7 are: 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 content of ammonium chloride 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 the triple-effect evaporator 8 for triple-effect evaporation crystallization to obtain the second ammonium chloride crystal, the triple-effect evaporation mother liquor and the triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are: 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; the material concentration in the triple-effect separator is 20wt%, the saturation temperature difference is 3°C, and the material liquid temperature in the triple-effect separator is 65°C. The second ammonium chloride crystal (ammonium chloride content is 92wt%) accounts for 9.8wt% of the total salt content (total ammonium chloride content in rare earth extraction wastewater and rare earth carbon precipitation wastewater), which can be directly used to produce agricultural-grade ammonium chloride products. A part of the mother liquor produced by triple-effect evaporation crystallization is returned to the high-density precipitation tank 5 for recycling, and a part is dried under negative pressure at 100 Pa by a negative pressure dryer 10 to produce impure salts, and the impure salts produced account for 0.2wt% 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 through reverse osmosis equipment 9, and the water inlet pressure is 30 bar. The RO concentrated water (TDS = 1000 mg / L) and RO fresh water (TDS = 100 mg / L) produced by reverse osmosis are respectively recycled to the rare earth production system to achieve the recycling of wastewater.

[0186] After calculation, the energy consumption cost for 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. The steam price is 200 yuan / ton, and the electricity price is 0.6 yuan / kW·h. The energy consumption cost of treating 1 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 under the condition of 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] 5t of rare earth zinc removal wastewater (ZnO: 0.2g / L, acidity 0.2mol / L), 5t of rare earth aluminum removal wastewater (Al2O3: 6g / L, pH value: 5) and 5t of rare earth iron removal wastewater (Fe2O3: 6g / L, acidity 0.6mol / L) are mixed to form the first mixed wastewater. The first mixed wastewater is passed into the flotation tank 1, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 7 to precipitate zinc ions, aluminum ions and iron ions. After precipitation, a PAC solution with a concentration of 10wt% of PAC solution is added in an amount of 500g per ton of wastewater for coagulation, and a PAM solution with a concentration of 0.2wt% per ton of wastewater is added for flocculation, and flotation slag and wastewater containing precipitation are obtained after flotation.

[0192] The wastewater containing the precipitate is passed into the inclined plate sedimentation tank 2, and a PAC solution is added at a dosage of 500 g of a 10 wt% PAC solution per ton of wastewater, and coagulation is performed again. A PAM solution is added at a dosage of 500 g of a 0.2 wt% PAM solution 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 filtering device 3 to obtain a sand filtrate. The sand filtrate is ultrafiltered through the ultrafiltration device 32 to obtain a first filtrate.

[0194] The pH value of the first filtrate is adjusted to 4 using a hydrochloric acid solution with a concentration of 1 mol / L, and then the first filtrate is passed into the disc tube reverse osmosis device 4 for disc tube reverse osmosis, with an inlet pressure of 120 bar. The DTRO fresh water (conductivity σ = 1500 μs / cm) produced by the disc tube reverse osmosis is passed into the reverse osmosis device 9 for reverse osmosis desalination, and the produced DTRO concentrated water (TDS = 15000 mg / L) is returned to the high-density sedimentation tank 5 for treatment, thereby realizing the recycling of wastewater.

[0195] 5t of rare earth extraction wastewater (TDS: 80000mg / L, CaO: 50mg / L, MgO: 30mg / L, NH4Cl 95g / L), 5t of rare earth carbon precipitation wastewater (TDS: 120000mg / L, CaO: 200mg / L, MgO: 150mg / L, NH4Cl 130g / L) and DTRO concentrated water are mixed to form a second mixed wastewater. The second mixed wastewater is passed into a high-density sedimentation tank 5, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 7.5. Oxalic acid is added at a concentration of 5wt% in excess of the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate is added at a concentration of 5wt% in excess of the theoretical amount to precipitate magnesium ions. After precipitation, 500g of a PAC solution with a concentration of 10wt% is added per ton of wastewater for coagulation, and 500g of a PAM solution with a concentration of 0.2wt% is added per ton of wastewater for flocculation to obtain a precipitate.

[0196] The precipitate is filtered by the first sand filter 6 to obtain a second filtrate. A hydrochloric acid solution with a concentration of 1 mol / L is used to adjust the pH value of the second filtrate to 7, and then the second filtrate is passed into the MVR evaporator 7 for evaporation and crystallization to obtain the first ammonium chloride crystal, the MVR evaporation mother liquor and the MVR secondary steam condensate. The operating parameters of the MVR evaporator 7 are: 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 99.3wt%) account for 85wt% of the total salt content (total content of ammonium chloride 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 the triple-effect evaporator 8 for triple-effect evaporation crystallization to obtain the second ammonium chloride crystal, the triple-effect evaporation mother liquor and the triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are: 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; the material concentration in the triple-effect separator is 30wt%, the saturation temperature difference is 6°C, and the material liquid temperature in the triple-effect separator is 65°C. The second ammonium chloride crystal (ammonium chloride content is 91.7wt%) accounts for 14.7wt% of the total salt content (total content of ammonium chloride in rare earth extraction wastewater and rare earth carbon precipitation wastewater), which can be directly used to produce agricultural-grade ammonium chloride products. Part of the mother liquor produced by triple-effect evaporation crystallization is returned to the high-density sedimentation tank 5 for recycling, and part of it is dried under negative pressure at 150 Pa by a negative pressure dryer 10 to produce impure salts, and the impure 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 through reverse osmosis equipment 9, with an inlet pressure of 50 bar. The RO concentrated water (TDS = 800 mg / L) and RO fresh water (TDS = 100 mg / L) produced by reverse osmosis are respectively recycled to the rare earth production system to achieve the recycling of wastewater.

[0199] After calculation, the energy consumption cost for 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. The steam price is 200 yuan / ton, and the electricity price is 0.6 yuan / kW·h. The energy consumption cost of treating 1 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 under the condition of 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] 5t of rare earth zinc removal wastewater (ZnO: 0.5g / L, acidity 0.2mol / L), 5t of rare earth aluminum removal wastewater (Al2O3: 8g / L, pH value: 4) and 5t of rare earth iron removal wastewater (Fe2O3: 8g / L, acidity 0.6mol / L) are mixed to form the first mixed wastewater. The first mixed wastewater is passed into the flotation tank 1, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 6 to precipitate zinc ions, aluminum ions and iron ions. After precipitation, a PAC solution with a concentration of 10wt% is added in an amount of 500g per ton of wastewater for coagulation, and a PAM solution with a concentration of 0.2wt% is added in an amount of 500g per ton of wastewater for flocculation, and a flotation slag and wastewater containing precipitation are obtained after flotation.

[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 10wt% per ton of wastewater at a rate of 500g, and coagulation is performed again. A PAM solution is added at a concentration of 0.2wt% per ton of wastewater at a rate of 500g, and flocculation is performed again to obtain a reprecipitate.

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

[0207] The pH value of the first filtrate is adjusted to 3 using a hydrochloric acid solution with a concentration of 1 mol / L, and then the first filtrate is subjected to disc-tube reverse osmosis treatment by a disc-tube reverse osmosis device 4, with an inlet pressure of 90 bar. The DTRO fresh water (conductivity σ=1800μs / cm) produced by the disc-tube reverse osmosis is passed into a reverse osmosis device 9 for reverse osmosis desalination, and the produced DTRO concentrated water (TDS=13000mg / L) is passed into a high-density sedimentation tank 5 for treatment, thereby realizing the recycling of wastewater.

[0208] 5t of rare earth extraction wastewater (TDS: 120000mg / L, CaO: 100mg / L, MgO: 50mg / L, NH4Cl 90g / L), 5t of rare earth carbon precipitation wastewater (TDS: 150000mg / L, CaO: 500mg / L, MgO: 350mg / L, NH4Cl 125g / L) and DTRO concentrated water are mixed to form a second mixed wastewater. The second mixed wastewater is passed into a high-density sedimentation tank 5, and ammonia water with a mass concentration of 24wt% is added to adjust the pH value to 7.5. Oxalic acid is added in excess of 5wt% of the theoretical amount to precipitate calcium ions, and diammonium hydrogen phosphate is added in excess of 5wt% 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 by the first sand filter 6 to obtain a second filtrate. A hydrochloric acid solution with a concentration of 1 mol / L is used to adjust the pH value of the second filtrate to 6, and then the second filtrate is passed into the 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: 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 content of ammonium chloride 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 the triple-effect evaporator 8 for triple-effect evaporation crystallization to obtain the second ammonium chloride crystal, the triple-effect evaporation mother liquor and the triple-effect secondary steam condensate. The operating parameters of the triple-effect evaporator 8 are: 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; the material concentration in the triple-effect separator is 25wt%, the saturation temperature difference is 5°C, and the material liquid temperature in the triple-effect separator is 65°C. The second ammonium chloride crystal (ammonium chloride content is 93wt%) accounts for 19.5wt% 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 agricultural-grade ammonium chloride products. Part of the mother liquor produced by triple-effect evaporation crystallization is returned to the high-density sedimentation tank 5 for recycling, and part of it is dried under negative pressure at 120 Pa in a negative pressure dryer 10 to produce impure salts, and the impure salts produced account for 0.2wt% of the total salt content.

[0211] The MVR secondary steam condensate, triple-effect secondary steam condensate and DTRO fresh water are subjected to reverse osmosis treatment through reverse osmosis equipment 9, with an inlet pressure of 20 bar. The RO concentrated water (TDS = 1200 mg / L) and RO fresh water (TDS = 100 mg / L) produced by reverse osmosis are respectively recycled to the rare earth production system to achieve the recycling of wastewater.

[0212] After calculation, the energy consumption cost for 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. The steam price is 200 yuan / ton, and the electricity price is 0.6 yuan / kW·h. The energy consumption cost of treating 1 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 under the condition of low treatment cost.

[0215] Comparative Example

[0216] The rare earth wastewater recycling and ammonium chloride co-production device 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, and the rare earth extraction wastewater and rare earth carbon precipitation wastewater are not treated. The other conditions are the same as those in Example 2. The energy consumption cost per unit of wastewater is calculated as follows:

[0217] Each ton of wastewater consumes 0.024 tons of steam and 22 kW·h of electricity. The steam price is 200 yuan / ton, and the electricity price is 0.6 yuan / kW·h. The energy consumption cost of treating 1 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, and does not treat the rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater. The other conditions are the same as those in Example 2. The energy consumption cost per unit of wastewater is calculated as follows:

[0219] Each ton of wastewater consumes 0.08 tons of steam and 50 kW·h of electricity. The steam price is 200 yuan / ton, and the electricity price is 0.6 yuan / kW·h. The energy consumption cost of treating 1 ton of wastewater is 46 yuan.

[0220] The energy consumption per unit of wastewater for separate treatment of rare earth zinc removal wastewater, rare earth aluminum removal wastewater and rare earth iron removal wastewater, and the energy consumption 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 embodiments 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. Without departing from the essential content of the present invention, any deformation, improvement and substitution that can be conceived by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A device for recycling rare earth wastewater and producing ammonium chloride, characterized in that: The device includes an air flotation tank, an inclined plate sedimentation tank, a filtering 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 flotate 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; 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 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 mixed solution including 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 device through a pipeline; The triple-effect evaporator is used to evaporate the crystallization MVR evaporation mother liquor to obtain the second ammonium chloride crystals, the triple-effect evaporation mother liquor and the 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 filtering 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 precipitation: 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 precipitation; 2) reprecipitation: passing the wastewater containing precipitate obtained in step 1) into the inclined plate sedimentation tank, adding PAC solution and PAM solution again for precipitation, and obtaining 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 mixed solution including rare earth extraction wastewater, rare earth carbon precipitation wastewater and 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 for treatment 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, 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 mass fraction of ammonium chloride in the first ammonium chloride crystals is at least 99.0wt%; 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 mass fraction of ammonium chloride in the second ammonium chloride crystals is 91-95wt%; 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) also 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 10-22wt%, 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 10-44wt%, 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 10-44wt%, 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 10-40wt%, the saturation temperature difference is 1-10°C, and the material liquid temperature 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 form 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 2-30wt%; based on each ton of wastewater, the amount of the PAC solution is 100-1000g; the mass concentration of the PAM solution is 0.01-0.5wt%; Based on each ton of wastewater, the usage of the PAM solution is 1 to 50 g.

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