Method for synergistically removing oxalate and carbonate in sodium aluminate solution
By adopting the method of synergistic removal of oxalate and carbonate in sodium aluminate solution, the problems of waste of raw materials and increased costs in the prior art are solved, an efficient and economical removal process is achieved, and production costs are reduced.
Patent Information
- Application Number
- CN202411646886.7
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-11-18
- Publication Date
- 2025-02-21
AI Technical Summary
The oxalate and carbonate removal process in the existing sodium aluminate solution has problems of waste of raw materials and increased costs.
Using a method of synergistic removal of oxalate and carbonate in sodium aluminate solution, the oxalate and carbonate are removed synergistically by evaporating the mother liquor and adsorbent, filtration separation, preheating and concentrating, etc. Salt.
This method removes the harmful effects of oxalate crystallization by synergistically removing oxalate and carbonate, improves the efficiency of the filtration and causticization process, reduces the energy loss of the system, and generates 3CaO·Al2O3·6H2O as a filter aid , saves the amount of lime milk and reduces production costs.
Smart Images
Figure CN119490212A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of metal smelting, and in particular relates to a method for collaboratively removing oxalate and carbonate in a sodium aluminate solution. Background Art
[0002] At present, the main production method of alumina in my country is the Bayer process, and the raw material used is mainly bauxite. In recent years, more and more domestic alumina plants have used imported ores. The organic matter in bauxite and the organic additives in the production process will decompose and enter the solution during the dissolution process. Some of the organic matter will be converted into oxalate, which will accumulate in the process. After the mother liquor is continuously recycled, some oxalate will be converted into carbonate. When the oxalate and carbonate in the process accumulate to a certain concentration, it will cause certain harm to production. The harmfulness of oxalate is more prominent in the seed decomposition process. During the seed decomposition process, oxalate will precipitate on the surface of the seed, induce secondary nucleation of the seed, reduce the agglomeration of fine particles, affect the particle size of aluminum hydroxide, and the strength of oxalate is poor. It will be wrapped in aluminum hydroxide and will break during calcination, reducing the strength of aluminum hydroxide; it will also cause difficulties in seed filtration and scarring on the surface of heat exchange equipment. When carbonate in the system accumulates to a certain concentration, it will precipitate on the surface of the heating equipment, reducing the heat exchange efficiency of the equipment, especially in the flash evaporation feed pipe during the dissolution process, blocking the feed pipe, causing the flash tank to carry the material due to lack of steam, causing scarring in the preheating section, increasing steam consumption, and reducing system production. Therefore, for Bayer process alumina companies using imported bauxite, efficient and economical removal of oxalate is an urgent problem to be solved.
[0003] Since the saturation concentration conditions of oxalate and carbonate in sodium aluminate solution are different, oxalate and carbonate cannot be removed at the same time. In the process of single removal, the removal of carbon alkali will be affected by the crystallization of oxalate, the viscosity of the material will increase, the filtering effect will deteriorate, and the removal efficiency will be affected; at the same time, the causticized product slag after the causticizing reaction is discharged into the red mud sedimentation washing tank, which reduces the washing efficiency of the red mud and increases the hydrolysis loss of the sodium aluminate solution; the feed dilution of the aluminum hydroxide classifier uses the seed and denominator liquor, resulting in a five-effect cycle of the seed and denominator liquor, which reduces the utilization efficiency of the alkali; when the sodium aluminate solution is refined, lime milk needs to be added to prepare the filter aid, which increases the lime consumption and the production cost. In summary, the existing process of removing oxalate and carbonate in sodium aluminate solution has the problems of waste of raw materials and increased costs.
[0004] In order to solve the above problems, a method for the synergistic removal of oxalate and carbonate in sodium aluminate solution is urgently needed. Summary of the invention
[0005] In order to solve the shortcomings and deficiencies of the prior art, a method for the coordinated removal of oxalate and carbonate in a sodium aluminate solution is provided, thereby solving the problems of waste of raw materials and increased costs in the existing process of removing oxalate and carbonate in a sodium aluminate solution.
[0006] A method for collaboratively removing oxalate and carbonate from a sodium aluminate solution provided in order to achieve the purpose of the present invention comprises the following steps:
[0007] Step 1: After the evaporated mother liquor is cooled by heat exchange in a heat exchanger, it is mixed with an adsorbent in a slurrying device to obtain a slurry to be removed of oxalate, which is then transported to an adsorption tank to stay for 3-5 hours. The oxalate in the slurry to be removed of oxalate is adsorbed to the adsorbent, and then filtered through a filtering device to separate a first filtrate and a first filter cake. The first filtrate is sent to a heat exchanger to increase the temperature, and the first filter cake is returned to the slurrying device as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged;
[0008] Step 2: preheating the first filtrate after the temperature is raised in step 1 through a preheater, and then continuing to use an evaporator to evaporate and concentrate to obtain a mother liquor to be decarbonized, and then mixing the decarbonized mother liquor with seeds in a slurrying device for slurrying for 0.5-2 hours, sending the slurried slurry into a sedimentation tank for sedimentation separation, separating the overflow and the underflow, and separating the underflow into a second filtrate and a second filter cake through a filtering device, the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank, a small part of the second filter cake is used as seeds and mixed with the mother liquor to be decarbonized for slurrying, and most of the remaining second filter cake is used for subsequent causticization;
[0009] Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution, and then the sodium carbonate solution is mixed with lime milk in a reaction tank for causticization reaction. The causticized slag obtained by the causticization reaction is filtered and separated by a filtering device, and the separated third filtrate is sent to the aluminum hydroxide classifier in the seed classification process to dilute the classifier feed slurry. The separated third filter cake and a part of the refined sodium aluminate solution produced by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into the coarse liquid tank;
[0010] Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
[0011] As a further improvement of the above scheme, in step 1, Na2O in the evaporation mother liquor is evaporated k The concentration is 200-225g / L and the temperature is 95-125℃.
[0012] As a further improvement of the above scheme, the heat exchanger in step one is arranged in multiple stages, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the 2nd to nth stages is the circulating water. After the first stage heat exchange, the first filtrate is heated to 70-90°C, and the evaporation mother liquor is cooled to 40-50°C after the nth stage heat exchange.
[0013] As a further improvement of the above scheme, the solid content of the slurry of the evaporated mother liquor and the adsorbent in step 1 is 40-80 g / L.
[0014] As a further improvement of the above scheme, the cold source of the preheater in step 2 is the first filtrate heated by the heat exchanger in step 1, and the heat source is the mixed solution of the second filtrate and overflow in step 2. The temperature of the first filtrate after heat exchange and heating in the preheater reaches 90-100°C.
[0015] As a further improvement of the above scheme, the Na2O in the decarbonized alkali mother liquor after being concentrated by the evaporator in step 2 k The concentration is 300-320g / L and the temperature is 100-105℃.
[0016] As a further improvement of the above scheme, the caustic soda concentration (in terms of Na2O k The total amount is 45-50g / L.
[0017] As a further improvement of the above scheme, the CaO in the lime milk in step 3 f The concentration is 150-180g / L, and the amount of lime milk added is 1.2 times the molecular weight of sodium carbonate.
[0018] As a further improvement of the above scheme, the time for the causticizing reaction of lime milk and sodium carbonate solution in step three is 2-5 hours, and the reaction temperature is 80-100°C.
[0019] As a further improvement of the above scheme, the third filter cake in step three and a part of the refined sodium aluminate solution produced by the leaf filter are slurried to obtain a slurry having a solid content of 250-300 g / L, and the slurrying time is 2-3 h.
[0020] The beneficial effects of the present invention are:
[0021] Compared with the prior art, the method for synergistically removing oxalate and carbonate from a sodium aluminate solution provided by the present invention has the advantages that oxalate has been removed from the alkali mother liquor to be decarbonized, the harmful effects of oxalate crystallization are eliminated, and subsequent filtration and causticization are facilitated; at the same time, the first filtrate and the second filtrate are heat recovered through a heat exchanger, thereby reducing the energy loss of the system; in addition, the filtrate filtered by the slurry after causticization is sent to a classifier, which will not affect the washing efficiency of the red mud sedimentation washing process, reduces the internal circulation of the mother liquor, and improves the utilization efficiency of the alkali; finally, the unreacted calcium hydroxide in the third filter cake obtained after the causticization slag is separated and slurried with the refined sodium aluminate solution to generate 3CaO·Al2O3·6H2O with good crystallinity as a filter aid with good effect, which can save the amount of lime milk and save production costs.
[0022] In summary, the synergistic removal process of oxalate and carbonate saves raw materials, can operate continuously with high efficiency and low operating costs, and is beneficial to purifying the solution and improving overall production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION
[0024] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings:
[0025] Embodiment 1
[0026] according to Figure 1 As shown, the present invention provides a method for synergistically removing oxalate and carbonate in a sodium aluminate solution, comprising the following steps:
[0027] Step 1: Evaporation of Na2O in mother liquor k The concentration is 215g / L and the temperature is 115℃. The evaporation mother liquor is cooled to 50℃ through the 1st, 2nd and 3rd stages of the wide channel plate heat exchanger, and then mixed with the adsorbent in the slurrying equipment to obtain the oxalate slurry to be removed. The slurry solid content of the evaporation mother liquor and the adsorbent is 50g / L. It is transported to the adsorption tank and stays for 5h. The oxalate in the oxalate slurry to be removed is adsorbed to the adsorbent, and then filtered through a vertical filter press to separate the first filtrate and the first filter cake. The first filtrate is sent to the heat exchanger to raise the temperature to 85℃, and the first filter cake is returned to the slurrying equipment as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged. The wide channel plate heat exchanger is set to 3 stages, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the 2nd-3rd stage is circulating water.
[0028] Step 2: The first filtrate after the temperature increase in step 1 is preheated to 95°C in a shell-type preheater and then concentrated in an evaporator to obtain a decarbonized alkali mother liquor, so that the Na2O in the decarbonized alkali mother liquor is kThe concentration is 320g / L and the temperature is 105°C; the decarbonized alkali mother liquor is mixed with the seeds and slurried in a slurrying device for 0.5h, the slurried slurry is sent to a sedimentation tank for sedimentation separation, and the overflow and the underflow are separated. The underflow is separated into a second filtrate and a second filter cake by a filtering device, the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank, a small part of the second filter cake is used as a seed and mixed with the decarbonized alkali mother liquor for slurry, and most of the remaining second filter cake is used for subsequent causticization; wherein the cold source of the preheater is the first filtrate after the temperature is increased by the heat exchanger in step one, and the heat source is the mixed solution of the second filtrate and the overflow in step two.
[0029] Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution. The caustic soda concentration (in terms of Na2O k Then the sodium carbonate solution and CaO f Lime milk with a concentration of 150 g / L is mixed in a reaction tank for causticizing reaction, the amount of lime milk added is 1.2 times the molecular weight of sodium carbonate, the time for the causticizing reaction of lime milk and sodium carbonate solution is 2 hours, and the reaction temperature is 80°C; the causticized slag obtained by the causticizing reaction is filtered and separated by a filtering device, and the separated third filtrate is sent to the aluminum hydroxide classifier of the seed classification process to dilute the feed slurry of the classifier, and the separated third filter cake and a part of the refined sodium aluminate solution produced by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into a coarse liquid tank, the solid content of the slurry after slurrying is 250 g / L, and the slurrying time is 3 hours;
[0030] Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
[0031] Embodiment 2
[0032] according to Figure 1 As shown, the present invention provides a method for synergistically removing oxalate and carbonate in a sodium aluminate solution, comprising the following steps:
[0033] Step 1: Evaporation of Na2O in mother liquor kThe concentration is 225g / L and the temperature is 125℃. The evaporation mother liquor is cooled to 45℃ through the 1st, 2nd and 3rd stage heat exchange of the spiral plate heat exchanger, and then mixed with the adsorbent in the slurrying equipment to obtain the oxalate slurry to be removed. The slurry solid content of the evaporation mother liquor and the adsorbent is 80g / L. It is transported to the adsorption tank and stays for 4 hours. The oxalate in the oxalate slurry to be removed is adsorbed to the adsorbent, and then filtered and separated by the filtration equipment to obtain the first filtrate and the first filter cake. The first filtrate is sent to the first stage of the heat exchanger to heat up to 90℃, and the first filter cake is returned to the slurrying equipment as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged. The heat exchanger is set to 3 stages, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the 2nd-3rd stage is circulating water.
[0034] Step 2: The first filtrate after the temperature increase in step 1 is preheated to 100°C in a shell-type preheater and then concentrated in an evaporator to obtain a mother liquor to be decarbonized. k The concentration is 310g / L and the temperature is 105°C; the decarbonized alkali mother liquor is mixed with the seeds and slurried in a slurrying equipment for 1 hour, and the slurry after slurrying is sent to a sedimentation tank for sedimentation separation to separate the overflow and the underflow. The underflow is separated into a second filtrate and a second filter cake by a filtering device, and the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank. A small part of the second filter cake is mixed with the decarbonized alkali mother liquor as seeds for slurrying, and most of the remaining second filter cake is used for subsequent causticization; wherein the cold source of the preheater is the first filtrate after the temperature is increased by the heat exchanger in step one, and the heat source is the mixed solution of the second filtrate and the overflow in step two.
[0035] Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution. The caustic soda concentration (in terms of Na2O k Then the sodium carbonate solution and CaO f Lime milk with a concentration of 160 g / L is mixed in a reaction tank for causticizing reaction, the amount of lime milk added is 1.2 times the molecular weight of sodium carbonate, the time for the causticizing reaction of lime milk and sodium carbonate solution is 3 hours, and the reaction temperature is 90°C; the causticized slag obtained by the causticizing reaction is filtered and separated by a filtering device, and the third filtrate obtained by separation is sent to the aluminum hydroxide classifier of the seed separation process to dilute the feed slurry of the classifier, and the third filter cake obtained by separation and a part of the refined sodium aluminate solution output by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into a coarse liquid tank, the solid content of the slurry after slurrying is 280 g / L, and the slurrying time is 2 hours;
[0036] Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
[0037] Embodiment 3
[0038] according to Figure 1 As shown, the present invention provides a method for synergistically removing oxalate and carbonate in a sodium aluminate solution, comprising the following steps:
[0039] Step 1: Evaporation of Na2O in mother liquor k The concentration is 200g / L and the temperature is 95°C. The evaporation mother liquor is cooled to 40°C through the first and second stages of the spiral plate heat exchanger and then mixed with the adsorbent in the slurrying equipment to obtain the oxalate slurry to be removed. The slurry solid content of the evaporation mother liquor and the adsorbent is 40g / L. It is transported to the adsorption tank and stays for 3 hours. The oxalate in the oxalate slurry to be removed is adsorbed to the adsorbent, and then filtered through a horizontal plate and frame filter press to separate the first filtrate and the first filter cake. The first filtrate is sent to the first stage of the heat exchanger to heat up to 70°C, and the first filter cake is returned to the slurrying equipment as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged. The heat exchanger is set to 2 stages, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the second stage is circulating water.
[0040] Step 2: The first filtrate after the temperature increase in step 1 is preheated to 90°C in a shell-type preheater and then concentrated in an evaporator to obtain a mother liquor to be decarbonized. k The concentration is 300g / L and the temperature is 100°C; the decarbonized alkali mother liquor is mixed with the seeds and slurried in a slurrying device for 2 hours, and the slurry after slurrying is sent to a sedimentation tank for sedimentation separation to separate the overflow and the underflow. The underflow is separated into a second filtrate and a second filter cake by a filtering device, and the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank. A small part of the second filter cake is mixed with the decarbonized alkali mother liquor as seeds for slurrying, and most of the remaining second filter cake is used for subsequent causticization; wherein the cold source of the preheater is the first filtrate after the temperature is increased by the heat exchanger in step one, and the heat source is the mixed solution of the second filtrate and the overflow in step two.
[0041] Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution. The caustic soda concentration (in terms of Na2O k Then the sodium carbonate solution and CaO fLime milk with a concentration of 180 g / L is mixed in a reaction tank for causticizing reaction, the amount of lime milk added is 1.2 times the molecular weight of sodium carbonate, the time for the causticizing reaction of lime milk and sodium carbonate solution is 5 hours, and the reaction temperature is 100°C; the causticized slag obtained by the causticizing reaction is filtered and separated by a filtering device, and the third filtrate obtained by separation is sent to the aluminum hydroxide classifier of the seed classification process to dilute the feed slurry of the classifier, and the third filter cake obtained by separation and a part of the refined sodium aluminate solution produced by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into a coarse liquid tank, the solid content of the slurry after slurrying is 300 g / L, and the slurrying time is 2 hours;
[0042] Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
[0043] Embodiment 4
[0044] according to Figure 1 As shown, the present invention provides a method for synergistically removing oxalate and carbonate in a sodium aluminate solution, comprising the following steps:
[0045] Step 1: Evaporation of Na2O in mother liquor k The concentration is 205g / L and the temperature is 105℃. The evaporation mother liquor is cooled to 45℃ through the 1st, 2nd and 3rd stage heat exchange of the spiral plate heat exchanger, and then mixed with the adsorbent in the slurrying equipment to obtain the oxalate slurry to be removed. The slurry solid content of the evaporation mother liquor and the adsorbent is 60g / L. It is transported to the adsorption tank and stays for 4 hours. The oxalate in the oxalate slurry to be removed is adsorbed to the adsorbent, and then filtered and separated by the filtration equipment to obtain the first filtrate and the first filter cake. The first filtrate is sent to the first stage of the heat exchanger to heat up to 80℃, and the first filter cake is returned to the slurrying equipment as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged. The heat exchanger is set to 3 stages, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the 2nd-3rd stage is circulating water.
[0046] Step 2: The first filtrate after the temperature increase in step 1 is preheated to 100°C in a shell-type preheater and then concentrated in an evaporator to obtain a mother liquor to be decarbonized. kThe concentration is 315g / L and the temperature is 100°C; the decarbonized alkali mother liquor is mixed with the seeds and slurried in a slurrying device for 1.5h; the slurried slurry is sent to a sedimentation tank for sedimentation separation to separate the overflow and the underflow; the underflow is separated into a second filtrate and a second filter cake by a filtering device; the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank; a small portion of the second filter cake is used as a seed and mixed with the decarbonized alkali mother liquor for slurrying, and the remaining majority of the second filter cake is used for subsequent causticization; wherein the cold source of the preheater is the first filtrate after the temperature is increased by the heat exchanger in step one, and the heat source is the mixed solution of the second filtrate and the overflow in step two.
[0047] Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution. The caustic soda concentration (in terms of Na2O k Then the sodium carbonate solution and CaO f Lime milk with a concentration of 170 g / L is mixed in a reaction tank for causticizing reaction. The amount of lime milk added is 1.2 times the molecular weight of sodium carbonate. The time for the causticizing reaction of lime milk and sodium carbonate solution is 4 hours, and the reaction temperature is 95°C. The causticized slag obtained by the causticizing reaction is filtered and separated by a filtering device. The third filtrate obtained by separation is sent to the aluminum hydroxide classifier of the seed separation process to dilute the feed slurry of the classifier. The third filter cake obtained by separation and a part of the refined sodium aluminate solution produced by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into a coarse liquid tank. The solid content of the slurry after slurrying is 275 g / L, and the slurrying time is 3 hours.
[0048] Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
[0049] The above embodiments are not limited to the technical solutions of the embodiments themselves, and the embodiments can be combined with each other to form new embodiments. The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Any modification or equivalent replacement that does not deviate from the spirit and scope of the present invention shall be included in the scope of the technical solutions of the present invention.
Claims
1. A method for the coordinated removal of oxalate and carbonate in a sodium aluminate solution, characterized in that: The following steps are involved: Step 1: After the evaporated mother liquor is cooled by heat exchange in a heat exchanger, it is mixed with an adsorbent in a slurrying device to obtain a slurry to be removed of oxalate, which is then transported to an adsorption tank to stay for 3-5 hours. The oxalate in the slurry to be removed of oxalate is adsorbed to the adsorbent, and then filtered through a filtering device to separate a first filtrate and a first filter cake. The first filtrate is sent to a heat exchanger to increase the temperature, and the first filter cake is returned to the slurrying device as a part of the adsorbent to adsorb oxalate until it can no longer be adsorbed and then discharged; Step 2: preheating the first filtrate after the temperature is raised in step 1 through a preheater, and then continuing to use an evaporator to evaporate and concentrate to obtain a mother liquor to be decarbonized, and then mixing the decarbonized mother liquor with seeds in a slurrying device for slurrying for 0.5-2 hours, sending the slurried slurry to a sedimentation tank for sedimentation separation, separating the overflow and the underflow, and separating the underflow into a second filtrate and a second filter cake through a filtering device, the second filtrate is mixed with the overflow and sent to a preheater for heat exchange and then to a blending tank, a small part of the second filter cake is used as seeds and mixed with the mother liquor to be decarbonized for slurrying, and most of the remaining second filter cake is used for subsequent causticization; Step 3: Most of the second filter cake remaining in step 2 is dissolved and diluted with hot water to obtain a sodium carbonate solution, and then the sodium carbonate solution is mixed with lime milk in a reaction tank for causticization reaction. The causticized slag obtained by the causticization reaction is filtered and separated by a filtering device, and the separated third filtrate is sent to the aluminum hydroxide classifier in the seed classification process to dilute the classifier feed slurry. The separated third filter cake and a part of the refined sodium aluminate solution produced by the leaf filter are slurried in a slurrying device to obtain a filter aid and then passed into the coarse liquid tank; Step 4: Add the filter aid obtained in step 3 to the coarse liquid tank as a filter aid for refining the sodium aluminate solution, and obtain the fourth filter cake and the refined sodium aluminate solution after separation by the leaf filter. The fourth filter cake is discharged into the sedimentation tank of the red mud sedimentation process, a part of the refined sodium aluminate solution enters the slurrying equipment for slurrying, and most of the refined sodium aluminate solution is introduced into the fine liquid tank.
2. The method for collaboratively removing oxalate and carbonate in a sodium aluminate solution according to claim 1, characterized in that: In the step 1, Na2O in the mother liquor is evaporated k The concentration is 200-225g / L and the temperature is 95-125℃.
3. The method for collaboratively removing oxalate and carbonate in a sodium aluminate solution according to claim 1, characterized in that: The heat exchanger in step 1 is configured to be multi-stage, the heat source is the evaporation mother liquor, the cold source of the first stage is the first filtrate, and the cold source of the 2nd to nth stages is the circulating water. After the first stage heat exchange, the first filtrate is heated to 70-90°C, and after the nth stage heat exchange, the evaporation mother liquor is cooled to 40-50°C.
4. The method for collaboratively removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: In the step 1, the slurry solid content of the evaporated mother liquor and the adsorbent is 40-80 g / L.
5. The method for collaboratively removing oxalate and carbonate in a sodium aluminate solution according to claim 1, characterized in that: The cold source of the preheater in step 2 is the first filtrate heated by the heat exchanger in step 1, and the heat source is the mixed solution of the second filtrate and overflow in step 2. The temperature of the first filtrate after heat exchange and heating in the preheater reaches 90-100°C.
6. The method for collaboratively removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: In step 2, the Na2O in the alkali mother liquor to be decarbonized after being concentrated by the evaporator k The concentration is 300-320g / L and the temperature is 100-105℃.
7. The method for collaboratively removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: The caustic soda concentration (in terms of Na2O k The total amount is 45-50g / L.
8. The method for collaboratively removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: The CaO in the lime milk in step 3 f The concentration is 150-180g / L, and the amount of lime milk added is 1.2 times the molecular weight of sodium carbonate.
9. The method for collaboratively removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: In the step 3, the time for the causticizing reaction of the lime milk and the sodium carbonate solution is 2-5 hours, and the reaction temperature is 80-100°C.
10. The method for synergistically removing oxalate and carbonate from a sodium aluminate solution according to claim 1, characterized in that: After the third filter cake in step 3 and a portion of the refined sodium aluminate solution produced by the leaf filter are slurried, the solid content of the slurry is 250-300 g / L, and the slurrying time is 2-3 hours.