Method for improving alumina seed decomposition rate in system for producing alumina by Bayer process

Abstract

The invention belongs to the technical field of alumina production, and particularly discloses a method for improving alumina seed decomposition rate in a Bayer process alumina production system. The method is used for solving the problems that an existing defoaming agent is difficult to uniformly mix when being added into a decomposing tank, symptoms are not treated, and causticizing liquid is reasonably utilized. Comprising the following steps: washing and filtering fine-particle seed crystals, and agglomerating the fine-particle seed crystals with fine liquid; agglomerated slurry and underflow seed crystal subjected to secondary grading enter a first decomposition tank for cooling decomposition; grading the seed crystal in the last decomposition tank twice; the overflow fine seed crystal subjected to secondary grading enters a fine seed crystal settling tank, settling overflow is decomposed mother liquor, underflow is filtered and washed, oxalate enters filtrate, and the filtrate containing oxalate enters a lime causticization system; the causticized underflow is subjected to filter pressing, filter pressing filtrate and causticized overflow enter a tubular filter to be filtered, and the filtered filtrate is fed into a decomposition intermediate tank after a defoaming agent is added into the filtered filtrate; foam of the decomposition tank is effectively reduced, and the decomposition power of the sodium aluminate solution is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of alumina production, and in particular relates to a method for improving the decomposition rate of alumina seeds in a Bayer process alumina production system. Background Art

[0002] In the existing Bayer process of producing alumina, the ore will bring a large amount of organic matter into the sodium aluminate decomposition solution during the production process, thus generating a large amount of foam in the decomposition process, making it difficult to lower the temperature of the decomposition system, causing serious scarring of the decomposition tank, reducing the effective volume, reducing the decomposition rate of the sodium aluminate solution, and periodically deteriorating the product particle size. Although most factories now add 10-30ppm of defoaming agent to the decomposition tank, it is difficult to mix evenly due to the large decomposition volume, and the effect is not good, which only treats the symptoms but not the root cause.

[0003] Whether the Bayer process uses domestic diaspore ore or imported diaspore ore or gibbsite ore, the inorganic carbon and organic carbon in the ore will react with NaOH to produce sodium carbonate and sodium oxalate during the production process, and enter the sodium aluminate solution. The traditional process is forced to discharge by evaporation and concentration, and lime milk is added for causticization. The causticized slurry or the causticized slurry is separated by the sedimentation tank and then the bottom flow is pumped into the washing and sedimentation system. The causticized slag is discharged with the red mud and stored, and the causticized liquid and the washing liquid are mixed and enter the dilution system. The Chinese invention patent "A method and system for improving the decomposition rate of alumina" with the publication number CN114873617A introduces that the direct entry of the causticized liquid into the red mud sedimentation and washing system will increase the amount of semen in the system, which not only increases the transport load of the semen system and shortens the decomposition time, but also causes the semen causticity ratio (ɑk), which is not conducive to improving the decomposition rate of the semen, especially as the carbon content of the ore gradually increases, the increase in the amount of liquid in the causticization system is more prominent.

[0004] Therefore, how to reasonably utilize the causticizing liquid is a current industry problem. Both the Chinese invention patent with publication number CN114873617A and the Chinese invention patent with publication number CN112499656A have conducted exploratory research but have obvious defects, as follows: The Chinese invention patent with publication number CN114873617A "A method and system for improving the decomposition rate of alumina seeds" discloses that the causticizing liquid produced by the causticizing system in the Bayer process alumina production is added to the refined sodium aluminate seed decomposition system, the causticizing liquid has a caustic concentration of 30-100 g / L, and a caustic ratio of 30-200, the refined sodium aluminate solution has a caustic concentration of 150-170 g / L, a caustic ratio of 1.38-1.50, an initial decomposition temperature of 58-63°C, and a final decomposition temperature of 45-52°C. In the above patent, the sodium carbonate causticizing needs to add excessive lime milk. There is unreacted Ca(OH)2 in the causticizing solution. The causticizing solution directly enters the decomposition system, resulting in excessive calcium in the alumina product, affecting product quality. Since the caustic concentration of the causticizing solution is 30-100g / L, it can play a dilution role when entering the decomposition system, but the excessively high ɑk (30-200) seriously hinders decomposition and affects the particle size of the alumina product. In actual production, in order to ensure the efficiency of sodium carbonate causticizing, the causticizing solution temperature is 80-95°C, while the temperature of the decomposition system is 45-63°C. Therefore, for substances that need to be cooled and decomposed, directly entering the decomposition tank will affect their decomposition rate.

[0005] The Chinese invention patent "A method for treating salt-removing causticized slurry in alumina production" with publication number CN112499656A discloses that after sodium carbonate causticized slurry is separated by solid-liquid separation equipment, a causticized filtrate with a caustic concentration of 60-90g / L is obtained, which enters a flat plate strong filtrate storage tank and is fully mixed with a strong filtrate with a caustic concentration of 140-160g / L to obtain a mixed solution with a caustic concentration of 100-120g / L, which is pumped into a decomposition system; the causticized slag enters a washing and sedimentation system, and is mixed with red mud and then stored by a red mud external drainage method. The sodium carbonate causticization in the above patent requires the addition of excessive lime milk, and there is unreacted Ca(OH)2 in the causticized liquid. The causticized liquid is directly mixed with the flat plate strong filtrate and enters the decomposition system, resulting in excessive calcium in the alumina product, affecting the product quality. The caustic soda concentration of the causticizing solution is 30-90g / L, which can dilute the solution when it enters the decomposition system, but too high ɑk (30-200) seriously hinders decomposition and affects the particle size of the alumina product. In actual production, in order to ensure the efficiency of sodium carbonate causticizing, the causticizing solution temperature is 80-95℃, while the temperature of the decomposition system is 45-63℃. Therefore, for substances that need to be cooled and decomposed, directly entering the decomposition tank will affect their decomposition rate. Summary of the invention

[0006] The purpose of the present invention is to provide a method for improving the decomposition rate of alumina seeds in a Bayer process alumina production system, effectively solving the problems in the prior art that the defoaming agent is difficult to mix in the decomposition tank and only treats the symptoms but not the root cause, and how to reasonably utilize the causticizing solution.

[0007] In order to solve the above technical problems, the technical solution adopted by the present invention is: a method for improving the decomposition rate of alumina seeds in a Bayer process alumina production system, comprising the following steps: S1, the fine particle seeds are washed and filtered and enter the agglomeration first tank together with the semen, the temperature of the agglomeration first tank is 75-80°C, and then they pass through the agglomeration intermediate tank and the agglomeration final tank in sequence for agglomeration.

[0008] S2, the seeds in the final decomposition tank are classified twice; the slurry after agglomeration and the bottom flow seeds of the second classification enter the first decomposition tank, the temperature of the first decomposition tank is 66-70°C, and then pass through the middle decomposition tank and the final decomposition tank in turn for cooling and decomposition, and the temperature of the final decomposition tank is 57-60°C.

[0009] The coarse particles in the bottom flow of the decomposition tank seeds for the first classification enter the finished product filtration process as finished products, and the overflow fine particles in the first classification are subjected to secondary classification.

[0010] S3. The overflow fine crystals after secondary classification enter the fine crystal seed sedimentation tank, the sedimentation overflow is the decomposition mother liquor, the bottom flow is filtered and washed with washing water through the filtering equipment, the oxalate enters the filtrate, and the filtrate containing oxalate enters the lime causticization system.

[0011] S4. In the lime causticizing system, the lime milk reacts with the oxalate in the filtrate in the reaction tank to generate calcium oxalate solid. The reaction time in the reaction tank is controlled to be 60-90 minutes, the temperature is 55-60°C, the alkalinity is 15-20 g / L, and the caustic ratio is 2.9-3.1.

[0012] S5. After causticization, the temperature of the causticized liquid is 55-60°C, the alkalinity is 16-26 g / L, and the caustic ratio is 3.3-3.6.

[0013] The causticized bottom flow is filtered through a filter press, and the filter residue after filtration is comprehensively utilized. The filtrate and causticized overflow enter the tubular filter for filtration to filter out calcium-containing particles with a particle size greater than or equal to 5μm. The filtrate after filtration is added with a defoaming agent and sent to the decomposition intermediate tank.

[0014] Furthermore, in step S4, the oxalate is sodium oxalate, and the molecular ratio of CaO to sodium oxalate is 2.0-2.5.

[0015] Further, in step S4, the reaction time in the reaction tank is controlled to be 60 min, the temperature to be 55° C., the alkalinity to be 16 g / L, and the caustic ratio to be 2.93.

[0016] Further, in step S5, the temperature of the causticized liquid after causticization is 56°C, the alkalinity is 22g / L, and the causticity ratio is 3.32.

[0017] Furthermore, there is one decomposition first tank and one decomposition last tank, and there are 13 to 15 decomposition intermediate tanks, which are numbered in sequence starting from No. 1; in step S5, the filtered filtrate is added with a defoaming agent and then sent to any one of the decomposition intermediate tanks No. 3 to No. 8.

[0018] Compared with the prior art, the beneficial technical effects of the present invention are:

[0019] The present invention utilizes a defoamer and oxalate causticizing solution in combination through creative process design, thereby effectively reducing the foam in the decomposition tank, thereby reducing the amount of scarring caused by the foam; increasing the effective volume of the decomposition tank, extending the decomposition time, significantly improving the natural cooling effect, and further increasing the decomposition power of the sodium aluminate solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0021] A method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system, such as Figure 1 As shown, the method comprises the following steps: S1, the fine particle seed crystals are washed and filtered and then enter the agglomeration first tank together with the semen. The temperature of the agglomeration first tank is 75-80°C, and then they pass through the agglomeration middle tank and the agglomeration final tank in sequence for agglomeration.

[0022] S2, the seeds in the final decomposition tank are classified twice. The slurry after agglomeration and the bottom flow seeds of the second classification enter the first decomposition tank, the temperature of the first decomposition tank is 66-70°C, and then pass through the middle decomposition tank and the final decomposition tank in turn for cooling and decomposition, and the temperature of the final decomposition tank is 57-60°C.

[0023] The coarse particles in the bottom flow of the decomposition tank seeds for the first classification enter the finished product filtration process as finished products, and the overflow fine particles in the first classification are subjected to secondary classification.

[0024] S3. The overflow fine crystals after secondary classification enter the fine crystal seed sedimentation tank, the sedimentation overflow is the decomposition mother liquor, the bottom flow is filtered and washed with washing water through the filtering equipment, the oxalate enters the filtrate, and the filtrate containing oxalate enters the lime causticization system.

[0025] S4. In the lime causticizing system, the lime milk reacts with the oxalate in the filtrate in the reaction tank to generate calcium oxalate solid, and the reaction time in the reaction tank is controlled to be 60-90 minutes, the temperature is 55-60° C., the alkalinity (NK) is 15-20 g / L, and the caustic ratio (ak) is 2.9-3.1. The oxalate is sodium oxalate, and the molecular ratio of CaO to sodium oxalate is 2.0-2.5.

[0026] S5. After causticization, the temperature of the causticized liquid is 55-60°C, the alkalinity is 16-26 g / L, and the caustic ratio is 3.3-3.6.

[0027] The causticized bottom flow is filtered through a filter press, and the filter residue after filtration is comprehensively utilized. The filtrate and causticized overflow enter the precision tubular filter for filtration, filtering out calcium-containing particles with a particle size greater than or equal to 5μm to prevent excessive calcium in the product. There is one decomposition first tank and one decomposition end tank, and there are 13 to 15 decomposition intermediate tanks, which are numbered in sequence starting from No. 1. After adding defoaming agent to the filtered filtrate, it is sent to any one of the decomposition intermediate tanks No. 3 to No. 8.

[0028] In this embodiment, the fine particles and fine seeds are particles mainly having a particle size of less than 45 μm, and the coarse particles and coarse seeds are particles mainly having a particle size of greater than or equal to 45 μm.

[0029] The 1.6 million tons / year Bayer process alumina production system produces 290-330m3 of oxalate caustic solution 3 / h, add the defoamer to the oxalate causticizing solution according to the amount added to the decomposition tank, and then inject it into the decomposition tank to mix very evenly, quickly defoam, and improve the decomposition power of the sodium aluminate solution. At the same time, the oxalate causticizing solution is only 55-60℃, which can play a role in cooling the decomposition tank; the alkalinity is as low as 16-26g / L, which reduces the alkalinity of the decomposed sodium aluminate solution; the caustic ratio is as low as 3.3-3.6, which can improve the decomposition power of the sodium aluminate solution. Since the decomposition of the sodium aluminate solution is a process of increasing alkali concentration, oxalate will precipitate in this process. The low alkalinity causticizing solution can inhibit and dilute the precipitation of oxalate and reduce the formation of foam, which can improve the decomposition power of the sodium aluminate solution.

[0030] In the Bayer process sodium aluminate solution, the solubility of sodium oxalate is proportional to the temperature and inversely proportional to the alkali concentration, and the decomposition in the Bayer process production is a process of cooling and slightly increasing the alkali concentration, which creates conditions for the crystallization of sodium oxalate. Because the sodium oxalate crystals are relatively fine and have a large specific surface area, under the interfacial force, it is easy to adhere to the Al(OH)3 surface as a fine seed, or deposit into the growing Al(OH)3 lattice. Sodium oxalate is circulated and enriched in the decomposition system along with a large amount of fine seed slurry. A large amount of sodium oxalate will hinder the agglomeration of fine seeds in the decomposition process and form a large amount of foam, which ultimately affects the stable operation of the decomposition section. The present invention improves the decomposition rate by combining the defoamer and the oxalate causticizing liquid, solves the problems of the prior art that the defoamer is difficult to mix in the decomposition tank, the effect is limited, the symptoms are not cured, and the decomposition rate is improved by the reasonable use of the oxalate causticizing liquid.

[0031] The present invention will be further described in detail below with reference to specific embodiments.

[0032] Example 1: In a 1.6 million t / a Bayer process alumina production system, the decomposition final tank seed crystals were classified twice.

[0033] After washing and filtration, the fine particle seeds and the semen enter the agglomeration first tank (temperature 79.2°C), and then pass through the agglomeration middle tank and the agglomeration final tank for agglomeration.

[0034] The slurry after agglomeration and the bottom flow seeds of the secondary classification enter the first decomposition tank (temperature 68.3°C), and then pass through the middle decomposition tank and the final decomposition tank (temperature 55.4°C) for cooling and decomposition.

[0035] The coarse particles at the bottom flow of the decomposition tank seeds after the first classification enter the finished product filtration process as finished products; the overflow fine particles of the first classification are subjected to secondary classification, and the overflow fine crystal seeds after the secondary classification enter the fine crystal seed sedimentation tank, and the sedimentation overflow is the decomposition mother liquor. The bottom flow filter equipment is filtered and washed with washing water, and oxalate enters the filtrate.

[0036] The oxalate-rich filtrate was concentrated at 320 m 3 / h enters the lime causticizing system, lime milk reacts with oxalate to form calcium oxalate solid, and the reaction time, temperature, alkalinity, and caustic ratio in the reaction tank are controlled to be 60min, 55℃, 16g / L, and 2.93; the molecular ratio of CaO to sodium oxalate is 2.2, and the temperature of the causticizing liquid after causticizing is 56℃, the alkalinity is 22g / L, and the caustic ratio is 3.32.

[0037] After causticization, most of the organic matter in the filtrate containing oxalate is causticized and the filtrate does not contain foam. The filter residue after causticization bottom flow is filtered by the filter press for comprehensive utilization, and the filtrate and causticization overflow enter the precision tubular filter for filtration to filter out calcium particles. After adding defoamer, the filtered filtrate is sent to the decomposition intermediate tank-No. 3 tank.

[0038] The original average temperature of tank No. 3 was 66.3℃, and the average temperature after adding the filtrate was changed to 64.4℃, a decrease of 1.9℃; the alkalinity changed from the previous average of 138.6g / L to the average of 136.2g / L after adding the filtrate, a decrease of 2.4g / L. After tank No. 3, the foam was significantly reduced, the amount of scarring caused by the foam was reduced by about 50%, the effective volume of the decomposition tank was increased, the decomposition time was extended, and the natural cooling effect was significantly improved compared with the past. Under the same working conditions, the average temperature of the first and last tanks of the decomposition was 10.6℃ before, and it can now reach 12.9℃; the decomposition power of the sodium aluminate solution has been improved, and the decomposition rate has been 49.3% before, and it can now reach 52.8%, an increase of 3.5%.

[0039] Example 2: In a 1.6 million t / a Bayer process alumina production system, the decomposition tank seed crystals were classified twice.

[0040] After washing and filtration, the fine particle seeds and the semen enter the agglomeration first tank (temperature 78.8℃), and then pass through the agglomeration middle tank and the agglomeration final tank for agglomeration.

[0041] The slurry after agglomeration and the bottom flow seeds of the secondary classification enter the first decomposition tank (temperature 68.1°C), and then pass through the middle decomposition tank and the final decomposition tank (temperature 55.8°C) for cooling and decomposition.

[0042] The coarse particles at the bottom flow of the first classification of the decomposition tank seeds enter the finished product filtration process as finished products, and the overflow fine particles of the first classification are subjected to secondary classification. The overflow fine seeds after the secondary classification enter the fine seed sedimentation tank. The sedimentation overflow is the decomposition mother liquor. The bottom flow filter equipment is filtered and washed with washing water, and oxalate enters the filtrate.

[0043] The oxalate-rich filtrate was concentrated at 320 m 3 / h enters the lime causticizing system, lime milk reacts with oxalate to generate calcium oxalate solid, and the reaction time is controlled to be 70min, temperature to be 58℃, alkalinity to be 18g / L, and caustic ratio to be 2.92 in the reaction tank; the molecular ratio of CaO to sodium oxalate is 2.3, and the temperature of the causticizing liquid after causticizing is 58℃, the alkalinity is 26g / L, and the caustic ratio is 3.48.

[0044] After causticizing, most of the organic matter in the filtrate containing oxalate is causticized, and there is no foam in the filtrate. The causticized bottom flow is filtered by the filter press and the filter residue is comprehensively utilized. The filter press filtrate and causticized overflow enter the precision tubular filter for filtration to filter out calcium particles. After adding the defoamer, the filtered filtrate is sent to the decomposition intermediate tank-tank No. 5.

[0045] The original average temperature of tank No. 5 was 63.8℃, and after adding the filtrate, the average temperature became 62.5℃, a decrease of 1.3℃; the alkalinity changed from the previous average of 139.7g / L to the average of 137.9g / L after adding the filtrate, a decrease of 1.8g / L.

[0046] After the No. 5 tank, the foam is significantly reduced, the amount of scarring caused by the foam is reduced by about 50%, the effective volume of the decomposition tank is increased, the decomposition time is extended, and the natural cooling effect is significantly improved compared with the past. Under the same working conditions, the average temperature of the first and last tanks of the decomposition was 10.6℃ before, and now it can reach 12.3℃; the decomposition power of the sodium aluminate solution is improved, and the decomposition rate is 49.3% before, and now it can reach 52.6%, an increase of 3.3%.

[0047] Example 3: In a 1.6 million t / a Bayer process alumina production system, the decomposition tank seed crystals were classified twice.

[0048] After washing and filtering, the fine particle seeds and the semen enter the agglomeration first tank (temperature 78.9℃), and then pass through the agglomeration middle tank and the agglomeration final tank for agglomeration.

[0049] The slurry after agglomeration and the bottom flow seeds of the secondary classification enter the first decomposition tank (temperature 68.5°C), and then pass through the middle decomposition tank and the final decomposition tank (temperature 56.8°C) for cooling and decomposition.

[0050] The coarse particles at the bottom flow of the first classification of the decomposition tank seeds enter the finished product filtration process as finished products, and the overflow fine particles of the first classification are subjected to secondary classification. The overflow fine seeds after the secondary classification enter the fine seed sedimentation tank. The sedimentation overflow is the decomposition mother liquor. The bottom flow filter equipment is filtered and washed with washing water, and oxalate enters the filtrate.

[0051] The oxalate-rich filtrate was concentrated at 320 m 3 / h enters the lime causticizing system, lime milk reacts with oxalate to form calcium oxalate solid, and the reaction time, temperature, alkalinity, and caustic ratio in the reaction tank are controlled to be 70min, 56℃, 16g / L, and 2.92; the molecular ratio of CaO to sodium oxalate is 2.0, and the temperature of the causticizing liquid after causticizing is 57℃, the alkalinity is 23g / L, and the caustic ratio is 3.43.

[0052] After causticizing, most of the organic matter in the filtrate containing oxalate is causticized, and there is no foam in the filtrate. The filter residue after causticizing bottom flow is filtered by the filter press for comprehensive utilization, and the filtrate and causticizing overflow enter the precision tubular filter for filtration to filter out the calcium particles. After the filtrate is filtered, the defoaming agent is added to the filtrate and sent to the decomposition intermediate tank-tank No. 7.

[0053] The original average temperature of tank No. 7 was 61.9℃, and the average temperature after adding the filtrate became 61.1℃, a decrease of 0.9℃; the alkalinity changed from the previous average of 140.2g / L to the average of 138.4g / L after adding the filtrate, a decrease of 1.8g / L.

[0054] After tank No. 7, the foam is significantly reduced, the amount of scarring caused by foam is reduced by about 50%, the effective volume of the decomposition tank is increased, the decomposition time is extended, and the natural cooling effect is significantly improved compared with the past. Under the same working conditions, the average temperature of the first and last tanks of the decomposition was 10.6℃ before, and now it can reach 11.7℃; the decomposition power of the sodium aluminate solution is improved, and the decomposition rate is 49.3% before, and now it can reach 52.1%, an increase of 2.8%.

[0055] Example 4: In a 1.6 million t / a Bayer process alumina production system, the decomposition final tank seed crystals were classified twice.

[0056] After washing and filtration, the fine particle seeds and the semen enter the agglomeration first tank (temperature 77.8℃), and then pass through the agglomeration middle tank and the agglomeration final tank for agglomeration.

[0057] The slurry after agglomeration and the bottom flow seeds of the secondary classification enter the first decomposition tank (temperature 67.9°C), and then pass through the middle decomposition tank and the final decomposition tank (temperature 56.8°C) for cooling and decomposition.

[0058] The coarse particles at the bottom flow of the first classification of the decomposition tank seeds enter the finished product filtration process as finished products, and the overflow fine particles of the first classification are subjected to secondary classification. The overflow fine seeds after the secondary classification enter the fine seed sedimentation tank. The sedimentation overflow is the decomposition mother liquor. The bottom flow filter equipment is filtered and washed with washing water, and oxalate enters the filtrate.

[0059] The oxalate-rich filtrate was concentrated at 320 m 3 / h enters the lime causticizing system, lime milk reacts with oxalate to form calcium oxalate solid, and the reaction time is controlled to be 70min, temperature to be 56℃, alkalinity to be 18g / L, and caustic ratio to be 2.93 in the reaction tank; the molecular ratio of CaO to sodium oxalate is 2.5, and the temperature of the causticizing liquid after causticizing is 56℃, the alkalinity is 25g / L, and the caustic ratio is 3.56.

[0060] After causticization, most of the organic matter in the filtrate containing oxalate is causticized and there is no foam in the filtrate. The residue after causticization bottom flow is filtered by the filter press for comprehensive utilization. The filtrate and causticization overflow enter the precision tubular filter for filtration to filter out the calcium particles. The filtrate after filtration is added with defoamer and sent to the decomposition intermediate tank-No. 8 tank.

[0061] The original average temperature of tank No. 8 was 60.7℃, and the average temperature after adding the filtrate became 60.2℃, a decrease of 0.5℃; the alkalinity changed from the previous average of 142.3g / L to the average of 140.2g / L after adding the filtrate, a decrease of 2.1g / L.

[0062] After the No. 8 tank, the foam is significantly reduced, the amount of scarring caused by the foam is reduced by about 50%, the effective volume of the decomposition tank is increased, the decomposition time is extended, and the natural cooling effect is significantly improved compared with the past. Under the same working conditions, the average temperature of the first and last tanks of the decomposition was 10.6℃ before, and now it can reach 11.1℃; the decomposition power of the sodium aluminate solution is improved, and the decomposition rate is 49.3% before, and now it can reach 51.5%, an increase of 2.2%.

[0063] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system, characterized in that: The following steps are involved: S1, fine particle seed crystals are washed and filtered and then enter the agglomeration first tank together with the semen. The temperature of the agglomeration first tank is 75-80°C, and then they pass through the agglomeration middle tank and the agglomeration final tank in sequence for agglomeration; S2, decomposing the final tank seed to perform two classifications; The slurry after agglomeration and the bottom flow seeds of the secondary classification enter the first decomposition tank, the temperature of the first decomposition tank is 66-70°C, and then pass through the middle decomposition tank and the final decomposition tank in turn for cooling and decomposition, the temperature of the final decomposition tank is 57-60°C; The coarse particles in the bottom flow of the decomposition tank seed for the first classification enter the finished product filtration process as the finished product, and the fine particles in the overflow of the first classification are subjected to secondary classification; S3, the overflow fine crystals after secondary classification enter the fine crystal seed sedimentation tank, the sedimentation overflow is the decomposition mother liquor, the underflow is filtered and washed with washing water through the filtering equipment, the oxalate enters the filtrate, and the filtrate containing oxalate enters the lime causticization system; S4. In the lime causticizing system, the lime milk reacts with the oxalate in the filtrate in the reaction tank to generate calcium oxalate solid. The reaction time in the reaction tank is controlled to be 60 to 90 minutes, the temperature is 55 to 60°C, the alkalinity is 15 to 20 g / L, and the caustic ratio is 2.9 to 3.1; S5. After causticization, the temperature of the causticized liquid is 55-60°C, the alkalinity is 16-26g / L, and the caustic ratio is 3.3-3.6; The causticized bottom flow is filtered through a filter press, and the filter residue after filtration is comprehensively utilized. The filtrate and causticized overflow enter the tubular filter for filtration to filter out calcium-containing particles with a particle size greater than or equal to 5μm. The filtrate after filtration is added with a defoaming agent and sent to the decomposition intermediate tank.

2. The method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system according to claim 1, characterized in that: In step S4, the oxalate is sodium oxalate, and the molecular ratio of CaO to sodium oxalate is 2.0-2.

5.

3. The method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system according to claim 1, characterized in that: In step S4, the reaction time in the reaction tank is controlled to be 60 minutes, the temperature to be 55° C., the alkalinity to be 16 g / L, and the caustic ratio to be 2.

93.

4. The method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system according to claim 3, characterized in that: In step S5, the temperature of the causticized liquid after causticization is 56° C., the alkalinity is 22 g / L, and the caustic ratio is 3.

32.

5. The method for increasing the decomposition rate of alumina seeds in a Bayer process alumina production system according to claim 1, characterized in that: There is one decomposition first slot and one decomposition last slot, and there are 13 to 15 decomposition middle slots. The decomposition middle slots are numbered in sequence starting from No. 1; In step S5, the filtered filtrate is added with a defoaming agent and then sent to any one of the decomposition intermediate tanks No. 3 to No. 8.

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