Carbon alkali salt elimination system and salt elimination method in process of producing aluminum oxide by Bayer process

Abstract

The invention relates to the technical field of salt elimination in the aluminum oxide production process, in particular to a carbon alkali salt elimination system and a salt elimination method in the process of producing aluminum oxide through a Bayer process, a feed port of a lime milk filter is connected with a discharge port of a lime milk tank, and a liquid outlet of the lime milk filter is connected with a liquid inlet of a lime milk filtrate tank; a discharge port of the lime milk filter is connected with a feed port of the pulping tank, a discharge port of the pulping tank is connected with a feed port of the activating tank, and a discharge port of the activating tank is connected with a feed port of the salt elimination filter; the salt discharge slurry tank comprises a first discharge port and a second discharge port, the first discharge port is connected with a feed port of the pulping tank, and the second discharge port is connected with a feed port of the salt discharge filter; a liquid outlet of the salt elimination filter is connected with a liquid inlet of the salt elimination filtrate tank, and a material outlet of the salt elimination filter is connected with a material inlet of the salt elimination filter cake tank. According to the invention, the lime milk filtration aiding system is introduced into the original salt elimination filtration system, so that the efficiency and the effect of the salt elimination process are remarkably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of salt removal in alumina production process, and in particular to a carbon alkali salt removal system and a salt removal method in a Bayer process for producing alumina. Background Art

[0002] During the Bayer process of alumina production, the carbon-to-alkali ratio (C / A) of the Bayer alkali system continuously increases due to factors such as impurities introduced by the ore, accumulation in the system's circulation, the addition of lime milk to the leaf filter as a filtration aid, the absorption of carbon dioxide from the air by the sodium aluminate solution, and the exchange of liquid volume with the sintering system. This increase in C / A not only affects the operating efficiency of the evaporator but also reduces key production indicators such as dissolution rate and circulation efficiency. Currently, the main methods used by the Bayer process to reduce the C / A content of the system are salt removal and causticization. The salt removal method involves filtering the concentrated mother liquor through a salt removal filter. The salt removal filter cake is then fed to the sintering batching, and the filtrate is returned to the Bayer batching. However, the carbonate crystals precipitated in the salt removal slurry are fine and easily clog the filter cloth, resulting in poor filtration efficiency. Furthermore, organic matter in the salt removal slurry increases the viscosity of the filter cake, causing it to adhere to the filter cloth, resulting in incomplete cake discharge and affecting the overall efficiency of the salt removal system. Summary of the Invention

[0003] In view of the problems in the prior art that filter cloth of the filter machine is easily clogged and filter cake is easily adhered to the filter cloth, the present invention provides a carbon alkali salt removal system and salt removal method for the Bayer process of producing alumina.

[0004] To achieve the above object, the technical solution of the present invention is as follows:

[0005] A carbon alkali salt removal system for a Bayer process of producing alumina comprises a lime milk tank, a lime milk filter, a lime milk filtrate tank, a beating tank, an activation tank, a salt removal slurry tank, a salt removal filter, a salt removal filtrate tank and a salt removal filter cake tank; the feed inlet of the lime milk filter is connected to the discharge port of the lime milk tank, the liquid outlet of the lime milk filter is connected to the liquid inlet of the lime milk filtrate tank, the discharge port of the lime milk filter is connected to the feed inlet of the beating tank, the discharge port of the beating tank is connected to the feed inlet of the activation tank, and the discharge port of the activation tank is connected to the feed inlet of the salt removal filter; the salt removal slurry tank comprises a first discharge port and a second discharge port, the first discharge port is connected to the feed inlet of the beating tank, and the second discharge port is connected to the feed inlet of the salt removal filter; the liquid outlet of the salt removal filter is connected to the liquid inlet of the salt removal filtrate tank, and the discharge port of the salt removal filter is connected to the feed inlet of the salt removal filter cake tank.

[0006] Furthermore, the lime milk filter is a vertical plate and frame filter press or a belt filter, and the salt removal filter is a vertical plate and frame filter press or a belt filter.

[0007] Furthermore, a first valve is provided at the first discharge port, a second valve is provided at the second discharge port, and a third valve is provided at the discharge port of the activation tank.

[0008] The present invention also includes the following technical solutions:

[0009] A method for removing salt from a carbon-alkali salt removal system in the above-mentioned Bayer process for producing alumina comprises the following steps:

[0010] S1, sending the lime milk in the lime milk tank into the lime milk filter for filtration and separation to obtain lime milk filtrate and lime milk filter cake;

[0011] S2, feeding the lime milk filter cake obtained in S1 into the beating tank, opening the first valve to feed the salt removal slurry in the salt removal slurry tank into the beating tank, wherein the molar ratio of the effective calcium CaO in the lime milk filter cake to the Al2O3 in the salt removal slurry is 1:2-3, and the lime milk filter cake and the salt removal slurry are evenly mixed to obtain a mixed slurry;

[0012] S3, sending the mixed slurry obtained in S2 into the activation tank, reacting for 2-3 hours to obtain activated slurry;

[0013] S4, closing the second valve, opening the third valve, and sending the activated slurry in the activation tank into the salt removal filter for a first filtration; then closing the third valve, opening the second valve, and sending the salt removal slurry in the salt removal slurry tank into the salt removal filter for a second filtration to obtain a mixed filter cake;

[0014] The filtrates in S5 and S4 enter the salt removal filtrate tank and are then sent to the evaporation process; the mixed filter cake in S4 is sent to the salt removal filter cake tank and is then sent to the sintering batching process.

[0015] Furthermore, in S1, the solid content of the lime milk is 200-300 g / L, and the content of effective calcium CaO accounts for 60-90%.

[0016] Furthermore, in S2 and S4, the salt removal slurry contains Na2O k , Na2O k The concentration is 280-320 g / L, and the temperature of the salt removal slurry is 90-100°C.

[0017] Furthermore, in S4, after the first filtration, the thickness of the filter cake is 2-3 mm.

[0018] The reaction mechanism involved in the present invention is as follows:

[0019] 3Ca(OH)2+2NaAlO2+4H2O=3CaO·Al2O3·6H2O+2NaOH

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention provides a carbon-alkali desalination system and method for the Bayer process of producing alumina. By introducing a lime milk filtration aid system into the existing desalination filtration system, the efficiency and effectiveness of the desalination process are significantly improved. Calcium hydroxide, the active ingredient in the lime milk, reacts with sodium metaaluminate in the desalination slurry to form porous, loose tricalcium aluminate hydrate particles. A first filtration process allows the tricalcium aluminate hydrate particles to be adsorbed on a filter cloth, followed by a second filtration process to remove carbonates from the desalination slurry. This design effectively improves the looseness of the filter cake, significantly reducing filtration resistance and making it easier to remove the filter cake during cake unloading, thereby significantly improving the filtration effect and efficiency of the filter. To address the problem of low active ingredient content in the lime milk phase and the resulting dilution of the desalination slurry when directly added, the present invention first filters and separates the lime milk, reducing the dilution effect of the lime milk on the desalination slurry. By optimizing the system flow and operating procedures, the present invention not only solves the filtration difficulties and low efficiency issues of traditional desalination processes but also provides strong support for the stable operation and efficient output of Bayer process alumina production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The embodiments of the present invention are further described below with reference to the accompanying drawings, in which:

[0023] Figure 1 The process flow diagram of the carbon alkali desalination system in the Bayer process for producing alumina is shown. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0025] Reference Attachment Figure 1A carbon alkali salt removal system for a Bayer process of producing alumina includes a lime milk tank, a lime milk filter, a lime milk filtrate tank, a beating tank, an activation tank, a salt removal slurry tank, a salt removal filter, a salt removal filtrate tank and a salt removal filter cake tank; the feed port of the lime milk filter is connected to the discharge port of the lime milk tank, the liquid outlet of the lime milk filter is connected to the liquid inlet of the lime milk filtrate tank, the discharge port of the lime milk filter is connected to the feed port of the beating tank, the discharge port of the beating tank is connected to the feed port of the activation tank, and the discharge port of the activation tank is connected to the feed port of the salt removal filter; the salt removal slurry tank includes a first discharge port and a second discharge port, the first discharge port is connected to the feed port of the beating tank, and the second discharge port is connected to the feed port of the salt removal filter; the liquid outlet of the salt removal filter is connected to the liquid inlet of the salt removal filtrate tank, and the discharge port of the salt removal filter is connected to the feed port of the salt removal filter cake tank.

[0026] In one embodiment of the present invention, the lime milk filter is a vertical plate and frame filter press or a belt filter, and the salt removal filter is a vertical plate and frame filter press or a belt filter.

[0027] In one embodiment of the present invention, a first valve is provided at the first discharge port, a second valve is provided at the second discharge port, and a third valve is provided at the discharge port of the activation tank.

[0028] Example 1

[0029] A carbon alkali salt removal method for producing alumina in a Bayer process comprises the following steps:

[0030] S1, sending the lime milk with a solid content of 200g / L and an effective calcium CaO content of 90% in the lime milk tank into a lime milk filter for filtration and separation to obtain a lime milk filtrate and a lime milk filter cake;

[0031] S2, send the lime milk filter cake obtained in S1 into the beating tank, open the first valve and send the salt removal slurry with a temperature of 90°C in the salt removal slurry tank into the beating tank, and the Na2O in the salt removal slurry k The concentration is 280g / L, the molar ratio of effective calcium CaO in the lime milk filter cake to Al2O3 in the salt removal slurry is 1:2, and the lime milk filter cake and the salt removal slurry are evenly mixed to obtain a mixed slurry;

[0032] S3, sending the mixed slurry obtained in S2 into an activation tank and reacting for 2 hours to obtain an activated slurry;

[0033] S4. Close the second valve, open the third valve, and send the activated slurry in the activation tank into the salt removal filter for the first filtration, forming a 2mm filter cake on the filter cloth; then close the third valve, open the second valve, and send the salt removal slurry at a temperature of 90°C in the salt removal slurry tank into the salt removal filter for the second filtration to obtain a mixed filter cake;

[0034] The filtrates in S5 and S4 enter the salt removal filtrate tank and are then sent to the evaporation process; the mixed filter cake in S4 is sent to the salt removal filter cake tank and is then sent to the sintering batching process.

[0035] In this embodiment, the slurry flow rate of the salt filter is 15m 3 / h, and the thickness of the obtained mixed filter cake was 15mm.

[0036] Example 2

[0037] A carbon alkali salt removal method for producing alumina in a Bayer process comprises the following steps:

[0038] S1, the lime milk with a solid content of 300g / L and an effective calcium CaO content of 60% in the lime milk tank is heated to 10m 3 / h flow rate is sent to the lime milk filter for filtration and separation to obtain lime milk filtrate and lime milk filter cake;

[0039] S2, send the lime milk filter cake obtained in S1 into the beating tank, open the first valve and let the salt slurry with a temperature of 100℃ in the salt slurry tank flow at a speed of 12m 3 / h flow rate is sent to the beating tank, and the Na2O in the salt slurry is discharged. k The concentration is 320g / L, the molar ratio of effective calcium CaO in the lime milk filter cake to Al2O3 in the salt removal slurry is 1:3, the lime milk filter cake and the salt removal slurry are evenly mixed to obtain a mixed slurry;

[0040] S3, sending the mixed slurry obtained in S2 into an activation tank and reacting for 3 hours to obtain an activated slurry;

[0041] S4, close the second valve, open the third valve, and send the activated slurry in the activation tank to the salt removal filter for the first filtration. The volume of the activated slurry filtered for the first time is 2m 3 , a 3mm filter cake is formed on the filter cloth; then the third valve is closed, the second valve is opened, and the salt slurry with a temperature of 100°C in the salt slurry tank is sent to the salt filter for the second filtration. The volume of the salt slurry filtered for the second time is 15m 3 , obtaining a mixed filter cake;

[0042] The filtrates in S5 and S4 enter the salt removal filtrate tank and are then sent to the evaporation process; the mixed filter cake in S4 is sent to the salt removal filter cake tank and is then sent to the sintering batching process.

[0043] In this embodiment, 15m 3 The time required for salt removal slurry is 600s.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that lime milk is not added, and other parameters remain unchanged. The salt slurry in the salt removal slurry tank is sent to the salt removal filter for filtration, the filtrate enters the salt removal filtrate tank, and then enters the evaporation process. The filter cake is sent to the salt removal filter cake tank and then sent to the sintering process.

[0046] The slurry flow rate of the salt removal filter in this comparative example is 8m 3 / h, and the thickness of the obtained mixed filter cake was 7 mm.

[0047] Comparative Example 2

[0048] The difference between this comparative example and Example 2 is that no lime milk is added, and other parameters remain unchanged. The salt slurry in the salt removal slurry tank is sent to the salt removal filter for filtration, the filtrate enters the salt removal filtrate tank, and then is sent to the evaporation process. The filter cake is sent to the salt removal filter cake tank and then sent to the sintering method batching process.

[0049] In this comparative example, 15m 3 The time required for salt removal slurry is 2000s.

[0050] The present invention provides a carbon-alkali desalination system and method for the Bayer process of producing alumina. By introducing a lime milk filtration aid system into the existing desalination filtration system, the efficiency and effectiveness of the desalination process are significantly improved. Calcium hydroxide, the active ingredient in the lime milk, reacts with sodium metaaluminate in the desalination slurry to form porous, loose tricalcium aluminate hydrate particles. A first filtration process allows the tricalcium aluminate hydrate particles to be adsorbed on a filter cloth, followed by a second filtration process to remove carbonates from the desalination slurry. This design effectively improves the looseness of the filter cake, significantly reducing filtration resistance and making it easier to remove the filter cake during cake unloading, thereby significantly improving the filtration effect and efficiency of the filter. To address the problem of low active ingredient content in the lime milk phase and the resulting dilution of the desalination slurry when directly added, the present invention first filters and separates the lime milk, reducing the dilution effect of the lime milk on the desalination slurry. By optimizing the system flow and operating procedures, the present invention not only solves the filtration difficulties and low efficiency issues of traditional desalination processes but also provides strong support for the stable operation and efficient output of Bayer process alumina production.

[0051] Some exemplary embodiments of the present invention are described above. It will be understood that the above embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. The features in these embodiments can be recombined in an appropriate manner, and the solutions obtained thereby are still within the scope of protection claimed by the present invention. Based on the above embodiments, all other embodiments obtained by those skilled in the art without making creative work, that is, all modifications, equivalent substitutions and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A carbon alkali salt removal system for the Bayer process of producing alumina, characterized in that: It includes a lime milk tank, a lime milk filter, a lime milk filtrate tank, a beating tank, an activation tank, a salt removal slurry tank, a salt removal filter, a salt removal filtrate tank and a salt removal filter cake tank; the feed port of the lime milk filter is connected to the discharge port of the lime milk tank, the liquid outlet of the lime milk filter is connected to the liquid inlet of the lime milk filtrate tank, the discharge port of the lime milk filter is connected to the feed port of the beating tank, the discharge port of the beating tank is connected to the feed port of the activation tank, and the discharge port of the activation tank is connected to the feed port of the salt removal filter; the salt removal slurry tank includes a first discharge port and a second discharge port, the first discharge port is connected to the feed port of the beating tank, and the second discharge port is connected to the feed port of the salt removal filter; the liquid outlet of the salt removal filter is connected to the liquid inlet of the salt removal filtrate tank, and the discharge port of the salt removal filter is connected to the feed port of the salt removal filter cake tank.

2. The carbon alkali salt removal system for the Bayer process of producing alumina according to claim 1, characterized in that: The lime milk filter is a vertical plate and frame filter press or a belt filter, and the salt removal filter is a vertical plate and frame filter press or a belt filter.

3. The carbon alkali salt removal system for the Bayer process of producing alumina according to claim 1 or 2, characterized in that: A first valve is provided at the first discharge port, a second valve is provided at the second discharge port, and a third valve is provided at the discharge port of the activation tank.

4. A method for removing salt from a carbon alkali salt removal system in a Bayer process for producing alumina according to claim 3, characterized in that: The following steps are involved: S1, sending the lime milk in the lime milk tank into the lime milk filter for filtration and separation to obtain lime milk filtrate and lime milk filter cake; S2, feeding the lime milk filter cake obtained in S1 into the beating tank, opening the first valve to feed the salt removal slurry in the salt removal slurry tank into the beating tank, wherein the molar ratio of the effective calcium CaO in the lime milk filter cake to the Al2O3 in the salt removal slurry is 1:2-3, and the lime milk filter cake and the salt removal slurry are evenly mixed to obtain a mixed slurry; S3, sending the mixed slurry obtained in S2 into the activation tank, reacting for 2-3 hours to obtain activated slurry; S4, closing the second valve, opening the third valve, and sending the activated slurry in the activation tank into the salt removal filter for a first filtration; then closing the third valve, opening the second valve, and sending the salt removal slurry in the salt removal slurry tank into the salt removal filter for a second filtration to obtain a mixed filter cake; The filtrates in S5 and S4 enter the salt removal filtrate tank and are then sent to the evaporation process; the mixed filter cake in S4 is sent to the salt removal filter cake tank and is then sent to the sintering batching process.

5. The carbon alkali salt removal method for producing alumina by the Bayer process according to claim 4, characterized in that: In S1, the solid content of the lime milk is 200-300 g / L, and the content of effective calcium CaO accounts for 60-90%.

6. The carbon alkali salt removal method for producing alumina by the Bayer process according to claim 4, characterized in that: In S2 and S4, the salt removal slurry contains Na2O k , Na2O k The concentration is 280-320 g / L, and the temperature of the salt removal slurry is 90-100°C.

7. The carbon alkali salt removal method for producing alumina by the Bayer process according to claim 4, characterized in that: In S4, after the first filtration, the thickness of the filter cake is 2-3 mm.

Images