A solution separation method based on the selective permeation mechanism of molecular sieve membranes

Abstract

The application relates to the technical field of alumina production, in particular to a solution separation method based on a molecular sieve membrane selective passing mechanism, which comprises the following steps: a Bayer method decomposition mother liquor is taken as a to-be-treated dialysate and is input into a dialysis chamber of a multistage molecular sieve membrane diffusion dialysis separator; the dialysate and diffusion liquid flow reversely on both sides of the molecular sieve membrane; Na + and OH ‑ are selectively passed from the dialysis chamber to the diffusion chamber by using the selective passing mechanism of the special regular pore channel structure of the molecular sieve membrane; Al 3+ and hydrated ions thereof are effectively intercepted by using the size screening effect of the molecular sieve membrane; the parameters of the feeding mother liquor are detected in real time, and the diffusion liquid flow and / or temperature are dynamically adjusted; after separation, the decomposition mother liquor with high Rp is returned to a decomposition procedure to continue decomposition, and the diffusion liquid with increased Na2O K concentration is sent to an evaporation procedure. The application replaces the traditional concentration difference driving mode by the molecular size selective passing mechanism of the molecular sieve membrane, and breaks through the limitation of single-stage static operation.

Description

Technical Field

[0001] This invention relates to the field of alumina production technology, specifically to a solution separation method based on the selective passage mechanism of molecular sieve membranes. Background Technology

[0002] The Bayer process is currently the mainstream technology for alumina production worldwide. Its core principle is to dissolve alumina from bauxite using sodium hydroxide solution, forming a sodium aluminate solution, which is then precipitated through seed crystal decomposition. In the Bayer process, alumina seed decomposition is the most time-consuming step, requiring the addition of many seed crystals, and even then, the decomposition rate is only around 55%. The decomposition process should aim to obtain a mother liquor with a relatively high molecular weight as the circulating alkali solution for dissolving bauxite, thus forming a closed-loop cycle in the Bayer process. Obtaining a mother liquor with a high molecular weight improves the decomposition rate and circulation efficiency, thereby reducing material flow and energy consumption in alumina production. Therefore, improving the decomposition rate and circulation efficiency while ensuring alumina product quality has always been a hot topic and a challenge in the alumina industry.

[0003] In the prior art, invention patent application number CN107585781A proposes a method for treating Bayer process decomposition mother liquor or evaporation mother liquor using cation exchange membrane diffusion dialysis. This method involves passing sodium aluminate solution and diffusion liquid into a cation exchange membrane diffusion dialysis separator for treatment, utilizing the Na+ on both sides of the membrane... + Sodium hydroxide diffuses from the dialysis chamber into the diffusion chamber due to the concentration difference, thereby reducing the caustic ratio of the sodium aluminate solution and returning the low caustic ratio solution to the decomposition process for further decomposition. However, this method, based on concentration difference-driven diffusion, has the following shortcomings: (1) The driving force of the concentration difference gradually weakens as the separation process proceeds, and the separation efficiency shows a downward trend; (2) The operating parameters are fixed values ​​and cannot be dynamically adjusted according to changes in the properties of the feed mother liquor, making it difficult to adapt to fluctuations in the composition of the mother liquor during the Bayer process; (3) Single-stage membrane separation is used, which limits the separation efficiency and flexibility, making it difficult to meet the dual requirements of high selectivity and high throughput; (4) The selectivity of the cation exchange membrane for ions is mainly based on charge repulsion rather than molecular size selectivity, which is not suitable for Al 3+ The retention efficiency is limited. Patent application CN105836771B proposes a method to improve the seed decomposition rate and recycling efficiency in alumina production. This method uses dilute alkali solution from red mud dealkalization as the diffusion liquid, achieving alkali recovery and process efficiency improvement simultaneously through single-stage diffusion dialysis. The application scenario is tied to the red mud dealkalization process, and the process is a single-stage static operation. Its limitations lie in the limited source of the diffusion liquid, weak application scope, and insufficient separation depth due to the lack of a staged separation design. Therefore, we propose a solution separation method based on the selective passage mechanism of molecular sieve membranes to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a solution separation method based on the selective passage mechanism of molecular sieve membranes, in order to solve the limitations of the prior art mentioned in the background, such as limited source of diffusion liquid, weak universality of application scenarios, and insufficient separation depth due to lack of hierarchical separation design.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a solution separation method based on the selective passage mechanism of a molecular sieve membrane, comprising the following steps:

[0006] S1: Take the decomposition mother liquor produced by the Bayer process decomposition and classification process as the sodium aluminate dialysis liquid to be treated, and take the low-concentration alkaline solution in the Bayer process as the diffusion liquid to be treated.

[0007] S2: Pass a portion of the dialysis liquid to be treated in step S1 into the dialysis chamber of the multi-stage molecular sieve membrane diffusion dialysis separator. The product of the first-stage membrane separation enters the dialysis chamber of the second-stage membrane separation for further processing. Each stage of membrane separation has an independent diffusion liquid supply system and operating parameters. An intermediate regulating tank is set between adjacent stages to regulate the temperature and flow rate of the intermediate product and ensure that the parameters of the feed liquid entering the next stage of membrane separation are stable.

[0008] S3: Simultaneously introduce the diffusion solution to be treated from step S1 into the diffusion chamber in step S2. The mother liquor and the diffusion solution react with each other on both sides of the molecular sieve membrane based on the regular pore structure of the molecular sieve membrane to react with Na. + The selective separation of Na+ and OH- occurs via reverse dialysis. The separation mechanism of molecular sieve membranes involves two aspects: firstly, based on the molecular size sieving effect—the regular channels of the molecular sieve membrane selectively allow permeation of hydrated ions of different sizes, such as Na+. + Hydrated ions (approximately 0.72 nm) and OH- - Hydrated ions (approximately 0.60 nm) can pass through the pores of a molecular sieve membrane with a suitable pore size, while Al 3+ Hydrated ions (approximately 0.95 nm) are trapped because their size is larger than the pores; secondly, based on cation exchange properties—the molecular sieve framework carries a negative charge and has the ability to exchange and conduct cations, which can promote the retention of Na+. + The targeted migration of Na. The two mechanisms work synergistically to achieve the targeted migration of Na. + and OH - High selectivity of Al 3+ Effective retention. During membrane separation, parameters such as the caustic alkali concentration, caustic ratio, and temperature of the feed mother liquor are monitored in real time, and the flow rate and temperature of the diffusion liquid are dynamically adjusted according to the detected values ​​and a preset control model;

[0009] S4: After dialysis separation, a high Rp decomposition mother liquor and increased Na2O are obtained. KThe sodium aluminate solution after concentration, and the final Na2O in the dialysis and diffusion solutions. K The concentration difference is 5–15 g / L. The high-Rp decomposition mother liquor is returned to the Bayer process for further decomposition, increasing the Na₂O content. K The sodium aluminate solution after concentration is sent to the evaporation process for concentration and then used for dissolution.

[0010] Preferably, the amount of the dialysis liquid to be treated in step S1 is 1% to 30% of the total amount of Bayer process decomposition mother liquor.

[0011] Preferably, the diffusion solution to be treated in step S1 is a low-concentration alkaline solution from the Bayer process, Na2O. K Concentration <100 g / L, including but not limited to aluminum hydroxide washing solution, red mud washing solution or fresh water in the Bayer process.

[0012] Preferably, the molecular sieve membrane in step S2 is at least one of NaA-type, NaX-type, MFI-type, or MOR-type molecular sieve membranes. The NaA-type molecular sieve membrane has a pore size of approximately 0.42 nm and exhibits high size selectivity for hydrated ions; the NaX-type molecular sieve membrane has a pore size of approximately 0.74 nm, similar to Na... + The hydrated ions have similar diameters (approximately 0.72 nm), which allows for optimal molecular sieving.

[0013] Preferably, the molecular sieve membrane diffusion dialysis separator described in step S2 includes a plate-and-frame type, a spiral wound type, or a hollow fiber type molecular sieve membrane assembly.

[0014] Preferably, the membrane module described in step S2 includes a certain number of repeating unit structures, that is, the dialysis liquid chamber and the diffusion liquid chamber separated by the ion exchange membrane constitute a repeating unit structure, and the diffusion liquid and the dialysis liquid flow in a countercurrent manner.

[0015] Preferably, the dynamic parameter adjustment described in step S3 is achieved through an automatic control system, including an online detection unit, a control unit, and an execution unit. The online detection unit collects the parameters of the feed mother liquor in real time, the control unit calculates the optimal diffusion liquid flow rate and temperature according to a preset control model, and the execution unit (such as a variable frequency pump or a heat exchanger regulating valve) executes the adjustment command.

[0016] Preferably, the dialysis separation described in step S3 refers to Na + and OH - Migrating from the dialysis chamber to the diffusion chamber, Al 3+ The pass rate is less than 3%.

[0017] Preferably, after the alumina decomposition rate and circulation efficiency are improved by about 1% to 5% in step S3 using this method, the process power consumption and steam consumption can be reduced by 1% to 5%.

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

[0019] This invention (1) uses a molecular sieve membrane to replace the traditional cation exchange membrane, utilizing the size sieving effect and cation exchange characteristics of the regular pore structure of the molecular sieve to achieve Na+ exchange. + and OH - Highly selective passage, while also affecting Al 3+ Al and its hydrated ions have excellent retention effects. 3+ The pass rate can be reduced to below 3%; (2) The separation driving force of the molecular sieve membrane comes from its inherent molecular size selectivity and does not depend on the concentration difference on both sides of the membrane, thus avoiding the problem of the driving force gradually decaying under the concentration difference driving mode, and the separation efficiency is more stable; (3) It is not limited by the ore grade, not limited to a specific diffusion liquid, and can be adapted to a variety of low-alkali solutions, making it more flexible in application; (4) The multi-stage series separation scheme of the diffusion dialysis device is adopted to more accurately control the concentration of the decomposition mother liquor material; (5) A new dynamic parameter adjustment system is added to adapt to the fluctuation of production conditions. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a solution separation method based on the selective passage mechanism of a molecular sieve membrane, provided by the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention. The proportional relationships involved in the text, such as mass ratio, molar ratio, etc., should be understood as the correspondence between the first and second terms of a proportional formula according to the order of description. The raw materials, reagents, instruments and equipment used in this article can all be obtained by purchasing from the market or by existing methods.

[0023] Please see Figure 1 The present invention provides an embodiment of a solution separation method based on the selective passage mechanism of molecular sieve membranes, comprising the following steps:

[0024] S1: Take the decomposition mother liquor produced by the Bayer process decomposition and classification process as the sodium aluminate dialysis liquid to be treated, and take the low-concentration alkaline solution in the Bayer process as the diffusion liquid to be treated.

[0025] S2: Pass a portion of the dialysis liquid to be treated in step S1 into the dialysis chamber of the multi-stage molecular sieve membrane diffusion dialysis separator. The product of the first-stage membrane separation enters the dialysis chamber of the second-stage membrane separation for further processing. Each stage of membrane separation has an independent diffusion liquid supply system and operating parameters. An intermediate regulating tank is set between adjacent stages to regulate the temperature and flow rate of the intermediate product and ensure that the parameters of the feed liquid entering the next stage of membrane separation are stable.

[0026] S3: Simultaneously introduce the diffusion solution to be treated from step S1 into the diffusion chamber in step S2. The mother liquor and the diffusion solution react with each other on both sides of the molecular sieve membrane based on the regular pore structure of the molecular sieve membrane to react with Na. + and OH - The selective separation is achieved through a mechanism of reverse dialysis. The separation mechanism of molecular sieve membranes includes two aspects: firstly, based on the molecular size sieving effect—the regular channels of the molecular sieve membrane have selective permeability to hydrated ions of different sizes, such as Na+. + Hydrated ions (approximately 0.72 nm) and OH- - Hydrated ions (approximately 0.60 nm) can pass through the pores of a molecular sieve membrane with a suitable pore size, while Al 3+ Hydrated ions (approximately 0.95 nm) are trapped because their size is larger than the pores; secondly, based on cation exchange properties—the molecular sieve framework carries a negative charge and has the ability to exchange and conduct cations, which can promote the retention of Na+. + The targeted migration of Na. The two mechanisms work synergistically to achieve the targeted migration of Na. + and OH - High selectivity of Al 3+ Effective retention. During membrane separation, parameters such as the caustic alkali concentration, caustic ratio, and temperature of the feed mother liquor are monitored in real time, and the flow rate and temperature of the diffusion liquid are dynamically adjusted according to the detected values ​​and a preset control model;

[0027] S4: After dialysis separation, a high Rp decomposition mother liquor and increased Na2O are obtained. K The sodium aluminate solution after concentration, and the final Na2O in the dialysis and diffusion solutions. K The concentration difference is 5–15 g / L. The high-Rp decomposition mother liquor is returned to the Bayer process for further decomposition, increasing the Na₂O content. K The sodium aluminate solution after concentration is sent to the evaporation process for concentration and then used for dissolution.

[0028] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0029] Example 1

[0030] The mother liquor from the decomposition process of a Bayer process alumina plant was used as the dialysis liquid, and the aluminum hydroxide washing liquid after filtration of the finished product was used as the diffusion liquid. The chemical composition is shown in Tables 1 and 2.

[0031] Table 1. Chemical composition and flow rate of mother liquor after decomposition in a Bayer process alumina plant.

[0032] Element <![CDATA[Al2O3(g / L)]]> <![CDATA[Na2O k (g / L)]]> <![CDATA[Na2O C (g / L)]]> Solution density (g / L) Mass (t / h) <![CDATA[Volume (m 3 / h)]]> content 89.45 154.22 18.52 1266.23 3896.03 3076

[0033] Table 2 Chemical composition and flow rate of aluminum hydroxide washing solution in a Bayer process alumina plant

[0034] Element <![CDATA[Al2O3(g / L)]]> <![CDATA[Na2O k (g / L)]]> <![CDATA[Na2O C (g / L)]]> Solution density (g / L) Mass (t / h) <![CDATA[Volume (m 3 / h)]]> content 34.96 60.27 7.24 1117.86 231.70 207

[0035] Considering the compatibility of the production equipment, approximately 6% of the decomposition mother liquor (233.76 t / h) was used as the dialysis liquid, and the aforementioned 231.7 t / h of aluminum hydroxide washing liquid was used as the diffusion liquid. A NaX-type molecular sieve membrane module (pore size approximately 0.74 nm, similar to Na...) was employed. + (Using hydrated ions with a diameter of approximately 0.72 nm) diffusion dialysis was performed to decompose the Na₂O in the mother liquor. k The concentration of Na2O in the aluminum hydroxide washing solution decreased from 154 g / L to 70 g / L. k The concentration was increased from 60 g / L to 145 g / L. The RP of this decomposition mother liquor increased from 0.58 to 1.07. Returning this decomposition mother liquor to the decomposition and classification process for further decomposition increases the decomposition rate from 50.63% to 52.07%. For a 1 million-ton alumina plant, this method is expected to reduce process power consumption by 2%, steam consumption by 2%, steam consumption by 0.038 t / t-AO, and power consumption by 4 kWh / t-AO, resulting in a cost saving of 7.7 yuan / t-AO and an annual cost saving of 7.7 million yuan.

[0036] Specific steps:

[0037] S1: Take the decomposition mother liquor produced by the Bayer process decomposition and classification process as the sodium aluminate dialysis liquid to be treated, and take the low-concentration alkaline solution in the Bayer process as the diffusion liquid to be treated.

[0038] S2: Pass a portion of the dialysis liquid to be treated in step S1 into the dialysis chamber of the multi-stage molecular sieve membrane diffusion dialysis separator. The product of the first-stage membrane separation enters the dialysis chamber of the second-stage membrane separation for further processing. Each stage of membrane separation has an independent diffusion liquid supply system and operating parameters. An intermediate regulating tank is set between adjacent stages to regulate the temperature and flow rate of the intermediate product and ensure that the parameters of the feed liquid entering the next stage of membrane separation are stable.

[0039] S3: Simultaneously introduce the diffusion solution to be treated from step S1 into the diffusion chamber in step S2. The mother liquor and the diffusion solution react with each other on both sides of the molecular sieve membrane based on the regular pore structure of the molecular sieve membrane to react with Na. + and OH - The selective separation is achieved through a mechanism of reverse dialysis. The separation mechanism of molecular sieve membranes includes two aspects: firstly, based on the molecular size sieving effect—the regular channels of the molecular sieve membrane have selective permeability to hydrated ions of different sizes, such as Na+. + Hydrated ions (approximately 0.72 nm) and OH- - Hydrated ions (approximately 0.60 nm) can pass through the pores of a molecular sieve membrane with a suitable pore size, while Al 3+ Hydrated ions (approximately 0.95 nm) are trapped because their size is larger than the pores; secondly, based on cation exchange properties—the molecular sieve framework carries a negative charge and has the ability to exchange and conduct cations, which can promote the retention of Na+. + The targeted migration of Na. The two mechanisms work synergistically to achieve the targeted migration of Na. + and OH - High selectivity of passage and Al 3+ Effective retention. During membrane separation, parameters such as the caustic alkali concentration, caustic ratio, and temperature of the feed mother liquor are monitored in real time, and the flow rate and temperature of the diffusion liquid are dynamically adjusted according to the detected values ​​and a preset control model;

[0040] S4: After dialysis separation, a high Rp decomposition mother liquor and increased Na2O are obtained. k The sodium aluminate solution after concentration, and the final Na2O in the dialysis and diffusion solutions. k The concentration difference is 5–15 g / L. The high-Rp decomposition mother liquor is returned to the Bayer process for further decomposition, increasing the Na₂O content. k The sodium aluminate solution after concentration is sent to the evaporation process for concentration and then used for dissolution. The above is all the specific methods of the present invention.

[0041] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A solution separation method based on the selective passage mechanism of molecular sieve membranes, characterized in that: Includes the following steps: S1: Use the decomposition mother liquor produced by the Bayer process decomposition and classification process as the dialysis liquid to be treated, and use the low-concentration alkaline solution in the Bayer process as the diffusion liquid to be treated. S2: The dialysis solution to be treated described in S1 is fed into the dialysis chamber of a multi-stage molecular sieve membrane diffusion dialysis separator. The multi-stage molecular sieve membrane diffusion dialysis separator includes at least a first-stage membrane separation and a second-stage membrane separation. The product of the first-stage membrane separation enters the dialysis chamber of the second-stage membrane separation for further processing. Each stage of membrane separation has an independent diffusion solution supply system and operating parameters. S3: Simultaneously introduce the diffusion solution to be treated from S1 into the diffusion chamber corresponding to the dialysis chamber in S2. The dialysis solution to be treated and the diffusion solution to be treated flow counterclockwise on both sides of the molecular sieve membrane, utilizing the regular pore structure of the molecular sieve membrane to treat Na. + and OH - The selectivity of Na is achieved through a mechanism. + and OH - Selective migration from the dialysis chamber to the diffusion chamber, while simultaneously utilizing the size sieving effect of the molecular sieve membrane to retain Al. 3+ During membrane separation, the parameters of the feed mother liquor are monitored in real time, and the flow rate and / or temperature of the diffusion liquid to be treated are dynamically adjusted according to the detected values ​​and a preset control model. S4: After membrane separation, a high-Rp decomposition mother liquor and increased Na2O are obtained. K The sodium aluminate solution with reduced concentration is returned to the Bayer process for further decomposition, along with the addition of Na₂O. K The sodium aluminate solution after concentration is sent to the evaporation process for concentration and then used for dissolution.

2. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The molecular sieve membrane is at least one of NaA type, NaX type, MFI type or MOR type molecular sieve membrane.

3. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: In the multi-stage cation membrane diffusion dialysis separator, an intermediate regulating tank is provided between adjacent stages to regulate the temperature and / or flow rate of the intermediate product.

4. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The ion-driven velocity in the diffusion dialysis separator depends on one, two, or three of the following: concentration difference, potential difference, and pressure difference.

5. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The molecular sieve membrane diffusion dialysis separator includes plate and frame type, spiral wound type or hollow fiber type molecular sieve membrane assembly.

6. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The dynamic adjustment is achieved through an automatic control system, which includes an online detection unit, a control unit, and an execution unit. The online detection unit collects parameters of the feed mother liquor in real time, the control unit calculates the target flow rate and target temperature of the diffusion liquid according to a preset control model, and the execution unit executes the adjustment command.

7. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The parameters of the feed mother liquor include at least one of the following: caustic alkali concentration, caustic ratio, and temperature.

8. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: After membrane separation, the final Na2O in the dialysis solution and the diffusion solution is... K The concentration difference is 5–15 g / L.

9. A solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The membrane module internally comprises a repeating unit structure consisting of a dialysis chamber and a diffusion chamber separated by an ion exchange membrane.

10. A solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: During the membrane separation process, Na + and OH - Migrating from the dialysis chamber to the diffusion chamber, Al 3+ The pass rate is less than 3%.

11. A solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The amount of the dialysis solution to be treated is 1% to 30% of the total amount of mother liquor from the Bayer process.

12. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The diffusion solution to be treated is a low-concentration alkaline solution from the Bayer process, containing Na2O. K Concentration <100 g / L, including but not limited to aluminum hydroxide washing solution, red mud washing solution or fresh water in the Bayer process.

13. The solution separation method based on the selective passage mechanism of a molecular sieve membrane according to claim 1, characterized in that: The method improves the alumina decomposition rate and circulation efficiency by 1% to 5%, and reduces process power consumption and steam consumption by 1% to 5%.

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