A bimodal distribution flocculant and a preparation method thereof

Abstract

The application provides a bimodal distribution flocculant and a preparation method, and belongs to the field of flocculants. The bimodal distribution flocculant is composed of a macromolecular flocculant and a small molecule reinforcing agent; wherein the macromolecular flocculant and the small molecule reinforcing agent are both hydroxamic acid flocculants; the molecular weight of the macromolecular flocculant is greater than or equal to 5 million, and the molecular weight of the small molecule reinforcing agent is less than or equal to 600 thousand. The bimodal distribution flocculant is formed by the macromolecular flocculant and the small molecule reinforcing agent. In the process of treating the red mud coarse liquid, the small molecule reinforcing agent is used to capture the extremely fine particles and promote the preliminary aggregation of the extremely fine particles to form small flocs. Then, the macromolecular flocculant further bridges the small flocs into large and stable flocs through the long chain structure and the bridging effect of the hydroxamic acid groups. The increase and stability of the flocs help to accelerate the sedimentation process, improve the sedimentation efficiency of the extremely fine particles and reduce the content of the floaters. Therefore, the sedimentation efficiency of the flocculant for the extremely fine particles in the red mud sedimentation process is improved.

Description

Technical Field

[0001] This application relates to the field of flocculant technology, and in particular to a bimodal distribution flocculant and its preparation method. Background Technology

[0002] In alumina production, the sedimentation separation of leached red mud from the crude liquid is the most crucial solid-liquid separation process, directly impacting production technical indicators and economic benefits. The key factors in the red mud separation process are the properties of the red mud slurry, namely its mineral composition, particle size distribution, and solution composition. Bayer process red mud generally has a very fine particle size; studies show that particles <0.4 mm account for over 90%, indicating that the leached red mud slurry is a fine particle suspension, sharing many properties with colloidal dispersions. In this suspension system, red mud particles are the dispersed phase, and sodium aluminate solution is the dispersion medium. Red mud particles possess extremely diffusive surfaces, exhibiting significant residual valence forces, van der Waals forces, and hydrogen bonding, leading to solvation.

[0003] In recent years, with the gradual depletion of domestic bauxite resources, aluminum companies have begun to use large quantities of bauxite from Guinea and other overseas sources to produce alumina. However, problems have arisen during the production process, including opaque red mud settling liquor, high suspended solids content, low clarity, and poor underflow compressibility, which have already affected the normal production of some companies. These problems arise because these overseas ores contain excessively high levels of goethite. Goethite in bauxite is mostly found in fine-cluster aggregates. During alumina production, due to grinding and leaching processes, it becomes extremely fine, irregular particles, with particle sizes ranging from 2 to 10 μm. These particles have high surface activity and severe solubilization. Therefore, these extremely fine red mud particles easily form a stable suspension in the slurry, and even if the goethite within them transforms into hematite, it is difficult to change their settling properties. Whether these extremely fine red mud particles can be captured and settled determines the suspended solids content and clarity of the settling liquor. Summary of the Invention

[0004] This application provides a bimodal distribution flocculant and its preparation method to solve the following technical problem: how to improve the settling efficiency of extremely fine particles in the red mud sedimentation process.

[0005] In a first aspect, this application provides a bimodal flocculant, which is composed of a macromolecular flocculant and a small-molecule reinforcing agent; wherein...

[0006] Both the macromolecular flocculant and the small molecule reinforcing agent are oxime acid flocculants;

[0007] The macromolecular flocculant has a molecular weight ≥ 5 million, and the small molecule reinforcing agent has a molecular weight ≤ 600,000.

[0008] Optionally, the mass ratio of the macromolecular flocculant to the small molecule reinforcing agent is (1-6):1.

[0009] Optionally, the mass ratio of the macromolecular flocculant to the small molecule reinforcing agent is (2-4):1.

[0010] Secondly, this application provides a method for preparing the bimodal distribution flocculant according to any embodiment of the first aspect, the method comprising:

[0011] A polyacrylamide with a set molecular weight, a solvent, and a hydroxylamine solution are mixed and the pH is adjusted to a first set pH. A first water bath reaction is carried out under the first set reaction conditions to obtain a macromolecular flocculant.

[0012] Acrylamide, solvent and initiator are mixed to carry out a polymerization reaction to obtain a mixture;

[0013] The mixture is mixed with a hydroxylamine solution, and the pH is adjusted to a second set pH to carry out a second water bath reaction under the second set reaction conditions to obtain a small molecule reinforcing agent.

[0014] By combining the macromolecular flocculant and the small molecule reinforcing agent, a bimodal distribution flocculant is obtained.

[0015] Optionally, the concentration of the polyacrylamide is 2% to 5%.

[0016] Optionally, the molar ratio of polyacrylamide to hydroxylamine is 1:(1.2 to 1.8).

[0017] Optionally, the first set reaction conditions include: a protective atmosphere of nitrogen, a reaction temperature of 50℃~80℃, a first set pH of 10~13, and a reaction time of 8h~20h.

[0018] Optionally, the concentration of acrylamide is 2% to 4%, and the concentration of the initiator is 0.3% to 0.6%, wherein the initiator includes one or more of ammonium persulfate and sodium bisulfite.

[0019] Optionally, the molar ratio of acrylamide to hydroxylamine is 1:(1.1 to 1.5).

[0020] Optionally, the second set reaction conditions include: a protective atmosphere of nitrogen, a reaction temperature of 50℃~80℃, a second set pH of 10~13, and a reaction time of 5h~10h.

[0021] The technical solutions provided in this application have the following advantages compared with the prior art:

[0022] This invention provides a bimodal flocculant composed of a macromolecular flocculant and a small-molecule reinforcing agent; wherein both the macromolecular flocculant and the small-molecule reinforcing agent are oxime acid flocculants; the molecular weight of the macromolecular flocculant is ≥5 million, and the molecular weight of the small-molecule reinforcing agent is ≤600,000. This invention forms a bimodal flocculant from macromolecular flocculants and small-molecule reinforcing agents. In the treatment of coarse red mud sedimentation liquid, the small-molecule reinforcing agent first captures extremely fine particles and promotes their initial aggregation, forming small flocs. Subsequently, the macromolecular flocculant, through its long-chain structure and the bridging effect of the oxime acid groups, further bridges these small flocs into large and stable flocs. The increase and stabilization of the flocs helps to accelerate the sedimentation process, improve the sedimentation efficiency of extremely fine particles, and reduce the suspended solids content. This improves the sedimentation efficiency of extremely fine particles during the red mud sedimentation process. Attached Figure Description

[0023] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0024] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic flowchart illustrating a method for preparing a bimodal flocculant according to an embodiment of this application. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0027] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0028] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. In this document, "and / or" describes the relationship between related objects, indicating that three relationships can exist; for example, A and / or B can represent: A alone, A and B simultaneously, or B alone. A and B can be singular or plural. In this document, "at least one" means one or more, and "more than" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c" or "at least one of a, b, and c" can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be a single or multiple.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0030] This application provides a bimodal flocculant, which is composed of a macromolecular flocculant and a small-molecule reinforcing agent; wherein...

[0031] Both the macromolecular flocculant and the small molecule reinforcing agent are oxime acid flocculants;

[0032] The macromolecular flocculant has a molecular weight ≥ 5 million, and the small molecule reinforcing agent has a molecular weight ≤ 600,000.

[0033] The macromolecular flocculant has a molecular weight ≥ 5 million, ensuring excellent bridging ability and a wide intermolecular contact surface, which helps to form larger floc structures in the suspension. The small molecule reinforcing agent has a molecular weight ≤ 600,000. Compared with the macromolecular flocculant, the small molecule reinforcing agent has a smaller molecular weight, so it can penetrate into the suspended particles more quickly, enhance the interaction force between particles, and make the flocs more compact and less prone to breakage. At the same time, both the macromolecular flocculant and the small molecule reinforcing agent are oxime acid flocculants. This consistency allows the two components to exert their respective advantages more efficiently when working synergistically, avoiding unnecessary chemical reactions or mutual interference. Therefore, this invention mixes the synthesized macromolecular flocculant and the small molecule reinforcing agent in a certain proportion to form a bimodal distribution flocculant. In the treatment of red mud sedimentation coarse liquid, the small molecule reinforcing agent is first used to capture extremely fine particles and promote their initial aggregation to form small flocs. Subsequently, the macromolecular flocculant, through its long chain structure and the bridging effect of the oxime acid groups, further bridges these small flocs into large and stable flocs. Finally, the increase and stabilization of the flocs help accelerate the sedimentation process, improve the sedimentation efficiency of ultrafine particles, and reduce the content of suspended solids. For example, the molecular weight of macromolecular flocculants can be 5 million, 7 million, 8 million, 9 million, 10 million, 11 million, 12 million, 13 million, 14 million, etc., while the molecular weight of small molecule enhancers can be 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, etc.

[0034] In some embodiments, the mass ratio of the macromolecular flocculant to the small molecule reinforcing agent is (1-6):1.

[0035] The mass ratio of macromolecular flocculant to small molecule enhancer is limited to (1-6):1, balancing the bridging effect of macromolecular flocculant and the particle-capturing ability of small molecule enhancer. Macromolecular flocculant can form larger floc structures, while small molecule enhancer can effectively capture and fix extremely fine particles, enhancing the overall flocculation effect. Furthermore, this invention allows for the selection of different proportions of macromolecular flocculant and small molecule enhancer to be compounded according to the needs of sodium aluminate solutions with different red mud compositions. Exemplary examples include mass ratios of 1:1, 2:1, 3:1, 4:1, 5:1, and 6:1.

[0036] In some embodiments, the mass ratio of the macromolecular flocculant to the small molecule reinforcing agent is (2-4):1.

[0037] Preferably, the mass ratio of macromolecular flocculant to small molecule enhancer is limited to (2-4):1, which can further enhance the overall flocculation effect.

[0038] Figure 1 This is a schematic flowchart illustrating a method for preparing a bimodal flocculant according to an embodiment of this application.

[0039] Based on a general inventive concept, please refer to... Figure 1 This application provides a method for preparing a bimodal distribution flocculant according to any embodiment of the first aspect, the method comprising:

[0040] S1. Mix polyacrylamide, solvent and hydroxylamine solution with a set molecular weight, and adjust the pH to the first set pH, so as to carry out the first water bath reaction under the first set reaction conditions to obtain macromolecular flocculant;

[0041] It should be noted that the molecular weight of polyacrylamide should be selected according to the molecular weight requirements of the target macromolecular flocculant. The reaction of polyacrylamide (PAM) with hydroxylamine (NH2OH) under alkaline conditions and water bath heating yields an oxoxamic acid (RCONHOH) group on the molecular chain through a nucleophilic substitution reaction. The specific reaction principle is as follows: In an alkaline environment, hydroxylamine is first converted into a hydroxylamine anion (NH2O-). This anion has strong nucleophilicity and can attack the carbonyl (C=O) carbon atom on the polyacrylamide molecular chain, forming an addition intermediate. Subsequently, this intermediate undergoes rearrangement and hydrolysis reactions, ultimately generating a polyacrylamide derivative containing an oxoxamic acid group, thus obtaining a macromolecular oxoxamic acid flocculant.

[0042] In some embodiments, the concentration of the polyacrylamide is 2% to 5%.

[0043] Limiting the mass concentration of polyacrylamide to 2% to 5% helps ensure that sufficient polyacrylamide molecules participate in the reaction in the solvent, while avoiding problems such as uneven reaction or difficulty in control that may occur due to excessively high concentrations. For example, the concentration of polyacrylamide can be 2%, 2.5%, 3%, 4%, 4.5%, 5%, etc.

[0044] In some embodiments, the molar ratio of polyacrylamide to hydroxylamine is 1:(1.2 to 1.8).

[0045] The molar ratio of polyacrylamide to hydroxylamine is limited to 1:(1.2–1.8) to balance reaction efficiency and byproduct formation. An excess of hydroxylamine over polyacrylamide ensures that more amide groups in the polyacrylamide are converted to oxime acid groups; however, excessive hydroxylamine may lead to unnecessary side reactions and excessive costs. For example, the molar ratio of polyacrylamide to hydroxylamine can be 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.75, 1:1.8, etc.

[0046] In some embodiments, the first set reaction conditions include: a protective atmosphere of nitrogen, a reaction temperature of 50°C to 80°C, a first set pH of 10 to 13, and a reaction time of 8 to 20 hours.

[0047] Using nitrogen as a protective atmosphere eliminates interference from oxygen in the reaction. A reaction temperature of 50°C–80°C promotes hydroxylation. Higher temperatures accelerate the reaction rate but may increase the risk of side reactions; lower temperatures may prolong the reaction time. A reaction pH of 10–13 provides the necessary alkaline conditions for hydroxylation. Within this pH range, the amide group reacts more readily with hydroxylamine to form an oxime acid group. A reaction time of 8–20 hours ensures the reaction proceeds fully and achieves a high conversion rate. For example, reaction temperatures can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, etc.; the initial pH can be 10, 10.5, 11, 11.5, 12, 12.5, 13, etc.; and reaction times can be 8 hours, 9 hours, 10 hours, 11 hours, 13 hours, 15 hours, 17 hours, 19 hours, 20 hours, etc.

[0048] This invention enables the preparation of macromolecular flocculants with expected molecular weight, high content of oxime acid groups, and good flocculation performance by precisely controlling the concentration of polyacrylamide, the molar ratio of polyacrylamide to hydroxylamine, and the conditions of the first water bath reaction (including protective atmosphere, reaction temperature, pH, and reaction time).

[0049] S2. Acrylamide, solvent and initiator are mixed to carry out polymerization reaction to obtain a mixture;

[0050] Small molecule reinforcing agents with oxime acid groups are generated on oligomers or prepolymers of polyacrylamide.

[0051] In some embodiments, the concentration of acrylamide is 2% to 4%, and the concentration of the initiator is 0.3% to 0.6%, wherein the initiator includes one or more of ammonium persulfate and sodium bisulfite.

[0052] Limiting the mass concentration of acrylamide to 2%–4% ensures the polymerization reaction proceeds while avoiding operational difficulties caused by excessive viscosity. Limiting the initiator mass concentration to 0.3%–0.6% is sufficient to initiate the polymerization of acrylamide without introducing excessive impurities. Ammonium persulfate and sodium bisulfite are commonly used free radical initiators; they can effectively generate free radicals, thereby initiating monomer polymerization. For example, the concentration of acrylamide can be 2%, 2.5%, 3%, 3.5%, 4%, etc., and the concentration of initiator can be 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, etc.

[0053] S3. Mix the mixture with the hydroxylamine solution and adjust the pH to the second set pH to carry out the second water bath reaction under the second set reaction conditions to obtain the small molecule reinforcing agent;

[0054] In some embodiments, the molar ratio of acrylamide to hydroxylamine is 1:(1.1 to 1.5).

[0055] By limiting the molar ratio of acrylamide to hydroxylamine to 1:(1.1 to 1.5), an excess of hydroxylamine is ensured, allowing more amide groups in the polyacrylamide oligomer to be converted into oxime acid groups. For example, the molar ratio of acrylamide to hydroxylamine can be 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc.

[0056] In some embodiments, the second set reaction conditions include: a protective atmosphere of nitrogen, a reaction temperature of 50°C to 80°C, a second set pH of 10 to 13, and a reaction time of 5 to 10 hours.

[0057] S4. The macromolecular flocculant and the small molecule reinforcing agent are compounded to obtain a bimodal distribution flocculant.

[0058] In some embodiments, the method further includes:

[0059] The bimodal flocculant is placed in a weakly alkaline aqueous solution until it is completely dissolved for sedimentation.

[0060] The product prepared by the preparation method of the bimodal distribution flocculant is the aforementioned bimodal distribution flocculant. The chemical composition and structure of the bimodal distribution flocculant prepared by the preparation method can be referred to the above embodiments. Since the preparation method of the bimodal distribution flocculant adopts some or all of the technical solutions of the bimodal distribution flocculant embodiments, it has at least all the beneficial effects brought about by the technical solutions of the bimodal distribution flocculant embodiments, which will not be elaborated here.

[0061] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0062] Example 1

[0063] Weigh out 5 million molecular weight polyacrylamide and slowly add it to a beaker containing a certain amount of distilled water while stirring. The concentration is 3.55%. After complete dissolution, transfer the viscous solution to a 250 mL three-necked flask and place the reaction flask in a constant temperature water bath at 50 °C. Weigh out a certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio and dissolve them in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. Add the hydroxylamine solution to the reaction flask. The molar ratio of polyacrylamide to hydroxylamine is 1:1.5. Adjust the pH to approximately 12.5. Stir magnetically and purge with 50 mL / min of high-purity N2 throughout the process. The reaction time is 12 h to synthesize a large molecular weight oxime acid flocculant.

[0064] Acrylamide was weighed and slowly added to a flask containing a certain amount of distilled water under stirring. The acrylamide concentration was 2.5%. Initiators: ammonium persulfate and sodium bisulfite, with an initiator concentration of 0.40%, were added, and the reaction time was 0.5 h. A certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio were dissolved in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. The hydroxylamine solution was added to the flask, with a molar ratio of acrylamide to hydroxylamine of 1:1.5, and the pH was adjusted to approximately 12.5. High-purity N2 was bubbled through the flask at a rate of 50 mL / min throughout the process, and the reaction time was 6 h, synthesizing a reinforcing agent with a molecular weight of approximately 400,000.

[0065] Two synthetic flocculants are combined to form a flocculant product with a bimodal distribution of large and small peaks.

[0066] Settling tests were conducted on the bimodal distribution flocculant product. When the addition amount of the bimodal distribution flocculant was 85 g / t, with a mass ratio of 400,000 molecular weight small molecule enhancer to 5 million molecular weight large molecule flocculant at 1:3, the settling velocity of the red mud coarse liquid was 27.81 m / h, the 5-minute compression zone height was 52 mL, and the suspended solids concentration was only 0.26 g / L. However, when 85 g / t of the 400,000 molecular weight small molecule enhancer was used alone, the red mud coarse liquid was difficult to settle; when 85 g / t of the 5 million molecular weight large molecule flocculant was used alone, the settling velocity was 23.46 m / h, the 5-minute compression zone height was 51 mL, and the suspended solids concentration was 0.45 g / L. Meanwhile, at a certain alumina company, the settling velocity of the flocculant (the main component of the flocculant is a large molecular weight polyacrylate anionic flocculant with a relatively uniform molecular weight distribution) was 15.08 m / h, the compression belt height was 50 mL in 5 minutes, and the concentration of suspended matter was 0.87 g / L.

[0067] Example 2

[0068] Polyacrylamide with a molecular weight of 14 million was weighed and slowly added to a beaker containing a certain amount of distilled water under stirring, resulting in a concentration of 3.55%. After complete dissolution, the viscous solution was transferred to a 250 mL three-necked flask, and the reaction flask was placed in a constant temperature water bath at 50 °C. A certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio were weighed and dissolved in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. This hydroxylamine solution was added to the reaction flask, with a polyacrylamide to hydroxylamine molar ratio of 1:1.5. The pH was adjusted to approximately 12.5. The mixture was magnetically stirred, and high-purity N2 was introduced at a rate of 50 mL / min throughout the reaction, which lasted for 10 hours.

[0069] Acrylamide was weighed and slowly added to a flask containing a certain amount of distilled water under stirring. The acrylamide concentration was 2.5%. 0.1% of initiator (ammonium persulfate and sodium bisulfite) was added, and the reaction time was 0.5 h. A certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio were dissolved in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. This hydroxylamine solution was added to the flask, with a polyacrylamide to hydroxylamine molar ratio of 1:1.5. The pH was adjusted to approximately 12.5. High-purity N2 was bubbled through the flask at a rate of 50 mL / min throughout the reaction, and the reaction time was 8 h. A small molecule reinforcing agent with a molecular weight of approximately 500,000 was synthesized.

[0070] Two synthetic flocculants are combined to form a flocculant product with a bimodal distribution of large and small peaks.

[0071] Sedimentation tests were conducted on the bimodal distribution flocculant product. When the addition amount of bimodal flocculant is 85 g / t, the mass ratio of the reinforcing agent with a molecular weight of 500,000 to the macromolecular flocculant with a molecular weight of 14 million is 1:3, the settling velocity is 32.08 m / h, the compression zone height in 5 minutes is 51 mL, and the concentration of suspended solids is only 0.20 g / L. When using 85 g / t of small molecule reinforcing agent with a molecular weight of 500,000 alone, the coarse red mud sedimentation liquid is difficult to settle. When using 85 g / t of macromolecular flocculant with a molecular weight of 14 million alone, the settling velocity of the coarse red mud sedimentation liquid is 28.77 m / h, the compression zone height in 5 minutes is 50 mL, and the concentration of suspended solids is 0.39 g / L. At the same time, the settling velocity of the flocculant used on-site by an alumina company (the main component of the flocculant is a macromolecular anionic polyacrylate flocculant with a relatively uniform molecular weight distribution) is 15.08 m / h, the compression zone height in 5 minutes is 50 mL, and the concentration of suspended solids is 0.87 g / L.

[0072] Example 3

[0073] Polyacrylamide with a molecular weight of 12 million was weighed and slowly added to a beaker containing a certain amount of distilled water under stirring, resulting in a concentration of 3.20%. After complete dissolution, the viscous solution was transferred to a 250 mL three-necked flask, and the reaction flask was placed in a constant temperature water bath at 50 °C. A certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio were weighed and dissolved in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. This hydroxylamine solution was added to the reaction flask, with a polyacrylamide to hydroxylamine molar ratio of 1:1.5. The pH was adjusted to approximately 12.5. The mixture was magnetically stirred, and high-purity N2 was introduced at a rate of 50 mL / min throughout the reaction, which lasted for 12 hours.

[0074] Acrylamide was weighed and slowly added to a flask containing a certain amount of distilled water under stirring. The acrylamide concentration was 2.5%. Initiators: ammonium persulfate and sodium bisulfite, with an initiator concentration of 0.40%, were added, and the reaction time was 0.5 h. A certain amount of hydroxylamine hydrochloride and sodium hydroxide in an equimolar ratio were dissolved in a certain amount of distilled water to obtain a neutralized hydroxylamine solution. The hydroxylamine solution was added to the flask, with a molar ratio of acrylamide to hydroxylamine of 1:1.5, and the pH was adjusted to approximately 12.5. High-purity N2 was bubbled through the flask at a rate of 50 mL / min throughout the process, and the reaction time was 6 h, synthesizing a reinforcing agent with a molecular weight of approximately 400,000.

[0075] Two synthetic flocculants are combined to form a flocculant product with a bimodal distribution of large and small peaks.

[0076] Sedimentation tests were conducted on the bimodal distribution flocculant product. When the addition amount of the bimodal distribution flocculant was 160 g / t, with a mass ratio of 400,000 molecular weight enhancer to 12 million molecular weight macromolecular flocculant of 1:3, the sedimentation velocity was 34.84 m / h, the compression belt height at 5 min was 53 mL, and the suspended solids concentration was 0.32 g / L. When using 160 g / t of the 400,000 molecular weight small molecule enhancer alone, the coarse red mud sedimentation liquid was difficult to settle. Using 160 g / t of the 12 million molecular weight small molecule enhancer alone... When using macromolecular flocculants, the settling velocity of the coarse red mud sediment was 32.58 m / h, the compression zone height was 51 mL in 5 minutes, and the concentration of suspended solids was 0.36 g / L. Meanwhile, at the same time, the settling velocity of the flocculant used on-site by an alumina company (the main component of the flocculant was a macromolecular sodium polyacrylate anionic flocculant with a relatively uniform molecular weight distribution) was 27.05 m / h, the compression zone height was 51 mL in 5 minutes, and the concentration of suspended solids was 0.75 g / L.

[0077] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:

[0078] In this embodiment of the invention, a macromolecular flocculant (molecular weight ≥ 5 million) is first synthesized by aqueous solution modification to ensure a high content of oxime acid groups in the molecule. Then, a small molecule reinforcing agent (molecular weight ≤ 600,000) is synthesized by acrylamide monomer polymerization modification as a sedimentation process reinforcing agent, which helps to capture extremely fine particles. Granulation is performed first, and then the flocculation effect is generated through the bridging effect of macromolecular flocs, thereby effectively improving and controlling the sedimentation process, and finally forming a high-efficiency flocculant with different molecular weight distributions.

[0079] In this embodiment of the invention, two flocculants with different molecular weights are selected and used in combination according to the different compositions of the red mud. This solves the problem of the difficulty in settling the extremely fine particles formed after the leaching of goethite during the sedimentation process, and improves the sedimentation efficiency of the flocculant. This method not only enables rapid sedimentation, but also produces a clear solution, reduces the content of suspended solids, is simple and convenient to use, and has high sedimentation efficiency.

[0080] In this embodiment of the invention, the settling velocity of the red mud sedimentation crude liquid is ≥25m / h, the compression belt height is ≤55mL after 5 minutes, and the concentration of suspended solids is ≤0.35g / L. The method of this invention can rapidly and effectively reduce the suspended solids content of the sedimentation crude liquid, achieving a better settling effect and providing timely guidance for alumina production.

[0081] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A bimodal flocculant for the settling of Bayer process red mud, characterized in that, The bimodal distribution flocculant is composed of a macromolecular flocculant and a small molecule reinforcing agent in a mass ratio of (1~6):1; wherein... Both the macromolecular flocculant and the small molecule reinforcing agent are oxime acid flocculants; The macromolecular flocculant has a molecular weight of 5 million to 14 million, and the small molecule reinforcing agent has a molecular weight of 100,000 to 600,000. The preparation method of the bimodal distribution flocculant includes: A polyacrylamide with a set molecular weight, a solvent, and a hydroxylamine solution are mixed and the pH is adjusted to a first set pH. A first water bath reaction is carried out under the first set reaction conditions to obtain a macromolecular flocculant. Acrylamide, solvent and initiator are mixed to carry out a polymerization reaction to obtain a mixture; The mixture is mixed with a hydroxylamine solution, and the pH is adjusted to a second set pH to carry out a second water bath reaction under the second set reaction conditions to obtain a small molecule reinforcing agent. The macromolecular flocculant and the small molecule reinforcing agent are compounded to obtain a bimodal distribution flocculant; The concentration of the polyacrylamide is 2%~5%, and the molar ratio of the polyacrylamide to hydroxylamine is 1:(1.2~1.8). The first set reaction conditions include: a nitrogen protective atmosphere, a reaction temperature of 50℃~80℃, a first set pH of 10~13, and a reaction time of 8h~20h. The concentration of the acrylamide is 2%~4%, and the concentration of the initiator is 0.3%~0.6%. The initiator includes one or more of ammonium persulfate and sodium bisulfite. The molar ratio of the acrylamide to hydroxylamine is 1:(1.1~1.5). The second set reaction conditions include: a nitrogen protective atmosphere, a reaction temperature of 50℃~80℃, a second set pH of 10~13, and a reaction time of 5h~10h.

2. The bimodal flocculant according to claim 1, characterized in that, The mass ratio of the macromolecular flocculant to the small molecule reinforcing agent is (2~4):

1.

3. A method for preparing a bimodal flocculant according to any one of claims 1 to 2, characterized in that, The preparation method includes: A polyacrylamide with a set molecular weight, a solvent, and a hydroxylamine solution are mixed and the pH is adjusted to a first set pH. A first water bath reaction is carried out under the first set reaction conditions to obtain a macromolecular flocculant. Acrylamide, solvent and initiator are mixed to carry out a polymerization reaction to obtain a mixture; The mixture is mixed with a hydroxylamine solution, and the pH is adjusted to a second set pH to carry out a second water bath reaction under the second set reaction conditions to obtain a small molecule reinforcing agent. The macromolecular flocculant and the small molecule reinforcing agent are compounded to obtain a bimodal distribution flocculant; The concentration of the polyacrylamide is 2%~5%, and the molar ratio of the polyacrylamide to hydroxylamine is 1:(1.2~1.8). The first set reaction conditions include: a nitrogen protective atmosphere, a reaction temperature of 50℃~80℃, a first set pH of 10~13, and a reaction time of 8h~20h. The concentration of the acrylamide is 2%~4%, and the concentration of the initiator is 0.3%~0.6%. The initiator includes one or more of ammonium persulfate and sodium bisulfite. The molar ratio of the acrylamide to hydroxylamine is 1:(1.1~1.5). The second set reaction conditions include: a nitrogen protective atmosphere, a reaction temperature of 50℃~80℃, a second set pH of 10~13, and a reaction time of 5h~10h.

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