Method for removing fluorine, oxalic acid and vanadium impurities without arsenic in aluminum oxide production process

Abstract

The invention belongs to the technical field of aluminum oxide production, and particularly relates to a method for removing fluorine, oxalic acid and vanadium impurities without arsenic in the aluminum oxide production process. The method comprises the following steps: (1) adding a sodium fluoride inducer and a sodium fluoride growth agent into evaporation mother liquor obtained by evaporating aluminum oxide, and then separating out sodium fluoride to obtain first mother liquor and first filter residues; (2) adding an oxalate inducer and an oxalate growth agent into the first mother liquor, and then separating out sodium oxalate to obtain second mother liquor and second filter residues; (3) performing sodium vanadate precipitation on the second mother liquor to obtain third mother liquor and third filter residues; the reaction temperature of sodium fluoride precipitation in the step (1), the reaction temperature of sodium oxalate precipitation in the step (2) and the reaction temperature of sodium vanadate precipitation in the step (3) are sequentially reduced. According to the method, the sodium fluoride slag, the sodium oxalate slag and the sodium vanadate slag can be obtained respectively, follow-up economic utilization of the waste slag is facilitated, and the slag does not contain arsenic.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of alumina production, and particularly relates to a method for removing fluorine, oxalic acid and vanadium impurities without arsenic in an alumina production process. BACKGROUND

[0002] Organics, vanadium (V) and arsenic (As) are extracted from bauxite into the Bayer liquor. These elements can exist in the Bayer liquor in the general form of vanadate (VO4 3- ), phosphate (PO4 3- ) and arsenate (AsO4 3- ) ions. Some of the organics will degrade to form oxalate, which has a low solubility in sodium aluminate solution. In the Bayer process for alumina production, impurities such as organic carbon, vanadium (V), phosphorus (P) and arsenic (As) can adversely affect the viscosity and density characteristics of the sodium aluminate solution and limit the productivity of the alumina plant. Due to the balance between inputs and outputs, the impurities in the sodium aluminate liquor reach an equilibrium concentration, and an increase in inputs and / or a restriction in outputs will naturally lead to accumulation. At a critical concentration, some impurities will spontaneously precipitate in the form of scale. Scaling increases the pressure drop in fluid transfer systems, affects the residence time in vessels, reduces heat transfer in heat exchangers, and reduces equipment availability, all of which increase the operating costs of the alumina plant, and are therefore undesirable. Measures are usually taken by the alumina plant to exclude these impurities.

[0003] In the existing alumina oxalate and / or vanadium removal process, fluorine and arsenic will be precipitated together, and the sodium fluoride, vanadate and arsenate in the sodium oxalate residue are usually 4% to 15%, 4% to 9% and 0.2% to 8% respectively, and the sodium fluoride, sodium oxalate and arsenate in the vanadate residue are 2% to 7%, 3% to 9% and 5 to 14% respectively. In the Bayer process for alumina production, the presence of sodium fluoride and arsenate in the discharged sodium oxalate residue and vanadate residue is analyzed. Because of the presence of arsenic, the waste such as sodium oxalate residue and vanadium residue has very high environmental problems and environmental hazards whether it is stored or utilized comprehensively. SUMMARY

[0004] The purpose of the present application is to provide a method for removing fluorine, oxalic acid and vanadium impurities without arsenic in an alumina production process. The method can obtain sodium fluoride residue, sodium oxalate residue and sodium vanadate residue respectively, and the sodium fluoride residue, sodium oxalate residue and sodium vanadate residue basically do not contain arsenic.

[0005] In order to achieve the above purpose, the present application provides the following technical scheme: The present application provides a method for removing fluorine, oxalic acid and vanadium impurities without arsenic in an alumina production process, which comprises: (1) adding sodium fluoride inducer and sodium fluoride growth agent into the evaporation mother liquor evaporated from the alumina, and then precipitating sodium fluoride to obtain first mother liquor and first filter residue; (2) adding oxalate inducer and oxalate growth agent into the first mother liquor, and then performing sodium oxalate precipitation to obtain a second mother liquor and a second filter residue; (3) performing sodium vanadate precipitation on the second mother liquor to obtain a third mother liquor and a third filter residue; The reaction temperature of sodium fluoride precipitation in step (1), the reaction temperature of sodium oxalate precipitation in step (2) and the reaction temperature of sodium vanadate precipitation in step (3) are sequentially reduced.

[0006] It is found in the research that the solubility of oxalate, V and As in the sodium aluminate solution has a general rule, specifically: the concentration of oxalate, As and V in the sodium aluminate solution increases with the increase of temperature, and decreases with the increase of caustic alkali. The concentration of fluorine also decreases with the increase of caustic alkali, but the dependence of fluorine concentration on temperature is obviously smaller and opposite. The increase of temperature will further precipitate fluorine. The concentration of As in the sodium aluminate solution depends on the concentration of fluoride. Fluoride has a strong inhibitory effect on the concentration of arsenate, resulting in the precipitation of sodium fluoroarsenate (Na7F(AsO4)2.xH2O) double salt.

[0007] In the present application, the evaporation mother liquor evaporated from alumina refers to the part of liquid returned to the system for recycling after the sodium aluminate solution (commonly known as "crude liquid") obtained in the dissolution process is evaporated and concentrated in the Bayer process production process. The present application does not have special limitations on the specific source of the evaporation mother liquor, as long as the purpose of the present application can be achieved. Preferably, the chemical composition of the evaporation mother liquor includes: N T The content of F - is 150-600 g / L, the content of AO is 50-400 g / L, the content of N K is 100-500 g / L, the content of V2O5 is 0.05-10 g / L, the content of As2O3 is 0.01-1 g / L, and the content of C2O4 2- is 2.635 g / L.

[0008] As an example, the chemical composition of the evaporation mother liquor evaporated from alumina includes: N T The content of F - is 220 g / L, the content of AO is 104.3 g / L, the content of N K is 196 g / L, the content of V2O5 is 1.012 g / L, the content of As2O3 is 0.052 g / L, and the content of C2O4 2- is 2.635 g / L.

[0009] In the present application, AO refers to the concentration of sodium aluminate in the evaporation mother liquor, which is expressed as the equivalent amount of Al2O3 g / L; N K表示Concentration of caustic soda (Na2O) in the mother liquor of evaporation k ); N T Indicates the total alkali concentration (Na2O) of the mother liquor from evaporation. T ) In step (1), sodium fluoride growth agent can play a role in fine particle agglomeration, etc. Preferably, the sodium fluoride growth agent is selected from polymers containing amine groups.

[0010] Preferably, the amine-containing polymer includes polyamine polymers.

[0011] Preferably, the polyamine polymer includes at least one of polydialkyldimethylammonium chloride, polyethyleneamine, and sodium polyethyleneamine-acrylate, with polyethyleneamine being the most preferred.

[0012] Preferably, the polyamine polymer has a weight-average molecular weight of not less than 100,000, more preferably not less than 500,000, more preferably not less than 1,000,000, and even more preferably 1,200,000 to 2,000,000.

[0013] Preferably, the amine-containing polymer further includes polydopamine. That is, in some preferred embodiments, the sodium fluoride growth agent includes a polyamine polymer (preferably polyethyleneamine) and polydopamine.

[0014] In this invention, polyvinylamine can achieve efficient charge neutralization and bridging aggregation of sodium fluoride microcrystals through its strong cationic properties, while polydopamine can form a strong adhesive coating on the crystal surface through its biomimetic mussel adhesion mechanism. The two work together to construct a dual "adhesion-bridging" mode, which can not only significantly promote the growth of sodium fluoride crystals into larger and denser particles and improve sedimentation and filtration efficiency, but more importantly, by forming a dense and regular crystal structure, it can effectively reduce the inclusion of harmful impurities such as arsenic during the crystallization process, so that the purity of the final sodium fluoride slag is increased to more than 90% and the arsenic content is less than 5 ppm.

[0015] Preferably, the polydopamine has a weight-average molecular weight of 100,000 to 1,000,000, and more preferably 350,000 to 500,000.

[0016] Preferably, the mass ratio of the polyamine polymer to polydopamine is 1:(0.5~1.5), more preferably 1:(0.8~1.2).

[0017] This invention controls the mass ratio of polyvinylamine (PVC) to polydopamine (PDA) within the range of 1:(0.8~1.2) to achieve optimal synergistic effects. At this ratio, the dominant "bridging and aggregation" effect of PVC and the auxiliary "adhesion and localization" effect of PDA are better balanced: PDA provides sufficient and robust binding sites for PVC, while PVC effectively connects multiple modified microcrystals, thereby forming dense and regular large-sized sodium fluoride crystals. This not only significantly improves crystallization efficiency and sedimentation filtration performance, but more importantly, it minimizes the inclusion of impurities such as arsenic in the crystals, ensuring high purity and low environmental risk of the slag.

[0018] Furthermore, when the proportion of polydopamine is too high, the excess polydopamine will form an excessively thick, sticky coating layer on the surface of the microcrystals, generating a steric hindrance effect that hinders the effective approach and aggregation between microcrystals. This not only inhibits the bridging function of polyvinylamine, leading to impaired crystal growth and finer particle size, but also forms loosely structured precipitates, increasing the chance of impurities such as arsenic being trapped, ultimately resulting in a decrease in the purity of the slag.

[0019] Preferably, in step (1), the amount of sodium fluoride growth agent added is 10~100ppm, for example, 10ppm, 20ppm, 30ppm, 40ppm, 50ppm, 60ppm, 70ppm, 80ppm, 90ppm or 100ppm, preferably 20~70ppm, and more preferably 30~50ppm.

[0020] In step (1), the sodium fluoride inducer acts as a crystal inducer, mainly by disrupting the stability of sodium fluoride in the sodium aluminate solution and inducing the crystallization of sodium fluoride. Preferably, the sodium fluoride inducer is selected from at least one of sodium fluorosilicate, potassium fluorosilicate, and sodium fluoride, and more preferably sodium fluorosilicate and / or potassium fluorosilicate.

[0021] This invention, through in-depth research, has discovered that to improve fluoride ion removal efficiency by reducing the apparent equilibrium concentration of fluoride ions, enhancing filtration performance, and reducing attached water in the filter cake, the addition of sodium fluoride inducing agents such as sodium fluorosilicate or potassium fluorosilicate to the sodium aluminate solution can significantly improve the precipitation efficiency of sodium fluoride. Simultaneously, the use of sodium fluoride growth promoters enhances the aggregation and growth of fine sodium fluoride crystals, thereby improving filtration performance and reducing the water content of the sodium fluoride filter cake.

[0022] Preferably, in step (1), the amount of sodium fluoride inducer added is 1 to 50 g / L, for example, 1 g / L, 3 g / L, 5 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, etc., preferably 3 to 30 g / L, and more preferably 5 to 20 g / L.

[0023] In step (2), the oxalate inducer plays a crystal-inducing role, mainly by disrupting the stability of oxalate in the sodium aluminate solution and inducing oxalate crystallization. Preferably, the oxalate inducer is selected from any one or more of lanthanum oxalate, cerium oxalate, and yttrium oxalate.

[0024] To improve the removal efficiency of oxalate ions by reducing the apparent equilibrium concentration of oxalate, enhancing filtration performance, and reducing attached water in the filter cake, an oxalate growth promoter was added to the sodium aluminate solution. This promoter acts as an oxalate crystallization inducer, increasing the precipitation efficiency of sodium oxalate. Simultaneously, the oxalate growth promoter also acts as a crystal growth agent for sodium oxalate, enhancing the aggregation and growth of fine sodium oxalate crystals, thereby improving filtration performance and reducing the moisture content of the sodium oxalate filter cake.

[0025] Preferably, in step (2), the amount of oxalate inducer added is 1 to 50 g / L, for example, 1 g / L, 3 g / L, 5 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, etc., preferably 3 to 30 g / L, and more preferably 5 to 20 g / L.

[0026] In step (2), the oxalate growth agent plays a role in inhibiting needle-like growth and fine particle aggregation. Preferably, the oxalate growth agent is a polysaccharide polymer.

[0027] Preferably, the polysaccharide polymer is selected from one or more of dextran, pullulan, aminopolysaccharide, chitosan and rhamnose, with chitosan being the most preferred.

[0028] Preferably, the weight-average molecular weight of the polysaccharide polymer is not less than 1 million, more preferably not less than 5 million, further preferably not less than 7.5 million, and even more preferably 8 million to 9 million.

[0029] Preferably, in step (2), the oxalate growth promoter is 10 to 100 ppm, for example, 10 ppm, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm or 100 ppm, more preferably 20 to 70 ppm, and even more preferably 30 to 50 ppm.

[0030] Preferably, in step (3), the sodium vanadate precipitation is carried out in the presence of acrylic acid-2-acrylamido-2-methylpropionic acid copolymer. That is, acrylic acid-2-acrylamido-2-methylpropionic acid copolymer is added to the second mother liquor to precipitate sodium vanadate.

[0031] Without the addition of acrylate-2-acrylamido-2-methylpropionic acid copolymer, sodium vanadate precipitates rapidly and randomly, forming a loose, amorphous precipitate. This precipitate is not only incompletely precipitated and of low purity, but its large specific surface area and disordered structure also adsorb and encapsulate a large amount of arsenic impurities, leading to an increase in the arsenic content of the third filter residue. In this invention, the phosphonic acid group and carboxyl group can specifically complex with vanadate ions, playing a role in "directional guidance" and "spatial regulation": on the one hand, it can effectively reduce the supersaturation of vanadate, inducing it to form well-structured crystals that are easy to settle and filter; on the other hand, these well-structured crystals can prevent harmful impurities such as residual arsenic (As) in the mother liquor from being encapsulated or co-precipitated into the final product.

[0032] Preferably, the amount of the acrylic acid-2-acrylamido-2-methylpropionic acid copolymer added is 0.5 to 20 g / L, for example, 0.5 g / L, 1 g / L, 3 g / L, 5 g / L, 8 g / L, 120 g / L, 15 g / L, 20 g / L, etc., more preferably 1 to 10 g / L, and more preferably 2 to 5 g / L.

[0033] Preferably, the preparation method of the acrylic acid-2-acrylamido-2-methylpropionic acid copolymer includes: S1. Prepare an acrylic acid aqueous solution with a mass concentration of 40%-45% using water; S2. Prepare an aqueous solution of 2-acrylamido-2-methylpropionic acid with a mass concentration of 40%-45% using water; S3. Under stirring and cooling in an ice-water bath, add a 10%-15% NaOH aqueous solution to a 2-acrylamido-2-methylpropionic acid aqueous solution, adjust the pH to 6-7, and obtain solution A; S4. Prepare an aqueous solution of ammonium persulfate with water, which has a mass concentration of 4%-5%. S5. Add water to the reactor, then use nitrogen to remove air from the reactor and heat to 78~82℃. Then, simultaneously add acrylic acid aqueous solution, solution A and ammonium persulfate aqueous solution. After the addition is complete, keep the reaction at the temperature for 1~1.5 hours to obtain the product. S6. After cooling the product to room temperature, it is poured into anhydrous ethanol for mixing, then filtered and the filter cake is dried to constant weight to obtain acrylic acid-2-acrylamido-2-methylpropionic acid copolymer.

[0034] Preferably, in step S5, the amount of water added is 2% to 5% of the mass of the acrylic acid aqueous solution.

[0035] Preferably, the dropping rate of the acrylic acid aqueous solution in step S5 is 3~4 mL / min.

[0036] Preferably, the dropping rate of solution A in step S5 is 1.5~2 mL / min.

[0037] Further research in this invention revealed that when the amount of acrylic acid increases, although the acrylate-2-acrylamido-2-methylpropionic acid copolymer can provide more initial nucleation sites, it cannot form a strong directional guide, resulting in small and irregular crystals, encapsulation of arsenic impurities, and reduced purity. When the amount of acrylic acid decreases, the enhanced hydrophobicity of the acrylate-2-acrylamido-2-methylpropionic acid copolymer may weaken its dispersion efficiency in the aqueous phase, thus failing to play a better role.

[0038] Preferably, the dropping rate of the ammonium persulfate aqueous solution in step S5 is 0.05~0.1 mL / min.

[0039] Preferably, in step S6, the volume ratio of the product to anhydrous ethanol is 1:(3~5).

[0040] Preferably, in step (1), the conditions for sodium fluoride precipitation include: a reaction temperature of 80-100°C. The temperature control is mainly determined by the temperature of the alumina production process, and generally no special adjustment is required.

[0041] Preferably, in step (1), the conditions for sodium fluoride precipitation include a reaction time of 1 to 4 hours, preferably 1 to 2 hours.

[0042] In step (1) of the present invention, the first mother liquor and the first filter residue can be separated by filtration.

[0043] Preferably, in step (2), the conditions for sodium oxalate precipitation include a reaction temperature of 55–65°C. That is, the temperature of the first mother liquor may be higher than this reaction temperature, and the temperature can be lowered to 55–65°C before adding the oxalate inducer and oxalate growth promoter to precipitate sodium oxalate.

[0044] Preferably, in step (2), the conditions for sodium oxalate precipitation include: a reaction time of 1 to 6 hours, preferably 2 to 5 hours, and more preferably 3 to 4 hours.

[0045] In step (2) of the present invention, the second mother liquor and the second filter residue can be obtained by filtration.

[0046] Preferably, in step (3), the conditions for sodium oxalate precipitation include a reaction temperature of 30~40℃. That is, the temperature of the second mother liquor may be higher than this reaction temperature, and the temperature can be lowered to 30~40℃ before adding the acrylic acid-2-acrylamide-2-methylpropionic acid copolymer to precipitate sodium vanadate.

[0047] Preferably, in step (3), the conditions for sodium oxalate precipitation include a reaction time of 4 to 10 hours.

[0048] The reactions involved in steps (1), (2), and (3) of this invention can be carried out under dynamic conditions, such as under stirring or under shaking conditions.

[0049] Preferably, the method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic includes: (1) Add sodium fluoride inducer and sodium fluoride growth agent to the mother liquor from the evaporation of alumina, then heat to 80-100℃ and shake in a constant temperature water bath for 1-2 hours to precipitate sodium fluoride. Then filter to obtain the first mother liquor and the first filter residue. (2) After cooling the first mother liquor to 55-65℃, add oxalate inducer and oxalate growth agent, then shake in a constant temperature water bath for 3-4 hours to precipitate sodium oxalate, and then filter to obtain the second mother liquor and the second filter residue. (3) After cooling the second mother liquor to 30~40℃, add acrylic acid-2-acrylamide-2-methylpropionic acid copolymer and shake in a constant temperature water bath for 4~10 hours to precipitate sodium vanadate, and obtain the third mother liquor and the third filter residue.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects: Existing technologies rely solely on the simple addition of inorganic salts and alteration of temperature conditions, resulting in a slow and disordered crystallization process. This leads to low purity and high residual levels of the target components in the slag at each stage, and the slag also contains arsenic. This invention, through the synergistic effect of sodium fluoride / oxalate inducers and growth promoters, and the precise control of vanadium crystallization by the copolymer, significantly improves crystallization efficiency and product purity, while also effectively reducing arsenic in the slag. In other words, the method of this invention can yield sodium fluoride slag, sodium oxalate slag, and sodium vanadate slag separately, facilitating the subsequent economic utilization of these waste residues. Furthermore, these slags are arsenic-free, completely eliminating the environmental hazards posed by these waste residues. Detailed Implementation

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] In the following examples The chemical components in the mother liquor from alumina evaporation include: N T The content was 205.8 g / L, F - The content of [unspecified substance] was 220 g / L, the content of AO was 104.3 g / L, and the content of N [unspecified substance] was [unspecified substance]. KThe content of [unspecified substance] is 196 g / L, the content of V2O5 is 1.012 g / L, the content of As2O3 is 0.052 g / L, and the content of C2O4 is [unspecified substance]. 2- The content was 2.635 g / L.

[0053] The weight-average molecular weight of polyethyleneamine is 1.7 million. The weight-average molecular weight of polydopamine is 420,000; The weight-average molecular weight of chitosan is 8.2 million.

[0054] Preparation example: Preparation Example 1 The preparation method of acrylic acid-2-acrylamide-2-methylpropionic acid copolymer includes: S1. Prepare an acrylic acid aqueous solution with a mass concentration of 45% using water; S2. Prepare an aqueous solution of 2-acrylamido-2-methylpropionic acid with a mass concentration of 40% using water; S3. Under stirring and cooling in an ice-water bath, add a 12% (w / w) NaOH aqueous solution to a 2-acrylamido-2-methylpropionic acid aqueous solution to adjust the pH to 6.8, thus obtaining solution A; S4. Prepare an aqueous solution of ammonium persulfate with water, resulting in a mass concentration of 4.6%. S5. Add water to the reactor (the amount of water added is 3% of the mass of the acrylic acid aqueous solution), then use nitrogen to remove air from the reactor and raise the temperature to 80°C. Then, simultaneously add the acrylic acid aqueous solution, solution A, and ammonium persulfate aqueous solution. After the addition is complete, keep the reaction at this temperature for 1 hour to obtain the product. The dropping rate of the acrylic acid aqueous solution is 4 mL / min, the dropping rate of solution A is 2 mL / min, and the dropping rate of the ammonium persulfate aqueous solution is 0.08 mL / min. S6. After the product material is cooled to room temperature, it is poured into anhydrous ethanol (the volume ratio of product material to anhydrous ethanol is 1:4) for mixing. Then, the mixture is filtered and the filter cake is dried to constant weight to obtain acrylic acid-2-acrylamido-2-methylpropionic acid copolymer (denoted as A).

[0055] Preparation Example 2 The method is the same as in Example 1, except that the dropping rate of the acrylic acid aqueous solution is 8 mL / min, and the dropping rate of solution A is 1 mL / min.

[0056] The rest is the same as in Preparation Example 1, and the final preparation yields acrylic acid-2-acrylamido-2-methylpropionic acid copolymer (denoted as B).

[0057] Preparation Example 3 The method is the same as in Example 1, except that the dropping rate of the acrylic acid aqueous solution is 1 mL / min, and the dropping rate of solution A is 4 mL / min.

[0058] The rest is the same as in Preparation Example 1, and the final product is acrylic acid-2-acrylamido-2-methylpropionic acid copolymer (denoted as C).

[0059] Examples 1-7 and Comparative Examples 1-7 (1) Sodium fluoride inducer and sodium fluoride growth agent are added to the mother liquor from the evaporation of alumina and then heated to 95°C and shaken in a constant temperature water bath for 2 hours to precipitate sodium fluoride. After that, the first mother liquor and the first filter residue are obtained by filtration. (2) After cooling the first mother liquor to 60°C, add oxalate inducer and oxalate growth agent, then shake in a constant temperature water bath for 4 hours to precipitate sodium oxalate, and then filter to obtain the second mother liquor and the second filter residue. (3) After cooling the second mother liquor to 40°C, add acrylic acid-2-acrylamide-2-methylpropionic acid copolymer, then shake in a constant temperature water bath for 4 hours to precipitate sodium vanadate, and then filter to obtain the third mother liquor and the third filter residue.

[0060] In step (1), the specific types and amounts of oxalate inducer and oxalate growth agent, as well as the F in the first mother liquor... - The content of NaF, the purity of NaF and the content of As in the first filter residue are shown in Table 1.

[0061] In step (2), the specific types and amounts of oxalate inducer and oxalate growth agent, as well as the C2O4 in the second mother liquor... 2- The content of , the purity of sodium oxalate and the content of As in the second filter residue are shown in Table 2.

[0062] In step (3), the specific types and amounts of acrylic acid-2-acrylamide-2-methylpropionic acid copolymer, as well as the V2O5 concentration in the third mother liquor, the purity of vanadium salt V2O5 in the second filter residue, and the As content are shown in Table 3.

[0063] Table 1

[0064] Table 2

[0065] Table 3

[0066] As can be seen from the test results in Table 1, the method of the present invention can obtain sodium fluoride slag, sodium oxalate slag, and sodium vanadate slag respectively, which is beneficial to the subsequent economic utilization of these waste residues. Moreover, these residues do not contain arsenic, which can completely eliminate the environmental hazards of these waste residues.

[0067] The comparative examples, lacking the necessary technical solutions, performed significantly worse than the examples in terms of performance testing. An improper or singular proportion of sodium fluoride growth agent resulted in numerous crystal defects and high As residue. In Comparative Example 3, the addition of acrylic acid-2-acrylamide-2-methylpropionic acid copolymer led to irregular precipitation of sodium vanadate, resulting in extensive As encapsulation. In Comparative Examples 4-5, the poor content of each structural unit in the acrylic acid-2-acrylamide-2-methylpropionic acid copolymer may have weakened complexing ability and resulted in high As residue. In Comparative Examples 6-8, the absence of sodium fluoride inducer or sodium fluoride growth agent may have led to incomplete crystallization, a large specific surface area, and easy As adsorption. In Comparative Examples 9-11, the lack of oxalate inducer or oxalate growth agent resulted in low sodium oxalate precipitation, disordered crystals, and As encapsulation.

[0068] The above experimental results further demonstrate the importance of the technical solution defined in this invention to its technical effect.

[0069] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for removing fluorine, oxalic acid, and vanadium impurities without arsenic during alumina production, characterized in that, The method includes: (1) Add sodium fluoride inducer and sodium fluoride growth agent to the mother liquor from the evaporation of alumina, and then precipitate sodium fluoride to obtain the first mother liquor and the first filter residue; (2) Add oxalate inducer and oxalate growth agent to the first mother liquor, and then precipitate sodium oxalate to obtain the second mother liquor and the second filter residue; (3) The second mother liquor is subjected to sodium vanadate precipitation to obtain the third mother liquor and the third filter residue; The reaction temperatures for sodium fluoride precipitation in step (1), sodium oxalate precipitation in step (2), and sodium vanadate precipitation in step (3) decrease sequentially.

2. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that... The chemical composition of the mother liquor includes: N T The content is 150~600g / L, F - The content of [unspecified substance] is 150~600g / L, the content of AO is 50~400g / L, and the content of N [unspecified substance] is [unspecified substance]. K The content of [unspecified substance] is 100~500 g / L, the content of V2O5 is 0.05~10 g / L, the content of As2O3 is 0.01~1 g / L, and the content of C2O4 is [unspecified substance]. 2- The content was 2.635 g / L.

3. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that... The sodium fluoride growth agent is selected from polymers containing amine groups; the sodium fluoride inducing agent is selected from at least one of sodium fluorosilicate, potassium fluorosilicate, and sodium fluoride.

4. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 3, is characterized in that... The amine-containing polymer includes polyamine polymers; the polyamine polymer includes at least one of polydialkyldimethylammonium chloride, polyethyleneamine, and sodium polyethyleneamine-acrylate; the weight-average molecular weight of the polyamine polymer is not less than 100,000.

5. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 4, is characterized in that... The amine-containing polymer also includes polydopamine; the weight-average molecular weight of the polydopamine is 100,000 to 1,000,000; the mass ratio of the polyamine polymer to the polydopamine is 1:(0.5 to 1.5).

6. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that... In step (1), the amount of sodium fluoride inducer added is 1 to 50 g / L; in step (1), the amount of sodium fluoride growth agent added is 10 to 100 ppm.

7. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that... The oxalate inducer is selected from any one or more of lanthanum oxalate, cerium oxalate and yttrium oxalate; the oxalate growth agent is a polysaccharide polymer; in step (2), the amount of oxalate inducer added is 1 to 50 g / L; in step (2), the amount of oxalate growth agent is 10 to 100 ppm.

8. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that... The precipitation of sodium vanadate is carried out in the presence of acrylate-2-acrylamido-2-methylpropionic acid copolymer; the amount of acrylate-2-acrylamido-2-methylpropionic acid copolymer added is 0.5-20 g / L.

9. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 8, is characterized in that... The preparation method of the acrylic acid-2-acrylamido-2-methylpropionic acid copolymer includes: S1. Prepare an acrylic acid aqueous solution with a mass concentration of 40%-45% using water; S2. Prepare an aqueous solution of 2-acrylamido-2-methylpropionic acid with a mass concentration of 40%-45% using water; S3. Under stirring and cooling in an ice-water bath, add a 10%-15% NaOH aqueous solution to a 2-acrylamido-2-methylpropionic acid aqueous solution, adjust the pH to 6-7, and obtain solution A; S4. Prepare an aqueous solution of ammonium persulfate with water, which has a mass concentration of 4%-5%. S5. Add water to the reactor, then use nitrogen to remove air from the reactor and heat to 78~82℃. Then, simultaneously add acrylic acid aqueous solution, solution A and ammonium persulfate aqueous solution. After the addition is complete, keep the reaction at the temperature for 1~1.5 hours to obtain the product. S6. After cooling the product to room temperature, it is poured into anhydrous ethanol for mixing, then filtered and the filter cake is dried to constant weight to obtain acrylic acid-2-acrylamido-2-methylpropionic acid copolymer.

10. The method for removing fluorine, oxalic acid, and vanadium impurities in the alumina production process without arsenic, according to claim 1, is characterized in that, In step (1), the conditions for sodium fluoride precipitation include: a reaction temperature of 80-100℃ and a reaction time of 1-4 hours; in step (2), the conditions for sodium oxalate precipitation include: a reaction temperature of 55-65℃ and a reaction time of 1-6 hours; in step (3), the conditions for sodium oxalate precipitation include: a reaction temperature of 30-40℃ and a reaction time of 4-10 hours.

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