A method for preparing low-lead antimony trioxide

Abstract

This invention relates to the field of inorganic materials, specifically to a method for preparing low-lead antimony trioxide. The method involves crushing antimony ingots, first melting and oxidizing them, then distilling to remove impurities to obtain a refined product. The refined product, organic acid, and polyol are mixed, heated, and reacted, followed by filtration to remove insoluble matter, yielding an antimony complex solution. A long-chain organic amine is dissolved in a mixed solvent of anhydrous ethanol and deionized water to obtain a long-chain organic amine solution. The antimony complex solution is added to the long-chain organic amine solution, and the pH is adjusted to 6-7. The reaction solution is transferred to a hydrothermal reactor, sealed, and subjected to hydrothermal reaction. The precipitate is collected, washed, and dried. The resulting nanosheet-like clustered antimony trioxide exhibits high purity, low impurity content, extremely high specific surface area, abundant active sites, high energy density, and good cycle performance, making it a highly promising pseudocapacitor electrode material.

Description

Technical Field

[0001] This invention relates to the field of inorganic materials, specifically to a method for preparing low-lead antimony trioxide. Background Technology

[0002] Antimony trioxide is an important inorganic chemical raw material, widely used in flame retardant synergists, plastics, rubber, coatings, glass clarifying agents, catalysts, and electronic ceramics. With the rapid development of new energy technologies, antimony trioxide, due to its unique structure and potential electrochemical activity, also shows great promise in lithium-ion batteries, sodium-ion batteries, and supercapacitor materials.

[0003] However, traditional industrial production of antimony trioxide mainly originates from antimony ore smelting or direct oxidation of antimony ingots. These two methods typically produce antimony trioxide with high impurity content, particularly lead, which is difficult to remove. These impurities remaining in the electrode material not only reduce electrochemical cycle stability but may also pose risks of biotoxicity and environmental pollution. Furthermore, the performance of antimony trioxide is closely related to its crystal morphology. Antimony trioxide with specific morphologies has a larger specific surface area and more active sites, exhibiting higher specific capacity and rate performance in electrochemical energy storage applications. However, traditional antimony ore smelting or direct oxidation methods make it difficult to precisely control the crystal growth process of antimony trioxide, resulting in products that are typically irregular particles or dense masses with small specific surface areas, failing to meet the demands of high-performance applications. Summary of the Invention

[0004] Objective of the invention: To address the above-mentioned technical problems, this invention proposes a method for preparing low-lead antimony trioxide.

[0005] The technical solution adopted is as follows: A method for preparing low-lead antimony trioxide: Antimony ingots are crushed, melted and oxidized, and then distilled to remove impurities to obtain a refined product. The refined product, organic acid, and polyol are mixed, heated, and reacted, followed by filtration to remove insoluble matter, yielding an antimony complex solution. Long-chain organic amines are dissolved in a mixed solvent of anhydrous ethanol and deionized water to obtain a long-chain organic amine solution. The antimony complex solution is added to the long-chain organic amine solution, and the pH is adjusted to 6-7. The reaction solution is transferred to a hydrothermal reactor, sealed, and heated to 55-65°C for 2-4 hours. The temperature is then increased to 75-95°C for 3-5 hours, and finally increased to 110-120°C for 2-4 hours. After returning to room temperature, the precipitate is collected, washed, and dried.

[0006] This invention first employs oxygen-enriched conditions to melt and oxidize antimony ingots, ensuring that metallic impurities (such as lead and bismuth) in the ingots are also oxidized to their corresponding oxides. Subsequently, distillation is performed under specific vacuum and temperature conditions to remove impurities. Since the saturated vapor pressure of antimony trioxide under these conditions is significantly higher than that of lead and bismuth oxides, by controlling the temperature gradient in the distillation condensation zone, the high-purity antimony trioxide vapor volatilized is preferentially condensed in the collection zone, while high-boiling-point oxides such as lead and bismuth oxides remain in the evaporation vessel, thus achieving physical separation and primary impurity removal.

[0007] The refined product (mainly high-purity antimony trioxide) reacts with organic acids and polyols. In this step, the anions ionized from the organic acids have extremely strong coordination ability, capable of forming stable water-soluble complexes with metal ions. The polyols, with their high boiling points, good polarity, and coordination ability with metal ions, can synergistically work with the organic acids to convert antimony trioxide into soluble antimony complexes, forming a homogeneous solution that provides a molecularly uniform precursor system for subsequent hydrolysis and precipitation. Furthermore, the polyols possess multiple hydroxyl groups, which may interact with the surface of the in-situ generated ionic liquid micelles through hydrogen bonds, regulating the surface curvature and hydrophilic / hydrophobic balance of the ionic liquid micelle template. Alternatively, they may act as steric hindrance regulators during crystal growth, preventing excessive stacking of nanosheets, thereby fine-tuning the thickness of the nanosheets and the density of the clusters, and influencing the electrochemical performance of the generated antimony trioxide.

[0008] When an antimony complex solution is added to a water-ethanol solution of a long-chain organic amine, the long-chain organic amine undergoes an acid-base neutralization reaction with the organic acid to generate a proton-type ionic liquid. This proton-type ionic liquid exhibits distinct amphiphilicity: the positively charged quaternary ammonium head group is hydrophilic, while the three long-chain alkyl groups are hydrophobic. In a water-ethanol-polyol mixed solvent, with increasing temperature and pH adjustment, these amphiphilic molecules reach a critical micelle concentration and self-assemble into dynamic, ordered aggregates. These self-assembled aggregates, known as "soft templates," typically range in size from a few nanometers to tens of nanometers, providing a confined microenvironment for subsequent inorganic crystal growth.

[0009] Preferably, the melt oxidation is carried out in an oxygen-enriched atmosphere. Appropriate oxygen-enriched conditions can accelerate the oxidation reaction, improve reaction efficiency, and reduce the formation of nitrogen oxides. A mixture of oxygen and argon is preferred, but oxygen-enriched air can also be selected for economic reasons.

[0010] Preferably, the oxygen volume concentration in the oxygen-enriched atmosphere is 25% to 40%. Within this range, both reaction efficiency and economy can be balanced.

[0011] Preferably, the vacuum degree for distillation is 50~250 Pa, and the distillation temperature is 450~550℃. Within this vacuum and temperature range, the volatilization rate of antimony trioxide is much higher than that of impurities such as lead oxide and bismuth oxide, thus achieving efficient separation.

[0012] Preferably, the mass ratio of the refined product, organic acid, and polyol is 1:(2-3):(5-15). This ratio range ensures that antimony trioxide can be fully complexed and dissolved. If there is too little organic acid, the dissolution will be incomplete, which is also not conducive to the subsequent formation of ionic liquids. If there is too little polyol, the system viscosity will be too high or the dissolving capacity will be insufficient; if there is too much organic acid or polyol, it will cause waste and increase the burden of subsequent processing.

[0013] Preferably, the organic acid is tartaric acid. Tartaric acid can react with Sb. 3+ It forms stable multi-cyclic chelates with good dissolution effect.

[0014] Preferably, the polyol is selected from at least one of ethylene glycol, glycerol, and pentaerythritol. The polyol not only acts as a solvent, but its hydroxyl groups may also participate in the coordination of antimony, and its high boiling point and good solubility contribute to the formation of a stable complex solution.

[0015] Preferably, the structural formula of the long-chain organic amine is as follows: R1, R2, and R3 are each an independent hydrocarbon group with ≥6 carbon atoms.

[0016] Long-chain hydrocarbon groups provide hydrophobic effects and are a key driving force for the formation of self-assembled structures such as micelles or vesicles.

[0017] Preferably, R1, R2, and R3 are the same. Long-chain tertiary amines with symmetrical structures are more likely to form regular ionic liquid structures, and their self-assembly behavior is more controllable.

[0018] Preferably, the long-chain organic amine is selected from at least one of tri-octylamine, tri-nonylamine, tri-decylamine, tri-undecylamine, and tri-dodecylamine. These long-chain tertiary amines, when combined with organic acids, form proton-type ionic liquids with suitable critical micelle concentrations and hydrophobic chain lengths, enabling them to effectively assemble into micelles under given hydrothermal conditions, thereby inducing the formation of antimony trioxide nanosheet clusters.

[0019] The present invention has the following outstanding beneficial effects: This invention achieves highly efficient primary physical removal of impurities such as lead and bismuth from antimony ingots through the synergistic effect of melt oxidation and vacuum distillation. Then, refined antimony trioxide is transformed into a molecularly dispersed antimony complex precursor via organic acid complexation. Furthermore, a long-chain organic amine and organic acid are used to generate an amphiphilic proton-type ionic liquid in situ under hydrothermal conditions. This ionic liquid spontaneously assembles into micelles or vesicles as soft templates, precisely inducing the two-dimensional growth of antimony trioxide crystals into nanosheets, which further self-assemble into regular nanosheet clusters. This simultaneously achieves deep impurity removal and morphology-controlled synthesis. The resulting antimony trioxide exhibits high purity, low impurity content, extremely high specific surface area, abundant active sites, high energy density, and excellent cycle performance, making it a highly promising pseudocapacitor electrode material. Simultaneously, this method is environmentally friendly, uses inexpensive raw materials, is simple to operate, and is easily scaled up industrially. The resulting product can be widely used in lithium-ion battery anodes and electrochemical energy storage devices. Attached Figure Description

[0020] Figure 1 This is a SEM image of the low-lead antimony trioxide prepared in Example 1. Detailed Implementation

[0021] Unless otherwise specified in the examples, the conditions were performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products. Techniques not mentioned in this invention refer to existing technologies. Unless otherwise specified, the following examples and comparative examples are parallel experiments, using the same processing steps and parameters. Example 1:

[0022] A method for preparing low-lead antimony trioxide includes the following steps: (1) Take 5 kg of industrial grade antimony ingot (purity of 99%, with the remaining impurities mainly being lead), crush it into antimony blocks with a particle size of 5-10 mm, heat and melt the antimony blocks in a vacuum induction melting furnace, and then atomize the antimony liquid with oxygen-enriched air (oxygen volume concentration of 30%) by pouring it out, and collect the atomization products to obtain 5.6 kg of crude antimony trioxide.

[0023] (2) The above crude antimony trioxide was loaded into a vacuum sublimation furnace, the vacuum degree was set to 100 Pa, heated to 500 °C, and kept at the temperature for 3 hours for distillation. The antimony trioxide vapor was collected on the condenser to obtain 5.2 kg of refined antimony trioxide with a purity of 99.93% and a lead content of 225 ppm.

[0024] (3) Weigh 100g of purified antimony trioxide, 250g of tartaric acid, and 800g of ethylene glycol. Add the three to a flask, stir and heat to 120℃, and react for 3 hours. During the reaction, the solid gradually dissolves, eventually forming a transparent pale yellow solution. Filter under vacuum while hot to remove insoluble matter, and obtain a clear filtrate, which is denoted as the antimony complex solution.

[0025] (4) Weigh 50g of tri-n-octylamine and dissolve it in a mixed solvent consisting of 200mL of anhydrous ethanol and 300mL of deionized water. Stir at room temperature for 30 minutes to completely dissolve it and obtain a tri-n-octylamine solution.

[0026] (5) Under mechanical stirring, the antimony complex solution was slowly added dropwise to the tri-n-octylamine solution at a rate of 10-20 mL / min. After the addition was complete, stirring was continued for 15 minutes. The pH of the mixed solution was adjusted dropwise to 6.5 using ammonia water. The pH-adjusted mixture was transferred to a hydrothermal reactor, sealed, and heated to 60°C at 2°C / min and held for 3 hours. Then, the temperature was increased to 85°C at 1.5°C / min and held for 4 hours. Finally, the temperature was increased to 115°C at 1°C / min and held for 3 hours. After the reaction was completed, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The reactor was opened, the reaction solution was centrifuged, and the precipitate was collected. After washing with deionized water and anhydrous ethanol, the precipitate was dried in a vacuum drying oven to obtain low-lead antimony trioxide. Its SEM image can be found in [reference needed]. Figure 1 It can be seen that it has a nanosheet cluster structure with a cluster diameter of 5~10μm, a purity of 99.998%, a lead content of 8ppm, and a yield of 92.4%. Example 2:

[0027] This embodiment is basically the same as that of Example 1, except that in step (3), ethylene glycol is replaced with glycerol, and the mass remains 800g. Scanning electron microscopy (SEM) shows that the product is a nanosheet cluster structure with a cluster diameter of 10~40μm, a purity of 99.992%, a lead content of 10ppm, and a yield of 91.9%. Example 3:

[0028] This embodiment is basically the same as that of Example 1, except that in step (4), tri-n-octylamine is replaced with tri-n-nonylamine, while the mass remains 50g. Scanning electron microscopy (SEM) shows that the product is a uniform nanosheet cluster structure with a cluster diameter of 5~10μm, a purity of 99.999%, a lead content of 5ppm, and a yield of 93.3%. Example 4:

[0029] This embodiment is basically the same as that of Example 1, except that in step (4), tri-n-octylamine is replaced with tri-n-decylamine, while the mass remains 50g. Scanning electron microscopy (SEM) shows that the product is a uniform nanosheet cluster structure with a cluster diameter of 5~10μm, a purity of 99.999%, a lead content of 4ppm, and a yield of 93.8%. Example 5:

[0030] This embodiment is basically the same as that of Example 1, except that in step (4), tri-n-octylamine is replaced with tri-n-undecylamine, while the mass remains 50g. Scanning electron microscopy (SEM) shows that the product is a uniform nanosheet cluster structure with a cluster diameter of 5~10μm, a purity of 99.997%, a lead content of 9ppm, and a yield of 93.5%. Example 6:

[0031] This embodiment is basically the same as that of Example 1, except that in step (4), tri-n-octylamine is replaced with tri-n-dodecylamine, while the mass remains 50g. Scanning electron microscopy (SEM) shows that the product is a uniform nanosheet cluster structure with a cluster diameter of 5~10μm, a purity of 99.996%, a lead content of 8ppm, and a yield of 93.0%. Example 7:

[0032] This embodiment is basically the same as embodiment 1, except that step (5) is different, as follows: (5) Under mechanical stirring, the antimony complex solution was slowly added dropwise to the tri-n-octylamine solution at a rate of 10-20 mL / min. After the addition was complete, stirring was continued for 15 minutes. The pH of the mixed solution was adjusted dropwise to 6.5 using ammonia water. The pH-adjusted mixture was transferred to a hydrothermal reactor, sealed, and heated to 65°C at 2°C / min and held for 2 hours. Then, the temperature was increased to 95°C at 1.5°C / min and held for 3 hours. Finally, the temperature was increased to 120°C at 1°C / min and held for 2 hours. After the reaction was completed, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The reactor was opened, the reaction solution was centrifuged, and the precipitate was collected. After washing with deionized water and anhydrous ethanol, the precipitate was dried in a vacuum drying oven to obtain low-lead antimony trioxide. Scanning electron microscopy (SEM) showed that the product was a nanosheet cluster structure with a purity of 99.997%, a cluster diameter of 5-10 μm, a lead content of 10 ppm, and a yield of 92.2%. Example 8:

[0033] This embodiment is basically the same as embodiment 1, except that step (5) is different, as follows: (5) Under mechanical stirring, the antimony complex solution was slowly added dropwise to the tri-n-octylamine solution at a rate of 10-20 mL / min. After the addition was complete, stirring was continued for 15 minutes. The pH of the mixed solution was adjusted dropwise to 6.5 using ammonia water. The pH-adjusted mixture was transferred to a hydrothermal reactor, sealed, and heated to 55°C at 2°C / min and held for 4 hours. Then, the temperature was increased to 75°C at 1.5°C / min and held for 5 hours. Finally, the temperature was increased to 110°C at 1°C / min and held for 4 hours. After the reaction was completed, the heating was turned off, and the mixture was allowed to cool naturally to room temperature. The reactor was opened, the reaction solution was centrifuged, and the precipitate was collected. After washing with deionized water and anhydrous ethanol, the precipitate was dried in a vacuum drying oven to obtain low-lead antimony trioxide. Scanning electron microscopy (SEM) showed that the product was a nanosheet cluster structure with a cluster diameter of 5-10 μm, a purity of 99.999%, a lead content of 4 ppm, and a yield of 94.1%.

[0034] Comparative Example 1: It is basically the same as Example 1, except that tartaric acid is not added in step (3).

[0035] (3) Weigh 100g of refined antimony trioxide and 800g of ethylene glycol. Add both to a flask, stir and heat to 120℃, and react for 3 hours. During the reaction, the solid hardly dissolves, and the system is white and turbid. Filter under vacuum while hot, collecting a large amount of undissolved white solid. The filtrate is a colorless and transparent liquid (tested to contain almost no antimony). This indicates that without the addition of tartaric acid, antimony trioxide cannot be effectively dissolved in ethylene glycol at the current temperature.

[0036] Comparative Example 2: It is basically the same as Example 1, except that tri-octylamine is not added in step (4).

[0037] Scanning electron microscopy (SEM) revealed that the product consisted of amorphous particle aggregates with irregular shapes, ranging from 0.5 to 15 μm in diameter. No nanosheets or cluster structures were observed. The product purity was 99.91%, with a lead content of 68 ppm and a yield of 91.5%. This indicates that without the addition of tri-n-octylamine, a proton-type ionic liquid soft template could not be generated in situ, thus preventing the induction of anisotropic growth and self-assembly. It also suggests that the formation of the proton-type ionic liquid soft template may contribute to the removal of impurities.

[0038] Comparative Example 3: It is basically the same as Example 1, except that in step (4), triethylamine is used instead of tri-n-octylamine.

[0039] Scanning electron microscopy (SEM) revealed that the product was a mixture of nanoparticles and short rod-like structures. The nanoparticles were 50–200 nm in size, the short rods were 200–500 nm in length and 10–20 nm in diameter, and no clustered structures of nanosheet assembly were formed. The product purity was 99.95%, the lead content was 32 ppm, and the yield was 92.1%. This indicates that the alkyl chain of triethylamine is too short. Although it can form a proton-type ionic liquid with organic acids, its hydrophobic effect is too weak to form stable micelles or vesicle soft templates in the water-ethanol-polyol system. Therefore, it cannot effectively induce anisotropic growth and three-dimensional self-assembly of nanosheets, resulting in uncontrolled morphology. Furthermore, the lead removal effect is inferior to that of Example 1.

[0040] Comparative Example 4: It is basically the same as Example 1, except that in step (4), tri-n-octylamine is replaced with tri-n-octylamine tartaric acid.

[0041] The preparation method of tri-n-octylamine tartaric acid is as follows: Tartaric acid and tri-n-octylamine in a molar ratio of 1:1 were dissolved in an appropriate amount of ethanol. The mixture was stirred and reacted at room temperature for 2 hours under nitrogen protection. After the reaction was completed, the solvent ethanol was removed by rotary evaporation, and the product was dried under vacuum.

[0042] Scanning electron microscopy (SEM) revealed that the product exhibited a nanosheet structure without the formation of clusters. The product purity was 99.93%, with a lead content of 40 ppm and a yield of 92.4%. While the pre-synthesized tri-n-octylamine tartrate might form micelles or vesicles in a water-ethanol-polyol mixed solvent upon addition to the reaction system, its self-assembly process was poorly synchronized with the hydrolysis and precipitation of the antimony complex. This made it difficult to effectively guide the directional growth and three-dimensional self-assembly of the nanosheets.

[0043] Performance testing: The low-lead antimony trioxide, acetylene black and polyvinylidene fluoride prepared in Examples 1-8 and Comparative Examples 1-4 were mixed in a mass ratio of 7:2:1 and ground thoroughly to obtain a mixture. The mixture was then added to an appropriate amount of N-methylpyrrolidone and ground thoroughly to obtain a slurry. The slurry was coated on a nickel foam disc and dried under vacuum at 60°C for 12 h to be used as the working electrode of the three-electrode system. Electrochemical performance tests were conducted using an electrochemical workstation with a three-electrode system. The counter electrode and reference electrode were platinum sheet and mercury / mercury oxide, respectively. A 2 mol / L KOH solution was used as the electrolyte. Cyclic voltammetry and constant current charge-discharge tests were performed with a voltage window of 0–0.5 V. The test current density was 2 A / g. The test results are shown in Table 1 below.

[0044] Table 1: As shown in Table 1 above, the low-lead antimony trioxide prepared by this invention has high energy density and good cycle performance, making it a very promising electrode material for pseudocapacitors.

[0045] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing low-lead antimony trioxide, characterized in that, Antimony ingots are crushed, melted and oxidized, and then distilled to remove impurities to obtain a refined product. The refined product, organic acid, and polyol are mixed, heated, and reacted, followed by filtration to remove insoluble matter, yielding an antimony complex solution. Long-chain organic amines are dissolved in a mixed solvent of anhydrous ethanol and deionized water to obtain a long-chain organic amine solution. The antimony complex solution is added to the long-chain organic amine solution, and the pH is adjusted to 6-7. The reaction solution is transferred to a hydrothermal reactor, sealed, and heated to 55-65°C for 2-4 hours. The temperature is then increased to 75-95°C for 3-5 hours, and finally increased to 110-120°C for 2-4 hours. After returning to room temperature, the precipitate is collected, washed, and dried.

2. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, Melt oxidation is carried out in an oxygen-rich atmosphere.

3. The method for preparing low-lead antimony trioxide as described in claim 2, characterized in that, The oxygen volume concentration in the oxygen-enriched atmosphere is 25% to 40%.

4. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, The vacuum degree for distillation to remove impurities is 50~250Pa, and the temperature for distillation to remove impurities is 450~550℃.

5. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, The mass ratio of the refined product, organic acid and polyol is 1:(2-3):(5-15).

6. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, The organic acid is tartaric acid.

7. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, The polyol is selected from at least one of ethylene glycol, glycerol, and pentaerythritol.

8. The method for preparing low-lead antimony trioxide as described in claim 1, characterized in that, The structural formula of the long-chain organic amine is as follows: R1, R2, and R3 are each an independent hydrocarbon group with ≥6 carbon atoms.

9. The method for preparing low-lead antimony trioxide as described in claim 8, characterized in that, R1, R2, and R3 are the same.

10. The method for preparing low-lead antimony trioxide as described in claim 9, characterized in that, The long-chain organic amine is selected from at least one of tri-octylamine, tri-nonylamine, tri-decylamine, tri-undecylamine, and tri-dodecylamine.

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