Method for synchronously preparing metastannic acid through ultrasonic enhancement and hydrolysis of low-concentration nitric acid

Abstract

The invention relates to a method for synchronously preparing metastannic acid through ultrasonic enhancement and hydrolysis of low-concentration nitric acid, and belongs to the technical field of metastannic acid preparation. The preparation method comprises the following steps: slowly adding high-purity tin sheets into a dilute nitric acid solution in batches under the stirring condition at the temperature of 35-60 DEG C, and uniformly mixing to obtain a mixed system; and at the temperature of 35-60 DEG C, ultrasonic waves are applied to the mixed system for an ultrasonic enhanced oxidation dissolution-hydrolysis reaction for 30-50 min, so that tin sheets are oxidized and dissolved and are synchronously hydrated to generate metastannic acid precipitates, solid-liquid separation is carried out, solids are sequentially washed and dried, and a high-purity metastannic acid product is obtained. A passivation layer on the surface of the tin sheet is destroyed by utilizing the mechanical effect of ultrasound, and mass transfer is accelerated; the ultrasonic cavitation effect is used for promoting particle refinement and gel network depolymerization, and tin ion hydrolysis is promoted. The method is carried out at normal pressure, low acidity and low temperature, no nitrogen oxide brown smoke is generated in the whole reaction process, the metastannic acid yield is larger than or equal to 95%, and the method has the advantages of being mild in reaction, environmentally friendly, high in efficiency and good in product purity.

Description

Technical Field

[0001] This invention relates to a method for the simultaneous preparation of metastannic acid by ultrasonic-enhanced low-concentration nitric acid-hydrolysis, belonging to the field of metastannic acid preparation technology. Background Technology

[0002] Stannic acid (SnO2·nH2O) is an important precursor for the preparation of tin dioxide functional materials and is widely used in ceramics, catalysts, gas sensors and lithium-ion batteries. Currently, the main industrial method for preparing stannic acid is the concentrated nitric acid oxidation method, which uses nitric acid with a concentration >40wt.% to react with metallic tin. This process has significant drawbacks: (1) The reaction of high-concentration nitric acid is violently exothermic, producing a large amount of nitrogen oxides (NOx). x (1) Brown smoke, causing serious environmental pollution; (2) High concentration of nitric acid is highly corrosive, has high requirements for equipment materials, and has a high operational risk factor; (3) The generated stannic acid is easy to form a viscous gel, which wraps unreacted tin or intermediates, resulting in incomplete tin oxidation and dissolution and low stannic acid production; (4) The product contains a lot of acidic impurities, which requires increasing the amount of neutralizing agent and increasing the burden of wastewater treatment.

[0003] To overcome the above shortcomings, existing technologies have proposed several improvement schemes, but all have obvious limitations. For example, patent application number 200410100843.5 proposes a pressurized nitric acid method, using tin powder or tin flowers as raw materials, reacting under the conditions of 40wt% high-concentration nitric acid as the oxidant, a high-pressure closed system (reaction pressure 0.7–2.0 MPa), with air or oxygen introduced (oxygen partial pressure 0.7–1.2 MPa), at a temperature of 100–160°C, and for 4–8 hours. Although this method effectively reduces NO... x While direct emission is possible, the equipment is complex, requires significant investment, carries high operational risks, and is difficult to control under high temperature and pressure. Patent application number 202210308061.9 proposes an atmospheric pressure co-oxidation method that uses nitric acid and hydrogen peroxide for synergistic oxidation, avoiding NO emissions. x While it's possible to reduce NO emissions, it requires excessive addition of hydrogen peroxide (20-25%) and reaction control agents (nitrates / ammonium salts), resulting in high reagent costs and concentrated exothermic reactions, making process control complex. Patent application number 201810135124.9 proposes a sulfuric acid process, using sulfuric acid instead of nitric acid to avoid NO emissions. x However, the reaction produces hydrogen, which poses a significant safety risk. Therefore, developing a green process for preparing metastannic acid that requires no high-pressure equipment, no external oxidant, no nitrogen oxide emissions, has a mild reaction, and produces high-purity products has important industrial application value. Summary of the Invention

[0004] To address the problems of high pollution from existing concentrated nitric acid methods, complex equipment in high-pressure methods, and the need for external oxidants and control agents in co-oxidation methods, this invention proposes a method for the simultaneous preparation of metastannic acid from low-concentration nitric acid via ultrasonic-enhanced hydrolysis. This method achieves one-step preparation of metastannic acid through ultrasonic physical field enhancement, utilizing the mechanical effect of ultrasound to disrupt the passivation layer on the tin sheet surface and accelerate mass transfer; and utilizing the ultrasonic cavitation effect to promote particle refinement and gel network depolymerization, thus accelerating tin ion hydrolysis. This method is carried out under normal pressure, low acidity, and low temperature, with no nitrogen oxides or brown fumes generated during the entire reaction process. The metastannic acid yield is ≥95%, and it has the advantages of mild reaction, environmental friendliness, high efficiency, and good product purity.

[0005] A method for simultaneously preparing metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) Under the conditions of temperature 35~60℃ and stirring, high-purity tin sheets are slowly added to dilute nitric acid solution in batches and mixed evenly to obtain a mixed system; (2) At a temperature of 35~60℃, ultrasonic waves are applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 30~50 min so that the tin sheet is oxidized and dissolved and simultaneously hydrated to form metastannic acid precipitate. The solid and liquid are separated, and the solid is washed with ammonium bicarbonate solution, deionized water and dried in sequence to obtain high-purity metastannic acid product.

[0006] Preferably, in step (1), the concentration of the dilute nitric acid solution is 20~30 wt.%, and the solid-liquid ratio of the high-purity tin sheet to the dilute nitric acid solution is 1:4~6 g:mL.

[0007] Preferably, the high-purity tin sheet in step (1) has a length of 0.3~2cm, a width of 0.3~2cm, and a thickness of 0.5~1.0mm.

[0008] Preferably, the ultrasonic frequency in step (2) is 20~40kHz and the output power is 150~300W.

[0009] Preferably, the concentration of the ammonium bicarbonate solution in step (2) is 0.6~1.2 mol / L.

[0010] The preparation principle of stannic acid in this invention: By introducing ultrasound, not only is it used as a means of mass transfer enhancement, but also through its cavitation effect and mechanical effect, the following synergistic effects are achieved: (1) Destroying the surface passivation layer: The ultrasonic micro-jet continuously scours the surface of the tin sheet, thinning its surface passivation layer (e.g. Figure 1 This facilitates contact between fresh metal surfaces and nitric acid, thereby improving the dissolution efficiency under low-concentration nitric acid conditions (e.g., Figure 2 (2) Inhibition of gel encapsulation: The local high temperature and pressure and strong shear force generated by the cavitation effect can effectively break the formed stannic acid gel network, optimize the hydrolysis process, and refine and homogenize the stannic acid particles (see Figure 3This prevents the encapsulation of unreacted tin and increases the yield of metastannic acid; it also enables the preparation of metastannic acid under low acid (20-30wt.%), low temperature (35-60℃), and normal pressure conditions, with no nitrogen oxide brown fumes generated throughout the process.

[0011] Unlike existing technologies that rely on enhancing the chemical oxidation atmosphere (increasing acid concentration, oxygen partial pressure, or adding chemical oxidants), this invention provides a novel one-step method for preparing metastannic acid via the oxidation-hydrolysis of low-concentration nitric acid, enhanced by a physical field. This method addresses reaction kinetic limitations by strengthening the physical process, rather than by increasing the chemical oxidation potential. Electrochemical test results (see...) Figure 4 As shown in the figure, the corrosion potential under ultrasonic conditions is similar to that under conventional conditions, indicating that the thermodynamic driving force of the reaction has not changed, meaning that ultrasound does not create a stronger chemical oxidation atmosphere. However, the corrosion current density (Ig) obtained by Tafel extrapolation is significantly higher than that under conventional conditions. corr This dynamic parameter is significantly different; I corr It is the kinetic parameter of the reaction, I corr A higher value indicates a faster corrosion reaction rate. Corrosion current I under ultrasonic conditions. corr It is 0.05567 A·cm -2 This is far higher than the 0.04233 A·cm under normal conditions. -2 It has been clearly demonstrated that ultrasound greatly accelerates reaction kinetics through physical action, without relying on enhancing the intrinsic oxidizing capacity of the system.

[0012] The beneficial effects of this invention are: (1) The method of the present invention uses low-concentration nitric acid (20 wt.%~30 wt.%), the reaction is mild, and no nitrogen oxide brown smoke is generated throughout the process, which meets the requirements of clean production; (2) The present invention simultaneously enhances the oxidation, dissolution and hydrolysis process of tin sheet using ultrasound, achieving a tin oxide yield of over 95%; (3) The product of this invention has high purity (SnO2≥88.50%), making it suitable as a precursor for high-end functional materials; (4) The method of the present invention operates at normal pressure and low temperature, without the need for high pressure equipment, external oxidant or reaction control agent, and nitric acid can be recycled, resulting in low production cost. The method of the present invention has low equipment requirements, short process flow, safe operation, and is suitable for large-scale production. Attached Figure Description

[0013] Figure 1 The images show the microstructure (SEM) of the tin sheets in Example 1 and Comparative Example 1. Figure 2 This is a comparison chart of tin dissolution rate and metastannic acid yield between Example 1 and Comparative Example 1; Figure 3The images show the particle size distribution and microstructure (SEM) of the stannic acid products of Example 1 and Comparative Example 1. Figure 4 This is a comparison chart of the electrochemical test results between Example 1 and Comparative Example 1. Detailed Implementation

[0014] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0015] Example 1: A method for the simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) Under the conditions of 60℃ and 200rpm, 50g of high-purity tin sheet (0.4cm×0.4cm in size and 0.8mm in thickness) was slowly added to a 20wt.% dilute nitric acid solution in 3 batches and mixed evenly to obtain a mixed system; the solid-liquid ratio of high-purity tin sheet to dilute nitric acid solution was 1:4 g:mL. (2) At a temperature of 60℃, ultrasonic waves (frequency of 40 kHz and power of 300 W) were applied to the mixed system to perform an ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 50 min, so that the tin sheet was completely oxidized and dissolved and simultaneously hydrated to form metastannic acid precipitate. The solid and liquid were separated, and the metastannic acid precipitate (acid residue of 2.1 mmol / g) was washed successively with 1.0 mol / L ammonium bicarbonate solution, deionized water, and dried to obtain high-purity metastannic acid product. In this embodiment, the tin sheet dissolution rate is 100%, the stannic acid yield is 98.3%, the SnO2 content in the stannic acid product is 88.93%, the acid residue in the stannic acid product is reduced to 0.5 mmol / g, the particle size range is 0.1~55 μm, and the pH=5.6; which meets the requirements for stannic acid products.

[0016] Comparative Example 1: The difference between this comparative example and Example 1 is that there is no ultrasound. When the reaction in this comparative example was carried out for 50 min, a large number of unreacted tin sheets were observed to be tightly wrapped by a dense layer of white stannic acid gel, and the reaction almost stopped. The tin sheet dissolution rate was 92.1%, and the stannic acid yield was only 87.1%. Compared with this comparative example, Example 1 showed an increase of 7.9% in tin sheet dissolution rate and 11.2% in stannic acid yield. When the reaction time in this comparative example was extended to 60 min, about 5% of the tin sheets were still not completely reacted. The final yield of the stannic acid product was only 89.3%, the SnO2 content in the stannic acid product was 86.93%, the particle size range was 10~65 μm, and the acid residue in the stannic acid precipitate was 2.4 mmol / g. After washing with 1.0 mol / L ammonium bicarbonate solution, washing with deionized water, and drying, the product was obtained (acid residue 0.9 mmol / g, pH=4.7), which did not meet the requirements for stannic acid products. The microstructure (SEM) results of the tin wafers in Example 1 and the comparative example are shown in the figure. Figure 1 The introduction of ultrasound effectively reduces the passivation layer on the tin sheet surface; a comparison of tin dissolution rate and metastannic acid yield between Example 1 and this comparative example is shown in the figure. Figure 2 The continuous ultrasonic microfluidic jet scouring of the tin sheet surface facilitates contact between the fresh metal surface and nitric acid, thereby improving the dissolution efficiency under low-concentration nitric acid. The particle size distribution and microstructure (SEM) results of the stannic acid products in Example 1 and this comparative example are shown below. Figure 3 The introduction of ultrasound breaks down the formed stannic acid gel network, effectively refining and homogenizing the stannic acid particles; a comparison of the electrochemical test results between Example 1 and this comparative example is shown in the figure. Figure 4 The corrosion potential under ultrasonic and conventional conditions is similar, indicating that the thermodynamic driving force of the reaction has not changed, meaning that ultrasound does not create a stronger chemical oxidation atmosphere; however, the corrosion current I under ultrasonic conditions... corr It is 0.05567 A·cm -2 This is far higher than the 0.04233 A·cm under normal conditions. -2 Therefore, ultrasound greatly accelerates the reaction kinetics through physical action, without relying on improving the intrinsic oxidation capacity of the system.

[0017] Comparative Example 2: The difference between this comparative example and Example 1 is that the concentration of the nitric acid solution in step (1) is 40 wt.%. The reaction process generates reddish-brown gas (NO2), and the product after the reaction has a high content of acidic impurities. The tin sheet dissolution rate is 63.8%, and the yield of metastannic acid is only 57.8%. However, in Example 1, by reducing the mass fraction of nitric acid, no NO2 is generated, the tin sheet dissolution rate is increased by 36.2%, and the yield of metastannic acid is increased by 40.5%. The SnO2 content in the metastannic acid product is 88.21%, the particle size range is 22~70 μm, and the acid residue in the metastannic acid precipitate is 3.8 mmol / g. After washing with 1.0 mol / L ammonium bicarbonate solution, washing with deionized water, and drying, the product obtained (acid residue 1.6 mmol / g, pH=3.4) does not meet the requirements for metastannic acid products.

[0018] Example 2: A method for the simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) At a temperature of 55℃ and a stirring speed of 160rpm, 50g of high-purity tin sheet (0.4cm×0.4cm in size and 0.8mm in thickness) was slowly added to a 25wt.% dilute nitric acid solution in 4 batches and mixed evenly to obtain a mixed system; the solid-liquid ratio of high-purity tin sheet to dilute nitric acid solution was 1:5 g:mL. (2) At a temperature of 55℃, ultrasonic waves (frequency of 24kHz and power of 240W) were applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 35 minutes to completely oxidize and dissolve the tin sheet and simultaneously hydrate it to form metastannic acid precipitate. The solid and liquid were separated, and the metastannic acid precipitate (acid residue of 2.1mmol / g) was washed successively with 0.6mol / L ammonium bicarbonate solution, deionized water, and dried to obtain high-purity metastannic acid product. In this embodiment, the tin sheet dissolution rate was 100%, the stannic acid yield was 98.5%, the SnO2 content in the stannic acid product was 88.37%, the acid residue in the stannic acid product was reduced to 0.6 mmol / g, and the particle size distribution D 50 It has a particle size of 20 μm and a pH of 5.2; it meets the requirements for stannic acid products.

[0019] Example 3: A method for the simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) Under the conditions of temperature 35℃ and stirring speed 180rpm, 50g of high-purity tin sheet (size 0.4 cm×0.4cm, thickness 0.8 mm) was slowly added to a 30wt.% dilute nitric acid solution in 4 batches and mixed evenly to obtain a mixed system; the solid-liquid ratio of high-purity tin sheet to dilute nitric acid solution g:mL was 1:6. (2) At a temperature of 35℃, ultrasonic waves (frequency of 20kHz and power of 180W) were applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 30 minutes to completely oxidize and dissolve the tin sheet and simultaneously hydrate it to form metastannic acid precipitate. Solid-liquid separation was performed, and the metastannic acid precipitate (acid residue of 2.3mmol / g) was washed sequentially with 1.2mol / L ammonium bicarbonate solution, deionized water, and dried to obtain high-purity metastannic acid product. In this embodiment, the tin sheet dissolution rate was 100%, the stannic acid yield was 95.6%, the SnO2 content in the stannic acid product was 88.99%, the acid residue in the stannic acid product was reduced to 0.3 mmol / g, and the particle size distribution D 50 It has a particle size of 32 μm and a pH of 6.1; it meets the requirements for stannic acid products.

[0020] Example 4: A method for the simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) Under the conditions of temperature 40℃ and stirring speed 150rpm, 50g of high-purity tin sheet (size 0.4 cm×0.4cm, thickness 0.8 mm) was slowly added to a 25wt.% dilute nitric acid solution in 3 batches and mixed evenly to obtain a mixed system; the solid-liquid ratio of high-purity tin sheet to dilute nitric acid solution g:mL was 1:6. (2) At a temperature of 40℃, ultrasonic waves (frequency of 28kHz and power of 200W) were applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 40min so that the tin sheet was completely oxidized and dissolved and simultaneously hydrated to form metastannic acid precipitate. Solid-liquid separation was performed, and the metastannic acid precipitate (acid residue of 2.1mmol / g) was washed sequentially with 0.8mol / L ammonium bicarbonate solution, deionized water, and dried to obtain high-purity metastannic acid product. In this embodiment, the tin sheet dissolution rate was 99.8%, the metastannic acid yield was 96.3%, the SnO2 content in the metastannic acid product was 88.78%, the acid residue in the metastannic acid product was reduced to 0.6 mmol / g, and the particle size distribution D 50 It has a particle size of 12 μm and a pH of 5.3; it meets the requirements for stannic acid products.

[0021] Example 5: A method for the simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis, the specific steps of which are as follows: (1) At a temperature of 45℃ and a stirring speed of 170rpm, 50g of high-purity tin sheet (0.4cm×0.4cm in size and 0.8mm in thickness) was slowly added to a 28wt.% dilute nitric acid solution in 3 batches and mixed evenly to obtain a mixed system; the solid-liquid ratio of high-purity tin sheet to dilute nitric acid solution was 1:6 g:mL. (2) At a temperature of 45℃, ultrasonic waves (frequency of 32kHz and power of 240W) were applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 25min so that the tin sheet was completely oxidized and dissolved and simultaneously hydrated to form metastannic acid precipitate. Solid-liquid separation was performed, and the metastannic acid precipitate (acid residue of 2.2mmol / g) was washed sequentially with 1.1mol / L ammonium bicarbonate solution, deionized water, and dried to obtain high-purity metastannic acid product. In this embodiment, the tin sheet dissolution rate was 99.1%, the metastannic acid yield was 96.2%, the SnO2 content in the metastannic acid product was 88.67%, the acid residue in the metastannic acid product was reduced to 0.7 mmol / g, and the particle size distribution D 50 It has a particle size of 21 μm and a pH of 5.1; it meets the requirements for stannic acid products.

[0022] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for simultaneously preparing metastannic acid by ultrasonic enhancement of low-concentration nitric acid-hydrolysis, characterized in that, The specific steps are as follows: (1) Under the conditions of temperature 35~60℃ and stirring, high-purity tin sheets are slowly added to dilute nitric acid solution in batches and mixed evenly to obtain a mixed system; (2) At a temperature of 35~60℃, ultrasonic waves are applied to the mixed system to perform ultrasonic-enhanced oxidation-dissolution-hydrolysis reaction for 30~50 min so that the tin sheet is oxidized and dissolved and simultaneously hydrated to form metastannic acid precipitate. The solid and liquid are separated, and the solid is washed with ammonium bicarbonate solution, deionized water and dried in sequence to obtain high-purity metastannic acid product.

2. The method for simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis according to claim 1, characterized in that: Step (1) The concentration of the dilute nitric acid solution is 20~30 wt.%, and the solid-liquid ratio of the high-purity tin sheet to the dilute nitric acid solution is 1:4~6 g:mL.

3. The method for simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis according to claim 1, characterized in that: Step (1) The length of the high-purity tin sheet is 0.3~2cm, the width is 0.3~2cm, and the thickness is 0.5~1.0mm.

4. The method for simultaneous preparation of metastannic acid by ultrasonic enhancement of low-concentration nitric acid-hydrolysis according to claim 1, characterized in that: Step (2) The ultrasonic frequency is 20~40kHz and the output power is 150~300W.

5. The method for simultaneous preparation of metastannic acid by ultrasound-enhanced low-concentration nitric acid-hydrolysis according to claim 1, characterized in that: Step (2) The concentration of ammonium bicarbonate solution is 0.6~1.2 mol / L.

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