A nano-amorphous silicon concentration dispersion liquid using potassium feldspar as raw material and a preparation method thereof

Abstract

The application discloses a kind of nanometer amorphous silicon concentration dispersion liquid with potassium feldspar as raw material and a preparation method thereof, and relates to the technical field of inorganic non-metallic material preparation.Nanometer amorphous silicon concentration dispersion liquid is prepared with potassium feldspar as raw material, and the preparation method includes pretreatment, catalytic thermal decomposition, second-stage quenching and ultrasonic hydration-concentration steps;The nanometer amorphous silicon concentration dispersion liquid with potassium feldspar as raw material and the preparation method thereof are prepared by catalytic thermal decomposition-second-stage quenching-ultrasonic hydration synergistic process, and the nanometer amorphous silicon concentration dispersion liquid with total silicon content of 80-110 g / L is obtained, the particle size is 5-50 nm, the amorphous state accounts for ≥90%, and the Zeta potential is-30--50 mV;After the dispersion liquid is sealed and light-proof at 25°C for 60 days, the silicon content retention rate is ≥94.5%, and the particle size change is only +2 nm;After the powder is dried and then added with water and ultrasonically treated for 10 minutes, it can be restored to uniform dispersion, and the recovery rate is ≥95%.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic material preparation technology, specifically to a nano-amorphous silicon concentrated dispersion using potassium feldspar as raw material and its preparation method. Background Technology

[0002] Silicon, existing in the form of soluble silicon or nano-silica, possesses unique bioactivity and shows broad application prospects in various fields such as food fortification, skin barrier repair, crop stress resistance and yield enhancement, and pharmaceutical active carriers. Among these, high-loading, high-stability, and small-particle-size nano-amorphous silicon concentrated dispersions have become a core research hotspot in related fields. Currently, the mainstream preparation processes for nano-silica in the industry include the gas phase method, precipitation method, and sol-gel method. The gas phase method uses silicon tetrachloride or organosilanes as raw materials and obtains the product through high-temperature hydrolysis, which has the disadvantages of high raw material costs and strong corrosivity, and the produced products are difficult to meet the safety requirements of food and cosmetic grades. The conventional precipitation method uses sodium silicate as raw material and prepares silicon dioxide through acid neutralization precipitation. The resulting products generally have large particle sizes (usually exceeding 100 nm), low specific surface areas, and insufficient amorphous purity. The loading of the accompanying dispersion is generally less than 30 g / L, and sedimentation and stratification are prone to occur during long-term storage.

[0003] Potassium feldspar, a natural mineral, is abundant in my country and has low mining costs, making it a highly promising silicon source. However, its highly stable crystal structure and high content of impurities such as aluminum, iron, and titanium make purification difficult. Existing purification processes for potassium feldspar mostly employ a combination of alkali fusion, acid leaching, and ion exchange. While this can yield a high-purity silica matrix, the product has extremely low reactivity, making it difficult to further convert into a high-loading, highly stable nanocrystalline amorphous silica dispersion that meets the requirements. Furthermore, there is a long-standing technical bias in this field: it is generally believed that metal oxides can only serve as auxiliary components to lower the reaction temperature of carbothermic reduction and cannot directly catalyze the thermal decomposition of silica. Conventional carbothermic reduction processes inevitably introduce carbonaceous impurities and are accompanied by large amounts of carbon dioxide emissions, which neither meets green manufacturing requirements nor produces products suitable for high-end applications such as food and cosmetics.

[0004] The core technological challenges currently facing this field are concentrated in five dimensions: First, conventional processes for preparing nano-silicon dispersions rely on carbonaceous reducing agents to achieve the decomposition and conversion of silica, inevitably introducing carbon impurities and resulting in excessive carbon content in the product, failing to meet the stringent safety requirements for food and cosmetic products; second, existing purification processes using potassium feldspar as raw material yield silica matrices with extremely low activity, making them unsuitable for direct use in efficient thermal decomposition reactions, resulting in consistently low raw material utilization; third, conventional silica thermal decomposition reactions require temperatures exceeding 1800℃, leading to extremely high energy consumption. Furthermore, the decomposition efficiency is less than 1%, making it completely unsuitable for industrial application. The industry has consistently lacked efficient catalytic solutions that can lower the reaction temperature to the 1200-1600℃ range. Fourth, the loading of nano-silicon dispersions produced by existing processes is generally below 30 g / L, resulting in poor long-term storage stability and a high tendency to settle and stratify, making high-concentration concentration and long-term stable storage impossible. Fifth, traditional carbothermic reduction processes produce 2-3 tons of carbon dioxide emissions per ton of product, which does not meet the current requirements for green and low-carbon industrial development. The industry has consistently lacked green preparation routes with low emissions and low energy consumption. Therefore, there is an urgent need to propose a nano-amorphous silicon concentration dispersion using potassium feldspar as a raw material and its preparation method to solve the problems of low silica activity, difficulty in thermal decomposition, easy crystallization of products, and low and unstable dispersion loading in nano-amorphous silicon concentration dispersions produced by existing methods. Summary of the Invention

[0005] The purpose of this invention is to provide a nano-amorphous silicon concentrate dispersion using potassium feldspar as raw material and its preparation method, in order to solve the problems of low silica activity, difficulty in thermal decomposition, easy crystallization of products, low and unstable dispersion loading in nano-amorphous silicon concentrate dispersions produced by existing methods.

[0006] To clarify the scope of protection of this invention, the following terms are defined:

[0007] Catalytic thermal decomposition refers to the process in which, without carbonaceous reducing agents, the surface oxygen vacancies provided by the CuO-MnO2-La2O3 catalyst lower the activation energy for Si-O bond breaking, allowing SiO2 to directly sublimate into gaseous SiO2. x This process differs fundamentally from carbothermic reduction (SiO2 + C → SiO + CO): the catalyst does not participate in the stoichiometric reaction, does not introduce carbon impurities, and the reaction product is SiO2. x And O2, not CO or CO2.

[0008] The three-step synergistic process refers to a technical system in which catalytic thermal decomposition, second-level rapid cooling, and ultrasonic hydration are indispensable and their order cannot be changed. Among these steps, catalytic thermal decomposition produces the metastable precursor SiO₂. xThe powder is "frozen" into amorphous nanoparticles by rapid cooling in seconds, and ultrasonic hydration utilizes the powder's high surface energy to achieve stable dispersion with high loading capacity. These three elements are interdependent and constitute an organically synergistic overall technical solution.

[0009] Highly active SiO2 matrix: refers to SiO2 powder obtained by pretreatment in step S1 of this invention that meets the following indicators: SiO2 content ≥ 99.5%, total alkali metal content ≤ 10 ppm, carbon ≤ 1 ppm, and total impurity elements other than SiO2, alkali metals and carbon ≤ 50 ppm (of which Al ≤ 15 ppm, Fe ≤ 10 ppm, Ti ≤ 8 ppm, Ca ≤ 5 ppm, Mg ≤ 5 ppm), as determined by ICP-MS.

[0010] Preferably, the surface oxygen vacancy concentration of the highly active SiO2 matrix is ​​1.0 × 10¹ 8 ~5.0×10¹ 8 pcs / cm³ (measured by EPR, instrument model: Bruker EMXplus, test conditions: microwave frequency 9.85GHz, power 2 mW, modulation amplitude 0.5 mT, temperature 77 K).

[0011] Non-equilibrium conditions: refers to the continuous purging of the reaction zone with an inert carrier gas, causing the gaseous product SiO2 to... x The inert carrier gas is rapidly removed, thereby disrupting the thermodynamic equilibrium and achieving the kinetic conditions for continuous decomposition. The inert carrier gas is continuously purged from the reaction zone at a flow rate of 2–100 L / min (adjusted according to reactor size), removing the gaseous product SiO₂. x Rapid removal from the reaction zone. Based on FactSage 8.0 thermodynamic calculations, at 1500℃ and a total pressure of 1 atm, when the partial pressure of SiO in the reaction zone is maintained at 10... -4 ~10 -5 At atm, the apparent Gibbs free energy ΔG of the reaction can be reduced to a negative value, satisfying the thermodynamic spontaneous condition. This partial pressure range is achieved by matching the carrier gas flow rate with the reactor size, and represents the preferred parameter range for the non-equilibrium conditions of this invention.

[0012] Quantitative indicators of nonequilibrium conditions: The "reduction of apparent Gibbs free energy ΔG to a negative value" described in this invention, under conditions of 1200–1600 °C and a total pressure of 1 atm, corresponds to a SiO partial pressure ≤10 in the reaction zone. -3 atm; preferably, the partial pressure of SiO2 is controlled at 10 by an inert carrier gas flow rate of 2-100 L / min. -4 ~10 -5 Within the atm range, ΔG is -8 to -52 kJ / mol.

[0013] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material, comprising the following steps:

[0014] S1. Pretreatment: Using potassium feldspar as raw material, a highly active SiO2 matrix is ​​obtained through alkali melting, leaching, precipitation, drying, calcination, acid leaching, and ion exchange.

[0015] S2. Catalytic thermal decomposition: Under inert gas protection, the highly active SiO2 matrix obtained in S1 is supplemented with a catalyst at a total addition amount of 1.0–1.5 wt%. The catalyst is composed of CuO, MnO2, and La2O3, with a mass ratio of (2.5–3.5):(1.5–2.5):(0.8–1.2). The catalytic thermal decomposition reaction is carried out in a reactor using a three-stage gradient heating to 1200–1600℃ and holding at that temperature for 0.5–1.5 hours, causing SiO2 to thermally decompose into gaseous SiO2. x , where x = 1.5 to 2.0;

[0016] The decomposition is a direct thermal decomposition of the catalyst mediated by surface oxygen vacancies, without the addition of any carbonaceous reducing agent. The catalytic thermal decomposition is carried out under non-equilibrium conditions: the reaction zone is continuously purged with an inert carrier gas at a flow rate of 2–100 L / min to maintain the SiO2 partial pressure in the reaction zone at 10. -4 ~10 -5 Based on FactSage 8.0 thermodynamic calculations, at 1200–1600 °C and a total pressure of 1 atm, the apparent Gibbs free energy ΔG of the reaction drops to a negative value, thus achieving continuous decomposition;

[0017] S3, Second-level rapid cooling: Gas jet rapid cooling is adopted, and high-pressure inert gas is injected through a supersonic nozzle to cool the gaseous SiO2 obtained in S2. x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to ≤100℃ within ≤2 seconds at a cooling rate of 500~2000℃ / s.

[0018] S4. Ultrasonic hydration-concentration: The nano-amorphous SiO2 powder obtained in S3 is mixed with deionized water, ultrasonically treated, filtered, and concentrated under reduced pressure until the solid content reaches the target value, resulting in a nano-amorphous silicon concentrated dispersion with a total silicon content of 80-110 g / L (calculated as SiO2), and the pH is adjusted to 10.5.

[0019] The catalytic thermal decomposition of S2, the second-level rapid cooling of S3, and the ultrasonic hydration-concentration of S4 are carried out sequentially and continuously, and the carrier gas flow rate of S2 and the rapid cooling gas flow rate of S3 are independently controlled.

[0020] Further, the pretreatment steps of S1 are as follows: First, potassium feldspar is crushed and ground to D50≤25μm, mixed with NaOH at a mass ratio of 1:2.5, and calcined at 750℃ for 3 hours to obtain clinker. Then, the clinker is mixed with deionized water at a ratio of 1:4 and leached at 80℃ for 2 hours. After leaching, CO2 is introduced to adjust the pH to 9.0, and precipitation is carried out at 30℃ for 4 hours. After precipitation, it is dried at 110℃ for 6 hours and calcined at 500℃ for 2 hours. Then, it is mixed with 10% hydrochloric acid at a ratio of 1:5 and leached at 80℃ for 4 hours. After centrifugation and washing, it is neutralized. After acid leaching, it is mixed with deionized water at a ratio of 1:8, 8% strong acid cation exchange resin is added, and it is treated at 30℃ for 3 hours to obtain a highly active SiO2 matrix.

[0021] Furthermore, the S1 pretreatment can also be performed using a one-step alkali fusion-hydrothermal method, with the following steps: potassium feldspar and NaOH are mixed at a mass ratio of 1:2.5 and hydrothermally reacted at 250°C and saturated vapor pressure for 6 hours to obtain a highly active SiO2 matrix.

[0022] Furthermore, the mass ratio of CuO, MnO2, and La2O3 in the catalyst of S2 is (2.8–3.2):(1.8–2.2):(0.9–1.1).

[0023] Furthermore, the mass ratio of CuO, MnO2, and La2O3 in the catalyst of S2 is 3:2:1.

[0024] Furthermore, the inert carrier gas in S2 is Ar or N2 with a purity ≥99.99%, and the flow rate is adjusted according to the reactor scale. The flow rate is 2-5 L / min in laboratory scale and 20-100 L / min in industrial scale.

[0025] Furthermore, the three-stage gradient heating parameters in S2 are as follows: the first stage heats up to 900℃ at a rate of 10-15℃ / min and holds for 0.5 hours; the second stage heats up to 1200℃ at a rate of 5-10℃ / min and holds for 0.5 hours; and the third stage heats up to 1500℃ at a rate of 3-5℃ / min and holds for 1 hour.

[0026] Furthermore, the reactor in S2 is a fluidized bed reactor with an apparent gas velocity of 0.2–0.5 m / s and a bed pressure drop of 3–8 kPa.

[0027] Furthermore, in S3, the gas jet quenching uses high-pressure inert gas, which is injected through a supersonic nozzle; the inert gas is Ar or N2, with a pressure of 0.5 to 2.0 MPa and a temperature of -50 to 20°C.

[0028] Furthermore, the ultrasonic treatment in S4 is carried out under N2 protection, with an ultrasonic frequency of 28-40 kHz, a power of 300-400 W, a temperature of 40-45°C, and a treatment time of 30-50 minutes.

[0029] Furthermore, the vacuum concentration in S4 is carried out at a temperature of 45–55°C and a vacuum degree of -0.085–-0.095 MPa.

[0030] Furthermore, the catalyst in S2 is recovered by magnetic separation after use. The recovered catalyst is regenerated by calcination at 400-600℃ and then recycled. The number of recycling cycles is 3-5 times, and 10%-20% of fresh catalyst is added each time.

[0031] This invention also discloses a nano-amorphous silicon concentrate dispersion using potassium feldspar as raw material, which is prepared by the above method. The total silicon content of the nano-amorphous silicon concentrate dispersion is 80-110 g / L (based on SiO2), the nano-SiO2 particle size is 5-50 nm, the amorphous content is ≥90%, the Zeta potential is -30 to -50 mV, and the carbon content is ≤1 ppm.

[0032] Furthermore, after the dispersion is left to stand for 60 days at 25°C in a sealed, light-protected environment, the silicon content retention rate is ≥94.5%.

[0033] Furthermore, after the dispersion is freeze-dried or dried at 60°C for 24 hours, a free-flowing white nanoparticle powder with a loose density of 50-150 g / L and an angle of repose of ≤45° is obtained. After the powder is re-added with deionized water and ultrasonically treated for 10 minutes, it can be restored to a uniform dispersion with a silicon content recovery rate of ≥95%.

[0034] Furthermore, the dispersion is applied in the fields of food fortification, cosmetic repair, agricultural stress resistance and yield increase, or pharmaceutical carrier.

[0035] Compared with the prior art, the present invention provides a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, which has the following beneficial effects:

[0036] (1) This invention uses a synergistic process of “catalytic thermal decomposition-second-level rapid cooling-ultrasonic hydration” to prepare a concentrated dispersion of nano-amorphous silicon with a total silicon content of 80-110 g / L, a particle size of 5-50 nm, an amorphous content of ≥90%, and a Zeta potential of -30 to -50 mV. After the dispersion is sealed and protected from light at 25°C for 60 days, the silicon content retention rate is ≥94.5%, and the particle size change is only +2 nm. After drying, the powder can be restored to uniform dispersion by adding water and sonicating for 10 minutes, with a recovery rate of ≥95%. In contrast, the loading of commercially available gas phase / sol-gel products after dispersion is usually only 30 g / L, and the particle size change after 60 days is +8 to +35 nm. This shows that this invention overcomes the technical bias of easy agglomeration of high-concentration nano-silica sol and achieves the synergy of high loading and ultra-long stability.

[0037] (2) This invention abandons carbonaceous reducing agents and uses a CuO-MnO2-La2O3 ternary catalyst to achieve direct thermal decomposition of SiO2 mediated by surface oxygen vacancies. The carbon content of the product is ≤1 ppm, which is two orders of magnitude lower than that of the carbothermic reduction method (>500 ppm), and it is free of chlorine, heavy metals and sodium ion stabilizers, which can directly meet the requirements of food / cosmetic grade; the reaction product is only SiO2. x It produces only O2 and no CO2, with a carbon footprint of only 0.12 kg CO2 / kg of product, which is 95.7% lower than the carbothermal reduction method (2.8 kg). It complies with green manufacturing and international environmental regulations, achieving simultaneous gains in product purity and zero carbon emission reduction.

[0038] (3) The catalyst of this invention, after wet magnetic separation (single-cycle recovery rate of 92% to 95%) and calcination at 400-600℃, showed no significant change in XRD crystal phase after 5 cycles of use. The SiO2 conversion rate only slightly decreased from 12.8% to 11.6%, and the activity recovery rate was ≥90%. The conversion rate could be maintained by adding 10% to 20% of fresh catalyst, which effectively solved the problem of catalyst sintering and deactivation and reduced the application cost. At the same time, the process adopts standardized equipment such as fluidized bed and supersonic gas jet quenching, and has been scaled up from 100g level to 10kg level with performance index differences ≤±5%, proving that the industrialization is reproducible. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0040] Figure 1 A flowchart illustrating a method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as a raw material, provided in an embodiment of the present invention;

[0041] Figure 2 A bar chart comparing the three-step synergistic effects provided in this embodiment of the invention;

[0042] Figure 3 XRD comparison images of crystalline and amorphous states provided in embodiments of the present invention;

[0043] Figure 4 This is a schematic diagram of the gas jet quenching device provided in an embodiment of the present invention;

[0044] Figure 5 This is a TG-MS verification comparison chart provided in an embodiment of the present invention;

[0045] Figure 6 A comprehensive characterization diagram of the catalyst and matrix provided in the embodiments of the present invention;

[0046] Figure 7 Comparison diagrams for process scale-up verification provided in embodiments of the present invention;

[0047] Figure 8 A radar chart comparing commercially available products provided for embodiments of the present invention;

[0048] Figure 9 The non-equilibrium condition verification data diagram (carrier gas flow rate-conversion rate-ΔG relationship curve) provided for the embodiments of the present invention. Detailed Implementation

[0049] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0050] Example 1:

[0051] Please see Figure 1-9 A concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, comprising the following steps:

[0052] S1. Pretreatment: Using potassium feldspar as raw material, a highly active SiO2 matrix is ​​obtained through alkali melting, leaching, precipitation, drying, calcination, acid leaching, and ion exchange.

[0053] The specific implementation method is to crush and grind potassium feldspar to D. 50=25μm, mixed with NaOH at a mass ratio of 1:2.5, and calcined at 750℃ for 3 hours to obtain clinker. Then, the clinker was mixed with deionized water at a ratio of 1:4 and leached at 80℃ for 2 hours. After leaching, CO2 was bubbled in to adjust the pH to 9.0, and precipitation was carried out at 30℃ for 4 hours. After precipitation, it was dried at 110℃ for 6 hours and calcined at 500℃ for 2 hours. Then, it was mixed with 10% hydrochloric acid at a ratio of 1:5 and leached at 80℃ for 4 hours, and centrifuged and washed until neutral. After acid leaching, it was mixed with deionized water at a ratio of 1:8, and 8% strong acid cation exchange resin was added. It was treated at 30℃ for 3 hours to obtain a highly active SiO2 matrix.

[0054] Acidic cation exchange resins include 001×7 type (732 type) strong acid styrene-based cation exchange resin, and food-grade 001×7FG or D001FD type macroporous strong acid cation exchange resin.

[0055] ICP-MS analysis: The pretreated highly reactive SiO2 matrix was analyzed by ICP-MS. The results are as follows: SiO2 content 99.6%, total alkali metals 8 ppm, Al 12 ppm, Fe 8 ppm, Ti 6 ppm, Ca 4 ppm, Mg 3 ppm, carbon <1 ppm. EPR analysis of surface oxygen vacancy concentration: 2.8 × 10⁻⁶ 18 pcs / cm 3 .

[0056] S2. Catalytic Thermal Decomposition: Under inert gas protection, the highly active SiO2 matrix obtained in S1 is supplemented with a catalyst of 1.0–1.5 wt%. The catalyst consists of CuO, MnO2, and La2O3 in a mass ratio of (2.5–3.5):(1.5–2.5):(0.8–1.2). The catalytic thermal decomposition reaction is carried out in a reactor using a three-stage temperature gradient to 1200–1600 °C, held for 0.5–1.5 hours, to thermally decompose SiO2 into gaseous SiO2. x , where x = 1.5 to 2.0;

[0057] The specific implementation method is as follows: 100g of highly active SiO2 matrix is ​​placed in a fluidized bed reactor, then high-purity Ar (purity ≥99.99%, flow rate 2 L / min) is introduced, followed by the addition of 1.2 wt% CuO-MnO2-La2O3 catalyst (mass ratio 3:2:1). Finally, a catalytic thermal decomposition reaction is carried out in the reactor to thermally decompose SiO2 into gaseous SiO2. x .

[0058] The apparent gas velocity of the fluidized bed reactor is 0.3 m / s, and the bed pressure drop is 5 kPa.

[0059] The three-stage gradient heating parameters are: 10℃ / min to 900℃, hold for 0.5h; 5℃ / min to 1200℃, hold for 0.5h; 3℃ / min to 1500℃, hold for 1h.

[0060] The catalyst decomposes into a direct thermal decomposition mediated by surface oxygen vacancies, without the addition of any carbonaceous reducing agent; such as Figure 9 As shown, the catalytic thermal decomposition was carried out under non-equilibrium conditions: the reaction zone was continuously purged with an inert carrier gas at a flow rate of 2–100 L / min to maintain the SiO2 partial pressure in the reaction zone at 10. -4 ~10 -5 Based on FactSage 8.0 thermodynamic calculations, at 1200–1600 °C and a total pressure of 1 atm, the apparent Gibbs free energy ΔG of the reaction drops to a negative value, thus achieving continuous decomposition.

[0061] TG-MS detection: The above gaseous SiO x TG-MS analysis was performed, and the results are as follows: mass loss 8.7%, peak height 0.32 nA at m / z=44, peak height 0.28 nA at m / z=32, SiO₂ + / O2 peak area ratio 1:0.95 (x≈1.7).

[0062] S3, Second-level rapid cooling: Gas jet rapid cooling is adopted, and high-pressure inert gas is injected through a supersonic nozzle to cool the gaseous SiO2 obtained in S2. x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to ≤100℃ within ≤2 seconds at a cooling rate of 500~2000℃ / s.

[0063] The specific implementation method is as follows: Figure 4 As shown, gas jet quenching is employed, with gas being injected through a supersonic nozzle under high pressure Ar (1.0 MPa, 20°C) to dissipate the gaseous SiO2 obtained from S2. x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to 60°C within 0.8 s at a cooling rate of 1500°C / s.

[0064] The obtained powder was tested, and the results are as follows: the particle size of the obtained powder is 22 nm (TEM), and the specific surface area is 320 m². 2 / g (BET), hydroxyl density 5.2 ions / nm 2 (FTIR), amorphous state accounts for 94.2% (XRD).

[0065] S4. Ultrasonic hydration-concentration: The nano-amorphous SiO2 powder obtained in S3 is mixed with deionized water, ultrasonically treated, filtered, and concentrated under reduced pressure until the solid content reaches the target value, resulting in a nano-amorphous silicon concentrated dispersion with a total silicon content of 80-110 g / L (calculated as SiO2), and the pH is adjusted to 10.5.

[0066] The specific implementation method is as follows: the nano-amorphous SiO2 powder obtained in S3 is mixed with deionized water at a ratio of 1:10, and then subjected to ultrasonic treatment, filtration, and vacuum concentration until the total silicon content is 105 g / L (calculated as SiO2) to obtain a nano-amorphous silicon concentrated dispersion.

[0067] The ultrasonic treatment was conducted at a frequency of 35 kHz, a power of 350 W, a temperature of 42℃, under nitrogen protection, for 40 min. A 0.22 μm filter membrane was used for filtration. The concentration was performed under reduced pressure at 45℃ and -0.09 MPa. The pH was adjusted to 10.5 using 0.1 M NaOH titration.

[0068] Properties of the concentrated dispersion of nano-amorphous silicon: total silicon content 105 g / L, nano-SiO2 particle size 22 nm, amorphous content 94.2%, Zeta potential -42 mV, carbon content <1 ppm. After being sealed and protected from light at 25℃ for 60 days, the silicon content retention rate was 97.5%, and no visible precipitation was observed.

[0069] The catalytic thermal decomposition of S2, the second-level rapid cooling of S3, and the ultrasonic hydration-concentration of S4 are carried out sequentially, forming an inseparable three-step synergistic process.

[0070] Example 2:

[0071] This embodiment provides a technical solution based on Embodiment 1: a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, comprising the following steps:

[0072] S1. Pre-treatment is the same as in Example 1.

[0073] S2. Catalytic Thermal Decomposition: 1 kg of highly active SiO2 matrix is ​​placed in a fluidized bed reactor (apparent gas velocity 0.3 m / s, bed pressure drop 5 kPa), then high-purity N2 (purity ≥99.99%, flow rate 15 L / min) is introduced, followed by the addition of 1.2 wt% CuO-MnO2-La2O3 catalyst (mass ratio 3:2:1). Finally, a catalytic thermal decomposition reaction is carried out in the reactor, causing SiO2 to thermally decompose into gaseous SiO2. x .

[0074] The three-stage gradient heating is the same as in Example 1, with a target temperature of 1500℃ and a holding time of 1 hour.

[0075] TG-MS analysis: mass loss 12.3%, peak height 0.48 nA at m / z=44 (50% improvement over fixed bed). Conversion rate 12.3%.

[0076] S3, Second-level rapid cooling: Gas jet rapid cooling is employed, using a supersonic nozzle to inject gaseous SiO2 obtained in S2 under high pressure Ar (pressure 1.0 MPa, temperature 20℃). x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to 60°C within 0.8 s at a cooling rate of 1500°C / s.

[0077] The resulting powder has a particle size of 20 nm, a specific surface area of ​​350 m² / g, a hydroxyl density of 5.5 hydroxyl groups / nm², and an amorphous content of 93.8%.

[0078] S4, Ultrasonic hydration-concentration: Same as in Example 1. Concentrate to a total silicon content of 102 g / L.

[0079] Product performance: Total silicon content 102 g / L, nano-SiO2 particle size 20 nm, amorphous state 93.8%, Zeta potential -45 mV, carbon content <1 ppm. 60-day retention rate 97.2%.

[0080] Example 3:

[0081] This embodiment provides a technical solution based on Embodiments 1 and 2: a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, comprising the following steps:

[0082] S1. Pretreatment: Potassium feldspar and NaOH are mixed at a mass ratio of 1:2.5 and placed in a high-pressure reactor. The mixture is then subjected to hydrothermal reaction at 250°C and saturated vapor pressure for 6 hours to directly obtain a highly active sodium silicate solution. After acidification precipitation, washing, and drying, a highly active SiO2 matrix is ​​obtained.

[0083] ICP-MS analysis: SiO2 content 99.5%, total impurities <50 ppm.

[0084] Steps S2-S4 are the same as in Example 2.

[0085] The properties of the obtained nano-amorphous silicon concentrated dispersion are as follows: total silicon content 103 g / L, nano-SiO2 particle size 21 nm, amorphous content 94.0%, Zeta potential -43 mV, carbon content <1 ppm. 60-day retention rate 97.0%.

[0086] Compared with Example 2, the advantage of using the one-step alkali fusion-hydrothermal method in the pretreatment step is that it reduces the traditional multi-step wet process from 7 steps to 1 step, shortens the operation time from 24 hours to 6 hours, and reduces energy consumption by 35%, making it more suitable for industrial promotion.

[0087] Example 4:

[0088] This embodiment provides a technical solution based on Embodiment 1: a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, comprising the following steps:

[0089] S1. Pre-treatment is the same as in Example 1.

[0090] S2. Catalytic thermal decomposition is the same as in Example 1, but a fixed-bed tubular furnace reactor is used (instead of a fluidized bed reactor).

[0091] S3, Second-level rapid cooling: Liquid nitrogen spray rapid cooling is adopted. Liquid nitrogen (-196℃) is sprayed through atomizing nozzles, with a cooling rate of 5000℃ / s, a rapid cooling time of 0.3s, and a final temperature of -50℃.

[0092] The obtained nano-amorphous SiO2 powder has a particle size of 15 nm, a specific surface area of ​​380 m² / g, a hydroxyl density of 5.8 hydroxyl groups / nm², and an amorphous content of 95.1%.

[0093] S4, Ultrasonic hydration-concentration: Same as in Example 1. Concentrate to a total silicon content of 108 g / L.

[0094] The properties of the obtained nano-amorphous silicon concentrated dispersion are as follows: total silicon content 108 g / L, nano-SiO2 particle size 15 nm, amorphous content 95.1%, Zeta potential -48 mV, and 60-day retention rate 98.1%. Liquid nitrogen is relatively expensive, making it suitable for high value-added products.

[0095] Example 5:

[0096] This embodiment provides a technical solution based on Embodiment 2:

[0097] The catalyst recycling was validated using a fluidized bed reactor.

[0098] A1. Pretreatment: Crushing and grinding potassium feldspar to D... 50 =25μm, mixed with NaOH at a mass ratio of 1:2.5, and calcined at 750℃ for 3 hours to obtain clinker. Then, the clinker was mixed with deionized water at a ratio of 1:4 and leached at 80℃ for 2 hours. After leaching, CO2 was bubbled in to adjust the pH to 9.0, and precipitation was carried out at 30℃ for 4 hours. After precipitation, it was dried at 110℃ for 6 hours and calcined at 500℃ for 2 hours. Then, it was mixed with 10% hydrochloric acid at a ratio of 1:5 and leached at 80℃ for 4 hours, and centrifuged and washed until neutral. After acid leaching, it was mixed with deionized water at a ratio of 1:8, and 8% strong acid cation exchange resin was added. It was treated at 30℃ for 3 hours to obtain a highly active SiO2 matrix.

[0099] A2. Catalytic Thermal Decomposition: 1 kg of highly active SiO2 matrix is ​​placed in a fluidized bed reactor (apparent gas velocity 0.3 m / s, bed pressure drop 5 kPa), then high-purity N2 (purity ≥99.99%, flow rate 15 L / min) is introduced, followed by the addition of 1.2 wt% CuO-MnO2-La2O3 catalyst (mass ratio 3:2:1). Finally, a catalytic thermal decomposition reaction is carried out in the reactor, causing SiO2 to thermally decompose into gaseous SiO2. x This is recorded as the first iteration.

[0100] A3. Catalyst Recovery: After the reaction, the catalyst is separated from the clinker by wet magnetic separation (magnetic field strength 1.2 T), with a single recovery rate of 93%. The recovered catalyst is regenerated by calcining in air at 600℃ for 2 hours.

[0101] A4. Cycles 2-5: Each cycle replenishes 15% fresh catalyst, repeating the steps of Example 2. Cycle stability data: Cycle 1 (fresh) TG mass loss 12.3%, conversion rate 12.3%, catalyst crystal phase characteristic peaks clear; Cycle 2 11.8%, 11.8%, characteristic peaks clear; Cycle 3 11.5%, 11.5%, characteristic peaks clear; Cycle 4 11.2%, 11.2%, characteristic peaks slightly broadened; Cycle 5 11.0%, 11.0%, characteristic peaks slightly broadened. In the 5th cycle, the conversion rate decreased to 89.4% of the first cycle (11.0% / 12.3%), but still remained above 11%, indicating catalyst crystal phase stability. This demonstrates that the catalyst has good cycle stability and economy.

[0102] Example 6:

[0103] Please see Figure 7 This embodiment provides a technical solution based on Embodiment 3: a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method, comprising the following steps:

[0104] S1. Pretreatment: Same as in Example 3, using a one-step alkali fusion-hydrothermal method, scaled up to 10 kg of potassium feldspar raw material.

[0105] S2. Catalytic Thermal Decomposition: 10 kg of highly active SiO2 matrix was placed in a fluidized bed reactor (apparent gas velocity 0.35 m / s, bed pressure drop 6 kPa), then high-purity N2 (flow rate 80 L / min) was introduced, followed by the addition of 1.2 wt% CuO-MnO2-La2O3 catalyst (mass ratio 3:2:1). Finally, a catalytic thermal decomposition reaction was carried out in the reactor, causing SiO2 to thermally decompose into gaseous SiO2. x .

[0106] The three-stage gradient heating parameters are as follows: 10℃ / min to 900℃, hold for 0.5h; 5℃ / min to 1200℃, hold for 0.5h; 3℃ / min to 1500℃, hold for 1h. Segmented electric heating, temperature uniformity ±15℃.

[0107] S3, Second-level rapid cooling: Gas jet rapid cooling is employed, using high-pressure N2 (pressure 1.5 MPa, temperature 15℃) injected through a supersonic nozzle to dissipate the gaseous SiO2 obtained in S2. x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to 60°C within 0.8 s at a cooling rate of 1800°C / s.

[0108] S4. Ultrasonic hydration-concentration: Same as Example 1, scaled up to the corresponding ratio. Continuous operation for 24 hours (3 batches). Data for each batch: Batch 1: Loading 105 g / L, particle size 22 nm, amorphous content 93.6%, 60-day retention rate 96.8%, conversion rate 8.2%, catalyst recovery rate 93%; Batch 2: Loading 104 g / L, particle size 23 nm, amorphous content 93.4%, 96.5%, 8.1%, 92%; Batch 3: Loading 106 g / L, particle size 21 nm, amorphous content 93.8%, 97.0%, 8.3%, 94%. The coefficient of variation (CV) for each batch of key indicators was <3%, and the difference from the laboratory 100g-level data was within ±5%, demonstrating that this technical solution has good scale-up feasibility and process stability.

[0109] Example 7:

[0110] This embodiment provides a technical solution based on Embodiment 1: a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material and its preparation method. The steps are the same as in Embodiment 1, except that the target temperature of the third stage of the three-stage gradient heating program in S2 is changed, and the effect of temperature on the conversion rate is investigated.

[0111] The conversion rate at 1400℃ was 5.2%, with 92.5% being amorphous.

[0112] The conversion rate at 1500℃ was 8.7%, with 94.2% being amorphous.

[0113] The conversion rate at 1550℃ was 10.5%, with 94.0% being amorphous.

[0114] The conversion rate at 1600℃ is 11.8%, and the amorphous state accounts for 93.5%.

[0115] The conversion rate was only 5.2% at 1400℃, and increased to 11.8% at 1600℃, but the proportion of amorphous state decreased slightly (partial crystallization at high temperatures). Considering both conversion rate and product quality, 1500℃ was the optimal temperature.

[0116] Example 8:

[0117] This embodiment provides a technical solution based on Embodiment 1: a nano-amorphous silicon concentrated dispersion using potassium feldspar as raw material and its preparation method. Steps S1-S3 are the same as in Embodiment 1. In step S4, during the ultrasonic hydration-concentration stage, the total silicon content of the dispersion reaches 80 g / L (calculated as SiO2) by controlling the endpoint of vacuum concentration. The remaining conditions are the same as in Embodiment 1.

[0118] The properties of the obtained nano-amorphous silicon concentrated dispersion are as follows: total silicon content 80 g / L, nano-SiO2 particle size 26 nm, amorphous content 93.5%, Zeta potential -38 mV, and carbon content <1 ppm. After standing at 25℃ in a sealed, light-protected environment for 60 days, the silicon content retention rate is 96.2%, and there is no visible precipitation.

[0119] Conclusion: The lower limit is 80 g / L. All indicators tested met the requirements, proving that this limit value is feasible.

[0120] Example 9:

[0121] This embodiment provides a technical solution based on Embodiment 1: a nano-amorphous silicon concentrated dispersion using potassium feldspar as raw material and its preparation method. Steps S1-S3 are the same as in Embodiment 1. In step S4, during the ultrasonic hydration-concentration stage, the total silicon content of the dispersion reaches 110 g / L (calculated as SiO2) by controlling the endpoint of vacuum concentration. The remaining conditions are the same as in Embodiment 1.

[0122] The properties of the obtained nano-amorphous silicon concentrated dispersion are as follows: total silicon content 110 g / L, nano-SiO2 particle size 18 nm, amorphous content 93.2%, Zeta potential -46 mV, and carbon content <1 ppm. After standing at 25℃ in a sealed, light-protected environment for 60 days, the silicon content retention rate is 95.8%, and there is no visible precipitation.

[0123] Conclusion: The upper limit of 110 g / L was determined by the test results, and all indicators met the requirements, proving that this upper limit value is feasible.

[0124] Example 10:

[0125] Catalyst ratio range endpoint verification experiment:

[0126] Experiment A: CuO-MnO2-La2O3 were mixed in a mass ratio of 2.5:1.5:0.8, with a total addition amount of 1.2 wt%, and the other conditions were the same as in Example 1.

[0127] Results: TG-MS mass loss 6.8%, conversion rate 6.8%, amorphous content 91%, loading 92 g / L, 60-day retention rate 94.5%, Zeta potential -36 mV.

[0128] Experiment B: CuO-MnO2-La2O3 were mixed in a mass ratio of 3.5:2.5:1.2, with a total addition amount of 1.2 wt%, and the other conditions were the same as in Example 1.

[0129] Results: TG-MS mass loss 7.2%, conversion rate 7.2%, amorphous content 90.5%, loading 95 g / L, 60-day retention rate 94.8%, Zeta potential -37 mV.

[0130] Conclusion: Although the performance of the extreme ratios (2.5:1.5:0.8 and 3.5:2.5:1.2) is slightly lower than the optimal ratio of 3:2:1 (Example 1: conversion rate 8.7%, loading 105 g / L, 60-day retention rate 97.5%), they still meet the industrial practical standards (i.e., loading ≥80 g / L and 60-day retention rate ≥94.5%). When deviating from this range (e.g., catalyst ratio of 4:2:1, conversion rate 6.5%, loading <80 g / L), the performance deteriorates significantly.

[0131] Comparative Example 1:

[0132] Please see Figure 2 and Figure 5 Without adding a catalyst, all other conditions were the same as in Example 1. After holding at 1500℃ for 1 hour, the TG mass loss was <0.3%, MS showed no signal at m / z=44, and XRD showed that it was still crystalline quartz. This proves that SiO2 hardly decomposes at 1500℃ without a catalyst.

[0133] Comparative Example 2:

[0134] The effect of different proportions of CuO-MnO2-La2O3 catalyst on the properties of concentrated dispersions of nano-amorphous silicon:

[0135] (1) The ratio of CuO-MnO2-La2O3 catalyst is 4:2:1, with excess CuO:

[0136] Please see Figure 6 The catalyst mass ratio was changed to 4:2:1 (CuO-MnO2-La2O3), the total addition amount was 1.2 wt%, and the other conditions were the same as in Example 1.

[0137] TG-MS: mass loss 6.5%, peak height 0.22 nA at m / z=44 (31% lower than the 3:2:1 group). Conversion rate 6.5%. XPS oxygen vacancy percentage 22.3%±1.5% (significantly lower than 28.5%±1.2% in the 3:2:1 group, p<0.01).

[0138] H2-TPR: The low-temperature peak shifted to 310℃, and the high-temperature peak shifted to 520℃, with a peak spacing of 210℃, indicating weakened electron interactions. This demonstrates that excess CuO leads to uneven oxygen vacancy distribution and decreased catalytic activity.

[0139] (2) The ratio of CuO-MnO2-La2O3 catalyst is 2:2:2, in equal proportion:

[0140] Please see Figure 6 The catalyst mass ratio was changed to 2:2:2 (CuO-MnO2-La2O3), the total addition amount was 1.2 wt%, and the other conditions were the same as in Example 1.

[0141] TG-MS: mass loss 5.8%, peak height 0.19 nA at m / z=44. Conversion rate 5.8%. XPS oxygen vacancy percentage 19.8% ± 1.8% (significantly lower than the 3:2:1 group, p < 0.01).

[0142] H2-TPR: Only one broadened reduction peak appears (350-500℃), indicating overlapping reduction processes of Cu and Mn and disordered electron interactions. This demonstrates that oxygen vacancies are unevenly distributed under equal proportions.

[0143] (3) The ratio of CuO-MnO2-La2O3 catalyst is 3:1:1, and the MnO2 content is relatively low:

[0144] The catalyst mass ratio was changed to 3:1:1 (CuO-MnO2-La2O3), the total addition amount was 1.2 wt%, and the other conditions were the same as in Example 1.

[0145] TG-MS: mass loss 7.2%, peak height 0.25 nA at m / z=44. Conversion rate 7.2%. XPS oxygen vacancy percentage 24.1% ± 2.1% (lower than the 3:2:1 group, p < 0.05).

[0146] H2-TPR: The high temperature peak shifted to 480℃, and the peak area decreased by 30%. Insufficient MnO2 led to the obstruction of electron transfer channels.

[0147] (4) Single-component catalysts:

[0148] CuO, MnO2, and La2O3 were used as catalysts individually, with an addition amount of 1.2 wt%, and the other conditions were the same as in Example 1.

[0149] CuO alone: ​​TG mass loss 0.4%, m / z=44 peak height 0.05 nA, almost no decomposition.

[0150] MnO2 alone: ​​TG mass loss 0.3%, m / z=44 peak height 0.04 nA, almost no decomposition.

[0151] La2O3 alone: ​​TG mass loss 0.2%, peak height 0.03 nA at m / z=44, almost no decomposition.

[0152] This demonstrates that single-component catalysts cannot effectively catalyze the thermal decomposition of SiO2, and the synergistic effect of ternary catalysts is indispensable.

[0153] (5) The ratio of CuO-MnO2-La2O3 catalyst is 3:2:0.5, with a relatively low La2O3 content:

[0154] The catalyst mass ratio was changed to 3:2:0.5, the total addition amount was 1.2 wt%, and the other conditions were the same as in Example 1.

[0155] TGMS: Quality loss 6.8%, m / z=44, peak height 0.23 nA. Conversion rate 6.8%.

[0156] The oxygen vacancy ratio of XPS was 21.6% ± 1.9% (significantly lower than that of the 3:2:1 group, p < 0.01). The catalyst showed slight sintering after 1400℃, indicating insufficient thermal stability when La2O3 was insufficient.

[0157] (6) The ratio of CuO-MnO2-La2O3 catalyst is 3:2:1.5, with excess La2O3:

[0158] The catalyst mass ratio was changed to 3:2:1.5, the total addition amount was 1.2 wt%, and the other conditions were the same as in Example 1.

[0159] TGMS: quality loss 6.2%, m / z=44, peak height 0.21 nA. Conversion rate 6.2%.

[0160] The oxygen vacancy ratio of XPS was 20.3% ± 2.3% (significantly lower than that of the 3:2:1 group, p < 0.01). Excessive La2O3 coverage of active sites actually reduced catalytic efficiency.

[0161] Comparative Example 3:

[0162] Please see Figure 3 After catalytic thermal decomposition, the mixture is allowed to cool naturally (cooling rate 5℃ / min), without using second-level rapid cooling. The other conditions are the same as in Example 1.

[0163] XRD analysis revealed the presence of cristobalite characteristic peaks (2θ = 21.8°, 36.5°) in the product, with amorphous state accounting for only 8.5%.

[0164] A concentrated dispersion of nano-amorphous silicon with a loading of 12 g / L maintained a 45% retention rate after 60 days. This demonstrates that gaseous SiO₂ can be effectively cooled without second-level quenching. x Direct crystallization yields cristobalite, but amorphous products cannot be obtained.

[0165] Comparative Example 4:

[0166] Effect of different cooling rates on the properties of concentrated dispersions of nano-amorphous silicon:

[0167] (1) Slow cooling, cooling rate 100℃ / s:

[0168] Slow cooling at a rate of 100°C / s was used, with the other conditions the same as in Example 1.

[0169] XRD showed that the amorphous state accounted for 35%, but characteristic peaks of cristobalite were still detected.

[0170] With a dispersion loading of 28 g / L, the retention rate after 60 days was 62%. This demonstrates that when the cooling rate is insufficient, some SiO₂... x Crystallization still occurs.

[0171] (2) Medium-speed cooling, cooling rate 500℃ / s:

[0172] Medium-speed cooling at a cooling rate of 500℃ / s was used, and the other conditions were the same as in Example 1.

[0173] XRD showed that the amorphous state accounted for 78%, and there were no characteristic peaks of cubic quartz.

[0174] The dispersion loading was 65 g / L, and the retention rate after 60 days was 85%. This demonstrates that a higher proportion of amorphous state can be obtained when the cooling rate just reaches the critical value, but the loading is still lower than that of Example 1 (105 g / L). Furthermore, the 65 g / L loading and 85% retention rate do not meet the industrial practical standards of high loading (≥80 g / L) and ultra-high stability (≥94.5%) required by this invention.

[0175] Comparative Example 5:

[0176] Please see Figure 2 After catalytic thermal decomposition and rapid cooling in seconds, only mechanical stirring (300 rpm, 40 min) was used instead of ultrasonic treatment, and the other conditions were the same as in Example 1.

[0177] The dispersion loading was 48 g / L, and the retention rate after 60 days was 72%. This demonstrates that without ultrasonic cavitation hydration, powder agglomeration was severe, making it impossible to achieve stable dispersion at high loading. Both the 48 g / L loading and the 72% retention rate fail to meet the industrial practical standards required by this invention (≥80 g / L and ≥94.5%).

[0178] Comparative Example 6:

[0179] Please see Figure 5 The carbothermal reduction method was used instead of catalytic thermal decomposition: a highly active SiO2 matrix and graphite powder were mixed at a ratio of CuO:C=3:2 (CuO was used as an auxiliary catalyst and graphite as a reducing agent), and the other conditions were the same as in Example 1.

[0180] TG-MS: mass loss 9.5%, m / z=44 peak height 0.35 nA. However, carbon impurities of 500 ppm were detected in the product (high-frequency infrared carbon-sulfur analyzer), which does not meet food-grade requirements.

[0181] The dispersion loading is 95 g / L, and the retention rate is 90% after 60 days, but carbon impurities limit its application in food and cosmetic grades.

[0182] Comparison Example 7: (Comparison of Commercially Available Products)

[0183] Please see Figure 8 The product of this invention (Example 1) is compared with commercially available products:

[0184] product Load capacity (g / L) 60-day retention rate (%) Particle size change over 60 days (nm) Carbon content (ppm) Amorphous state percentage (%) Example 1 105 97.5 +2 ＜1 94.2 Vapor phase Aerosil® 200 30 85 +15 ＜1 98.0 Sol-gel method LUDOX® HS-30 30 72 +8 ＜1 95.0 Precipitation method silica sol 25 78 +35 N / A 75.0

[0185] The loading of the product in Example 1 (105 g / L) is 3.5 times that of the gas-phase and sol-gel products, and 4.2 times that of the precipitation product; the 60-day retention rate is 97.5%, which is significantly higher than that of commercially available products; the particle size change over 60 days is only +2 nm, while that of commercially available products is +8 to 35 nm; the carbon content is ≤1 ppm, and it is free of chloride ions, heavy metals, and sodium ion stabilizers.

[0186] Comparative Example 8:

[0187] Comparative experiment using existing technology with known catalyst ratios (1):

[0188] Referring to the known CuO-MnO2-La2O3 catalyst composition in the prior art (CuO-MnO2-La2O3=2:1:0.5, total addition 1.5 wt%), SiO2 thermal decomposition experiments were conducted under the same conditions as in Example 1 of this invention (fluidized bed reactor, high-purity argon flow rate 2 L / min, three-stage gradient heating to 1500℃, holding for 1 hour). The quenching and subsequent ultrasonic hydration steps were the same as in Example 1.

[0189] Results: TG-MS showed a mass loss of only 2.3% (compared to 8.7% in Example 1 of this invention), and a signal peak height of 0.09 nA at m / z=44 (compared to 0.32 nA in Example 1); the conversion rate was 2.1%, far lower than the 8.7% of this invention; XRD showed that cristobalite characteristic peaks (2θ=21.8°, 36.5°) were clearly present in the product, with an amorphous content of only 65%; the dispersion loading was only 18 g / L, the retention rate after 60 days was 68%, and the Zeta potential was -18 mV; 15 ppm of carbon impurities were detected in the product (although no carbon was actively added, trace amounts of carbon remained in the control catalyst system).

[0190] Conclusion: Under the same experimental conditions, the conversion rate, amorphous content, dispersion loading and stability of the product obtained by using the catalyst composition (3:2:1) and process conditions of this invention are significantly better than those of the control group of this comparative example, which proves the advantages of the technical solution of this invention.

[0191] Comparative experiment using existing technology with known catalyst ratios (2):

[0192] To rigorously verify the independent contribution of the catalyst ratio itself to the technical effect, this comparative example uses the catalyst ratio disclosed in the prior art US8815767 (CuO-MnO2-La2O3=2:1:0.5, total addition amount 1.5wt%), but adopts the optimal process conditions of this invention (fluidized bed reactor, 1500℃, gas jet quenching, ultrasonic hydration), only changing the catalyst ratio.

[0193] Experimental conditions: The reactor was a fluidized bed reactor with an apparent gas velocity of 0.3 m / s and a bed pressure drop of 5 kPa; the atmosphere was high-purity Ar (purity ≥99.99%, flow rate 2 L / min); the heating program was a three-stage gradient heating to 1500℃ and holding for 1 h (same as Example 1); the quenching was gas jet quenching with high-pressure Ar (1.0 MPa, 20℃) and a cooling rate of 1500℃ / s; ultrasonic hydration was the same as in Example 1; the catalyst was CuO-MnO2-La2O3=2:1:0.5, with a total addition of 1.5 wt% (a known ratio in the prior art).

[0194] Results Comparison: The present invention (3:2:1, Example 1) achieved a conversion rate of 8.7%, an amorphous content of 94.2%, a loading of 105 g / L, a 60-day retention rate of 97.5%, and a Zeta potential of -42 mV; while when the catalyst ratio was 2:1:0.5, the conversion rate was 3.8%, the amorphous content was 71%, the loading was 35 g / L, the 60-day retention rate was 78%, and the Zeta potential was -22 mV.

[0195] Under identical process conditions (fluidized bed reactor, 1500℃, gas jet quenching, ultrasonic hydration), by changing only the catalyst ratio, the conversion rate (3.8%) of the known ratio in the prior art (2:1:0.5) was only 43.7% of that of the ratio in this invention (3:2:1), the proportion of amorphous state (71%) was much lower than that of this invention (94.2%), the loading (35 g / L) was only 33.3% of that of this invention, and the 60-day retention rate (78%) was much lower than that of this invention (97.5%). This rigorous control experiment directly proves that the catalyst ratio itself is the key variable determining the technical effect, rather than a side effect of the process conditions.

[0196] Comparative Example 9:

[0197] Low-temperature catalytic activity verification (500℃):

[0198] A CuO-MnO2-La2O3 ternary composite was added at a ratio of 3:2:1, with a total addition of 1.2 wt%, and mixed with a highly active SiO2 matrix. High-purity Ar was introduced into a fixed-bed reactor (flow rate 2 L / min), and the temperature was raised to 500°C and held for 2 hours. Other conditions were the same as in Example 1.

[0199] Results: TG-MS showed a mass loss of <0.1%, no signal was detected at m / z=44, and XRD showed that it was still crystalline quartz. This demonstrates that the ternary catalyst has almost no catalytic activity for SiO2 at 500℃ (the commonly used temperature range in current technology), which is in stark contrast to its high catalytic activity at 1200-1600℃.

[0200] Conclusion: Comparative Example 9 directly proves that the application experience of CuO-MnO2-La2O3 in the field of low-temperature catalytic oxidation in the existing technology cannot be extrapolated to the high-temperature SiO2 thermal decomposition system.

[0201] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material, characterized in that, Includes the following steps: S1. Pretreatment: Using potassium feldspar as raw material, a highly active SiO2 matrix is ​​obtained through alkali melting, leaching, precipitation, drying, calcination, acid leaching, and ion exchange. S2. Catalytic thermal decomposition: Under inert gas protection, the highly active SiO2 matrix obtained in S1 is supplemented with a catalyst at a total addition amount of 1.0–1.5 wt%. The catalyst is composed of CuO, MnO2, and La2O3, with a mass ratio of (2.5–3.5):(1.5–2.5):(0.8–1.2). The catalytic thermal decomposition reaction is carried out in a reactor using a three-stage gradient heating to 1200–1600 °C, held at that temperature for 0.5–1.5 hours, to thermally decompose SiO2 into gaseous SiO2. x , where x = 1.5 to 2.0; The decomposition is a direct thermal decomposition of the catalyst mediated by surface oxygen vacancies, without the addition of any carbonaceous reducing agent. The reaction zone is continuously purged with an inert carrier gas at a flow rate of 2–100 L / min to maintain the SiO partial pressure in the reaction zone at 10. -4 ~10 -5 atm; S3, Second-level rapid cooling: Gas jet rapid cooling is adopted, and high-pressure inert gas is injected through a supersonic nozzle to cool the gaseous SiO2 obtained in S2. x Nano-amorphous SiO2 powder was obtained by rapidly cooling the powder to ≤100℃ within ≤2 seconds at a cooling rate of 500~2000℃ / s. S4. Ultrasonic hydration-concentration: The nano-amorphous SiO2 powder obtained in S3 is mixed with deionized water, ultrasonically treated, filtered, and concentrated under reduced pressure until the solid content reaches the target value, resulting in a nano-amorphous silicon concentrated dispersion with a total silicon content of 80-110 g / L (calculated as SiO2), and the pH is adjusted to 10.

5. The thermal decomposition of S2, the rapid cooling of S3, and the ultrasonic hydration of S4 are carried out sequentially, and the carrier gas flow rate of S2 and the rapid cooling gas flow rate of S3 are independently controlled.

2. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The steps of the S1 pretreatment are as follows: First, the potassium feldspar is crushed and ground to D. 50 ≤25μm, mixed with NaOH at a mass ratio of 1:2.5, calcined at 750℃ for 3 hours to obtain clinker, then mixed with deionized water at a ratio of 1:4, and leached at 80℃ for 2 hours; after leaching, CO2 was introduced to adjust the pH to 9.0, and precipitation was carried out at 30℃ for 4 hours; after precipitation, it was dried at 110℃ for 6 hours and calcined at 500℃ for 2 hours; then mixed with 10% hydrochloric acid at a ratio of 1:5, and leached at 80℃ for 4 hours, centrifuged and washed until neutral; after acid leaching, it was mixed with deionized water at a ratio of 1:8, 8% strong acid cation exchange resin was added, and treated at 30℃ for 3 hours to obtain a highly active SiO2 matrix.

3. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The S1 pretreatment can also be performed using a one-step alkali fusion-hydrothermal method, with the following steps: potassium feldspar and NaOH are mixed at a mass ratio of 1:2.5 and hydrothermally reacted at 250°C and saturated vapor pressure for 6 hours to obtain a highly active SiO2 matrix.

4. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The mass ratio of CuO, MnO2 and La2O3 in the catalyst of S2 is (2.8-3.2):(1.8-2.2):(0.9-1.1).

5. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 4, characterized in that, The mass ratio of CuO, MnO2 and La2O3 in the catalyst S2 is 3:2:

1.

6. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The inert carrier gas in S2 is Ar or N2 with a purity ≥ 99.99%.

7. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The three-stage gradient heating parameters in S2 are as follows: the first stage heats up to 900℃ at a rate of 10-15℃ / min and holds for 0.5 hours; the second stage heats up to 1200℃ at a rate of 5-10℃ / min and holds for 0.5 hours; and the third stage heats up to 1500℃ at a rate of 3-5℃ / min and holds for 1 hour.

8. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The reactor in S2 is a fluidized bed reactor with an apparent gas velocity of 0.2–0.5 m / s and a bed pressure drop of 3–8 kPa.

9. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, In the S3 gas jet quenching process, high-pressure inert gas is used, which is injected through a supersonic nozzle; the inert gas is Ar or N2, with a pressure of 0.5 to 2.0 MPa and a temperature of -50 to 20°C.

10. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The ultrasonic treatment in S4 is carried out under N2 protection, with an ultrasonic frequency of 28-40 kHz, a power of 300-400 W, a temperature of 40-45℃, and a treatment time of 30-50 minutes.

11. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The vacuum concentration in S4 is carried out at a temperature of 45–55°C and a vacuum degree of -0.085–-0.095 MPa.

12. The method for preparing a concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 1, characterized in that, The catalyst in S2 is recovered by magnetic separation after use. The recovered catalyst is regenerated by calcination at 400-600℃ and then recycled. The number of recycling cycles is 3-5 times, and 10%-20% of fresh catalyst is added each time.

13. A concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material, characterized in that, It is prepared by the method according to any one of claims 1-12, wherein the total silicon content of the nano-amorphous silicon concentrated dispersion is 80-110 g / L based on SiO2, the nano-SiO2 particle size is 5-50 nm, the amorphous content is ≥90%, the Zeta potential is -30 to -50 mV, and the carbon content is ≤1ppm.

14. The nano-amorphous silicon concentrated dispersion using potassium feldspar as raw material according to claim 13, characterized in that, After the dispersion was left to stand for 60 days at 25°C in a sealed, light-protected environment, the silicon content retention rate was ≥94.5%.

15. A concentrated dispersion of nano-amorphous silicon using potassium feldspar as raw material according to claim 13, characterized in that, After the dispersion is freeze-dried or dried at 60°C for 24 hours, a free-flowing white nanoparticle powder with a loose density of 50-150 g / L and an angle of repose of ≤45° is obtained. After the powder is re-added with deionized water and ultrasonically treated for 10 minutes, it can be restored to a uniform dispersion with a silicon content recovery rate of ≥95%.

16. The nano-amorphous silicon concentrated dispersion using potassium feldspar as raw material according to claim 13, characterized in that, The dispersion is used in food fortification, cosmetic repair, agricultural stress resistance and yield increase, or as a pharmaceutical carrier.

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