Method and device for extracting silicon from polycrystalline silicon production byproducts and polycrystalline silicon production system

Abstract

The embodiment of the invention provides a method and device for extracting silicon from polycrystalline silicon production byproducts and a polycrystalline silicon production system. The method comprises the following steps: carrying out first cleaning on a mixed system containing silica fume generated by a cold hydrogenation process and an alkaline solution to obtain a first silicon-containing alkaline solution; an oxidizing agent is added into the first silicon-containing alkali liquor for second cleaning, and second silicon-containing alkali liquor is obtained; performing first filtration on the second silicon-containing alkali liquor to obtain initial silicon powder and copper-containing filtrate; adding the initial silicon powder into an acidic solution for third cleaning to obtain a silicic acid-containing solution; carrying out second filtration on the silicic acid-containing liquid to obtain pure silicon powder; the alkaline solution comprises ammonia water and a urea water solution. The method is used for realizing efficient recovery of silicon in the silica fume.

Description

Technical Field

[0001] This application relates to the field of polysilicon production, and more particularly to a method, apparatus, and polysilicon production system for extracting silicon from byproducts of polysilicon production. Background Technology

[0002] Cold hydrogenation is a core step in polysilicon production, primarily used to process the reduction byproduct silicon tetrachloride (SiCl4). In cold hydrogenation, hydrogen, silicon tetrachloride (SiCl4), and metallurgical-grade silicon powder are used as raw materials. Under high temperature and pressure conditions (565-590℃ / 2.5-2.9MPa), they react with a copper chloride catalyst to produce a mixture of chlorosilanes, including trichlorosilane (SiHCl3). This chlorosilane mixture is then processed through a cyclone separator and a silicon powder filter to remove most of the fine silicon powder, resulting in discharged microsilicon powder.

[0003] The silicon content in the discharged microsilica powder is about 80%. However, in the existing process, the discharged microsilica powder is usually used in industries such as construction and metallurgy, which leads to a reduction in the utilization value of microsilica powder and a waste of silicon resources.

[0004] Currently, there is no technology for recovering silicon from microsilica powder. Therefore, there is an urgent need to provide a method for extracting silicon from the byproducts of cold hydrogenation reactions, so as to achieve efficient recovery of silicon resources from microsilica powder, a byproduct of cold hydrogenation reactions. Summary of the Invention

[0005] This application provides a method, apparatus, and polysilicon production system for extracting silicon from byproducts of polysilicon production, so as to achieve the effect of recovering silicon from the microsilicon powder discharged as a byproduct of polysilicon production.

[0006] In a first aspect, embodiments of this application provide a method for extracting silicon from a byproduct of polysilicon production, comprising:

[0007] The mixture containing microsilicon powder generated by the cold hydrogenation process and an alkaline solution is first cleaned to obtain a first silicon-containing alkaline solution.

[0008] An oxidant is added to the first silicon-containing alkaline solution for a second cleaning to obtain a second silicon-containing alkaline solution.

[0009] The second silicon-containing alkaline solution is filtered first to obtain initial silicon powder and copper-containing filtrate.

[0010] The initial silicon powder is added to an acidic solution for a third cleaning to obtain a silicic acid solution;

[0011] The silica-containing solution was subjected to a second filtration to obtain pure silicon powder.

[0012] The alkaline solution includes an aqueous solution of ammonia and urea.

[0013] In one possible implementation, the ammonia solution has a mass fraction of 25%-30%.

[0014] And / or, the urea aqueous solution comprises urea and water, wherein the mass fraction of urea in the urea aqueous solution is 35%-45%;

[0015] And / or, the mass ratio of the silica powder to the ammonia and the urea is 1:(0.3-0.5):(0.6-0.8);

[0016] And / or, the oxidant includes at least one of hydrogen peroxide and hypochlorite at a mass fraction of 28%-32%, wherein the hypochlorite contains 10wt%-15wt% available chlorine;

[0017] And / or, the mass ratio of the microsilica powder to the oxidant is 1:(0.1-0.3).

[0018] In one possible implementation, the first cleaning includes:

[0019] The mixture was stirred at a stirring speed of 800 r / min-1000 r / min at 80℃-100℃ for 0.5 h-1 h;

[0020] And / or, the second cleaning includes:

[0021] The first silicon-containing alkaline solution and the oxidant are mixed and stirred at a stirring speed of 800 r / min-1000 r / min at 80℃-100℃ for 0.5 h-1 h.

[0022] In one possible implementation, the pH of the first silicon-containing alkaline solution is 8-10;

[0023] And / or, the pH of the second silicon-containing alkaline solution is 8-10.

[0024] In one possible implementation, the acidic solution comprises at least one of the following: 20%-30% hydrochloric acid, 68wt%-70wt% nitric acid, 95wt%-98wt% sulfuric acid, and 80wt%-85wt% phosphoric acid.

[0025] And / or, the mass ratio of the initial silicon powder to the acidic solution is 1:(1.5-2).

[0026] In one possible implementation, the third cleaning includes:

[0027] The initial silicon powder and the acidic solution were mixed at 70°C-80°C with a stirring speed of 800r / min-1000r / min for 0.5h-1h.

[0028] In one possible implementation, after the third cleaning, filtration, washing with water, and drying are also included.

[0029] Secondly, embodiments of this application provide an apparatus for extracting silicon from by-products of polysilicon production, the apparatus being used in the aforementioned method for extracting silicon from by-products of polysilicon production;

[0030] The device includes:

[0031] A first heated and stirred reactor is used for performing the first cleaning and the second cleaning.

[0032] A first filter is used to perform the first filtration on the second silicon-containing alkaline solution;

[0033] The second heated and stirred reactor is used for the third cleaning process;

[0034] A second filter is used to perform the second filtration on the silica-containing solution;

[0035] The heated and stirred reactor includes a first inlet and a first outlet. The first inlet is used to feed raw materials into the heated and stirred reactor, and the first outlet is connected to the first filter.

[0036] The first filter includes a second inlet and a second outlet, the second inlet being connected to the first outlet, and the second outlet being connected to the second heating and stirring reactor;

[0037] The second heating and stirring reactor includes a third inlet and a third outlet, the third inlet being connected to the second outlet, and the third outlet being connected to the second filter;

[0038] The second filter includes a fourth inlet and a fourth outlet, the fourth inlet being connected to the third outlet, and the fourth outlet being used to discharge the pure silicon powder and filtrate.

[0039] In one possible implementation, the device further includes:

[0040] An evaporator for evaporating and concentrating the copper-containing filtrate;

[0041] A settling tank is used to filter the copper-containing filtrate after evaporation and concentration.

[0042] The evaporator includes a fifth inlet and a fifth outlet. The fifth inlet is connected to the third outlet of the first filter and is used to supply the copper-containing filtrate to the first filter.

[0043] The settling tank includes a sixth inlet and a sixth outlet. The sixth inlet is connected to the fifth outlet, and the sixth outlet is used to discharge copper slag and waste acid.

[0044] Thirdly, embodiments of this application provide a polysilicon production system, including: a by-product discharge device and the aforementioned device for extracting silicon from polysilicon production by-products;

[0045] The by-product discharge device includes a by-product discharge port, which is connected to the first feed port of the first heated and stirred reactor.

[0046] The method, apparatus, and polysilicon production system for extracting silicon from polysilicon production byproducts provided in this application utilize the synergistic effect of ammonia-urea mixed alkaline washing and acid washing of microsilicon powder: ammonia provides an alkaline environment, forming soluble complexes between ammonium ions and metal ions, while hydrogen peroxide oxidizes low-valence metal ions to high-valence states, promoting their precipitation or complexation removal; urea hydrolyzes under heating conditions to replenish ammonium ions, maintaining a stable pH value of the alkaline washing solution and preventing excessive corrosion of the silicon powder matrix; achieving the directional removal of metal chlorides, metal oxides, and high-valence metal ions from the microsilicon powder discharged by cold hydrogenation process, and simultaneously achieving silicon extraction and stabilization treatment of the silicon powder surface structure, resulting in pure silicon powder with a purity of not less than 90%. Attached Figure Description

[0047] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0048] Figure 1 A schematic diagram of the cold hydrogenation process provided in this application;

[0049] Figure 2 This is a schematic diagram of an apparatus for extracting silicon from byproducts of polysilicon production, as provided in this application.

[0050] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0051] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0052] First, let me explain the terms used in this application:

[0053] Cold hydrogenation process: This refers to the low-temperature hydrogenation process of silicon tetrachloride (SiCl4), a key technology in modern polysilicon production. Its main purpose is to convert the large amount of byproduct generated during polysilicon production—silicon tetrachloride (SiCl4)—into the production raw material—trichlorosilane (SiHCl3), thereby achieving material recycling, reducing costs, and minimizing environmental pollution.

[0054] Polycrystalline silicon: This refers to high-purity polycrystalline silicon, a form of elemental silicon. It is composed of countless tiny single-crystal silicon particles randomly combined. These grains have different crystal orientations, thus grain boundaries exist between the grains.

[0055] Microsilica powder, also known as silica fume, is an ultrafine powder byproduct produced during industrial smelting processes. Specifically, it is collected by special dust collection devices from the flue gas emitted from high-temperature furnaces during the production of metallic silicon or ferrosilicon alloys.

[0056] Figure 1 A schematic diagram of the cold hydrogenation process provided in this application is shown below. Figure 1 As shown, the cold hydrogenation process uses purchased silicon powder as raw material and, through a series of reactions, produces byproduct hydrogen and byproduct silicon tetrachloride. This application can be specifically applied to the recovery of the byproduct micro silicon powder.

[0057] Based on the above scenarios, it can be seen that in the existing technology, there is a problem of wasted silicon resources in the microsilica powder, a byproduct of the cold hydrogenation process.

[0058] The method for extracting silicon from polysilicon production byproducts provided in this application solves the technical problem of extracting silicon from microsilicon powder, a byproduct of cold hydrogenation process, through a mixed alkaline washing technique using ammonia-urea water.

[0059] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0060] This application provides a method for extracting silicon from a byproduct of polysilicon production. The method includes: first cleaning a mixture containing microsilicon powder generated by a cold hydrogenation process and an alkaline solution to obtain a first silicon-containing alkaline solution; adding an oxidant to the first silicon-containing alkaline solution for a second cleaning to obtain a second silicon-containing alkaline solution; first filtering the second silicon-containing alkaline solution to obtain initial silicon powder and a copper-containing filtrate; adding the initial silicon powder to an acidic solution for a third cleaning to obtain a silicic acid solution; and second filtering the silicic acid solution to obtain pure silicon powder. The alkaline solution includes an aqueous solution of ammonia and urea.

[0061] In this application, the alkaline environment provided by ammonia water causes the surfaces of the microsilica powder and impurity particles to become negatively charged. This electrostatic repulsion prevents impurity particles from re-adsorbing onto the microsilica powder surface. This electrostatic repulsion prevents removed impurities from re-attaching to the silicon powder surface. Furthermore, ammonia water corrodes the oxide layer on the surface of the microsilica powder, weakening the bonding force between impurity particles and the silicon substrate, thus promoting particle detachment. This corrosion helps to disrupt the oxide layer structure on the silicon powder surface, exposing the metallic impurities encased within the oxide layer, facilitating subsequent complexation reactions. The alkaline environment of ammonia water and the buffering effect of urea can, through a complexation reaction, convert Cu... 2+ It transforms into [Cu(NH3)4] 2+ The complex is dissolved and removed, along with some metal oxides (such as Fe2O3 and Al2O3) from the microsilica powder. Simultaneously, silicon's resistance to weak alkalis prevents its bulk from dissolving, achieving initial separation of impurity metal ions from silicon. Then, oxidation by an oxidant promotes the separation of lower valence metal ions (such as Fe...). 2+ The initial silicon powder and copper-containing filtrate are obtained by removing the precipitate or complex with the copper. The initial silicon powder is then acid-washed to finally obtain high-purity pure silicon powder.

[0062] In some specific implementations, the mass fraction of ammonia is 25wt%-30wt%.

[0063] It should be understood that typical impurities in microsilica powder include metal oxides (Fe2O3, Al2O3, CaO, etc.) and acidic impurities (such as chlorine and sulfides). The metal oxides can partially dissolve under alkaline conditions to form soluble complexes or precipitates, while acidic impurities can be removed through alkaline hydrolysis or ion exchange. In some embodiments, Fe... 3+ Reaction with ammonia: Fe 3+ +3NH3•H2O→Fe(OH)3↓+3NH4 + When ammonia is in excess, Fe(OH)3 will further form a complex with NH3: Fe(OH)3 + 6NH3 → (Fe(NH3)6) 3+ +3OH - Al 3+It reacts with ammonia to form Al(OH)3 precipitate: Al 3+ +3NH3•H2O→Al(OH)3↓+3NH4 + Because Al(OH)3 has amphoteric properties, it will dissolve in the presence of excess ammonia: Al(OH)3 + OH- - →AlO2 - +2H2O.

[0064] Therefore, in this embodiment, by controlling the mass fraction of ammonia water used to be 25%-30%, the pH of the mixed system can be precisely controlled, avoiding excessive alkalinity that could cause the silicon powder to dissolve (SiO2 reacts slowly in strong alkali), while ensuring efficient removal of impurities. Furthermore, appropriately increasing the ammonia water concentration can enhance the complexing ability, promoting the detachment of metallic impurities from the surface of the micro-silicon powder and their entry into the solution.

[0065] Urea hydrolyzes under alkaline heating conditions to produce NH3 and CO2, gradually releasing ammonia gas, which acts as a corrosion inhibitor and pH buffer. Therefore, controlling the initial ammonia concentration can prevent drastic pH fluctuations during the initial stage of urea hydrolysis, maintain a stable alkaline environment, and improve the uniformity of impurity removal.

[0066] For example, the mass fraction of ammonia water can be a range of 25 wt%, 26 wt%, 27 wt%, 28 wt%, 29 wt%, 30 wt%, or any combination thereof.

[0067] In some specific embodiments, the urea aqueous solution comprises urea and water, wherein the mass fraction of urea in the urea aqueous solution is 35wt%-45wt%.

[0068] In this embodiment, the corrosion inhibition rate of ammonia is controlled by adjusting the mass fraction of urea in the urea aqueous solution to 35wt%-45wt%, thus achieving a stable dynamic change in the alkaline environment. Furthermore, the CO2 produced by urea hydrolysis reacts with OH- in the solution to generate CO3. 2- Therefore, controlling the mass fraction of urea solution means controlling CO3. 2- The amount of urea produced can be specifically used to remove impurities rich in alkaline earth metals. Furthermore, urea molecules themselves are excellent polar molecules and surfactants. An appropriate concentration of urea aqueous solution can reduce the surface tension of water, enhance the penetration and wetting ability of the cleaning solution on microsilica agglomerates, resulting in more thorough cleaning, and help disperse fine microsilica particles, preventing their re-agglomeration and increasing the contact area with the cleaning solution.

[0069] For example, the mass fraction of urea in the urea aqueous solution can be a range of 35wt%, 36wt%, 37wt%, 38wt%, 39wt%, 40wt%, 41wt%, 42wt%, 43wt%, 44wt%, 45wt%, or any combination thereof.

[0070] In some specific implementations, the mass ratio of microsilica powder to ammonia and urea is 1:(0.3-0.5):(0.6-0.8).

[0071] In the mixed system, ammonia provides the initial alkalinity (OH-). - Urea has strong complexing ability (NH3), which is responsible for rapidly initiating the reaction and dissolving acidic impurities and some metals; urea undergoes a decomposition reaction upon heating: (NH2)2CO + 3H2O → 2NH4 + +CO3 2- +2OH - Ammonia is continuously and steadily replenished to maintain the alkalinity of the system and generate CO3. 2- Alkaline earth metal ions react with carbonate ions in a uniform alkaline environment to form relatively uniform carbonate particles, which gradually precipitate, thereby removing alkaline earth metal ions from microsilica powder. By controlling the mixing mass ratio of microsilica powder, ammonia, and urea to 1:(0.3-0.5):(0.6-0.8), the chemical reaction process and kinetics can be precisely controlled, achieving targeted and thorough impurity removal. This results in cleaning the surface and pores while maintaining the particle size distribution and chemical stability of the silica powder, yielding a high-purity product with a high recovery rate.

[0072] For example, the mass ratio of microsilica powder to ammonia and urea can be 1:0.3:0.6, 1:0.4:0.6, 1:0.5:0.6, 1:0.3:0.7, 1:0.4:0.7, 1:0.5:0.7, 1:0.3:0.8, 1:0.4:0.8, 1:0.5:0.8, or any combination thereof.

[0073] In some specific embodiments, the oxidant includes at least one of hydrogen peroxide and hypochlorite in a mass fraction of 28wt%-32wt%, wherein the hypochlorite contains 10wt%-15wt% available chlorine.

[0074] Specifically, hypochlorite can be sodium hypochlorite, potassium hypochlorite, etc.

[0075] For example, the mass fraction of hydrogen peroxide can be in the range of 28 wt%, 29 wt%, 30 wt%, 31 wt%, 32 wt%, or any two of these; the mass fraction of available chlorine in hypochlorite can be in the range of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, or any two of these.

[0076] In some specific implementations, the mass ratio of microsilica powder to oxidant is 1:(0.1-0.3).

[0077] It is understandable that, in addition to Fe, the silica fume filtrate contains... 2+ It may also contain other metal ions (such as Mn). 2+ Cr 3+ Excessive oxidizing agents may oxidize these ions to higher oxidation states, forming soluble colored ions (such as purple MnO4). - Compounds, or other more difficult-to-process compounds, can affect the purity of silicon. Insufficient oxidant (too low a mass ratio) can also lead to Fe... 2+ It cannot be completely oxidized to Fe. 3+ The remaining Fe 2+ It will not precipitate during subsequent pH adjustments, thus remaining in the solution and ultimately unable to be removed by filtration, which will also affect the purity of silicon.

[0078] Therefore, the mass of oxidant used can be determined by calculation and oxidation reaction equations to ensure that the added oxidant is exactly or slightly more than the total amount of Fe. 2+ Oxidized to Fe 3+ The required stoichiometry. Based on the determination of the elemental content in the silica fume, the approximate iron content in the silica fume can be determined. Then, according to the oxidation reaction equation, the theoretical stoichiometric ratio can be calculated to obtain the theoretical molar amount of the required oxidant. To obtain silica fume with higher purity, the mass ratio of silica fume to oxidant used is 1:(0.1-0.3).

[0079] For example, the mass ratio of microsilica powder to oxidant can be 1:0.1, 1:0.11, 1:0.12, 1:0.13, 1:0.14, 1:0.15, 1:0.16, 1:0.17, 1:0.18, 1:0.19, 1:0.2, 1:0.25, 1:0.3 or any combination thereof.

[0080] In some specific embodiments, the first cleaning includes: stirring the mixture at a stirring speed of 800 r / min-1000 r / min at 80℃-100℃ for 0.5 h-1 h.

[0081] It is understandable that the reaction rate constants of processes such as urea hydrolysis, ammonia complexation with metal ions, and the dissolution of impurity oxides in alkali all increase exponentially with increasing temperature (following the Arrhenius equation). By controlling the temperature of the first cleaning step, the process cycle can be significantly shortened, and production efficiency improved. Moreover, the hydrolysis rate of urea is extremely sensitive to temperature; controlling the temperature can control the ammonia generation rate, thereby controlling the rate of pH rise and stability of the entire system, facilitating "on-demand alkali supply" and preventing pH runaway. In addition, at 80℃-100℃, the viscosity of the mixed system decreases, and the fluidity is further improved, which, in conjunction with a stirring speed of 800r / min-1000r / min, can further improve mass transfer and mixing effects.

[0082] For example, the stirring speed of the first cleaning can be a range of 800 r / min, 850 r / min, 900 r / min, 950 r / min, 1000 r / min or any two of these; the temperature of the first cleaning can be a range of 80°C, 85°C, 90°C, 95°C, 100°C or any two of these.

[0083] In some specific embodiments, the second cleaning includes: mixing and stirring the first silicon-containing alkaline solution and the oxidant at a stirring speed of 800 r / min-1000 r / min at 80℃-100℃ for 0.5 h-1 h.

[0084] By controlling the stirring speed of the second cleaning cycle to 800-1000 rpm, the added oxidant can be rapidly dispersed throughout the reaction system, avoiding localized concentration buildup, significantly reducing waste caused by non-target decomposition of the oxidant, and ensuring that impurities in all areas receive equal oxidation opportunities, thereby improving overall oxidation efficiency. Simultaneously, it keeps the solid phase (silicon powder, newly formed precipitate) in suspension, ensuring sufficient contact between the oxidant and impurities.

[0085] Increasing the temperature accelerates most oxidation reactions. By controlling the temperature, target impurities (such as Fe) can be preferentially oxidized. 2+ Rapid oxidation to Fe 3+ This method avoids or slows down adverse oxidation of the silicon substrate or other components, achieving selective oxidation that protects the host silicon while efficiently removing impurities. It also maximizes the use of the oxidant in the target reaction, significantly reducing oxidant consumption costs.

[0086] In some embodiments, during the oxidant addition stage, a relatively high stirring speed and strictly controlled medium-low temperature are used. High-speed stirring ensures instantaneous dispersion of the oxidant, avoiding localized high heat and high concentration; medium-low temperature suppresses the decomposition of the oxidant upon addition from a global perspective. During the oxidation reaction maintenance stage, the stirring speed can be appropriately reduced to maintain uniform suspension, and the temperature can be maintained or slightly increased to promote complete oxidation reaction.

[0087] For example, the stirring speed of the second cleaning can be a range of 800 r / min, 850 r / min, 900 r / min, 950 r / min, 1000 r / min or any two of these; the temperature of the second cleaning can be a range of 80°C, 85°C, 90°C, 95°C, 100°C or any two of these.

[0088] In some specific implementations, the pH of the first silicon-containing alkaline solution is 8-10.

[0089] In some specific implementations, the pH of the second silicon-containing alkaline solution is 8-10.

[0090] It should be understood that transition metal ions (such as Fe) 2+ Cu 2+ The formation of ammonia (NH3) is not only affected by precipitation equilibrium but also dominated by complexation effects. Furthermore, the pH of the system directly influences the form of complexing agents such as ammonia (NH3) (at low pH, it is in the form of NH4). + (It exists in a form with weak complexing ability). By controlling the pH of the first and / or second silicon-containing alkaline solutions to 8-10, it is possible to control whether it is removed in the form of a precipitate or retained in the solution as a soluble complex, thus achieving selective separation.

[0091] In some specific embodiments, the acidic solution includes at least one of the following: hydrochloric acid (20wt%-30wt%), nitric acid (68wt%-70wt%), sulfuric acid (95wt%-98wt%), and phosphoric acid (80wt%-85wt%).

[0092] For example, the mass fraction of hydrochloric acid can be in the range of 22 wt%, 24 wt%, 26 wt%, 28 wt%, 30 wt%, or any two of these; the mass fraction of nitric acid can be in the range of 68 wt%, 69 wt%, 70 wt%, or any two of these; the mass fraction of sulfuric acid can be in the range of 95 wt%, 96 wt%, 97 wt%, 98 wt%, or any two of these; and the mass fraction of phosphoric acid can be in the range of 80 wt%, 81 wt%, 82 wt%, 83 wt%, 84 wt%, 85 wt%, or any two of these.

[0093] In some specific implementations, the initial silicon powder to acidic solution mass ratio is 1:(1.5-2).

[0094] The initial silica powder surface retains a large number of OH⁻ ions (from ammonia and urea hydrolysis products), requiring neutralization with an acidic solution. By optimizing the mass ratio of initial silica powder to acidic solution to 1:(1.5-2), the final pH can be stabilized within a preset weakly acidic or near-neutral range (e.g., pH=5-7), achieving complete neutralization while creating an optimal environment for selective acid dissolution. Simultaneously, the acidity and ionic strength of the system are controlled, thus preferentially dissolving target impurities while minimizing impact on the bulk silica. Under suitable acidic conditions, the silica powder surface may protonate, resulting in a high concentration of H⁻ ions. + This compresses the diffused electric double layer around the particles, significantly reducing the electrostatic barrier and decreasing electrostatic repulsion between particles. Furthermore, the presence of impurity ions or uneven particle surface properties in the system leads to local charge neutralization or the generation of oppositely charged points, thus promoting aggregation and sedimentation. Moreover, after protonation of the silicon powder surface, the resulting ≡Si-OH2... + It is a strong hydrogen bond donor, which can bond with ≡Si-O on the surface of adjacent particles. - Alternatively, strong hydrogen bonds can form between ≡Si-OH, tightly binding the particles together, overcoming residual electrostatic repulsion, and facilitating subsequent filtration or centrifugal separation.

[0095] For example, the mass ratio of the initial silicon powder to the acidic solution can be 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.0, or any combination thereof.

[0096] In some specific embodiments, the third cleaning includes: mixing the initial silicon powder and the acidic solution at 70°C-80°C with a stirring speed of 800r / min-1000r / min for 0.5h-1h.

[0097] For example, the temperature of the third cleaning can be a range of 70°C, 72°C, 74°C, 76°C, 78°C, 80°C, or any combination thereof.

[0098] In some specific implementations, the third cleaning process also includes filtration, washing with water, and drying.

[0099] Specifically, the system obtained from the third cleaning is filtered using a plate and frame filter press and backwashed with water (silicon powder:water = 1:(2-3)) to remove acid. After hot air drying, the silicon powder is recovered. The acid washing waste liquid is mixed with copper-containing solid waste precipitate and treated with acid-base neutralization.

[0100] The method for extracting silicon from polysilicon production byproducts provided in this application employs a synergistic effect of ammonia-urea mixed alkaline washing and acid washing on microsilicon powder: ammonia provides an alkaline environment, forming soluble complexes between ammonium ions and metal ions, while the oxidation of low-valence metal ions by an oxidant converts them into high-valence states, promoting their precipitation or complexation removal; urea hydrolyzes under heating conditions to replenish ammonium ions, maintaining a stable pH value of the alkaline washing solution and avoiding excessive corrosion of the silicon powder matrix; it achieves the targeted removal of metal chlorides, metal oxides, and high-valence metal ions from the microsilicon powder discharged by a cold hydrogenation process, and simultaneously achieves silicon extraction and stabilization treatment of the silicon powder surface structure, resulting in pure silicon powder with a purity of not less than 90%.

[0101] Figure 2 This is a schematic diagram of an apparatus for extracting silicon from by-products of polysilicon production, as provided in this application. This apparatus is used to perform the aforementioned method for extracting silicon from by-products of polysilicon production. Figure 2 As shown, the device includes: a first heated and stirred reactor for performing a first cleaning and a second cleaning; a first filter for performing a first filtration of a second silicon-containing alkaline solution; a second heated and stirred reactor for performing a third cleaning; and a second filter for performing a second filtration of a silicon-containing acid solution.

[0102] In this apparatus, the first heated and stirred reactor includes a first inlet and a first outlet. The first inlet is used to supply the cold hydrogenation process byproducts, silica powder and alkaline solution, to the first heated and stirred reactor. The first outlet is connected to a first filter. In some embodiments, the silica powder and alkaline solution can be pre-stored in a silica powder storage tank and an alkaline solution storage tank, respectively, and then connected to the first inlet through their respective delivery pipes. Specifically, the ammonia water and urea aqueous solution in the alkaline solution can enter the first heated and stirred reactor from the ammonia water storage tank and the urea aqueous solution storage tank, respectively, through separate pipes.

[0103] After the silica powder and alkaline solution are first cleaned in the first heated and stirred reactor, an oxidant is added to the first heated and stirred reactor to perform a second cleaning on the resulting first silica-containing alkaline solution, thereby obtaining a second silica-containing alkaline solution. The second silica-containing alkaline solution can enter the first filter through the first outlet.

[0104] The first filter includes a second inlet and a second outlet, with the second inlet connected to the first outlet, for conveying the obtained second silicon-containing alkaline solution to the first filter. In some embodiments, the first filter can be a plate and frame filter press to filter the second silicon-containing alkaline solution to obtain initial silicon powder and copper-containing filtrate. The initial silicon powder enters the second heated and stirred reactor through the second outlet.

[0105] The second heated and stirred reactor includes a third inlet and a third outlet. The third inlet is connected to the second outlet and is used to receive the initial silicon powder. Simultaneously, an acidic solution is added to the second heated and stirred reactor through the third inlet to perform a third washing of the initial silicon powder, resulting in a mixture containing silicon powder. The mixture then enters a second filter through the third outlet for filtration.

[0106] The second filter includes a fourth inlet and a fourth outlet, connected to each other, for conveying the mixture obtained from the third washing process to the second filter. In some embodiments, the second filter can be a plate and frame filter press to filter the mixture, obtaining pure silica powder and filtrate.

[0107] In some specific embodiments, the apparatus for extracting silicon from polysilicon production byproducts further includes: an evaporator for evaporating and concentrating copper-containing filtrate; and a settling tank for filtering the evaporated and concentrated copper-containing filtrate.

[0108] The evaporator includes a fifth inlet and a fifth outlet. The fifth inlet is connected to the second outlet of the first filter and is used to supply copper-containing filtrate to the evaporator. The settling tank includes a sixth inlet and a sixth outlet. The sixth inlet is connected to the fifth outlet, and the sixth outlet is used to discharge copper slag and waste acid. Specifically, the evaporator can be a multi-effect evaporator, the settling tank can be an inclined plate settling tank, and the waste acid can be neutralized by adding alkali.

[0109] In some embodiments, pure silicon powder can be backwashed with water from an industrial water storage tank in a plate and frame filter press to remove the acidic solution on the surface, and then dried with hot air and ball milled to obtain silicon of the target particle size that can be used as a polycrystalline silicon raw material.

[0110] The apparatus for extracting silicon from polysilicon production byproducts provided in this embodiment can perform the method provided in the above-described method embodiments. Its implementation principle and technical effects are similar, and will not be described in detail here.

[0111] This application also provides a polysilicon production system, including a by-product discharge device and the aforementioned device for extracting silicon from polysilicon production by-products; the by-product discharge device includes a by-product discharge port, which is connected to the first feed port of a first heated and stirred reactor.

[0112] The technical solution of this application will be further illustrated by specific embodiments below.

[0113] Example 1

[0114] A method for extracting silicon from a byproduct of polysilicon production, comprising the following steps:

[0115] The mixture obtained by mixing microsilica powder with ammonia water with a mass fraction of 25 wt% and urea water with a mass fraction of 35% at a mass ratio of 1:0.3:0.6 was placed in a first heated and stirred reaction vessel and stirred and heated at 80℃ and 800 r / min for 1 h to perform the first cleaning, thereby obtaining the first silicon-containing alkaline solution.

[0116] 30% hydrogen peroxide was added to the first heated and stirred reactor, and the reaction was continued under the same conditions for 0.5 hours. At the same time, the pH of the reaction system was controlled at 8, and a second cleaning was performed to obtain a second silicon-containing alkaline solution. The mass ratio of microsilica powder to added 30% hydrogen peroxide was 1:0.1.

[0117] The second silicon-containing alkaline solution is filtered through a plate and frame filter to obtain initial silicon powder and copper-containing filtrate. The copper-containing filtrate is then processed through a multi-effect evaporator to recover ammonium, which is used to prepare ammonia water. Finally, it is processed through a settling tank to obtain copper-containing precipitate.

[0118] Initial silicon powder and hydrochloric acid with a mass fraction of 20% were mixed at a mass ratio of 1:1.5 and placed in a second heated and stirred reactor. The mixture was stirred at 80°C for 1 hour for a third wash. The product obtained from the third wash was then separated by plate and frame filtration through a second filter to obtain crude silicon powder and acid washing waste liquid.

[0119] The crude silica powder is backwashed with water and dried with hot air to obtain pure silica powder; the mass ratio of crude silica powder to water is 1:2.

[0120] Example 2

[0121] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder, 25wt% ammonia water, and 35% urea aqueous solution is 1:0.2:0.6.

[0122] Example 3

[0123] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder, 25wt% ammonia water, and 35% urea aqueous solution is 1:0.4:0.6.

[0124] Example 4

[0125] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 3, except that the mass ratio of microsilicon powder, 25wt% ammonia water, and 35% urea aqueous solution is 1:0.5:0.6.

[0126] Example 5

[0127] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 4, except that the mass ratio of microsilicon powder, 25 wt% ammonia water, and 35 wt% urea aqueous solution is 1:0.6:0.6.

[0128] Example 6

[0129] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of ammonia is 24 wt%.

[0130] Example 7

[0131] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of ammonia is 28 wt%.

[0132] Example 8

[0133] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of ammonia is 30 wt%.

[0134] Example 9

[0135] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 8, except that the mass fraction of ammonia is 31 wt%.

[0136] Example 10

[0137] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder, 25wt% ammonia water, and 35wt% urea aqueous solution is 1:0.3:0.5.

[0138] Example 11

[0139] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder, 25 wt% ammonia water, and 35 wt% urea aqueous solution is 1:0.3:0.7.

[0140] Example 12

[0141] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder, 25 wt% ammonia water, and 35 wt% urea aqueous solution is 1:0.3:0.8.

[0142] Example 13

[0143] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 12, except that the mass ratio of microsilicon powder, 25 wt% ammonia water, and 35 wt% urea aqueous solution is 1:0.3:0.9.

[0144] Example 14

[0145] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of the urea aqueous solution is 32 wt%.

[0146] Example 15

[0147] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of the urea aqueous solution is 40 wt%.

[0148] Example 16

[0149] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass fraction of the urea aqueous solution is 45 wt%.

[0150] Example 17

[0151] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 16, except that the mass fraction of the urea aqueous solution is 48 wt%.

[0152] Example 18

[0153] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 17, except that the mass ratio of microsilicon powder to 30% hydrogen peroxide is 1:0.05.

[0154] Example 19

[0155] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder to 30% hydrogen peroxide is 1:0.2.

[0156] Example 20

[0157] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of microsilicon powder to 30% hydrogen peroxide is 1:0.3.

[0158] Example 21

[0159] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 20, except that the mass ratio of microsilicon powder to 30% hydrogen peroxide is 1:0.32.

[0160] Example 22

[0161] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 20, except that a sodium hypochlorite solution is used instead of hydrogen peroxide, wherein the available chlorine in the sodium hypochlorite solution is 12 wt%.

[0162] Example 23

[0163] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the concentration of hydrochloric acid used is 15 wt%.

[0164] Example 24

[0165] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the concentration of hydrochloric acid used is 30 wt%.

[0166] Example 25

[0167] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 24, except that the concentration of hydrochloric acid used is 35 wt%.

[0168] Example 26

[0169] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of initial silicon powder to hydrochloric acid is 1:1.2.

[0170] Example 27

[0171] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of initial silicon powder to hydrochloric acid is 1:1.8.

[0172] Example 28

[0173] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that the mass ratio of initial silicon powder to hydrochloric acid is 1:2.

[0174] Example 29

[0175] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 28, except that the mass ratio of initial silicon powder to hydrochloric acid is 1:2.2.

[0176] Comparative Example 1

[0177] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that no urea aqueous solution is added.

[0178] Comparative Example 2

[0179] A method for extracting silicon from a byproduct of polysilicon production, the steps of which are basically the same as those in Example 1, except that ammonia is not added.

[0180] Comparative Example 3

[0181] A method for extracting silicon from polysilicon production byproducts, the steps of which are basically the same as those in Example 1, except that a first cleaning is not performed.

[0182] Comparative Example 4

[0183] A method for extracting silicon from polysilicon production byproducts, the steps of which are basically the same as those in Example 1, except that a third cleaning is not performed.

[0184] The following performance tests were performed on the above embodiments and comparative examples:

[0185] The purity of the silicon powder and the content of copper, aluminum, iron and calcium elements were determined using inductively coupled plasma mass spectrometry (Thermo Fisher iCAP RQplus ICP-MS).

[0186] The test results are detailed in Table 1.

[0187] Table 1

[0188]

[0189]

[0190] According to the data in Table 1, the method provided in this application can purify silicon in microsilica powder to obtain pure silicon powder with a purity greater than 89.8%, and the copper content is less than 7400 ppm, the aluminum content is less than 2600 ppm, the iron content is less than 68000 ppm, and the calcium content is less than 1600 ppm.

[0191] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method of extracting silicon from a by-product of polysilicon production, characterized in that, The method comprises the following steps: carrying out first cleaning on a mixed system containing micro-silicon powder generated by a cold hydrogenation process and an alkaline solution to obtain a first silicon-containing alkaline solution; adding an oxidizing agent to the first silicon-containing alkaline solution to carry out second cleaning to obtain a second silicon-containing alkaline solution; carrying out first filtration on the second silicon-containing alkaline solution to obtain initial silicon powder and a copper-containing filtrate; adding the initial silicon powder to an acidic solution to carry out third cleaning to obtain a silicon-containing acid solution; carrying out second filtration on the silicon-containing acid solution to obtain pure silicon powder. The alkaline solution comprises ammonia water and a urea aqueous solution.

2. The method of extracting silicon from by-products of polysilicon production according to claim 1, characterized in that, The mass fraction of the ammonia water is 25%-30%; And / or, the urea aqueous solution comprises urea and water, and the mass fraction of the urea in the urea aqueous solution is 35%-45%; And / or, the mass ratio of the micro-silicon powder to the ammonia water and the urea is 1:(0.3-0.5):(0.6-0.8); And / or, the oxidizing agent comprises at least one of hydrogen peroxide with a mass fraction of 28%-32% and hypochlorite containing 10wt%-15wt% available chlorine; And / or, the mass ratio of the micro-silicon powder to the oxidizing agent is 1:(0.1-0.3).

3. The method of extracting silicon from by-products of polysilicon production according to claim 1 or 2, characterized in that, The first cleaning comprises the following steps: stirring the mixed system at a stirring speed of 800r / min-1000r / min at 80℃-100℃ for 0.5h-1h; And / or, the second cleaning comprises the following steps: mixing and stirring the first silicon-containing alkaline solution and the oxidizing agent at a stirring speed of 800r / min-1000r / min at 80℃-100℃ for 0.5h-1h.

4. The method of extracting silicon from by-products of polysilicon production according to any one of claims 1 to 3, characterized in that, The pH of the first silicon-containing alkaline solution is 8-10; And / or, the pH of the second silicon-containing alkaline solution is 8-10.

5. The method of extracting silicon from by-products of polysilicon production according to any one of claims 1-4, characterized in that, The acidic solution comprises at least one of hydrochloric acid with a mass fraction of 20wt%-30wt%, nitric acid with a mass fraction of 68wt%-70wt%, sulfuric acid with a mass fraction of 95wt%-98wt%, and phosphoric acid with a mass fraction of 80wt%-85wt%; And / or, the mass ratio of the initial silicon powder to the acidic solution is 1:(1.5-2).

6. The method of extracting silicon from by-products of polysilicon production according to any one of claims 1-5, characterized in that, The third cleaning comprises the following steps: mixing and stirring the initial silicon powder and the acidic solution at a stirring speed of 800r / min-1000r / min at 70℃-80℃ for 0.5h-1h.

7. The method of extracting silicon from by-products of polysilicon production according to any one of claims 1-6, characterized in that, After the third cleaning, water washing and drying are further included.

8. An apparatus for extracting silicon from by-products of polysilicon production, characterized by, The device is used to execute the method for extracting silicon from by-products in the production of polysilicon according to any one of claims 1-7; The device comprises: a first heating and stirring reaction kettle used to carry out the first cleaning and the second cleaning; a first filter used to carry out the first filtration on the second silicon-containing alkaline solution; a second heating and stirring reaction kettle used to carry out the third cleaning; a second filter used to carry out the second filtration on the silicon-containing acid solution; the first heating and stirring reaction kettle comprises a first feeding port and a first discharging port, the first feeding port is used to deliver raw materials to the first heating and stirring reaction kettle, and the first discharging port is connected to the first filter; The first filter comprises a second inlet and a second outlet, the second inlet is connected with the first outlet, and the second outlet is connected with the second heating and stirring reaction kettle; The second heating and stirring reaction kettle comprises a third inlet and a third outlet, the third inlet is connected with the second outlet, and the third outlet is connected with the second filter; The second filter comprises a fourth inlet and a fourth outlet, the fourth inlet is connected with the third outlet, and the fourth outlet is used for discharging the pure silicon powder and filtrate.

9. The apparatus for extracting silicon from by-products of polysilicon production according to claim 8, characterized in that, The device further comprises: an evaporator used for evaporating and concentrating the copper-containing filtrate; a settling tank used for filtering the copper-containing filtrate after evaporating and concentrating; The evaporator comprises a fifth inlet and a fifth outlet, the fifth inlet is connected with the second outlet of the first filter, and is used for conveying the copper-containing filtrate to the first filter; The settling tank comprises a sixth inlet and a sixth outlet, the sixth inlet is connected with the fifth outlet, and the sixth outlet is used for discharging copper residue and waste acid.

10. A polycrystalline silicon production system, characterized in that, The device for extracting silicon from by-products in the production of polysilicon comprises a by-product discharging device and the device for extracting silicon from by-products in the production of polysilicon according to any one of claims 8-9; The by-product discharging device comprises a by-product discharging port, which is connected with the first inlet of the first heating and stirring reaction kettle.

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