Method for enhancing removal of impurity boron in industrial silicon by using potassium-sodium-rich biomass composite ash additive

Abstract

The invention relates to a method for enhancing removal of impurity boron in industrial silicon by using a potassium-sodium-rich biomass composite ash additive, and belongs to the technical field of industrial silicon refining and purification. The method comprises the following steps: crushing and screening blocky industrial silicon to obtain silicon powder; drying and crushing the biomass rich in potassium and sodium to obtain biomass powder; heating the biomass powder to 600-900 DEG C, and roasting the biomass powder in air for 60-120 minutes to obtain a potassium-sodium-rich biomass composite ash additive; the method comprises the following steps: uniformly mixing silicon powder and a potassium-sodium-rich biomass composite ash additive, filling a high-purity graphite crucible with the mixture, putting the high-purity graphite crucible into an induction furnace, heating to 1450-1800 DEG C at a constant speed in a protective gas atmosphere, preserving heat for 1-4 hours to remove impurity boron, cooling to room temperature along with the furnace, and removing slag to obtain high-purity silicon. According to the method, the potassium-sodium-rich biomass composite ash additive is adopted to reinforce and refine industrial silicon so as to remove the impurity boron, after optimization, the boron content can be reduced to 4 ppmw or below through one-time refining treatment, and the total removal rate of other impurities is larger than or equal to 17%.

Description

Technical Field

[0001] The invention relates to a method for strengthening the removal of impurity boron in industrial silicon using a potassium-sodium-rich biomass composite ash additive, and belongs to the technical field of industrial silicon refining and purification. Background Art

[0002] The photovoltaic industry is mainly based on silicon materials. Most photovoltaic modules are made of silicon materials, and the raw material of solar cells is polycrystalline silicon. Industrial silicon is a front-end product and a raw material of high-quality industrial silicon. It is the main raw material of solar cells and is very important. In the development history of industrial silicon, it is very important in our lives. Whether in the information industry or in new energy products, industrial silicon occupies an important position.

[0003] Boron, as an impurity element in solar-grade silicon, has a serious impact on the photoelectric conversion rate and stability of solar cells. In the process of preparing solar-grade silicon by metallurgical method, the boron content in silicon materials should be reduced as much as possible. Industrial silicon is a front-end product of solar-grade silicon. In the process of industrial silicon smelting, special attention should be paid to B impurities. Therefore, in order to meet the requirements of solar-grade silicon cells, B impurities need to be reduced as much as possible.

[0004] The existing methods for removing B impurities in solar-grade silicon include slag refining, gas blowing, plasma refining, and wet treatment. Slag treatment can effectively remove boron from silicon, but a larger slag-silicon ratio is required for refining silicon, and it is difficult for slag particles to fully contact with liquid silicon; gas blowing may cause silicon to be oxidized, with part of the silicon being oxidized into silicon monoxide and silicon dioxide, resulting in silicon loss; plasma refining has a good effect on removing impurities in silicon, but its equipment is complex, costly, and energy-intensive; wet treatment uses inorganic acids to treat silicon, which can cause equipment corrosion and difficulty in handling waste liquid.

[0005] The research team previously studied the process of synergistically enhancing the removal of impurity boron by biomass and additives and applied for patent 2024111964714; it requires the biomass to be calcined and then combined with alkali metal carbonates and / or alkali metal hydroxides to achieve deboronization. Based on this, the present invention further discovered that it is possible to completely remove the external additives and directly use the biomass calcination products to achieve rapid deboronization of industrial silicon. At the same time, based on research and development, it was also discovered that by optimizing the composition of potassium-sodium-rich biomass composite ash additives, the removal rate of certain impurity elements can be improved while ensuring the deboronization efficiency, thereby forming the present invention. Summary of the invention

[0006] In view of the problems of complicated operation and high cost in the existing methods for removing B impurities in solar-grade silicon, the present invention proposes a method for strengthening the removal of impurity boron in industrial silicon by using potassium-sodium-rich biomass composite ash additives based on previous research. The present invention uses potassium-sodium-rich biomass composite ash additives to strengthen the refining of industrial silicon. The carbonates of sodium and potassium alkali metal elements in the biomass composite ash react with the impurity boron element to generate boron oxides that volatilize or enter the slag phase to remove the impurity boron. After optimization, a single refining treatment can reduce the boron content to less than 4ppmw and the total removal rate of other impurities is greater than or equal to 17%. At the same time, the present invention can further improve the purity of silicon while removing boron.

[0007] A method for enhancing the removal of impurity boron in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0008] (1) crushing and screening blocky industrial silicon to obtain silicon powder, the particle size of which is 80 to 200 meshes;

[0009] (2) drying and crushing the potassium-sodium rich biomass to obtain biomass powder; heating the biomass powder to 600-900° C. and roasting in air for 60-120 min to obtain a potassium-sodium rich biomass composite ash additive;

[0010] (3) The silicon powder and the potassium-sodium-rich biomass composite ash additive are mixed evenly, placed in a high-purity graphite crucible, and then placed in an induction furnace. Under a protective gas atmosphere, the temperature is uniformly raised to above 1410° C., preferably 1450-1800° C. and kept warm for 1-4 hours to remove the impurity boron, and the furnace is cooled to room temperature, and the slag is removed to obtain high-purity silicon.

[0011] The boron content in the silicon powder in step (1) is greater than 10 ppmw, which of course includes greater than or equal to 50 ppmw and greater than 100 ppmw.

[0012] The potassium-sodium-rich biomass in step (2) is one or more of coffee husks, rice husks, rice straws, tobacco straws, and cotton straws.

[0013] The total mass content of potassium and sodium in the potassium-sodium rich biomass composite ash additive in step (2) is greater than or equal to 6%.

[0014] The total mass contents of potassium and sodium in the potassium-sodium-rich biomass composite ash additive obtained by roasting coffee husks, rice husks, rice straws, tobacco straws, and cotton straws are 21.2657%, 6.16%, 9.22%, 61.56%, and 44.27%, respectively. In order to improve the deboronization efficiency, the potassium-sodium-rich biomass composite ash obtained by roasting at least one of tobacco straws, cotton straws, and coffee husks is selected as an additive, or

[0015] The additive is composed of A and B, wherein A is a potassium-sodium-rich biomass composite ash obtained by roasting at least one of tobacco straw, cotton straw, and coffee husk; and B is a potassium-sodium-rich biomass composite ash obtained by roasting at least one of rice husk and rice straw.

[0016] The amount of the potassium-sodium biomass composite ash additive added in step (3) is 1-9% of the mass of the silicon powder, preferably 4-9%, and more preferably 7-9%. In the study, it was found that excessive ash addition makes it difficult to form silicon ingots, and it is difficult to separate impurities and product silicon.

[0017] The uniform heating rate in step (3) is 8-12°C / min.

[0018] As a further preference, on the basis of ensuring that the boron removal rate is greater than 96%, in order to remove as much iron as possible, the available scheme is: drying and crushing potassium-sodium-rich biomass tobacco straw, cotton straw and coffee shell, and mixing them in a ratio of 3:2:1 to obtain biomass powder; heating the biomass powder to 900°C at a rate of 10°C / min, and roasting in air for 120min to obtain a potassium-sodium-rich biomass composite ash additive; mixing silicon powder and the potassium-sodium-rich biomass composite ash additive evenly, loading them in a high-purity graphite crucible, and then placing them in an induction furnace, and in a protective gas atmosphere, uniformly heating them to 1800°C at a rate of 10°C / min and keeping them warm for 4h to remove impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder.

[0019] As a further preference, on the basis of ensuring that the boron removal rate is greater than 96%, in order to remove as much calcium as possible, the available solutions are:

[0020] Potassium-sodium-rich tobacco straw and cotton straw are dried and crushed, and mixed in a ratio of 1:1 to obtain biomass powder; the biomass powder is heated to 900°C at a rate of 10°C / min, and roasted in air for 120 minutes to obtain a potassium-sodium-rich biomass composite ash additive; silicon powder and the potassium-sodium-rich biomass composite ash additive are evenly mixed, loaded into a high-purity graphite crucible, and then placed in an induction furnace, and under a protective atmosphere, the temperature is uniformly increased to 1800°C at a rate of 10°C / min and kept warm for 4 hours to remove impurity boron, and the furnace is cooled to room temperature, and the slag is removed to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder.

[0021] The principle of potassium-sodium biomass composite ash additive to enhance the removal of impurity boron in industrial silicon: biomass is rich in potassium and sodium elements. Through high-temperature roasting, composite ash rich in potassium and sodium carbonates is obtained. The ash is mixed with industrial silicon powder. During the refining process, the carbonates of sodium and potassium alkali metal elements react with the impurity boron element in industrial silicon to generate boron oxides that volatilize or enter the slag phase to remove the impurity boron. Through the selection of biomass, while ensuring efficient boron removal, the purity of industrial silicon is improved as much as possible, providing the necessary conditions for the subsequent stable production of high-purity silicon.

[0022] After one treatment, the boron removal rate of the present invention is greater than 84%, and the total removal rate of other impurities is greater than 13.5%. After optimization, the boron removal rate of the present invention is greater than 95.8%, and the total removal rate of other impurities is greater than 17%.

[0023] The beneficial effects of the present invention are: The present invention calcines potassium-sodium rich biomass at high temperature so that only potassium-sodium rich composite ash remains. The potassium-sodium rich composite ash contains a large amount of carbonates of sodium and potassium alkali metal elements, which are used as additives to strengthen industrial silicon refining. During the refining process, the carbonates of sodium and potassium alkali metal elements react with the impurity boron element in industrial silicon to generate boron oxides that volatilize or enter the slag phase to remove the impurity boron, thereby reducing the boron content to below 3.12ppmw.

[0024] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described in detail below in conjunction with specific implementation modes, but the protection scope of the present invention is not limited to the described contents.

[0026] The potassium and sodium contents in the biomass coffee husks, rice husks, rice straws, tobacco straws and cotton straws in the embodiments of the present invention are shown in Table 1.

[0027] Table 1 Potassium and sodium content in biomass coffee husk, rice husk, rice straw, tobacco straw and cotton straw

[0028]

[0029] The potassium and sodium contents in different potassium- and sodium-rich biomass composite ash additives in the embodiments of the present invention are shown in Table 2;

[0030] Table 2 Potassium and sodium content in different potassium-sodium-rich biomass composite ash additives

[0031]

[0032] The total mass contents of potassium and sodium in the potassium-sodium-rich biomass composite ash additive of the present invention are 21.2657%, 6.16%, 9.22%, 61.56% and 44.27% respectively.

[0033] Example 1: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0034] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 80-100 mesh; the boron content in the silicon powder of this embodiment is 100.46 ppmw, and the sum of other impurities is 5415 ppmw, and the types of other impurities are: Fe, Al, Ca, Ti (Fe3470 ppmw, Al 1330 ppmw, Ca 210 ppmw, Ti 405 ppmw);

[0035] (2) drying and crushing the potassium-sodium-rich biomass rice husk to obtain biomass powder; heating the biomass powder to 600° C. at a rate of 10° C. / min, and roasting in air for 60 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 6.16%;

[0036] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1450°C in a protective gas (argon) atmosphere and keeping them warm for 2 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 2% of the mass of the silicon powder;

[0037] The boron content of the impurity in the high-purity silicon of this embodiment is 15.46 ppmw (boron removal rate is 84.6%), and the sum of other impurities is 4725 ppmw (other impurity removal rate is 13.7%). The types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 3221 ppmw, Al remaining 1160 ppmw, Ca remaining 115 ppmw, Ti remaining 229 ppmw)

[0038] Example 2: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0039] (1) crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 100 to 120 mesh, which is the same batch of material as in Example 1;

[0040] (2) drying and crushing the potassium-sodium-rich biomass rice straw to obtain biomass powder; heating the biomass powder to 700° C. at a rate of 10° C. / min, and roasting in air for 60 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 9.22%;

[0041] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them at a rate of 10°C / min to 1500°C and keeping them warm for 2.5 hours in a protective gas (argon) atmosphere to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 3% of the mass of the silicon powder;

[0042] The impurity boron content in the high-purity silicon of this embodiment is 11.58 ppmw (boron removal rate is 88.5%), and the sum of other impurities is 4689 ppmw, and the types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 3350 ppmw, Al remaining 1194 ppmw, Ca remaining 65 ppmw, Ti remaining 80 ppmw)

[0043] Example 3: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0044] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 120-140 mesh; the silicon powder in this embodiment and that in embodiment 1 are from the same batch of materials;

[0045] (2) drying and crushing the potassium- and sodium-rich biomass coffee shells to obtain biomass powder; heating the biomass powder to 800° C. at a rate of 10° C. / min, and roasting in air for 90 min to obtain a potassium- and sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium- and sodium-rich biomass composite ash additive is 21.2657%;

[0046] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1600°C in a protective gas (argon) atmosphere and keeping them warm for 3 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 4% of the mass of the silicon powder;

[0047] The impurity boron content in the high-purity silicon of this embodiment is 8.71 ppmw (boron removal rate is 91.3%), and the sum of other impurities is 4578 ppmw, and the types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 3052 ppmw, Al remaining 1228 ppmw, Ca remaining 95 ppmw, Ti remaining 203 ppmw)

[0048] Example 4: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0049] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 140-160 mesh; the silicon powder in this embodiment and that in embodiment 1 are from the same batch of materials;

[0050] (2) drying and crushing the potassium-sodium-rich biomass cotton straw to obtain biomass powder; heating the biomass powder to 800° C. at a rate of 10° C. / min, and roasting in air for 100 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 44.27%;

[0051] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1650°C in a protective gas (argon) atmosphere and keeping them warm for 3.5 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 5% of the mass of the silicon powder;

[0052] The impurity boron content in the high-purity silicon of this embodiment is 5.36 ppmw (boron removal rate is 94.6%), the sum of other impurity contents is 4465 ppmw, and the types of other impurities are: Fe, Al, Ca, Ti (Fe remaining 3250 ppmw, Al remaining 815 ppmw, Ca remaining 20 ppmw, Ti remaining 380 ppmw).

[0053] Example 5: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0054] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 160-180 mesh; the silicon powder in this embodiment and that in embodiment 1 are from the same batch of materials;

[0055] (2) drying and crushing the potassium-sodium-rich biomass cotton straw to obtain biomass powder; heating the biomass powder to 900° C. at a rate of 10° C. / min, and roasting in air for 120 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 44.27%;

[0056] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1750°C in a protective gas (argon) atmosphere and keeping them warm for 4 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 7% of the mass of the silicon powder;

[0057] The impurity boron content in the high-purity silicon of this embodiment is 4.26ppmw (boron removal rate is 95.8%), and the sum of other impurities is 4272ppmw. The types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 2985ppmw, Al remaining 753ppmw, Ca remaining 165ppmw, Ti remaining 365ppmw)

[0058] Example 6: A method for enhancing the removal of impurity boron in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0059] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 180-200 mesh; the silicon powder used in this embodiment is from the same batch as that in Embodiment 1;

[0060] (2) drying and crushing the potassium-sodium-rich biomass tobacco straw to obtain biomass powder; heating the biomass powder to 900° C. at a rate of 10° C. / min, and roasting in air for 120 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 61.56%;

[0061] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1800°C in a protective gas (argon) atmosphere and keeping them warm for 4 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder;

[0062] The impurity boron content in the high-purity silicon of this embodiment is 3.12ppmw (boron removal rate is 96.9%), and the sum of other impurities is 4015ppmw. The types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 3185ppmw, Al remaining 653ppmw, Ca remaining 73ppmw, Ti remaining 104ppmw)

[0063] Example 7: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0064] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 180-200 mesh; the silicon powder in this embodiment and that in embodiment 1 are from the same batch of materials;

[0065] (2) drying and crushing potassium-sodium-rich biomass tobacco straw and cotton straw, and mixing them in a ratio of 1:1 to obtain biomass powder; heating the biomass powder to 900° C. at a rate of 10° C. / min, and roasting in air for 120 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 52.92%;

[0066] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1800°C in a protective gas (argon) atmosphere and keeping them warm for 4 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder;

[0067] The impurity boron content in the high-purity silicon of this embodiment is 3.58 ppmw (boron removal rate is 96.5%), and the sum of other impurities is 4178 ppmw. The types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 3062 ppmw, Al remaining 939 ppmw, Ca remaining 45 ppmw, Ti remaining 132 ppmw)

[0068] Example 8: A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, the specific steps are as follows:

[0069] (1) Crushing and sieving blocky industrial silicon to obtain silicon powder with a particle size of 180-200 mesh; the silicon powder used in this embodiment is from the same batch as that in Embodiment 1;

[0070] (2) drying and crushing potassium-sodium-rich biomass tobacco straw, cotton straw and coffee husk, and mixing them in a ratio of 3:2:1 to obtain biomass powder; heating the biomass powder to 900° C. at a rate of 10° C. / min, and roasting in air for 120 min to obtain a potassium-sodium-rich biomass composite ash additive; the total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive is 49.08%;

[0071] (3) mixing silicon powder and potassium-sodium-rich biomass composite ash additive uniformly, placing them in a high-purity graphite crucible, and then placing them in an induction furnace, heating them uniformly at a rate of 10°C / min to 1800°C in a protective gas (argon) atmosphere and keeping them warm for 4 hours to remove the impurity boron, cooling them to room temperature with the furnace, and removing the slag to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder;

[0072] The boron content of the impurity in the high-purity silicon of this embodiment is 3.75ppmw (boron removal rate is 96.3%), and the sum of other impurities is 4368ppmw (the total removal rate of other impurities is 19.4%). The types of other impurities are: Fe, Al, Ca, Ti. (Fe remaining 2837ppmw, Al remaining 1121ppmw, Ca remaining 175ppmw, Ti remaining 235ppmw)

[0073] This solution can ensure the removal of boron while also achieving good iron removal effects.

[0074] Comparative Example 1

[0075] Other conditions are the same as those in Example 6, except that:

[0076] The amount of the potassium-sodium-rich biomass composite ash additive added is 12% of the mass of the silicon powder; this makes it difficult to form a silicon ingot, and it is impossible to separate silicon from silicon slag, resulting in an inability to accurately measure the content of impurities in the silicon after smelting.

[0077] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive, characterized in that The steps include: (1) crushing and screening blocky industrial silicon to obtain silicon powder, wherein the particle size of the silicon powder is 80 to 200 mesh; in step (1), the boron content in the silicon powder is greater than 10 ppmw; (2) drying and crushing the potassium-sodium rich biomass to obtain biomass powder; heating the biomass powder to 600-900° C. and roasting in air for 60-120 min to obtain a potassium-sodium rich biomass composite ash additive; (3) The silicon powder and the potassium-sodium-rich biomass composite ash additive are mixed evenly, placed in a graphite crucible, and then placed in an induction furnace. Under a protective gas atmosphere, the temperature is uniformly increased to above 1410° C. and kept warm for 1 to 4 hours to remove the impurity boron, and the furnace is cooled to room temperature, and the slag is removed to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive in step (3) is 1 to 9% of the mass of the silicon powder.

2. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: The potassium-sodium-rich biomass in step (2) is one or more of coffee husks, rice husks, rice straws, tobacco straws, and cotton straws.

3. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: The total mass content of potassium and sodium in the potassium-sodium-rich biomass composite ash additive in step (2) is greater than or equal to 6%.

4. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: The potassium-sodium-rich biomass composite ash obtained by roasting at least one of tobacco straws, cotton straws and coffee husks is selected as an additive.

5. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: The additive is composed of A and B, wherein A is a potassium-sodium-rich biomass composite ash obtained by roasting at least one of tobacco straw, cotton straw, and coffee husk; and B is a potassium-sodium-rich biomass composite ash obtained by roasting at least one of rice husk and rice straw.

6. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: In step (3), the amount of potassium-sodium-rich biomass composite ash additive added is 4-9% of the mass of silicon powder.

7. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: In step (3), the amount of potassium-sodium-rich biomass composite ash additive added is 7-9% of the mass of silicon powder.

8. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: The uniform heating rate in step (3) is 8-12°C / min.

9. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: In the step (3), the temperature is raised to 1450-1800° C. and kept at this temperature for 1-4 hours to remove the impurity boron.

10. The method for enhancing the removal of boron impurities in industrial silicon using a potassium-sodium-rich biomass composite ash additive according to claim 1, characterized in that: Potassium-sodium-rich biomass tobacco straw, cotton straw and coffee shell are dried and crushed, and mixed in a ratio of 3:2:1 to obtain biomass powder; the biomass powder is heated to 900°C at a rate of 10°C / min, and roasted in air for 120min to obtain a potassium-sodium-rich biomass composite ash additive; silicon powder and the potassium-sodium-rich biomass composite ash additive are evenly mixed, loaded into a high-purity graphite crucible, and then placed in an induction furnace, and in a protective gas atmosphere, the temperature is uniformly increased to 1800°C at a rate of 10°C / min and kept warm for 4h to remove impurity boron, and the furnace is cooled to room temperature, and the slag is removed to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder; or Potassium-sodium-rich tobacco straw and cotton straw are dried and crushed, and mixed in a ratio of 1:1 to obtain biomass powder; the biomass powder is heated to 900°C at a rate of 10°C / min, and roasted in air for 120 minutes to obtain a potassium-sodium-rich biomass composite ash additive; silicon powder and the potassium-sodium-rich biomass composite ash additive are evenly mixed, loaded into a high-purity graphite crucible, and then placed in an induction furnace, and under a protective atmosphere, the temperature is uniformly increased to 1800°C at a rate of 10°C / min and kept warm for 4 hours to remove impurity boron, and the furnace is cooled to room temperature, and the slag is removed to obtain high-purity silicon; the addition amount of the potassium-sodium-rich biomass composite ash additive is 9% of the mass of the silicon powder.

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