Impurity removal and utilization method of silicon-containing waste residue in polycrystalline silicon production process

Abstract

The invention relates to the technical field of impurity removal and recycling of silicon-containing waste residues, and discloses an impurity removal and utilization method of silicon-containing waste residues in a polycrystalline silicon production process, which comprises the following steps: immersing the silicon-containing waste residues in the polycrystalline silicon production process into a leaching solution containing hydrofluoric acid and copper nitrate, adding hydrogen peroxide, and carrying out a metal-assisted chemical etching reaction, obtaining silicon powder attached with copper; and the silicon powder attached with copper is annealed and then put into a cold hydrogenation reaction. According to the method, the purification of the silicon-containing waste residues and the loading of copper can be realized in one step by utilizing a metal-assisted chemical etching method, and a cuprous chloride catalyst does not need to be additionally added in a subsequent cold hydrogenation process. The silicon powder in the silicon-containing waste residue is recycled, the production cost is reduced, the waste of resources is avoided, and the method conforms to the criterion of harmless treatment.

Description

Technical Field

[0001] The invention relates to the technical field of impurity removal and recycling of silicon-containing waste slag, and in particular to a method for removing impurities and recycling silicon-containing waste slag in a polysilicon production process. Background Art

[0002] Polysilicon is widely used in the solar photovoltaic industry and the optoelectronics industry. More than 90% of polysilicon is produced by the modified Siemens process. The raw material for producing polysilicon by the modified Siemens process is trichlorosilane, which is specifically synthesized by silicon powder, silicon tetrachloride and hydrogen in a fluidized bed reactor. During the synthesis process, the gas will take away some silicon particles from the reactor and enter the slurry treatment system after rapid cooling. The slurry is a mixture with a pungent odor and strong corrosiveness. It mainly contains a small amount of trichlorosilane, silicon tetrachloride, some high-boiling chlorosilanes, and a certain amount of Si powder and metal chlorides. The current method for treating the slurry is to first separate the solid and liquid by sedimentation. The separated chlorosilane is fractionated, the monosilane is returned to the separation process, the high-boiling chlorosilane is also returned to the separation system after cracking, and the siloxane that cannot be cracked is hydrolyzed. The solid composed of Si powder and metal chloride is mainly landfilled. This treatment method will cause waste of this part of Si powder and will also cause a certain degree of environmental problems, which does not meet the principles of resource conservation and harmless treatment.

[0003] Patent CN112142055A discloses a method for recycling slurry in a cold hydrogenation process and a recycling system used therein. The slurry in the cold hydrogenation process is subjected to solid-liquid separation, and the obtained solid is heated to 1100-1250°C with zircon sand, a carbonaceous reducing agent, and chlorine gas, and reacted under the catalysis of cuprous chloride to produce zirconium tetrachloride, silicon tetrachloride, and carbon monoxide. Zirconium tetrachloride is a production product, and silicon powder and chlorine gas synthesize silicon tetrachloride and return to the cold hydrogenation system. However, this recovery method uses a relatively high reaction temperature, and the chlorination and reduction products need to be separated later, and the process is relatively complicated.

[0004] Patent CN219429722U discloses the recycling of waste residues in the slurry produced during the production of polysilicon. The recovered chlorosilane is sent to a distillation tank, and the silicon powder obtained is dried to obtain silicon mud, which is then smelted and recovered to obtain silicon ingots, thereby realizing the recycling of silicon powder. However, the above Si powder utilization method is mainly to use it as a reducing agent through heat treatment, and it cannot return to the cold hydrogenation process.

[0005] In addition to silicon powder, the solids in the slurry also contain impurities such as Fe, Al, Ca, and Ti. Directly returning to the cold hydrogenation reaction process will increase the content of metal impurities in chlorosilane. In addition, the literature reports that a higher impurity content weakens the catalytic effect of the copper catalyst in the cold hydrogenation reaction process, thereby affecting the efficiency of the cold hydrogenation reaction. Summary of the invention

[0006] In order to solve the problem that slag slurry is generated in the cold hydrogenation process, and silicon-containing waste slag is generated after solid-liquid separation, and this part of the waste slag cannot be put into the production section again, resulting in a large amount of silicon powder being wasted, the purpose of the present invention is to provide a method for removing impurities and utilizing silicon-containing waste slag in the production process of polysilicon, and the silicon powder purified by the method can be directly put into the cold hydrogenation reaction without the need to add additional cuprous chloride.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0008] A method for removing impurities and utilizing silicon-containing waste slag in a polysilicon production process comprises the following steps:

[0009] The silicon-containing waste residue in the polysilicon production process is immersed in a leaching solution containing hydrofluoric acid and copper nitrate, and hydrogen peroxide is added to perform a metal-assisted chemical etching reaction to obtain silicon powder with copper attached;

[0010] The copper-attached silicon powder is annealed and then put into a cold hydrogenation reaction.

[0011] Furthermore, the mass concentration of hydrofluoric acid in the leaching solution containing hydrofluoric acid and copper nitrate is 4% to 11%, and the mass concentration of copper nitrate in the leaching solution containing hydrofluoric acid and copper nitrate is 0.7 to 7%.

[0012] Furthermore, the mass ratio of hydrofluoric acid to copper nitrate is 1:0.00625-0.0625.

[0013] Furthermore, the mass concentration of hydrogen peroxide is 3% to 5%, and the mass ratio of hydrogen peroxide to copper nitrate is 1:0.00625 to 0.0625.

[0014] Furthermore, the mass ratio of silicon-containing waste slag to copper nitrate is 1:0.01098-0.1098.

[0015] Furthermore, the temperature of the metal-assisted chemical etching reaction is 50-60° C. and the time is 2 hours.

[0016] Furthermore, the annealing temperature is 350° C. to 650° C., and the time is 3 to 4 hours.

[0017] Furthermore, the temperature of the cold hydrogenation reaction is 500°C.

[0018] Furthermore, during the cold hydrogenation reaction, the hydrogen flow rate is 200-250 mL / min.

[0019] Furthermore, during the cold hydrogenation reaction, the molar ratio of hydrogen to silicon tetrachloride is 4:1.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention not only removes metal impurities in Si powder, but also uniformly deposits copper into the pores of silicon particles through the principle of metal-assisted etching, and converts copper into catalytic active material Cu3Si during the cold hydrogenation reaction. The method can effectively recycle Si powder, and the recycled Si powder can be directly used in the cold hydrogenation reaction, which reduces production costs, avoids waste of resources, and meets the principle of harmless treatment.

[0022] The metal-assisted chemical etching method is a process of locally oxidizing and dissolving the silicon substrate in a hydrofluoric acid solution in the presence of an oxidant. Metal nanoparticles are introduced on the surface of the silicon substrate to form a primary battery between the silicon substrate and the metal nanoparticles. The metal nanoparticles act as micro-cathode and the silicon substrate acts as an anode. The oxidant in the etching solution injects holes into the valence band of silicon under the catalytic action of the metal nanoparticles, causing the silicon in contact with the metal nanoparticles to be oxidized, and the electrons provided by the oxidized silicon further promote the reduction of the oxide, thereby forming a spontaneous electrochemical reaction on the silicon surface. The main reactions are as follows:

[0023] Cathode: H2O2+2H + →2H2O+2h +

[0024] Anode: Si+6HF+NH + →H2SiF6+nH + +[(4-n) / 2]H2↑

[0025] Overall reaction: Si+6HF+n / 2H2O2→H2SiF6+nH2O+[(4-n) / 2]H2↑

[0026] The metal-assisted chemical etching method can form a certain pore structure on the surface of the silicon substrate. Compared with the acid leaching method, the pore structure formed by this method is conducive to improving the contact between the impurities in the silicon and the leaching solution, thereby strengthening the removal of impurities in the silicon-containing waste slag. The removal rate of metal impurities Fe, Ti, and Ca can reach more than 99%, and the removal rate of Al can reach more than 96%. At the same time, this method can deposit copper nanoparticles on the silicon surface, and after annealing, a catalytic active substance Cu3Si for cold hydrogenation reaction can be formed. After directly putting it into the cold hydrogenation reaction without adding a catalyst, the conversion rate of silicon tetrachloride can reach 17.75%. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 The SEM images of the samples of silicon-containing waste slag after treatment and their corresponding EDS element mapping images, where (a) is the SEM image of the treated silicon-containing waste slag, (b) is the distribution diagram of the surface elements after treatment, (c) is the Si element mapping image of the sample surface after treatment, and (d) is the Cu element mapping image of the sample surface after treatment;

[0028] Figure 2 This is a comparison chart of the conversion rate of silicon tetrachloride. DETAILED DESCRIPTION

[0029] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly and comprehensively understood.

[0030] Example 1

[0031] Weigh 20g of silicon-containing waste residue from the production process of polycrystalline silicon with a mesh size of about 100 after grinding, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, wherein the mass concentration of hydrofluoric acid in the mixture is 11% and the mass concentration of copper nitrate is 0.7%. Etch for 1min, slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter to neutral, and vacuum dry at 80°C for 6h to obtain silicon powder with copper attached, recorded as pSi-1.

[0032] The removal rates of Fe, Al, Ti and Ca are 99.81%, 96.21%, 98.38% and 98.45% respectively.

[0033] 10 g of pSi-1 was put into a tube furnace, and heated to 450°C at a rate of 10°C / min in a nitrogen atmosphere and maintained for 3 h to obtain a mixture of catalytically active substances and silicon powder, which was recorded as Cu3Si / pSi-1.

[0034] 9.6 g of Cu3Si / pSi-1 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 14.70%.

[0035] Example 2

[0036] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, the mass concentration of hydrofluoric acid in the mixture is 4%, and the mass concentration of copper nitrate is 0.7%. Etch for 1 minute, slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-2.

[0037] The removal rates of Fe, Al, Ti and Ca were 98.67%, 94.07%, 97.15% and 95.17% respectively.

[0038] Take 10g of pSi-2 and put it into a tubular furnace. Under a nitrogen atmosphere, heat it to 450℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-2.

[0039] 9.6 g of Cu3Si / pSi-2 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 10.21%.

[0040] Example 3

[0041] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, etch for 1min, the mass concentration of hydrofluoric acid in the mixture is 11%, and the mass concentration of copper nitrate is 0.7%, slowly add 170mL of 5% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-3.

[0042] The removal rates of Fe, Al, Ti and Ca are 99.50%, 94.98%, 97.67% and 98.30% respectively.

[0043] Take 10g of pSi-3 and put it into a tubular furnace. Under a nitrogen atmosphere, heat it to 450℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-3.

[0044] 9.6 g of Cu3Si / pSi-3 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 11.76%.

[0045] Example 4

[0046] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, and etch it for 1min. The mass concentration of hydrofluoric acid in the mixture is 11%, and the mass concentration of copper nitrate is 7%. Slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-4.

[0047] The removal rates of Fe, Al, Ti and Ca are 99.91%, 96.89%, 99.02% and 99.38% respectively.

[0048] Take 10g of pSi-4 and put it into a tube furnace. In a nitrogen atmosphere, heat it to 450℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-4.

[0049] 9.6 g of Cu3Si / pSi-4 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 17.75%.

[0050] Example 5

[0051] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, etch for 1min, the mass concentration of hydrofluoric acid in the mixture is 11%, and the mass concentration of copper nitrate is 0.7%, slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-1.

[0052] The removal rates of Fe, Al, Ti and Ca are 99.81%, 96.21%, 98.38% and 98.45% respectively.

[0053] Take 10g of pSi-1 and put it into a tube furnace. Under a nitrogen atmosphere, heat it to 350℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-5.

[0054] 9.6 g of Cu3Si / pSi-5 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 14.09%.

[0055] Example 6

[0056] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, etch for 1min, the mass concentration of hydrofluoric acid in the mixture is 11%, and the mass concentration of copper nitrate is 0.7%, slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-1.

[0057] The removal rates of Fe, Al, Ti and Ca are 99.81%, 96.21%, 98.38% and 98.45% respectively.

[0058] Take 10g of pSi-1 and put it into a tube furnace. Under a nitrogen atmosphere, heat it to 550℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-6.

[0059] 9.6 g of Cu3Si / pSi-6 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 14.23%.

[0060] Example 7

[0061] Weigh 20g of silicon-containing waste residue of about 100 mesh, dissolve it in a mixture of 170mL of hydrofluoric acid solution and 60mL of copper nitrate solution, etch for 1min, the mass concentration of hydrofluoric acid in the mixture is 11%, and the mass concentration of copper nitrate is 0.7%, slowly add 170mL of 3% hydrogen peroxide, react at 55°C for 2h, filter until neutral, and vacuum dry at 80°C for 6h to obtain pSi-1.

[0062] The removal rates of Fe, Al, Ti and Ca are 99.81%, 96.21%, 98.38% and 98.45% respectively.

[0063] Take 10g of pSi-1 and put it into a tube furnace. Under a nitrogen atmosphere, heat it to 650℃ at a rate of 10℃ / min and keep it for 3h to obtain Cu3Si / pSi-7.

[0064] 9.6 g of Cu3Si / pSi-7 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 9.07%.

[0065] Example 8

[0066] Weigh 20g of silicon-containing waste residue in the production process of polysilicon with a mesh size of about 100 after grinding, dissolve it in a leachate containing hydrofluoric acid and copper nitrate, etch for 1min, slowly add hydrogen peroxide, react at 50℃ for 2h, filter to neutral, vacuum dry at 80℃ for 6h, and obtain silicon powder with copper attached, which is recorded as pSi-1. Among them, the mass concentration of hydrofluoric acid in the leachate containing hydrofluoric acid and copper nitrate is 4%, and the mass concentration of copper nitrate in the leachate containing hydrofluoric acid and copper nitrate is 0.7%. The mass ratio of hydrogen peroxide, hydrofluoric acid and copper nitrate is 1:0.01. The mass concentration of hydrogen peroxide is 3%, and the mass ratio of silicon-containing waste residue to copper nitrate is 1:0.05.

[0067] 10 g of pSi-1 was put into a tube furnace, and heated to 550° C. at a rate of 10° C. / min in a nitrogen atmosphere and maintained for 3.5 h to obtain a mixture of catalytically active substances and silicon powder, which was recorded as Cu3Si / pSi-1.

[0068] 9.6 g of Cu3Si / pSi-1 was filled into a fixed bed reactor, and trichlorosilane was synthesized under the conditions of a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1.

[0069] Example 9

[0070] Weigh 20g of silicon-containing waste residue in the production process of polysilicon with a mesh size of about 100 after grinding, dissolve it in a leachate containing hydrofluoric acid and copper nitrate, etch for 1min, slowly add hydrogen peroxide, react at 60℃ for 2h, filter to neutral, vacuum dry at 80℃ for 6h, and obtain silicon powder with copper attached, which is recorded as pSi-1. Among them, the mass concentration of hydrofluoric acid in the leachate containing hydrofluoric acid and copper nitrate is 11%, and the mass concentration of copper nitrate in the leachate containing hydrofluoric acid and copper nitrate is 7%. The mass ratio of hydrogen peroxide, hydrofluoric acid and copper nitrate is 1:0.0625. The mass concentration of hydrogen peroxide is 5%, and the mass ratio of silicon-containing waste residue to copper nitrate is 1:0.1098.

[0071] 10 g of pSi-1 was put into a tube furnace, and heated to 650°C at a rate of 10°C / min in a nitrogen atmosphere and maintained for 3 h to obtain a mixture of catalytically active substances and silicon powder, which was recorded as Cu3Si / pSi-1.

[0072] 9.6 g of Cu3Si / pSi-1 was filled into a fixed bed reactor, and trichlorosilane was synthesized under the conditions of a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1.

[0073] Example 10

[0074] Weigh 20g of silicon-containing waste residue in the production process of polysilicon with a mesh size of about 100 after grinding, dissolve it in a leachate containing hydrofluoric acid and copper nitrate, etch for 1min, slowly add hydrogen peroxide, react at 55℃ for 2h, filter to neutral, vacuum dry at 80℃ for 6h, and obtain silicon powder with copper attached, which is recorded as pSi-1. Among them, the mass concentration of hydrofluoric acid in the leachate containing hydrofluoric acid and copper nitrate is 7%, and the mass concentration of copper nitrate in the leachate containing hydrofluoric acid and copper nitrate is 3%. The mass ratio of hydrogen peroxide, hydrofluoric acid and copper nitrate is 1:0.00625. The mass concentration of hydrogen peroxide is 4%, and the mass ratio of silicon-containing waste residue to copper nitrate is 1:0.01098.

[0075] 10 g of pSi-1 was put into a tube furnace, and heated to 350° C. at a rate of 10° C. / min in a nitrogen atmosphere and maintained for 4 h to obtain a mixture of catalytically active substances and silicon powder, which was recorded as Cu3Si / pSi-1.

[0076] 9.6 g of Cu3Si / pSi-1 was filled into a fixed bed reactor, and trichlorosilane was synthesized under the conditions of a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1.

[0077] Comparative Example 1

[0078] Weigh 20 g of silicon-containing waste residue of about 100 mesh, dissolve it in 400 mL of 19% hydrochloric acid, react at 55° C. for 6 h, filter it until it is neutral, and vacuum dry it at 80° C. for 6 h to obtain HCl-Si.

[0079] The removal rates of Fe, Al, Ti and Ca were 68.49%, 94.45%, 80.39% and 94.91% respectively.

[0080] Take 10g HCl-Si and 2g cuprous chloride and mix them evenly. Put the mixture into a tube furnace, and heat it to 450°C at 10°C / min under a nitrogen atmosphere and keep it for 3h to obtain Cu3Si / Si-1.

[0081] 9.6 g of Cu3Si / Si-1 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 16.77%.

[0082] Comparative Example 2

[0083] Weigh 20 g of silicon-containing waste residue of about 100 mesh, dissolve it in 400 mL of 4% hydrofluoric acid, react at 55° C. for 6 h, filter it until it is neutral, and vacuum dry it at 80° C. for 6 h to obtain HF-Si.

[0084] The removal rates of Fe, Al, Ti and Ca are 99.21%, 85.55%, 95.73% and 96.86% respectively.

[0085] Take 10g HF-Si and 12g cuprous chloride and mix them evenly. Put the mixture into a tube furnace, and heat it to 450°C at 10°C / min under a nitrogen atmosphere and keep it for 3h to obtain Cu3Si / Si-2.

[0086] 9.6 g of Cu3Si / Si-2 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 5.72%.

[0087] Comparative Example 3

[0088] Weigh 20 g of silicon-containing waste residue of about 100 mesh, dissolve it in 400 mL of a mixture of hydrochloric acid and hydrofluoric acid, wherein the mass concentration of hydrochloric acid is 19% and the mass concentration of hydrofluoric acid is 4%, react at 55°C for 6 h, filter to neutrality, and vacuum dry at 80°C for 6 h to obtain HCl-HF-Si.

[0089] The removal rates of Fe, Al, Ti and Ca were 74.41%, 93.78%, 91.09% and 96.24% respectively.

[0090] Take 10g HCl-HF-Si and 2g cuprous chloride and mix them evenly. Put the mixture into a tube furnace, and heat it to 450℃ at 10℃ / min under a nitrogen atmosphere and keep it for 3h to obtain Cu3Si / Si-3.

[0091] 9.6 g of Cu3Si / Si-3 was filled into a fixed bed reactor, and trichlorosilane was synthesized at a reaction temperature of 500°C, normal pressure, a hydrogen flow rate of 200 mL / min, and a molar ratio of hydrogen to silicon tetrachloride of 4:1. The conversion rate of silicon tetrachloride was 11.89%.

[0092] The silicon content of the solid silicon-containing waste residue after solid-liquid separation is 47.97 wt %. The silicon content can reach 98 wt % by removing the metal impurities in the waste residue by metal-assisted chemical etching. See Table 1 for specific values.

[0093] Table 1 Impurity content in silicon-containing waste slag and silicon powder after treatment

[0094]

[0095] It can be seen from Table 1 that the silicon content of the sample treated by the metal-assisted chemical etching method can reach 98%, while the content of other metal impurities is less than 0.01%.

[0096] Table 2 Summary of specific surface area and pore size of silicon-containing waste slag after treatment under different conditions

[0097]

[0098] It can be seen from Table 2 that by adjusting the concentration of each solution in the metal-assisted chemical etching method, a porous structure is formed on the surface of the treated sample.

[0099] Table 3 Comparison of silicon-containing waste slag removal rates under different treatment conditions

[0100]

[0101]

[0102] It can be seen from Table 3 that compared with the acid leaching method for treating silicon-containing waste slag, the metal-assisted chemical etching method can remove deep-level impurities in the silicon-containing waste slag, and the reaction time is shorter, which is 2 hours. Under the optimized experimental conditions, the removal rates of metal impurities Fe, Ti, and Ca in silicon-containing waste slag are all above 99%, and the removal rate of Al can reach 96.89%.

[0103] Table 4 Comparison of the effects of different treatment conditions on cold hydrogenation reaction

[0104]

[0105]

[0106] As can be seen from Table 4, the best conversion rate of SiCl4 in the sample treated with acid washing of silicon-containing waste slag is 16.77% under the condition of adding 20% ​​catalyst; the best conversion rate of SiCl4 in the sample treated with metal-assisted chemical etching method is 17.75% under the condition of not adding catalyst. The results of exploring the effect of different temperatures on the catalytic activity of the treated samples show that when the reaction temperature is 450℃, the best conversion rate of SiCl4 is 17.75%.

[0107] See also Figure 1 In (a), (b), (c) and (d), it can be seen that a regular pore structure is formed on the surface of the sample after treatment with metal-assisted chemical etching, and copper is evenly distributed on the surface of the Si substrate and in the pores.

[0108] See also Figure 2 It can be seen that among Example 1, Example 2, Example 3, Example 4 and Comparative Example 1, Comparative Example 2, Comparative Example 3, the best conversion rate of SiCl4 in Example 4 after being recycled for cold hydrogenation reaction is 17.75%.

[0109] The above description is only for the best embodiment of the present invention, but it should not be understood as limiting the claims. The present invention is not limited to the above embodiments, and its specific structure is allowed to be changed. However, all changes made within the protection scope of the independent claims of the present invention are within the protection scope of the present invention.

[0110] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

Claims

1. A method for removing impurities and utilizing silicon-containing waste slag in a polysilicon production process, characterized in that: The following steps are involved: The silicon-containing waste residue in the polysilicon production process is immersed in a leaching solution containing hydrofluoric acid and copper nitrate, and hydrogen peroxide is added to perform a metal-assisted chemical etching reaction to obtain silicon powder with copper attached; The copper-attached silicon powder is annealed and then put into a cold hydrogenation reaction.

2. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The mass concentration of hydrofluoric acid in the leaching solution containing hydrofluoric acid and copper nitrate is 4% to 11%, and the mass concentration of copper nitrate in the leaching solution containing hydrofluoric acid and copper nitrate is 0.7% to 7%.

3. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The mass ratio of hydrofluoric acid to copper nitrate is 1:0.00625~0.0625.

4. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The mass concentration of hydrogen peroxide is 3% to 5%, and the mass ratio of hydrogen peroxide to copper nitrate is 1:0.00625 to 0.0625.

5. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The mass ratio of silicon-containing waste slag to copper nitrate is 1:0.01098-0.1098.

6. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The temperature of the metal-assisted chemical etching reaction is 50-60° C. and the time is 2 hours.

7. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The annealing temperature is 350°C to 650°C, and the time is 3 to 4 hours.

8. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: The temperature of the cold hydrogenation reaction is 500°C.

9. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: During the cold hydrogenation reaction, the hydrogen flow rate is 200-250 mL / min.

10. The method for removing impurities and utilizing silicon-containing waste slag in the polysilicon production process according to claim 1, characterized in that: During the cold hydrogenation reaction, the molar ratio of hydrogen to silicon tetrachloride is 4:1.

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