A method for removing metallic and non-metallic impurities from industrial silicon by secondary refining

Abstract

The application provides a method for removing metal and nonmetal impurities in industrial silicon by off-oven refining, comprising the following steps: S1, collecting industrial silicon melt obtained by smelting industrial silicon in a silicon ladle; S2, continuously introducing gas from the bottom of the silicon ladle, and adding a slagging agent obtained by calcining a raw material containing barium salt into the silicon ladle while the gas is being introduced, maintaining the temperature of the industrial silicon melt at 1500-1700 DEG C by blowing the gas, and keeping the temperature for 20-60 min; S3, after the temperature-keeping reaction is completed, tilting the silicon ladle to pour out the industrial silicon melt in the silicon ladle, and leaving the impurities floating on the surface and sinking to the bottom in the silicon ladle for subsequent pouring out; wherein the removed metal and nonmetal impurities at least include calcium, aluminum, phosphorus, boron and titanium. The application can effectively reduce the content of various impurities, is simple to operate, and is suitable for industrial large-scale production.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of industrial silicon purification, and particularly relates to a method for removing metal and non-metal impurities in industrial silicon by furnace refining. BACKGROUND

[0002] With the gradual increase of the quality requirements of downstream chemical industry and electronic industry on the industrial silicon product, the industrial silicon production enterprises generally adopt the furnace refining technology to improve the quality of the industrial silicon product. Meanwhile, with the rapid development of the photovoltaic industry, the low-cost preparation of solar-grade polysilicon by metallurgical method has attracted more and more attention, and the requirements for the quality of the industrial silicon product as raw material are also more and more stringent. The existing industrial silicon production technology cannot meet the requirements. In order to further reduce the production cost of solar-grade polysilicon, the new process of low-cost preparation of solar-grade polysilicon by metallurgical method gradually extends to the industrial silicon smelting and refining process, and especially the furnace refining process of industrial silicon has become an important and indispensable process of the new process of low-cost preparation of solar-grade polysilicon by metallurgical method.

[0003] The furnace refining methods of industrial silicon mainly include two types, namely, gas blowing refining and slagging refining. The gas blowing refining is usually achieved by blowing single gas or mixed gas such as hydrogen, oxygen, nitrogen, argon and water vapor into the industrial silicon melt. The slagging refining is usually achieved by adding common oxides such as silicon oxide, calcium oxide and aluminum oxide into the industrial silicon melt.

[0004] In the prior art, in order to solve the problems of difficult separation of silicon slag in the slagging refining and easy introduction of new impurities, a solution of increasing the amount of ZnO in the ternary slagging agent and controlling the reaction temperature and time is proposed. However, the method involves the use of zinc oxide material and the amount is relatively large, which greatly increases the cost of impurity removal. Meanwhile, the components in the slagging agent are not treated, and it is difficult to mix uniformly in actual operation. In addition, the method does not show the removal effect of Ti, and there is a certain limitation in impurity removal.

[0005] Therefore, there is an urgent need for a refining slagging method with less amount, no introduction of new impurities, easy separation of silicon slag, significant impurity removal effect and low cost. SUMMARY

[0006] The present application aims to overcome the shortcomings of the prior art and provide a method for removing calcium, aluminum, phosphorus, boron and titanium impurities in industrial silicon melt by furnace refining, which is simple in process, low in cost and does not introduce new impurities.

[0007] A method for removing metal and non-metal impurities in industrial silicon by off-oven refining, comprising:

[0008] Step S1, collecting industrial silicon melt obtained by industrial silicon smelting in a silicon ladle;

[0009] Step S2, continuously introducing gas from the bottom of the silicon ladle, while adding a slagging agent obtained by calcining raw materials containing barium salt into the silicon ladle, maintaining the temperature of the industrial silicon melt at 1500-1700°C by blowing gas, and keeping the reaction for 20-60 min; after the reaction, the impurities with large density sink to the bottom of the industrial silicon melt, the impurities with small density float on the surface of the industrial silicon melt, and the volatile impurities directly volatilize and overflow the industrial silicon melt;

[0010] Step S3, after the heat preservation reaction is completed, the industrial silicon melt in the silicon ladle is poured out, and the impurities floating on the surface and sinking to the bottom are left in the silicon ladle for subsequent pouring; before pouring the silicon liquid, the surface dross is raked off, and the impurities sinking to the bottom are raked off after the casting is completed;

[0011] The removed metal and non-metal impurities at least include calcium, aluminum, phosphorus, boron, and titanium.

[0012] Optionally, in step S2, the gas is oxygen or compressed air.

[0013] Optionally, in step S2, the gas flow is 500-1500 L / h, the pressure is 0.2-1 MPa, and the gas introduction time starts from when the industrial silicon melt is collected in the silicon ladle, accounting for 1 / 3 of the total volume of the silicon ladle, and ends when the refining heat preservation is completed and the industrial silicon melt is poured out. Under this condition, the gas introduction can play the roles of heat preservation and stirring. The introduction of gas can make the industrial silicon melt constantly boil, achieving the effect of stirring the industrial silicon melt; maintaining the relatively stable temperature of the industrial silicon melt; and oxidizing the calcium, aluminum, phosphorus, boron, titanium, and other impurities in the industrial silicon melt.

[0014] Optionally, the preparation raw materials of the slagging agent are silica, calcium oxide, and barium salt, or silica, sodium carbonate, and barium salt; and preferably, silica, sodium carbonate, and barium salt are used.

[0015] Optionally, the preparation method of the slagging agent is: mixing a certain proportion of silica, calcium oxide, and barium salt, or silica, sodium carbonate, and barium salt, and then calcining at 1200-1500°C for 30 min to obtain a blocky slagging agent.

[0016] Optionally, the slagging agent raw material silicon dioxide purity ≥98wt%, calcium oxide purity ≥90wt%, sodium carbonate purity ≥98wt%, barium salt purity ≥98wt%, can be used industrial grade raw material; barium salt is selected from one or more of barium oxide, barium carbonate, barium hydroxide, barium sulfate, barium chloride; preferably the slagging agent raw material is crushed to not more than 5cm.

[0017] Optionally, the weight percentage of the slagging agent raw material silicon dioxide, calcium oxide, barium salt or silicon dioxide, sodium carbonate, barium salt is 30-50:30-50:5-40, the total weight percentage of the three raw materials is 100%.

[0018] Optionally, the amount of slagging agent is 2-25% of the total mass of the industrial silicon melt used for refining, and the method of adding the slagging agent to the industrial silicon melt is to take a sufficient amount of slagging agent, immediately after the completion of the collection of the industrial silicon melt, add the first batch of slagging agent, the amount is 1 / 4 of the total mass of the required slagging agent, then every 5-10min, add the slagging agent of 1 / 4 of the total mass of the required slagging agent, until all the slagging agent is added. The batch addition can make the slag system and the silicon melt fully mixed, and if added at once, the slag phase may be concentrated at the bottom or top.

[0019] The principle of the present application is that: in the refining process, the steam bubble of the barium-containing slag system can contact with the silicon water surface, and can react with phosphorus, boron, titanium and other impurities in the silicon melt to form complex oxides, which can help the aggregation and removal of metal inclusions. In addition, barium salt can change the vapor pressure, density, melting point and other properties of impurity elements in the silicon melt, which can enhance the effect of the slag system, change the morphology of inclusions, and improve the utilization rate and the effect of removing impurities.

[0020] The technical scheme provided by the present application brings at least the following beneficial effects:

[0021] 1. The content of aluminum, calcium, phosphorus, boron, titanium and other impurities in the industrial silicon product is effectively reduced, the performance of the industrial silicon product is improved, and higher economic value is created;

[0022] 2. The temperature of the industrial silicon melt inside the silicon package is maintained by the bottom blowing method during the refining process, and the internal silicon melt is stirred, without the need for additional heat preservation equipment and stirring equipment, thereby reducing the energy consumption required in the refining process;

[0023] 3. The slagging agent is prepared from relatively low-cost raw materials such as silicon dioxide, calcium oxide, sodium carbonate, and barium salt, and the method of mixing and firing the raw materials ensures that the raw materials are fully mixed and uniform, thereby improving the effect of refining and removing impurities;

[0024] 4. After the refining is completed, the separation of silicon and slag is realized by simple twice pouring, which is simple to operate and suitable for industrial large-scale production. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Table 1. Impurity Composition of Raw Materials

[0029] Element Al Ca P B Ti Content 0.38％ 0.2％ 63 ppm 36 ppm 597 ppm

[0030] Example 1

[0031] When the industrial silicon melt collected in the silicon bag reaches 1 / 3 of the total volume of the bag, oxygen is introduced from the bottom of the bag at a pressure of 0.2 MPa and a flow rate of 600 L / h. After the silicon melt is collected, a slagging agent obtained by calcining raw materials with a mass percentage of silicon dioxide:sodium carbonate:barium carbonate of 45%:45%:10% at 1200℃ for 30 min is added to the silicon bag in batches at 5-minute intervals. The amount of slagging agent is 5% of the weight of industrial silicon. The temperature is controlled at 1680℃, and the bag is continuously purged and kept at this temperature for 25 min to allow impurities to form different compounds and fully detach from the industrial silicon melt. The bag is then poured to obtain refined industrial silicon. After the industrial silicon naturally solidifies, samples are obtained from different locations by cutting. After being sieved using the quartering method, powder samples with an average particle size of 200 mesh are prepared. The content of aluminum, calcium, phosphorus, boron, and titanium is detected by inductively coupled plasma atomic emission spectrometry.

[0032] Example 2

[0033] When the industrial silicon melt collected in the silicon package reaches 1 / 3 of the total volume of the silicon package, compressed air is introduced from the bottom of the silicon package, the compressed air pressure is 0.8 MPa, the gas flow is 1400 L / h, after the collection of the silicon melt is completed, the raw materials with a mass percentage of 30%:30%:40% of silicon dioxide:sodium carbonate:barium oxide are fired at 1300°C for 30 min to obtain a slagging agent, which is added to the silicon package in batches at intervals of 10 min, the amount of the slagging agent is 10% of the weight of the industrial silicon, the temperature is controlled at 1550°C, and the gas blowing is continued for 60 min to make the impurities form different compounds and fully separate from the industrial silicon melt, and then the refined industrial silicon is poured. After the industrial silicon is naturally condensed, samples at different positions are obtained by cutting, the samples are screened by quartering method to obtain powder samples with an average particle size of 200 mesh, and the contents of aluminum, calcium, phosphorus, boron and titanium are detected by inductively coupled plasma atomic emission spectrometer.

[0034] Example 3

[0035] When the industrial silicon melt collected in the silicon package reaches 1 / 3 of the total volume of the silicon package, compressed air is introduced from the bottom of the silicon package, the compressed air pressure is 0.6 MPa, the gas flow is 1000 L / h, after the collection of the silicon melt is completed, the raw materials with a mass percentage of 40%:40%:20% of silicon dioxide:calcium oxide:barium carbonate are fired at 1400°C for 30 min to obtain a slagging agent, which is added to the silicon package in batches at intervals of 8 min, the amount of the slagging agent is 20% of the weight of the industrial silicon, the temperature is controlled at 1600°C, and the gas blowing is continued for 50 min to make the impurities form different compounds and fully separate from the industrial silicon melt, and then the refined industrial silicon is poured. After the industrial silicon is naturally condensed, samples at different positions are obtained by cutting, the samples are screened by quartering method to obtain powder samples with an average particle size of 200 mesh, and the contents of aluminum, calcium, phosphorus, boron and titanium are detected by inductively coupled plasma atomic emission spectrometer.

[0036] Example 4

[0037] When the industrial silicon melt collected in the silicon package reaches 1 / 3 of the total volume of the silicon package, oxygen is introduced from the bottom of the silicon package, the oxygen pressure is 0.3 MPa, the gas flow is 1000 L / h, after the collection of the silicon melt is completed, the raw materials with a mass percentage of 45%:45%:10% of silicon dioxide:calcium oxide:barium hydroxide are fired at 1500°C for 30 min to obtain a slagging agent, which is added to the silicon package in batches at intervals of 5 min, the amount of the slagging agent is 10% of the weight of the industrial silicon, the temperature is controlled at 1700°C, and the gas blowing is continued for 30 min to make the impurities form different compounds and fully separate from the industrial silicon melt, and then the refined industrial silicon is poured. After the industrial silicon is naturally condensed, samples at different positions are obtained by cutting, the samples are screened by quartering method to obtain powder samples with an average particle size of 200 mesh, and the contents of aluminum, calcium, phosphorus, boron and titanium are detected by inductively coupled plasma atomic emission spectrometer.

[0038] Comparative Example 1

[0039] When the industrial silicon melt collected in the silicon ladle reaches 1 / 3 of the total volume of the silicon ladle, oxygen is introduced from the bottom of the silicon ladle, the oxygen gas pressure is 0.2 MPa, the gas flow is 600 L / h, after the collection of the silicon melt is completed, no slagging agent is added, the temperature is controlled at 1680℃, and the gas blowing is continued for 25 min to make the impurities form different compounds fully separate from the industrial silicon melt, and then the refined industrial silicon is obtained by pouring. After the industrial silicon is naturally condensed, samples at different positions are obtained by cutting, the samples are screened by quartering method to obtain powder samples with an average particle size of 200 mesh, and the contents of aluminum, calcium, phosphorus, boron and titanium elements are detected by inductively coupled plasma atomic emission spectrometer.

[0040] Comparative Example 2

[0041] When the industrial silicon melt collected in the silicon ladle reaches 1 / 3 of the total volume of the silicon ladle, oxygen is introduced from the bottom of the silicon ladle, the oxygen gas pressure is 0.2 MPa, the gas flow is 600 L / h, after the collection of the silicon melt is completed, the slagging agent obtained by calcining raw materials with a mass percentage of 45%:45%:10% of silicon dioxide:calcium oxide:sodium carbonate at 1500℃ for 30 min is added into the silicon ladle in batches at intervals of 5 min, the amount of the slagging agent is 20% of the weight of the industrial silicon, the temperature is controlled at 1700℃, and the gas blowing is continued for 30 min to make the impurities form different compounds fully separate from the industrial silicon melt, and then the refined industrial silicon is obtained by pouring. After the industrial silicon is naturally condensed, samples at different positions are obtained by cutting, the samples are screened by quartering method to obtain powder samples with an average particle size of 200 mesh, and the contents of aluminum, calcium, phosphorus, boron and titanium elements are detected by inductively coupled plasma atomic emission spectrometer.

[0042] Table 2: Impurity contents in each example and comparative example

[0043] Impurities Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Al(％) 0.16 0.2 0.19 0.22 0.35 0.3 Ca (%) 0.09 0.05 0.16 0.12 0.19 0.15 P (ppm) 21 18 25 23 60 55 B (ppm) 8 9 13 12 35 30 Ti (ppm) 156 207 224 271 600 601

[0044] The above merely provides a specific implementation of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for removing metallic and non-metallic impurities from industrial silicon through ladle refining, characterized in that, include: Step S1: Collect the industrial silicon melt obtained from industrial silicon smelting in a silicon package; Step S2: Continuously introduce gas from the bottom of the silicon bag. At the same time, add the slagging agent obtained by calcining the barium salt-containing raw material into the silicon bag in batches. Maintain the temperature of the industrial silicon melt at 1500-1700℃ by blowing in the gas and keep the reaction at this temperature for 20-60 minutes. Step S3: After the heat preservation reaction is completed, tilt the silicon bag to pour out the industrial silicon melt inside. Impurities floating on the surface and settling at the bottom will remain in the silicon bag and be poured out later. Among them, the removed metallic and non-metallic impurities include at least calcium, aluminum, phosphorus, boron, and titanium; In step S2, the gas flow rate is 500-1500 L / h and the pressure is 0.2 MPa-1 MPa. The gas flow time starts when the industrial silicon melt collected from the silicon bag occupies 1 / 3 of the total volume of the silicon bag and ends when the refining and heat preservation are completed and the industrial silicon melt is poured out. The slag-forming agent is prepared by mixing a certain proportion of silicon dioxide, calcium oxide, and barium salt, or silicon dioxide, sodium carbonate, and barium salt, and then calcining it at 1200-1500℃ for 30 minutes to obtain the slag-forming agent.

2. The method according to claim 1, characterized in that, In step S2, the gas is oxygen or compressed air.

3. The method according to claim 1, characterized in that, The slag-forming agent raw materials have a purity of ≥98wt% for silica, ≥90wt% for calcium oxide, ≥98wt% for sodium carbonate, and ≥98wt% for barium salts, all of which can be industrial-grade raw materials; the barium salts are selected from one or more of barium oxide, barium carbonate, barium hydroxide, barium sulfate, and barium chloride.

4. The method according to claim 3, characterized in that, The raw materials for the slag-forming agent are crushed to a size not exceeding 5cm.

5. The method according to claim 1, characterized in that, The weight percentage of the raw materials silicon dioxide, calcium oxide and barium salt or silicon dioxide, sodium carbonate and barium salt in the slag-forming agent is 30-50:30-50:5-40, and the total weight percentage of the three raw materials is 100%.

6. The method according to claim 1, characterized in that, The amount of slagging agent used is 2-25% of the total mass of the industrial silicon melt used for refining. The method of adding the slagging agent to the industrial silicon melt is to take a sufficient amount of slagging agent and add the first batch of slagging agent immediately after the industrial silicon melt is collected. The amount added is 1 / 4 of the total mass of the required slagging agent. Then, add 1 / 4 of the total mass of the required slagging agent every 5-10 minutes until all the slagging agent is added.

7. The application of the method according to any one of claims 1-6 in the purification of industrial silicon.

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