A method for purifying metallurgical grade silicon by high-temperature chlorination process

Abstract

The present invention discloses a method for purifying metallurgical grade silicon by high-temperature chlorination method, which specifically comprises the following steps: (1) performing crushing treatment on metallurgical grade silicon; (2) performing pickling on the crushed metallurgical grade silicon, and the acid used is a mixed acid of HF, HCl and HNO3; (3) collecting the pickled metallurgical grade silicon and further crushing it into silicon powder; (4) performing pickling on the silicon powder to remove metal impurities, and drying it after the pickling is completed, wherein: the acid used is one or several of HCl, H2SO4 and citric acid; (5) mixing the silicon powder pickled in step (4) with a chloride evenly, then placing it into a polycrystalline furnace, evacuating and heating up to obtain the purified metallurgical grade silicon, wherein: the chloride is one or more of NaCl, ZnCl2, BaCl2 and MgCl2; this method can prepare high-purity and high-quality metallurgical grade silicon, and has low cost and is easy to operate.

Description

Technical Field

[0001] The present invention relates to a purification method, specifically to a method for purifying metallurgical grade silicon by high-temperature chlorination, belonging to the technical field of metallurgical grade silicon purification. Background Art

[0002] Metallurgical grade silicon, also known as semi-metallic silicon, is a commodity name that emerged in the mid-1960s. Metallurgical grade silicon is a product smelted from silica and carbonaceous reducing agents in a submerged arc furnace. The content of the main component silicon element is about 98% (in recent years, those with a Si content of 99.99% are also classified as metallurgical grade silicon). It is divided into various specifications according to its uses. According to the contents of iron, aluminum, and calcium in semi-metallic silicon, semi-metallic silicon can be divided into different grades such as 553, 441, 411, 421, 3303, 3305, 2202, 2502, 1501, 1101, etc. The by-products of semi-metallic silicon include microsilica powder, edge silicon, black silicon, metallurgical grade silicon slag, etc. Among them, microsilica powder is also called silica fume, which is widely used in the refractory and concrete industries. Metallurgical grade silicon contains a large amount of metal impurities such as Fe, Al, and Ca, which seriously affect the quality of the product and subsequent production and processing.

[0003] Currently, Patent CN101293654A discloses a method for purifying metallurgical grade silicon under pressure. In this method, metallurgical grade silicon is crushed and then put into a pressure purification reactor for purification, and then pickling and soaking are used for purification. However, the acid used is not easily decomposed, which will pollute the raw materials, and it has high requirements for equipment.

[0004] Patent CN103183351B discloses a method for purifying silica ore by chlorination roasting-leaching method. In this method, chlorination is used for purification. However, the chlorides used have a greater impact on the environment. Especially, the volatilization of hydrogen chloride has a particularly strong corrosiveness to equipment. At the same time, the volatilization of these chlorides has a pungent smell and great harm to the human body.

[0005] In order to overcome the existing technical problems, it has become an urgent technical problem for those skilled in the art to provide a method for removing metal impurities in metallurgical grade silicon by high-temperature chlorination, improving the quality of silicon, and reducing the subsequent production and processing costs. Summary of the Invention

[0006] The technical problem to be solved by the present invention is, aiming at the above-mentioned disadvantages existing in the prior art, to provide a method for purifying metallurgical grade silicon by high-temperature chlorination. This method can prepare high-purity and high-quality metallurgical grade silicon, and has low cost and easy operation.

[0007] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0008] A method for purifying metallurgical grade silicon by high-temperature chlorination specifically includes the following steps:

[0009] (1) Crush the metallurgical grade silicon.

[0010] (2) Pickle the crushed metallurgical grade silicon with a mixed acid of HF, HCl and HNO3.

[0011] (3) Collect the pickled metallurgical grade silicon and further crush it into silicon powder.

[0012] (4) Pickle the silicon powder to remove metal impurities, and dry it after pickling. Among them:

[0013] The acid used is one or more of HCl, H2SO4, and citric acid.

[0014] (5) Mix the silicon powder pickled in step (4) with a chloride evenly, then place it in a polycrystalline furnace, evacuate and heat it up to obtain purified metallurgical grade silicon. Among them:

[0015] The addition amount of the chloride is 1% - 50% of the silicon powder.

[0016] The chloride is one or more of NaCl, ZnCl2, BaCl2, and MgCl2.

[0017] The further limited technical solution of the present invention is:

[0018] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (1), the metallurgical grade silicon is crushed, and the size after crushing is not more than 10 cm.

[0019] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (2), when pickling, by mass percentage, HF:HCl:HNO3 = 0 - 30%:0 - 50%:0 - 50%.

[0020] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (2), the pickling time is 0.5 - 5 h.

[0021] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (3), when the metallurgical grade silicon is crushed into silicon powder, the particle size of the silicon powder is 0.5 mm - 2 mm.

[0022] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (4), the pickling time is 2 - 8 h, and the drying temperature is 120 °C.

[0023] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, in step (4), the mass fraction of the acid is 1% - 30%.

[0024] In the method for purifying metallurgical grade silicon by the foregoing high-temperature chlorination method, when pickling in step (4), by mass percentage, HCl:H2SO4:citric acid = 0 - 50%:0 - 30%:1 - 100%;.

[0025] Technical effect: Citric acid belongs to organic acid and decomposes at high temperature without contaminating the raw materials. However, if other acids are not completely processed, they will contaminate the raw materials. At the same time, the requirements for equipment are relatively high, and the post-treatment of other acids is also relatively difficult, especially the treatment of chloride ions.

[0026] In the method for purifying metallurgical grade silicon by the high-temperature chlorination method described above, in step (5), the vacuum degree in the polycrystalline furnace is not higher than 0.1 Mpa, and the temperature is controlled at 1420 - 1750 °C during heating and temperature rise.

[0027] In the method for purifying metallurgical grade silicon by the high-temperature chlorination method described above, the purity of the metallurgical grade silicon obtained after the treatment in step (5) is detected, and the silicon purity detection is ≥ 5N (99.999%).

[0028] The beneficial effects of the present invention are as follows:

[0029] The present invention performs pickling multiple times. The main function of pickling in step 2 is to remove SiO2 generated during the smelting process of metallurgical grade silicon and preliminarily pickle to remove impurities in the metallurgical grade silicon.

[0030] In the present invention, one or more of NaCl, ZnCl2, BaCl2, and MgCl2 are used during chlorination. The main function of this step is to directly remove Fe. Generally, the method for removing Fe in industry is directional solidification, which has a complex process and high energy consumption. The present invention uses the chlorination method in combination with chlorides to directly remove Fe, with a simple process and low energy consumption. Moreover, the chlorides added in this patent have low solubility in silicon and have little impact on the minority carrier lifetime of polysilicon wafers, and can be effectively removed during the subsequent directional solidification process. Specific embodiments Example 1

[0031] This example provides a method for purifying metallurgical grade silicon by the high-temperature chlorination method, which specifically includes the following steps:

[0032] (1) Crush the metallurgical grade silicon, and the size after crushing is not greater than 10 cm;

[0033] (2) Pickle the crushed metallurgical grade silicon. The pickling time is 1 h, and the acid used is a mixed acid of HF, HCl, and HNO3. During pickling, by mass ratio, HF:HCl:HNO3 = 5%:45%:50%;

[0034] (3) Collect the pickled metallurgical grade silicon and further crush it into silicon powder with a particle size of 0.5 mm;

[0035] (4) Pickle the silicon powder to remove metal impurities. The pickling time is 8 h, and after pickling, it is dried at a drying temperature of 120 °C, where:

[0036] The acid used is citric acid; the mass fraction of the acid is 30%;

[0037] (5)The silicon powder after pickling in step (4) is mixed evenly with the chloride and then placed in a polycrystalline furnace for vacuum pumping and heating up. The temperature is controlled at 1500 °C and the vacuum degree is not higher than 0.1 Mpa to obtain purified industrial silicon, where:

[0038] The chloride is NaCl and ZnCl2, and the mass ratio is 80%:20%. The addition amount of the chloride is 20% of the silicon powder;

[0039] In this embodiment, the purity of the industrial silicon obtained after the treatment in step (5) is detected, and the silicon purity detection is ≥5N (99.999%).

[0040] In addition to the above embodiments, the present invention may also have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope required by the present invention. Example 2

[0041] This embodiment provides a method for purifying industrial silicon by high-temperature chlorination, which specifically includes the following steps:

[0042] (1)The industrial silicon is subjected to crushing treatment, and the size after crushing is not greater than 10 cm;

[0043] (2)The crushed industrial silicon is pickled. The pickling time is 1 h. The acid used is a mixed acid of HF, HCl and HNO3. When pickling, by mass ratio, HF:HCl:HNO3 = 15%:35%:50%;

[0044] (3)The pickled industrial silicon is collected and further crushed into silicon powder, and the particle size of the silicon powder is 2 mm;

[0045] (4)The silicon powder is pickled to remove metal impurities. The pickling time is 5 h. After pickling, it is dried, and the drying temperature is 120 °C, where:

[0046] The acid used is citric acid and HCl; the mixed acid accounts for 20% of the solution mass, and the mass fractions of citric acid and HCl are 15%:85%;

[0047] (5)The silicon powder after pickling in step (4) is mixed evenly with the chloride and then placed in a polycrystalline furnace for vacuum pumping and heating up. The temperature is controlled at 1600 °C and the vacuum degree is not higher than 0.1 Mpa to obtain purified industrial silicon, where:

[0048] The chloride is NaCl, and the addition amount of NaCl is 15% of the silicon powder;

[0049] In this embodiment, the purity of the industrial silicon obtained after the treatment in step (5) is detected, and the silicon purity detection is ≥5N (99.999%).

[0050] In addition to the above embodiments, the present invention may have other implementation manners. All technical solutions formed by equivalent replacement or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for purifying metallurgical grade silicon by high-temperature chlorination method, characterized in that, Specifically, it includes the following steps: (1) Crush industrial silicon; (2) Pickle the crushed industrial silicon with a mixed acid of HF, HCl and HNO3; (3) Collect the pickled industrial silicon and further crush it into silicon powder; (4) Pickle the silicon powder to remove metal impurities, and dry it after pickling. Among them: The acid used is one or more of HCl, H2SO4, and citric acid; (5) Mix the silicon powder pickled in step (4) with a chloride evenly, then place it in a polycrystalline furnace, evacuate and heat it up to obtain purified industrial silicon. Among them: The addition amount of the chloride is 1%-50% of the silicon powder; The chloride is one or more of NaCl, ZnCl2, BaCl2, and MgCl2.

2. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, wherein: In step (1), the industrial silicon is crushed, and the size after crushing is not more than 10 cm.

3. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: In step (2), when pickling, by mass percentage, HF:HCl:HNO3 = 1~30%:0~50%:0~50%.

4. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, wherein: In step (2), the pickling time is 0.5 - 5 h.

5. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: When the industrial silicon is crushed into silicon powder in step (3), the particle size of the silicon powder is 0.5 mm - 2 mm.

6. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: In step (4), the pickling time is 2 - 8 h, and the drying temperature is 120 °C.

7. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, wherein: In step (4), the mass fraction of the acid is 1% - 30%.

8. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: When pickling in step (4), by mass percentage, the acid used is HCl:H2SO4:citric acid = 0~50%:0~30%:1~100%.

9. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: In step (5), when placed in a polycrystalline furnace, the vacuum degree of evacuation is not higher than 0.1 MPa, and the temperature is controlled at 1420 - 1750 °C during heating up.

10. The method for purifying metallurgical grade silicon by high-temperature chlorination according to claim 1, characterized in that: Conduct a purity test on the industrial silicon obtained after the treatment in step (5), and the silicon purity test ≥ 5N (99.999%).