CN100579902C - A method for preparing ultra-metallurgical grade silicon - Google Patents

Abstract

A method of preparing hypermetallurgical grade silicon. The invention relates to a method for preparing high-purity silicon, in particular to a method for preparing ultra-metallurgical-grade silicon with a purity greater than 99.99% from metallurgical-grade silicon. In the present invention, after cleaning, crushing, ball milling, sieving, preliminary impurity removal and other processes, the bulk metallurgical grade silicon is put into an ultrasonic and microwave field for metallurgical acid leaching treatment, and the metallurgical grade silicon powder after intensive treatment is reused The combination of atmospheric pressure wet leaching and high temperature and high pressure leaching enables metal impurities in metallurgical grade silicon powder to enter the leachate as soon as possible. The leachate is recycled after extraction, and the extractant is also recycled after stripping. This method combines microwave metallurgy, ultrasonic metallurgy, high temperature and high pressure leaching and other special field strengthening technologies, and the purity of the prepared silicon is more than 99.99%, which meets the requirements of the solar cell industry for ultra-metallurgical grade silicon, and has low equipment investment and low energy consumption. The impact on the environment is relatively small and the cost is low.

Description

A method for preparing ultra-metallurgical grade silicon

technical field

The invention relates to a method for preparing high-purity silicon, in particular to a method for preparing ultra-metallurgical-grade silicon with a purity greater than 99.99 percent from metallurgical-grade silicon.

Background technique

As we all know, traditional fossil energy can no longer meet the rapidly growing energy demand of mankind. The solar photovoltaic industry meets the requirements of the sustainable development strategy, and has maintained a high-speed development with an annual growth rate of more than 30% in the past ten years. The solar photovoltaic industry relies on polysilicon for solar cells.

At present, solar cell materials mainly come from waste and defective products of the semiconductor industry. Polysilicon for solar cells directly produced by the traditional hydrogen reduction method of trichlorosilane (SiHCl ₃ ), that is, the Siemens method, has large investment, high production cost, poor safety performance, and shortage of raw material supply. Research on new methods of solar-grade silicon production has begun at home and abroad.

my country's Wen Ruimei and others applied for a method for producing polysilicon with a mixed source of trichlorosilane and silicon tetrachloride (the patent number is 02137592.5, and the announcement date is March 19, 2003). This invention involves a brand-new Hydrogen reduction process to produce polysilicon. In the polysilicon production process, the invention makes full use of SiCl ₄ and HCl produced in the production process to ensure high quality and high yield. It also reduces the consumption of raw material industrial silicon, hydrogen and chlorine, and reduces the cost.

Japan has developed a new method to purify crude silicon for use in solar cells. The raw material used in this technology is crude silicon with a purity of about 95%. First, it is melted at 1500°C under vacuum conditions, and the phosphorous in the crude silicon is vaporized with a 750kW electron beam. Using directional solidification technology, silicon crystals are arranged in one direction, and metal impurities such as iron and aluminum are separated, while boron and carbon are removed by plasma melting and oxidation processes. A second directional solidification technique is then used to remove trace metals. Finally, the high-purity silicon is melted and solidified into an ingot by electromagnetic casting technology, which prevents the silicon from coming into contact with the walls of the melting pot.

Take advantage of the characteristics of Si-Al alloy melt, proposed a new process of preparing solar-grade silicon at low temperature using metallurgical-grade silicon as raw material, and conducted in-depth research on the physical and chemical processes of the process, but the silicon obtained so far The aluminum content is relatively high, and further optimization research is needed.

Ma Wenhui et al. applied for a method for preparing solar-grade polysilicon (patent number 200610010654.8, announced on July 19, 2006). The invention relates to a method for preparing solar-grade polysilicon, using metallurgical-grade silicon as a raw material After preliminary acid leaching treatment, vacuum refining treatment is carried out in a vacuum furnace. Vacuum refining is divided into two stages, namely, vacuum oxidation refining stage, vacuum distillation refining and vacuum degassing stage, and finally through directional solidification and head cutting. Get solar grade polysilicon products. The purity of its silicon is above 99.9999%, which meets the requirements of silicon raw materials required by the solar cell industry.

Ultra metallurgical grade silicon is an intermediate product in the production process of solar grade polysilicon, its purity is greater than 99.99%, and it is mainly produced through the acid leaching pretreatment process. Due to the inhomogeneity of impurities in metallurgical grade silicon, it is very difficult to purify metallurgical grade silicon. Most metal impurities can be removed through the pretreatment process, reducing the difficulty of the subsequent vacuum smelting process; in addition, the process of crushing metallurgical-grade silicon blocks into silicon powder itself is a mixing process, which plays an important role in ensuring quality stability in post-processing.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing ultra-metallurgical grade silicon, which has high production efficiency, less equipment investment, low energy consumption, relatively small impact on the environment, low cost, high purity of silicon produced, and energy Meet the requirements of the solar cell industry for ultra-metallurgical grade silicon.

The technical solution adopted to solve the technical problem of the present invention is: after cleaning, crushing, ball milling, sieving, preliminary impurity removal and other processes, the massive metallurgical grade silicon is placed in an ultrasonic and microwave field for metallurgical acid leaching treatment, and after strengthening The treated metallurgical-grade silicon powder is combined with atmospheric pressure wet leaching and high-temperature and high-pressure leaching, so that metal impurities in metallurgical-grade silicon powder can enter the leaching solution as soon as possible. The leaching solution is recycled after extraction, and the extractant is also stripped. Recycle later.

The main technical conditions of the present invention are:

(1) The concentration of the leaching solution: the concentration of sulfuric acid is 2mol/L to 6mol/L, the concentration of hydrochloric acid is 0.5mol/L to 8mol/L, and the concentration of nitric acid is 1mol/L to 8mol/L;

(2) The weight-liquid-solid ratio during microwave treatment and ultrasonic treatment is 1:1 to 5:1, the temperature is 40°C to 90°C, and the treatment time is 0.5 hours to 3 hours;

(3) The weight-liquid-solid ratio during atmospheric pressure leaching is 1:1 to 10:1, the temperature is 40°C to 90°C, and the treatment time is 1 day to 5 days;

(4) The weight-liquid-solid ratio during high-temperature and high-pressure leaching is 1:1-8:1, the pressure is 0.3MPa-2.5MPa, the temperature is 110°C-190°C, and the treatment time is 0.5-12 hours.

(5) The silicon powder separated after high temperature and high pressure leaching is finally leached with hydrofluoric acid with a concentration of 1mol/L to 5mol/L, the concentration of the reaction solution is 1mol/L to 5mol/L, and the reaction temperature is 40°C to 80°C. The reaction time is 1 hour to 8 hours;

Cleaning: Using commercially available bulk metallurgical-grade silicon with a purity of 98% to 99.5% as raw material, use cleaning agents and ultrasonic equipment to clean the sundries on the surface for 30 to 60 minutes to reduce metallurgical damage caused by the increase of these sundries. The increase in the total amount of impurities in grade silicon.

Crushing: After the cleaned metallurgical grade silicon is crushed several times by a crusher, it is put into a ball mill for grinding to obtain a silicon powder material of 50 mesh to 300 mesh, which is then processed in the next step.

Screening: Put the pulverized silicon powder material into the sieving machine to classify the silicon powder particles, and obtain the silicon powder material of 50 mesh to 300 mesh, which can be processed in the next step and can also be sold as a product; and the silicon powder smaller than 50 mesh can be re-introduced Go to the ball mill for repeated ball milling.

Preliminary impurity removal: The sieved metallurgical grade silicon is put into the electromagnetic magnetic separator for multiple magnetic separations to reduce the iron and iron oxide content brought in during the crushing and ball milling process.

Microwave and ultrasonic treatment: the metallurgical grade silicon powder after preliminary impurity removal is added to the acid solution according to the weight-liquid-solid ratio, heated and reacted in a microwave equipment with a power of 300W-1000W for 30min-120min, and then under the action of 500W-800W ultrasonic wave Acid leaching for 5 minutes to 180 minutes. This process is mainly to increase the acid leaching temperature, shorten the reaction time, and remove a large part of metal impurities in metallurgical grade silicon.

Hydrometallurgical treatment under atmospheric pressure: the metallurgical-grade silicon powder after the above treatment is leached for a second time with hydrochloric acid or aqua regia with a concentration of 0.5mol/L-7mol/L in a water bath at a temperature of 40°C to 90°C for 1 day to 5 days. sky. The main purpose of this process is to enable the metallurgical grade silicon powder to fully contact and react with the leaching solution. Impurities can be better removed.

Hydrometallurgical treatment in autoclave: After atmospheric pressure acid leaching, silicon powder is mixed with sulfuric acid and hydrochloric acid solutions with a concentration of 2mol/L~6mol/L according to the liquid-solid ratio of 1:1~8:1, and then put into high-pressure reaction In the equipment, keep the reaction pressure at 0.3MPa-2.5MPa, the reaction temperature at 110-190°C, and the stirring speed at 300rpm-700rpm for 0.5-12 hours. Then, the liquid and solid phases are separated by a vacuum separation method such as vacuum filtration. The separated silicon powder is finally soaked with hydrofluoric acid with a concentration of 1-5mol/L at a temperature of 40°C-80°C for 1-8 hours; to remove silicon dioxide and some impurities on the surface of the silicon powder material, and then use a third-stage After washing with deionized water for 3 to 5 times, filter under reduced pressure and dry. The product can be sold after packaging. The lining material of the autoclave is metal titanium or resin.

Recycling of leaching agent: extracting and separating the leaching solution after decompression separation by using the extracting liquid. The separated leachate is put back into the above pretreatment process to realize the recycling of the leachate; the reacted extract is back-extracted with soda ash solution or sodium hydroxide solution, and the extract is also recycled. The metal impurity elements produced are non-toxic and harmless, and can be treated as waste.

The beneficial effects of the present invention are:

① High production efficiency. The combined leaching technology of microwave metallurgy, ultrasonic metallurgy and high-pressure high-temperature hydrometallurgy has solved the problem of difficult purification of metallurgical-grade silicon, resulting in qualitative changes in the purification effect and production efficiency;

② Less infrastructure investment. This method mainly adopts the all-hydrometallurgical technology, and its infrastructure investment can be reduced by 70% compared with the same production scale of the pyrometallurgical manufacturer;

③The equipment is simple and safe. Since this process is all a hydrometallurgical process, its equipment is relatively simple, with few auxiliary systems and high safety;

④Low energy consumption and low production cost. During the production process, the power consumption can be reduced by more than 60%, and the production cost can be reduced by 50%;

⑤Less environmental pollution. Because the leaching agent used in this process is recycled, there is no need to discharge a large amount of acid solution during the production process. Therefore, the new process has less pressure on the environment, can achieve clean production, and meets the requirements of green metallurgy.

Description of drawings

Fig. 1 is a process flow diagram of the present invention.

Detailed ways

Embodiment one

Metallurgical grade silicon with a silicon content of 98.5wt% is used as a raw material, wherein the main impurity components include Al content of 1100ppmw, Fe content of 1620ppmw, and Ca content of 420ppmw.

The raw material is crushed by a crusher, ball milled by a ball mill, and the metallurgical grade silicon powder is screened by a sieving machine to obtain a silicon powder material with a particle size of 150 mesh, and then an electromagnetic separator is used to remove the iron brought in during the crushing and ball milling process. Impurities.

Use hydrochloric acid with a concentration of 4mol/L to react the silicon powder material under the action of ultrasonic waves with a power of 800W for 5 minutes according to the liquid-solid ratio of 1:1, and then carry out acid leaching treatment under the action of microwaves with a power of 300W for 60 minutes, and then remove it Place in a water bath at a temperature of 50°C for leaching for 5 days, and finally react in an autoclave for 2 hours. The reaction temperature in the autoclave is 110°C, the pressure is 2.5 MPa, and the stirring speed is 300 rpm. The reacted material is separated by vacuum filtration from the acid solution and the silicon powder material, and washed 4 times with distilled water, and the reacted acid solution is subjected to an extraction reaction with an extract to separate metal ions in the acid solution. The extracted acid solution is put into a new round of acid leaching experiment after adding a certain amount of new acid; and a small amount of soda ash solution or sodium hydroxide solution is added to the extract for back extraction, so that the extract can also be recycled. . After treatment under three different conditions, the iron impurity content has been reduced by 96%, the aluminum impurity content has been reduced by 95%, the impurity nickel content has been reduced by 87%, and the impurity titanium has been removed by 83%. 5mol/L hydrofluoric acid for 5 hours to remove silicon dioxide and some impurities on the surface of the particles, and use tertiary deionized water to wash 6 times.

Implementation results: After metallurgical grade silicon is processed, its purity is 99.991%, the content of iron impurities is 18ppmw, the content of aluminum impurities is 14ppmw, the content of calcium impurities is 8ppmw, the content of titanium impurities is 15ppmw, and the impurities of other metals are total The amount is less than 15ppmw.

Embodiment two

Metallurgical grade silicon with a silicon content of 99.5wt% is used as a raw material, and its main impurity components are Al content of 540ppmw, Fe content of 850ppmw, and Ca content of 200ppmw.

The raw materials are crushed by a crusher, ball milled by a ball mill, and the metallurgical grade silicon powder is screened by a sieving machine to obtain a silicon powder material with a particle size of 200 mesh, and then an electromagnetic separator is used to remove iron impurities brought in during the crushing and ball milling process .

Use nitric acid with a concentration of 8 mol/L to carry out acid leaching treatment on the silicon powder material according to the liquid-solid ratio of 5:1. First, treat it under the condition of ultrasonic power of 600W for 30min, then treat it under the condition of microwave for 40min, the microwave power is 600W, and then leaching in a water bath at 60°C for 3 days, then use vacuum filtration to separate the acid solution from the material, and use Wash with distilled water for 4 times, then use sulfuric acid solution with a concentration of 4mol/L to leach the silicon powder material under high temperature and high pressure according to the liquid-solid ratio of 5:1. After 10 hours, the reaction temperature in the autoclave is 190 ℃, and the pressure is 0.3MPa, the stirring speed is 500 rpm, the acid liquid and the silicon powder material are separated by vacuum filtration, and washed 4 times with three-stage deionized water, and the acid liquid after the reaction is extracted with the extraction liquid to separate Metal ions in acid solution. The extracted acid solution is put into a new round of acid leaching experiment after adding a certain amount of new acid; and a small amount of soda ash solution or sodium hydroxide solution is added to the extract for back extraction, so that the extract can also be recycled. . After treatment under three different conditions, the iron impurity content has been reduced by 97%, the aluminum impurity content has been reduced by 93%, the nickel impurity content has been reduced by 85%, and the titanium impurity has been removed by 87%. 1mol/L hydrofluoric acid for 1 hour to remove silicon dioxide and some impurities on the surface of the particles, and use tertiary deionized water to wash 6 times.

Implementation results: After metallurgical grade silicon is processed, its purity reaches 99.995%. Among them, the content of iron impurities is 10ppmw, the content of aluminum impurities is 7ppmw, the content of calcium impurities is 8ppmw, the content of titanium impurities is 3ppmw, and the content of other metal impurities The total amount of impurities is less than 5ppmw.

Embodiment three

Metallurgical grade silicon with a silicon content of 99.3wt% is used as a raw material, and its main impurity component A1 content is 930ppmw, Fe content is 1320ppmw, and Ca content is 420ppmw.

The raw material is crushed by a crusher, ball milled by a ball mill, and the metallurgical grade silicon powder is screened by a sieving machine to obtain a silicon powder material with a particle size of 100 mesh, and then an electromagnetic separator is used to remove iron impurities brought in during the crushing and ball milling process .

Use hydrochloric acid with a concentration of 3mol/L according to the liquid-solid ratio of 8:1 to treat the silicon powder material under ultrasonic conditions for 5 minutes, the power is 500W, and then treat it under microwave conditions for 120 minutes, the microwave power is 1000W, and then at 90 ° C leaching in a water bath for 2 days, and then use vacuum filtration to separate the acid solution from the material, and then use a sulfuric acid solution with a concentration of 2mol/L to pickle the silicon powder material at high temperature and pressure for 0.5h, and the reaction temperature in the autoclave is 190 ℃, the pressure is 1.5MPa, the stirring speed is 700 rpm, and then the acid solution and the silicon powder material are separated by vacuum filtration, and washed 4 times with tertiary deionized water, and the acid solution after the reaction is treated with the extract Extraction reaction to separate metal ions in acid solution. The extracted acid solution is put into a new round of acid leaching experiment after adding a certain amount of new acid; and a small amount of soda ash solution or sodium hydroxide solution is added to the extract for back extraction, so that the extract can also be recycled. . After treatment under three different conditions, the iron impurity content has been reduced by 98%, the aluminum impurity content has been reduced by 97%, the nickel impurity content has been reduced by 83%, and the titanium impurity has been removed by 85%. 3mol/L hydrofluoric acid for 8 hours to remove silicon dioxide and some impurities on the surface of the particles, and use tertiary deionized water to wash 6 times.

Implementation results: After metallurgical grade silicon is processed, its purity reaches 99.991%. Among them, the content of iron impurities is 17ppmw, the content of aluminum impurities is 13ppmw, the content of calcium impurities is 10ppmw, the content of titanium impurities is 15ppmw, and the content of other metal impurities The total amount of impurities is less than 8ppmw.

Embodiment four

Metallurgical grade silicon with a silicon content of 99.0wt% is used as a raw material, and its main impurity components are Al content of 1030ppmw, Fe content of 1430ppmw, and Ca content of 400ppmw.

The raw materials are crushed by a crusher, ball milled by a ball mill, and the metallurgical grade silicon powder is screened by a sieving machine to obtain a silicon powder material with a particle size of 300 mesh, and then an electromagnetic separator is used to remove iron impurities brought in during the crushing and ball milling process .

Use hydrochloric acid with a concentration of 1mol/L according to the liquid-solid ratio of 10:1 to treat the silicon powder material under ultrasonic conditions for 180min at a power of 800W, then treat it under microwave conditions for 80min at a microwave power of 800W, and then heat it at 70°C leached in a water bath for 4 days, then vacuum filtration was used to separate the acid solution from the material, and washed 3 times with distilled water, and then the silicon powder material was acid-leached at high temperature and high pressure for 12 hours with a sulfuric acid solution with a concentration of 6mol/L. The reaction temperature in the kettle is 150° C., the pressure is 1.0 MPa, and the stirring speed is 600 rpm. Afterwards, vacuum filtration is used to separate the acid solution from the silicon powder material, and the tertiary deionized water is used to wash 4 times, and the acid solution after the reaction is subjected to an extraction reaction with an extraction liquid to separate metal ions in the acid solution. The extracted acid solution is put into a new round of acid leaching experiment after adding a certain amount of new acid; and a small amount of soda ash solution or sodium hydroxide solution is added to the extract for back extraction, so that the extract can also be recycled. . After being treated under three different conditions, the iron impurity content has been reduced by 95%, the aluminum impurity content has been reduced by 98%, the nickel impurity content has been reduced by 87%, and the titanium impurity has been removed by 93%. 4mol/L hydrofluoric acid for 8 hours to remove silicon dioxide and some impurities on the surface of the particles, and use tertiary deionized water to wash 6 times.

Implementation results: After metallurgical grade silicon is processed, its purity reaches 99.992%. Among them, the content of iron impurities is 12ppmw, the content of aluminum impurities is 14ppmw, the content of calcium impurities is 6ppmw, the content of titanium impurities is 17ppmw, and the content of other metal impurities The total amount of impurities is less than 11ppmw.

Embodiment five

Metallurgical grade silicon with a silicon content of 99.4wt% is used as a raw material, and its main impurity components are Al content of 850ppmw, Fe content of 1220ppmw, and Ca content of 320ppmw.

The raw material is crushed by a crusher, ball milled by a ball mill, and the metallurgical grade silicon powder is screened by a sieving machine to obtain a silicon powder material with a particle size of 250 mesh, and then an electromagnetic separator is used to remove iron impurities brought in during the crushing and ball milling process .

Use nitric acid with a concentration of 1mol/L according to the liquid-solid ratio of 5:1 to treat the silicon powder material under ultrasonic conditions for 150min at a power of 500W, then treat it under microwave conditions for 50min at a microwave power of 1000W, and then heat it at 60°C. leaching in a water bath for 5 days, and then use vacuum filtration to separate the acid solution from the material, and use distilled water to wash 3 times, and then use a hydrochloric acid solution with a concentration of 6mol/L to pickle the silicon powder material at high temperature and high pressure for 6 hours, and then The reaction temperature in the kettle is 170° C., the pressure is 2.0 MPa, and the stirring speed is 690 rpm. Afterwards, vacuum filtration is used to separate the acid solution from the silicon powder material, and the tertiary deionized water is used to wash 4 times, and the acid solution after the reaction is subjected to an extraction reaction with an extraction liquid to separate metal ions in the acid solution. The extracted acid solution is put into a new round of acid leaching experiment after adding a certain amount of new acid; and a small amount of soda ash solution or sodium hydroxide solution is added to the extract for back extraction, so that the extract can also be recycled. . After treatment under three different conditions, the iron impurity content has been reduced by 98%, the aluminum impurity content has been reduced by 94%, the nickel impurity content has been reduced by 89%, and the titanium impurity has been removed by 85%. 2mo1/L of hydrofluoric acid for 6 hours to remove silicon dioxide and some impurities on the surface of the particles, and wash 6 times with tertiary deionized water.

Implementation results: After metallurgical grade silicon is processed, its purity reaches 99.993%. Among them, the content of iron impurities is 10ppmw, the content of aluminum impurities is 8ppmw, the content of calcium impurities is 10ppmw, the content of titanium impurities is 17ppmw, and the content of other metal impurities The total amount of impurities is less than 9ppmw.

Claims (5)

1. A method for preparing ultra-metallurgical-grade silicon, characterized in that: after cleaning, crushing, ball milling, screening, preliminary impurity removal and other processes, the bulk metallurgical-grade silicon is successively put into ultrasonic and microwave fields for metallurgical acid leaching After intensive treatment, the metallurgical-grade silicon powder is leached by normal pressure wet method and high-temperature and high-pressure leaching successively, and the separated silicon powder after high-temperature and high-pressure leaching is then leached with hydrofluoric acid, so that the metal impurities in the metallurgical-grade silicon powder It can enter the leachate as soon as possible, the leachate is recycled after extraction, and the extractant is also recycled after stripping. 2. The method for preparing ultra-metallurgical grade silicon according to claim 1, characterized in that the main technical conditions are: (1) The concentration of the leaching solution: the concentration of sulfuric acid is 2mol/L to 6mol/L, the concentration of hydrochloric acid is 0.5mol/L to 8mol/L, and the concentration of nitric acid is 1mol/L to 8mol/L; (2) The weight-liquid-solid ratio during microwave treatment and ultrasonic treatment is 1:1 to 5:1, the temperature is 40°C to 90°C, and the treatment time is 0.5 hours to 3 hours; (3) The weight-liquid-solid ratio during atmospheric pressure leaching is 1:1 to 10:1, the temperature is 40°C to 90°C, and the treatment time is 1 day to 5 days; (4) The weight-liquid-solid ratio during high-temperature and high-pressure leaching is 1:1 to 8:1, the pressure is 0.3MPa to 2.5MPa, the temperature is 110°C to 190°C, and the treatment time is 0.5 hours to 12 hours; (5) The silicon powder separated after high temperature and high pressure leaching is finally leached with hydrofluoric acid with a concentration of 1mol/L to 5mol/L, the concentration of the reaction solution is 1mol/L to 5mol/L, and the reaction temperature is 40°C to 80°C. The reaction time is 1 hour to 8 hours. 3. The method for preparing ultra-metallurgical-grade silicon according to claim 2, characterized in that: the raw material is metallurgical-grade silicon with a purity of 98%-99.5%. 4. The method for preparing ultra-metallurgical grade silicon according to claim 2 or 3, characterized in that: after the raw materials are washed, they are crushed to a particle size of 50 mesh to 300 mesh, and the preliminary removal of impurities is carried out by sieving Metallurgical grade silicon powder is subjected to magnetic separation to reduce the content of iron and iron oxide brought in during crushing and ball milling. 5. A method for preparing ultra-metallurgical silicon according to claim 2 or 3, characterized in that the lining material of the autoclave used for high temperature and high pressure leaching is metal titanium or resin.

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