JPH06107406A - Method for refining metallic silicon - Google Patents

Abstract

PURPOSE:To easily and inexpensively obtain high-purity metallic silicon by crushing high-purity metallic silicon, treating the crushed silicon with aq. HF having specified concn. at normal temps. and then subjecting the product to filtration and water washing. CONSTITUTION:The metallic silicon having >=99.5% purity is crushed to <=50mum, and the crushed silicon is treated with 1-5wt.% aq. HF at normal temps., then filtered, washed with water and refined. When a smaller amt. of aq. HF is added, the concn. of the granular silicon is increased in a reactor, the grains are aggregated, the liq. dispersion is increased in viscosity, and the silicon is not uniformly treated. Conversely, when a larger amt. of HF is added, the treating effect is not improved, HF is wasted, the load in the succeeding HF recovery stage is inefficiently increased. Accordingly, the weight ratio of the HF to silicon is controlled to 2-10, preferably to 3-6.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for purifying metallic silicon,
In particular, it relates to a method for refining metallic silicon that can be used as a raw material for solar cells and ceramics.

[0002]

2. Description of the Related Art Metallic silicon used in the chemical industry is usually considered to have a purity of 99.5% or higher. However, since it contains impurities such as Fe, Al, and Ca near 1,000 ppm, However, it cannot be used as it is as a raw material for solar cells and ceramics that require high purity. On the other hand, it is known that impurities are present at the grain interface in metal silicon obtained by metallurgy, and this is because the size of crystal grains and the segregation degree of impurities can be adjusted by changing the cooling rate after melting. In this regard, there has been proposed a method in which industrial metal silicon is melted and recrystallized, and this is crushed to 100 μm or less and treated with an acid (Japanese Patent Laid-Open No. 60-195015).
(See Japanese Patent Laid-Open No. 60-195016).

[0003]

However, this method has a drawback in that the energy cost such as an electric bill is large and expensive because the metal silicon is once melted at a high temperature of 1,500 ° C. or higher. For this reason, a method has been proposed in which the metal silicon is not melted, and the metal silicon particles having a large particle size are heat-treated at a temperature of 40 to 90 ° C. with a high concentration of an acid such as HF, HCl or HNO _3. However, the purification efficiency is low because impurities scattered inside the particles cannot be removed.In this case, there is corrosion of the equipment, and the washing with water to remove the acid is strengthened. There is a drawback that the treatment cost increases due to the increased load of collection and wastewater treatment.

For this high-purity silicon, semiconductor grade purified silicon by the zone melting method, the single crystal pulling method, etc. is also known, but it is very expensive, so it is used for general purposes. It cannot be used. Therefore, as a method for purifying this metallic silicon, a method for obtaining a highly pure metallic silicon at a low cost by a simple method is required.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for refining metal silicon which solves the above disadvantages and drawbacks. This is a method of purifying metal silicon having a purity of 99.5% or more to 50 μm.
It is characterized in that it is ground into the following, treated with a 1 wt% to 5 wt% HF aqueous solution at room temperature, and then filtered and washed with water.

That is, the inventors of the present invention conducted various studies on a method for purifying chemical industry grade metal silicon, and as a result,
When metal silicon for the chemical industry with a purity of 99.5% or more is first crushed to a particle size of 50 μm or less, the surface of the crystal grains of metal silicon and the surface of the particles that have been segregated and the impurities segregated inside Since it is exposed to, the impurities can be removed at room temperature by treating it with an HF aqueous solution.
According to this, since the natural oxide film on the surface of the metal silicon can be removed, if it is then filtered and washed with water, Fe as impurities is 15 ppm or less, Al is 130 ppm or less, and Ca is
It was found that high-purity metal silicon with U reduced to 2.2 ppb or less at 30 ppm can be obtained with a yield of 95% or more, and research on the concentration and amount of HF used here was conducted. Then, the present invention was completed. This will be described in more detail below.

[0007]

The present invention relates to a method for purifying metal silicon, which comprises crushing metal silicon having a purity of 99.5% or more to 50 μm or less and using a 1% to 5% by weight HF aqueous solution at room temperature. After treatment, it is characterized by being filtered and washed with water. According to this, it is possible to easily and inexpensively obtain high-purity metallic silicon that can be used for solar cells and ceramics. Gender is given.

The method for refining metallic silicon according to the present invention is carried out using chemical industry grade metallic silicon as a starting material. This chemical grade metal silicon is a method of reducing silica with carbon in an electric furnace or magnesium,
Made with a method of reduction with aluminum, which has a purity of 9
Although it is 9.5%, it usually contains F as an impurity.
e, Al, Ca, etc. around 1,000ppm,
Radioactive elements such as U and Th also contain tens to hundreds of ppb, and these impurities are investigated by scanning electron microscope (SEM) photographs of the fracture surface of this metal silicon by electromicroprobe analysis (EPMA). Fe, A,
l and Ca are segregated and scattered at the crystal grain interface and inside, and the size of the impurity aggregates scattered inside is from 20 μm on average to 2 μm.
It was found that it was in the range of 00 μm, and particularly distributed from 50 μm to 100 μm.

In the present invention, the metal silicon is first pulverized to 50 μm or less. When pulverized in this way, most of the impurities segregated or scattered at the crystal grain interface and inside of the metal silicon, It has been found that this removal is facilitated because it becomes exposed on the surface of the crushed metal silicon powder particles. The smaller the particle size obtained by this pulverization, the higher the purification efficiency in the post-treatment step.However, if the particle size is made too fine, the inclusion of foreign matter during pulverization will increase, and the efficiency of solid-liquid separation operation after acid treatment and water washing described below The particle size is 1μm or more, 50μ
It is preferably m or less.

Incidentally, this crushing is performed by a rotating cylindrical ball sill,
It may be done with a vibrating ball mill, etc., and after crushing, sieve with a JIS325 mesh (opening 44 μm) sieve, or
Coarse particles of 50 μm or more may be removed using a classifier such as a cyclone.

In the present invention, the metal silicon thus crushed is treated with an aqueous HF solution to remove impurities exposed on the surface of the particles. This is the addition of the aqueous HF solution to the metallic silicon powder. Then, these impurities are removed from the metal silicon by the reaction with HF. However, this reaction is carried out at room temperature for 20 minutes to 2 hours, so heating at this time is required. do not have to.

The metal silicon obtained by the above-mentioned pulverization rapidly reacts with oxygen in the air on the surface of the particles to form a thin natural oxide film on the surface, which is amorphous silica in the atmosphere at room temperature. In storage, the thickness is 2-3 nm. However, in order to remove impurities, HC
When treated with l, HNO ₃ , H ₂ SO _4, etc., this natural oxide film interferes with the removal of impurities that are inside the natural oxide film and segregated on the surface of the metal silicon. The removal of the natural oxide film is indispensable for removing the impurities.

However, when the metal silicon pulverized according to the present invention is treated with an HF aqueous solution, this natural oxide film (SiO ₂ ) reacts with the HF aqueous solution, and SiO ₂ + 4HF → SiF ₄ + 2H ₂ O SiF ₄ + 2HF → Since it is removed with H ₂ SiF ₆ , this eliminates the disadvantage that impurities cannot be removed due to the presence of natural oxides.

In this case, the native oxide film in this case has a specific surface area (m ² / g) and an oxide thickness (nm) of which it is calculated from the specific gravity of silica (2.20). , Usually around 1% by weight, which is the above-mentioned F
Since the amount of impurities such as e, Al, and Ca is larger than that, the concentration and addition amount of HF used here may be determined based on this silica amount.

When the amount of the HF aqueous solution added in the present invention is small, the concentration of powdery particles of metallic silicon in the reactor becomes high, and the particles are aggregated together and the viscosity of the dispersion is increased, so that uniform treatment is performed. If it is too much, the treatment effect will not be improved, waste of HF will be wasted, and the burden of the recovery process of HF in the subsequent process will increase and it will not be efficient, so this is 2% by weight relative to the metal silicon. As described above, 10 or less, preferably 3 or more and 6 or less is desirable.

If the concentration of the HF aqueous solution used here is less than 1% by weight, the reaction with silica becomes slow,
The removal of impurities became insufficient, and even if it was 5% by weight or more, the purification efficiency did not change, and if it was more than 5%, HF wasted and HF remained in the solid-liquid separation after the treatment, increasing the load of the washing process. As this is not preferable, this is 1 weight or more,
It is required to be 5% by weight or less.

The particulate silicon metal treated with the HF aqueous solution may be separated by filtration to remove the HF aqueous solution containing impurities, and the residual liquid may be further washed with water and filtered repeatedly to be diluted and removed. After filtering and washing with water, the metallic silicon is treated in the same way as normal powder drying in a clean container that does not cause contamination.
It may be dried in an atmosphere, but the HF aqueous solution used for processing in these series of steps should be a high-purity product with a purity of 99.9% or more,
Ion-exchanged water or distilled water may be used as water for HF dilution and water washing.

The reaction vessel used here may be made of Teflon or polyvinyl chloride, but as an industrial apparatus, it is made of iron lined with Teflon or polyvinyl chloride, and a stirrer made of the same material. You can use the one equipped with. In addition, this filter also has a corrosion resistant material,
There is no need to limit the model as long as it can be efficiently filtered and washed.

[0019]

EXAMPLES Next, examples and comparative examples of the present invention will be described. Example 1 Chemical industry grade metal silicon having a purity of 99.5% or more was crushed to a particle size of 1 to 30 μm, and 5 kg of this was placed in a stainless steel 50 liter container having an inner surface of Teflon lining, and the purity was 99.5%. , 15 kg of concentrated HF water with a concentration of 55% by weight diluted with ion-exchanged water to 2% by weight was added,
The mixture was stirred at room temperature of 20 ° C for 1 hour.

Then, the acid-treated suspension was transferred to a filter, HF water was removed by pressure filtration, washed with ion-exchanged water, filtered, and vacuum dried at 100 ° C. and -740 mmHg for 8 hours. The treated metal silicon powder was taken out, and the amounts of Fe, Al, and Ca as impurities contained in this powder were measured by atomic absorption spectrometry, and the amount of U contained therein was inductively coupled. High frequency plasma gravimetric method (ICP-M
As a result of analysis by S), the results shown in Table 1 below were obtained, and it was confirmed that this was high-purity metal silicon.

Example 2 The concentration of HF water in Example 1 was changed from 2% by weight to 5% by weight.
The same procedure as in Example 1 was carried out to refine the silicon metal, except that the results were as shown in Table 1 below for the amount of impurities in the obtained silicon metal. .

The amount of HF water added in Example 1 was changed from 30 to 15 kg.
When the metal silicon was purified by the same treatment as in Example 1 except that the amount was changed to kg, the results shown in Table 1 below regarding the amount of impurities in the obtained metal silicon were obtained. It was

Comparative Examples 1 to 6 Metallic silicon as a starting material in Example 1 having a particle size of 50 to 200 μm (Comparative Example 1) and HF concentration of 0.5% by weight (Comparative Example) 2), 55 wt% of this (Comparative Example 3), HF water addition amount of 36 kg (Comparative Example 4), treatment temperature of 50 ° C. (Comparative Example 5), treatment time of 4 When the metal silicon was purified in the same manner as in Example 1 except that these conditions were used as the time (Comparative Example 6), the amount of impurities in the obtained metal silicon is shown in Table 1 below. The exact result was obtained.

[0024]

[Table 1]

Comparative Examples 7 to 8 The same treatment as in Example 1 was carried out except that the HF solution in Example 1 was changed to HCl having a concentration of 36% (Comparative Example 7) and HNO _{3 having} a concentration of 30% (Comparative Example 8). After refining the metal silicon with the following method, the amount of impurities in the obtained metal silicon is shown in Table 2 below.
The result as shown in was obtained.

[0026]

[Table 2]

[0027]

Industrial Applicability The present invention relates to a method for purifying metallic silicon, which has a purity of 99.5% or more and is crushed to 50 μm or less by 1% to 5% by weight.
It is characterized in that it is treated with an HF aqueous solution of, and then filtered and washed with water. According to this method, the natural oxide film on the surface of the metal silicon can also be removed. Less than 130ppm, Ca less than 30p
This gives an advantage that high-purity metal silicon having U reduced to 2.2 ppb or less can be obtained in a yield of 95% or more.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Yukiko Wakao 1 Hitomi, Katsumi, Matsuida-cho, Usui-gun, Gunma 10 Silicon Research Institute for Electronic Materials, Shin-Etsu Chemical Co., Ltd. (72) Akio Ohori Isobe, Gunma Prefecture Isobe 2-13-1 Shin-Etsu Kagaku Kogyo Co., Ltd. Isobe Plant (72) Inventor Junsei Kamiya 1 Toyota-cho, Toyota-shi, Aichi Toyota Motor Corporation (72) Inventor Abe Fujioka-cho, Nishikamo-gun Aichi Ishihito 177-9

Claims (3)

[Claims] 1. A metal characterized by crushing metal silicon having a purity of 99.5% or more to 50 μm or less, treating it with a 1 wt% to 5 wt% HF aqueous solution at room temperature, and then filtering and washing with water. Purification method of silicon 2. The method for purifying metal silicon according to claim 1, wherein the amount of the HF aqueous solution added is 2 or more and 10 or less in weight ratio to the metal silicon. 3. The method for purifying metal silicon according to claim 1, wherein the water for diluting HF and the water for washing are ion-exchanged water or distilled water.