JPH10226510A - Preliminary treatment of metal silicon powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high purity metal silicon capable of being a main material for a silicon for solar cell by treating an unreacted metal silicon powder with a chemical, which is discharged from a synthetic process of silane and is in a metallic state though containing a large quantity of copper. SOLUTION: A preliminary treating method of the metal silicon powder is for removing copper in the metal silicon powder by charging the metal silicon powder in an aq. solution containing sulfuric acid and mixing the metal silicon powder and the aq. solution by stirring while supplying oxygen (including a case of incorporating in air). In such a case, as the metal silicon powder, a metal silicon powder containing a spent copper catalyst discharged from the synthetic process of silane can be used. The metal silicon powder is preferably used after chlorine contained therein is removed by previously washing. The concentration of sulfuric acid is preferably 10-100g/l in excess of the quantity equivalent to copper, the concentration of the slurry is preferably 100-500g/l and the feed flow rate of oxygen is preferably 0.2-0.51/min per 1kg of metal silicon powder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for synthesizing low-purity metallic silicon, for example, silane, as a raw material of a method for purifying metallic silicon for obtaining high-purity metallic silicon which can be used as a main material of silicon for solar cells. The present invention relates to a pretreatment method for metal silicon powder so that metal silicon discharged from a process can be used.

[0002]

2. Description of the Related Art In a silicon resin manufacturing process, silane is synthesized using metallic silicon powder. In this step, copper powder or the like is used as a catalyst for accelerating the reaction. Therefore, unreacted metallic silicon powder discharged from the silane synthesis step contains a large amount of copper. The amount of copper added varies depending on the type of silane to be synthesized, and the copper content in the unreacted metallic silicon powder also shows various values corresponding to the silane type. It is about 15% by weight.

[0003] The unreacted metallic silicon powder contains about 0.8 to 3.0% by weight of iron in addition to copper. This iron originates from iron already contained at the time of the metal silicon mass and iron mixed from an iron pulverizer that supplies the metal silicon mass to the silane synthesis process.

[0004] Among the impurities contained in the unreacted metallic silicon powder, those containing less than 1% by weight of aluminum include 0.2 to 0.5% by weight of aluminum and 0.1 to 0.1% by weight of zinc.
It contains about 3% by weight, about 0.1 to 0.2% by weight of calcium, and about 1 to 10 ppm of boron. Further, about 0.2 to 0.5% by weight of chlorine remains in the unreacted metallic silicon powder. The purity of metallic silicon is about 75 to 90% by weight.

[0005] Among such unreacted metallic silicon powders, those having a copper content of 10% by weight or more are reused in copper smelting as a copper raw material and a fermenting agent. However, those having a copper content of less than 10% by weight are not so preferred for copper smelting applications, and are mostly disposed of in landfills.

[0006]

Since the above-mentioned unreacted metallic silicon powder is in a metallic state, it is treated with a chemical to obtain a high-purity metallic silicon which can be used as a main material of silicon for solar cells. It would be very convenient to convert low value items into expensive products.

However, since the unreacted metallic silicon powder has an extremely high content of impurities, particularly copper, as described above, it is difficult to immediately purify high-purity metallic silicon with a chemical as it is.

An object of the present invention is to provide a method for pre-treating metal silicon powder which enables use of low-purity metal silicon as a raw material for a method for purifying metal silicon to obtain high-purity metal silicon. .

[0009]

Means for Solving the Problems To solve the above problems, the present inventors have decided to leaching out Cu and the like contained in metallic silicon powder with sulfuric acid which is easily available and easy to handle, and repeated tests. As a result, a predetermined sulfuric acid concentration (amount required for Cu leaching + 10 to 100 g / l), a predetermined slurry concentration (100 to 500 g / l) and a predetermined air blowing amount (0.9 to 2.0 g / kg of metal silicon powder). was established technique for stirring leaching 7 liters / min ... range of O ₂ in terms 0.2 to 0.5 liters / minute).

Here, as the metal silicon powder, for example, a metal silicon powder containing a used copper catalyst discharged from a silane synthesis step can be used, but the metal silicon powder having the same impurity concentration can be used. If so, other metallic silicon may be used. Further, the aqueous solution leached with copper may be used as a copper sulfate source in a zinc refining process. When the aqueous solution is used for such purposes, it is preferable that the metal silicon powder be washed with water and dechlorinated in advance.

Sulfuric acid concentration: Sulfuric acid is a main chemical for reacting with Cu in metallic silicon powder to perform leaching. The reaction equation for leaching copper is simply expressed as Cu ° + H ₂ SO ₄ → CuSO ₄ + H ₂ ↑. If the amount of excess sulfuric acid is less than 10 g / l in this leaching reaction, the leaching rate is low, so
0 g / l is preferred. The leaching rate of copper also increases as the sulfuric acid concentration increases, but when it exceeds 100 g / liter, the leaching rate becomes almost constant, and there is no improvement in the leaching rate. Therefore, in consideration of the corrosion resistance of the equipment, the safety of work, and the like, the upper limit of the amount of excess sulfuric acid is preferably 100 g / liter, but may be more than 100 g / liter.

Slurry concentration: When performing the stirring leaching reaction, the lower the slurry concentration, the better the leaching rate, and the higher the slurry concentration, the worse the leaching rate. If it exceeds 500 g / l, the leaching rate will be extremely deteriorated, so the upper limit of the slurry concentration is 500 g / l. On the other hand, the leaching rate increases as the slurry becomes lower in concentration, but becomes almost constant at less than 100 g / liter. Therefore, in consideration of productivity, the lower limit of the slurry concentration is preferably 100 g / liter, but may be less than 100 g / liter. .

Oxygen supply amount: Copper is a relatively noble metal, and when leaching metallic copper with sulfuric acid, the leaching rate is not very good even if it is simply leached with an aqueous solution of sulfuric acid. Therefore, it is necessary to promote the oxidation of metallic copper by blowing air (O ₂ ) as a reaction assistant (oxidizing agent), for example, to improve the leaching rate. The reaction equation for leaching metallic copper at the time of blowing air is simply expressed as Cu ° + ／ O ₂ + H ₂ SO ₄ → CuSO ₄ + H ₂ O.

In this leaching reaction, the oxygen supply rate is less than 0.2 liter / min in terms of O ₂ per kg of metallic silicon powder, so the leaching rate is poor, so the lower limit is 0.2 liter / min. The leaching rate increases as the oxygen supply increases,
At 0.5 liter / min or more, it is almost constant. Therefore, the upper limit is preferably 0.5 liter / minute, but 0.5 liter / minute is preferable.
You may exceed a minute. In the present invention, not only a case where pure oxygen is blown but also a case where a gas containing oxygen such as air is blown.

Dechlorination treatment: F, C in wet zinc refining
l and the like cause a process abnormality. Therefore, in order to effectively use the dissolved copper in the zinc refining process, it is required that the liquid in which the copper is dissolved contains as little chlorine as possible. For this reason,
Pretreatment dechlorination is required to remove chlorine before dissolving the copper. In the present invention, this dechlorination is performed by washing and filtering the metal silicon powder.

The metal silicon powder obtained by this method can be used as a raw material for obtaining a metal silicon powder having a higher purity, but the use of the metal silicon powder is not limited thereto. Instead, it can of course be used for a reducing agent for magnesium scouring, a raw material for silicon nitride or silicon carbide, and other ordinary uses commensurate with its purity.

[0017]

【Example】

Example 1 Using a mechanical stirring type leaching apparatus as shown in FIG. 1, as shown in Table 1, 1 kg of metallic silicon powder, 300 g / l of slurry concentration, and 0.38 liter of oxygen supply in terms of O ₂ gas supply Under conditions of 5 to 1 in excess of sulfuric acid equivalent to copper leaching.
The mixture was changed to several levels of 30 g / liter, and agitated and leached for 3 hours. The liquid temperature during stirring and leaching was not particularly adjusted, but was about 50 to 60 ° C. Then, the metallic silicon powder in the slurry was separated by filtration, washed with water, and dried.

Next, when the copper in the obtained metal silicon powder was analyzed, it was as shown in Table 1 and FIG. As is clear from these results, it is found that when the excess amount of sulfuric acid is less than 10 g / liter, the leaching and removal of copper is insufficient.
Further, it can be seen that even if the excess amount of sulfuric acid exceeds 100 g / liter, there is no further improvement in the leaching removal rate, and the residual copper content becomes constant.

In FIG. 1, 1 is a slurry composed of metallic silicon powder and an aqueous sulfuric acid solution, 2 is a 5-liter beaker containing the slurry 1, 3 is a stirrer for stirring the slurry 1, and 4 is a slurry 1 The glass tube 5 inserted in the inside is a ball type glass filter attached to the tip of the glass tube 4.

Example 2 Using a mechanical stirring type leaching apparatus as shown in FIG.
As shown in the following table: 30 g / liter of sulfuric acid in excess of the amount equivalent to the leaching of copper, and an oxygen supply amount of 0.38 liter / minute in terms of O ₂ gas. 55
The mixture was changed to several levels of 0 g / liter, and agitated and leached for 3 hours. The liquid temperature during stirring and leaching was not particularly adjusted, but was about 50 to 60 ° C. Then, the metallic silicon powder in the slurry was separated by filtration, washed with water, and dried.

Next, when copper in the obtained metallic silicon powder was analyzed, it was as shown in Table 1 and FIG. As is evident from the results, it is found that when the slurry concentration is 500 g / liter or more, the leaching of copper is poor. Also, the lower the slurry concentration, the higher the leaching rate, but 100 g /
It can be seen that the degree of leaching is constant below 1 liter.

Example 3 Using a mechanical stirring type leaching apparatus as shown in FIG.
As shown in at & metallic silicon powder 1 kg-slurry concentration 300 g / liter of copper leaching considerable excess than content of sulfuric acid 30 g / l conditions, the oxygen supply in O ₂ terms 0.15 to 0. 6
The mixture was changed to several liters / minute and stirred and leached for 3 hours. The liquid temperature during stirring leaching was not particularly adjusted,
It was about 50-60 ° C. Then, the metallic silicon powder in the slurry was separated by filtration, washed with water, and dried.

Next, when the copper in the obtained metal silicon powder was analyzed, it was as shown in Table 1 and FIG. As is clear from this result, 0.2 kg / kg of metallic silicon powder was used.
It can be seen that leaching and removal of copper is insufficient at an oxygen supply rate (O ₂ gas conversion) of less than liter / minute. In addition, the removal rate of copper leaching increases with an increase in oxygen supply,
It can be seen that it becomes constant at 0.5 liter / min or more in terms of O ₂ gas.

[0024]

According to the present invention, a low-purity metal silicon powder containing a large amount of copper and other impurities, for example, a metal silicon powder containing a used copper catalyst discharged from a synthesis process of silane and containing copper and other impurities is used. Since impurities can be removed to a considerable extent, there is an effect that such low-purity metal silicon powder can be regenerated as a raw material for obtaining high-purity metal silicon powder.

Further, the present invention is to increase the added value of what should be waste by using the copper component removed from the metallic silicon powder as a substitute for copper sulfate used in the zinc refining process. As a result, there is an effect that the cost of refining the metal silicon powder can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a stirring device used in the present invention.

FIG. 2 is a graph showing the relationship between the amount of excess sulfuric acid and the copper content in leached metal silicon powder.

FIG. 3 is a graph showing the relationship between the slurry concentration and the copper content in the leached metal silicon powder.

FIG. 4 is a graph showing a relationship between an oxygen supply amount per 1 kg of metal silicon powder and a copper content in a leached metal silicon powder.

[Explanation of symbols]

 Reference Signs List 1 slurry 2 beaker 3 stirrer 4 glass tube 5 ball type glass filter

Claims (7)

[Claims] 1. A method in which a metal silicon powder is put into an aqueous solution containing sulfuric acid, and the metal silicon powder and the aqueous solution are stirred and mixed while supplying oxygen (including a case where the metal silicon powder is contained in air). A pretreatment method for metal silicon powder, which comprises removing copper from the metal silicon powder. 2. The method according to claim 1, wherein the metal silicon powder is a metal silicon powder containing a used copper catalyst discharged from a silane synthesis step. 3. The method according to claim 1, wherein said metal silicon powder is washed with water in advance to remove contained chlorine, and then said copper removal is performed. 4. The method according to claim 1, wherein the aqueous solution which contains copper by the decoppering is used as a copper sulfate source in a zinc refining step. 5. The method according to claim 1, wherein the concentration of sulfuric acid in the aqueous solution is 10 to 100 g / L in excess of a copper equivalent. 6. The metal silicon powder having a slurry concentration of 10
The method according to any one of claims 1 to 5, wherein the amount is 0 to 500 g / liter. 7. The method according to claim 1, wherein the supply amount of oxygen is 0.2 to 0.5 liter / minute in terms of O ₂ per kg of the metal silicon powder. .