JPH0687607A - Method for recovering silicon - Google Patents

Abstract

PURPOSE:To recover silicon from suspension of silicon particles. CONSTITUTION:Inorganic acid, water soluble inorganic salt and their mixture are added to suspension of silicon particles to give the silicon sedimentation. And if necessary, the separated silicon is washed with water to be made to have high purity. And further, after the suspension is given sedimentation with inorganic acid, the recovered silicon is heated to be made to have high purity. Thus silicon is effectively recovered from suspension of silicon particles and if necessary, the recovered silicon is also made to have high purity. As a result, it is effectively recycled.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for recovering silicon from an aqueous solution in which fine silicon particles are suspended.

[0002]

2. Description of the Related Art Semiconductor silicon chips are manufactured by cutting a silicon wafer cut and polished from a silicon ingot. The shavings generated during the cutting of the ingot and the polishing process of the cut wafer become a state where fine particles of silicon are suspended in the water used for the cutting and polishing process, and with the development of the semiconductor industry, This amount is enormous.

[0003]

The silicon particles generated in the above process are so fine that they are suspended in water and do not easily settle. For this reason, it is difficult to separate silicon from water, and until now, it was treated as a suspension without being reused, and was treated and discarded together with other waste liquids. But not reusing expensive, pure silicon
This is a big problem in terms of effective use of resources.

[0004] Generally, as a method of collecting particles, a method of filtering and separating is known, but the above-mentioned silicon particles are not practical because the particle size is too fine and they are easily clogged with the filter paper. There is also a centrifuge method, but the concentration of silicon particles is too thin with respect to water, the efficiency of centrifuge is poor, and the equipment and operation are expensive, and this method is also not practical.

The present invention has been made in view of the above circumstances, in which silicon particles suspended in water are chemically treated to be efficiently separated by sedimentation and further, if necessary, recovered. The purpose is to make the purified silicon highly purified.

[0006]

In order to achieve the above object, the method for recovering silicon from a suspension of silicon particles according to the present invention is a method for recovering silicon from an aqueous solution in which silicon particles are suspended. There
An inorganic acid is added to the silicon particle suspension to separate the silicon particles settled in the liquid.

Further, there is provided a silicon recovery method for recovering silicon particles from an aqueous solution in which silicon particles are suspended,
A water-soluble inorganic salt is added to a silicon particle suspension to separate the silicon particles settled in the liquid.

A method of recovering silicon from an aqueous solution in which silicon particles are suspended,
A mixture of an inorganic acid and an inorganic salt is added to a suspension of silicon particles to separate the silicon particles precipitated in the liquid.

Further, the silicon particles separated from the aqueous solution are subjected to a water washing treatment to highly purify the recovered silicon.

Further, the silicon particles separated from the aqueous solution are heated to highly purify the recovered silicon.

[0011]

According to the present invention, by adding an inorganic acid, a water-soluble inorganic salt or a mixture of an inorganic acid and a water-soluble inorganic salt to a silicon particle suspension, the silicon particles are precipitated and separated to recover silicon. , To purify the recovered silicon.

The silicon particle suspension of the present invention refers to a suspension of silicon particles in an aqueous solution.
An aqueous solution containing fine silicon particles generated in a silicon ingot cutting step, a silicon wafer polishing step, or the like can be used.

The average particle diameter of these actual silicon particles is generally about 10 μ to 0.1 μ. In addition to the above, the present invention is applicable to all aqueous solutions in which silicon particles that are suspended and hardly settle are wholly or partially present.

Next, the inorganic acid added to this suspension refers to an inorganic acid that dissociates well in water, and examples thereof include sulfuric acid, hydrochloric acid, hydrofluoric acid, nitric acid, and mixtures thereof. The addition amount of these is 0.01 mol /
It is preferably 1 or more. If it is less than 0.01 mol / l, the effect of improving the sedimentation rate of silicon particles becomes small.

The upper limits of the amounts of these added are not particularly limited, except for hydrofluoric acid and mixtures thereof with other acids, but the purity of the recovered silicon decreases, so it is preferable that it is as low as possible. When hydrofluoric acid or other acids are mixed, the amount of hydrofluoric acid added to the suspension is 1 mol / l.
Less than is preferred. Above this, the tendency of silicon to dissolve becomes strong, and the recovery rate of silicon decreases.

Examples of the water-soluble inorganic salt added to this suspension include calcium chloride, sodium chloride, ferric chloride, aluminum sulfate, ferrous sulfate, ferric sulfate and the like. The addition amount of these is 0.005 mol / l
The above is preferable. Below this, the effect of improving the sedimentation rate becomes small.

The upper limit of the amount of addition of these is not particularly limited as long as they are dissolved in the suspension, but since the purity of the recovered silicon decreases, it is preferable that the amount of addition is as small as possible.

When a mixture of these inorganic acids and water-soluble inorganic salts is added, their total amount is 0.005mo.
It is preferably 1 / l or more. Below this, the effect of improving the sedimentation speed becomes small. These upper limits are not particularly limited as long as they are well dissolved in the suspension, except that hydrofluoric acid is mixed with the other and added.

However, since the purity of the recovered silicon decreases, it is preferable that the amount is as small as possible. When hydrofluoric acid is added as a mixture with an inorganic salt, the amount of hydrofluoric acid added is preferably less than 1 mol / l with respect to the suspension. Above this, the tendency for the silicon to dissolve becomes stronger, and the recovery rate of silicon decreases.

The silicon thus precipitated from the suspension can be separated by decanting or filtering the supernatant and then removing water by drying or the like.

Further, the removal of the inorganic acid or the inorganic salt attached to the silicon separated by the above method to improve the purity can be carried out by washing these with water.
Specifically, it can be performed by repeating decantation or washing the silicon residue with water during filtration. At this time, in the present invention, since the precipitated silicon particles are strongly aggregated, they are not resuspended even if washed, and the sedimentation and separation do not become difficult.

When the inorganic acid is added alone to precipitate and separate the silicon, the recovered silicon can be highly purified by heating the separated silicon.

The suspended silicon fine particles can be easily separated by sedimentation by adding an inorganic acid, a water-soluble inorganic salt or a mixture thereof, and can be highly purified thereafter. The reason for this is that the surface of the silicon particles in the suspension was charged and floated due to this repulsive force, but by adding an inorganic acid or an inorganic salt, the surface charge was eliminated and It is conceivable that the powder was modified to cause strong aggregation. Therefore, it is considered that the recovered silicon could be highly purified without being resuspended when washed with water.

When the inorganic acid is added and the silicon is separated by sedimentation, it is considered that the acid adhering to the silicon can be evaporated by heating the adhering acid, resulting in high purification.

[0025]

EXAMPLES Examples of the present invention will be described below.

Mixtures shown in Examples 1 to 11 were prepared by adding an inorganic acid and a water-soluble inorganic salt to a suspension of silicon particles. For example, for Example 1, 90 m of an aqueous solution in which 0.5% by weight of silicon particles having an average particle size of 0.6 μ are suspended.
10 ml of 10 N sulfuric acid was added to 1 to give 1 mol / l.
The concentration is set to. The procedure is the same for Examples 2 to 11.

Table 1 shows the average particle size of silicon particles, the silicon concentration, the type of the added inorganic acid and the type of the inorganic salt, and the addition amount thereof for each example.

[0028]

[Table 1]

Next, the samples of the respective examples were stirred for 3 minutes and then allowed to stand, and the sedimentation rate of silicon was measured. The sedimentation speed was determined by collecting the supernatant liquid at a fixed time and measuring the turbidity of the liquid. The turbidity measurement method is JIS KO101.
According to 9.2, a calibration curve was prepared using a kaolin standard solution. The measurement results are shown in Table 2.

[0030]

[Table 2]

Further, the sedimented and separated silicon of the samples of Examples 3, 4 and 10 was filtered, and 10 ml of pure water was added to the silicon residue on the filter paper and suction was repeated three times for washing.

The washed silicon was transferred to a beaker, 100 ml of pure water was added, and the mixture was stirred for 3 minutes, and the reprecipitation property was measured. The sedimentation velocity was measured by the same method as described above. The measurement results are shown in Table 2 as Examples 12, 13 and 14, respectively.

Further, with respect to the samples of Examples 7 and 11, the sedimentation-separated supernatants of silicon were decanted, 100 ml of pure water was added, and the mixture was stirred and allowed to stand, followed by decanting three times. . Then, 100 ml of pure water was added and stirred, and then the sedimentation rate was measured in the same manner as in the previous example. The measurement results are shown in Examples 15 and 1.
6 is shown in Table 2.

Further, in Examples 12 to 16, the electrical conductivity of the supernatant liquid when the sedimentation property was observed was measured to examine the cleaning degree of silicon. The measurement results are shown in Table 3.

[0035]

[Table 3]

In Table 3, Examples 17 and 18 correspond to Example 3,
For the sample of No. 4, after filtering the precipitated and separated silicon respectively, air-drying and further heating at 300 ° C. for 5 hours, adding 100 ml of pure water and stirring, and measuring the electric conductivity of the solution. is there. The measurement result represents the acid removability.

For comparison, with respect to the samples of Comparative Examples 1 and 2 shown in Table 1 in which no inorganic acid or inorganic salt was added, the sedimentation rate of silicon was measured after stirring the suspensions for 3 minutes. The measurement results are shown in Table 2. Furthermore, the electrical conductivity of the silicon suspensions of Comparative Examples 1 and 2 was measured. The measurement results are shown in Table 3 as Comparative Examples 3 and 4, respectively.

As is clear from the comparison between the examples and the comparative examples, it was found that silicon can be easily precipitated and separated by adding an inorganic acid, a water-soluble inorganic salt, and a mixture thereof to a silicon particle suspension.

Further, it has been found that the recovered silicon can be washed with water to be highly purified, and the sedimentation / separation property after washing with water is good, and resuspension is difficult. It was also found that the product separated by sedimentation with an inorganic acid can be highly purified by heating.

[0040]

As described above, according to the present invention, silicon can be efficiently separated and recovered from a silicon particle suspension, and the recovered silicon can be highly purified, if necessary. As a result, there is an effect that these can be effectively recycled.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sadahiko Yokoyama 5-7-1 Shiba, Minato-ku, Tokyo Inside NEC Corporation (72) Inventor Minoru Tsurumi 30-2-1 Engaoka, Midori-ku, Yokohama-shi, Kanagawa − 103

Claims (5)

[Claims] 1. A method for recovering silicon from an aqueous solution in which silicon particles are suspended, which comprises adding an inorganic acid to a suspension of silicon particles and separating the silicon particles precipitated in the liquid. A method for recovering silicon, which is characterized by being present. 2. A method of recovering silicon particles from an aqueous solution in which silicon particles are suspended, comprising adding a water-soluble inorganic salt to a suspension of silicon particles, and separating the silicon particles precipitated in the liquid. A method for recovering silicon, which is characterized in that 3. A silicon recovery method for recovering silicon particles from an aqueous solution in which silicon particles are suspended, which comprises adding a mixture of an inorganic acid and an inorganic salt to a suspension of silicon particles, and depositing the silicon in a liquid. A method for recovering silicon, which comprises separating particles. 4. The method for recovering silicon according to claim 1, wherein the silicon particles separated from the aqueous solution are washed with water to highly recover the recovered silicon. 5. The method for recovering silicon according to claim 1, wherein the silicon particles separated from the aqueous solution are heated to highly purify the recovered silicon.