JP5001589B2 - Method for producing silicon from waste sludge - Google Patents

Description

  The present invention relates to a method for producing silicon, and more particularly, for example, to a method for producing high-purity silicon from waste sludge containing impurities such as silicon particles and abrasive grains that are generated when a silicon crystal is cut.

  One method of obtaining IC wafers, solar cell wafers, etc. from silicon single crystal or silicon polycrystal ingots is to use a device called a wire saw and press the silicon ingot against the wire while rotating the wire at high speed. There is a method of slicing a silicon crystal by supplying a slurry containing abrasive grains to a contact portion between a silicon ingot and a wire.

  In this method, the slurry containing the above-mentioned abrasive grains is circulated and used. However, when the slurry is repeatedly used, silicon cutting powder, crushed abrasive grains, metal powder that is a worn piece of the wire, and the like accumulate, resulting in deterioration of cutting performance such as reduction in cutting speed and slicing accuracy. Therefore, by replacing part of the slurry with new slurry as appropriate, the cutting performance is maintained by maintaining the solid content concentration such as metal powder that is the chip, crushed abrasive grains, and wire wear pieces in the slurry within the specified range. I try to keep it.

  By the way, most of the waste slurry discharged from the wire saw in the silicon ingot slicing process as described above is discarded despite containing silicon particles (swarf) which are effective resources. Is the actual situation.

  On the other hand, as a method of recovering silicon from waste slurries (waste sludge) containing silicon particles as described above, waste slurries discharged in the process of cutting or polishing silicon single crystals or polycrystals are solid-liquid separated. A method is proposed in which the solid content is washed with an organic solvent to remove the dispersant contained in the solid content, and then silicon oxide and abrasive grains are removed from the solid content to obtain a silicon-based powder. (See Patent Document 1).

  In Patent Document 1, as a method for obtaining silicon-based powder by removing silicon oxide and abrasive grains from the solid content, an airflow classifier is used, and the solid content (powder) is introduced into the airflow. Thus, a method for separation is disclosed.

  However, in the case of the method of Patent Document 1, even if the solid content is washed with an organic solvent, it is difficult to sufficiently remove impurities such as a dispersant contained in the solid content, and the solid content remains in the solid content. There is a problem that the purity of the recovered silicon is hindered.

In the case of the method of Patent Document 1, as a method of obtaining silicon-based powder by removing silicon oxide and abrasive grains from solid content, the solid content (powder) is introduced into an air stream and separated. In this method, silicon oxide and abrasive grains cannot always be sufficiently removed. When silicon obtained by this method is used, high purity suitable for use in solar cells is used. There is a problem that it is difficult to obtain silicon.
JP 2001-278612 A

  The present invention solves the above-mentioned problems. For example, high-purity silicon is reliably and efficiently produced from waste sludge containing impurities such as silicon particles and abrasive grains generated when cutting silicon crystals. An object of the present invention is to provide a silicon manufacturing method that can be manufactured.

In order to solve the above problems, the method for producing silicon from waste sludge according to the present invention (Claim 1),
A method for producing high-purity silicon from waste sludge containing silicon particles, powdered inorganic substances other than silicon particles, magnetic impurities, and organic impurities,
(a) a first magnetic material separation step of separating the magnetic material from waste sludge by magnetic force;
(b) A first centrifuge that separates the waste sludge from which the magnetic material has been separated in the first magnetic material separation step into a silicon dispersion in which silicon particles are dispersed and a sedimented layer containing a sedimented substance. A separation process;
(c) a metal impurity dissolving step in which an acid is added to the silicon dispersion separated in the first centrifugation step to dissolve metal impurities contained in the silicon dispersion;
(d) a silicon particle separation step of separating silicon particles from the silicon dispersion in which metal impurities are dissolved in the metal impurity dissolution step;
(e) a cleaning step of cleaning the silicon particles separated in the silicon particle separation step to remove an adhesion liquid containing an acid attached to the silicon particles;
(f) heat-treating the silicon particles cleaned in the cleaning step to remove organic substances contained in the silicon particles;
(g) a heating and melting step for heating and melting the silicon particles heat-treated in the heat treatment step;
(h) a unidirectional solidification purification step of obtaining high-purity silicon by unidirectionally solidifying a silicon ingot obtained by solidifying the silicon melted in the heating and melting step.

Further, a method for producing silicon from waste sludge according to claim 2 is the structure of the invention according to claim 1,
(i) a second magnetic material separation step of separating the magnetic material by magnetic force from the silicon dispersion separated in the immediately preceding centrifugation step;
(j) After performing the second magnetic substance separation step (i), the silicon dispersion is centrifuged, and the second centrifugation step for separating solid impurities as a sedimentation layer is used as one cycle for purification. The cycle is performed once or more after the first centrifugation step (b).

According to a third aspect of the present invention, there is provided a method for producing silicon from waste sludge according to the second aspect of the present invention. It shifts to a process, Then, the process of said (d)-(h) is implemented.

Moreover, the manufacturing method of the silicon | silicone from the waste sludge of Claim 4 is the structure of the invention in any one of Claims 1-3,
The cleaning of the silicon particles in the cleaning step (e) is performed using water,
Between the cleaning step (e) and the heat treatment step (f), a drying step for drying the silicon particles to remove moisture is provided.

  A method for producing silicon from waste sludge according to claim 5 is characterized in that, in the configuration of any one of claims 1 to 4, the heat treatment step (f) is performed at 450 to 600 ° C. .

  A method for producing silicon from the waste sludge according to claim 6 is the cutting waste generated when the waste sludge cuts silicon crystals in the configuration according to any one of claims 1 to 5. It is characterized by sludge.

  The method for producing silicon from waste sludge according to claim 7 is characterized in that, in the structure of any one of claims 1 to 6, it is used for obtaining high-purity silicon for solar cells. It is said.

  The method for producing silicon from waste sludge according to the present invention (Claim 1) is high purity from waste sludge containing silicon particles, powdered inorganic substances other than silicon particles, magnetic impurities, and organic impurities. (A) a first magnetic material separation step of separating magnetic material from waste sludge by magnetic force, and (b) centrifuging the waste sludge from which the magnetic material has been separated in the first magnetic material separation step. A first centrifugal separation step of separating into a silicon dispersion liquid in which silicon particles are dispersed and a sedimentation layer containing a sedimented substance, and (c) the silicon dispersion separated in the first centrifugation step. A metal impurity dissolving step in which an acid is added to dissolve metal impurities contained in the silicon dispersion, and (d) silicon particles from the silicon dispersion in which the metal impurities are dissolved in the metal impurity dissolving step. A silicon particle separation step for separating, (e) a cleaning step for washing the silicon particles separated in the silicon particle separation step to remove an adhering liquid containing an acid attached to the silicon particles, and (f) in the washing step. A heat treatment step of heat-treating the cleaned silicon particles to remove organic substances contained in the silicon particles; (g) a heat-melting step of heat-melting the silicon particles heat-treated in the heat treatment step; and (h) a heat-melting step. It is equipped with a unidirectional solidification purification process to obtain high-purity silicon by unidirectionally solidifying the silicon ingot obtained by solidifying the silicon melted in, so that it is a powdery inorganic substance such as abrasive grains, organic To reliably separate silicon impurities, metal impurities, etc., and waste slurries containing silicon particles, powdered inorganic substances other than silicon particles, magnetic impurities, and organic impurities The high purity silicon it is possible to efficiently produce from.

  A typical example of waste sludge used as a raw material in the present invention is waste sludge containing silicon particles and abrasive grains, which is generated when a silicon ingot is sliced using an apparatus called a wire saw. , Not limited to this, waste sludge generated when cutting silicon ingots by other methods, and other silicon particles, powdered inorganic substances other than silicon particles, magnetic impurities, Various waste sludges containing organic impurities can be used as a raw material.

  In the present invention, examples of the powdered inorganic substance include silicon carbide (SiC) used as abrasive grains. However, abrasive grains made of other materials may be included.

  Examples of the magnetic impurities include iron powder generated by wear of the wire constituting the wire saw and oxides thereof.

  Examples of the organic impurities include organic substances derived from a dispersion medium used for dispersing abrasive grains, a coolant used in a cutting process, and the like.

In the heating and melting step (g) in which the silicon particles are heated and melted, usually, the silicon particles can be efficiently heated and melted by a known induction heating method.
Further, the unidirectional solidification purification step of obtaining the high-purity silicon by the unidirectional solidification treatment in the above (h) can be carried out by applying a known method, and its specific methods and conditions There are no special restrictions.

  Examples of the acid that can be used in the metal impurity dissolution step (c) include hydrochloric acid, sulfuric acid, and nitric acid. Usually, it is desirable to use hydrochloric acid, but in the present invention, there are no particular restrictions on the type of acid, and various acids as described above can be used.

  In addition, as the centrifugal separation means used in the first centrifugal separation step, for example, a wet type in which only a coarse particle having a predetermined diameter or more is selectively settled and separated by rotating a classification rotor containing a liquid to be treated at high speed. A centrifugal classifier is exemplified as a suitable centrifugal separation means.

  In addition, since the silicon particles in the waste sludge are colloidal, for example, using a centrifugal classifier as described above, when the centrifugal separation process is performed, the silicon particles hardly settle and powdery solids such as abrasive grains. And can be classified efficiently.

  On the other hand, the present invention includes a metal impurity dissolving step in which an acid is added to the silicon dispersion separated in the first centrifugation step to dissolve metal impurities contained in the silicon dispersion. Since the colloidal state is destroyed by adding an acid in the step, in the silicon particle separation step (d), for example, the wet centrifugal classifier used in the first centrifugation step (b) is used. By using the same centrifugal classifier, it is possible to efficiently separate silicon particles.

  Moreover, like the manufacturing method of the silicon | silicone from the waste sludge of Claim 2, in the structure of invention of Claim 1, the 2nd magnetic body isolation | separation process of (i) and the 2nd centrifugation process of (j) When the purification cycle is performed once or more after the first centrifugation step of (b), the magnetic substance as impurities and the solid impurities are efficiently removed, It becomes possible to produce high-purity silicon from waste sludge.

In addition, as in the method for producing silicon from waste sludge according to claim 3, in the configuration of the invention according to claim 2 , after performing the purification cycle until the magnetic reaction by the magnetic substance is eliminated, the metal impurities of (c) By going to the melting step and then carrying out the steps (d) to (h), it becomes possible to remove the magnetic material with certainty and to produce high purity silicon more reliably. become.

  Further, as in the method for producing silicon from waste sludge according to claim 4, in the configuration of any one of claims 1 to 3, the washing of the silicon particles in the washing step (e) is performed using water. And performing a drying step of drying the silicon particles to remove moisture between the cleaning step of (e) and the heat treatment step of (f), compared with a case where no drying step is provided, It is possible to improve the silicon recovery rate by suppressing the generation of silicon oxide when the silicon particles come into contact with water.

  Moreover, like the manufacturing method of the silicon | silicone from the waste sludge of Claim 5, in the structure of the invention in any one of Claims 1-4, by performing the heat processing process of said (f) at 450-600 degreeC, Various organic substances such as organic substances derived from dispersion media used to disperse abrasive grains and coolants used in the cutting process can be efficiently removed by evaporation, decomposition, and combustion. In the subsequent heating and melting step (g), the silicon particles can be efficiently heated and melted and purified.

  In addition, as in the method for producing silicon from waste sludge according to claim 6, in the configuration according to any one of claims 1 to 5, the cutting waste sludge generated when cutting silicon crystals is used. Thus, high-purity silicon can be efficiently produced. That is, a large amount of cutting waste sludge generated when cutting silicon crystals is generated. By using this as a raw material, high-purity silicon can be efficiently produced under stable conditions. Become.

Moreover, according to the method for producing silicon from the waste sludge of the present invention, it is possible to obtain high-purity silicon exceeding 99.99% by weight. Therefore, the present invention is extremely effectively used as a method for obtaining high-purity silicon for solar cells from waste sludge containing powdery inorganic substances such as silicon particles and abrasive grains, magnetic impurities, organic impurities, etc. can do.
Moreover, this invention can be utilized also as a method of obtaining the silicon | silicone for sealing agents for semiconductors.
Furthermore, the present invention is not limited to silicon intended for the above applications, but can also be used as a method for producing silicon intended for other applications.

  The features of the present invention will be described in more detail below with reference to examples of the present invention.

  In Example 1, a method for producing silicon from waste sludge generated when a silicon ingot is sliced with a wire saw will be described as an example.

  Waste sludge is a powdered inorganic substance such as silicon particles that are cutting powder, SiC that is abrasive grains, an organic dispersion medium that disperses abrasive grains, organic impurities derived from grinding coolant, and wire wear. It contains magnetic impurities derived from powder and the like, silica colloid generated when silicon particles react with moisture, and the like.

The waste sludge contains about 50 to 65% by weight of a dispersion medium with respect to a solid content of 25 to 45% by weight, and the composition of main substances in this solid content is as follows.
(a) Silicon particles and silicon oxide (SiO ₂ ): 40 to 60% by weight,
(b) Abrasive grains (silicon carbide): 40 to 60% by weight,
(c) Metal powder: 3 to 6% by weight

Note that SiO ₂ contained in the silicon particles is a substance covering the surface of the silicon particles, which is generated when silicon is exposed to high temperature or in contact with moisture during the cutting process. Further, the metal powder is a substance generated by, for example, wire wear, and may include iron (Fe), copper (Cu), aluminum (Al), and the like.

A method for producing silicon using the waste sludge as described above will be described below with reference to FIG.
FIG. 1 is a flowchart showing a procedure of a method for producing silicon from waste sludge according to an embodiment of the present invention.

(1) First, a first magnetic material separation step is performed to separate magnetic materials from waste sludge by magnetic force (first magnetic material separation step) (step 1 in FIG. 1).
In this step, the main part of the magnetic material such as metal powder (iron powder) which is a wear piece of the wire and iron oxide which is an oxide thereof is separated.
In addition, although this 1st magnetic body isolation | separation process is implemented by making a magnet contact waste sludge, there is no special restriction | limiting in the specific method.

(2) Then, by centrifuging the waste sludge from which the magnetic material has been separated in the first magnetic material separation step of (1) above, the silicon dispersion liquid in which the silicon particles are dispersed and SiC as the abrasive grains are the main components. (First centrifugation step) (step 2 in FIG. 1).
In the first centrifugal separation step, a centrifugal classifier is used to separate the silicon dispersion liquid in which the silicon particles are dispersed and the sedimented layer containing SiC as a main component.
At this time, the volume ratio of the silicon dispersion to be separated and the sedimented layer is about 8: 1.
The sedimented layer separated in this step is a non-magnetic solid material that has not been separated in the first magnetic material separation step (1), that is, SiC powder that is abrasive grains, or a solid material that is a non-magnetic material. In general, the silicon dispersion liquid formed and separated from each other contains approximately 80% by weight or more of silicon particles in the waste sludge.

(3) Next, the magnetic material is separated by magnetic force from the silicon dispersion separated in the first centrifugation step (second magnetic material separation step) (step 3 in FIG. 1).
In this step, the magnetic material that has not been separated in the first magnetic material separation step (1) and has not moved to the sedimented layer side in the first centrifugation step (2) is separated. . Since the magnetic substance is an impurity of silicon to be finally produced, it is desirable to remove it as much as possible at this stage.

(4) Then, the silicon dispersion obtained by further separating the magnetic material in the second magnetic material separation step of (3) is subjected to the same kind of centrifugal separation as the centrifugal classifier used in the first centrifugation step of (2). Centrifugation is performed using a classifier, and solid impurities remaining in the silicon dispersion are separated as a sedimentation layer (second centrifugation step) (step 4 in FIG. 1).
Then, the above step (3) and the subsequent step (4) are taken as one purification cycle, and this purification cycle is performed until there is no magnetic reaction due to the magnetic substance.

(5) Then, the above purification cycle is repeated until the magnetic reaction disappears, and hydrochloric acid is added to the silicon dispersion sufficiently separated from the magnetic substance and the solid impurities to dissolve the metal impurities contained in the silicon dispersion ( Metal impurity dissolution step) (Step 5 in FIG. 1).
In this metal impurity dissolution step, the nonmagnetic metal contained in the silicon dispersion is dissolved in acid and moves to the liquid phase.
In this metal impurity dissolving step, about 15 g of an aqueous hydrochloric acid solution having a concentration of 35 wt% is added to 1 kg of the silicon dispersion in a state where the solid concentration of the silicon dispersion is about 8 wt%, The metal impurities were dissolved by stirring.

(6) Next, silicon particles are separated from the silicon dispersion in which the metal impurities are dissolved in the metal impurity dissolution step (5) (silicon particle separation step) (step 6 in FIG. 1).
Since the colloidal state is destroyed by adding an acid to the silicon dispersion in the metal impurity dissolution step (5), the wet centrifugal classifier used in the first centrifugation step (2) By using a similar centrifugal classifier or the like, silicon particles can be efficiently separated.

(7) Thereafter, the silicon particles separated in the silicon particle separation step are sufficiently washed to remove the adhering liquid containing hydrochloric acid adhering to the silicon particles (washing step) (step 7 in FIG. 1).
In this cleaning step, the silicon particles are cleaned using water. However, if cleaning is performed using water, some of the silicon particles react with water to form silicon hydrates, oxides (SiO ₂ ), etc. In range, it is desirable to reduce contact with water.

(8) Then, the silicon particles washed in the washing step (7) are dried at 110 to 150 ° C. to remove moisture (drying step) (step 8 in FIG. 1).
Desirably, drying is performed as quickly as possible to suppress the formation of silicon hydrates or oxides due to the contact of silicon with water.

(9) Next, the silicon particles dried in the drying step (8) are heat-treated at 600 ° C. to remove organic substances contained in the silicon particles (heat treatment step) (step 9 in FIG. 1).
The silicon particles in the state dried in the drying step (8) are usually a variety of organic substances derived from a dispersion medium used for dispersing abrasive grains, a coolant used in the cutting step, and the like. Although it contains an organic substance, the organic substance can be efficiently removed by evaporating, decomposing, and burning by using this heat treatment step.

  (10) Then, the silicon particles that have been heat-treated in the heat treatment step (9) and from which the organic material has been removed are heated and melted by a method such as induction heating (heat-melting step) (step 10 in FIG. 1).

(11) Further, the silicon ingot obtained by solidifying the silicon melted in the heating and melting step of (10) is subjected to unidirectional solidification to obtain high purity silicon (unidirectional solidification purification step) (FIG. 1 step 11).
Thereby, a high purity silicon crystal is obtained.

In addition, as a result of measuring the purity of the silicon manufactured by the method of the above example, it was confirmed that the silicon purity was 99.99% by weight or more and could be used as a raw material for solar cells.
In addition, according to the method of this example, about 70 to 80 g of high-purity silicon could be obtained from 100 g of silicon particles in the waste sludge.

  In this embodiment, the second magnetic material separation step (3) and the second centrifugation step (4) for separating solid impurities remaining in the silicon dispersion liquid as a sedimentation layer are performed. “Purification cycle” is carried out, but if the magnetic substance and solid impurities such as SiC can be sufficiently separated in the first magnetic substance separation step and the first centrifugation step, It is possible to omit the implementation of the cycle.

  The present invention is not limited to waste sludge generated when slicing a silicon ingot as described above with a wire saw, but waste sludge containing silicon particles, powdered inorganic substances, magnetic impurities, and organic impurities. Can be widely applied to the production of silicon.

  The invention of the present application is not limited to the above embodiment in other points as well, and the type of waste sludge and the magnet and waste sludge for carrying out the first and second magnetic substance separation steps are brought into contact with each other. A specific method including a method for the above, a specific configuration of a centrifuge used in the first and second centrifugation steps, a type of acid used in the metal impurity dissolving step, and a condition for dissolving the metal impurities by the acid The type and configuration of the separation means used in the silicon particle separation process, the cleaning method of the silicon particles separated in the silicon particle separation process, its conditions, the configuration and drying conditions of the drying means in the drying process, Heat treatment conditions for removing organic substances contained in particles, equipment and operating conditions used for heating and melting silicon particles, Respect such conditions procoagulant process, within the scope of the invention, may be added various applications and modifications.

As described above, according to the present invention, waste sludge containing silicon particles, powdered inorganic substances, magnetic impurities, and organic impurities, typically when a silicon ingot is sliced with a wire saw. High-purity silicon can be efficiently produced from the generated waste sludge.
Therefore, the present invention can be widely applied to the production of high-purity silicon as a raw material for solar cells from waste sludge containing silicon.

It is a flowchart which shows the procedure of the manufacturing method of the silicon | silicone from waste sludge concerning one Example of this invention.

Claims (7)

A method for producing high-purity silicon from waste sludge containing silicon particles, powdered inorganic substances other than silicon particles, magnetic impurities, and organic impurities,
(a) a first magnetic material separation step of separating the magnetic material from waste sludge by magnetic force;
(b) A first centrifuge that separates the waste sludge from which the magnetic material has been separated in the first magnetic material separation step into a silicon dispersion in which silicon particles are dispersed and a sedimented layer containing a sedimented substance. A separation process;
(c) a metal impurity dissolving step in which an acid is added to the silicon dispersion separated in the first centrifugation step to dissolve metal impurities contained in the silicon dispersion;
(d) a silicon particle separation step of separating silicon particles from the silicon dispersion in which metal impurities are dissolved in the metal impurity dissolution step;
(e) a cleaning step of cleaning the silicon particles separated in the silicon particle separation step to remove an adhesion liquid containing an acid attached to the silicon particles;
(f) heat-treating the silicon particles cleaned in the cleaning step to remove organic substances contained in the silicon particles;
(g) a heating and melting step for heating and melting the silicon particles heat-treated in the heat treatment step;
(h) unidirectionally solidifying and purifying a silicon ingot obtained by solidifying the silicon melted in the heating and melting step to obtain high purity silicon, A method for producing silicon from waste sludge. (i) a second magnetic material separation step of separating the magnetic material by magnetic force from the silicon dispersion separated in the immediately preceding centrifugation step;
(j) After performing the second magnetic substance separation step (i), the silicon dispersion is centrifuged, and the second centrifugation step for separating solid impurities as a sedimentation layer is used as one cycle for purification. The method for producing silicon from waste sludge according to claim 1, wherein the cycle is performed at least once after the first centrifugation step (b). The purification cycle is performed until the magnetic reaction due to the magnetic substance disappears, and then the step (c) is performed to dissolve the metal impurities, and then the steps (d) to (h) are performed. A method for producing silicon from waste sludge according to claim 2 . The cleaning of the silicon particles in the cleaning step (e) is performed using water,
4. A drying step for drying the silicon particles to remove moisture is provided between the cleaning step (e) and the heat treatment step (f). A method for producing silicon from waste sludge as described in 1.   The method for producing silicon from waste sludge according to any one of claims 1 to 4, wherein the heat treatment step (f) is performed at 450 to 600 ° C.   The method for producing silicon from waste sludge according to any one of claims 1 to 5, wherein the waste sludge is cutting waste sludge generated when cutting silicon crystals.   The method for producing silicon from waste sludge according to any one of claims 1 to 6, which is used for obtaining high-purity silicon for solar cells.

Images