JP2003147455A - Method of recovering tantalum compound from wire saw slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of recovering a tantalum compound from oily low concentration tantalum-containing precipitates which are disposed as industrial waste heretofore. SOLUTION: The method consists of a first stage where wire saw slurry after use containing a tantalum compound and abrasive grains in cutting oil is dissolved in a solvent compatible with the cutting oil to disperse the tantalum compound and the abrasive grains into the solvent, and a second stage where powders are wetly classified into fine powders and coarse powders from the solvent. The fine powders are reused as wire saw slurry, and the tantalum compound is recovered from the coarse powders. Desirably, beforehand measurement for specifying the maximum grain diameter of the tantalum compound is performed, and, with the specified maximum grain diameter as a cut size, the wet classification in the second stage is performed by using a wet cyclone.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wire saw slurry, which is generated during the process of manufacturing an oxide crystal wafer containing tantalum such as lithium tantalate, and contains a tantalum compound and abrasive grains in cutting oil, The present invention relates to a method for recovering a tantalum compound by concentrating and separating the tantalum compound.

[0002]

2. Description of the Related Art In the process of manufacturing an oxide crystal wafer containing tantalum, such as lithium tantalate, when cutting an oxide crystal containing tantalum (hereinafter referred to as a tantalum compound), a wire saw is conventionally used. The method has been done.

In this method of cutting with a wire saw, cutting oil in which abrasive grains are dispersed is used. Therefore, the precipitates generated during the cutting of the wire saw include cutting oil, fine cutting powder, and coarser abrasive grains. Are collected as a mixture (an oily low-concentration tantalum-containing starch containing tantalum compound particles). A method for recovering such abrasive grains is described in, for example, Japanese Patent Laid-Open No. 8-39430. However, in the wire saw cutting, since the amount of abrasive grains used is large, the content of the tantalum compound in the starch becomes 20% by mass or less,
The tantalum concentration was low. Therefore, when trying to recover the tantalum compound from the above-mentioned starch generated during the wire saw cutting, the recovery rate is poor due to the low tantalum concentration, and a large amount of industrial waste is generated after the recovery of the tantalum compound. To do. Thus, the recovery of tantalum compounds from the starch generated during the wire saw cutting is economically unacceptable, and thus the starch has conventionally been disposed of as industrial waste.

However, from the viewpoint of effectively utilizing the tantalum resource which tends to be insufficient, the tantalum compound is economically recovered from the precipitate generated during the cutting of the wire saw, and a large amount of industrial waste is generated. There is a strong demand for ways to reduce the amount of

[0005]

DISCLOSURE OF THE INVENTION The present invention reduces the amount of industrial waste generated from an oily low-concentration tantalum-containing starch containing fine particles of tantalum compound, which has been conventionally disposed of as industrial waste. The purpose is to provide a method for separating.

[0006]

A method for recovering a tantalum compound from a wire saw slurry of the present invention is a method in which a used wire saw slurry containing a tantalum compound and abrasive grains in a cutting oil is used as a solvent compatible with the cutting oil. A first step of dissolving and dispersing a tantalum compound and abrasive grains in the solvent;
A second step of wet classification from the solvent into a slurry containing fine powder and a slurry containing coarse powder, the coarse powder is reused as a wire saw slurry, and the tantalum compound is recovered from the fine powder.

It is desirable that the solvent is a cutting oil of the same kind as the cutting oil.

The difference between the measured particle size distribution of the starch obtained from the used wire saw slurry and the measured particle size distribution of the starch after removing the tantalum compound from the starch is defined as the particle size distribution of the tantalum compound. It is desirable to perform a preliminary measurement to identify the maximum particle size of the tantalum compound by identification, and to perform the wet classification of the second step using a liquid cyclone with the identified maximum particle size of the tantalum compound as a classification point. .

During at least one of the first step and the second step, it is desirable to remove the magnetic substance contained in the slurry by using a magnet.

By identifying the measured particle size distribution of the starch after removing the tantalum compound from the starch obtained from the used wire saw slurry as the particle size distribution of the abrasive grains,
A means for performing a pre-measurement for specifying the maximum grain size of the abrasive grains to remove foreign matter having a size larger than the maximum grain size of the specified abrasive grains is provided in at least one of the first step and the second step. Is desirable.

The mass of the abrasive grains in the precipitate containing the abrasive grains and the tantalum compound obtained by centrifugal separation from the slurry containing fine powder was measured, and the unused abrasive grains were removed by the mass of the measured abrasive grains or less. It is desirable to add it to the slurry containing the coarse powder and reuse it as a wire saw slurry.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below.

FIG. 1 is a flow chart showing an embodiment of the present invention.

First, the method of recovering a tantalum compound according to the present invention comprises at least the following first step and second step, and the coarse powder mainly obtained by the second step and containing abrasive grains is used as a wire saw slurry. To reuse. The small amount of tantalum compound remaining in the coarse powder is finally separated and collected as fine powder mainly containing the tantalum compound.

(1) First Step In the first step, the cutting oil in the used wire saw slurry is dissolved in a solvent that is compatible with the cutting oil, and the tantalum compound and abrasive grains in the wire saw slurry are diluted.・ Disperse.

The tantalum compound and the abrasive grains in the wire saw slurry are dispersed in the solvent for the following reason.

That is, the abrasive grains at the time of cutting the wire saw are usually dispersed in the cutting oil in a high concentration, and the wire saw slurry has a high viscosity. Therefore, in the second step, it may be insufficient to remove the abrasive grains from the tantalum compound and the abrasive grains in the wire saw slurry by wet classification.

If the abrasive particles can be removed by wet classification, a solvent other than cutting oil, such as kerosene, may be used as the solvent.

However, when the coarse powder which is separated by the wet classification in the second step and mainly contains abrasive grains is reused as the wire saw slurry, the residual solvent may adversely affect the cutting characteristics. It is preferable to use cutting oil itself as the solvent.

(2) Second Step In the second step, in order to remove the abrasive particles from the solvent in which the tantalum compound and the abrasive particles are dispersed, fine powder mainly containing the tantalum compound and abrasive particles are mainly contained. Wet classification with coarse powder.

As the wet classification, a natural sedimentation method or a filtration method using a filter having an opening diameter larger than fine powder and smaller than coarse powder can be applied, but continuous treatment is possible and economical. The method using a liquid cyclone is preferable.

Regarding the setting of the classification point in the hydrocyclone, the following setting method is exemplified.

That is, after a part of the wire saw slurry was sampled and dried, the obtained precipitate was treated with an etching solution for dissolving a tantalum compound, for example, a hydrofluoric acid-nitric acid mixed solution, The particle size distribution of the starch before and after the treatment is measured, and the particle size distributions of the respective starches are compared (that is, the particle size distribution of the starch before the treatment including the tantalum compound and the abrasive grains (in the case of FIG. 1, before removing the magnetic substance / foreign matter) After the treatment in which the tantalum compound is removed and the abrasive grains are contained (compared with the particle size distribution of the starch after the wet classification in the case of FIG. 1), the particle size distribution of the tantalum compound contained in the starch Is measured in advance, and the classification point in the liquid cyclone may be set to about the maximum particle size of the measured tantalum compound.

When it is confirmed in the preliminary measurement that the precipitate contains a magnetic substance such as a wire piece of a wire saw, at least one of the first step and the second step ( In the case of FIG. 1, before dissolution), magnetic substances such as wire pieces contained in the solvent are removed using a magnet. By this magnetic substance removal treatment, it is possible to omit the complicated Fe removal treatment that is required before the recovery as tantalum, and also to mix the wire pieces into the coarse particles to be reused as the wire saw slurry. It can be reduced.

Furthermore, in order to prevent foreign matters from adversely affecting the cutting characteristics when the coarse powder mainly containing abrasive grains is reused as the wire saw slurry in the second step, the first step is carried out. It is preferable to have means for removing foreign matters larger than the maximum grain size of the abrasive grains during at least one of the second step (before melting in the case of FIG. 1).

When the coarse powder is reused as a wire saw slurry, the mass of the abrasive grains in the slurry containing fine powder is added to the abrasive grains separated in the slurry containing fine powder by wet classification. Below, new abrasive grains are added to the slurry containing coarse powder to adjust the slurry concentration. As described above, cutting characteristics and life equivalent to those when using new abrasive grains can be realized.

Even if the mass of the new abrasive grains to be added is more than the mass of the abrasive grains in the slurry containing fine powder, there is no problem in the cutting characteristics and life at the time of reuse, but the slurry containing fine powder. More than the mass of abrasive grains in, when adding new abrasive grains, the mass of abrasive grains in the regenerated wire saw slurry,
The mass of the abrasive grains in the initial wire saw slurry is more than the mass, and the amount of the regenerated slurry is more than the initial amount of slurry, and eventually it must be discarded as industrial waste. Therefore, although the tantalum compound remains in the coarse powder to be discarded as industrial waste and has a low content rate mainly containing abrasive grains, the tantalum compound to be discarded cannot be ignored because the mass of the coarse powder is large.

Therefore, in order to improve the recovery rate of the tantalum compound, which is the object of the present invention, and to maintain the effect of reducing the amount of industrial waste generated, a new abrasive having a mass equal to or less than the mass of the abrasive grains in the fine powder is maintained. Add the grains to the slurry containing the coarse powder.

In the used wire saw slurry, the tantalum compound concentration is about 20% by mass. However, by classifying, the fine powder mainly containing the tantalum compound has a tantalum compound concentration of up to about 40% by mass. Concentrated.

Thereafter, usually, tantalum pentoxide is produced from the tantalum compound, and the tantalum content is recovered and recycled. Specifically, the tantalum compound containing the concentrated abrasive grains is incinerated to remove the oil content. After pulverization, the product is dissolved in a nitric acid-hydrofluoric acid solution, and then subjected to general chemical treatment to purify tantalum pentoxide.

[0031]

EXAMPLES Examples of the present invention will be specifically described below.

The wire saw slurry after cutting the lithium tantalate single crystal was left to stand and was allowed to spontaneously settle to remove the supernatant oil component, and the precipitate (first-time starch) was treated as follows.

The first-time starch contains lithium tantalate cutting powder, abrasive grains containing SiC as a main component, and cutting oil.

The results of the analysis of the first-time starch are shown in Table 1.

[0035]

[Table 1]

Further, a part of the first-time starch was sampled, dried, and then treated with a hydrofluoric acid-nitric acid mixed solution,
The particle size distribution before and after the treatment was measured. Figure 2 shows the measured particle size distribution before and after removal of lithium tantalate.
Shown in.

From the comparison of the particle size distributions before and after the removal of lithium tantalate shown in FIG. 2, it is estimated that the lithium tantalate contained in the first starch has a particle size of 5 μm or less. It should be noted that this measurement can be carried out in a steady operation by partially collecting as shown in FIG.

Next, 21.0 kg of the first-time starch (containing 4095 g of lithium tantalate) was put into 140 liters of cutting oil, and after stirring and dispersing, a permanent magnet was put in, and what was adsorbed to the magnet was taken. After removal, a first dispersion liquid was obtained.

Further, the obtained first dispersion liquid was mixed with 100
After filtering with a μm filter, wet classification was performed with a liquid cyclone at 5 μm as a boundary, and about 131 liters of the first upstream dispersion liquid (containing fine powder) mainly containing the tantalum compound and the first downstream dispersion liquid mainly containing the abrasive grains. Liquid (including coarse powder) About 1
I got 4 liters.

About 131 liters of the first upstream dispersion obtained by this wet classification treatment was centrifuged to obtain 8.2 kg (lithium tantalate content 3600 g) of solid content.

On the other hand, about 14 liters of the first downstream dispersion liquid was spontaneously settled, and the supernatant oil was removed to obtain 12.9 kg.
A solid content of (lithium tantalate content 495 g) was obtained.

Table 2 shows the analysis results of the solid content of the first upstream dispersion liquid and the solid content of the first downstream dispersion liquid.

[0043]

[Table 2]

After adding the amount of abrasive grains in the solid content of the first upstream dispersion liquid, that is, 3.73 kg of new abrasive grains to the solid content of the first downstream dispersion liquid, the specific gravity was adjusted using cutting oil, and the solid content was adjusted again. Used as a wire saw slurry for cutting a lithium tantalate single crystal.

It should be noted that no difference in cutting characteristics was observed when using a wire saw slurry prepared from new abrasive grains.

The wire saw slurry after cutting is left to stand and is allowed to spontaneously settle to remove the supernatant oil component, and the second precipitation 2
1.5 kg was obtained.

The results of the second-time analysis of the starch are shown in Table 3.

[0048]

[Table 3]

Next, 21.5 kg of the second-time precipitate (lithium tantalate content 4236 g) was put into 140 liters of cutting oil, and after stirring and dispersing, a permanent magnet was put in to remove what was attracted to the magnet. A second dispersion was obtained.

Further, the obtained second dispersion liquid is mixed with 100
After filtering with a μm filter, wet classification was performed with a liquid cyclone at 5 μm as a boundary, and the second upstream dispersion liquid (contains fine powder) about 131.5 liters in which the tantalum compound was concentrated and the second time mainly containing abrasive grains About 14 liters of the downstream dispersion liquid (including coarse powder) was obtained.

About 131.5 liters of the second upstream dispersion obtained by this wet classification treatment was centrifuged to give 8.5 kg.
A solid content of (lithium tantalate content 3715 g) was obtained.

On the other hand, about 14 liters of the second downstream dispersion liquid was spontaneously sedimented, and the supernatant oil was removed to obtain 13.3 kg.
A solid content of (tantalum content 507 g) was obtained.

Table 4 shows the analysis results of the solid content of the second upstream dispersion liquid and the solid content of the second downstream dispersion liquid.

No difference was found between the concentration of lithium tantalate in the solid content of the first downstream liquid in Table 2 and the concentration of lithium tantalate in the solid content of the second downstream liquid in Table 4.

[0055]

[Table 4]

[0056]

As described above, according to the method for recovering the tantalum compound from the wire saw slurry of the present invention, the coarse powder mainly containing the abrasive grains is not disposed as industrial waste,
Since it is reused as wire saw slurry, the generation of industrial waste can be greatly reduced.

Further, every time the coarse powder to be reused as the wire saw slurry is circulated and used, a small amount of the remaining tantalum compound is finally transferred to the fine powder and can be separated / collected.

[Brief description of drawings]

FIG. 1 is a flowchart showing an embodiment of the present invention.

FIG. 2 is a graph showing a particle size distribution of a starch before and after etching with a hydrofluoric acid-nitric acid mixed solution.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C22B 1/00 601 C22B 1/00 601 7/00 7/00 Z

Claims (6)

[Claims] 1. A first step in which a used wire saw slurry containing a tantalum compound and abrasive grains in cutting oil is dissolved in a solvent compatible with the cutting oil to disperse the tantalum compound and abrasive grains in the solvent. And a second step of wet classification from the solvent into a slurry containing fine powder and a slurry containing coarse powder, wherein the coarse powder is reused as a wire saw slurry, and the tantalum compound is recovered from the fine powder. A method for recovering tantalum compounds from a wire saw slurry. 2. The method for recovering a tantalum compound from a wire saw slurry according to claim 1, wherein the solvent is a cutting oil of the same kind as the cutting oil. 3. The difference between the measured particle size distribution of the starch obtained from the used wire saw slurry and the measured particle size distribution of the starch after removal of the tantalum compound from the starch is determined by the particle size of the tantalum compound. Performing a preliminary measurement to identify the maximum particle size of the tantalum compound by identifying it as a distribution, and performing the wet classification of the second step using a liquid cyclone with the identified maximum particle size of the tantalum compound as the classification point. The method for recovering a tantalum compound from the wire saw slurry according to claim 1, wherein. 4. The wire source according to claim 1, wherein a magnetic substance contained in the slurry is removed by using a magnet during at least one of the first step and the second step. Recovery method of tantalum compounds from rally. 5. The maximum grain size of the abrasive grains is determined by identifying the grain size distribution of the measured grain after removing the tantalum compound from the grain obtained from the used wire saw slurry as the grain size distribution of the grain. A method for performing a pre-measurement for identifying a foreign matter having a particle size equal to or larger than the maximum grain size of the identified abrasive grains is provided in at least one of the first step and the second step. Item 2. A method for recovering a tantalum compound from the wire saw slurry according to Item 1. 6. An abrasive grain obtained by centrifuging from a slurry containing fine powder and the mass of the abrasive grain in the precipitate containing the tantalum compound are measured, and only the mass of the abrasive grain measured or less is unused. The method of recovering a tantalum compound from a wire saw slurry according to claim 1, wherein abrasive grains are added to the slurry containing the coarse powder and reused as a wire saw slurry.