JP2011074475A - Method for recovering gallium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a technique which can recover gallium with high purity from the scrap, polishing waste or the like of a gallium compound. <P>SOLUTION: The method for recovering gallium includes: a solid-liquid separation step of subjecting gallium-arsenic-containing sediment to solid-liquid separation into oil and solid residue by a filter press using an oil resistant filter with an air permeability of ≤18 cc/cm<SP>2</SP>/min; an oil removal step of holding the solid residue after the solid-liquid separation to an inert gas atmosphere in the temperature range higher than the boiling point of the oil and lower than the evaporation temperature of arsenic and controlling the oil contained in the solid residue after the solid-liquid separation to ≤1 wt.%; an arsenic removal step of holding the solid residue after the oil removal to an atmosphere of ≥1,000°C for ≥5 min and removing arsenic; a dissolution step of dissolving the solid residue after the arsenic removal into acid or alkali; an insoluble matter filtration step of filtering a solution and insoluble matter obtained in the dissolution step by a filter; and a gallium recovering step of neutralizing a solution obtained in the insoluble matter filtration step, so as to obtain a gallium oxide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for recovering gallium, and more particularly to a method for recovering gallium from a gallium arsenide-containing starch.

  Gallium is a semiconductor material having excellent characteristics, but is a rare element with almost no concentrate, and is mainly obtained as a by-product of refining aluminum and zinc. For this reason, in order to effectively use gallium resources that tend to be deficient, and to reduce industrial waste, semiconductor waste generated when manufacturing electronic components such as ICs, slurry generated when cutting with scrap or wire saw, Gallium is collected from a slurry or the like generated by polishing after cutting (for example, Patent Document 1 and Patent Document 2).

  However, the method disclosed in Patent Document 1 is a method for concentrating and recovering gallium from a gallium arsenide compound by solvent extraction, and there is a problem that the process becomes expensive because an organic solvent needs to be prepared separately.

  Therefore, from the gallium phosphorus compound-containing starch generated as cutting waste when cutting a semiconductor crystal of a compound containing gallium such as gallium phosphide, concentration by wet classification, solid-liquid separation by liquid cyclone or membrane separation, acid dissolution, A method of recovering gallium through a process called concentration recovery (Patent Document 2) is disclosed.

  However, only solid-liquid separation by liquid cyclone or membrane separation inevitably leaves about 10% of the cutting oil in the separated solid, and the acid in such a state containing organic matter (cutting oil) is unavoidable. Dissolution caused carbon contamination during the recovery of gallium, and had a problem of reducing the purity of the recovered gallium.

Japanese Patent Laid-Open No. 61-215214 Japanese Patent No. 3436304

  For this reason, development of the technique which can collect | recover high purity gallium without raising a cost from the cutting waste, the grinding | polishing waste, etc. which arise when a gallium compound is cut | disconnected or grind | polished has been desired.

  The present inventor has found that the above-mentioned problems can be solved by the inventions of the following claims, and has completed the present invention. The invention of each claim will be described below.

The invention described in claim 1
A method for recovering gallium from a gallium arsenide-containing starch,
A solid-liquid separation step of subjecting the gallium arsenide-containing starch to solid-liquid separation into an oil component and a solid residue with a filter press using an oil-resistant filter having an air permeability of 18 cc / cm ² / min or less;
The solid residue after solid-liquid separation obtained in the solid-liquid separation step is maintained in an inert gas atmosphere in a temperature range higher than the boiling point of the oil and lower than the evaporation temperature of arsenic, An oil removing step in which the oil contained in the residue is 1% by weight or less;
An arsenic removing step of removing arsenic by holding the solid residue after oil removal obtained in the oil removing step in an air atmosphere of 1000 ° C. or higher for 5 minutes or more;
A dissolution step of dissolving the solid residue after removal of arsenic obtained in the arsenic removal step in an acid or alkali;
An insoluble matter filtering step of filtering the solution and insoluble matter obtained in the dissolving step with a filter;
A gallium recovery step for obtaining a gallium oxide by neutralizing the solution obtained in the insoluble matter separation step;
It is a gallium collection | recovery method characterized by having.

In the present invention, since gallium is recovered in the form of gallium oxide after removing oil and arsenic such as cutting oil and polishing oil, high purity gallium can be recovered efficiently.
Hereinafter, each step will be described in the order of steps (see FIG. 1).

(1) Solid-liquid separation step The first step, the solid-liquid separation step, is a gallium arsenide-containing starch produced during cutting or polishing of a gallium arsenide compound (since it is in the form of a slurry, it is also referred to as “waste slurry” hereinafter). Is a process of solid-liquid separation into oil and solid residue with a filter press.

  That is, this gallium arsenide-containing starch contains a gallium arsenide compound, abrasive grains (usually SiC is used), and cutting oil or polishing oil (usually A heavy oil is used). And a solid residue containing gallium arsenide compound and abrasive grains and an oil component.

  In this step, since a filter press is used, most (90% or more) of the oil contained in the gallium arsenide-containing starch can be recovered. The recovered oil can be reused as cutting oil or polishing oil.

When the air permeability of the filter exceeds 18 cc / cm ² / min, the solid content passes through the filter, and the Ga recovery rate is lowered, which is not preferable.

(2) Oil component removal step In the oil component removal step, the solid residue obtained in the solid-liquid separation step remains in the solid residue after solid-liquid separation by heating at a temperature higher than the boiling point of the oil component. In this step, the oil is boiled and evaporated to reduce it to 1% by weight or less.

  In the solid residue obtained in the solid-liquid separation step, although it is a small amount, an oil content of about 3 wt% remains. Since the oil content of the solid residue after the solid-liquid separation is reduced to 1% by weight or less by this step, it is possible to suppress carbon from being mixed into the finally obtained gallium.

  In this step, as described above, the solid residue after solid-liquid separation is heated at a temperature higher than the boiling point of the oil component, but if the heating temperature is too high, specifically about 500 ° C., the oil component is evaporated. In addition, harmful arsenic also evaporates, which is not preferable. Accordingly, the heating temperature is set higher than the boiling point of the oil component and lower than the evaporation temperature of arsenic.

  For example, in the case of the A heavy oil described above, the boiling point is 240 to 250 ° C, and thus heating is performed at about 300 to 400 ° C.

  This heating is performed in an inert gas atmosphere in order to prevent the oil vapor from exploding even when the explosion limit concentration is reached. For example, the explosion limit concentration in the case of the A heavy oil is 1 to 7 vol%. An example of the inert gas is nitrogen gas. In addition, what is necessary is just to set a heating time suitably according to the density | concentration of residual oil content, However About 1 to 5 hours are preferable.

(3) Arsenic removal step The next arsenic removal step is the thermal decomposition of arsenic by holding the solid residue whose oil content is 1% by weight or less in the oil removal step in an air atmosphere of 1000 ° C or higher for 5 minutes or longer. It is the process of removing by doing.

  That is, in this step, by maintaining in an air atmosphere at 1000 ° C. or higher for 5 minutes or longer, arsenic of the gallium arsenide compound in the solid residue after oil removal is thermally decomposed and removed from the solid residue after oil removal. . Specifically, the thermally decomposed arsenic is oxidized by oxygen in the atmosphere and sublimated to be removed from the solid residue after oil removal. By collecting the sublimated arsenic oxide vapor with a water trap, toxic arsenic can be reliably recovered without diffusing outside. Note that the recovered arsenic oxide is reused as arsenic by appropriately reducing it.

In this step, as described above, the solid residue after oil removal is heated at a temperature of 1000 ° C. or higher. However, if the heating temperature is too high, specifically over about 1200 ° C., the abrasive SiC is oxidized and SiO ₂ is generated, making it difficult to reuse the abrasive grains. Therefore, the heating temperature is preferably about 1000 to 1200 ° C, and particularly preferably 1150 ° C. The holding time is preferably 5 minutes or longer, and more preferably 30 minutes or longer.

(4) Dissolution Step The next dissolution step is a step of dissolving the solid residue from which arsenic has been removed in acid or alkali. The solid residue after removal of arsenic from which arsenic has been removed contains gallium and abrasive grains, but when contacted with acid or alkali, only gallium dissolves and the abrasive grains precipitate as insoluble matter.

As the acid, reverse aqua regia obtained by mixing hydrochloric acid and nitric acid in a ratio of 1: 3 to 1 (volume ratio) is preferably used, and dissolution takes, for example, a temperature of 90 ° C. over 1 hour. Performing for a short time is preferable. As the alkali, such as aqueous NaOH or aqueous ammonia _(NH 4 OH) is preferably used.

(5) Insoluble matter filtering step The next insoluble matter filtering step is a step of filtering the solution and insoluble matter obtained in the above dissolving step with a filter. The insoluble abrasive grains separated by filtration are reused after being washed with water.

  Generally, SiC is used as the abrasive grains when cutting the gallium arsenide compound. In this case, the insoluble matter filtered off in this step is SiC abrasive grains, which are reused as SiC abrasive grains after washing with water.

(6) Gallium recovery step The final gallium recovery step is a step of obtaining the gallium oxide by neutralizing the solution, and is a step of recovering gallium in the form of gallium oxide.

  As described above, as shown in each step of (1) to (6), according to the invention of this claim, the waste slurry from which oil and arsenic have been removed is dissolved in acid or alkali to recover gallium. Therefore, high purity gallium can be recovered. In addition, the acid and alkali used in the dissolution step, for example, nitric acid and hydrochloric acid constituting reverse aqua regia can be procured at a lower cost than an organic solvent, so that the cost does not increase. Furthermore, since the recovered oil and arsenic can be used again in each step, this is also preferable from the viewpoint of cost. And according to the invention of this claim, since it becomes possible to construct | assemble the collection | recovery method of a closed system, it is preferable also from the surface of an environment and safety | security.

The invention described in claim 2
Prior to the solid-liquid separation step,
2. The gallium recovery method according to claim 1, wherein an iron content removing step for removing iron content from the waste slurry is provided using a magnet. 3.

  In some cases, the waste slurry may contain iron such as a wire piece. If this iron content remains unremoved, it affects the purity of the collected gallium, so it is preferably removed. As a specific means for removing iron, a magnet is preferably used.

The invention according to claim 3
The arsenic removal step includes
The solid residue after removal of the oil from which the oil was removed in the temperature raising process up to 400 ° C. was held at 400 ° C. for 1 hour or more to oxidize arsenic, 3. The process of vaporizing arsenic oxide by slowly raising the temperature at a heating rate of less than or equal to a minute and then holding at a high temperature of 1000 ° C. or more for 5 minutes or more. This is a gallium recovery method.

  Since thermal decomposition of gallium arsenide compound into gallium and arsenic and subsequent oxidation are performed, arsenic can be efficiently removed.

The invention according to claim 4
A constant potential electrolysis step is provided between the dissolution step and the gallium recovery step, in which a constant potential electrolysis treatment is performed on the solution obtained in the dissolution step to selectively remove arsenic. The gallium recovery method according to any one of claims 1 to 3.

  Even after the arsenic removal step, arsenic having a concentration higher than a predetermined value may remain depending on the situation. In this case, arsenic is selectively removed by subjecting the solution to a constant potential electrolytic treatment. As a result, gallium can be recovered in a state where arsenic has been sufficiently removed, and it is possible to recover the presence or absence of high purity. In addition, this constant potential electrolysis process should just be performed between a melt | dissolution process and a gallium collection | recovery process, and does not ask | require before and after an insoluble matter filtration process.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to collect | recover high-purity gallium, without raising a cost from the cutting waste, polishing waste, etc. which arise when a gallium compound is cut | disconnected or grind | polished.

It is a figure which shows the outline of the process of collect | recovering gallium from the gallium arsenide containing starch in one embodiment of this invention. It is a graph showing the vaporization rate of degradation in the 1273K of Ga ₂ O ₃ and _As 2 _{O 3.} Is a graph showing the As ₂ O ₃ in relation separation rate and the heat treatment temperature by the heat treatment. It is a figure which shows the SEM image and fluorescent X-ray-measurement result of the solid residue after heat processing in one embodiment of this invention. It is a figure which shows the SEM image and fluorescent X-ray-measurement result of the SiC particle collect | recovered in one embodiment of this invention. Is a diagram showing an SEM image and fluorescent X-ray measurement results of the Ga ₂ O ₃ of recovered particles in one embodiment of the present invention.

  Hereinafter, the present invention will be described based on embodiments. Note that the present invention is not limited to the following embodiments. Various modifications can be made to the following embodiments within the same and equivalent scope as the present invention.

  This embodiment is a method for recovering gallium from a slurry-like gallium arsenide-containing starch (waste slurry) produced when a GaAs (gallium arsenide) substrate is cut using SiC as abrasive grains and A heavy oil as cutting oil. About. Hereinafter, the present embodiment will be described with reference to the drawings.

  FIG. 1 is a diagram showing an outline of a process for recovering Ga from waste slurry. Each step will be described below.

1. Composition of Waste Slurry First, as a waste slurry in the present embodiment, a waste slurry composed of 2% by weight of GaAs, 28% by weight of SiC, and 70% by weight of A heavy oil was prepared.

2. Method for recovering Ga from waste slurry (1) Iron content removal step First, iron was removed from a gallium arsenide-containing starch using a magnet.

(2) Solid-Liquid Separation Step Next, 200 kg of waste slurry from which iron has been removed was measured according to JIS P 8117: 1998 “Paper and paperboard—Air permeability test method—Gurley test machine method” and the air permeability was 18 cc. / (Cm ² · min) or less of polypropylene separation membrane (membrane area: 5 m ² ) and filtered under pressure at a processing rate of 300 cc / min with a filter press under a pressure of 0.4 MPa. By this step, 60 kg of solid residue and 140 kg of separation liquid (A heavy oil) could be obtained by solid-liquid separation.

  The obtained separated liquid (A heavy oil) had a solid content of 1% or less and could be sufficiently reused as cutting oil.

(3) Cutting oil removal process When the above-mentioned solid residue was inspected, 3 wt% A heavy oil was still contained. Next, this solid residue is kept in a nitrogen gas stream at 390 ° C., which is a temperature between 300 ° C. and 400 ° C., for 120 minutes using a heat treatment furnace, and the heavy oil A remaining in the solid residue is retained. It was removed by boiling and evaporation, and A heavy oil in the solid residue was adjusted to 1 wt% or less, specifically 0.01 wt% or less.

(4) Arsenic removal step Next, the solid residue after removal of A heavy oil is placed in a heat treatment furnace, and the solid residue after oil removal is introduced at 1150 ° C. while introducing air into the furnace from one direction of the heat treatment furnace. Heated for 60 minutes.

As a condition for removing arsenic by heating, an experiment was performed using 200 g of SiC / GaAs (GaAs: 3 wt%) in advance with respect to the amount of air. As a result, in the case of this 200 g example, an oxygen amount of about 2.8 L is required, and Ga and As are oxidized to generate Ga ₂ O ₃ and As ₂ O ₃ at a temperature of 450 to 500 ° C. It was found that it was necessary to raise the range at 0.5 ° C./min. That is, when this treatment is performed for 100 minutes, an oxygen flow rate of 28 mL / min (140 mL / min in terms of air) is required.

  In the present embodiment, 0.2 L / min of air exceeding the required amount was introduced based on the above experimental results.

This step utilizes the difference in vaporization decomposition rate between Ga ₂ O ₃ and As ₂ O ₃ produced when the solid residue after oil removal is heated in the atmosphere, and this is shown in FIG. FIG. 2 is a graph showing the relationship between the vapor decomposition rate at 1000 ° C. of the produced Ga ₂ O ₃ and As ₂ O ₃ and time. As shown in FIG. 2, Ga ₂ O ₃ hardly vaporizes and decomposes and is non-volatile, while As ₂ O ₃ sublimates and vaporizes and decomposes.

Further, the heating temperature and the heating time in this step were set based on FIG. FIG. 3 (a) is a graph showing the relationship between the amount of As ₂ O ₃ separated from the solid residue after oil removal and the heat treatment temperature when the heat treatment time is constant, and FIG. 3 (b) shows the heat treatment temperature. it is a graph showing the relationship between the amount of separation and the heat treatment time from the solid residue after oil removal of as ₂ O ₃ in the case of a constant. FIG. 3A shows that when the treatment time is 30 minutes, the As concentration is almost 0 wt% when the treatment temperature is 1150 ° C., and FIG. 3B shows that the treatment time is when the heat treatment temperature is 1000 ° C. It can be seen that the concentration of As is close to 0 wt% if it is 5 minutes or longer.

  The heating temperature and heating time (1150 ° C., 60 minutes) in this step are set based on these findings obtained in advance.

Necessary oxygen can be supplied without hindrance by introducing air from one direction of the heat treatment furnace. On the other hand, when air is introduced from both directions, the air is disturbed and the generated Ga ₂ O ₃ may be scattered, which is not preferable.

The sublimated As ₂ O ₃ was collected with a water trap and collected. The amount of As ₂ O ₃ recovered was about 1.8 kg.

(5) Dissolution process In this Embodiment, the reverse aqua regia which is an acid was used as a solution. The solid residue after separating and removing As by heat treatment was put into reverse aqua regia (1 L) prepared in a SUS tank lined with polypropylene, and over 300 minutes at a temperature of 90 ° C. The solid residue after removal of arsenic with respect to 1 L was dissolved at a ratio of 200 g (corresponding to 6 g / L in terms of Ga dissolution concentration). At this time, SiC did not dissolve in the reverse aqua regia and precipitated as an insoluble material.

(6) Constant potential electrolysis process a. Investigation of solid residue after heat treatment As a result of observing the solid residue after separating and removing As by the heat treatment with SEM and analyzing the composition by fluorescent X-ray analysis, it was found that As remained, although in a small amount. (See FIG. 4). And Fe was detected in the place where As remained. Therefore, after dissolution in reverse aqua regia, the remaining As was removed by constant potential electrolysis. Note that Fe was removed in advance using a magnet.

B. Constant-potential electrolysis Specifically, a Ti electrode is inserted into the reverse aqua regia in which the solid residue after arsenic removal is dissolved, and the positive electrode potential is maintained at a constant potential of 0.5 V with respect to the silver / silver chloride reference electrode. While performing electrolysis for 2 hours at a current of 100 mA or less, gas (arsenic oxide) generated from the positive electrode during this period was recovered. Thereby, the As concentration in the reverse aqua regia was greatly reduced from 620 ppm before electrolysis to 49 ppm. In addition, Ga dissolved in the reverse aqua regia was 560 ppm before electrolysis, and was 570 ppm after electrolysis, since water content was somewhat reduced.

  As described above, when the concentration of As contained in the solid residue after arsenic removal is sufficiently low, it is not necessary to perform electrolytic treatment. Further, the electrolytic treatment may be performed after the next SiC separation and recovery.

(7) Insoluble matter filtration step As described above, when the solid residue after arsenic removal is dissolved in the reverse aqua regia, SiC precipitates without dissolving, so it is filtered under reduced pressure using a membrane filter (Nippon Millipore). Then, insoluble matters were separated by filtration, and SiC was recovered. When the collected SiC particles were subjected to SEM observation and fluorescent X-ray analysis, it was confirmed that they were pure SiC particles containing no Ga or As (see FIG. 5), and it was found that they could be reused as abrasives. . The recovered amount was about 56 kg.

(8) Gallium recovery process The reverse aqua regia from which SiC and As were removed was neutralized with NaOH to adjust the pH to 4-6, thereby precipitating Ga as Ga ₂ O ₃ (white powder). The obtained precipitate was filtered through a membrane filter (Nippon Millipore) under reduced pressure, washed with water and collected. Recovered amount is about 1.9kg as _Ga 2 _{O 3,} the recovery rate versus about 2.4kg of _Ga 2 _{O 3,} which is converted from the initial charge amount was 83%. The recovered Ga ₂ O ₃ was observed with an SEM, and composition analysis was performed by fluorescent X-ray analysis. As a result, it was confirmed to be pure Ga ₂ O ₃ having a particle size of 0.2 to 0.5 μm. (See FIG. 6).

Claims (4)

A method for recovering gallium from a gallium arsenide-containing starch,
A solid-liquid separation step of subjecting the gallium arsenide-containing starch to solid-liquid separation into an oil component and a solid residue with a filter press using an oil-resistant filter having an air permeability of 18 cc / cm ² / min or less;
The solid residue after solid-liquid separation obtained in the solid-liquid separation step is maintained in an inert gas atmosphere in a temperature range higher than the boiling point of the oil and lower than the evaporation temperature of arsenic, An oil removing step in which the oil contained in the residue is 1% by weight or less;
An arsenic removing step of removing arsenic by holding the solid residue after oil removal obtained in the oil removing step in an air atmosphere of 1000 ° C. or higher for 5 minutes or more;
A dissolution step of dissolving the solid residue after removal of arsenic obtained in the arsenic removal step in an acid or alkali;
An insoluble matter filtering step of filtering the solution and insoluble matter obtained in the dissolving step with a filter;
A gallium recovery step for obtaining a gallium oxide by neutralizing the solution obtained in the insoluble matter separation step;
A gallium recovery method characterized by comprising: Prior to the solid-liquid separation step,
The method for recovering gallium according to claim 1, wherein an iron content removing step for removing iron content from the waste slurry is provided using a magnet. The arsenic removal step includes
The solid residue after removal of the oil from which the oil was removed in the temperature raising process up to 400 ° C. was held at 400 ° C. for 1 hour or more to oxidize arsenic, 3. The process of vaporizing arsenic oxide by slowly raising the temperature at a heating rate of less than or equal to a minute and then holding at a high temperature of 1000 ° C. or more for 5 minutes or more. Gallium recovery method.   A constant potential electrolysis step is provided between the dissolution step and the gallium recovery step, in which a constant potential electrolysis treatment is performed on the solution obtained in the dissolution step to selectively remove arsenic. The gallium recovery method according to any one of claims 1 to 3.