JP4781555B2 - Collection method of valuable metals - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a valuable metal recovery method for efficiently separating and recovering valuable metals such as gallium and arsenic from alloy scrap such as compound semiconductor scrap containing gallium and arsenic.
[0002]
[Prior art]
Gallium arsenide is well known as a compound semiconductor containing gallium and arsenic. The demand for gallium arsenide is rapidly increasing for semiconductor devices with the spread of mobile devices such as mobile phones. However, compound semiconductors have a very low commercialization rate from raw materials to products, and members that do not transition to products are discharged as scraps in various forms such as single-crystal end face cut parts, damaged wafers, cutting scraps, and polishing scraps. Since these gallium arsenide scraps contain expensive gallium and the toxic arsenic, establishment of an effective recovery method is desired.
[0003]
Conventionally, as a method for recovering gallium and arsenic from gallium arsenide scrap, an alkali fusion decomposition method, a combination of acid decomposition method and electrolytic extraction, or a vacuum thermal decomposition method has been used, and the recovered gallium is subjected to acid cleaning and recrystallization. Purified and reused as 99.9999% gallium, which can be used as a semiconductor raw material. On the other hand, arsenic has not been industrially recovered, and recovery and reuse are important propositions to prevent environmental pollution.
[0004]
In the combination of the alkali melting method and electrowinning, an alkali hydroxide, alkali carbonate and gallium arsenide scrap are put into a nickel or zirconium crucible, heated and decomposed, and then leached with water. Gallium hydroxide is precipitated by adjusting the leachate to about pH 7 with an acid, and the filtered gallium hydroxide is dissolved in an aqueous caustic soda solution to obtain an electrolytic solution.
[0005]
In the electrowinning, gallium is electrodeposited on the cathode by electrolysis using platinum, carbon or stainless steel as an electrode and collected. Electrolysis is performed at a current density of 2000 A / m ² at a maximum with a gallium concentration of 30% or less and a sodium hydroxide concentration of 30-50% in the electrolytic solution. In electrowinning, the main purpose is to deposit gallium from gallium oxide or gallium hydroxide as a raw material, and its purity is about 99%. In order to perform these operations, many additional facilities such as a scrap decomposition heating furnace, an electrolytic solution preparation tank, a filtration device, a direct current power source, and an electrolytic tank are required, and the amount of waste tends to increase and the cost tends to increase.
[0006]
The combination of the acid decomposition method and electrowinning is carried out by putting gallium arsenide scrap into a quartz container, adding aqua regia, and then heating to decompose it into a solution. The solution is adjusted to a pH of around 7 with a caustic soda solution, gallium hydroxide is precipitated, filtered and dissolved in an aqueous caustic soda solution to obtain an electrolyte.
Electrolytic extraction is the same as in the case of a combination of the alkaline melt decomposition method and electrolytic extraction, and the purity of gallium that can be recovered is about 99%. In order to perform these operations, a large number of incidental facilities such as a crystal scrap decomposition tank, a heating source, an electrolytic solution preparation tank, a filtration device, a DC power supply, an electrolytic tank are necessary, and a combination of an alkali melting decomposition method and electrolytic collection is required. As in the case, the amount of waste tends to be high and the cost tends to be high.
[0007]
The vacuum thermal decomposition method is a method of sublimating and separating arsenic having a higher vapor pressure than gallium by utilizing the difference in vapor pressure when decomposing gallium arsenide scrap. It is possible to thermally decompose gallium arsenide scrap to 1,000 ° C or higher at a vacuum of 13 Pa or less, and to reduce arsenic with a high vapor pressure to 1 ppm in the remaining gallium. In addition, since all the steps can be performed in a dry process, the cost can be reduced as compared with the combination of the alkali melt decomposition method or the acid decomposition method and electrowinning. In the vacuum pyrolysis method, operating conditions are selected so as to prevent contamination of impurities from the container that may occur by heating to 1,000 ° C. or higher, and to further suppress gallium evaporation loss.
[0008]
In the vacuum pyrolysis method, a vacuum heating furnace is used, and the heating method is electrical resistance heating or high frequency induction heating. Although electrical resistance heating is relatively inexpensive, the core tube material is inevitably in the form of quartz, alumina, or a protective tube sheathed for heating by heat conduction and radiation. For example, when quartz is used for the reactor core tube, it is necessary to limit the amount of gallium arsenide scrap charged as a safety measure for preventing damage or to externally coat the reactor core tube with a protective tube. Stainless steel is suitable as a protective tube, but it usually takes 1 to 5 hours to raise the temperature and 6 to 12 hours to lower the temperature, so the processing time per batch becomes longer, and the temperature increases and decreases many times. Since the strength of the protective tube decreases due to repeated, there is a problem in safety.
[0009]
On the other hand, since the container containing the gallium arsenide scrap is directly heated in the high frequency induction heating, it becomes possible to heat the gallium arsenide scrap directly, and while it is possible to shorten the temperature raising and lowering time, temperature control is difficult, for example, When the diameter of the container is increased, the gallium arsenide scrap has a high temperature only in the vicinity of the container until the decomposition progresses to some extent, and uniform decomposition cannot be performed. In addition, when the rate of temperature increase is increased, the gallium arsenide scrap near the container becomes overheated, causing gallium evaporation loss.
[0010]
The vacuum pyrolysis method has to be batch processing because the processing is performed under reduced pressure, and if the processing time per batch is long, the recovery rate decreases due to evaporation loss resulting from it, and the cost increases. .
[0011]
[Problems to be solved by the invention]
As described above, a method for recovering valuable metals such as gallium and arsenic from alloy scrap such as compound semiconductors containing gallium and arsenic at low cost is required. This combination requires a lot of ancillary equipment, increases the amount of waste and increases costs, and the vacuum pyrolysis method requires a long period of time for temperature rise, fall, and heat cracking, resulting in metal evaporation loss. There is a problem of being big.
[0012]
The present invention provides a method for recovering valuable metals that does not require a long time for heating, lowering, and thermal decomposition of alloy scrap in a vacuum pyrolysis method, and that can recover valuable metals with low evaporation loss at low cost. Objective.
[0013]
[Means for Solving the Problems]
In the method for recovering valuable metals of the present invention, a vacuum heating facility comprising a raw material chamber composed of a quartz glass window and a water-cooled metal casing, an infrared condensing heating device, an evaporative substance recovery trap, and a vacuum pump is provided. The alloy scrap charged in the raw material chamber is decomposed into a component having a high vapor pressure and a component having a low vapor pressure by heating with an infrared condensing heating device under reduced pressure, and the respective components are recovered, respectively. Reduce scrap decomposition time and improve recovery rate.
[0014]
The quartz glass window must have a thickness sufficient to withstand pressure so that it is not damaged when the pressure inside the raw material chamber is reduced. A thickness of 10 mm is appropriate for an area of 400 mm × 400 mm, but other values may be used as long as safety can be ensured. Further, as a method for increasing the strength, the shape may be a semi-cylindrical shape. If it is made semi-cylindrical, the volume of the raw material chamber can be increased, and the throughput per batch increases.
[0015]
Quartz as a glass window material has high infrared transmittance, heat resistance, pressure strength and corrosion resistance, and this material is optimal. For the water-cooled metal casing, a material having excellent corrosion resistance, heat resistance, thermal conductivity, and strength is used. The material is preferably SUS316, SUS304, Al or the like. Moreover, overheating of the metal casing is prevented by water cooling.
[0016]
Infrared condensing heating devices are installed above and below the raw material chamber. In the infrared condensing heating device, an infrared lamp is mounted in a gold-plated ellipsoidal or parabolic reflector so that the collected infrared rays are irradiated to the entire alloy scrap charged in the raw material chamber. .
Ellipsoidal reflectors are suitable for heating small areas with relatively low power, and parabolic reflectors that consume large power temporarily but can heat large areas are suitable for increasing throughput. ing. The reflector has a jacket structure and is cooled with water to prevent overheating. As the infrared lamp, a halogen or xenon lamp is used, and its rated power varies depending on the number and shape used, but when heating an area of 300 mm × 300 mm, a total of about 52 kW is considered good.
[0017]
The evaporative substance recovery trap is attached between the metal casing and the vacuum pump in order to supplementarily collect components with high vapor pressure that could not be aggregated by the metal casing in the raw material chamber. Without the evaporative substance recovery trap, a part of the high vapor pressure component flows into the vacuum pump, which not only causes a failure of the vacuum pump but also reduces the recovery rate. In order to improve the recovery rate of components having a high vapor pressure, it is important to keep the evaporative substance recovery trap at a low temperature, but water cooling is suitable as the method. Further, SUS316, SUS304, etc., which are excellent in corrosion resistance, are suitable for the material, but should be determined in consideration of the nature of the component having a high vapor pressure, particularly its corrosion resistance.
[0018]
The vacuum pump is provided to depressurize the raw material chamber and the evaporative substance recovery trap. The vacuum pump only needs to be able to maintain a degree of vacuum of 10 ^{−3 to} 13 Pa. Usually, an oil rotary pump is sufficient, but an oil diffusion pump is preferably added in the case of alloy scrap that hardly decomposes.
Quartz with high infrared transmittance, heat resistance, and corrosion resistance is optimal as the material for containers for alloy scrap. The alloy scrap is filled in a container and charged into the raw material chamber, and after the pressure in the raw material chamber and the evaporative substance recovery trap is reduced by a vacuum pump, the infrared condensing heating device is energized and heated.
[0019]
The component with high vapor pressure in the alloy scrap is preferentially evaporated by heating, and the vapor is condensed in the metal casing and the evaporative substance recovery trap in the raw material chamber, and the component with low vapor pressure remains, so the raw material after cooling The chamber and evaporant recovery trap are returned to atmospheric pressure and the decomposition products are recovered. When undecomposed alloy scrap remains with a component having a low vapor pressure, the decomposition is repeated again as it is, or after separating a component having a low vapor pressure, only the undecomposed alloy scrap is decomposed again.
[0020]
At this time, if the degree of vacuum is higher than 10 ⁻³ Pa, components having a low vapor pressure are easily vaporized, not only reducing the purity of components having a high vapor pressure, but also improving the recovery rate of components having a low vapor pressure. Reduce. On the other hand, if the degree of vacuum is lower than 13 Pa, the decomposition rate of the alloy scrap is slow, which is not practical.
When the heating temperature is lower than 700 ° C., the decomposition rate of the alloy scrap is generally slow, and when it is higher than 1200 ° C., the evaporation loss of the vapor pressure component increases, which is inefficient.
[0021]
In the infrared condensing heating, since rapid heating and cooling are possible, the temperature raising time can be performed between 0.3 and 60 min, and the cooling is also performed within 60 min within room temperature to 40 ° C. The processing time is shortened. In addition, since infrared rays can be condensed and heated only on alloy scrap, metal casings in the raw material chamber kept at a low temperature have no corrosion deterioration due to substances with high vapor pressure, and components with higher vapor pressure Since it is rapidly agglomerated by the metal casing in the raw material chamber, the vapor partial pressure in the raw material chamber is kept low, and the decomposition rate becomes much faster than the conventional heating method.
[0022]
If the infrared condensing heating device is movable, a large number of raw material chambers can be heated with a set of infrared condensing heating devices, so that charging, thermal decomposition, and removal can be performed continuously, increasing work efficiency and maximum power. Can be kept low. It is also possible to fix an infrared condensing heating device and make a large number of raw material chambers movable.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in the case of decomposing gallium arsenide scrap as alloy scrap will be described.
FIG. 1 is a block diagram showing an example of a vacuum heating facility used in carrying out the valuable metal recovery method of the present invention.
[0024]
The vacuum heating equipment includes a raw material chamber 1, an infrared condensing heating device 2, an evaporated substance recovery trap 3, and a vacuum pump 4, and between the raw material chamber 1 and the evaporated substance recovery trap 3 and between the evaporated substance recovery trap 3, The vacuum pump 4 is connected with pipes 11 and 12 made of SUS316 or SUS304.
The raw material chamber 1 is composed of a quartz glass window 5 and a housing 6 made of SUS316 or SUS304. The quartz glass window 5 has a length of 400 mm, a width of 400 mm, and a thickness of 10 mm. One is closely fixed to the housing 6 and the other is an openable upper lid. The housing 6 of the raw material chamber 1, the infrared condensing heating device 2 and the evaporative substance recovery trap 3 have a water cooling jacket structure and are provided with an inlet and an outlet (not shown) of cooling water. An oil rotary pump is used as the vacuum pump 4.
[0025]
The infrared condensing heating device 2 installed above and below the raw material chamber 1 is provided with a halogen lamp 7 and a parabolic reflecting mirror 8, and the irradiation area is 300 mm long × 300 mm wide. .
The gallium arsenide scrap 10 is uniformly filled into a vat-like quartz container 9 having a length of 300 mm, a width of 300 mm, and a depth of 50 mm, and the quartz container 9 is loaded and installed in the center of the raw material chamber 1 and then a quartz glass window. Close the top cover consisting of 5. The thickness of the quartz container 9 is preferably 2 to 5 mm, but may be determined with sufficient consideration of the strength. The gallium arsenide scrap 10 has a faster decomposition rate for finer particles, but 0.5 to 2.36 mm is appropriate in consideration of scattering loss associated with evacuation. Further, the filling amount of the gallium arsenide scrap 10 is set so as not to spill from the quartz container 9, and normally 5 to 10 kg is appropriate for the bat-shaped quartz container 9 having a length of 300 mm × width of 300 mm × depth of 50 mm. is there.
[0026]
Cooling water is supplied to the housing 6 of the raw material chamber 1, the infrared condensing heating device 2, and the water cooling jacket of the evaporative substance recovery trap 3, and the raw material chamber 1 and the evaporative substance recovery trap 3 are vacuumed using the vacuum pump 4. The degree is maintained at 10 ^{−3 to} 13 Pa.
The infrared condensing heating device 2 is energized, heated up to 700 ° C. to 1200 ° C. in 0.3 to 60 minutes, held for 1 to 4 hours, and then energized and cooled. When cooling is started, arsenic adheres to the quartz glass window 5, but a part of the arsenic remaining in the decomposition product is sublimated, so that it can be easily removed by irradiating infrared rays in the next processing. However, if the temperature is maintained at 600 to 700 ° C. for 5 to 60 minutes after decomposition, arsenic is not sublimated from the decomposition product at this temperature, so that arsenic can be prevented from adhering to the quartz glass window 5, but the processing time per batch is long. Become. Considering the operating conditions, it is better to select which one is more efficient.
[0027]
Cooling is performed within 60 minutes even in furnace cooling, and the internal temperature of the raw material chamber 1 becomes room temperature to 40 ° C., but an inert gas such as nitrogen or argon may be introduced into the raw material chamber 1 in order to increase the cooling rate.
After cooling, the raw material chamber 1 and the evaporative substance recovery trap 3 are returned to atmospheric pressure, the upper cover of the raw material chamber 1 is opened, and the decomposition product remaining in the quartz container 9 is taken out.
[0028]
Since the housing 6, the evaporative substance recovery trap 3 and the pipes 11 and 12 of the raw material chamber 1 are water-cooled, there is no corrosion deterioration of equipment members due to arsenic or the like. The sublimated arsenic aggregates in the housing 6 and the evaporative substance recovery trap 3 in the raw material chamber 1, and is peeled off and recovered. On the other hand, since gallium and undecomposed gallium arsenide remain in the quartz container 9, after recovery, the polypropylene non-woven fabric is used to separate it into gallium and gallium arsenide. It becomes possible.
[0029]
【Example】
[Example 1]
Gallium arsenide scrap 10 was made into a powder of 0.5 to 2.36 mm with a blow-type crusher, and 8 kg was filled in a quartz container 9 (length 300 mm × width 300 mm × depth 50 mm).
[0030]
After the quartz container 9 is placed and placed in the center of the raw material chamber 1 of the vacuum heating equipment shown in FIG. 1, the upper cover of the quartz glass window 5 is closed, and the housing 6 of the raw material chamber 1, the infrared condensing heating device 2 and the evaporating substance. Cooling water was allowed to flow through the water cooling jacket of the recovery trap 3 at 10 L / min, and the raw material chamber 1 and the evaporated substance recovery trap 3 were maintained at a vacuum degree of 8 Pa using the vacuum pump 4.
[0031]
The infrared condensing heating device 2 is energized and heated up to 1050 ° C. for 20 minutes and then held for 2 hours. After decomposition, the temperature is lowered to 700 ° C. for 0.5 minutes and held for 30 minutes, so that arsenic adheres to the quartz glass window 5 The furnace was cooled. The cooling time from 700 ° C. to 40 ° C. was 50 min.
Since the sublimated arsenic adhered to the housing 6 and the evaporative substance recovery trap 3 in the raw material chamber 1, it was removed by applying a light impact with a hammer and recovered. On the other hand, since gallium and undecomposed gallium arsenide remain in the quartz container 9, after recovery, they were separated into gallium and gallium arsenide using a polypropylene nonwoven fabric.
[0032]
Through the above operation, the recovery rate of gallium was 96%, and the recovery rate of arsenic was 97%. 3% of arsenic was not recovered from undecomposed gallium arsenide, the housing 6 of the raw material chamber 1 and the evaporative substance recovery trap 3. On the other hand, 4% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed in arsenic.
The time required for the vacuum decomposition of 8 kg / batch was 3.68 h, and it was completed in 5 h including charging and recovery operations.
[0033]
[Example 2]
Example 1 except that the infrared ray condensing heating device 2 was energized while maintaining the raw material chamber 1 and the evaporative substance recovery trap 3 at a vacuum degree of 10 ⁻¹ Pa, heated to 1050 ° C. in 20 minutes, and then maintained for 1.5 hours. Operated.
With the above operation, the recovery rate of gallium was 95%, and the recovery rate of arsenic was 96%. 4% of arsenic was not recovered from undecomposed gallium arsenide, the casing 6 of the raw material chamber 1 and the evaporative substance recovery trap 3. On the other hand, 5% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed in arsenic.
[0034]
The time required for the vacuum decomposition of 8 kg / batch was 3.18 h, and it was completed in 4.5 h including charging and recovery operations.
Example 3
The same operation as in Example 1 was performed except that the infrared ray condensing heating device 2 was energized while maintaining the raw material chamber 1 and the evaporative substance recovery trap 3 at a vacuum degree of 8 Pa, heated to 1000 ° C. for 20 minutes, and then maintained for 2.18 h.
[0035]
With the above operation, the recovery rate of gallium was 94% and the recovery rate of arsenic was 95%. 5% of arsenic was not recovered from undecomposed gallium arsenide, the casing 6 of the raw material chamber 1 and the evaporative substance recovery trap 3. On the other hand, 6% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed into arsenic.
The time required for the vacuum decomposition of 8 kg / batch was 4.2 h, and was completed in 5.5 h including charging and collecting operations.
[0036]
【The invention's effect】
According to the valuable metal recovery method of the present invention, it is possible to shorten the time required for heating, lowering, and thermal decomposition of the alloy scrap in the vacuum pyrolysis method, and to recover the valuable metal at a low cost because of less evaporation loss. Can do.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an example of a vacuum heating facility used in carrying out the valuable metal recovery method of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Raw material chamber 2 Infrared condensing heating apparatus 3 Evaporative substance collection trap 4 Vacuum pump 5 Quartz glass window 6 Housing 7 Halogen lamp 8 Reflector 9 Quartz container 10 Gallium arsenide scrap 11 Piping 12 Piping

Claims (2)

Depressurize the gallium arsenide scrap charged in the raw material chamber using a vacuum heating facility equipped with a quartz glass window, a water-cooled metal enclosure, an infrared condensing heating device, an evaporative substance recovery trap, and a vacuum pump. A valuable metal recovery method comprising: arsenic , which is a component having a high vapor pressure, and gallium , which is a component having a low vapor pressure, which are heated by an infrared ray condensing heating device, and each component is recovered. . Vacuum degree of gallium arsenide scrap 10 ^-3 It is decomposed into arsenic, which has a high vapor pressure, and gallium, which has a low vapor pressure, by heating to 700 to 1200 ° C. with an infrared condensing heating device equipped with a parabolic reflector under a reduced pressure of ˜13 Pa And each component is collect | recovered, respectively, The recovery method of the valuable metal of Claim 1 characterized by the above-mentioned.

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