JP2002327217A - Method for collecting valuable metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To collect valuable metals at low cost by shortening necessary time for raising and lowering the temperature and for decomposing alloy scrap with heat, and consequently by reducing vaporization loss, in a vacuum heat decomposition method. SOLUTION: A vacuum heating apparatus comprises a material chamber 1 composed of a glass window 5 made of quartz and a water cooled type of a metallic body 6, a heating device 2 with condensed infrared-rays, a trap 3 for collecting a vaporized material, and a vacuum pump 4. The method for separately collecting each constituent is characterized by decomposing the alloy scrap 10 charged in the material chamber 1 into two elements having high and low vapor pressures, and by heating it in the heating device 2 with condensed infrared-rays of the vacuum heating apparatus, under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of recovering valuable metals such as gallium and arsenic from alloy scraps such as compound semiconductor scraps containing gallium and arsenic.

[0002]

2. Description of the Related Art As a compound semiconductor containing gallium and arsenic, gallium arsenide is well known. Demand for gallium arsenide for semiconductor devices is rapidly increasing with the spread of mobile devices such as mobile phones.
However, compound semiconductors have a very low production rate from raw materials to products, and members that do not migrate to products are discharged as scrap in various forms such as single crystal end face cuts, damaged wafers, cutting chips, and polishing chips. Since these gallium arsenide scraps contain expensive gallium and toxic arsenic, establishment of an effective recovery method is demanded.

Conventionally, as a method of recovering gallium and arsenic from gallium arsenide scrap, a combination of an alkali melting decomposition method or an acid decomposition method and electrowinning, or a vacuum heat decomposition method has been used. Purity purified by recrystallization and usable as a semiconductor raw material
Reused as 9999% gallium. On the other hand, arsenic has not been recovered industrially, and recovery and reuse are regarded as important propositions in order to prevent environmental pollution.

[0004] In the combination of the alkali melting decomposition method and the electrolytic extraction, an alkali hydroxide, an alkali carbonate and gallium arsenide scrap are put into a nickel or zirconium crucible,
After heat melting and decomposition, it is leached with water. PH of leachate with acid
Gallium hydroxide is precipitated by adjusting the value to about 7, and the filtered gallium hydroxide is dissolved in an aqueous solution of sodium hydroxide to prepare an electrolyte.

In the electrowinning, gallium is electrodeposited on a cathode by electrolysis using platinum, carbon or stainless steel as an electrode and collected. The concentration of gallium in the electrolyte is 30% or less, the concentration of sodium hydroxide is 30 to 50%, and the maximum is 2000 A /
Electrolyze at a current density of m ² . The main purpose of electrowinning is to deposit gallium from gallium oxide or gallium hydroxide as a raw material, and its purity is about 99%. To perform these operations, many auxiliary facilities such as a heating furnace for scrap disassembly, an electrolytic solution preparation tank, a filtration device, a DC power supply, and an electrolytic tank are required, and the amount of waste tends to be large and the cost is high.

[0006] In the combination of the acid decomposition method and the electrowinning, gallium arsenide scrap is put in a quartz container, aqua regia is added, and the mixture is heated to be decomposed into a solution. The solution is adjusted to a pH of about 7 with a caustic soda solution to precipitate gallium hydroxide, and filtered to dissolve gallium hydroxide in an aqueous caustic soda solution to form an electrolytic solution. The electrowinning is the same as the case of the combination of the alkali melting decomposition method and the electrowinning, and the purity of gallium that can be recovered is about 99%. In order to perform these operations, many additional facilities such as a crystal decomposing tank, a heating source, an electrolytic solution preparing tank, a filtration device, a DC power supply, and an electrolytic tank are required. As in the case, the amount of waste tends to be large 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 a difference in vapor pressure during decomposition of gallium arsenide scrap. Gallium arsenide scrap can be thermally decomposed at a vacuum of 13 Pa or less to 1,000 ° C. or more, and arsenic with a high vapor pressure can be reduced to 1 ppm in the remaining gallium. Separation and recovery can be performed with a relatively simple device. In addition to the fact that the entire process can be performed in a dry manner, the cost can be reduced as compared with a combination of the alkali melting decomposition method or the acid decomposition method and the electrolytic extraction. In the vacuum pyrolysis method, operating conditions are selected so as to prevent contamination of the container from impurities that may occur by heating to 1,000 ° C. or higher, and to further suppress evaporation loss of gallium.

In the vacuum thermal decomposition method, a vacuum heating furnace is used, and the heating method is electric resistance heating or high frequency induction heating. Although electric resistance heating is relatively inexpensive in equipment, the material of the furnace tube is inevitably quartz, alumina, or a form in which they are covered with a protective tube for heating by heat conduction and radiation. For example, when quartz is used for the furnace tube, it is necessary to limit the amount of gallium arsenide scrap to be charged or to cover the furnace tube with a protective tube as safety measures such as damage prevention.
Stainless steel is suitable for the protective tube, but the time required for temperature rise is usually 1 to 5 hours, and the time required for temperature decrease is 6 to 12 hours. There is a problem in safety because the strength of the protective tube is reduced by repeated use.

On the other hand, the high-frequency induction heating directly heats the container containing the gallium arsenide scrap, which makes it possible to directly heat the gallium arsenide scrap, thereby shortening the time for raising and lowering the temperature. Difficult,
For example, when the diameter of the container is increased, the temperature of the gallium arsenide scrap becomes high only in the vicinity of the container until the decomposition proceeds to some extent, so that uniform decomposition cannot be performed. In addition, when the heating rate is increased, the gallium arsenide scrap in the vicinity of the container becomes overheated, causing gallium evaporation loss.

[0010] In the vacuum pyrolysis method, since the treatment is performed under reduced pressure, the treatment must be performed in a batch process. If the treatment time per batch is long, the recovery rate is reduced due to evaporation loss caused by the treatment, and the cost is increased. There are drawbacks.

[0011]

As described above, there is a demand for a method of recovering valuable metals such as gallium and arsenic from alloy scraps such as compound semiconductors containing gallium and arsenic at low cost. In the combination of decomposition or acid decomposition and electrowinning, many additional facilities are required, and the amount of waste is high and the cost is high.
Further, the vacuum thermal decomposition method has a problem that a long time is required for raising and lowering the temperature and thermal decomposition, and there is a problem that the evaporation loss of the metal is large.

The present invention provides a method for recovering valuable metals, which does not require a long time for raising and lowering the temperature of alloy scrap and thermal decomposition in the vacuum pyrolysis method, and which can recover valuable metals at a low cost with little evaporation loss. The purpose is to do.

[0013]

According to the method for recovering valuable metals of the present invention, a raw material chamber composed of a quartz glass window and a water-cooled metal frame, an infrared ray condensing and heating device, an evaporative substance recovery trap, and a vacuum Using a vacuum heating facility equipped with a pump, the alloy scrap charged into the raw material chamber is heated under reduced pressure by an infrared condensing heating device to be decomposed into a component having a high vapor pressure and a component having a low vapor pressure. By recovering the respective components, it is possible to shorten the decomposition time of the alloy scrap and improve the recovery rate.

The quartz glass window must be thick enough to withstand pressure so as not to be damaged when the inside of the raw material chamber is depressurized. The thickness is suitably 10 mm for an area of 400 mm × 400 mm, but any value other than this value may be used as long as safety can be ensured. Further, as a method of increasing the strength, a semi-cylindrical shape can be used. If it is made semi-cylindrical, the capacity of the raw material chamber can be increased, and the throughput per batch increases.

Quartz as a glass window material has high infrared transmittance, heat resistance, compressive strength and corrosion resistance.
This material is optimal. A material having excellent corrosion resistance, heat resistance, heat conductivity, and strength is used for the water-cooled metal frame. The material is preferably SUS316, SUS304, Al or the like. Water cooling prevents overheating of the metal frame.

Above and below the raw material chamber, infrared condensing and heating devices are installed. The infrared condensing heating device has an infrared lamp mounted in a gold-plated elliptical or parabolic reflector so that the condensed infrared light can be radiated to the entire alloy scrap loaded in the raw material chamber. . Ellipsoidal reflectors are suitable for heating small areas with relatively low power, and in order to increase the throughput, a parabolic reflector that consumes large power temporarily but can heat large areas is suitable ing. The reflector has a jacket structure and is cooled with water to prevent overheating. A halogen or xenon lamp is used as the infrared lamp, and its rated power varies depending on the number and shape of the lamp used, but when heating an area of 300 mm × 300 mm, a total of about 52 kW is considered to be good.

The evaporative substance recovery trap is mounted between the metal frame and the vacuum pump in order to supplementarily collect components having a high vapor pressure that could not be coagulated by the metal frame in the raw material chamber. Without the evaporative substance recovery trap, some of the components having a high vapor pressure flow into the vacuum pump, which not only causes a failure of the vacuum pump but also lowers the recovery rate. In order to improve the recovery of components having a high vapor pressure, it is important to keep the evaporant recovery trap at a low temperature, and water cooling is suitable as a method for this. The material is S which has excellent corrosion resistance.
US316 and SUS304 are suitable, but should be determined in consideration of the nature of the component having a high vapor pressure, particularly its corrosion resistance.

A vacuum pump is provided to reduce the pressure in the raw material chamber and the evaporant recovery trap. The vacuum pump only needs to be able to maintain a degree of vacuum of 10 ^{−3 to} 13 Pa, and an oil rotary pump is usually sufficient. However, in the case of alloy scrap that does not easily decompose, it is preferable to add an oil diffusion pump. As the material of the container for containing the alloy scrap, quartz having high infrared transmittance, excellent heat resistance and excellent corrosion resistance is optimal. The alloy scrap is filled in a container and charged into the raw material chamber. The pressure in the raw material chamber and the evaporative substance recovery trap is reduced by a vacuum pump, and then the infrared condensing heating device is energized and heated.

Due to the heating, the components having a high vapor pressure in the alloy scrap evaporate preferentially, and the vapor condenses on the metal frame and the evaporative substance recovery trap in the raw material chamber, and the components having a low vapor pressure remain. After cooling, the raw material chamber and the evaporative substance recovery trap are returned to atmospheric pressure, and the decomposition products are recovered.
If the undecomposed alloy scrap remains together with the component having a low vapor pressure, the decomposition is repeated again, or only the undecomposed alloy scrap is decomposed again after filtering the component having a low vapor pressure.

At this time, if the degree of vacuum is made higher than 10 ^-3 Pa, the components having a low vapor pressure are also easily vaporized, which not only lowers the purity of the components having a high vapor pressure but also reduces the purity of the components having a low vapor pressure. Decreases recovery. In addition, the degree of vacuum is 13 Pa
If the vacuum is lower, the decomposition rate of the alloy scrap is low, which is not practical. When the heating temperature is lower than 700 ° C., the decomposition rate of alloy scrap is generally slow,
If the temperature is higher than 0 ° C., the evaporation loss of the components of the vapor pressure increases, which is inefficient.

In the case of infrared condensing heating, rapid heating and cooling are possible, so that the temperature can be raised within a time period of 0.3 to 60 minutes, and cooling can be performed within a period of 60 minutes or less.
Since the temperature is lowered, the processing time per batch is reduced. In addition, since infrared rays can be focused and heated only on the alloy scrap, the metal frame of the raw material room kept at a low temperature is not corroded and deteriorated by substances with high vapor pressure.
Further, components having a high vapor pressure are rapidly agglomerated in the metal frame of the raw material chamber, so that the partial pressure of the vapor in the raw material chamber is suppressed to a low level, and the decomposition rate is significantly higher than that of the conventional heating method.

If the infrared condensing and heating device is made movable, a large number of raw material chambers can be heated by a single set of infrared condensing and heating devices, so that charging, thermal decomposition, and removal can be performed continuously, thereby increasing work efficiency. Also, the maximum power can be kept low. Further, it is also possible to fix the infrared ray condensing and heating device and make many raw material chambers movable.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which gallium arsenide scrap is decomposed as an alloy scrap will be described below. FIG. 1 is a configuration diagram showing an example of a vacuum heating facility used in carrying out the method for recovering valuable metals of the present invention.

The vacuum heating equipment includes a raw material chamber 1, an infrared ray condensing and heating device 2, an evaporative substance recovery trap 3, and a vacuum pump 4, and the space between the raw material chamber 1 and the evaporative substance recovery trap 3 and the evaporative substance recovery The pipes 11 and 12 made of SUS316 or SUS304 are connected between the trap 3 and the vacuum pump 4. The raw material chamber 1 has a quartz glass window 5 and an SU
And a frame 6 made of S316 or SUS304. The quartz glass window 5 has a length of 400 mm and a width of 400 mm.
mm × 10 mm in thickness, one of which is tightly fixed to the frame 6, and the other is an openable top cover. Raw material room 1
The frame 6, the infrared ray condensing and heating device 2 and the evaporant recovery trap 3 have a water-cooled jacket structure, and are provided with an inlet and an outlet (not shown) for cooling water. As the vacuum pump 4, an oil rotary pump is used.

A halogen lamp 7 and a parabolic reflecting mirror 8 are provided in the infrared ray condensing and heating device 2 installed above and below the raw material chamber 1, and the irradiation area is 300 mm long × 300 mm wide. Has become. Gallium arsenide scrap 10
Is uniformly filled in a bat-shaped quartz container 9 having a length of 300 mm × a width of 300 mm × a depth of 50 mm. Close. The thickness of the quartz container 9 is preferably 2 to 5 mm, but may be determined in consideration of the strength. The gallium arsenide scrap 10 has a higher decomposition rate as the finer the grains, but in consideration of the scattering loss caused by evacuation, it is 0.5 to 2.36 mm.
Is appropriate. The filling amount of the gallium arsenide scrap 10 is set so as not to spill from the quartz container 9 and usually 5 to 10 kg is appropriate for the bat-shaped quartz container 9 having a length of 300 mm × a width of 300 mm × a depth of 50 mm. is there.

The frame 6 of the raw material chamber 1 and the infrared condensing heating device 2
And evaporated substance recovery trap 3 of the water-cooling jacket cooling water flow 5~20L / min, a feed chamber 1 and the evaporation material recovery trap 3 vacuum degree of 10 ^-3 to using a vacuum pump 4
It is kept at 13 Pa. Power is supplied to the infrared condensing heating device 2 and 7
The temperature is raised from 00 ° C to 1200 ° C in 0.3 to 60 minutes,
After holding for 1 to 4 hours, the power supply is stopped and cooling is performed. When cooling is started, arsenic adheres to the quartz glass window 5, but part of the arsenic remaining in the decomposition product is sublimated, so that it is easily removed by irradiating infrared rays at the next processing. However,
After decomposition, if the temperature is maintained at 600 to 700 ° C for 5 to 60 minutes,
At this temperature, there is no sublimation of arsenic from the decomposition product, so that arsenic can be prevented from adhering to the quartz glass window 5, but the processing time per batch becomes longer. It is better to select which one is more efficient in consideration of operating conditions.

Cooling is performed within 60 minutes even in a furnace.
The internal temperature becomes from room temperature to 40 ° C. In order to increase the cooling rate, an inert gas such as nitrogen or argon may be introduced into the raw material chamber 1. After cooling, the raw material chamber 1 and the evaporating substance recovery trap 3 are returned to atmospheric pressure, the upper lid of the raw material chamber 1 is opened, and the decomposition products remaining in the quartz container 9 are taken out.

Since the body 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 is agglomerated in the skeleton 6 of the raw material chamber 1 and the evaporative substance recovery trap 3, and is stripped and collected. On the other hand, since gallium and undecomposed gallium arsenide remain in the quartz container 9, after recovery, the gallium and gallium arsenide are filtered off using a nonwoven fabric made of polypropylene, and the gallium arsenide is again decomposed by heating under vacuum for efficient operation. It becomes possible.

[0029]

EXAMPLES Example 1 A gallium arsenide scrap 10 was made into a powder having a size of 0.5 to 2.36 mm by a percussion crusher, and a quartz container 9 (300 mm long × 300 mm wide × 50 m deep) was used.
m) was filled with 8 kg.

After the quartz container 9 is placed in the center of the raw material chamber 1 of the vacuum heating equipment shown in FIG. 1, the upper lid of the quartz glass window 5 is closed, and the frame 6 of the raw material chamber 1 and the infrared condensing heating device 2 Then, cooling water is supplied at a flow rate of 10 L / min to the water cooling jacket of the evaporant recovery trap 3, and the raw material chamber 1 is
Further, the evaporant recovery trap 3 was maintained at a vacuum degree of 8 Pa.

Electric power is supplied to the infrared condensing heating device 2 at 1050 ° C.
After heating for 20 min, hold for 2 h and decompose,
The temperature was lowered to 700 ° C. in 0.5 min and maintained for 30 min to prevent arsenic from adhering to the quartz glass window 5 and the furnace was cooled. Cooling time from 700 ° C to 40 ° C is 50min
Met. Since the sublimed arsenic adhered to the frame 6 of the raw material chamber 1 and the evaporant recovery trap 3, the arsenic was peeled off with a light impact with a hammer and collected. On the other hand, since gallium and undecomposed gallium arsenide remain in the quartz container 9, they were collected and separated into gallium and gallium arsenide using a nonwoven fabric made of polypropylene.

With the above operation, the recovery rate of gallium is 96%,
The recovery of arsenic was 97%. 3% of arsenic could not be recovered from undecomposed gallium arsenide, the skeleton 6 of the raw material chamber 1 and the evaporant recovery trap 3. On the other hand, 4% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed with arsenic. The time required for vacuum decomposition of 8 kg / batch was 3.68 h, and the operation was completed in 5 h including the operations of charging and recovery.

Example 2 While keeping the raw material chamber 1 and the evaporating substance recovery trap 3 at a degree of vacuum of 10 ^-1 Pa, the infrared ray condensing and heating apparatus 2 was energized, heated to 1050 ° C. for 20 minutes, and held for 1.5 hours. Other than that, it operated similarly to Example 1.
By the above operation, the recovery rate of gallium was 95%, and the recovery rate of arsenic was 96%. 4% of arsenic could not be recovered from undecomposed gallium arsenide, the skeleton 6 of the raw material chamber 1 and the evaporant recovery trap 3. On the other hand, 5% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed with arsenic.

The time required for vacuum decomposition of 8 kg / batch was 3.18 h, and 4.5 hours including the charging and recovery operations.
h. Example 3 The procedure was the same as that of Example 1 except that the raw material chamber 1 and the evaporating substance recovery trap 3 were kept at a vacuum degree of 8 Pa, and the infrared ray condensing and heating apparatus 2 was energized, heated to 1000 ° C. in 20 minutes, and then held for 2.18 h. The same operation was performed.

By the above operation, the recovery rate of gallium is 94%,
The recovery of arsenic was 95%. 5% of arsenic could not be recovered from undecomposed gallium arsenide, the frame 6 of the raw material chamber 1 and the evaporant recovery trap 3. On the other hand, 6% of gallium is undecomposed gallium arsenide, gallium adhering thereto, and evaporated and mixed with arsenic. The time required for the vacuum decomposition of 8 kg / batch was 4.2 h, and was completed in 5.5 h including the charging and recovery operations.

[0036]

According to the method for recovering valuable metals of the present invention,
In the vacuum thermal decomposition method, the time required for raising and lowering the temperature of the alloy scrap and the time required for thermal decomposition can be shortened, and valuable metals can be recovered at low cost because the evaporation loss is small.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an example of a vacuum heating facility used in carrying out a valuable metal recovery method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Raw material chamber 2 Infrared condensing heating device 3 Evaporation substance collection trap 4 Vacuum pump 5 Quartz glass window 6 Frame 7 Halogen lamp 8 Reflector 9 Quartz container 10 Gallium arsenide scrap 11 Piping 12 Piping

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K001 AA03 AA11 BA22 EA01 EA02

Claims (1)

[Claims] 1. A raw material chamber composed of a quartz glass window and a water-cooled metal frame, a vacuum heating facility equipped with an infrared condensing heating device, an evaporating substance recovery trap, and a vacuum pump were charged into the raw material chamber. A method for recovering valuable metals, comprising heating an alloy scrap under reduced pressure with an infrared condensing heating device to decompose it into a component having a high vapor pressure and a component having a low vapor pressure, and recovering each component.