JP4073551B2 - Gallium recovery method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gallium recovery method for recovering gallium from a compound semiconductor scrap containing gallium phosphide as a main component at a low cost.
[0002]
[Prior art]
Gallium oxide is recovered as a by-product from the buyer's liquid used in the production of alumina from bauxite, or from the retort residue of zinc distillate zinc distillate or the sulfuric acid leaching residue of zinc roasting ore. After gallium is dissolved in caustic soda solution, it is produced as 98 to 99% low purity gallium by electrowinning. This low-purity gallium is further purified by a combination of vacuum heating, acid cleaning, and recrystallization steps, and is highly purified to 99.9999% or more. However, there are few buyer liquids, retort residues or sulfuric acid leaching residues that meet the recovery costs, and the total amount of gallium demand cannot be covered by the production from them.
[0003]
Therefore, about 50% or more of gallium currently used in Japan is covered by compound semiconductor scrap such as gallium arsenide or gallium phosphide, or a recycled product of scrap from the liquid phase epitaxial growth process of compound semiconductor.
[0004]
Compound semiconductor scraps containing gallium phosphide as the main component include polycrystalline or single crystal end cuts, damaged wafers, cutting scraps, lapping scraps, exhaust gases in vapor phase epitaxial growth processes, and wafer damage after circuit formation There are things. In order to recover gallium from these compound semiconductor scraps, it is necessary to decompose gallium and phosphorus, which are the main components thereof, and an acid dissolution method and a vacuum heat decomposition method are known because of the difference in decomposition methods.
[0005]
In the acid dissolution method, gallium hydroxide is precipitated by adding an alkaline solution to a solution obtained by decomposing and dissolving gallium phosphide in aqua regia and adjusting the pH, and then separating the precipitated gallium hydroxide by filtration, Gallium is recovered by electrolytic collection from an electrolytic solution in which is dissolved in an alkaline solution.
[0006]
The acid dissolution method has the advantage that the initial investment in equipment is relatively small and gallium can be recovered relatively safely from wet processing, but the number of processing steps is large, and by-products to be disposed of as industrial waste Since a large amount of products are generated, there are disadvantages that the cost is high and it is difficult to obtain high-purity gallium, and it is gradually becoming unusable.
[0007]
The vacuum pyrolysis method uses the difference in vapor pressure between gallium and phosphorus when heating gallium phosphide scrap in vacuum and decomposing it, giving priority to phosphorus and impurities with higher vapor pressure than gallium. It is a method of evaporating and separating.
[0008]
The vacuum pyrolysis method has the advantage that there are few processing steps, so there is relatively little contamination during processing, and gallium can be recovered at the same time as scrap decomposition, but the decomposed phosphorus condenses to yellow phosphorus, and yellow phosphorus becomes oxygen. On the other hand, since it is active, there exists a fault that a process is difficult.
[0009]
In view of this, in the vacuum thermal decomposition method, there is a method in which yellow phosphorus separated by decomposition is converted into red phosphorus in the apparatus and scraped with a scraper (see Japanese Patent Application No. 63-270430). In this method, yellow phosphorus is converted into red phosphorus in the apparatus, so that it can be stably handled in the atmosphere.
[0010]
In addition, as a method for treating yellow phosphorus, a method has been proposed in which dry air is allowed to react slowly with yellow phosphorus while controlling the flow rate to recover it as phosphorus pentaphosphide stable in air.
[0011]
As described above, the vacuum heat decomposition method has a high scrap processing speed and can recover high-purity gallium, but it cannot be continuously operated because yellow phosphorus produced by decomposition is processed by the above method. An excessive dust collector is required.
[0012]
Gallium recovered by vacuum pyrolysis is purified by vacuum heating, electrolytic purification, acid cleaning, recrystallization purification methods alone or in combination as necessary, and again as a compound semiconductor crystal or liquid phase epitaxial growth raw material used.
[0013]
[Problems to be solved by the invention]
As described above, in the conventional vacuum pyrolysis method, phosphorus produced during the decomposition of gallium phosphide scrap is condensed into yellow phosphorus. However, it is converted into red phosphorus by long-time heat treatment or gradually with dry air. Reacted and recovered as phosphorus pentoxide or removed.
[0014]
Conversion to red phosphorus takes a long time of 4 to 5 days at 250 ° C., and it is difficult to convert 100% even over a long time. Therefore, the remaining yellow phosphorus is usually separated from red phosphorus, oxidized, reacted with water, and washed and removed as phosphoric acid.
[0015]
On the other hand, when phosphorous pentoxide is used, the amount of heat generated by yellow phosphorus is large, so that phosphorous pentoxide is generated in the form of fine particles and white smoke, making it difficult to remove. In order to avoid this difficulty, it is necessary to increase the particle size of phosphorus pentoxide produced by adjusting the oxidation rate of yellow phosphorus by air. Moreover, in order to process the high temperature phosphoric acid produced | generated by contact with a water | moisture content, the apparatus material with corrosion resistance is required, and there are many restrictions in the selection.
[0016]
The waste liquid generated when removing the phosphorus pentoxide particles by wet treatment contains phosphoric acid, which may cause red tides and eutrophication of seawater and lakes. It is necessary to solidify in a form that can be discarded, such as calcium phosphate.
[0017]
As described above, in the vacuum thermolysis method, it is an object of cost reduction to find a phosphorus treatment method that is easy to control and has a small calorific value, and to enable continuous operation. More preferably, the material obtained by the phosphorus treatment is valuable.
[0018]
The present invention solves the above-described problem in a gallium recovery method in which compound semiconductor scrap containing gallium phosphide as a main component is thermally decomposed by vacuum to separate gallium and phosphorus and recover gallium. A gallium recovery method that enables rapid operation of the vacuum thermal decomposition method by rapidly processing phosphorus without generating white smoke and converting it into a material that can be handled in the atmosphere, enabling gallium to be recovered at low cost. The purpose is to provide.
[0019]
[Means for Solving the Problems]
The present invention relates to a method for recovering gallium in which compound semiconductor scrap containing gallium phosphide as a main component is subjected to vacuum pyrolysis to separate gallium and phosphorus to recover gallium, and the generated phosphorus is brought into contact with a zinc melt or vapor. Thus, the above problem is solved by generating zinc phosphide.
[0020]
The boiling point of liquid phosphorus is 280.5 ° C. under 1 atm. The boiling point of gallium is 2403 ° C., and the vapor pressure at 1000 ° C. is 0.003 mmHg. Gallium phosphide is a compound having a melting point of 1450 ° C. under the vapor pressure of phosphorus of 760 mmHg.
[0021]
In synthesizing gallium phosphide, a method is adopted in which the vapor pressure of phosphorus is increased to 10 atm to bring it close to the stoichiometric ratio. When synthesizing gallium phosphide, the higher the vapor pressure of phosphorus, the higher the melting point of the gallium phosphide produced, and the P / Ga stoichiometric ratio approaches 1.
[0022]
The vacuum thermolysis method is an application of the above principle in reverse, and the decomposition of gallium phosphide scrap is promoted by lowering the phosphorus vapor partial pressure by heating to a high temperature and raising the degree of vacuum.
[0023]
Phosphorus generated by vacuum pyrolysis is processed quickly without generation of white smoke by contact with zinc melt or vapor to form zinc phosphide, and the substance produced by the treatment is also in the atmosphere. Since it can be handled, continuous operation of the vacuum pyrolysis method becomes possible, and as a result, gallium is recovered at a low cost.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
The vacuum pyrolysis apparatus used in the method of the present invention comprises a preliminary vacuum chamber for scrap material supply, a vacuum pyrolysis chamber, a preliminary vacuum chamber for zinc supply, a zinc chamber, a gallium chamber, a zinc chloride chamber, and a surplus zinc recovery chamber. Each chamber is connected with a duct, and a heater and a duct and a valve that enable vacuuming are attached.
[0025]
The positional relationship among the scrap material supply preliminary vacuum chamber, the vacuum pyrolysis chamber, and the gallium chamber is arranged in the above order from the top to the bottom. A multi-stage zinc chamber is connected to the upper side surface of the vacuum pyrolysis chamber, a surplus zinc recovery chamber is connected to the upper part of the final stage zinc chamber, and an adjacent zinc chamber is connected to the lower part.
[0026]
A vacuum pump for depressurizing main processing steps from vacuum pyrolysis to surplus zinc recovery is attached to the surplus zinc recovery chamber. The multi-stage zinc chamber is installed at a position that is slightly lowered for each stage. In order to completely remove phosphorus, it is better to connect at least three chambers.
[0027]
It is appropriate to use an electric resistance heater as the heating method, but other heating methods may be used as long as the temperature can be raised to a target temperature.
The material of the device must be selected from materials that do not react with gallium and phosphorus, and the device body is preferably made of stainless steel because it has high strength and oxidation resistance. Carbon, silicon carbide, or boron nitride coating is suitable for the inner surface. It is.
[0028]
The specific gravity of gallium is 5.9, and the specific gravity of gallium phosphide is 4.13. Gallium phosphide scraps are various, such as lumps, particles, fine powder, or slurries in which particles and fine powder are dispersed. All the particulate scrap is made into fine particles by pulverization so that vacuum thermal decomposition is promoted. Generally, lump scraps are roughly crushed with a jaw crusher or the like and then crushed into a fine powder using a stainless steel ball mill or the like. The smaller the particle size, the easier the decomposition during heating proceeds, so the gallium recovery improves the pulverization.
[0029]
The pulverized gallium phosphide scrap is supplied from a hopper to a preliminary vacuum chamber for supplying scrap raw material, and vacuum deaerated. The feed rate must be determined according to the size of the device. The preliminary vacuum chamber for supplying scrap raw material is supplied with a small amount of nitrogen gas to prevent entry of phosphorus from the vacuum thermal decomposition chamber, and gallium phosphide scrap is put into the vacuum thermal decomposition chamber.
[0030]
In other words, the pressure in the preliminary vacuum chamber for scrap material supply is reduced as much as possible, the air in the preliminary vacuum chamber for scrap material supply is discharged, and then a small amount of nitrogen gas is supplied. Next, after opening the valve which connects the preliminary vacuum chamber for scrap material supply and the vacuum pyrolysis chamber heated to 1000 ° C. or higher in a reduced pressure state of about 50 mmHg in advance, the gallium phosphide scrap is put into the vacuum pyrolysis chamber Then close the valve again. As the gallium phosphide scrap is heated, it begins to decompose, producing gallium and phosphorus.
[0031]
In vacuum decomposition, a higher decomposition rate can be expected at higher temperatures and higher vacuums, but the temperature conditions must be determined in consideration of the material of the apparatus. The decomposition time per unit weight kg of gallium phosphide scrap is generally 1 to 5 hours, and an optimum value is arbitrarily determined and set according to the particle diameter and charged weight of gallium phosphide scrap. In order to accelerate the decomposition, it is effective to stir the gallium phosphide scrap with a mechanical or aerated stirrer.
[0032]
The vacuum heat decomposition is performed at a heating temperature of 1000 ° C. or more and a vacuum degree of about 50 mmHg. However, if the degree of vacuum is higher, a further decomposition effect can be expected. The decomposition time is determined by setting an optimum value arbitrarily according to the weight of scrap.
[0033]
Gallium produced by vacuum pyrolysis of scrap in the vacuum pyrolysis chamber is discharged from the bottom of the vacuum pyrolysis chamber through the U-shaped tube to the gallium chamber due to the difference in specific gravity with gallium phosphide.
[0034]
The zinc supply preliminary vacuum chamber is connected to the top of the zinc chamber closest to the vacuum pyrolysis chamber. Zinc supplied from the hopper is vacuum degassed in a preliminary vacuum chamber for supplying zinc, and then a small amount of nitrogen gas is supplied to prevent the entry of phosphorus and zinc vapor from the zinc chamber, and the zinc is supplied to the zinc chamber. The Zinc is introduced into the zinc chamber in a timely manner corresponding to the amount of phosphorus generated by vacuum thermal decomposition of gallium phosphide scrap.
[0035]
Here, the granular form of zinc is 5 to 10 mm. Zinc with large grains and complex shapes is likely to cause a delay in the supply to the zinc chamber, and in the fine powder form, the amount of oxygen contained in the zinc increases, so that gallium is oxidized and the recovery rate of gallium deteriorates. Become. The supply rate of zinc is determined from the amount of phosphorus generated by the decomposition of gallium phosphide scrap.
[0036]
The phosphorus produced by the vacuum cracking is induced by the exhaust flow from the vacuum pump, blown into the zinc melt in the zinc chamber connected to the vacuum heat cracking chamber, and passes through the zinc melt in the multistage zinc chamber. A compound is produced. The temperature of the zinc chamber must be lower than the temperature of the vacuum pyrolysis chamber and not less than the melting point of zinc phosphide, and is suitably controlled in the range of 700 to 800 ° C.
[0037]
The zinc chamber is at least three-stage connected, and the zinc melt in each chamber is controlled at 700 to 800 ° C. At this time, the temperature of the zinc chamber is the lowest in the final stage, and the temperature is gradually increased toward the vacuum pyrolysis chamber to maintain the entire system at a higher vacuum. Phosphorus that has not reacted with zinc in the first stage is absorbed by reacting with the zinc melt again in the next stage.
[0038]
Thus, the zinc chamber can be completely removed by using a multistage system, and at the same time, the specific gravity of zinc phosphide is 3.14 to 4.5, and the specific gravity of zinc is 7.9. Can be concentrated before reaching the final stage while overflowing from the zinc chamber of each stage. Zinc phosphide is discharged from the zinc chamber in the final stage into a container in the zinc phosphide chamber by overflow and solidified.
[0039]
The surplus zinc recovery chamber is connected to the upper part of the final zinc chamber via a condenser tube heated to 420 to 450 ° C. The vapor pressure of zinc is 0.39 mmHg at 450 ° C, 62 mmHg at 700 ° C, and 234 mmHg at 800 ° C. This is for condensing unreacted zinc in a condenser tube and recovering the melt.
[0040]
Metals that form phosphides include lead, aluminum, tin, and copper in addition to zinc. Zinc has a melting point of 420 ° C and a boiling point of 907 ° C, both of which are relatively low, and the reaction rate with phosphorus is appropriate. It is most preferable because of its low price and low toxicity. Since zinc has a lower boiling point than other metals, it is possible to react zinc vapor with phosphorus.
[0041]
Two types of compounds have been identified for zinc phosphide. One is ZnP and the other is Zn ₃ P ₂ . When phosphorus vapor is reacted with a solution or vapor of zinc, a mixture of ZnP and Zn ₃ P ₂ is formed. In general, Zn ₃ P ₂ is easier to produce, and when making a ZnP single phase with a high phosphorus content, the vapor pressure of phosphorus must be kept higher than atmospheric pressure in a sealed container.
[0042]
Zinc phosphide is the only metal phosphide that is stable to cold and hot water, excluding copper phosphide, and can be handled safely in the atmosphere. At the same time, zinc phosphide has a use as a rodenticide. It can be recovered as a valuable resource. Regarding copper phosphide, the melting point of copper is as high as 1087 ° C., and the melting point varies greatly depending on the composition, so that it is difficult to control, making operation complicated, and not suitable for use.
[0043]
The zinc phosphide moves while being concentrated in the zinc chamber from the first stage to the final stage while overflowing, and is discharged from the final stage to the container in the zinc phosphide chamber. The solidified product is a mixture of zinc and zinc phosphide (ZnP and Zn ₃ P ₂ ), but only zinc phosphide is used when the amount of zinc input is appropriate. In addition to copper phosphide, zinc phosphide is the only metal phosphide that is stable to cold and hot water and can be handled safely in the atmosphere.
[0044]
In addition, gallium is taken out from the vacuum pyrolysis chamber using the specific gravity difference between gallium phosphide and gallium, and only the gallium melt accumulated at the bottom of the vacuum pyrolysis chamber can be overflowed and discharged by a U-tube. As a result, continuous operation is possible.
[0045]
【Example】
[Example 1]
After crushing 1000 g of bulk gallium phosphide bulk scraps with a jaw crusher into particles of 5 mm or less, it was pulverized at 100 rpm for 30 minutes with 2000 g of φ15 stainless balls in a 2-liter stainless steel ball mill. 3 mm or less.
[0046]
990 g of the crushed scrap powder is put into a preliminary vacuum chamber for supplying scrap raw material through a hopper, and after vacuum degassing, nitrogen gas is supplied to a pressure of 100 mmHg, and then the scrap powder is supplied to the vacuum pyrolysis chamber at a supply rate of 990 g per hour. Intermittently. The vacuum pyrolysis chamber was previously depressurized to 50 mmHg, filled with gallium to the overflow line, and heated to 1100 ° C. The third-stage zinc chamber was heated to 700 ° C., and zinc was filled up to the overflow discharge line of the zinc chamber. Zinc was introduced intermittently at a supply rate of 1000 g / hour.
[0047]
48 hours after the start of the continuous treatment, the amount of gallium and metal phosphide per hour flowing into the gallium chamber and the zinc phosphide chamber were measured. The recovered gallium was 680 g. As a metal phosphide, 1290 g of a mixture composed of zinc, ZnP, and Zn ₃ P ₂ was obtained, and the phosphorus content was 23.6 wt%.
[0048]
The recovery rate of gallium was about 98%, and the recovery rate of phosphorus was about 99%.
[0049]
【The invention's effect】
According to the gallium recovery method of the present invention, when compound semiconductor scrap containing gallium phosphide as a main component is thermally decomposed by vacuum to separate gallium and phosphorus and recover gallium, the decomposed phosphorus is converted into white smoke. Since it can be processed quickly without generation, and the substance produced by the treatment can be handled in the atmosphere, continuous operation of the vacuum pyrolysis method is possible, and as a result, gallium can be recovered at low cost.

Claims (1)

A method of recovering gallium by separating compound semiconductor scrap containing gallium phosphide as a main component by vacuum pyrolysis to recover gallium and phosphorus, and contacting the generated phosphorus with a melt or vapor of zinc. A method for recovering gallium, characterized by producing zinc phosphide.