Method for efficiently removing gallium from aluminum oxide polycrystal for sapphire

Abstract

The invention relates to an aluminum oxide high-frequency smelting gallium removal method, and belongs to the technical field of material purification and resource recovery. According to the method, the nano carbon black is used as a reducing agent, gallium oxide is reduced into gallium monoxide steam through heating of a high-frequency induction furnace, and efficient separation of gallium is achieved in combination with a condensation system. The method is suitable for preparation of high-purity aluminum oxide and recycling of gallium resources in the fields of semiconductors, photovoltaics and the like, and has high efficiency, environmental friendliness and economical efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of material purification, and particularly relates to a method for efficiently removing gallium (Ga) impurities by adding carbon black during the high-frequency melting process of high-purity alumina produced by the improved Bayer process, which is applicable to the field of preparing high-purity alumina polycrystals for sapphire. Background Art

[0002] Aluminum oxide (Al2O3) is the core raw material of the aluminum industry, and its purity is crucial for downstream applications. However, trace amounts of gallium (Ga) impurities (0.01 - 0.5%) are often associated with its natural ore or recycled aluminum raw materials. The gallium element index in the high-purity alumina produced by the Bayer process is relatively high, while the Bayer process is the method with the lowest production cost and the widest application for producing alumina. The presence of gallium oxide will significantly reduce the current efficiency of aluminum electrolysis and affect the application of high-purity alumina in high-end fields such as semiconductors and sapphires. Therefore, an efficient method is needed to remove gallium from alumina (produced by the Bayer process).

[0003] The existing gallium removal methods mainly include acid leaching method, solvent extraction method, electrolysis method, etc. However, these methods have problems such as high energy consumption, large consumption of chemical reagents, and environmental pollution. Therefore, providing an efficient, economical, and environmentally friendly alumina gallium removal method has become an industry demand. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for purifying alumina powder based on high-temperature carbon reduction, which can improve the purity of alumina by selectively reducing and volatilizing gallium, and simultaneously achieve the efficient recovery of gallium.

[0005] To achieve the above purpose, the present invention provides a method for efficiently removing gallium from alumina polycrystals for sapphire, including the following steps:

[0006] (1) Take gallium-containing alumina powder and control the particle size to be 50 - 100 μm;

[0007] (2) Select carbon black with a purity ≥ 99.99% and a particle size ≤ 50 μm, and uniformly mix it with the alumina powder in step (1) according to a mass ratio of (0.5% - 5%);

[0008] (3) Add the mixture into a high-temperature reaction furnace, and raise the temperature to 2000 - 2100 °C; the melting time is 30 - 600 minutes;

[0009] (4) Recover the gallium-containing vapor through a condenser to obtain metal gallium nanoparticles;

[0010] (5) Screen the alumina out of the furnace to remove the unreacted carbon black.

[0011] By adding carbon black to alumina powder and under the action of high-frequency electromagnetic field at high temperature, using the reduction property and gasification reaction characteristics of carbon, gallium is converted into volatile substances (such as Ga2O) to achieve efficient removal of gallium (removal rate ≥ 95%), while avoiding the introduction of secondary pollution.

[0012] Technical advantages:

[0013] 1. The removal rate of gallium ≥ 95%, and the purity of alumina reaches more than 99.999%;

[0014] 2. The process is integrated, without other complex gallium removal process steps, and the cost is reduced by 40%;

[0015] 3. Carbon black has a wide source and low price, and the reaction product (CO) can be recycled as fuel, which is green and environmentally friendly;

[0016] 4. Recover the crude gallium ash powder rich in gallium;

[0017] 1. Raw material pretreatment:

[0018] The high-purity alumina produced by the Bayer process (gallium content is about 0.002 - 0.02 wt%) is uniformly mixed with carbon black (particle size ≤ 50 μm, purity > 99.99%) according to the mass ratio (0.5% - 5%).

[0019] 2. High-frequency melting:

[0020] The mixture is added to a high-frequency induction furnace (frequency 100 - 600 kHz), heated to 2000 - 2100 °C, and the melting time is 30 - 600 minutes.

[0021] 3. Separation and capture of gallium:

[0022] The volatile gallium compound (Ga2O) enters the condensation system through the top exhaust port of the furnace and is condensed into rich gallium ash powder for recovery.

[0023] 4. Product treatment:

[0024] The purified alumina melt is directly produced into sapphire alumina raw materials, and the gallium ash powder is purified by acid leaching (recovery rate ≥ 98%).

[0025] Core reaction mechanism:

[0026] Reduction reaction:

[0027] C + Ga2O3 → Ga2O + CO

[0028] Under the high-temperature molten state, Ga2O3 is reduced by carbon black into volatile Ga2O, which volatilizes from the molten state, and the remaining carbon black reacts with oxygen in the air to generate CO or CO2 gasification.

[0029] Further, the temperature gradient of the condenser is 10°C → 600°C, which can provide the recovery rate of gallium.

[0030] Further, the specific surface area of carbon black ≥ 200 m 2 / g. The high specific surface area and active sites of nano-carbon black can increase the reaction rate. Through nano-scale dispersion, carbon black agglomeration is avoided, ensuring the uniformity of the reduction reaction.

[0031] Further, the reaction furnace is a high-frequency induction furnace with a frequency of 50 - 100 kHz and a heating power density of 50 - 200 W / cm 3 , and the specific frequency matches the dielectric properties of alumina to achieve rapid and uniform heating inside the material. The control of power density avoids local overheating and ensures the stable volatilization of gallium vapor. Specific Embodiments

[0032] The following is a further detailed description through specific embodiments:

[0033] Example 1:

[0034] Raw materials: 20 kg of alumina powder containing 102 PPM of gallium, adding 0.1 kg of carbon black (the addition amount of carbon black is 0.5% of the amount of alumina, particle size D50 = 10 um, purity 99.999%), igniting through 4 graphite rods stacked in a square shape under high frequency, and removing the graphite rods after ignition;

[0035] Smelting conditions: 2050 - 2100°C, 300 kHz, 100 minutes;

[0036] During the process, the exhaust port at the top of the furnace enters the condensation system (condenser temperature 100°C), and brown substances appear in the condenser, and the brown substances are recovered.

[0037] Results: The gallium removal rate from alumina is 97.8%, and the purity of alumina ≥ 99.999%.

[0038] Example 2:

[0039] Raw materials: 20 kg of alumina powder containing 102 PPM of gallium, adding 0.2 kg of carbon black (the addition amount of carbon black is 1% of the amount of alumina, carbon black particle size D50 = 10 um, carbon black purity 99.999%), igniting through 4 graphite rods stacked in a square shape under high frequency, and removing the graphite rods after ignition;

[0040] Smelting conditions: temperature 2050 - 2100°C, frequency 300 kHz, smelting for 100 minutes;

[0041] During the process, the exhaust port at the top of the furnace enters the condensation system (condenser temperature 100°C), and brown substances appear in the condenser, and the brown substances are recovered.

[0042] Results: The removal rate of gallium in alumina is 98.48%, and the purity of alumina is ≥99.999%.

[0043] Example 3:

[0044] Raw materials: 20 kg of alumina powder containing 102 PPM of gallium, adding 0.4 kg of carbon black (the addition amount of carbon black is 2% of the alumina amount, the particle size D50 of carbon black = 10 um, and the purity of carbon black is 99.999%). Ignite under high frequency by stacking 4 graphite rods into a mouth shape, and remove the graphite rods after ignition;

[0045] Smelting conditions: temperature 2050 - 2100 °C, frequency 300 kHz, smelting for 100 minutes;

[0046] During the process, the top exhaust port of the furnace enters the condensation system (condenser temperature 100 °C), and brown substances appear in the condenser, and the brown substances are recovered.

[0047] Results: The removal rate of gallium in alumina is 99.66%, and the purity of alumina is ≥99.999%.

[0048] Example 4:

[0049] Raw materials: 20 of alumina powder containing 102 PPM of gallium, without adding carbon black. Ignite under high frequency by stacking 4 graphite rods into a mouth shape, and remove the graphite rods after ignition;

[0050] Smelting conditions: temperature 2050 - 2100 °C, frequency 300 kHz, smelting for 100 minutes;

[0051] During the process, the top exhaust port of the furnace enters the condensation system (condenser temperature 100 °C), and almost no brown substances appear in the condenser.

[0052] Results: The removal rate of gallium in alumina is 9.51%.

[0053] The following table shows the polycrystalline indexes of Example 1, Example 2, Example 3, and Example 4.

[0054] Powder Index Index of Example 1 Index of Example 2 Index of Example 3 Index of Example 4 P (ppm) 0.5 0.36 0.34 0.41 0.4 Zn (ppm) 0.1 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Co (ppm) 0 ＜0.05 ＜0.05 ＜0.05 ＜0.05 Ni (ppm) 0.05 ＜0.05 ＜0.05 ＜0.05 ＜0.05 B (ppm) 0.5 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Si (ppm) 2 1.5 1.76 2.13 1.61 Fe (ppm) 0.2 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Cr (ppm) 0 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Mn (ppm) 0 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Mg (ppm) 0.1 ＜0.1 ＜0.1 ＜0.1 ＜0.1 V (ppm) 0.1 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Ga (ppm) 102 2.2 1.55 0.35 92.3 Be (ppm) 0.2 ＜0.05 ＜0.05 ＜0.05 ＜0.05 Cu (ppm) 0.1 ＜0.05 ＜0.05 ＜0.05 ＜0.05 Ca (ppm) 1.2 ＜0.05 ＜0.05 ＜0.05 ＜0.05 Na (ppm) 2 0.2 0.22 0.26 0.36 Li (ppm) 0.1 ＜0.05 ＜0.05 ＜0.05 ＜0.05 K (ppm) 0.5 ＜0.05 ＜0.05 ＜0.05 ＜0.05 Ti (ppm) 0.1 ＜0.1 ＜0.1 ＜0.1 ＜0.1 Zr (ppm) 0.2 0.18 0.18 0.18 0.17

[0055] The above are only the embodiments of the present invention, and common knowledge such as the specific structures and characteristics in the solutions is not described in detail here. It should be noted that for those skilled in the art, without departing from the structure of the present invention, several deformations and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the present invention. The specific implementation manners and the like in the specification can be used to explain the content of the claims.

Claims

1. A method for efficiently removing gallium from polycrystalline alumina for sapphire, characterized in that, It includes the following steps: (1) Take gallium-containing alumina powder, control the particle size to be 50 - 100 μm, and the moisture content ≤ 0.5%; (2) Select carbon black with a purity ≥ 99.99% and a particle size ≤ 50 μm, and uniformly mix it with the alumina powder in step (1) at a mass ratio of 0.5% - 5%; (3) Add the mixture into a high-temperature reaction furnace, heat it up to 2000 - 2100 °C; the smelting time is 30 - 600 minutes; (4) Recover the gallium-containing vapor through a condenser to obtain metal gallium nanoparticles; (5) Screen the as-furnace alumina to remove the unreacted carbon black.

2. The method according to claim 1, wherein The temperature gradient of the condenser is 10 °C → 600 °C.

3. The method according to claim 2, wherein The specific surface area of the carbon black is ≥ 200 m 2 / g.

4. The method according to any one of claims 1-3, characterized in that, The high-temperature reactor is a high-frequency induction furnace with a frequency of 50 - 100 kHz and a heating power density of 50 - 200 W / cm 3 .