Method for removing alkali metal from electrolytic aluminum liquid

Abstract

The invention relates to the technical field of electrolytic aluminum impurity removal, in particular to a method for removing alkali metal from electrolytic aluminum liquid. The method comprises the following steps: in a closed reaction device filled with electrolytic aluminum liquid, injecting silicon tetrachloride gas into the electrolytic aluminum liquid through a gas inlet formed in the bottom of the closed reaction device. According to the invention, the silicon tetrachloride gas obtained by preheating the silicon tetrachloride liquid is creatively utilized to remove alkali metals and alkaline earth metals in the electrolytic aluminum liquid; the silicon tetrachloride gas is decomposed under high-temperature micro-aerobic conditions to generate silicon dioxide particles and chlorine; the characteristic that the density of silicon dioxide particles is smaller than that of aluminum is utilized, so that the silicon dioxide particles float to the surface of molten aluminum to form slag; the silicon tetrachloride does not contain C and H; the reduction of the performance of the aluminum product due to the introduction of C and H is avoided.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the technical field of electrolytic aluminum impurity removal, in particular to a method for removing alkali metals from electrolytic aluminum liquid. BACKGROUND

[0002] Alkali metals and alkaline earth metals in aluminum melt mainly come from alkali metals and alkaline earth metals elements such as Na, Li, Ca, etc. in the aluminum electrolysis process, and also come from fluxes for aluminum alloys, which are generally composed of chlorides and fluorides of alkali metals and alkaline earth metals, and the main components are KCl, NaCl, NaF, CaF, Na3AlF6, Na2SiF6, etc. After using the flux, the above-mentioned alkali metals and alkaline earth metals will be left in the melt. Taking sodium as an example, sodium is almost insoluble in aluminum, with a maximum solid solubility of less than 0.0025%. In Al-Mg alloy, when the magnesium content exceeds 2%, magnesium will take silicon and precipitate free sodium. During the solidification process of Na element, it exists in the grain boundary. During the plastic deformation process, due to its low melting point, it will recover to the free state again, thereby forming a crack source. With the increase of deformation, cracks are gathered to form cracking, which is the so-called sodium brittleness phenomenon. Calcium in aluminum alloy will form new phases CaAl4 and CaAl2 with aluminum, and the formation of these new phases will reduce the strengthening phase in aluminum alloy. The new phase does not dissolve into the aluminum matrix and cannot occur precipitation strengthening, so the as-cast hardness of the aluminum alloy is reduced, and when the calcium content increases, the hardness of the aluminum alloy after heat treatment is also reduced. In addition, Ca will also make the fluidity of the aluminum alloy melt worse, easy to absorb air and cause micro pinholes or porosity, and even cause segregation of hard brittle compounds, which will significantly increase the scrap rate of castings and reduce the heat treatment strengthening effect of aluminum alloy.

[0003] In the prior art, the method that can remove alkali metals in aluminum melt is to use chlorine gas, chlorine-containing refining agents (such as hexachloroethane, carbon tetrachloride, etc.) or fluoride-containing refining agents in the holding furnace to refine the melt. For common chlorine-containing refining agents, there are inevitably the following shortcomings: (1) organic matters such as hexachloroethane and carbon tetrachloride inevitably produce carbon pollution and form new Al4Cl3 phase; (2) as a liquid, carbon tetrachloride releases chlorine gas with a volume much larger than its own volume, which will cause violent release, and a large amount of chlorine gas cannot completely react and separate from the aluminum liquid, which not only leads to waste and environmental pollution, but also causes corrosion of the reaction device and affects the service life. SUMMARY

[0004] The present disclosure provides a method for removing alkali metals from electrolytic aluminum liquid to solve the problems in the related art.

[0005] According to a first aspect of an embodiment of the present disclosure, a method for removing alkali metals from electrolytic aluminum liquid is provided, and the method comprises the following steps: In a closed reaction device containing electrolytic aluminum liquid, silicon tetrachloride gas is injected into the electrolytic aluminum liquid through a gas inlet arranged at the bottom of the closed reaction device.

[0006] In one aspect of the embodiments of the present disclosure, the atmosphere in the closed reaction device can be a mixed gas of argon and oxygen; the partial pressure of the oxygen is 10 -8 to 10 -6 atm; the volume fraction of the oxygen is 0.001-0.015% of the volume fraction of the argon.

[0007] In one aspect of the embodiments of the present disclosure, the atmosphere in the closed reaction device can be a mixed gas of carbon dioxide and carbon monoxide; the volume ratio of the carbon monoxide to the carbon dioxide is selected from (75-85):(15-25).

[0008] In one aspect of the embodiments of the present disclosure, the atmosphere in the closed reaction device can be pure argon.

[0009] In one aspect of the embodiments of the present disclosure, the silicon tetrachloride gas is pre-dried and heated, the purity of the silicon tetrachloride gas is ≥99.9%, and the silicon tetrachloride gas is free of organic solvents and water.

[0010] In one aspect of the embodiments of the present disclosure, the silicon tetrachloride gas is decomposed to generate silicon dioxide particles and chlorine gas under a high-temperature micro-oxygen environment; the density of the silicon dioxide particles is less than that of the aluminum liquid, and a slag layer is formed on the surface of the aluminum liquid; the chlorine gas reacts with the floated alkali metal and alkaline earth metal to generate a chloride, the density of the chloride is less than that of the aluminum liquid, and the chloride is enriched in the slag layer.

[0011] In one aspect of the embodiments of the present disclosure, the closed reaction device is a sealed heat preservation bag; a gas outlet and a slag outlet are arranged at the top of the sealed heat preservation bag; a gas inlet and a liquid outlet are arranged at the bottom of the sealed heat preservation bag.

[0012] In one aspect of the embodiments of the present disclosure, the silicon tetrachloride gas is pre-heated to 100-150°C to prevent local supercooling of the electrolytic aluminum liquid.

[0013] In one aspect of the embodiments of the present disclosure, the treatment temperature of the electrolytic aluminum liquid is selected from 730-750°C; the treatment time is selected from 5-10 min.

[0014] In one aspect of the embodiments of the present disclosure, the mixed gas discharged from the gas outlet is recovered for silicon tetrachloride through a condensing device.

[0015] Compared with the prior art, the present disclosure has the following beneficial effects: This disclosure creatively utilizes silicon tetrachloride gas obtained by preheating silicon tetrachloride liquid to remove alkali metals and alkaline earth metals from electrolytic aluminum liquid; the silicon tetrachloride gas decomposes under high temperature and micro-oxygen conditions to produce silicon dioxide particles and chlorine gas; this disclosure utilizes the characteristic that the density of silicon dioxide particles is less than that of aluminum, causing the silicon dioxide particles to float to the surface of the aluminum liquid and form slag; furthermore, silicon tetrachloride itself does not contain C and H; it avoids the introduction of C and H causing a decrease in the performance of aluminum products. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0017] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0018] In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0019] In this disclosure, under high-temperature, oxygen-free conditions, SiCl4 is difficult to decompose into Si and Cl2, and it remains essentially stable in molten aluminum; however, under high-temperature, low-oxygen conditions (oxygen partial pressure approximately 10), it remains stable. -6 Under the conditions of atm), the main reaction is: SiCl4 + 2O2 → SiO2(s) + 2Cl2(g), ΔG = -450 kJ / mol; while the side reaction is: SiCl4 → Si(s) + 2Cl2(g), ΔG = +85 kJ / mol (suppressed); since silicon dioxide and aluminum do not react, the method used in this disclosure introduces almost no silicon impurities.

[0020] In this disclosure, the partial pressure of oxygen is 10. -8 Up to 10 -6 atm; specifically, it can be 1×10 -6 atm, 5×10 -7 atm, 8×10 -7 atm, 2.5×10 -7 atm, 10 -7 atm, etc.

[0021] In this disclosure, the volume fraction of oxygen is 0.001-0.015% of the volume fraction of argon gas; specifically, it can be 0.001%, 0.005%, 0.010%, or 0.015%.

[0022] In this disclosure, the rate of silicon tetrachloride gas introduced after drying and heating can be 5-20 L / min; however, this disclosure is not limited to this; it can be specifically set according to the size of the reaction apparatus and the amount of molten aluminum.

[0023] In this disclosure, silicon tetrachloride gas is preheated to 100°C-150°C to prevent localized overcooling of the electrolytic aluminum liquid; specifically, it can be preheated to 105°C, 110°C, 115°C, 120°C, 125°C, 130°C, 135°C, 140°C, 145°C, or 150°C; this disclosure is not limited thereto.

[0024] In this disclosure, the density of the generated silica particles is 2.2 g / cm³. 3 The chlorine gas automatically floats to the surface of the molten aluminum to form a slag layer; the chlorine gas reacts with the floating sodium, potassium and calcium metals to generate chlorides, which are enriched in the slag layer; the tail gas after the reaction is condensed and recovered, and the increase in silicon in the molten aluminum is controlled within 10 ppm, and the sodium, potassium and calcium contents are all ≤5 ppm.

[0025] In this disclosure, the slag layer is removed by skimming.

[0026] In this disclosure, the treatment temperature of the electrolytic aluminum liquid is selected from 730℃-750℃, specifically 730℃, 735℃, 740℃, 745℃, or 750℃. The treatment time of the electrolytic aluminum liquid is selected from 5-10 minutes, specifically 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, or 10 minutes; more specifically, the treatment temperature of the electrolytic aluminum liquid is 740℃, and the treatment time is 10 minutes.

[0027] In this disclosure, the oxygen flow rate within the reaction apparatus is precisely regulated by a mass flow controller.

[0028] In this disclosure, the mixed gas discharged from the top of the reaction device is condensed to recover silicon tetrachloride, and the uncondensed gas is absorbed by alkaline solution to remove chlorine. The argon gas is then returned to the reactor for reuse via a circulating pump.

[0029] The present disclosure will be further described below by way of specific embodiments.

[0030] Example 1 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet, slag outlet and oxygen sensor interface at the top, and a gas inlet and liquid outlet at the bottom.

[0031] Argon: Purity ≥ 99.999%, dried by molecular sieve before use; Oxygen: Purity ≥ 99.9%, precisely regulated by mass flow controller (MFC); Oxygen volume fraction: 0.0010% (oxygen partial pressure pO2 = 8 × 10⁻⁶). -7 SiCl4 is stored in a liquid storage tank made of 316L stainless steel, with a built-in molecular sieve desiccant. The SiCl4 is preheated to 125±5℃ using a vaporizer to obtain SiCl4 gas, and the SiCl4 gas flow rate is controlled at approximately 20L / min using a gas flow valve.

[0032] 300 kg of molten aluminum was poured into the insulation bag, sealed, and then evacuated to 10 Pa. An argon-oxygen mixture was then introduced. Heating was started, and the temperature of the molten aluminum was stabilized at 740 ± 2 °C. The bottom gas inlet was opened, and SiCl4 gas was injected through the gas flow valve. After 5 minutes of injection, the injection was stopped, and the mixture was allowed to stand for 5 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0033] The composition of the molten aluminum was determined using ICP-OES: Na was 2.8 ppm, Ca was 1.5 ppm, and Si increased by 3.2 ppm. The slag layer was analyzed using a LECO analyzer, revealing a NaCl + CaCl2 content of approximately 12 wt% and a SiO2 content of approximately 82%.

[0034] Example 2 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet and slag outlet at the top, and a gas inlet and liquid outlet at the bottom.

[0035] Argon: purity ≥99.999%, used after being dried by molecular sieve; SiCl4 is stored in a liquid storage tank made of 316L stainless steel with built-in molecular sieve desiccant; SiCl4 is preheated to 125±5℃ using a vaporizer to obtain SiCl4 gas, and the SiCl4 gas flow rate is controlled to be about 20L / min using a gas flow valve.

[0036] 300 kg of molten aluminum was poured into the insulation bag, sealed, and then evacuated to 10 Pa before being filled with argon gas. Heating was started to stabilize the temperature of the molten aluminum at 740 ± 2 °C. The gas inlet at the bottom was opened, and SiCl4 gas was injected through the gas flow valve. After 5 minutes of injection, the injection was stopped, and the mixture was allowed to stand for 5 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0037] The composition of the molten aluminum was determined by ICP-OES: Na was 66.7 ppm, Ca was 23.5 ppm, and Si increased by 14.2 ppm.

[0038] Example 3 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet, slag outlet and oxygen sensor interface at the top, and a gas inlet and liquid outlet at the bottom.

[0039] Argon: Purity ≥ 99.999%, dried by molecular sieve before use; Oxygen: Purity ≥ 99.9%, precisely regulated by mass flow controller (MFC); Oxygen volume fraction: 0.0010% (oxygen partial pressure pO2 = 8 × 10⁻⁶). -7 SiCl4 is stored in a liquid storage tank made of 316L stainless steel, with a built-in molecular sieve desiccant. The SiCl4 is preheated to 125±5℃ using a vaporizer to obtain SiCl4 gas, and the SiCl4 gas flow rate is controlled at approximately 20L / min using a gas flow valve.

[0040] 300 kg of molten aluminum was poured into the insulation bag, sealed, and then evacuated to 10 Pa. An argon-oxygen mixture was then introduced. Heating was started, and the temperature of the molten aluminum was stabilized at 770 ± 2 °C. The bottom gas inlet was opened, and SiCl4 gas was injected through the gas flow valve. After 5 minutes of injection, the injection was stopped, and the mixture was allowed to stand for 5 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0041] The composition of the molten aluminum was determined using ICP-OES: Na was 4.2 ppm, Ca was 1.9 ppm, and Si increased by 4.0 ppm. The slag layer was analyzed using a LECO analyzer, revealing a NaCl + CaCl2 content of approximately 11 wt% and a SiO2 content of approximately 83%.

[0042] Example 4 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet, slag outlet and oxygen sensor interface at the top, and a gas inlet and liquid outlet at the bottom.

[0043] Argon: Purity ≥ 99.999%, dried by molecular sieve before use; Oxygen: Purity ≥ 99.9%, precisely regulated by mass flow controller (MFC); Oxygen volume fraction: 0.0010% (oxygen partial pressure pO2 = 8 × 10⁻⁶). -7SiCl4 is stored in a liquid storage tank made of 316L stainless steel, with a built-in molecular sieve desiccant. The SiCl4 is preheated to 125±5℃ using a vaporizer to obtain SiCl4 gas, and the SiCl4 gas flow rate is controlled at approximately 20L / min using a gas flow valve.

[0044] 300 kg of molten aluminum was poured into the insulation bag, sealed, and then evacuated to 10 Pa. An argon-oxygen mixture was then introduced. Heating was started, and the temperature of the molten aluminum was stabilized at 710 ± 2 °C. The bottom gas inlet was opened, and SiCl4 gas was injected through the gas flow valve. After 5 minutes of injection, the injection was stopped, and the mixture was allowed to stand for 5 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0045] The composition of the molten aluminum was determined using ICP-OES: Na was 5.4 ppm, Ca was 2.7 ppm, and Si increased by 3.6 ppm. The slag layer was analyzed using a LECO analyzer, revealing a NaCl + CaCl2 content of approximately 11 wt% and a SiO2 content of approximately 83%.

[0046] Comparative Example 1 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet, slag outlet and graphite tube at the top, and a liquid discharge port at the bottom.

[0047] Argon: purity ≥99.999%, dried with molecular sieve before use; carbon tetrachloride is injected into the molten aluminum via a graphite tube using a dripping method. A pumping system is used to maintain a constant flow rate; the dripping volume is controlled at 450g, and the dripping time is controlled at 12 minutes (to prevent burst release). A graphite tube with an inner diameter of 8mm is used, inserted to a depth of 125mm from the bottom of the ladle.

[0048] 300 kg of molten aluminum was injected into the insulation bag, sealed, and evacuated to 10 Pa before being filled with argon gas. Heating was started to stabilize the temperature of the molten aluminum at 740 ± 2 °C. The pumping system was turned on to maintain a constant flow rate. The dripping volume was controlled at 450 g, and the dripping time was controlled at 12 minutes. Carbon tetrachloride was injected through a graphite tube. After 12 minutes, the injection was stopped, and the mixture was allowed to stand for 8 minutes. The slag layer on the surface was then removed by opening the slag port.

[0049] The composition of the molten aluminum was determined by ICP-OES: Na was 12.0 ppm, Ca was 9.5 ppm, and the increase in C was 20.6 ppm.

[0050] Comparative Example 2 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet and slag outlet at the top, and a gas inlet and liquid outlet at the bottom.

[0051] Argon: purity ≥99.999%, used after being dried by molecular sieve; carbon tetrachloride is stored in a liquid storage tank made of 316L stainless steel with built-in molecular sieve desiccant; carbon tetrachloride is preheated to 105±5℃ using a vaporizer to obtain carbon tetrachloride gas, and the flow rate of carbon tetrachloride gas is controlled at about 20L / min using a gas flow valve.

[0052] 300 kg of molten aluminum was poured into the insulation bag, sealed, and then evacuated to 10 Pa before being filled with argon gas. Heating was started to stabilize the temperature of the molten aluminum at 740 ± 2 °C. The gas inlet at the bottom was opened, and carbon tetrachloride gas was injected through the gas flow valve. After 5 minutes of injection, the injection was stopped, and the mixture was allowed to stand for 5 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0053] The composition of the molten aluminum was determined by ICP-OES: Na was 15.4 ppm, Ca was 11.7 ppm, and the increase in C was 14.6 ppm.

[0054] Comparative Example 3 It adopts a 500L sealed insulation bag, lined with silicon nitride refractory material, with a gas outlet and slag outlet at the top, a liquid discharge outlet at the bottom, and a closed screw feeder in the middle.

[0055] Argon: purity ≥99.999%, dried by molecular sieve before use; hexachloroethane is added to the molten aluminum via a closed screw feeder. A pumping system is used to maintain a constant feed rate; the total mass of the material is controlled at 400g, and the feeding time is controlled at 8 minutes (to prevent burst release).

[0056] 300 kg of molten aluminum was injected into the insulation bag, sealed, and then evacuated to 10 Pa before being filled with argon gas. Heating was started to stabilize the temperature of the molten aluminum at 740 ± 2 °C. The pumping system was turned on to maintain a constant feeding rate. The total mass of the material was controlled at 400 g, and the feeding time was controlled at 8 minutes. Hexachloroethane was added to the molten aluminum through a closed screw feeder. After 8 minutes, the injection was stopped, and the mixture was allowed to stand for 6 minutes. The slag layer on the surface was then removed by opening the slag outlet.

[0057] The composition of the molten aluminum was determined by ICP-OES: Na was 9.5 ppm, Ca was 7.3 ppm, and the increase in C was 14.4 ppm.

[0058] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein.

Claims

1. A method for removing alkali metals from electrolytic aluminum liquid, characterized in that, The method includes the following: In a closed reaction apparatus containing molten aluminum, silicon tetrachloride gas is injected into the molten aluminum through a gas inlet located at the bottom of the closed reaction apparatus.

2. The method for removing alkali metals from electrolytic aluminum liquid according to claim 1, characterized in that, The atmosphere inside the sealed reaction device is a slightly oxygenated atmosphere formed by argon and oxygen; the partial pressure of the oxygen is 10. -8 Up to 10 -6 atm; the volume fraction of oxygen is 0.001-0.015% of the integral of argon gas.

3. The method for removing alkali metals from electrolytic aluminum liquid according to claim 1, characterized in that, The atmosphere inside the closed reaction device is a mixture of carbon dioxide and carbon monoxide; the volume ratio of carbon monoxide to carbon dioxide is selected from (75-85):(15-25).

4. The method for removing alkali metals from electrolytic aluminum liquid according to claim 1, characterized in that, The silicon tetrachloride gas is pre-dried and heated, and the purity of the silicon tetrachloride gas is ≥99.9%, and it does not contain organic solvents or water.

5. The method for removing alkali metals from electrolytic aluminum liquid according to claim 1, characterized in that, The sealed reaction device is a sealed insulated bag; the top of the sealed insulated bag is provided with a gas outlet and a slag outlet; the bottom of the sealed insulated bag is provided with a gas inlet and a liquid outlet.

6. The method for removing alkali metals from electrolytic aluminum liquid according to claim 4, characterized in that, The silicon tetrachloride gas is preheated to 100℃-150℃ to prevent localized overcooling of the electrolytic aluminum liquid.

7. The method for removing alkali metals from electrolytic aluminum liquid according to any one of claims 1-6, characterized in that, The treatment temperature of the electrolytic aluminum liquid is selected from 730℃-750℃; the treatment time is selected from 5-10min.

8. The method for removing alkali metals from electrolytic aluminum liquid according to claim 7, characterized in that, The mixed gas discharged from the gas outlet is condensed to recover silicon tetrachloride.