CN109652813B - Method for preparing non-metallurgical-grade aluminum oxide by using electrolytic method - Google Patents
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- CN109652813B CN109652813B CN201811459011.0A CN201811459011A CN109652813B CN 109652813 B CN109652813 B CN 109652813B CN 201811459011 A CN201811459011 A CN 201811459011A CN 109652813 B CN109652813 B CN 109652813B
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Abstract
The invention relates to the technical field of aluminum hydroxide manufacturing, in particular to a method for preparing non-metallurgical-grade aluminum oxide by an electrolytic method, which is characterized in that the caustic ratio of a sodium aluminate solution is reasonably controlled, electrolysis, washing and microwave radiation treatment are combined, so that the content of sodium oxide in the prepared aluminum oxide is greatly reduced to be below 0.1%, the cost is low, the efficiency is high, the purity of an aluminum oxide product is high, the yield is high, a byproduct sodium hydroxide is obtained, and the regeneration and utilization of the sodium hydroxide are realized.
Description
Technical Field
The invention relates to the technical field of aluminum hydroxide manufacturing, in particular to a method for preparing non-metallurgical-grade aluminum oxide by using an electrolytic method.
Background
The low-sodium non-metallurgical-grade aluminum oxide has wide application in the aspects of refractory materials, fine ceramics, electrical appliances, insulating ceramic devices, catalyst carriers and the like, and the sale price of the low-sodium non-metallurgical-grade aluminum oxide is more than 2 times higher than that of the metallurgical-grade aluminum oxide, so that the low-sodium non-metallurgical-grade aluminum oxide is an important means for improving the benefit of various aluminum oxide production enterprises.
The low-sodium alumina is alumina with sodium content less than 0.1%, alumina purity over 99.5% and grain size less than 10 microns. Currently, low sodium alumina is mainly prepared by thermal decomposition of high purity ultra fine aluminum hydroxide. The high-purity superfine aluminium hydroxide is prepared by adding high-purity superfine aluminium hydroxide seed crystal into sodium aluminate solution for decomposition and crystallization by using a seed precipitation method. However, since the aluminum hydroxide seed crystal and the aluminum hydroxide obtained by decomposing the seed crystal from the sodium aluminate solution contain a high sodium oxide content, the sodium oxide content of the seed crystal is increased when the seed crystal is thermally decomposed into aluminum oxide. The reasons for this phenomenon are mainly: sodium ions exist in the aluminum hydroxide crystal lattice to perform isomorphous substitution on hydrogen ions in the hydroxide ion layer, so that the sodium ions cannot be removed by washing. At present, in the production process of alumina by a seed precipitation method, the obtained aluminum hydroxide has phenomena of alkali adhesion, intercrystalline alkali and crystalline alkali, the content of sodium oxide of the aluminum hydroxide respectively reaches 40-50%, 50-60% and 1-3% of the total alkali content of the aluminum hydroxide, and after the aluminum hydroxide is washed, the content of the sodium oxide is difficult to reduce from 0.6% to below 0.1%, and the water consumption for washing is large.
Based on the technical defects, researchers filter the aluminum hydroxide micropowder slurry obtained by the decomposition reaction of the sodium aluminate solution to obtain a filter material; adding the filter material into hot water at the temperature of 70-90 ℃ for neutralization and dispersion to obtain a mixed solution; adding 0.005-0.01 times of penetrant into the mixed solution, fully stirring, reacting for 3 hours, then adding 0.0005-0.005 times of dispersant, fully stirring, reacting for 1 hour, filtering and washing; the temperature of the two reactions is 70-90 ℃, the penetrating agent is one of pyrophosphoric acid, oxalic acid, benzenesulfonic acid, formic acid, dicarboxylic acid, tannic acid, citric acid and tartaric acid, and the dispersing agent is one of nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, hypochlorous acid, perchloric acid and acetic acid. The water consumption for washing the aluminum hydroxide is reduced, and the content of the sodium oxide in the aluminum hydroxide is lower than 0.1 percent, so that the content of the sodium oxide in the aluminum oxide is reduced. The method has simple treatment process flow, but needs to consume a large amount of penetrant, and has higher cost. Some researchers also add mineralizer or organic reagent to react with sodium oxide to generate volatile compounds, and then calcine the volatile compounds to decompose the volatile compounds into aluminum hydroxide, which not only has high production cost, but also easily causes the change of the application performance of the aluminum oxide. Therefore, in view of the current production level of alumina, in order to produce low-sodium high-purity non-metallurgical-grade alumina, unconventional means must be adopted to improve the purity and the granularity of aluminum hydroxide crystals to reach the level of superfine nanometer, so that high-quality aluminum hydroxide can be separated from sodium aluminate solution and obtained by calcination, which inevitably needs to increase the cost and prolong the treatment process.
Disclosure of Invention
In order to solve the technical problems in the prior art, the invention provides a method for preparing non-metallurgical-grade aluminum oxide by an electrolytic method, which aims at the defects, adopts direct current electrolysis of a sodium aluminate solution to obtain a mixture with main components of aluminum hydroxide crystals and part of aluminum hydroxide on an anode and an anode area, and obtains a low-sodium high-purity non-metallurgical-grade aluminum oxide product through washing and microwave radiation treatment.
The method is realized by the following technical scheme:
a method of electrolytically preparing non-metallurgical grade alumina, comprising the steps of:
(1) removing iron and silicon from industrial-grade sodium aluminate leachate to obtain a sodium aluminate solution with iron content less than 0.3g/L and silicon dioxide content less than 0.5 g/L;
(2) injecting the sodium aluminate solution obtained in the step (1) into a direct current electrolytic tank, taking a stainless steel or titanium plate as an anode and a stainless steel plate as a cathode, and arranging a separation net or a screen mesh on a cathode piece and an anode piece to separate a cathode chamber and an anode chamber;
(3) controlling the electrolysis condition to be 3.5-5V of bath pressure and 800A/m of anode current density2The electrolysis temperature is 50-60 ℃, electrolyte is added from the anode chamber, electrolysis residual liquid flows out from an overflow port of the cathode chamber and flows into a storage tank after being collected, and the flow speed is 0.2-0.6m3Controlling the causticity ratio of the electrolysis residual liquid to be 1.5-1.7 and the concentration of sodium hydroxide to be 180-200 g/L;
(4) filtering and collecting the electrolytic sediment, washing the electrolytic sediment by hot water at 60-80 ℃ until the electrolytic sediment contains less than 0.1% of sodium oxide, generating microwave radiation with the frequency of 2-3GHz for 20-30min by adopting the power of a microwave oven of 2-5kW, and controlling the temperature in the microwave oven in the radiation process to be 250-400 ℃.
Preferably, the step (1) further comprises adjusting the caustic ratio of the sodium aluminate solution to be 1.2-1.3, and the concentration of sodium hydroxide to be 140-150 g/L.
Preferably, in the step (2), the anode chamber and the cathode chamber are separated by a plastic screen or a stainless steel screen with the porosity of 0.1-0.5mm, and the same polar distance is 100-150 mm; the top end of the screen is horizontal to the top of the electrolytic cell, the lower part of the screen is 50-150mm away from the bottom of the electrolytic cell, so that the bottom of the cathode chamber and the anode chamber are communicated, and the bottom of the electrolytic cell is provided with a discharge hole valve.
Preferably, each electrolytic tank is provided with more than 10 groups of cathode and anode plates, and each group consists of a cathode plate and an anode plate.
Preferably, in the step (4), the sodium oxide content in the filtrate is washed to be less than 0.1%.
Preferably, when the caustic ratio of the electrolysis raffinate is less than 1.5 and the concentration of sodium hydroxide is less than 180g/L, the electrolysis raffinate electrolytic cell is electrolyzed again.
In the invention, sodium aluminate exists in two forms in caustic solution, namely Na+(AlO2)-、Na+[Al(OH)4]-When α k value (causticity ratio) is high, Na is mainly used+[Al(OH)4]-In the form of Na or vice versa+(AlO2)-Predominantly in the form of, but not exclusively, αkThe value is more or less, the two forms can not be separated completely, when the aluminum hydroxide seed crystal is directly used for the seed precipitation method in the sodium aluminate solution, the Al (OH) is mainly used4 -And (3) decomposing to obtain a large amount of aluminum hydroxide crystals, and introducing carbon dioxide for seed precipitation to obtain aluminum hydroxide seed crystals and then performing seed precipitation to obtain a large amount of aluminum hydroxide crystals. When a large amount of aluminum hydroxide crystals are produced, the caustic ratio of the sodium aluminate solution increases, promoting AlO2 -To Al (OH)4 -And (4) transformation. Therefore, the decomposition of sodium aluminate by the seed precipitation method can only obtain aluminum hydroxide crystals, the seed precipitation time is long, generally more than 20 hours is needed, the seed precipitation rate is only about 50%, and the sodium aluminate is placed in a direct current electric field to generate the following electrochemical reaction: NaAlO2→Na++AlO2 -，NaAl(OH)4→Na++Al(OH)4 -. The sodium ions move to the cathode and react with the cathode of water to obtain hydroxide ions to form ion pairs during discharging, and the obtained sodium hydroxide is regenerated. AlO (aluminum oxide)2 -，Al(OH)4 -Moving to the anode and discharging electricity on the anode, AlO2 -The electrochemical reaction generated by the discharge on the anode is 2AlO2 -→Al2O3+1/2O to obtain alumina crystals. And Al (OH)4 -Discharging to generate electrochemical reaction of Al (OH)4 -→Al(OH)3+OH-，2OH-→H2O + 1/2O. The overall reaction is 2Al (OH)4 -→2Al(OH)3+H2O +1/2 O. α of sodium aluminate solutionkAt smaller values, the main discharge occurring at the anode is AlO2 -α as the alumina crystallizes outkIncreased value of Al (OH)4 -The three decomposition reactions exist in a direct current electric field simultaneously and can not be separated completely, the obtained anode deposition product is a mixture of aluminum oxide and aluminum hydroxide, the former two reactions have a close relation with the pressure of an electrolytic bath and the current density of an anode and are fast reactions, fresh electrolyte is required to be rapidly supplemented, and the ion diffusion speed at a certain temperature is requiredkThe sodium aluminate solution is electrolyzed, the electrolyte is supplemented at the same time, the crystal quantity of the obtained alumina is larger than that of the aluminum hydroxide, the homogeneous isomorphous phenomenon of sodium ions and hydrogen ions in hydroxide radicals and the phenomenon of intercrystalline alkali and crystalline alkali do not exist in the alumina crystal, only the phenomenon of alkali adsorption exists, and the sodium ion content in the product can be reduced to be below 0.1 percent as long as sufficient hot water washing is carried out.
And the mixture of the aluminum oxide and the aluminum hydroxide obtained by electrolysis is fully washed and dealkalized, and then calcined by adopting a microwave radiation technology, so that the aluminum hydroxide in the mixture is decomposed into the aluminum oxide and water, and the aluminum hydroxide is more easily penetrated into a material layer and aluminum hydroxide crystal molecules because the high microwave and low frequency microwave radiation absorption penetrating power of the aluminum hydroxide is greater than that of high frequency microwave radiation, and the aluminum hydroxide is simultaneously decomposed into the aluminum oxide from the inside and the outside of the material, so that the decomposition temperature is low, the speed is high, the decomposition is thorough, and other chemical components are not brought in, and the obtained aluminum oxide is fine in granularity, low in agglomeration rate and high in purity.
In conclusion, the invention reasonably controls the caustic ratio of the sodium aluminate solution, combines electrolysis, washing and microwave radiation treatment, greatly reduces the content of sodium oxide in the prepared alumina to be below 0.1 percent, has lower cost and high efficiency, has higher purity and yield of the alumina product, obtains the byproduct sodium hydroxide, and realizes the recycling of the sodium hydroxide.
Detailed Description
The technical solution of the present invention is further defined below with reference to the specific embodiments, but the scope of the claims is not limited to the description.
The specific implementation mode of the invention is that industrial sodium aluminate is placed in an electrolytic bath, a stainless steel or titanium plate is used as an anode, the same stainless steel plate is used as a cathode, a plastic screen or a stainless steel screen with the porosity of 0.1-0.5mm is arranged between the anode and the cathode to separate the anode chamber and the cathode chamber, continuous direct current electrolysis is carried out by controlling certain electrolytic bath pressure, anode current density, electrolysis temperature and electrolyte circulation speed to obtain a mixture of aluminum oxide and aluminum hydroxide, the mixture is washed by hot water until the content of sodium ions is less than 0.1 percent, and then microwave treatment is carried out, thus obtaining a high-quality non-metallurgical aluminum oxide grade product.
Example 1
After iron removal by sodium sulfide and desilication by calcium oxide, industrial sodium aluminate produced by a certain enterprise contains 105mg/L of iron and 350mg/L of silicon dioxide, and is prepared to caustic ratio by using industrial alumina or aluminum hydroxide (α)k) 1.2, the concentration of caustic soda (sodium hydroxide) is 140g/L, then the mixture is added into an electrolytic tank, a 316 stainless steel plate is used as a cathode and an anode simultaneously, the homopolar distance is 120mm, a plastic screen with the porosity of 0.2mm is used for separating an anode chamber and a cathode chamber, the upper parts of the two chambers are horizontal to the top of the electrolytic tank, and the lower parts of the two chambers are 100mm away from the bottom of the electrolytic tank. The bottom of the electrolytic tank is provided with a stainless steel valve with the diameter of 60mm for discharging sediments, and the electrolytic tank is internally provided with a cathode and anode 12 group (12 anodes and 13 cathodes). The electrolytic bath voltage is controlled to be 4V, and the anode current density is 400A/m2The electrolysis temperature is 50-55 ℃, electrolyte is added from the anode chamber and naturally flows out from an overflow port of the cathode chamber, flows into an electrolysis residual liquid storage tank after being converged in a chute,the flow rate of the electrolyte is 400L/h, and the electrolytic sediment (suspension slurry) is sucked from the bottom of the electrolytic tank by a vacuum suction pipe every 10 hours and filtered, the filtered substance is washed by hot water at 70 ℃ until the content of sodium oxide in the solid is less than 0.1 percent, and the washing water is recycled until the content of sodium hydroxide reaches more than 10g/L, and the sodium hydroxide returns to the α which is used for matching alkali to leach the bauxite or is used for adjusting the electrolytekValue of electrolysis raffinate αkThe value was 1.56, caustic concentration (sodium hydroxide) 188 g/L.
The hot water washings are placed in 3 microwave ovens connected in series, the microwave radiation frequency is controlled to be 2.4GHz, the total power is 6kW, the temperature in the ovens is 250 ℃, and the radiation time is 25 minutes.
Sampling and detecting for 5 times, and taking an average value to detect that the alumina product contains 99.7 percent of alumina, 0.02 percent of aluminum hydroxide, 0.08 percent of iron, 0.16 percent of silicon dioxide, 0.03 percent of sodium oxide, 5.2 microns of alumina granularity and 72 percent of alumina yield (alumina in alumina/alumina in sodium aluminate x 100 percent).
Example 2
After iron removal and desilication of sodium aluminate of a certain enterprise, the α k value of the sodium aluminate is 1.25, the caustic soda concentration is 150g/L, electrolysis is carried out by using the electrolytic cell of the embodiment 1, the electrolytic condition is controlled to 4.5V of cell pressure, the anode current density is 700A/m2, the electrolytic temperature is 60 ℃, the electrolyte flow rate is 500L/h, electrolytic sediments are extracted every 8 hours and filtered, the electrolytic sediments are washed by hot water at 80 ℃ and then placed in a single microwave oven for microwave radiation treatment, the microwave radiation frequency is controlled to be 3GHz, the power is 0.8-2kW, the temperature in the oven is 300 ℃, the radiation time is 30 minutes, and an alumina powder product is obtained.
Sampling and detecting for 5 times, and averaging to obtain the detection results of the alumina particle size of 2.3 microns, the purity of 99.85 percent, the sodium oxide content of 0.053 percent and the electrolysis residual liquid αkThe value is 1.7, the caustic soda concentration is 205g/L, and the yield of the alumina product is 78.5 percent.
Example 3
The iron-removing and desiliconized sodium aluminate solutions of example 1 and example 2 were produced by the seed precipitation method, respectively, and the obtained aluminum hydroxide crystals were washed with hot water at 80 ℃ in an amount of 1.5 to 3 times the mass of example 1 or example 2. Then calcining the mixture in an electric heating furnace at the temperature of between 250 and 300 ℃ for 2 to 3 hours. Sampling, testing and detecting for 5 times respectively, and displaying the result: the purity of the product is 94.5-95.2% of alumina, 4.3-5.5% of aluminum hydroxide, 0.65-0.92% of sodium oxide, the particle size is 50-85 microns, agglomeration phenomenon occurs, and the yield of alumina is 52.3%.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (5)
1. A method of electrolytically preparing non-metallurgical grade alumina, comprising the steps of:
(1) removing iron and silicon from industrial-grade sodium aluminate leachate to obtain a sodium aluminate solution with iron content less than 0.3g/L and silicon dioxide content less than 0.5 g/L;
(2) injecting the sodium aluminate solution obtained in the step (1) into a direct current electrolytic tank, taking a stainless steel or titanium plate as an anode and a stainless steel plate as a cathode, and arranging a separation net or a screen mesh between the anode and the cathode to separate a cathode chamber and an anode chamber;
(3) controlling the electrolysis condition to be 3.5-5V of bath pressure and 800A/m of anode current density2The electrolysis temperature is 50-60 ℃, electrolyte is added from the anode chamber, electrolysis residual liquid flows out from an overflow port of the cathode chamber and flows into a storage tank after being collected, and the flow speed is 0.2-0.6m3Controlling the causticity ratio of the electrolysis residual liquid to be 1.5-1.7 and the concentration of sodium hydroxide to be 180-200 g/L;
(4) filtering and collecting the electrolytic sediment, washing the electrolytic sediment by hot water at 60-80 ℃ until the electrolytic sediment contains less than 0.1% of sodium oxide, generating microwave radiation with the frequency of 2-3GHz for 20-30min by adopting the power of a microwave oven of 2-5kW, and controlling the temperature in the microwave oven in the radiation process to be 250-400 ℃.
2. The method of claim 1, wherein step (1) further comprises adjusting the caustic ratio of the sodium aluminate solution to 1.2-1.3 and the sodium hydroxide concentration to 150 g/L.
3. The process for the preparation of non-metallurgical alumina by electrolysis according to claim 1 wherein in step (2), the anode and cathode compartments are separated by a plastic or stainless steel mesh having a porosity of 0.1-0.5mm, and the homopolar distance is 100-150 mm; the top end of the screen is horizontal to the top of the electrolytic cell, the lower part of the screen is 50-150mm away from the bottom of the electrolytic cell, so that the bottom of the cathode chamber and the anode chamber are communicated, and the bottom of the electrolytic cell is provided with a discharge hole valve.
4. A process for the electrolytic production of non-metallurgical grade alumina as claimed in claim 1 or claim 3 in which the cells are each provided with more than 10 sets of cathode and anode plates, each set consisting of a cathode plate and an anode plate.
5. The process for the electrolytic production of non-metallurgical grade aluminum oxide according to claim 1 wherein the caustic ratio of the raffinate is < 1.5 and the sodium hydroxide concentration is < 180g/L, the raffinate is fed to the cell for re-electrolysis.
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| CN1792801A (en) * | 2006-01-10 | 2006-06-28 | 中国铝业股份有限公司 | Process for producing aluminium hydroxide |
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