CN114455618B - Method for preparing low-sodium low-iron superfine alpha-alumina and large-pore-volume pseudo-boehmite - Google Patents
Method for preparing low-sodium low-iron superfine alpha-alumina and large-pore-volume pseudo-boehmite Download PDFInfo
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Abstract
The invention provides a method for preparing low-sodium low-iron superfine alpha-alumina and large-pore-volume pseudo-boehmite, which comprises the steps of leaching, purifying and deironing, neutralizing and the likeStep (a) to obtain alpha-Al 2 O 3 Product, fe 2 O 3 Not higher than 0.016wt% of Na 2 O content not higher than 0.032wt%, particle size (D50) not greater than 2 μm. Wherein the sodium content is far lower than that of Na in low-sodium alumina 2 O content not higher than 0.2wt% (YS/T89-2011 calcined alpha alumina). The specific surface area of the pseudo-boehmite product obtained by the invention is higher than 350m 2 Per gram, the pore volume is more than 1.2 ml/gram, the pore diameter is more than 8nm 2 O 3 Not more than 0.01wt% of Na 2 The content of O is not higher than 0.02wt percent, and the content of O and O is far lower than that of pseudo-boehmite Fe on the market at present 2 O 3 0.03-0.05 wt% of Na 2 The content of O is 0.1-0.3 wt%. The invention selects the circulating fluidized bed fly ash with high activity as the raw material, the cost of the raw material is low, and the process is simple; the method has the advantages of direct iron removal in an acid system, less washing water, simple operation steps, good iron removal effect and low iron content and sodium content in the product.
Description
Technical Field
The invention relates to a method for preparing alumina and pseudo-boehmite, in particular to a method for preparing low-sodium low-iron superfine alpha-alumina and large-pore-volume pseudo-boehmite by using circulating fluidized bed fly ash.
Background
Low-sodium superfine alpha-alumina refers to Na 2 alpha-Al with O content less than 0.2% and D50 particle size less than or equal to 2 mu m 2 O 3 . The superfine low-sodium alumina can be used for manufacturing cutters, toughening precise alumina ceramics, various products produced by a mirror polishing isostatic pressing method and has wide application prospect. Low-sodium alumina is usually produced by using aluminum hydroxide or alumina obtained by an alkaline process (sintering process or Bayer process) as a raw material, adding aluminum fluoride, boric acid, fluorite, etc., and then subjecting the mixture to high-temperature calcination to obtain Na 2 O volatilization removing method. The production process is complicated, the use of additives and high temperature increases the production cost, and more importantly, the high temperature calcination easily causes hard agglomeration of powder, and the product has larger particles although the powder is obtainedThe particle size can be reduced by mechanical crushing, but the particle size distribution is wide, and the low-sodium superfine alumina product with uniform size is difficult to obtain.
Pseudo boehmite (γ -AlOOH. NH2O, n =0.08 to 0.62), also called colloidal boehmite or pseudo boehmite, has a crystal phase structure similar to that of boehmite, but has an incomplete crystal. The pseudoboehmite has the characteristics of large pore volume, high specific surface area, good peptization performance and the like, can be used as a catalyst carrier, a catalyst, a ceramic base material and the like to be widely applied to the petrochemical industry, and can also be used for preparing gamma-Al 2 O 3 And an important precursor of a series of products, namely alumina. Pseudoboehmite as a catalyst support generally needs to have a large pore volume, a large specific surface area, a low sodium content, and a suitable pore size distribution. The existing production methods of pseudo-boehmite can be roughly divided into two types, namely an organic aluminum alkoxide method and an acid-base neutralization method, and the production of the macroporous pseudo-boehmite is realized by controlling reaction conditions or adding a surfactant, a pore-expanding agent and the like on the basis of the methods. The prior art utilizes an aluminum alkoxide method, and a surfactant is added to obtain the specific surface area of 270m 2 The pseudo-boehmite with the pore volume of more than 1.3ml/g has the problems of high cost, complex production process, easy explosion and the like. The acid-base neutralization method can be classified into an alkaline method and an acid method. The alkaline process is to introduce carbon dioxide (or add hydrochloric acid, nitric acid, ammonium bicarbonate, sodium bicarbonate and other acids) into the sodium aluminate solution prepared by Bayer process or sintering process, and react under proper conditions to obtain pseudo-boehmite. The alkaline process is mature, but the sodium aluminate solution contains high sodium ions, the specific surface area of the pseudo-boehmite is large and porous, so that the sodium content in the product is high, the washing process is complex, the washing water amount is large, the washing water amount per ton of the pseudo-boehmite can reach 100 tons, the sodium content in the washing mother solution is low, and the recycling is difficult. The acid process is a process of neutralizing an aluminum salt (e.g., aluminum sulfate, aluminum nitrate) solution with a base to precipitate hydrated alumina. Compared with the alcohol aluminum method and the alkali method, the acid method has the advantages that the material consumption cost is low, sodium ions are not introduced, the washing procedure is simplified, but the method is very complex and difficult to control through intermediate formation and crystal transformation processes. And due to metals such as ironThe ions are very soluble in the acid, which introduces high levels of iron impurities. Therefore, it is necessary to find a technical route which can obtain the macroporous pseudoboehmite and ensure low impurity content on the premise of lower cost.
The fly ash is waste discharged from coal-fired power plants, wherein the alumina in the fly ash of the circulating fluidized bed has good activity and can be used as a raw material for producing alumina and pseudo-boehmite. In the method for preparing alumina by using fly ash as a raw material, an alkaline process is mainly adopted. The alkaline process introduces excessive alkali in the production process, so that the washing procedure is complicated, the production cost is increased, and the strengthened washing can only reduce the impurity content of sodium oxide to a limited extent. In another acid method, although the introduction of sodium oxide impurities can be avoided, higher iron impurities are brought in, and the color and the performance of the polymer product are adversely affected. In order to remove iron impurities from the acid solution, further treatment is usually carried out by an alkaline process. The process is long, and sodium ions are introduced in the process of adding alkali to remove iron. In the prior art, the method for preparing pseudo-boehmite by utilizing fly ash comprises the steps of mixing the fly ash with Na 2 CO 3 Roasting, leaching with hydrochloric acid to obtain coarse AlCl 3 A solution; mixing coarse AlCl 3 Neutralizing the solution to obtain aluminum hydroxide precipitate, filtering to remove iron, and adding sodium hydroxide to prepare a purified sodium metaaluminate solution; adding NaHCO 3 Neutralization of the solution to pH =9-11 yielded pseudoboehmite Dan Chengpin. The process route adopted by the method is alkali (Na) 2 CO 3 ) Acid (hydrochloric acid), base (sodium hydroxide) and weak acid (NaHCO) 3 ) The method has the advantages of complex process route, more raw material consumption, large amount of sodium ions introduced in the preparation process and large washing water amount. In the prior art, the fly ash is subjected to acid leaching, impurity removal and other processes to obtain crystalline aluminum chloride, the aluminum chloride is calcined to obtain activated alumina, and finally the activated alumina is mixed with water to perform hydrothermal reaction to obtain pseudo-boehmite. The method also has the problems of complex process route, high energy consumption and increased cost.
The invention aims to solve the problem of how to prepare a high-quality superfine nano alumina product with low sodium and low iron and a pseudo-boehmite product with large pore volume by using fly ash, particularly circulating fluidized bed fly ash as a raw material through a simple process method, and can obtain an ammonium chloride product simultaneously.
Disclosure of Invention
In order to solve the technical problems, the invention provides a method for preparing low-sodium low-iron superfine alpha-alumina and large-pore volume pseudo-boehmite, which comprises the following steps:
a) Leaching: under a closed condition, the fly ash of the circulating fluidized bed is leached by hydrochloric acid with the concentration of 20 to 37 weight percent, and the following reaction is carried out on alumina and hydrochloric acid: al (Al) 2 O 3 +6HCl→2AlCl 3 +3H 2 O, adding 50-80% of hydrochloric acid according to the concentration of the hydrochloric acid and the content of alumina in the circulating fluidized bed fly ash, so that the obtained leaching solution only contains a small amount of free acid, has no volatility, and has small environmental pollution and small corrosion to equipment; controlling the pH value of the leaching solution to be 2.0-3.0, preferably 2.0-2.5, leaching at 150-250 ℃ by using autogenous pressure for 1.5-5 hours, wherein the leaching rate of alumina in the fly ash is higher than 85%; settling, filtering and washing the reacted slurry to obtain leaching solution; the leaching solution contains iron impurities, most of which are Fe 2+ Is present in a minor part as Fe 3+ When Fe is present in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L;
b) Purifying and deironing: keeping the temperature of the leaching solution at 60-90 ℃, introducing oxygen-enriched gas into the leaching solution while stirring, controlling the gas flow to keep Fe in the leaching solution 3+ Concentration is always lower than 1g/L, fe 2+ Gradual oxidation to Fe 3+ ，Fe 3+ FeO (OH) is formed according to the following reaction: fe 3+ +2H 2 O→FeO(OH)+3H + The FeO (OH) forms a precipitate at the pH value of more than 2.0, the pH value of the precipitate formed by the aluminum hydroxide is 3.7, the leaching solution is purified according to the difference of the pH values of the precipitates formed by the FeO and the aluminum hydroxide, and the formed precipitate is aged at the temperature of between 50 and 85 ℃ for 5 to 15 hours and then filtered to obtain a refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, and neutralizing the refined aluminum chloride solution by using an ammonium-containing alkali liquor until the pH value of the solution is 5.5-7.5 to obtain colloidal precipitate;
d) Preparation of alpha-alumina: aging the mixed solution obtained in the step c) for 1 to 24 hours at the temperature of between 10 and 55 ℃, settling, filtering, washing, pulping, and spray-drying at the temperature of between 160 and 230 ℃ to obtain powder; calcining the powder at 1200-1500 ℃ for 1-4 hours to obtain a low-sodium low-iron superfine alpha-alumina product;
e) Preparing pseudo-boehmite: adding a pore-expanding agent aqueous solution with the concentration of 0.5-10 wt% into the mixed solution obtained in the step c), wherein the addition amount of the pore-expanding agent aqueous solution is 1-5% of the volume of the mixed solution, adjusting the aperture and the specific surface area of the colloidal precipitate, and aging for 5-24 hours at the temperature of 10-55 ℃; after settling, filtering, washing and pulping, carrying out spray drying at 160-230 ℃ to obtain macroporous pseudo-boehmite powder;
f) Preparing ammonium chloride: the filtrate obtained by filtration in step d) and step e) contains mainly NH 4 + And Cl - And further contains a small amount of Al 3+ Crystallizing and purifying the filtrate to obtain ammonium chloride product, and the mother liquid contains small amount of Al 3+ 、NH 4 + And Cl - And c), adding hydrochloric acid according to the concentration and the dosage of the hydrochloric acid required in leaching, and returning to the step a) for recycling.
Further, in the step a), the circulating fluidized bed fly ash is subjected to magnetic separation for pre-removing iron before being leached by hydrochloric acid, so that the iron content in the fly ash is reduced to below 1.0 wt%; preferably, wet magnetic separation is adopted for removing iron: pulverizing fly ash to below 100 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation to remove iron so as to reduce the iron content in the fly ash to below 1.0wt%, and filtering to obtain a filter cake.
Further, in the step a), the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution.
Further, in the step b), the oxygen-enriched gas is one of air, oxygen-enriched air or oxygen, and the aeration speed is 3-5 m 3 /h。
Further, in the step c), adding an ammonium-containing alkali liquor into the refined aluminum chloride solution during neutralization, or mixing the ammonium-containing alkali liquor and the refined aluminum chloride solution in a concurrent flow manner; in order to keep the pH constant, the refined aluminum chloride solution and the ammonium-containing lye are preferably mixed in cocurrent.
The ammonium-containing alkali liquor is one of ammonium carbonate aqueous solution, ammonium bicarbonate aqueous solution or ammonia water, and the concentration is NH in the solution 4 + The concentration of the ions is 1 to 12mol/L.
Further, in step e), the pore-expanding agent is one or more of ammonium carbonate, ammonium bicarbonate, ammonium chloride, polyethylene glycol or urea.
Further, in step f), the crystallization method is a cold precipitation, salting out or evaporation concentration method, and in order to prevent introduction of new impurities, the crystallization is preferably performed by a cold precipitation and evaporation concentration method.
The invention has the beneficial effects that:
compared with the prior art, the invention selects the circulating fluidized bed fly ash with high activity as the raw material, has low cost and easy acquisition of the raw material, adopts the methods of direct acid dissolution, ammonia water addition neutralization and calcination to obtain the superfine alpha-alumina product and the pseudo-boehmite product, and has simple process; because no alkali is added, the introduction of sodium oxide impurities is avoided, the washing procedure is simplified, the washing water quantity is small, the iron is directly removed in an acid system, compared with the prior art of removing iron by an alkali method, the operation steps are simple, the iron removing effect is good, and the iron content and the sodium content in the product are lower. alpha-Al obtained by the invention 2 O 3 Fe in the product 2 O 3 Not higher than 0.016wt% of Na 2 O content not higher than 0.032wt%, particle size (D50) not greater than 2 μm. Wherein the sodium content is far lower than that of Na in low-sodium alumina 2 A standard (YS/T89-2011 calcined alpha alumina) in which the O content is not higher than 0.2 wt%. The specific surface area of the pseudo-boehmite product obtained by the invention is higher than 350m 2 Per g, the pore volume is more than 1.2ml/g, the pore diameter is more than 8nm 2 O 3 Not more than 0.01wt% of Na 2 The content of O is not higher than 0.02wt percent, and the content of O and O is far lower than that of pseudo-boehmite on the market at presentStone Fe 2 O 3 0.03-0.05 wt% of Na 2 The content of O is 0.1-0.3 wt%.
Drawings
FIG. 1 is a schematic overall flow diagram of the present invention;
FIG. 2 is a schematic flow chart of examples 2 to 4 of the present invention;
FIG. 3 is a schematic flow chart of examples 5 to 7 of the present invention.
Detailed Description
The present invention is further illustrated by the following examples, but the content of the present invention is not limited to the contents of the examples.
The raw material adopts circulating fluidized bed fly ash produced by a certain thermal power plant, and the chemical components of the circulating fluidized bed fly ash are shown in table 1.
TABLE 1 circulating fluidized bed fly ash chemical composition (wt%)
| SiO 2 | Al 2 O 3 | TiO 2 | CaO | MgO | TFe 2 O 3 | FeO | K 2 O | Na 2 O | LOS | SO 3 | Sum of |
| 34.70 | 46.28 | 1.48 | 3.61 | 0.21 | 1.54 | 0.22 | 0.39 | 0.17 | 7.17 | 1.32 | 95.77 |
Example 1:
the embodiment provides a method for preparing low-sodium low-iron superfine alpha-alumina and large-pore volume pseudo-boehmite, which comprises the following steps:
a) Leaching: pulverizing fly ash of a circulating fluidized bed to 200 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation and deironing by using a vertical ring magnetic separator to reduce the iron content in the fly ash to 0.8wt%, and filtering to obtain a filter cake; putting the fly ash filter cake into an acid-resistant reaction kettle, and under a closed condition, according to the solid-liquid ratio of the fly ash to hydrochloric acid of the circulating fluidized bed being 1Kg:3.18Kg (corresponding to 80% of theory) of industrial hydrochloric acid with a concentration of 25% by weight are added and the leaching is carried out at 250 ℃ and with autogenous pressure for 1.5 hours; settling the reacted slurry, performing pressure filtration by using a plate and basket filter press, and washing to obtain leaching solution with the pH value of 2.5; when Fe is in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L; the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution;
b) Purifying and deironing: heat exchanging the leaching solution, cooling to 80 deg.C, introducing oxygen into the leaching solution under stirring at a speed of 3m 3 H, keeping Fe in the leaching solution 3+ The concentration is always lower than 1g/L, precipitates formed after 2 hours are aged for 10 hours at 75 ℃ and then filtered, and refined aluminum chloride solution is obtained;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, and mixing the refined aluminum chloride solution and an ammonium bicarbonate solution with the concentration of 5mol/L in a parallel flow manner until the pH value of the solution is 5.8 to obtain colloidal precipitate;
d) Preparation of alpha-alumina: aging the mixed solution obtained in the step c) for 1 hour at 45 ℃, filtering and washing the aged mixed solution by using a plate-and-frame filter press, pulping the mixed solution, and performing spray drying at 180 ℃ to obtain powder; calcining the powder at 1300 ℃ for 1.5 hours to obtain a low-sodium low-iron superfine alpha-alumina product, and determining Fe in the alpha-alumina product 2 O 3 0.012wt% of Na 2 O content of 0.026wt%, particle diameter (D50) of 1.2 μm;
e) Preparing pseudo-boehmite: adding 1wt% polyethylene glycol (molecular weight 4000) solution into the mixed solution of the step c), wherein the addition amount is 2% of the volume of the solution, aging at 45 ℃ for 7 hours, filtering and washing by using a plate-and-frame filter press, pulping, and then performing spray drying at 180 ℃ to obtain pseudo-boehmite powder; the specific surface area of the product is 364m 2 (ii)/g, pore volume of 1.28ml/g, pore diameter of 9nm 2 O 3 0.01wt% of Na 2 The O content is 0.018wt%;
f) Preparing ammonium chloride: the filtrate obtained by filtration in step d) and step e) contains mainly NH 4+ Ions and Cl + Ions, and further contains a small amount of Al 3+ Crystallizing and purifying the filtrate to obtain ammonium chloride product, and the mother liquid contains small amount of Al 3+ 、NH 4+ And Cl + And c), adding hydrochloric acid according to the concentration and the dosage of the hydrochloric acid required in leaching, and returning to the step a) for recycling.
Example 2
The embodiment provides a method for preparing low-sodium low-iron superfine alpha-alumina, which comprises the following steps:
a) Leaching: pulverizing fly ash of a circulating fluidized bed to 200 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation and deironing by using a vertical ring magnetic separator to reduce the iron content in the fly ash to 0.8wt%, and filtering to obtain a filter cake; putting the fly ash filter cake into an acid-resistant reaction kettle, and under a closed condition, according to the solid-liquid ratio of 1Kg of fly ash to hydrochloric acid of a circulating fluidized bed: 3.16Kg (corresponding to 70% of theory) of industrial hydrochloric acid with a concentration of 22% by weight are added and the leaching is carried out at 200 ℃ and with autogenous pressure for 2 hours; settling the slurry after the reaction, performing pressure filtration by using a plate and basket filter press, and washing to obtain an extract with the pH value of 2.3; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L, and the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution;
b) Purifying and deironing: cooling the leaching solution to 90 deg.C by heat exchange, introducing oxygen-enriched gas with oxygen content of 70% into the leaching solution under stirring at a speed of 5m 3 H, keeping Fe in the leaching solution 3+ The concentration is always lower than 1g/L, and precipitates formed after 1.5 hours are aged for 5 hours at 82 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, adding ammonia water with the concentration of 10mol/L under strong stirring until the pH value of the solution is 6.2, and obtaining colloidal precipitate;
d) Preparation of alpha-alumina: aging at 45 deg.C for 1 hr, filtering with plate-and-frame filter press, washing, pulping, and spray drying at 180 deg.C to obtain powder; calcining the powder at 1200 ℃ for 3 hours to obtain a low-sodium low-iron superfine alpha-alumina product, and determining Fe in the alpha-alumina product 2 O 3 0.01wt% of Na 2 The O content was 0.021wt%, and the particle diameter (D50) was 0.8. Mu.m.
And c, inputting the filtrate after solid-liquid separation into a cold separation crystallizer, carrying out cold separation at 10 ℃, carrying out centrifugal separation to obtain an ammonium chloride product, adding hydrochloric acid into the crystallization mother liquor according to the concentration and the dosage of the hydrochloric acid required in leaching, and returning to the step a) for recycling.
Example 3
The embodiment provides a method for preparing low-sodium low-iron superfine alpha-alumina, which comprises the following steps:
a) Leaching: same as example 2, step a);
b) Purifying and deironing: the same step b) as in example 2 was carried out to obtain a refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, and mixing the refined aluminum chloride solution and an ammonium carbonate solution with the concentration of 2mol/L in a parallel flow manner until the pH value of the solution is 6.0 to obtain colloidal precipitate;
d) Preparation of alpha-alumina: aging at 45 deg.C for 4 hr, filtering with plate-and-frame filter press, washing, pulping, and spray drying at 180 deg.C to obtain powder; calcining the powder at 1400 ℃ for 2.5 hours to obtain a low-sodium low-iron superfine alpha-alumina product, and determining that the Fe in the alpha-alumina product 2 O 3 0.015wt% of Na 2 O content was 0.027wt%, particle diameter (D50) was 0.8. Mu.m.
And (4) inputting the filtrate after solid-liquid separation into a triple-effect evaporator for concentration and crystallization, and performing centrifugal separation to obtain an ammonium chloride product.
Example 4
The embodiment provides a method for preparing low-sodium low-iron superfine alpha-alumina, which comprises the following steps:
a) Leaching: the procedure is as in step a) of example 2;
b) Purifying and deironing: the procedure is the same as in step b) of example 2 to obtain a refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, adding an ammonium bicarbonate solution with the concentration of 10mol/L under strong stirring until the pH value of the solution is-5.5, and obtaining colloidal precipitate;
d) Preparation of alpha-alumina: aging at 40 deg.C for 8 hr, filtering with plate-and-frame filter press, washing, pulping, and spray drying at 180 deg.C to obtain powder; calcining the powder at 1200 ℃ for 3 hours to obtain a low-sodium low-iron superfine alpha-alumina productMeasured as Fe in the alpha-alumina product 2 O 3 0.008wt% of Na 2 O content was 0.018wt%, and particle diameter (D50) was 0.8. Mu.m.
And (4) inputting the filtrate after solid-liquid separation into a triple-effect evaporator for concentration and crystallization, and performing centrifugal separation to obtain an ammonium chloride product.
Example 5
The embodiment provides a method for preparing low-sodium low-iron large-pore-volume pseudo-boehmite, which comprises the following steps of:
a) Leaching: pulverizing fly ash of a circulating fluidized bed to 200 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation and deironing by using a vertical ring magnetic separator to reduce the iron content in the fly ash to 0.8wt%, and filtering to obtain a filter cake; putting the fly ash filter cake into an acid-resistant reaction kettle, and under a closed condition, according to the solid-liquid ratio of the fly ash to hydrochloric acid of the circulating fluidized bed being 1Kg:3.16Kg (corresponding to 70% of theory) of industrial hydrochloric acid with a concentration of 22% by weight are added and the leaching is carried out at 180 ℃ and under autogenous pressure for 1.5 hours; settling the reacted slurry, performing pressure filtration by using a plate and basket filter press, and washing to obtain leaching solution with the pH value of 2.3; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L, and the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution;
b) Purifying and removing iron: heat exchanging the leaching solution, cooling to 90 deg.C, introducing oxygen-enriched air with oxygen content of 70% into the leaching solution under stirring at a speed of 5m 3 H, keeping Fe in the leaching solution 3+ The concentration is always lower than 1g/L, and precipitates formed after 2.5 hours are aged for 10 hours at 80 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, adding ammonia water with the concentration of 10mol/L under strong stirring till the pH value of the solution is 6.5, and obtaining colloidal precipitate;
d) Preparing pseudo-boehmite: adding 1wt% ammonium bicarbonate in an amount of 3% of the volume of the solution, aging at 45 deg.C for 5 hr, and passing through a plate frameFiltering and washing by a filter press, pulping, and then spray-drying at 180 ℃ to obtain pseudo-boehmite powder; the specific surface area of the product is determined to be 382m 2 (ii)/g, pore volume of 1.31ml/g, pore diameter of 10nm 2 O 3 0.008wt% of Na 2 The O content was 0.017wt%.
And c, inputting the filtrate after solid-liquid separation into a cold separation crystallizer, carrying out cold separation at 10 ℃, carrying out centrifugal separation to obtain an ammonium chloride product, adding hydrochloric acid into the crystallization mother liquor according to the concentration and the dosage of the hydrochloric acid required in leaching, and returning to the step a) for recycling.
Example 6
The embodiment provides a method for preparing low-sodium low-iron large-pore-volume pseudo-boehmite, which comprises the following steps of:
a) Leaching: pulverizing fly ash of a circulating fluidized bed to 200 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation and deironing by using a vertical ring magnetic separator to reduce the iron content in the fly ash to 0.8wt%, and filtering to obtain a filter cake; putting the fly ash filter cake into an acid-resistant reaction kettle, and under a closed condition, according to the solid-liquid ratio of the fly ash to hydrochloric acid of the circulating fluidized bed being 1Kg:3.18Kg (corresponding to 80% of theory) of industrial hydrochloric acid with a concentration of 25% by weight are added and the leaching is carried out at 250 ℃ and with autogenous pressure for 1.5 hours; settling the slurry after the reaction, performing pressure filtration by using a plate and basket filter press, and washing to obtain an extract with the pH value of 2.5; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L;
b) Purifying and deironing: cooling the leaching solution to 80 deg.C by heat exchange, introducing oxygen into the leaching solution under stirring at a speed of 3m 3 H, keeping Fe in the leaching solution 3+ The concentration is always lower than 1g/L, precipitates formed after 2 hours are aged for 10 hours at 75 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, and mixing the refined aluminum chloride solution and an ammonium bicarbonate solution with the concentration of 5mol/L in a parallel flow manner until the pH value of the solution is 7.2 to obtain colloidal precipitate;
d) Preparing pseudo-boehmite: then adding 2wt% of ureaAdding 3% of the solution by volume, aging at 50 deg.C for 5 hr, filtering with plate-and-frame filter press, washing, pulping, and spray drying at 180 deg.C to obtain pseudoboehmite powder; the specific surface area of the product is determined to be 375m 2 (ii)/g, pore volume of 1.26ml/g, pore diameter of 10nm 2 O 3 0.008wt% of Na 2 The O content was 0.017wt%.
And (3) inputting the filtrate after solid-liquid separation into a cold separation crystallizer, carrying out cold separation at 10 ℃, carrying out centrifugal separation to obtain ammonium chloride, and feeding the mother solution after the cold separation into a triple-effect evaporator to carry out evaporation, concentration and crystallization to obtain an ammonium chloride product.
Example 7
The embodiment provides a method for preparing low-sodium low-iron large-pore-volume pseudo-boehmite, which comprises the following steps of:
a) Leaching: the procedure is as in step a) of example 5;
b) Purifying and removing iron: the procedure is the same as in step b) of example 5 to obtain a refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, adding an ammonium bicarbonate solution with the concentration of 10mol/L under strong stirring until the pH value of the solution is 5.5, and obtaining colloidal precipitate;
d) Preparing pseudo-boehmite: adding 2wt% ammonium chloride solution, aging at 30 deg.C for 8 hr, filtering with plate-and-frame filter press, washing, pulping, and spray drying at 180 deg.C to obtain pseudo-boehmite powder; the specific surface area of the pseudo-boehmite product is 379m 2 (ii)/g, pore volume of 1.26ml/g, pore diameter of 9nm 2 O 3 0.007wt% of Na 2 The O content was 0.016wt%.
And (4) inputting the filtrate after solid-liquid separation into a triple-effect evaporator, and evaporating, concentrating and crystallizing to obtain an ammonium chloride product.
Claims (6)
1. A method for preparing low-sodium low-iron superfine alpha-alumina and large-pore volume pseudo-boehmite is characterized by comprising the following steps of: the method comprises the following steps:
a) Leaching: under the closed condition, the fly ash of the circulating fluidized bed is leached by hydrochloric acidAdopting wet magnetic separation deironing before: pulverizing fly ash to below 100 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation to remove iron so that the iron content in the fly ash is reduced to below 1.0wt%, and filtering to obtain a filter cake; leaching with hydrochloric acid of concentration 20wt% -37 wt%, adding hydrochloric acid of 50% -80% of theoretical value according to the concentration of hydrochloric acid and the content of alumina in the circulating fluidized bed fly ash, and controlling the pH value of leaching solution to be 2.0-3.0; leaching under autogenous pressure at 150-250 ℃ for 1.5-5 hours, wherein the leaching rate of alumina in the fly ash is higher than 85%; settling, filtering and washing the reacted slurry to obtain leaching solution; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L; the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution;
b) Purifying and deironing: keeping the temperature of the leaching solution at 60-90 ℃, introducing oxygen-enriched gas into the leaching solution under stirring at the aeration speed of 3-5 m 3 H, controlling the gas flow to keep Fe in the leaching solution 3+ The concentration is always lower than 1g/L, and the formed precipitate is aged for 5 to 15 hours at the temperature of between 50 and 85 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, and neutralizing the refined aluminum chloride solution by using an ammonium-containing alkali liquor until the pH value of the solution is 5.5-7.5 to obtain colloidal precipitate;
d) Preparing alpha-alumina: aging the mixed solution obtained in the step c) for 1 to 24 hours at the temperature of between 10 and 55 ℃, settling, filtering, washing, pulping, and spray-drying at the temperature of between 160 and 230 ℃ to obtain powder; calcining the powder at 1200-1500 ℃ for 1-4 hours to obtain a low-sodium low-iron superfine alpha-alumina product;
e) Preparing pseudo-boehmite: adding a pore-expanding agent aqueous solution with the concentration of 0.5wt% -10 wt% into the mixed solution obtained in the step c), wherein the addition amount of the pore-expanding agent aqueous solution is 1% -5% of the volume of the mixed solution, adjusting the aperture and the specific surface area of the colloidal precipitate, and aging for 5-24 hours at the temperature of 10-55 ℃; after settling, filtering, washing and pulping, carrying out spray drying at 160-230 ℃ to obtain macroporous pseudo-boehmite powder;
f) Preparing ammonium chloride: crystallizing and purifying the filtrate obtained by filtering in the step d) and the step e) to obtain an ammonium chloride product.
2. The method for preparing low-sodium low-iron superfine alpha-alumina and large-pore volume pseudo-boehmite according to claim 1, which is characterized in that: in step c), the ammonium-containing alkali liquor is one of ammonium carbonate aqueous solution, ammonium bicarbonate aqueous solution or ammonia water, and the concentration is determined by NH in the solution 4 + The concentration of the ions is 1 to 12mol/L.
3. The method for preparing low-sodium low-iron superfine alpha-alumina and large-pore volume pseudo-boehmite according to claim 1, which is characterized in that: in the step e), the pore-expanding agent is one or more of ammonium carbonate, ammonium bicarbonate, ammonium chloride, polyethylene glycol or urea.
4. A method for preparing low-sodium low-iron superfine alpha-alumina is characterized by comprising the following steps: the method comprises the following steps:
a) Leaching: under a closed condition, carrying out wet magnetic separation on the fly ash of the circulating fluidized bed before hydrochloric acid leaching for removing iron: pulverizing fly ash to below 100 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation to remove iron so that the iron content in the fly ash is reduced to below 1.0wt%, and filtering to obtain a filter cake; leaching with hydrochloric acid with the concentration of 20wt% -37 wt%, wherein the amount of the added hydrochloric acid is 50% -80% of the theoretical value according to the concentration of the hydrochloric acid and the content of alumina in the circulating fluidized bed fly ash, and the pH value of the leaching solution is controlled to be 2.0-3.0; leaching under autogenous pressure at 150-250 ℃ for 1.5-5 hours, wherein the leaching rate of alumina in the fly ash is higher than 85%; settling, filtering and washing the reacted slurry to obtain leaching solution; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ The concentration is lower than 1g/L; the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/LAdding into the leaching solution;
b) Purifying and deironing: keeping the temperature of the leaching solution at 60-90 ℃, introducing oxygen-enriched gas into the leaching solution under stirring at the aeration speed of 3-5 m 3 H, controlling the gas flow to keep Fe in the leaching solution 3+ The concentration is always lower than 1g/L, and the formed precipitate is aged for 5 to 15 hours at the temperature of between 50 and 85 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, neutralizing the refined aluminum chloride solution by using an ammonium-containing alkali liquor until the pH value of the solution is 5.5-7.5 to obtain colloidal precipitate, wherein the concentration of the ammonium-containing alkali liquor is equal to NH in the solution 4 + The concentration of the ions is 1 to 12mol/L;
d) Preparation of alpha-alumina: aging the mixed solution obtained in the step c) for 1 to 24 hours at the temperature of between 10 and 55 ℃, settling, filtering, washing, pulping, and spray-drying at the temperature of between 160 and 230 ℃ to obtain powder; calcining the powder at 1200-1500 ℃ for 1-4 hours to obtain a low-sodium low-iron superfine alpha-alumina product;
e) Preparing ammonium chloride: crystallizing and purifying the filtrate obtained by filtering in the step d) to obtain an ammonium chloride product.
5. A method for preparing low-sodium low-iron large pore volume pseudo-boehmite is characterized by comprising the following steps: the method comprises the following steps:
a) Leaching: under a closed condition, carrying out wet magnetic separation on the fly ash of the circulating fluidized bed before hydrochloric acid leaching for removing iron: pulverizing fly ash to below 100 meshes, adding water to prepare slurry with the solid content of 20-40wt%, carrying out wet magnetic separation to remove iron so that the iron content in the fly ash is reduced to below 1.0wt%, and filtering to obtain a filter cake; leaching with hydrochloric acid with the concentration of 20wt% -37 wt%, wherein the amount of the added hydrochloric acid is 50% -80% of the theoretical value according to the concentration of the hydrochloric acid and the content of alumina in the circulating fluidized bed fly ash, and the pH value of the leaching solution is controlled to be 2.0-3.0; leaching under autogenous pressure at 150-250 ℃ for 1.5-5 hours, wherein the leaching rate of alumina in the fly ash is higher than 85%; settling, filtering and washing the reacted slurry to obtain leaching solution; when Fe is contained in the leaching solution 3+ When the concentration is higher than 1g/L, reducing agent is added into the solution to lead Fe 3+ Concentration ofLess than 1g/L; the reducing agent is one of hydroxylamine hydrochloride and ascorbic acid; when in use, the reducing agent is dissolved in water to prepare an aqueous solution with the concentration of 0.5-5 mol/L, and the aqueous solution is added into the leaching solution;
b) Purifying and deironing: keeping the temperature of the leaching solution at 60-90 ℃, introducing oxygen-enriched gas into the leaching solution under stirring at the aeration speed of 3-5 m 3 H, controlling the gas flow to keep Fe in the leaching solution 3+ The concentration is always lower than 1g/L, and the formed precipitate is aged for 5 to 15 hours at the temperature of between 50 and 85 ℃ and then filtered to obtain refined aluminum chloride solution;
c) Neutralizing: controlling the temperature of the refined aluminum chloride solution to be 10-60 ℃, neutralizing the refined aluminum chloride solution by using an ammonium-containing alkali liquor until the pH value of the solution is 5.5-7.5 to obtain colloidal precipitate, wherein the concentration of the ammonium-containing alkali liquor is equal to NH in the solution 4 + The concentration of the ions is 1 to 12mol/L;
d) Preparing pseudo-boehmite: adding a pore-expanding agent aqueous solution with the concentration of 0.5wt% -10 wt% into the mixed solution obtained in the step c), wherein the addition amount of the pore-expanding agent aqueous solution is 1% -5% of the volume of the mixed solution, adjusting the aperture and the specific surface area of the colloidal precipitate, and aging for 5-24 hours at the temperature of 10-55 ℃; after settling, filtering, washing and pulping, carrying out spray drying at 160-230 ℃ to obtain macroporous pseudo-boehmite powder;
e) Preparing ammonium chloride: crystallizing and purifying the filtrate obtained by filtering in the step d) to obtain an ammonium chloride product.
6. The method for preparing low-sodium low-iron large pore volume pseudoboehmite according to claim 5, characterized by comprising the following steps: in the step d), the pore-expanding agent is one or more of ammonium carbonate, ammonium bicarbonate, ammonium chloride, polyethylene glycol or urea.
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