CN115403364A - Method for preparing columnar mullite by using rapid sintering process after pretreatment of high-alumina fly ash - Google Patents
Method for preparing columnar mullite by using rapid sintering process after pretreatment of high-alumina fly ash Download PDFInfo
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Abstract
The invention discloses a method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash, which comprises the steps of firstly extracting partial silicon oxide from the high-alumina fly ash to form desiliconized fly ash, then removing impurities from different types of impurities in the desiliconized fly ash step by step, and then carrying out secondary deep desiliconization by adopting desiliconized alkali liquor and deep impurity-removed desiliconized fly ash to obtain desiliconized fly ash with high aluminum-silicon ratio; the invention combines the microcrystalline mullite grain characteristics of the desiliconized fly ash with high aluminum-silicon ratio, promotes the formation of liquid phase by adding a small amount of sintering aid, has the sintering time of only 9-18min in a high-temperature section, has the total sintering time of 60-80min, greatly reduces the sintering time compared with 48h, greatly shortens the whole sintering time compared with the sintering time of the traditional mullite sintering process, and realizes the purpose of rapid sintering.
Description
Technical Field
The invention belongs to the technical field of mullite, and particularly relates to a method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash.
Background
The main chemical components of the high-alumina fly ash, namely alumina and silicon oxide, account for more than 85 percent of the total chemical components, are solid wastes generated after coal burning of a thermal power plant, and particularly the main phase compositions of the high-alumina fly ash after the high-alumina coal is calcined by a pulverized coal furnace are mullite, corundum and glass and the like.
The mineral component of the conventional mullite is 3Al 2 O 3 ·2SiO 2 Is Al 2 O 3 -SiO 2 The most stable crystal mineral of the system under normal pressure has the excellent performances of good high-temperature volume stability, high refractoriness, strong chemical erosion resistance, high thermal shock resistance and the like, is a most popular refractory material in the current industrialization, and is widely applied to the industries of ceramics, metallurgy, glass, cement and the like.
The synthesis of mullite is mainly divided into an electric melting method and a sintering method. The electric melting method is obtained by mixing an aluminum-containing raw material and a silicon-containing raw material and then melting in an electric arc furnace, has the main defects of higher reaction temperature, harsh conditions and high power consumption, and is mainly used for preparing high-end mullite refractory materials. The industrial common sintering method is generally formed by mixing natural minerals such as flint clay, andalusite, high-alumina bauxite, kaolin and the like according to different required chemical compositions and then calcining the mixture in a kiln at high temperature, and the method has the advantages of simple operation, controllable components, simple and convenient production and moderate production cost; the disadvantages are high energy consumption, high exploitation cost of natural minerals, no elimination of natural mineral impurities, low mullite conversion efficiency and the like.
Recently, the related technologies of adding different proportions of high-alumina bauxite and industrial aluminum hydroxide or industrial oxide into fly ash and sintering at high temperature to obtain mullite have appeared, and although the useful components of alumina and silica in fly ash are utilized, the technologies have the disadvantage that the added raw materials adopt industrial aluminum hydroxide or industrial oxide, so that the raw material cost is high; in addition, the resource amount of the bauxite and the high bauxite in China is reduced year by year, so that the supply amount of the raw materials is gradually reduced, the selling price is increased year by year, the cost of mullite production enterprises is high, and the sustainable and healthy development of the refractory material industry is greatly influenced.
CN 102092734A relates to a method for preparing mullite refractory material and sodium silicate solution, the invention takes fly ash after magnetic separation and iron removal as raw material, and the fly ash is subjected to high-temperature high-pressure alkali dissolution and desilication reaction to obtain solid-phase desiliconized fly ash and liquid-phase sodium silicate solution, and the low-sodium desiliconized fly ash is obtained after washing and drying. And mixing the low-sodium fly ash, kaolin and a powdery aluminum source with water, pressing and molding, and calcining in a high-temperature tunnel to obtain the mullite refractory material. The technical scheme of the invention needs high-temperature and high-pressure alkali dissolution in the preparation process, and has higher requirements on the process and equipment; meanwhile, kaolin and a powdery aluminum source are additionally added into the raw material system, so that the production cost is increased.
CN 102583409A relates to a method for producing mullite and calcium silicate by using high-alumina fly ash, the high-alumina fly ash after magnetic separation and iron removal is used as a raw material, the high-alumina fly ash is subjected to alkali dissolution in a medium-temperature and medium-pressure reaction kettle, desiliconization reaction and filtration are carried out, desiliconized fly ash is obtained after sodium removal, calcium removal and iron removal by acid washing with 20% hydrochloric acid, and the desiliconized fly ash is calcined at high temperature (1200-1600 ℃) for 1-2 hours to obtain the mullite refractory material. And causticizing the desiliconized filtrate by lime milk to prepare calcium silicate. According to the technical scheme, medium-temperature and medium-pressure alkali dissolution (120 ℃) is required in the preparation process, the raw materials are required to be subjected to ball milling treatment, and the requirements on the process and equipment are high; meanwhile, the high-temperature sintering time is longer, the energy consumption is higher, and the production cost is increased; finally, the content of alumina in the mullite obtained after sintering is between 55 and 64 percent, and the requirement of M70 (the content of alumina is more than 70 percent) cannot be met.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide the method for preparing the columnar mullite by the rapid sintering process after the pretreatment of the high-alumina fly ash, the method has the advantages of wide raw material source, low energy consumption and low production cost, and the columnar mullite product is directly produced by the high-alumina fly ash without adding any industrial mineral and aluminum-containing component besides the high-alumina fly ash; the rest components can be co-produced into mature industrial products, the utilization of 100 percent of the high-alumina fly ash is realized, secondary solid waste is not generated, the method is suitable for industrial production, and higher economic and environmental benefits can be generated.
The purpose of the invention is realized by the following technical scheme.
A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash comprises the following steps:
1) Uniformly mixing high-alumina fly ash and a sodium hydroxide aqueous solution to obtain a mixed slurry, reacting the mixed slurry at 30-60 ℃ for 4-12 h under the condition of stirring, carrying out solid-liquid separation after the reaction is finished, carrying out solid-liquid separation to obtain desiliconized fly ash after the solid-liquid separation is finished, and carrying out solid-liquid separation to obtain liquid which is desiliconized alkaline solution, wherein the ratio of the mass parts of the high-alumina fly ash to the volume parts of the sodium hydroxide aqueous solution is 1: (4-8), wherein the unit of the mass parts is kg, and the unit of the volume parts is L;
in the step 1), the rotation speed of the stirring condition is 150 to 1000r/min, preferably 250 to 350r/min.
In the step 1), water is used for cleaning.
In said step 1), the concentration of sodium hydroxide in the aqueous sodium hydroxide solution is 25 to 35wt%, preferably 25 to 30wt%.
In the step 1), the average particle diameter of the high-alumina fly ash is 50 to 80 μm.
In the step 1), the mixed slurry is reacted at 30-60 ℃ for 4-12 h, preferably 50-60 ℃ for 6-8 h.
2) Mixing the desiliconized fly ash obtained in the step 1) with a liquid with a pH value of less than 4, stirring and reacting for 1-6 h at 30-60 ℃, and performing solid-liquid separation to obtain a solid, namely the desiliconized fly ash with sodium and calcium removed;
in the step 2), the liquid with the pH value less than 4 is dilute hydrochloric acid.
In the step 2), the concentration of the dilute hydrochloric acid is 1-5 wt%.
In the step 2), the ratio of the mass part of the desiliconized fly ash to the volume part of the dilute hydrochloric acid is 1: (4 to 8), preferably 1: (5-7).
In the step 2), the reaction is carried out for 1 to 6 hours at a temperature of between 30 and 60 ℃ with stirring, and preferably for 2 to 4 hours at a temperature of between 40 and 50 ℃.
In the step 2), the stirring rate of the stirring reaction is 150 to 1000r/min, preferably 250 to 350r/min.
3) Mixing the sodium-calcium-removing desiliconized fly ash with concentrated sulfuric acid, reacting for 4-8 h at 50-80 ℃ under the condition of stirring, and performing solid-liquid separation to obtain solid which is the deep impurity-removing desiliconized fly ash after being washed with water;
in the step 3), the concentration of the concentrated sulfuric acid is 20 to 50wt%, preferably 30 to 40wt%.
In the step 3), the ratio of the mass parts of the sodium-removing, calcium-removing and desiliconizing fly ash to the volume parts of concentrated sulfuric acid is 1: (6 to 10), preferably 1: (6-8).
In the step 3), the rotation speed of the stirring condition is 150 to 1000r/min, preferably 250 to 400r/min.
In the step 3), the reaction is carried out at 50-80 ℃ for 4-8 h, preferably at 60-75 ℃ for 4-6 h.
4) Mixing the cleaned deeply impurity-removed and desilicified fly ash with the desilicified alkali liquor obtained in the step 1), reacting for 2-6 h at 30-60 ℃ under the condition of stirring, and performing solid-liquid separation to obtain the desilicified fly ash with high aluminum-silicon ratio as solid, wherein the ratio of the mass part of the deeply impurity-removed and desilicified fly ash to the volume part of the desilicified alkali liquor is 1: (4-8).
In the step 4), the reaction is carried out at 30-60 ℃ for 2-6 h, preferably at 40-50 ℃ for 2-4 h.
In the step 4), the rotation speed of the stirring condition is 150 to 1000r/min, preferably 250 to 400r/min.
In the step 4), the ratio of the mass parts of the deeply impurity-removed and desiliconized fly ash to the volume parts of the desiliconized alkali liquor is 1: (4-6).
5) Uniformly mixing the desiliconized fly ash with high aluminum-silicon ratio obtained in the step 4) with a sintering aid to obtain a to-be-granulated substance, granulating the to-be-granulated substance, molding, heating to T ℃, and sintering for T min to obtain columnar mullite, wherein T = 1500-1700, T = 9-18, and the sintering aid is TiO 2 、WO 3 And Nd 2 O 5 The sintering aid is 1-8 wt% of the desiliconized fly ash with high aluminum-silicon ratio.
In the step 5), the sintering aid is 1-4 wt% of the desiliconized fly ash with high aluminum-silicon ratio.
In the step 5), the method for preparing the granulating agent used for granulation comprises the following steps: mixing water and polyvinyl alcohol (PVA), stirring in a water bath at 80-90 ℃ for 8-11 h to obtain the granulating agent, wherein the ratio of the water to the PVA is (90-93) to (7-10) in parts by weight.
In the step 5), the granulating agent is 0.1-0.8 wt%, preferably 0.1-0.3 wt% of the high-alumina-silica ratio desiliconized fly ash.
In the step 5), the mixture is granulated and sieved by a 40-60 mesh sieve.
In the step 5), the pressure used for the molding is 100 to 300Mpa, preferably 150 to 200Mpa.
In the step 5), T =1600 to 1650, T =12 to 15.
In the step 5), the rate of heating to T ℃ is 30-50 ℃/min, preferably 30-40 ℃/min.
The columnar mullite obtained by the method.
In the technical scheme, the columnar mullite has the breaking strength of 120-180 MPa, the volume density of 2.6-3.03 g/cm < 3 >, the porosity of 0.2-2%, the apparent porosity of 0.3-2.5%, the mullite phase content in the columnar mullite is more than 93%, and the refractoriness is not lower than CN 180.
Extracting partial silicon oxide from the high-alumina fly ash to form desiliconized fly ash, then removing impurities from different types of impurities in the desiliconized fly ash step by step, and then carrying out secondary deep desiliconization by adopting desiliconized alkaline liquor and deep impurity-removed desiliconized fly ash to obtain desiliconized fly ash with high aluminum-silicon ratio; compared with the prior art of directly synthesizing the mullite from natural minerals and synthesizing the mullite by adding aluminum-containing industrial raw materials into the fly ash, the method has the following advantages that:
1) The raw material source of the mullite is mainly from a large amount of industrial solid wastes of a pulverized coal furnace power plant, the mullite is directly synthesized after pretreatment, no additional natural aluminum-containing ore or industrial aluminum-containing mineral is needed to be added, the main raw materials are all from high-alumina fly ash, high value-added utilization of the industrial solid wastes can be realized, no secondary solid wastes and waste liquids are generated, and the environmental benefit and the social benefit are remarkable.
2) The high-alumina fly ash aluminum-silicon high-efficiency separation is realized through the pre-desilication reaction of the high-alumina fly ash under the low-temperature condition, all separation processes are carried out under the normal-pressure condition, the production can be realized only by a conventional reaction tank, the process is compared with a process needing a reaction kettle, and the investment cost and the process cost of production operation are greatly reduced.
3) As can be seen from comparative examples 4 to 6, if only the desiliconized fly ash is directly added with the acid solution for reaction and impurity removal, the water content of the desiliconized fly ash reaches up to 60 to 65 percent, and the drying cost is increased. Through twice grading and impurity removal of different acid solutions, the moisture content of the desiliconized fly ash is less than 45%, and the reduction of drying and drying costs in the actual production process is facilitated.
4) Through twice impurity removal and twice desiliconization, the alumina content in the finally obtained desiliconized fly ash with high aluminum-silicon ratio is up to 70-79.5%, the silica content is 18.9-21.3%, and the molar ratio of alumina to silica is (3.36-3.92): 1.
5) The traditional mullite sintering process adopts tunnel kiln sintering, the total time from entering the tunnel kiln to leaving the tunnel kiln is about 48 hours, and the time of the high-temperature period is at least more than 3 hours.
6) Step 4) carrying out secondary desiliconization by using desiliconized alkali liquor after primary desiliconization without adding sodium hydroxide additionally, and if the step 4) adopts new sodium hydroxideA second desilication with sodium hydroxide is then carried out, so that a low concentration (SiO) is produced 2 Concentration of the silicon-removing liquid), the whole process needs similar treatment for many times, the working procedures are increased, the investment is increased, and the efficiency is also reduced. Step 4) carrying out secondary desiliconization by utilizing desiliconized alkali liquor after the primary desiliconization so as to ensure that SiO in the liquid obtained after the solid-liquid separation in the step 4) 2 Increased concentration of SiO 2 The concentration increase of the (C) is beneficial to improving the efficiency, reducing the material consumption in the production process and reducing the material conveying capacity for synthesizing 4A zeolite or synthesizing calcium silicate by using the (C) for the subsequent step; the concentration of the acid leaching solution can also be improved by recycling different acid treatment liquid phases; the liquid phases are finally reasonably and comprehensively utilized, amorphous alumina and amorphous silica in the high-alumina fly ash are fully utilized, and the 'dry-method squeezing' of solid-waste utilization is realized.
Drawings
FIG. 1 is an XRD pattern of different intermediate materials of example 1;
FIG. 2 is an SEM of columnar mullite made in example 1;
FIG. 3 is an SEM of columnar mullite made in example 2;
fig. 4 is an SEM of the preparation of columnar mullite in example 3.
Detailed Description
A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash comprises the following steps:
1) Pre-desiliconizing the high-alumina fly ash: the high-alumina fly ash is subjected to normal-pressure pre-desiliconization reaction by using a sodium hydroxide aqueous solution.
2) Removing calcium and sodium from the desiliconized fly ash by using liquid with pH less than 4: mixing the desiliconized fly ash with a liquid with the pH value of less than 4, then carrying out low-temperature dilute hydrochloric acid calcium and sodium removal, filtering after the reaction is finished, wherein the solid phase is the desiliconized fly ash with the sodium removed and the calcium removed, the filtrate is a mixed salt solution of aluminum chloride and calcium chloride, the filtrate can be continuously used for calcium and sodium removal when the pH value of the filtrate is less than 4, and the filtrate is used as a raw material for preparing the water purifying agent after the concentration of the aluminum chloride is increased. The purpose of the step 2) is to remove sodium aluminosilicate in the desiliconized fly ash and calcium oxide in the desiliconized fly ash in the step 1) by using a liquid with the pH value of less than 4 so as to prevent a calcium sulfate solid phase from being formed in subsequent treatment and reduce the water content of the deeply impurity-removed desiliconized fly ash obtained in the step 3).
3) Deep impurity removal by concentrated sulfuric acid: mixing the sodium-removing, calcium-removing and desiliconized fly ash obtained in the step 2) with concentrated sulfuric acid, then removing impurities at normal pressure, after the reaction is finished, filtering, washing with water, and then obtaining a solid phase which is the deep impurity-removing and desiliconized fly ash, wherein the filtrate is an aluminum sulfate aqueous solution, and after evaporation and concentration are carried out, the aluminum sulfate concentration is increased, and the obtained solid phase is used as a raw material for preparing a water purifying agent. The purpose of the step 3) is to remove iron oxide and titanium oxide in the sodium-removing, calcium-removing and desiliconized fly ash of the step 2) by using concentrated sulfuric acid, so as to reduce the impurity content in desiliconized ash. The water content of the deeply impurity-removed and desiliconized fly ash obtained in the step 3) is less than 50 percent.
4) Secondary desiliconization of desiliconized solution: mixing the desiliconized alkali liquor obtained in the step 1) and the deeply impurity-removed desiliconized fly ash obtained in the step 3), stirring, carrying out secondary desiliconization, washing and filtering after the reaction is finished, wherein the solid phase is the desiliconized fly ash with high aluminum-silicon ratio (initial aluminum-silicon mixture after impurity removal), the filtrate is sodium silicate aqueous solution, carrying out causticization by lime milk to obtain sodium hydroxide aqueous solution, evaporating and concentrating, and returning to the step 1 for recycling (Na is used for recycling) 2 SiO 3 +Ca(OH) 2 ＝CaSiO 3 ↓ + NaOH); step 4) the amorphous silicon dioxide in the sodium aluminosilicate decomposed in the step 2) and the step 3 is further reacted to achieve the purpose of deep desiliconization (the reaction process in the step 2 is Na) 2 O·Al 2 O 3 ·SiO 2 + HCl → NaCl (liquid phase) + AlCl 3 (liquid phase) + SiO 2 (gel-like solid), the reaction process of step 1 is NaOH + SiO 2 (gel-like solid) → Na 2 SiO 3 (liquid phase)). The desiliconized fly ash with high aluminum-silicon ratio contains 70-79.5% of alumina, 18.9-21.3% of silicon oxide, and the molar ratio of the alumina to the silicon oxide is (3.36-3.92): 1, the water content is less than 45 percent.
5) And (3) rapid sintering: and 4) adding a sintering aid into the desiliconized fly ash with high aluminum-silicon ratio obtained in the step 4), uniformly mixing, granulating, molding, and then quickly sintering to obtain the columnar mullite. The sintering aid can promote the formation of low-temperature liquid phases such as aluminum titanate, aluminum tungstate and the like, and accelerate the growth of mullite grains, thereby accelerating the secondary mullite process.
The technical scheme of the invention is further explained by combining specific examples.
The following high-alumina fly ash comes from a certain thermal power plant in inner Mongolia.
In the following examples, parts by mass are in kg and parts by volume are in L.
The model of the normal pressure stirring container: IKA EUROSTAR 60.
Example 1
A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash comprises the following steps:
1) High alumina fly ash (Al) with an average particle size of 55 mu m 2 O 3 ：49.55wt％，SiO 2 ：41.02wt％，CaO:3.82wt％，TiO 2 :1.47wt％，Na 2 O:0.17wt％，Fe 2 O 3 1.94 wt%) and sodium hydroxide aqueous solution to obtain mixed slurry, placing the mixed slurry into a normal pressure stirring container, reacting at 45 deg.C for 6h under the stirring condition of 300r/min, after the reaction is completed, making solid-liquid separation, and cleaning the solid obtained by solid-liquid separation with water whose mass is 0.9 times that of the above-mentioned material to obtain desiliconized flyash (Al) 2 O 3 ：58.37，SiO 2 ：26.07％，CaO:4.02％，TiO 2 :1.62％，Na 2 O:3.64％，Fe 2 O 3 2.07 percent of water content, 49.56 percent of aluminum-silicon ratio, 2.24 percent of aluminum-silicon ratio, 1), and performing solid-liquid separation to obtain a liquid which is desiliconized alkali liquor, wherein the ratio of the mass parts of the high-alumina fly ash to the volume parts of the sodium hydroxide aqueous solution is 1:4.5, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 25.4wt%;
2) Mixing the desiliconized fly ash obtained in the step 1) with dilute hydrochloric acid, putting the mixture into a normal-pressure stirring container, stirring and reacting for 2 hours at 35 ℃ at the speed of 300r/min, and performing solid-liquid separation to obtain desiliconized fly ash (Al) with solid as sodium and calcium removed 2 O 3 ：63.01wt％，SiO 2 ：28.86wt％，CaO:0.36wt％，TiO 2 :1.65wt％，Na 2 O:0.21wt％，Fe 2 O 3 1.96wt%, water content 46.23wt%, ratio of aluminum to silicon 2.18: 1) (the liquid obtained by solid-liquid separation can be recycled after being diluted by adding concentrated hydrochloric acid), wherein the diluted saltThe concentration of the acid is 2.5wt%, and the ratio of the mass part of the desiliconized fly ash to the volume part of the dilute hydrochloric acid is 1:8;
3) Mixing the sodium-calcium-removing desiliconized fly ash and concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 6 hours at 70 ℃ under the stirring condition of 350r/min, performing solid-liquid separation to obtain solid, cleaning the solid with water with the mass of 1.5 times that of the solid, and then deeply removing impurities and desiliconized fly ash (Al) 2 O 3 ：61.71wt％，SiO 2 ：30.76wt％，CaO:0.21wt％，TiO 2 :0.85wt％，Na 2 O:0.12wt％，Fe 2 O 3 0.34wt%, water content of 44.56wt%, al/Si ratio of 2.01: 1) (the liquid obtained by solid-liquid separation can be diluted by adding concentrated sulfuric acid for recycling), wherein the concentration of the concentrated sulfuric acid is 35wt%, and the ratio of the mass portion of the sodium-removing, calcium-removing and desiliconizing fly ash to the volume portion of the concentrated sulfuric acid is 1:6.5;
4) Mixing the deeply-purified and desiliconized fly ash with the desiliconized alkali liquor obtained in the step 1), introducing the mixture into a normal-pressure stirring container, reacting for 3 hours at 40 ℃ under the stirring condition of the speed of 250r/min, carrying out solid-liquid separation to obtain a solid, washing the solid with 0.85 time of water, and then obtaining the desiliconized fly ash (Al) with high aluminum-silicon ratio 2 O 3 ：75.16wt％，SiO 2 ：20.16wt％，CaO:0.24wt％，TiO 2 :0.88wt％，Na 2 O:0.14wt％，Fe 2 O 3 0.39wt%, water content of 43.12wt%, aluminum-silicon ratio of 3.73: 1), the ratio of the mass parts of the deep impurity-removing desiliconized fly ash to the volume parts of the desiliconized alkali liquor is 1:5.
5) Mixing the desiliconized fly ash with high Al/Si ratio obtained in the step 4) with a sintering aid, ball-milling for 1 hour at the rotating speed of 750r/min to obtain a substance to be granulated, adding a granulating agent into the substance to be granulated for granulation, sieving by a 40-mesh sieve, pressing in a mould for 60 seconds by adopting the pressure of 196MPa for molding, heating to 1650 ℃ in a muffle furnace at the speed of 30 ℃/min, and sintering for 12min to obtain columnar mullite; wherein the sintering aid is TiO 2 And WO 3 Of (2), tiO 2 And WO 3 The mass ratio of the sintering aid to the desiliconized fly ash is 1.2 to 1.3, the sintering aid is 2.5wt% of the desiliconized fly ash with high alumina-silica ratio, the granulating agent is 0.3wt% of the desiliconized fly ash with high alumina-silica ratio, and the method for preparing the granulating agent comprises the following steps: mixing water and polyethyleneMixing alcohol (PVA), and stirring in a water bath at 85 ℃ for 10 hours to obtain a granulating agent, wherein the ratio of water to polyvinyl alcohol is 92.
The test shows that the column mullite has the breaking strength of 163.7MPa and the volume density of 2.92g/cm 3 The porosity was 0.55%, the apparent porosity was 1.23%, the mullite phase content was 94.6%, and the refractoriness was CN 184. As shown in FIG. 2, the SEM of the columnar mullite obtained in example 1 shows that the length of the columnar mullite is about 7-18 μm, the columnar structure is obvious, and almost no pores exist, so that the structural foundation is laid for high breaking strength and low porosity.
As shown in FIG. 1, the main crystal phases of the high-alumina fly ash are mullite and corundum phases, and a small amount of amorphous glass is contained. The desiliconized fly ash obtained after the treatment in the step 1) contains a small amount of P-type zeolite phase (namely sodium aluminosilicate solid) besides the main crystal phases of mullite and corundum; the deeply impurity-removed and desiliconized fly ash obtained after the treatment in the step 3) contains corundum and mullite phases and a small amount of amorphous silica; the desiliconized fly ash with high aluminum-silicon ratio obtained by the treatment of the step 4) only remains corundum and mullite phases.
Comparative example 1
A method of producing columnar mullite, substantially the same as in example 1, except that no sintering aid is present in step 5). The columnar mullite has the flexural strength of 116.9MPa and the bulk density of 2.64g/cm 3 The porosity was 2.46%, the apparent porosity was 5.23%, the mullite phase content was 89.2%, and the refractoriness was CN 180.
Example 2
A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash comprises the following steps:
1) High alumina fly ash (Al) with an average particle size of 55 mu m 2 O 3 ：49.55wt％，SiO 2 ：41.02wt％，CaO:3.82wt％，TiO 2 :1.47wt％，Na 2 O:0.17wt％，Fe 2 O 3 1.94 wt%) and sodium hydroxide aqueous solution to obtain mixed slurry, placing the mixed slurry into a normal pressure stirring container, reacting at 35 deg.C for 4h under the condition of stirring at 350r/min, and finishing the reactionThen solid-liquid separation is carried out, solid obtained by solid-liquid separation is washed by water with the mass of 1.1 times that of the solid, and the washed solid is desiliconized fly ash (Al) 2 O 3 ：59.67wt％，SiO 2 ：25.87wt％，CaO:4.13wt％，TiO 2 :1.64wt％，Na 2 O:5.12wt％，Fe 2 O 3 2.12wt%, water content of 51.34wt%, aluminum-silicon ratio of 2.31), and solid-liquid separation to obtain a liquid which is desiliconized alkali liquor, wherein the ratio of the mass parts of the high-alumina fly ash to the volume parts of the sodium hydroxide aqueous solution is 1:5, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 31.5wt%;
2) Mixing the desiliconized fly ash obtained in the step 1) with dilute hydrochloric acid, putting the mixture into a normal-pressure stirring container, stirring and reacting for 4 hours at 50 ℃ at the speed of 350r/min, and performing solid-liquid separation to obtain desiliconized fly ash (Al) with solid being sodium and calcium removed 2 O 3 ：63.42wt％，SiO 2 ：28.54wt％，CaO:0.26wt％，TiO 2 :1.68wt％，Na 2 O:0.17wt％，Fe 2 O 3 1.98wt%, water content of 47.18wt%, and aluminum-silicon ratio of 2.22 (the liquid obtained by solid-liquid separation can be recycled after being diluted by adding concentrated hydrochloric acid), wherein the concentration of the dilute hydrochloric acid is 4wt%, and the ratio of the mass part of the desiliconized fly ash to the volume part of the dilute hydrochloric acid is 1:7;
3) Mixing the sodium-calcium-removing desiliconized fly ash and concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 7 hours at 60 ℃ under the stirring condition of 300r/min, carrying out solid-liquid separation to obtain solid, washing the solid with water with the mass of 1.3 times of that of the solid, and then deeply removing impurities and desiliconized fly ash (Al) 2 O 3 ：62.45wt％，SiO 2 ：30.88wt％，CaO:0.21wt％，TiO 2 :0.88wt％，Na 2 O:0.15wt％，Fe 2 O 3 0.30wt%, water content of 44.26wt%, and aluminum-silicon ratio of 2.02 (liquid obtained by solid-liquid separation can be recycled after concentrated sulfuric acid is added for dilution), wherein the concentration of the concentrated sulfuric acid is 45wt%, and the ratio of the mass parts of the sodium-removing, calcium-removing and desiliconizing fly ash to the volume parts of the concentrated sulfuric acid is 1:7.5;
4) Mixing the deeply impurity-removed desiliconized fly ash with the desiliconized alkali liquor obtained in the step 1), introducing the mixture into a normal-pressure stirring container, and carrying out reverse reaction at 50 ℃ under the stirring condition of the speed of 350r/minAfter 2 hours, solid-liquid separation is carried out, the obtained solid is washed by 0.95 time of water to obtain desiliconized fly ash (Al) with high aluminum-silicon ratio 2 O 3 ：77.42wt％，SiO 2 ：19.85wt％，CaO:0.18wt％，TiO 2 :0.92wt％，Na 2 O:0.11wt％，Fe 2 O 3 0.42wt%, water content 42.12wt%, aluminum-silicon ratio 3.90: 1), the ratio of the mass parts of the deep impurity-removing desiliconized fly ash to the volume parts of desiliconized alkali liquor is 1:6.
5) Mixing the desiliconized fly ash with high aluminum-silicon ratio obtained in the step 4) with a sintering aid, ball-milling for 1 hour at the rotating speed of 600r/min to obtain a substance to be granulated, adding a granulating agent into the substance to be granulated for granulation, sieving by a 40-mesh sieve, pressing in a mould for 60 seconds by adopting the pressure of 234MPa for molding, heating to 1670 ℃ in a muffle furnace at the speed of 40 ℃/min, and sintering for 15 minutes to obtain columnar mullite; wherein the sintering aid is Nd 2 O 5 And WO 3 Mixture of (1) Nd 2 O 5 And WO 3 The mass ratio of the sintering aid to the desiliconized fly ash is 2.1 to 1.6, the sintering aid is 3.7wt% of the desiliconized fly ash with high alumina-silica ratio, the granulating agent is 0.5wt% of the desiliconized fly ash with high alumina-silica ratio, and the method for preparing the granulating agent comprises the following steps: mixing water and polyvinyl alcohol (PVA), and stirring in a water bath at 90 ℃ for 8 hours to obtain a granulating agent, wherein the ratio of the water to the PVA is 90.
The test shows that the column mullite (1) has the breaking strength of 172.6MPa and the volume density of 2.98g/cm 3 The porosity was 0.48%, the apparent porosity was 0.92%, the mullite phase content was 93.7%, and the refractoriness was CN 185. The SEM of the columnar mullite obtained in the example 2 is shown in a figure 3, and the figure shows that the length of the columnar mullite is about 5-15 mu m, the short columnar structure and part of long columnar mullite structures are alternately arranged, and a structural foundation is laid for high breaking strength and low porosity.
Comparative example 2
A method of producing columnar mullite, substantially the same as that of example 2, except that no sintering aid is present in step 5). The columnar mullite has the rupture strength of 121.8MPa and the volume density of 2.69g/cm 3 The porosity was 1.32%, the apparent porosity was 3.15%, the mullite phase content was 88.9%, and the refractoriness was CN 182.
Example 3
A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash comprises the following steps:
1) High alumina fly ash (Al) with an average particle size of 60.4 μm 2 O 3 ：45.89wt％，SiO 2 ：42.18wt％，CaO:2.92wt％，TiO 2 :1.54wt％，Na 2 O:0.22wt％，Fe 2 O 3 1.87wt%, the ratio of aluminum to silicon is 1.09) 2 O 3 ：56.29wt％，SiO 2 ：27.42wt％，CaO:3.51wt％，TiO 2 :1.61wt％，Na 2 O:4.65wt％，Fe 2 O 3 1.92wt%, water content of 49.18wt%, aluminum-silicon ratio of 2.05: 4, the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 33wt%;
2) Mixing the desiliconized fly ash obtained in the step 1) with dilute hydrochloric acid, putting the mixture into a normal-pressure stirring container, stirring and reacting for 1h at the temperature of 30 ℃ at the speed of 400r/min, and performing solid-liquid separation to obtain desiliconized fly ash (Al) with solid as sodium and calcium removed 2 O 3 ：59.32wt％，SiO 2 ：29.95wt％，CaO:0.21wt％，TiO 2 :1.69wt％，Na 2 O:0.15wt％，Fe 2 O 3 1.97wt%, water content of 46.11wt%, and aluminum-silicon ratio of 1.98) (the liquid obtained by solid-liquid separation can be recycled after being diluted by adding concentrated hydrochloric acid), wherein the concentration of the dilute hydrochloric acid is 2wt%, and the ratio of the mass part of the desiliconized fly ash to the volume part of the dilute hydrochloric acid is 1:6.5;
3) Mixing the sodium-calcium-removing desiliconized fly ash and concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 4.5 hours at 75 ℃ under the stirring condition of the speed of 300r/min, carrying out solid-liquid separation to obtain a solid, washing the solid with water with the mass of 1.4 times that of the solid, and then carrying out solid-liquid separationFly ash (Al) for deep impurity removal and desilication 2 O 3 ：58.32wt％，SiO 2 ：32.11wt％，CaO:0.18wt％，TiO 2 :0.95wt％，Na 2 O:0.11wt％，Fe 2 O 3 0.28wt%, water content of 44.19wt%, and aluminum-silicon ratio of 1.82 (liquid obtained by solid-liquid separation can be diluted by concentrated sulfuric acid for recycling), wherein the concentration of the concentrated sulfuric acid is 50wt%, and the ratio of the mass parts of the sodium-removing, calcium-removing and desiliconizing fly ash to the volume parts of the concentrated sulfuric acid is 1:6;
4) Mixing the deeply-purified and desiliconized fly ash with the desiliconized alkali liquor obtained in the step 1), introducing the mixture into a normal-pressure stirring container, reacting for 3 hours at the temperature of 60 ℃ under the stirring condition at the speed of 300r/min, and carrying out solid-liquid separation to obtain the desiliconized fly ash (Al) with high aluminum-silicon ratio after cleaning the solid with 0.9 times of water 2 O 3 ：72.26wt％，SiO 2 ：21.30wt％，CaO:0.19wt％，TiO 2 :0.99wt％，Na 2 O:0.13wt％，Fe 2 O 3 0.45wt%, water content of 43.86wt%, aluminum-silicon ratio of 3.39 to 1), the ratio of the mass parts of the deeply impurity-removed desiliconized fly ash to the volume parts of desiliconized alkali liquor is 1:8.
5) Mixing the desiliconized fly ash with high Al/Si ratio obtained in the step 4) with a sintering aid, ball-milling for 1 hour at the rotating speed of 650r/min to obtain a substance to be granulated, adding a granulating agent into the substance to be granulated for granulation, sieving by a 60-mesh sieve, pressing in a mould for 60 seconds by adopting the pressure of 168MPa for molding, heating to 1600 ℃ in a muffle furnace at the speed of 50 ℃/min, and sintering for 9min to obtain columnar mullite; wherein the sintering aid is Nd 2 O 5 And WO 3 Mixture of (1) Nd 2 O 5 And WO 3 The mass ratio of the sintering aid to the desiliconized fly ash is 1: mixing water and polyvinyl alcohol (PVA), and stirring in a water bath at 85 ℃ for 10 hours to obtain a granulating agent, wherein the ratio of the water to the PVA is 92.
The test shows that the column mullite has the breaking strength of 123.4MPa and the volume density of 2.69g/cm 3 The porosity is 1.23%, the apparent porosity is 1.89%, and the mullite phase content is 93.2%And refractoriness CN 182. As shown in FIG. 4, the SEM of the columnar mullite obtained in example 3 shows that the length of the columnar mullite is about 3-8 μm, the columnar structure is not obvious, the blocky structure appears, and the porosity is small, so that the flexural strength is reduced and the porosity is improved compared with the former two examples.
Comparative example 3
A method of producing columnar mullite, substantially the same as in example 3, except that no sintering aid is present in step 5). The mullite has the breaking strength of 102.3MPa and the volume density of 2.51g/cm 3 The porosity was 2.37%, the apparent porosity was 4.13%, the mullite phase content was 88.1%, and the refractoriness was CN 180.
Comparative example 4
Mixing the desiliconized fly ash obtained in the step 1) in the embodiment 1 with concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 6 hours at 70 ℃ under the stirring condition of 350r/min, carrying out solid-liquid separation, washing the solid obtained by the solid-liquid separation with water with the mass being 1.5 times that of the solid, and then deeply removing impurities and desiliconizing the fly ash (Al) 2 O 3 ：59.28wt％，SiO 2 ：31.02wt％，CaO:1.32wt％，TiO 2 :0.79wt％，Na 2 O:0.14wt％，Fe 2 O 3 0.36wt%, water content 62.18wt%, al/Si ratio 1.91: 1) Wherein the concentration of the concentrated sulfuric acid is 35wt%, and the ratio of the mass part of the desiliconized fly ash to the volume part of the concentrated sulfuric acid is 1:6.5.
comparative example 5
Mixing the desiliconized fly ash obtained in the step 1) in the embodiment 2 with concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 7 hours at 60 ℃ under the stirring condition of the speed of 300r/min, carrying out solid-liquid separation, washing the solid obtained by the solid-liquid separation with water with the mass being 1.3 times that of the solid, and then deeply removing impurities and desiliconizing the fly ash (Al) by using the solid 2 O 3 ：61.23wt％，SiO 2 ：31.18wt％，CaO:1.36wt％，TiO 2 :0.86wt％，Na 2 O:0.17wt％，Fe 2 O 3 0.32wt%, water content of 63.16wt%, and aluminum-silicon ratio of 1.96, wherein the concentration of concentrated sulfuric acid is 45wt%, and the ratio of the mass part of the desiliconized fly ash to the volume part of the concentrated sulfuric acid is 1:7.5.
comparative example 6
Mixing the desiliconized fly ash obtained in the step 1) in the embodiment 3 with concentrated sulfuric acid, putting the mixture into a normal-pressure stirring container, reacting for 4.5 hours at 75 ℃ under the stirring condition of the speed of 300r/min, carrying out solid-liquid separation, washing the solid obtained by the solid-liquid separation with water with the mass of 1.4 times that of the solid, and then deeply removing impurities and desiliconizing the fly ash (Al) by using the solid 2 O 3 ：57.89wt％，SiO 2 ：32.91wt％，CaO:1.42wt％，TiO 2 :0.97wt％，Na 2 O:0.14wt％，Fe 2 O 3 0.29wt%, water content of 61.82wt%, and aluminum-silicon ratio of 1.76, wherein the concentration of concentrated sulfuric acid is 50wt%, and the ratio of the mass part of desiliconized fly ash to the volume part of concentrated sulfuric acid is 1:6.
the invention has been described in an illustrative manner, and it is to be understood that any simple variations, modifications or other equivalent changes which can be made by one skilled in the art without departing from the spirit of the invention fall within the scope of the invention.
Claims (10)
1. A method for preparing columnar mullite by a rapid sintering process after pretreatment of high-alumina fly ash is characterized by comprising the following steps:
1) Uniformly mixing high-alumina fly ash and a sodium hydroxide aqueous solution to obtain a mixed slurry, reacting the mixed slurry at 30-60 ℃ for 4-12 h under the condition of stirring, carrying out solid-liquid separation after the reaction is finished, carrying out solid-liquid separation to obtain desiliconized fly ash after the solid-liquid separation is finished, and carrying out solid-liquid separation to obtain liquid which is desiliconized alkaline solution, wherein the ratio of the mass parts of the high-alumina fly ash to the volume parts of the sodium hydroxide aqueous solution is 1: (4-8), wherein the unit of the mass parts is kg, and the unit of the volume parts is L;
2) Mixing the desiliconized fly ash obtained in the step 1) with a liquid with the pH value of less than 4, stirring and reacting for 1-6 h at the temperature of 30-60 ℃, and performing solid-liquid separation to obtain solid, namely the desiliconized fly ash with sodium and calcium removed;
3) Mixing the sodium-removing, calcium-removing and desiliconized fly ash with concentrated sulfuric acid, reacting for 4-8 h at 50-80 ℃ under the condition of stirring, and carrying out solid-liquid separation to obtain solid which is the deeply impurity-removing and desiliconized fly ash after being washed by water;
4) Mixing the cleaned deeply impurity-removed desiliconized fly ash with the desiliconized alkali liquor obtained in the step 1), reacting for 2-6 h at 30-60 ℃ under the condition of stirring, and carrying out solid-liquid separation to obtain the desiliconized fly ash with high aluminum-silicon ratio as solid, wherein the ratio of the mass part of the deeply impurity-removed desiliconized fly ash to the volume part of the desiliconized alkali liquor is 1: (4-8);
5) Uniformly mixing the desiliconized fly ash with the high aluminum-silicon ratio obtained in the step 4) and a sintering aid to obtain a to-be-granulated substance, granulating the to-be-granulated substance, molding, heating to T ℃, and sintering for T min to obtain columnar mullite, wherein T = 1500-1700, T = 9-18, and the sintering aid is TiO 2 、WO 3 And Nd 2 O 5 The sintering aid is 1-8 wt% of the desiliconized fly ash with high alumina-silica ratio.
2. The method according to claim 1, wherein in step 1), the rotation speed of the stirring conditions is 150 to 1000r/min, preferably 250 to 350r/min;
in the step 1), water is adopted for cleaning;
in the step 1), the concentration of sodium hydroxide in the sodium hydroxide aqueous solution is 25 to 35wt%, preferably 25 to 30wt%;
in the step 1), the average particle size of the high-alumina fly ash is 50-80 μm;
in the step 1), the mixed slurry is reacted for 4 to 12 hours at a temperature of between 30 and 60 ℃, preferably for 6 to 8 hours at a temperature of between 50 and 60 ℃.
3. The method according to claim 1, wherein in the step 2), the liquid with the pH less than 4 is diluted hydrochloric acid;
in the step 2), the concentration of the dilute hydrochloric acid is 1-5 wt%;
in the step 2), the ratio of the mass part of the desiliconized fly ash to the volume part of the dilute hydrochloric acid is 1: (4 to 8), preferably 1: (5-7);
in the step 2), stirring and reacting at 30-60 ℃ for 1-6 h, preferably at 40-50 ℃ for 2-4 h;
in the step 2), the stirring rate of the stirring reaction is 150 to 1000r/min, preferably 250 to 350r/min.
4. The method according to claim 1, wherein in the step 3), the concentrated sulfuric acid has a concentration of 20 to 50wt%, preferably 30 to 40wt%;
in the step 3), the ratio of the mass parts of the sodium-removing, calcium-removing and desiliconizing fly ash to the volume parts of concentrated sulfuric acid is 1: (6 to 10), preferably 1: (6-8);
in the step 3), the rotating speed of the stirring condition is 150-1000 r/min, preferably 250-400 r/min;
in the step 3), the reaction is carried out at 50-80 ℃ for 4-8 h, preferably at 60-75 ℃ for 4-6 h.
5. The method according to claim 1, wherein in step 4), the reaction is carried out at 30-60 ℃ for 2-6 h, preferably at 40-50 ℃ for 2-4 h;
in the step 4), the rotating speed of the stirring condition is 150-1000 r/min, preferably 250-400 r/min;
in the step 4), the ratio of the mass parts of the deeply impurity-removed and desiliconized fly ash to the volume parts of the desiliconized alkali liquor is 1: (4-6).
6. The method according to claim 1, wherein in the step 5), the sintering aid is 1-4 wt% of the high-Al-Si ratio desiliconized fly ash;
in the step 5), the method for preparing the granulating agent used for granulation comprises the following steps: mixing water and polyvinyl alcohol, stirring in a water bath at 80-90 ℃ for 8-11 h to obtain the granulating agent, wherein the ratio of the water to the polyvinyl alcohol is (90-93) to (7-10) in parts by weight;
in the step 5), the granulating agent is 0.1-0.8 wt% of the high-aluminum-silicon ratio desiliconized fly ash, and preferably 0.1-0.3 wt%;
in the step 5), after granulation, sieving the granules by a sieve of 40 to 60 meshes;
in the step 5), the pressure for molding is 100 to 300MPa, preferably 150 to 200MPa;
in the step 5), T =1600 to 1650, T =12 to 15;
in the step 5), the rate of heating to T ℃ is 30-50 ℃/min, preferably 30-40 ℃/min.
7. Columnar mullite obtained by the process according to any one of claims 1 to 6.
8. The columnar mullite according to claim 7, wherein the columnar mullite has a flexural strength of 120 to 180MPa and a bulk density of 2.6 to 3.03g/cm 3 。
9. The columnar mullite according to claim 7, wherein the columnar mullite has a porosity of 0.2 to 2% and an apparent porosity of 0.3 to 2.5%.
10. The columnar mullite according to claim 7, wherein the mullite phase content in the columnar mullite is greater than 93% and the refractoriness is not less than CN 180.
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