Process for extracting alumina from high-alumina fly ash

Abstract

The application discloses a method for extracting alumina from high-alumina fly ash. The method comprises the following steps: crushing the high-alumina fly ash and a low-temperature mineralizer in a ball mill to form crushed mixed raw materials, so as to realize preliminary activation of the raw materials; after the crushed mixed raw materials are formed into a shape, high-temperature roasting is performed, so as to obtain active mineral phase chamotte; the active mineral phase chamotte is crushed, stirred and alkali leached in an alkali liquor, and then separated, so as to obtain a filtrate and a filter residue; aluminum hydroxide seeds are added into the filtrate, so as to induce C 12 A7, the CA solution is converted into aluminum hydroxide crystals, and finally, the aluminum hydroxide product is obtained through filtration and separation. The extraction method is simple in process, easy to operate, low in reaction temperature and energy consumption, free of environmental pollution, convenient for large-scale popularization and use, and capable of solving the environmental problems caused by the high-alumina fly ash storage and the alumina resource shortage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of valuable metal extraction, in particular to a method for extracting alumina from high-aluminum fly ash. BACKGROUND

[0002] The amount of solid waste in China is large and wide, and its safe disposal is directly related to the national ecological and environmental safety. With the rapid development of China's industry, the increase of power consumption, the emission of fly ash also increases year by year. The central region of Inner Mongolia, the northern region of Shanxi and the eastern region of Ningxia are important large coal energy bases in China. The special geographical location makes a large number of associated boehmite and kaolinite and other aluminum-rich minerals in coal, forming a characteristic high-aluminum coal resource, with a prospective reserve of more than 100 billion tons. A large amount of high-aluminum fly ash (HAFA) is generated by high-aluminum coal after combustion for power generation, with an annual production of more than 30 million tons, an alumina content of more than 40%, a potential resource of more than 10 billion tons, and a clear strategic resource property, which has great recycling and recycling value.

[0003] However, the comprehensive utilization rate of high-aluminum fly ash is less than 30% at present, and the remaining part not used is long-term stacked in the ash storage yard. According to the statistics of the Ministry of Industry and Information Technology of China, for every 100 million tons of solid waste, 5,000 mu of land will be newly occupied. According to the existing stacking amount of high-aluminum fly ash in China, the land resources occupied by the cumulative stacking of high-aluminum fly ash have exceeded 25,000 mu.

[0004] The stacking of high-aluminum fly ash has the following problems:

[0005] First, high-aluminum fly ash in China is mainly produced in the northwest region, where the climate fluctuates greatly, the natural conditions are harsh, the ecological system is relatively fragile and has poor self-repairing ability. The stacking of high-aluminum fly ash in the local area may seriously damage the local vegetation growth environment, aggravate soil desertification, and cause air and water pollution;

[0006] Second, the salts and alkalis in high-aluminum fly ash may diffuse into the surrounding soil along with the penetration of rainwater during the stacking and landfill process, causing the surrounding land to be salinized, which is not conducive to the growth of crops and the production of aquaculture and animal husbandry;

[0007] Third, if the heavy metal elements and radioactive elements contained in high-aluminum fly ash diffuse into the soil and are absorbed by plants, they will eventually accumulate in the human body through the food chain, which will seriously endanger human health.

[0008] At the same time, the demand of alumina in China is greater than the output, and the demand gap mainly comes from imports, the dependence on foreign countries is high, the alumina content of high-aluminum fly ash is equivalent to that of medium-grade bauxite, and efficient extraction of alumina is a resource utilization approach with great social and environmental benefits. At present, the extraction of alumina from high-aluminum fly ash in China mainly includes pre-desilication-lime sintering method, limestone sintering-Bayer method, one-step acid dissolution method, ammonium sulfate sintering method and the like. These extraction methods of alumina have the following problems:

[0009] Firstly, the traditional alkali sintering has the defects of too high reaction temperature (1200-1300℃), narrow sintering temperature range, difficult control, high energy consumption and the like;

[0010] Secondly, the acid dissolution method has short process, but needs a complex purification process to ensure the quality of alumina products, has high requirements for corrosion resistance of equipment, and has problems of acid vapor pollution and the like;

[0011] Thirdly, the ammonium sulfate sintering method has the problems of serious material adhesion during heating, difficult recovery of ammonia gas and sulfur dioxide, equipment corrosion, sintering adhesion, low concentration of leaching solution and long process flow. SUMMARY

[0012] In view of the deficiencies of the prior art, the present application provides a method for extracting alumina from high-aluminum fly ash, which has the advantages of simple process, easy operation, low reaction temperature, low energy consumption and no environmental pollution, and is convenient for large-scale popularization and use.

[0013] In order to achieve the above-mentioned purpose, the method for extracting alumina from high-aluminum fly ash designed by the present application has the following steps:

[0014] S1) high-aluminum fly ash and low-temperature mineralizer are crushed in a ball mill, under the action of high-energy ball milling, the mixture is mechanically broken by repeated rolling and collision, the particle size of the mixture is reduced, the surface area is increased, at the same time, mullite in the high-aluminum fly ash produces surface defects or is converted into amorphous substance, and the mixture is preliminarily activated;

[0015] The low-temperature mineralizer includes carbide slag and calcium fluoride;

[0016] S2) the preliminarily activated mixture is pressed into a shape and is activated by high-temperature calcination, the low-temperature mineralizer participates in the conversion of mullite in the high-aluminum fly ash from mineral phase to clinker active mineral phase during the high-temperature calcination activation;

[0017] The specific participation process of the low-temperature mineralizer is as follows:

[0018] The calcareous compound in the low-temperature mineralizer decomposes into CaO in the calcination process, and CaO participates in the reaction of Al2O3 and SiO2 in the mullite phase in the high-aluminum fly ash under high-temperature sintering, and a clinker active mineral is generated, which contains 12CaO·7Al2O3, CaO·Al2O3 and 2CaO·SiO2 that are easily dissolved in alkali liquor and difficult to dissolve in alkali liquor;

[0019] The calcium fluoride and sulfate in the low-temperature mineralizer act as fluxes, reduce the liquid phase formation temperature, promote the formation of liquid phase in the sintering process, thereby reducing the calcination temperature and realizing low-temperature mineral phase reconstruction;

[0020] S3) crushing the clinker active mineral and alkali leaching in alkali liquor, wherein 12CaO·7Al2O3 and CaO·Al2O3 that are easily dissolved in alkali liquor are dissolved in the alkali liquor, and 2CaO·SiO2 that is difficult to dissolve in alkali liquor is in the form of suspended solid in the alkali liquor, and the solid and liquid are separated to obtain filtrate and residue;

[0021] S4) adding aluminum hydroxide seeds to the filtrate to induce the conversion of 12CaO·7Al2O3 and CaO·Al2O3 solution in the filtrate into aluminum hydroxide crystals, and finally filtering to separate the aluminum hydroxide product.

[0022] Further, in S1), the high-aluminum fly ash needs to be dried before being crushed in the ball mill, and the oven temperature is set to 105-110°C.

[0023] Further, in S1), the low-temperature mineralizer is added in an amount of 30%-75%.

[0024] Further, in S1), the ball mill is a high-energy ball mill, the ball milling speed is 300-600 rpm, and the ball milling time is 20-60 min.

[0025] Further, in S1), the low-temperature mineralizer further includes calcium carbonate and sulfate.

[0026] Further, in S2), the pressed mixture is placed in a muffle furnace for high-temperature calcination and activation, and the calcination conditions of the muffle furnace are as follows: heating rate 3-7°C / min, calcination temperature 950-1050°C, calcination time 1-3h, and natural cooling.

[0027] Further, in S2), the decomposition of the calcareous compound in the low-temperature mineralizer into CaO in the calcination process is as follows:

[0028] Ca(OH)2→CaO+H2O(1)

[0029] CaCO3→CaO+CO2(2)

[0030] The reaction equation of CaO participating in the Al2O3 in the mullite phase in the high-aluminum fly ash under high-temperature sintering is as follows formula (3) and (4)

[0031] 7(CaO·Al2O3)+5CaO→12CaO·7Al2O3 (3)

[0032] Al2O3+CaO→CaO·Al2O3 (4)

[0033] The reaction equation of CaO participating in the SiO2 in the mullite phase in the high-aluminum fly ash under high-temperature sintering is as follows formula (5)

[0034] 2CaO+SiO2→2CaO·SiO2 (5)

[0035] Further, in S3), the alkali liquor is NaOH / Na2CO3 double alkali liquor, the liquid-solid ratio of the double alkali liquor to the clinker active mineral is 5:1-10:1, the concentration of NaOH in the double alkali liquor is 2-8 g / L, and the concentration of Na2CO3 is 60-120 g / L.

[0036] Further, in S3), while alkali leaching in the alkali liquor, the mixed liquid of solid and liquid is heated by water bath stirring, the water bath temperature is 50-80 DEG C, and the stirring time is 15-45 min.

[0037] Further, in S3), the mixed liquid of solid and liquid is separated by vacuum filtration to obtain the filtrate.

[0038] The present application has the advantages that:

[0039] 1. The low-temperature mineralizer raw material used in the present application has wide sources and low cost, and the extraction process is simple and easy to operate, which is conducive to large-scale use.

[0040] 2. The equipment used in the present application is simple, the calcination temperature is 950-1050 DEG C, which is lower than the reaction temperature of the limestone sintering method (1300-1400 DEG C) and the alkali lime sintering method (1200 DEG C), the calcination energy consumption is relatively low, the feasibility is high, and good social benefits can be brought.

[0041] 3. The extraction rate of alumina in the present application can reach about 90%, which can realize efficient extraction of alumina in high-aluminum fly ash.

[0042] The method for extracting alumina from high-aluminum fly ash has the advantages of simple extraction process, easy operation, low reaction temperature, low energy consumption, no environmental pollution, and is convenient for large-scale popularization and use, and solves the environmental problems caused by high-aluminum fly ash storage and the present situation of alumina resource shortage. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 Physical diagram of the shaped material of the present application;

[0044] Figure 2 Process flow diagram of the present application;

[0045] Figure 3 XRD pattern of high-alumina fly ash used in the embodiment of the present application;

[0046] Figure 4 XRD pattern of clinker used in the embodiment of the present application. DETAILED DESCRIPTION

[0047] The present application is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] As shown in Figure 2 the method for extracting alumina from high-alumina fly ash, comprising the following steps:

[0049] S1) grinding the high-alumina fly ash and low-temperature mineralizer in a ball mill, under the action of high-energy ball milling, the mixture is mechanically broken by repeated rolling and collision, the particle size of the mixture is reduced, the surface area is increased, and at the same time, mullite in the high-alumina fly ash produces surface defects or is converted into amorphous material, achieving preliminary activation of the mixture.

[0050] The low-temperature mineralizer includes carbide slag and calcium fluoride.

[0051] Preferably, the high-alumina fly ash and the low-temperature mineralizer need to be dried before being ground in the ball mill, and the oven temperature is set to 105-110°C.

[0052] Preferably, the amount of the low-temperature mineralizer added is 30%-75%.

[0053] Preferably, the ball mill is a high-energy ball mill, the ball milling speed is 100-600 rpm, the ball milling time is 20-60 min, and the ball-to-material ratio is 1-5:1.

[0054] Preferably, the low-temperature mineralizer further includes calcium carbonate and sulfate.

[0055] High-energy ball milling is to mechanically change the raw material mixture by repeated welding, fracturing, re-welding and other ways to crush, increase the surface area, reduce the grain size, introduce surface defects and other physical changes. These changes will produce unsaturated groups, free ions and electrons, thus promoting chemical reactions. If the ball milling speed is small or the ball milling time is too short, it is difficult to achieve the effect of stimulating the reaction, but if the ball milling speed reaches a certain degree or the ball milling time is excessively prolonged, the increase of the ball milling speed and the ball milling time has little effect on the subsequent high-alumina fly ash mineral conversion, and even the mechanical equipment is worn and the energy consumption is increased. Therefore, more preferably, the ball milling speed is 300 rpm to 500 rpm, the ball milling time is 30 to 45 min, and the ball-to-material ratio is 1 to 3:1.

[0056] S2) The mixture after preliminary activation is pressed into a shape and high-temperature calcination activation is carried out, and the low-temperature mineralizer participates in the conversion of mullite in the high-alumina fly ash from a mineral phase to a clinker active mineral phase in the high-temperature calcination activation process.

[0057] The specific participation process of the low-temperature mineralizer is as follows:

[0058] The calcareous compound in the low-temperature mineralizer decomposes into CaO in the calcination process, and CaO participates in the reaction of Al2O3 and SiO2 in the mullite phase in the high-alumina fly ash under high-temperature sintering to generate clinker active minerals, which contain 12CaO·7Al2O3 (dodecacalcium aluminate), CaO·Al2O3 (monocalcium aluminate) and 2CaO·SiO2 (dicalcium silicate) that are easily dissolved in alkali liquor and difficult to dissolve in alkali liquor.

[0059] Calcium fluoride and sulfate in the low-temperature mineralizer act as fluxing agents to reduce the liquid phase formation temperature and promote the liquid phase formation in the sintering process, thereby reducing the calcination temperature and realizing low-temperature mineral phase reconstruction.

[0060] Specifically, 12CaO·7Al2O3 is dodecacalcium aluminate, abbreviated as C 12 A7, which is crystallized from the melt at 1450°C in the form of round particles without definite glass luster grain boundaries and definite cleavage. In clinker with high CaO content or under-fired clinker, this crystal form is often found. The coordination of aluminum and calcium in the crystal is very irregular, and the structure has many voids, with strong water absorption. The water absorption is maximum at 950°C, and it is difficult to make dry C 12 A7.

[0061] CaO·Al2O3 is monocalcium aluminate, abbreviated as CA, which is generated at 1100°C under normal conditions, and the optimal generation temperature is 1400°C. In the clinker prepared by sintering method, CA shows microcrystalline or skeleton-like crystal nucleus under a polarizing microscope, without pleochroism and with directional arrangement.

[0062] 2CaO·SiO2 is dicalcium silicate, abbreviated as C2S, mostly needle-shaped crystal, white powder. Odorless, non-toxic, soluble in strong acid, insoluble in water, alcohol and alkali.

[0063] Preferably, the mixture material pressed into shape is placed in a muffle furnace for high-temperature calcination, and the muffle furnace is calcined at a temperature rising rate of 3-7℃ / min, a calcination temperature of 950-1050℃, a calcination time of 1-3h, and natural cooling.

[0064] The calcination mechanism has an important influence on the sintering of the product. Too low a temperature rising rate increases energy consumption, and the solid-phase reaction process is slow. Too high a temperature rising rate causes the reactants to fail to undergo a fluxion reaction, and irreversible reactions inhibit the formation of the target mineral. Too low a calcination temperature or too short a holding time makes it difficult to reach the reaction conditions and fully react. Too high a calcination temperature or too long a holding time increases energy consumption. Therefore, more preferably, the muffle furnace is calcined at a temperature rising rate of 5℃ / min, a calcination temperature of 950-980℃, and a calcination time of 2h.

[0065] Compared with the limestone sintering method at 1300-1400℃ and the soda lime sintering method at 1200℃, the reaction temperature of the present application is lower, the calcination energy consumption is relatively low, the feasibility is high, and good social benefits can be brought.

[0066] Specifically, the calcium compound in the low-temperature mineralizer decomposes into CaO in the calcination process, and the equations are as follows (1) and (2)

[0067] Ca(OH)2→CaO+H2O (1)

[0068] CaCO3→CaO+CO2 (2)

[0069] CaO participates in the reaction of Al2O3 in the mullite phase in high-aluminum fly ash under high-temperature sintering, and the equations are as follows (3) and (4)

[0070] 7(CaO·Al2O3)+5CaO→12CaO·7Al2O3 (3)

[0071] Al2O3+CaO→CaO·Al2O3 (4)

[0072] CaO participates in the reaction of SiO2 in the mullite phase in high-aluminum fly ash under high-temperature sintering, and the equation is as follows (5)

[0073] 2CaO+SiO2→2CaO·SiO2 (5)

[0074] Preferably, the mass ratio of the low-temperature mineralizer to the total material is 0.45-0.55:1, and the addition of the low-temperature mineralizer can promote the occurrence of the solid-phase reaction, reduce the sintering temperature, save energy and accelerate the formation of the active mineral components of the clinker. If the addition amount of the low-temperature mineralizer is too low, the sintering temperature cannot be effectively reduced, and if the addition amount is too high, the content of the low-temperature mineralizer reaches saturation. Therefore, the mass ratio of the low-temperature mineralizer to the total material is more preferably 0.50.

[0075] The carbide slag includes Ca(OH)2 and a small amount of CaCO3, and the carbide slag provides an alkaline activator for the activation of the high-alumina fly ash. The carbide slag can be decomposed into CaO through mechanical activation and calcination, and the quicklime plays an important role in the mineral transformation of the high-alumina fly ash. If the proportion of the carbide slag is too low, the high-alumina fly ash cannot be effectively transformed into target minerals, and when the proportion of the quicklime is relatively high, the crystal phase transformation reaction can be more sufficient, but when the content of the carbide slag reaches saturation, increasing the addition amount of the carbide slag has little effect on the mineral transformation efficiency of the high-alumina fly ash. Therefore, the mass ratio of the carbide slag to the high-alumina fly ash is preferably 1.5-2.5:1, and more preferably 2.0-2.3:1.

[0076] Preferably, the addition amount of CaF2 is 6.5%-8%. The addition of CaF2 plays a role of fluxing agent, which can further reduce the sintering temperature of the mixed raw material and greatly reduce the energy consumption of subsequent industrial production. If the addition amount of CaF2 is too low, the effect of the fluxing agent is insufficient, and if the addition amount of CaF2 is too high and even supersaturated, the cost of the additive will be increased. Therefore, the addition amount of CaF2 is more preferably 7.5%.

[0077] Preferably, the addition of the sulfate also plays a role of fluxing agent, which can further reduce the sintering temperature of the mixed raw material and greatly reduce the energy consumption of subsequent industrial production. The mass ratio of the sulfate to the high-alumina fly ash is 0.25-0.85.

[0078] S3) crushing the clinker active mineral and alkali leaching in an alkali liquor, wherein 12CaO·7Al2O3 and CaO·Al2O3 that are easily soluble in the alkali liquor are dissolved in the alkali liquor, 2CaO·SiO2 that is difficult to dissolve in the alkali liquor is in a suspended solid state in the alkali liquor, and the solid and liquid are separated to obtain a filtrate and a filter residue.

[0079] Specifically, the alkali liquor is a NaOH / Na2CO3 double alkali liquor, the liquid-solid ratio of the double alkali liquor to the clinker active mineral is 5:1-10:1, the concentration of NaOH in the double alkali liquor is 2-8 g / L, and the concentration of Na2CO3 is 60-120 g / L.

[0080] Preferably, while alkali leaching in the alkali liquor, the mixture of the solid and the liquid is heated by water bath stirring, the water bath temperature is 50-80°C, and the stirring time is 15-45 min.

[0081] Preferably, the mixture of solid and liquid is subjected to solid-liquid separation by vacuum filtration to obtain a filtrate.

[0082] S4) adding aluminum hydroxide seeds into the filtrate to induce the conversion of 12CaO-7Al2O3, CaO-Al2O3 solution in the filtrate into aluminum hydroxide crystals, and finally filtering to separate the aluminum hydroxide product.

[0083] The high-alumina fly ash used in this example is from Shuozhou Goden Power Plant in Shanxi Province, and its XRD pattern is shown in Figure 3 , and its chemical composition is shown in Table 1 below:

[0084] Table 1 X-ray fluorescence (XRF) analysis results of high-alumina fly ash

[0085] Ingredients SiO2 Al2O3 SO3 CaO Fe2O3 TiO2 [K2O] MgO Others Content / % 41.96 36.72 7.38 6.24 3.35 1.95 0.623 0.498 1.279

[0086] Example 1:

[0087] First step, the high-alumina fly ash and low-temperature mineralizer are dried in a 105℃ oven, the mass ratio of calcium carbide slag to high-alumina fly ash is 1.6:1, the CaF2 external doping amount is 6.5% of the high-alumina fly ash, and the mixed raw materials are placed in a planetary ball mill jar according to the above mass ratio. After setting the rotation speed of the planetary ball mill to 350 rpm, the ball mill jar is opened, and the mechanical ball milling time is 30 min.

[0088] Second step, after ball milling, the uniformly mixed raw materials after ball milling are taken out, and a pressure machine is used to press into a pie shape with a thickness of 1 cm, as shown in Figure 1 , and the test block is placed in a muffle furnace, heated to 950℃ at a heating rate of 5℃ / min, and kept for 1h. After the heating program is completed, it is naturally cooled to room temperature.

[0089] Third step, the calcined clinker in the muffle furnace is taken out and crushed by mortar grinding, 10g of powdered clinker is placed in a single-necked flask, and mixed with the prepared NaOH / Na2CO3 double-alkali solution at a liquid-solid ratio of 10:1, wherein the concentration of Na2CO3 is 120g / L and the concentration of NaOH is 7g / L. Turn on the power of the digital constant-temperature water bath, turn on the power switch and heating switch in turn, and adjust the rotation speed to 400 rpm. The water bath in the water bath is stirred at 75℃ for 30 min.

[0090] Fourth step, after the mixture is cooled to room temperature, it is transferred to a vacuum filtration device, and the solid-liquid is fully separated by vacuum filtration. Aluminum hydroxide seeds are added to the filtrate to induce the conversion of calcium aluminate solution in the filtrate into aluminum hydroxide crystals. After filtering, the aluminum hydroxide product is obtained.

[0091] After this embodiment, the extraction rate of alumina is calculated to be 86.41%.

[0092] Example 2:

[0093] In the first step, the high-aluminum fly ash and the low-temperature mineralizer are dried in a 105°C oven. The mass ratio of carbide slag to high-aluminum fly ash is 1.8:1, and the CaF2 external addition amount is 6.5% of the high-aluminum fly ash. The mixed materials are placed in a planetary ball mill jar according to the above mass ratio, and the planetary ball mill is started after being set at a speed of 350 rpm. Mechanical ball milling is performed for 30 min.

[0094] In the second step, after the ball milling is completed, the uniformly mixed materials after ball milling are taken out and pressed into a pie with a thickness of 1 cm using a press at a pressure of 30 MPa, as shown in FIG. 1. Figure 1 The test block is placed in a muffle furnace, heated to 980°C at a heating rate of 5°C / min, and kept for 1 h. After the heating program is completed, it is naturally cooled to room temperature.

[0095] In the third step, the calcined clinker in the muffle furnace is taken out and crushed by pot grinding. 10 g of the powdered clinker is placed in a single-necked flask and mixed with the prepared NaOH / Na2CO3 double-alkali solution at a liquid-solid ratio of 10:1. The concentration of Na2CO3 is 120 g / L, and the concentration of NaOH is 7 g / L. The digital constant-temperature water bath pot is turned on, and the power switch and heating switch are turned on in sequence. The speed is adjusted to 400 rpm, and the water bath in the water bath pot is uniformly stirred at 75°C for 30 min.

[0096] In the fourth step, after the mixed solution is cooled to room temperature, it is transferred to a vacuum filtration device for full separation of solid and liquid. Aluminum hydroxide seeds are added to the filtrate to induce the conversion of calcium aluminate solution in the filtrate to aluminum hydroxide crystals. After filtration, the solid and liquid are separated to obtain the aluminum hydroxide product.

[0097] After this embodiment, the extraction rate of alumina is calculated to be 87.74%.

[0098] Example 3:

[0099] In the first step, the high-aluminum fly ash and the low-temperature mineralizer are dried in a 105°C oven. The mass ratio of carbide slag to high-aluminum fly ash is 1.8:1, and the CaF2 external addition amount is 6.5% of the high-aluminum fly ash. The mixed materials are placed in a planetary ball mill jar according to the above mass ratio, and the planetary ball mill is started after being set at a speed of 350 rpm. Mechanical ball milling is performed for 30 min.

[0100] In the second step, after the ball milling is completed, the uniformly mixed materials after ball milling are taken out and pressed into a pie with a thickness of 1 cm using a press at a pressure of 30 MPa, as shown in FIG. 1. Figure 1As shown, the test block was placed in a muffle furnace, heated to 950℃ at a heating rate of 5℃ / min, and kept for 2h, and after the heating program was over, it was allowed to cool to room temperature naturally.

[0101] Thirdly, the calcined clinker in the muffle furnace was taken out and crushed by mortar grinding, 10g of the powdered clinker was placed in a single-necked flask, mixed with the prepared NaOH / Na2CO3 double alkali solution at a liquid-solid ratio of 10:1, wherein the concentration of Na2CO3 was 120g / L and the concentration of NaOH was 7g / L, the power of the digital constant temperature water bath was turned on, the power switch and the heating switch were turned on in turn, the speed was adjusted to 400rpm, and the water bath in the water bath at 75℃ was stirred uniformly for 30min.

[0102] Fourthly, after the mixture was cooled to room temperature, it was transferred to a vacuum filtration device, and the solid-liquid was fully separated by vacuum filtration, aluminum hydroxide seeds were added to the filtrate, and the calcium aluminate solution in the filtrate was induced to convert into aluminum hydroxide crystals, and then the solid-liquid was separated by filtration to obtain the aluminum hydroxide product.

[0103] After this embodiment, the extraction rate of alumina was calculated to be 91.08%.

[0104] Example 4:

[0105] Firstly, the high-aluminum fly ash and the low-temperature mineralizer were dried in a 105℃ oven, the mass ratio of carbide slag to high-aluminum fly ash was 2.2:1, the mass ratio of calcium sulfate to high-aluminum fly ash was 0.55:1, and the CaF2 external doping amount was 8% of the high-aluminum fly ash, the mixture was placed in a planetary ball mill jar according to the above mass ratio, the planetary ball mill was started after setting the speed to 350rpm, and the ball mill jar was started.

[0106] Secondly, after the ball milling was completed, the uniformly mixed material after ball milling was taken out and pressed into a pie with a thickness of 1cm using a press at a pressure of 30MPa, as shown in Figure 1 As shown, the test block was placed in a muffle furnace, heated to 950℃ at a heating rate of 5℃ / min, and kept for 2h, and after the heating program was over, it was allowed to cool to room temperature naturally. Figure 4 .

[0107] Thirdly, the calcined clinker in the muffle furnace was taken out and crushed by mortar grinding, 10g of the powdered clinker was placed in a single-necked flask, mixed with the prepared NaOH / Na2CO3 double alkali solution at a liquid-solid ratio of 10:1, wherein the concentration of Na2CO3 was 120g / L and the concentration of NaOH was 7g / L, the power of the digital constant temperature water bath was turned on, the power switch and the heating switch were turned on in turn, the speed was adjusted to 400rpm, and the water bath in the water bath at 75℃ was stirred uniformly for 30min.

[0108] The fourth step, after the mixed solution is cooled to room temperature, it is transferred to a vacuum filtration device, and solid-liquid is fully separated by vacuum filtration. Aluminum hydroxide seeds are added to the filtrate to induce the conversion of calcium aluminate solution in the filtrate into aluminum hydroxide crystals. After filtration, solid-liquid separation is performed to obtain an aluminum hydroxide product.

[0109] After the embodiment, it is calculated that the extraction rate of aluminum oxide is 92.83%.

[0110] From the above embodiments 1-4, the method for extracting aluminum oxide from high-aluminum fly ash has an extraction rate of aluminum oxide higher than 85%.

[0111] The key technical solution of the present application is to use high-energy ball milling to reduce the particle size of each material, increase the surface area, and improve the chemical reaction activity of the mixture. Then, through the muffle furnace roasting method, the internal mineral structure is directionally converted to produce calcium aluminate and calcium silicate that is easily soluble in alkali solution and difficult to dissolve in alkali solution, realizing efficient separation of silicon and aluminum and achieving the purpose of efficient extraction of aluminum oxide.

[0112] The above embodiments are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above embodiments. Any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.

Claims

1. A method of extracting alumina from a high alumina fly ash, characterized by, The method comprises the following steps: S1) grinding high-alumina fly ash and low-temperature mineralizer in a ball mill, under the action of high-energy ball milling, the mixture is mechanically broken by repeated rolling and collision, the particle size of the mixture is reduced and the surface area is increased, at the same time, mullite in the high-alumina fly ash is converted into amorphous substance or has surface defects, and the mixture is preliminarily activated; The low-temperature mineralizer comprises carbide slag and calcium fluoride. The ball mill is a high-energy ball mill, the ball milling speed is 300 rpm to 600 rpm, and the ball milling time is 20 to 60 min. S2) the preliminarily activated mixture is pressed into a shape and is subjected to high-temperature calcination and activation, and the low-temperature mineralizer participates in the conversion of mullite in the high-alumina fly ash from a mineral phase to a clinker active mineral phase during the high-temperature calcination and activation. The high-temperature calcination conditions are as follows: the temperature rising speed is 3 to 7 ℃ / min, the calcination temperature is 950 to 1050 ℃, the calcination time is 1 to 3 h, and the temperature is naturally cooled down. The specific participation process of the low-temperature mineralizer is as follows: In the calcination process, the calcareous compound in the low-temperature mineralizer is decomposed into CaO, the CaO participates in the reaction of Al2O3 and SiO2 in the mullite phase in the high-alumina fly ash under high-temperature sintering, and a clinker active mineral is generated, the clinker active mineral contains 12CaO·7Al2O3, CaO·Al2O3 which are easily soluble in lye and 2CaO·SiO2 which is difficult to dissolve in lye; The calcium fluoride and sulfate in the low-temperature mineralizer act as fluxing agents, reduce the liquid phase formation temperature, promote the liquid phase formation in the sintering process, thereby reducing the calcination temperature and realizing low-temperature mineral phase reconstruction; S3) the clinker active mineral is ground and is subjected to alkali leaching in lye, 12CaO·7Al2O3 and CaO·Al2O3 which are easily soluble in lye are dissolved in the lye, 2CaO·SiO2 which is difficult to dissolve in lye is in a suspended solid state in the lye, and the lye and the solid are separated to obtain a filtrate and a filter residue; The lye is NaOH / Na2CO3 double lye, the liquid-solid ratio of the double lye to the clinker active mineral is 5:1 to 10:1, the concentration of NaOH in the double lye is 2 to 8 g / L, and the concentration of Na2CO3 is 60 to 120 g / L; S4) aluminum hydroxide seeds are added to the filtrate to induce the 12CaO·7Al2O3 and CaO·Al2O3 solution in the filtrate to be converted into aluminum hydroxide crystals, and finally, the aluminum hydroxide product is obtained by filtration and separation.

2. The method of extracting alumina from high alumina fly ash according to claim 1, characterized by: In S1), the high-alumina fly ash and the low-temperature mineralizer need to be dried before being ground in the ball mill, and the oven temperature is set to 105 to 110 ℃.

3. The method of extracting alumina from high alumina fly ash according to claim 2, characterized by: In S1), the addition amount of the low-temperature mineralizer is 30% to 75%.

4. The method of extracting alumina from a high alumina fly ash according to claim 3, characterized in that: In S1), the low-temperature mineralizer further comprises calcium carbonate and sulfate.

5. The method of extracting alumina from high alumina fly ash as claimed in claim 1, wherein: In S2), the pressed mixture is placed in a muffle furnace for high-temperature calcination and activation.

6. The method of extracting alumina from a high alumina fly ash as claimed in claim 5, wherein: In S2), the equations for the decomposition of the calcareous compound in the low-temperature mineralizer into CaO in the calcination process are as follows: ​ ​ The reaction equation of CaO participating in Al2O3 of the mullite phase in the high-alumina fly ash under high-temperature sintering is as follows: formula (3) and (4) 7(CaO-Al2O3)+5CaO→12CaO-7Al2O3 (3) Al2O3+CaO→CaO-Al2O3 (4) The reaction equation of CaO participating in SiO2 of the mullite phase in the high-alumina fly ash under high-temperature sintering is as follows: formula (5) 2CaO+SiO2→2CaO-SiO2 (5).

7. The method of extracting alumina from high alumina fly ash according to claim 1, characterized by: In S3), the mixed liquid of solid and liquid is heated by water bath stirring, the water bath temperature is 50-80°C, and the stirring time is 15-45 min.

8. The method of extracting alumina from a high alumina fly ash according to claim 7, characterized in that: In S3), the mixed liquid of solid and liquid is separated by vacuum filtration to obtain the filtrate.

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