Method for extracting aluminum oxide from fly ash

Abstract

The invention discloses a method for extracting alumina from fly ash, which comprises the following steps: S1, carrying out pre-desiliconization and solid-liquid separation on high-alumina fly ash to obtain a sodium silicate solution and desiliconized ash, and is characterized by further comprising the following steps: S2, mixing the desiliconized ash in the S1 with sodium carbonate, limestone and a binder, granulating, and sintering to obtain clinker; and S3, the clinker prepared in the S2 is subjected to countercurrent leaching. The preparation method has the advantages that 1) the combustion improver is added during proportioning, so that a bonding effect can be achieved, granulation and forming are facilitated, the reaction heat value is increased, the use amount of sintered natural gas is greatly reduced, and the energy consumption is greatly reduced; according to the preparation method, the solid-state ion reaction degree is increased and the follow-up leaching effect is improved in the batching, granulating and sintering procedures. In addition, the sintering condition of the furnace kiln in the sintering process is relieved, and the service life of the sintering furnace kiln is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of harmless resource treatment of solid waste and hazardous waste, and specifically to a method for extracting aluminum oxide from fly ash, and in particular to a method for improving the desiliconization rate and reducing energy consumption in the process of extracting aluminum oxide from high-aluminum fly ash. Background Art

[0002] Fly ash is the main solid waste discharged from thermal power generation, and its main component is Al 2 O 3 、SiO 2 , Fe 2 O 3 、TiO 2 , CaO, MgO, etc. The main mineral phases in fly ash from different origins were analyzed, and it was found that the mineral phase composition of fly ash from different origins was also quite different. It mainly contained two types of mineral phases, one in the form of crystal mineral phase; the other mainly in the form of glass, which may include low-temperature quartz, mullite, high-iron glass, low-iron glass, glassy SiO 2 、Glass Al 2 O 3 wait.

[0003] my country started research on extracting alumina from fly ash early, and the main methods are divided into acid method and alkaline method.

[0004] Acid method for utilizing Al in fly ash 2 O 3 Soluble in acid and SiO 2 The insoluble nature enables the separation of silicon and aluminum. The acid method is used to process widely distributed high-silicon, low-iron aluminum-containing raw materials. Because the silicon dioxide in fly ash does not react with acid, it is easier to separate silicon and aluminum than the alkaline method, and the large amount of acid used can be recycled to reduce costs, but it requires high corrosion resistance of the equipment, and impurity ions such as Fe and Ca in fly ash will also be leached with Al, which requires high impurity removal and it is difficult to produce metallurgical grade alumina products.

[0005] The alkaline process has simple process steps and mature technology. The extracted alumina has high purity. It is the first choice for producing high-quality alumina from high-alumina fly ash. The existing industrial process is the pre-desiliconization-alkali lime sintering method, which involves first leaching fly ash with NaOH solution to make the amorphous silicon dioxide in the ash react with NaOH to form sodium silicate. 2 Total SiO in fly ash 2 The content is about 50.8%, and alkali desiliconization can extract part of the amorphous SiO 2 , which is beneficial to reduce the amount of silicon-calcium slag produced during the extraction of alumina and remove part of the silicon in advance. 2 CO3 As the main sintering agent, it reacts with fly ash at high temperature to generate easily soluble aluminates and insoluble silicates. After the separation of silicon and aluminum, it is calcined to obtain alumina or directly dissolved with high-concentration alkali solution and then separated by crystallization. Compared with the simple soda-lime sintering method, pre-desiliconization reduces the consumption of alkali (Na 2 CO 3 ) amount is reduced, and the desiliconization solution can be further processed and utilized to improve economic benefits.

[0006] Disadvantages of the pre-desiliconization-soda lime sintering method: high sintering temperature leads to high energy consumption, and the large amount of raw material limestone used also leads to a large amount of waste slag, which cannot be effectively utilized and pollutes the environment. 2 CO 3 With calcium orthosilicate (CaO·SiO 2 ) secondary reaction (forming Na 2 SiO 3 +CaCO 3 ), resulting in SiO 2 It precipitates with aluminum hydroxide into the finished alumina product, increasing the impurity content of alumina. 2 High content will cause scarring of the evaporator tube wall, reduce the conduction efficiency, and affect the smooth evaporation operation. For alumina production, the depth of desiliconization and the stability of indicators are crucial to the quality of alumina. In addition, pressurized desiliconization is a high-energy-consuming process, and the improvement of its equipment and process flow has a significant impact on the steam consumption and cost of alumina (the processing fee of the desiliconization process can account for more than 10% of the total cost at the highest).

[0007] In 2008, Datang International used the above-described pre-desiliconization-soda lime sintering process in Inner Mongolia to build a demonstration production line with an annual output of 200,000 tons of alumina and a co-production of 160,000 tons of calcium-silicon slag. The entire process was completed in 2010, and the production capacity was stabilized in 2013. The production line has undergone a large number of technical transformations in the later period, and the production situation has improved year by year. The process technology indicators are also being continuously optimized and improved. However, due to the high energy consumption, high cost, and low added value of silicon byproducts, the production line is in a state of suspension.

[0008] A Chinese patent with publication number CN106348323A discloses a method for producing alumina using raw material balls, comprising the following steps: reacting high-aluminum fly ash with a sodium hydroxide solution for pre-desiliconization to obtain a fly ash filter cake and a desiliconized liquid; adding the desiliconized fly ash filter cake into a sodium carbonate solution to form a mixed slurry, then adding limestone, quicklime, anthracite and other powders under stirring conditions, stirring and solidifying, using a ball making machine to make balls to obtain raw material balls, drying the raw material balls outside the kiln and then entering a rotary kiln to calcine into clinker, mixing the clinker with an adjustment liquid for dissolution, performing solid-liquid separation after dissolution to obtain a dissolution slag and a sodium aluminate crude liquid, performing one or two stage desiliconization on the obtained sodium aluminate crude liquid, obtaining a sodium aluminate concentrate, and then performing carbon decomposition to obtain an aluminum hydroxide product. The desiliconization rate of this scheme needs to be improved, and the energy consumption and cost need to be reduced. Summary of the invention

[0009] The object of the present invention is to provide a method for extracting aluminum oxide from fly ash, thereby improving the desiliconization rate of a pre-desiliconization-soda lime sintering method and reducing energy consumption and production costs.

[0010] In order to achieve the above object, the technical solution adopted by the present invention is:

[0011] A method for extracting aluminum oxide from fly ash, comprising S1, pre-desiliconizing high-aluminum fly ash, solid-liquid separation to obtain sodium silicate solution and desiliconized ash, and S2, mixing the desiliconized ash in S1 with sodium carbonate, limestone, and a binder, granulating, and sintering to obtain clinker; S3, countercurrent leaching the clinker obtained in S2 to obtain a leachate and a leaching residue;

[0012] The binder in S2 is lignite or petroleum coke; preferably, the binder in S2 is lignite.

[0013] Under the combined action of limestone and sodium carbonate, an ion exchange reaction occurs to form CaO.SiO 2 and NaAlO which is easily soluble in water 2 The more complete the reaction is, the better the desiliconization effect is, and the higher the recovery rate of alumina and the purity of the product are. The traditional method is to mix the powder into balls and then roast them, which is not conducive to the occurrence of ion exchange reactions at high temperatures. Therefore, adding a binder for granulation can increase the contact area between fly ash and sodium carbonate, limestone, and binder, increase the degree of ion reaction in the solid state, and make the sintering reaction more complete. In addition, the addition of the binder increases the calorific value of the reaction and reduces the energy consumption of the sintering reaction.

[0014] The clinker is subjected to countercurrent leaching, and the liquid-to-solid ratio of countercurrent leaching is low, which can reduce equipment specifications and equipment quantity, and reduce investment costs.

[0015] After passing through S3, most of the Si element in the solution is precipitated in the form of sodium silicon slag, reducing the loss of alumina.

[0016] The high-aluminum fly ash comprises the following components in parts by weight: Al 2 O 3 40-50 parts, SiO 2 40-50 parts, Fe 2 O 3 5-10 parts, CaO2-5 parts, MgO1-5 parts.

[0017] According to the embodiments of the present invention, the present invention can be further optimized. The following is the technical solution formed after optimization:

[0018] The binder in S2 is lignite or petroleum coke; preferably, the binder in S2 is lignite.

[0019] Compared with anthracite as a binder, the present invention uses blue coke or petroleum coke, which can improve the bonding performance, increase the heat conduction efficiency, reduce the material scattering loss due to the tight structure, and promote the complete sintering reaction.

[0020] In one of the preferred embodiments, in S1, the mass ratio of the desiliconized ash to the sodium carbonate and the limestone is (1-1.1):(1-1.1):(1-1.3), and the mass of the added binder is 1.5% to 3% of the mass of the desiliconized ash.

[0021] In one preferred embodiment, the particle size of the granules in S2 is 8-10 mm. The small particle size of the present application promotes complete sintering reaction.

[0022] In one preferred embodiment, the sintering temperature in S2 is 1000-1400°C, the sintering time is 30-60min, and the residence time in the kiln is 120-180min; preferably, the sintering temperature in S2 is 1100-1200°C, the sintering time is 30-35min, and the residence time in the kiln is 120-150min.

[0023] Part of the flue gas is returned for secondary use to further reduce energy consumption.

[0024] In one preferred embodiment, the liquid-to-solid ratio of the countercurrent leaching in S3 is 0.6-2, three to five levels of countercurrent leaching are performed at room temperature, and the leaching time is 48-96 hours.

[0025] In one preferred embodiment, in S3, the leached residue after countercurrent leaching is washed once, and the washing liquid is preferably returned to the countercurrent leaching for recycling.

[0026] In one preferred embodiment, the method for extracting alumina from fly ash further comprises S4, deeply desiliconizing the leaching solution in S3 to obtain a secondary desiliconized liquid;

[0027] S5, carbon dioxide is introduced into the secondary desiliconized semen, sodium aluminate forms aluminum hydroxide precipitation, and the precipitation is filtered and washed to obtain an aluminum hydroxide filter cake;

[0028] S6. The aluminum hydroxide filter cake is calcined.

[0029] Further heating and pressurizing desiliconization is performed to achieve deep desiliconization. The desiliconized semen is then decomposed by carbonation, solid-liquid separation, and calcined to obtain metallurgical grade alumina.

[0030] In one of the preferred embodiments, S2 and S3 also include sintering solid waste heat utilization; preferably, the sintering solid waste heat utilization adopts a solid waste heat boiler to cool the clinker to 100-150°C, and use the clinker heat to produce hot water and saturated steam.

[0031] By adding a solid waste heat utilization process after sintering, the sintering heat can be recovered to generate steam and hot water, which can be used in other work sections to reduce the energy consumption of the entire process.

[0032] In one preferred embodiment, the pre-desiliconization in S1 is specifically to add NaOH to the high-alumina fly ash, the mass fraction of NaOH is 10-20%, the reaction temperature is 90-100°C, the reaction time is 1-3h, the liquid-solid ratio is 2-4, and the desiliconization time is 1-3h.

[0033] After pre-desiliconization, the soluble silicon dissolves and reacts with the sodium hydroxide solution to form a sodium silicate solution. The sodium silicate can be further utilized for high value, and the insoluble crystalline silicon remains in the desiliconization ash. The desiliconization ash (wet basis) is mixed with sodium carbonate, limestone, and a binder in a certain proportion and then granulated.

[0034] In one preferred embodiment, the deep desiliconization in S4 includes one-stage desiliconization and two-stage desiliconization; the one-stage desiliconization is to add seed crystals to the leachate obtained in S3 for pressure boiling desiliconization to obtain sodium silicate slag and solution; the two-stage desiliconization is to add lime milk to the solution obtained in S3 after precise filtration for reaction; preferably, the calcium oxide content in the lime milk is 8-10g / L, and the temperature is 90-100°C.

[0035] Part of the produced sodium silicon slag can be ground and recycled as seed crystals.

[0036] Furthermore, the solid-liquid ratio of washing in S5 is 1-2:1-2.

[0037] Furthermore, the calcination temperature in S6 is 700-900° C., and the calcination time is 3-5 h.

[0038] Furthermore, in S3, the countercurrent leaching device adopts an underground pool and does not require stirring.

[0039] Furthermore, in S3, a slag remover is used to remove slag and drain water, or a material remover is used in combination with a belt filter to separate solid and liquid.

[0040] The main principles of the present invention are as follows:

[0041] The raw materials are pre-desiliconized, sintered, dissolved, desiliconized, carbonated and decomposed, and calcined.

[0042] Pre-desiliconization: wet method, essentially alkali leaching, Na 2 SiO 3 The modulus is 0.86.

[0043] SiO 2 +2NaOH → Na 2 SiO 3 +H 2 O

[0044] Na 2 SiO 3 +Ca(OH) 2 →CaSiO 3 ↓+2NaOH

[0045] Sintering: Fire method, 1100~1200℃, essentially replacing SiO with CaO 2 , Al 2 O 3 with Na 2 CO 3 Forming NaAlO which is easily soluble in water 2 .

[0046] 3Al 2 O 3 ·2SiO 2 +4CaO+3Na 2 CO 3 →2(2CaO·SiO 2 )+6NaAlO 2 +3CO 2 ↑

[0047] Dissolution: Wet method, using dilute alkali or water to dissolve the clinker to achieve silicon and aluminum separation.

[0048] CaO·SiO 2 +Na 2 CO 3 →Na 2 SiO 3 +CaCO 3

[0049] Desiliconization: wet method, refined liquid is obtained after desiliconization.

[0050] The first stage of desiliconization produces sodium silicon slag (hydrated sodium aluminosilicate). The reaction is very slow at room temperature and pressure without stirring. It requires high temperature and high pressure to add seed crystals. For every 1 gram of SiO precipitated 2 1 to 1.2 grams of aluminum oxide is lost and 3 grams of silicon slag is generated.

[0051] 2Na 2 SiO 3 +2NaAl(OH) 4 →Na 2 O.Al 2 O 3 ·2SiO 2 ·nH2O↓+4NaOH

[0052] Second stage desiliconization, adding lime milk, producing calcium silicate slag (hydrated garnet), each precipitate 1 gram SiO 2 17 to 18 grams of alumina are lost and 60 grams of silicon slag are generated.

[0053] 3Ca(OH) 3 +2NaAl(OH) 4 →(3CaO·Al 2 O 3 6H2O)+2NaOH

[0054] ×Na 2 SiO 3 +3CaO·Al 2 O 3 ·6H2O→3CaO·Al 2 O 3 ×SiO 2 ·(6-2×)H2O↓+2×NaOH(×=0.1~0.2)

[0055] Carbonization: wet method.

[0056] 2NaAlO 2 +CO 2 +3H 2 O→Na 2 CO 3 +2Al(OH) 3 ↓

[0057] 2NaOH+CO 2 →Na 2 CO 3 +H 2 O

[0058] Calcination: fire method, 500-800℃.

[0059] 2Al(OH) 3 →Al 2 O 3+3H 2 O

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] 1) The combustion aid is added during the batching of the present invention, which can not only play a bonding role and help granulation molding, but also increase the reaction heat value, greatly reduce the use of sintering natural gas, and greatly reduce energy consumption.

[0062] 2) The batching, granulating and sintering process of the present invention increases the degree of solid-state ion reaction and improves the subsequent leaching effect. In addition, the kiln stagnation during the sintering process is reduced, and the service life of the sintering kiln is extended.

[0063] 3) The present invention adds a solid waste heat recovery process, and the self-produced steam can be used in other processes, especially in the pressurized desiliconization section, which greatly reduces the consumption of natural gas steam production.

[0064] 4) The present invention adopts countercurrent leaching, with a small solid-liquid ratio and good leaching effect, which can reduce the specifications of the desiliconization process equipment. The leaching device can adopt a ground pool to replace the traditional leaching tank, which greatly reduces the equipment investment and power load.

[0065] 5) The present invention improves the removal rate of silicon dioxide in the method of extracting aluminum oxide from fly ash and improves the recovery rate of aluminum oxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 It is a process flow chart in one embodiment of the present invention. DETAILED DESCRIPTION

[0067] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0068] Comparative Example 1 (no granulation, excluding waste heat recovery)

[0069] 1) Selection of raw materials:

[0070] High alumina fly ash components: Al 2 O 3 : 47.5%, SiO 2 :41.46,Fe 2 O 3 :5.8%, CaO: 2.86%, MgO: 1.58%.

[0071] 2) Pre-desiliconization

[0072] The above raw materials were pre-desiliconized at a reaction temperature of 95°C, a reaction time of 2h, a liquid-to-solid ratio of 3, a NaOH mass fraction of 15%, and a desiliconization time of 2h. After the reaction, solid-liquid separation was performed by a filter press. After separation, sodium silicate solution and desiliconized ash (i.e., aluminum silicate ash) were obtained. The aluminum silicate ash was dried in a drying cylinder at 105°C until the water content was controlled to about 15%, and the sodium silicate solution was used for further high-value utilization. Under this condition, the desiliconization rate reached 42%.

[0073] Desiliconization rate = (Silicon in raw material - Silicon in solution) / Silicon in raw material * 100%

[0074] Silicon carried into the next stage in the slag: 1000 × 41.46% × (1-42%) = 240.5 g

[0075] 3) Dissolved silicon

[0076] The cooled sintered clinker is transported by chain plates to the leaching tank, and industrial water is added to carry out downstream leaching of silicon and aluminum separation. The liquid-to-solid ratio is 2, leaching is carried out at room temperature, and the leaching time is 72 hours. The solid-liquid separation is carried out by a filter. The leaching liquid contains soluble sodium aluminate and sodium silicate, and the soluble silicon is 7g / L. The next step of deep desiliconization is carried out.

[0077] Desiliconization rate: (240.5-6L×7g / L) / (1000g×41.46%)=47.9%

[0078] 4) Deep desiliconization

[0079] Deep desiliconization includes one-stage desiliconization and two-stage desiliconization. The silicon dioxide in the leachate is precipitated in the form of hydrated garnet. Seedlings are added under high temperature and high pressure conditions for pressure boiling and desiliconization. The product of this desiliconization is called sodium silicate slag in production. Part of the produced sodium silicate slag can be ground and recycled as seedlings. For every gram of silicon dioxide precipitated, 1-1.2g of alumina is lost, and 3-4g of silicon slag is produced. After precise filtration, the solution is added with lime milk (calcium oxide content is 8-10g / L), and secondary desiliconization is carried out at 90-100℃ and normal pressure. All silicon is precipitated. For every gram of silicon dioxide precipitated, 17-18g of alumina is lost, and 60-65g of hydrated garnet is produced. The solution is mainly sodium aluminate and sodium hydroxide, which is called secondary desiliconization concentrate and enters the next stage. The maximum loss of aluminum and the maximum energy consumption in the method of producing alumina from fly ash are both in this step. The loss of alumina this time is: 125g / L solution.

[0080] 5) Carbonation decomposition

[0081] Carbon dioxide is introduced into the secondary desiliconization liquid, and sodium aluminate forms aluminum hydroxide precipitation. Sodium hydroxide reacts with carbon dioxide to form sodium carbonate and water. After plate and frame filtration, stirring and washing are performed once, and the washing liquid-solid ratio is 1:1. After filtration, aluminum hydroxide filter cake is formed. The filtrate and washing water are added to the secondary desiliconization for recycling. The direct recovery rate of aluminum is improved.

[0082] 6) Calcination

[0083] The aluminum hydroxide filter cake is calcined in a tunnel kiln at 800°C for 4 hours to generate α-Al 2 O 3 product.

[0084] Example 1 (adding ingredients for granulation and sintering, solid waste heat recovery, and countercurrent leaching and desiliconization)

[0085] 1) Selection of raw materials:

[0086] High aluminum fly ash components: Al 2 O 3 : 47.5%, SiO 2 :41.46,Fe 2 O 3 :5.8%, CaO: 2.86%, MgO: 1.58%.

[0087] The pre-desiliconization process in Comparative Example 1 was repeated, and batch granulation sintering and solid waste heat recovery were added.

[0088] 2) Ingredients, granulation and sintering

[0089] The pre-desiliconized aluminum ash is mixed with sodium carbonate and limestone at a ratio of 1:1:1.05, and 2% blue carbon is added as an auxiliary agent. A disc pelletizer is used for pelletizing, and the particle size is 8-10mm. Sintering is carried out in a rotary kiln at 1100-1200℃. The sintering time is 35min, and the residence time in the kiln is 135min. Part of the flue gas is returned for secondary use. The natural gas consumption is 75Nm 3 / t clinker. Compared with the method of comparative example 1, 17Nm 3 / t clinker, greatly reducing energy consumption. Loss on ignition rate was reduced from 21% to 17%.

[0090] 3) Solid waste heat recovery

[0091] The clinker temperature after sintering in the rotary kiln is 1000℃ and the bulk density is: 0.9t / m 3 , enter the solid waste heat boiler for cooling and waste heat recovery. The boiler outlet temperature is ≤150℃, and can produce 1.1t / t clinker of hot water and 0.3t / t clinker of saturated steam. Both steam and hot water can be used for further utilization in other sections.

[0092] 4) Countercurrent leaching and desiliconization

[0093] The silicon dissolution process in Comparative Example 1 was modified to countercurrent leaching and desiliconization.

[0094] The cooled sintered clinker is transported by chain plates and distributed to the ground pool. Industrial water is added for countercurrent leaching of silicon and aluminum separation. The liquid-to-solid ratio is 1 times, and the four-stage countercurrent leaching is carried out at room temperature for 72 hours. The leaching slag is removed from the ground pool by slag removal equipment. Most of the silicon will form calcium silicate and enter the slag for further resource utilization. The leaching liquid contains soluble sodium aluminate and sodium silicate. The soluble silicon dioxide is 3.5g / L. It is conducive to the next step of deep desiliconization.

[0095] Desiliconization rate: (240.5-1L×3.5g / L) / (1000g×41.46%)=57.1%

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 1 is:

[0098] (1) The binder is anthracite.

[0099] (2) Addition ratio: 1.5%.

[0100] (3) Granulation size 15-20mm (traditional pelletizing particle size).

[0101] The loss on ignition rate is analyzed by thermogravimetric analysis (TGA). The porosity is tested by destructive testing, and the pore volume is calculated based on the mass change of the material before and after it is soaked in liquid.

[0102]

[0103] Comparative Example 3:

[0104] The difference between this comparative example and Example 1 is that there is no binder.

[0105]

[0106] Conclusion: The absence of binder leads to loose granulation, 23% increase in sintering energy consumption, increased loss on ignition, high silicon content in leached slag and significantly increased aluminum loss.

[0107] Comparative Example 4:

[0108] The difference between this comparative example and Example 1 is that there is no waste heat boiler.

[0109]

[0110] A comparison shows that waste heat recovery reduces overall energy consumption by 28%, reduces carbon emissions by 31%, realizes energy recycling, and the recovered energy meets 60% of the hot water demand in the leaching section.

[0111] Example 2

[0112] The difference between this comparative example and Example 1 is that the process parameters of countercurrent leaching and desiliconization are different.

[0113] The cooled sintered clinker is transported by chain plates and distributed to the ground pool. Industrial water is added for countercurrent leaching of silicon and aluminum separation. The liquid-to-solid ratio is 1 times, and the four-stage countercurrent leaching is carried out at room temperature for 72 hours. The leaching slag is removed from the ground pool by slag removal equipment. Most of the silicon will form calcium silicate and enter the slag for further resource utilization. The leaching liquid contains soluble sodium aluminate and sodium silicate. The soluble silicon dioxide is 3.5g / L. It is conducive to the next step of deep desiliconization.

[0114] Comparative Example 5

[0115] The difference between this comparative example and Example 1 is that conventional downstream leaching is adopted with a liquid-to-solid ratio of 6.

[0116]

[0117] A comparison shows that the four-stage countercurrent makes the solid-liquid contact more complete, reduces aluminum loss by 39%, and reduces equipment investment cost by 67%.

[0118] Comparative Example 5: Desiliconization rate: (240.5-6L×5.2g / L) / (1000g×41.46%)=50.5%

[0119] Comparative analysis of key data

[0120] (1) Desiliconization rate and aluminum loss: The total desiliconization rate of Example 1 is 57.1%; the desiliconization rate of Comparative Example 1 is 47.9%; the desiliconization rate of Comparative Example 5 is 50.5%, and the aluminum loss is more than 100 g / L.

[0121] Technological progress: Through the synergistic effect of countercurrent leaching + blue carbon binder, aluminum loss is reduced by 36% to 60%.

[0122] (2) Energy consumption and cost: Example 1 Natural gas consumption: 75 Nm 3 / t(Compared with the traditional process 92Nm 3 / t); Equipment investment cost: The volume of countercurrent leaching equipment is reduced by 67%; Economic benefit: The production cost of each ton of alumina is reduced by 15% to 20%.

[0123] 5) Deep desiliconization

[0124] The deep desiliconization in Comparative Example 1 was repeated, and the loss of alumina in this stage was 64 g / L solution, which was much lower than that in Example 1.

[0125] Repeat the deep desiliconization, carbonation decomposition, and calcination steps in Comparative Example 1 to generate α-Al2 O 3 product.

[0126] Comprehensive benefit comparison:

[0127] The industrialization comparison of this application and the process of the Chinese patent with publication number CN106348323A (annual production scale of 500,000 tons):

[0128]

[0129]

[0130] Difference in technical inspiration: The Chinese patent with publication number CN106348323A does not disclose the correlation between the binder and the sintering porosity and aluminum loss. This application achieves low energy consumption and high separation efficiency through blue carbon binder + particle size control.

[0131] Replace anthracite with lignite: The volatility of lignite (≤5%) is significantly lower than that of anthracite (8% to 12%), and the sintering temperature and time need to be re-optimized (35 min in Example 1 versus the traditional 45 min).

[0132] Compared with "GB / T 39201-2020 Technical Specification for Extraction of Alumina from Fly Ash", this application highlights the leading position in aluminum recovery rate (90% vs. industry average 75%) and energy consumption (420kWh / t vs. 550kWh / t).

[0133] The present invention relates to a method for improving the desiliconization rate in the process of extracting aluminum oxide from fly ash, comprising the following steps: adding batching granulation, rotary kiln sintering, and solid waste heat recovery processes to the traditional pre-desiliconization-soda lime sintering process. The countercurrent leaching process is used to improve the leaching rate, reduce aluminum loss, and reduce energy consumption. The treatment method of the present invention can achieve the desiliconization rate of SiO2 in fly ash. 2 The extraction rate of Al 2 O 3 The extraction rate reaches more than 90%, which reduces the energy consumption of the whole process, reduces equipment investment, and has good economic benefits. Through the technical synergy of binder innovation-particle size control-waste heat recovery-leaching optimization, a low-cost, low-energy consumption, and high-resource technology system for extracting aluminum from fly ash has been constructed. The experimental data fully confirms that each improved feature has produced unexpected technical effects and has a significant degree of creativity.

[0134] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the embodiments made by those skilled in the art fall within the scope defined by the claims attached to the present invention.

Claims

1. A method for extracting aluminum oxide from fly ash, comprising: S1, pre-desiliconizing high-aluminum fly ash, and solid-liquid separation to obtain sodium silicate solution and desiliconized ash, characterized in that: The process also includes mixing the desiliconized ash in S2 and S1 with sodium carbonate, limestone and a binder, granulating and sintering the mixture to obtain clinker; and S3, countercurrently leaching the clinker obtained in S2 to obtain a leachate and a leach residue. The binder in S2 is lignite or petroleum coke; preferably, the binder in S2 is lignite.

2. The method for extracting aluminum oxide from fly ash according to claim 1, characterized in that: In S1, the mass ratio of the desiliconized ash to the sodium carbonate and the limestone is (1-1.1): (1-1.1): (1-1.3), the mass of the added binder is 1.5% to 3% of the mass of the desiliconized ash.

3. The method for extracting aluminum oxide from fly ash according to claim 1, characterized in that: The particle size of the granulation in S2 is 8 to 10 mm.

4. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: The sintering temperature in S2 is 1000-1400°C, the sintering time is 30-60min, and the residence time in the kiln is 120-180min; preferably, the sintering temperature in S2 is 1100-1200°C, the sintering time is 30-35min, and the residence time in the kiln is 120-150min.

5. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: The liquid-to-solid ratio of countercurrent leaching in S3 is 0.6-2, three to five levels of countercurrent leaching are carried out at room temperature, and the leaching time is 48-96h.

6. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: In S3, the leached residue after the countercurrent leaching is washed once, and the preferred washing liquid is returned to the countercurrent leaching for recycling.

7. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: The invention also includes S4, deeply desiliconizing the leaching solution in S3 to obtain a secondary desiliconized semen; S5, carbon dioxide is introduced into the secondary desiliconized semen, sodium aluminate forms aluminum hydroxide precipitation, and the precipitation is filtered and washed to obtain an aluminum hydroxide filter cake; S6. The aluminum hydroxide filter cake is calcined.

8. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: S2 and S3 also include the utilization of sintered solid waste heat; preferably, the utilization of sintered solid waste heat adopts a solid waste heat boiler to cool the clinker to 100-150°C, and use the heat of the clinker to produce hot water and saturated steam.

9. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: The pre-desiliconization in S1 is specifically to add NaOH to the high-aluminum fly ash, the mass fraction of NaOH is 10-20%, the reaction temperature is 90-100°C, the reaction time is 1-3h, the liquid-solid ratio is 2-4, and the desiliconization time is 1-3h.

10. The method for extracting aluminum oxide from fly ash according to any one of claims 1 to 3, characterized in that: The deep desiliconization in S4 includes one-stage desiliconization and two-stage desiliconization; the one-stage desiliconization is to add seed crystals to the leachate obtained in S3 for pressure boiling desiliconization to obtain sodium silicate slag and solution; the two-stage desiliconization is to add lime milk to the solution obtained in S3 after precise filtration for reaction; preferably, the calcium oxide content in the lime milk is 8-10g / L and the temperature is 90-100°C.

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