Method for preparing aluminum oxide based on flash firing of coal solid waste

Abstract

The invention relates to the technical field of coal solid waste resource utilization. The invention provides a method for preparing aluminum oxide based on flash firing of coal solid waste. The method comprises the following steps: S1, calcining coal gangue in a flash firing suspension kiln to obtain clinker; s2, pre-desiliconization through dilute alkali treatment; (S3) dissolving the low-silicon clinker by using dilute sulphuric acid: adding 18-21 wt% of dilute sulphuric acid into the high-temperature reaction kettle, heating to 130-165 DEG C, stirring and reacting for 2-3 hours, when the PH is 4-5, completing the reaction, and carrying out solid-liquid separation and filtration to obtain an aluminum-containing leachate and silicon-containing residues; heating and concentrating the aluminum-containing leachate, cooling to form crystallized aluminum sulfate, heating at the rate of 10-20 DEG C / h, removing crystal water at 300-600 DEG C, heating to 950-960 DEG C at the rate of 15-30 DEG C / h, and firing to form crude aluminum oxide; and S4, performing low-temperature concentrated alkali purification to obtain the metallurgical-grade aluminum oxide. The method has the advantages of high reaction efficiency, high aluminum utilization rate, low impurity content, low acid, alkali and water consumption, low cost and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal solid waste resource utilization, in particular to a method for preparing alumina based on coal solid waste flash burning. BACKGROUND

[0002] Coal seams are often associated with a black rock, coal gangue. China is a major coal producer, and a large amount of coal gangue is discharged in the process of coal mining and coal washing, which is difficult to effectively utilize, and accounts for nearly half of the total amount of industrial waste generated in the country. The main treatment method for coal gangue is stacking, but stacking occupies a large amount of land and pollutes the ecological environment, so more methods for resource utilization of coal gangue must be sought.

[0003] The coal gangue in China is mainly clay, and most of it contains aluminum elements. The main components of coal gangue are Al2O3, SiO2, and also contain varying amounts of Fe2O3, CaO, MgO, TiO2, Na2O, K2O, P2O5, SO3 and trace amounts of rare elements (gallium, vanadium, titanium, cobalt). Extracting alumina from aluminum rock coal gangue is a very promising way of coal gangue resource utilization.

[0004] Currently, the main methods for extracting alumina from coal gangue are acid method, alkali method and sintering method.

[0005] The sintering method has high energy consumption and is not suitable for large-scale promotion.

[0006] The alkali method in the prior art uses NaOH strong alkali solution to efficiently decompose coal gangue at normal pressure and low temperature to improve the leaching rate of aluminum elements, but the dissolution rate of aluminum elements is only 60%. In the prior art, the crushed coal gangue is calcined at high temperature, then leached with sodium hydroxide solution, the residue is filtered, CO2 gas is introduced into the filtrate to precipitate Al(OH)3, vacuum filtration, high temperature dehydration to obtain Al2O3 product. However, in this method, aluminum and silicon elements are simultaneously dissolved out, the purity of the obtained Al2O3 product is not high, and the utilization rate of aluminum is low. In addition, the alkali method also has the problems of large amount of alkali, low reaction efficiency, the need for high temperature, high alkali concentration and other conditions, large environmental pollution, equipment corrosion, low aluminum recovery rate, large amount of residue, secondary pollution and unreasonable resource utilization.

[0007] The acid method, coal gangue acid leaching refers to the process of directly leaching valuable metals in coal-containing waste by using acid solution to dissolve and recover them. The "one-step acid dissolution method" process mainly consists of raw material and dissolution, sedimentation, impurity removal, evaporation crystallization, calcination, and acid absorption processes. Specifically, coal gangue is mixed with HCl and water in a certain proportion to form a slurry. After high-temperature and high-pressure dissolution to achieve the predetermined dissolution rate, it is sent to the sedimentation unit for solid-liquid separation. The liquid phase is purified by impurity removal to obtain an aluminum chloride solution, which is evaporated to form aluminum chloride hexahydrate crystals by three-effect counter-flow evaporation. In the calcination process, the crystallized aluminum chloride is calcined at high temperature to form the final product, aluminum oxide. The calcined flue gas (mainly composed of hydrogen chloride) is washed and dusted, and then absorbed by multiple stages to form hydrochloric acid, which is returned to the raw material and dissolution unit for recycling. The sulfuric acid leaching method is to mix coal gangue with sulfuric acid in a certain proportion, and react under certain temperature and pressure. The aluminum oxide in coal gangue reacts with sulfuric acid to form Al2(SO4)3, while SiO2 in coal gangue does not participate in the reaction, thus achieving the separation of silicon and aluminum. However, in the direct acid dissolution method, coal gangue contains varying amounts of Fe2O3, CaO, MgO, TiO2, Na2O, K2O, P2O5, SO3, and trace amounts of rare elements (gallium, vanadium, titanium, cobalt), which are dissolved and then re-enter the subsequent process. These impurities are removed through a complex impurity removal process, resulting in a long process flow, high impurity removal cost, and low aluminum recovery rate. For example, the iron content cannot meet the metallurgical first-grade product requirement of w(iron)≤0.02% in Al2O3; the subsequent process has high impurity removal cost and difficulty.

[0008] The acid-alkali compound method, the prior art provides a method for extracting aluminum oxide, silicon oxide, and iron oxide from coal gangue combustion ash, which includes acidification: adding thick slurry to a stirred reactor, adding sulfuric acid solution to the slurry, after the acidification reaction is complete, filtering the mixed liquid, and the filtrate is a mixed solution containing aluminum sulfate and iron sulfate; washing the filter residue with deionized water 2-4 times and pressure filtering to obtain silicon residue, which is used for further extraction of silicon oxide; extracting iron from the filtrate; then calcining the aluminum sulfate to form aluminum oxide; alkali dissolution of silicon oxide: adding the obtained silicon residue to a caustic solution, allowing it to naturally settle in a reactor, and extracting the supernatant for subsequent process to extract silicon, and the sediment continues to react after being prepared; however, the mixed solution containing aluminum sulfate and iron sulfate obtained by acid dissolution reaction in the above process contains a large amount of impurities, and the removal cost is high; the acid filter residue is treated with alkali, which consumes a large amount of alkali and water, and the overall process is complex, consumes a large amount of alkali and water, has high impurity content, is difficult to effectively remove, and has low aluminum recovery rate.

[0009] In summary, in the efficient recovery of aluminum from coal gangue, the prior art has many different technologies, but all have the problems of complex process, high impurity removal cost, high acid or alkali consumption, low aluminum recovery rate, and low purity when using acid leaching, alkali leaching, or a combination of acid and alkali, which restricts the efficient and low-cost recovery and utilization of coal gangue. SUMMARY

[0010] To overcome the deficiencies of the prior art, the present application provides a method for preparing alumina based on coal solid waste flash calcination, which has the advantages of high reaction efficiency, high aluminum utilization rate, low impurity content, low consumption of acid, alkali and water, and low cost.

[0011] Embodiments of the present application are implemented as follows:

[0012] In a first aspect, the present application provides a method for preparing alumina based on coal solid waste flash calcination, which comprises:

[0013] S1, calcine the coal gangue in a flash calcination suspension kiln to obtain clinker: the coal gangue is pretreated by crushing and grinding in sequence; the crushing is to crush the coal gangue to 5-25 mm; the grinding is to grind the crushed coal gangue powder to a particle size of 325 mesh or less; after grinding, the coal gangue is sent into the flash calcination suspension kiln for calcination at 750-900℃ for 20-120 min to obtain clinker;

[0014] S2, pre-desiliconization by dilute alkali treatment: add NaOH solution to the clinker in a high-temperature reaction kettle and heat to 100-120℃, then perform solid-liquid separation to obtain low-silicon clinker and sodium silicate solution; the concentration of the NaOH solution is 20-30wt%;

[0015] S3, dissolve the low-silicon clinker with dilute sulfuric acid: add 18-21wt% dilute sulfuric acid to the high-temperature reaction kettle and heat to 130-165℃, then stir and react for 2-3h; when the PH is 4-5, the reaction is complete; after solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained; the aluminum-containing leaching solution is heated and concentrated, then cooled to form crystalline aluminum sulfate; the temperature is increased at a rate of 10-20℃ / h to 300-600℃ to remove crystallization water; the temperature is increased at a rate of 15-30℃ / h to 950-960℃ to calcine the crude alumina;

[0016] S4, obtain metallurgical-grade alumina by low-temperature concentrated alkali purification: add the crude alumina to a sodium hydroxide solution in a high-temperature reaction kettle and heat to 110-130℃, then stir and react for 1-2h; the concentration of the sodium hydroxide solution is 31-36wt%; perform solid-liquid separation to obtain a hydroxide aluminum precipitate; calcine the hydroxide aluminum precipitate at a high temperature of 1200-1300℃ to obtain metallurgical-grade alumina.

[0017] Optionally, in step S1, the calcination in the flash calcination suspension kiln is first calcined at 605-623℃ for a first time, and then calcined at 881-895℃ for a second time; the first time: the second time is 2-3:1.

[0018] Optionally, in step S2, when the dilute alkali treatment pre-desiliconization is performed, high-temperature water vapor is introduced; the temperature of the water vapor is 110-120℃; the total amount of water vapor introduced is 0.5-1% of the NaOH solution by mass.

[0019] Optionally, in the step S4, during the reaction of the crude alumina with the sodium hydroxide solution, ultrasonic is applied, the power is 100-500 W, the power density is 0.3-0.5 W / cm 3 , the frequency is 20-40 kHz, and the pulse mode is duty cycle 50%-70%.

[0020] Optionally, in the step S4, during the application of the ultrasonic, a surfactant is added into the sodium hydroxide solution, and the surfactant is rhamnose, polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA).

[0021] Optionally, in the step S4, the amount of the surfactant added accounts for less than 0.1% of the total mass of the crude alumina and the sodium hydroxide solution.

[0022] Optionally, in the step S4, the mass ratio of the rhamnose, the polyethylene glycol, the polyacrylic acid and the polyvinyl alcohol is (1.3-1.4):(1.2-1.3):(0.2-0.3):1.

[0023] Optionally, in the step S1, the raw material composition of the coal gangue is as follows: loss on ignition 18.5-19.5 wt%, silicon dioxide 42-43 wt%, diatomic aluminum oxide 36.3-37.2 wt%, diatomic iron oxide 0.1-0.2 wt%, calcium oxide 0.1-0.3 wt%, magnesium oxide 0.1-0.3 wt%, and titanium dioxide 0.9-1.1 wt%.

[0024] Optionally, in the step S2, the silicon content of the low-silicon clinker is reduced to less than 5 wt%, and the concentration of the NaOH solution is 22-27 wt%.

[0025] Optionally, in the step S4, the amount of the surfactant added accounts for 0.03-0.1% of the total mass of the crude alumina and the sodium hydroxide solution.

[0026] The beneficial effects include:

[0027] The method for preparing alumina based on coal solid waste flash calcination provided by the application realizes the double-low-temperature alkali treatment of the suspension kiln calcination, the low-temperature silicon removal by dilute alkali, the low-temperature separation of silicon and aluminum by dilute acid, the preparation of the crude alumina, and the preparation of the metallurgical-grade alumina by low-temperature concentrated alkali, the high efficiency of the intermediate acid treatment, and the process for obtaining the high-purity alumina product at a low treatment temperature. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0029] Those skilled in the art can understand that, unless otherwise defined, all the terms (including technical terms and scientific terms) used herein have the same meaning as that generally understood by those skilled in the art to which the present application belongs. It should also be understood that the terms such as those defined in a general dictionary should be understood as having meanings consistent with those in the context of the prior art, and should not be interpreted to have idealized or overly formal meanings unless specifically defined as such. The reagents used herein can be commercially available related products, and the performance test standards refer to the industry or national standards.

[0030] Those skilled in the art can understand that, unless otherwise stated, the singular forms "a", "an" and "the" used herein also include the plural forms. It should be further understood that the phrase "comprising" used in the specification of the present application means that the features, integers, steps, operations, elements and / or components exist, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or their combinations. The phrase "and / or" used herein includes all or any single unit and all combinations of the associated listed items.

[0031] In view of the problems of acid leaching, alkali leaching and mixed use of acid and alkali in the efficient recovery of aluminum from coal gangue, the process is complex, the cost of impurity removal is high, the acid or alkali consumption is large, and the aluminum recovery rate is low. The embodiments of the present application provide a method for preparing alumina based on coal solid waste flash calcination.

[0032] Exemplarily, a method for preparing alumina based on coal solid waste flash calcination is provided, which comprises:

[0033] S1, calcine the coal gangue in a flash calcination suspension kiln to obtain clinker:

[0034] The coal gangue is sent to the laboratory for sampling and analysis of raw material components: loss on ignition 18.5-19.5 wt%, silicon dioxide 42-43 wt%, aluminum oxide 36.3-37.2 wt%, ferric oxide 0.1-0.2 wt%, calcium oxide 0.1-0.3 wt%, magnesium oxide 0.1-0.3 wt%, titanium dioxide 0.9-1.1 wt%. In the prior art, materials with aluminum oxide / silicon dioxide greater than 1 in coal gangue materials are generally selected, and the aluminum oxide content is high, which is used for preparing aluminum oxide, but the proportion of coal gangue materials with high aluminum content is relatively small, which undoubtedly affects the utilization of coal gangue materials. The application adopts coal gangue raw materials with aluminum oxide / silicon dioxide less than 1, and the silicon dioxide content is higher than the aluminum oxide content, which is difficult to process, but the development of its effective utilization process will also be applicable to materials with aluminum oxide / silicon dioxide greater than 1, and has more application prospects.

[0035] After the raw material components are qualified, pretreatment is performed, and crushing and grinding are sequentially performed; wherein the control requirement of the crushing process is to crush the coal gangue to 5-25 mm; and the control requirement of the grinding process is to grind the crushed coal gangue powder to a particle size of 325 mesh or less, and preferably, a particle size of 500-800 mesh. The application adopts coal gangue raw materials with aluminum oxide / silicon dioxide less than 1, and the silicon dioxide content is higher than the aluminum oxide content, by reducing the particle size after grinding, the heat transfer area is increased, the calcination decomposition time can be reduced, the efficient utilization under the condition of low aluminum oxide content is beneficial, the carbon and volatile matter contained in the coal gangue are beneficial to combustion and volatilization, the calcination effect is improved, and the calcination temperature of the flash calcination suspension kiln is reduced.

[0036] After the grinding is completed, the flash calcination suspension kiln is sent for calcination: the clinker is obtained by calcining at 750-900 ℃ (which can be selected as 750 ℃, 753 ℃, 762 ℃, 773 ℃, 786 ℃, 792 ℃, 804 ℃, 812 ℃, 826 ℃, 834 ℃, 849 ℃, 857 ℃, 866 ℃, 873 ℃, 886 ℃, 892 ℃, 900 ℃, etc.) for 20-120 min in the flash calcination suspension kiln. When the flash calcination suspension kiln is calcined, by using a lower calcination temperature, it is beneficial to avoid the generation of cristobalite (dense SiO2) at high temperature (>900 ℃), and improve the solubility of silicon.

[0037] Preferably, the first time of calcination at 605-623℃ (optionally 605℃, 607℃, 611℃, 613℃, 615℃, 617℃, 619℃, 621℃, 622℃, 623℃, etc.) is followed by the second time of calcination at 881-895℃, and the first time: second time is 2-3:1. In the prior art, calcination at high temperature is often used to improve efficiency, but calcination at high temperature for too long time will make the particles dense and large in size, and the reactivity will be reduced. Low-temperature calcination at 605-623℃ avoids premature sintering of the particles, and the main mineral kaolinite and other crystalline aluminum-containing minerals in coal gangue are converted into semi-crystalline or even amorphous metakaolin and other minerals, and their structure is in a thermodynamic metastable state. The main structure of hydroxyl (-OH) is removed, the interlayer hydrogen bond of the layered silicate is broken, the layered structure is loose, more SiO2 active sites are exposed, more amorphous SiO2 is produced, and the subsequent reaction with sodium hydroxide solution is facilitated. Calcination at low temperature for a longer time overcomes the shortcomings of the original high-temperature direct sintering of the layered structure, which cannot be fully converted into a loose structure, and the reactivity cannot be improved. Subsequent high-temperature calcination for a short time is beneficial to the further decomposition of coal gangue minerals, and higher temperature causes atomic rearrangement, thereby forming a mixed structure of solidified pores, disorder and amorphous state, releasing residual hydroxyl and gas, and fully burning, which also increases the porosity and avoids the residue of carbon; and a shorter time is used to avoid closed pores at high temperature, sintering between particles to increase the particle size, and to reduce the alkali solubility of alumina at high temperature. The above treatment is beneficial to improving the effect of pre-desiliconization by alkali treatment at low temperature and low concentration.

[0038] The calcined clinker is sampled and analyzed for composition in the laboratory: loss on ignition 0.2-0.3wt%, silicon dioxide 51.5-52.6wt%, aluminum trioxide 44-45wt%, iron trioxide 0.1-0.2wt%, calcium oxide 0.2-0.4wt%, magnesium oxide 0.2-0.4wt%, and titanium dioxide 1-1.2wt%. Through the treatment, the loss on ignition is significantly reduced.

[0039] The flash suspension kiln is a calcination furnace provided with a cyclone, and the coal gangue material enters the furnace body in a suspended state and is calcined at high temperature to rapidly amorphize the kaolinite in the coal gangue and completely burn the volatile matter and carbon.

[0040] S2, pre-desiliconization by dilute alkali treatment:

[0041] The amount of sodium hydroxide and clinker is calculated by the chemical equation: SiO2+2NaOH=Na2SiO3+H2O. The control requirements are as follows: the NaOH solution and the clinker are heated to 100-120°C (optionally 100°C, 102°C, 104°C, 105°C, 107°C, 109°C, 111°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, etc.) in a high-temperature reaction kettle, and stirred for 1-2 hours to dissolve SiO2. Low-silicon clinker (the silicon content is reduced to <5 wt%, preferably <2 wt%) and a sodium silicate solution are obtained by solid-liquid separation. The NaOH solution concentration is 20-30 wt%, preferably 22-27 wt%, 24-25 wt%. The porous and highly reactive product obtained in step S1, especially the clinker with stronger SiO2 reactivity and inhibited Al2O3 reactivity, is treated under low-temperature and dilute-alkali conditions, which is conducive to the reaction of SiO2 and NaOH solution and inhibits the dissolution of Al2O3 (which requires higher temperature and alkali amount to continuously dissolve more). In the past, the reaction of coal gangue and NaOH dilute solution was carried out at a temperature of less than 100°C and a NaOH solution concentration of less than 20% to inhibit the dissolution of Al2O3, but the reaction efficiency was not high, the removal rate of SiO2 was low, and the silicon content of the silicon clinker obtained by solid-liquid separation was more than 15 wt%. The porous and highly reactive product obtained in step S1, especially the clinker with stronger SiO2 reactivity and inhibited Al2O3 reactivity, is treated under higher temperature and NaOH solution concentration than the low-temperature and low-alkali conditions in the past, which realizes efficient production of low-silicon clinker and does not increase the dissolution of Al2O3. The dilute-alkali pretreatment and desilication process also has a certain dilution and impurity removal effect.

[0042] Preferably, high-temperature water vapor is introduced during the dilute-alkali pretreatment and desilication process, and the temperature of the water vapor is 110-120°C (optionally 110°C, 111°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 120°C, etc.). The total amount of water vapor introduced accounts for 0.5-1% of the NaOH solution by mass, which avoids excessive dilution of the NaOH solution and ensures the effect of water vapor introduction. The introduction of water vapor reduces the concentration of the NaOH solution, which is conducive to the inhibition of the reaction between Al2O3 and NaOH. The introduction of water vapor can maintain the reaction temperature, the appropriate high temperature, and the enhanced solution kinetics, which can enhance the reactivity of SiO2 and NaOH, promote the preferential reaction of SiO2 and OH - The reaction generates soluble sodium silicate, which is conducive to reducing the viscosity of the system, accelerating the diffusion of silicate ions, and promoting the stable dissolution of sodium silicate, thereby further reducing the silicon content and improving the purity of the low-silicon clinker.

[0043] S3, dilute sulfuric acid dissolves low-silicon clinker, separates silicon and aluminum, and after solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained, the leaching solution is heated into a viscous liquid, cooled into crystalline aluminum sulfate, and the crystallization water is removed and calcined into coarse aluminum oxide:

[0044] In the dilute acid separation of silicon and aluminum, the amount of sulfuric acid and low-silicon clinker is calculated through the chemical equation Al2O3+3H2SO4→Al2(SO4)3+3H2O. Control requirements: dilute 98wt% concentrated sulfuric acid to 18-21wt% (optional 18wt%, 19wt%, 20wt%, 21wt%, etc.) by adding water, heat to 130-165°C (optional 130°C, 132°C, 137°C, 139°C, 142°C, 145°C, 147°C, 149°C, 152°C, 153°C, 155°C, 157°C, 161°C, 163°C, 165°C, etc.) in a high-temperature reaction kettle, and stir for 2-3h, when the PH is 4-5, it is a complete reaction. After desiliconization, the diffusion resistance of the material after sulfuric acid leaching of aluminum is reduced, the reaction rate is improved, and the leaching time is shortened; through the S2 step, low-silicon clinker is obtained, which greatly reduces the acid consumption, and also avoids the direct acid treatment of calcined coal gangue, which cannot fully utilize the porous reaction activity of calcined coal gangue, and needs to add more excess acid to achieve higher acid dissolution effect, which is not economical, and improves the reaction rate, so relatively low concentration of acid and relatively low reaction temperature can be used.

[0045] After solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained. The leaching solution is heated into a viscous liquid, and cooled into crystalline aluminum sulfate. Through multiple experiments, the dissolution rate is determined, which is as high as 90% or even more than 96%.

[0046] The cooled crystalline aluminum sulfate is heated up at a faster rate of 10-20 ℃ / h, and the crystal water is removed at 300-600 ℃ (optionally 300 ℃, 314 ℃, 334 ℃, 351 ℃, 365 ℃, 382 ℃, 397 ℃, 430 ℃, 460 ℃, 475 ℃, 482 ℃, 524 ℃, 536 ℃, 547 ℃, 557 ℃, 568 ℃, 579 ℃, 583 ℃, 596 ℃, 600 ℃, etc.). The faster heating-up rate facilitates the removal of the crystal water and the overflow of the generated decomposition gas, reduces the decomposition time, and promotes the formation of a dispersed loose structure. At a low temperature, the agglomeration is reduced, and the crystalline aluminum sulfate is partially decomposed to form amorphous or γ-Al2O3, with a small particle size (nanometer to sub-micron level). The gas (SO2, H2O) escapes sufficiently during calcination, and a more dispersed loose structure can be obtained. Preferably, the temperature is 336-432 ℃, and a lower temperature can slow down the decomposition of the particles and facilitate the formation of a dispersed loose structure, which is beneficial to increasing the reactivity of the subsequent treatment and improving the purity. The temperature is rapidly increased to 950-960 ℃ at a rate of 15-30 ℃ / h. In the rapid heating-up mode, the alumina is in a transition phase of γ-Al2O3 and θ-Al2O3. As the temperature increases, the θ-Al2O3 gradually converts to α-Al2O3 (corundum). The transition phase has a rich surface hydroxyl group and many structural defects, which provide more reaction sites. The rapid heating-up rate causes incomplete conversion of the transition phase during the conversion process, and the many transition phases result in more cracks on the surface of the particles and an increase in the particle size, thereby increasing the reactivity of the calcined alumina.

[0047] The high-temperature calcination at 950-960 ℃ (optionally 950 ℃, 951 ℃, 952 ℃, 953 ℃, 954 ℃, 955 ℃, 956 ℃, 957 ℃, 958 ℃, 959 ℃, 960 ℃, etc.) for 140-150 minutes produces coarse alumina. The alumina is completely converted to a stable α phase only at a temperature of 1200 ℃ or above. The low-temperature calcination ensures sufficient calcination of the coarse alumina, thereby increasing the reactivity of the calcined alumina, avoiding sintering of the particles at a high temperature, increasing the reactivity of the subsequent treatment, shortening the reaction time, reducing the re-entry of impurities, and improving the purity.

[0048] The sulfur dioxide flue gas generated by the high-temperature calcination is recovered and utilized by an acid recovery device.

[0049] (Chemical equation: Al2(SO4)3+ 3O2→ 2Al2O3+ 3SO2)

[0050] The burned alumina is sent to the laboratory for sampling and analysis of components: 0-0.1wt% of silicon dioxide, 97-98wt% of aluminum trioxide, 0.7-0.8wt% of iron trioxide, 0.6-0.7wt% of calcium oxide, 0.5-0.6wt% of magnesium oxide, and 1.1-1.2wt% of titanium dioxide. Thus, the content of silicon dioxide is greatly reduced, the effective separation of silicon dioxide and aluminum trioxide is realized, and the impurity components such as iron trioxide, calcium oxide, magnesium oxide, and titanium dioxide are effectively reduced.

[0051] S4, low-temperature concentrated alkali purification to obtain metallurgical-grade alumina:

[0052] The coarse alumina is reacted with a sodium hydroxide solution to generate aluminum hydroxide; the required amount of sodium hydroxide is calculated according to the chemical equation: Al2O3+2NaOH→2NaAlO2+H2O, NaAlO2+2H2O→NaOH+Al(OH)3↓, the temperature in the high-temperature reaction kettle is raised to 110-130°C (which can be selected as 110°C, 111°C, 113°C, 114°C, 115°C, 116°C, 117°C, 118°C, 119°C, 121°C, 123°C, 124°C, 126°C, 128°C, 130°C, etc.), and is preferably 121-129°C, the stirring reaction is performed for 1-2h, and the aluminum hydroxide precipitate is separated from the liquid; the aluminum hydroxide precipitate is calcined at a high temperature of 1200-1300°C to obtain metallurgical-grade alumina according to the chemical equation: 2Al(OH)3→Al2O3+3H2O↑. In the prior art, high-concentration sodium hydroxide (50% or more) and a high temperature of 200°C or more (e.g., molten alkali) are used to improve the reactivity of alumina, but at the same time, the possibility of impurity components such as silicon dioxide and iron trioxide, calcium oxide, magnesium oxide, and titanium dioxide participating in the reaction increases, which affects the further improvement of the purity of alumina, and a large-cost impurity removal process is required to meet the high-purity requirement. The coarse alumina obtained in the S3 step has high reactivity, and can have high reaction efficiency at a relatively low temperature and a relatively moderate high-alkali concentration (a high-alkali concentration that is higher than the high-alkali concentration that affects the reduction of impurities, and a high-alkali concentration that is higher than the alkali concentration for pre-silicon removal), and the possibility of the dissolution of residual silicon dioxide and other impurities is extremely low, thereby realizing efficient purification for improving the purity.

[0053] The metallurgical-grade alumina is sent to the laboratory for sampling and analysis of components: 0-0.03wt% of silicon dioxide, 97.5-99.7wt% of aluminum trioxide, 0-0.02wt% or less of iron trioxide, 0-0.6wt% of calcium oxide, 0-0.5wt% of magnesium oxide, and 0-0.9wt% of titanium dioxide. The impurity content of the metallurgical-grade alumina is extremely low, and the purity is high.

[0054] Preferably: during the reaction of the crude alumina with the sodium hydroxide solution to generate aluminum hydroxide, ultrasound is applied, the cavitation bubbles generated by the ultrasound can effectively break up the alumina agglomerates, increase the active sites, the microjet and turbulent effects induced by the ultrasound accelerate the diffusion of OH - The ions diffuse to the surface of the alumina, eliminate the diffusion boundary layer restriction, and improve the reaction efficiency.

[0055] The power is 100-500 W, and the power density is 0.3-0.5 W / cm 3 , to ensure effective cavitation effect and avoid excessive impact on the surface of alumina; select 20-40 kHz, select high frequency band, enhance cavitation intensity and reduce the damage of low frequency to particle agglomeration; pulse mode: duty cycle 50%-70%, which can maintain cavitation efficiency and reduce temperature rise caused by continuous energy input, and maintain favorable low temperature conditions. Through the optimization of the above conditions, the dissolution reaction efficiency of alumina is improved.

[0056] Preferably: during the application of ultrasound, a surfactant is added to the sodium hydroxide solution, and the surfactant is rhamnose, polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA); the above surfactants, by introducing the calcined surfactant which does not produce new residues, weaken the agglomeration of the crude alumina, expose more reaction sites, which is beneficial to improve the reaction rate, shorten the reaction time, reduce the dissolution of impurities and improve the purity. The sodium hydroxide solution has a certain influence on the surfactant, and it is beneficial to compound a variety of different surfactants. Rhamnose is a biological surfactant that reduces the solid-liquid interfacial tension, enhances the wettability, and expands the reaction contact area. Polyethylene glycol (PEG) is non-ionic, which forms hydrogen bonds with the surface of alumina through hydroxyl groups, reduces the van der Waals force between particles, and provides steric hindrance effect through long chain structure, stabilizes the particles through steric hindrance effect, and reduces the agglomeration caused by van der Waals force; polyacrylic acid (PAA) is partially dissociated in NaOH solution and carries negative charge, which inhibits agglomeration through electrostatic repulsion and steric hindrance mechanism; polyvinyl alcohol (PVA) wraps the surface of the particles; the above different types of surfactants improve the reactivity through different mechanisms such as reducing agglomeration and enhancing wettability, cooperate with ultrasonic treatment, and the coating layer dynamically changes during the dissolution process, which is beneficial to achieve better dispersed particles, reduce agglomeration, improve reactivity, improve reaction rate, shorten reaction time, reduce impurities, and improve purity.

[0057] Preferably, the amount of surfactant added is less than 0.1% of the total mass of the crude alumina and sodium hydroxide solution, preferably 0.03-0.1% (optionally 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc.). A small amount of addition is advantageous, and excessive addition of the surfactant will be affected by the sodium hydroxide solution, resulting in complex and adverse reactions, and failing to achieve the desired effect. Meanwhile, excessive addition will result in the residual of new impurities such as carbon after decomposition.

[0058] Preferably, the total mass of the surfactant is (1.3-1.4):(1.2-1.3):(0.2-0.3):1. By increasing the proportion of rhamnose and polyethylene glycol and reducing the proportion of polyacrylic acid, the wettability improvement effect can be improved, the agglomeration can be reduced, and the unexpected changes in components caused by the decomposition of polyacrylic acid can be reduced.

[0059] In the above method, S1, gangue flash calcination suspension kiln calcination to obtain clinker, S2, dilute alkali treatment to pre-desiliconize, S3, dilute acid dissolution of low-silicon clinker to separate silicon and aluminum, and after solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained, the leaching solution is heated into a viscous liquid, cooled into crystalline aluminum sulfate, and the crystal water is removed to be fired into crude alumina, S4, low-temperature concentrated alkali purification to obtain metallurgical grade alumina, realizing double low-temperature alkali treatment of suspension kiln calcination, dilute alkali low-temperature desiliconization, dilute acid low-temperature separation of silicon and aluminum to obtain crude alumina, and then low-temperature concentrated alkali to obtain metallurgical grade alumina, high efficiency of intermediate acid treatment, and low processing temperature to obtain high-purity alumina product process.

[0060] The features and performance of the present application are further described in detail below in conjunction with the following examples:

[0061] Example 1

[0062] A method for preparing alumina based on coal solid waste flash calcination, the method comprising:

[0063] S1, gangue flash calcination suspension kiln calcination to obtain clinker: the coal gangue is sampled and analyzed for raw material composition in the laboratory: loss on ignition 19.5wt%, silicon dioxide 43wt%, aluminum oxide 36.3wt%, iron trioxide 0.1wt%, calcium oxide 0.1wt%, magnesium oxide 0.1wt%, titanium dioxide 0.9wt%. The raw material is sequentially crushed and ground; wherein the coal gangue is crushed to 15mm; the crushed coal gangue powder is ground to a particle size of 550 mesh (average particle size). First calcination at 612°C for a first time, and then calcination at 894°C for a second time, the first time: second time is 2.5:1; the total calcination time is 60min to obtain clinker.

[0064] The calcined clinker is sent to the laboratory for sampling and analysis of the composition: loss on ignition 0.2wt%, silicon dioxide 52.6wt%, aluminum trioxide 45wt%, iron trioxide 0.2wt%, calcium oxide 0.4wt%, magnesium oxide 0.4wt%, titanium dioxide 1.2wt%.

[0065] S2, dilute alkali treatment pre-desilication: the clinker is reacted with NaOH solution in a high-temperature reaction kettle, heated to 117°C, stirred for 1h, and SiO2 is dissolved out, and low-silicon clinker (silicon content 0.8wt%) and sodium silicate solution are obtained by solid-liquid separation; the concentration of NaOH solution is 25wt%. When the dilute alkali treatment pre-desilication is carried out, high-temperature water vapor is introduced, the temperature of the water vapor is 118°C; the total amount of water vapor introduced accounts for 0.7% of the mass of the NaOH solution.

[0066] S3, dilute sulfuric acid dissolves low-silicon clinker, 98wt% concentrated sulfuric acid is diluted to 19wt%, heated to 161°C in a high-temperature reaction kettle, stirred for 2h, and when the PH is 4-5, it is completely reacted. After solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained. The leaching solution is heated to a viscous liquid, and cooled to crystalline aluminum sulfate. The dissolution rate is as high as 98.5%.

[0067] The cooled crystalline aluminum sulfate is heated at a faster rate of 18°C / h, and the crystallization water is removed at 423°C; it is quickly heated to a high temperature of 958°C at a rate of 29°C / h, and is burned for 140 minutes to form coarse aluminum oxide.

[0068] The burned aluminum oxide is sent to the laboratory for sampling and analysis of the composition: silicon dioxide 0.1wt%, aluminum trioxide 97wt%, iron trioxide 0.7wt%, calcium oxide 0.6wt%, magnesium oxide 0.5wt%, titanium dioxide 1.1wt%.

[0069] S4, low-temperature concentrated alkali purification to obtain metallurgical grade aluminum oxide: heated to 127°C in a high-temperature reaction kettle, stirred for 1h, and solid-liquid separation to obtain aluminum hydroxide precipitate; the aluminum hydroxide precipitate is calcined at a high temperature of 1250°C to obtain metallurgical grade aluminum oxide, and the concentration of NaOH solution is 34wt%.

[0070] During the reaction of coarse aluminum oxide and sodium hydroxide solution to generate aluminum hydroxide, ultrasonic waves are applied, the power is 425W, the power density is 0.4W / cm 3 , the frequency is 35kHz, and the pulse mode is duty cycle 55%. During the application of ultrasonic waves, a surfactant is added to the sodium hydroxide solution, the surfactant is rhamnose, polyethylene glycol (PEG), polyacrylic acid (PAA) and polyvinyl alcohol (PVA); the amount of surfactant added accounts for 0.06% of the total mass of coarse aluminum oxide and sodium hydroxide solution. Based on the total mass of the surfactant, the ratio of rhamnose: polyethylene glycol: polyacrylic acid: polyvinyl alcohol is 1.4:1.3:0.2:1.

[0071] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.01wt% of SiO2, 98.94wt% of Al2O3, 0.01wt% or less of Fe2O3, 0.17wt% of CaO, 0.17wt% of MgO, and 0.7wt% of TiO2. The metallurgical grade alumina had very low impurity content and high purity.

[0072] Example 2

[0073] The method for preparing the alumina based on the coal solid waste flash calcination in Example 1 was basically the same, and the main difference was that the ground product was sent into a flash calcination suspension kiln for calcination at 900°C.

[0074] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.03wt% of SiO2, 98.7wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.25wt% of CaO, 0.4wt% of MgO, and 0.8wt% of TiO2.

[0075] Example 3

[0076] The method for preparing the alumina based on the coal solid waste flash calcination in Example 1 was basically the same, and the main difference was that high-temperature water vapor was not introduced during the dilute alkali treatment for pre-desiliconization.

[0077] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.03wt% of SiO2, 98.76wt% of Al2O3, 0.01wt% or less of Fe2O3, 0.2wt% of CaO, 0.3wt% of MgO, and 0.7wt% of TiO2.

[0078] Example 4

[0079] The method for preparing the alumina based on the coal solid waste flash calcination in Example 1 was basically the same, and the main difference was that no ultrasonic was applied during the reaction of the crude alumina with the sodium hydroxide solution to generate aluminum hydroxide in the S4 step.

[0080] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.03wt% of SiO2, 98.35wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.4wt% of CaO, 0.4wt% of MgO, and 0.8wt% of TiO2.

[0081] Example 5

[0082] The method for preparing the alumina based on the coal solid waste flash calcination in Example 1 was basically the same, and the main difference was that no surfactant was added to the sodium hydroxide solution during the application of ultrasonic in the S4 step.

[0083] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.02wt% of SiO2, 98.46wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.5wt% of CaO, 0.3wt% of MgO, and 0.7wt% of TiO2.

[0084] Example 6

[0085] The method for preparing the alumina based on the coal solid waste flash in Example 1 was basically the same, and the main difference was that in the S4 step, the amount of the surfactant added accounted for 0.02% of the total mass of the crude alumina and the sodium hydroxide solution.

[0086] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.02wt% of SiO2, 98.46wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.5wt% of CaO, 0.3wt% of MgO, and 0.7wt% of TiO2.

[0087] Example 7

[0088] The method for preparing the alumina based on the coal solid waste flash in Example 1 was basically the same, and the main difference was that in the S4 step, the amount of the surfactant added accounted for 0.02% of the total mass of the crude alumina and the sodium hydroxide solution.

[0089] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.02wt% of SiO2, 98.46wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.5wt% of CaO, 0.3wt% of MgO, and 0.7wt% of TiO2.

[0090] Comparative Example 1

[0091] The method for preparing the alumina based on the coal solid waste flash in Example 1 was basically the same, and the main difference was that in the S4 step, the amount of the surfactant added accounted for 0.02% of the total mass of the crude alumina and the sodium hydroxide solution.

[0092] The metallurgical grade alumina was sampled and analyzed in the laboratory, and the components were as follows: 0.02wt% of SiO2, 98.46wt% of Al2O3, 0.02wt% or less of Fe2O3, 0.5wt% of CaO, 0.3wt% of MgO, and 0.7wt% of TiO2.

[0093] Comparative Example 2

[0094] The method for preparing the alumina based on the coal solid waste flash in Example 1 was basically the same, and the main difference was that in the S4 step, the amount of the surfactant added accounted for 0.02% of the total mass of the crude alumina and the sodium hydroxide solution.

[0095] The metallurgical grade alumina is sampled and analyzed in the laboratory for the following components: silicon dioxide 0.5wt%, aluminum trioxide 96.15wt%, ferric trioxide 0.45wt% or less, calcium oxide 0.9wt%, magnesium oxide 1.0wt%, titanium dioxide 1.0wt%.

[0096] Comparative Example 3

[0097] The process for preparing the alumina based on the coal solid waste flash combustion of Example 1 is substantially the same, with the main difference being that the cooled crystalline aluminum sulfate is heated at a rate of 5°C / h; and the crude alumina is calcined at a high temperature of 958°C at a rapid heating rate of 10°C / h.

[0098] The metallurgical grade alumina is sampled and analyzed in the laboratory for the following components: silicon dioxide 0.9wt%, aluminum trioxide 95.14wt%, ferric trioxide 0.56wt% or less, calcium oxide 1.2wt%, magnesium oxide 1.1wt%, titanium dioxide 1.1wt%.

[0099] The above detailed the preferred embodiments of the present application, only to illustrate the technical solutions of the present application, rather than limit it; although the present application is described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still be modified to the technical solutions described in the foregoing examples, or part or all of the technical features are replaced by the equivalent; and these modifications or replacements, do not make the corresponding technical solutions of the essence of the present application, out of the scope of the embodiments of the present application technical solutions.

Claims

1. A method for producing alumina based on coal solid waste flash burning, characterized in that: The method comprises: S1, coal gangue is calcined in a flash calcining suspension kiln to obtain clinker: the coal gangue is pretreated by crushing and grinding in sequence; the crushing is to crush the coal gangue to 5-25 mm; the grinding is to grind the crushed coal gangue powder to a particle size of below 325 mesh; after the grinding is completed, the coal gangue is sent into the flash calcining suspension kiln and calcined at 750-900 DEG C for 20-120 min to obtain the clinker; S2, pre-desiliconization by dilute alkali treatment: the clinker is heated to 100-120 DEG C in a high-temperature reaction kettle with the addition of NaOH solution, and then solid-liquid separation is performed to obtain low-silicon clinker and sodium silicate solution; the concentration of the NaOH solution is 20-30 wt%; S3, dissolving the low-silicon clinker with dilute sulfuric acid: the low-silicon clinker is heated to 130-165 DEG C in a high-temperature reaction kettle with the addition of 18-21 wt% dilute sulfuric acid, and then stirred and reacted for 2-3 h; when the PH value is 4-5, the reaction is complete; after solid-liquid separation and filtration, an aluminum-containing leaching solution and a silicon-containing residue are obtained; the aluminum-containing leaching solution is heated and concentrated, and then cooled to form crystalline aluminum sulfate; the crystalline aluminum sulfate is heated at a rate of 10-20 DEG C / h, and then dehydrated at 300-600 DEG C; the crystalline aluminum sulfate is heated at a rate of 15-30 DEG C / h to 950-960 DEG C to obtain coarse aluminum oxide; S4, obtaining metallurgical-grade aluminum oxide by low-temperature concentrated alkali purification: the coarse aluminum oxide is heated to 110-130 DEG C in a high-temperature reaction kettle with the addition of sodium hydroxide solution, and then stirred and reacted for 1-2 h; the concentration of the sodium hydroxide solution is 31-36 wt%; the aluminum hydroxide precipitate is obtained by solid-liquid separation; the aluminum hydroxide precipitate is calcined at a high temperature of 1200-1300 DEG C to obtain the metallurgical-grade aluminum oxide.

2. The method for producing alumina based on coal solid waste flash combustion according to claim 1, characterized in that, In the S1 step, the calcination in the flash calcining suspension kiln is performed at 605-623 DEG C for a first time, and then at 881-895 DEG C for a second time; the first time: the second time is 2-3:

1.

3. The method for producing alumina based on coal solid waste flash combustion according to claim 1, characterized in that, In the S2 step, high-temperature water vapor is introduced during the pre-desiliconization by dilute alkali treatment; the temperature of the water vapor is 110-120 DEG C; the total amount of the water vapor introduced accounts for 0.5-1% of the NaOH solution in terms of mass.

4. The method for preparing alumina based on coal solid waste flash burning according to claim 1, wherein in the step S4, during the reaction of the crude alumina with the sodium hydroxide solution to generate aluminum hydroxide, ultrasonic waves are applied, the power is 100-500 W, the power density is 0.3-0.5 W / cm2, the frequency is 20-40 kHz, and the pulse mode is 50%-70% duty cycle. 3 .

5. The method of claim 4, wherein the coal solid waste is selected from the group consisting of coal ash, coal cinder, and coal combustion residue. In the S4 step, a surfactant is added to the sodium hydroxide solution during the ultrasonic treatment; the surfactant is rhamnose, polyethylene glycol (PEG), polyacrylic acid (PAA), and polyvinyl alcohol (PVA).

6. The method of claim 5, wherein the coal solid waste is selected from the group consisting of coal ash, coal cinder, and coal combustion residue. In the S4 step, the amount of the surfactant added accounts for less than 0.1% of the total mass of the coarse aluminum oxide and the sodium hydroxide solution.

7. The method of claim 6, wherein the coal solid waste is selected from the group consisting of coal ash, coal cinder, and coal combustion residue. In the S4 step, the mass ratio of rhamnose:polyethylene glycol:polyacrylic acid:polyvinyl alcohol is (1.3-1.4):(1.2-1.3):(0.2-0.3):1 in terms of the total mass of the surfactants.

8. The method for producing alumina based on coal solid waste flash combustion according to claim 1, characterized in that, In the S1 step, the raw material composition of the coal gangue is as follows: loss on ignition 18.5-19.5 wt%, silicon dioxide 42-43 wt%, diatomic aluminum oxide 36.3-37.2 wt%, diatomic iron oxide 0.1-0.2 wt%, calcium oxide 0.1-0.3 wt%, magnesium oxide 0.1-0.3 wt%, and titanium dioxide 0.9-1.1 wt%.

9. The method for producing alumina based on coal solid waste flash combustion according to claim 1, characterized in that, In the S2 step, the silicon content of the low-silicon clinker is reduced to <5 wt%; the concentration of the NaOH solution is 22-27 wt%.

10. The method for producing alumina based on coal solid waste flash combustion according to claim 6, characterized in that, In the S4 step, the amount of the surfactant added accounts for 0.03-0.1% of the total mass of the coarse aluminum oxide and the sodium hydroxide solution. In the S4 step, the amount of the surfactant added accounts for 0.03-0.1% of the total mass of the coarse aluminum oxide and the sodium hydroxide solution.