A method for efficiently extracting silica white and alumina from fly ash and its application

Abstract

The present invention provides a method for efficiently extracting silica white and alumina from fly ash, comprising the following steps: mixing fly ash with an alkali agent for roasting; subjecting the roasted product to acidification treatment after dissolution to obtain filtrate A and residue A; removing moisture from filtrate A to obtain a solid, redissolving the solid and performing solid-liquid separation to obtain filtrate B and residue B; heating residue B to obtain silica white, adding an alkali solution to filtrate B to obtain ferric hydroxide precipitate, and adjusting the pH to obtain aluminum hydroxide precipitate; heating the precipitate to obtain magnetic iron oxide and alumina. Compared with the prior art, the method provided by the present invention realizes the efficient separation of silicon and aluminum, increases the extraction rate of silicon and aluminum to over 90%, which is much higher than that of the existing process technology. Meanwhile, the amount of ash residue generated is small, and the ash residue accounts for only about 30% of the fly ash usage. The purity of the obtained silica white and alumina products is both as high as over 95%. The present invention also has the advantages of simple process, low cost, and relatively low roasting temperature.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-value reduction of solid waste, and specifically relates to a method for efficiently extracting silica white and alumina from fly ash, and also relates to the application of the above method in the high-value utilization of fly ash. Background Technique

[0002] According to statistics, currently thermal power generation in China accounts for more than 71% of the total national power generation, and it is still the main source of power supply in China, playing an important role in ensuring power supply. Fly ash is an ash product formed after pulverized coal burns in a high-temperature coal-fired boiler and is the main by-product of modern coal-fired power plants. In recent years, with the rapid development of the power industry, the discharge of fly ash has increased sharply, posing a huge pressure on China's national economic construction and ecological environment. The technology for high-value utilization of fly ash is an important means to improve the comprehensive utilization rate and economic benefits of fly ash, and is highly regarded both at home and abroad.

[0003] Fly ash is mainly composed of oxides such as silicon, aluminum, and iron. The content of aluminum and silicon oxides is usually above 75%. Many technologies have been developed for the separation and extraction of aluminum and silicon.

[0004] The methods for extracting silica white from fly ash mainly include two categories: precipitation method and gas phase method (CN101214961B). Compared with the gas phase method, the precipitation method has the advantage of low cost. The current precipitation method mainly uses alkaline conditions to dissolve silicon, and then carbonization precipitation is used to prepare silica white (CN101306819B, CN101591020A, CN104556056B, and CN104649279A). At present, industrialization has not been truly realized. On the one hand, the silicon and aluminum in fly ash are low in activity as high-temperature sintered products, resulting in a low alkaline dissolution rate. Therefore, many studies use the silicon dissolved in the pre-desilication process to prepare silica white, and the other undissolved parts are transformed into calcium silicate through high-temperature solid-phase reaction for desilication and aluminum extraction (CN101306926B); on the other hand, the silicon dissolved by alkali leaching or alkali co-melting method is also accompanied by the dissolution of aluminum, and the purity of silica white is low due to the strong adsorption of aluminum and other cations by silicic acid during carbonization silicon precipitation. Therefore, extracting high-purity and high-extraction-rate silica white from fly ash remains a difficult problem to be solved at present.

[0005] The method of extracting alumina from fly ash generally requires prior desilication and then alumina extraction due to the solubility of silicon and aluminum under alkaline conditions and the strong adsorption of silicic acid to aluminum, calcium, iron, etc. under acidic conditions. The main problem is that affected by the current desilication methods, whether it is the acidic carbonation desilication method or the alkali co-fusion roasting clinker method, etc., the alumina extraction efficiency is not very high. The method of alumina extraction usually involves first removing iron and then precipitating alumina. The method of removing iron usually uses alkaline conditions to convert iron into iron hydroxide precipitate for removal (CN105197973B, CN100457628C), and precipitating alumina is a method of converting alumina into aluminum hydroxide precipitate for extraction by carbonation to pH = 10 - 12.

[0006] The invention patent with the publication number CN101891224A provides a method for producing alumina and white carbon black using red mud and fly ash. This method proportionally mixes fly ash and red mud with sodium hydroxide or sodium carbonate, and through processes such as calcination, acid leaching, concentration, crystallization, thermal decomposition, water washing, seeding, and roasting, alumina and white carbon black are produced. This method leaches the calcined materials with acid to obtain a solution and acid slag with the main component of SiO2, and then directly extracts white carbon black from the acid slag and thermally removes acid and dissolves and extracts alumina from the solution. In fact, due to the strong adsorption of white carbon black (silica hydrate) produced under acidic conditions to aluminum, iron, etc., most of the aluminum and iron coexist with silicon, either in the solution (before the polymerization and gelation of silicic acid molecules) or in the acid slag (after the polymerization and gelation of silicic acid molecules). Therefore, this process cannot effectively separate aluminum and silicon, and the purity of the obtained white carbon black and aluminum is relatively low.

[0007] In summary, efficient desilication from fly ash and effective separation of aluminum and silicon are the keys restricting the extraction efficiency and purity of silicon and aluminum. Therefore, to improve the extraction efficiency of silicon and aluminum from fly ash, a more effective method for silicon extraction or silicon-aluminum separation needs to be established to reduce the loss of aluminum during the desilication process. Summary of the Invention

[0008] One of the objectives of the present invention is to provide a method for efficiently extracting white carbon black and alumina from fly ash.

[0009] Another objective of the present invention is to provide the application of a method for efficiently extracting white carbon black and alumina from fly ash in the high-value utilization of fly ash.

[0010] The technical solution adopted by the present invention to achieve the first objective is: A method for efficiently extracting white carbon black and alumina from fly ash, characterized by including the following steps:

[0011] S1. Mix fly ash with an alkali agent in a certain proportion and obtain a calcined product through calcination treatment;

[0012] S2. Dissolve the calcined product in water to obtain a first mixture, acidify the first mixture until the pH < 4, and perform solid-liquid separation to obtain filtrate A and filter residue A;

[0013] S3. Remove the moisture from the filtrate A to obtain a solid, redissolve the solid in water to obtain a second mixture, and perform solid-liquid separation to obtain filtrate B and filter residue B;

[0014] S4. Heat-treat the filter residue B to obtain white carbon black;

[0015] S5. Under the condition of continuous stirring, add an aqueous solution of an alkali to the filtrate B, adjust the pH to pH > 12.5, perform solid-liquid separation and wash the precipitate to obtain filtrate C and iron hydroxide precipitate;

[0016] S6. Under the condition of continuous stirring, acidify the filtrate C until the pH = 6 - 10, and perform solid-liquid separation to obtain aluminum hydroxide precipitate;

[0017] S7. Heat-treat the aluminum hydroxide precipitate to obtain aluminum oxide.

[0018] In the method provided by the present invention, in order to achieve the efficient separation of silicon and aluminum, solid-liquid separation is immediately carried out after acidifying the calcined product to remove the insoluble solids in fly ash. Compared with the existing lime desilication technology, the reduction of ash and slag can be effectively achieved; at this time, all components such as aluminum, silicon, and iron leached out are transferred to the solution, and then dehydration treatment is carried out instead of precipitating silicic acid and immediately separating silicon and aluminum. The dehydrated solid is redissolved in water, aluminum and iron enter the liquid phase while silicon is deactivated and exists in the solid phase, thereby realizing the efficient separation of silicon from aluminum, iron, etc. The present invention effectively solves the problem of difficult separation of silicon and aluminum at present and provides a more economical and effective method for the high-value utilization of fly ash industry.

[0019] Further, in step S1, the mass ratio of fly ash to the alkali agent is 1:(0.5 - 4), and the alkali agent includes one or a combination of more of sodium carbonate, sodium hydroxide, and potassium hydroxide.

[0020] Further, in step S1, the temperature of the calcination treatment is 600 - 900 °C, and the time is 0.2 - 2 h.

[0021] Further, in step S2, the acidification treatment uses hydrochloric acid and / or sulfuric acid with a concentration of 0.1 - 10 mol / L.

[0022] Preferably, in step S2, the mass ratio of filter residue A to fly ash in step S1 ≤ 30%.

[0023] Further, in step S3, the moisture removal is carried out by heating, and the heating time is 1 - 10 h.

[0024] Further, in step S3, the solid is redissolved in water to obtain a second mixture, and the solid-liquid ratio is 1:10 to 5:1 by mass.

[0025] Further, in step S4, the temperature of the heat treatment is 80 to 450 °C, and the time is 0.5 to 2 h.

[0026] Further, in step S5, the aqueous solution of the base is selected from the aqueous solution of NaOH with a concentration of 0.1 to 2 mol / L. Preferably, the concentration of the aqueous solution of NaOH is 1 mol / L.

[0027] Further, in step S6, the acidification treatment is carried out by adding hydrochloric acid and / or sulfuric acid to filtrate C, or by introducing CO2 into filtrate C.

[0028] Further, step S7 further includes: heating the iron hydroxide precipitate to obtain magnetic iron oxide.

[0029] Preferably, in step S7, the temperature of the heat treatment is 500 to 900 °C, and the time is 20 to 80 min.

[0030] The technical solution adopted to achieve the second object of the present invention is: to provide an application of the method according to the first object of the present invention in the high-value utilization of fly ash.

[0031] Further, after the fly ash is treated, the purities of the obtained white carbon black and alumina are both higher than 95%. At the same time, the extraction efficiency of white carbon black and alumina in the fly ash by this method is as high as more than 90%, far higher than the extraction rate of the existing process technology, and the amount of ash slag generated is small, and the amount of ash slag is less than 30% of the fly ash usage. The filtrate generated during this treatment process can also be used to recover sodium chloride and / or sodium sulfate salts, realizing the high-value utilization and reduction of fly ash.

[0032] Compared with the prior art, the beneficial effects of the present invention are:

[0033] (1) A method for efficiently extracting white carbon black and alumina from fly ash provided by the present invention, after acidifying the calcined product, a mixed acid leaching solution containing aluminum, silicon and iron and a filter residue without aluminum, silicon and iron are obtained. By first heating the acid leaching solution to obtain a solid and then redissolving and separating the solid, a filter residue with a high silicon content is obtained. Compared with the conventional method of directly extracting silicon from the acid leaching residue, this method not only realizes the efficient separation of silicon and aluminum, increases the extraction rate of silicon and aluminum to more than 90%, far higher than the extraction rate of the existing process technology, but also generates less ash slag, and the amount of ash slag only accounts for about 30% of the fly ash usage, and the purities of the obtained white carbon black and alumina products are as high as more than 95%.

[0034] (2) The method provided by the present invention for efficiently extracting silica white and alumina from fly ash significantly improves the separation effect of silicon and aluminum through the optimization and adjustment of each step. The extraction efficiency of silicon and aluminum is much higher than that of the existing process technology, and the obtained silica white and alumina products both have high purity. The present invention also has the advantages of simple process, low cost, low roasting temperature, easy industrialization and batch operation, etc., and has broad promotion and application prospects in the field of high-value utilization of fly ash. Brief Description of the Drawings

[0035] Figure 1 It is a process schematic diagram of the method provided by the present invention for efficiently extracting silica white and alumina from fly ash;

[0036] Figure 2 It is the EDS spectrum of the high-purity silica white and alumina prepared in Example 1 of the present invention; among them, (a) is the EDS spectrum of the product silica white, and (b) is the EDS spectrum of the product alumina. Detailed Embodiments

[0037] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0038] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0039] The present invention provides a method for efficiently extracting silica white and alumina from fly ash for the recycling treatment of fly ash. The operation process of this method is as Figure 1 shown, and this method includes the following steps:

[0040] Step 1: Mix fly ash with one or more of alkali agents such as sodium carbonate, sodium hydroxide, and potassium hydroxide in a mass ratio of 1:(0.5 - 4), and perform roasting treatment at 600 - 900 °C for 0.2 - 2 h to obtain a roasted product;

[0041] Step 2: Dissolve the roasted product in water to obtain a first mixture, acidify the first mixture with hydrochloric acid and / or sulfuric acid with a concentration of 0.1 - 10 mol / L until the pH < 4, and immediately perform solid-liquid separation to obtain filtrate A and filter residue A;

[0042] Step 3: Heat the filtrate A for 1 - 10 h to remove water and obtain a solid. Mix the solid with water at a solid - liquid ratio (mass ratio) of 1:10 - 5:1, redissolve to obtain a second mixture, and immediately perform solid - liquid separation to obtain filtrate B and residue B;

[0043] Step 4: Heat - treat the residue B at 80 - 450 °C for 0.5 - 2 h to obtain white carbon black;

[0044] Step 5: Under continuous stirring, add an aqueous solution of NaOH with a concentration of 0.1 - 2 mol / L to the filtrate B, adjust the pH to pH > 12.5, perform solid - liquid separation and wash the precipitate to obtain filtrate C and iron hydroxide precipitate;

[0045] Step 6: Under continuous stirring, acidify the filtrate C until pH = 6 - 10, perform solid - liquid separation to obtain aluminum hydroxide precipitate and filtrate D;

[0046] Step 7: Heat - treat the iron hydroxide precipitate and the aluminum hydroxide precipitate at 500 - 900 °C for 20 - 80 min to obtain magnetic iron oxide and alumina;

[0047] Step 8: Collect and treat the filtrate D to recover sodium chloride and / or sodium sulfate.

[0048] The present invention will be further described below in conjunction with specific embodiments, but it is not intended to limit the present invention.

[0049] For the fly ash used in each embodiment of the present invention, by weight percentage, the silica content is 41.96% - 54.75%, the alumina content is 29.95% - 44.45%, the iron oxide content is 0.67% - 3.66%, the calcium oxide content is 0.37% - 6.24%, the titanium dioxide content is 0.98% - 1.95%, and the content of other components is less than 5%.

[0050] Example 1

[0051] Weigh 4 g of a mixture of fly ash and 12 g of sodium carbonate, heat - roast it at 900 °C for 1 h, dissolve it in water, acidify it with hydrochloric acid until pH < 4, and after filtration, the ash residue yield is 27.8% of the fly ash mass. Heat the filtrate for 5.6 h, redissolve the obtained solid in water, stir evenly, then filter, wash, and dry at 150 °C to obtain white carbon black with a purity of 97.4% and a recovery rate of 92.3%. Adjust the pH of the filtrate with sodium hydroxide to pH > 12.5, filter and wash to obtain an iron hydroxide precipitate. Adjust the pH of the filtrate to pH = 7 with hydrochloric acid and filter to obtain an aluminum hydroxide precipitate. Heat - dehydrate the iron hydroxide and aluminum hydroxide precipitates to obtain magnetic iron oxide and alumina, where the purity of alumina is 95.8% and the recovery rate is 93.8%.

[0052] The EDS spectra of the silica white and alumina products obtained in this example are as follows Figure 2 shown. It can be seen from Figure 2 that the purities of the silica white and alumina products are both greater than 95%, and there is no aluminum in the silica white component and no silicon in the alumina. This proves that the method provided by the present invention can efficiently desilicate fly ash, reduce the loss of aluminum during the desilication process, effectively achieve the separation of aluminum and silicon, ensure the extraction efficiency of silicon and aluminum, and ensure the high purity of the products.

[0053] Example 2

[0054] Weigh 2 g of fly ash and 5 g of sodium hydroxide, heat and roast the mixture at 850 °C for 1 h, dissolve it in water, acidify it with hydrochloric acid to pH < 4, filter, and the ash residue yield is 28.2% of the fly ash mass. Heat the filtrate for 4.5 h, redissolve the obtained solid in water, stir evenly, filter, wash, and dry at 200 °C to obtain silica white with a purity of 98.2% and a recovery rate of 90.8%. Adjust the pH of the filtrate with sodium hydroxide to pH > 12.5, filter and wash to obtain ferric hydroxide precipitate. Adjust the pH of the filtrate with hydrochloric acid to pH = 9, filter to obtain aluminum hydroxide precipitate. Heat and dehydrate the ferric hydroxide and aluminum hydroxide precipitates to obtain magnetic iron oxide and alumina, where the purity of alumina is 98.6% and the recovery rate is 92.4%.

[0055] Example 3

[0056] Weigh 2 g of fly ash and 5 g of sodium carbonate, heat and roast the mixture at 800 °C for 1 h, dissolve it in water, acidify it with hydrochloric acid to pH < 4, filter, and the ash residue yield is 29% of the fly ash mass. Heat the filtrate for 6.7 h, redissolve the obtained solid in water, stir evenly, filter, wash, and dry at 300 °C to obtain silica white with a purity of 98.2% and a recovery rate of 93.8%. Adjust the pH of the filtrate with sodium hydroxide to pH > 12.5, filter and wash to obtain ferric hydroxide precipitate. Pass CO2 through the filtrate to pH = 7.4, filter to obtain aluminum hydroxide precipitate. Heat and dehydrate the ferric hydroxide and aluminum hydroxide precipitates to obtain magnetic iron oxide and alumina, where the purity of alumina is 98.9% and the recovery rate is 90.2%.

[0057] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the content of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for efficiently extracting silica white and alumina from fly ash, characterized in that, It includes the following steps: S1. Mix fly ash and an alkali agent in a certain ratio, and obtain a calcined product through calcination treatment; S2. Dissolve the calcined product in water to obtain a first mixture, perform acidification treatment on the first mixture until pH < 4, and immediately perform solid-liquid separation to obtain filtrate A and filter residue A; S3. Heat the filtrate A for 1 - 10 h to remove moisture to obtain a solid, mix the solid and water in a mass ratio of 1:10 - 5:1, redissolve to obtain a second mixture, and immediately perform solid-liquid separation to obtain filtrate B and filter residue B; S4. Heat-treat the filter residue B at a temperature of 80 - 450 °C for 0.5 - 2 h to obtain white carbon black; S5. Under the condition of continuous stirring, add an aqueous solution of an alkali to the filtrate B to adjust the pH to pH > 12.5, perform solid-liquid separation and wash the precipitate to obtain filtrate C and iron hydroxide precipitate; S6. Under the condition of continuous stirring, perform acidification treatment on the filtrate C until pH = 6 - 10, and perform solid-liquid separation to obtain aluminum hydroxide precipitate; S7. Perform heat treatment on the aluminum hydroxide precipitate to obtain alumina; The extraction efficiency of white carbon black and alumina in fly ash by the method is over 90%; the purity of the obtained white carbon black and alumina is higher than 95%; the ash residue generated is less than 30% of the fly ash dosage.

2. The method according to claim 1, characterized in that, In step S1, the mass ratio of fly ash to the alkali agent is 1:(0.5 - 4), and the alkali agent includes one or a combination of more of sodium carbonate, sodium hydroxide, and potassium hydroxide.

3. The method according to claim 1, wherein In step S1, the temperature of the calcination treatment is 600 - 900 °C, and the time is 0.2 - 2 h.

4. The method according to claim 1, wherein In step S2, the acidification treatment uses hydrochloric acid and / or sulfuric acid with a concentration of 0.1 - 10 mol / L.

5. The method according to claim 1, wherein In step S5, the aqueous solution of the alkali is selected from an aqueous solution of NaOH with a concentration of 0.1 - 2 mol / L.

6. The method according to claim 1, wherein In step S6, the acidification treatment is carried out by adding hydrochloric acid and / or sulfuric acid to the filtrate C, or by introducing CO2 into the filtrate C.

7. The method according to claim 1, wherein In step S7, the temperature of the heat treatment is 500 - 900 °C, and the time is 20 - 80 min.

8. An application of the method according to any one of claims 1 - 7 in the high-value utilization of fly ash.

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