Method for preparing aluminum chloride by leaching fly ash with hydrochloric acid under assistance of chlorine

Abstract

The invention discloses a method for preparing aluminum chloride by leaching fly ash with hydrochloric acid under the assistance of chlorine, and belongs to the technical field of resource utilization of fly ash and preparation of aluminum oxide. The method comprises the following steps: utilizing hypochlorous acid with strong oxidizing property generated when chlorine is dissolved in an aqueous solution to promote decomposition of fly ash, promoting aluminum oxide components in the fly ash to be dissolved into the solution and exist in the solution in the form of AlCl3, simultaneously or crosswise introducing hydrogen into the solution, and enabling the chlorine and the hydrogen to react in a solution environment, so as to obtain the aluminum oxide in the fly ash. And chemical energy released during complexing of chlorine and hydrogen is directly converted into chemical energy required by decomposition of fly ash. According to the method, the hydrochloric acid concentration, the leaching temperature and the leaching pressure required in the leaching process can be reduced. And the corrosion problem of leaching equipment is relieved. And meanwhile, the energy cost consumed for maintaining a relatively high leaching temperature is reduced.

Description

Technical Field

[0001] The invention relates to the technical fields of fly ash resource utilization and aluminum chloride / aluminum oxide preparation, and in particular to a method for obtaining aluminum chloride concentrate by leaching fly ash with chlorine-assisted hydrochloric acid. Background Art

[0002] Fly ash is a fine solid waste produced by coal combustion in coal-fired power generation, heating, metal smelting and other coal-fired industries. The direct emission of this substance will cause environmental pollution and ecological damage, so the resource utilization of fly ash is urgent. Fly ash, especially high-aluminum fly ash, can contain 40% to 60% alumina. It is generally believed that when the aluminum oxide content in fly ash is greater than 40%, it has the potential for aluminum extraction. The higher the aluminum oxide content, the more conducive it is to the recovery of aluminum components. Therefore, high-aluminum fly ash is a good raw material for extracting aluminum compound-related chemical products, including aluminum oxide, aluminum chloride, aluminum sulfate, aluminum nitrate, aluminum fluoride, aluminum hydroxide, etc. By developing and improving relevant extraction technologies, not only can the high added value of fly ash be achieved, but also the current shortage of bauxite resources in my country can be alleviated.

[0003] The main components of fly ash are aluminum oxide and silicon dioxide, and it also contains associated elements such as iron, lead, mercury, arsenic, chromium, cadmium, copper, zinc, and gallium. At present, the technology of extracting alumina from high-aluminum fly ash can be roughly divided into alkali method and acid method. The alkali method is based on the Bayer process, which mainly uses alkali to react with alumina to generate soluble sodium aluminate, realizes the separation of aluminum elements and impurities in fly ash, and finally obtains alumina through high-temperature roasting and other process flows. The advantage of the alkali method is that the process flow can refer to the existing alumina extraction process, which is a mature technology and has undergone long-term production practice. However, the disadvantage is that it is limited by the low mass ratio of aluminum oxide to silicon dioxide (aluminum-silicon ratio) in fly ash, and cannot be directly used to extract alumina from fly ash. The acid process has the advantages of reduction, easy comprehensive utilization, suitable for processing low aluminum-silicon ratio silicate ores, and low energy consumption. It is the main method for fly ash treatment. The acid method is mainly divided into sulfuric acid method and hydrochloric acid method. The sulfuric acid method is to dissolve fly ash with concentrated sulfuric acid, separate the silicon dioxide that is insoluble in concentrated sulfuric acid, obtain an aluminum-containing extract, and then concentrate and crystallize the extract to obtain aluminum sulfate crystals, and finally roast it to obtain alumina. The difficulty faced by the sulfuric acid method is that it is very difficult to remove impurities from the sulfate solution, which is mainly reflected in the high precision required for impurity removal and the wide variety of impurity ions in the solution.

[0004] The hydrochloric acid method mixes fly ash and hydrochloric acid in an autoclave for acid dissolution, and separates the silicon dioxide in the fly ash to obtain a crude concentrate rich in aluminum chloride. The crude concentrate is then removed, concentrated, and crystallized to obtain hydrated aluminum chloride crystals, and finally roasted to obtain alumina. The hydrochloric acid method for extracting fly ash has the advantages of short process, low energy consumption, and the ability to recycle acid. It is not only beneficial to protect the ecological environment and reduce technical costs, but also can extract some valuable elements other than alumina. The process is relatively simple and the alumina obtained is of high quality, so it is widely used.

[0005] The current mainstream leaching technology is to use hydrochloric acid with a mass fraction of 25% to 30%, a fly ash-hydrochloric acid mass ratio (solid-liquid ratio) of 1:3 to 1:4, a leaching temperature of 130°C to 160°C, a leaching pressure of 0.27MPa to 0.62MPa, and a leaching time of 5h to 6h to complete the leaching. The actual alumina leaching rate can usually reach 85% to 90%. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid. The method uses chlorine and hydrochloric acid to complete the leaching step of aluminum oxide in fly ash. The fly ash (main component is Al2O3·xSiO2) is decomposed by using the strong oxidizing hypochlorous acid (Cl2+H2O=HClO+HCl) generated when chlorine is dissolved in an aqueous solution, so as to promote the aluminum oxide (Al2O3) component in the fly ash to dissolve into the solution and exist in the solution in the form of AlCl3. At the same time, as an auxiliary, hydrogen is introduced into the solution simultaneously or crosswise. Chlorine and hydrogen react chemically in the solution environment, and the chemical energy released when chlorine and hydrogen are complexed (Cl2+H2=2HCl) is directly converted into the chemical energy required for the decomposition of fly ash (Al2O3·xSiO2=Al2O3+xSiO2). The silicon dioxide (SiO2) component is insoluble in the acid solution, and the silicon dioxide component can be separated from the system by filtering, thereby obtaining a leachate rich in aluminum chloride.

[0007] The present invention provides a method for preparing aluminum chloride by leaching fly ash with hydrochloric acid assisted by chlorine, comprising the following steps:

[0008] (1) Fly ash and hydrochloric acid solution are mixed and slurried, and then loaded into a reaction kettle with stirring and gas blowing functions;

[0009] (2) setting the temperature and pressure of the reactor for leaching;

[0010] (3) During the leaching process, chlorine gas, or a mixture of chlorine gas and air, carbon dioxide, etc., is continuously or intermittently introduced into the reactor;

[0011] (4) During the leaching process, hydrogen is introduced into the reactor continuously, intermittently, or crosswise with chlorine to allow the hydrogen to react rapidly with the chlorine dissolved in the solution.

[0012] The above-mentioned method for preparing aluminum chloride by leaching fly ash with hydrochloric acid assisted by chlorine gas, wherein:

[0013] In the step (1), the mass concentration of hydrochloric acid is 20% to 27%, and the mass ratio of fly ash to hydrochloric acid solution is 1:3 to 1:5.

[0014] In the step (2), the leaching temperature is between 80°C and 130°C, and the leaching pressure is between 0.1MPa and 0.27MPa (absolute pressure).

[0015] In the step (3), the total mass of the chlorine gas introduced is 3% to 15% of the mass of the slurry to be treated.

[0016] In the step (4), the total mass of the hydrogen introduced is less than or equal to 5% of the total mass of the chlorine introduced.

[0017] In the steps (2) to (4), the leaching time is 3h to 5h. If the reactor (device) used is a vertical or horizontal tank reactor, the production method is generally intermittent, and the leaching time of a single tank is 3h to 5h. If the reactor (device) used is a pipeline leaching, the leaching time is the residence time of the material in the leaching pipeline section, which is 3h to 5h.

[0018] In the steps (1) to (4), the gas blowing methods include top blowing, side blowing and bottom blowing.

[0019] By adopting the method of the present invention, the leaching rate of aluminum oxide in fly ash can reach 85% to 95%.

[0020] Beneficial effects of the present invention:

[0021] 1. Fly ash is the residue produced after coal powder is burned in the process of coal-fired power generation. During the high-temperature combustion of coal, part of the fly ash is converted into glass, which has stable properties and is not easily decomposed by acid or alkali. Therefore, high-concentration acid or alkali solution is often required to destroy its structure, so as to efficiently extract the alumina component therein. The method of the present invention utilizes the strong oxidizing hypochlorite ions generated by the reaction of chlorine with aqueous solution and hydrogen to promote the rapid disintegration of glass fly ash under milder reaction conditions, thereby obtaining a higher alumina leaching rate.

[0022] 2. The main problem of the current hydrochloric acid leaching process is that the leaching process needs to be carried out in a high hydrochloric acid concentration, high temperature, and high pressure environment, which leads to corrosion of the leaching equipment and high investment problems. The method of the present invention can reduce the hydrochloric acid concentration, leaching temperature, and leaching pressure required in the leaching process, thereby alleviating the corrosion problem of the leaching equipment. At the same time, it reduces the energy cost consumed by maintaining a high leaching temperature.

[0023] 3. The method of the present invention is suitable for commercial-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a schematic diagram of a device for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid.

[0025] In the figure: 1. Reactor, 2. Stirring paddle, 3. Chlorine gas storage tank, 4. Gas filtering and drying equipment, 5. Air pump I, 6. Hydrogen gas storage tank, 7. Air pump II.

[0026] Figure 2 This is the XRD spectrum of the fly ash raw material used in the embodiments of the present invention. DETAILED DESCRIPTION

[0027] A method for preparing aluminum chloride by leaching fly ash with hydrochloric acid assisted by chlorine gas, the experimental device used is as shown in the attached Figure 1 The device comprises a reaction kettle 1, a stirring paddle 2, a chlorine gas storage tank 3, a gas filtering and drying device 4, an air pump I 5, a hydrogen gas storage tank 6 and an air pump II 7.

[0028] The chemical composition of fly ash used in the experiment is:

[0029] element Al Si Na Fe P Mass fraction % 23.08 16.88 1.61 1.36 1.42

[0030] The XRD phase composition of the fly ash used in the experiment is a mixed phase of silicon dioxide and mullite, see the attached Figure 2 .

[0031] The specific operation process is as follows:

[0032] (1) Weigh the fly ash sample Mg and place it in a laboratory high-pressure reactor.

[0033] (2) Prepare a hydrochloric acid solution with a mass concentration of A% (20% to 27%). Mix the fly ash and the hydrochloric acid solution in a reaction kettle at a fly ash-hydrochloric acid solution mass ratio (solid-liquid ratio) of B (1:3 to 1:5). The actual mass of the hydrochloric acid solution added is bg.

[0034] (3) After closing the reactor cover, set the reactor temperature so that the reaction temperature is stable at T°C (80°C to 130°C). Since the reactor is in a closed state, the temperature and reaction pressure P MPa (0.1 MPa to 0.27 MPa, absolute pressure) in the reactor can be directly converted according to the following table using the vapor pressure of the aqueous solution.

[0035] Water vapor pressure-temperature comparison table

[0036] Temperature, °C Absolute pressure, MPa <100 0.101 100 0.101 110 0.143 120 0.199 130 0.270 140 0.361 150 0.476 160 0.618 170 0.793 180 1.004 190 1.256 200 1.555

[0037] (4) Start stirring the reactor to ensure that the slurry in the reactor is fully mixed. Continue to introduce chlorine gas into the reactor from the side blowing port of the reactor. The rate of introduction of chlorine gas is:

[0038] v=(m×X) / t

[0039] Where, v is the chlorine gas introduction rate, g / h;

[0040] X is the ratio of the total mass of chlorine gas introduced into the reaction to the total mass of the slurry in the reactor, %; in the present invention, the value of X is between 3 and 15;

[0041] m is the total mass of the slurry in the reactor, m = the mass of fly ash added to the reactor M + the mass of hydrochloric acid solution actually added to the reactor b, g;

[0042] t is the reaction time, h. In the present invention, the reaction time is 3 h to 5 h.

[0043] (5) Hydrogen is intermittently introduced into the reactor from the side blowing port of the reactor, and the total mass of the hydrogen introduced is x% of the total mass of the chlorine introduced; in the present invention, the value of x is less than or equal to 5.

[0044] (6) After the reaction is completed, stop introducing chlorine and hydrogen, stop stirring, release the pressure of the reactor, and discharge the slurry material. The slurry material is subjected to solid-liquid separation and filter cake washing. The obtained filtrate is a crude aluminum chloride concentrate, and the obtained filtrate volume is VL. After chemical analysis, the aluminum element concentration is C2 g / L, and the obtained filter cake is white mud rich in silicon dioxide. The leaching rate of aluminum oxide in fly ash is defined as:

[0045] Y=(V×C2) / (M×C1)×100%

[0046] Where, Y is the leaching rate of alumina in fly ash, %;

[0047] V is the volume of the filtrate, L;

[0048] C2 is the concentration of aluminum in the filtrate, g / L;

[0049] M is the mass of fly ash, g;

[0050] C1 is the mass fraction of aluminum in fly ash, %.

[0051] The present invention is described below by 10 embodiments. The present invention is designed for the following contents: mass concentration of hydrochloric acid solution A%, mass ratio of fly ash to hydrochloric acid solution (solid-liquid ratio) B, leaching reaction temperature T°C, leaching reaction pressure PMPa (absolute pressure), ratio of total mass of chlorine gas introduced in the reaction to total mass of slurry in the reactor X%, total mass of hydrogen introduced is x% of total mass of chlorine gas introduced, leaching reaction time th, leaching rate of aluminum oxide in fly ash Y%.

[0052] Under the above conditions, fly ash Mg with a mass fraction of aluminum of C1% was added, bg of hydrochloric acid solution was added, and vg / h of chlorine gas was introduced into the m=(M+b)g slurry to carry out a leaching experiment.

[0053] After the reaction is completed, a filtrate VL with an aluminum concentration of C2 g / L is obtained by filtration.

[0054] Table 1 Core process parameters in Examples 1-10

[0055] A B T P X x t Y Example 1 27 0.2 130 0.27 15 5 5 95 Example 2 20 0.2 130 0.27 15 5 5 92 Example 3 27 0.333 130 0.27 15 5 5 85 Example 4 27 0.2 80 0.10 15 5 5 88 Example 5 27 0.2 130 0.27 5 5 5 85 Example 6 27 0.2 130 0.27 15 5 3 87 Example 7 24 0.25 110 0.14 10 2.5 4 91 Example 8 22 0.28 95 0.10 10 2 5 92 Example 9 25 0.29 95 0.10 12 2 4 94 Example 10 25 0.3 110 0.14 10 0 3 90

[0056] Table 2 Specific experimental parameters in Examples 1-10

[0057]

[0058]

Claims

1. A method for preparing aluminum chloride by leaching fly ash with hydrochloric acid assisted by chlorine, characterized in that: The method uses chlorine and hydrochloric acid to jointly complete the leaching step of aluminum oxide in fly ash, and utilizes the hypochlorous acid with strong oxidizing property generated when chlorine is dissolved in aqueous solution to promote the decomposition of fly ash, so as to cause the aluminum oxide component in the fly ash to dissolve into the solution and exist in the solution in the form of AlCl3, and hydrogen is introduced into the solution simultaneously or crosswise, and the chlorine and hydrogen react chemically in the solution environment, so that the chemical energy released when the chlorine and hydrogen are complexed is directly converted into the chemical energy required for the decomposition of the fly ash.

2. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 1, characterized in that: The silicon dioxide component in the fly ash is insoluble in the acid solution. The silicon dioxide component is stripped from the system by filtering to obtain a leaching solution rich in aluminum chloride.

3. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 1, characterized in that: The following steps are involved: (1) Fly ash and hydrochloric acid solution are mixed and slurried, and then loaded into a reaction kettle with stirring and gas blowing functions; (2) setting the temperature and pressure of the reactor for leaching; (3) During the leaching process, chlorine gas, or a mixture of chlorine gas, air, or carbon dioxide, is continuously or intermittently introduced into the reactor; (4) During the leaching process, hydrogen is introduced into the reactor continuously, intermittently, or crosswise with chlorine to allow the hydrogen to react rapidly with the chlorine dissolved in the solution.

4. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: In the step (1), fly ash and hydrochloric acid solution with a mass concentration of 20% to 27% are mixed at a fly ash-hydrochloric acid solution mass ratio of 1:3 to 1:5, slurried, and loaded into a reaction kettle with stirring and gas blowing functions.

5. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: Gas blowing methods include top blowing, side blowing and bottom blowing.

6. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: In the step (3), the total mass of the chlorine gas introduced is 3% to 15% of the mass of the slurry to be treated.

7. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: In the step (4), the total mass of the hydrogen introduced is less than or equal to 5% of the total mass of the chlorine introduced.

8. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: The leaching temperature is 80°C to 130°C, the leaching pressure is 0.1MPa to 0.27MPa, and the leaching time is 3h to 5h.

9. The method for preparing aluminum chloride by leaching fly ash with chlorine-assisted hydrochloric acid according to claim 3, characterized in that: The leaching rate of alumina in fly ash reaches 85% to 95%.

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