Method for purifying aluminum chloride hexahydrate and application thereof

Abstract

The invention provides a method for purifying aluminum chloride hexahydrate and application thereof. The method comprises the following steps: evaporating a mixed solution containing aluminum chloride for the first time, and obtaining a mixture A when the concentration of AlCl3 is in a saturated state; performing secondary evaporation on the mixture A, and stopping the secondary evaporation when the content of the solid-phase matter is 20-40% to obtain a mixture B; cooling and crystallizing the mixture B, and obtaining a mixture C when the content of a solid-phase substance is 20-50%; filtering the mixture C under a constant temperature condition to obtain a precipitate and a supernatant; wherein the precipitate is aluminum chloride hexahydrate; wherein the rate v of the second evaporation is equal to x * V, v is the evaporation rate, and kg H2O / h; x is a rate coefficient and is 40%-50% / h; and V is the mass of the mixture A, kg. The method is helpful for promoting the development of circular economy.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a method for purifying aluminum chloride hexahydrate and application thereof. Background Art

[0002] Aluminum chloride hexahydrate (AlCl3·6H2O) is a colorless crystal with a melting point of 204°C. It is mainly used as a water purifier in industry. It has the advantages of good flocculation effect, low cost, and large processing capacity. It is widely used in various fields such as industry, agriculture, commerce, and animal husbandry. Aluminum chloride hexahydrate has also been widely used in solvent extraction and ion exchange processes. Aluminum chloride hexahydrate, as a solvent extractant, can be used as an ion exchanger in the solvent extraction process to adsorb various metal ions. Aluminum chloride hexahydrate can also be used as a catalyst, precipitant, electroplating agent, water treatment agent, disinfectant, preservative, flame retardant, drilling mud stabilizer, adhesive and other raw materials.

[0003] By using hydrochloric acid to leach fly ash (solid residue obtained after coal combustion for power generation), the main components of fly ash, silicon and aluminum, can be separated. Most of the aluminum enters the leachate to form an aluminum chloride solution. Silicon cannot be leached by hydrochloric acid, and after solid-liquid separation, it enters the "white mud" filter residue. During the hydrochloric acid treatment of fly ash, some other inclusions in the fly ash, such as Ca, Fe, Li, K, Mg, Cr, Cu, Zn, Ti, Na, As, Si, Pb, Ga, etc., will also enter the leachate with the Al element, forming a "crude aluminum chloride concentrate" with aluminum chloride as the main component.

[0004] This crude semen needs to be further impurity-removed and purified to obtain a crystalline aluminum chloride product that meets the purity standard. Common purification methods include: adding strong alkaline sulfides such as sodium sulfide, potassium sulfide, and zinc sulfide to react aluminum ions with iron ions, titanium ions, silicon ions, etc. to form a precipitate, separating it by filtering, and then evaporating and crystallizing the filtrate to obtain aluminum chloride hexahydrate; adding aluminum hydroxide flocculant, flocculating and filtering; introducing weak alkaline salts such as ammonium bicarbonate, sodium bicarbonate, and sodium carbonate to react with aluminum ions to form a precipitate, separating it by filtering, and then evaporating and crystallizing the filtrate to obtain aluminum chloride hexahydrate. The aluminum content purified by the above method can reach more than 99%, but the purity of AlCl3 in aluminum chloride hexahydrate is low, the product is easily affected by humidity, easy to agglomerate, and has poor strength. In addition, the added flocculants, precipitants, etc. will increase production costs and have a large consumption. Therefore, it is crucial to develop a method for extracting high-purity aluminum chloride hexahydrate. Summary of the invention

[0005] The main purpose of the present invention is to provide a method for purifying aluminum chloride hexahydrate and application thereof, so as to solve the problem of low purity of purified aluminum chloride hexahydrate in the prior art.

[0006] In order to achieve the above object, according to a first aspect of the present invention, a method for purifying aluminum chloride hexahydrate is provided, the method comprising:

[0007] Step 1, evaporating the mixed solution containing aluminum chloride for the first time, and when the concentration of AlCl3 is saturated, a mixture A is obtained;

[0008] Step 2, evaporating the mixture A for a second time, and when the content of the solid phase is 20% to 40%, stopping the second evaporation to obtain a mixture B;

[0009] Step 3, cooling and crystallizing the mixture B, and when the solid content is 20% to 50%, a mixture C is obtained;

[0010] Step 4, filtering the mixture C under constant temperature conditions to obtain a precipitate and a supernatant; wherein the precipitate is aluminum chloride hexahydrate;

[0011] The rate of the second evaporation is v=x×V, where v is the evaporation rate, kg H2O / h; x is the rate coefficient, 40% to 50% / h; and V is the mass of the mixture A, kg.

[0012] The mixed solution containing aluminum chloride contains AlCl3 solute with a mass volume concentration of <350g / L, HCl with a volume concentration of <5%, and any one or more of the following components: Ca element with a mass concentration of <1%, Fe element with a mass concentration of <2%, Li element with a mass concentration of <1%, K element with a mass concentration of <1%, Mg element with a mass concentration of <1%, Cr element with a mass concentration of <1%, Cu element with a mass concentration of <1%, or Zn element with a mass concentration of <1%.

[0013] Furthermore, the first evaporation and the second evaporation are performed in an evaporator.

[0014] Furthermore, the evaporator is selected from any one of the following: a single-effect evaporator, a multiple-effect evaporator or an MVR evaporator.

[0015] Furthermore, the rate of the first evaporation is greater than the rate of the second evaporation.

[0016] Furthermore, the temperature of the first evaporation is 60-120°C.

[0017] Furthermore, the first evaporation and the second evaporation are both performed in a vacuum system.

[0018] Furthermore, the absolute pressure of the vacuum system in which the first evaporation is performed is 0.005-0.02 MPa.

[0019] Furthermore, the absolute pressure of the vacuum system where the second evaporation is performed is 0.01-0.03 MPa.

[0020] Furthermore, the mixed solution containing aluminum chloride is a leachate of fly ash leached with hydrochloric acid.

[0021] In order to achieve the above object, according to a second aspect of the present invention, there is provided an application of the above method in purifying aluminum chloride hexahydrate in a leachate of hydrochloric acid leaching of fly ash.

[0022] By applying the technical solution of the present invention, the purity and yield of aluminum chloride hexahydrate are effectively improved by controlling the evaporation rate (two-stage evaporation) and the solid content. In practical applications, the method can not only significantly reduce the content of impurity elements, but also optimize the crystallization process, so that the final product has advantages such as high purity.

[0023] In addition, in some preferred embodiments, by performing evaporation in a vacuum system, energy consumption is effectively reduced, production efficiency is improved, and an economically feasible solution is provided for industrial-scale purification of aluminum chloride hexahydrate.

[0024] The application of this method, especially when applied to the purification of aluminum chloride hexahydrate in the leachate of hydrochloric acid leaching fly ash, is of great significance to resource recovery and environmental protection, can promote the development of circular economy, and reduce the impact of industrial waste on the environment. At the same time, the method can also be widely used in the treatment of other aluminum-containing waste liquids, such as bauxite, aluminum processing waste liquid, etc., opening up a new way for the comprehensive utilization of aluminum resources. Through the method of the present invention, not only can the yield and purity of aluminum chloride hexahydrate be improved, but also the production cost can be reduced, and the economic benefit can be improved, which plays an important role in promoting the sustainable development of the aluminum chemical industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 A process flow chart for purifying aluminum chloride hexahydrate according to the present invention is shown.

[0027] Figure 2 The XRD phase analysis spectrum of the aluminum chloride hexahydrate product obtained in Example 1 of the present invention is shown. DETAILED DESCRIPTION

[0028] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below in conjunction with the embodiments.

[0029] Terminology explanation:

[0030] Liquid attachment rate: refers to the degree to which the gaps between solid particles are filled with liquid during the accumulation of solid particles. In the present invention, it refers to the content of unseparated aluminum chloride mother liquor in the prepared aluminum chloride hexahydrate product.

[0031] As mentioned in the background art, the method for purifying aluminum chloride hexahydrate in the prior art has the problem of low extraction purity. In the present invention, the inventor attempts to separate multiple impurity elements by regulating the evaporation rate of the mixed solution containing aluminum chloride, so that the purity of the purified aluminum chloride hexahydrate is high, and thus proposes the protection scheme of the present invention.

[0032] In a first typical embodiment of the present invention, a method for purifying aluminum chloride hexahydrate is provided, such as Figure 1 As shown, the above method includes:

[0033] Step 1, evaporating the mixed solution containing aluminum chloride for the first time, and when the concentration of AlCl3 is saturated, a mixture A is obtained;

[0034] Step 2, evaporating the mixture A for a second time, and when the content of the solid phase is 20% to 40%, stopping the second evaporation to obtain a mixture B;

[0035] Step 3, cooling and crystallizing the mixture B, and when the solid content is 20% to 50%, a mixture C is obtained;

[0036] Step 4, filtering the mixture C under constant temperature conditions to obtain a precipitate and a supernatant; wherein the precipitate is aluminum chloride hexahydrate;

[0037] The rate of the second evaporation is v=x×V, where v is the evaporation rate, kg H2O / h; x is the rate coefficient, 40% to 50% / h; and V is the mass of the mixture A, kg.

[0038] The mixed solution containing aluminum chloride contains AlCl3 solute with a mass volume concentration of <350g / L, HCl with a volume concentration of <5%, and any one or more of the following components: Ca element with a mass concentration of <1%, Fe element with a mass concentration of <2%, Li element with a mass concentration of <1%, K element with a mass concentration of <1%, Mg element with a mass concentration of <1%, Cr element with a mass concentration of <1%, Cu element with a mass concentration of <1%, or Zn element with a mass concentration of <1%.

[0039] The inventor has conducted many experiments and found that by regulating the evaporation rate of the mixed solution containing aluminum chloride, especially the second evaporation rate, the aluminum chloride hexahydrate in the mixed solution containing aluminum chloride can be effectively purified. In the present invention, the second evaporation rate is v=x×V (v is the evaporation rate, kg H2O / h; x is the rate coefficient, 40% to 50% / h; V is the mass of the above-mentioned mixture A, kg), and its size is affected by the rate coefficient and the mass of the mixture A. The inventor has conducted many experiments and found that when the rate coefficient is 40% to 50% / h, the purity of the aluminum chloride hexahydrate crystals precipitated from a certain volume of saturated aluminum chloride mother liquor is high. The application of this method, especially when applied to the purification of aluminum chloride hexahydrate in the leachate of hydrochloric acid leaching fly ash, is of great significance to resource recovery and environmental protection, can promote the development of circular economy, and reduce the impact of industrial waste on the environment. Through the method of the present invention, not only can the yield and purity of aluminum chloride hexahydrate be improved, but also the production cost can be reduced, the economic benefit can be improved, and it plays an important role in promoting the sustainable development of the aluminum chemical industry.

[0040] The purpose of the first evaporation is to quickly concentrate the mixed solution containing aluminum chloride, so that the concentration of AlCl3 in the mixed solution is concentrated to a saturated state to obtain a mixture A. Since the first evaporation is only for the purpose of concentration, not purification, its evaporation rate does not affect the final purification process. It is usually recommended to set the first evaporation rate to the maximum evaporation rate of the equipment. Increasing the rate of the first evaporation is more conducive to improving production efficiency. In some embodiments, the rate of the first evaporation is 0.5 to 1.5 kg H2O / h. Using this evaporation rate for the first evaporation can quickly concentrate the mixed solution containing aluminum chloride to a saturated state.

[0041] The purpose of the second evaporation is to purify, so at a lower evaporation rate, aluminum chloride crystals are slowly precipitated from the solution. At this time, the slower crystal precipitation rate makes the newly precipitated aluminum chloride crystals from the solution system mixed with as few solution impurities as possible. When the content of the solid phase in the above-mentioned mixture A is 20% to 40%, the above-mentioned second evaporation is stopped because as the aluminum chloride crystals are continuously precipitated from the solution system, the concentration ratio of the body (including impurities and aluminum chloride) in the solution gradually increases, which is not conducive to the precipitation of clean aluminum chloride crystals from the solution. When the content of the solid phase in the mixture A exceeds 40%, the purity of the newly precipitated aluminum chloride crystals will decrease. In some embodiments, the rate of the first evaporation is greater than the rate of the second evaporation.

[0042] It should be noted that there are many factors that affect the evaporation rate, including the evaporation temperature and the absolute pressure of the vacuum system. Different evaporation equipment may have different corresponding evaporation temperatures and absolute pressures of the vacuum system to achieve the above two evaporation rates. Specifically, the evaporation temperature and the absolute pressure of the vacuum system and other parameters can be set according to the evaporation equipment actually used, so that the evaporation rate eventually reaches the above first evaporation rate and the second evaporation rate. In a preferred embodiment of the present invention, the temperature of the first evaporation is 60-120°C. The use of this evaporation temperature helps to increase the first evaporation rate and promote the rapid first evaporation.

[0043] In another preferred embodiment of the present invention, the first evaporation and the second evaporation are both carried out in a vacuum system. Evaporation in a vacuum system can reduce the evaporation temperature, reduce energy consumption, and improve evaporation efficiency. In a more preferred embodiment of the present invention, the absolute pressure of the vacuum system where the first evaporation is located is 0.005-0.02MPa. In another more preferred embodiment of the present invention, the absolute pressure of the vacuum system where the second evaporation is located is 0.01-0.03MPa. The absolute pressure of the vacuum system helps to promote the evaporation rate and improve the purification efficiency of aluminum chloride hexahydrate.

[0044] In a preferred embodiment of the present invention, the first evaporation and the second evaporation are carried out in an evaporator. The use of an evaporator for two-stage evaporation (the first evaporation and the second evaporation) can better control the evaporation conditions, improve the evaporation efficiency, and is suitable for large-scale industrial production, which can significantly reduce production costs and improve economic benefits.

[0045] The evaporator is selected from any one of the following: single-effect evaporator, multi-effect evaporator or MVR evaporator. Different evaporators are suitable for different production scales and energy consumption requirements, and can be flexibly adjusted to adapt to different industrial application scenarios, such as large chemical plants, small laboratories, etc.

[0046] The purpose of the cooling crystallization is to allow aluminum chloride crystals in the solution to further precipitate, so as to increase the yield of aluminum chloride crystal products, that is, to improve the production efficiency of a single evaporation-crystallization cycle. In the present invention, the mixture B is cooled and crystallized, and the content of the solid phase in the mixture B is controlled to be 20% to 50%, so as to ensure that the precipitated aluminum chloride crystals are mixed with other impurities as little as possible and have a high chemical purity.

[0047] The temperature of cooling crystallization may affect the time of cooling crystallization, thereby further affecting the production efficiency of aluminum chloride hexahydrate. Conventional cooling crystallization temperatures are applicable to the present invention, and the solid content of the mixture after cooling crystallization should be 20% to 50%. It should be noted that when filtering after cooling crystallization, it is necessary to make the filtering temperature the same as the cooling crystallization temperature and keep a constant temperature. Filtration under this condition can avoid a substantial increase in the solid content of the solution during the filtering process.

[0048] In a preferred embodiment of the present invention, the mixed solution containing aluminum chloride is a leachate of fly ash leached with hydrochloric acid. Generally, the mass volume concentration of AlCl3 in the leachate of fly ash leached with hydrochloric acid is less than 350g / L, the volume concentration of HCl is less than 5%, and the mass concentration of elements such as Ca, Li, K, Mg, C, Cu and Zn is less than 1%, and the mass concentration of elements such as Fe is less than 2%. The method of the present invention is used to purify hexahydrate and aluminum chloride in the leachate of fly ash leached with hydrochloric acid, which has the advantage of high purification purity. In some embodiments, the mixed solution containing aluminum chloride is a leachate of coal gangue, nepheline or low-grade bauxite leached with hydrochloric acid.

[0049] In a second typical embodiment of the present invention, an application of the above method to purify aluminum chloride hexahydrate in the leachate of fly ash leached with hydrochloric acid is provided. The leachate of fly ash leached with hydrochloric acid contains rich aluminum elements. Through the purification method provided by the present invention, these aluminum elements can be effectively recovered and utilized to produce high-purity (more than 98%) aluminum chloride hexahydrate, which can not only improve resource utilization and reduce environmental pollution, but also provide high-quality raw materials for related industries and promote the development of circular economy.

[0050] The present invention is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed by the present invention.

[0051] The experimental process of the embodiment of the present invention is as follows:

[0052] (1) The components of the aluminum chloride crude concentrate to be treated are: AlCl3 A1 g / L, HC concentration B1%; impurities CaC1%, FeD1%, LiE1%, KF1%, MgG1%, CrH1%, CuI1%, ZnJ1%.

[0053] (2) 500 mL of the aluminum chloride crude solution in (1) was placed in a laboratory rotary evaporator for evaporation, and the evaporation rate was controlled in two stages according to the evaporation degree of the solution (the rotary evaporator model used in the present invention is RE2000A, manufactured by Shanghai Yarong). The first stage evaporation temperature is T1°C, the absolute pressure of the vacuum system is K1 MPa, the evaporation rate is about v1 kg H2O / h, and after t1 h, the AlCl3 concentration in the solution reaches saturation.

[0054] (3) The second stage evaporation temperature is T2℃, the absolute pressure of the vacuum system is K2 MPa, the evaporation rate is about v2 gH2O / min, and the evaporation rate is controlled as follows: v2=x×V, where v2 is the evaporation rate, kg H2O / h; x is the rate coefficient, 0.25~1.0% / h; and V is the amount of mother liquor in the evaporator, kg.

[0055] (4) After t2 h, when the solid content in the solution reaches L%, the mother liquor is discharged from the evaporator.

[0056] (5) The mother liquor discharged is further cooled and crystallized in the crystallizer, but the solid content in the solution should be controlled to be maintained within the range of M%.

[0057] (6) Constant temperature filtration to achieve solid-liquid separation.

[0058] (7) The solid phase obtained after filtration is dried to remove the attached water on the surface of the solid phase, and aluminum chloride hexahydrate product N kg is obtained. The chemical purity of the product is A2%, Ca C2 ppm (mass concentration), Fe D2 ppm, Li E2 ppm, K F2ppm, Mg G2 ppm, Cr H2 ppm, Cu I2 ppm, Zn J2 ppm, and the liquid attachment rate is K%.

[0059] The mass concentration of each impurity element in the present invention is obtained by ICP-OES detection. The liquid attachment rate is the mass loss rate of the sample after drying at 100 degrees Celsius for 24 hours.

[0060] The calculation formula of the chemical purity A2 of aluminum chloride hexahydrate (AlCl3·6H2O) is:

[0061] A2={1-[C2*(MCaCl2) / (MCa)-D2*(MFeCl3) / (MFe)-E2*(MLiCl) / (MLi)-F2*

[0062] (MKCl) / (MK)-G2*(MMgCl2) / (MMg)-H2*(MCrCl3) / (MCr)-I2*(MCuCl2) / (MCu)-J2*(MZnCl2) / (MZn)] / 1000000-K / 100}*100%, wherein MCaCl2 is the relative molecular mass of calcium chloride, 111 g / mol; MCa is the relative atomic mass of calcium, 40 g / mol; the relative molecular mass and relative atomic mass of other impurity chlorides and elements are the same.

[0063] Example 1

[0064] The experimental parameters and experimental results of Example 1 are shown in Table 1.

[0065] Table 1

[0066]

[0067]

[0068] Figure 2 This is the XRD phase analysis spectrum of the aluminum chloride hexahydrate product obtained after the experiment. It can be seen that the product is AlCl3·6H2O crystals with good crystallinity.

[0069] Example 2

[0070] The experimental parameters and experimental results of Example 2 are shown in Table 2.

[0071] Table 2

[0072]

[0073] Example 3

[0074] The experimental parameters and experimental results of Example 3 are shown in Table 3.

[0075] Table 3

[0076]

[0077] Example 4

[0078] The experimental parameters and experimental results of Example 4 are shown in Table 4.

[0079] Table 4

[0080]

[0081] Example 5

[0082] The experimental parameters and experimental results of Example 5 are shown in Table 5.

[0083] Table 5

[0084]

[0085] Example 6

[0086] The experimental parameters and experimental results of Example 6 are shown in Table 6.

[0087] Table 6

[0088]

[0089]

[0090] Example 7

[0091] The experimental parameters and experimental results of Example 7 are shown in Table 7.

[0092] Table 7

[0093]

[0094] Example 8

[0095] The experimental parameters and experimental results of Example 8 are shown in Table 8.

[0096] Table 8

[0097]

[0098]

[0099] Example 9

[0100] The experimental parameters and experimental results of Example 9 are shown in Table 9.

[0101] Table 9

[0102]

[0103] Example 10

[0104] The experimental parameters and experimental results of Example 10 are shown in Table 10.

[0105] Table 10

[0106]

[0107] Comparative Example 1

[0108] This comparative example adopts the evaporation crystallization method in the patent application document CN101837998A to treat the crude aluminum chloride concentrate in Example 1, and finally obtains crystalline aluminum chloride.

[0109] The experimental parameters and experimental results of Comparative Example 1 are shown in Table 11.

[0110] Table 11

[0111]

[0112] Comparative Example 2

[0113] This comparative example adopts the evaporation crystallization method in the patent application document CN101837998A to treat the crude aluminum chloride concentrate in Example 1, and finally obtains crystalline aluminum chloride.

[0114] The experimental parameters and experimental results of Comparative Example 2 are shown in Table 12.

[0115] Table 12

[0116]

[0117] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: the present invention can separate a variety of impurity elements by controlling the evaporation rate at different stages (two-stage) of the evaporation of the aluminum chloride solution, and the process is low-cost and high-efficiency. The concentration of impurity elements in the aluminum chloride hexahydrate product obtained by this method is: Ca<1000ppm, Fe<2600ppm, Li<100ppm, K<600ppm, Mg<400ppm, Cr<100ppm, Cu<100ppm, Zn<100ppm (ppm is mass fraction).

[0118] This method can not only significantly reduce the content of impurity elements, but also optimize the crystallization process, so that the final product has advantages such as high purity. In addition, by evaporating in a vacuum system, energy consumption is effectively reduced, production efficiency is improved, and an economically feasible solution is provided for the purification of aluminum chloride hexahydrate on an industrial scale. The application of this method, especially the purification of aluminum chloride hexahydrate in the leachate of hydrochloric acid leaching fly ash, is of great significance for resource recovery and environmental protection, and can promote the development of a circular economy and reduce the impact of industrial waste on the environment.

[0119] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for purifying aluminum chloride hexahydrate, characterized in that: The method comprises: Step 1, evaporating the mixed solution containing aluminum chloride for the first time, and when the concentration of AlCl3 is saturated, a mixture A is obtained; Step 2, evaporating the mixture A for a second time, and when the content of the solid phase is 20% to 40%, stopping the second evaporation to obtain a mixture B; Step 3, cooling and crystallizing the mixture B, and when the content of the solid phase is 20% to 50%, a mixture C is obtained; Step 4, filtering the mixture C under a constant temperature condition to obtain a precipitate and a supernatant; wherein the precipitate is the aluminum chloride hexahydrate; Wherein, the rate of the second evaporation is v=x×V, v is the evaporation rate, kg H2O / h; x is the rate coefficient, 40% to 50% / h; V is the mass of the mixture A, kg; The mixed solution containing aluminum chloride contains AlCl3 solute with a mass volume concentration of less than 350g / L, HCl with a volume concentration of less than 5%, and any one or more of the following components: Ca element with a mass concentration of less than 1%, Fe element with a mass concentration of less than 2%, Li element with a mass concentration of less than 1%, K element with a mass concentration of less than 1%, Mg element with a mass concentration of less than 1%, Cr element with a mass concentration of less than 1%, Cu element with a mass concentration of less than 1%, or Zn element with a mass concentration of less than 1%.

2. The method according to claim 1, characterized in that The first evaporation and the second evaporation are performed in an evaporator.

3. The method according to claim 2, characterized in that The evaporator is selected from any one of the following: a single-effect evaporator, a multiple-effect evaporator or an MVR evaporator.

4. The method according to claim 1, characterized in that: The rate of the first evaporation is greater than the rate of the second evaporation.

5. The method according to claim 4, characterized in that The temperature of the first evaporation is 60-120°C.

6. The method according to claim 5, characterized in that The first evaporation and the second evaporation are both performed in a vacuum system.

7. The method according to claim 6, characterized in that The absolute pressure of the vacuum system where the first evaporation occurs is 0.005-0.02 MPa.

8. The method according to claim 6, characterized in that The absolute pressure of the vacuum system where the second evaporation is performed is 0.01-0.03 MPa.

9. The method according to claim 1, characterized in that: The mixed solution containing aluminum chloride is a leaching solution of fly ash leached with hydrochloric acid.

10. Use of the method according to any one of claims 1 to 9 in purifying aluminum chloride hexahydrate in a leachate of fly ash leached with hydrochloric acid.

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