Method for removing iron impurities in coal ash leachate

Abstract

The invention provides a method for removing iron impurities in coal ash lixivium. The removal method comprises the following steps: pretreating the coal ash leachate, adding iron powder, and carrying out reduction reaction to obtain aluminum chloride clear liquid; sequentially performing a first electrolytic reaction, a second electrolytic reaction and a third electrolytic reaction on the aluminum chloride clear liquid to obtain an aluminum chloride refined liquid; wherein the cathode current density in the first electrolytic reaction, the cathode current density in the second electrolytic reaction and the cathode current density in the third electrolytic reaction are p1, p2 and p3 respectively, and the size relation of the cathode current density in each electrolytic reaction is selected from any one of the following relations: p1 > p2 > p3, p1 = p2 > p3 or p1 > p2 = p3. By adjusting the multi-stage current density in the electrolysis process, the removal efficiency of iron impurities is effectively improved, the energy consumption is reduced, meanwhile, a large amount of waste generated in a traditional chemical precipitation method is avoided, the method is environmentally friendly, removal of the iron element can be accurately controlled, and the aluminum chloride refined solution with high purity is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to a method for removing iron impurities in fly ash leaching solution. Background Art

[0002] 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, and most of the aluminum enters the leaching solution to form aluminum chloride solution. Silicon cannot be leached by hydrochloric acid, and after solid-liquid separation, it enters the "white mud" filter residue.

[0003] During the hydrochloric acid treatment of fly ash, some other inclusions in the fly ash, such as iron, lithium, gallium, magnesium, potassium, calcium, sodium, etc., will also enter the leaching solution along with aluminum, forming a "rough aluminum chloride concentrate" with aluminum chloride as the main component. This crude concentrate needs to be further impurity-removed and purified to obtain a crystalline aluminum chloride product. As a bulk industrial chemical, crystalline aluminum chloride can be used for a variety of purposes. The higher the purity of the aluminum product obtained in the aluminum extraction process, the higher the economic value.

[0004] The iron in fly ash mainly exists in the form of hematite and magnetite. For iron oxide before acid leaching, the iron removal method of solid minerals such as bauxite and kaolin can be used, such as magnetic separation. However, magnetic separation cannot remove all iron impurities. No matter what form of iron is present, it will react with hydrochloric acid during the fly ash acid leaching process and enter the leaching solution as Fe 2+ and Fe 3+ If the iron is not purified, the iron impurities will be 3+ Entering the next step of crystallization affects the purity of aluminum salt. For iron ions after acid leaching, the main removal methods are precipitation and extraction.

[0005] Among them, the precipitation method is to add a precipitant to precipitate aluminum ions or iron ions. There are mainly goethite method and jarosite method. Goethite method can be used for iron removal at normal pressure and low temperature, with simple process equipment and low iron removal cost; however, the process requires strict control of the solution pH (generally around 3.5-4.0) and Fe 3+ concentration to avoid the formation of colloidal Fe(OH)3 which is difficult to filter, and the pH control process will also lead to the Al 3+ with Fe 3+ Co-precipitation occurs. The jarosite method can precipitate iron into jarosite vanadium crystals that are easy to clarify and filter, but the resulting precipitate has a low iron content and a low iron removal efficiency. In addition, the jarosite method requires the introduction of SO4 into the leaching mother liquor. 2- , so it is not suitable for the fly ash acid treatment process developed based on the hydrochloric acid method.

[0006] In addition, the extraction method of iron removal often uses ion exchange resin, which has good iron removal effect (up to ppm level), wide application range, and iron removal resin also has good adsorption effect on heavy metal impurities in the leachate, such as lead, mercury, arsenic, chromium, cadmium, copper, zinc, etc. However, due to the high price and slow adsorption rate of iron removal resin, when meeting high production efficiency, the valve system and adsorption system are huge, the resin eluent uses a large amount of water, and the amount of Fe(OH)3 wet cake produced is large and difficult to handle.

[0007] Therefore, how to provide a method with high iron removal efficiency and simple operation is of great significance for the purification and reuse of aluminum chloride. Summary of the invention

[0008] The main purpose of the present invention is to provide a method for removing iron impurities in fly ash leachate, so as to solve the problem of low purity of fly ash leachate after electrolytic removal of impurities in the prior art.

[0009] In order to achieve the above-mentioned purpose, according to a first aspect of the present invention, a method for removing iron impurities in fly ash leachate is provided, and the removal method comprises: pretreating the fly ash leachate, adding iron powder, and performing a reduction reaction to obtain a clear aluminum chloride solution; sequentially performing a first electrolysis reaction, a second electrolysis reaction, and a third electrolysis reaction on the clear aluminum chloride solution to obtain a refined aluminum chloride solution; wherein the cathode current density in the first electrolysis reaction, the second electrolysis reaction, and the third electrolysis reaction are p1, p2, and p3, respectively, and the cathode current density in each electrolysis reaction is selected from any one of the following: p1>p2>p3, p1=p2>p3, or p1>p2=p3.

[0010] Furthermore, the concentration of aluminum chloride in the pretreated fly ash leachate is 50-200 g / L, and the concentration of iron is ≤20 g / L; preferably, the pH value of the pretreated fly ash leachate is 0-2; preferably, the temperature of the pretreated fly ash leachate is 10-70°C.

[0011] Furthermore, the theoretical addition amount of iron powder is calculated using formula I, and the actual addition amount of iron powder is 105-110% of the theoretical addition amount; m = [C1(Fe 3+ )×V1×M(Fe)] / 2Formula Ⅰ; where C1(Fe 3+ ) is the Fe content in the fly ash leachate after pretreatment 3+ concentration, V1 is the volume of the fly ash leachate after pretreatment, and M(Fe) is the relative atomic mass of iron.

[0012] Furthermore, the concentration of iron in the aluminum chloride solution for the first electrolysis reaction is 5-20 g / L; preferably, the cathode current density in the first electrolysis reaction is 0.12-0.15 A / cm 2 .

[0013] Furthermore, the concentration of iron in the aluminum chloride solution for the second electrolysis reaction is 1-5 g / L; preferably, the cathode current density in the second electrolysis reaction is 0.08-0.12 A / cm 2 .

[0014] Furthermore, the concentration of iron in the aluminum chloride solution for the third electrolysis reaction is 0.1-1 g / L; preferably, the cathode current density in the third electrolysis reaction is 0.05-0.08 A / cm 2 .

[0015] Furthermore, the clear aluminum chloride solution sequentially undergoes a first electrolysis reaction, a second electrolysis reaction and a third electrolysis reaction in the diaphragm electrolytic cell; wherein, according to the flow direction of the clear aluminum chloride solution, the diaphragm electrolytic cell comprises a first electrolytic cell unit, a second electrolytic cell unit and a third electrolytic cell unit sequentially connected in series, and the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit are separated by an anion diaphragm respectively; wherein the first electrolysis reaction is carried out in the first electrolytic cell unit, the second electrolysis reaction is carried out in the second electrolytic cell unit, and the third electrolysis reaction is carried out in the third electrolytic cell unit.

[0016] Further, the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit each independently include a plurality of anode chambers and cathode chambers alternately arranged in series, and the anode chamber and the cathode chamber are separated by an anion diaphragm, the plurality of anode chambers are connected by a first pipe, and the plurality of cathode chambers are connected by a second pipe; preferably, each electrolytic cell unit includes 3 anode chambers and 2 cathode chambers, and the anode chambers and the cathode chambers are alternately connected in series in sequence according to the flow direction of the aluminum chloride clear solution; preferably, the aluminum chloride clear solution is passed into the first cathode chamber of the first electrolytic cell unit away from the second electrolytic cell unit, the anions in the aluminum chloride clear solution diffuse into the anode chamber through the anion diaphragm, and the cation solution in the aluminum chloride clear solution passes through the cathode chambers of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit in sequence through the second pipe to perform a reduction reaction; the anion solution in the aluminum chloride clear solution passes through the anode chambers of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit in sequence through the first pipe to perform an oxidation reaction.

[0017] Furthermore, the pH value of the reduction reaction is 0-7.

[0018] Furthermore, the anode cavity contains an anode, and the cathode cavity contains a cathode; preferably, the material of the cathode includes: non-metal or an alloy with a metal layer plated on the surface; preferably, the metal of the metal layer includes: iron, titanium, copper or lead.

[0019] The technical solution of the present invention is applied to effectively improve the removal efficiency of iron impurities and reduce energy consumption by adjusting the multi-stage current density during the electrolysis process, while avoiding the large amount of waste generated in the traditional chemical precipitation method, being environmentally friendly, and being able to more accurately control the removal of iron elements. The resulting aluminum chloride refined liquid has high purity and is suitable for a variety of industrial applications, such as water treatment, papermaking, textile and other industries, with significant economic and environmental benefits. In addition, the method is simple to operate, easy to realize industrial production, and provides a new way for fly ash resource utilization. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings constituting a part of the present application 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 drawings:

[0021] Figure 1 A schematic diagram of the process of electrolytically removing iron impurities in fly ash leachate in Example 1 of the present application is shown;

[0022] Figure 2 A schematic diagram of an apparatus for performing electrolysis in the present application is shown;

[0023] Figure 3 The schematic diagram of the structure of the cathode chamber and the anode chamber constituting the diaphragm electrolyzer unit of the present application is shown;

[0024] Figure 4 The XRD phase analysis spectrum of iron precipitated on the cathode plate after electrolysis in Example 1 of the present application is shown;

[0025] Figure 5 The SEM microscopic morphology image of iron precipitated on the cathode plate after electrolysis in Example 1 of the present application is shown;

[0026] Among them, the above Figure 3 The following reference numerals are included:

[0027] 1. Anode gas outlet; 2. Anode liquid outlet; 3. Anode liquid inlet; 4. Anode chamber; 5. Anion diaphragm; 6. Cathode plate; 7. Cathode chamber; 8. Anode plate; 9. Cathode liquid inlet; 10. Cathode gas outlet; 11. Cathode liquid outlet. DETAILED DESCRIPTION

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

[0029] In a first typical embodiment of the present application, a method for removing iron impurities in a fly ash leachate is provided, the removal method comprising: pretreating the fly ash leachate, adding iron powder, and performing a reduction reaction to obtain a clear aluminum chloride solution; sequentially performing a first electrolysis reaction, a second electrolysis reaction, and a third electrolysis reaction on the clear aluminum chloride solution to obtain a refined aluminum chloride solution; wherein the cathode current densities in the first electrolysis reaction, the second electrolysis reaction, and the third electrolysis reaction are p1, p2, and p3, respectively, and the relationship between the cathode current densities in each electrolysis reaction is selected from any one of the following: p1>p2>p3, p1=p2>p3, or p1>p2=p3.

[0030] The main component of fly ash leaching solution is aluminum chloride solution. In the aluminum chloride solution electrolytic iron removal method, Fe 2+ / Fe 3+ Reduction and H + The products of the two reduction reactions are Fe and H2. The two reduction reactions are competitive reactions. The former reaction can convert Fe 2+ / Fe 3+ The latter reaction is a side reaction, which actually decomposes HCl in the solution, causing the composition of the aluminum chloride solution to fluctuate.

[0031] Fe in solution 2+ / Fe 3+ The concentration of H+ has a great influence on the precipitation of iron impurities in the solution. 2+ / Fe 3+ The concentration decrease will lead to Fe 2+ / Fe 3+ The deposition overpotential on the cathode plate increases sharply, which causes most of the cathode current to be used to precipitate H2 instead of elemental Fe. Therefore, in order to improve the Fe deposition efficiency, it is very important to adjust the cathode current in the electrolytic cell.

[0032] Therefore, after the removal method of the present application performs preliminary iron reduction on the fly ash leachate, the iron impurities in the aluminum chloride clear solution are more effectively removed by using cathode current densities of different sizes in different electrolytic reactions, which can improve the recovery rate of aluminum chloride and reduce resource waste. It is suitable for the preliminary treatment stage of fly ash resource utilization, laying the foundation for the subsequent refining and application of aluminum chloride. In addition, the current efficiency of the present application has also been improved. The current efficiency is the ratio of the electric energy consumed by the iron precipitation in the present application to the total electric energy in the electrolytic reaction of the present application. The current efficiency of iron removal in general aluminum chloride is about 10%.

[0033] In order to further reduce the ferric chloride in the fly ash leachate to ferrous iron with higher efficiency, in a preferred embodiment, the concentration of aluminum chloride in the pretreated fly ash leachate is 50-200 g / L, and the concentration of iron element is ≤20 g / L; preferably, the pH value of the pretreated fly ash leachate is 0-2; preferably, the temperature of the pretreated fly ash leachate is 10-70° C. By optimizing the pretreatment conditions, the subsequent reduction of ferric chloride can be promoted while stabilizing the properties of aluminum chloride, reducing the occurrence of side reactions, being suitable for large-scale industrial production, and significantly improving production efficiency and product quality.

[0034] In order to further completely remove the iron impurities in the aluminum chloride solution and avoid the waste of resources caused by excessive iron powder, in a preferred embodiment, the theoretical addition amount of iron powder is calculated using formula I, and the actual addition amount of iron powder is 105-110% of the theoretical addition amount; m = [C1(Fe 3+ )×V1×M(Fe)] / 2Formula Ⅰ; where C1(Fe 3+ ) is the Fe content in the fly ash leachate after pretreatment 3+ concentration, V1 is the volume of the pretreated fly ash leachate, and M(Fe) is the relative atomic mass of iron. By controlling the amount of iron powder added, the iron ions in the ferric chloride can be reduced more completely, and the unreacted iron powder can be removed from the solution by filtering or magnetic attraction.

[0035] The cathode current density in different electrolysis reactions is adjusted according to the difference in the iron concentration in different electrolysis reactions. In a preferred embodiment, the iron concentration in the aluminum chloride clear solution for the first electrolysis reaction is 5-20 g / L; preferably, the cathode current density in the first electrolysis reaction is 0.10-0.15 A / cm 2 In a preferred embodiment, the concentration of iron in the aluminum chloride solution for the second electrolysis reaction is 1-5 g / L; preferably, the cathode current density in the second electrolysis reaction is 0.08-0.12 A / cm 2 In a preferred embodiment, the concentration of iron in the aluminum chloride solution for the third electrolysis reaction is 0.1-1 g / L; preferably, the cathode current density in the third electrolysis reaction is 0.05-0.08 A / cm 2 The above cathode current density setting can effectively remove low-concentration iron impurities while maintaining high purity of aluminum chloride clear solution, which is suitable for removing iron from aluminum chloride in industrial production and can significantly improve the purity and market competitiveness of the product.

[0036] In order to be able to appropriately adjust various parameters in different electrolysis reactions, the above-mentioned electrolysis reactions are carried out in a diaphragm electrolytic cell. In a preferred embodiment, the aluminum chloride clear solution is sequentially subjected to a first electrolysis reaction, a second electrolysis reaction and a third electrolysis reaction in the diaphragm electrolytic cell; wherein, according to the flow direction of the aluminum chloride clear solution, the diaphragm electrolytic cell comprises a first electrolysis cell unit, a second electrolysis cell unit and a third electrolysis cell unit sequentially connected in series, and the first electrolysis cell unit, the second electrolysis cell unit and the third electrolysis cell unit are respectively separated by an anion diaphragm; wherein the first electrolysis reaction is carried out in the first electrolysis cell unit, the second electrolysis reaction is carried out in the second electrolysis cell unit, and the third electrolysis reaction is carried out in the third electrolysis cell unit.

[0037] In order to further improve the removal efficiency of iron impurities, while maintaining the fluidity and stability of aluminum chloride, and making full use of the electrochemical reaction in the electrolysis process, in a preferred embodiment, the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit each independently include a plurality of anode chambers and cathode chambers alternately connected in series, and the anode chamber and the cathode chamber are separated by an anion diaphragm, the plurality of anode chambers are connected by a first pipe, and the plurality of cathode chambers are connected by a second pipe; preferably, each electrolytic cell unit includes 3 anode chambers and 2 cathode chambers, and the anode chambers and the cathode chambers are alternately connected in series in sequence according to the flow direction of the aluminum chloride clear solution.

[0038] In order to further improve the electrolytic reaction efficiency of electrolytic iron removal, in a preferred embodiment, aluminum chloride clear solution is passed into the first cathode cavity away from the second electrolytic cell unit in the first electrolytic cell unit, and the anions in the aluminum chloride clear solution diffuse into the anode cavity through the anion diaphragm, and the cationic solution in the aluminum chloride clear solution passes through the cathode cavities of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit in sequence through the second pipeline to perform a reduction reaction; the anionic solution in the aluminum chloride clear solution passes through the anode cavities of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit in sequence through the first pipeline to perform an oxidation reaction.

[0039] In order to further improve the removal efficiency of iron impurities and reduce energy consumption, in a preferred embodiment, the pH value of the reduction reaction is 0-7. By controlling the pH value and flow rate, the electrolytic iron removal process can be optimized, which is suitable for process control in industrial production and can significantly improve production efficiency and economic benefits.

[0040] Any conductive metal or non-metal material that does not easily react with hydrochloric acid or chlorine is suitable for this application. In a preferred embodiment, the anode cavity contains an anode, and the cathode cavity contains a cathode; preferably, the cathode material includes: non-metal or alloy with a metal layer on the surface; preferably, the metal of the metal layer includes: iron, titanium, copper or lead. Selecting suitable anode / cathode materials can improve electrolysis efficiency and reduce equipment corrosion and maintenance costs. The selection of materials suitable for electrolysis equipment can significantly improve the service life and economic benefits of the equipment.

[0041] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0042] The fly ash leaching solution used for iron removal in the present application is usually the filtrate obtained by leaching fly ash with hydrochloric acid in industrial production and filtering and separating silicon mud.

[0043] Example 1 (operation process as shown in Figure 1 (shown)

[0044] 1. Pretreating the fly ash leachate, including adjusting the concentration, pH value and temperature of the fly ash leachate, to obtain the pretreated fly ash leachate: the concentration of aluminum chloride is Ag / L, the concentration of iron is B g / L, the pH value is C, and the temperature is E°C.

[0045] 2. Add iron powder F g to the pretreated fly ash leachate and stir it thoroughly. After the reaction is complete, remove the unreacted iron powder from the solution by filtering or magnetic attraction to obtain a clear aluminum chloride solution.

[0046] 3. Pass the aluminum chloride solution into Figure 2 In the diaphragm electrolyzer shown in FIG. 1 , the specific cathode chamber and anode chamber structures are as follows: Figure 3 The clear aluminum chloride solution is introduced into the cathode liquid inlet 9 of the first cathode chamber 7 of the first electrolytic cell unit away from the second electrolytic cell to perform the first electrolysis reaction, wherein a reduction reaction occurs in the cathode chamber 7, iron filings are precipitated on the cathode plate 6, and hydrogen is discharged from the cathode gas outlet 10. The anions Cl in the clear aluminum chloride solution are - The chlorine enters the anode chamber 4 through the anion diaphragm 5 (the commercial diaphragm model is JRAM-G, produced by Beijing Jie Rui Environmental Protection Technology Co., Ltd.), an oxidation reaction occurs in the anode chamber 4, and the chlorine is discharged from the anode gas outlet 1. Then, the cationic solution and the anionic solution in the anode chamber 4 and the cathode chamber 7 respectively pass through the anode liquid outlet 2 and the cathode liquid outlet 11 through the first pipeline and the second pipeline from the anode liquid inlet 3 and the cathode liquid inlet 9 to enter the next anode chamber 4 and the cathode chamber 7 to continue the subsequent second electrolysis reaction and the third electrolysis reaction for iron removal.

[0047] The anode plate 8 is made of K and has a geometric size of 5 cm × 5 cm; the cathode plate 6 is made of L and has a geometric size of 5 cm × 5 cm; the first electrolytic cell unit has a total of 5 chambers from the aluminum chloride clear solution, including 3 anode chambers and 2 cathode chambers. The cathode has a total of 4 working surfaces, and the actual cathode working area is 5 cm × 5 cm × 4 = 100 cm 2 .

[0048] The aluminum chloride clear liquid flows through the first, second and third electrolytic cell units in sequence at a flow rate of GL / h and is discharged into the product tank.

[0049] The cathode current density in the first electrolytic cell unit is I1 A / cm 2 , the cathode current density in the second electrolytic cell unit is I2A / cm 2 , the cathode current density in the third electrolytic cell unit is I3 A / cm 2 .

[0050] The total iron precipitation current efficiency of the diaphragm electrolytic cell is J%.

[0051] 4. After the electrolysis is completed, the solution is discharged from the cathode chamber of the diaphragm electrolytic cell to obtain the refined aluminum chloride solution after iron removal.

[0052] The specific values ​​of the parameters represented by the above letters are shown in Table 1 below.

[0053] Table 1:

[0054] A 200 <![CDATA[I1]]> 0.15 B 5 <![CDATA[I2]]> 0.12 C 2 <![CDATA[I3]]> 0.08 E 60 J 20 F 5.5 K graphite G 3.0 L titanium

[0055] The iron content in the final aluminum chloride refined liquid is reduced to 250ppm. The byproduct iron purity obtained is >99%, the hydrogen purity is >99%, and the chlorine purity is >95% (with a little oxygen). Figure 4 and Figure 5 They are the XRD phase analysis spectrum and SEM microscopic morphology image of iron precipitated on the cathode plate after the electrolysis.

[0056] from Figure 4 It can be seen that the product on the cathode surface is alpha-phase elemental iron with good crystallinity. No other impurity phases are found, which proves that the purity of the byproduct iron is high. Figure 5 It shows that the cathode product iron is granular and evenly distributed on the cathode surface, and the surface of the electroplating layer is flat and uniform, indicating that the electrode behavior is stable during the electrolytic iron removal process and that the electrolysis method has the potential for further industrial expansion.

[0057] Embodiment 2

[0058] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 2 below.

[0059] Table 2:

[0060] A 180 <![CDATA[I1]]> 0.15 B 10 <![CDATA[I2]]> 0.12 C 2 <![CDATA[I3]]> 0.08 E 50 J 23 F 11 K graphite G 2.5 L lead

[0061] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 290ppm. The byproduct iron purity obtained is >99%, the hydrogen purity is >99%, and the chlorine purity is >95% (with a little oxygen).

[0062] Embodiment 3

[0063] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 3 below.

[0064] Table 3:

[0065] A 150 <![CDATA[I1]]> 0.15 B 15 <![CDATA[I2]]> 0.12 C 2 <![CDATA[I3]]> 0.08 E 40 J 27 F 16.5 K graphite G 2.0 L iron

[0066] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 180ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0067] Embodiment 4

[0068] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 4 below.

[0069] Table 4:

[0070]

[0071]

[0072] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 200ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0073] Embodiment 5

[0074] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 5 below.

[0075] Table 5:

[0076] A 50 <![CDATA[I1]]> 0.13 B 5 <![CDATA[I2]]> 0.10 C 2 <![CDATA[I3]]> 0.06 E 70 J 22 F 5.5 K graphite G 2.5 L titanium

[0077] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 240ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0078] Embodiment 6

[0079] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 6 below.

[0080] Table 6:

[0081] A 200 <![CDATA[I1]]> 0.12 B 5 <![CDATA[I2]]> 0.08 C 1 <![CDATA[I3]]> 0.05 E 50 J 26 F 5.5 K graphite G 1.5 L silver

[0082] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 270ppm. The purity of the by-product iron is>99%, the purity of hydrogen is>99%, and the purity of chlorine is>95% (with a little oxygen).

[0083] Embodiment 7

[0084] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 7 below.

[0085] Table 7:

[0086] A 180 <![CDATA[I1]]> 0.12 B 3 <![CDATA[I2]]> 0.08 C 0.5 <![CDATA[I3]]> 0.05 E 20 J 17 F 3.3 K graphite G 2.5 L gold

[0087] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 290ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0088] Embodiment 8

[0089] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 8 below.

[0090] Table 8:

[0091] A 150 <![CDATA[I1]]> 0.10 B 2 <![CDATA[I2]]> 0.07 C 0 <![CDATA[I3]]> 0.05 E 10 J 15 F 2.2 K graphite G 2.5 L platinum

[0092] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 300ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0093] Embodiment 9

[0094] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 9 below.

[0095] Table 9:

[0096]

[0097]

[0098] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 140ppm. The purity of the byproduct iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0099] Embodiment 10

[0100] The specific steps in this embodiment are the same as those in the first embodiment, and the parameters represented by the letters are different. The specific values ​​are shown in Table 10 below.

[0101] Table 10:

[0102] A 180 <![CDATA[I1]]> 0.12 B 3 <![CDATA[I2]]> 0.12 C 2.5 <![CDATA[I3]]> 0.08 E 60 J 15 F 3.3 K iron G 3.5 L titanium

[0103] The iron content in the aluminum chloride refined liquid in the product tank is reduced to 150ppm. The purity of the by-product iron is >99%, the purity of hydrogen is >99%, and the purity of chlorine is >95% (with a little oxygen).

[0104] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: by flexibly adjusting the cathode current density in different electrolytic units, the iron element in the fly ash leachate can be effectively removed, the purity of the aluminum chloride refined liquid can be improved, and a new way for fly ash resource utilization is provided. In addition, the method is simple to operate, easy to realize industrial production, has significant economic and environmental benefits, and is suitable for application in a variety of industrial fields such as water treatment, papermaking, textile and other industries.

[0105] 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 removing iron impurities in fly ash leachate, characterized in that: The removal method comprises: Pre-treating the fly ash leaching solution, adding iron powder, and performing a reduction reaction to obtain a clear aluminum chloride solution; The aluminum chloride clear solution is subjected to a first electrolysis reaction, a second electrolysis reaction and a third electrolysis reaction in sequence to obtain the aluminum chloride refined solution; Wherein, the cathode current densities in the first electrolysis reaction, the second electrolysis reaction and the third electrolysis reaction are p1, p2 and p3 respectively, and the magnitude relationship of the cathode current density in each electrolysis reaction is selected from any one of the following: p1>p2>p3, p1=p2>p3 or p1>p2=p3.

2. The removal method according to claim 1, characterized in that: The concentration of aluminum chloride in the fly ash leaching solution after the pretreatment is 50-200 g / L, and the concentration of iron is ≤20 g / L; Preferably, the pH value of the fly ash leachate after the pretreatment is 0-2; Preferably, the temperature of the fly ash leachate after the pretreatment is 10-70°C.

3. The removal method according to claim 1, characterized in that: The theoretical addition amount of the iron powder is calculated using formula I, and the actual addition amount of the iron powder is 105-110% of the theoretical addition amount; m = [C1(Fe 3+ ) × V1 × M(Fe)] / 2 Equation Ⅰ; Wherein, the Cl(Fe 3+ ) is the Fe in the fly ash leachate after the pretreatment 3+ concentration, V1 is the volume of the fly ash leachate after the pretreatment, and M(Fe) is the relative atomic mass of iron.

4. The removal method according to claim 1, characterized in that: The concentration of iron in the aluminum chloride clear solution for the first electrolysis reaction is 5-20 g / L; Preferably, the cathode current density in the first electrolysis reaction is 0.12-0.15 A / cm 2 .

5. The removal method according to claim 4, characterized in that: The concentration of iron in the aluminum chloride clear solution for the second electrolysis reaction is 1-5 g / L; Preferably, the cathode current density in the second electrolysis reaction is 0.08-0.12 A / cm 2 .

6. The removal method according to claim 5, characterized in that: The concentration of iron in the aluminum chloride clear solution for the third electrolysis reaction is 0.1-1 g / L; Preferably, the cathode current density in the third electrolysis reaction is 0.05-0.08 A / cm 2 .

7. The removal method according to claim 1, characterized in that: The aluminum chloride clear solution sequentially performs the first electrolysis reaction, the second electrolysis reaction and the third electrolysis reaction in a diaphragm electrolytic cell; Wherein, according to the flow direction of the aluminum chloride clear solution, the diaphragm electrolytic cell comprises a first electrolytic cell unit, a second electrolytic cell unit and a third electrolytic cell unit connected in series in sequence, and the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit are respectively separated by an anion diaphragm; The first electrolysis reaction is carried out in the first electrolytic cell unit, the second electrolysis reaction is carried out in the second electrolytic cell unit, and the third electrolysis reaction is carried out in the third electrolytic cell unit.

8. The removal method according to claim 7, characterized in that: The first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit each independently include a plurality of anode chambers and cathode chambers alternately arranged in series, and the anode chamber and the cathode chamber are separated by an anion diaphragm, the plurality of anode chambers are connected by a first pipe, and the plurality of cathode chambers are connected by a second pipe; Preferably, each of the electrolytic cell units comprises three anode chambers and two cathode chambers, and the anode chambers and the cathode chambers are alternately connected in series in sequence according to the flow direction of the aluminum chloride clear solution; Preferably, the aluminum chloride clear solution is introduced into the first cathode chamber of the first electrolytic cell unit away from the second electrolytic cell unit, and anions in the aluminum chloride clear solution diffuse into the anode chamber through the anion diaphragm. The cationic solution in the aluminum chloride clear solution passes through the cathode chambers of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit in sequence through the second pipeline to perform a reduction reaction; The anion solution in the aluminum chloride clear solution passes through the first pipeline in sequence through the anode chambers of the first electrolytic cell unit, the second electrolytic cell unit and the third electrolytic cell unit to undergo an oxidation reaction.

9. The removal method according to claim 8, characterized in that: The pH value of the reduction reaction is 0-7.

10. The removal method according to claim 8, characterized in that: The anode cavity contains an anode, and the cathode cavity contains a cathode; Preferably, the cathode material includes: non-metal or alloy with a metal layer plated on the surface; Preferably, the metal of the metal layer includes iron, titanium, copper or lead.

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