Method for preparing polyaluminum chloride through electro-catalytic activation of fly ash

Abstract

The invention provides a method for preparing polyaluminum chloride through electro-catalytic activation of fly ash, and belongs to the technical field of fly ash reutilization, the method comprises the following steps: crushing fly ash, adding an electrolyte containing sodium bicarbonate, taking carbon paper as a cathode and an anode respectively, electrifying to carry out electro-catalytic reaction, after the electro-catalytic reaction is completed, filtering and adjusting the pH value to obtain Al (OH) 3 precipitate, and drying the Al (OH) 3 precipitate to obtain the polyaluminum chloride. And polymerizing the Al (OH) 3 precipitate to obtain polyaluminum chloride. The invention overcomes the problems of high energy consumption and high pollution of the existing alkali activation, and provides a green and efficient method for preparing polyaluminum chloride by electrocatalytically activating fly ash. The fly ash is activated by adopting an electro-catalytic activation method, the reaction temperature is normal temperature, the energy consumption can be remarkably reduced, the energy utilization efficiency is improved, and meanwhile, the dissolution rate of aluminum oxide can reach 95% or above.

Description

Technical Field

[0001] This invention relates to the field of fly ash recycling technology, and in particular to a method for preparing polyaluminum chloride by electrocatalytic activation of fly ash. Background Technology

[0002] Fly ash is a major solid waste discharged from coal-fired power plants, with an annual output exceeding 600 million tons and a cumulative stockpile exceeding 3 billion tons. It not only occupies a large amount of land but also poses serious environmental risks due to dust and heavy metal leaching. The Al2O3 content in fly ash is generally 15-35%, and can reach over 45% in some high-alumina coal types, making it an important non-traditional aluminum resource. Efficiently extracting the aluminum from fly ash and preparing it into a high-value-added flocculant—polyaluminum chloride (PAC)—can alleviate the pressure on bauxite supply and achieve large-scale, high-value utilization of solid waste, aligning with the needs of the dual-carbon strategy and the development of a circular economy.

[0003] Currently, the mainstream industrial route for extracting aluminum from fly ash and preparing PAC is the high-temperature alkali activation-acid dissolution-basicity control process, as detailed below:

[0004] 1) Activation stage: After mixing fly ash with additives such as Na2CO3, CaO or CaCl2·2H2O, it is calcined at 800~1300℃ for 0.5~2h to transform the inert mullite and quartz phase into easily soluble clinker such as nepheline, calcium aluminum feldspar or calcium aluminum garnet.

[0005] 2) Leaching stage: The clinker is leached with hydrochloric acid or sulfuric acid to obtain Al. 3+ An aluminum salt solution with a concentration of approximately 80~120 g / L;

[0006] 3) Polymerization stage: The basicity is adjusted to 60-80% by adding calcium aluminate powder or NaOH, and liquid PAC is obtained after aging.

[0007] Although this technology has achieved a demonstration scale of thousands of tons, it still has the following prominent problems:

[0008] ① High energy consumption: The roasting temperature is ≥800℃, and the comprehensive energy consumption per ton of Al2O3 reaches 2.8~3.5 tons of standard coal, which is seriously inconsistent with the dual carbon target; ② High pollution: High-temperature alkaline combustion releases a large amount of CO2, SO2 and dust. The CO2 emission per ton of Al2O3 is ≥2t, and the amount of alkaline waste residue generated is as high as 0.6~0.8t; ③ Stringent equipment: High-temperature equipment such as rotary kilns and vertical kilns need to be fire-resistant, corrosion-resistant and operate continuously, resulting in high investment and maintenance costs; ④ Limited leaching rate: Due to the limitation of fly ash conversion rate, the leaching rate of Al2O3 is generally only 70~85%, and the aluminum content of tailings is still >10%, resulting in low resource utilization; ⑤ Secondary pollution risk: High basicity waste liquid and alkaline residue are difficult to dispose of, which can easily cause soil salinization and water eutrophication.

[0009] Therefore, it is necessary to develop a new fly ash activation technology that operates at normal temperature and pressure, with low energy consumption, low emissions, and high Al2O3 leaching rate. Summary of the Invention

[0010] To address the above-mentioned problems, this invention relates to a method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0011] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0012] A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash. The method involves crushing fly ash, adding an electrolyte containing sodium bicarbonate, using carbon paper as the cathode and anode, and conducting an electrocatalytic reaction. After the electrocatalytic reaction is completed, the mixture is filtered and the pH value is adjusted to obtain Al(OH)3 precipitate. The Al(OH)3 precipitate is then polymerized to obtain polyaluminum chloride.

[0013] Furthermore, the method includes the following steps:

[0014] Crushing: The fly ash is crushed and sieved to obtain sieved fly ash;

[0015] Preparation of electrolyte: Take NaOH and / or KOH and NaHCO3 and add water to prepare the electrolyte;

[0016] Electrocatalysis: Sievened fly ash is added to the electrolyte. Both the cathode and anode are carbon paper. Electrocatalysis is carried out by applying electricity. After the electricity is stopped, the reaction continues to obtain the electrocatalyzed system.

[0017] Precipitation: After electrocatalysis, the system is filtered, and the pH of the filtrate is adjusted to precipitate Al(OH)3. After drying, Al(OH)3 is obtained.

[0018] Polymerization: Al(OH)3 is dissolved in hydrochloric acid, reacted, and then an initiator is added to polymerize, resulting in solid polyaluminum chloride (PAC).

[0019] Furthermore, the voltage for the electrocatalytic reaction is 0.3~0.8V and the energizing time is 1~3h.

[0020] Furthermore, the weight-to-volume ratio of fly ash to electrolyte is 1:30~100.

[0021] Furthermore, after filtration, the final pH value is adjusted to 9.5~10.5.

[0022] Furthermore, during the electrocatalytic process, the total concentration of NaOH and / or KOH in the electrolyte is 0.5~1.5M, and the concentration of NaHCO3 is 0.5~1.2M.

[0023] Furthermore, during the electrocatalytic process, the reaction continues for 1 to 5 hours after the power is stopped.

[0024] Furthermore, during the polymerization process, the weight-to-volume ratio of Al(OH)3 to hydrochloric acid is 1:10~50;

[0025] The hydrochloric acid concentration is 15~36wt%.

[0026] Furthermore, during the polymerization process, the weight-to-volume ratio of hydrochloric acid to initiator is 10~2:1.

[0027] Furthermore, during the polymerization process, the initiator is calcium aluminate or sodium hydroxide.

[0028] The beneficial effects of the method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to the present invention are as follows:

[0029] The traditional alkaline activation method for extracting aluminum from fly ash to prepare polyaluminum chloride (PAC) requires mixing it with sodium carbonate or calcium oxide in equal proportions and then calcining it at a high temperature of 800-1300℃ (in the literature "Research on Aluminum Extraction Process from Fly Ash by Activation of Calcium Chloride Dihydrate in Pulverized Coal Furnace", calcium chloride and fly ash were calcined at 1100℃ in a 1:1 ratio, achieving an alumina extraction rate of 93%). This invention overcomes the high energy consumption and high pollution problems of existing alkaline activation methods, providing a green and efficient method for preparing PAC by electrocatalytic activation of fly ash. This invention uses electrocatalytic activation to activate fly ash at room temperature, which can significantly reduce energy consumption and improve energy utilization efficiency. Simultaneously, the alumina dissolution rate can reach over 95%. Specifically, it includes:

[0030] ① Significantly reduced energy consumption: The electrocatalytic activation method of this invention can complete the crystalline phase reconstruction of fly ash at room temperature and pressure, completely eliminating the traditional high-temperature roasting process of 800~1300℃. The comprehensive energy consumption per ton of Al2O3 is reduced from 2.8~3.5t of standard coal to ≤0.3t of standard coal, a reduction of >85%, directly reducing CO2 emissions by more than 2t, which is in line with the national dual-carbon strategy;

[0031] ② Significantly improved dissolution rate: Under the electric field of this invention - HCO4 - Under the synergistic effect of active particles, the Si-O and Al-O bonds in fly ash are broken, and the Al2O3 dissolution rate can be stably increased to ≥95% in 1~3h, realizing near-full recovery of aluminum resources from fly ash.

[0032] ③ Significantly reduced equipment investment and operating costs: The high-temperature rotary kiln, refractory materials, and denitrification and desulfurization devices have been eliminated, and the core equipment has been replaced by an electrocatalytic reaction, resulting in a reduction of more than 40% in equipment investment per ton of PAC; operation at room temperature eliminates thermal stress corrosion, extends the maintenance cycle by 3 times, and reduces operating costs by 45%;

[0033] ④ Simple process and high-quality products: The three steps of electrocatalytic activation, acid precipitation and polymerization are completed in one continuous process, shortening the process by 30% and reducing the number of employees by 50%. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Example 1: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0036] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0037] S1. Crushing: Grind fly ash (containing 39.2% SiO2 and 36.9% Al2O3) and pass the resulting powder through a 300-mesh standard sieve to obtain sieved fly ash.

[0038] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1M and 0.8M, respectively.

[0039] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 100mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.5V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0040] During the electrocatalytic reaction, H2O2 is generated at the cathode; the generated H2O2 and HCO3 - The BAP system is formed, thereby generating HCO4 with high oxidizing activity. - The generated HCO4 - Under the influence of electrical energy, active particles attack defects (≡Si•, ≡Al•) on the surface of fly ash to generate ≡Si. + and ≡Al + ,≡Si + and ≡Al + It strongly attracts water molecules or OH-. - This leads to the breaking of Si-O and Al-O bonds, and OH -Ions can penetrate and react more deeply along these opened channels, further damaging the glassy protective layer on the surface of fly ash, and causing soluble SiO2 and Al2O3 inside to dissolve and form Al(OH)4. - SiO3 2- The chemical reaction formulas involved are as follows:

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[0050]

[0051] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 using 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 1.086g of Al(OH)3 was obtained (the alumina dissolution rate was 96.2%). The alumina dissolution rate is calculated as: weight of alumina obtained ÷ (weight of fly ash × alumina content in fly ash).

[0052] S5. Polymerization: Dissolve 1.086g Al(OH)3 in 20mL of 17wt% hydrochloric acid, react at 65℃ for 0.5h, then add 4g of calcium aluminate initiator and polymerize for 3h to obtain 6g of solid polyaluminum chloride (PAC).

[0053] Example 2: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0054] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0055] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 250-mesh standard sieve to obtain the sieved fly ash.

[0056] S2. Prepare electrolyte: Take KOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of KOH and NaHCO3 are 0.5M and 1.2M, respectively.

[0057] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 200mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.3V and the energizing time to 3h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 5h to obtain the electrocatalyzed system.

[0058] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 1.075g of Al(OH)3 was obtained (the dissolution rate of aluminum oxide was 95.2%).

[0059] S5. Polymerization: Dissolve 1.075g Al(OH)3 in 30mL of 30wt% hydrochloric acid, react at 60℃ for 1 h, then add 10g of calcium aluminate initiator and polymerize for 3h to obtain 12g of solid polyaluminum chloride.

[0060] Example 3: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0061] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0062] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0063] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1.2M and 1M respectively.

[0064] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 60mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.8V and the energizing time to 2h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 1h to obtain the electrocatalyzed system.

[0065] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 15wt% hydrochloric acid to precipitate Al(OH)3. After drying, 1.100g of Al(OH)3 was obtained (the dissolution rate of aluminum oxide was 97.4%).

[0066] S5. Polymerization: Dissolve 1.1g Al(OH)3 in 50mL of 15wt% hydrochloric acid, react at 70℃ for 0.3h, then add 8g of calcium aluminate initiator and polymerize for 4h to obtain 10g of solid polyaluminum chloride (PAC).

[0067] Example 4: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0068] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0069] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0070] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1.5M and 0.5M, respectively.

[0071] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 120mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. The voltage is set to 0.6V and the energizing time is 1.5h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 2h to obtain the electrocatalyzed system.

[0072] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 20wt% hydrochloric acid to precipitate Al(OH)3. After drying, 1.090g of Al(OH)3 was obtained (the dissolution rate of aluminum oxide was 96.5%).

[0073] S5. Polymerization: Dissolve 1.090g Al(OH)3 in 10mL of 36wt% hydrochloric acid, react at 65℃ for 0.2h, then add 4g of calcium aluminate initiator and polymerize for 3h to obtain 6g of solid polyaluminum chloride.

[0074] Comparative Example 1: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0075] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0076] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0077] S2. Preparation of electrolyte: Take NaOH and NaHCO3 and add water to prepare an electrolyte, wherein the concentrations of NaOH and NaHCO3 are 0.1M and 0.1M, respectively.

[0078] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 100mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.5V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0079] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 0.510g of Al(OH)3 was obtained (the dissolution rate of alumina was 45.2%).

[0080] S5. Polymerization: Dissolve 0.51g Al(OH)3 in 10mL of 17wt% hydrochloric acid, react at 65℃ for 0.3h, then add 2g of calcium aluminate initiator and polymerize for 3h to obtain 3g of solid polyaluminum chloride.

[0081] Comparative Example 2: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash

[0082] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0083] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0084] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 2M and 2M respectively.

[0085] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 100mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.5V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0086] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 0.920g of Al(OH)3 was obtained (the dissolution rate of alumina was 81.5%).

[0087] S5. Polymerization: Dissolve 0.920g Al(OH)3 in 10mL of 17wt% hydrochloric acid, react at 65℃ for 0.5h, then add 2g of calcium aluminate initiator and polymerize for 3h to obtain 4g of solid polyaluminum chloride.

[0088] Comparative Example 3: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0089] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0090] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0091] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1M and 0.8M, respectively.

[0092] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 100mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.1V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0093] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 0.620g of Al(OH)3 was obtained (the dissolution rate of aluminum oxide was 54.9%).

[0094] S5. Polymerization: Dissolve 0.620g Al(OH)3 in 10mL of 17wt% hydrochloric acid, react at 65℃ for 0.4h, then add 2g of calcium aluminate initiator and polymerize for 4h to obtain 3g of solid polyaluminum chloride.

[0095] Comparative Example 4: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0096] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0097] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0098] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1M and 0.8M, respectively.

[0099] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 100mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 1.5V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0100] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 0.970g of Al(OH)3 was obtained (the dissolution rate of alumina was 85.9%).

[0101] S5. Polymerization: Dissolve 0.970g Al(OH)3 in 10mL of 17wt% hydrochloric acid, react at 65℃ for 0.3h, then add 2g of calcium aluminate initiator and polymerize for 4h to obtain 4g of solid polyaluminum chloride.

[0102] Comparative Example 5: A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash.

[0103] This embodiment describes a method for preparing polyaluminum chloride (PAC) from fly ash through electrocatalytic activation. The PAC is obtained through steps including electrocatalytic activation, filtration, acid leaching, concentration, and polymerization, as detailed below:

[0104] S1. Crushing: Grind the fly ash (containing 39.2% SiO2 and 36.9% Al2O3, the same batch of fly ash as in Example 1) and pass the resulting powder through a 300-mesh standard sieve to obtain the sieved fly ash.

[0105] S2. Prepare electrolyte: Take NaOH and NaHCO3 and add water to prepare electrolyte, wherein the concentrations of NaOH and NaHCO3 are 1M and 0.8M, respectively.

[0106] S3. Electrocatalysis: Weigh 2g of sieved fly ash and add it to 20mL of electrolyte. Stir in an open container. Both the cathode and anode are carbon paper. Set the voltage to 0.5V and the energizing time to 1h to carry out the electrocatalytic reaction. After stopping the energizing, continue stirring for 3h to obtain the electrocatalyzed system.

[0107] S4. Precipitation: After electrocatalysis, the system was filtered. The pH of the filtrate was adjusted to 9.5-10.5 with 17wt% hydrochloric acid to precipitate Al(OH)3. After drying, 0.740g of Al(OH)3 was obtained (the dissolution rate of alumina was 65.5%).

[0108] S5. Polymerization: Dissolve 0.740g Al(OH)3 in 10mL of 17wt% hydrochloric acid, react at 65℃ for 0.4h, then add 2g of calcium aluminate initiator and polymerize for 3h to obtain 3g of solid polyaluminum chloride.

[0109] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for preparing polyaluminum chloride by electrocatalytic activation of fly ash, characterized in that, The method involves crushing fly ash, adding an electrolyte containing sodium bicarbonate, using carbon paper as the cathode and anode, and conducting an electrocatalytic reaction. After the electrocatalytic reaction is completed, the mixture is filtered and the pH value is adjusted to obtain Al(OH)3 precipitate. The Al(OH)3 precipitate is then polymerized to obtain polyaluminum chloride.

2. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 1, characterized in that, The method includes the following steps: Crushing: The fly ash is crushed and sieved to obtain sieved fly ash; Preparation of electrolyte: Take NaOH and / or KOH and NaHCO3 and add water to prepare the electrolyte; Electrocatalysis: Sievened fly ash is added to the electrolyte. Both the cathode and anode are carbon paper. Electrocatalysis is carried out by applying electricity. After the electricity is stopped, the reaction continues to obtain the electrocatalyzed system. Precipitation: After electrocatalysis, the system is filtered, and the pH of the filtrate is adjusted to precipitate Al(OH)3. After drying, Al(OH)3 is obtained. Polymerization: Al(OH)3 is dissolved in hydrochloric acid, reacted, and then an initiator is added to polymerize, yielding solid polyaluminum chloride.

3. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 1 or 2, characterized in that, The voltage for the electrocatalytic reaction is 0.3~0.8V, and the energizing time is 1~3h.

4. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 1 or 2, characterized in that, The weight-to-volume ratio of fly ash to electrolyte is 1:30~100.

5. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 1 or 2, characterized in that, After filtration, adjust the pH value to a final value of 9.5~10.

5.

6. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 2, characterized in that, During the electrocatalysis process, the total concentration of NaOH and / or KOH in the electrolyte is 0.5~1.5M, and the concentration of NaHCO3 is 0.5~1.2M.

7. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 2 or 6, characterized in that, During the electrocatalysis process, the reaction continues for 1 to 5 hours after the power is stopped.

8. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 2 or 6, characterized in that, During the polymerization process, the weight-to-volume ratio of Al(OH)3 to hydrochloric acid is 1:10~50; The hydrochloric acid concentration is 15~36wt%.

9. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 2 or 6, characterized in that, The weight-to-volume ratio of hydrochloric acid to initiator is 10~2:

1.

10. The method for preparing polyaluminum chloride by electrocatalytic activation of fly ash according to claim 2 or 6, characterized in that, The initiator is calcium aluminate or sodium hydroxide.

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