A method for targeted heavy metal removal in fly ash water washing process
By combining graded water washing with targeted chelating agents, the problems of low heavy metal removal efficiency and secondary pollution in traditional water washing methods are solved, achieving efficient and stable removal of heavy metals from fly ash and meeting environmental protection standards.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANTONG LEER ENVIRONMENTAL TECH CO LTD
- Filing Date
- 2026-02-26
- Publication Date
- 2026-05-29
AI Technical Summary
Traditional water washing methods have low efficiency in removing different forms of heavy metals from fly ash, are prone to causing secondary pollution, and have unstable heavy metal leaching concentrations after treatment, making it difficult to meet environmental protection standards.
The method employs a staged water washing process. First, soluble chloride salts and some acid-soluble heavy metals are dissolved with sodium dihydrogen phosphate. Then, ferrous sulfate is added in a carbon dioxide environment to reduce hexavalent chromium. Next, heavy metal chelating agents and MOF materials are used for targeted chelation and adsorption. Finally, metal sulfides are loaded using a hydrothermal method for highly selective adsorption.
It achieves efficient and targeted removal of heavy metals from fly ash, ensuring stable heavy metal leaching concentrations after treatment, meeting environmental standards, and reducing the risk of secondary pollution.
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Figure SMS_1
Abstract
Description
Technical Field
[0001] This invention relates to the field of wastewater treatment technology, specifically a method for targeted removal of heavy metals during fly ash washing. Background Technology
[0002] Fly ash is a hazardous waste generated during waste incineration or coal combustion. It contains large amounts of leached heavy metals such as Pb, Cd, Cr, Zn, Cu, Ni, and As, and must be properly treated before landfilling or resource utilization. Water washing is a commonly used technology for pre-treatment of fly ash, but traditional water washing methods have the following bottlenecks:
[0003] 1) Low removal efficiency and lack of specificity: Traditional water washing mainly removes soluble chloride salts, and has limited effect on removing heavy metals that exist in different forms (such as oxides, complexes, and residues). In addition, it usually adopts a "one-size-fits-all" acid washing or complexing agent rinsing, which lacks specificity.
[0004] 2) It is easy to cause secondary pollution: Blindly using strong acids or general complexing agents may lead to an increase in the leaching concentration of certain heavy metals (such as acid washing may cause large amounts of Pb and Cd to dissolve), or introduce new chemical pollution, and the heavy metals in the washing wastewater are difficult to treat.
[0005] 3) Stability cannot be guaranteed: The heavy metal leaching concentration of the treated fly ash may still be unstable, posing a long-term environmental risk and making it difficult to consistently meet increasingly stringent environmental standards.
[0006] Therefore, there is an urgent need to find a method for targeted removal of heavy metals during fly ash washing to achieve efficient deep purification. Summary of the Invention
[0007] The purpose of this invention is to provide a method for targeted removal of heavy metals during fly ash washing, in order to solve the problems raised in the prior art.
[0008] To achieve the above objectives, the present invention provides the following technical solution:
[0009] A method for targeted removal of heavy metals during fly ash washing specifically includes the following process steps:
[0010] Step 1: Place the fly ash sample in deionized water, add sodium dihydrogen phosphate for primary water washing treatment, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0011] Step 2: Place the primary water-washed fly ash in deionized water, add the primary water-washed filtrate, treat with CO2 atmosphere, then treat with ferrous sulfate. After the treatment, add a heavy metal chelating agent and adjust the pH of the system. Perform secondary water washing treatment, filter to obtain secondary water-washed fly ash residue and secondary water-washed filtrate. After separating the heavy metal chelating agent from the secondary fly ash residue, dry to obtain secondary water-washed fly ash.
[0012] Step 3: Place the secondary washed fly ash in deionized water, add heavy metal adsorbent for tertiary washing treatment, filter to obtain tertiary washed fly ash residue and tertiary washed filtrate, separate the heavy metal adsorbent from the tertiary washed fly ash residue, and dry to obtain tertiary washed fly ash.
[0013] Preferably, in step 1, the ratio of fly ash sample, deionized water, and sodium dihydrogen phosphate is 10g:(100-120)mL:(0.3-0.5)g;
[0014] Preferably, the process parameters for the primary water washing treatment are: rotation speed of 150-300 r / min and water washing time of 30-50 min;
[0015] Preferably, in step 2, the flow rate of the CO2 atmosphere is 1-2 mL / min, and the concentration is 8-15%.
[0016] More preferably, ferrous sulfate is added 8-10 minutes after the CO2 atmosphere is introduced;
[0017] More preferably, the heavy metal chelating agent is added after stirring ferrous sulfate for 20-30 minutes;
[0018] More preferably, the pH of the system is adjusted to 4-6 after the addition of the heavy metal chelating agent;
[0019] Preferably, the process parameters for the secondary water washing treatment are: rotation speed of 200-300 r / min and water washing time of 1-2 h;
[0020] More preferably, in step 2, the mass of ferrous sulfate is 1-3 wt% of the primary water-washed fly ash; the mass of the heavy metal chelating agent is 5-8 wt% of the primary water-washed fly ash; the preparation steps of the heavy metal chelating agent are as follows:
[0021] s1.1: Zirconium chloride and 2-aminoterephthalic acid were mixed, N,N-dimethylformamide and glacial acetic acid were added, and the mixture was ultrasonically stirred and then transferred to an oven. After reacting at 120-125℃ for 10-12 h, the mixture was centrifuged, washed and dried to obtain an aminated MOF. The aminated MOF was dispersed in N,N-dimethylformamide, methacrylic anhydride was added and stirred for 2-3 days, and then filtered and dried to obtain a double bond modified MOF.
[0022] s1.2: Triacryloylhexahydrotriazine and piperazine were placed in N,N-dimethylformamide and stirred for 4-6 h. The mixture was then heated to 40-50 °C and stirred for 20-24 h. After sedimentation, the mixture was separated, freeze-dried, and then mixed with double bond modified MOF, azobisisobutyronitrile and N,N-dimethylformamide. The mixture was heated to 70-80 °C and stirred for 8-10 h. After centrifugation, piperazine-modified MOF material was obtained.
[0023] s1.3: Sodium carboxymethyl cellulose was placed in deionized water and stirred for 10-20 min. Then piperazine-modified MOF material dispersion was added, stirred for 1-2 h, and then freeze-dried to obtain heavy metal chelating agent;
[0024] Preferably, the mass ratio of zirconium chloride to 2-aminoterephthalic acid in s1.1 is 1:(0.6-0.8); and the mass ratio of aminated MOF to methacrylic anhydride is 1:(8-12).
[0025] Preferably, the mass ratio of double-bond modified MOF, triacryloylhexahydrotriazine, piperazine, and azobisisobutyronitrile in s1.2 is 1:(1.5-3):(0.5-0.8):(0.01-0.02).
[0026] More preferably, the mass ratio of sodium carboxymethyl cellulose and piperazine-modified MOF material in the heavy metal chelating agent s1.3 is 1:(0.5-1).
[0027] Preferably, the preparation steps of the heavy metal adsorbent in step 3 are as follows: Cobalt chloride hexahydrate, manganese chloride tetrahydrate, and aminated MOF are ultrasonically dispersed in deionized water for 10-20 min, sodium sulfide is added and stirred for 6-8 h, cooled, filtered, and washed to obtain sulfide composite MOF material; Trimethylol chloride powder and sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 50-60℃ for 10-12 h, cooled, washed, and then placed in deionized water and stirred at 45-50℃ for 10-12 h, centrifuged and dried, and placed in ethanol with aminothiourea, heated to 70-80℃ for 40-48 h, washed, and dried to obtain functionalized MOF material; Sodium carboxymethyl cellulose is placed in deionized water and stirred for 10-20 min, then the functionalized MOF material dispersion is added, stirred for 1-2 h, and then freeze-dried to obtain heavy metal adsorbent;
[0028] More preferably, the mass ratio of cobalt chloride hexahydrate, manganese chloride tetrahydrate, aminated MOF, and sodium sulfide in the sulfide composite MOF material is (0.08-0.12):(0.03-0.05):1:(0.03-0.07); the mass ratio of the sulfide composite MOF material, trimesoyl chloride, and aminothiourea is 1:(1.5-2.0):(1.0-1.5); and the mass ratio of sodium carboxymethyl cellulose and functionalized MOF material is 1:(0.5-1).
[0029] Preferably, the process parameters for the three-stage water washing treatment are: rotation speed of 400-500 r / min, water washing time of 1-3 h; and the mass of the heavy metal adsorbent is 2-3 wt% of the fly ash from the second-stage water washing.
[0030] Compared with the prior art, the beneficial effects of the present invention are:
[0031] 1. This invention involves graded water washing of fly ash. In the first stage of water washing, sodium dihydrogen phosphate is added to dissolve soluble chlorides, sulfates, and some acid-soluble heavy metals, which are then reused in the second stage of water washing. Ferrous sulfate, a reducing agent, is added to reduce hexavalent chromium to trivalent chromium in a weakly acidic environment created by carbon dioxide. Then, a heavy metal chelating agent is used to target and chelate cationic heavy metals, such as trivalent chromium and divalent copper. This heavy metal chelating agent is obtained by polymerizing piperazine and triacryloylhexahydrotriazine to obtain a polyamine polymer with terminal double bonds, which is grafted onto a double-bond modified MOF material through an addition reaction. Through the synergistic effect of physical adsorption of the MOF material and chelation of polyamine functional groups, heavy metals are precipitated during the second stage of water washing.
[0032] 2. In the third stage of treatment, metal sulfides are loaded onto amino-modified MOF materials via a hydrothermal method. The metal sulfides can rapidly capture Hg and As, which can then be used for subsequent grafted complex adsorption. The sulfide composite MOF material is then subjected to gas-phase grafting to introduce carbonyl groups. The carbonyl groups on the MOF surface react with the amino groups of aminothiourea in a Schiff base reaction, fixing the aminothiourea onto the MOF material as a targeting core. This allows for highly selective complexation and stabilization of Hg, thereby achieving targeted adsorption. The above-mentioned targeting material is then combined with sodium carboxymethyl cellulose to form a three-dimensional porous material, facilitating the separation and recovery of the adsorbent. Detailed Implementation
[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0034] In the experiment, the preparation steps of the aminated MOF were as follows: by mass, 10 parts of zirconium chloride and 7 parts of 2-aminoterephthalic acid were mixed, 200 parts of N,N-dimethylformamide and 10 parts of glacial acetic acid were added, the mixture was ultrasonically stirred and then transferred to an oven. After reacting at 120℃ for 12 h, the mixture was centrifuged, washed and dried to obtain the aminated MOF.
[0035] The preparation steps of double bond modified MOF are as follows: by mass, 5 parts of aminated MOF are dispersed in 100 parts of N,N-dimethylformamide, 50 parts of methacrylic anhydride are added and stirred for 3 days, filtered and dried to obtain double bond modified MOF;
[0036] The chemical composition of fly ash includes: 45.43% CaO, 15.33% Cl. - 4.13% SiO2, 3.33% Fe2O3, 1.25% Al2O3, 2.21% MgO, 6.33% Na2O, 5.35% K2O and the balance being impurities;
[0037] A CO2 atmosphere consists of 95% nitrogen and 5% carbon dioxide.
[0038] Example 1: This example provides a method for washing fly ash with water, specifically including the following steps:
[0039] Step 1: By mass, place 10 parts of fly ash sample in 100 parts of deionized water, add 0.3 parts of sodium dihydrogen phosphate for primary water washing treatment, treat at 200 r / min for 40 min, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0040] Step 2: By weight, place the primary washed fly ash in 20 parts of deionized water, add the primary washed filtrate, and treat with a CO2 atmosphere at a flow rate of 1 mL / min for 10 min. Then, add ferrous sulfate and stir for 30 min. Add a heavy metal chelating agent and adjust the pH of the system to 4 for secondary washing treatment at a speed of 300 r / min for 2 h. Filter to obtain secondary washed fly ash residue and secondary washed filtrate. Separate the heavy metal chelating agent from the secondary fly ash residue and dry it to obtain secondary washed fly ash. The mass of ferrous sulfate and heavy metal chelating agent are 2% and 6% of the primary washed fly ash, respectively.
[0041] Step 3: By weight, place the secondary washed fly ash in 100 parts of deionized water, add heavy metal adsorbent for tertiary washing, filter to obtain tertiary washed fly ash residue and tertiary washed filtrate, separate the heavy metal adsorbent from the tertiary washed fly ash residue, and dry to obtain tertiary washed fly ash; wherein, the mass of the heavy metal adsorbent is 3% of the secondary washed fly ash.
[0042] The preparation steps of the heavy metal chelating agent are as follows: By mass, 2 parts of triacryloylhexahydrotriazine and 0.5 parts of piperazine are placed in 100 parts of N,N-dimethylformamide and stirred for 6 hours. The mixture is then heated to 50°C and stirred for 24 hours. After sedimentation in diethyl ether, the mixture is separated, freeze-dried, and then mixed with 1 part of double-bond modified MOF, 0.02 parts of azobisisobutyronitrile, and 100 parts of N,N-dimethylformamide. The mixture is heated to 80°C and stirred for 8 hours. After centrifugation, the piperazine-modified MOF material is obtained. 1.2 parts of sodium carboxymethyl cellulose are placed in 20 parts of deionized water and stirred for 10 minutes. 1 part of the piperazine-modified MOF material is dispersed in 20 parts of N,N-dimethylformamide, stirred for 2 hours, and then freeze-dried to obtain the heavy metal chelating agent.
[0043] The preparation steps of the heavy metal adsorbent are as follows: 0.10 parts by mass of cobalt chloride hexahydrate, 0.05 parts by mass of manganese chloride tetrahydrate, and 1 part by mass of aminated MOF are ultrasonically dispersed in deionized water for 20 min. Then, 0.05 parts by mass of sodium sulfide are added, stirred for 8 h, cooled, filtered, and washed to obtain sulfide composite MOF material. 1.8 parts by mass of trimesoyl chloride powder and 1 part by mass of sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 60℃ for 12 h, cooled, washed, and then placed in deionized water and stirred at 50℃ for 12 h. After centrifugation and drying, 1.5 parts by mass of aminothiourea are placed in ethanol, heated to 80℃ for 48 h, washed, and dried to obtain functionalized MOF material. 1.2 parts by mass of sodium carboxymethyl cellulose are placed in deionized water and stirred for 15 min. Then, 1 part by mass of functionalized MOF material dispersion is added, stirred for 2 h, and then freeze-dried to obtain the heavy metal adsorbent.
[0044] Example 2: This example provides a method for washing fly ash with water, specifically including the following steps:
[0045] Step 1: By mass, place 10 parts of fly ash sample in 100 parts of deionized water, add 0.4 parts of sodium dihydrogen phosphate for primary water washing treatment, treat at 150 r / min for 50 min, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0046] Step 2: By weight, place the primary washed fly ash in 20 parts of deionized water, add the primary washed filtrate, and treat with a CO2 atmosphere at a flow rate of 1 mL / min for 8 min. Then, add ferrous sulfate and stir for 20 min. Add a heavy metal chelating agent and adjust the pH of the system to 5 for secondary washing treatment at a speed of 200 r / min for 2 h. Filter to obtain secondary washed fly ash residue and secondary washed filtrate. Separate the heavy metal chelating agent from the secondary washed fly ash residue and dry it to obtain secondary washed fly ash. The mass of ferrous sulfate and heavy metal chelating agent are 1% and 7% of the primary washed fly ash, respectively.
[0047] Step 3: By weight, place the secondary washed fly ash in 100 parts of deionized water, add heavy metal adsorbent for tertiary washing, filter to obtain tertiary washed fly ash residue and tertiary washed filtrate, separate the heavy metal adsorbent from the tertiary washed fly ash residue, and dry to obtain tertiary washed fly ash; wherein, the mass of the heavy metal adsorbent is 2% of the secondary washed fly ash.
[0048] The preparation steps of the heavy metal chelating agent are as follows: By weight, 2 parts of triacryloylhexahydrotriazine and 0.5 parts of piperazine are placed in 100 parts of N,N-dimethylformamide, stirred for 6 hours, heated to 50°C and stirred for 24 hours, poured into diethyl ether for sedimentation and separation, freeze-dried, and mixed with 1 part of double-bond modified MOF, 0.02 parts of azobisisobutyronitrile and 100 parts of N,N-dimethylformamide, heated to 80°C and stirred for 10 hours, and centrifuged to disperse to obtain piperazine-modified MOF material; 1.2 parts of sodium carboxymethyl cellulose are placed in 20 parts of deionized water and stirred for 10 minutes, then 1 part of piperazine-modified MOF material is dispersed in 20 parts of N,N-dimethylformamide, stirred for 2 hours and freeze-dried to obtain the heavy metal chelating agent;
[0049] The preparation steps of the heavy metal adsorbent are as follows: 0.10 parts by mass of cobalt chloride hexahydrate, 0.05 parts by mass of manganese chloride tetrahydrate, and 1 part by mass of aminated MOF are ultrasonically dispersed in deionized water for 20 min. Then, 0.05 parts by mass of sodium sulfide are added, stirred for 6 h, cooled, filtered, and washed to obtain sulfide composite MOF material. 1.8 parts by mass of trimesoyl chloride powder and 1 part by mass of sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 50℃ for 10 h, cooled, washed, and then placed in deionized water and stirred at 50℃ for 10 h. After centrifugation and drying, it is placed in ethanol with 1.5 parts by mass of aminothiourea, heated to 75℃ for 48 h, washed, and dried to obtain functionalized MOF material. 1.2 parts by mass of sodium carboxymethyl cellulose are placed in deionized water and stirred for 15 min. Then, 1 part by mass of functionalized MOF material dispersion is added, stirred for 2 h, and then freeze-dried to obtain the heavy metal adsorbent.
[0050] Example 3: This example provides a method for washing fly ash with water, specifically including the following steps:
[0051] Step 1: By mass, place 10 parts of fly ash sample in 100 parts of deionized water, add 0.5 parts of sodium dihydrogen phosphate for primary water washing treatment, treat at 150 r / min for 50 min, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0052] Step 2: By weight, place the primary washed fly ash in 20 parts of deionized water, add the primary washed filtrate, and treat with a CO2 atmosphere at a flow rate of 1 mL / min for 10 min. Then, add ferrous sulfate and stir for 30 min. Add a heavy metal chelating agent and adjust the pH of the system to 4 for secondary washing treatment at a speed of 300 r / min for 2 h. Filter to obtain secondary washed fly ash residue and secondary washed filtrate. Separate the heavy metal chelating agent from the secondary fly ash residue and dry it to obtain secondary washed fly ash. The mass of ferrous sulfate and heavy metal chelating agent are 3% and 5% of the primary washed fly ash, respectively.
[0053] Step 3: By weight, place the secondary washed fly ash in 100 parts of deionized water, add heavy metal adsorbent for tertiary washing, filter to obtain tertiary washed fly ash residue and tertiary washed filtrate, separate the heavy metal adsorbent from the tertiary washed fly ash residue, and dry to obtain tertiary washed fly ash; wherein, the mass of the heavy metal adsorbent is 3% of the secondary washed fly ash.
[0054] The preparation steps of the heavy metal chelating agent are as follows: By mass, 2 parts of triacryloylhexahydrotriazine and 0.5 parts of piperazine are placed in 100 parts of N,N-dimethylformamide, stirred for 4 hours, heated to 50℃ and stirred for 24 hours, poured into diethyl ether for sedimentation and separation, freeze-dried, and mixed with 1 part of double-bond modified MOF, 0.02 parts of azobisisobutyronitrile and 100 parts of N,N-dimethylformamide, heated to 80℃ and stirred for 10 hours, and centrifuged to disperse to obtain piperazine-modified MOF material; 1.2 parts of sodium carboxymethyl cellulose are placed in 20 parts of deionized water and stirred for 10 minutes, then 1 part of piperazine-modified MOF material is dispersed in 20 parts of N,N-dimethylformamide, stirred for 2 hours and freeze-dried to obtain the heavy metal chelating agent;
[0055] The preparation steps of the heavy metal adsorbent are as follows: 0.10 parts by mass of cobalt chloride hexahydrate, 0.05 parts by mass of manganese chloride tetrahydrate, and 1 part by mass of aminated MOF are ultrasonically dispersed in deionized water for 20 min. Then, 0.05 parts by mass of sodium sulfide are added, stirred for 8 h, cooled, filtered, and washed to obtain sulfide composite MOF material. 1.8 parts by mass of trimesoyl chloride powder and 1 part by mass of sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 60℃ for 12 h, cooled, washed, and then placed in deionized water and stirred at 50℃ for 12 h. After centrifugation and drying, 1.5 parts by mass of aminothiourea are placed in ethanol, heated to 80℃ for 48 h, washed, and dried to obtain functionalized MOF material. 1.2 parts by mass of sodium carboxymethyl cellulose are placed in deionized water and stirred for 15 min. Then, 1 part by mass of functionalized MOF material dispersion is added, stirred for 2 h, and then freeze-dried to obtain the heavy metal adsorbent.
[0056] Comparative Example 1: As a comparative experiment of Example 3, the fly ash sample was not subjected to secondary water washing. The specific process steps included:
[0057] Step 1: By mass, place 10 parts of fly ash sample in 100 parts of deionized water, add 0.5 parts of sodium dihydrogen phosphate for primary water washing treatment, treat at 150 r / min for 50 min, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0058] Step 2: By weight, place the primary washed fly ash in 100 parts of deionized water, add heavy metal adsorbent for secondary washing, filter to obtain secondary washed fly ash residue and tertiary washed filtrate, separate the heavy metal adsorbent from the secondary washed fly ash residue, and dry to obtain secondary washed fly ash; wherein, the mass of the heavy metal adsorbent is 3% of the primary washed fly ash.
[0059] The preparation steps of the heavy metal adsorbent are as follows: 0.10 parts by mass of cobalt chloride hexahydrate, 0.05 parts by mass of manganese chloride tetrahydrate, and 1 part by mass of aminated MOF are ultrasonically dispersed in deionized water for 20 min. Then, 0.05 parts by mass of sodium sulfide are added, stirred for 8 h, cooled, filtered, and washed to obtain sulfide composite MOF material. 1.8 parts by mass of trimesoyl chloride powder and 1 part by mass of sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 60℃ for 12 h, cooled, washed, and then placed in deionized water and stirred at 50℃ for 12 h. After centrifugation and drying, 1.5 parts by mass of aminothiourea are placed in ethanol, heated to 80℃ for 48 h, washed, and dried to obtain functionalized MOF material. 1.2 parts by mass of sodium carboxymethyl cellulose are placed in deionized water and stirred for 15 min. Then, 1 part by mass of functionalized MOF material dispersion is added, stirred for 2 h, and then freeze-dried to obtain the heavy metal adsorbent.
[0060] Comparative Example 2: As a comparative experiment for Example 3, the fly ash sample was not subjected to three-stage water washing treatment. The specific process steps included:
[0061] Step 1: By mass, place 10 parts of fly ash sample in 100 parts of deionized water, add 0.5 parts of sodium dihydrogen phosphate for primary water washing treatment, treat at 150 r / min for 50 min, and filter to obtain primary water washed fly ash and primary water washed filtrate.
[0062] Step 2: By weight, place the primary washed fly ash in 20 parts of deionized water, add the primary washed filtrate, and treat with a CO2 atmosphere at a flow rate of 1 mL / min for 10 min. Then, add ferrous sulfate and stir for 30 min. Add a heavy metal chelating agent and adjust the pH of the system to 4 for secondary washing treatment at a speed of 300 r / min for 2 h. Filter to obtain secondary washed fly ash residue and secondary washed filtrate. Separate the heavy metal chelating agent from the secondary fly ash residue and dry it to obtain secondary washed fly ash. The mass of ferrous sulfate and heavy metal chelating agent are 3% and 5% of the primary washed fly ash, respectively.
[0063] The preparation steps of the heavy metal chelating agent are as follows: 2 parts by mass of triacryloylhexahydrotriazine and 0.5 parts by mass of piperazine are placed in 100 parts by mass of N,N-dimethylformamide, stirred for 4 hours, heated to 50°C and stirred for 24 hours, poured into diethyl ether for sedimentation and separation, freeze-dried, and mixed with 1 part by mass of double bond modified MOF, 0.02 parts by mass of azobisisobutyronitrile and 100 parts by mass of N,N-dimethylformamide, heated to 80°C and stirred for 10 hours, and centrifuged to disperse to obtain piperazine-modified MOF material; 1.2 parts by mass of sodium carboxymethyl cellulose are placed in 20 parts by mass of deionized water and stirred for 10 minutes, then 1 part by mass of piperazine-modified MOF material is dispersed in 20 parts by mass of N,N-dimethylformamide, stirred for 2 hours and freeze-dried to obtain the heavy metal chelating agent.
[0064] Testing and Experiment
[0065] Referring to the method of HJ 557-2010, water was used as the leaching agent to analyze the heavy metal leaching toxicity of fly ash samples, the three-stage water-washed fly ash prepared in Examples 1-3, and the final water-washed fly ash prepared in Comparative Examples 1-2. After filtering the leachate, it was digested with nitric acid and the contents of Hg, As, and Cr were detected and analyzed by ICP-OES. The purification rate was calculated and recorded as data in Table 1.
[0066] Table 1
[0067]
[0068] Conclusion: The process flow and specific parameter design of Example 3 achieved better heavy metal removal effect than the other examples; Comparative Example 1, as the control experiment of Example 3, did not perform secondary water washing treatment, that is, it did not add heavy metal chelating agent, ferrous iron and carbon dioxide, so hexavalent chromium was not reduced, and the final Cr content was relatively high; Comparative Example 2 did not perform tertiary water washing treatment and did not add heavy metal adsorbent, so the heavy metal purification rate of Hg and As decreased.
[0069] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.
Claims
1. A method for targeted removal of heavy metals during fly ash washing, characterized in that, Specifically, the process steps include the following: Step 1: Place the fly ash sample in deionized water, add sodium dihydrogen phosphate for primary water washing treatment, and filter to obtain primary water washed fly ash and primary water washed filtrate. Step 2: Place the primary water-washed fly ash in deionized water, add the primary water-washed filtrate, treat with CO2 atmosphere, then treat with ferrous sulfate. After the treatment, add a heavy metal chelating agent and adjust the pH of the system. Perform secondary water washing treatment, filter to obtain secondary water-washed fly ash residue and secondary water-washed filtrate. After separating the heavy metal chelating agent from the secondary fly ash residue, dry to obtain secondary water-washed fly ash. Step 3: Place the secondary water-washed fly ash in deionized water, add heavy metal adsorbent for tertiary water washing treatment, filter to obtain tertiary water-washed fly ash residue and tertiary water-washed filtrate, separate the heavy metal adsorbent from the tertiary water-washed fly ash residue, and dry to obtain tertiary water-washed fly ash. In step 2, the mass of ferrous sulfate is 1-3 wt% of the primary water-washed fly ash; the mass of the heavy metal chelating agent is 5-8 wt% of the primary water-washed fly ash; the preparation steps of the heavy metal chelating agent are as follows: s1.1: Zirconium chloride and 2-aminoterephthalic acid were mixed, N,N-dimethylformamide and glacial acetic acid were added, and the mixture was ultrasonically stirred and then transferred to an oven. After reacting at 120-125℃ for 10-12 h, the mixture was centrifuged, washed and dried to obtain an aminated MOF. The aminated MOF was dispersed in N,N-dimethylformamide, methacrylic anhydride was added and stirred for 2-3 days, and then filtered and dried to obtain a double bond modified MOF. s1.2: Triacryloylhexahydrotriazine and piperazine were placed in N,N-dimethylformamide and stirred for 4-6 h. The mixture was then heated to 40-50 °C and stirred for 20-24 h. After sedimentation, the mixture was separated, freeze-dried, and then mixed with double bond modified MOF, azobisisobutyronitrile and N,N-dimethylformamide. The mixture was heated to 70-80 °C and stirred for 8-10 h. After centrifugation, piperazine-modified MOF material was obtained. s1.3: Sodium carboxymethyl cellulose was placed in deionized water and stirred for 10-20 min. Then piperazine-modified MOF material dispersion was added, stirred for 1-2 h, and then freeze-dried to obtain heavy metal chelating agent; The preparation steps of the heavy metal adsorbent in step 3 are as follows: Cobalt chloride hexahydrate, manganese chloride tetrahydrate, and aminated MOF are ultrasonically dispersed in deionized water for 10-20 min, sodium sulfide is added and stirred for 6-8 h, cooled, filtered and washed to obtain sulfide composite MOF material; Trimethylol chloride powder and sulfide composite MOF material are placed separately at both ends of a sealed tube, heated to 50-60℃ for 10-12 h, cooled and washed, then placed in deionized water and stirred at 45-50℃ for 10-12 h, centrifuged and dried, and placed in ethanol with aminothiourea, heated to 70-80℃ for 40-48 h, washed and dried to obtain functionalized MOF material; Sodium carboxymethyl cellulose is placed in deionized water and stirred for 10-20 min, then the functionalized MOF material dispersion is added, stirred for 1-2 h and freeze-dried to obtain heavy metal adsorbent.
2. The method for targeted removal of heavy metals during fly ash washing according to claim 1, characterized in that, In step 1, the ratio of fly ash sample, deionized water and sodium dihydrogen phosphate is 10g:(100-120)mL:(0.3-0.5)g; the process parameters for the first-stage water washing treatment are: rotation speed of 150-300r / min and water washing time of 30-50min.
3. The method for targeted removal of heavy metals during fly ash washing according to claim 1, characterized in that, In step 2, the flow rate of the CO2 atmosphere is 1-2 mL / min, and the concentration is 8-15%; ferrous sulfate is added 8-10 min after the CO2 atmosphere is introduced; heavy metal chelating agent is added after stirring for 20-30 min after adding ferrous sulfate; the pH of the system is adjusted to 4-6 after adding the heavy metal chelating agent; the process parameters for the secondary water washing treatment are: rotation speed of 200-300 r / min and water washing time of 1-2 h.
4. The method for targeted removal of heavy metals during fly ash washing according to claim 1, characterized in that, In s1.1, the mass ratio of zirconium chloride to 2-aminoterephthalic acid is 1:(0.6-0.8); the mass ratio of aminated MOF to methacrylic anhydride is 1:(8-12); in s1.2, the mass ratio of double bond modified MOF, triacryloylhexahydrotriazine, piperazine, and azobisisobutyronitrile is 1:(1.5-3):(0.5-0.8):(0.01-0.02); in s1.3, the mass ratio of sodium carboxymethyl cellulose and piperazine-modified MOF material in the heavy metal chelating agent is 1:(0.5-1).
5. A method for targeted removal of heavy metals during fly ash washing according to claim 1, characterized in that, The mass ratio of cobalt chloride hexahydrate, manganese chloride tetrahydrate, aminated MOF, and sodium sulfide in the sulfide composite MOF material is (0.08-0.12):(0.03-0.05):1:(0.03-0.07); the mass ratio of the sulfide composite MOF material, trimesoyl chloride, and aminothiourea is 1:(1.5-2.0):(1.0-1.5); and the mass ratio of sodium carboxymethyl cellulose and functionalized MOF material is 1:(0.5-1).
6. A method for targeted removal of heavy metals during fly ash washing according to claim 1, characterized in that, The process parameters for the three-stage water washing treatment are: rotation speed of 400-500 r / min, water washing time of 1-3 h; and the mass of the heavy metal adsorbent is 2-3 wt% of the fly ash from the second-stage water washing.