Selenium-containing fly ash anaerobic biological curing baking-free brick and preparation method thereof
The preparation of non-fired bricks by bioreduction of hexavalent selenium using an anaerobic mixed bacterial system solves the passivation problem of hexavalent selenium in fly ash, achieving efficient, low-cost resource utilization and environmentally friendly treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-02
- Publication Date
- 2026-03-17
AI Technical Summary
Existing technologies are insufficient for efficiently passivating hexavalent selenium in fly ash, and traditional treatment methods are characterized by high energy consumption, large resource consumption, and the risk of secondary pollution. Biological passivation technology also faces problems such as the inhibition of bacterial activity during fly ash disposal.
An anaerobic mixed bacterial system containing Clostridium acetonebutanol, Bacillus jiunifolia, Bacteroides propionitum, commensal bacteria of wine cellars, and desulfurized Vibrio desulfurization was used to convert hexavalent selenium into stable elemental selenium through anaerobic biological reduction reaction, and then combined with cementing materials to prepare non-fired bricks.
It achieves a high passivation rate of hexavalent selenium (>95%), reduces processing costs and energy consumption, and the prepared non-fired bricks have high compressive strength, which is in line with the concept of green and low-carbon development and provides a balance between economic benefits and environmental protection.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of hazardous waste resource utilization technology, specifically relating to a selenium-containing fly ash anaerobic biological solidification non-fired brick and its preparation method. Background Technology
[0002] With the acceleration of urbanization and the growth of energy demand, the amount of fly ash generated by industrial activities such as waste incineration and coal-fired power generation continues to rise. According to the "National Hazardous Waste List (2021 Edition)," fly ash is clearly listed as HW18 hazardous waste, which contains heavy metals such as mercury, lead, and cadmium, metalloids such as arsenic and selenium, and persistent organic pollutants such as dioxins. If not properly disposed of, it may enter the environment through dust, leaching, and other pathways, posing a serious threat to ecosystems and human health.
[0003] Currently, fly ash treatment technologies mainly include two approaches: harmless disposal and resource utilization. In harmless disposal technologies, while cement solidification / stabilization can temporarily fix heavy metals, its long-term stability is affected by environmental pH and does not reduce fly ash volume. High-temperature melting treatment can effectively degrade dioxins, but energy consumption is as high as 1200-1500℃, and it may generate secondary pollution. Regarding resource utilization, traditional sintering brick making consumes clay resources and emits greenhouse gases, while existing non-fired brick technologies mostly use physical coating methods to treat fly ash, which have limited effectiveness in solidifying easily migrating elements such as selenium. Of particular concern is that selenium in fly ash often exists in the forms of selenate (hexavalent selenium) and selenite (tetravalent selenium). Existing chemical passivation technologies can achieve a removal rate of over 80% for selenite, but the removal rate for selenate is generally below 40%. This is mainly because hexavalent selenium has higher mobility in alkaline fly ash environments. Although biopassivation technology is widely used in wastewater treatment and soil remediation, traditional single-strain technology faces technical bottlenecks such as inhibited bacterial activity and poor system adaptability when directly applied to fly ash disposal.
[0004] Therefore, there is an urgent need to develop a treatment technology that can efficiently passivate hexavalent selenium while adapting to the complex environment of fly ash. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of the prior art and to provide a selenium-containing fly ash anaerobic biological solidification non-fired brick and its preparation method.
[0006] The specific technical solution adopted in this invention is as follows:
[0007] In a first aspect, the present invention provides a method for preparing selenium-containing fly ash anaerobic bio-solidified non-fired bricks, the specific steps of which are as follows:
[0008] S1: Prepare an anaerobic mixed bacterial system with selenate reduction function; use the anaerobic mixed bacterial system that passes the bacterial growth test and selenate reduction test as the fly ash solidification bacterial solution;
[0009] S2: Mix the pretreated fly ash to be solidified with the nutrient broth culture medium, adjust the pH to neutral, and obtain fly ash slurry;
[0010] S3: Mix fly ash solidified bacterial solution and fly ash slurry, and let them react under anaerobic conditions to achieve selenium passivation and obtain passivated fly ash slurry;
[0011] S4: After adding cementitious materials to the passivated fly ash slurry, curing is carried out to obtain solidified non-fired bricks.
[0012] Preferably, the anaerobic mixed bacterial system comprises Clostridium acetobutylicum, Paludibacter jiangxiensis, Bacteroides propionicigenes, Syntrophomonas cellicola, and Desulfovibrio desulfuricans; the Clostridium acetobutylicum, Paludibacter jiangxiensis, Bacteroides propionicigenes, Syntrophomonas cellicola, and Desulfovibrio desulfuricans are all deposited at the China General Microbiological Culture Collection Center, with accession numbers CGMCC 1.133, CGMCC 1.5150, CGMCC 1.17886, CGMCC 1.5041, and CGMCC 1.5189, respectively.
[0013] Preferably, the bacterial growth test is performed as follows: the prepared anaerobic mixed bacterial system is inoculated into the growth test medium at a volume ratio of 1% to 2%, and anaerobically cultured at 25 to 35°C for 1 to 5 days. The OD value is then selected. 600 The bacterial solution has a pH value between 0.5 and 1.5; the growth test medium is a nutrient broth medium containing fly ash to be solidified or Luria-Bertani medium.
[0014] Furthermore, the selenate reduction test is specifically performed as follows: The OD value of the sample, which has undergone bacterial growth testing, is then tested. 600 Add Na2SeO4 to the bacterial culture at a concentration of 0.5-1.5 to make the selenium content in the system 100-1000 mg / L. Then, anaerobic culture at 25-35℃ for 1-5 days until the selenate in the culture medium is reduced to selenium precipitate.
[0015] Preferably, the fly ash to be solidified in step S2 is pretreated by screening with a 50-200 mesh screen; the fly ash to be solidified and the nutrient broth culture medium are mixed at a mass ratio of 10:(1-5), and the pH is adjusted to 6.5-7.5 using sulfuric acid, hydrochloric acid or phosphoric acid solution.
[0016] Preferably, in step S3, the amount of fly ash solidification bacterial solution added to the fly ash slurry is 2%~20%, and the mixture is anaerobically cultured at 25~35℃ for 1~5 days.
[0017] Preferably, the cementing material in step S4 is calcium oxide, cement, gypsum, water glass, magnesia, asphalt, or epoxy resin; the amount of cementing material added is 2% to 20%.
[0018] Preferably, the curing temperature in step S4 is 20~60℃, the curing humidity is 60~80%, and the curing time is 3~10 days.
[0019] Preferably, the fly ash contains less than 50 mg / kg of total selenium, of which the content of hexavalent selenium is less than 30 mg / kg, the moisture content is less than 20%, and the pH is less than 12.
[0020] Secondly, the present invention provides a selenium-containing fly ash anaerobic bio-curing non-fired brick obtained by the preparation method described in the first aspect.
[0021] Compared with the prior art, the present invention has the following advantages:
[0022] (1) Compared with the traditional chemical passivation technology, which has low efficiency (<40%) in treating hexavalent selenium and poses a risk of secondary pollution, this invention can efficiently convert highly mobile hexavalent selenium in fly ash into stable elemental selenium through the bioreduction of anaerobic bacteria. The passivation rate of hexavalent selenium is >95%, and the treatment process is carried out at room temperature and pressure without introducing foreign toxic and harmful substances and without secondary pollution.
[0023] (2) Compared with the traditional sintering brick-making process, which consumes clay resources, has high energy consumption (900~1100℃) and causes serious pollution, this invention adopts microbial solidification-bonding synergistic technology to directly convert fly ash into non-fired bricks with a compressive strength of 5.5~9.0 MPa. This not only solves the problem of hazardous waste disposal, but also realizes resource recycling, which is in line with the concept of green and low-carbon development.
[0024] (3) Compared with the problem that the bacterial activity is easily inhibited in practical applications of conventional single-strain biotechnology, the present invention adopts anaerobic bacterial community technology and establishes a dual adaptive testing mechanism of bacterial growth test and selenate reduction test to ensure the effectiveness of the bacterial community and the reliability of the process in the complex environment of fly ash.
[0025] (4) This invention transforms the cost of fly ash treatment into the benefits of resource utilization. Each ton of fly ash treatment can generate a net profit of 200 to 400 yuan, and the carbon emission is only 1 / 5 to 1 / 8 of that of sintered bricks. It achieves the unity of environmental protection and economic benefits and provides a feasible technical path for the resource utilization of hazardous waste. Detailed Implementation
[0026] The present invention will be further described and illustrated below with reference to specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly, provided that there is no mutual conflict.
[0027] The following examples used *Clostridium acetobutylicum*, deposited at the China General Microbiological Culture Collection Center (CGMCC) with accession number CGMCC 1.133; *Paludibacter jiangxiensis* with accession number CGMCC 1.5150; *Bacteroides propionicigenes* with accession number CGMCC 1.17886; *Syntrophomonas cellicola* with accession number CGMCC 1.5041; and *Desulfovibrio desulfuricans* with accession number CGMCC 1.5189. All of these strains are publicly available.
[0028] Example 1
[0029] (1) Fly ash acquisition and pretreatment
[0030] Fly ash A was collected from the flue gas purification system of enterprise A's coal combustion and passed through a 100-mesh sieve (approximately 0.15 mm in diameter) to remove large particulate impurities. Testing revealed that fly ash A contained a total selenium content of 2.78 mg / kg, hexavalent selenium of 2.03 mg / kg, a moisture content of 8%, and a pH of 10.9.
[0031] Slowly add 10 mL of concentrated sulfuric acid to 10 mL of pure water, stir and cool to obtain a sulfuric acid (1+1) solution, and set aside. Take 50 g of sieved fly ash A, add 15 mL of nutrient broth culture medium, adjust the pH to 7.5 with the sulfuric acid (1+1) solution, and stir evenly to obtain fly ash slurry A.
[0032] (2) Preparation of anaerobic bacteria
[0033] Dissolve 2.5 g of nutrient broth culture medium powder in 100 mL of pure water and sterilize at 121℃ for 20 min to obtain nutrient broth culture medium. Inoculate *Clostridium acetonebutanol*, *Sphaerophyte jiengensis*, *Bacteroides propionitum*, *Sphaerophyte jiengensis* commensalomorpha*, and *Desulfovibrio desulfurization* into an anaerobic serum bottle containing 100 mL of nutrient broth culture medium and culture to obtain an anaerobic mixed bacterial system.
[0034] (3) Bacterial adaptability test
[0035] Disperse 15 g of fly ash slurry A in 150 mL of pure water, shake at 35℃ and 150 rpm for 30 min, centrifuge (4000 rpm, 10 min), and collect the supernatant as fly ash solution. Add 2.5 g of nutrient broth culture medium powder to 100 mL of fly ash solution, sterilize at 121℃ for 20 min, and obtain growth test medium.
[0036] The growth test medium was transferred to an anaerobic serum bottle, and 1 mL of the anaerobic bacterial culture obtained in step (2) was inoculated. After aeration with nitrogen for 20 min, the bottle was sealed and cultured with shaking at 30℃ and 150 rpm for 2 days. OD was measured. 600 Value. OD 600 A value greater than 1.0 indicates that the bacterial growth test is passed.
[0037] Subsequently, 0.1 g of Na2SeO4 was added, and the mixture was cultured for another 2 days under the same conditions. A large amount of red precipitate was produced, indicating that the mixed bacterial system reduced selenate to elemental selenium, which was verified by the selenate reduction test.
[0038] Both tests passed, indicating that the anaerobic bacteria obtained in step (2) are suitable for the solidification of fly ash A, and a fly ash solidified bacterial solution was obtained.
[0039] (4) Passivation of heavy metals in fly ash
[0040] Take 50 g of fly ash slurry A from step (1), add 4 mL of fly ash solidification bacterial solution that has passed the test, mix well and put into a sealed bag, let stand at 30℃ for 2 days to obtain passivated fly ash slurry.
[0041] (5) Fly ash brick making
[0042] Experimental group: Take 54 g of the passivated fly ash slurry after reaction, add 2 g of calcium oxide and 3 g of ordinary silicate cement (PO 42.5 grade), mix well and pour into a cylindrical silicone mold (diameter 2.5 cm, height 5 cm), vibrate and compact (50 Hz, 5 min), cure for 5 days at 30℃ and 70% humidity, and demold to obtain non-fired brick samples.
[0043] Control group: Take 40 g of sieved fly ash A, add 14 mL of pure water, 2 g of calcium oxide and 3 g of ordinary silicate cement, and prepare the control group's non-fired brick sample using the same method.
[0044] (6) Performance testing and results analysis
[0045] Compressive strength: The compressive strength of the above-mentioned non-fired brick samples was tested according to the "Test Method for Masonry Bricks" (GB / T 2542-2012). The compressive strength of the control group was 1.8 MPa, and that of the experimental group was 5.5 MPa, an increase of 3.06 times.
[0046] Leaching toxicity: Samples were treated according to the "Leaching Method for Solid Waste - Horizontal Oscillation Method" (HJ 557-2010), and the concentrations of selenium were determined by atomic fluorescence spectrometry and the concentrations of other heavy metals were determined by inductively coupled plasma mass spectrometry.
[0047] The results are shown in Table 1: The total selenium leaching concentration in the experimental group decreased from 0.0238 mg / L to 0.0075 mg / L (reduction rate 68.7%), the total arsenic decreased from 0.2042 mg / L to 0.0089 mg / L (reduction rate 95.6%), and the cadmium decreased from 0.0075 mg / L to 0.0014 mg / L (reduction rate 81.3%). All indicators of the leachate met the Class III water limit of the Groundwater Quality Standard (GB / T 14848-2017).
[0048] Example 2
[0049] (1) Fly ash acquisition and pretreatment
[0050] Fly ash B was collected from the waste incineration flue gas purification system of Enterprise B, passed through a 100-mesh sieve, and the total selenium content was measured to be 8.05 mg / kg, hexavalent selenium was 6.83 mg / kg, the moisture content was 10%, and the pH was 11.2.
[0051] (2) The preparation of anaerobic bacteria, bacterial adaptability testing, fly ash heavy metal passivation, fly ash brick making and performance testing processes are the same as in Example 1, except that the fly ash used is different.
[0052] (3) Results Analysis
[0053] Compressive strength: The compressive strength of the control group was 5.3 MPa, while that of the experimental group was 9.0 MPa, an increase of 1.70 times.
[0054] Leaching toxicity: As shown in Table 1, the total selenium leaching concentration in the experimental group decreased from 0.0177 mg / L to 0.0024 mg / L (reduction rate 86.3%), the total arsenic decreased from 0.1975 mg / L to 0.0096 mg / L (reduction rate 95.1%), and the cadmium decreased from 0.4004 mg / L to 0.0002 mg / L (reduction rate 99.95%). All indicators of the leachate met the Class III water limit values of the "Groundwater Quality Standard" (GB / T 14848-2017).
[0055] Table 1. Compressive strength and heavy metal leaching concentration of unfired bricks
[0056]
[0057] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention. Therefore, all technical solutions obtained through equivalent substitution or transformation fall within the protection scope of the present invention.
Claims
1. A process for the preparation of selenium containing fly ash anaerobically biosolidified unfired bricks, characterized by, The specific steps are as follows: S1: preparing an anaerobic mixed bacteria system with selenate reduction function; the anaerobic mixed bacteria system passing bacterial growth test and selenate reduction test is used as a fly ash solidification bacteria liquid; S2: mixing the pretreated fly ash to be solidified and a nutrient broth culture solution, and adjusting the pH to neutral to obtain a fly ash slurry; S3: mixing the fly ash solidification bacteria liquid and the fly ash slurry, and standing and reacting under anaerobic conditions to realize selenium passivation, thereby obtaining a passivated fly ash slurry; S4: adding a cementing material to the passivated fly ash slurry and curing to obtain a solidified and unfired brick.
2. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, The anaerobic mixed bacteria system is a mixed bacteria system comprising Clostridium acetobutylicum, Paludibacter jiangxiensis, Bacteroides propionicigenes, Syntrophomonas cellicola and Desulfovibrio desulfuricans; the Clostridium acetobutylicum, Paludibacter jiangxiensis, Bacteroides propionicigenes, Syntrophomonas cellicola and Desulfovibrio desulfuricans are preserved in the China General Microbiological Culture Collection Center, and the preservation numbers are CGMCC 1.133, CGMCC 1.5150, CGMCC 1.17886, CGMCC 1.5041 and CGMCC 1.5189, respectively.
3. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, The bacterial growth test is specifically as follows: inoculate the prepared anaerobic mixed bacteria system into a growth test culture medium at a volume ratio of 1% to 2%, and anaerobically culture at 25 to 35°C for 1 to 5 days, select a bacterial liquid with an OD 600 value of 0.5 to 1.5; and the growth test culture medium is a nutrient broth culture medium or a Luria-Bertani culture medium containing the fly ash to be solidified.
4. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 3 wherein, The selenate reduction test is carried out as follows: the bacteria liquid with OD value of 0.5-1.5, which has passed the bacterial growth test, is added with Na2SeO4, so that the selenium content in the system is 100-1000 mg / L, and the system is cultured anaerobically at 25-35°C for 1-5 days until the selenate in the culture medium is reduced into selenium precipitate. 600 The selenate reduction test is carried out as follows: the bacteria liquid with OD value of 0.5-1.5, which has passed the bacterial growth test, is added with Na2SeO4, so that the selenium content in the system is 100-1000 mg / L, and the system is cultured anaerobically at 25-35°C for 1-5 days until the selenate in the culture medium is reduced into selenium precipitate.
5. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, The fly ash to be solidified in step S2 is pretreated by screening through a 50-200 mesh sieve; the fly ash to be solidified and the nutrient broth culture solution are mixed at a mass ratio of 10: (1-5), and the pH is adjusted to 6.5-7.5 by using a sulfuric acid, hydrochloric acid or phosphoric acid solution.
6. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, In step S3, the fly ash solidification bacteria liquid is added to the fly ash slurry at an amount of 2%-20%, and anaerobic culture is carried out at 25-35℃ for 1-5 days.
7. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, In step S4, the cementing material is calcium oxide, cement, gypsum, water glass, magnesia, pitch or epoxy resin; and the cementing material is added at an amount of 2%-20%.
8. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, In step S4, the curing temperature is 20-60℃, the curing humidity is 60-80%, and the curing time is 3-10 days.
9. The process for the production of seleniferous fly ash anaerobically biosolidified unfired brick as claimed in claim 1 wherein, The total selenium content in the fly ash is less than 50 mg / kg, the content of hexavalent selenium is less than 30 mg / kg, the water content is less than 20%, and the pH is less than 12.
10. A selenium-containing fly ash anaerobic biological solidification unfired brick prepared by the preparation method of any one of claims 1-9.