CN114314811B - Iron-carbon composite material and preparation method and application thereof - Google Patents
Iron-carbon composite material and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the field of application of microbial technology, and particularly provides an iron-carbon composite material, and a preparation method and application thereof, wherein the preparation method comprises the following steps: and a cross-linking and curing step: crosslinking and solidifying the iron powder and the biological activated carbon by adopting alkaline earth metal salt and a crosslinking agent; mineralizing treatment: soaking the cross-linked and solidified iron-carbon composite material in mineralized bacteria liquid for 5-15min, and drying to obtain the product. The mineralized bacteria form alkaline earth metal carbonate structures on the surface of the iron-carbon composite material by using alkaline earth metal ions, so that the strength of the iron-carbon composite material is greatly enhanced, and meanwhile, the time for soaking in mineralized bacteria liquid is controlled, so that the effect of affecting the active ingredients in the iron-carbon composite material due to the formation of a compact metal carbonate film is avoided.
Description
Technical Field
The invention relates to the field of application of microbial technology, in particular to an iron-carbon composite material and a preparation method and application thereof.
Background
The zero-valent iron has active chemical properties and stronger reducing capability, and a large number of researches show that the zero-valent iron can not only degrade chlorinated organic matters in water, but also reduce and remove heavy metals, azo dyes, nitroaromatics, nitrate, perchlorate, herbicide and other pollutants, thereby greatly promoting the application of the zero-valent iron in the aspect of environmental pollution control. Because of its low cost, it is commonly used as a filler or injection agent in osmotic reaction walls and in situ injection techniques. However, with the reaction of zero-valent iron, hydroxide gradually deposits on the surface of iron, blocking the iron powder in the iron from participating in the reaction, reducing the oxidation-reduction reaction, and reducing the capability of treating pollutants.
The iron-carbon composite material is formed by solidifying and combining carbon and zero-valent iron, and is used as a micro-electrolysis filler, so that the enrichment of sediment on the surface of iron powder can be effectively prevented, and pollutants can be treated more efficiently. Currently, carbon and iron can be combined to form stable micro-electrolytic materials by both cross-linking curing and sintering curing. Crosslinking curing combinations refer to the use of crosslinking curing agents to block and cure iron-carbon together, for example: the patent application CN111377497A uses sodium alginate and calcium chloride as crosslinking curing agents to cure and combine iron, carbon and medical stone to form a material, and phosphorus particles in water are removed. The patent application CN110330082A uses sodium alginate and calcium chloride as crosslinking curing agents to cure iron and carbon into a material, and uses the material as a catalyst to catalyze sodium persulfate to treat ibuprofen pollution. However, the pure crosslinking curing mode has large usage amount of the curing agent, the obtained iron-carbon material has lower strength, the requirement of high mechanical strength operation of in-situ injection or permeation reaction wall technology cannot be met, and the iron-carbon material can be rapidly disintegrated in water environment with microorganisms and loses structural characteristics.
Sintering and curing solve the problem of the strength of the material. However, the sintering process requires processing the material for a plurality of hours at a high temperature of hundreds of DEG C, the energy consumption is extremely high, the material can be hardened at a high Wen Zhongbiao surface, the original slow release pore canal is sealed, part of active materials such as iron powder and carbon powder are locked in the cured material and cannot react with the outside, and the material utilization rate is low.
Therefore, the iron-carbon composite material with high compressive strength and good sewage treatment effect is sought, and the iron-carbon composite material is a technical problem which needs to be solved in the popularization and the utilization of the current iron-carbon catalyst products.
Disclosure of Invention
Therefore, the invention aims to provide an iron-carbon composite material with high compressive strength and good sewage treatment effect, and a preparation method and application thereof.
Therefore, the invention provides a preparation method of an iron-carbon composite material, which comprises the following steps:
and a cross-linking and curing step: crosslinking and solidifying the iron powder and the carbon powder by adopting alkaline earth metal salt and a crosslinking agent;
mineralizing treatment: soaking the cross-linked and solidified iron-carbon composite material in mineralized bacteria liquid for 5-15min, and drying to obtain the product.
Preferably, the soaking time is 5-10min.
Preferably, the mineralization bacteria are selected from one or more of myxococcus xanthus, sulfate reducing bacteria, denitrifying bacteria and bacillus pasteurizus.
Preferably, the sulfate reducing bacteria are selected from one or more of common vibrio desulphurisation, mollusca desulphurisation and vibrio desulphurisation.
Preferably, the denitrifying bacteria are selected from one or more of the genera thiobacillus denitrificans, pseudomonas and alcaligenes.
Preferably, the pseudomonas genus comprises one or more of pseudomonas aeruginosa, pseudomonas fluorescens, pseudomonas meliotidis and pseudomonas pseudomeliotidis.
Preferably, the alcaligenes comprises one or more of alcaligenes, alcaligenes denitrificans and alcaligenes aromaticum.
Preferably, the mineralization bacteria solution has absorbance (OD 600 ) 1-5; preferably 1-3.
Preferably, the preparation method of the mineralized bacterial liquid comprises the following steps: mixing mineralized bacteria powder, ammonium sulfate, urea and water, and culturing.
Preferably, the culture temperature is 25-37 ℃ and the culture time is 24-72h.
Preferably, the mass ratio of mineralized bacteria powder, ammonium sulfate, urea and water is as follows: (20-30): (15-20): (10-15): (800-1200).
Preferably, the mineralized bacteria powder is mixed with ammonium sulfate, urea and water and then comprises the step of adjusting the pH; preferably, the pH is adjusted to 6.5-9.5.
Preferably, the drying step is preceded by a step of dispersing the iron-carbon composite material and leaching the bacterial liquid.
Preferably, a screen with the aperture of 2.0-4.0mm is adopted for dispersion, and the bonded iron-carbon composite material is dispersed by horizontal vibration for 30-60 s.
Preferably, the bacterial liquid is leached out by adopting a screen with the particle size of 0.5-3.0mm, and horizontally oscillating for 30-60s, so as to leach out the redundant bacterial liquid.
Preferably, the drying temperature is 40-60 ℃ and the drying time is 3-5h.
Preferably, the carbon powder is selected from one or two of activated carbon and graphite.
Preferably, the alkaline earth metal salt is selected from one or more of calcium chloride, calcium nitrate, zinc chloride, zinc nitrate.
Preferably, the cross-linking agent is sodium alginate.
Preferably, the crosslinking curing step includes: mixing iron powder, carbon powder, a cross-linking agent and water, adding the mixture into alkaline earth metal salt solution, standing, separating solid from liquid, and drying to obtain the cross-linked and solidified iron-carbon composite material.
Preferably, the mass ratio of the iron powder to the carbon powder to the cross-linking agent is (40-80): (10-30): (3-6).
Preferably, the carbon powder has a particle size of 200-400 mesh.
Preferably, the iron powder is acid-washed iron powder; preferably, the preparation method of the acid-washed iron powder comprises the following steps: soaking iron powder in 0.05-0.5mol/L acid solution for at least 3min, separating solid from liquid, and washing to neutrality.
Preferably, the particle size of the iron powder is 200-400 meshes.
Preferably, the acid solution is selected from one or more of hydrochloric acid solution, sulfuric acid solution and nitric acid solution.
Preferably, in the crosslinking curing step, the water temperature is 50-70 ℃.
Preferably, the mass ratio of the total mass of the acidified iron powder, the carbon powder and the cross-linking agent to water is (3-5): 20.
preferably, the mass percentage concentration of the alkaline earth metal salt solution is 2-6%.
Preferably, the rate of addition to the alkaline earth metal salt solution in the crosslinking curing step is from 5 to 15mL/min.
Preferably, in the crosslinking curing step, the standing time is 30-90min.
Preferably, in the crosslinking curing step, the drying temperature is 40-60 ℃ and the drying time is 6-10h.
Preferably, the particle size of the obtained cross-linked and solidified iron-carbon composite material is 1.2-3mm.
The invention further provides the iron-carbon composite material prepared by the preparation method.
Preferably, the particle size of the iron-carbon composite material is 1.5-3.5mm.
The invention also provides application of the iron-carbon composite material prepared by the preparation method in sewage treatment.
The technical scheme of the invention has the following advantages:
1. the invention provides a preparation method of an iron-carbon composite material, which comprises the following steps: and a cross-linking and curing step: crosslinking and solidifying the iron powder and the carbon powder by adopting alkaline earth metal salt and a crosslinking agent; mineralizing treatment: soaking the cross-linked and solidified iron-carbon composite material in mineralized bacteria liquid for 5-15min, and drying to obtain the product. Mineralized bacteria form alkaline earth metal carbonate on the surface of the iron-carbon composite material by utilizing alkaline earth metal ions, the alkaline earth metal carbonate is mutually connected and wrapped on the surface of the pellets to finally form a coating structure, so that the strength of the iron-carbon composite material is greatly enhanced; meanwhile, the time of soaking in mineralized bacteria liquid is controlled to be 5-15min, so that mineralized bacteria can only convert part of alkaline earth metal ions on the surface of the iron-carbon composite material, but not excessively convert the alkaline earth metal ions in the iron-carbon composite material, and therefore, the iron-carbon composite material can still maintain the slow release structure of the iron-carbon composite material in the iron-carbon composite material, and the formation of a compact alkaline earth metal carbonate film is avoided to influence the action of active ingredients in the iron-carbon composite material, so that the iron-carbon composite material with high compressive strength and good slow release performance is obtained.
2. According to the preparation method of the iron-carbon composite material, the soaking time of the iron-carbon composite material in the bacterial liquid is controlled to be 5-10min, so that the alkaline earth metal carbonate film structure formed by mineralized bacteria on the surface of the iron-carbon composite material is more reasonable, and the reduction of the active ingredients in the iron-carbon composite material is facilitated.
3. The invention provides a preparation method of an iron-carbon composite material, wherein mineralized bacteria are selected from one or more of myxococcus xanthus, sulfate reducing bacteria, denitrifying bacteria and bacillus pasteurizus. The mineralized bacteria can form alkaline earth metal carbonate films on the surface of the iron-carbon composite material more rapidly, so that the compressive strength of the iron-carbon composite material is improved; the carbon powder is selected from one or two of active carbon and graphite, and can form a micro-electrolysis structure with the iron powder; the alkaline earth metal-containing salt is selected from one or more of calcium chloride, calcium nitrate, zinc chloride and zinc nitrate, and can bond iron powder and carbon powder together with a cross-linking agent into a whole, and simultaneously provides a material basis for mineralization of mineralized bacteria.
4. The invention provides a preparation method of an iron-carbon composite material, which is used for mineralizing the OD of bacterial liquid 600 When the ratio is 1-5, the mineralization speed is favorably controlled, the structure for forming the alkaline earth metal carbonate film is more proper, on one hand, the strength of the iron-carbon composite material is improved, and on the other hand, the reduction effect of the treated sewage is prevented from being lost due to the fact that the dense film is formed by the alkaline earth metal carbonate film to wrap the iron-carbon composite material.
5. The preparation method of the iron-carbon composite material provided by the invention comprises the following steps of controlling the mass ratio of iron powder to carbon powder to cross-linking agent to be (40-80): (10-30): (3-6) improving the oxidation-reduction reaction efficiency of the iron-carbon composite material.
6. According to the preparation method of the iron-carbon composite material, the acid-washed iron powder is used as a raw material, and the oxide film on the surface of the iron powder is removed through acid washing treatment, so that the reduction activity of the iron powder is improved.
7. According to the preparation method of the iron-carbon composite material, provided by the invention, the carbon-iron combination is of a micro-electrolysis structure, so that the electron exchange in a reaction system is accelerated, the oxidation of iron and the reduction of pollutants are promoted, the pollutant treatment capacity is higher, and the efficiency is higher. Meanwhile, the iron powder is separated by the carbon powder, the deposition points of the hydroxide are dispersed, and the reaction activity is kept for a longer time, the main component of the iron-carbon composite material provided by the invention is alginate, organic matters are decomposed by mineralized bacteria, alkaline earth metal carbonate is formed on the surface of carbon-iron under the condition of alkaline earth metal ions, the mechanical strength is obviously increased, the iron-carbon composite material cannot be easily disintegrated in the process of medicament mixing and wall construction, and meanwhile, the wrapped alkaline earth metal carbonate is of a porous structure and cannot prevent the internal iron-carbon material from playing a role.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a photograph showing the appearance of a cross-linked and cured iron-carbon composite material in the preparation method of example 1 of the present invention;
FIG. 2 is an appearance picture of the mineralized bacteria liquid treated iron-carbon composite material prepared by the preparation method of the embodiment 1;
FIG. 3 is a graph showing the relationship between the particle size of the iron-carbon composite material and the different times of soaking in mineralized bacteria liquid in experimental example 3;
FIG. 4 shows the Cr-containing treatment of the iron-carbon composite material immersed in mineralized bacterial liquid for different times for 1h in experimental example 3 6+ After sewage of Cr 6+ A relation diagram of reduction rate and soaking time;
FIG. 5 shows the Cr-containing composition of experimental example 3 after immersing the iron-carbon composite material in mineralized bacteria solution for different periods of time for 3 days 6+ After sewage of Cr 6+ A relation diagram of reduction rate and soaking time;
FIG. 6 is a graph showing the relationship between the time of immersing the iron-carbon composite material in mineralized bacteria liquid and the compressive strength of the iron-carbon composite material in experimental example 3.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The specific experimental procedures or conditions are not noted in the examples and may be followed by the operations or conditions of conventional experimental procedures described in the literature in this field. The reagents or apparatus used were conventional reagent products commercially available without the manufacturer's knowledge.
In the following examples of the invention, the Bacilluspastoris accession numbers: ATCC 11859, available from american type culture collection. Myxococcus xanthus used, accession number: ATCC 25232, available from American type culture Collection.
In the experimental example of the invention, 1000 mug/mL hexavalent chromium solution standard substance is purchased from the company of biological technology of the national institute of advanced and the company of North of the commercial company, and the product number BWZ6851-2016.
In the following examples of the present invention, reduced iron powder was purchased from ultrafine high purity iron powder of alloy materials limited in the middle of south palace; the biological activated carbon powder is obtained from Henan Songshan technology Co., ltd, and comprises peach shell, coconut shell, apricot shell and walnut shell; sodium alginate powder is purchased from Guangzhou Chang device chemical industry Co., ltd., model HG80; graphite powder was purchased from 1000 mesh graphite powder, east Kai graphite Co., ltd.
Example 1
The preparation method of the iron-carbon composite material comprises the following steps:
(1) Acid washing iron powder preparation: grinding 500g of reduced iron powder to 200 meshes, placing in 1000mL of 0.1mol/L hydrochloric acid, stirring for 5min, filtering under reduced pressure, washing with deionized water until the pH value of the filtrate is 7.2, drying in a vacuum oven at 50 ℃ for 2h, and storing in an anaerobic environment;
(2) Crosslinking and curing: grinding the biological activated carbon to 200 meshes to obtain activated carbon powder; taking 375g of dry acid-washing iron powder, 100g of activated carbon powder and 25g of sodium alginate powder to prepare a total of 500g of mixtureMixing the powder, adding into 2kg of 60 ℃ water during stirring, and continuously stirring for 10min, wherein the whole suspension is uniform and free of particle agglomeration and has a certain viscosity to obtain a suspension; the suspension was pumped through a hose with an inner diameter of 0.5mm under stirring at a pump speed of 10mL/min into CaCl having a mass percent concentration of 3% 2 And (3) standing in the solution for 60min, dispersing the iron-carbon composite material by using a sieve with the aperture of 1mm, placing in a vacuum drying oven, and drying at 50 ℃ for 8h to obtain the cross-linked and solidified iron-carbon composite material, preserving the cross-linked and solidified iron-carbon composite material in an oxygen-free manner, randomly taking 25 particles, and measuring the particle size of the cross-linked and solidified iron-carbon composite material within the range of 1.2-3mm by using a vernier caliper, wherein the average particle size is 1.84mm.
(3) Mineralization of mineralization bacteria:
preparing bacterial liquid: weighing and mixing 20g of bacillus barbituric bacteria powder, 20g of ammonium sulfate and 10g of urea, adding 1L of water, adjusting the pH value to 7.54, fermenting and culturing for 72h at 25 ℃ to obtain bacterial liquid OD 600 4.7;
mineralizing: placing the cross-linked and solidified iron-carbon composite material obtained in the step (2) in a screen with the aperture of 1mm, soaking in bacterial liquid for 10min, and taking out;
dispersing and leaching bacterial liquid: placing the iron-carbon composite material in a level oscillating screen, and horizontally oscillating for 60s; the aperture of the upper layer is 3.0mm, so that the dispersion of the iron-carbon composite material is realized; the aperture of the lower layer is 1.5mm, and redundant bacterial liquid is leached out;
and (3) drying: and (3) placing the mineralized iron-carbon composite material in a vacuum drying box, drying at 50 ℃ for 4 hours, and randomly taking 25 particles, wherein the measured particle sizes are all within the range of 1.9-3.5mm, and the average particle size is 2.6mm.
Example 2
The preparation method of the iron-carbon composite material comprises the following steps:
(1) Acid washing iron powder preparation: grinding 500g of reduced iron powder to 400 meshes, placing in 1000mL of 0.05mol/L sulfuric acid, stirring for 4min, filtering under reduced pressure, washing deionized water until the pH value of the filtrate is 7.3, drying in a vacuum oven at 50 ℃ for 2h, and storing in an anaerobic environment;
(2) Crosslinking and curing: grinding graphite to 400 meshes to obtain graphite powder; taking 400g of dry acid-washing iron powder, 50g of graphite powder and 15g of sodium alginate powder, preparing 465g of mixed powder in total, and stirringAdding into 1.86kg of 70 ℃ water, continuously stirring for 10min, and obtaining a suspension, wherein the whole suspension is uniform and free of particle agglomeration and has a certain viscosity; the suspension was pumped through a hose having an inner diameter of 0.5mm under stirring at a pump speed of 5mL/min into ZnCl having a mass percentage concentration of 2% 2 And (3) standing for 30min, dispersing the iron-carbon composite material by using a sieve with the aperture of 1mm, placing in a vacuum drying oven, and drying at 40 ℃ for 10h to obtain the cross-linked and solidified iron-carbon composite material, preserving the cross-linked and solidified iron-carbon composite material in an oxygen-free manner, randomly taking 25 particles, and measuring the particle size of the cross-linked and solidified iron-carbon composite material within the range of 1.2-3mm by using a vernier caliper, wherein the average particle size is 1.82mm.
(3) Mineralization of mineralization bacteria:
preparing bacterial liquid: weighing 25g of myxococcus xanthus bacterial powder, 20g of ammonium sulfate and 12g of urea, mixing, adding 1L of water, adjusting the pH value to 6.55, fermenting and culturing at 28 ℃ for 36h to obtain bacterial liquid OD 600 3.2;
mineralizing: placing the cross-linked and solidified iron-carbon composite material obtained in the step (2) in a screen with the aperture of 1mm, soaking in bacterial liquid for 5min, and taking out;
dispersing and leaching bacterial liquid: placing the iron-carbon composite material in a level oscillating screen, and horizontally oscillating for 30s; the aperture of the upper layer is 2.0mm, so that the dispersion of the iron-carbon composite material is realized; the aperture of the lower layer is 0.5mm, and redundant bacterial liquid is leached out;
and (3) drying: and (3) placing the mineralized iron-carbon composite material in a vacuum drying box, drying at 60 ℃ for 3 hours, randomly taking 25 particles, and measuring the particle size by using a vernier caliper to be in the range of 1.5-3.3mm, wherein the average particle size is 2.19mm.
Example 3
The preparation method of the iron-carbon composite material comprises the following steps:
(1) Acid washing iron powder preparation: grinding 500g of reduced iron powder to 300 meshes, placing in 1000mL of 0.5mol/L phosphoric acid, stirring for 3min, filtering under reduced pressure, washing the filtrate with deionized water until the pH value is 7.1, drying in a vacuum oven at 50 ℃ for 3h, and storing in an anaerobic environment;
(2) Crosslinking and curing: grinding the biological activated carbon to 300 meshes to obtain activated carbon powder; 200g of dry acid-washing iron powder, 150g of activated carbon powder and 30g of sodium alginate powder are taken to prepare 380g of mixed powder in total, and stirredAdding 2.53kg of 50 ℃ water into the mixture, continuously stirring for 15min, and obtaining a suspension, wherein the whole suspension is uniform and free of particle agglomeration and has a certain viscosity; the suspension was pumped through a hose having an inner diameter of 0.5mm under stirring at a pump speed of 15mL/min into CaCl having a concentration of 6% by mass 2 And (3) standing in the solution for 90min, dispersing the iron-carbon composite material by using a sieve with the aperture of 1mm, placing in a vacuum drying oven, and drying at 60 ℃ for 6h to obtain the cross-linked and solidified iron-carbon composite material, preserving the cross-linked and solidified iron-carbon composite material in an oxygen-free manner, randomly taking 25 particles, and measuring the particle size of the cross-linked and solidified iron-carbon composite material within the range of 1.2-3mm by using a vernier caliper, wherein the average particle size is 1.80mm.
(3) Mineralization of mineralization bacteria:
preparing bacterial liquid: weighing 30g of bacillus barbitarus bacterial powder, 15g of ammonium sulfate and 15g of urea, mixing, adding 1L of water, adjusting pH to be 9.0, and fermenting and culturing for 24 hours at 37 ℃ to obtain bacterial liquid OD 600 1.5;
mineralizing: placing the cross-linked and solidified iron-carbon composite material obtained in the step (2) in a screen with the aperture of 1mm, immersing the material in a bacterial liquid for 7min, and taking out the material;
dispersing and leaching bacterial liquid: placing the iron-carbon composite material in a level oscillating screen, and horizontally oscillating for 45s; the aperture of the upper layer is 4.0mm, so that the dispersion of the iron-carbon composite material is realized; the aperture of the lower layer is 3.0mm, and redundant bacterial liquid is leached out;
and (3) drying: and (3) placing the mineralized iron-carbon composite material in a vacuum drying box, drying at 40 ℃ for 5 hours, randomly taking 25 particles, and measuring the particle size by using a vernier caliper to be in the range of 1.7-3.3mm, wherein the average particle size is 2.47mm.
Example 4
The present embodiment provides a method for preparing an iron-carbon composite material, which is different from embodiment 1 in that the mineralization treatment in step (3) is performed, the iron-carbon composite material after cross-linking and curing is immersed in a bacterial liquid for 15min, and the other steps and parameter conditions are the same.
Comparative example 1
The comparative example provides a method for preparing an iron-carbon composite material, which is different from example 1 only in that mineralization step of mineralization bacteria is omitted, and other steps and parameter conditions are the same.
Comparative example 2
The comparative example provides a method for preparing an iron-carbon composite material, which is different from the method in the embodiment 1 in that the mineralization treatment in the step 3 is carried out, the iron-carbon composite material after crosslinking and solidification is immersed in bacterial liquid for 1min, and the rest steps and parameter conditions are the same.
Comparative example 3
The comparative example provides a method for preparing an iron-carbon composite material, which is different from the method in the embodiment 1 in that the mineralization treatment in the step 3 is carried out, the iron-carbon composite material after crosslinking and solidification is immersed in bacterial liquid for 30min, and the rest steps and parameter conditions are the same.
Comparative example 4
The comparative example provides a method for preparing an iron-carbon composite material, which is different from example 1 in that the iron-carbon composite material is prepared by sintering and solidifying in the step (2), and the rest steps and parameters are the same. The sintering and curing steps are as follows:
grinding the biological activated carbon to 200 meshes to obtain activated carbon powder; taking 375g of dry acid-washed iron powder, 100g of activated carbon powder, 135g of water and 340RF 75g of bear brand heat stabilizer, mixing 685g of mixed powder, and granulating by a disc granulator after mixing; then heating to 200 ℃ under the anaerobic condition, sintering for 30min, and cooling to room temperature in a vacuum drying environment.
Experimental example 1
The iron-carbon composite materials prepared in examples 1-4 and comparative examples 1-2 were subjected to compressive strength testing, and were measured according to GB/T10516-2012 measurement of average crushing resistance of nitrophosphate granules;
simultaneously, 10g of the iron-carbon composite material is respectively weighed and placed in 100mL of Cr with the concentration of 30mg/L 6+ After 3 days in solution, the shape of the iron-carbon composite was observed, and the results are shown in table 1.
Table 1 compressive strength and shape after use of different iron-carbon composites
As can be seen from the data in the table, the alkaline earth metal carbonate protective film is formed on the surface of the iron-carbon composite material by mineralization bacteria mineralization technology, so that the compressive strength of the iron-carbon composite material is obviously improved, and the mechanical strength requirement of in-situ injection or permeation type reaction wall technology can be met; after the iron-carbon composite material is used for 3 days, the original shape can be still maintained, no disintegration or crushing phenomenon exists, and the iron-carbon composite material can continuously play a role in treating sewage. The mineralization treatment step of mineralization bacteria is omitted in comparative example 1, the mineralization treatment time of mineralization bacteria in comparative example 2 is 1min, the compressive strength of the iron-carbon composite material is low, the iron-carbon composite material disintegrates after being used for 3 days, the sewage treatment effect cannot be continuously exerted, and further, the mineralization treatment can improve the strength of the iron-carbon composite material, so that the iron-carbon composite material maintains the original shape, and the service life is prolonged.
Experimental example 2
Examining the capacity of the iron-carbon composite material prepared in examples 1-4 and comparative examples 3-4 for sewage treatment, the specific method is as follows: 10g of the iron-carbon composite material is respectively weighed and placed in a conical flask, and 100mL of 30mg/L Cr is added 6+ Placing the conical flask in a shaker, shaking at 110rpm for 1 hr, and sampling to determine Cr according to GB/T7467-1987 method for determining dibenzoyl dihydrazide spectrophotometry for determining hexavalent chromium in water quality 6+ Is a concentration of (2); then standing, sampling at 12h, 24h, 48h and 72h respectively, and measuring Cr 6+ Calculating the concentration of Cr 6+ The reduction rate and the result are shown in Table 2.
Cr 6+ Reduction rate (%) = (Cr in the sewage before treatment) 6+ Concentration of Cr in treated wastewater 6+ Concentration of (2)/Cr in the pre-treatment wastewater 6+ Is a concentration of (3).
Wherein, 30mg/L Cr 6+ The preparation method of the solution comprises the following steps: taking 3mL of 1000 mug/mL hexavalent chromium solution standard substance, and adding water to fix the volume to 100 mL.
TABLE 2 reduction of Cr by different iron carbon composites 6+ Capability of
As can be seen from the data in the table, the mineralization time of the embodiment 1-4 is 5-15min, and the obtained iron-carbon composite material can effectively treat Cr in sewage 6+ . The mineralization time of the comparative example 3 is 30min, and the coating time is too long, so that an alkaline earth metal carbonate film formed on the surface of the iron-carbon composite material is compact and cannot be contacted with sewage for sewage restoration, and the hexavalent chromium restoration efficiency is obviously reduced; comparative example 4 an iron-carbon composite material was prepared by sintering and curing, and then mineralized in the same manner, but the effect of treating sewage was poor because the slow-release channels inside the iron-carbon composite material were closed by sintering and curing.
Experimental example 3
The cross-linked and solidified iron-carbon composite material was prepared according to the preparation method of example 1, and was divided into 7 groups, wherein one group was not mineralized by mineralization bacteria (recorded as 0 min), the other 6 groups were mineralized by mineralization bacteria, and immersed in mineralization bacteria liquid for 5, 10, 15, 30, 60, 120min, respectively, and the other step parameters were the same as those of example 1. Examining particle size and Cr of iron-carbon composite material with different mineralization time 6+ Influence of reducing ability and compressive strength, wherein compressive strength and Cr 6+ The reducing power was measured by a vernier caliper for the same manner as in examples 1 and 2, and 5 particles were randomly selected from each group, and their straight particle diameters were measured, and the average value was obtained, and the results are shown in Table 3 and FIGS. 3 to 6.
TABLE 3 influence of different soaking times on the iron-carbon composite properties
As can be seen from the above table data, regarding the particle size of the iron-carbon composite material, calcium carbonate films are formed on the surface of the iron-carbon composite material due to mineralization of mineralization bacteria, and the growth process of the calcium carbonate films can be simplified into three stages: during the contact period before 5min, the microorganisms just contact with the calcium ions on the surface of the slow-release material at this stage, and the calcium carbonate film is relatively slow to synthesize due to the lack of crystal nuclei and supporting frameworks. After the fast growth period of 5-60min and the contact of the first 5min, the microbe synthesizes calcium carbonate in several points on the surface of the slow released material, and the subsequent microbe synthesizes great amount of calcium carbonate with 5min of the synthesized calcium carbonate as crystal nucleus and skeleton and gradually connects to form complete calcium carbonate coating. In the stable period of more than 60 minutes, calcium carbonate formed in the early stage gradually forms a cover on the surface of the particles, so that external microorganisms are prevented from continuously reacting with calcium ions released inside the particles, and further, calcium carbonate cannot be continuously formed to wrap the surfaces of the particles, and therefore, the particle size tends to be stable and unchanged.
For Cr at 1h 6+ The reduction rate, although the calcium carbonate coating formed in the initial stage of mineralization has a large influence on the particle size, is not a dense calcium carbonate structure, so that the reduced material in the iron-carbon composite material can be released. However, after 15min, the generation of calcium carbonate is to simultaneously increase the particle size and the density of the calcium carbonate film, so that the internal reduced iron-carbon composite material is more and more difficult to release, and the reduction effect is gradually weakened.
Treatment of Cr 6+ After 3 days, the treatment immersed for less than 15 minutes still has further reduction effect in the standing process, and the treatment longer than 15 minutes hardly reduces Cr further 6+ . It is shown that the calcium carbonate produced by long-term immersion is dense, preventing the release of the internal reducing material.
The change of the mineralized film compactness degree can be clearly seen for the compressive strength. The mineralized film generated before 5min has low strength, and between 10 and 60min, the mineralized film grows rapidly and becomes more compact, so that the compressive strength of the material is obviously increased, and the hardness is obviously improved.
In summary, the immersion time is controlled to be 5-15min, especially 5-10min, on the one hand, the generated calcium carbonate does not seal the surface of the pellets, and the reduction effect of the material can be maintained; on the other hand, the compressive strength of the iron-carbon composite material can be improved to a certain extent, and the material is prevented from being broken in the use process.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (10)
1. The preparation method of the iron-carbon composite material is characterized by comprising the following steps of:
and a cross-linking and curing step: crosslinking and solidifying the iron powder and the carbon powder by adopting alkaline earth metal salt and a crosslinking agent;
mineralizing treatment: soaking the cross-linked and solidified iron-carbon composite material in mineralized bacteria liquid for 5-15min, and drying to obtain the iron-carbon composite material;
the cross-linking agent is sodium alginate;
the mineralized bacteria liquid OD 600 1-5;
the mass ratio of the iron powder to the carbon powder to the cross-linking agent is (40-80): (10-30): (3-6).
2. The method of claim 1, wherein the soaking time is 5-10min.
3. The preparation method according to claim 1 or 2, wherein the mineralization bacteria are selected from one or more of myxococcus xanthus, sulfate reducing bacteria, denitrifying bacteria, and bacillus pasteurizus;
and/or the carbon powder is selected from one or two of active carbon and graphite;
and/or the alkaline earth metal salt is selected from one or two of calcium chloride and calcium nitrate.
4. The method according to claim 1, wherein the mineralization bacterial liquid OD 600 1-3.
5. The production method according to claim 1 or 2, wherein the crosslinking curing step comprises: mixing iron powder, carbon powder, a cross-linking agent and water, adding the mixture into alkaline earth metal salt solution, standing, separating solid from liquid, and drying to obtain the cross-linked and solidified iron-carbon composite material.
6. The method of manufacturing according to claim 1 or 2, characterized in that the iron powder is a pickled iron powder.
7. The method of producing the acid-washed iron powder according to claim 6, comprising: soaking iron powder in 0.05-0.5mol/L acid solution for at least 3min, separating solid from liquid, and washing to neutrality.
8. The method according to claim 5, wherein the alkaline earth metal salt solution has a mass percentage concentration of 2 to 6%.
9. An iron-carbon composite material prepared by the preparation method of any one of claims 1 to 8.
10. The use of the iron-carbon composite material prepared by the preparation method of any one of claims 1 to 8 in sewage treatment.
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