CN114477698B - Application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas - Google Patents
Application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas Download PDFInfo
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- B01J2220/4812—Sorbents characterised by the starting material used for their preparation the starting material being of organic character
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- B01J2220/4875—Sorbents characterised by the starting material used for their preparation the starting material being a waste, residue or of undefined composition
- B01J2220/4887—Residues, wastes, e.g. garbage, municipal or industrial sludges, compost, animal manure; fly-ashes
Abstract
The invention discloses an application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas, wherein the cyanobacteria-based biochar is prepared by firstly adopting a hot-pressing filtering technology to process cyanobacteria mud, and an obtained cyanobacteria filter cake is rich in iron ions and organic matters and can be used for preparing the cyanobacteria-based biochar with an iron catalysis function, and the biochar can be applied to flue gas treatment containing zero-valent mercury; and mixing the obtained blue algae filtrate with municipal sludge, feeding the mixture into a filter press, carrying out secondary filter pressing to obtain a sludge filter cake and secondary filtrate, drying the sludge filter cake, and then using the dried sludge filter cake for incineration power generation to realize resource utilization, wherein the secondary filtrate is brought into a wastewater treatment system. The blue algae filtrate and the municipal sludge are cooperated with the deep dehydration method, so that the pollution components in the blue algae filtrate are reduced by utilizing the adsorption effect of the municipal sewage, the municipal sludge is flocculated by utilizing soluble iron ions in the blue algae filtrate, the deep dehydration of the municipal sludge is facilitated, and the processing difficulty of the blue algae filtrate is reduced.
Description
Technical Field
The invention relates to application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas, and belongs to the field of environmental engineering.
Background
The water content of the obtained algae mud is still as high as 85-95 percent after the primary dehydration treatment of mechanical wall breaking, flocculation sedimentation and centrifugal separation is carried out on the blue algae slurry salvaged to the shore. The high-water-content algae mud is not beneficial to subsequent drying incineration treatment and resource utilization, and needs to be further deeply dehydrated to the water content of about 60 percent.
Patent CN110342779A (an integrated method for sludge and algae mud cooperative treatment) and patent CN111807626A (a wastewater treatment system and process for sludge and blue algae cooperative deep dehydration) disclose an integrated method for sludge and algae mud cooperative treatment, which directly mixes municipal sludge and blue algae mud, then adds calcium oxide and ferric chloride, and carries out filter pressing under alkaline conditions. Although this process can improve the dehydration performance of the cyanobacteria puree, the obtained filter cake contains a large amount of inorganic substances due to the addition of a large amount of calcium oxide before dehydration, and further resource utilization is difficult. The obtained filtrate contains a large amount of calcium ions, which brings adverse effects to the subsequent water treatment process.
The conventional deep dehydration process of the blue algae mud needs to add ferric chloride, a large amount of calcium oxide and dilution water, the content of inorganic components in the obtained algae cake reaches 40-60% of the total dry mass, the combustion heat value of the algae cake is reduced, and the subsequent resource utilization is not facilitated. The hot pressing filtration technology reduces the viscosity of the algae mud by heating the raw materials, releases the macromolecular polymer outside the blue algae cells, can effectively reduce the usage amount of the flocculating agent and the coagulant aid, can reserve the characteristic of high organic matter content of the blue algae cells, and can further expand the resource treatment of the blue algae mud to lay a material foundation. By cooperatively treating the blue algae mud heat filter pressing filtrate and the municipal sludge, the comprehensive cost of the blue algae mud heat filter pressing process can be further reduced, the difficulty in treating the blue algae mud heat filter pressing filtrate is reduced, and the aims of saving energy, reducing consumption and expanding the blue algae mud resource utilization approach are fulfilled.
Mercury in flue gas discharged from coal combustion is one of the main sources of mercury pollution, and accounts for about 25% of the total mercury discharge. Mercury is present in flue gas in three main forms: zero valent mercury (Hg) 0 ) Bivalent mercury (Hg) 2+ ) And mercury (Hg) in particulate form P ). Wherein Hg is 2+ And Hg P Can be respectively removed by a wet denitration device and a dust removal device, and the rest Hg 0 Is difficult to remove from the smoke due to the characteristics of water insolubility and volatility. The method of spray addition of activated carbon or biochar is considered to be the most promising. Compared with common biocharThe blue algae-based biochar obtained by using the blue algae mud already contains more abundant functional group types and higher nitrogen content, is beneficial to the metal catalytic reaction and adsorption process, and can be applied to Hg in smoke 0 And (4) removing.
Disclosure of Invention
In order to solve the problems, the invention provides an application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas, the preparation of the cyanobacteria-based biochar is that cyanobacteria mud is treated by a hot pressing filtration technology, the cyanobacteria filter cake is rich in iron ions and organic matters, the cyanobacteria-based biochar can be used for preparing the cyanobacteria-based biochar with an iron catalysis function, and the biochar can be applied to flue gas treatment containing zero-valent mercury; simultaneously, the obtained blue algae filtrate can be mixed with municipal sludge, so that the pollution components in the blue algae filtrate can be reduced by utilizing the adsorption effect of municipal sewage, and the municipal sludge is flocculated by utilizing soluble iron ions in the blue algae filtrate, thereby being beneficial to deep dehydration of the municipal sludge and reducing the treatment difficulty of the blue algae filtrate.
In order to achieve the purpose, the specific technical scheme of the invention is as follows:
the invention provides an application of ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas,
the ferric chloride mediated cyanobacteria-based biochar takes cyanobacteria mud as a raw material;
the application method comprises the following steps: removing zero-valent mercury pollutants in the flue gas by using blue algae-based biochar through an adsorption fixed bed system;
the ferric chloride mediated cyanobacteria-based biochar is prepared by the following method:
(3) Putting the cyanobacteria mud into a closed container, adding ferric chloride, stirring, and carrying out first thermal filter pressing to obtain a cyanobacteria filter cake containing ferric salt and a cyanobacteria filtrate;
(4) And adding a saturated KOH solution into the blue algae filter cake, kneading, neutralizing, drying and pyrolyzing to obtain the blue algae-based biochar.
The application is further that the specific surface area of the cyanobacteria-based biochar is 20m 2 /g～200m 2 Per g, pore volume 0.02cm 3 /g～0.2cm 3 /g。
In the application, further, in the step (1), the cyanobacteria mud is from a cyanobacteria water separation station, the solid content is 5-15% (w), and the cyanobacteria mud can be salvaged and primarily dehydrated on the same day, or can be from an aged cyanobacteria mud of a storage pool with an aging period of 3-60 days.
The application further comprises the specific steps that in the step (1), the cyanobacteria mud is placed in a closed container, ferric chloride is added and stirred, and the cyanobacteria filter cake containing the ferric salt and the cyanobacteria filtrate are obtained through first hot press filtration: introducing steam into the closed container, heating the blue algae mud to 80-95 ℃, adding 1.5% -2.5% of ferric chloride, stirring and mixing, pumping the blue algae mud into a filter press, deeply dehydrating under the condition of 0.2-1.5 MPa, and performing first filter pressing to obtain a blue algae filter cake and blue algae filtrate.
The application is further that in the step (2), the specific method for preparing the ferric chloride mediated cyanobacteria-based biochar by adding a saturated KOH solution into the cyanobacteria filter cake, kneading, neutralizing, drying and pyrolyzing the mixture comprises the following steps: adding 40% (w/v) KOH solution into the blue algae filter cake, kneading and uniformly mixing, adjusting the pH of the mixture to be neutral, then sending the mixture into drying equipment for drying at 105-135 ℃, obtaining blue algae powder after drying, and then pyrolyzing at 450-800 ℃ to obtain the blue algae-based charcoal.
In the application, further, the pyrolysis method at 450-800 ℃ is specifically that the temperature in the rotary furnace is increased to 450 ℃ at the speed of 10 ℃/min, the temperature is kept at 450 ℃ for 60min, then the temperature is continuously increased to 800 ℃ at the speed of 10 ℃/min, and then the temperature is kept at 800 ℃ for activation for 60min.
The application further comprises the step of treating the blue algae filtrate obtained in the step (1) by the method comprising the following steps: mixing the blue algae filtrate with municipal sludge, feeding the mixture into a filter press, carrying out secondary filter pressing to obtain a sludge filter cake and secondary filtrate, and further drying the sludge filter cake for subsequent resource utilization, so as to apply the sludge filter cake to incineration power generation; the secondary filtrate is brought into a wastewater treatment system;
the application is further characterized in that the municipal sludge is derived from excess sludge of municipal sewage treatment plants, and the solid content is 10-20% (w); the blue algae filtrate is mixed with the municipal sludge while the filtering temperature is kept at 70-90 ℃, and the volume mixing ratio is as follows: the municipal sludge is = 1.0-3.0, calcium oxide is added, the pH is adjusted to 5.0 by stirring, and the temperature of the blue algae filtrate is kept between 50 ℃ and 75 ℃ after the blue algae filtrate is mixed with the municipal sludge.
In the above application, further, the second pressure filtration is carried out under the condition of 0.2-1.5 MPa; the solid content of the sludge filter cake is 30-40%.
The application method further comprises the following steps: removing zero-valent mercury pollutants in the flue gas by using blue algae-based biochar through an adsorption fixed bed system; the concentration of the zero-valent mercury in the mercury-containing flue gas is 20-100 mu g/m 3 The gas flow rate of the adsorbent per unit mass is 1-10L/g.min, and the adsorption temperature is 120-180 ℃.
Advantageous effects
5. The blue algae mud treated by the hot pressing filtration process can realize deep dehydration of the blue algae mud under the condition of adding a small amount of ferric chloride, the content of inorganic matters in the obtained blue algae filter cake is low, the characteristic that the blue algae filter cake is high in organic matters is kept, the basic condition can be laid for subsequent resource utilization of the blue algae filter cake, the blue algae filter cake can be used for preparing blue algae-based biochar, and the obtained blue algae-based biochar can be applied to removal of pollutants such as zero-valent mercury in smoke and can also be applied to sewage treatment.
6. Iron ions in the blue algae filter cake and macromolecular substances in blue algae are chelated to form metalloid organic framework Material (MOF) molecules, and fine iron oxide compound crystals are formed under the catalytic action of KOH in the pyrolysis process and are dispersed in the blue algae-based biochar to form fine granular ferrite compounds, so that the fine granular ferrite compounds are favorable for carrying out redox reaction with zero-valent mercury in flue gas, are converted into granular mercury and are retained in the blue algae-based biochar.
7. The blue algae-based biochar prepared by the method plays an adsorption role of the blue algae-based biochar and a reaction role of a ferrite compound in a mercury-containing flue gas treatment process, and the removal efficiency of zero-valent mercury is remarkably improved.
8. The blue algae filtrate contains iron ions, municipal sludge can be flocculated, the deep dehydration of the municipal sludge is facilitated, and meanwhile the municipal sludge can adsorb pollutants in the blue algae filtrate, particularly adsorb biological resistant substances, and the biodegradability of the secondary filtrate is facilitated to be improved.
Drawings
FIG. 1 is a process flow diagram of synergistic treatment of cyanobacteria mud and municipal sludge
FIG. 2 scanning electron microscope image of cyanobacteria-based biochar prepared from cyanobacteria mud
FIG. 3 shows the effect of blue algae-based biochar in removing zero-valent mercury in waste gas
FIG. 4 Effect of different dewatering treatment methods on municipal sludge dewatering
Detailed Description
Total Hg 0 Removal efficiency (. Eta.) T )、Hg 0 Adsorption efficiency (. Eta.) ads ) And Hg 0 Efficiency of oxidation (. Eta.) oxi ) The definition is as follows:
in the formula, the first step is that,
and
respectively representing the concentration of zero-valent mercury in the inlet flue gas and the outlet flue gas;
representing the concentration of total mercury in the outlet flue gas. t represents the reaction time for each set of experiments, and in our work t =180min. BCs to Hg 0 Is calculated by equation 4, Q (μ g/g) represents the adsorption capacity of the carbon material; v represents the flue gas flow rate (v = 0.5L/min); m represents the mass of the adsorbent (m =50 mg).
The invention discloses a method for preparing blue algae-based biochar from dehydrated blue algae and applying the biochar to Hg 0 And (3) an adsorption process. Deep dehydration of ferric chloride in blue algae, preparation of blue algae-based biochar and Hg 0 The removal plays a key role in flocculation, activation and reaction respectively.
Example 1
The processing process flow for preparing the cyanobacteria-based biochar by using the cyanobacteria mud is shown in figure 1, and the specific method comprises the following steps:
(1) Heating 100kg of blue algae mud with solid content of 10%, heating to 90 deg.C, adding 6.7L of 30% ferric chloride solution, stirring and mixing completely, pumping to hot pressing filter for first deep dehydration, wherein the feeding pressure and the filter pressing time are 0.1MPa and 20min in turn; 0.2MPa,10min;0.4MPa,10min;0.6MPa,10min;1.0MPa,10min; squeezing under 1.2MPa for 20min to obtain 34kg blue algae filter cake and 72L blue algae filtrate.
(2) And (3) taking 34kg of blue algae filter cake obtained by the hot filter pressing process, and stirring about 0.5L of saturated 40% (w/v) KOH solution in a kneader in a spraying manner to enable the pH value of the blue algae filter cake to be close to neutral. The blue algae filter cake is crushed into small particles and then is sent into a drier for drying, and blue algae powder with the water content of about 10% -15% is obtained. Preparing granules with the diameter of 8mm and the length of 20-50 mm by using a ring die granulator, and then sending the granules into a rotary furnace for carbonization in nitrogen atmosphere, wherein the carbonization process comprises the following steps: the temperature in the rotary furnace is increased to 450 ℃ at the speed of 10 ℃/min, and is kept at 450 ℃ for 60min; and then, continuously heating to 800 ℃ at the speed of 10 ℃/min, and then keeping at 800 ℃ for activating for 60min to prepare the blue algae-based biochar. The obtained blue algae-based biochar is crushed by a crusher to obtain powdered biochar, the granularity is about 200-400 meshes, and the powdered biochar can be applied to purification treatment of mercury-containing flue gas. The different raw material compositions and the product surface properties of the biochar prepared by using the cyanobacteria sludge are shown in table 1.
TABLE 1 raw material composition and code for preparing blue algae-based biochar from blue algae mud
The electron scanning microscope photograph of the cyanobacteria-based biochar prepared from different raw material compositions is shown in fig. 2, and the cyanobacteria-based biochar (code number BCF, fig. 2 b) prepared by adding ferric chloride and the cyanobacteria-based biochar (code number BC, fig. 2 a) prepared from single cyanobacteria mud have a rougher surface and show a larger specific surface area. Furthermore, after a ferric chloride flocculant is added and a hot-pressing filtration dehydration process is performed, a blue algae filter cake is obtained, the pH value is adjusted to be neutral by KOH, the obtained ferric hydroxide, blue algae cells and macromolecular substances thereof form a structure of a metal organic framework composite (MOF), in a drying process, part of ferric chloride reacts with KOH to generate a ferric oxide compound, the ferric oxide compound and the ferric chloride compound are uniformly dispersed in blue algae powder, and in a process of preparing blue algae-based biochar through pyrolysis, more ferric oxide is formed and well dispersed in the obtained blue algae-based biochar (figure 2 c). The obtained blue algae-based biochar has better specific surface area and porosity, and the specific surface area can reach 195.82m 2 /g。
Example 2
In order to verify the adsorption performance of the prepared blue algae-based biochar and the mercury removal efficiency of the blue algae-based biochar in the flue gas treatment process, the prepared blue algae-based biochar is put into a quartz reactor, and the reactor is communicated with a gas inlet and a gas outlet. Flue gas composition (nitrogen 78%, oxygen 21%, hydrogen chloride 10ppm, mercury 10 μ g/m) 3 ) Then, the temperature is raised to 150 ℃ by an electric furnace at a heating rate of 10 ℃/min for heat preservation, namely Hg 0 The removal reaction provides the required temperature. After the temperature of the electric furnace is stabilized at 150 ℃, opening a gas inlet valve switch, and keeping the flow of inlet gas at 0.5L/min by a flow control program, wherein N is simultaneously added 2 As balance gas to keep inlet flue gas flow stable. After blue algae-based biochar adsorption, hg in the flue gas is discharged 0 The concentration of the (D) is detected on line by using a cold vapor atomic absorption spectrophotometer (CVAAS, lumex R-915M), and the obtained product is indirectly condensed by ice water and then discharged. The Hg0 removal amount of different cyanobacteria-based biochar under different conditions is shown in the following table 2:
TABLE 2 blue algae-based biochar for Hg under different conditions 0 Amount of removal of
As can be seen from Table 2, hg of cyanobacterial-based biochar (code BC) prepared from single cyanobacterial mud 0 The removal capacity is the worst, and is only 25.91 mu g/g; via FeCl 3 Activated cyanobacteria-based biochar (code number BCF) for Hg 0 The removal of the sodium-zinc-manganese-zinc alloy is obviously improved and is increased from 25.91 to 73.55 mu g/g; in contrast, KOH and FeCl 3 The blue algae-based biochar (code number BCFK) obtained by co-activation shows the effect on Hg 0 The best removal capacity is 85.91 mu g/g, which is 3.3 times of the removal capacity of the cyanobacteria-based biochar prepared from single cyanobacteria mud.
FIG. 3a shows different cyanobacterial-based biochar in N 2 +O 2 Hg under HCl atmosphere 0 Outlet concentration of (2). As the reaction proceeded, the outlet Hg of BC was found 0 The concentration gradually increased. In contrast, outlet Hg of BCF and BCFK 0 The concentration is relatively stable. Hg at outlet of BCFK even when the reaction proceeded to 390min (FIG. 3 b) 0 No significant increase in concentration occurred. This shows that the blue algae-based biochar passes through KOH and FeCl 3 Removal of Hg after co-activation 0 Showing good stability.
FIGS. 3c and 3d show Hg in outlet flue gas from BCFK, respectively 2+ In relation to Hg 0 The adsorption and oxidation efficiency of (a). In the first reaction stage (0-20 min), the outlet total mercury concentration was lowest. This indicates that BCFK is on Hg 0 The adsorption of (b) is most pronounced at this stage. In addition, a large amount of Hg was detected in the outlet flue gas 2+ It shows that the oxidation and the adsorption both act on Hg 0 The removal contributes. The outlet total mercury concentration then gradually increases. The outlet concentration stabilized at 95. Mu.g/m when the test was run for 40min 3 Left and right and held until the end of the experiment. However, the outlet Hg 0 The concentration rose slowly during this phase (40-180 min), indicating that the adsorption sites gradually tended to saturate. During the whole reaction process, hg in the total mercury is discharged 2+ The ratio of the mercury to the mercury is up to 80 percent and is obviously higher than the Hg at the outlet 0 The concentration of (c). This indicates that the oxidation active site is in Hg 0 The removal process plays a major role.
Example 3
The flow of the blue algae filtrate and municipal sludge collaborative dehydration treatment process is shown in figure 1, and the specific method is as follows:
stirring and mixing the blue algae filtrate obtained in the example 1 and municipal sludge with the water content of 80% according to a volume ratio of 2; 0.2MPa,10min;0.4MPa,10min;0.6MPa,10min;1.0MPa,10min; and then pressing for 20min under the condition of 1.2MPa to obtain 91L of secondary filtrate and 17kg of sludge filter cake. The obtained sludge filter cake is dried and then sent to a sludge treatment plant for incineration, and can be used for power generation. And sending the secondary filtrate to a biochemical treatment workshop for further treatment and discharging the secondary filtrate through a nano pipe.
The conventional deep dehydration process comprises the following steps: taking 100kg of blue algae mud with the solid content of 10 percent and 33.3kg of municipal sludge with the solid content of 20 percent, adding 122L of water, stirring and mixing completely, then adding 3.6L of 30 percent ferric chloride solution and 7.67kg of calcium oxide, stirring and mixing completely, pumping into a filter press for filter pressing and deep dehydration, wherein the feeding pressure and the filter pressing time are 0.1MPa and 20min in sequence; 0.2MPa,10min;0.4MPa,10min;0.6MPa,10min;1.0MPa,10min; squeezing under 1.2MPa for 20min to obtain 153L filtrate and 113kg filter cake. Adding 44L of water, 0.7L of 30% ferric chloride and 0.85kg of calcium oxide into the residual 26.7kg of municipal sludge, stirring and mixing completely, pumping into a filter press for filter pressing deep dehydration, wherein the feeding pressure and the filter pressing time are 0.1MPa and 20min in sequence; 0.2MPa,10min;0.4MPa,10min;0.6MPa,10min;1.0MPa,10min; squeezing under 1.2MPa for 20min to obtain 50L filtrate and 21kg filter cake.
Through the synergistic treatment and the adsorption effect of the municipal sludge, the concentration and the total amount of pollutants in the blue algae filtrate obtained by the first hot filter pressing are obviously reduced, the pH value also tends to be neutral, and the indexes of the pollutants in the blue algae filtrate and the second filtrate are shown in the table 3. The cooperative treatment method is to reuse the blue algae filtrate for municipal sludge, and can reduce the generation of the total filtrate and the pollutant concentration in the filtrate when deep dehydration is carried out. The filtrate amount generated by the synergistic treatment method is 45 percent less than that of the conventional deep dehydration process, the COD content is 56.6 percent less, the concentration of other pollutants is reduced in different degrees, and the treatment difficulty of the blue algae filtrate is reduced. The concentration change of the pollutants in the filtrate is large and is caused by inconsistent rotting degrees of the cyanobacteria mud, and intracellular substances are released after the cyanobacteria mud is rotted, so that the concentration fluctuation of the pollutants in the filtrate is large. And secondly, when the municipal sludge is treated by the synergistic treatment process, only a small amount of calcium oxide is added to adjust the pH value, so that the cost of chemical agents of the conventional deep dehydration process of the municipal sludge is reduced on the premise of achieving the dehydration effect. Finally, the filter cake obtained by deep dehydration of the cooperative treatment process has the potential of resource utilization due to only adding a small amount of ferric chloride, has high heat value and can be prepared into blue algae-based biochar for adsorbing heavy metals, and the filter cake of the conventional deep dehydration process is not beneficial to further resource utilization due to high content of inorganic matters.
TABLE 3 comparison of the synergistic treatment Process with the conventional deep dehydration Process
Note: the raw materials for treatment are 100kg of blue algae mud with a solid content of 10% and 60kg of municipal sludge with a solid content of 20%.
In order to further prove the synergistic deep dehydration effect of the blue algae filtrate and the municipal sludge, a control group is respectively arranged1: mixing municipal sludge and water until the solid content is 6%, and then performing pressure filtration and dehydration under the condition of 0.2 MPa; control group 2: mixing municipal sludge and water until the solid content is 6%, adding ferric chloride accounting for 5% of the dry weight of the municipal sludge and calcium oxide accounting for 20%, stirring and mixing completely, and performing pressure filtration and dehydration under the condition of 0.2 MPa; experimental group a: mixing the blue algae hot-pressing filtration filtrate with municipal sludge until the solid content is 6%, and then performing pressure filtration and dehydration under the condition of 0.2 MPa. FIG. 4 compares the effect of the above different filter pressing conditions on the municipal sludge deep dewatering effect. In the industrial treatment process, the municipal sludge is deeply dehydrated under the common condition that 2 times of water and a small amount of ferric chloride and calcium oxide are added and then subjected to pressure filtration. The most common municipal sludge deep dehydration process is to add ferric chloride accounting for 3-5% of the dry weight of the sludge and calcium oxide accounting for 10-20% of the dry weight of the sludge, so as to be beneficial to ensuring the dehydration efficiency of the municipal sludge. As can be seen from FIG. 4, the deep dehydration effect of the co-treatment of the hot-pressing filtration filtrate and the municipal sludge is not good as that of the conventional deep dehydration effect, but the specific resistance of the filter cake is less than 5X 10 11 m/kg, completely meets the requirement of industrial deep dehydration treatment efficiency, and does not need to add ferric chloride and calcium oxide. Compared with the conventional deep dehydration process, the method (1) can reduce the concentration of pollutants in the filtrate of the thermal pressure filtration; (2) The deep dehydration process of the municipal sludge can be realized under the condition of not adding an auxiliary agent; and (3) the volume discharge amount of the filtrate can be reduced by nearly half.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be apparent to those skilled in the art that various changes in the embodiments and/or modifications of the invention can be made, and equivalents may be substituted for elements thereof without departing from the scope of the invention.
Claims (6)
1. The application of the ferric chloride mediated cyanobacteria-based biochar in removing zero-valent mercury in flue gas is characterized in that the ferric chloride mediated cyanobacteria-based biochar is prepared from cyanobacteria mud as a raw material;
the application method comprises the following steps: removing zero-valent mercury pollutants in the flue gas by using blue algae-based biochar through an adsorption fixed bed system;
the ferric chloride mediated cyanobacteria-based biochar is prepared by the following method:
(1) Putting the cyanobacteria mud into a closed container, adding ferric chloride, stirring, and carrying out first thermal filter pressing to obtain a cyanobacteria filter cake containing ferric salt and a cyanobacteria filtrate;
(2) Adding a saturated KOH solution into the blue algae filter cake, kneading, neutralizing, drying and pyrolyzing to prepare the ferric chloride mediated blue algae-based biochar;
in the step (2), the specific method for preparing the ferric chloride mediated blue algae-based biochar after adding the saturated KOH solution into the blue algae filter cake, kneading, neutralizing, drying and pyrolyzing comprises the following steps: adding a KOH solution with the concentration of 40% (w/v) into the blue algae filter cake, kneading and uniformly mixing, adjusting the pH value of the mixture to be neutral, then sending the mixture into drying equipment for drying at 105-135 ℃, obtaining blue algae powder after drying, and then pyrolyzing the blue algae powder at 450-800 ℃ to obtain the blue algae-based charcoal.
2. The use according to claim 1, wherein the ferric chloride-mediated cyanobacteria-based biochar has a specific surface area of 20m 2 /g～200m 2 Per g, pore volume 0.02cm 3 /g～0.2cm 3 /g。
3. The use of claim 1, wherein in the step (1), the cyanobacteria mud is sourced from a cyanobacteria water separation station, the solid content is 5-15% (w), and the cyanobacteria mud is the cyanobacteria mud which is salvaged and primarily dehydrated on the day or the aged cyanobacteria mud which is sourced from a storage pool and has an aging period of 3-60 days.
4. The application of claim 1, wherein in the step (1), the specific method for obtaining the ferric salt-containing cyanobacteria filter cake and the cyanobacteria filtrate through first hot filter pressing by putting the cyanobacteria mud into a closed container, adding ferric chloride and stirring comprises the following steps: introducing steam into the closed container, heating the cyanobacteria mud to 80-95 ℃, adding 1.5-2.5% (w/v) of ferric chloride, stirring and mixing, pumping the cyanobacteria mud into a filter press, deeply dehydrating under the condition of 0.2-1.5 MPa, and performing first filter pressing to obtain a cyanobacteria filter cake and a cyanobacteria filtrate.
5. The use according to claim 1, wherein in the step (2), the pyrolysis at 450-800 ℃ is carried out by raising the temperature in a rotary furnace to 450 ℃ at a rate of 10 ℃/min, maintaining the temperature at 450 ℃ for 60min, further raising the temperature to 800 ℃ at a rate of 10 ℃/min, and then maintaining the temperature at 800 ℃ for 60min.
6. The use according to any one of claims 1 to 5, wherein the application method is specifically: removing zero-valent mercury pollutants in the flue gas by using blue algae-based biochar through an adsorption fixed bed system; the concentration of zero-valent mercury in the flue gas is 20-100 mu g/m 3 The gas flow rate of the adsorbent per unit mass is 1-10L/g.min, and the adsorption temperature is 120-180 ℃.
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