CN113332952B - Modified fly ash adsorbent and preparation method and application thereof - Google Patents
Modified fly ash adsorbent and preparation method and application thereof Download PDFInfo
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Abstract
The invention provides a modified fly ash adsorbent and a preparation method and application thereof. The preparation method of the modified fly ash adsorbent comprises the following steps: A) grinding and sieving the fly ash to obtain pretreated fly ash; B) performing primary modification on the pretreated fly ash at normal temperature by using ferrous salt and ferric salt to obtain primary modified fly ash; C) carrying out secondary modification on the primary modified fly ash by adopting calcium hydroxide to obtain secondary modified fly ash; D) and filtering, drying, roasting and crushing the secondary modified fly ash to obtain the modified fly ash adsorbent. The modified fly ash adsorbent has low production cost, high heavy metal removing efficiency and good economic and environmental benefits.
Description
Technical Field
The invention relates to the technical field of environmental protection, in particular to a modified fly ash adsorbent and a preparation method and application thereof.
Background
With the rapid development of the industry in China, various industrial production activities including energy mining, power generation, metallurgy, electroplating, mining and the like all involve the processing and use of a large amount of heavy metal-containing minerals and raw materials, so that a large amount of heavy metal polluted wastewater is generated, and the universality and the persistence of the heavy metal pollution to the human health and the environmental safety are increasingly concerned.
In the aspect of heavy metal wastewater treatment technology, the traditional neutralization flocculation precipitation method is mainly to add Ca (OH)2Traditional water treatment chemicals such as aluminum salts, iron salts, organic sulfur, etc. remove numerous heavy metals, howeverThe chemical mechanism involved in the class treatment process is single, mainly chemical precipitation and adsorption precipitation are taken as main mechanisms, certain limitations are realized, and especially for heavy metals with higher emission requirements, the heavy metals are difficult to reach the standard only through chemical precipitation.
Electrochemical methods, such as electrodialysis (electrodialysis) and electrolytic flocculation (electroflocculation), can also be used for treating heavy metal wastewater. However, despite some unique advantages, electrochemical methods still face economic and technical obstacles, are complex to operate and control, and often cannot meet the latest strict discharge standards.
The adsorption method is a stable and effective removal technology and plays an important role in heavy metal wastewater treatment. However, most of the prior applications are artificially synthesized adsorbents, and the material cost is high. Meanwhile, coal-fired power plants generate a large amount of fly ash every day, the fly ash has natural porous property, is a good adsorbing material base material, and has poor adsorbing effect on heavy metals, so that the fly ash needs to be modified into an adsorbing material with high adsorbing performance.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a modified fly ash adsorbent, a preparation method and application thereof.
The invention provides a preparation method of a modified fly ash adsorbent, which comprises the following steps:
A) grinding and sieving the fly ash to obtain pretreated fly ash;
B) performing primary modification on the pretreated fly ash at normal temperature by using ferrous salt and ferric salt to obtain primary modified fly ash;
C) carrying out secondary modification on the primary modified fly ash by adopting calcium hydroxide to obtain secondary modified fly ash;
D) and filtering, drying, roasting and crushing the secondary modified fly ash to obtain the modified fly ash adsorbent.
The inventor of the invention discovers that when the fly ash is modified, if the mixed modifier of ferrous salt and ferric salt is firstly adopted for primary modification, the primary modification of the fly ash can be realized at normal temperature, the modification effect is obviously improved, and especially the removal efficiency of heavy metals is greatly improved; in addition, the calcium hydroxide is adopted for secondary modification, which is beneficial to increasing the specific surface area of the fly ash particles, so that the surfaces of the fly ash particles are roughened, and the adsorption performance of the modified fly ash adsorbent is further improved.
In the step A), the particle size of the pretreated fly ash can be controlled to be 60-200 microns; the fly ash is ground and sieved to control the particle size of the fly ash, so that the modification effect of subsequent primary modification and secondary modification is favorably ensured.
In step B), the ferrous salt and ferric salt used are not particularly limited, and ferrous salts such as ferrous sulfate and the like, ferric salts such as ferric chloride and the like are used. It can be understood that when the pretreated fly ash is subjected to primary modification, a ferrous salt solution and a ferric salt solution can be adopted, and water can be added as required; wherein, the ratio of the mass of the pretreated fly ash to the total mass of ferrous salt and ferric salt can be controlled to be (20-100): 1, preferably 80 to 100: 1, more preferably 100: 1; and the molar ratio of ferrous salt to ferric salt can be controlled to be 1: (1.5-2.5), preferably 1: 2.
further, in the step B), the first modification can be carried out under the conditions of stirring and pH value control; wherein, the stirring speed can be controlled to be less than or equal to 180r/min, such as 140-; the pH value of the primary modification system can be controlled to be 7.5-9.5; in addition, the primary modification time can be controlled to be 20-120min, preferably 40-80min, and more preferably 60 min.
In the step C), the mass ratio of the primary modified fly ash to the calcium hydroxide can be controlled to be 100: (1-10), preferably 100: (5-10), more preferably 10: 1. further, the secondary modification may include: slowly stirring for 20-40min, and aging for 2-5 h; wherein, the slow stirring speed can be controlled to be 40-60 r/min.
In step D), the drying temperature can be controlled at 100-105 ℃; the roasting temperature is 600-750 ℃, preferably 600-700 ℃, and more preferably 650 ℃; the roasting time is 40-120min, preferably 60-100min, and more preferably 80 min. In addition, the particle size of the modified fly ash adsorbent can be controlled to be 100-800 microns.
The invention also provides a modified fly ash adsorbent prepared according to the preparation method.
The invention also provides a heavy metal wastewater treatment method, which comprises the following steps: and (3) carrying out contact reaction on the heavy metal wastewater and the modified fly ash adsorbent in a reactor.
Further, heavy metal wastewater is pretreated before contact reaction, so that the SS of the heavy metal wastewater is less than or equal to 300mg/L, and the pH value is greater than 6.
The reactor employed in the present invention is not critical and may be a conventional reactor in the art, such as a packed bed reactor or the like.
In a conventional packed bed reactor, a packing layer is directly arranged in the reactor; however, the research finds that the traditional packed bed reactor cannot optimize the treatment effect of the heavy metal wastewater. Therefore, the invention also modifies the structure of the reactor; specifically, at least two stages of packing layers are arranged in the reactor at intervals up and down, a settling zone is arranged below the packing layers, the modified fly ash adsorbent is filled in the packing layers, and the heavy metal wastewater flows through the packing layers from top to bottom and is in contact reaction with the modified fly ash adsorbent in the packing layers. It can be understood that the reactor has a shell, the packing layer and the settling zone are arranged inside the shell; the material of the filler layer is not particularly limited, and for example, a porous material such as porous sponge can be used.
Furthermore, an arc top can be arranged between the adjacent packing layers, and a plurality of through holes are formed in the arc top; the arc top is mainly used for collecting the filler lost from the filler layer above the arc top and uniformly filling the filler to the next filler layer, can be set into a smooth arc top, and can be an arc in section shape, the central angle of the arc can be 90-120 degrees, and the chord length can be the diameter of the shell; the aperture of the through-hole may be set to 0.4-0.6 mm. By arranging at least two stages of packing layers and arranging the arc tops between the adjacent packing layers, the modified fly ash adsorbent can be uniformly distributed, thereby being beneficial to improving the treatment effect.
Further, the settling zone may include a primary settling zone having a tapered bottom and disposed below the packing layer located lowermost, and a secondary settling zone disposed outside the primary settling zone and communicating with an upper portion of the primary settling zone; at the moment, a water inlet is arranged on the shell above the filler area, and a water outlet is arranged at the upper part of the secondary sedimentation area. Wherein the total height of the packing layer can be set to 1/3 to 1/2; 3/4, the height of the primary settling zone is no greater than the height of the secondary settling zone; the height of the secondary settling zone is from 1/4 to 1/3 of the shell height. The arrangement of the primary settling zone and the secondary settling zone can ensure that the concentration of the effluent suspended matters is kept at a low level.
The implementation of the invention has at least the following advantages:
1) when the mixed modifier of ferrous salt and ferric salt is used for carrying out primary modification on the pretreated fly ash, the primary modification of the fly ash can be realized at normal temperature, and the energy consumption and the production cost of the modified fly ash are reduced; meanwhile, the introduction of ferrous salt obviously improves the modification effect of the fly ash, and particularly greatly improves the removal efficiency of heavy metals;
2) the structure of the reactor is improved, so that the uniform distribution of the modified fly ash adsorbent is ensured, the reusability of the modified fly ash adsorbent is improved, the reaction energy consumption is effectively reduced, the treatment effect is greatly improved, and the water quality of treated effluent is ensured;
3) the method fully utilizes the low-value fly ash for modification to obtain the high-value adsorption material, realizes the resource utilization of the fly ash, has low production cost of the modified fly ash, high heavy metal removal efficiency and good economic and environmental benefits; in addition, the modified fly ash adsorbent is flexible in use mode and can be flexibly used according to different water qualities, so that the optimal treatment effect is achieved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is a schematic view of the structure of a reactor used in example 3.
Description of reference numerals:
1; a housing; 2; a filler layer; 3: arc top; 4: a primary precipitation zone; 5: a secondary sedimentation zone; 6: an oxygenation pump; 7: an ultrasonic device; 8: and (5) a primary sedimentation tank.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present application. As used herein, the singular forms also include the plural forms unless the context clearly dictates otherwise, and further, it is understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of the stated features, steps, operations, devices, components, and/or combinations thereof.
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Firstly, preparing modified fly ash adsorbent
Taking fly ash of a certain power plant, grinding and sieving to obtain pretreated fly ash with the particle size of about 100 microns.
Adding a proper amount of water, a ferrous sulfate solution and a ferric chloride salt solution into the pretreated fly ash, adjusting the pH value to 8.5, and controlling the mass ratio of the fly ash to the total mass of ferrous sulfate and ferric chloride to be 100: 1, the molar ratio of ferrous sulfate to ferric chloride is 1: 2, carrying out primary modification for 60 minutes at normal temperature and under the condition of 160r/min to obtain the primary modified fly ash.
Adding calcium hydroxide into the primary modified fly ash, and controlling the mass ratio of the primary modified fly ash to the calcium hydroxide to be 10: 1, slowly stirring for 30 minutes at the speed of 60r/min, and then aging for 2 hours to obtain the secondary modified fly ash.
And filtering the obtained secondary modified fly ash, drying at 105 ℃, roasting at 650 ℃ for 80min, and crushing to obtain the modified fly ash adsorbent with the particle size of about 400 microns.
Second, heavy metal wastewater treatment method
The actual desulfurization wastewater of a certain power plant is taken as a treatment object, the conventional packed bed reactor and the prepared modified fly ash adsorbent are used for treatment, the packing layer of the reactor is porous sponge, and the modified fly ash adsorbent is filled in the packing layer, wherein the filling amount is 2% of the wastewater in the reactor. The wastewater was taken from the raw water of an existing wastewater treatment system, and the concentrations of the main pollutants in the raw water are shown in table 1.
Table 1 concentration of major contaminants in raw water
| Index (I) | Unit of | Numerical value |
| Hg | mg/L | 1.02 |
| Pb | mg/L | 3.40 |
| Cd | mg/L | 0.21 |
| Cr | mg/L | 3.42 |
| As | mg/L | 2.43 |
| SS | mg/L | 34500 |
Pumping the wastewater into the reactor from the upper part of the reactor for treatment, performing hydraulic retention for 30min, sampling and filtering from the lower part of the reactor, and detecting the concentration of metal ions in the filtrate, wherein the results are shown in Table 2.
Example 2
Firstly, preparing modified fly ash adsorbent
Taking fly ash of a certain power plant, grinding and sieving to obtain pretreated fly ash with the particle size of about 200 microns.
Adding a proper amount of water, a ferrous sulfate solution and a ferric chloride salt solution into the pretreated fly ash, adjusting the pH value to 8.5, and controlling the mass ratio of the fly ash to the total mass of ferrous sulfate and ferric chloride to be 80: 1, the molar ratio of ferrous sulfate to ferric chloride is 1: 2, carrying out primary modification for 80 minutes at normal temperature and under the condition of 140r/min to obtain the primary modified fly ash.
Adding calcium hydroxide into the primary modified fly ash, and controlling the mass ratio of the primary modified fly ash to the calcium hydroxide to be 20: 1, slowly stirring for 40 minutes at 40r/min, and then aging for 5 hours to obtain the secondary modified fly ash.
And filtering the obtained secondary modified fly ash, drying at 105 ℃, roasting at 700 ℃ for 60min, and crushing to obtain the modified fly ash adsorbent with the particle size of about 300 microns.
Second, heavy metal wastewater treatment method
The actual desulfurization wastewater of a certain power plant is taken as a treatment object, the conventional packed bed reactor and the prepared modified fly ash adsorbent are used for treatment, the packing layer of the reactor is porous sponge, and the modified fly ash adsorbent is filled in the packing layer, wherein the filling amount is 2% of the wastewater in the reactor. The wastewater was taken from the raw water of an existing wastewater treatment system, and the concentrations of the main pollutants in the raw water are shown in table 1.
Pumping the wastewater into the reactor from the upper part of the reactor for treatment, performing hydraulic retention for 30min, sampling and filtering from the lower part of the reactor, and detecting the concentration of metal ions in the filtrate, wherein the results are shown in Table 2.
Example 3
The procedure was as in example 1 except that the reactor configuration was changed.
Referring to fig. 1, the reactor structure of this example is as follows:
the reactor of this embodiment has a shell 1, a packing layer 2 which is arranged in the shell 1 at least in two stages at intervals up and down is arranged, a settling zone is arranged below the packing layer 2, the modified fly ash adsorbent of embodiment 1 is filled in the packing layer 2, heavy metal wastewater flows through the packing layer 2 from top to bottom and is in contact reaction with the modified fly ash adsorbent in the packing layer 2, and the filling amount of the modified fly ash adsorbent is 2% of the wastewater in the reactor.
The shell 1 is cylindrical, the packing layer 2 is made of porous sponge, and the total height of the packing layer 2 is the same as that of the packing layer in the embodiment 1; an arc top 3 is arranged between the adjacent packing layers 2, the cross section of the arc top is in the shape of an arc, the central angle of the arc is 90-120 degrees, and the chord length is the diameter of the shell 1; the arc top 3 is provided with a plurality of through holes, and the aperture of each through hole is 0.4-0.6 mm.
The sedimentation zone includes primary sedimentation zone 4 and second grade sedimentation zone 5, and primary sedimentation zone 4 has the toper bottom and sets up in the packing layer 2 below that is located the below, and second grade sedimentation zone 5 sets up in the outside of primary sedimentation zone 4 and communicates with the upper portion of primary sedimentation zone 4, is equipped with the water inlet on the casing 1 that is located the packing zone top, is equipped with the delivery port on the upper portion of second grade sedimentation zone 5. The cone angle of the conical bottom of the primary settling zone 4 is set to be not more than 90 °; the height of the primary settling zone 4 may be set to be no greater than 3/4 of the height of the secondary settling zone 5; the height of the secondary sedimentation zone 5 may be set at 1/4 to 1/3 of the height of the shell 1.
Further, a primary sedimentation tank 8 can be arranged at the front end of the reactor to carry out primary sedimentation on the wastewater; in addition, the reactor can be provided with an aeration device and an ultrasonic device 7 for aeration and ultrasonic treatment, and the aeration device can be provided with an oxygenation pump 6 for oxygenation.
Pumping the wastewater into the reactor from the upper part of the reactor for treatment, performing hydraulic retention for 30min, sampling and filtering from the lower part of the reactor, and detecting the concentration of metal ions in the filtrate, wherein the results are shown in Table 2.
Comparative example 1
Except for the step of preparing the modified fly ash adsorbent, only ferric chloride salt solution is adopted to modify the pretreated fly ash at normal temperature for one time, and the mass ratio of the fly ash to the ferric chloride is 100: 1; the rest is basically the same as in example 1.
Pumping the wastewater into the reactor from the upper part of the reactor for treatment, performing hydraulic retention for 30min, sampling and filtering from the lower part of the reactor, and detecting the concentration of metal ions in the filtrate, wherein the results are shown in Table 2.
Comparative example 2
Except for the step of preparing the modified fly ash adsorbent, only ferric chloride salt solution is adopted to modify the pretreated fly ash at 80 ℃ for one time, and the mass ratio of the fly ash to the ferric chloride is 100: 1; the rest is basically the same as in example 1.
Pumping the wastewater into the reactor from the upper part of the reactor for treatment, performing hydraulic retention for 30min, sampling and filtering from the lower part of the reactor, and detecting the concentration of metal ions in the filtrate, wherein the results are shown in Table 2.
TABLE 2 concentration of main contaminants in the treated effluent
| Index (I) | Unit of | Example 1 | Example 2 | Example 3 | Comparative example 1 | Comparative example 2 |
| Hg | mg/L | 0.002 | 0.003 | 0.001 | 0.042 | 0.032 |
| Pb | mg/L | 0.1 | 0.11 | 0.06 | 0.21 | 0.16 |
| Cd | mg/L | 0.03 | 0.07 | 0.015 | 0.1 | 0.08 |
| Cr | mg/L | 0.28 | 0.15 | 0.02 | 0.46 | 0.39 |
| As | mg/L | 0.016 | 0.026 | 0.008 | 0.127 | 0.115 |
As can be seen from table 2:
1. if the fly ash is modified by adopting the iron salt for one time, the modification effect is poor, and the removal efficiency of the modified fly ash on heavy metals in the desulfurization wastewater cannot be greatly improved;
2. compared with a conventional packed bed reactor, the reactor with the improved structure in the embodiment 3 has better effect of removing heavy metals in wastewater and more excellent effluent quality, and the reactor with the improved structure can greatly improve the treatment effect of desulfurization wastewater, so that the effluent quality is ensured;
3. when the coal ash modified by the method of each embodiment of the invention is used for treating desulfurization wastewater, the heavy metals in the desulfurization wastewater are far lower than the current emission standard, which shows that the modified coal ash adsorbent prepared by each embodiment has good effect of removing the heavy metals in the wastewater.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (8)
1. The preparation method of the modified fly ash adsorbent is characterized by comprising the following steps:
A) grinding and sieving the fly ash to obtain pretreated fly ash;
B) performing primary modification on the pretreated fly ash at normal temperature by using ferrous salt and ferric salt to obtain primary modified fly ash; wherein the ratio of the mass of the pretreated fly ash to the total mass of ferrous salt and ferric salt is (20-100): 1; the molar ratio of ferrous salt to ferric salt is 1: (1.5-2.5);
C) carrying out secondary modification on the primary modified fly ash by adopting calcium hydroxide to obtain secondary modified fly ash;
D) filtering, drying, roasting and crushing the secondary modified fly ash to obtain a modified fly ash adsorbent; wherein the roasting temperature is 600-750 ℃; the roasting time is 40-120 min.
2. The preparation method according to claim 1, wherein in the step A), the particle size of the pretreated fly ash is controlled to be 60-200 microns.
3. The preparation method according to claim 1, wherein in the step B), the primary modification is performed under the conditions of stirring and pH value control, wherein the stirring speed is controlled to be less than or equal to 180r/min, the pH value is controlled to be 7.5-9.5, and the primary modification time is controlled to be 20-120 min.
4. The preparation method according to claim 1, wherein in the step C), the mass ratio of the primary modified fly ash to the calcium hydroxide is 100: (1-10); the secondary modification comprises the following steps: slowly stirring for 20-40min, and aging for 2-5 h.
5. The method as claimed in claim 1, wherein in step D), the drying temperature is controlled to be 100-105 ℃; the particle size of the modified fly ash adsorbent is controlled to be 100-800 microns.
6. A modified fly ash adsorbent, characterized by being produced by the production method according to any one of claims 1 to 5.
7. A heavy metal wastewater treatment method is characterized by comprising the following steps: carrying out contact reaction on heavy metal wastewater and the modified fly ash adsorbent in claim 6 in a reactor; the reactor is provided with at least two packing layers which are arranged at intervals up and down, a settling zone is arranged below the packing layers, the modified fly ash adsorbent is filled in the packing layers, heavy metal wastewater flows through the packing layers from top to bottom and reacts with the modified fly ash adsorbent in the packing layers in a contact manner, an arc top is arranged between the adjacent packing layers, and a plurality of through holes are formed in the arc top.
8. The heavy metal wastewater treatment method according to claim 7, wherein the heavy metal wastewater is pretreated before the contact reaction, so that the SS of the heavy metal wastewater is less than or equal to 300mg/L and the pH value is greater than 6.
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| CN109126684A (en) * | 2018-10-30 | 2019-01-04 | 常熟理工学院 | A kind of preparation method of base iron load type mixed ash adsorbent |
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| CN107376829A (en) * | 2017-08-28 | 2017-11-24 | 云南圣清环保科技有限公司 | A kind of preparation method for carrying iron powder coal ash arsenic-removing adsorption agent |
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