CN115634668A - Preparation and use methods of sodium bentonite-loaded chitosan heavy metal stabilizing agent - Google Patents
Preparation and use methods of sodium bentonite-loaded chitosan heavy metal stabilizing agent Download PDFInfo
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Abstract
The invention provides a preparation method and a use method of a sodium bentonite loaded chitosan heavy metal stabilizing agent, and relates to the field of environmental engineering. The preparation method of the heavy metal stabilizing agent comprises the following steps: (1) Mixing and stirring sodium bentonite and an oxalic acid solution at normal temperature, acidifying, modifying and filtering; (2) Roasting and activating the acidified sodium bentonite in a muffle furnace; (3) Dissolving chitosan powder in acetic acid solution to prepare chitosan solution; (4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution; infiltrating and heating; (5) adjusting the pH value, stirring and precipitating to remove unreacted chitosan; (6) Washing the precipitate, centrifugally separating, taking the lower layer precipitate, drying, grinding and sieving to prepare the heavy metal stabilizing agent. The invention takes natural and easily obtained sodium bentonite and chitosan as raw materials, and the prepared bottom mud stabilizer has the characteristics of good heavy metal adsorption performance, low cost and easily obtained raw materials.
Description
Technical Field
The invention relates to the field of environmental engineering, in particular to a preparation method and a use method of a heavy metal stabilizing agent for river and lake bottom mud.
Background
Heavy metal means a density of 4.5g/cm 3 Above, or a metal having a specific gravity greater than 5. The common heavy metal species in the river sediment comprise Cd, as, cu, cr, zn, ni, fe, mn and the like. The waste water discharged by human beings in production and life contains a certain amount of heavy metals, once the waste water enters a water body, the effects of adsorption, complexation, sedimentation and the like can be generated, the waste water is enriched in the bottom mud on the surface layers of rivers and lakes, and the content of the waste water in the bottom mud can exceed the content of overlying water bodies by multiple orders of magnitude. When the environmental conditions change, part of heavy metals may be released from the bottom mud through desorption, dissolution, oxidation reduction and other actions, so that secondary pollution of the water body is caused. The continuous accumulation of heavy metals in the bottom mud not only poses serious threats to aquatic organisms, drinking water of residents along rivers and safe irrigation of farmlands, but also can damage human health through a food chain. Therefore, safe disposal of the heavy metal polluted bottom mud is particularly necessary.
At present, the stabilization treatment is one of the widely applied technologies for treating the heavy metal pollution of the river and lake bottom mud at home and abroad. The selection of the stabilizing agent is the key of the heavy metal bottom mud repairing technology. Currently, common heavy metal stabilizing agents mainly include limes, phosphorus-containing agents, natural minerals and organic substances:
the lime stabilizer mainly comprises calcium carbonate, lime and the like. The stabilizing mechanism of the alkaline stabilizer to the heavy metals is mainly to increase the pH value of the heavy metal bottom mud, on one hand, the adsorption effect of the bottom mud to the heavy metals is increased, on the other hand, heavy metal ions are converted into a precipitate form which is not easy to transfer, so that the leaching and biotoxicity of the heavy metal ions are reduced, but the hardening and alkalization of the bottom mud can be caused.
The phosphorus-containing heavy metal stabilizer comprises phosphate, hydroxyapatite and the like. The stabilization mechanism is mainly that phosphate reacts with heavy metal to generate insoluble complex or mineral, meanwhile, the reaction efficiency of the phosphate and the heavy metal can be increased due to the electronegativity of the phosphate, so as to achieve the purpose of stabilizing the heavy metal, but due to the precipitation of phosphorus, water eutrophication can be caused.
The natural mineral heavy metal stabilizer comprises sepiolite, bentonite, red mud, diatomite and the like. The action mechanism is mainly that the stabilizer has larger specific surface area, and fixes heavy metal through the actions of adsorption, complexation, precipitation and the like with the heavy metal, so that the mobility and the biotoxicity of the heavy metal are reduced, the raw materials are cheap and easy to obtain, but the adsorption is saturated, and natural minerals can be modified to a certain extent to enhance the adsorption capacity of the natural minerals.
The organic heavy metal stabilizer comprises chitosan, tannic acid and the like. The action mechanism is mainly to reduce the heavy metal content in the bottom mud to a certain extent by utilizing the chelation of the organic chelating agent and the heavy metal. The organic chelating agent can react with heavy metal in the bottom sediment to form hydrophobic and insoluble chelate, so that the chelate is converted into a more stable form, the toxicity and the bioavailability of the heavy metal in the environment are reduced, the raw materials are easy to obtain, but the processed stabilizer is high in price and is generally subjected to composite modification with other cheap stabilizers, so that the cost is reduced.
And, the treatment of heavy metals in river and lake bottom sludge is more complicated than the treatment of heavy metals in water. Firstly, the stabilizing agent for treating heavy metals in water can be recovered and removed in a flocculation precipitation mode, but the stabilizing agent and the bottom mud are difficult to separate after being mixed, so that the material for preparing the stabilizing agent needs to be nontoxic and harmless, and has no adverse effect on the ecological environment and the production and life of human beings; secondly, a part of heavy metals in the bottom sediment are adsorbed on the bottom sediment particles, a part of heavy metals exist in water, and the heavy metals on the bottom sediment particles have various existing forms and are divided into an acid-extractable state, a reducible state, an oxidizable state and a residue state, so that the heavy metal stabilizing agent not only needs to remove the heavy metals in the water through a series of chemical reactions, but also needs to convert the existing forms of the heavy metals in the bottom sediment and the heavy metals captured from the water into more stable oxidizable states and residue states, and the heavy metals are difficult to separate out from the bottom sediment under extreme conditions.
The traditional bottom mud stabilizing agent has the defects of large dosage, soil hardening and influence on the quality of effluent water, and is difficult to adapt to the requirement of current heavy metal treatment of the bottom mud of rivers and lakes, so that the development of the heavy metal stabilizing agent with good treatment effect, low price, easy obtainment and no secondary pollution becomes a key technology for heavy metal remediation of the bottom mud of rivers and lakes, and the exploration of the important research direction for preparing the heavy metal stabilizing agent based on natural materials such as chitosan, bentonite and the like to become the remediation of the bottom mud of rivers and lakes polluted by heavy metal.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a preparation method and a use method of a sodium bentonite-loaded chitosan heavy metal stabilizing agent (NaBent-CTS). The invention takes natural and easily obtained sodium bentonite (NaBent) and Chitosan (CTS) as raw materials, and the prepared bottom mud stabilizer has the characteristics of good heavy metal adsorption performance, low cost and easily obtained raw materials.
The technical scheme of the invention is as follows:
the preparation method of the sodium bentonite loaded chitosan heavy metal stabilizing agent comprises the following steps:
(1) Mixing and stirring sodium bentonite and an oxalic acid solution at normal temperature for 0.5-1.5h for acidification modification, then carrying out suction filtration, and collecting the acidified sodium bentonite;
(2) Roasting and activating the acidified sodium bentonite in a muffle furnace;
(3) Dissolving chitosan powder in acetic acid solution to obtain chitosan solution, and slowly stirring for dissolving;
(4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution; fully soaking, and stirring and heating for 2.5-3h at the temperature of 60-65 ℃;
(5) Adding sodium hydroxide solution, adjusting pH to 8.5-9.5, slowly stirring for 10-15min, and removing unreacted chitosan by precipitation;
(6) Washing the precipitate with distilled water until the pH value is 7-8, performing centrifugal separation, taking the lower layer precipitate, drying, grinding and sieving to obtain the sodium bentonite loaded chitosan heavy metal stabilizing agent.
Preferably, the mass concentration of the oxalic acid solution in the step (1) is 18-23%; the liquid-solid ratio of the oxalic acid solution to the sodium bentonite is 1-42 mL/g.
Preferably, the temperature for roasting activation in the step (2) is 430-470 ℃ and the time is 1.5-2.5h.
Preferably, the mass concentration of the acetic acid solution in the step (3) is 3-5%; the mass concentration of the prepared chitosan solution is 3-5%.
Preferably, the mass ratio of the chitosan powder in the step (3) to the sodium bentonite powder in the step (4) is 1; the time for full infiltration is 2.5-3.5h.
Preferably, the precipitation in step (5) removes unreacted chitosan for 2-3h.
Preferably, the centrifugal separation condition in the step (6) is 15-20min under the condition that the rotating speed is 3400-3600 r/min; the drying temperature is 80-90 ℃; the sieving condition was 0.074mm.
The invention also provides application of the sodium bentonite-loaded chitosan heavy metal stabilizing agent obtained by the preparation method, and the sodium bentonite-loaded chitosan heavy metal stabilizing agent is used for adsorbing and stabilizing the heavy metals in the bottom mud of rivers and lakes.
Further, the heavy metals in the bottom sludge of rivers and lakes comprise Cu 2+ 、Zn 2+ 、Cd 2+ 。
Further, when adsorbing and stabilizing heavy metals in the bottom mud of rivers and lakes, the dosage of the sodium bentonite loaded chitosan is 4-6% of the weight of the dry bottom mud, and the treatment time is 6-8 days.
The beneficial technical effects of the invention are as follows:
1. the technical problems to be solved by the invention include two points, firstly, the heavy metal stabilizer needs to be nontoxic and harmless to human beings and ecological environment; secondly, the stabilizing effect of heavy metal is good, the heavy metal in both liquid phase and solid phase can be treated, and the existing form of the heavy metal can be converted to the stable form.
According to the invention, the effect of stabilizing the heavy metal can be synergistically enhanced after two stabilizing agents of sodium bentonite and chitosan are compounded, the leaching rate of the heavy metal leaching toxicity of the stabilized river and lake bottom mud can meet the relevant requirements of hazardous waste identification standard leaching toxicity identification (GB 5085.3-2007), and the existing form of the heavy metal is changed from an acid extractable state and a reducible state to a more stable oxidizable state and a residue state.
2. The sodium bentonite has high adsorption speed but is easy to adsorb and saturate; chitosan is a carbohydrate, has abundant groups and large adsorption capacity, but is dissolved in water to easily cause COD (chemical oxygen demand) rise and water quality pollution, so that the chitosan is adsorbed on sodium bentonite through chemical action, the adsorption capacity of the sodium bentonite can be improved, and the water quality cannot be influenced. However, the mass ratio of the two is too small, so that the chitosan is easy to block the gap of the sodium bentonite; the chitosan loaded on the sodium bentonite is easy to be unloaded due to overhigh temperature and overlong stirring time, so that the invention carries out a great deal of research on the composite technology of the sodium bentonite and the chitosan and finally obtains the optimal mass ratio and preparation process.
3. The sodium bentonite has abundant mineral resources, low price, and has the advantages of large surface area, good adsorptivity, ion exchange property, cohesiveness and the like; the chitosan is the second largest natural linear compound, has the characteristics of no toxicity, harmlessness, biodegradability, capability of complexing heavy metals through self-abundant groups and the like, and is a good material for adsorbing the heavy metals. After the chitosan is loaded on the sodium bentonite, the sodium bentonite has larger adsorption surface area, contains rich groups, has stronger adsorption and chelation effects on heavy metals, has wide sources and low manufacturing cost, and has relatively low stabilizing treatment cost.
4. The invention aims at the single or compound heavy metal polluted sediment with the sediment pH of 7-9 and the respective leaching concentrations of Cu, zn and Cd within 40mg/L, the adding amount is 5% of the weight of the dry sediment, and the medicament needs to be fully mixed with the sediment and subjected to stabilization treatment for 14 days, thus achieving remarkable effect. The heavy metal polluted bottom mud subjected to the medicament stabilization treatment is still lower than the limit value in the identification standard of hazardous wastes in the leaching concentration of heavy metals in an acidic environment, the toxicity risk is obviously reduced, the heavy metals are converted into more stable forms, and the stabilization effect is obviously improved compared with that of sodium bentonite.
Drawings
Fig. 1 is an infrared spectrum of a stabilizer for chitosan, sodium bentonite and chitosan-modified sodium bentonite, wherein three curves from top to bottom represent Chitosan (CTS), sodium bentonite (NaBent) and the sodium bentonite-loaded chitosan heavy metal stabilizing agent (NaBent-CTS) prepared in example 1.
Fig. 2 is an XRD pattern of the sodium bentonite-supported chitosan heavy metal stabilizing agent prepared in example 1.
Fig. 3 is an SEM image of the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in example 1 (the left image is sodium bentonite, and the right image is sodium bentonite-loaded chitosan heavy metal stabilizing agent).
FIG. 4 shows that NaBent-CTS respectively adsorb Cu 2+ 、Zn 2+ 、Cd 2+ Infrared spectrograms before and after heavy metals.
FIG. 5 shows that NaBent-CTS respectively adsorb Cu 2+ 、Zn 2+ 、Cd 2+ XPS spectra before and after heavy metals.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the 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:
(1) Mixing and stirring sodium bentonite and 20% oxalic acid solution at normal temperature for 1h according to the liquid-solid ratio of 1.
Oxalic acid is used in this step because oxalic acid is an organic substance and can be decomposed at 105 deg.C to produce H by oxalic acid + Removing partial organic matters in the sodium bentonite, and carrying out ion exchange on Al with larger ion radius in the sodium bentonite layer 3+ 、Mg 2+ 、Ca 2+ The metal ions are replaced out of the layers, so that the acting force between the layers is weakened, the interlayer distance is enlarged, the exchange between cations is facilitated, and the adsorption capacity is improved.
(2) And roasting and activating the acidified sodium bentonite in a muffle furnace for 2 hours at the temperature of 450 ℃.
The purpose of this step is in order to remove sodium bentonite interlamination hydrone and organic matter to increase sodium bentonite interlamellar spacing and pore volume, provide the basis for follow-up chitosan to get into between the sodium bentonite interlamellar.
(3) Dissolving a certain amount of chitosan powder in 4% acetic acid solution to prepare 4% chitosan solution, and slowly stirring and dissolving the chitosan solution.
(4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution, wherein the mass ratio of the chitosan powder to the sodium bentonite powder is 1:5; fully soaking for 3h, and stirring and heating for 3h at the temperature of 65 ℃.
In the step, the stirring time is too long, so that the chitosan can fall off from the sodium bentonite; at 65 ℃, the molecular kinetic energy between the sodium bentonite layers is increased, the molecular repulsion force is also followed to increase, in order to reach new balance, the interlayer distance is also increased, chitosan is easier to enter the sodium bentonite layers, and the chitosan has larger volume, so that the interlayer distance is increased after entering the sodium bentonite layers, the specific surface area is increased, and ion exchange reaction is favorably carried out between the layers to adsorb heavy metals.
(5) Adding a certain amount of sodium hydroxide solution, adjusting the pH to 9, slowly stirring for 10min, and removing unreacted chitosan by precipitation for 2h.
The step is to prevent the chitosan which is not loaded on the sodium bentonite from entering the overlying water after being mixed with the bottom mud with high water content, so that the COD of the overlying water is increased to cause the deterioration of the water quality.
(6) Washing the precipitate with distilled water until the pH value is 7-8, performing centrifugal separation for 15min at the rotation speed of 3500r/min, taking the lower layer precipitate, putting the lower layer precipitate into an oven, drying at 85 ℃, grinding, and sieving with a 0.074mm sieve to obtain the sodium bentonite loaded chitosan heavy metal stabilizing agent with the chitosan load rate of 9.23%. The chitosan can not be hydrolyzed at the temperature of 85 ℃, and the activity of the chitosan is kept.
The infrared spectrum of the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in example 1 and the chitosan and sodium bentonite is shown in figure 1.
3438cm, known from CTS -1 The absorption peak is the stretching vibration absorption peak of amino N-H and hydroxyl O-H, 2926cm -1 The absorption peak is C-H stretching vibration absorption peak, 1657cm -1 The absorption peak is the absorption peak of amide band I, 1593cm -1 The absorption peak is the absorption peak of amide II band, 1420cm -1 The absorption peak is 1161cm of bending vibration absorption in the hydroxyl O-H plane -1 Is at 1072cm and is an absorption peak of primary hydroxyl O-H -1 The absorption peak of secondary hydroxyl O-H is shown.
3618cm from NaBent -1 Is located at the O-H stretching vibration peak of Si-Al-OH hydroxyl in a sodium bentonite structure, 3476cm -1 Located at 1632cm from the O-H hydroxyl stretching vibration peak of interlayer water molecules -1 Is positioned at 990cm of O-H bending vibration peak of interlayer water molecule of sodium bentonite -1 Is located at an asymmetric stretching vibration peak of Si-O-Si of 515cm -1 The peak is the bending vibration peak of Si-O-Al.
3624cm, known from NaBent-CTS -1 The absorption peak is obviously enhanced, the peak area is enlarged, which indicates that chitosan enters the interlayer of sodium bentonite, so that the O-H hydroxyl groups between the layers are increased, and the thickness is 1428cm -1 And 1113cm -1 The absorption peaks are hydroxyl bending vibration absorption peaks, which indicates that the chitosan is loaded in the sodium bentonite; 3434cm -1 The vibration peak is the expansion vibration peak of water molecules O-H hydroxyl between sodium bentonite layers and the bending vibration peak of amino N-H in chitosan; 507cm -1 The absorption peak area and intensity of Si-O-Al are increased, and no aluminum ion is added, so that chemisorption occurs at Si-O-Al, 1657 and 1593cm -1 The absorption peak of the amide band disappears, which shows that the chemical adsorption is generated between the amide on the chitosan and the Si-O-Al; 994cm -1 The vibration peaks of Si-O-Si and hydroxyl O-H are shown.
The XRD curve of the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in example 1 is shown in fig. 2. As can be seen from FIG. 2, the first peak positions of the NaBent and NaBent-CTS diffraction peaks are significantly changed. According to the Bragg equation:
2dsinθ＝nλ
in the formula: d-layer spacing
Angle between incident ray and reflecting crystal plane
Lambda-wavelength, cu target Ka ray (lambda =0.15406 nm)
n-order of reflection, first order diffraction n =1
The theta of NaBent is 3.66 degrees, the theta of NaBent-CTS is 3.2 degrees, and the calculation shows that the interlamellar spacing of NaBent-CTS is 1.38nm, the interlamellar spacing of NaBent is 1.21nm, and the interlamellar spacing of NaBent is obviously changed after the CTS is loaded, because the CTS molecules have larger volume, the interlamellar spacing is enlarged after entering the NaBent layers, and the ion exchange effect of heavy metal ions entering the layers is facilitated.
SEM of the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in example 1, chitosan and sodium bentonite are shown in fig. 3, and BET specific surface area test results of NaBent and NaBent-CTS are shown in table 1.
TABLE 1
| BET | Surface/m 2 *g -1 |
| NaBent | 14.609 |
| NaBent-CTS | 51.036 |
As can be seen from fig. 3 and table 1, before and after modification, the appearance of the NaBent is greatly changed, the surface structure of the NaBent particles is relatively flat, the number of pores is small, and the surface of the NaBent-CTS particles is rougher than that of the sodium bentonite particles, the specific surface area is larger, and the NaBent-CTS particles are beneficial to adsorbing heavy metals.
Example 2:
(1) Mixing and stirring sodium bentonite and 18% oxalic acid solution at the normal temperature according to the liquid-solid ratio of 1:42mL/g for 0.5h for acidification modification, then performing suction filtration, and collecting the acidified sodium bentonite.
(2) And roasting and activating the acidified sodium bentonite in a muffle furnace for 2.5h at the temperature of 430 ℃.
(3) Dissolving a certain amount of chitosan powder in 3% acetic acid solution to prepare 3% chitosan solution, and slowly stirring and dissolving the chitosan solution.
(4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution, wherein the mass ratio of chitosan to sodium bentonite is 1; fully soaking for 2.5h, and stirring and heating for 3h at the temperature of 60 ℃.
(5) Adding a certain amount of sodium hydroxide solution, adjusting the pH to 9, slowly stirring for 10min, and removing unreacted chitosan by precipitation for 2h.
(6) Washing the precipitate with distilled water until the pH value is 7-8, performing centrifugal separation for 15min at the rotation speed of 3400r/min, taking the lower-layer precipitate, putting the lower-layer precipitate into an oven, drying at 80 ℃, grinding, and sieving by a 0.074mm sieve to obtain the sodium bentonite-loaded chitosan heavy metal stabilizing agent with the chitosan load rate of 9.25%.
In the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in the embodiment 2, the interlamellar spacing of NaBent and NaBent-CTS is 1.20nm and 1.39nm respectively; the BET specific surface areas of NaBent and NaBent-CTS are 14.609m 2 ·g -1 、50.755m 2 ·g -1 . The space between the layers of the NaBent and the specific surface area are obviously increased after the CTS is loaded, and the adsorption of heavy metals is facilitated.
Example 3:
(1) Mixing and stirring sodium bentonite and 23% oxalic acid solution at normal temperature according to a liquid-solid ratio of 1 38mL/g for 1.5h for acidification modification, then performing suction filtration, and collecting the acidified sodium bentonite.
(2) And roasting and activating the acidified sodium bentonite in a muffle furnace for 1.5h at 470 ℃.
(3) Dissolving a certain amount of chitosan powder in 5% acetic acid solution to prepare 4% chitosan solution, and slowly stirring for dissolving.
(4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution, wherein the mass ratio of chitosan to sodium bentonite is 1; fully soaking for 3.5h, and stirring and heating for 3h at the temperature of 65 ℃.
(5) Adding a certain amount of sodium hydroxide solution, adjusting the pH to 9, slowly stirring for 15min, and removing unreacted chitosan by precipitation for 3h.
(6) Washing the precipitate with distilled water until the pH value is 7-8, performing centrifugal separation for 20min at the rotation speed of 3600r/min, taking the lower-layer precipitate, putting the lower-layer precipitate into an oven, drying at 90 ℃, grinding, and sieving by a 0.074mm sieve to obtain the sodium bentonite-loaded chitosan heavy metal stabilizing agent with the chitosan load rate of 9.24%.
In the sodium bentonite-loaded chitosan heavy metal stabilizing agent prepared in the embodiment 3, the interlamellar spacing of NaBent and NaBent-CTS is 1.21nm and 1.40nm respectively; the BET specific surface areas of the NaBent and the NaBent-CTS are 14.605m respectively 2 ·g -1 、51.732m 2 ·g -1 . The space between the layers of the NaBent and the specific surface area are obviously increased after the CTS is loaded, and the adsorption of heavy metals is facilitated.
Application example 1:
to Cu 2+ 、Zn 2+ 、Cd 2+ The stabilization agent (prepared in example 1) with 5% of dry bottom mud weight is added into the composite polluted bottom mud, and Cu detection shows that 2+ 、Zn 2+ 、Cd 2+ The concentration of TCLP leachate is 24.714mg/L, 23.598mg/L and 20.701mg/L respectively;
wherein, cu 2+ The proportions of the weak acid extraction state, reducible state, oxidizable state and residue state are respectively 12.28%, 79.58%, 19.53% and 26.38%;
Zn 2+ the proportions of the weak acid extraction state, the reducible state, the oxidizable state and the residue state are 41.15%, 30.29%, 5.85% and 26.44% respectively;
Cd 2+ the proportions of the weak acid extraction state, reducible state, oxidizable state and residue state are 83.14%, 22.19%, 1.20% and 0.53%, respectively.
Use the shellTreating the bottom mud for 14 days by using the polysaccharide modified sodium bentonite stabilizer, and detecting Cu 2+ The concentration of the leachate is reduced from 24.714mg/L before stabilization to 0.400mg/L after stabilization, and the stabilization rate is 98.38 percent; zn 2+ The concentration of the leachate is reduced from 23.598mg/L before stabilization to 0.911mg/L after stabilization, and the stabilization rate is 96.14 percent; cd [ Cd ] 2+ The concentration of the leachate is reduced from 20.701mg/L before stabilization to 0.76mg/L after stabilization, the stabilization rate is 96.33%, the concentration is lower than the detection limit of hazardous waste identification standard leaching toxicity identification (GB 5085.3-2007), and the treatment effect is remarkable.
The bottom mud which is stabilized for 30 days by using the chitosan modified sodium bentonite stabilizer is detected, and Cu is obtained 2+ The proportions of the weak acid extraction state, reducible state, oxidizable state and residue state are respectively 2.12%, 25.82%, 35.06% and 35%; zn 2+ The proportions of the weak acid extraction state, reducible state, oxidizable state and residue state are respectively 14.22%, 20.82%, 27.32% and 37.64%; cd [ Cd ] 2+ The proportions of the weak acid extraction state, reducible state, oxidizable state and residue state are respectively 72.72%, 12.03%, 12.97% and 2.28%, and Cu 2+ 、Zn 2+ 、Cd 2+ The ratio of the oxidizable state to the residual state of the catalyst is greatly improved.
Respectively adsorbing Cu by NaBent-CTS 2+ 、Zn 2+ 、Cd 2+ The infrared spectra before and after heavy metals are shown in FIG. 4. As can be seen from FIG. 4, naBent-CTS adsorbs Cu 2+ 、Zn 2+ 、Cd 2+ After that, no new peak appears, 3624, 3405, 1636, 1428, 1113, 987cm -1 The characteristic peak of hydroxyl and amino is shifted and the peak intensity is reduced, namely, the heavy metal and the hydroxyl and amino groups are subjected to complexation reaction; 507cm -1 The characteristic peak of Si-O-Al shows wave number shift and strength reduction, which is caused by ion exchange reaction between heavy metal and metal cation in the stabilizer. Adsorb Cu 2+ And Zn 2+ Then, hydroxyl and amino adsorb Cd compared with Si-O-Al absorption peak intensity 2+ The post-weakening is obvious, which indicates that NaBent-CTS is applied to Cu 2+ 、Zn 2+ And Cd 2+ Has selective adsorption, and weakens the strength according to characteristic peakIt is known that the heavy metal adsorption capacity of the curing agent is: cu 2+ >Zn 2+ >Cd 2+ 。
Respectively adsorbing Cu by NaBent-CTS 2+ 、Zn 2+ 、Cd 2+ XPS spectra before and after heavy metal adsorption are shown in FIG. 5, and it can be seen from the full spectrum that Cu is adsorbed 2+ 、Zn 2+ And Cd 2+ Then, orbital peaks of Cu2p, zn2p and Cd3d appeared, and it was fully confirmed that Cu was present 2+ 、Zn 2+ And Cd 2+ Successfully adsorbed on NaBent-CTS, and the previous infrared characterization results are also verified.
The strong Na1s spectral peak almost disappears after adsorption, which shows that the content of sodium element in NaBent-CTS is reduced rapidly after adsorption. The content change of sodium ions before and after the addition of heavy metals indicates that ion exchange reaction exists in the process of removing the heavy metals, and the heavy metals exchange metal cations in the NaBent-CTS into a solution, so that the infrared analysis result is further proved.
Comparative example 1:
the substrate sludge was treated with untreated sodium bentonite stabilizer alone for 14 days and tested for Cu 2+ The concentration of the leachate is reduced from 24.714mg/L before stabilization to 13.294mg/L after stabilization, and the stabilization rate is 46.21 percent; zn 2+ The concentration of the leachate is reduced from 23.598mg/L before stabilization to 16.431mg/L after stabilization, and the stabilization rate is 30.37 percent; cd (cadmium-doped cadmium) 2+ The concentration of the leachate is reduced from 20.701mg/L before stabilization to 12.731mg/L after stabilization, the stabilization rate is 38.5 percent, and the stabilization effect is poor.
Comparative example 2:
treating the bottom mud by using the bentonite stabilizer alone for 14 days, and detecting Cu 2+ The concentration of the leachate is reduced from 24.714mg/L before stabilization to 16.623mg/L after stabilization, and the stabilization rate is 32.74 percent; zn 2+ The concentration of the leachate is reduced from 23.598mg/L before stabilization to 18.395mg/L after stabilization, and the stabilization rate is 22.05 percent; cd [ Cd ] 2+ The concentration of the leachate is reduced from 20.701mg/L before stabilization to 16.836mg/L after stabilization, the stabilization rate is 18.67 percent, and the stabilization effect is poor.
While the embodiments of the invention have been described in detail, it is not intended to limit the invention to the exact construction and operation illustrated and described, and it will be appreciated by those skilled in the art that various changes, modifications, substitutions and alterations can be made herein without departing from the spirit and scope of the invention.
Claims (10)
1. The preparation method of the sodium bentonite loaded chitosan heavy metal stabilizing agent is characterized by comprising the following steps:
(1) Mixing and stirring sodium bentonite and an oxalic acid solution at normal temperature for 0.5-1.5h for acidification modification, then performing suction filtration, and collecting acidified sodium bentonite;
(2) Roasting and activating the acidified sodium bentonite in a muffle furnace;
(3) Dissolving chitosan powder in acetic acid solution to obtain chitosan solution, and slowly stirring for dissolving;
(4) Slowly adding acidified and activated sodium bentonite powder into the chitosan solution; fully soaking, and stirring and heating for 2.5-3h at the temperature of 60-65 ℃;
(5) Adding sodium hydroxide solution, adjusting pH to 8.5-9.5, slowly stirring for 10-15min, and removing unreacted chitosan by precipitation;
(6) Washing the precipitate with distilled water until the pH value is 7-8, performing centrifugal separation, taking the lower layer precipitate, drying, grinding and sieving to obtain the sodium bentonite loaded chitosan heavy metal stabilizing agent.
2. The preparation method according to claim 1, wherein the mass concentration of the oxalic acid solution in the step (1) is 18-23%; the liquid-solid ratio of the oxalic acid solution to the sodium bentonite is 1-42 mL/g.
3. The preparation method of claim 1, wherein the temperature for the roasting activation in the step (2) is 430-470 ℃ and the time is 1.5-2.5h.
4. The preparation method according to claim 1, wherein the mass concentration of the acetic acid solution in the step (3) is 3-5%; the mass concentration of the prepared chitosan solution is 3-5%.
5. The production method according to claim 1, wherein the mass ratio of the chitosan powder of step (3) to the sodium bentonite powder of step (4) is 1; the time for full infiltration is 2.5-3.5h.
6. The method of claim 1, wherein the precipitation of step (5) removes unreacted chitosan for a period of 2-3 hours.
7. The method according to claim 1, wherein the centrifugal separation in step (6) is carried out at a rotation speed of 3400-3600r/min for 15-20min; the drying temperature is 80-90 ℃; the sieving condition was 0.074mm.
8. The application of the sodium bentonite-loaded chitosan heavy metal stabilizing agent obtained by the preparation method of any one of claims 1 to 7, wherein the sodium bentonite-loaded chitosan heavy metal stabilizing agent is used for adsorbing and stabilizing bottom mud heavy metals in rivers and lakes.
9. The use according to claim 8, wherein the heavy metals of the bottom sludge of rivers and lakes comprise Cu 2+ 、Zn 2+ 、Cd 2+ 。
10. The use of claim 8, wherein the amount of the sodium bentonite-loaded chitosan is 4-6% of the weight of dry bottom mud when adsorbing and stabilizing heavy metals in the bottom mud of rivers and lakes, and the treatment time is 6-8 days.
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