CN113860468A - Composite material for efficiently treating hexavalent chromium pollution in environment and preparation method and application thereof - Google Patents
Composite material for efficiently treating hexavalent chromium pollution in environment and preparation method and application thereof Download PDFInfo
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Abstract
The invention belongs to the field of environmental pollution remediation, and discloses a composite material for efficiently remedying hexavalent chromium in an environment, and a preparation method and application thereof. The preparation method comprises the following steps: under the nitrogen environment, uniformly dispersing a certain amount of ascorbic acid in deoxygenated water, sequentially adding a ferrous sulfate solution and a sodium sulfide solution, carrying out coprecipitation reaction to obtain an ascorbic acid modified nano ferrous sulfide suspension, standing, and carrying out vacuum freeze drying on the obtained solid phase to obtain the ascorbic acid modified nano ferrous sulfate composite material. The invention utilizes ascorbic acid to modify nano ferrous sulfide, which can effectively improve the problem that nano material is easy to agglomerate and oxidize; meanwhile, the ascorbic acid has good oxidation resistance, so that the composite material is not easy to deteriorate and convenient to store, and the hexavalent chromium can be efficiently removed.
Description
Technical Field
The invention belongs to the field of environmental pollution remediation, and particularly relates to a composite material for efficiently remedying hexavalent chromium in an environment, and a preparation method and an application thereof, which are mainly applied to treatment and remediation of hexavalent chromium-polluted wastewater and soil.
Background
With the rapid development of industrialization, the pollution problem of heavy metal chromium is increasingly serious. According to statistics, the annual discharge amount of chromium in 2016 industrial wastewater reaches 131.8 tons, and the chromium becomes the heavy metal pollutant with the largest discharge amount. Chromium and compounds thereof are used as main raw materials in industrial production and mainly come from wastewater discharge in the industries of electroplating, tanning, metallurgy, chemical industry and the like. In addition, the consumption of chromium salt in China is at the top of the world, and more than 400 ten thousand tons of chromium slag are directly discharged into the environment without treatment, thereby causing serious pollution to water environment and soil. The heavy metal chromium in the environment mainly has two forms of trivalent chromium (Cr (III)) and hexavalent chromium (Cr (VI)), wherein the biotoxicity of the hexavalent chromium is 100 times of that of the trivalent chromium, and the hexavalent chromium has stronger mobility and bioaccumulation. Therefore, the reduction of hexavalent chromium to trivalent chromium is one of the common methods in the treatment of environmental chromium pollution.
At present, the hexavalent chromium pollution is treated by widely applying a direct chemical reduction method and an immobilization technology at home and abroad, the technology has high treatment efficiency, small disturbance to the environment and low repair cost, and the core is that hexavalent chromium is quickly reduced by utilizing an efficient reducing agent (Zhang Hui, pay de-ice, Guo Xiao, Song Feng, Chen Xiao Hua. reduction and stabilization repair of chromium polluted soil [ J ] environmental engineering report, 2017,11(11):6163 and 6168.). Wherein, the nanometer ferrous sulfide is used as an excellent reducing agent and has the advantages of large specific surface area, strong reaction activity and the like. However, the bare nano ferrous sulfide is easy to agglomerate and oxidize, so that the surface area and the activity of the bare nano ferrous sulfide are reduced, and the processing performance of the bare nano ferrous sulfide is greatly reduced. Therefore, the nano ferrous sulfide needs to be modified to avoid agglomeration or oxidation in a short time, so that the stability and the reaction activity of the nano material are improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to prepare the ascorbic acid modified nano ferrous sulfide composite material which is easy to operate and has good Cr (VI) reduction performance aiming at the defects of easy agglomeration, easy oxidation and the like of the nano iron sulfide. Researches show that the ascorbic acid is utilized to modify the nano ferrous sulfide, so that nano ferrous sulfide particles are effectively dispersed, the problem that nano materials are easy to agglomerate and oxidize is effectively solved, and the reaction activity of the nano materials is ensured; meanwhile, the preparation method is simple and efficient, and the material can efficiently remove hexavalent chromium in soil, is environment-friendly and nontoxic, and does not pollute the environment. Finally, the present invention has been completed.
The invention provides a preparation method of a hexavalent chromium composite material in an efficient restoration environment, which is characterized in that the reduction component of the composite material is ferrous sulfide, the modifier is ascorbic acid, and the hexavalent chromium composite material is prepared by a chemical coprecipitation method under the environment of continuously introducing nitrogen.
In a preferred embodiment, the specific steps are as follows: under the protection of protective gas, adding an aqueous solution of ferrous sulfate into an aqueous solution of ascorbic acid, and then slowly adding an aqueous solution of sodium sulfide (preferably, the slow addition of the sodium sulfide refers to a dropwise adding mode); continuously introducing protective gas into the mixed solution, stirring, sealing and standing after the reaction is finished to obtain ascorbic acid modified nano ferrous sulfide composite material suspension; the reaction time is more than 20 min; the standing time is more than 12 hours.
More preferably, the solid phase obtained is subjected to a step of vacuum drying, more preferably vacuum freeze drying, and then stored in a vacuum drier.
In a specific embodiment, the ferrous sulfate is ferrous sulfate heptahydrate, and the sodium sulfide is sodium sulfide nonahydrate as a raw material, wherein the molar ratio of the two is 0.8-1.2: 1, more specifically, to a 0.01 to 0.03M aqueous solution.
In a preferred embodiment, the content of the ascorbic acid in the mixed solution is 0.025wt% to 0.2 wt%.
In a more preferred embodiment, the water used in the preparation process is deionized water subjected to oxygen removal treatment, more specifically, pure water is placed in a liquid storage bottle, and protective gas is continuously introduced for more than 20min to remove dissolved oxygen in the water.
Further preferably, the protective gas is nitrogen.
In a very specific embodiment, the preparation steps are as follows:
(1) preparing a ferrous sulfate solution: 0.316g of ferrous sulfate heptahydrate is dissolved in 50ml of deoxygenated water, ultrasonic treatment is carried out until complete dissolution is achieved, and nitrogen is continuously introduced for standby.
(2) Preparing a sodium sulfide solution: 0.237g of sodium sulfide nonahydrate is dissolved in 50ml of deoxygenated water, the solution is sonicated until completely dissolved, and nitrogen is continuously introduced for standby.
(3) The coprecipitation method is used for preparing the material: adding 0.1g of ascorbic acid into 100ml of deoxygenated water, stirring for 5min under the protection of nitrogen, adding the ferrous sulfate solution obtained in the step (1), stirring for 5min, uniformly mixing, dropwise adding the sodium sulfide solution obtained in the step (2), finally continuously stirring for 20min, sealing and standing after the reaction is finished, and obtaining the ascorbic acid modified nano ferrous sulfide composite suspension with the concentration of 0.5 g/L.
The invention also provides the ascorbic acid modified nano ferrous sulfide composite material prepared by the preparation method. Further provides application of the ascorbic acid modified nano ferrous sulfide composite material in treatment of heavy metal-containing industrial wastewater, industrial solid waste or remediation of heavy metal contaminated soil, and specifically the heavy metal is hexavalent chromium.
Preferably, the suspension of the ascorbic acid modified nano ferrous sulfide composite material is mixed with soil, stirred uniformly and placed for more than 3 days; more specifically, the ascorbic acid modified nano ferrous sulfide composite material is used in an amount such that the molar ratio of the reduced component ferrous sulfide to hexavalent chromium is 1.2-1.8:1, preferably 1.5: 1.
The advantages and the beneficial effects of the invention are embodied in that: firstly, the ascorbic acid is utilized to modify the nano ferrous sulfide, so that nano ferrous sulfide particles are effectively dispersed, the problem that nano materials are easy to agglomerate and oxidize can be effectively solved, and the reaction activity of the nano materials is ensured. Meanwhile, the ascorbic acid has good oxidation resistance, so that the composite material is not easy to deteriorate and convenient to store. Moreover, the preparation method is simple, convenient and efficient, can synthesize the material by a coprecipitation method in one step, and has short preparation period, low cost and good effect. From the aspect of use effect, the application of the ascorbic acid modified nano ferrous sulfide composite material in the treatment of heavy metal-containing wastewater can quickly remove hexavalent chromium in an aqueous solution, and has high removal efficiency, so that the ascorbic acid modified nano ferrous sulfide composite material can be applied to in-situ remediation of soil polluted by hexavalent chromium, hexavalent chromium in soil can be efficiently removed, and meanwhile, the material is environment-friendly, non-toxic and free of environmental pollution.
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FIG. 1 is a comparison graph of an object and an electron microscope observation comparison graph of the ascorbic acid nano ferrous sulfide composite material and an unmodified nano material prepared according to example 1 of the present invention.
Fig. 2 is a graph comparing the reduction efficiency of the obtained ascorbic acid nano ferrous sulfide composite material and the unmodified nano material to hexavalent chromium in water according to the embodiment 2 of the invention.
FIG. 3 is a graph comparing the oxidation resistance of the obtained ascorbic acid nano ferrous sulfide composite material and unmodified nano material to hexavalent chromium in water according to example 3 of the present invention.
Fig. 4 is a graph comparing the reduction efficiency of the obtained ascorbic acid nano ferrous sulfide composite material to hexavalent chromium in water under different dosage conditions according to example 4 of the present invention.
Fig. 5 is a graph comparing the removal rate of hexavalent chromium in water under different pH conditions of the obtained ascorbic acid nano ferrous sulfide composite material according to example 5 of the present invention.
FIG. 6 determination of ascorbic acid dosage in example 1.
Detailed Description
In order to more clearly describe the technical scheme of the invention, the invention is further illustrated by the following specific examples, which should be understood that the specific examples described herein are only for explaining the invention and are not used for limiting the invention.
Example 1
The preparation method of the composite material for efficiently repairing hexavalent chromium in the environment comprises the following specific steps:
(1) placing 400ml of pure water in a liquid storage bottle, and continuously introducing nitrogen for more than 20min to remove dissolved oxygen in the water;
(2) preparing a 0.023M ferrous sulfate solution by using the deoxygenated water in the step (1);
(3) preparing 0.023M of sodium sulfide solution by using the deoxygenated water in the step (1);
(4) taking 100ml of deoxygenated water in the step (1), adding 0.1g of ascorbic acid, and stirring under the protection of nitrogen to dissolve the ascorbic acid in the water;
(5) under the protection of nitrogen, adding 50ml of ferrous sulfate solution prepared in the step (2) into the solution obtained in the step (4);
(6) dropwise adding 50ml of the sodium sulfide solution prepared in the step (3) into the solution obtained in the step (4) under the protection of nitrogen;
(7) and (4) continuously introducing nitrogen into the mixed system obtained in the step (6), stirring for 20min, sealing and standing for 12h after the reaction is finished, and preparing the ascorbic acid modified nano ferrous sulfide composite material suspension with the concentration of 0.5 g/L.
Further, the prepared composite material for efficiently restoring hexavalent chromium in the environment is subjected to solid-liquid separation after standing, and the obtained solid phase is subjected to vacuum freeze drying and is stored in a vacuum drier.
The composite material after freeze-drying is directly added into air-dried soil, and is activated by adding water after being uniformly mixed.
The Zeta potential of the ascorbic acid modified nano ferrous sulfide suspension and the nano ferrous sulfide material suspension prepared in the embodiment is measured, and the higher the absolute value of the Zeta potential is, the more stable the system is, namely, the dissolution or dispersion can resist aggregation.
The determination result shows that the Zeta potential determination result of the unmodified nano ferrous sulfide material is-15.13 mV, and the dispersion system stability is poor; the Zeta potential measurement result of the modified nano material obtained in the embodiment is-38.21 mV, the absolute value of the Zeta potential measurement result is more than 30mV, and the stability is better.
According to the chemical formula Fe2++S2-→ FeS determines that the ratio of ferrous sulfate to sodium sulfide is optimally a 1:1 molar ratio, while the amount of ascorbic acid needs to be determined experimentally:
different dosages of ascorbic acid are preferably used in the experiment: the material preparation process is substantially the same as that of example 1 except that the modifier ascorbic acid is added in an amount of 0.025wt%, 0.05wt%, 0.075wt%, 0.1wt%, 0.15wt%, 0.2wt%, respectively, during the material preparation process. Preparing 6 groups of simulated wastewater with the initial concentration of hexavalent chromium of 60ml/L, 200ml of each group, adjusting the initial pH =7, respectively adding the same amount of the prepared nano material suspension with different modifier adding amounts to ensure that the molar ratio of the reduction component ferrous sulfide to the hexavalent chromium is 1.5:1, reacting for 180min in a constant-temperature shaking table at 25 ℃ under the condition of the rotating speed of 200rpm, filtering by a 0.22um filter membrane, and detecting the hexavalent chromium in the filtrate by using a dibenzoyl dihydrazide spectrophotometry method for measuring water quality hexavalent chromium. As shown in FIG. 6, the wastewater removal rate was 95.19% for the modified nanomaterial prepared by adding 0.025wt% of the modifier, and the wastewater removal rate was 99% or more for all the other groups of modified nanomaterials, and the optimum amount of VC added was 0.05wt% considering the small amount of the modifier and the good stability of the nanomaterial.
In addition, the prepared ascorbic acid nano ferrous sulfide composite material and the unmodified nano material are compared in physical appearance (shown as A and B in figure 1 respectively), the unmodified nano material is changed from black to dark brown, an oxidation phenomenon occurs, and the modified ascorbic acid nano ferrous sulfide composite material is kept unchanged, so that the modified nano material has good oxidation resistance.
In addition, by comparing scanning electron micrographs of the prepared ascorbic acid nano ferrous sulfide composite material and the unmodified nano material (as shown in C and D in figure 1 respectively), it can be seen that a large-area layered structure appears on the surface of the unmodified nano material, and an agglomeration phenomenon occurs, while the majority of the ascorbic acid nano ferrous sulfide composite material is spherical or ellipsoidal fine particles, which shows that the ascorbic acid nano ferrous sulfide composite material has good dispersibility.
Example 2
Dynamics experiment for removing hexavalent chromium in aqueous solution: preparing two groups of simulated wastewater with the initial concentration of hexavalent chromium of 60ml/L, 200ml of each group, adjusting the initial pH =7, respectively adding the modified nano-material suspension and the unmodified nano-material suspension prepared in the example 1 in equal amount, so that the molar ratio of the reduced component ferrous sulfide to the hexavalent chromium is 1.5:1, reacting for 180min in a constant-temperature shaking table at 25 ℃ under the condition of the rotating speed of 200rpm, respectively sampling at 2min, 5min, 10min, 15min, 20min, 40min, 60min, 90min, 120min and 180min after the reaction starts, filtering by a 0.22um filter membrane, and detecting the hexavalent chromium in the filtrate by using a dibenzoyl dihydrazide spectrophotometry method for measuring the hexavalent chromium in water.
The reduction efficiency of the modified nano-material and the unmodified nano-material to hexavalent chromium in water in the embodiment is shown in fig. 2. The experimental result shows that under the same dosage condition, the concentration of the wastewater treated by the unmodified nano material is 1.72mg/L, and the wastewater does not meet the requirements of the III-class standard (less than or equal to 0.05 mg/L) of underground water, the removal rate of hexavalent chromium by the modified nano material obtained in the embodiment 1 of the invention reaches more than 99%, and the I-class standard (less than or equal to 0.005 mg/L) of the underground water can be met, and the removal efficiency of the modified nano material obtained in the invention is integrally higher than that of the unmodified nano material, so that the modified material has greater potential in repairing hexavalent chromium polluted water.
Example 3
The oxidation resistance of the modified nano material is researched: the modified nano-material suspension and the unmodified nano-material suspension prepared in the example 1 are subpackaged into a plurality of 50ml centrifugal tubes, and are kept stand at a constant temperature for 2d, 3d, 5d and 10d respectively, and then the kept modified nano-material and unmodified material suspensions are shaken up again for ultrasonic dispersion for 15min to carry out a hexavalent chromium removal experiment. The environmental conditions and the material addition amount are the same as those in example 2, and the experimental method is basically the same as that in example 2, except that continuous time point sampling is not performed in the present example, and only the final equilibrium concentration of hexavalent chromium is measured after the continuous reaction time of 180 min.
The oxidation resistance of the modified nanomaterial and the unmodified nanomaterial of this example is shown in fig. 3. After standing for 10 days, the removal efficiency of the unmodified nano material to the hexavalent chromium in the water is only 60.37%, and the concentration of the hexavalent chromium in the treated wastewater is 28.32mg/L and far exceeds the concentration limit value specified by the underground water quality standard. Due to good oxidation resistance of the modified nano material, after standing for 10 days, the concentration of hexavalent chromium in the treated wastewater is 0.01mg/L, the treated wastewater can meet the II-class standard (less than or equal to 0.01 mg/L) of underground water, the removal rate of the hexavalent chromium is still more than 99%, and the oxidation resistance of the modified nano material is remarkably higher than that of an unmodified material, so that the modified nano material can be better stored in practical application.
Example 4
And (3) comparing the reduction efficiency of the modified nano material in different adding amounts: the operation flow and the detection mode are the same as those of example 2, and the experimental method related to the example is basically the same as that of example 2, except that 4 groups of simulated wastewater are prepared, and different amounts of the modified nano-material suspension prepared in example 1 are respectively added, so that the molar ratios of the reduction component ferrous sulfide and hexavalent chromium are respectively 1:1, 1.5:1, 2:1 and 2.5: 1.
The reduction efficiency ratio of the modified nano-material in the present example under different dosage conditions is shown in fig. 4. The experimental result shows that when the molar ratio is 1:1, the removal rate of the modified material to hexavalent chromium in water after reacting for 180min is 75.29 percent, and the removal rate does not reach the concentration limit value specified by the quality standard of underground water; with the increase of the adding amount, the reaction rate is improved, and when the molar ratio is 2:1, the removal rate of the hexavalent chromium in the water by the modified material after 20min of reaction reaches 99%; at a molar ratio of 2.5:1, equilibrium is reached after 2min of reaction. The experimental data are subjected to pseudo-second-order kinetic fitting analysis, and four different adding steps are carried outThe experimental results under quantitative treatment all fit well (R)2> 0.999) and the equilibrium adsorption capacities are calculated to be 386.1mg/g, 392.16 mg/g, 295.85 mg/g and 236.41 mg/g respectively, so that the optimum adding amount of the modified material is 1.5: 1.
Example 5
The modified nano material treats hexavalent chromium in water under different pH conditions: the experimental conditions and the detection method are basically the same as those of the example 2, and the difference is that 100ml of each of 8 groups of simulated wastewater with the pH value of 3-10 is prepared, and the final equilibrium concentration of hexavalent chromium is measured after the continuous reaction is carried out for 180 min.
The experimental results of the modified nanomaterial for treating hexavalent chromium in water under different pH conditions are shown in fig. 5, the removal rates of two sets of experiments, namely pH =9 and pH =10, on hexavalent chromium are 96.45% and 95.01%, respectively, and the removal rates of the two sets of experiments do not reach the concentration limit value specified by the quality standard of groundwater, and the removal rates of the six sets of experiments on hexavalent chromium reach more than 99%, which indicates that the material has a good removal effect on hexavalent chromium in water in a large pH range; the pH value of the treated water solution is 6-9. In contrast, the pH of the unmodified nanomaterial treated simulated wastewater with pH 7 was 10.1, indicating that the modified nanomaterial has excellent potential for improving alkaline wastewater.
Example 6
The research on the performance of the modified nano ferrous sulfide material for treating hexavalent chromium contaminated soil comprises the following steps: taking 100g of actual polluted soil after pretreatment, putting two parts of actual polluted soil into a polyethylene jar, weighing and adding a certain mass of modified nano ferrous sulfide particles prepared in the embodiment 1 to ensure that the molar ratio of the reduced component ferrous sulfide to hexavalent chromium is 1.5:1, fully mixing, adding 40ml of pure water, uniformly stirring, placing in a constant temperature room at 25 ℃ for culture, respectively taking one part of soil after 3d and 7d, freeze-drying, and sieving with a 100-mesh sieve for later use. Extracting and measuring the mass concentration of hexavalent chromium in the soil according to an alkaline solution extraction-flame atomic absorption spectrophotometry for measuring soil and sediment hexavalent chromium, and measuring the leaching toxicity according to a solid waste leaching toxicity leaching method-a sulfuric acid-nitric acid method and a water quality hexavalent chromium measuring-a dibenzoyl dihydrazide spectrophotometry. In the embodiment, the pH value of the soil is 4.91, the content of hexavalent chromium in the soil is 15.29mg/kg, and the concentration of the hexavalent chromium leached by a sulfuric acid-nitric acid method is 0.152 mg/L.
As shown in Table 1, in the soil treated by the method for treating the hexavalent chromium in the invention for 3d and 7d, the hexavalent chromium concentration leached by the nitric acid sulfate method is 0.007mg/L after 3d, which meets the II-class standard (less than or equal to 0.01 mg/L) of underground water; no detection is carried out after 7 days, and the standard of I type underground water (less than or equal to 0.005 mg/L) is met. The ascorbic acid modified nano ferrous sulfide composite material has a good removal effect on hexavalent chromium contaminated soil, and has a wide application prospect in the remote remediation of heavy metal contaminated soil.
TABLE 1 comparison of hexavalent chromium contaminated soil before and after treatment
| Item | Before treatment | After 3d of treatment | After 7d of treatment |
| Soil hexavalent chromium (mg/kg) | 15.61±2.552 | - | - |
| Leaching toxicity (mg/L) | 0.156±0.005 | 0.007±0.162 | - |
The above examples are merely illustrative for clearly illustrating the present invention and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. The preparation method of the composite material for efficiently repairing hexavalent chromium in the environment is characterized in that the composite material is prepared by a chemical coprecipitation method under the environment of continuously introducing nitrogen, wherein a reducing component of the composite material is ferrous sulfide, and a modifier is ascorbic acid.
2. The preparation method according to claim 1, comprising the following steps:
under the protection of protective gas, adding a ferrous sulfate aqueous solution into an ascorbic acid aqueous solution, and then slowly adding a sodium sulfide aqueous solution; continuously introducing protective gas into the mixed solution, stirring, sealing and standing after the reaction is finished to obtain ascorbic acid modified nano ferrous sulfide composite material suspension; the reaction time is more than 20 min; the standing time is more than 12 hours.
3. The method according to claim 2, further comprising a step of subjecting the ascorbic acid-modified nano ferrous sulfide composite suspension to solid-liquid separation, and subjecting the obtained solid phase to vacuum drying, more preferably vacuum freeze drying, and then storing in a vacuum dryer.
4. The process according to any one of claims 1 to 3, wherein the ferrous sulfate is ferrous sulfate heptahydrate, and the sodium sulfide is sodium sulfide nonahydrate, which is used as a raw material, in a molar ratio of 0.8 to 1.2: 1, more specifically, to a 0.01 to 0.03M aqueous solution.
5. The method according to claim 4, wherein the ascorbic acid is contained in the mixed solution in an amount of 0.025wt% to 0.2 wt%.
6. The method according to any one of claims 1 to 3, wherein the water used in the preparation process is deionized water subjected to oxygen removal treatment, more specifically, the deionized water is placed in a liquid storage bottle, and the protective gas is continuously introduced for more than 20min to remove dissolved oxygen in the water.
7. The process according to any one of claims 1 to 3, wherein the shielding gas is nitrogen.
8. The method of claim 2, wherein the slow addition of the sodium sulfide solution is in a dropwise manner.
9. The ascorbic acid-modified nano ferrous sulfide composite material obtained by the production method according to any one of claims 1 to 8.
10. Use of the ascorbic acid-modified nano-ferrous sulfide composite of claim 9 in the treatment of industrial wastewater, industrial solid waste or heavy metal contaminated soil remediation containing heavy metals, in particular the heavy metal is hexavalent chromium; preferably, the suspension of the ascorbic acid modified nano ferrous sulfide composite material is mixed with soil, stirred uniformly and placed for more than 3 days; more specifically, the dosage of the ascorbic acid modified nano ferrous sulfide composite material is up to the molar ratio of the reduced component ferrous sulfide to hexavalent chromium of 1.2-1.8: 1.
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| CN116037632A (en) * | 2022-11-21 | 2023-05-02 | 南开大学 | Method for in-situ reconstruction of underground aquifer and application |
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