CN111234832B - FeS-containing2Composite material and reduced iron, preparation method and application thereof - Google Patents

FeS-containing2Composite material and reduced iron, preparation method and application thereof Download PDF

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CN111234832B
CN111234832B CN202010050625.4A CN202010050625A CN111234832B CN 111234832 B CN111234832 B CN 111234832B CN 202010050625 A CN202010050625 A CN 202010050625A CN 111234832 B CN111234832 B CN 111234832B
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soil
fes
hexavalent chromium
composite material
microwave
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CN111234832A (en
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杨卫春
李琦
闵小波
杨志辉
张晓明
廖骐
石岩
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Central South University
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    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K17/00—Soil-conditioning materials or soil-stabilising materials
    • C09K17/40—Soil-conditioning materials or soil-stabilising materials containing mixtures of inorganic and organic compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09C—RECLAMATION OF CONTAMINATED SOIL
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    • B09C1/08—Reclamation of contaminated soil chemically

Abstract

The invention provides a FeS-containing catalyst2And a reduced iron composite material, a method for preparing the same and use thereof. FeS is prepared2And mixing the substances with the content of more than 95% with the reducing iron powder, adding the chelating agent, fully mixing, taking out after ball milling, and sieving to obtain the repair material. The soil to be repaired is added into the soil polluted by hexavalent chromium, and the reduction rate of the hexavalent chromium reaches more than 99 percent. The hexavalent chromium contaminated soil remediation material which is economical and easy to prepare is expected to fully utilize metal tailings, is prepared in one step, is simple in preparation method and low in cost, and is expected to solve the problem of difficult tailing stockpiling in large-scale preparation; the prepared restoration material has good restoration effect on the hexavalent chromium contaminated soil by utilizing the external field conditions such as microwave and the like, has short time, and can be efficiently used for restoring the hexavalent chromium contaminated soil.

Description

FeS-containing2Composite material and reduced iron, preparation method and application thereof
Technical Field
The invention relates to the technical field of soil pollution remediation, in particular to an economic and easily prepared FeS-containing fertilizer2And a reduced iron repair material and methods of making and using the same.
Background
Chromium and its compounds are typical heavy metal pollutants produced in the chromium chemical industry. At present, more than 40 chromium slag piling yards and more than 30 waste chromium salt plants are still available in China. Due to lack of environmental risk control measures such as pollutant migration and obstruction, the soil of chromium waste residue storage yards and waste plant sites in the chromium chemical industry is seriously polluted. Chromium is generally present in two forms of Cr (VI) and Cr (III), the toxicity of Cr (VI) is about 100 times higher than that of Cr (III), hexavalent chromium in the environment can enter soil through various ways, and water-soluble Cr (VI) is listed as one of 8 chemical substances with the greatest harm to human bodies.
At present, the Cr (VI) polluted soil is mainly repaired by two ideas: firstly, the existing form of chromium in soil is changed, and Cr (VI) is reduced into Cr (III) with relatively low toxicity, so that the migration capability and the bioavailability in the environment are reduced; secondly, chromium is removed from the contaminated soil. Around the two ideas, researches on various repair technologies such as reduction stabilization, electric repair, soil leaching, ex-situ cleaning, phytoremediation and the like have been carried out on chromium-contaminated soil. The reduction stabilization technology is considered as a chromium-contaminated soil remediation technology with high maturity and treatment efficiency, short remediation time and moderate treatment cost and operability, and has attracted wide attention. Therefore, the remediation agent is of great importance in the reduction stabilization remediation of chromium-contaminated sites. The traditional reduction and stabilization repairing agents such as ferrous sulfate, zero-valent iron powder, sodium sulfide and the like have the problems of low repairing efficiency, secondary pollution and the like. Some commonly reported high-efficiency synthetic materials, such as nano zero-valent iron, have complex preparation methods and high price and are difficult to be applied in engineering, so that the research on the high-efficiency green and relatively economic remediation material and the preparation method thereof are the key for solving the problem of hexavalent chromium polluted soil.
Disclosure of Invention
The invention aims to provide an economic and easily prepared FeS-containing material2And a reduced iron composite material and a method for producing the same. The material can efficiently repair the heavy metal contaminated soil, and particularly can realize low-cost, quick, efficient and green toxicity-reducing treatment on hexavalent chromium contaminated soil.
In order to solve the problems, the invention adopts the following technical scheme:
FeS-containing2And a process for producing a reduced iron composite material by reacting FeS2Mixing the substances with the content of more than 95% with reducing iron powder, adding a chelating agent, fully mixing, taking out after ball milling, and sieving to obtain the product.
Further, the FeS2The substance with content of more than 95% comprises FeS2Natural pyrite or lead-zinc metal ore dressing tailings with the mass fraction of more than 95 percent.
The iron powder of the invention can also be replaced by industrial iron chips.
FeS2The substances with the content of more than 95 percent mainly mean that the substances which are not beneficial to removing heavy metals in the invention are not contained, and the requirements of the invention on raw materials can be met.
Further, the FeS2The natural pyrite or lead-zinc metal ore dressing tailings, iron powder or industrial scrap iron with the mass fraction of more than 95 percent preferably pass through 20 meshes.
Further, FeS2The mol ratio of the iron powder to the reducing iron powder is 7:3-9: 1.
Further, FeS2The molar ratio to the reduced iron powder is preferably 8:2 to 9: 1.
Further, FeS2The molar ratio to the reduced iron powder is preferably 9: 1.
The above FeS2The molar ratio of the iron powder to the reduced iron powder has a very important influence on the effect of the product of the invention on removing heavy metals. The invention discovers that FeS is used as the catalyst for the first time2The mol ratio of the Cr (VI) to the reducing iron powder is within the range of 7:3-9:1, and the Cr (VI) removal rate of the prepared material is greater than that of FeS2And iron powder are independently subjected to mechanical ball milling activation, and the combination degree of the pyrite and the iron powder in the molar ratio range is better than that of other molar ratios. From SEM images in different molar ratio ranges, compared with materials prepared by other molar ratios, when n (pyrite: iron powder) is 9:1, more nano-scale fine particles are adhered to the surface of the pyrite, and the specific surface area and the reaction activity of the particles are greatly increased. The invention adopts mechanical ball milling activation technology, utilizes the characteristic of high sulfur (mass fraction is 53.33%) of the pyrite as a vulcanizing agent to vulcanize the zero-valent iron, compounds the two, and enables the grain diameters of the two to become finer after ball milling, thereby achieving the purposes of removing passivation layers of the two and increasing specific surface area, and simultaneously utilizing the high-efficiency electron transfer effect caused by the generated sulfide to improve the catalytic performance.
Further, the FeS-containing2And a process for preparing a reduced iron composite, said chelating agent comprising: one or more of citric acid or citrate.
Further, the chelating agent preferably comprises one or more of citric acid, calcium citrate and potassium citrate.
Further, the chelating agent is preferably added in an amount of 1 to 8 mass percent of the total material.
Further, the chelating agent is added in an amount of preferably 1 to 4% by mass of the total material.
Further, the chelating agent is added in an amount of preferably 1 to 3% by mass of the total material.
The in-situ chemical reduction of hexavalent chromium (Cr (VI)) to trivalent chromium (Cr (III)) by using natural iron-containing minerals is one of the important directions of green chemistry, and a great deal of related research is carried out at home and abroad. Research shows that the reduction of Cr (VI) by pyrite can be divided into three stages of adsorption, oxidation reduction and coprecipitation. With regard to the reduction of hexavalent chromium from pyrite, the reaction process which is currently relatively approved at home and abroad comprises:
Cr2O7 2-+H2O＝2HCrO4 -
3FeS2+15HCrO4 -+57H+＝3Fe3++15Cr3++6SO4 2-+36H2O
xCr3++(1-x)Fe3++3OH-＝(CrxFe1-x)(OH)3(s)
fe (II) and S upon pyrite production2 2-The iron-chromium coprecipitation ((Cr) is generated on the surface of the pyrite) by the electron exchange with Cr (VI)xFe1-x)(OH)3) Thus, the formation of surface oxidation products blocks further reaction of pyrite functional groups with cr (vi), resulting in incomplete reaction. Most organic acids have strong pH buffering capacity, so that the efficiency of removing Cr (VI) from the pyrite-based material can be improved, but at the same time, the organic ligand can be adsorbed on the pyrite to block active sites on the surface of the pyrite, so that the selection of the appropriate organic ligand as the chelating agent is particularly important. Thus, the chelating agent prevents the passivation of the pyrite surface by removing the surface oxide layer by forming soluble Fe-Cr ligand complexes; the redox cycle for reducing Fe is enhanced to promote regeneration of new surface sites.
Compared with the material without citric acid, the material prepared by adding citric acid has obviously improved Cr (VI) removal efficiency, but when the addition amount of citric acid is too large, the Cr (VI) removal rate is reduced, which possibly causes the organic ligand to be adsorbed on the surface of pyrite by excessive addition of citric acid to prevent the reaction from fully proceeding, and the addition amount of citric acid is selected to be 1% in combination with the economy of material preparation. The FeS-containing2The mass ratio of the total material to the grinding balls is 1:5-1:20, the ball milling rotation speed is 200 plus 500 r/min, the ball milling time is 2-6 hours, and the composite material is sieved by a 100-mesh sieve after ball milling.
The omnibearing planetary ball mill is preferably selected during ball milling, and the grinding balls and the ball milling pot are made of hard stainless steel or agate.
It is a secondary object of the present invention to provide the above-mentioned FeS-containing2And the application of the composite material of the reduced iron in repairing the heavy metal polluted soil.
Further, the heavy metals include: hexavalent chromium and/or antimony.
Further, the application is as follows: adding the repairing material into heavy metal contaminated soil, and then adding pure water, wherein the mass ratio range is as follows: repairing materials: 100 parts of water: (1-6): (30-50), uniformly stirring the mixture, and reducing and detoxifying the hexavalent chromium into trivalent chromium after 1-30 days, so as to realize in-situ remediation of the heavy metal contaminated soil.
The soil repair material additive amount is too little to lead to the effect not good, and the additive amount is too big then can become high with high costs, consequently combines repair effect and economic nature principle, soil: repairing materials: 100 parts of water: 5: (30-50) is preferable.
Further, the application specifically can also be as follows: adding the repairing material into heavy metal contaminated soil, and then adding pure water, wherein the mass ratio range is as follows: repairing materials: 100 parts of water: (1-6): (50-200), stirring the mixture to be uniform, applying microwave external field treatment to the mixture, wherein the microwave power is 0.3KW-0.7KW, and the microwave time is controlled within 1min-10min, so as to finish the quick repair of the hexavalent chromium polluted soil.
During microwave treatment:
soil: repairing materials: water is preferably 100: (1-6): (100-200).
The microwave power is preferably 0.5KW-0.7 KW.
The microwave time is preferably 5-10min, and more preferably 8-10 min.
During microwave treatment, a great deal of exploration experiments are carried out on microwave power and microwave time in the early stage, when the microwave power is too high (0.7KW), the removal rate of Cr (VI) in soil is 95.21% and the concentration of the residual Cr (VI) is 21.51mg/kg when the microwave treatment is carried out for 10min, when the microwave power is too low (0.2KW), the removal rate of Cr (VI) in soil is 92.58%, the concentration of the residual Cr (VI) is 33.25mg/kg, when the microwave power is between the two, and 0.35KW is selected, the removal rate of Cr (VI) in soil is more than 99% and the concentration of the residual Cr (VI) is 3.79mg/kg when the microwave treatment is carried out for 10 min; for the microwave time, when the microwave time is too short, the microwave power is 0.35KW, and the microwave treatment is carried out for 5min, the removal rate of Cr (VI) in the soil is 90.89%, the concentration of the residual Cr (VI) is 40.82mg/kg, when the microwave is carried out for 8min, the removal rate of Cr (VI) in the soil continues to rise but is still less than 95%, and when the microwave is carried out for 10min, the removal rate of Cr (VI) in the soil reaches more than 99%, the concentration of the residual Cr (VI) is 3.79mg/kg, and the repair target is basically reached; as for the water addition amount of microwave treatment, early-stage experiments show that the repair efficiency can be improved more than 2:1 when the solid-liquid ratio is 1:1, and the microwave repair time can be saved by improving the water amount within a certain range, mainly because water is also a wave-absorbing medium, has large dielectric constant and strong microwave absorption capacity, can accelerate the temperature rise rate of a system and accelerate the reaction rate of a material.
Microwave heating is different from traditional heating methods, and microwave heating is whole heating, and the microwave can pierce through the material, realizes the simultaneous heating of surface and interior, and the heating is fast, simultaneously can also the selective heating, this is mainly because different microwave absorbing media have different dielectric constants. The influencing factors of microwave heating comprise wave-absorbing medium, power, water content and the like, wherein the wave-absorbing medium has a key influence on the microwave heating, and the material capable of absorbing the microwave and converting the microwave into heat energy is called wave-absorbing medium, which often has larger dielectric constant and dielectric loss coefficient and mainly contains water and fatAnd polar and magnetic compounds. The FeS prepared by the invention2the/Fe composite material has strong magnetism, is a good wave-absorbing medium, has strong wave-absorbing capability, can quickly absorb energy under a microwave field, and quickly raises the reaction temperature, which is an advantage that the traditional repair materials such as sodium sulfide, ferrous sulfate and the like do not have.
The advantages of the invention are mainly reflected in that:
(1) the economical and easily prepared preparation method of the heavy metal contaminated soil remediation material provided by the invention has the advantages that the main raw material pyrite is wide in source and low in price, can be obtained from metal tailings, is expected to solve the problem of difficult stockpiling of the tailings, is simple in preparation method, low in cost, easy to prepare in a large scale, and is suitable for remediation of actual heavy metal contaminated sites, especially chromium contaminated sites.
(2) The invention utilizes pyrite and adopts a high-energy ball-milling activation technology to vulcanize and modify reducing iron powder, so that the originally smooth material becomes very rough and the particle size is reduced, meanwhile, the pyrite becomes a main body by controlling the proportion of the pyrite and the iron powder, a plurality of nano-scale fine particles are adhered to the surface of the material, and the specific surface area and the reaction activity of the particles are greatly increased as shown in figure 2. XRD spectrogram of the material obtained after high-energy ball milling activation modification is shown in figure 3, and except FeS in the XRD spectrogram of the material prepared by the molar ratio of pyrite to iron powder of 9:1 and 5:52And no diffraction peak other than that of Fe, which indicates that FeS is generated during ball milling2And Fe did not undergo significant chemical reaction or formed undetectable amorphous material. However, the diffraction peak intensity of the composite material after ball milling is obviously weaker than that of ball milling iron powder or pyrite, which shows that the amorphous degree and the activity of the composite material after ball milling are improved. EDS analysis of the nanoscale fine particles adhered to the surface of the material prepared by the molar ratio of 9:1, as shown in FIG. 4, shows that the relative atomic ratio of Fe to S in the nanoscale fine particles is about 1:3, as shown in Table 1, and is greater than the relative atomic ratio of Fe to S in pyrite (1:2), which indicates that the nanoscale fine particle substances may be formed amorphous FeSx. The polysulfide thus formed causes efficient electron transfer and improved catalysisThe performance is one of the important reasons that the composite material has better reaction performance compared with the ball-milling pyrite or iron powder.
TABLE 1
Figure BDA0002371030390000051
Figure BDA0002371030390000061
The influence of the molar ratio on the product cannot be determined only by performing phase analysis on the ball-milled product. Therefore, the XRD patterns of the ball-milled products were analyzed for crystallinity using the Jade software, and the obtained results are shown in table 2. The crystallinity of the compound after the high-energy ball milling activation modification is greatly reduced, namely the crystallinity is the complete degree of crystallization. The crystal with high crystallinity is complete, good in crystal form, large in crystal grain and orderly arranged in inner mass points. The crystal with low crystallinity, fine crystal grains and more crystal defects. The poorer the crystallinity, the more defects the sample has, the lowest the crystallinity of the material and the most crystal defects of the material at a molar ratio of 9:1 in the following table, FeS2The compounding degree of Fe and Fe is best; that is, the pyrite is substantially combined with the iron powder during the ball milling process, as can be confirmed by the adhesion of many nano-sized fine particles to the surface of the material as reflected in the SEM image of fig. 2.
TABLE 2
Figure BDA0002371030390000062
(3) The molar ratio of the pyrite to the reducing iron powder is 7:3-9:1, and the effects of preparing materials with different pyrite/reducing iron powder molar ratios are compared, and as a result, as shown in fig. 5, when n (pyrite: iron powder) is (7:3-9:1), the removal rate of Cr (VI) of the prepared materials is greater than that of the materials prepared by mechanically ball-milling and activating the pyrite and the iron powder independently, which shows that the compounding degree of the pyrite and the iron powder is better than that of other molar ratios in the range of the molar ratios, and as shown in an SEM picture (fig. 6) of different molar ratios, compared with the materials prepared by other molar ratios, when n (pyrite: iron powder) is 9:1, more nano-scale fine particles are adhered to the surface of the pyrite, and the specific surface area and the reaction activity of the particles are greatly increased.
(4) Citric acid or citrate is added in the process of high-energy ball milling activation modification, and the action of the method mainly has two aspects: 1) the addition of citric acid is beneficial to forming Fe (III) -S on the surface of the pyrite, and the redox cycle of Fe is enhanced to promote the regeneration of new surface sites; 2) the strong complexing ability of citric acid can prevent the passivation of the surface of pyrite by forming soluble iron-chromium citric acid complex, and enhance the reaction activity. Compared with a repair material without citric acid, the material prepared by adding citric acid (3%) under the same condition has the efficiency of removing Cr (VI) in water improved to nearly 90% from 75% and the removal rate of hexavalent chromium is obviously improved.
(5) The synthesized hexavalent chromium contaminated soil remediation material which is economical and easy to prepare shows high-efficiency reduction remediation performance, is stable in chemical property, has an obvious effect in traditional hexavalent chromium contaminated soil remediation, can achieve the purpose of quickly reducing toxicity of hexavalent chromium contaminated soil under the condition of a microwave outfield, and is suitable for treatment of hexavalent chromium contaminated soil.
Drawings
FIG. 1 is a TEM image of example 1;
FIG. 2 is an SEM photograph of example 1;
FIG. 3 is the XRD spectrum of example 1;
FIG. 4 is EDS analysis of the nano-sized fine particles adhered to the surface of the material prepared in example 1;
FIG. 5 is a graph showing the effect of different molar ratios of pyrite to reduced iron powder in preparing a material on hexavalent chromium removal;
FIG. 6 is an SEM image of materials prepared with different pyrite to reduced iron powder molar ratios (a)10:0, (b)9:1, (c)5: 5;
FIG. 7 is a graph showing the effect of example 1 in repairing hexavalent chromium-contaminated soil;
FIG. 8 is a graph showing the results of searching for the amount of citric acid added.
Detailed Description
The preparation of the hexavalent chromium contaminated soil remediation material which is economical and easy to prepare and the method for using the same are further described below, but the invention is not limited thereto.
Example 1
Selection of FeS2Drying, vibrating, grinding and screening the pyrite with the mass fraction of more than 95% through a 20-mesh sieve to obtain pyrite particles; fully mixing pyrite and iron powder (passing through 20 meshes) according to a molar ratio of 9:1, adding citric acid with the total material mass fraction of 1%, putting the mixture into a hard stainless steel ball milling tank, adding grinding balls according to a ball-to-material ratio of 15:1, setting the ball milling speed to be 400 r/min, mechanically milling for 4h, and screening through 100 meshes to obtain the required hexavalent chromium polluted soil remediation material.
Example 2
Selecting certain iron ore tailings, crushing, taking a high-purity pyrite sample, cleaning, air-drying, grinding, and sieving with a 20-mesh sieve (the contents of Fe and S are 47.33% and 51.68% respectively by chemical component analysis) to obtain pyrite particles; fully mixing pyrite and iron powder (passing through 20 meshes) according to a molar ratio of 9:1, adding citric acid with the total material mass fraction of 1%, putting the mixture into a hard stainless steel ball milling tank, adding grinding balls according to a ball-to-material ratio of 15:1, setting the ball milling speed to be 400 r/min, mechanically milling for 4h, and screening through 100 meshes to obtain the required hexavalent chromium polluted soil remediation material.
Example 3
Weighing 20g of polluted soil with the hexavalent chromium content of 448.1mg/kg, placing the polluted soil in a polytetrafluoroethylene beaker, adding 1g of the economical and easily prepared hexavalent chromium polluted soil remediation material described in the embodiment 1, adding pure water according to the soil-water mass ratio of 2:1, and stirring the mixture until the mixture is uniform. Sampling in reaction time of 1, 2, 5, 7, 14 and 30 days respectively, drying at 60 deg.C for 6h, extracting hexavalent chromium content in soil by alkaline digestion METHOD (EPA METHOD 3060B), and measuring hexavalent chromium concentration by dibenzoyl dihydrazide spectrophotometry. The experimental result is shown in fig. 7, after 30d of treatment, the concentration of the total hexavalent chromium in the soil is 2.5mg/kg, and the removal rate of the total hexavalent chromium in the soil reaches 99.44%.
Example 4
Weighing 20g of hexavalent chromium contaminated soil with the hexavalent chromium content of 448.1mg/kg, placing the soil into a 250ml conical flask, adding 1g of the economical and easily prepared hexavalent chromium contaminated soil remediation material described in the embodiment 1, adding pure water according to the soil-water mass ratio of 1:1, stirring until the soil is uniform, applying microwave treatment to the mixture, wherein the microwave power is 0.35KW, the treatment time is 10min, cooling to the room temperature after the treatment is finished, extracting the hexavalent chromium content in the soil by using an alkaline digestion METHOD (EPA METHOD 3060B), measuring the hexavalent chromium concentration by using dibenzoyl dihydrazide spectrophotometry, analyzing, determining the total hexavalent chromium concentration in the restored soil to be 3.79mg/kg, and achieving the removal rate of more than 99%.
Example 5:
weighing 20g of hexavalent chromium contaminated soil with the hexavalent chromium content of 448.1mg/kg, placing the soil into a 250ml conical flask, adding 1g of the economical and easily prepared hexavalent chromium contaminated soil remediation material described in the embodiment 2, adding pure water according to the soil-water mass ratio of 1:1, stirring until the soil-water mass ratio is uniform, applying microwave treatment to the mixture, wherein the microwave power is 0.35KW, the treatment time is 10min, cooling to room temperature after the treatment is finished, drying for 6h at 60 ℃, extracting the hexavalent chromium content in the soil by using an alkaline digestion METHOD (EPA MethOD 3060B), measuring the hexavalent chromium concentration by using dibenzoyl dihydrazide spectrophotometry, and analyzing to obtain the total hexavalent chromium concentration in the repaired soil of 3.96mg/kg, wherein the removal rate is more than 99%.
Example 6
The materials prepared in this example were prepared by the same method and reaction conditions as in example 1, except that different pyrite/reduced iron powder molar ratios, 100mg/L hexavalent chromium solution, and 1g/L material were added, and the results after 6 hours of reaction are shown in FIG. 5. It can be seen that when n (pyrite: iron powder) is in a range of (7:3-9:1), the removal rates of cr (vi) in the prepared material are all greater than those of the pyrite and the iron powder after the separate mechanical ball milling activation, which indicates that the compounding degree of the pyrite and the iron powder in the range of the molar ratio is better than that of other molar ratios, and as can be seen from the SEM image of fig. 6 of different molar ratios, more nano-scale fine particles are adhered to the surface of the pyrite, and the specific surface area and the reaction activity of the particles are greatly increased compared with the material prepared in other molar ratios, especially when n (pyrite: iron powder) is 9: 1.
Example 7
No citric acid added: selection of FeS2Drying, vibrating, grinding and screening the pyrite with the mass fraction of more than 95% through a 20-mesh sieve to obtain pyrite particles; fully mixing the pyrite and the iron powder (passing through a 20-mesh sieve) according to a molar ratio of 9:1, putting the mixture into a hard stainless steel ball milling tank, adding grinding balls according to a ball-to-material ratio of 15:1, setting the ball milling speed to be 400 r/min, mechanically milling for 4h, and taking out the compound to obtain the needed hexavalent chromium polluted soil remediation material.
Weighing 20g of hexavalent chromium contaminated soil with the hexavalent chromium content of 448.1mg/kg, placing the soil into a 250ml conical flask, adding 1g of the hexavalent chromium contaminated soil remediation material in the embodiment, adding pure water according to the soil-water mass ratio of 1:1, stirring the mixture until the mixture is uniform, and performing microwave treatment on the mixture, wherein the microwave power is 0.35KW, and the treatment time is 10 min;
through analysis, the total hexavalent chromium concentration of the soil after remediation in the embodiment is 38.4mg/kg, while the remediation effect of the material prepared in the embodiment 4 is that the total hexavalent chromium concentration of the soil after remediation is 3.79mg/kg, the removal rate is more than 99%, and it can be obviously seen that the remediation effect of the material prepared by citric acid is obviously improved.
Example 8
The addition amount of citric acid is explored on the basis of example 1, 100mg/L hexavalent chromium solution is treated, 1g/L material is added, the reaction lasts for 6 hours, when the addition amount is too large, the removal rate of Cr (VI) is reduced, and the phenomenon that organic ligands are adsorbed on the surface of pyrite due to excessive addition of citric acid can be possibly caused, so that the reaction is prevented from being fully carried out. The results are shown in FIG. 8.
Example 9
Microwave treatment exploration experiment: hexavalent chromium soil was treated according to the method of example 4 using the material prepared in example 1. When the microwave power is too high (0.7KW) and the microwave treatment is carried out for 10min, the removal rate of polluted soil with the hexavalent chromium content of 448.1mg/kg is 95.21%, the concentration of the residual Cr (VI) is 21.51mg/kg, when the microwave power is too low (0.2KW), the removal rate of Cr (VI) is 92.58%, the concentration of the residual Cr (VI) is 33.25mg/kg, when the microwave power is between the two, 0.35KW is selected, the removal rate of Cr (VI) reaches more than 99% and the concentration of the residual Cr (VI) is 3.79mg/kg after the microwave treatment is carried out for 10 min; for the microwave time, when the microwave time is too short, the microwave power is 0.35KW, and the microwave treatment is carried out for 5min, the removal rate of Cr (VI) is 90.89%, the concentration of the residual Cr (VI) is 40.82mg/kg, the removal rate of Cr (VI) continues to increase but is still less than 95% when the microwave treatment is carried out for 8min, and the removal rate of Cr (VI) reaches more than 99% when the microwave treatment is carried out for 10min, the concentration of the residual Cr (VI) is 3.79mg/kg, thereby basically achieving the repair target; as for the water addition amount of microwave treatment, early-stage experiments show that the repair efficiency can be improved more than 2:1 when the solid-liquid ratio is 1:1, and the microwave repair time can be saved by improving the water amount within a certain range, mainly because water is also a wave-absorbing medium, has large dielectric constant and strong microwave absorption capacity, can accelerate the temperature rise rate of a system and accelerate the reaction rate of a material.
Example 10
Weighing 20g of antimony-contaminated soil, placing the antimony-contaminated soil in a polytetrafluoroethylene beaker, adding 1g of the economical and easily prepared repair material described in example 1, adding pure water according to the soil-water mass ratio of 2:1, and stirring the mixture until the mixture is uniform. Samples were taken at 2 days reaction time. 10g of the treated soil sample was weighed, 100ml of ultrapure water was added thereto, and the mixture was placed on a shaker at 30 ℃ and shaken at 175rpm for two hours. Standing for precipitation, filtering with a filter membrane, and detecting the content of antimony in the clear liquid by utilizing ICP. The removal rate of the water-soluble antimony after repairing reaches 94.68 percent.

Claims (7)

1. FeS-containing2The application of the composite material containing the reduced iron in repairing heavy metal hexavalent chromium polluted soil is characterized in that the composite material containing FeS2The preparation method of the composite material with reduced iron comprises the following steps of2Mixing the substances with the content of more than 95% with reducing iron powder, adding a chelating agent, fully mixing, taking out after ball milling, and sieving to obtain the product; FeS2The mol ratio of the iron powder to the reducing iron powder is 9: 1; the chelating agent comprises: one or more of citric acid or citrate; the added chelating agent accounts for 1-4% of the total mass of the materials; the mass ratio of the total materials to the grinding balls is 1:5-1:20, the ball milling rotating speed is 200-Then sieving the mixture by a 100-mesh sieve.
2. Use according to claim 1, wherein said FeS2The substance with content of more than 95% comprises FeS2Natural pyrite or lead-zinc metal ore dressing tailings with the mass fraction of more than 95 percent.
3. Use according to claim 2, wherein said FeS2The substances with the content of more than 95 percent pass through a 20-mesh sieve.
4. The use of claim 1, wherein said chelating agent comprises: one or two of citric acid and potassium citrate.
5. Use according to claim 1, wherein the chelating agent is added in an amount of 1-3% by mass of the total mass of the material.
6. The application of the composite material as claimed in claim 1, wherein the composite material is added into heavy metal contaminated soil, and pure water is added, wherein the mass ratio range is that of the soil: the composite material comprises the following components: water = 100: (1-6): (30-50), uniformly stirring the mixture, and reducing and detoxifying the hexavalent chromium into trivalent chromium after 1-30 days, so as to realize in-situ remediation of the heavy metal contaminated soil.
7. The application of the composite material as claimed in claim 1, wherein the composite material is added into heavy metal contaminated soil, and pure water is added, wherein the mass ratio range is that of the soil: the composite material comprises the following components: water = 100: (1-6): (50-200), stirring the mixture to be uniform, applying microwave external field treatment to the mixture, wherein the microwave power is 0.3KW-0.7KW, and the microwave time is controlled within 1min-10min, so as to finish the quick repair of the hexavalent chromium polluted soil.
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