Method for remediation of heavy metal contaminated groundwater in a metallurgical plant area

Abstract

The application discloses a kind of metallurgical plant area heavy metal pollution groundwater remediation method, comprising the following steps: S1, reaction wall construction: S1-1, first reaction wall construction;S1-2, second reaction wall construction;S1-3, third reaction wall construction;The internal filler of the permeable reaction box body of first reaction wall is quartz sand layer and sulfur modified straw;The internal filler of the permeable reaction box body of second reaction wall is quartz sand layer and straw biochar;The internal filler of the permeable reaction box body of third reaction wall is bentonite layer, nano zero-valent iron, zeolite and fly ash;S2, filler replacement.The application carries out hierarchical processing to the groundwater of metallurgical plant area heavy metal component more complex, wherein, to finally realize the comprehensive efficient remediation of complex heavy metal component groundwater, and the polluted groundwater with Hg, Cu, Fe, Zn, Cd and other complex heavy metal elements has good repair effect.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of groundwater remediation, in particular to a method for remediation of heavy metal contaminated groundwater in a metallurgical plant. BACKGROUND

[0002] Groundwater refers to water that can flow in the rock-soil body below the ground, is an important part of global water resources, and plays a very important role in human production and life. Under the industrial production activities in the metallurgical area, the surrounding soil and groundwater will be contaminated by heavy metals or at risk of heavy metal contamination.

[0003] Therefore, research on groundwater remediation has been ongoing. The permeable reactive barrier (PRB) technology is an in-situ groundwater remediation technology that constructs a permeable reaction wall or reaction zone underground. When contaminated groundwater flows through the reaction wall or reaction zone, the pollutants can be removed. When selecting the active material of PRB, attention needs to be paid to various problems. The active material of PRB needs to be suitable for the underground environment. When the reaction material reacts with the pollutants, no harmful chemical reaction or byproduct is generated. The reaction material is stable in the reaction and is not easy to dissolve or consume. The most common active material of PRB is zero-valent iron, which can effectively adsorb and degrade various heavy metals and organic matter, is easy to obtain, and is inexpensive, so it has been widely valued and practically used. Other active materials include activated carbon, zeolite, limestone, ion exchange resin, iron oxides and hydroxides, phosphates and organic materials.

[0004] However, for the heavy metal component complex and high concentration groundwater pollution in the metallurgical area, the traditional permeable reactive barrier (PRB) technology has limited treatment effect, so it is necessary to find a groundwater remediation method that is more suitable for the groundwater pollution in the metallurgical area on this basis. The invention patent with the authorized publication number CN106277406B discloses a series connection progressive in-situ groundwater heavy metal pollution remediation system: a row of pumping well groups is arranged perpendicularly to the groundwater flow direction and in parallel at the downstream boundary of the pollution plume according to the groundwater flow direction, a plurality of rows of recharge well groups are arranged in parallel at the upstream corresponding pumping well group, and the most upstream row of recharge well groups is arranged outside the pollution source. A repair reaction zone is arranged between the recharge well of each row of recharge well groups and the recharge well of the adjacent recharge well group. The effluent treated by the repair reaction zone flows into the recharge well of the row of recharge well groups through a pipeline. The repair reaction zone is filled with active material that reacts with heavy metals. The recharge well mouth is filled with modified zeolite. A water quality sensor is arranged in each well with pumping function and is connected to a PLC programmable controller to automatically control the opening and closing of the water pump. The patent product can deal with some remediation of heavy metal contaminated groundwater, but further research on the principle of heavy metal adsorption is still lacking, and frequent extraction will also disturb the flow rule of groundwater. SUMMARY

[0005] In view of the above problems, the present application provides a metallurgical plant heavy metal contaminated groundwater remediation method.

[0006] The technical scheme of the present application is:

[0007] A metallurgical plant heavy metal contaminated groundwater remediation method, comprising the following steps:

[0008] S1, reaction wall construction:

[0009] S1-1, first reaction wall construction: a first reaction wall is constructed in the groundwater channel in the downstream direction of the groundwater pollution plume;

[0010] S1-2, second reaction wall construction: a second reaction wall is constructed in the groundwater channel in the downstream direction of the first reaction wall;

[0011] S1-3, third reaction wall construction: a third reaction wall is constructed in the groundwater channel in the downstream direction of the second reaction wall;

[0012] Wherein, the first reaction wall, the second reaction wall and the third reaction wall are all stacked by a plurality of permeable reaction box bodies;

[0013] The internal filler of the permeable reaction box body of the first reaction wall is a quartz sand layer and a thio-modified straw;

[0014] The internal filler of the permeable reaction box body of the second reaction wall is a quartz sand layer and a straw biochar;

[0015] The internal filler of the permeable reaction box body of the third reaction wall is a bentonite layer, nano zero-valent iron, zeolite and fly ash;

[0016] S2, filler replacement: the permeable reaction box body is taken out and the filler is replaced;

[0017] Wherein, the straw biochar is obtained by calcining a composite straw powder, and the composite straw powder comprises 0-60% of recycled thio-modified straw and 40-100% of fresh straw powder by mass percentage.

[0018] Further, in S1-2, the spacing between the second reaction wall and the first reaction wall is 3-8m, and in S1-3, the spacing between the third reaction wall and the second reaction wall is 5-15m.

[0019] Note: By adjusting the spacing between each reaction wall, good remediation efficiency is ensured while not interfering with each other.

[0020] Further, the thickness of the first reaction wall, the second reaction wall and the third reaction wall is 1-3 m, and the thickness of the permeable reaction box is 20-60 cm.

[0021] Description: The reaction wall is composed of the permeable reaction box, which is convenient for disassembly and replacement of the filler.

[0022] Further, the inside of the permeable reaction box of the first reaction wall is filled with a 5-10 cm thick quartz sand layer at both ends and a thio-modified straw in the middle, the inside of the permeable reaction box of the second reaction wall is filled with a 5-10 cm thick quartz sand layer at both ends and a straw biochar in the middle, and the inside of the permeable reaction box of the third reaction wall is filled with a 5-10 cm thick bentonite layer at both ends and a nano zero-valent iron, a zeolite and a fly ash of the same thickness in the middle.

[0023] Description: The quartz sand layer or the bentonite layer is filled at both sides of the inside of the permeable reaction box to prevent the filler from leaking.

[0024] Further, the preparation method of the thio-modified straw is as follows:

[0025] The fresh straw is crushed to obtain straw segments of 1-5 mm in size, the straw segments are anaerobically fermented to obtain humus straw, and the humus straw is thio-modified: the humus straw is placed in a container, a NaOH standard solution and a CS2 standard solution are added, wherein the addition ratio of the humus straw, the NaOH standard solution and the CS2 standard solution is 1-2 g: 55-75 mL: 2-5 mL, the molar concentration of the NaOH standard solution is 1 mol / L, and the mass concentration of the CS2 standard solution is 1 mg / mL, after stirring and reaction, the thio-modified straw powder is obtained by centrifugal filtration, water washing and freeze-drying in sequence.

[0026] Description: The thio-modified straw is mainly used to enhance its adsorption capacity for Hg and Cu, and the reaction of CS2 with the hydroxyl group (-OH) or the amino group (-NH2) in the straw obtains a sulfur-containing functional group CSS - , which improves the complexing capacity, ion exchange efficiency and selective adsorption capacity of the straw.

[0027] Further, the stirring speed of the stirring reaction is 100-150 rpm, the stirring reaction time is 20-30 h, the centrifugal filtration speed is 4000-5000 rpm, the water washing is deionized water washing for 3 times until neutral, and the freeze-drying includes low-temperature freezing and vacuum drying, wherein the low-temperature freezing temperature is -45 to -35℃, the low-temperature freezing time is 20-30 h, and the vacuum drying time is 6-8 h.

[0028] Note: Selecting different freeze-drying temperatures has certain influence on the adsorption effect of the final filler; lower freeze-drying temperature makes the surface of the filler more uniform and dense, so that the secondary reuse is easy to regenerate, and higher freeze-drying temperature can maintain a certain porosity, and the one-time adsorption efficiency is more obvious.

[0029] Further, the method for anaerobic fermentation of the straw section is:

[0030] The straw section is mixed with anaerobic sludge, the mass ratio of the straw section to the anaerobic sludge is 10:1-3, and is placed in a fermentation tank for fermentation at 15-25 DEG C for 20-40 days; urea is added to control the carbon-nitrogen ratio in the fermentation tank to be 20-30:1, and lime water is added to adjust the pH to 6.5-7.5.

[0031] Note: By means of putrefactive treatment of the straw, the cell wall of the straw is decomposed by microorganisms, the originally compact structure becomes loose gradually, and more pores are formed; however, with decomposition and transformation of the organic components, the number of polar functional groups such as hydroxyl groups and carboxyl groups in the straw is reduced; however, excessive putrefactive treatment will inhibit the generation of sulfur-containing functional groups CSS - , therefore, the time of putrefactive treatment should be controlled within a reasonable range.

[0032] Further, the preparation method of the straw biochar in S2 is:

[0033] The composite straw powder is calcined under inert gas, the calcination temperature is 400-600 DEG C, the calcination time is 30-60 min, and Hg vapor or pyrolysis biogas is collected by condensation.

[0034] Note: Hg is recovered and utilized by means of pyrolysis to obtain biochar, FeOx-biochar or FsS-biochar.

[0035] Further, S3, monitoring, is further included, that is, monitoring wells are constructed between the first reaction wall and the second reaction wall and between the second reaction wall and the third reaction wall, and the content of heavy metal pollutants in groundwater is monitored in real time.

[0036] Note: The content of heavy metal pollutants in groundwater is monitored in real time, so that the permeable reaction box bodies of the reaction walls are replaced or added as required.

[0037] The beneficial effects of the present application are:

[0038] (1) The present invention provides a method for remediating groundwater contaminated with heavy metals in a metallurgical plant area. By setting up permeable reactive walls with different remediation effects and purposes in sections, the groundwater with complex heavy metal composition in the metallurgical plant area can be treated in stages. The first reactive wall mainly targets the adsorption of most Hg and a small amount of Cu in the groundwater. The second reactive wall mainly targets Pb, Cd, Cu and Zn in the groundwater. The third reactive wall mainly targets the remaining heavy metal elements in the groundwater. Thus, the comprehensive and efficient remediation of groundwater with complex heavy metal composition can be achieved. It has a good remediation effect on groundwater contaminated with complex heavy metal elements such as Hg, Cu, Fe, Zn and Cd.

[0039] (2) The present invention provides a method for remediating heavy metal contaminated groundwater in metallurgical plant areas by sulfidating humic straw that has been properly decomposed, enabling it to complex and chelate with heavy metals Hg and Cu in groundwater. In particular, the adsorption capacity for Hg is significantly increased, generating insoluble sulfides (HgS, CuS) loaded in the pores of the straw. Hg is recovered by high-temperature calcination, and biochar is obtained simultaneously. More importantly, the sulfidated straw is soaked in groundwater containing heavy metals for a long time, and is modified by combining with potential FeCl3 and FeS. After calcination, FeOx-biochar or FsS-biochar is obtained. When used as the main filler in the subsequent second reaction wall, the effect is better than that of simple straw biochar, realizing resource reuse and providing a new idea for the construction of permeable reaction walls. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the groundwater flow direction after the reaction wall is constructed in a method for remediating heavy metal contaminated groundwater in a metallurgical plant area according to the present invention.

[0041] Figure 2 This is a circumferential schematic diagram of the groundwater flow direction after the construction of the reaction wall in a method for remediating heavy metal contaminated groundwater in a metallurgical plant area according to the present invention. Detailed Implementation

[0042] Example 1: A method for remediating heavy metal contaminated groundwater in a metallurgical plant area, comprising the following steps:

[0043] S1. Construction of the reactive wall:

[0044] S1-1, Construction of the first reaction wall: Construct the first reaction wall in the groundwater channel downstream of the groundwater pollution plume;

[0045] S1-2, Construction of the second reaction wall: A second reaction wall is constructed in the underground water channel downstream of the first reaction wall, with a distance of 5m between the second reaction wall and the first reaction wall;

[0046] S1-3, third reaction wall construction: a third reaction wall is constructed in the groundwater channel in the downstream direction of the second reaction wall, and the spacing between the third reaction wall and the second reaction wall is 10 m;

[0047] The first reaction wall, the second reaction wall and the third reaction wall are all stacks of a plurality of permeable reaction boxes, and the thickness of the first reaction wall, the second reaction wall and the third reaction wall is 2 m, and the thickness of the permeable reaction box is 40 cm;

[0048] The internal filler of the permeable reaction box of the first reaction wall is a quartz sand layer and a sulfur-modified straw;

[0049] The internal filler of the permeable reaction box of the second reaction wall is a quartz sand layer and a straw biochar;

[0050] The internal filler of the permeable reaction box of the third reaction wall is a bentonite layer, nano zero-valent iron, zeolite and fly ash;

[0051] The internal filler of the permeable reaction box of the first reaction wall is a quartz sand layer with a thickness of 8 cm at both ends and a sulfur-modified straw in the middle, the internal filler of the permeable reaction box of the second reaction wall is a quartz sand layer with a thickness of 8 cm at both ends and a straw biochar in the middle, and the internal filler of the permeable reaction box of the third reaction wall is a bentonite layer with a thickness of 8 cm at both ends, and nano zero-valent iron, zeolite and fly ash with the same thickness in the middle;

[0052] The preparation method of the sulfur-modified straw is as follows:

[0053] Fresh wheat straw is crushed to obtain straw segments with a size of 2 mm, the straw segments are anaerobically fermented to obtain humus straw, and the humus straw is sulfur-modified: the humus straw is placed in a container, NaOH standard solution and CS2 standard solution are added, wherein the addition ratio of the humus straw, the NaOH standard solution and the CS2 standard solution is 1.5 g:65 mL:3 mL, the molar concentration of the NaOH standard solution is 1 mol / L, and the mass concentration of the CS2 standard solution is 1 mg / mL, after stirring reaction, centrifugal filtration, water washing and freeze-drying are sequentially performed to obtain sulfur-modified straw powder, the stirring speed of the stirring reaction is 120 rpm, the stirring time of the stirring reaction is 24 h, the centrifugal filtration speed is 4500 rpm, the water washing is deionized water washing for 3 times until neutral, and the freeze-drying includes low-temperature freezing and vacuum drying, wherein the low-temperature freezing temperature is-40℃, the low-temperature freezing time is 24 h, and the vacuum drying time is 7 h;

[0054] The method for anaerobic fermentation of the straw segments is as follows:

[0055] The straw segments are mixed with anaerobic sludge, the mass ratio of straw segments to anaerobic sludge is 10:2, and are placed in a fermentation tank for fermentation at 20℃ for 30 days, urea is added during the fermentation process to control the carbon-nitrogen ratio in the fermentation tank to be 25:1, and lime water is added to adjust the pH to 7;

[0056] S2, filler replacement: the permeable reaction box body is taken out, and the filler is replaced, the internal filler replacement period of the permeable reaction box body of the first reaction wall is 0.5 years, the internal filler replacement period of the permeable reaction box body of the second reaction wall is 1 year, and the internal filler replacement period of the permeable reaction box body of the third reaction wall is 2 years;

[0057] The straw biochar is obtained by calcining the composite straw powder, and the composite straw powder comprises, by mass percentage, 30% of the recovered thio-modified straw and 70% of the fresh straw powder;

[0058] The preparation method of the straw biochar is as follows:

[0059] The composite straw powder is calcined under inert gas, the calcination temperature is 500℃, the calcination time is 40min, and the Hg vapor and pyrolysis biogas are collected by condensation;

[0060] S3, monitoring: monitoring wells are constructed between the first reaction wall and the second reaction wall, and between the second reaction wall and the third reaction wall, to monitor the content of heavy metal pollutants in groundwater in real time;

[0061] The monitoring well comprises a monitoring station on the ground and a water quality detector underground, the monitoring station transmits the collected water quality data to the monitoring center by wireless transmission, and the monitoring station is powered by a high-energy lithium battery; the water quality detector is a commercially available integrated multi-parameter water quality analyzer, which can detect water level, water temperature, pH value, heavy metal content, etc., and the collection frequency is once every 1 to 4 hours.

[0062] Embodiment 2: The difference between this embodiment and embodiment 1 is that,

[0063] S1-2, second reaction wall construction: the distance between the second reaction wall and the first reaction wall is 3m;

[0064] S1-3, third reaction wall construction: the distance between the third reaction wall and the second reaction wall is 5m;

[0065] The first reaction wall, the second reaction wall and the third reaction wall are all stacks of a plurality of permeable reaction box bodies, the thickness of the first reaction wall, the second reaction wall and the third reaction wall is 1m, and the thickness of the permeable reaction box body is 20cm;

[0066] The first reaction wall is filled with 5cm thick quartz sand layers at both ends and sulfur-modified straw in the middle. The second reaction wall is filled with 5cm thick quartz sand layers at both ends and straw biochar in the middle. The third reaction wall is filled with 5cm thick bentonite layers at both ends and, in the middle, nanometer zero-valent iron, zeolite and fly ash of the same thickness.

[0067] Example 3: The difference between this example and Example 1 is that,

[0068] S1-2, second reaction wall construction: the distance between the second reaction wall and the first reaction wall is 8m;

[0069] S1-3, third reaction wall construction: the distance between the third reaction wall and the second reaction wall is 15m;

[0070] The first reaction wall, the second reaction wall and the third reaction wall are all stacks of several permeable reaction boxes, and the thickness of the first reaction wall, the second reaction wall and the third reaction wall is 3m, and the thickness of the permeable reaction box is 60cm.

[0071] The first reaction wall is filled with 10cm thick quartz sand layers at both ends and sulfur-modified straw in the middle. The second reaction wall is filled with 10cm thick quartz sand layers at both ends and straw biochar in the middle. The third reaction wall is filled with 10cm thick bentonite layers at both ends and, in the middle, nanometer zero-valent iron, zeolite and fly ash of the same thickness.

[0072] Note: If the corresponding groundwater pollution area of the metallurgical plant is large, the interval between each reaction wall should be appropriately lengthened, and the thickness of the permeable reaction box should be appropriately increased.

[0073] Example 4: The difference between this example and Example 1 is that,

[0074] The preparation method of the sulfur-modified straw is as follows: fresh straw is crushed to obtain 1mm straw segments, the addition ratio of humus straw, NaOH standard solution and CS2 standard solution is 1g:55mL:2mL, the stirring speed of the stirring reaction is 100rpm, the stirring time of the stirring reaction is 20h, the centrifugal filtration speed is 4000rpm, the water washing is deionized water washing 3 times until neutral, and the freeze-drying includes low-temperature freezing and vacuum drying, wherein the low-temperature freezing time is 20h, and the vacuum drying time is 6h.

[0075] Example 5: The difference between this example and Example 1 is that,

[0076] The preparation method of the thio-modified straw is as follows: fresh straw is crushed to obtain straw segments with a size of 5 mm, the addition ratio of humus straw, NaOH standard solution and CS2 standard solution is 2 g:75 mL:5 mL, the stirring speed of stirring reaction is 150 rpm, the stirring time of stirring reaction is 30 h, the centrifugal speed of centrifugal filtration is 5000 rpm, water washing is deionized water washing for 3 times until neutral, and freeze-drying includes low-temperature freezing and vacuum drying, wherein the low-temperature freezing time is 30 h, and the vacuum drying time is 8 h.

[0077] Example 6: The difference between this example and example 1 is that the low-temperature freezing temperature is -35 DEG C.

[0078] Example 7: The difference between this example and example 1 is that the low-temperature freezing temperature is -45 DEG C.

[0079] Example 8: The difference between this example and example 1 is that,

[0080] The method for anaerobic fermentation of the straw segments is as follows:

[0081] The straw segments are mixed with anaerobic sludge, the mass ratio of the straw segments to the anaerobic sludge is 10:1, and the mixture is placed in a fermentation tank for fermentation at 25 DEG C for 20 days, urea is added to control the carbon-nitrogen ratio in the fermentation tank to be 20:1 during the fermentation process, and lime water is added to adjust the pH to 6.5.

[0082] Example 9: The difference between this example and example 1 is that,

[0083] The method for anaerobic fermentation of the straw segments is as follows:

[0084] The straw segments are mixed with anaerobic sludge, the mass ratio of the straw segments to the anaerobic sludge is 10:3, and the mixture is placed in a fermentation tank for fermentation at 15 DEG C for 40 days, urea is added to control the carbon-nitrogen ratio in the fermentation tank to be 30:1 during the fermentation process, and lime water is added to adjust the pH to 7.5.

[0085] Description: When the fermentation temperature is relatively low, the fermentation time can be appropriately prolonged.

[0086] Example 10: The difference between this example and example 1 is that,

[0087] The composite straw powder includes, in terms of mass percentage, 60% of the recycled thio-modified straw and 40% of the fresh straw powder.

[0088] Example 11: The difference between this example and example 1 is that,

[0089] The composite straw powder includes, in terms of mass percentage, 0% of the recycled thio-modified straw and 100% of the fresh straw powder.

[0090] Note: In the early stage of repair, no recovered thio-modified straw is produced, so the amount of recovered thio-modified straw added is 0. As the repair progresses, more recovered thio-modified straw is produced, so recovered thio-modified straw can be used to replace fresh straw.

[0091] Example 12: The difference between this example and Example 1 is that,

[0092] The preparation method of straw biochar is to calcine the composite straw powder under inert gas, the calcination temperature is 400℃, the calcination time is 30min, and Hg vapor is collected by condensation.

[0093] Example 13: The difference between this example and Example 1 is that,

[0094] The preparation method of straw biochar is to calcine the composite straw powder under inert gas, the calcination temperature is 600℃, the calcination time is 60min, and pyrolysis bio-gas is collected by condensation.

[0095] Note: The calcination temperature and calcination time are inversely proportional. If no recovered thio-modified straw is added to the composite straw powder, no Hg vapor is produced. If a large amount of recovered thio-modified straw is added in the later stage of repair, Hg vapor is the main recovered gas.

[0096] Example 14: The difference between this example and Example 1 is that the straw is corn straw.

[0097] Example 15: The difference between this example and Example 1 is that,

[0098] S2, filler replacement: take out the permeable reaction box body, and replace the filler, the internal filler replacement period of the permeable reaction box body of the first reaction wall is 0.5 years, the internal filler replacement period of the permeable reaction box body of the second reaction wall is 0.5 years, and the internal filler replacement period of the permeable reaction box body of the third reaction wall is 1 year.

[0099] Example 16: The difference between this example and Example 1 is that,

[0100] S2, filler replacement: take out the permeable reaction box body, and replace the filler, the internal filler replacement period of the permeable reaction box body of the first reaction wall is 1 year, the internal filler replacement period of the permeable reaction box body of the second reaction wall is 2 years, and the internal filler replacement period of the permeable reaction box body of the third reaction wall is 3 years.

[0101] Experimental Example 1

[0102] We study the feasibility of the method of the application by means of indoor simulation experiment, in the experimental example, the comprehensive removal effect of the method of the application on various heavy metals is mainly discussed, and comparative experiments are set, wherein, the comparative example 1 is only provided with the first reaction wall, the comparative example 2 is only provided with the second reaction wall, and the second reaction wall is provided with the filler in the embodiment 11, and the recovered sulfur-modified straw is not added, the comparative example 3 is only provided with the second reaction wall, and the second reaction wall is provided with the filler in the embodiment 10, and more biochar prepared from the recovered sulfur-modified straw is added, and the comparative example 4 is only provided with the third reaction wall;

[0103] 100mL of the simulated wastewater contains 0.5mg / L of Hg, 5mg / L of Cu, 5mg / L of Fe, 0.5mg / L of Cd, 5mg / L of Zn and 0.5mg / L of Pb;

[0104] According to the method in the embodiment 1, each reaction wall is provided with one permeable reaction box body, the flow rate of the simulated wastewater is 5mL / min, the reaction time is 6h, the content of each heavy metal element in the solution after the reaction is determined, the removal rate is calculated, and the results are shown in Table 1.

[0105] Table 1: Removal rate of each heavy metal element under different experimental conditions

[0106] Case Hg % Cu % Fe % Cd % Zn % Pb % Example 1 99.5 99.2 87.7 98.7 94.1 97.3 Comparative Example 1 92.3 90.6 45.5 73.2 60.0 79.6 Comparative Example 2 64.2 77.4 50.8 76.8 62.5 84.1 Comparative Example 3 65.3 79.8 46.7 78.9 61.4 86.4 Comparative Example 4 88.7 89.2 85.6 97.8 90.3 98.8

[0107] It can be seen that each heavy metal element is removed with a high removal rate after the simulated wastewater is treated according to the method in the embodiment 1, so we further compare the comparative examples to analyze the reasons.

[0108] Firstly, the comparative example 1 adopts the first reaction wall, that is, the filler is the humus straw modified by sulfur, and it can be seen that it mainly removes Hg and Cu in the wastewater by adsorption, because the humus straw modified by sulfur can be complexed and chelated with the heavy metals Hg and Cu in the groundwater, especially the adsorption amount of Hg is obviously increased, and the insoluble sulfide (Hg S, Cu S) is generated and loaded in the straw pores, and the adsorption effect on Cd is also certain, but the effect on other heavy metal elements is limited;

[0109] Subsequently, the second reaction wall is adopted in the comparative example 2, and the recovered sulfur-modified straw is not added, and it can be seen that the adsorption removal effect of each heavy metal element in the wastewater is limited, that is, the single straw biochar has a limited adsorption efficiency when various heavy metal elements are interwoven to form cross pollution;

[0110] However, when the biochar prepared from the recycled thio-modified straw was used in Comparative Example 3, the removal rates of multiple heavy metal elements were all increased compared with Comparative Example 2, for example, the removal rates of Pb and Cd were increased, and it was speculated that the adsorption of FeOOH surface complexation + straw functional groups (—COOH, —OH) in the FeOOH-biochar or FsS-biochar was involved, and the specific chemical formula was as follows:

[0111] Pb 2+ +FeOOH→FeO—Pb + +H +

[0112] At the same time, the adsorption rates of Fe and Zn decreased, which might be caused by the occupation of the original adsorption sites by other heavy metal elements;

[0113] Finally, we found that the removal rates of various heavy metals in the simulated wastewater were relatively balanced in Comparative Example 4, but the overall removal rates were lower than those in Example 1, which might be caused by the influence of the adsorption efficiency of the filler when multiple heavy metal elements were intertwined to form cross contamination, for example, the removal rate of the third reaction wall could reach more than 99% when the filler was used to treat Pb-contaminated wastewater, but when it was used to treat multiple heavy metal elements intertwined to form cross contamination, the adsorption efficiency decreased;

[0114] It might also be that when the content of one or more heavy metal elements decreased (Hg, Cu), the adsorption efficiency of the filler for the remaining heavy metal pollutants increased.

[0115] Example 2

[0116] Subsequently, we explored the influence of freeze-drying temperature on the adsorption efficiency of the modified straw biofiller of the present application, mainly by comparing the freeze-drying temperatures of the fillers in Examples 1, 6, and 7. We first set up only the first reaction wall, and then followed the method in Experimental Example 1 to treat the simulated wastewater. After roasting, we set up the second reaction wall and again followed the method in Experimental Example 1 to treat the simulated wastewater. The purpose of this was to observe the influence of freeze-drying temperature on the adsorption effect. The remaining parameters were in accordance with Example 1, and were respectively denoted as Examples 1', 6', and 7'. At the same time, Comparative Examples were set up, in which the freeze-drying temperature of Comparative Example 4 was -55°C, and the freeze-drying temperature of Comparative Example 5 was -15°C.

[0117] Table 2 Influence of freeze-drying temperature

[0118] Example Primary adsorption Hg removal % Secondary adsorption Hg removal % Example 1 92.3 64.2 Example 6 93.5 63.6 Example 7 91.7 65.5 Comparative Example 4 87.5 58.4 Comparative Example 5 89.3 56.5

[0119] It can be seen that the selection of different freeze-drying temperature has a certain influence on the adsorption effect of the final filler. Lower freeze-drying temperature makes the surface of the modified straw biological filler more uniform and dense, thereby ensuring easy regeneration during secondary reuse. Higher freeze-drying temperature can maintain a certain porosity, and the one-time adsorption efficiency is more obvious.

Claims

1. A method for remediating heavy metal-contaminated groundwater in a metallurgical plant area, characterized in that, Includes the following steps: S1. Construction of the reactive wall: S1-1, Construction of the first reaction wall: Construct the first reaction wall in the groundwater channel downstream of the groundwater pollution plume; S1-2, Construction of the second reactive wall: A second reactive wall is constructed in the underground water channel downstream of the first reactive wall; S1-3, Construction of the third reaction wall: Construct a third reaction wall in the underground water channel downstream of the second reaction wall; The first reaction wall, the second reaction wall, and the third reaction wall are all composed of several permeable reaction chambers stacked together. The filling material inside the permeable reaction box of the first reaction wall is a layer of quartz sand and thiolated straw. The permeable reaction chamber of the second reaction wall is filled with a layer of quartz sand and straw biochar. The internal filler of the permeable reaction box of the third reaction wall is a bentonite layer, nano-zero valent iron, zeolite and fly ash; S2. Packing material replacement: Remove the permeable reaction chamber and replace the packing material; The straw biochar is obtained by roasting composite straw powder, wherein the composite straw powder comprises, by mass percentage, 0-60% recycled sulfur-modified straw and 40-100% fresh straw powder; The first reaction wall has a permeable reaction box with 5-10cm thick quartz sand layer at both ends and sulfur-modified straw in the middle. The second reaction wall has a permeable reaction box with 5-10cm thick quartz sand layer at both ends and straw biochar in the middle. The third reaction wall has a permeable reaction box with 5-10cm thick bentonite layer at both ends and nano-zero valent iron, zeolite and fly ash of the same thickness in the middle. The method for preparing the sulfur-modified straw is as follows: Fresh straw is crushed to obtain straw segments of 1-5 mm in size. The straw segments are then anaerobically fermented to obtain humic straw. The humic straw is then subjected to sulfide modification: Humic straw is placed in a container, and NaOH standard solution and CS2 standard solution are added. The addition ratio of humic straw to NaOH standard solution and CS2 standard solution is 1-2 g: 55-75 mL: 2-5 mL. The molar concentration of NaOH standard solution is 1 mol / L, and the mass concentration of CS2 standard solution is 1 mg / mL. After stirring and reacting, the mixture is successively centrifuged, filtered, washed with water, and freeze-dried to obtain sulfide-modified straw powder. The stirring speed of the stirring reaction is 100~150 rpm, the stirring reaction time is 20~30 h, the centrifugal filtration speed is 4000~5000 rpm, the water washing is three times with deionized water until neutral, and the freeze drying includes low temperature freezing and vacuum drying. The low temperature freezing temperature is -45~-35℃, the low temperature freezing time is 20~30 h, and the vacuum drying time is 6~8 h.

2. The method for remediating heavy metal-contaminated groundwater in a metallurgical plant area according to claim 1, characterized in that, In S1-2, the distance between the second reaction wall and the first reaction wall is 3~8m. In S1-3, the distance between the third reaction wall and the second reaction wall is 5~15m.

3. The method for remediating heavy metal-contaminated groundwater in a metallurgical plant area according to claim 1, characterized in that, The thickness of the first reaction wall, the second reaction wall and the third reaction wall is 1~3m, and the thickness of the permeable reaction box is 20~60cm.

4. The method for remediating heavy metal-contaminated groundwater in a metallurgical plant area according to claim 1, characterized in that, The method for anaerobic fermentation of the straw segments is as follows: The straw segments are mixed with anaerobic sludge at a mass ratio of 10:1 to 3, and placed in a fermentation tank. The mixture is fermented at 15 to 25°C for 20 to 40 days. During the fermentation process, urea is added to control the carbon-nitrogen ratio in the fermentation tank to be 20 to 30:1, and lime water is added to adjust the pH to 6.5 to 7.

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5. A method for remediating heavy metal-contaminated groundwater in a metallurgical plant area according to claim 1, characterized in that, The preparation method of straw biochar in S2 is as follows: The composite straw powder is calcined under an inert gas at a temperature of 400-600°C for 30-60 minutes, and Hg vapor or pyrolysis biogas is collected by condensation.

6. The method for remediating heavy metal-contaminated groundwater in a metallurgical plant area according to claim 1, characterized in that, It also includes S3, monitoring: monitoring wells are constructed between the first and second reaction walls and between the second and third reaction walls to monitor the content of heavy metal pollutants in groundwater in real time.

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