CN114044571B

CN114044571B - Permeable reactive barrier composite material and preparation method and application thereof

Info

Publication number: CN114044571B
Application number: CN202111272984.5A
Authority: CN
Inventors: 郭红岩; 李业朴; 尹颖; 叶博
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2021-10-29
Filing date: 2021-10-29
Publication date: 2022-11-25
Anticipated expiration: 2041-10-29
Also published as: CN114044571A

Abstract

The invention discloses a permeable reactive barrier composite material for groundwater heavy metal pollution remediation and a preparation method and application thereof, the composite material comprises a high-permeability hard shell layer and a heavy metal remediation functional layer, wherein the high-permeability hard shell is prepared from an inorganic bonding material, plastic clay and a porous material containing microchannels, by mass, 22.3-32.9%:50.1-66.9%:10.7-20%, wherein the functional material of the heavy metal repairing functional layer is composed of an inorganic reducing agent, a natural organic carbon-releasing material, a carbonate mineral, biomass carbon and plastic clay according to the mass percentage of 5% -10%:40% -50%:10% -20%:10%:20 percent, the permeable reactive barrier composite material prepared by the invention can be applied to remediation of heavy metal polluted underground water, and the material has the advantages of low cost, no secondary pollution and simple preparation method, and has the potential of large-scale popularization and application.

Description

Permeable reactive barrier composite material and preparation method and application thereof

Technical Field

The invention relates to the field of in-situ remediation of polluted underground water, in particular to a permeable reactive barrier composite material for remediation of heavy metal pollution of underground water and application of a preparation method thereof.

Background

With the increase of industrial production activities, more and more heavy metals are generated, and the heavy metals enter a groundwater system through ways of atmospheric sedimentation, sewage irrigation and the like, so that the pollution of groundwater is aggravated, and the serious harm is caused to the human health and production and operation activities. From the current situation of heavy metal pollution of underground water in China, the method has the characteristics of wide pollution range, high pollution speed, serious pollution and the like, so that the metal pollution of the underground water becomes a threat factor which endangers the healthy life of human beings and hinders the sustainable development of social economy, and the treatment of the heavy metal pollution of the underground water is urgent.

At present, two main approaches for treating heavy metal underground water pollution are provided: firstly, the existing form of metal ions is changed into a simple substance or compound precipitate, the stability of the metal ions is enhanced, and the mobility of the metal ions in the environment is reduced; another is to change the valence state of the metal ion to reduce its toxicity.

Aiming at the heavy metal pollution remediation, the ex-situ remediation technology is mainly a pumping-surface treatment technology. According to the statistics of the United states environmental protection agency, in the period of 1982-2002, the application proportion of the repair technology on engineering application is as high as 68% compared with other repair technologies. But sometimes the tailing and bouncing phenomenon may occur and there is a problem in that the running cost is high. The in-situ remediation technology is used for in-situ remediation of polluted underground water without destroying the natural environment of soil and underground water, and has the advantages of low treatment cost, few surface treatment facilities and low environmental disturbance, and comprises a permeable reactive barrier technology, an in-situ electric remediation technology, an in-situ chemical remediation technology and an in-situ biological remediation technology. Permeable Reactive Barrier (PRB) technology in these in-situ repair technologies has the advantages of low operation cost, good repair effect and wide application range compared with other in-situ repair technologies, and therefore, people are receiving more and more attention.

The publication number CN107473321A discloses a permeable reactive barrier active material, which comprises the following components in percentage by weight: 20-40% of aluminum powder; 20-40% of iron powder; 30-40% of activated carbon; 5-10% of zeolite; and the sum of the components is 100 percent; in addition, aluminum powder, iron powder, activated carbon and zeolite are mixed according to a specific proportion, and after the permeable reactive barrier is loaded, various heavy metal ions (Cr (VI) and Cd) in acidic water can be removed simultaneously ²⁺ 、Cu ²⁺ 、Zn ²⁺ ) The effective period of the active material is 2-3 times that of the single zero-valent iron as the active material. Chinese patent with publication number CN111233069A discloses a permeable reactive barrier active material, which comprises modified iron powder, modified ferroferric oxide and modified medical stone, wherein the mass ratio of the modified iron powder to the modified ferroferric oxide to the modified medical stone is 1-2:1-3:1-9. After the material runs for 2 months, the removal rate of heavy metals Cd (II) and Cr (VI) is still more than 99%. However, the two materials are in loose powder structures, and the flow of groundwater can be blocked after long-term operation, so that the capability of repairing groundwater is lost. The document discloses a double-layer permeable reactive barrier repair system and a preparation method and application thereof, and PRB materials used by Matbeidou and the like, flow rate and flow state numerical simulation in permeable reactive barrier walls of _ Wang Jiang and the like overcome loose powder structures, but the manufactured PRB pellets do not distinguish a functional layer from an outer shell layer. Article (Chinese character)The research on the carbon source materials for restoring the nitrate-polluted groundwater by PRB and the research on the removal of the nitrate in the groundwater by simulating PRB by the loofah sponge carbon source are carried out by adding the carbon source in the wall materials, but the carbon source used in the literature has the defects of high release speed and difficulty in obtaining.

Disclosure of Invention

Aiming at the problems of high manufacturing cost, low activity and easiness in damage of the permeable reactive barrier composite material, the invention provides the permeable reactive barrier composite material for repairing heavy metal pollution of underground water and the preparation method thereof. The material has the characteristics of good removal effect and good economic applicability in the process of repairing the heavy metal polluted underground water.

Specifically, the invention is realized by the following technical scheme:

firstly, the application provides a permeable reactive barrier composite material which is of a spherical structure, wherein the spherical structure consists of a heavy metal repairing functional layer and a high-permeability hard shell layer wrapped outside the heavy metal repairing functional layer;

the high-permeability hard shell layer consists of an inorganic bonding material, plastic clay and a permeable material containing micro-channels;

the heavy metal restoration functional layer is composed of a functional material and a natural bonding material, wherein the functional material is composed of an inorganic reducing agent, a natural organic carbon-releasing material, a carbonate mineral, biomass carbon and plastic clay.

Furthermore, in the permeable reactive barrier composite material provided by the invention, in the high-permeability hard shell layer, the inorganic binding material, the plastic clay and the permeable material containing the micro-channels are 22.3-32.9% in sequence according to the mass percentage: 50.1-66.9%:10.7 to 20 percent; further, the inorganic binder is preferably at least one of portland cement and hydrated lime; the plastic clay is preferably at least one of attapulgite, kaolin and montmorillonite; the water permeable material containing the micro-channels is preferably diatomite.

Furthermore, in the permeable reactive wall composite material provided by the invention, the functional material is composed of an inorganic reducing agent, a natural organic carbon-releasing material, a carbonate mineral, biomass carbon and plastic clay, and the mass percentages of the functional material, the natural organic carbon-releasing material, the carbonate mineral, the biomass carbon and the plastic clay are 5-10% in sequence: 40-50%:10-20%:10%:20 percent; further, the inorganic reducing agent is preferably at least one of secondary reduced iron powder, copper powder and aluminum powder; the natural organic carbon-releasing material is preferably at least one of wood chips (such as pine wood chips), fermented chicken manure and crop straws; the carbonate mineral is preferably at least one of ground calcium carbonate, sodium carbonate, calcium carbonate and magnesium carbonate, the biomass carbon is preferably at least one of poplar biochar, coconut shell biochar, bamboo charcoal and fruit core biochar, and the plastic clay is preferably at least one of attapulgite, kaolin and montmorillonite.

Furthermore, in the permeable reactive barrier composite material provided by the invention, the natural adhesive material is a sodium alginate solution with the mass percentage of 0.5-1%; the mass-to-volume ratio of the functional material to the natural adhesive material is preferably 1.

Furthermore, in the permeable reactive wall composite material provided by the invention, the particle size of the spherical structure is preferably 1-1.5 cm, and the thickness of the high-permeability hard shell layer is preferably 0.1-0.2 cm.

Secondly, the application also provides a method for preparing the permeable reactive barrier composite material, which comprises the following steps:

1) Respectively sieving an inorganic bonding material, plastic clay, a permeable material containing micro-channels, an inorganic reducing agent, carbonate minerals, biomass carbon and the plastic clay with a 80-mesh sieve for later use;

sieving natural organic carbon-releasing material with 20 mesh sieve;

preparing 0.5-1% sodium alginate solution for later use;

2) Sequentially mixing the inorganic reducing agent obtained in the step 1), the natural organic carbon-releasing material, the carbonate mineral, the biomass carbon and the plastic clay according to the mass percentage of 5-10%:40-50%:10-20%:10%: mixing 20% of the above materials, and making into functional powder;

3) Mixing the sodium alginate solution (volume) and the functional powder (mass) prepared in the step 2) in a container according to the volume-mass ratio of 1;

4) Pouring the pellets prepared in the step 3) into a sugar coating machine, rolling the pellets at a rotating speed of 30-40 r/min, and spraying a sodium alginate solution to form pellets with compact structures, wherein the pellets are used as core pellets for further preparing a heavy metal repair functional layer;

5) Pouring the small inner core balls prepared in the step 4) into a sugar coating machine, rolling the small inner core balls at the rotating speed of 30-40 r/min, adding the functional powder in the step 2), and spraying a sodium alginate solution to enable the small inner core balls to grow into primary heavy metal repairing functional layer balls with the grain size of 0.6-1.1 cm;

6) Sieving the primary heavy metal restoration functional layer pellets prepared in the step 5), and selecting pellets with the particle size not smaller than (i.e. not larger than) 0.6 cm as the sieved heavy metal restoration functional layer pellets for later use; repeating step 5) with pellets of less than 0.6 cm particle size;

7) Sequentially mixing an inorganic binding material, plastic clay and a permeable material containing micro-channels according to the mass percentage of 22.3-32.9%:50.1-66.9%:10.7 to 20 percent of the raw materials are uniformly mixed to prepare the shell powder for standby.

8) Putting the small balls with the heavy metal repairing functional layer screened in the step 6) into a sugar coating machine, adding the shell powder prepared in the step 7), rolling at the rotating speed of 30-40 r/min, and spraying tap water to form small balls;

9) Naturally air-drying the pellets prepared in the step 8) to obtain a permeable reactive barrier composite material (PRB material); the material is a spherical structure with the grain diameter of 1-1.5 cm, and comprises a heavy metal repairing functional layer and a high-permeability hard shell layer wrapping the outside of the heavy metal repairing functional layer, wherein the thickness of the high-permeability hard shell layer is 0.1-0.2 cm.

The application also provides application of the permeable reactive barrier composite material prepared by the method in repairing underground water polluted by heavy metal. Excavating a ditch in the flowing direction downstream of underground water polluted by heavy metal, and then uniformly mixing permeable reactive barrier materials and sand according to the mass ratio of 1:1 and then piling the mixture into the ditch to form a permeable reactive barrier; the top end of the permeable reactive wall material is flush with the water level of the underground water, and finally the excavated soil is backfilled to the ditch, so that the polluted underground water is repaired. The heavy metals include Cd, as and Pb.

Compared with the existing permeable reactive barrier, the permeable reactive barrier composite material for repairing heavy metal pollution of underground water prepared by the application has the following advantages:

1) In the prior art, underground water pollutants are usually removed by only utilizing one or two principles, the permeable reactive barrier composite material prepared by the method removes heavy metals (Cd, as and Pb) in underground water under the comprehensive action of precipitation, complexation, adsorption, reduction and microorganism enrichment in an anaerobic environment, has the advantages of high removal efficiency, stability and wide application range, and has the removal rate of the heavy metals (Cd, as and Pb) of more than 99 percent after 91 days of stable operation;

2) The composite material has low preparation cost which is 1500-2000 yuan/t (other PRB materials are more than 5000 yuan/t according to market price);

3) The carbon source used by the permeable reactive barrier composite material is the combination of the biochar and the wood chips, is stable in carbon source release (used for complexing pollutants and providing nutrition for microbial growth) and easy to obtain, and can be stabilized to be more than 35 mg/L after 91 days;

4) The reduced iron powder, the biochar, the attapulgite and the carbonate minerals in the permeable reactive wall composite material prepared by the method can maintain alkaline pH for a long time, and the pH can be stabilized to be more than 10 after 91 days, so that heavy metal precipitation is facilitated;

5) The permeable reactive wall composite material (PRB) prepared by the method is in a small sphere shape and comprises a heavy metal restoration functional layer and a high-permeability hard shell layer outside the heavy metal restoration functional layer, and the hardness of the material is guaranteed while the strong water permeability of the shell layer is guaranteed, so that the material is not easy to break underground and block underground water channels.

Drawings

FIG. 1 is a graph showing the trend of pH of effluent over time in example 1.

FIG. 2 is a graph showing the trend of the total organic carbon concentration (TOC) of effluent water with time in example 1.

FIG. 3 is a schematic diagram showing the change of Cd concentration in outlet water with time in example 1.

FIG. 4 is a graph showing the trend of pH of effluent over time in example 2.

FIG. 5 is a graph showing the trend of the total organic carbon concentration (TOC) of effluent water with time in example 2.

FIG. 6 is a schematic diagram showing the change trend of Cd concentration in effluent with time in example 2.

FIG. 7 is a graph showing the trend of pH of effluent over time in example 3.

FIG. 8 is a graph showing the trend of the Pb concentration of the effluent over time in example 3.

FIG. 9 is a graph showing the trend of the Pb concentration of the effluent over time in example 4.

FIG. 10 is a graph showing the time-dependent trend of As concentration in effluent in examples 5 and 6.

FIG. 11 is a schematic diagram showing the change trend of the pH value of effluent with time in examples 5 and 6.

FIG. 12 is a schematic diagram of an experimental apparatus, a composite material structure diagram and a pollutant removal mechanism for heavy metal contaminated groundwater remediation.

Fig. 13 is a photograph of the pellet as a heavy metal repairing functional layer.

Fig. 14 is a photograph of a finished product with PRB material.

Detailed Description

The invention is further described with reference to specific examples. Materials/equipment sources referred to in the examples: the secondary reduced iron powder, poplar biochar, ground calcium carbonate and sodium alginate are purchased from Nanjing Ningqing glass instruments Limited; portland cement (425) was purchased from Endoconcha Sepiae Cement, inc.; fermented chicken manure was purchased from Shenyang Hao Yuan environmental services Co., ltd; in the experiment, the standard solution of Cd, pb and As (1000 mg/L) purchased from Beijing Zhongke quality inspection biotechnology limited is used for preparing polluted underground water; sugar coating machines (YB-400) were purchased from Guangzhou Yangying medical devices, inc. The determination of Cd, pb and As in the effluent was carried out by ICP-MS. TOC was analyzed using a TOC analyzer (Mettler-Tollido 5000 TOCi).

Example 1

The composite material for repairing the heavy metal polluted underground water is prepared and comprises a heavy metal repairing functional layer and a high-permeability hard outer shell layer wrapped outside the heavy metal repairing functional layer; the high-permeability hard shell layer comprises the following components in percentage by mass: 10.7 percent of diatomite, 59.1 percent of attapulgite and 30.2 percent of Portland cement.

The functional material of the heavy metal restoration functional layer comprises the following components in percentage by mass: 10% of secondary reduced iron powder, 25% of pine and cypress sawdust, 25% of fermented chicken manure, 10% of ground calcium carbonate, 10% of poplar charcoal and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is sodium alginate solution with the concentration of 0.5 percent. The particle size of the raw materials for preparing the composite material is larger than 80 meshes except for the pine and cypress sawdust and the fermented chicken manure which are 20 meshes.

The preparation method of the composite material for repairing the heavy metal polluted underground water comprises the following steps:

1) Diatomite, attapulgite, portland cement, secondary reduced iron powder, ground calcium carbonate, poplar biochar and attapulgite which are sieved by a sieve of 80 meshes are reserved, pine and cypress sawdust and fermented chicken manure which are sieved by a sieve of 20 meshes are reserved, and sodium alginate solution is reserved.

2) The secondary reduced iron powder, pine and cypress sawdust, fermented chicken manure, heavy calcium carbonate, poplar biochar and attapulgite in the step 1) are mixed according to the mass percentage of 10 percent: 25%:25%:10%:10%: mixing 20% of the above materials, and making into functional powder.

3) Taking out a part of the functional powder in the step 2) according to the volume of the sodium alginate solution: the powder mass ratio of 1.

4) Pouring the pellets prepared in the step 3) into a sugar coating machine, rolling the pellets at the rotating speed of 30 r/min, and spraying a sodium alginate solution to form pellets with compact structures, wherein the pellets are used as core pellets for further preparing the heavy metal repairing functional layer.

5) Pouring the inner core pellets prepared in the step 4) into a sugar coating machine, rolling the pellets at the rotating speed of 30 r/min, adding the functional powder prepared in the step 2), and spraying a sodium alginate solution to enable the inner core pellets to grow into primary heavy metal restoration functional layer pellets with the grain size of 0.6-1.1 cm.

6) Sieving the primary heavy metal restoration functional layer pellets prepared in the step 5), and selecting pellets with the particle size of more than or equal to 0.6 cm as sieved heavy metal restoration functional layer pellets for later use, wherein the photo is shown in fig. 13; the pellets with the grain diameter less than 0.6 cm are used as the inner cores for manufacturing the heavy metal restoration functional layer pellets next time.

7) The Portland cement, the attapulgite and the diatomite are mixed according to the mass percentage of 22.3%: 66.9%:10.7 percent of the raw materials are uniformly mixed to prepare the shell powder for standby.

8) Putting the small balls with the heavy metal repairing functional layer screened in the step 6) into a sugar coating machine, adding the shell powder prepared in the step 7), rolling at the rotating speed of 30 r/min, spraying tap water to form small balls with the particle size of 1-1.5 cm, and naturally air-drying to obtain the permeable reactive wall composite material (PRB material), wherein the photo of the permeable reactive wall composite material is shown in figure 14, and the thickness of the high-permeability hard shell layer obtained in the embodiment is about 0.1-0.2 cm.

The permeable reactive wall composite material (fig. 12 is simply referred to as composite material) prepared in the embodiment and quartz sand are filled in a settling tube which is 50 cm long and 5 cm in the mass ratio of 1:1 (see fig. 12 for device and principle).

A water sample simulating Cd contamination of groundwater (Cd initial concentration 500 μ g/L, pH = 4) was supplied to the precipitation tube by a peristaltic pump at a flow rate of 19.6 μ L/min with a hydraulic retention time of about 31 days.

The pH value, the TOC concentration and the Cd concentration of the effluent are respectively detected, the detection results are sequentially shown in figure 1, figure 2 and figure 3, the effluent concentration of heavy metal Cd after 91 days of operation is 0.05 mu g/L, the removal rate is more than 99%, the pH value is 10.05, and the Total Organic Carbon (TOC) is 38.2 mg/L.

Example 2

In the permeable reactive barrier composite material prepared by the embodiment, the high-permeability hard outer shell layer consists of the following components in percentage by mass: 15% of diatomite, 55% of attapulgite and 30% of portland cement; the functional material of the heavy metal restoration functional layer comprises the following components in percentage by mass: 5% of secondary reduced iron powder, 50% of pine and cypress sawdust, 15% of heavy calcium carbonate, 10% of poplar charcoal and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is 0.5 percent of sodium alginate solution. The particle sizes of other raw materials are larger than 80 meshes except for the raw materials for preparing the composite material, namely the pine and cypress sawdust and the fermented chicken manure are 20 meshes.

The steps of the preparation method of the composite material are the same as those of the embodiment 1, the difference is that the rotating speed of the sugar coating machine is 40 r/min, and the thickness of the high-permeability hard shell prepared by the embodiment is about 0.1-0.15 cm.

The composite functional material prepared in the embodiment and quartz sand are filled in a settling tube which is 50 cm long and 5 cm in diameter according to the mass ratio of 1:1 (same as embodiment 1). The water sample simulating Cd pollution of the underground water is supplied to a precipitation tube by a peristaltic pump at the flow rate of 19.6 mu L/min, the hydraulic retention time is about 31 days, the initial concentration of Cd is 500 mu g/L, and the pH =4.

The pH, the TOC concentration and the Cd concentration of the effluent are respectively detected, the detection results are shown in figures 4, 5 and 6, the effluent concentration of heavy metal Cd after 91 days of operation is 0.14 mu g/L, the removal rate is more than 99%, the pH value is 10.33, and the Total Organic Carbon (TOC) is 35.8 mg/L. The former is superior to the latter in the removal effect in example 2 as compared with example 1.

Example 3

In the permeable reactive barrier composite material prepared by the embodiment, the high-permeability hard outer shell layer consists of the following components in percentage by mass: 17% of diatomite, 50.1% of attapulgite and 32.9% of portland cement. The functional material of the heavy metal restoration functional layer comprises the following components in percentage by mass: 7% of secondary reduced iron powder, 50% of fermented chicken manure, 13% of ground calcium carbonate, 10% of poplar biochar and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is 0.5 percent of sodium alginate solution. The particle size of the raw materials for preparing the composite material is larger than 80 meshes except for 20 meshes of fermented chicken manure.

The composite material of this example was prepared in the same manner as in example 1, except that the coating machine was operated at a speed of 35 r/min, the resulting high permeability hard outer shell had a thickness of about 0.1 to 0.15 cm, and the poplar biochar was prepared using 10% KOH in a ratio of 1 (poplar biochar mass, g): 10 (volume of KOH, ml) for 24 hours, vacuum filtering with 200 mesh nylon filter cloth, drying at 85 ℃ and sieving with 80 mesh sieve.

The composite functional material prepared in the embodiment and quartz sand are filled in a precipitation tube which is 50 cm in length and 5 cm in diameter according to the mass ratio of 1:1 (same as embodiment 1). A water sample simulating Pb contamination of groundwater was supplied to the settling tube by a peristaltic pump at a flow rate of 19.6 μ L/min for a hydraulic retention time of about 31 days, with an initial concentration of Pb of 500 μ g/L and pH =4.

The pH and Pb concentration of the water were measured, and the measurement results are shown in fig. 7 and 8: after 91 days of operation, the effluent concentration of heavy metal Pb is 0.09 mu g/L, the removal rate is more than 99 percent, and the pH of the effluent is 9.80.

Example 4

In the permeable reactive barrier composite material prepared by the embodiment, the high-permeability hard outer shell layer consists of the following components in percentage by mass: 20% of diatomite, 52% of attapulgite and 28% of portland cement. The functional material of the heavy metal restoration functional layer comprises the following components in percentage by mass: 10% of secondary reduced iron powder, 40% of fermented chicken manure, 20% of ground calcium carbonate, 10% of poplar biochar and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is 1% sodium alginate solution. The particle sizes of other raw materials except for 20 meshes of fermented chicken manure are larger than 80 meshes.

The composite material of this example was prepared in the same manner as in example 1, except that the coating machine was operated at a speed of 35 r/min, the high permeability hard jacket thickness was about 0.1-0.15 cm, and the attapulgite was coated with 10% KOH in a ratio of 1 (attapulgite mass, g): 15 (volume of KOH, ml) for 24 hours, vacuum filtering with 200 mesh nylon filter cloth, drying at 85 ℃ and sieving with 80 mesh sieve.

The composite functional material prepared in the embodiment and quartz sand are filled in a settling tube which is 50 cm long and 5 cm in diameter according to the mass ratio of 1:1 (same as embodiment 1). A water sample simulating Pb contamination of groundwater was supplied to the settling tube by a peristaltic pump at a flow rate of 19.6 μ L/min for a hydraulic retention time of about 31 days, with an initial concentration of Pb of 500 μ g/L and pH =4.

The Pb concentration of the effluent was detected, and the detection results are shown in fig. 9: after 91 days of operation, the effluent concentration of heavy metal Pb is 0.05 mu g/L, and the removal rate is more than 99 percent.

Example 5

In the permeable reactive barrier composite material prepared by the embodiment, the high-permeability hard outer shell layer consists of the following components in percentage by mass: 12.1 percent of diatomite, 62.9 percent of attapulgite and 25 percent of portland cement. The functional material of the heavy metal restoration functional layer comprises the following components in percentage by mass: 10% of secondary reduced iron powder, 40% of pine and cypress sawdust, 20% of heavy calcium carbonate, 10% of poplar charcoal and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is 1% sodium alginate solution. The particle sizes of the raw materials for preparing the composite material are all larger than 80 meshes except for the pine and cypress sawdust of 20 meshes.

The preparation steps of the composite material of the embodiment are the same as the embodiment 1, and the difference is that the rotating speed of the sugar coating machine is 35 r/min, and the thickness of the high-permeability hard outer shell is 0.1-0.15 cm. The attapulgite was treated with 6 mol/L hydrochloric acid in accordance with the following formula (1) (attapulgite mass, g): 15 (hydrochloric acid volume, ml) for 24 hours, vacuum filtering with 200 mesh nylon filter cloth, drying at 85 ℃, and sieving with 80 mesh sieve.

The composite functional material prepared in the embodiment and quartz sand are filled in a precipitation tube which is 50 cm in length and 5 cm in diameter according to the mass ratio of 1:1 (same as embodiment 1). A water sample simulating As contamination of groundwater was supplied to the settling tube by a peristaltic pump at a flow rate of 19.6 μ L/min for a hydraulic retention time of about 31 days, with an initial concentration of As of 500 μ g/L and pH =4.

The Pb concentration and pH value of the water were detected, and the detection results are shown in fig. 10 and 11: after the operation for 91 days, the effluent concentration of heavy metal As is 4.09 mu g/L, the removal rate is more than 99 percent, and the pH of the effluent is 7.42.

Example 6

In the permeable reactive barrier composite material prepared by the embodiment, the high-permeability hard shell layer consists of the following components in percentage by mass: 10.7 percent of diatomite, 66.9 percent of attapulgite and 22.3 percent of Portland cement. The heavy metal restoration functional layer comprises the following components in percentage by mass: 10% of secondary reduced iron powder, 20% of pine and cypress sawdust, 30% of fermented chicken manure, 10% of ground calcium carbonate, 10% of poplar charcoal and 20% of attapulgite. The adhesive of the heavy metal restoration functional layer is 0.7 percent of sodium alginate solution. The particle sizes of the raw materials for preparing the composite material are all larger than 80 meshes except for the pine and cypress sawdust of 20 meshes.

The preparation steps of the composite material of the embodiment are the same as the embodiment 1, and the difference is that the rotating speed of the sugar coating machine is 35 r/min, and the thickness of the high-permeability hard outer shell is about 0.1-0.15 cm. The attapulgite is prepared by mixing 3 mol/L hydrochloric acid according to the mass ratio of 1 (attapulgite mass, g): 15 (hydrochloric acid volume, ml) for 24 hours, vacuum filtering with 200 mesh nylon filter cloth, drying at 85 ℃, and sieving with 80 mesh sieve.

The composite functional material prepared in the embodiment and quartz sand are filled in a settling tube which is 50 cm long and 5 cm in diameter according to the mass ratio of 1:1. A water sample simulating As contamination of groundwater was supplied to the settling tube by a peristaltic pump at a flow rate of 19.6 μ L/min for a hydraulic retention time of about 31 days, with an initial concentration of As of 500 μ g/L and pH =4.

The Pb concentration and the pH value of the water are respectively detected, and the detection results are shown in fig. 10 and fig. 11: after 91 days of operation, the effluent concentration of heavy metal As is 3.72 mu g/L, the removal rate is more than 99 percent, and the pH of the effluent is 7.44.

The above-mentioned embodiments only express the embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several modifications can be made without departing from the inventive concept, and these modifications all fall within the scope of protection of the present invention.

Claims

1. An application of permeable reactive wall composite material in repairing underground water polluted by heavy metal,

the heavy metal comprises at least one of Cd, as and Pb;

the permeable reactive barrier composite material is of a spherical structure consisting of a heavy metal restoration functional layer and a high-permeability hard shell layer wrapped outside the heavy metal restoration functional layer;

the high-permeability hard shell layer is composed of an inorganic bonding material, plastic clay and a permeable material containing micro-channels;

the heavy metal restoration functional layer is composed of a functional material and a natural adhesive material; the functional material consists of an inorganic reducing agent, a natural organic carbon-releasing material, carbonate minerals, biomass carbon and plastic clay;

the inorganic binding material comprises at least one of Portland cement and hydrated lime; the plastic clay comprises at least one of attapulgite, kaolin and montmorillonite; the permeable material containing the micro-channels is diatomite;

in the functional material, the inorganic reducing agent comprises at least one of secondary reduced iron powder, copper powder and aluminum powder; the natural organic carbon-releasing material comprises at least one of wood chips, fermented chicken manure and crop straws;

the carbonate mineral comprises at least one of sodium carbonate, calcium carbonate and magnesium carbonate;

the natural adhesive material is sodium alginate solution;

in the high-permeability hard shell layer, the mass percentages of the inorganic binding material, the plastic clay and the permeable material containing the micro-channels are 22.3-32.9% in sequence: 50.1-66.9%:10.7 to 20 percent;

the functional material comprises 5-10% of inorganic reducing agent, natural organic carbon releasing material, carbonate mineral, biomass carbon and plastic clay in sequence by mass percent: 40-50%:10-20%:10%:20 percent.

2. The application of claim 1, wherein the mass percent of the sodium alginate solution is 0.5-1% of the sodium alginate solution, and the mass ratio of the functional material to the natural adhesive material is 1.

3. Use according to claim 1, wherein the spherical structures have a particle size of 1-1.5 cm.

4. The use of claim 3, wherein the high permeability hard skin layer has a thickness of 0.1-0.2 cm.