Method for repairing heavy metal polluted underground water based on slow-release repairing agent

Abstract

The invention discloses a method for repairing heavy metal polluted underground water based on a slow-release repairing agent. The method comprises the following steps: S1, preparing an external slow-release material; s2, preparing an internal sustained-release material; s3, designing a dosing well; and S4, calculating the dosage. According to the invention, two different sustained-release materials are used as the basis and are coated with each other to form the sustained-release repairing agent, and the inner sustained-release material has stronger adsorption capacity, so that the problem of poor effect of the outer sustained-release material under the condition of high-concentration heavy metal polluted underground water can be solved; meanwhile, the outer slow-release material can further assist and slow down release of the inner slow-release material, finally, a set of long-term treatment scheme suitable for various complex heavy metal polluted groundwater is formed by matching with the special repairing agent tubular column and a dosage correction formula, and the effective repairing effect on groundwater heavy metal pollution can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of groundwater remediation, and specifically relates to a method for remediating heavy metal-polluted groundwater based on a slow-release remediation agent. Background Art

[0002] Groundwater refers to the water stored in the rock voids below the ground surface. Narrowly speaking, it refers to the water in the saturated aquifer below the groundwater table. The strata below the ground surface are complex, and the flow of groundwater is extremely slow. Therefore, groundwater pollution is characterized by a slow process, being difficult to detect, and being difficult to treat. Once groundwater is polluted, even if the pollution source is completely eliminated, it will take more than ten years, or even decades, to restore the water quality. Groundwater pollution is a phenomenon of deterioration of groundwater quality caused by human factors. The main reasons for groundwater pollution are as follows: direct discharge of industrial wastewater into the ground, intrusion of polluted surface water into the underground aquifer, infiltration of human and animal feces or water polluted by excessive use of pesticides into the ground, etc. The result of the pollution is an increase in the content of harmful components in the groundwater, such as phenols, chromium, mercury, arsenic, radioactive substances, bacteria, organic substances, etc. Polluted groundwater is harmful to human health and industrial and agricultural production.

[0003] Currently, the main methods for remediating heavy metal-polluted groundwater are as follows: Extraction and treatment method: Polluted groundwater is pumped to the ground through a well group, treated, and then re-injected into the ground or discharged into surface water bodies. Adsorption method: Materials with adsorption capacity, such as activated carbon, clay minerals, zeolites, etc., are used to adsorb heavy metal ions in groundwater. Chemical precipitation method: Chemical agents are added to groundwater to cause heavy metal ions to react chemically with the agents to form insoluble precipitates, thereby reducing the concentration of heavy metal ions in groundwater. Oxidation-reduction method: Oxidants or reductants are used to convert heavy metal ions in groundwater into forms that are easier to remove. For example, as mentioned above, aeration oxidation can oxidize some heavy metal ions to high-valent states, and then form precipitates for removal. Bioremediation method, etc. Among them, the materials for slow-release remediation of heavy metal-polluted groundwater are a type of materials that can slowly release remediation components in groundwater and reduce the concentration of heavy metal ions through precipitation, adsorption, ion exchange, etc.

[0004] Hydroxyapatite is a commonly used slow-release remediation agent. Calcium ions on its surface, etc., undergo ion exchange reactions with heavy metal ions, and at the same time, phosphate ions will form insoluble phosphate precipitates with some heavy metal ions, thereby fixing heavy metal ions. For example, for lead pollution, phosphate in apatite reacts with lead ions to form lead phosphate precipitates, achieving the removal of lead. In order to improve the remediation effect of apatite, it is often modified, such as by surface loading of metal oxides such as iron and manganese to increase the adsorption sites and reaction activity for heavy metals. However, for groundwater polluted by high-concentration heavy metals, its treatment effect is limited, and further research needs to be carried out on it. Summary of the Invention

[0005] In view of the above problems, the present invention provides a method for repairing heavy metal contaminated groundwater based on a slow-release repair agent.

[0006] The technical solution of the present invention is as follows:

[0007] A method for repairing heavy metal contaminated groundwater based on a slow-release repair agent, comprising the following steps:

[0008] S1. Preparation of the outer slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:4 to 8, and co-encapsulate them with an organosilica gel skeleton to obtain the outer slow-release material;

[0009] S2. Preparation of the inner slow-release material: Load FeS on the surface of mesoporous SiO2 nanospheres with a pore size of 5 to 10 nm, and then modify polyacrylic acid on its surface to obtain the inner slow-release material;

[0010] S3. Design of the dosing well: Excavate the contaminated groundwater area as the dosing well. Use the outer slow-release material to encapsulate the inner slow-release material as the slow-release repair agent. The mass ratio of the outer slow-release material to the inner slow-release material in the slow-release repair agent is 4 to 5:1 to 2, and a screen is wrapped around the slow-release repair agent to form a continuous repair agent string, which is lowered below the groundwater level in the dosing well;

[0011] S4. Calculation of the dosing amount: The calculation formula for the dosing amount is as follows:

[0012]

[0013] In the formula, M is the total dosage of the slow-release repair agent, in g; C0 is the initial heavy metal concentration, in mg / L; Q is the groundwater flow rate, in m 3 / d; T is the expected repair time, 30 to 60 d; f is the safety factor, taken as 1.2; η is the utilization rate of the slow-release repair agent, taken as 0.7; A is the proportion of the inner slow-release material in the total mass of the slow-release repair agent, in %.

[0014] Further, the preparation method of the acid-modified carbon nanotubes in S1 is: Add carbon nanotubes to the mixed acid solution, stir and mix for 20 to 30 min, then heat up to 70 to 80 °C and disperse for 0.5 to 1 h under ultrasonic conditions, and then take it out and dry it to obtain the acid-modified carbon nanotubes;

[0015] Among them, the mass-volume ratio of the carbon nanotubes to the mixed acid solution is 1 g:80 to 100 mL, and the mixed acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 3 to 4:1.

[0016] Description: By acid-modifying carbon nanotubes, they are aggregated with hydroxyapatite particles and interpenetrated therein, providing more heavy metal adsorption channels. After modification, a large number of oxygen-containing functional groups are introduced into the carbon nanotubes, increasing its specific surface area and surface activity.

[0017] Furthermore, the method of co-coating with the organosilica gel framework in S1 is as follows: Add the acid-modified carbon nanotubes and hydroxyapatite according to the above mass ratio to absolute ethanol, and ultrasonically disperse for 0.5 - 1 h to obtain solution A, and the solid content in the solution A is 20 - 30 wt%.

[0018] Take organosilica gel particles with a volume of 1 - 2 cm 3 and add them to the solution A. At the same time, add sulfomethylated phenolic resin. The mass-volume ratio of the organosilica gel particles, sulfomethylated phenolic resin to the solution A is 1 g: 0.2 - 0.4 g: 2 - 3 mL. Stir and mix at 30 - 35 °C for 12 - 24 h, take out the loaded organosilica gel particles, wash them 3 times with absolute ethanol, and then air dry naturally to obtain the outer slow-release material.

[0019] Description: By selecting organosilica gel particles as the loading framework material for acid-modified carbon nanotubes and hydroxyapatite, it has good physical and chemical stability, a large specific surface area and porosity, and can effectively load and achieve slow release. Among them, the added sulfomethylated phenolic resin (SMP) has good high-temperature resistance, salt resistance and hydrophobic properties, and can effectively control the loss of the repair agent in high-concentration heavy metal-polluted groundwater.

[0020] Further, in S2, the preparation method of the mesoporous SiO2 nanospheres is as follows: Dissolve tetraethyl orthosilicate in absolute ethanol and stir evenly to form solution B. The molar concentration of tetraethyl orthosilicate in the solution B is 0.5 - 1 mol / L. Dissolve cetyltrimethylammonium bromide in deionized water and add ammonia water, and stir to form solution C. The molar concentration of cetyltrimethylammonium bromide in the solution C is 0.05 - 0.1 mol / L, and the molar concentration of ammonia water is 2 - 5 mol / L. Then, drop solution B into solution C at a dropping rate of 1 - 5 mL / min. After dropping, continue to stir and react for 2 - 6 hours, and the reaction temperature is 50 - 60 °C. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres, and then wash it several times with absolute ethanol and deionized water, and dry it at 60 - 65 °C to obtain the mesoporous SiO2 nanospheres.

[0021] Description: Mesoporous SiO2 nanospheres have a large specific surface area and a regular pore structure, which can provide abundant adsorption sites. Its surface carries a certain charge and can adsorb heavy metal ions in groundwater through electrostatic attraction.

[0022] Further, the method for loading FeS on mesoporous SiO2 nanospheres in S2 is as follows: Dissolve FeCl2·4H2O and Na2S·9H2O separately in deionized water, stir and mix to obtain solution D and solution E. The molar concentration of Fe in solution D is 0.01 - 0.05 mol / L, and the molar concentration of S in solution E is 0.02 - 0.08 mol / L. Add the mesoporous SiO2 nanospheres into solution D, ultrasonically disperse for 10 - 30 min, then under stirring conditions, dropwise add solution E, with the dropping rate controlled at 1 - 3 mL / min, the reaction temperature controlled at 40 - 60 °C, and the reaction time is 2 - 4 hours. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres loaded with FeS, then wash it several times with absolute ethanol and deionized water, and dry it at 60 - 65 °C to obtain the mesoporous SiO2 nanospheres loaded with FeS.

[0023] Note: After loading FeS on the mesoporous SiO2 nanospheres, the surface properties of the material change, enhancing the adsorption capacity for certain pollutants. It can reduce some heavy metal ions in groundwater, such as Cr(VI), Hg(II), etc., to less toxic or more easily precipitated valence states. FeS will slowly release S in water. 2- , S 2- can react with various heavy metal ions such as Pb 2+ , Cd 2+ , Cu 2+ etc. to form insoluble sulfide precipitates.

[0024] Preferably, the method for surface modification with polyacrylic acid in S2 is as follows: Take an acrylic acid solution with a molar concentration of 0.1 - 1.0 mol / L, add potassium persulfate, and the potassium persulfate is 1 - 5% of the mass of acrylic acid. Add the mesoporous SiO2 nanospheres loaded with FeS into the acrylic acid solution, ultrasonically disperse for 10 - 15 min, heat to 70 - 80 °C under a nitrogen atmosphere, stir and react for 6 - 8 hours. After centrifugation, wash the solid product several times with deionized water, and dry it at 60 - 65 °C to obtain the internal slow-release material.

[0025] Note: Polyacrylic acid can form a protective film on the surface of FeS, reducing the direct contact between FeS and certain substances in the groundwater environment, reducing the oxidation or dissolution rate of FeS, thereby improving the stability of FeS, extending the service life of the material, and ensuring its continuous role in groundwater treatment.

[0026] Further, in S3, the internal slow-release material is located at the center of the repair agent column, and the external slow-release material is located on the outer ring of the repair agent column. The length of the repair agent column is 1 - 2 m, and the radius of the repair agent column is 10 - 20 cm.

[0027] Description: By wrapping two kinds of sustained-release materials around each other, the release of the internal sustained-release material is further slowed down. At the same time, the strong adsorption capacity of the internal sustained-release material is used to make up for the limited effect of the external sustained-release material when remediating groundwater with high heavy metal concentration.

[0028] Furthermore, in S3, the bottom of the repair agent pipe column is always located 20 - 40 cm below the groundwater level.

[0029] Description: By keeping the bottom of the repair agent pipe column at a certain height below the groundwater level all the time, it is ensured that the released repair agent can act on the groundwater completely and evenly.

[0030] Further, in S3, an aeration pipe is arranged side by side beside the repair agent pipe column, and aeration is carried out while the repair agent pipe column is working to keep the dissolved oxygen content in the groundwater at 4 - 8 mg / L.

[0031] Description: By aeration, the oxygen content in the groundwater is increased, making the water body in an oxidation environment and oxidizing heavy metal ions into a more easily removable form.

[0032] The beneficial effects of the present invention are:

[0033] (1) A method for remediating heavy metal - contaminated groundwater based on a sustained - release repair agent of the present invention is based on two different sustained - release materials, which form a sustained - release repair agent after wrapping around each other. Among them, the internal sustained - release material has stronger adsorption capacity, which can make up for the poor effect of the external sustained - release material under the condition of high - concentration heavy metal - contaminated groundwater. At the same time, the external sustained - release material can further assist and slow down the release of the internal sustained - release material. Finally, combined with the special repair agent pipe column and the dosing amount correction formula of the present invention, a set of long - term treatment schemes suitable for various complex heavy metal - contaminated groundwater is formed, which can effectively repair the heavy metal pollution in groundwater.

[0034] (2) In the preparation of the external sustained - release material of a method for remediating heavy metal - contaminated groundwater based on a sustained - release repair agent of the present invention, sulfomethylated phenolic resin (SMP) is added, so that the external sustained - release material has good high - temperature resistance, salt resistance, and hydrophobic properties, can effectively control the filter loss amount of the repair agent in high - concentration heavy metal - contaminated groundwater, and enables the two internal and external sustained - release materials to have good compatibility. Description of the Drawings

[0035] Figure 1 is a schematic structural diagram of a repair agent pipe column in a dosing well of a method for remediating heavy metal - contaminated groundwater based on a sustained - release repair agent of the present invention;

[0036] Figure 2 is a cross - sectional view of a repair agent pipe column in a dosing well of a method for remediating heavy metal - contaminated groundwater based on a sustained - release repair agent of the present invention;

[0037] Figure 3 It is the treatment result diagram of each experimental group under the condition of single heavy metal ion treatment in Experimental Example 1 of the present invention;

[0038] Figure 4 It is the treatment result diagram of each experimental group under the condition of multiple heavy metal ion treatment in Experimental Example 1 of the present invention. Detailed implementation manners

[0039] Example 1

[0040] A method for repairing heavy metal contaminated groundwater based on a slow-release repair agent, comprising the following steps:

[0041] S1. Preparation of outer slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite according to a mass ratio of 1:6, and co-encapsulate them with an organosilica gel skeleton to obtain the outer slow-release material;

[0042] The preparation method of the acid-modified carbon nanotubes is: Add carbon nanotubes to the mixed acid solution, stir and mix for 25 min, then heat up to 73 °C and disperse for 0.75 h under ultrasonic conditions, take out and dry to obtain the acid-modified carbon nanotubes;

[0043] Among them, the mass-volume ratio of the carbon nanotubes to the mixed acid solution is 1 g: 90 mL, the mixed acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid according to a volume ratio of 3.5:1, the mass fraction of the concentrated nitric acid is 75%, and the mass fraction of the concentrated sulfuric acid is 75%;

[0044] The method of co-encapsulating with the organosilica gel skeleton is: Add the acid-modified carbon nanotubes and hydroxyapatite to anhydrous ethanol according to the mass ratio, ultrasonically disperse for 0.75 h to obtain solution A, and the solid content in solution A is 26 wt%;

[0045] Take an organosilica gel particle with a volume of 1.2 cm 3 and add it to solution A, and at the same time add sulfomethylated phenolic resin. The mass-volume ratio of the organosilica gel particle, sulfomethylated phenolic resin to solution A is 1 g: 0.3 g: 2.5 mL, stir and mix at 33 °C for 16 h, take out the loaded organosilica gel particle, wash it 3 times with anhydrous ethanol, and then air-dry naturally to obtain the outer slow-release material;

[0046] S2. Preparation of inner slow-release material: Load FeS on the surface of mesoporous SiO2 nanospheres with a pore size of 8 nm, and then modify polyacrylic acid on its surface to obtain the inner slow-release material;

[0047] The preparation method of mesoporous SiO2 nanospheres is as follows: Tetraethyl orthosilicate is dissolved in anhydrous ethanol and stirred evenly to form solution B. The molar concentration of tetraethyl orthosilicate in solution B is 0.6 mol / L. Cetyltrimethylammonium bromide is dissolved in deionized water, and ammonia water is added, and then stirred to form solution C. The molar concentration of cetyltrimethylammonium bromide in solution C is 0.08 mol / L, and the molar concentration of ammonia water is 3 mol / L. Subsequently, solution B is dropped into solution C at a dropping rate of 3 mL / min. After the dropping is completed, stirring reaction is continued for 3 hours, the reaction temperature is 55 °C, and mesoporous SiO2 nanosphere crude products are obtained by centrifugation. Then, they are washed 3 times with anhydrous ethanol and deionized water, and dried at 63 °C to obtain mesoporous SiO2 nanospheres;

[0048] The method for loading FeS on mesoporous SiO2 nanospheres is as follows: FeCl2·4H2O and Na2S·9H2O are respectively dissolved in deionized water, and stirred and mixed to obtain solution D and solution E. The molar concentration of Fe in solution D is 0.03 mol / L, and the molar concentration of S in solution E is 0.05 mol / L. Mesoporous SiO2 nanospheres are added to solution D and ultrasonically dispersed for 20 min. Then, under stirring conditions, solution E is dropped, and the dropping rate is controlled at 2 mL / min, the reaction temperature is controlled at 50 °C, and the reaction time is 3 hours. The crude products of mesoporous SiO2 nanospheres loaded with FeS are obtained by centrifugation. Then, they are washed 3 times with anhydrous ethanol and deionized water, and dried at 63 °C to obtain mesoporous SiO2 nanospheres loaded with FeS;

[0049] The method for surface modification with polyacrylic acid is as follows: Take an acrylic acid solution with a molar concentration of 0.3 mol / L, add potassium persulfate, and the mass of potassium persulfate is 3% of the mass of acrylic acid. Mesoporous SiO2 nanospheres loaded with FeS are added to the acrylic acid solution and ultrasonically dispersed for 12 min. Heat to 75 °C under a nitrogen atmosphere and stir and react for 7 hours. After centrifugation, the solid product is washed 3 times with deionized water and dried at 62 °C to obtain the internal slow-release material;

[0050] S3. Design of dosing well: Excavate the polluted groundwater area as the dosing well. Coating the internal slow-release material with the external slow-release material as the slow-release repair agent. The mass ratio of the external slow-release material to the internal slow-release material in the slow-release repair agent is 4.5:1.5. And a screen is coated outside the slow-release repair agent to form a continuous repair agent string, which is lowered below the groundwater level in the dosing well. The internal slow-release material is located at the center of the repair agent string, and the external slow-release material is located in the outer ring of the repair agent string. The length of the repair agent string is 1.5 m, the radius of the repair agent string is 15 cm, and the bottom of the repair agent string is always 30 cm below the groundwater level. An aeration pipe is arranged side by side beside the repair agent string, and aeration is carried out while the repair agent string is working to keep the dissolved oxygen content in the groundwater at 6 mg / L;

[0051] S4. Dosage calculation: The calculation formula for the dosage is as follows:

[0052]

[0053] In the formula, M is the total dosage of the slow-release repair agent, in g; C0 is the initial heavy metal concentration, in mg / L; Q is the groundwater flow rate, in m 3 / d; T is the expected repair time, 45 d; f is the safety factor, taken as 1.2; η is the utilization rate of the slow-release repair agent, taken as 0.7; A is the proportion of the internal slow-release material in the total mass of the slow-release repair agent, taken as 25%.

[0054] Example 2

[0055] The difference between this example and Example 1 is:

[0056] S1. Preparation of the external slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:4.

[0057] Example 3

[0058] The difference between this example and Example 1 is:

[0059] S1. Preparation of the external slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:5.

[0060] Example 4

[0061] The difference between this example and Example 1 is:

[0062] S1. Preparation of the external slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:7.

[0063] Example 5

[0064] The difference between this example and Example 1 is:

[0065] S1. Preparation of the external slow-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:8.

[0066] Example 6

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

[0068] The preparation method of the acid-modified carbon nanotubes is as follows: Add carbon nanotubes to the mixed acid solution, stir and mix for 20 min, then heat up to 70 °C and disperse for 0.5 h under ultrasonic conditions, and then take out and dry to obtain the acid-modified carbon nanotubes;

[0069] Among them, the mass-volume ratio of carbon nanotubes to the mixed acid solution is 1 g: 80 mL, and the mixed acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 3:1;

[0070] The method for co-coating the silicone gel skeleton is as follows: Add acid-modified carbon nanotubes and hydroxyapatite in a mass ratio to absolute ethanol, and ultrasonically disperse for 0.5 h to obtain solution A. The solid content in solution A is 20 wt%;

[0071] Take 1 cm 3 of silicone gel particles, add them to solution A, and simultaneously add sulfomethylated phenolic resin. The mass-volume ratio of silicone gel particles, sulfomethylated phenolic resin to solution A is 1 g: 0.2 g: 2 mL. Stir and mix at 30 °C for 12 h, take out the loaded silicone gel particles, wash them 3 times with absolute ethanol, and then air dry naturally to obtain the outer sustained-release material.

[0072] Example 7

[0073] The difference between this example and Example 1 is as follows:

[0074] The preparation method of acid-modified carbon nanotubes is as follows: Add carbon nanotubes to the mixed acid solution, stir and mix for 30 min, then heat up to 80 °C under ultrasonic conditions and disperse for 1 h. Take out and dry to obtain acid-modified carbon nanotubes;

[0075] Among them, the mass-volume ratio of carbon nanotubes to the mixed acid solution is 1 g: 100 mL, and the mixed acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 4:1;

[0076] The method for co-coating the silicone gel skeleton is as follows: Add acid-modified carbon nanotubes and hydroxyapatite in a mass ratio to absolute ethanol, and ultrasonically disperse for 1 h to obtain solution A. The solid content in solution A is 30 wt%;

[0077] Take 2 cm 3 of silicone gel particles, add them to solution A, and simultaneously add sulfomethylated phenolic resin. The mass-volume ratio of silicone gel particles, sulfomethylated phenolic resin to solution A is 1 g: 0.4 g: 3 mL. Stir and mix at 35 °C for 24 h, take out the loaded silicone gel particles, wash them 3 times with absolute ethanol, and then air dry naturally to obtain the outer sustained-release material.

[0078] Note: The addition amounts of silicone gel particles and sulfomethylated phenolic resin are adjusted proportionally. It is difficult to control the volume of silicone gel particles at an accurate value. Therefore, those with a volume of 1-2 cm 3 are acceptable, and the other parameters are adjusted within a reasonable range.

[0079] Example 8

[0080] The difference between this example and Example 1 is as follows:

[0081] S2. Preparation of the inner slow-release material: Load FeS on the surface of mesoporous SiO2 nanospheres with a pore size of 5 nm, and then modify polyacrylic acid on its surface to obtain the inner slow-release material;

[0082] The preparation method of the mesoporous SiO2 nanospheres is as follows: Dissolve tetraethyl orthosilicate in absolute ethanol and stir evenly to form solution B. The molar concentration of tetraethyl orthosilicate in solution B is 0.5 mol / L. Dissolve cetyltrimethylammonium bromide in deionized water and add ammonia water, and stir to form solution C. The molar concentration of cetyltrimethylammonium bromide in solution C is 0.05 mol / L, and the molar concentration of ammonia water is 2 mol / L. Subsequently, drop solution B into solution C at a dropping rate of 1 mL / min. After the dropping is completed, continue to stir and react for 2 hours at a reaction temperature of 50 °C. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres, and then wash it twice with absolute ethanol and deionized water, and dry it at 60 °C to obtain the mesoporous SiO2 nanospheres;

[0083] The method for loading FeS on the mesoporous SiO2 nanospheres is as follows: Dissolve FeCl2·4H2O and Na2S·9H2O in deionized water respectively, and stir and mix to obtain solution D and solution E. The molar concentration of Fe in solution D is 0.01 mol / L, and the molar concentration of S in solution E is 0.02 mol / L. Add the mesoporous SiO2 nanospheres to solution D, ultrasonically disperse for 10 min, and then, under stirring conditions, drop solution E with a dropping rate controlled at 1 mL / min and a reaction temperature controlled at 60 °C for a reaction time of 2 hours. Centrifuge to obtain the crude product of the mesoporous SiO2 nanospheres loaded with FeS, and then wash it twice with absolute ethanol and deionized water, and dry it at 60 °C to obtain the mesoporous SiO2 nanospheres loaded with FeS;

[0084] The method for surface modification with polyacrylic acid is as follows: Take an acrylic acid solution with a molar concentration of 0.1 mol / L, add potassium persulfate, and the potassium persulfate is 1% of the mass of acrylic acid. Add the mesoporous SiO2 nanospheres loaded with FeS to the acrylic acid solution, ultrasonically disperse for 10 min, heat to 80 °C under a nitrogen atmosphere, stir and react for 6 hours, centrifuge, wash the solid product twice with deionized water, and dry it at 60 °C to obtain the inner slow-release material.

[0085] Example 9

[0086] The difference between this example and Example 1 is as follows:

[0087] S2. Preparation of the inner slow-release material: Load FeS on the surface of mesoporous SiO2 nanospheres with a pore size of 10 nm, and then modify polyacrylic acid on its surface to obtain the inner slow-release material;

[0088] The preparation method of mesoporous SiO2 nanospheres is as follows: Dissolve tetraethyl orthosilicate in absolute ethanol, stir evenly to form solution B, and the molar concentration of tetraethyl orthosilicate in solution B is 1 mol / L. Dissolve cetyltrimethylammonium bromide in deionized water, add ammonia water, and stir to form solution C. The molar concentration of cetyltrimethylammonium bromide in solution C is 0.1 mol / L, and the molar concentration of ammonia water is 5 mol / L. Subsequently, drip solution B into solution C at a dripping rate of 5 mL / min. After dripping, continue to stir and react for 6 hours at a reaction temperature of 60 °C. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres, then wash it twice with absolute ethanol and deionized water, and dry it at 65 °C to obtain mesoporous SiO2 nanospheres;

[0089] The method for loading FeS on mesoporous SiO2 nanospheres is as follows: Dissolve FeCl2·4H2O and Na2S·9H2O in deionized water respectively, stir and mix to obtain solution D and solution E. The molar concentration of Fe in solution D is 0.05 mol / L, and the molar concentration of S in solution E is 0.08 mol / L. Add mesoporous SiO2 nanospheres into solution D, disperse them ultrasonically for 30 min, then under stirring conditions, drip solution E, control the dripping rate at 3 mL / min, control the reaction temperature at 40 °C, and the reaction time is 4 hours. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres loaded with FeS, then wash it twice with absolute ethanol and deionized water, and dry it at 65 °C to obtain mesoporous SiO2 nanospheres loaded with FeS;

[0090] The method for surface modification with polyacrylic acid is as follows: Take an acrylic acid solution with a molar concentration of 1.0 mol / L, add potassium persulfate, and the potassium persulfate is 5% of the mass of acrylic acid. Add the mesoporous SiO2 nanospheres loaded with FeS into the acrylic acid solution, disperse them ultrasonically for 15 min, heat to 70 °C under a nitrogen atmosphere, stir and react for 8 hours. After centrifugation, wash the solid product twice with deionized water, and dry it at 65 °C to obtain the internal slow-release material.

[0091] Note: The parameters for preparing the internal slow-release material can be appropriately adjusted within a given range. For example, when the reaction temperature is relatively high, the reaction time can be appropriately reduced.

[0092] Example 10

[0093] The difference between this example and Example 1 is as follows:

[0094] S3. Design of the dosing well: Excavate the contaminated groundwater area as the dosing well, and use the outer slow-release material coated with the inner slow-release material as the slow-release repair agent. The mass ratio of the outer slow-release material to the inner slow-release material in the slow-release repair agent is 4:1;

[0095] Correspondingly, A is the proportion of the inner slow-release material in the total mass of the slow-release repair agent, taking 20%.

[0096] Example 11

[0097] The difference between this example and Example 1 is as follows:

[0098] S3. Design of the dosing well: Excavate the contaminated groundwater area to serve as the dosing well. Coating the inner slow-release material with the outer slow-release material as the slow-release repair agent, the mass ratio of the outer slow-release material to the inner slow-release material in the slow-release repair agent is 4:2.

[0099] Correspondingly, A is the proportion of the inner slow-release material in the total mass of the slow-release repair agent, taking 33.3%.

[0100] Example 12

[0101] The difference between this example and Example 1 is as follows:

[0102] S3. Design of the dosing well: Excavate the contaminated groundwater area to serve as the dosing well. Coating the inner slow-release material with the outer slow-release material as the slow-release repair agent, the mass ratio of the outer slow-release material to the inner slow-release material in the slow-release repair agent is 5:1.

[0103] Correspondingly, A is the proportion of the inner slow-release material in the total mass of the slow-release repair agent, 16.6%.

[0104] Example 13

[0105] The difference between this example and Example 1 is as follows:

[0106] S3. Design of the dosing well: Excavate the contaminated groundwater area to serve as the dosing well. Coating the inner slow-release material with the outer slow-release material as the slow-release repair agent, the mass ratio of the outer slow-release material to the inner slow-release material in the slow-release repair agent is 5:2.

[0107] Correspondingly, A is the proportion of the inner slow-release material in the total mass of the slow-release repair agent, 28.5%.

[0108] Example 14

[0109] The difference between this example and Example 1 is as follows:

[0110] A screen mesh is coated on the slow-release repair agent to form a continuous repair agent pipe string, which is lowered into the injection well below the groundwater level. The inner slow-release material is located at the center of the repair agent pipe string, and the outer slow-release material is located in the outer ring of the repair agent pipe string. The length of the repair agent pipe string is 1 m, the radius of the repair agent pipe string is 20 cm, and the bottom of the repair agent pipe string is always 20 cm below the groundwater level. An aeration pipe is arranged side by side beside the repair agent pipe string, and aeration is carried out while the repair agent pipe string is working to keep the dissolved oxygen content in the groundwater at 4 mg / L.

[0111] Example 15

[0112] The difference between this example and Example 1 is as follows:

[0113] A screen mesh is coated on the slow-release repair agent to form a continuous repair agent pipe string, which is lowered into the injection well below the groundwater level. The inner slow-release material is located at the center of the repair agent pipe string, and the outer slow-release material is located in the outer ring of the repair agent pipe string. The length of the repair agent pipe string is 2 m, the radius of the repair agent pipe string is 10 cm, and the bottom of the repair agent pipe string is always 40 cm below the groundwater level. An aeration pipe is arranged side by side beside the repair agent pipe string, and aeration is carried out while the repair agent pipe string is working to keep the dissolved oxygen content in the groundwater at 8 mg / L.

[0114] Note: When the groundwater level is relatively shallow, the repair agent pipe string can be appropriately thickened and shortened. At the same time, when the groundwater level is relatively deep, the aeration volume needs to be appropriately increased.

[0115] Example 16

[0116] The difference between this example and Example 1 is as follows:

[0117] T is the expected repair time, taking 30 d.

[0118] Example 17

[0119] The difference between this example and Example 1 is as follows:

[0120] T is the expected repair time, taking 60 d.

[0121] Experimental Example 1

[0122] Next, we conduct a study on the feasibility of the method of the present invention. We prepare the outer slow-release material, the inner slow-release material, and the slow-release repair agent according to the methods of S1 and S2 in Example 1, and treat the simulated heavy metal wastewater in the laboratory.

[0123] (1) Treatment of single heavy metal ion

[0124] Several groups of 100 mL of simulated wastewater containing 50 μg / mL of heavy metal nickel were prepared, and the external slow-release materials in Examples 1 to 5 were added respectively. At the same time, the external slow-release material of Comparative Example 1 was added. Comparative Example 1 was basically the same as Example 1, except that sulfomethylated phenolic resin was not added. After continuous stirring and reaction for 12 days, the results were as follows Figure 3 shown.

[0125] It can be seen that the release rate of the external slow-release material is slow, and the controlled-release effect can be achieved. During the initial stage of release, the adsorption rate begins to increase significantly. By the 9th day, the release amount is about 60-70%. The entire repair process is relatively stable;

[0126] At the same time, the external slow-release materials in several groups of examples can finally achieve good removal effects on heavy metal nickel in wastewater. Among them, after adding more acid-modified carbon nanotubes (Examples 4 and 5), the removal rate of heavy metal nickel in the final wastewater can be improved. However, according to the trend in the figure, it can be judged that further increasing the proportion of acid-modified carbon nanotubes on the basis of Example 5 will no longer further improve the removal rate of heavy metal nickel in wastewater;

[0127] In addition, the results in Comparative Example 1 are close to the repair effect of Example 1, indicating that adding an appropriate amount of sulfomethylated phenolic resin does not affect the repair effect of the external slow-release material.

[0128] (2) Treatment of multiple metal ions

[0129] Several groups of 100 mL of simulated wastewater containing 50 μg / mL of heavy metal nickel, cadmium, and lead were prepared, and the repair agent columns made of the materials in Example 1, Example 11, and Example 12 were added respectively. The bottom end was kept in the middle of the simulated wastewater. As the slow-release material inside the repair agent column was gradually released, the repair agent column was lowered. At the same time, Comparative Example 2 was introduced. Comparative Example 2 was basically the same as Example 1, except that sulfomethylated phenolic resin was not added. After continuous stirring and reaction for 24 days, the results were as follows Figure 4 shown.

[0130] It can be seen that the adsorption and removal rate of the slow-release material inside the repair agent column for the multiple metal ion wastewater increases with time. Among them, in the initial stage of the reaction (0-10 days), the removal rate of the slow-release material in Example 11 increased the fastest, and the adsorption and removal effect was the best. This may be because more internal slow-release material was added in Example 11 and the external slow-release material was thinner. Therefore, the internal slow-release material with better short-term adsorption was released more quickly; while in the later stage of the repair, the slow-release material in Example 12 could obviously achieve a higher final adsorption and removal rate, because the external slow-release material was thicker and the internal slow-release material was released slower. Although the adsorption and removal effect was poor in the early stage, the persistence was stronger. Reasonably select the parameters in Example 1 or Example 11, Example 12 according to the groundwater pollution situation;

[0131] In addition, sulfomethylated phenolic resin was not added in Comparative Example 2, and its final adsorption and removal effect was slightly lower than that of Example 1. This may be because sulfomethylated phenolic resin (SMP) was added in the preparation of the outer sustained-release material, so that the outer sustained-release material has good high-temperature resistance, salt resistance and hydrophobic properties, and can effectively control the loss of the repair agent in the groundwater polluted by heavy metals at high concentrations, prompting the two kinds of inner and outer sustained-release materials to have good compatibility.

[0132] Experimental Example 2

[0133] Next, we demonstrate the calculation formula of the dosage in S4, the dosage calculation of the present invention. During the actual monitoring of groundwater in a certain place, the content of heavy metal Cd pollutant is 12.8 mg / L. Assuming that the repair duration of a repair cycle is 120 d and the groundwater flow rate is 16 m 3 / d, then substituting into the formula in Example 1, the calculation result is:

[0134]

[0135] The total dosage M of the sustained-release repair agent in this repair cycle is calculated to be 168.5 kg. The length and thickness of the repair agent column are designed according to the total dosage and volume.

[0136] If calculated with the parameters in Example 11, the total dosage M of the sustained-release repair agent obtained changes. According to the analysis results in Experimental Example 1, more inner sustained-release material and thinner outer sustained-release material were added in Example 11. Therefore, the inner sustained-release material with better short-term adsorption property is released more quickly. Therefore, the repair cycle should be appropriately shortened to 90 d. At this time, substituting into the formula in Example 11, the calculation result is:

[0137]

[0138] The total dosage M of the sustained-release repair agent is calculated to be 95.7 kg. The length and thickness of the repair agent column are designed according to the total dosage and volume.

Claims

1. A method for repairing heavy metal-contaminated groundwater based on a slow-release repair agent, characterized in that, It includes the following steps: S1. Preparation of outer sustained-release material: Mix acid-modified carbon nanotubes and hydroxyapatite in a mass ratio of 1:4 to 8, and co-encapsulate them with an organosilica gel skeleton to obtain the outer sustained-release material; S2. Preparation of inner sustained-release material: Load FeS on the surface of mesoporous SiO2 nanospheres with a pore size of 5 to 10 nm, and then modify polyacrylic acid on its surface to obtain the inner sustained-release material; S3. Design of dosing well: Excavate at the location of contaminated groundwater to serve as the dosing well. Coating the inner sustained-release material with the outer sustained-release material as the sustained-release repair agent. The mass ratio of the outer sustained-release material to the inner sustained-release material in the sustained-release repair agent is 4 to 5:1 to 2, and a screen is coated outside the sustained-release repair agent to form a continuous repair agent string, which is lowered below the groundwater level in the dosing well; S4. Calculation of dosing amount: The calculation formula for the dosing amount is as follows: Wherein, M is the total dosage of the slow-release repair agent, in g; C0 is the initial heavy metal concentration, in mg / L; Q is the groundwater flow rate, in m 3 / d; T is the expected repair time, 30 - 60 d; f is the safety factor, taken as 1.2; η is the utilization rate of the slow-release repair agent, taken as 0.7; A is the proportion of the internal slow-release material in the total mass of the slow-release repair agent, in %.

2. The method for repairing heavy metal-contaminated groundwater based on a sustained-release repair agent according to claim 1, wherein The preparation method of the acid-modified carbon nanotubes in S1 is: Add carbon nanotubes to the mixed acid solution, stir and mix for 20 to 30 minutes, then heat up to 70 to 80 °C under ultrasonic conditions and disperse for 0.5 to 1 hour, and after taking out, dry to obtain the acid-modified carbon nanotubes; Among them, the mass-volume ratio of carbon nanotubes to the mixed acid solution is 1 g: 80 to 100 mL, and the mixed acid solution is obtained by mixing concentrated nitric acid and concentrated sulfuric acid in a volume ratio of 3 to 4:

1.

3. The method for repairing heavy metal contaminated groundwater based on a slow-release repair agent according to claim 2, wherein, The method of co-encapsulation with the organosilica gel skeleton in S1 is: Add the acid-modified carbon nanotubes and hydroxyapatite in the said mass ratio to absolute ethanol, and ultrasonically disperse for 0.5 to 1 hour to obtain solution A, and the solid content in solution A is 20 to 30 wt%; Take silicone gel particles with a volume of 1 - 2 cm 3 and add them to the solution A. At the same time, add sulfomethylated phenolic resin. The mass - volume ratio of the silicone gel particles, sulfomethylated phenolic resin to the solution A is 1 g: 0.2 - 0.4 g: 2 - 3 mL. Stir and mix at 30 - 35 °C for 12 - 24 h. Take out the loaded silicone gel particles, wash them 3 times with absolute ethanol, and then air - dry naturally to obtain the outer sustained - release material.

4. A method for repairing heavy metal contaminated groundwater based on a slow-release repair agent according to claim 1, characterized in that, In S2, the preparation method of the mesoporous SiO2 nanospheres is: Dissolve tetraethyl orthosilicate in absolute ethanol and stir evenly to form solution B. The molar concentration of tetraethyl orthosilicate in solution B is 0.5 to 1 mol / L. Dissolve cetyltrimethylammonium bromide in deionized water and add ammonia water, and stir to form solution C. The molar concentration of cetyltrimethylammonium bromide in solution C is 0.05 to 0.1 mol / L, and the molar concentration of ammonia water is 2 to 5 mol / L. Then, drip solution B into solution C at a dripping speed of 1 to 5 mL / min. After dripping, continue to stir and react for 2 to 6 hours, and the reaction temperature is 50 to 60 °C. Centrifuge to obtain the crude product of mesoporous SiO2 nanospheres, and then wash several times with absolute ethanol and deionized water, and dry at 60 to 65 °C to obtain the mesoporous SiO2 nanospheres.

5. A method for repairing heavy metal contaminated groundwater based on a sustained-release repair agent according to claim 4, characterized in that, The method for loading FeS on mesoporous SiO2 nanospheres in S2 is as follows: Dissolve FeCl2·4H2O and Na2S·9H2O separately in deionized water, stir and mix to obtain solution D and solution E. The molar concentration of Fe in solution D is 0.01 - 0.05 mol / L, and the molar concentration of S in solution E is 0.02 - 0.08 mol / L. Add the mesoporous SiO2 nanospheres into solution D, ultrasonically disperse for 10 - 30 min, then under stirring conditions, dropwise add solution E with the dropping rate controlled at 1 - 3 mL / min, control the reaction temperature at 40 - 60 °C, react for 2 - 4 hours, centrifuge to obtain the crude product of mesoporous SiO2 nanospheres loaded with FeS, then wash it several times with absolute ethanol and deionized water, and dry it at 60 - 65 °C to obtain the mesoporous SiO2 nanospheres loaded with FeS.

6. The method for repairing heavy metal contaminated groundwater based on a slow-release repair agent according to claim 5, characterized in that, The method for surface modification with polyacrylic acid in S2 is as follows: Take an acrylic acid solution with a molar concentration of 0.1 - 1.0 mol / L, add potassium persulfate, and the potassium persulfate is 1 - 5% of the mass of acrylic acid. Add the mesoporous SiO2 nanospheres loaded with FeS into the acrylic acid solution, ultrasonically disperse for 10 - 15 min, heat to 70 - 80 °C under a nitrogen atmosphere, stir and react for 6 - 8 hours, centrifuge, wash the solid product with deionized water several times, and dry it at 60 - 65 °C to obtain the internal slow-release material.

7. A method for repairing heavy metal contaminated groundwater based on a sustained-release repair agent according to claim 1, characterized in that, In S3, the internal slow-release material is located at the center of the repair agent pipe column, and the external slow-release material is located on the outer ring of the repair agent pipe column. The length of the repair agent pipe column is 1 - 2 m, and the radius of the repair agent pipe column is 10 - 20 cm.

8. A method for repairing heavy metal contaminated groundwater based on a slow-release repair agent according to claim 1, characterized in that, In S3, the bottom of the repair agent pipe column is always 20 - 40 cm below the groundwater level.

9. A method for repairing heavy metal contaminated groundwater based on a slow-release repair agent according to claim 1, characterized in that, In S3, an aeration pipe is arranged side by side beside the repair agent pipe column, and aeration is carried out while the repair agent pipe column is working to keep the dissolved oxygen content in the groundwater at 4 - 8 mg / L.

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