Iron-based synthetic humic acid heavy metal composite passivator as well as preparation method and application thereof

Abstract

The invention discloses an iron-based synthetic humic acid heavy metal composite passivator as well as a preparation method and application thereof. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator comprises the following steps that S1, catechol and glycine are added into an aqueous solution, manganese dioxide is added after the catechol and the glycine are dissolved, and a first mixed solution is obtained; s2, stirring the first mixed solution for reaction, and separating after stirring to obtain synthetic humic acid; s3, mixing the aqueous solution containing the synthetic humic acid with an aqueous solution of ferric salt, and adjusting the pH value to obtain a second mixed solution; and S4, the second mixed solution is stirred for a reaction, separation is conducted after stirring is completed, and the iron-based synthetic humic acid heavy metal composite passivator is obtained. In the iron-based synthetic humic acid heavy metal composite passivator, by introducing the synthetic humic acid, on one hand, the stability of an iron base can be improved, and the iron base is not prone to deterioration; on the other hand, more active functional groups can be introduced, the heavy metal binding capacity is enhanced, and the synergistic remediation effect is generated.

Description

Technical Field

[0001] The present invention relates to the technical field of heavy metal contaminated soil remediation, and particularly to a preparation method of a soil heavy metal passivator. Background Art

[0002] With the acceleration of China's industrialization and urbanization processes, heavy metal pollution in farmland soil is serious. The "National Soil Pollution Survey Bulletin" in 2014 pointed out that the total over-standard rate of heavy metals in China's soil is 16.1%, and the site over-standard rate of cultivated land soil reaches 19.4%. The situation of heavy metal pollution in farmland soil is severe. In-situ passivation remediation is one of the soil heavy metal pollution remediation technologies advocated in China's "14th Five-Year Plan for Soil, Groundwater and Rural Ecological Environment Protection". Due to its advantages such as low cost, high efficiency, and simple operation, this technology is widely used in the remediation of heavy metal contaminated farmland. Among them, the development of passivators with good performance is particularly crucial.

[0003] A soil heavy metal passivator refers to a substance that can chemically react with heavy metal ions in the soil, convert them into compounds that are poorly soluble in water or stable forms, thereby reducing their toxicity and mobility. Commonly used passivators include inorganic materials such as clay minerals, lime, phosphorus-containing substances, as well as organic materials such as biochar and humus. Using natural humic acid as a passivator is one of the effective ways to repair soil heavy metal pollution. However, due to various sources, there are significant differences in the structural characteristics of different natural humic acids. Some natural humic acids have low active site content and poor biological stability, resulting in unsatisfactory passivation effects. In addition, natural humic acid also has problems such as a long formation period, complex extraction process, and high cost. These limitations significantly restrict its applicability. Synthetic humic acid refers to an artificially synthesized humic acid-like substance prepared through an abiotic humification pathway. It is weakly acidic and has various functional groups such as carboxyl groups, phenolic hydroxyl groups, and quinone groups. Its structural properties are controllable, and it has a higher content of active functional groups. It is considered a high-quality alternative material to natural humic acid. However, like natural humic acid, synthetic humic acid has the problem of poor biological stability. Iron salts are also a commonly used passivator. Although they can promote the conversion of heavy metals in the soil to the residual state to a certain extent, due to their limited passivation effect and easy deterioration, they usually cannot be used alone. Summary of the Invention

[0004] The purpose of the present invention is to provide a preparation method of an iron-based synthetic humic acid heavy metal composite passivator, aiming to provide a more efficient soil heavy metal passivator and solve the problem of poor passivation effect on composite heavy metal contaminated soil containing lead, cadmium, and zinc. The iron-based synthetic humic acid provided by the present invention has good stability, controllable structural properties, and a large number of active functional groups are distributed on the surface, which can provide more binding sites for heavy metals such as lead, cadmium, and zinc, and reduce their mobility and bioavailability in the soil.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a preparation method of an iron-based synthetic humic acid heavy metal composite passivator, comprising the following steps:

[0007] S1. Add catechol and glycine to an aqueous solution, and after dissolution, add manganese dioxide to obtain a first mixed solution;

[0008] S2. Stir the first mixed solution for reaction, and after completion of stirring, separate to obtain synthetic humic acid;

[0009] S3. Mix the aqueous solution containing the synthetic humic acid with an aqueous solution of an iron salt, and adjust the pH value to obtain a second mixed solution;

[0010] S4. Stir the second mixed solution for reaction, and after completion of stirring, separate to obtain the iron-based synthetic humic acid heavy metal composite passivator.

[0011] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, the aqueous solution is a phosphate buffer solution with a pH value of 6-8, such as a phosphate buffer solution with a pH of 8 (0.1 mol / L, Na2HPO4-NaH2PO4);

[0012] The molar ratio of the catechol to the glycine is 1:(1-^4), such as 1:1;

[0013] The concentration of the catechol in the aqueous solution is 0.05-0.5 mol / L, such as 0.25 mol / L;

[0014] The concentration of the manganese dioxide in the first mixed solution is 5-30 g / L, such as 25 g / L.

[0015] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, in step S2, the reaction is carried out under light-shielded conditions;

[0016] In step S2, the temperature of the reaction is 20-45 °C, such as 25 °C;

[0017] In step S2, the stirring time is 96-240 h, such as 240 h.

[0018] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, in step S2, the separation step includes:

[0019] 1) Centrifuge the reaction system and collect the supernatant;

[0020] 2) Filter the supernatant, adjust the pH value of the obtained filtrate to 1, stand still, and collect the precipitate.

[0021] In the above separation step, the centrifugation can specifically be carried out at 4°C, with a rotation speed of 10,000 rpm and a time of 10 min;

[0022] The filtration can specifically use a 0.45 μm filter membrane;

[0023] The standing time can specifically be 24 h;

[0024] Preferably, in the separation step, after collecting the precipitate, the following steps are further included:

[0025] HCl and HF are added to the precipitate, stirred, allowed to stand, and the precipitate is collected;

[0026] The precipitate is successively dialyzed and freeze-dried to obtain the synthetic humic acid.

[0027] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, the iron salt includes at least one of FeCl3 (added in the form of FeCl3·6H2O) and Fe(NO3)3;

[0028] The C / Fe molar ratio in the second mixed solution is (0.5 - 12):1, preferably 6:1;

[0029] Among them, the C / Fe molar ratio is based on the feeding amounts of the synthetic humic acid and the iron salt, and the molar amount of carbon can specifically be calculated according to the mass percentage content of carbon in the synthetic humic acid.

[0030] The aqueous solution containing the synthetic humic acid is composed of the synthetic humic acid and an aqueous solution of an inorganic base (such as a 0.04 mol / L NaOH solution), for example, every 1.306 g of the synthetic humic acid is dissolved in 40 mL of the 0.04 mol / L NaOH solution;

[0031] The pH value of the second mixed solution is 7.5 - 7.8.

[0032] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, in step S4, the stirring time is 2 h.

[0033] In the above preparation method of the iron-based synthetic humic acid heavy metal composite passivator, in step S4, the separation step includes: allowing the stirred system to stand and collecting the precipitate; preferably, the standing time is 20 minutes;

[0034] After the separation in step S4, it further includes: washing the separated product and freeze-drying.

[0035] Second aspect, the present invention provides an iron-based synthetic humic acid heavy metal composite passivator prepared by the preparation method described in any one of the above.

[0036] Among them, the iron-based synthetic humic acid heavy metal composite passivator may specifically be a passivator for heavy metal passivation including Pb 2+ and Cd 2+ heavy metals.

[0037] Third aspect, the present invention provides a method for passivating heavy metal ions in soil, comprising the following steps:

[0038] Applying the iron-based synthetic humic acid heavy metal composite passivator to the soil to be passivated can achieve the passivation of heavy metal ions.

[0039] In the above method for passivating heavy metal ions in soil, the heavy metal ions include at least one of Pb 2+ , Cd 2+ and Zn 2+ ; and / or,

[0040] the pH value of the soil to be passivated is 5.4 to 8.5, such as 5.48; and / or,

[0041] the available lead content in the soil to be passivated is 22.9 to 175.4 mg / kg, and the available cadmium content is 0.5 to 85.9 mg / kg; and / or,

[0042] Based on the mass percentage, the application amount of the iron-based synthetic humic acid heavy metal composite passivator is 1% to 5% of the soil, preferably 5%.

[0043] The present invention has the following beneficial effects:

[0044] In the technical solution provided by the present invention, iron-based can form an iron-based synthetic humic acid composite material with synthetic humic acid through mechanisms such as coprecipitation. The introduction of synthetic humic acid can, on the one hand, improve the stability of iron-based, making it not easily deteriorate; on the other hand, it can also introduce more active functional groups, strengthen the heavy metal binding ability, and produce a synergistic remediation effect.

[0045] The iron-based synthetic humic acid composite material has a good heavy metal binding effect, and its performance is superior to that of single iron-based or synthetic humic acid. The iron-based synthetic humic acid composite material combines the advantages of synthetic humic acid and iron-based and overcomes the deficiencies of the two materials when used alone, and has broad application prospects.

[0046] The results of the examples show that the iron-based synthetic humic acid prepared by the present invention has a high adsorption capacity for lead, cadmium and zinc ions, and can reduce the availability of lead, cadmium and zinc ions in the soil. The iron-based synthetic humic acid of the present invention has a better treatment effect on acidic soil and is suitable for the passivation of soil polluted by high-concentration heavy metals. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is the X-ray diffraction pattern (XRD) of the iron-based synthetic humic acid passivation composite material with different carbon-iron ratios in the embodiment of the present invention.

[0048] Figure 2 It is the SEM-EDS image of the iron-based synthetic humic acid passivation material in Example 1 of the present invention.

[0049] Figure 3 It is the adsorption performance of the iron-based synthetic humic acid passivation composite material with different carbon-iron ratios in Example 2 of the present invention for Pb 2+ and Cd 2 .

[0050] Figure 4 It is the adsorption performance of the iron-based synthetic humic acid passivation composite material in Example 3 of the present invention for Pb 2+ and Cd 2 at different initial pH values. DETAILED DESCRIPTION OF THE INVENTION

[0051] In-situ passivation technology has become one of the most commonly used soil heavy metal pollution remediation technologies due to its simple operation and relatively low cost. Synthetic humic acid is a high-molecular organic compound, which is weakly acidic and has various functional groups such as carboxyl, phenolic hydroxyl and quinone groups. It can interact with various heavy metals through mechanisms such as adsorption, ion exchange, complexation and redox. Compared with single synthetic humic acid, iron-based synthetic humic acid has more types of active functional groups and multiple stable mechanisms, which helps to improve its soil heavy metal passivation performance.

[0052] In view of this, the present invention proposes a preparation method of a heavy metal composite passivator of iron-based synthetic humic acid, aiming to provide a more efficient soil heavy metal passivator and solve the problem of poor effect of passivating soil contaminated with composite heavy metal ions containing lead, cadmium and zinc.

[0053] To achieve the above object, the present invention provides a preparation method of a heavy metal composite passivator of iron-based synthetic humic acid, including the following steps: S1. Add catechol and glycine to an aqueous solution, and after dissolution, add manganese dioxide to obtain a first mixed solution; S2. Stir the first mixed solution for reaction, and after the reaction is completed, separate to obtain synthetic humic acid; S3. Mix the aqueous solution of the synthetic humic acid and the aqueous solution of an iron salt to obtain a second mixed solution; S4. Stir the second mixed solution for reaction, and after the reaction is completed, separate to obtain the heavy metal composite passivator of iron-based synthetic humic acid. In the present invention, the introduction of synthetic humic acid can, on the one hand, improve the stability of the iron-based material and make it not easy to deteriorate; on the other hand, it can also introduce more active functional groups, strengthen the heavy metal binding ability, and produce a synergistic remediation effect.

[0054] The present invention will be further described in detail below in conjunction with specific embodiments. The provided embodiments are only for clarifying the present invention, rather than limiting the scope of the present invention. The following provided embodiments can be used as a guide for those of ordinary skill in the art to make further improvements, and do not limit the present invention in any way.

[0055] The methods used in the following embodiments are all conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials, reagents, etc. used in the following embodiments can be obtained from commercial sources unless otherwise specified.

[0056] The test method for the C / Fe molar ratio in the following embodiments is as follows: The molar mass of Fe in 2.365 g of FeCl3·6H2O is 0.00875 mol (2.365 / 270.3 = 0.00875 mol); the carbon content of the synthesized humic acid is 48.2%, then the molar masses of C in 0.109 g, 0.218 g, 0.436 g, 0.654 g, 1.306 g, and 2.612 g of the synthesized humic acid are 0.0004375 mol, 0.00875 mol, 0.0175 mol, 0.035 mol, 0.0525 mol, and 0.105 mol, respectively. Weigh 0.109 g, 0.218 g, 0.436 g, 0.654 g, 1.306 g, and 2.612 g of the synthesized humic acid (carbon content is 48.2%) and dissolve them in 40 mL of 0.04 mol / L NaOH solution in a beaker to obtain a synthesized humic acid solution; weigh 2.365 g of FeCl3·6H2O in a beaker, dissolve it with 360 mL of deionized water, place it on a magnetic stirrer to dissolve, and then slowly add the dissolved artificial synthesized humic acid solution to the FeCl3 solution placed on the magnetic stirrer, and adjust the pH value to 7.5 - 7.8 with 0.1 M NaOH solution to obtain iron salt and synthesized humic acid mixtures with C / Fe molar ratios of 0.5, 1, 2, 3, 6, and 12, respectively.

[0057] In the following embodiments, the contents of available Pb, Cd, and Zn in the soil are determined by the diethylenetriaminepentaacetic acid (DTPA) extraction method. Referring to the method of "Determination of available lead and cadmium in soil quality" (GBT 23739 - 2009), the extraction is carried out at a soil-to-water ratio of 5:1 (V:m), and the heavy metal content in the extract is determined by inductively coupled plasma optical emission spectrometry (ICP-OES, Prodigy7, Lee man Labs, USA).

[0058] Example 1

[0059] This embodiment provides a preparation method of an iron-based synthetic humic acid heavy metal composite passivator, and the specific steps are as follows:

[0060] S1. Prepare a phosphate buffer solution (0.1 mol / L, Na2HPO4-NaH2PO4) with a pH of 8. Add catechol and glycine to the above buffer solution, control the concentrations of catechol and glycine to be both 0.25 mol / L, and after dissolving until it turns pink, add manganese dioxide, control the mass concentration of manganese dioxide to be 25 g / L, to obtain a first mixed solution;

[0061] S2. Place the first mixed solution in the dark at a temperature of 25 °C and stir for 240 h. After stirring, extract the synthetic humic acid by the standard method of IHSS. For details, refer to the public website (https: / / humic-substances.org / ). The specific steps are as follows: After the cultivation is completed, centrifuge the suspension at a high speed (10000 rpm, 4 °C, 10 min). First filter the supernatant obtained by centrifugation through a 0.45 μm filter membrane, adjust the pH of the filtrate to 1 with concentrated HCl, let it stand for 24 h, and then centrifuge to obtain the synthetic humic acid precipitate 1. Add 2 mL of HCl and HF each, stir, and after standing for 24 h, centrifuge again to obtain the synthetic humic acid precipitate 2. Dialyze and freeze-dry this precipitate to finally obtain a synthetic humic acid sample.

[0062] S3. Take 1.306 g of the synthetic humic acid and dissolve it in 40 mL of 0.04 mol / L NaOH solution to obtain a synthetic humic acid solution; Weigh 2.365 g of FeCl3·6H2O in a beaker, dissolve it with 360 mL of deionized water, place it on a magnetic stirrer to dissolve, and then slowly add the dissolved artificial synthetic humic acid solution to the FeCl3 solution placed on the magnetic stirrer. Add 0.1 M NaOH solution to adjust the pH value to 7.5 - 7.8 to obtain an iron salt and synthetic humic acid mixed solution with a C / Fe molar ratio of 6, that is, a second mixed solution;

[0063] S4. Place the second mixed solution on a magnetic stirrer and continuously stir for 2 h. After standing for 20 min, use the siphon method to suck out the supernatant, then add deionized water and centrifuge and wash the precipitate at a speed of 4000 r / min, repeat 5 times, and freeze-dry to obtain an iron-based synthetic humic acid with a C / Fe molar ratio of 6.

[0064] The XRD pattern of the iron-based synthetic humic acid in Example 1 is shown in Figure 1 , and it can be seen from Figure 1 that two relatively obvious broad peaks appear at 2θ of 35° and 62°, which are consistent with the peaks of ferrihydrite, indicating that the iron-containing material is successfully loaded.

[0065] The SEM-EDS image of the iron composite artificial humic acid passivation material in Example 1 is shown inFigure 2 , it can be seen that C, O, N, and Fe elements exist in the iron-based synthetic humic acid and are relatively evenly distributed on the surface of the sample, indicating that the iron-based synthetic humic acid has been successfully prepared. The specific surface area and total pore volume of the iron-based synthetic humic acid in Example 1 are 34.15 m2 / g and 0.0507 cm 3 / g, respectively. The surface of the iron composite artificial humic acid passivation material of the present invention is rough and irregular, which helps to increase the specific surface area of the composite material.

[0066] Comparative Example 1

[0067] This comparative example provides a preparation method of a synthetic humic acid heavy metal passivator, which is only different from that in Example 1 in that the preparation steps of the synthetic humic acid are retained. The specific steps are as follows:

[0068] S1. Prepare a phosphate buffer solution (0.1 mol / L, Na2HPO4-NaH2PO4) with a pH of 8. Add catechol and glycine to the above buffer solution, control the concentrations of catechol and glycine to be both 0.25 mol / L, and after dissolution to a pink color, add manganese dioxide, control the mass concentration of manganese dioxide to be 25 g / L, to obtain a first mixed solution;

[0069] S2. Place the first mixed solution in the dark at a temperature of 25 °C and stir for 240 h. After stirring, extract the synthetic humic acid by the standard method of IHSS. For details, refer to the public website (https: / / humic-substances.org / ). The specific steps are as follows: After the culture is completed, centrifuge the suspension at a high speed (10000 rpm, 4 °C, 10 min). First, filter the supernatant obtained by centrifugation through a 0.45 μm filter membrane, adjust the pH of the filtrate to 1 with concentrated HCl, let it stand for 24 h, and then centrifuge to obtain a synthetic humic acid precipitate 1. Add 2 mL of HCl and HF each, stir and let it stand for 24 h, and then centrifuge again to obtain a synthetic humic acid precipitate 2. The precipitate is dialyzed and freeze-dried to finally obtain a synthetic humic acid sample.

[0070] Comparative Example 2

[0071] This comparative example provides a preparation method of an iron salt heavy metal passivator, which is only different from that in Example 1 in that the preparation steps of the iron salt are retained. The specific steps are as follows:

[0072] Dissolve 2.365 g of FeCl3·6H2O in 350 mL of deionized water, slowly add 1 mol / L NaOH solution to adjust the pH to 7.5-7.8, continuously stir for 2 h under dark conditions, then centrifuge at a speed of 4000 rpm for 20 min to separate the sample, wash it 5 times with deionized water, and store it at 4 °C after freeze-drying for later use.

[0073] Example 2

[0074] This example provides the effect of iron-based synthetic humic acids with different C / Fe molar ratios on the adsorption performance of heavy metal ions. The specific steps are as follows:

[0075] The preparation method is the same as that in Example 1, only the masses of synthetic humic acid and FeCl3·6H2O are adjusted to obtain mixed solutions of iron salts and synthetic humic acids with C / Fe molar ratios of 6, 3, 2, 1, and 0.5, and finally iron-based synthetic humic acids with C / Fe molar ratios of 6, 3, 2, 1, and 0.5 are obtained. The XRD patterns of the iron-based synthetic humic acids with different C / Fe molar ratios are shown in Figure 1 , indicating that the iron-containing materials are successfully loaded.

[0076] Test the adsorption rates of iron-based synthetic humic acids with different C / Fe molar ratios for Pb 2+ and Cd 2+ . The specific steps are as follows: Add 30.0 mg of iron-based synthetic humic acids with different C / Fe molar ratios to 30.0 mL of a solution of Pb 2+ or Cd 2+ with a concentration of 50 mg / L. Oscillate at 250 rpm for 24 h using an orbital shaker at 25 °C, filter through a 0.45 μm PES syringe filter, and dilute with 5% HNO3 solution. Determine the concentration of Pb 2+ or Cd 2+ in the solution using inductively coupled plasma optical emission spectrometry (ICP-OES; Prodigy 7 type, Leeman Labs, USA). The adsorption rates (Equation 1) and adsorption capacities Q 2+ of Pb 2+ or Cd e are calculated using the following formulas:

[0077]

[0078]

[0079] where: Q e is the adsorption capacity of the iron-based synthetic humic acid for Pb 2+ or Cd 2+ , mg·g -1 ; C0 and C e are the mass concentrations of Pb 2+ or Cd 2+ at the initial and adsorption equilibrium, respectively, mg·g -1 ; V0 is the volume of the added Pb 2+ solution or Cd 2+ solution, L; m is the dosage of the passivator, g.

[0080] The results are shown in Figure 3It can be seen from Figure 3 that when the C / Fe molar ratio is ≥1, there is no obvious change in the adsorption performance for Pb 2+ . When the C / Fe molar ratio = 6, the adsorption performance for Cd 2+ is the strongest. Therefore, the C / Fe molar ratio = 6 is determined as the optimal carbon-iron molar ratio of the composite material of the present invention.

[0081] Example 3

[0082] This example provides the influence of iron-based synthetic humic acid on the adsorption performance of heavy metal ions at different initial pH values. The specific steps are as follows: Only adjust the initial pH values in the adsorption experiment in Example 2 to 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, and 8.0 respectively.

[0083] Test the adsorption rates of iron-based synthetic humic acid for Pb 2+ and Cd 2+ at different initial pH values. The results are shown in Figure 4 It can be seen from Figure 4 that the iron-based synthetic humic acid of the present invention has good adsorption ability for heavy metals in the pH range of 5-8, showing a wide pH adaptability.

[0084] Example 4

[0085] Mix the passivators prepared in the above Example 1 and Comparative Examples 1-2 with the tested soil (0-20 cm surface farmland soil collected from Shizuishan City, Ningxia) at mass ratios of 1%, 2%, and 5% respectively, and place them in a plastic beaker. Incubate at 25°C in a constant temperature incubator, keep the gas flowing, and after 90 days of incubation, take samples to measure the contents of soil available lead, soil available cadmium, and soil available zinc. The calculation formulas for the adsorption capacity and removal rate of heavy metal ions are the same as those in Example 2. The experimental results are shown in Table 1.

[0086] Table 1. Contents of soil available lead, soil available cadmium, and soil available zinc in the soil

[0087]

[0088] It can be seen from Table 1 that after treating the heavy metal-contaminated soil with the iron-based synthetic humic acid heavy metal composite passivator prepared in Example 1, the contents of soil available lead, available cadmium, and available zinc in the soil all decreased significantly. Compared with the single addition of pure goethite and pure synthetic humic acid, the passivation effect was significantly improved, indicating that after the combination of iron-based and synthetic humic acid, a synergistic repair effect will occur.

[0089] Example 5

[0090] Example 1 was mixed with the tested acidic soil (0-20 cm surface farmland soil in Nanning, Guangxi, pH = 5.48) at a mass ratio of 5% and placed in a plastic beaker. It was cultured at 25 °C in a constant temperature incubator while maintaining gas circulation. After 30 days of cultivation, samples were taken to measure the available lead and available cadmium in the soil. The results are shown in Table 2.

[0091] Table 2. Contents of available lead and available cadmium in the soil

[0092] experimental group available lead content in soil available cadmium content in soil untreated acidic soil for test 175.44 mg / kg 7.93 mg / kg 5% treatment (Example 1) 22.63 mg / kg 3.74 mg / kg

[0093] As can be seen from Table 2, after the acidic soil contaminated with heavy metals was treated with the iron composite artificial humic acid passivation material prepared in Example 1, the contents of available lead and cadmium in the soil decreased significantly. As can be seen from Tables 1 and 2, in acidic soil, the passivation rates of iron-based synthetic humic acid for cadmium and lead are 87.1% and 52.8% respectively, which are higher than its passivation rates in alkaline soil (80.8% and 47.1%), indicating that its treatment effect on acidic soil is better.

[0094] Example 6

[0095] Example 1 was mixed with the tested heavy metal contaminated soil (0-20 cm surface farmland soil in Hengxian, Guangxi) at a mass ratio of 5% and placed in a plastic beaker. It was cultured at 25 °C in a constant temperature incubator while maintaining gas circulation. After 30 days of cultivation, samples were taken to measure the available lead and available cadmium in the soil. The results are shown in Table 3.

[0096] Table 3. Contents of available lead and available cadmium in the soil

[0097]

[0098] As can be seen from Table 3, after the heavily polluted soil contaminated with heavy metals was treated with the iron composite artificial humic acid passivation material prepared in Example 1, the contents of available lead and cadmium in the soil decreased significantly. The iron composite artificial humic acid passivation material prepared in Example 1 is suitable for the remediation of heavily polluted soil in scenarios where the cadmium concentration does not exceed 100 mg / kg.

[0099] As can be seen from Tables 1, 2, and 3, after the soil contaminated with heavy metals was treated with the iron-based synthetic humic acid composite heavy metal passivator prepared in the examples of the present invention, the contents of available lead, available cadmium, and available zinc in the soil decreased significantly.

[0100] In summary, the iron-based synthetic humic acid composite heavy metal passivator provided by the present invention has controllable structural properties, good stability, a large specific surface area and total pore volume, and a large number of active functional groups on the surface, which can provide more reaction sites for binding heavy metals. Iron-based synthetic humic acid for Pb 2+ 、Cd 2+and Zn 2+ Both have good binding properties. Using iron-based synthetic humic acid can significantly improve the binding strength and passivation efficiency of heavy metals in soil, and reduce the mobility and ecological risk of heavy metals in soil.

[0101] The present invention has been described in detail above. For those skilled in the art, without departing from the purpose and scope of the present invention, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to cover any modification, use or improvement of the present invention, including changes made by using conventional techniques known in the art that are outside the scope disclosed in this application.

Claims

1. A preparation method of an iron-based synthetic humic acid heavy metal composite passivator, comprising the following steps: S1. Add catechol and glycine to an aqueous solution. After dissolution, add manganese dioxide to obtain a first mixed solution; S2. Stir the first mixed solution for reaction. After stirring, separate to obtain synthetic humic acid; S3. Mix the aqueous solution containing the synthetic humic acid with an aqueous solution of an iron salt, and adjust the pH value to obtain a second mixed solution; S4. Stir the second mixed solution for reaction. After stirring, separate to obtain the iron-based synthetic humic acid heavy metal composite passivator.

2. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to claim 1, characterized in that: The aqueous solution is a phosphate buffer solution with a pH value of 6-8; The molar ratio of catechol to glycine is 1:(1-4); The concentration of catechol in the aqueous solution is 0.05-0.5 mol / L; The concentration of manganese dioxide in the first mixed solution is 5-30 g / L.

3. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to any one of claims 1-2, characterized in that: In step S2, the reaction is carried out under light-shielded conditions; In step S2, the reaction temperature is 20-45 °C; In step S2, the stirring time is 96-240 h.

4. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to any one of claims 1-3, characterized in that: In step S2, the separation step includes: 1) Centrifuge the reacted system and collect the supernatant; 2) Filter the supernatant, adjust the pH value of the obtained filtrate to 1, let it stand, and collect the precipitate.

5. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to any one of claims 1-4, characterized in that: The iron salt includes at least one of FeCl3 and Fe(NO3)3; The C / Fe molar ratio in the second mixed solution is (0.5-12):1; The aqueous solution containing the synthetic humic acid is composed of the synthetic humic acid and an aqueous solution of an inorganic base; The pH value of the second mixed solution is 7.5-7.

8.

6. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to any one of claims 1-5, characterized in that: In step S4, the stirring time is 2 h.

7. The preparation method of the iron-based synthetic humic acid heavy metal composite passivator according to any one of claims 1-6, characterized in that: In step S4, the separation step includes: Let the stirred system stand and collect the precipitate; preferably, the standing time is 20 minutes; After the separation in step S4, it further includes: washing the separated product with water and freeze-drying.

8. An iron-based synthetic humic acid heavy metal composite passivator prepared by the preparation method according to any one of claims 1-7.

9. A method for passivating heavy metal ions in soil, comprising the following steps: Applying the iron-based synthetic humic acid heavy metal composite passivator according to claim 8 to the soil to be passivated can achieve the passivation of heavy metal ions.

10. The passivation method for heavy metal ions in soil according to claim 9, wherein: The heavy metal ions include Pb 2+ , Cd 2+ and Zn 2+ and / or at least one of them; The pH value of the soil to be passivated is 5.4-8.5; and / or, The content of available lead in the soil to be passivated is 22.9-175.4 mg / kg, and the content of available cadmium is 0.5-85.9 mg / kg; and / or, Calculated by mass percentage, the application amount of the iron-based synthetic humic acid heavy metal composite passivator is 1%-5% of the soil.

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