Preparation method of modified clay mineral for soil heavy metal cadmium and lead pollution treatment

Abstract

The invention relates to the technical field of soil heavy metal pollution treatment, in particular to a preparation method of a modified clay mineral for soil heavy metal cadmium and lead pollution treatment, and the preparation method comprises the following steps: S100, removing crystal water in a duty void channel in the clay mineral; s200, the clay minerals are soaked in diluted hydrochloric acid, washed to be neutral and then dried; s300, drying under the protection of inert gas; s400, adding the clay minerals into sodium hydroxide, stirring, washing to be neutral, and drying; s500, adding a sodium silicate solution into the clay minerals to form primary clay minerals; s600, the primary clay minerals are added into a kiln, and ammonia gas is introduced for drying; and S700, the dried clay minerals are crushed and sieved. The adsorption, immobilization and complexation capabilities of heavy metal ions are improved through the prepared clay mineral.

Description

Technical Field

[0001] The invention relates to the technical field of soil heavy metal pollution control, and in particular to a method for preparing a modified clay mineral for soil heavy metal cadmium and lead pollution control. Background Art

[0002] Heavy metal pollution in soil is a global environmental problem that poses a serious threat to ecosystem health, agricultural production, and human health.

[0003] According to the research on the analysis and evaluation of heavy metal pollution in farmland soil in China, the average values ​​of the contents of eight heavy metal elements (arsenic As, cadmium Cd, chromium Cr, copper Cu, mercury Hg, nickel Ni, lead Pb and zinc Zn) in farmland soil in China show that, compared with the soil background value, except for arsenic, other heavy metal elements have a certain accumulation, especially cadmium and mercury, which have the largest accumulation, exceeding the soil background value by 177.9% and 340.3% respectively. The sources of heavy metals in soil may include industrial emissions, agricultural activities (such as the use of fertilizers and pesticides), traffic emissions, mining activities, etc., and natural sources are also a factor that cannot be ignored. Heavy metal pollution in soil will affect the growth of crops, resulting in excessive heavy metal content in crops, which in turn poses a threat to human health through the food chain. In addition, heavy metal pollution in soil will also affect the balance of the soil ecosystem.

[0004] The treatment of heavy metal pollution in soil includes physical, chemical and biological remediation methods. For example, the publication number CN114292652A discloses a heavy metal stabilization material in contaminated soil and its preparation method and application. After the soil is treated, it is coated with a stabilization material to reduce the transformation of heavy metal forms, thereby stabilizing the heavy metal ions. However, the above treatment methods are cumbersome to operate and require more raw materials, which is not conducive to large-scale promotion.

[0005] Therefore, those skilled in the art are committed to developing a method for preparing modified clay minerals for the treatment of soil heavy metal cadmium and lead pollution, by improving the adsorption, fixation and complexing capabilities of heavy metal ions through the prepared clay minerals. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing a modified clay mineral for treating soil heavy metal cadmium and lead pollution, and to improve the adsorption, fixation and complexing capabilities of heavy metal ions through the prepared clay mineral.

[0007] The technical solution of the present invention to solve the above technical problems is as follows:

[0008] A method for preparing a modified clay mineral for treating soil heavy metal cadmium and lead pollution comprises the following steps:

[0009] S100. Add clay minerals into a kiln, dry them under the protection of inert gas, and then gradually increase the temperature to dry the clay minerals, so that the crystal water occupying the void channels inside the clay minerals is stripped to form dry clay;

[0010] S200. Add the dry clay prepared in step S100 into a dilute hydrochloric acid solution, soak and stir it, then rinse it with pure water until neutral, and then add it into the kiln for secondary drying;

[0011] S300. When the washed clay minerals are dried for the second time in the kiln, dry them under the protection of inert gas, and then gradually increase the temperature to dry the clay minerals to obtain dried clay;

[0012] S400. Add the dried clay in step S300 into a sodium hydroxide solution and stir it, then rinse it with pure water until neutral, and then dry it for the third time;

[0013] S500. Add sodium silicate solution to the dried clay minerals in step S400, after the reaction ends, dehydrate, filter, and crush to form primary clay minerals;

[0014] S600. Add the primary clay minerals in step S500 into the kiln, introduce ammonia gas and heat to dry;

[0015] S700. Place the dried primary clay minerals in step S600 in a cool and ventilated place to remove the residual ammonia gas, then crush and screen them to finally form modified clay minerals.

[0016] The beneficial effects of adopting the above solution are as follows: By dredging, expanding, ion-exchanging and fixing the internal pores of the clay mineral materials, and then cooperating with silicon element catalysis and ammonium ion attachment to increase the complexing ability for heavy metal ions, the adsorption, fixation and complexing abilities of the minerals for heavy metal ions are greatly improved, so as to reduce the activity of heavy metal ions, and the modified clay minerals have a good passivation effect on heavy metal elements such as cadmium and lead.

[0017] On the basis of the above technical solution, the present invention can also be improved as follows.

[0018] Further, in step S100, the clay mineral is one or more of bentonite, attapulgite, sepiolite, zeolite, and kaolin;

[0019] When the clay minerals are dried under the protection of inert gas, the drying temperature is 100°C - 150°C, and the drying time is 1.5h - 2.5h;

[0020] When gradually increasing the temperature, first increase the temperature to 250°C, keep warm for 30min - 60min, and then increase the temperature to 450°C and keep it constant for 4h - 6h.

[0021] The beneficial effects of adopting the above further solution are as follows: First, the free water on the surface and in the pores of the clay minerals is dried at a low temperature. Subsequently, the temperature is slowly raised to a high temperature (the crystal water in the clay minerals can be stripped out at a temperature above 300 °C), and the crystal water inside the clay minerals is stripped. The purpose is to dredge the pores and cavities inside the clay minerals. The entire process requires protection by an inert gas, and its functions are as follows: The evaporated water vapor can be quickly carried away, and through gas flow, the heat distribution becomes more uniform.

[0022] Further, in step S200, the concentration of the dilute hydrochloric acid is 0.07 mol / L - 0.16 mol / L, the soaking time is 3 h to 5 h, and the stirring speed is 40 r / min - 60 r / min.

[0023] The beneficial effects of adopting the above further solution are as follows: The impurities in the internal pores of the clay minerals are removed by the dilute hydrochloric acid aqueous solution, improving the pore conductivity; Hydrochloric acid can react with free metal ions such as aluminum, sodium, and calcium in the clay minerals, expanding the original internal channels and cavities, and further removing water-insoluble impurities.

[0024] Further, in step S300, when the clay minerals are dried for the second time, in the temperature range of 0 °C - 300 °C during the heating stage, the temperature is raised at a rate of 5 °C - 10 °C per minute;

[0025] In the temperature range of 300 °C - 450 °C, the temperature is raised at a rate of 3 °C - 5 °C per minute;

[0026] In the temperature range of 450 °C - 600 °C, the temperature increase rate per minute is controlled at 1 °C - 3 °C,

[0027] After the temperature is raised to 600 °C, it enters the heat preservation stage, and the heat preservation time is 1.5 h - 2.5 h.

[0028] The beneficial effects of adopting the above further solution are as follows: The purpose of the heat treatment is to further expand the pores and cavities inside the clay minerals using the principle of high-temperature expansion.

[0029] Further, in step S400, the concentration of the sodium hydroxide solution is 0.35 mol / L - 0.8 mol / L, the volume ratio of the clay minerals to the sodium hydroxide solution is 1:0.6 - 1:1.1, the set range of the soaking temperature is a constant temperature of 35 °C - 42 °C, the soaking treatment time is 40 min - 70 min, and the stirring speed is controlled at 40 r / min - 60 r / min;

[0030] The temperature range for the third drying is 180 °C - 220 °C.

[0031] The beneficial effects of adopting the above further scheme are as follows: using an alkaline solution to remove a part of the silicon element in the clay mineral to improve its polarity, and at the same time, under the action of ion exchange, replacing Ca2+, Mg2+ in the zeolite structure with Na+ to further open the internal pores, and enhancing the specific surface area and cation exchange capacity of the clay mineral.

[0032] Further, in step S500, the concentration range of the sodium silicate solution is 10 g / L - 20 g / L, and the weight ratio range of sodium silicate to the clay mineral is 1.5:1 - 2:1.

[0033] The beneficial effects of adopting the above further scheme are as follows: silicon element has the property of being negatively charged and can adsorb positively charged heavy metal ions, which will further enhance the passivation effect on heavy metals.

[0034] Further, in step S600, the heating temperature is 80°C - 120°C, the heating time is 3 h - 5 h, and the ammonia gas flow rate range is 0.12 L / min - 4 L / min.

[0035] The beneficial effects of adopting the above further scheme are as follows: under the water-containing condition of the clay mineral, ammonia gas is introduced to form ammonia water, which will be adsorbed and fixed on the clay mineral, and the NH4+ ions are left in the clay mineral. The purpose is that ammonium ions will displace heavy metal ions such as Pb, and the latter is more easily adsorbed and fixed by the clay mineral.

[0036] Further, in step S100, the clay mineral is crushed before being added to the kiln and filtered through a 20-mesh sieve;

[0037] In step S700, the modified clay mineral is crushed and filtered through a 20-mesh sieve.

[0038] The beneficial effects of adopting the above further scheme are as follows: sieving is used to remove large particle clays, making the reaction of small particle clays more sufficient.

[0039] Further, after step S700, it further includes:

[0040] S800. Place the modified clay mineral prepared in step S700 in an ultrasonic container and perform ultrasonic treatment on the modified clay mineral.

[0041] The beneficial effects of adopting the above further scheme are as follows: ultrasonic waves further disperse the sepiolite particles and enhance their surface activity and adsorption performance.

[0042] Further, after step S700, it further includes:

[0043] S900. Disperse the modified clay minerals prepared in step S700 into absolute ethanol, add the nanomaterial precursor, and magnetically stir to prepare a suspension with a stirring rate of 40 r / min - 60 r / min and a stirring time of 10 min - 30 min;

[0044] Hydrothermally prepare the suspension into a modified clay mineral precursor at a hydrothermal temperature of 160°C - 200°C and a hydrothermal time of 3 h - 8 h;

[0045] Finally, add the modified clay mineral precursor to a kiln and calcine it under the protection of an inert gas at a calcination temperature of 350°C - 500°C and a calcination time of 1 h - 3 h to prepare the modified clay minerals loaded with nanomaterials.

[0046] The beneficial effect of adopting the above further scheme is: modifying the nanomaterials on the surface of the clay minerals to improve the catalytic performance and simultaneously enhancing the rate and effect of the photocatalytic reaction. Brief Description of the Drawings

[0047] Figure 1 It is the flow chart of the preparation method steps of the modified clay minerals for treating soil heavy metal cadmium and lead pollution in the present invention;

[0048] Figure 2 It is the graph of the effective cadmium concentration and passivation rate at an addition amount of 0.3% in Example 1 of the present invention;

[0049] Figure 3 It is the graph of the effective lead concentration and passivation rate at an addition amount of 0.3% in Example 1 of the present invention;

[0050] Figure 4 It is the graph of the effective cadmium concentration and passivation rate of the test plot in Example 2 of the present invention;

[0051] Figure 5 It is the graph of the effective lead concentration and passivation rate of the test plot in Example 2 of the present invention;

[0052] Figure 6 It is the graph of the effective cadmium concentration and passivation rate of the test plot in Example 3 of the present invention;

[0053] Figure 7 It is the graph of the effective lead concentration and passivation rate of the test plot in Example 3 of the present invention. Detailed Embodiments

[0054] The principles and features of the present invention are described below with reference to the drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0055] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "center", "length", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "inner", "outer", "peripheral side", "circumferential direction", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the system or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0056] In the description of the present invention, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0057] In the present invention, unless otherwise clearly specified and defined, the terms "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0058] As Figure 1 shown, a preparation method of a modified clay mineral for treating soil heavy metal cadmium and lead pollution includes the following steps:

[0059] S100. Add the clay mineral into a kiln furnace, dry it under the protection of an inert gas, and then gradually increase the temperature step by step to dry the clay mineral, so that the crystal water in the internal void channels of the clay mineral is stripped to form dry clay;

[0060] Specifically, the clay mineral is one or more of bentonite, attapulgite, sepiolite, zeolite, kaolin. The clay mineral is crushed before being added to the kiln furnace and filtered through a 20-mesh sieve. The kiln furnace can be one or more of an atmosphere sintering furnace, a box furnace, a tunnel kiln, and a rotary kiln, and its maximum temperature is not lower than 750 degrees Celsius.

[0061] When the clay mineral is dried under the protection of an inert gas, the drying temperature is 100°C - 150°C, the drying time is 1.5h - 2.5h, and the inert gas is one of argon, helium, and neon.

[0062] When increasing the temperature step by step, first increase the temperature to 250°C, keep it warm for 30min - 60min, and then increase the temperature to 450°C and keep it constant for 4h - 6h.

[0063] S200. Add the dried clay prepared in step S100 to a dilute hydrochloric acid solution, soak and stir it, then rinse it with pure water until it is neutral, and then add it to a kiln for secondary drying;

[0064] Specifically, the concentration of the dilute hydrochloric acid is 0.07 mol / L - 0.16 mol / L, the soaking time is 3 h to 5 h, and the stirring speed is 40 r / min - 60 r / min.

[0065] S300. When the washed clay minerals are secondarily dried in a kiln, dry them under the protection of an inert gas, and then stepwise increase the temperature to dry the clay minerals to obtain dried clay;

[0066] Specifically, when the clay minerals are secondarily dried, in the temperature range of 0 °C - 300 °C during the heating stage, the temperature is increased at a rate of 5 °C - 10 °C per minute;

[0067] In the temperature range of 300 °C - 450 °C, the temperature is increased at a rate of 3 °C - 5 °C per minute;

[0068] In the temperature range of 450 °C - 600 °C, the temperature increase rate per minute is controlled at 1 °C - 3 °C,

[0069] After the temperature is increased to 600 °C, enter the heat preservation stage, and the heat preservation time is 1.5 h - 2.5 h.

[0070] S400. Add the dried clay in step S300 to a sodium hydroxide solution and stir it, then rinse it with pure water until it is neutral, and then perform the third drying;

[0071] Specifically, the concentration of the sodium hydroxide solution is 0.35 mol / L - 0.8 mol / L, the volume ratio of the clay minerals to the sodium hydroxide solution is 1:0.6 - 1:1.1, the set range of the soaking temperature is a constant temperature of 35 °C - 42 °C, the soaking treatment time is 40 min - 70 min, and the stirring speed is controlled at 40 r / min - 60 r / min;

[0072] The temperature range of the third drying is 180 °C - 220 °C.

[0073] S500. Add a sodium silicate solution to the dried clay minerals in step S400, and after the reaction ends, dehydrate, filter, and crush them to form primary clay minerals;

[0074] Specifically, the concentration range of the sodium silicate solution is 10 g / L - 20 g / L, and the weight ratio of sodium silicate to clay minerals is 1.5:1 - 2:1.

[0075] S600. Add the primary clay minerals in step S500 to a kiln, introduce ammonia gas and heat to dry;

[0076] Specifically, in step S600, the heating temperature is 80°C - 120°C, the heating time is 3h - 5h, and the ammonia gas flow rate ranges from 0.12 L / min to 4 L / min.

[0077] S700. Place the primary clay minerals dried in step S600 in a cool and ventilated place to remove residual ammonia, and then crush and screen them to finally form modified clay minerals. After crushing, the modified clay minerals are filtered through a 20-mesh sieve.

[0078] After step S700, it further includes:

[0079] S800. Place the modified clay minerals prepared in step S700 in an ultrasonic container and perform ultrasonic treatment on the modified clay minerals.

[0080] After step S700, it further includes:

[0081] S900. Disperse the modified clay minerals prepared in step S700 into anhydrous ethanol, add a nanomaterial precursor, and magnetically stir to prepare a suspension. The stirring rate is 40 r / min - 60 r / min, and the stirring time is 10 min - 30 min;

[0082] Hydrothermally prepare the suspension into a modified clay mineral precursor. The hydrothermal temperature is 160°C - 200°C, and the hydrothermal time is 3h - 8h;

[0083] Finally, add the modified clay mineral precursor to a kiln and calcine it under the protection of an inert gas. The calcination temperature is 350°C - 500°C, and the calcination time is 1h - 3h to prepare modified clay minerals loaded with nanomaterials.

[0084] Example 1

[0085] As shown in the figure, Figure 2 and Figure 3 shown:

[0086] 1. Clay mineral modification method

[0087] (1) Take sepiolite and zeolite, pass them through a 20-mesh sieve, and then put them into a blender according to the ratio of sepiolite:zeolite = 3:2 and stir evenly.

[0088] (2) Put the mixed clay minerals into an atmosphere sintering furnace and dry them at 150°C for 2h. Then, heat them up to 250°C at a heating rate of 8°C / min, hold for 30min, and then heat them up to 450°C at a heating rate of 1.5°C / min and perform a constant temperature treatment for 4h. The whole process needs to be protected by introducing an inert gas.

[0089] (3) The clay minerals processed in step (2) are stirred and soaked with 0.08 mol / L dilute hydrochloric acid at a stirring speed of 60 r / min for 3 h. After the soaking is completed, it is washed with pure water until the waste water is nearly neutral.

[0090] (4) The clay minerals are put into an atmosphere sintering furnace for heat treatment. The temperature is raised at a rate of 10 °C per minute in the temperature range of 0 - 300 °C, 5 °C per minute in the temperature range of 300 - 450 °C, and 3 °C per minute in the temperature range of 450 - 600 °C. After heating to 600 °C, it is held for 2 h. An inert gas needs to be introduced for protection during the heat treatment process.

[0091] (5) The clay minerals and 0.5 mol / L sodium hydroxide solution are added to a magnetic heating stirrer according to a volume ratio of 1:0.8. The set temperature is 40 °C, and the treatment stirring speed is 40 / min. After soaking and treating for 40 min, it is washed with pure water until the waste water is nearly neutral, and then dried at a low temperature of 200 °C.

[0092] (6) The clay minerals and a sodium silicate solution with a concentration of 10 g / L are mixed according to a weight ratio in the range of 1:2, and then placed in an oven at 150 °C for reaction for 3 h, followed by filtration, drying, and crushing.

[0093] (7) The clay minerals are placed in an atmosphere sintering furnace with a set temperature of 120 °C, and ammonia gas is introduced at a flow rate of 150 mL / min for 3 h.

[0094] (8) After the modified clay minerals are placed in a ventilated place, they are crushed, passed through a 20-mesh sieve, and then packed in a sealed bag for use.

[0095] 2. Performance indicators of modified clay minerals

[0096] The performance indicators and detection methods of clay minerals before and after modification are shown in Table 1 below

[0097]

[0098] Table 1

[0099] 3. Basic information of the test soil

[0100] The test soil is sampled on-site. The source is paddy field soil downstream of a mine in a certain place in Zhejiang. The heavy metal elements of pollution are cadmium and lead. The soil pH value is 6.34. The average concentrations of heavy metal elements in the soil are shown in the following table. The total amount of each element is in accordance with HJ803 - 2016 and HJ608 - 2013. The detection standard for the available state of cadmium and lead elements is HJ804 - 2016.

[0101]

[0102] Table 2

[0103] 4. Test method

[0104] (1) Put the test soil into the oven and dry it at 40 °C, then crush it, pick out the sundries and reserve it for use.

[0105] (2) Weigh 200 g of the treated soil, and weigh 2 portions in total. Add 0.6 g of modified clay mineral respectively. That is, the addition ratio is 0.3%.

[0106] (3) Add 40 ml of pure water to each, stir evenly, stand for curing, and ensure that the soil is moist during the curing period.

[0107] (4) Sampling is carried out at the initial stage, the 3rd day, the 5th day, the 7th day, and the 15th day respectively. Test the concentrations of available cadmium and available lead in the samples. The detection standard is HJ804-2016.

[0108] 5. Experimental data

[0109]

[0110] Table 3

[0111] From Figure 2 、 Figure 3 and Table 3, it can be seen that after 15 days of treatment, the available concentrations of cadmium and lead in the test soil are significantly reduced, and the passivation rate is above 40%.

[0112] Example 2

[0113] 1. Clay mineral modification method

[0114] (1) Take sepiolite, zeolite, and bentonite, sieve them through a 20-mesh sieve, and then put them into a screw mixer according to the ratio of sepiolite: zeolite: bentonite = 4:4:2 for stirring and mixing evenly.

[0115] (2) Put the mixed clay mineral into a tunnel kiln and dry it at 150 °C for 2 h, then heat it up to 250 °C at a heating rate of 5 °C / min, keep it warm for 60 min, and then heat it up to 450 °C at a heating rate of 1 °C / min and carry out constant temperature treatment for 6 h. An inert gas needs to be introduced for protection during the whole process.

[0116] (3) Put the clay mineral treated in step (2) and 0.13 mol / L dilute hydrochloric acid into a planetary mixer for stirring and soaking, the stirring speed is 60 r / min, and the stirring and soaking time is 2 h. After soaking, wash it with pure water until the waste water is close to neutral.

[0117] (4) Put the clay minerals into a tunnel kiln for heat treatment. Heat up at a rate of 5°C per minute in the temperature range of 0 - 300°C, 3°C per minute in the temperature range of 300 - 450°C, and 1°C per minute in the temperature range of 450 - 600°C. After heating up to 600°C, keep it at this temperature for 2 hours. An inert gas needs to be introduced for protection during the heat treatment process.

[0118] (5) Add the clay minerals and 0.75 mol / L sodium hydroxide solution to a planetary mixer according to a volume ratio of 1:0.7. Set the temperature to 42°C, the processing stirring speed to 60 / min. After soaking for 45 minutes, wash with pure water until the wastewater is nearly neutral, and then dry at a low temperature of 200°C.

[0119] (6) Mix the clay minerals and a sodium silicate solution with a concentration of 15 g / L according to a weight ratio in the range of 1:1.8. After mixing, put them into an oven at 120°C and react for 5 hours, then filter, dry, and crush.

[0120] (7) Place the clay minerals in a rotary kiln with a set temperature of 80°C, and introduce ammonia gas at a flow rate of 3 L / min for 4 hours.

[0121] (8) After the modified clay minerals are placed in a ventilated area, crush them with a ball mill, sieve them through a 20 - mesh sieve, and then pack and store for use.

[0122] 2. Basic situation of the test plot

[0123] The test plot is located in a certain place in Zhejiang. The soil types are irrigated land and vegetable fields, the polluting elements are heavy metals cadmium and lead pollution, and the soil pH value is 6.18. The average concentrations of soil heavy metal elements are shown in the following table. The total amounts of each element are in accordance with HJ803 - 2016 and HJ608 - 2013. The detection standards for the available forms of cadmium and lead elements are HJ804 - 2016.

[0124]

[0125] Table 4

[0126] 3. Treatment process

[0127] (1) Use a rotary tiller to rotary till the top 0 - 30 cm of the test plot to preliminarily crush the soil.

[0128] (2) Uniformly sprinkle the modified clay minerals at a ratio of 400 kg / mu. After sprinkling, use a rotary tiller to rotary till back and forth 3 times to make the minerals and the soil evenly mixed.

[0129] (3) Moisten it with pollution - free surface water and then carry out maintenance, ensuring that the soil is moist during the maintenance period.

[0130] Samples were taken on the 7th, 15th, 30th, 60th, and 90th days respectively. The concentrations of available cadmium and available lead in the test samples were measured. The detection standard was HJ804-2016.

[0131] 4. Test data

[0132]

[0133] Table 5

[0134] As Figure 4 、 Figure 5 and Table 5 show, after 90 days of treatment, the concentrations of available cadmium and available lead in the tested soil decreased significantly, and the passivation rate was over 40%.

[0135] Example 3

[0136] The difference between Example 3 and Example 1 is only that the following steps are further included:

[0137] (9) The crushed and sieved modified clay minerals were placed in an ultrasonic container for ultrasonic treatment. The ultrasonic treatment time was 10 min - 30 min, and in this example, the ultrasonic treatment time was 20 min.

[0138] (10) The ultrasonically treated modified clay minerals were dispersed in absolute ethanol, and a nanomaterial precursor was added, and then magnetically stirred to prepare a suspension. The stirring rate was 40 r / min - 60 r / min, and the stirring time was 10 min - 30 min. In this example, the nanomaterial precursor was titanium tetrabutoxide-supported titanium dioxide, the stirring rate was 50 r / min, and the stirring time was 20 min;

[0139] The suspension was hydrothermally prepared into a modified clay mineral precursor. The hydrothermal temperature was 180 °C, and the hydrothermal time was 5 h;

[0140] Finally, the modified clay mineral precursor was added to a kiln and calcined under the protection of an inert gas. The calcination temperature was 500 °C, and the calcination time was 2 h to prepare modified clay minerals loaded with nanomaterials.

[0141] As Figure 6 and Figure 7 show, after 90 days of treatment, the concentrations of available cadmium and available lead in the tested soil decreased significantly, and the passivation rate was over 45%.

[0142] This may be because ultrasonic treatment can increase the specific surface area and surface activity of clay minerals, making them have stronger adsorption ability. After loading nanomaterials, the surface properties of clay minerals change further, which may increase the adsorption sites for heavy metals, thus improving the adsorption capacity for cadmium and lead;

[0143] Meanwhile, nanomaterials may form stable complexes or chelates with cadmium and lead, and these complexes are more difficult to be absorbed by plants than free ions, thus reducing the effective state concentration of heavy metals;

[0144] Moreover, the addition of clay minerals and nanomaterials may increase the pH value of the soil, which will affect the hydrolysis equilibrium and adsorption-desorption equilibrium of heavy metal ions. At a higher pH value, heavy metals are more likely to form hydroxide or carbonate precipitates, thereby reducing their bioavailability. Due to the stabilization effect of nanomaterials, even after 90 days, this passivation effect is still significant, indicating that the passivation effect of the treated clay minerals on cadmium and lead in the soil has temporal stability.

[0145] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0146] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a modified clay mineral for treating cadmium and lead pollution in soil, characterized in that, It includes the following steps: S100. Add clay minerals into a kiln, dry them under the protection of inert gas, and then gradually increase the temperature to dry the clay minerals, so that the crystal water in the internal void channels of the clay minerals is stripped to form dry clay; S200. Add the dry clay prepared in step S100 into a dilute hydrochloric acid solution, soak and stir it, then rinse it with pure water until neutral, and then add it into the kiln for secondary drying; S300. When the washed clay minerals are dried for the second time in the kiln, dry them under the protection of inert gas, and then gradually increase the temperature to dry the clay minerals to obtain dried clay; S400. Add the dried clay in step S300 into a sodium hydroxide solution and stir it, then rinse it with pure water until neutral, and dry it for the third time; S500. Add a sodium silicate solution to the clay minerals dried in step S400, dehydrate, filter, and crush them after the reaction ends to form primary clay minerals; S600. Add the primary clay minerals in step S500 into the kiln, introduce ammonia gas and heat to dry; S700. Place the primary clay minerals dried in step S600 in a cool and ventilated place to remove the residual ammonia gas, then crush and screen them to finally form modified clay minerals.

2. The preparation method of the modified clay mineral for treating soil heavy metal cadmium and lead pollution according to claim 1, characterized in that: In step S100, the clay minerals are one or more of bentonite, attapulgite, sepiolite, zeolite, and kaolin; When the clay minerals are dried under the protection of inert gas, the drying temperature is 100°C - 150°C, and the drying time is 1.5h - 2.5h; When gradually increasing the temperature, first increase the temperature to 250°C, keep it warm for 30 min - 60 min, and then increase the temperature to 450°C and keep it constant for 4h - 6h.

3. The preparation method of the modified clay mineral for treating cadmium and lead pollution in soil according to claim 1, characterized in that: In step S200, the concentration of the dilute hydrochloric acid is 0.07 mol / L - 0.16mol / L, the soaking time is 3h to 5h, and the stirring speed is 40 r / min - 60r / min.

4. The preparation method of the modified clay mineral for treating cadmium and lead pollution in soil according to claim 1, characterized in that: In step S300, when the clay minerals are dried for the second time, the temperature in the heating stage from 0°C to 300°C is increased at a rate of 5°C - 10°C per minute; The temperature range from 300°C to 450°C is increased at a rate of 3°C - 5°C per minute; The heating rate per minute in the temperature range from 450°C to 600°C is controlled at 1°C - 3°C, After increasing the temperature to 600°C, enter the heat preservation stage, and the heat preservation time is 1.5h - 2.5h.

5. The preparation method of the modified clay mineral for treating cadmium and lead pollution in soil according to claim 1, characterized in that: In step S400, the concentration of the sodium hydroxide solution is 0.35mol / L - 0.8mol / L, the volume ratio of the clay minerals to the sodium hydroxide solution is 1:0.6 - 1:1.1, the set range of the soaking temperature is a constant temperature of 35°C - 42°C, the soaking treatment time is 40min - 70min, and the stirring speed is controlled at 40 r / min - 60r / min; The temperature range for the third drying is 180°C - 220°C.

6. The preparation method of the modified clay mineral for treating soil heavy metal cadmium and lead pollution according to claim 1, wherein: In step S500, the concentration range of the sodium silicate solution is 10g / L - 20g / L, and the weight ratio of sodium silicate to clay minerals is 1.5:1 - 2:

1.

7. The preparation method of the modified clay mineral for treating soil heavy metal cadmium and lead pollution according to claim 1, wherein: In step S600, the heating temperature is 80°C - 120°C, the heating time is 3h - 5h, and the ammonia gas flow rate range is 0.12L / min - 4L / min.

8. The preparation method of the modified clay mineral for treating cadmium and lead pollution in soil according to claim 1, characterized in that: In step S100, the clay minerals are crushed before being added to the kiln and filtered through a 20-mesh sieve. In step S700, the modified clay minerals are crushed and filtered through a 20-mesh sieve.

9. The preparation method of the modified clay mineral for treating soil heavy metal cadmium and lead pollution according to claim 1, characterized in that, After step S700, it further includes: S800. Place the modified clay minerals prepared in step S700 in an ultrasonic container and perform ultrasonic treatment on the modified clay minerals.

10. The preparation method of the modified clay mineral for treating soil heavy metal cadmium and lead pollution according to claim 9, wherein, After step S700, it further includes: S900. Disperse the modified clay minerals prepared in step S700 in absolute ethanol, add the nanomaterial precursor, and magnetically stir to prepare a suspension. The stirring rate is 40 r / min - 60 r / min, and the stirring time is 10 min - 30 min; Hydrothermally prepare the suspension into a modified clay mineral precursor. The hydrothermal temperature is 160 °C - 200 °C, and the hydrothermal time is 3 h - 8 h; Finally, add the modified clay mineral precursor to the kiln and calcine it under the protection of an inert gas. The calcination temperature is 350 °C - 500 °C, and the calcination time is 1 h - 3 h to prepare the modified clay minerals loaded with nanomaterials.

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