Hydrotalcite-biochar composite material, preparation method and application thereof

Abstract

The present application relates to the technical field of soil remediation, and particularly relates to a hydrotalcite biochar compounded material, a preparation method and application thereof. The present application selects specific hydrotalcite and biochar as raw materials, and adopts a simple mixing method to prepare the compounded material. The preparation method is simple, the obtained material does not need high-temperature calcination and ball milling post-treatment processes, and can be produced on a large scale, thereby effectively saving the cost. The present application can simultaneously achieve the three purposes of improving the soil pH value, fixing heavy metals and improving the organic matter content, and the fixation rate of effective cadmium and effective lead is higher, and is suitable for large-scale application.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soil remediation, in particular to a hydrotalcite biochar compound material, a preparation method and application thereof. BACKGROUND

[0002] Farmland soil heavy metal pollution has the characteristics of concealment, long-term and irreversibility, which not only leads to soil fertility and crop yield and quality decline, but also easily causes groundwater pollution. At the same time, soil heavy metal pollution is often accompanied by soil acidification and infertility (low organic matter content), which also enhances the mobility and toxicity of heavy metals in soil. At present, methods such as electrodynamic remediation, chemical leaching, hyperaccumulating plant absorption and guest soil are often used, but due to high remediation cost, large workload and long remediation period, the above methods are not suitable for large-scale remediation of contaminated farmland soil.

[0003] In recent years, hydrotalcite and biochar are hotspots in the research of remediation materials. Hydrotalcite is a layered double hydroxide (LDH), also known as hydrotalcite-like compound or anionic clay, which is widely used in catalysis, adsorption and other reactions, nanotechnology and biotechnology due to its unique interlayer anion exchange, memory effect, super-stable mineralization and other characteristics. Hydrotalcite is often used as an acid soil conditioner to adsorb and fix heavy metals due to its high pH value, but its high cost and difficulty in preparation limit its large-scale production and application. Biochar is a porous, stable and carbon-rich solid material prepared by pyrolysis of biomass under anaerobic or limited oxygen conditions, with a pyrolysis temperature of 300-700℃. The production raw material cost of biochar is low and the source is wide, mainly being agricultural and forestry solid waste (such as rice straw) and kitchen waste and other biomass. Therefore, converting biomass into biochar as an adsorbent is an effective way to reduce pollution and carbon and realize resource utilization. In addition, biochar has the advantages of high cost-effectiveness, wide application range and environmental friendliness, and is often used for the improvement of infertile and acidic soil, and the improvement of soil organic matter content and pH value. However, the adsorption capacity of biochar for heavy metals is weak and the durability is not strong, which has the risk of secondary release, seriously limiting its application in environmental governance.

[0004] At present, many studies are devoted to repairing heavy metal contaminated soil by simply applying hydrotalcite or biochar, but it is difficult to simultaneously consider soil acid improvement, organic matter content improvement and heavy metal pollution control. Some studies have begun to modify hydrotalcite and biochar composite materials by hydrothermal method and coprecipitation method, but these techniques are complicated and not suitable for large-scale application and promotion. In addition, patent application document CN115647023A reports that by combining the technology of turning over Astragalus sinicus, the technology of applying magnesium-calcium-aluminum hydrotalcite, and the technology of returning rice straw biochar to the field, the biological availability of cadmium in soil is reduced, but the technical process is complicated and not conducive to popularization and application. Therefore, it is of great significance to invent an application technology that can fix heavy metals, improve soil pH value and increase soil organic matter content. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a hydrotalcite-biochar composite material, a preparation method and application thereof. The preparation method of the hydrotalcite-biochar composite material provided by the present application is simple, the cost is low, the soil pH value and organic matter content can be improved, and the fixation rate of effective cadmium and effective lead is high.

[0006] The present application provides a hydrotalcite-biochar composite material prepared from raw materials including iron-based hydrotalcite and biochar.

[0007] The mass ratio of the iron-based hydrotalcite to the biochar is 1-3:7-9.

[0008] Preferably, the iron-based hydrotalcite is calcium-iron hydrotalcite.

[0009] The present application also provides a preparation method of the hydrotalcite-biochar composite material described above, comprising the following steps:

[0010] Mixing the calcium-iron hydrotalcite and the biochar to obtain the composite material.

[0011] Preferably, the composite material can be obtained by directly mixing the calcium-iron hydrotalcite and the biochar without other treatment steps.

[0012] The present application also provides an application of the hydrotalcite-biochar composite material described above, or the hydrotalcite-biochar composite material prepared by the preparation method described above as a soil remediation agent.

[0013] Preferably, the application is the application of the hydrotalcite-biochar composite material in the treatment of acid heavy metal contaminated farmland soil and the improvement of organic matter.

[0014] The present application also provides a use method of the hydrotalcite-biochar composite material, comprising the following steps:

[0015] After the soil to be treated is dried, the soil is ground and sieved, and the hydrotalcite biochar compound material is uniformly mixed, and the soil moisture content is maintained for a period of time;

[0016] The hydrotalcite biochar compound material is the hydrotalcite biochar compound material described above, or the hydrotalcite biochar compound material prepared by the preparation method described above.

[0017] Preferably, in the soil to be treated, the effective state cadmium content is 0.5-1.0 mg / kg, the effective state lead content is 30-50 mg / kg, and the organic carbon content is 30-40 g / kg; the pH value of the soil to be treated is 3.0-6.0.

[0018] Preferably, after the soil to be treated is dried, it further includes removing plant residues;

[0019] The soil is ground and sieved to 10 mesh;

[0020] The hydrotalcite biochar compound material accounts for 1%-3% of the mass of the soil after being ground and sieved.

[0021] Preferably, the soil moisture content is maintained at 50%-70%;

[0022] The maintenance time is 7-60 days.

[0023] The present application provides a hydrotalcite biochar compound material, which is prepared from raw materials including iron-based hydrotalcite and biochar; the mass ratio of the iron-based hydrotalcite and the biochar is 1-3:7-9. The present application uses a stirrer to simply mix specific hydrotalcite and biochar, and the preparation method is simple, easy to implement in practical application, and relatively low in cost, which can achieve three purposes of improving the soil pH value, fixing heavy metals, and improving the organic matter content, among which the fixing rate of effective state cadmium and effective state lead is relatively high, and it is suitable for large-scale application. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The pH value improvement effect of BC (simple addition of biochar), C (simple addition of calcium-iron hydrotalcite), H19C (hydrotalcite: biochar mass ratio of 1:9 compound material), and H37C (hydrotalcite: biochar mass ratio of 3:7 compound material) applied to the soil to be treated for 15d Figure 1 a), 30d Figure 1 b), and 45d Figure 1 c) is shown in the following table:

[0025] Figure 2 The effective state cadmium fixing rate of BC, C, H19C, and H37C applied to the soil to be treated for 15d Figure 2 a), 30d Figure 2 b), and 45d Figure 2 c) is shown in the following table:

[0026] Figure 3 The effective state lead fixation rate after the treatment BC, C, H19C and H37C are applied to the soil to be treated for 15d Figure 3 a), 30d Figure 3 b) and 45d Figure 3 c);

[0027] Figure 4 The organic carbon content increase rate after the treatment BC, C, H19C and H37C are applied to the soil to be treated for 45d;

[0028] Figure 5 The effective state cadmium fixation rate after the treatment BC, C, H19C and H37C are applied to the soil to be treated for 45d and the 1m 3 The price of the soil to be treated effective state cadmium concentration is reduced by 1mg / kg;

[0029] Figure 6 The comparative effect diagram of the compound material (ordinary mixing) obtained from the step 1) of the embodiment 1-2 of the present application and K19C (ball milling compound material of the mass ratio of hydrotalcite to biochar is 1:9) and K37C (ball milling compound material of the mass ratio of hydrotalcite to biochar is 3:7) obtained by using the ball milling technology; the ball milling technology is specifically as follows: the calcium-iron hydrotalcite and the biochar are mixed according to the mass ratio of 1:9 and then are put into a planetary mixing instrument (the mass ratio of the mixture to the ball milling beads is 9:1), 500rpm / min, ball milling for 3h, to obtain K19C; the calcium-iron hydrotalcite and the biochar are mixed according to the mass ratio of 3:7 and then are put into a planetary mixing instrument (the mass ratio of the mixture to the ball milling beads is 9:1), 500rpm / min, ball milling for 3h, to obtain K37C.

[0030] Figure 7 The effective state cadmium and effective state lead fixation rates after the compound material obtained from the step 1) of the embodiment 1 of the present application and the compound material obtained from the comparative example 1-2 are applied to the soil to be treated for 15d. DETAILED DESCRIPTION

[0031] The technical solutions of the present application will be described clearly and completely below by combining with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by the ordinary skilled in the art without creative labor are within the protection scope of the present application.

[0032] The present application provides a hydrotalcite biochar compound material, which is prepared from raw materials including iron-based hydrotalcite and biochar;

[0033] The mass ratio of the iron-based hydrotalcite to the biochar is 1-3:7-9.

[0034] In some embodiments of the present application, the iron-based hydrotalcite is calcium iron hydrotalcite, such as calcium iron hydrotalcite with model number SR-02-21.

[0035] The present application also provides a preparation method of the hydrotalcite biochar compound material described above, comprising the following steps:

[0036] Mixing the calcium iron hydrotalcite and the biochar to obtain the compound material.

[0037] The hydrotalcite biochar compound material provided by the present application only needs to be directly mixed with the calcium iron hydrotalcite and the biochar to obtain, without other processing steps. The mixing is carried out in a stirrer.

[0038] The present application also provides an application of the hydrotalcite biochar compound material described above as a soil remediation agent. Specifically, an application of the hydrotalcite biochar compound material described above in the treatment of acid heavy metal contaminated farmland soil and the improvement of organic matter is provided.

[0039] The present application also provides a use method of the hydrotalcite biochar compound material described above, comprising the following steps:

[0040] After the soil to be treated is dried, it is ground and sieved, mixed with the hydrotalcite biochar compound material described above, and maintained for a period of time at a soil moisture content.

[0041] In some embodiments of the present application, in the soil to be treated, the effective state cadmium content is 0.5-1.0 mg / kg, the effective state lead content is 30-50 mg / kg, and the organic carbon content is 30-40 g / kg; the pH value of the soil to be treated is 3.0-6.0. Specifically, in the soil to be treated, the effective state cadmium content is 1.0 mg / kg, the effective state lead content is 35 mg / kg, and the organic carbon content is 35 g / kg; the pH value of the soil to be treated is 4.5.

[0042] In some embodiments of the present application, after the soil to be treated is dried, it further comprises removing plant residues.

[0043] In some embodiments of the present application, the grinding is through a 10-mesh sieve.

[0044] In some embodiments of the present application, the hydrotalcite biochar compound material accounts for 1%-3% of the mass of the soil after grinding and sieving, such as 1.5% and 3%.

[0045] In some embodiments of the present application, the maintenance of the soil moisture content is carried out in a culture pot. The mass of each soil sample in the culture pot is 500-1000 g, such as 800 g.

[0046] In some embodiments of the present application, the soil moisture content is maintained at 50-70%, such as 50%.

[0047] In some embodiments of the present application, the curing time is 7-60 days, such as 15 days, 30 days, or 45 days.

[0048] The raw materials used in the present application are not particularly limited and can be commercially available.

[0049] Advantages:

[0050] 1) The present application selects specific hydrotalcite and biochar as raw materials, and uses a simple mixing method to prepare a compounded material. The preparation method is simple, and the obtained material does not require high-temperature calcination and ball milling post-treatment processes, but still can increase the soil pH value and organic matter content, and has a high fixation rate for effective cadmium and effective lead, and can be produced on a large scale, effectively saving costs.

[0051] 2) The present application can simultaneously achieve the three purposes of increasing the soil pH value, fixing heavy metals, and increasing the organic matter content.

[0052] In order to further illustrate the present application, the hydrotalcite-biochar compounded material, its preparation method and application provided by the present application are described in detail below, but it should not be understood as limiting the scope of protection of the present application.

[0053] In the examples, the effective cadmium content in the soil to be treated is 1.0 mg / kg, the effective lead content is 35 mg / kg, and the organic carbon content is 35 g / kg; the pH value of the soil to be treated is 4.5.

[0054] Example 1

[0055] 1) Preparation of hydrotalcite-biochar compounded material:

[0056] The calcium-iron hydrotalcite (model SR-02-21) and biochar were mixed in a mass ratio of 1:9 in a stirrer to obtain a compounded material, denoted as H19C.

[0057] 2) After the soil to be treated was dried, plant residues were removed, ground through a 10-mesh sieve, and the soil to be repaired was obtained. H19C (the H19C accounted for 1.5% of the mass of the soil to be repaired) was added to the soil to be repaired, mixed uniformly, and then loaded into a culture pot. The mass of each soil sample in the culture pot was 800 g, the soil moisture content was maintained at 50%, and the samples were taken after curing for 15, 30, and 45 days for detection and evaluation of the repair performance of the material. As shown in Table 1.

[0058] Example 2

[0059] 1) Preparation of hydrotalcite-biochar compounded material:

[0060] Calcium iron hydrotalcite (model SR-02-21) and biochar were mixed in a stirrer at a mass ratio of 3:7 to obtain a compound material, denoted as H37C.

[0061] 2) After drying the soil to be treated, remove plant residues, grind it through a 10-mesh sieve to obtain the soil to be remediated; add H37C (H37C accounts for 3% of the mass of the soil to be remediated) to the soil to be remediated, mix well, and put it into a culture pot. The mass of each soil sample in the culture pot is 800g, and the soil moisture content is maintained at 50%. After 15, 30, and 45 days of curing, samples are taken for testing to evaluate the remediation performance of the material. As shown in Table 1.

[0062] Table 1. Fixation rates of Cd and Pb in soil by the compound materials in Examples 1-2

[0063]

[0064] Figure 1 To treat soil samples treated with BC (with biochar alone), C (with calcium-iron hydrotalcite alone), H19C (a mixture of hydrotalcite and biochar at a mass ratio of 1:9), and H37C (a mixture of hydrotalcite and biochar at a mass ratio of 3:7), the following solutions were applied to the soil sample 15 days later. Figure 1 a) 30d ( Figure 1 b) and 45d Figure 1 c) The effect of increasing pH value. Figure 1 It can be seen that H19C and H37C treatments have a significant effect on increasing soil pH, with pH increasing by 1.08 to 1.85. The effect is more obvious with the increase of the amount added. Among them, the C treatment has the best effect due to its high pH, ​​with the highest pH increase of 1.99. The soil pH remains stable within 45 days. The other three materials reach their maximum at 30 days and then slowly decrease.

[0065] Figure 2 To treat the soil, BC, C, H19C and H37C were applied for 15 days. Figure 2 a) 30d ( Figure 2 b) and 45d Figure 2 c) Effective cadmium fixation rate.

[0066] Figure 3 To treat the soil, BC, C, H19C and H37C were applied for 15 days. Figure 3 a) 30d ( Figure 3 b) and 45d Figure 3 c) Effective lead fixation rate.

[0067] Depend on Figures 2-3It can be seen that the fixing ability of H37C treatment with high proportion of hydrotalcite to effective cadmium in soil is better than that of H19C treatment, with the highest fixing rate of 37.42%, and the highest fixing rate of effective lead is 40%; and with the increase of the amount of the compound material, the effect is more obvious, and the effect is similar to that of C treatment; with the extension of the repair time, the fixing effect of the material on heavy metals is relatively stable.

[0068] Figure 4 The organic carbon increase rate of BC, C, H19C and H37C applied to the soil to be treated after 45 days is shown in Table 2. Figure 4 It can be seen that C treatment has no effect on the improvement of soil organic matter, BC treatment has a significant effect, and the improvement effect of the compound material on soil organic matter is mainly due to the proportion of biochar in it, but the overall effect is relatively good.

[0069] The repair price Q of unit cubic meter of contaminated soil is shown in formula (1);

[0070] Q=M×P / M HMS Formula (1);

[0071] In formula (1), M is the material addition amount of unit cubic meter of contaminated soil, unit kg / m 3 ; the quality of contaminated soil is calculated as 2.3t / m 3 ;

[0072] P is the price of BC, C, H19C and H37C, which is 2000, 20000, 3800 and 7400 yuan / t respectively; BC represents biochar; C represents calcium iron hydrotalcite;

[0073] M HMS is the mass of heavy metals removed from unit cubic meter of contaminated soil.

[0074] Figure 5 The effective cadmium fixing rate of BC, C, H19C and H37C applied to 1m 3 of soil to be treated after 30 days, and the price of each material to reduce the effective cadmium concentration of 1mg / kg in the soil to be treated are shown in Table 3. Figure 5 It can be seen that the fixing ability of H37C treatment to effective cadmium is the best, and considering the repair cost, the price of H37C treatment is 690 yuan / m 3 , which is 73% less than that of C treatment (2553 yuan / m 3 ) and 20% less than that of BC treatment (828 yuan / m 3 ).

[0075] Figure 6The comparative effect of the compound material (ordinary mixing) obtained in step 1) of the present application embodiment 1-2 with K19C and K37C obtained by using a ball milling technique; the ball milling technique is as follows: calcium-iron hydrotalcite and biochar are mixed in a mass ratio of 1:9 and then put into a planetary mixer (the mass ratio of the mixture to the ball milling beads is 9:1), 500 rpm / min, ball milling for 3 h to obtain K19C; calcium-iron hydrotalcite and biochar are mixed in a mass ratio of 3:7 and then put into a planetary mixer (the mass ratio of the mixture to the ball milling beads is 9:1), 500 rpm / min, ball milling for 3 h to obtain K37C. Figure 6 It can be seen that: compared with the common ball milling technique, the ordinary mixing technique of the present application is obviously superior to the ball milling technique when the addition amount of the material is 3%, and the power consumption and the complicated operation of the ball milling technique can only be used for small-scale production; while the present application is suitable for large-scale batch production, and the preparation cost is relatively lower.

[0076] Comparative example 1

[0077] The difference from example 1 is that:

[0078] The calcium-iron hydrotalcite is replaced by magnesium-aluminum hydrotalcite (Al2Mg6(OH) 16 CO3·4H2O), and the magnesium-aluminum hydrotalcite and biochar are mixed in a mass ratio of 1:9 in a stirrer to obtain a compound material, which is recorded as H19M. The remaining steps and parameters are carried out according to the steps and parameters of example 1.

[0079] Comparative example 2

[0080] The difference from comparative example 1 is that:

[0081] In step 1), the magnesium-aluminum hydrotalcite and biochar are mixed in a mass ratio of 3:7 in a stirrer to obtain a compound material, which is recorded as H37M. The remaining steps and parameters are carried out according to the steps and parameters of example 1.

[0082] Figure 7 The effective state cadmium fixation rate of the compound material obtained in step 1) of example 1 of the present application and the compound material obtained in comparative examples 1-2 after being applied to the soil to be treated for 15 days; from Figure 7 It can be seen that: the effective state cadmium fixation rate under the treatment of H19M and H37M of magnesium-aluminum hydrotalcite used in comparative examples 1-2 is significantly lower than that under the treatment of H19C and H37C of calcium-iron hydrotalcite, which indicates that the hydrotalcite-biochar compound material prepared by using calcium-iron hydrotalcite in the present application has better effect. In summary, the compound material prepared in the present application has certain advantages in terms of price and effect.

[0083] The foregoing description of the disclosed embodiments enables a person skilled in the art to make or use the application. Modifications of these embodiments will occur to persons of skill in the art, and, while certain modifications are discussed, it is desired to be protected in accordance with the spirit and scope of the application. Therefore, the application is not limited to the specific embodiments shown and described, but only by the scope of the appended claims, unless otherwise specified.

Claims

1. A method for using a hydrotalcite biochar compound material, comprising the following steps: After the soil to be treated is dried, the soil is ground and sieved, mixed with the hydrotalcite biochar compound material, and maintained for a period of time at a soil moisture content; The hydrotalcite biochar compound material is obtained by directly mixing iron-based hydrotalcite and biochar; The mass ratio of the iron-based hydrotalcite to the biochar is 1-3:7-9; The iron-based hydrotalcite is calcium iron hydrotalcite; In the soil to be treated, the content of available lead is 30-50 mg / kg, and the content of organic carbon is 30-40 g / kg; the pH value of the soil to be treated is 3.0-6.

0.

2. The method of use of claim 1, wherein, In the soil to be treated, the content of available cadmium is 0.5-1.0 mg / kg.

3. The method of use of claim 1, wherein, After the soil to be treated is dried, plant residues are removed; The soil is ground and sieved to 10 mesh; The hydrotalcite biochar compound material accounts for 1-3% of the mass of the soil after being ground and sieved.

4. The method of use of claim 1, wherein, The soil moisture content is maintained at 50-70%; The maintenance time is 7-60 days.

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