Calcium humic acid modified charcoal composite material as well as preparation method and application thereof

Abstract

The invention provides a calcium humic acid modified biochar composite material as well as a preparation method and application thereof. The preparation method specifically comprises the following steps: preparing calcium modified biochar powder from biochar powder and a calcium source; mixing humic acid with the calcium modified charcoal powder, filtering and drying to obtain a calcium humic acid modified charcoal composite material; wherein the mass ratio of the humic acid to the calcium modified charcoal powder is 1: (2-20). When the calcium humic acid modified biochar composite material is used as a soil remediation agent for soil remediation, the pH value, the organic matter content and the cation exchange capacity of soil can be improved, the soil hardening degree is relieved, heavy metal lead and cadmium and ions thereof can be immobilized in the modes of ion exchange, electrostatic adsorption, surface complexing, deposition and the like, and the soil remediation efficiency is improved. The soil heavy metal content is further reduced.

Description

Technical Field

[0001] The present invention relates to the field of soil remediation, and specifically, to a calcium humic acid modified biochar composite material, a preparation method thereof, and an application thereof. Background Art

[0002] To improve the fertilizer efficiency of soil and improve soil productivity, the commonly used methods are physical, chemical, and biological methods. The physical remediation method is to repair the soil by means of mechanical means. The biological remediation technology includes animal remediation, microbial remediation, and phytoremediation. The chemical remediation method is to add a remediation agent to the soil to improve the soil aggregate structure and inhibit the environmental migration ability of heavy metals in the soil, so as to achieve the purpose of improving the soil health quality.

[0003] The invention patent application with the authorization announcement number CN119056406A discloses a method for preparing artificial humic acid-activated magnesium modified biochar and its application in repairing zinc and cadmium in soil or water bodies. In order to solve the problems of poor adsorption effect and poor material stability of using metal oxide modified biochar in the existing method. It includes preparing magnesium modified biochar, mixing magnesium modified biochar and artificial humic acid KOH solution, stirring for a period of time, and then pyrolyzing in a tube furnace to obtain artificial humic acid-activated magnesium modified biochar. The artificial humic acid-activated magnesium modified biochar prepared by this method has a larger specific surface area and more active sites on the surface compared with unmodified biochar and magnesium modified biochar. Due to its unique physical and chemical properties, it can achieve efficient adsorption of zinc and cadmium in soil and water bodies. However, this method does not disclose how to improve soil fertility and reduce soil compaction while reducing the heavy metal content in the soil. Summary of the Invention

[0004] In order to improve soil fertility, increase soil organic matter content, reduce soil compaction, and reduce soil heavy metal content, the technical solution adopted by the present invention is: a preparation method of a calcium humic acid modified biochar composite material, comprising the following steps:

[0005] Step 1: Prepare calcium modified biochar powder by using biochar powder and a calcium source, wherein the specific surface area of the biochar powder is 35m 2 / g to 43m 2 / g, and the pore volume is 0.045cm 3 / g to 0.090cm 3 / g;

[0006] Step 2: Mix humic acid with the calcium modified biochar powder, and obtain a calcium humic acid modified biochar composite material after filtration and drying; wherein, the mass ratio of the humic acid to the calcium modified biochar powder is 1:(2-20). Preferably, the mass ratio of the humic acid to the calcium modified biochar powder is 1:(5-15).

[0007] Based on the above, Step 1 specifically includes transferring the biochar powder into a calcium chloride solution for mixing, and obtaining the calcium-modified biochar powder after filtration, drying, grinding, and sieving.

[0008] Based on the above, Step 1 specifically includes mixing the carbonized eggshell powder and the biochar powder, and obtaining the calcium-modified biochar powder after ball milling, drying, and calcination.

[0009] Based on the above, the biochar powder is obtained by carbonizing agricultural waste after alkali washing to remove lignin.

[0010] Based on the above, the temperature of the carbonization treatment is 400°C to 800°C, the heating rate is 3°C / min to 8°C / min, and the carbonization time is 1h to 3h;

[0011] Based on the above, the agricultural waste is mushroom stick residue, peanut shell, or wood chip.

[0012] The present invention also provides a calcium humic acid-modified biochar composite material, which is prepared by the above preparation method. The specific surface area of the calcium humic acid-modified biochar composite material is 69.28 m 2 / g to 92.62 m 2 / g, and the pore volume is 0.112 cm 3 / g to 0.226 cm 3 / g.

[0013] The present invention also provides an application of the calcium humic acid-modified biochar composite material. The calcium humic acid-modified biochar composite material is used as a soil repair agent to repair soil. Specifically, when repairing soil, the mass ratio of the calcium humic acid-modified biochar composite material to the soil is 1:(5 - 15).

[0014] The present invention has prominent substantial features and significant progress compared with the prior art. Specifically, a calcium humic acid-modified biochar composite material, its preparation method and application provided by the present invention use humic acid to modify the calcium-modified biochar powder, increasing the specific surface area of the particles and enriching the pore structure. At the same time, the modification treatment reduces the aromatization degree of the biochar powder, increases the hydrophilicity and surface polar functional groups of the biochar powder. And grafting humic acid onto the surface of the calcium-modified biochar can significantly increase the content of oxygen-containing groups, benzene rings, and carbon chains, which can provide necessary organic matter for the soil and provide potential possibilities for inhibiting the migration of heavy metal ions in the soil.

[0015] Furthermore, when the calcium humic acid modified biochar composite is applied to problematic soils, its surface is rich in polar groups and a large number of inorganic mineral ions. It can not only increase the pH value, organic matter content, and cation exchange capacity of the soil, alleviate the soil compaction degree, but also immobilize heavy metals such as lead and cadmium and their ions through ion exchange, electrostatic adsorption, surface complexation, and deposition, thereby inhibiting their migration and transfer in the soil.

[0016] Furthermore, by applying the calcium humic acid modified biochar composite to the test soil, the growth of pakchoi plants is good, and their germination rate, plant height, dry weight, and fresh weight are all high. The chlorophyll content and soluble protein content in the pakchoi plants are also relatively high. Moreover, it can effectively passivate the heavy metal ions in the soil, resulting in little difference in the content and morphological distribution of available lead in the soil before and after pakchoi planting, and the same phenomenon is also shown in the content and morphological distribution of available cadmium in the soil before and after pakchoi planting. Description of the Drawings

[0017] Figure 1 SEM photos of calcium humic acid modified biochar composites and their matrices prepared from different biomass raw materials. Among them, Figure 1 A, D, and G respectively refer to biochar, calcium modified biochar, and humic acid modified calcium modified biochar prepared from mushroom stick residues; B, E, and H respectively refer to biochar, calcium modified biochar, and humic acid modified calcium modified biochar prepared from peanut shells; C, F, and I respectively refer to biochar, calcium modified biochar, and humic acid modified calcium modified biochar prepared from wood chips; J-L respectively refer to three kinds of humic acid modified calcium modified biochars prepared by the ball milling method.

[0018] Figure 2 SEM photos of calcium modified biochars modified with different concentrations of humic acid. Among them, Figure 2 A refers to mushroom stick residue biochar; B-D are humic acid modified calcium modified biochars, where the mass ratio of biochar to humic acid is 15:1, 10:1, and 5:1 respectively.

[0019] Figure 3 Infrared spectra of calcium humic acid modified biochar composites and their matrices.

[0020] Figure 4 Infrared spectra of calcium modified biochars modified with different concentrations of humic acid powder.

[0021] Figure 5 Soil pH change diagram at different remediation times.

[0022] Figure 6 Soil conductivity change diagram at different remediation times.

[0023] Figure 7 Soil organic matter content change diagram for different repair times.

[0024] Figure 8 Soil urease activity change diagram for different repair times.

[0025] Figure 9 Soil sucrase activity change diagram for different repair times.

[0026] Figure 10 Soil alkaline phosphatase activity change diagram for different repair times.

[0027] Figure 11 Soil catalase activity change diagram for different repair times.

[0028] Among them, Figures 5 to 11 in which A, B, C, and D respectively refer to the soil pH values at the 15th d, 30th d, 45th, and 60th d of repair; 1-1, 1-3, and 1-5 respectively represent adding soil repair agent QCa@PSC-600@HA-1 to the soil sample at ratios of 1%, 3%, and 5%; 2-1, 2-3, and 2-5 respectively represent adding soil repair agent QCa@PSC-600@HA-2 to the soil sample at ratios of 1%, 3%, and 5%; 3-1, 3-3, and 3-5 respectively represent adding soil repair agent QCa@PSC-600@HA-3 to the soil sample at ratios of 1%, 3%, and 5%; 4-1, 4-3, and 4-5 respectively represent adding soil repair agent QCa@MDC-600@HA-2 to the soil sample at ratios of 1%, 3%, and 5%; the control means no soil repair agent is added to the soil sample.

[0029] Figure 12 Morphological distribution diagrams of Pb and Cd elements in improved soil sample No. 1 at different time periods.

[0030] Figure 13 Morphological distribution diagrams of Pb and Cd elements in improved soil sample No. 2 at different time periods.

[0031] Among them, Figure 12 and Figure 131-1, 2-1, 3-1, and 4-1 respectively refer to the soils of Specimen No. 1 or No. 2 with the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 1% respectively. 1-3, 2-3, 3-3, and 4-3 respectively refer to the soils of Specimen No. 1 or No. 2 with the remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 3% respectively. 1-5, 2-5, 3-5, and 4-5 respectively refer to the soils of Specimen No. 1 or No. 2 with the soil remediation agents QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3, and QCa@MDC-600@HA-2 added at a dose of 5% respectively.

[0032] Figure 14 It is a comparison chart of the growth of pakchoi. Among them, in the first row from left to right are the control and the soils added with different types of biochar-based composites; the second row is the pakchoi potted plants planted in the flowerpots corresponding to the first row; the third row is the pakchoi plants (36d) in the flowerpots corresponding to the first row; the fourth row is the pakchoi (30d) planted in large quantities in the greenhouse simulating the externally collected soil.

[0033] Figure 15 It is a chart showing the effect of calcium humic acid modified biochar composite on the chlorophyll content in pakchoi.

[0034] Figure 16 It is a chart showing the effect of calcium humic acid modified biochar composite on the soluble protein content in pakchoi.

[0035] Figure 17 It is a chart showing the effect of calcium humic acid modified biochar composite on the soluble sugar content in pakchoi.

[0036] Among them, Figures 15 to 17 1-1, 1-2, and 1-3 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-1 at a ratio of 1%, 3%, and 5%. 2-1, 2-2, and 2-3 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-2 at a ratio of 1%, 3%, and 5%. 2-1, 2-2, and 2-3 respectively refer to the soil samples added with the soil remediation agent QCa@PSC-600@HA-3 at a ratio of 1%, 3%, and 5%. Control - the soil without the soil remediation agent.

[0037] Figure 18 It is a morphological distribution chart of Pb and Cd in the soil before and after the pakchoi is planted and harvested. Detailed implementation manners

[0038] The technical solution of the present invention will be further described in detail below through specific implementation manners.

[0039] Example

[0040] This example provides a preparation method of a calcium-humic acid modified biochar composite material, including the following steps:

[0041] Preparation of biochar powder: First, wash and dry agricultural waste with deionized water, then crush and screen it with a crusher (through a 60-mesh steel sieve). The obtained agricultural waste powder is stirred in hot alkaline solution (5% NaOH solution) for 6 h to remove part of the lignin in its components. Finally, wash the filter residue with deionized water until neutral, dry, grind, and screen to obtain a biomass pretreatment sample. The agricultural wastes used are respectively the waste mushroom stick residues (MD) from a mushroom planting base in Biyang County, Zhumadian, the peanut shells (PS) locally planted and shelled, and the sawdust (SD) from the woodworking workshop in the school-based innovation and entrepreneurship park of Huanghuai University.

[0042] Carbonize the pretreated agricultural waste powder in a tubular heating furnace under N2 atmosphere. The carbonization temperatures are set at 400 °C, 600 °C, and 800 °C respectively, and the heating rate and carbonization time are 5 °C / min and 2 h respectively. After the reaction is completed, the obtained black solid is biochar powder. According to the yield and infrared spectrum of biochar obtained from the same biomass raw material at different carbonization temperatures, biochar products with higher carbonization yields and rich surface groups are selected, and their naming numbers are MDC-600, PSC-600, and SDC-600 respectively.

[0043] Preparation of calcium-modified biochar powder: Method 1: Using calcium chloride as the calcium source: Weigh 5 g of biochar powder and transfer it to 250 mL of 1 mol / L calcium chloride solution. Stir the solution at room temperature for 24 h. After the reaction is completed, filter the reaction solution by suction. The obtained filter residue is washed with deionized water and then dried in an oven at 105 °C. The obtained black solid is ground and screened to obtain calcium-modified biochar powder, and its name numbers are: HCa@PSC-600, HCa@MDC-600, and HCa@SDC-600.

[0044] Method 2: The eggshells are carbonized at 600 °C for 2 h, and the heating rate is set at 5 °C / min. Before carbonizing the eggshells, operations such as cleaning, air-drying, crushing, and sieving (100 mesh) need to be carried out in advance. Then, the eggshell powder and biochar powder are mixed in a mass ratio of 5:1, and ball milling is carried out under the action of an ethanol solvent. The temperature and rotation speed of ball milling are set at 70 °C and 30 r / min respectively. After 4 h, the solid is separated, and the dried solid powder is placed in a tube furnace at 800 °C under N2 atmosphere for calcination, and the heating rate of the furnace is adjusted to 20 °C / min. After 1.5 h, the calcium-modified biochar samples are obtained, and their name numbers are: QCa@PSC-600, QCa@MDC-600, and QCa@SDC-600 respectively.

[0045] Preparation of calcium humic acid-modified biochar composite: Mix the calcium-modified biochar powder and humic acid according to the set ratio, transfer it to 50 mL of deionized water, and stir the reaction solution at room temperature. After 8 h, filter the reaction solution, and the obtained filter residue is naturally air-dried to obtain the calcium humic acid-modified biochar composite. Among them, the mixing ratios of calcium-modified biochar and humic acid are set as: 15:1 (w / w), 10:1 (w / w), and 5:1 (w / w) respectively, and the corresponding product numbers are: HCa@PSC-600@HA-1, HCa@MDC-600@HA-1, HCa@SDC-600@HA-1, QCa@PSC-600@HA-1, QCa@MDC-600@HA-1, QCa@SDC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, HCa@SDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, QCa@SDC-600@HA-2, HCa@PSC-600@HA-3, HCa@MDC-600@HA-3, HCa@SDC-600@HA-3, QCa@PSC-600@HA-3, QCa@MDC-600@HA-3, and QCa@SDC-600@HA-3. The experiment conducts physical and chemical property tests on a series of humic acid-modified calcium-modified biochars obtained by modifying with different calcium sources and modifying with different concentrations of humic acid, and the relevant results are shown in Table 1.

[0046] It can be seen from Table 1 that before the three agricultural wastes are carbonized, they need to be pretreated with alkali, and the resulting biochars are all alkaline. Compared with the modified biochars, the three unmodified biochars all show lower ash content and pore volume, higher yield and specific surface area. As for the three unmodified biochars, the biochar prepared from the mushroom stick residue has the characteristics of low ash content, high yield, large specific surface area and low pore volume. In the preparation process of modified biochar, as the amount of humic acid increases, the pH value of the obtained carbon-based composite material decreases more significantly.

[0047] The reason for this phenomenon is that the humic acid solution is somewhat acidic. In addition, there is about 8% ash in the newly prepared humic acid-modified calcium biochar, and as the amount of humic acid used increases, the ash content in the biochar composite material gradually decreases.

[0048] By comparing the specific surface area and pore volume of calcium-modified biochar modified by humic acid at different concentrations, it was found that for the biochar obtained by carbonization of the same biomass, when the mass ratio of humic acid to calcium-modified biochar was 1:10, the specific surface area and pore volume of humic acid-modified calcium-modified biochar were large. The specific surface area and porosity of humic acid-modified calcium-modified biochars obtained by modification with humic acid solution of the same concentration were different for different types of biochar raw materials. However, the difference in the type of biochar raw materials had relatively little effect on the specific surface area and pore volume of the modified biochar.

[0049] Table 1 Basic physicochemical properties of humic acid-modified calcium biochar

[0050]

[0051] Structural characterization

[0052] The morphological characteristics of humic acid-modified calcium-modified biochar and its precursor prepared from mushroom residue, peanut shell and sawdust are shown in Figure 2. Figure 1 As shown. Figure 1 It can be seen that for the biochar made from the residue of the mushroom stick, its surface presents a hollow tubular fiber structure with a relatively smooth tube wall. After modification, the biochar made from the residue of the mushroom stick has a fragmented structure with a smaller particle size. Some obvious holes appear on the surface of the particles, and some tiny holes appear, indicating that the humic acid modification and calcium modification treatment have changed the surface morphology of the biochar made from the mushroom stick. At the same time, there are some irregular ellipsoidal substances on the surface of the biochar after modification, indicating that the surface of the biochar is doped with some calcium (calcium chloride or carbonized eggshell) elements.

[0053] In the case of peanut shell-based biochar, after carbonization, the surface of the biochar still retains the original fibrous structure of the biomass, with micropores of different sizes distributed on its surface and many surface wrinkles. Compared with the unmodified biochar, in addition to being covered with more pores and wrinkles, the surface of the modified biochar shows more fine particles, its structure is more fluffy, and the layered structure is more obvious. In the case of wood chip-based biochar, after carbonization of the wood chips, the surface of the wood chip biochar presents a rough surface morphology and has many impurities attached, with relatively few pores. After modification treatment, the impurity residues and ash on the surface of the sawdust biochar are removed and it becomes smooth. At the same time, after modification treatment, the pore structure on the surface of the wood chip-based biochar increases and its structure is more fluffy.

[0054] The apparent morphological characteristics of calcium humic acid-modified biochar composites prepared by modification with different concentrations of humic acid are shown in Figure 2 as follows. From Figure 2 it can be seen that as the concentration of the humic acid modifier increases, the fine pores on the surface of the modified biochar become more numerous, indicating that humic acid can destroy the microscopic structure of the biochar surface. However, with a further increase in the dosage of humic acid, some of the pores on the biochar surface are blocked. In summary, when using humic acid to modify calcium-modified biochar, in order to ensure the high specific surface area and well-developed pore structure of the modified biochar, biochar-based composites with relatively strong remediation ability for problem soils are screened out, which are QCa@PSC-600@HA-1, HCa@PSC-600@HA-2, HCa@MDC-600@HA-2, QCa@PSC-600@HA-2, QCa@MDC-600@HA-2, HCa@PSC-600@HA-3 and QCa@PSC-600@HA-3 respectively.

[0055] Infrared spectrum analysis

[0056] The infrared spectra of calcium humic acid-modified biochar composites and their matrices prepared from waste mushroom stick residues are shown in Figure 3 as follows. From Figure 3 it can be seen that in the case of the infrared spectrum of the unmodified mushroom stick residue biochar, the strong and broad vibration absorption peak at a wavenumber of 3422 cm -1 belongs to the stretching vibration of hydroxyl groups, the vibration absorption peak at a wavenumber of 2834 cm -1 is caused by the C-H stretching vibration on -CH2, the absorption peak at a wavenumber of 1365 cm -1 is caused by the skeletal bending vibration of the benzene ring, the absorption peak at a wavenumber of 1628 cm -1 is caused by the C=O stretching vibration, and the absorption peak at 1147 cm -1The characteristic absorption peak at the wavenumber is caused by the C-O stretching vibration. Compared with the unmodified mushroom stick residue biochar, the overall change in the functional group composition of the mushroom stick biochar modified by calcium chloride and humic acid is not significant. However, the intensity of the absorption peak of the mushroom stick biochar modified by calcium chloride and humic acid has increased. At the same time, the positions and intensities of the vibration absorptions on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 are almost the same, indicating that the differences in the functional group composition and content on the surfaces of these two modified biochars are not obvious.

[0057] In addition, new absorption peaks appear at 775 cm -1 and 776 cm -1 wavenumbers on the spectra of HCa@PSC-600@HA-2 and QCa@PSC-600@HA-2, respectively. This is attributed to the effect of the C-Ca bond on the surface of the modified biochar. At the same time, humic acid is modified on the surface of the biochar, and a large number of oxygen-containing functional groups are introduced onto the biochar surface during this process, resulting in enhanced vibration absorptions at 3422 cm -1 and 1628 cm -1 wavenumbers on the spectra of HCa@PSC-600@HA-2, QCa@PSC-600@HA-2, indicating an increase in the content of acidic groups on the surface of the humic acid-modified calcium-modified biochar.

[0058] The infrared spectra of the calcium-modified biochar modified with different concentrations of humic acid are shown in Figure 4 . As can be seen from Figure 4 , changing the concentration of humic acid has little effect on the chemical composition of the humic acid-modified calcium-modified biochar, indicating that the changes in the content of oxygen-containing polar groups and organic matter composition on the surface of the calcium humic acid-modified biochar composite prepared with different concentrations of humic acid are not reflected in the infrared spectra. However, due to the abundant polar groups on the surface of the modified biochar, when it is applied to farmland with problems of soil compaction and heavy metal pollution, it can improve the air permeability and water retention capacity of the soil by changing the soil aggregate structure, and can also adsorb heavy metal ions in the soil through ion exchange, surface complexation, etc.

[0059] At the same time, there is no difference in the morphological characteristics between the modified biochar prepared by the ball milling method and the modified biochar prepared by the chemical impregnation method. Since the preparation of calcium-modified biochar by the ball milling method can reduce the types and amounts of chemical reagents, subsequent experiments will be carried out using QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 as raw materials.

[0060] Elemental analysis

[0061] The percentage contents of C, H, N, and S elements in the biochar samples were determined using an elemental analyzer, and the content of O element was calculated by the difference method. The organic elemental compositions and contents of the calcium humic acid-modified biochar composite and its precursor are shown in Table 2.

[0062] Table 2 Elemental analysis of the calcium humic acid-modified biochar composite and its matrix

[0063]

[0064] Specifically, the H / C molar ratio of the biochar material can be used as an index to measure its degree of aromatization, and the O / C molar ratio is positively correlated with the oxygen-containing functional groups on its surface. At the same time, it can also be used as a basis for judging the hydrophilicity of the biochar material. Moreover, the larger the O / C molar ratio of the biochar, the better its hydrophilicity. In addition, the (O + N) / C molar ratio of the carbon-rich material can reflect the polarity of the material. The larger the (O + N) / C molar ratio of the biochar, the greater its polarity.

[0065] It can be seen from Table 2 that for the unmodified biochar, although the types of agricultural waste used to make the biochar are different, when carbonized at the same temperature, the aromatization degrees of the obtained biochars are not different, and their hydrophilicities and polarities are also similar. Compared with the unmodified biochar, the biochar modified by humic acid and calcium modification has higher aromaticity, hydrophilicity, and polarity, indicating that the content of polar functional groups on the surface of the modified biochar is higher, and it also indicates that humic acid has been successfully grafted onto the surface of the calcium-modified biochar. This conclusion is consistent with the analysis results of the infrared spectrum of the humic acid-modified calcium-modified biochar mentioned above. Regarding the concentration of the modifier humic acid, as the amount of humic acid used increases, the aromaticity of the obtained modified biochar increases, while its hydrophilicity and polarity do not change significantly, indicating that an appropriate addition amount of humic acid is a necessary condition for increasing the organic matter content in the modified biochar.

[0066] Soil saturation experiment

[0067] The calcium humic acid modified biochar composites labeled as QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, QCa@PSC-600@HA-3 and QCa@MDC-600@HA-2 were selected for the soil remediation experiment. The specific steps were as follows: The soil samples were respectively mixed with the above 4 kinds of calcium humic acid modified biochar composites in proportion and placed in pots, then watered. After the water seeped out from the water outlet holes at the bottom of the pots, they were left standing for 12 h, and then watered again until water came out from the bottom of the pots. Then the flower pots were placed in a greenhouse and watered thoroughly once a week. When there was no obvious decrease in the soil body, it was in an equilibrium state. After reaching the equilibrium state, it was left for 15 d. Thereafter, soil samples were taken through a 18-mesh sieve every 15 d for measuring the physical and chemical properties of the soil. The sampling time interval for measuring the content of heavy metal ions in the soil was 30 d.

[0068] The experiment took 4 kinds of calcium humic acid modified biochar composites as soil remediation agents as the research object, adopted the indoor simulation test method, and added the soil remediation agents at one time according to 0%, 1.0%, 3.0% and 5.0% of the soil quality. And soil samples were collected on the 15th d, 30th d, 45th d and 60th d. For each soil type, 13 groups of soil samples were designed in the experiment, and each group of experimental operations was repeated 3 times. The soil samples without adding any amendments were used as the blank control group.

[0069] Change of soil pH value: During the soil remediation process, the change rules of soil pH in different treatment groups are shown in Figure 5 as follows. From Figure 5 it can be seen that generally speaking, after applying the soil remediation agent, the pH value of the soil generally shows an increasing trend. However, the pH value of the soil without adding the soil remediation agent changed little during the whole incubation period and was always weakly acidic. After adding the soil remediation agent to the problem soil, its pH value increased with the increase of the soil incubation time, and the pH value of the soil reached the maximum after 45 d of soil incubation. In addition, it can also be seen from the figure that in terms of the types of soil remediation agents, compared with other types of soil remediation materials, the soil remediation agent QCa@PSC-600@HA-3 has good effects on increasing the pH values of the three kinds of soils, and increasing the usage amount of the soil remediation material, the pH value of the soil after its action increases. The above comprehensive analysis shows that adding soil amendments can improve the pH value of the soil to a certain extent, and among them, the soil remediation agent QCa@PSC-600@HA-3 has the most significant treatment effect on the acidified farmland.

[0070] Change of soil electrical conductivity: During the remediation process, the change trends of the soil electrical conductivity in different treatment groups are shown in Figure 6 as follows. From Figure 6It can be seen that, compared with the soil without the addition of calcium humic acid modified biochar composite, the electrical conductivity of the soil in the farmland with the addition of calcium humic acid modified biochar composite has decreased. For different types of calcium humic acid modified biochar composites, the electrical conductivity value in the soil with the addition of QCa@PSC-600@HA-2 has decreased most significantly, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing biochar are different, the changing trend of their influence on the electrical conductivity in the soil is the same.

[0071] Take the calcium humic acid modified biochar composite QCa@PSC-600@HA-2 as an example. Different mixing dosages of it with the test soil result in different electrical conductivities of the soil after remediation. As the dosage of the biochar-based composite increases, the decrease in the electrical conductivity value in the affected soil becomes more obvious. When the mass ratio of the calcium humic acid modified biochar composite to the test soil is 1:10, the electrical conductivity value in the affected soil is the lowest, and this research result is valid for both soil samples. Applying QCa@PSC-600@HA-2 to the test soil at a ratio of 1:10 (w / w), its electrical conductivity value decreases significantly within 0 - 45 days, while the change in the electrical conductivity value is not obvious after more than 45 days, indicating that the calcium humic acid modified biochar composite can improve the fertility of degraded soil in a relatively short time.

[0072] Change in soil organic matter content: The changing trend of the organic matter content in the remediated soil of different treatment groups is shown in Figure 7 as follows. It can be seen from Figure 7 that, compared with the soil without the addition of calcium humic acid modified biochar composite, the organic matter content in the soil with the addition of calcium humic acid modified biochar composite has increased. For different types of calcium humic acid modified biochar composites, the increase in the organic matter content in the soil with the addition of QCa@PSC-600@HA-2 is the largest, followed by QCa@MDC-600@HA-2, indicating that although the raw materials for preparing biochar are different, the changing trend of their influence on the organic matter content in the soil is the same. For the biochar-based composite QCa@PSC-600@HA-2, different mixing dosages of it with the soil sample result in different organic matter contents in the soil after remediation.

[0073] With the increase in the dosage of carbon-based composites, the increase in the organic matter content in the affected soil becomes more obvious. When the mass ratio of carbon-based composites to the sample soil is 1:10, the organic matter content in the affected soil is the highest, and this research result is valid for both soil samples. When QCa@PSC-600@HA-2 is applied to the sample soil at a ratio of 1:10 (w / w), the organic matter content in the soil increases significantly within 30 days of soil incubation. After more than 45 days, the change trend of the organic matter content in the soil is not obvious. Since the organic matter content in the soil is an important indicator to measure the soil fertility, the calcium humic acid modified biochar composite can significantly increase the organic matter content in the soil in a short time, indirectly indicating that when the modified biochar is applied to the soil with degraded fertility, the improvement and repair effect can be gradually achieved in a short time.

[0074] Change in soil urease activity: The change rule of urease activity in the soil after repair in different groups is shown in Figure 8 the following figure. It can be seen from Figure 8 the figure that with the extension of soil incubation time, the change in urease activity in the control group is not obvious, while the urease activity in other groups of soil increases with the increase of repair time, but the increase amplitude of urease activity in different groups at the same time period is different. In the initial stage of soil incubation (0 - 30 days), the urease activity in the repaired soil of groups 1 - 1 and 3 - 1 increases slowly. However, when the incubation time exceeds 30 days, the increase rate of urease activity in the repaired soil of groups 2 - 5 and 4 - 5 accelerates, while the growth of urease activity in the repaired soil of group 3 - 3 is the slowest. During the whole repair process, the urease activity in the repaired soil of groups 2 - 3 and 4 - 3 has been showing a stable upward trend, and the numerical increase rate is the fastest.

[0075] Since the urease activity in the soil is closely related to the number of microorganisms in it. When the calcium humic acid modified biochar composite is applied to the soil, the biochar interacts with the microbial community in the soil, resulting in an accelerated increase rate of urease activity. Therefore, applying the calcium humic acid modified biochar composites QCa@PSC-600@HA-2 and QCa@PSC-600@HA-2 to the problematic soil can significantly increase the number of microorganisms, and then cause an accelerated increase rate of urease activity in the soil.

[0076] Change in soil sucrase activity: During the soil incubation process, the change rule of sucrase activity in the repaired soil of different groups is as shown in Figure 9 the following figure. As shown in Figure 9It can be seen that by prolonging the soil incubation time, the change in the sucrase activity in the control group is not obvious. The sucrase activities in the repaired soils of other groups all increase with the increase of the repair time. However, at the same time period, the increase amplitudes of the sucrase activities in different groups are different. In the initial stage of soil incubation (0 - 30 d), the sucrase activities in groups 1 - 1 and 3 - 1 increase slowly. However, when the incubation time exceeds 30 d, the increase rates of the sucrase activities in the repaired soils of groups 2 - 5 and 4 - 5 accelerate, while the increase rate of the sucrase activity in the repaired soil of group 3 - 3 is the slowest. During the whole repair process, the sucrase activities in the repaired soils of groups 2 - 3 and 4 - 3 are always in a stable upward trend, and the numerical increase rate is the fastest. Since the sucrase activity in the soil is closely related to the number of microorganisms in it. When the calcium humic acid modified biochar composite is applied to the soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated increase rate of the sucrase activity. Therefore, applying the calcium humic acid modified biochar composites QCa@PSC - 600@HA - 2 and QCa@PSC - 600@HA - 2 to the problematic soil can significantly increase the number of microorganisms, and further cause the increase rate of the sucrase activity in the soil to reach the fastest.

[0077] Changes in soil alkaline phosphatase activity: The change rules of the alkaline phosphatase activities in the repaired soils of different groups are as Figure 10 shown. As can be seen from Figure 10 , the change trends of the alkaline phosphatase activities in the repaired soils of different groups are different. For the soils repaired with the calcium humic acid modified biochar composite, with the increase of the soil incubation time, the alkaline phosphatase activities in the repaired soils of all groups increase with the increase of the repair time. However, at the same time period, the increase amplitudes of the alkaline phosphatase activities in the repaired soils of different groups are different. In the initial stage of soil incubation (0 - 30 d), the alkaline phosphatase activities in the repaired soils of groups 1 - 1 and 3 - 1 increase slowly. However, when the incubation time exceeds 30 d, the increase rates of the alkaline phosphatase activities in the repaired soils of groups 2 - 5 and 4 - 5 accelerate, while the increase of the alkaline phosphatase activity in the repaired soil of group 3 - 3 is the slowest. During the whole repair process, the alkaline phosphatase activities in the soils of groups 2 - 3 and 4 - 3 are always in a steady upward trend, and the numerical growth rate is the fastest.

[0078] Since the alkaline phosphatase activity in the soil is closely related to the number of its microorganisms. When the calcium humic acid modified biochar composite is applied to the test soil, the modified biochar interacts with the microbial community in the soil, resulting in an accelerated growth rate of its alkaline phosphatase activity. Therefore, applying the calcium humic acid modified biochar composites QCa@PSC - 600@HA - 2 and QCa@PSC - 600@HA - 2 to the problematic soil can cause the alkaline phosphatase activity in the soil to reach the maximum.

[0079] Changes in soil catalase activity: Different types and dosages of calcium humic acid modified biochar composites were applied to the test soil. The changing trends of catalase activity in the soil at different incubation stages after incubation are shown in Figure 11 the following figure. It can be seen from Figure 11 the figure that the changing rules of catalase activity in the repaired soil of each treatment group are different from those of urease, sucrase, and alkaline phosphatase activities in the soil. The catalase activity in the repaired soil of the control group is higher than that of other groups, and its enzyme activity basically does not change with the increase of soil incubation time. However, the catalase activity in the repaired soil of other groups shows a decreasing trend with the increase of time. In the initial stage of soil incubation (0 - 45 d), the catalase activity in the repaired soil of groups 2 - 5 and 4 - 5 decreases the fastest. After more than 45 d, the decrease in its catalase activity is not obvious, indicating that the soil repair material can reduce the catalase activity in the soil, and its reduction rate will change with the incubation time of the soil sample. Based on the above analysis, it can be known that the pH value, organic matter content, conductivity, and enzyme activity in the soil are related to the types and dosages of the added calcium humic acid modified biochar composites, and have nothing to do with the types of biomass used to prepare the biochar.

[0080] Content of available lead and cadmium in the soil after repairing the problem soil: Using soil samples No. 1 and No. 2 collected in the laboratory as research objects respectively, the effects of the types and dosages of calcium humic acid modified biochar composites on the existing effective forms and contents of lead and cadmium elements in the problem soil at different incubation time periods were studied. After applying the calcium humic acid modified biochar composite to soil sample No. 1, the available state contents and their morphological distributions of Pb and Cd elements at different time periods are shown in Table 3 and Figure 12 the following figure.

[0081] Table 3 Available state contents of Pb and Cd elements in the improved soil sample No. 1 at different time periods

[0082]

[0083] Note: 1 - 1, 1 - 3, and 1 - 5 respectively refer to the soil samples added with soil repair agent QCa@PSC - 600@HA - 1 at a ratio of 1%, 3%, and 5%. 2 - 1, 2 - 3, and 2 - 5 respectively refer to the soil samples added with soil repair agent QCa@PSC - 600@HA - 2 at a ratio of 1%, 3%, and 5%. 3 - 1, 3 - 3, and 3 - 5 respectively refer to the soil samples added with soil repair agent QCa@PSC - 600@HA - 3 at a ratio of 1%, 3%, and 5%. 4 - 1, 4 - 3, and 4 - 5 respectively represent the soil samples added with soil repair agent QCa@MDC - 600@HA - 2 at a ratio of 1%, 3%, and 5%.

[0084] As can be seen from the table, compared with the soil without the application of the biochar-based composite, after 60 days of soil incubation experiment on Soil Sample No. 1, the content of available Pb in it decreased significantly, and its content reached the lowest after 90 days of soil incubation. At the same time, the change trend of the content of available cadmium in Soil No. 1 was basically the same as that of available lead during different incubation periods. Regarding different types of calcium humic acid modified biochar composites, when QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 were respectively applied to the soil samples, their passivation effects on available Pb and Cd in the soil were better than those of other types of calcium humic acid modified biochar composites. Regarding the addition amount of the calcium humic acid modified biochar composite, increasing the dosage of the calcium humic acid modified biochar composite, the contents of available Pb and Cd in the sample soil decreased. When the addition amount of the calcium humic acid modified biochar composite reached 5% (percentage with respect to the sample soil), the contents of available Pb and Cd in it reached the lowest, basically reaching the level of the control soil sample (Soil Sample No. 3) in this study.

[0085] Content of available lead and cadmium in the soil after remediation of the problematic soil: At the end of soil incubation, the present invention analyzed the morphological distributions of Pb and Cd in the experimental soil respectively. From Figure 12 it can be seen that when different types and different proportions of calcium humic acid modified biochar composites were applied to Soil Sample No. 1, the morphological distributions of Pb and Cd in it were different.

[0086] Generally speaking, compared with the soil without the application of the calcium humic acid modified biochar composite, the content of fixed Pb in the improved sample soil No. increased significantly, while the contents of acid-soluble and exchangeable Pb in it decreased significantly. Regarding different types of calcium humic acid modified biochar composites, QCa@MDC-600@HA-2 and QCa@MDC-600@HA-2 were respectively used to adsorb and immobilize the available lead Pb in the remediated sample soil, and their passivation abilities for Pb were almost equivalent.

[0087] Regarding the different dosages of the same humic acid-modified biochar composite with calcium, during the soil incubation process, as the amount of the humic acid-modified biochar composite with calcium increases, the content of acid-soluble and exchangeable Pb in the repaired soil decreases, while the content of fixed Pb increases. When the ratio of the humic acid-modified biochar composite with calcium to the sample soil is 1:10, the contents of acid-soluble and exchangeable Pb and fixed Pb in the repaired soil are 18.59% and 46.83% respectively. Compared with the corresponding values of the soil repaired without using the humic acid-modified biochar composite with calcium, the two are decreased by 25.87% and increased by 25.97% respectively. In addition, the influence of the humic acid-modified biochar composite with calcium on the Cd form in the repaired soil is similar to that of the Pb form. Therefore, for the soil sample repaired by the humic acid-modified biochar composite with calcium, the content of fixed Cd in it has increased by 21.89% compared with the soil before repair. Applying the humic acid-modified biochar composite with calcium to soil sample No. 2, the available content and its form distribution of Pb and Cd elements at different time periods are shown in Table 4 and Figure 13 as follows.

[0088] As can be seen from Table 4, at the initial stage of soil incubation, the change trend of the available Pb content in the soil is relatively similar to that of the available Cd content, and both show varying degrees of decrease. However, when the soil incubation time exceeds 60 days, the decreasing trends of the available Pb content and the available Cd content in the soil are not obvious, and these values reach the lowest after 90 days of soil incubation. The reason for this phenomenon is that when the humic acid-modified biochar composite with calcium acts on the lead and cadmium contaminated soil, the adsorption sites on the surface of the modified biochar are basically occupied by lead and cadmium. In addition, when the humic acid-modified biochar composite with calcium acts on soil sample No. 2, the influence it has on the available lead and cadmium content in the soil is similar to that of soil sample No. 1, and this result is also consistent with the research conclusions on the pH value, organic matter content, electrical conductivity and various enzyme activities in the repaired soil, which further confirms that the humic acid-modified biochar composite with calcium has potential market promotion prospects in the treatment of farmland suffering from soil compaction and lead and cadmium pollution.

[0089] Table 4 Available content of Pb and Cd elements in improved soil sample No. 2 at different time periods

[0090]

[0091] Note: 1-1, 1-3, and 1-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-1 at ratios of 1%, 3%, and 5% respectively; 2-1, 2-3, and 2-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-2 at ratios of 1%, 3%, and 5% respectively; 3-1, 3-3, and 3-5 refer to soil samples added with soil remediation agent QCa@PSC-600@HA-3 at ratios of 1%, 3%, and 5% respectively; 4-1, 4-3, and 4-5 refer to soil samples added with soil remediation agent QCa@MDC-600@HA-2 at ratios of 1%, 3%, and 5% respectively.

[0092] Figure 13 It shows the morphological distribution and content change rules of cadmium elements at the end of soil incubation. By comparing the contents of fixed lead and fixed cadmium in the repaired soils of different groups, it can be seen that the content of fixed Cd is slightly lower than that of fixed Pb, indicating that the passivation effect of the calcium humic acid modified biochar composite material on available lead in the soil is better than that on available cadmium. This may be due to the hydrolysis constant of Pb(II) being lower than that of Cd(II), and it is more easily fixed by the modified biochar through ion exchange.

[0093] From Figure 13 it can also be seen that when different types and ratios of calcium humic acid modified biochar composite materials are applied to sample soil No. 2, there are slight differences in the contents of various forms of Pb and various forms of Cd. Generally speaking, compared with the soil without the application of calcium humic acid modified biochar composite material, the content of fixed Cd in the improved sample soil No. 2 increases significantly, while the content of acid-soluble and exchangeable Cd decreases significantly. For different types of calcium humic acid modified biochar composite materials, QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 are used to adsorb and immobilize available Cd in the repaired sample soil respectively, and their passivation abilities for Cd are almost the same.

[0094] Regarding different dosages of the same type of calcium humic acid modified biochar composite material, during the soil incubation process, as the dosage of the calcium humic acid modified biochar composite material increases, the content of acid-soluble and exchangeable Cd in the repaired soil decreases, while the content of fixed Cd increases. When the ratio of the calcium humic acid modified biochar composite material to the sample soil is set to 1:10 (W / W), the contents of acid-soluble and exchangeable Cd and fixed Cd in the repaired soil are 11.23% and 38.82% respectively. Compared with the corresponding values of the soil without the application of the biochar-based composite material, the two are reduced by 18.63% and increased by 21.48% respectively.

[0095] Based on the above analysis, it can be seen that there are obvious differences in the contents of various forms of Pb and various forms of Cd in the two tested soil samples. This may be related to the differences in the initial concentrations of lead and cadmium in the sample soil and the competitive adsorption between heavy metal elements on the surface of the modified biochar. Since the effects of the calcium humic acid modified biochar composites QCa@PSC-600@HA-2 and QCa@MDC-600@HA-2 on the physical and chemical properties, available lead and cadmium contents and their morphological distributions in the repaired soil are consistent, in order to avoid a lot of useless work and simplify the workload, the calcium humic acid modified biochar composites QCa@PSC-600@HA-1, QCa@PSC-600@HA-2 and QCa@PSC-600@HA-3 are determined to be used as soil repair agents for the subsequent bioavailability experiments of soil samples.

[0096] Bioavailability evaluation of improved soil

[0097] According to the conclusions drawn from the aforementioned experiments, applying the calcium humic acid modified biochar composite to the problematic soil can not only increase the pH value, organic matter content and electrical conductivity of the acidified soil, but also improve the activities of urease, sucrase and alkaline phosphatase in the soil. In order to further evaluate the production quality of the calcium humic acid modified biochar composite for repairing the sample soil, an experiment on Chinese cabbage varieties was carried out in the on-campus greenhouse.

[0098] Three different calcium humic acid modified biochar composites (QCa@PSC-600@HA-1, QCa@PSC-600@HA-2 and QCa@PSC-600@HA-3) were used in the experiment. Their mixing mass ratios with the sample soil were 1:5, 1:10 and 1:15 respectively, and the soil without adding the calcium humic acid modified biochar composite was selected for comparison. Based on the growth trend and quality indexes of Chinese cabbage in the pot experiment, the repair ability of the prepared calcium humic acid modified biochar composite to the selected problematic soil was evaluated, and the contents and morphological distributions of available Pb and available Cd in the sample soil and Chinese cabbage plants were studied respectively.

[0099] The two problematic soils collected were used as the research objects in the experiment. By applying different types and concentrations of the calcium humic acid modified biochar composite to them and planting Chinese cabbage on them, the growth of Chinese cabbage, the physical and chemical properties of the soil and the heavy metal contents in them were observed. The detailed experimental steps are described as follows:

[0100] The calcium humic acid modified biochar composite was mixed with the sample soil at ratios of 1:5 (w / w), 1:10 (w / w), and 1:15 (w / w), respectively, and then filled into flower pots. The carefully selected pakchoi seeds were evenly sown into each flower pot, with 18 pakchoi seeds sown in each pot experiment. Before the seeds germinated, water was poured once every other day. After the seeds germinated, water was poured once a day, and it was ensured that the soil in the pakchoi pots remained moist, and the germination rate of the pakchoi seeds was observed regularly. Thinning of the pakchoi was started 16 days after sowing. After the pakchoi grew for 36 days, the pakchoi was pulled out from the planted pakchoi pots, and the growth indexes of the pakchoi plants in each group of pots were observed.

[0101] Two small plots of land were found in the on-campus greenhouse, and the external sampled soil was simulated respectively. With the calcium humic acid modified biochar composite QCa@PSC-600@HA-2 as the soil remediation agent, it was mixed and incubated with two kinds of simulated soils (soil sample No. 1 and soil sample No. 2) at a mass ratio of 1:10 respectively. After 90 days, pakchoi was planted on them respectively. After the pakchoi grew for 30 days, the growth status of the pakchoi was observed and the heavy metal contents in the soil and pakchoi plants were determined.

[0102] By conducting a pakchoi planting experiment in the greenhouse and dynamically monitoring the growth indexes (germination rate, fresh and dry weights of plants, plant height) and quality indexes (chlorophyll, soluble protein, and soluble sugar) of pakchoi planted in the soil incubated with the calcium humic acid modified biochar composite, the effect of the soil remediation agent on the growth status of pakchoi was studied.

[0103] Effect on the growth of pakchoi: Figure 14 These are the physical pictures of pakchoi planted in the soil before and after being repaired by the selected calcium humic acid modified biochar composite. From Figure 14 it can be seen that overall, compared with the pakchoi plants planted in the soil without the calcium humic acid modified biochar composite repair, the pakchoi plants in the soil with the calcium humic acid modified biochar composite have better growth; and when the same type and concentration of calcium humic acid modified biochar composite are applied to soil sample No. 1 and soil sample No. 2 respectively, the growth of the planted pakchoi plants is better. For different types of calcium humic acid modified biochar composites, QCa@PSC-600@HA-2 as the soil remediation agent is better than QCa@PSC-600@HA-1 and QCa@PSC-600@HA-3 in terms of the plant height and leaf greenness of pakchoi.

[0104] This indicates that during the preparation of modified biochar, an appropriate amount of HA is beneficial for the biochar surface to immobilize more oxygen-containing groups; moreover, as the dosage of the soil conditioner increases, the heights of the pakchoi plants in the repaired soil samples No. 1 and No. 2 both increase. This shows that in the soil applied with the calcium humic acid modified biochar composite, both the modified biochar and the humic acid on its surface contribute to improving the soil air permeability, electrical conductivity and organic matter content, thereby alleviating the soil compaction degree and promoting the growth of pakchoi.

[0105] The biological trait parameters of pakchoi (such as germination rate, plant fresh weight, plant dry weight, plant height, etc.) can reflect its growth status. Table 5 lists the biological trait parameters of pakchoi in the soil repaired by different soil conditioners.

[0106] The changes in the soil environment can directly affect plant growth. Table 5 lists the biological trait parameters of pakchoi after 36 days of planting. It can be seen from the table that compared with the soil without the calcium humic acid modified biochar composite, the germination rate of pakchoi in the soil repaired by the calcium humic acid modified biochar composite has increased significantly. For different types of calcium humic acid modified biochar composites, when adding QCa@PSC-600@HA-2 to the test soil at a ratio of 1:10 (w / w), the germination rate of pakchoi planted on it is relatively high, followed by the pakchoi planted in the soil treated with QCa@PSC-600@HA-3 at the same ratio. Regarding the dosage of the same type of calcium humic acid modified biochar composite, when applying the calcium humic acid modified biochar composite to the test soil at a mass ratio of 1:10, the germination rate of pakchoi is relatively high; when the mass ratio of the two decreases to 1:15, the germination rate of pakchoi in the repaired soil is relatively low, indicating that the dosage of the soil conditioner has a significant impact on improving the fertilizer efficiency of degraded soil.

[0107] Table 5 Biological trait parameters of pakchoi

[0108]

[0109] Note: 1-1, 2-1, and 3-1 were prepared by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:5 (w / w), respectively; 2-1, 2-2, and 2-3 were prepared by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:10 (w / w), respectively; 3-1, 3-2, and 3-3 were prepared by adding QCa@PSC-600@HA-1, QCa@PSC-600@HA-2, and QCa@PSC-600@HA-3 to the test soil No. 1 at a ratio of 1:15 (w / w), respectively.

[0110] In addition, compared with the unamended test soil, the fresh weight, dry weight, and plant height of pakchoi grown in the amended test soil increased. For different types of calcium humic acid modified biochar composites, when QCa@PSC-600@HA-2 was added to the test soil at a ratio of 1:10 (w / w), the increases in the fresh weight, dry weight, and plant height of pakchoi reached 99.6%, 113.8%, and 146.1%, respectively. The increases in the fresh weight, dry weight, and plant height of pakchoi in the soil treated with QCa@PSC-600@HA-1 were relatively small. Regarding the dosage of the same type of calcium humic acid modified biochar composite, the highest increases in the fresh weight, dry weight, and plant height of pakchoi were observed in the soil treated with the carbon-based composite at a mass ratio of 1:10, while the smallest increases were found in the soil treated with the repair agent at a mass ratio of 1:5. This result was the same as that of the pakchoi germination rate.

[0111] In addition, the ability of the calcium humic acid modified biochar composite to improve the test soil No. 2 was almost the same as that of the test soil No. 1, indicating the universality of the developed calcium humic acid modified biochar composite in improving problem soils.

[0112] Effect on the quality of pakchoi: To further explore the remediation effect of the calcium humic acid modified biochar composite on compacted and heavy metal contaminated soils, the physiological and biochemical indexes of pakchoi in the remediated soil (such as chlorophyll, soluble sugar, and protein) were measured to indirectly reflect the improvement ability of the calcium humic acid modified biochar composite on problem soils. The relevant test results are shown in Figure 15 、 Figure 16 and Figure 17 as shown. The chlorophyll contents of pakchoi in the soils remediated with different concentrations and different types of calcium humic acid modified biochar composites are shown in Figure 15As shown in the figure. It can be seen from the figure that in the pakchoi planting experiment with soil sample No. 1, compared with the pakchoi planted in the soil without applying the biochar-based composite material, the chlorophyll content in the leaves of pakchoi in the improved soil has increased, and the increase rate is as high as 124.68%.

[0113] Regarding different types of calcium humic acid modified biochar composites, the chlorophyll content in pakchoi in the soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the chlorophyll content of pakchoi in the soil treated with the same type of calcium humic acid modified biochar composite at different dosages, it is found that the chlorophyll content increases with the increase in the dosage of the modified biochar. The change law of the chlorophyll content obtained from the pakchoi planting experiment with soil sample No. 1 is consistent with that of the pakchoi planting experiment with soil sample No. 2. Of course, during the soil remediation process, the dosage of the calcium humic acid modified biochar composite is not the more the better, and this phenomenon has been verified in the determination of the chlorophyll content of pakchoi in both soil samples. When the mass ratio of the biochar-based composite material to the sample soil is 1:10, the chlorophyll content of pakchoi in the improved soil reaches the maximum. At this time, the chlorophyll contents of pakchoi in soil sample No. 1 and soil sample No. 2 are 2.53 mg / g and 2.62 mg / g respectively.

[0114] Effect on the soluble protein content in pakchoi plants: Among them, the soluble protein content of pakchoi in the soil treated with different concentrations and different types of calcium humic acid modified biochar composites is shown in Figure 16 as shown. From Figure 16 it can be seen that in the pakchoi planting experiment with soil sample No. 1, compared with the pakchoi in the soil without applying the calcium humic acid modified biochar composite, the soluble protein content in the leaves of pakchoi in the improved soil has increased, and the increase rate is as high as 32.87%. Regarding different types of calcium humic acid modified biochar composites, the soluble protein content of pakchoi in the soil modified by QCa@PSC-600@HA-2 is higher than that of other types. By comparing the soluble protein content of pakchoi in the repaired soil with the same type of calcium humic acid modified biochar composite at different dosages, it is found that the soluble protein content can increase with the increase in the dosage of the modified biochar. The change law of the soluble protein content obtained from the pakchoi planting experiment with soil sample No. 1 is consistent with that of the pakchoi planting experiment with soil sample No. 2. Of course, during the soil remediation process, the dosage of the calcium humic acid modified biochar composite is not the more the better, and this phenomenon has been verified in the determination of the soluble protein content of pakchoi in both soil samples. When the mass ratio of the calcium humic acid modified biochar composite to the sample soil is 1:10, the soluble protein content of pakchoi planted in the improved soil is the highest, and the chlorophyll contents of pakchoi in soil sample No. 1 and No. 2 are 27.69 mg / g and 28.92 mg / g respectively.

[0115] Effect on the soluble sugar content in pakchoi plants: The soluble sugar contents of pakchoi in soils repaired with calcium humic acid modified biochar composites at different concentrations and of different types are shown in Figure 17 the following. It can be seen from Figure 17 this that generally speaking, in the pakchoi planting experiment in soil sample No. 1, the calcium humic acid modified biochar composite has little correlation with the soluble sugar content of pakchoi in the repaired soil. For the test soils treated with calcium humic acid modified biochar composites of the same dose and different types, there is no regularity in the soluble sugar content of pakchoi planted on them. However, when comparing the test soils treated with calcium humic acid modified biochar composites of the same type and different dosages, the changes in the soluble sugar content in the harvested pakchoi leaves basically do not show regularity. Moreover, in soil sample No. 1 and soil sample No. 2 treated with calcium humic acid modified biochar composites of the same type and the same dose respectively, the soluble sugar contents of the planted pakchoi are not very different, indicating that the soluble sugar content in plants is not only affected by the nutrients in the soil, but also the growth environment will have a great impact on its soluble sugar content.

[0116] Content and morphological distribution of available lead and cadmium in soil after pakchoi maturation: Given that no heavy metals were detected in the pakchoi planted in two small simulated field soils in the school greenhouse, the experiment also measured the content and morphological distribution of available lead and cadmium in the soils of the simulated plots before and after applying the soil remediation agent. The relevant test results are shown in Table 7 and Figure 18 the following. The contents of available lead and cadmium in the soil of the simulated plot after 90 days of repair with the calcium humic acid modified biochar composite QCa@PSC-600@HA-2, before and after pakchoi harvesting, are listed in Table 6.

[0117] Table 6 Contents of available Pb and available Cd in soil before and after pakchoi planting

[0118]

[0119] It can be seen from Table 6 that when pakchoi is planted in soil sample No. 1 repaired with the calcium humic acid modified biochar composite, comparing the available Pb content in the soil before and after pakchoi planting, the numerical changes are not obvious, indicating that the available lead in the soil has not been transferred to the pakchoi plants. The reason for this phenomenon is that when the calcium humic acid modified biochar composite is applied to the test soil, the polar oxygen-containing groups on the biochar surface may adsorb and complex with some heavy metals in the soil, thereby achieving the purpose of passivating heavy metals. Moreover, PO4 3- and CO3 2-Oxyacid root ions such as etc. may also react with lead and cadmium ions to form precipitates.

[0120] In addition, the difference in the available Cd content in the soil before and after the planting and harvesting of pakchoi is not significant, indicating that the available Cd in the soil has not been transferred to the pakchoi plants. In addition, pakchoi was planted in soil samples No. 1 and No. 2 after being repaired with the biochar-based composite material. The difference in the available lead content in the soil before and after sowing is not significant. Since no available lead and available cadmium were detected in the harvested pakchoi plants in this study, the accuracy of the experimental results was verified. Pakchoi was planted in soil sample No. 1 repaired with the calcium humic acid modified biochar composite material, and the morphological distributions of Pb (or / and Cd) in the soil before and after the planting of pakchoi were measured respectively. The relevant results are shown in Figure 18 as follows.

[0121] From Figure 18 it can be seen that for soil sample No. 1 repaired with the calcium humic acid modified biochar composite material, comparing the content of fixed Pb in the soil before and after the sowing of pakchoi, the change is not significant, and the difference in the content of other forms of Pb (such as acid-soluble and exchangeable Pb, oxidized Pb and reduced Pb) is not obvious. At the same time, the difference in the content of each form of Cd in the soil before and after the sowing of pakchoi is not significant. In summary, during the growth of pakchoi, the available lead and available cadmium in the soil have not been transferred to the pakchoi plants. In addition, when pakchoi was planted in soil sample No. 2 repaired with the calcium humic acid modified biochar composite material, the content of available lead and cadmium in the soil before and after the sowing of pakchoi did not change significantly.

[0122] Analysis of the mechanism of action of the calcium humic acid modified biochar composite material in repairing compacted and heavy metal contaminated soil: When the calcium humic acid modified biochar composite material is applied to farmland suffering from soil compaction and heavy metal pollution, there are interactions between the biochar and the anions, cations, heavy metals, microorganisms, etc. in the soil. When the calcium humic acid modified biochar composite material enters the heavy metal contaminated soil, the negative charges and polar oxygen-containing functional groups on its surface respectively have electrostatic adsorption effects on the positively charged lead ions and cadmium ions. And a large number of inorganic mineral ions (such as Ca 2+ ) and oxygen-containing anions are contained on the surface of the calcium modified biochar, and they can all undergo ion exchange reactions with heavy metal ions (such as lead and cadmium) in the soil, thereby inhibiting the migration and transfer of heavy metal ions in the soil.

[0123] Meanwhile, the surface of humic acid-modified biochar contains a large number of polar oxygen-containing groups (such as hydroxyl, carboxyl, carbonyl, etc.), which can achieve the purpose of immobilization by oxidizing heavy metals such as lead and cadmium. In addition, biochar with a high specific surface area and a developed pore structure has more adsorption sites on its surface or in the pores, and can fix heavy metals on the surface or inside the pores of biochar through intermolecular forces, thereby achieving the effect of passivating heavy metals. When humic acid-modified calcium-modified biochar acts on compacted soil, the abundant oxygen-containing groups on its surface increase the soil pH value, while also increasing the organic matter content and decreasing the electrical conductivity in the soil. The introduction of biochar changes the microbial community structure in the soil, increasing the activities of urease, sucrase, and alkaline phosphatase in the soil, and thus achieving the purpose of soil carbon sequestration and stabilizing nitrogen and phosphorus contents. In addition, the surface of biochar prepared from waste mushroom stick residues contains a large number of inorganic mineral ions. When it enters the soil, it improves the cation exchange capacity in the soil and enhances the water holding capacity of the soil, reducing the compactness of the soil.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that: it is still possible to modify the specific implementation manners of the present invention or perform equivalent replacements on some technical features; without departing from the spirit of the technical solutions of the present invention, they should all be covered within the scope of the technical solutions claimed by the present invention.

Claims

1. A preparation method of a calcium humic acid modified biochar composite material, comprising the following steps: Step 1. Prepare calcium-modified biochar powder using biochar powder and a calcium source, where the specific surface area of the biochar powder is 35 m 2 / g to 43 m 2 / g, and the pore volume is 0.045 cm 3 / g to 0.090 cm 3 / g; Step 2: Mix humic acid with the calcium modified biochar powder, and obtain the calcium humic acid modified biochar composite material after filtration and drying; wherein, the mass ratio of the humic acid to the calcium modified biochar powder is 1:(2-20).

2. The preparation method of the calcium humic acid modified biochar composite material according to claim 1, characterized in that: The specific steps of Step 1 include transferring the biochar powder into a calcium chloride solution for mixing, and obtaining the calcium modified biochar powder after filtration, drying, grinding and sieving.

3. The preparation method of the calcium humic acid modified biochar composite material according to claim 1, characterized in that: The specific steps of Step 1 include mixing the carbonized eggshell powder with the biochar powder, and obtaining the calcium modified biochar powder after ball milling, drying and calcination.

4. The preparation method of the calcium humic acid modified biochar composite material according to claim 1 or 2 or 3, characterized in that: The biochar powder is obtained by carbonizing agricultural waste after alkali washing to remove lignin.

5. The preparation method of the calcium humic acid modified biochar composite according to claim 4, characterized in that: The temperature of the carbonization treatment is 400 °C to 800 °C, the heating rate is 3 °C / min to 8 °C / min, and the carbonization time is 1 h to 3 h.

6. The preparation method of the calcium humic acid modified biochar composite material according to claim 4, characterized in that: The agricultural waste is mushroom stick residue, peanut shell or wood chip.

7. A calcium humic acid modified biochar composite material, characterized in that, The composite material is obtained by the preparation method according to any one of claims 1 to 6.

8. An application of a calcium humic acid modified biochar composite material as a soil repair agent in soil repair.

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