Composition for repairing heavy metal polluted alkaline soil and application thereof, and method for repairing heavy metal polluted alkaline soil

Abstract

The present invention belongs to the technical field of contaminated soil treatment, and specifically relates to a composition for repairing heavy metal-contaminated alkaline soil, its application, and a method for repairing heavy metal-contaminated alkaline soil. Hydroxyapatite and humic acid in the present invention can reduce active heavy metals in alkaline soil, reduce the toxic effects of heavy metals on giant fungus grass, and increase the biomass of giant fungus grass. Hydroxyapatite combined with humic acid and giant fungus grass treatment has no obvious effect on the pH value and conductivity of alkaline soil, while increasing the organic matter in alkaline soil and reducing the available phosphorus, which is beneficial to improving soil fertility. There is no risk of secondary pollution caused by exogenous phosphorus, showing a certain degree of environmental friendliness. The presence of giant fungus grass can also increase the number of alkaline soil microorganisms, enrich the diversity of soil microbial communities, and promote the improvement of the ecological environment of alkaline soil.

Description

Technical Field

[0001] The invention belongs to the technical field of contaminated soil treatment, and specifically relates to a composition for repairing heavy metal contaminated alkaline soil and an application thereof, and a method for repairing heavy metal contaminated alkaline soil. Background Art

[0002] In-situ passivation remediation is an economically effective way to treat heavy metal pollution in farmland. Compared with other remediation methods, in-situ passivation remediation has the advantages of strong operability, low cost, quick results and less disturbance to the pollution site, but it may also have the risk of reactivation of pollutants. At present, the commonly used in-situ passivators are usually single passivators, such as lime and phosphorus-based materials. Lime is considered to be a common substance for treating soil Cd pollution. However, excessive application of lime will lead to soil calcification, causing soil compaction and reducing crop yields; excessive application of phosphorus-based materials may cause secondary phosphorus pollution and cause eutrophication of surrounding groundwater and rivers. In addition, single passivation agent treatment is often only effective for one heavy metal, and its application amount is usually large or needs to be applied repeatedly, which may cause damage to the soil structure, cause plant nutrient deficiency, and increase the risk of surface and groundwater pollution. Summary of the invention

[0003] In view of this, the purpose of the present invention is to provide a composition for repairing heavy metal contaminated alkaline soil and its application, and a method for repairing heavy metal contaminated alkaline soil. The hydroxyapatite and humic acid in the composition provided by the present invention can reduce the active state proportion of various heavy metals in the soil, increase the number of soil microorganisms, enrich the diversity of soil microbial communities, and at the same time reduce the risk of secondary pollution caused by exogenous phosphorus in hydroxyapatite.

[0004] In order to achieve the above object, the present invention provides the following technical solutions:

[0005] The invention provides a composition for repairing alkaline soil polluted by heavy metals, comprising hydroxyapatite, humic acid and giant fungus grass.

[0006] Preferably, the ratio of the mass of hydroxyapatite, the mass of humic acid and the number of giant fungus grass plants is (7.2-10.2) kg: (3.6-5.6) kg: (4-20) plants.

[0007] The present invention also provides the use of the composition described in the above technical solution in in-situ repair of heavy metal-contaminated alkaline soil.

[0008] Preferably, the heavy metal includes one or more of Cd, Pb, Cu and Zn.

[0009] The present invention also provides a method for repairing heavy metal-contaminated alkaline soil, comprising the following steps:

[0010] Hydroxyapatite and humic acid are applied to the tillage layer of alkaline soil contaminated by heavy metals, and giant fungus grass is planted on the tillage layer for restoration.

[0011] Preferably, the depth of the tillage layer is 5 to 30 cm.

[0012] Preferably, the mass of the hydroxyapatite is 0.1-2% of the total mass of the cultivated layer soil.

[0013] Preferably, the mass of the humic acid is 0.1-2% of the total mass of the cultivated layer soil.

[0014] Preferably, based on the area of ​​the heavy metal-contaminated alkaline soil, the planting amount of the giant fungus grass is 4 to 20 plants / m 2 .

[0015] Preferably, the repairing time is 30 to 300 days.

[0016] The present invention provides a composition for repairing heavy metal-contaminated alkaline soil, comprising hydroxyapatite, humic acid and giant fungus grass. The surface of the hydroxyapatite contains PO4 3- , Ca 2+ OH - Substances such as PO4 3- Easy to use with Pb 2+ Formation of phosphate rock precipitation, Cd 2+ With Ca 2+ Prone to isostructural substitution and OH - Formation of Cd(OH) 2 precipitation; the surface of humic acid contains rich functional groups, and functional groups such as carboxyl and phenolic hydroxyl groups also have strong binding ability to Cu, Zn, Cd, and Pb. Therefore, hydroxyapatite and humic acid can significantly reduce the acid-soluble content of heavy metals in the soil, and convert heavy metals from a highly active state to a stable state; and giant fungus grass has a significant absorption effect on heavy metals in the soil. Hydroxyapatite and humic acid can reduce the toxic effects of heavy metals on giant fungus grass, reduce the antioxidant stress response of giant fungus grass, and increase the content of chlorophyll a, b and total chlorophyll in giant fungus grass, which is beneficial to the light energy capture and conversion of giant fungus grass, promote the production and development of giant fungus grass, and thus increase the biomass of giant fungus grass. Giant fungus grass can produce root secretions such as organic acids, which increase the content of organic matter in the soil. In addition, the growth of giant fungus grass will absorb phosphorus, thereby reducing the available phosphorus in the soil. Under the combined action of giant fungus grass, hydroxyapatite combined with humic acid can increase soil organic matter and reduce available phosphorus. At the same time, it has no obvious effect on the pH value and conductivity of alkaline soil, which is beneficial to improving soil fertility. There is no risk of secondary pollution caused by exogenous phosphorus, and it shows a certain degree of environmental friendliness. Giant fungus grass can also increase the number of soil microorganisms, enrich the diversity of soil microbial communities, and promote the improvement of soil ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The graphs are the trend of the chemical forms of Cd in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 with different treatments;

[0018] Figure 2 The graphs are trend diagrams of the chemical forms of Pb in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 with different treatments;

[0019] Figure 3 The graphs are the trend of the chemical forms of Cu in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 with different treatments;

[0020] Figure 4 The graphs are the trend of the chemical forms of Zn in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 with different treatments;

[0021] Figure 5 The Cd content of the aboveground and underground parts of the giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0022] Figure 6 The graphs of Pb content in the aboveground and underground parts of the giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0023] Figure 7 The Cu content diagram of the aboveground and underground parts of the giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0024] Figure 8 It is a graph of Zn content in the aboveground and underground parts of giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0025] Fig. 9 The transport coefficient and enrichment coefficient of heavy metals under the action of single giant fungus grass in comparative example 1;

[0026] Fig.10 The figure is the transport coefficient and enrichment coefficient of heavy metals in giant grass under the action of hydroxyapatite and humic acid in comparative example 3;

[0027] Fig.11 The transport coefficient and enrichment coefficient of heavy metal Cd in giant fungus grass in Examples 1 to 3 and Comparative Examples 2 to 6 are shown;

[0028] Fig.12 The pH and EC diagrams of the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0029] Fig.13 Graph showing the available phosphorus content in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0030] Fig.14 It is a graph of organic matter content in soil samples of Examples 1 to 3 and Comparative Examples 1 to 6;

[0031] Fig.15 The graph is a graph showing the changes in the number of bacterial species in the soil samples of Example 3, Comparative Examples 1, 2 and 6;

[0032] Fig.16 The bacterial community composition and abundance change diagram in the soil samples of Example 3 and Comparative Examples 1, 2 and 6. DETAILED DESCRIPTION

[0033] The invention provides a composition for repairing alkaline soil polluted by heavy metals, comprising hydroxyapatite, humic acid and giant fungus grass.

[0034] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products known to those skilled in the art may be used.

[0035] In the present invention, the ratio of the mass of hydroxyapatite, the mass of humic acid and the number of giant grass plants is preferably (7.2-10.2) kg: (3.6-5.6) kg: (4-20) plants.

[0036] The present invention also provides the use of the composition described in the above technical solution in in-situ repair of heavy metal-contaminated alkaline soil.

[0037] In the present invention, the heavy metal preferably includes one or more of Cd, Pb, Cu and Zn, and more preferably Cd, Pb, Cu and Zn. When the heavy metal is the above-mentioned heavy metals, the present invention has no special restrictions on the ratio of different types of heavy metals, and any ratio can be used; the pH value of the heavy metal-contaminated alkaline soil is preferably 7.5 to 9, and more preferably 8 to 8.5.

[0038] The present invention also provides a method for repairing heavy metal-contaminated alkaline soil, comprising the following steps:

[0039] Hydroxyapatite and humic acid are applied to the tillage layer of alkaline soil contaminated by heavy metals, and giant fungus grass is planted on the tillage layer for restoration.

[0040] The invention applies hydroxyapatite and humic acid to the tillage layer of the alkaline soil polluted by heavy metals and mixes them evenly.

[0041] In the present invention, the depth of the cultivated layer of soil is preferably 5 to 30 cm, more preferably 10 to 30 cm, and most preferably 15 to 25 cm; the cultivated layer of soil preferably refers to the soil extending downward from the soil surface as 0 cm.

[0042] In the present invention, the mass of the hydroxyapatite is preferably 0.1-2% of the total mass of the cultivated layer soil, and more preferably 0.5-2%.

[0043] In the present invention, the mass of the humic acid is preferably 0.1-2% of the total mass of the cultivated layer soil, and more preferably 0.5-2%.

[0044] The present invention has no particular limitation on the application and mixing process, and any application and mixing process known in the art may be used.

[0045] The surface of hydroxyapatite in the present invention contains PO4 3- , Ca 2+ OH - Substances such as PO4 3- Easy to use with Pb 2+ Formation of phosphate rock precipitation, Cd 2+ With Ca 2+ Prone to isostructural substitution and OH - Formation of Cd(OH) 2 precipitation; the surface of humic acid contains rich functional groups, and functional groups such as carboxyl and phenolic hydroxyl groups also have strong binding ability to Cu, Zn, Cd, and Pb. Therefore, hydroxyapatite and humic acid can significantly reduce the acid-soluble content of heavy metals in the soil, and convert heavy metals from a highly active state to a stable state; and giant fungus grass has a significant absorption effect on heavy metals in the soil. Hydroxyapatite and humic acid can reduce the toxic effects of heavy metals on giant fungus grass, reduce the antioxidant stress response of giant fungus grass, and increase the content of chlorophyll a, b and total chlorophyll in giant fungus grass, which is beneficial to the light energy capture and conversion of giant fungus grass, promote the production and development of giant fungus grass, and thus increase the biomass of giant fungus grass.

[0046] After the mixing is completed, the present invention plants giant fungus grass on the tillage layer for repair.

[0047] In the present invention, the planting method of the giant fungus grass is preferably transplanting seedlings; based on the area of ​​the heavy metal-contaminated alkaline soil, the planting amount of the giant fungus grass is preferably 4 to 20 plants / m 2 , more preferably 9 to 15 plants / m 2 .

[0048] In the present invention, the repairing time is preferably 30 to 300 days, more preferably 30 to 180 days.

[0049] The present invention has no particular limitation on the planting process, and any planting process known in the art may be used.

[0050] Giant fungus grass is a high-yield, high-quality fungus grass. Its salt-alkali resistance, heavy metal resistance, and drought resistance make it highly adaptable, so it is widely planted in arid and desert areas. Giant fungus grass can accelerate microbial reproduction and has a certain effect on the number of soil microorganisms, which is beneficial to improving the ecological environment of the soil and curbing soil degradation. Through the joint repair of Cu and Cd-contaminated alkaline soils by hydroxyapatite and plants, it was found that compared with hyperaccumulators such as Elsholtzia haizhouensis and Sedum commensalata, giant fungus grass showed better advantages due to its large biomass. Giant fungus grass can produce root secretions such as organic acids, increase the content of organic matter in the soil, and the growth of giant fungus grass will absorb phosphorus, thereby reducing the effective phosphorus in the soil. At the same time, it has no obvious effect on the pH value and conductivity of alkaline soil, which is beneficial to improve soil fertility. There is no risk of secondary pollution caused by exogenous phosphorus, and it has a certain degree of environmental friendliness. Giant fungus grass can also increase the number of soil microorganisms, enrich the diversity of soil microbial communities, and promote the improvement of soil ecological environment.

[0051] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention.

[0052] Examples and Comparative Examples

[0053] In an area of ​​0.1m 2 , the soil in the area with a depth of 30 cm was excavated and piled on the plastic film to be fully mixed to form a soil with uniform texture, and then 10 kg of soil was weighed respectively, and hydroxyapatite and humic acid were added according to the mass ratio of soil according to Table 1. After mixing, it was backfilled in each area with an impermeable membrane on all sides, and then one giant fungus grass seedling of similar size was uniformly planted in each area T0~T7, and a field cultivation experiment lasting 30 days was carried out. During the period, watering was carried out uniformly according to the degree of soil drought, and the same amount of compound fertilizer was uniformly applied according to the optimal fertilization amount of farmland soil. The specific masses of hydroxyapatite and humic acid are shown in Table 1.

[0054] Table 1 Treatment settings of Examples 1 to 3 and Comparative Examples 1 to 6

[0055]

[0056] Sample collection and pretreatment

[0057] The giant fungus grass in each area of ​​Examples 1 to 3 and Comparative Examples 1 to 6 was destructively collected. At the same time, the soil in each area was collected in triplicate, bagged, numbered, and brought back to the laboratory.

[0058] After cleaning, the giant fungus grass is divided into above-ground and underground parts. After weighing the fresh weight of each part, it is placed in an oven at 101°C for two hours, then dried at 71°C to constant weight and crushed for later use.

[0059] The soil samples were placed in a ventilated place to dry naturally for 2 to 3 days, and then sieved with a 2 mm sieve and a 0.11 mm sieve, respectively, and numbered and bagged for testing. The basic physical and chemical properties of the original soil are shown in Table 2.

[0060] Table 2 Basic physical and chemical properties of soil

[0061]

[0062] Performance Testing

[0063] 1) Effects of hydroxyapatite and humic acid on the distribution of heavy metal forms in soil

[0064] The soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 were tested for soil metal morphology, and the results are shown in 1 to 4, where Figure 1 The changing trends of Cd chemical forms under different treatments are shown in Figure 2. Figure 2 The change trend of each chemical form of Pb with different treatments is shown in Figure 2. Figure 3 The changing trends of Cu chemical forms with different treatments are shown in Figure 2. Figure 4 The changing trends of various chemical forms of Zn with different treatments.

[0065] Depend on Figure 1It can be seen that under the condition of planting giant fungus grass, different treatments of hydroxyapatite and humic acid have different degrees of influence on the distribution of chemical forms of soil Cd. The main manifestation of each treatment soil is that the weak acid extractable Cd decreases, and the oxidizable and residual Cd increases. The weak acid extractable, oxidizable, reducible and residual states of Cd in CK soil account for 18.9%, 13.08%, 2.03% and 21.99% respectively. It can be seen that the active Cd in the soil accounts for a large proportion, which is easy to migrate or be absorbed by plants, thereby endangering human health. After hydroxyapatite and humic acid (T1-T7) treatment, the Cd in the soil is mainly converted from the weak acid extractable state to the oxidizable state, and the conversion trend increases with the increase in the amount of addition. The percentage of weak acid extractable Cd is reduced by 4.63%, 8.37% and 18.19% respectively compared with CK, and the oxidizable Cd is increased by 7.01%, 14.67% and 18.72% respectively compared with CK. The changes in various forms of Cd in the soil treated with single application of hydroxyapatite (T2-4) were basically the same as those in the treatment of hydroxyapatite combined with humic acid, and the acid-soluble state was reduced by 6.04%, 10.0%, and 13.79%, respectively. In addition, the weakly acid-extractable Cd in the soil under the action of 1% humic acid alone (T1) and only giant fungus grass (T0) also decreased to a certain extent, by 8.2% and 7.67%, respectively. It is worth noting that the residual Cd increased the most under the T0 treatment, significantly increasing to 36.16%. Among all the treatments, the application of high proportion of hydroxyapatite combined with humic acid T7 was the best in reducing the percentage of weakly acid-extractable Cd in the soil. Comprehensive comparison showed that the application of high proportion of hydroxyapatite combined with humic acid T7 was the best in reducing the percentage of weakly acid-extractable Cd in the soil when giant fungus grass was planted.

[0066] Depend on Figure 2It can be seen that the form of Pb in the soil is different from that of Cd. The content of weakly acid extractable Pb is low, and the oxidizable Pb occupies the vast majority. The application of hydroxyapatite and humic acid further reduces the percentage of weakly acid extractable Pb in the soil. The weakly acid extractable, oxidizable, reducible and residual forms of Pb in CK soil account for 9.82%, 76.41%, 3.13% and 10.24% respectively. After hydroxyapatite and humic acid (T1-7) treatment, Pb in the soil is mainly converted from weakly acid extractable and residual forms to oxidizable forms, and the conversion trend increases with the increase of the addition amount. The percentages of weakly acid extractable and residual Pb are reduced by 7.43%, 8.64%, 9.12% and 1.88%, 4.33%, 4.37% respectively compared with CK, and the oxidizable Pb is increased by 9.11%, 13.1% and 13.86% respectively compared with CK. The Pb in the soil treated with hydroxyapatite (T2-4) was mainly transformed from weakly acid extractable to residual state, and the acid-soluble Pb decreased by 6.43%, 8.22%, and 9.02%, respectively. Among them, the residual Pb percentage of the soil treated with medium-proportion hydroxyapatite T3 was the highest, reaching 23.9%, an increase of 13.66% compared with CK. When 1% humic acid (T1) was applied alone, the percentage of weakly acid extractable Pb in the soil decreased, and the percentage of residual Pb increased, but the change was not obvious. It is also worth noting that the percentage of weakly acid extractable Pb increased instead of decreasing under the action of a single giant fungus grass T0.

[0067] Depend on Figure 3It can be seen that the forms of Cu in the soil are mainly distributed in three states: weakly acid extractable, oxidizable, and residual. The application of hydroxyapatite and humic acid reduced the percentage of weakly acid extractable Cu in the soil to varying degrees. The weakly acid extractable, oxidizable, reducible, and residual states of Cu in CK soil accounted for 21.79%, 41.03%, 1.66%, and 31.11%, respectively. Under the condition of planting giant fungus grass, the percentage of weakly acid extractable Cu in the soil was significantly reduced by hydroxyapatite and humic acid (T1-7), among which T7 treatment had the best effect, and the percentage of weakly acid extractable Cu decreased by 9.63%, 10.13%, and 11.83%, respectively. On the contrary, the oxidizable and residual Cu increased, but there was no significant difference between different proportions. The percentage of weakly acid extractable Cu in the soil treated with hydroxyapatite (T2-4) was 18.8%, 18.21%, and 11.36%, respectively. The percentage of Cu in each form of the soil was slightly transformed under low and medium doses, but the percentage of weakly acid extractable Cu was significantly reduced by 10.43% under high dose T3 treatment, and the percentage of residual Cu increased the most, reaching 42.11%, an increase of 11.04% compared with CK. The percentage of weakly acid extractable Cu in the soil treated with 1% humic acid T1 alone decreased to 11.11%, and the percentage of residual Cu increased to 37.4%. The single effect of giant fungus grass T0 also reduced the percentage of weakly acid extractable Cu to a certain extent and increased the percentage of residual Cu.

[0068] Depend on Figure 4It can be seen that the morphological distribution of Zn in the soil is similar to that of Cu, and Zn is also mainly distributed in three states: weakly acid extractable, oxidizable, and residual. In general, there was no significant difference in the percentage change of weakly acid extractable Zn in the soil among the treatments. The weakly acid extractable, oxidizable, reducible, and residual states of Zn in CK soil accounted for 36.8%, 27.19%, 1.81%, and 33.7%, respectively. Under the combined action of giant fungus grass, the percentage of weakly acid extractable Zn in the soil treated with hydroxyapatite and humic acid (T1-7) was 31.91%, 31.41%, and 33.47%, respectively, which was not significantly reduced compared with CK; the percentage of residual Zn showed a trend of first increasing, then decreasing, and then increasing with the increase of dosage. The percentage of weakly acid extractable Zn in the soil treated with hydroxyapatite (T2-4) was 33.98%, 34.13%, and 29.32%, respectively. The percentage of residual Zn also showed a trend of increasing first, then decreasing, and then increasing with the increase of dosage. Among them, T4 had the most ideal effect on Zn form transformation in all treatments. The percentage of weakly acid extractable Zn was 7.14% lower than that of CK, and the percentage of residual Zn was 46.08%, which was 12.38% higher than that of CK. In addition, the percentage of weakly acid extractable Zn in the soil treated with 1% humic acid T1 was reduced to 32.81%, and the percentage of residual Zn increased to 41.11%. The single giant fungus grass T0 also reduced the weakly acid extractable Zn to a certain extent, with a percentage content of 32.87%, and increased the residual Zn, with a percentage content of 43.19%.

[0069] 2) Effects of hydroxyapatite and humic acid on the heavy metal contents in the aboveground and underground parts of giant fungus grass

[0070] The contents of heavy metals absorbed by different parts of the giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6 were tested, and the results are shown in Figures 5 to 8, where Figure 5 The effects of different treatments on the Cd content in the aboveground and underground parts of giant fungus grass are shown in Figure 2. Figure 6 The effects of different treatments on the Pb content in the aboveground and underground parts of giant fungus grass are shown in Figure 2. Figure 7 The effects of different treatments on the Cu content in the aboveground and underground parts of giant fungus grass are shown in Figure 2. Figure 8 Effects of different treatments on Zn content in the aboveground and underground parts of giant fungus grass.

[0071] Depend on Figure 5 It can be seen that the content of heavy metals absorbed by different parts of the giant fungus grass is different. In general, the content of heavy metals in the underground part is higher than that in the aboveground part. The addition of different proportions of hydroxyapatite and humic acid has a significant effect on the absorption of heavy metals in the underground part of the giant fungus grass, but has little effect on the aboveground part. Without the addition of passivation agent (T0), the Cd content absorbed by the aboveground part of the giant fungus grass is 1.18 mg kg -1 , the Cd content in the underground part is 7.6 mg kg -1After adding different proportions of hydroxyapatite and humic acid, the Cd content absorbed by the aboveground part of the giant fungus grass had no significant difference compared with T0, while the heavy metal Cd content in the underground part was significantly reduced in the treatments of single hydroxyapatite T3, T4 and its combination with humic acid T1, T7, which decreased to 1.17, 4.83, 1.14, and 1.96 mg kg, respectively. -1 , which were reduced by 27.3%, 36.9%, 27.7% and 22.2% respectively compared with T0. There was no significant difference in Cd content in the understory of giant fungus grass under other treatments compared with T0.

[0072] Depend on Figure 6 It can be seen that the Pb content in the aboveground part of the giant fungus grass without adding passivation agent is 1.78 mg kg -1 Although the Pb content in the aboveground part of the giant fungus grass was different under each treatment, the difference was not significant compared with T0. The Pb content in the underground part of the giant fungus grass planted without the addition of passivation agent was 17.96 mg kg -1 Except for the addition of 0.1% hydroxyapatite in T2, the other treatments had no significant difference from T0. The Pb content in the understory of giant fungus grass in T2 treatment was 24.19 mg kg -1 , which significantly increased by 6.63 mg·kg compared with T0 -1 , an increase of 36.9%.

[0073] Depend on Figure 7 It can be seen that the Cu content in the aboveground part of the giant fungus grass without adding passivation agent is 9.14 mg kg -1 The Cu content in the aboveground part of the giant fungus grass was different under each treatment, which was consistent with the situation of Cd and Pb, but the difference was not significant compared with T0. The Cu content in the underground part of the giant fungus grass without adding passivation agent was 21.61 mg kg -1 The treatments of single application of hydroxyapatite T3 and T4 and combined application of humic acid T7 had the best effect on reducing the Cu content in the lower part of the giant fungus grassland, which was reduced to 20.86, 20.21, and 20.13 mg·kg respectively compared with T0. -1 , respectively reduced by 4.71, 1.4, and 1.48 mg·kg -1 The decrease was 18.1-21.4%. However, the low-dose hydroxyapatite T2 treatment promoted the absorption of Cu by the understory of giant fungus grass, and its content increased significantly to 31.99 mg kg -1 , an increase of 6.38 mg kg compared to T0 -1 , an increase of 24.9%.

[0074] Depend on Figure 8 It can be seen that the Zn content in the aboveground part of the giant fungus grass without the addition of passivation agent is 39.34 mg kg -1Slightly different from the situation of Cd, Pb, and Cu, the single high-dose hydroxyapatite T4 treatment increased the Zn content in the aboveground part of the giant fungus grass, which increased by 13.14 mg kg -1 , an increase of 13.8 mg kg compared to T0 -1 , an increase of 31.1%, and no significant difference in the aboveground Zn content of the other treatments. The Zn content in the underground part of the giant fungus grass planted without the addition of passivation agent was 41.91 mg kg -1 The Cu content in the lower part of the giant fungus grassland decreased the most under the treatment of single hydroxyapatite T4, with a numerical value of 32.77 mg kg -1 , which was reduced by 9.18 mg·kg compared with T0 -1 , with a decrease of 21.9%; there was no significant difference in Zn in the underground part of the other treatments. In summary, the single high-dose hydroxyapatite (T4) and its combination with humic acid (T7) treatments had the best inhibitory effect on the absorption of Cd, Pb, Cu, and Zn by giant fungus grass, and significantly reduced the heavy metal content in the roots of giant fungus grass; but it is worth noting that the low-dose hydroxyapatite T2 treatment promoted the absorption of heavy metals by the roots of giant fungus grass. Overall, the heavy metal content in giant fungus grass exceeded the "National Feed Hygiene Standard" (GB13078-2017).

[0075] 3) Effects of hydroxyapatite and humic acid on the transport and accumulation of heavy metals in Giant Juncao

[0076] The transport coefficient and enrichment coefficient of heavy metal Cd in the giant fungus grass samples of Examples 1 to 3 and Comparative Examples 1 to 6 were tested. The results are as follows: Figures 9-11 As shown, Fig. 9 The transport coefficient and enrichment coefficient of heavy metals under the action of single giant fungus grass in comparative example 1; Fig.10 The figure is the transport coefficient and enrichment coefficient of heavy metals in giant grass under the action of hydroxyapatite and humic acid in comparative example 3; Fig.11 The transport coefficient and enrichment coefficient of heavy metal Cd in giant fungus grass in Examples 1 to 3 and Comparative Examples 2 to 6 are shown.

[0077] Depend on Fig. 9 It can be seen that the transport coefficient and enrichment coefficient reflect the ability of plants to remove heavy metals in the soil. The higher the transport and enrichment coefficients, the more beneficial the plants are to remove heavy metals. In the complex heavy metal soil, the transport coefficient of giant fungus grass for Zn is the highest, and its enrichment ability for Cd is stronger. The transport coefficients of giant fungus grass treatment (T0) for Cu, Cd, Pb, and Zn are all less than 1, ranging from 0.36 to 0.94, and the transport capacity is Zn>Cd>Cu>Pb, indicating that the giant fungus grass treatment is more conducive to the migration of Zn from underground to above ground. The Cd enrichment coefficient of giant fungus grass is significantly higher than that of the other three heavy metals, with a value of 0.31, indicating that giant fungus grass has a stronger ability to enrich Cd.

[0078] Depend on Fig.10 It can be seen that the transfer coefficient and enrichment capacity of the four heavy metals in the treatment of adding hydroxyapatite and humic acid (T7) are basically the same as those in the case of the single treatment of giant fungus grass. The transport of Zn is still the strongest, and the enrichment of is the highest. However, the addition of hydroxyapatite and humic acid has a certain increase in the transfer coefficients of Cu, Cd, and Zn, and slightly reduced the enrichment coefficients of Cu, Cd, and Pb. This may be because the passivation effect reduces the toxic effects of heavy metals, promotes the transport of heavy metals in giant fungus grass, and reduces the absorption of heavy metals by the roots.

[0079] Depend on Fig.11 It can be seen that by comparing the Cd transport coefficient and enrichment coefficient of giant grass under different treatments, the research results show that there is no significant change in either the transport coefficient or the enrichment capacity between the treatment group with added passivators and the group without added passivators (complementary interference, changes in their respective efficacy, and modified expressions), indicating that single or combined application of hydroxyapatite and humic acid does not affect the transport and enrichment of Cd by giant grass.

[0080] 4) Effects of hydroxyapatite and humic acid combined with giant fungus grass on soil pH and EC

[0081] The pH and EC of the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 were tested. The results are as follows: Fig.12 shown.

[0082] Depend on Fig.12 It can be seen that when giant fungus grass is planted, the treatment of hydroxyapatite with humic acid has no significant change on soil pH and conductivity, indicating that the addition of passivation agent combination will not affect the soil microenvironment. After treatment, the soil pH value ranged from 8.14 to 8.44 from T0 to T7, which was lower than that of CK. Among them, the soil pH value decreased significantly (P<0.01) under the treatment of no material addition (T0) and 1% humic acid (T1), from 8.68 to 8.14 and 8.27, respectively, which decreased by 0.14 and 0.41 units. However, the decrease in soil pH value under the treatment of hydroxyapatite alone (T2~T4) and its combination with humic acid (T1~T7) did not reach a significant level, and there was no significant difference with the change of addition amount. The change in soil conductivity values ​​shows that the conductivity values ​​under T0~T7 treatments are between 108.9 and 127.1μs·cm -1 There were no significant differences compared with CK, indicating that different treatments of plants and passivators did not affect soil electrical conductivity.

[0083] 5) Effects of hydroxyapatite and humic acid combined with giant fungus grass on available phosphorus in field soil

[0084] The available phosphorus content in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 was tested. The results are as follows: Fig.13 shown.

[0085] Depend on Fig.13 It can be seen that when planting giant fungus grass, different treatments of hydroxyapatite and humic acid significantly reduced the available phosphorus content in the soil, and there was no significant difference with the change of the addition amount, indicating that there is no risk of secondary pollution with the addition of hydroxyapatite. The available phosphorus content in the soil of each treatment was T1<T3<T7<T4<T1<T6<T2<CK. Compared with CK, the available phosphorus content in the soil of the single giant fungus grass T0 treatment was reduced by 9.2 mg·kg -1 , the decrease was 22.8%; the soil available phosphorus content in T1 treated with 1% humic acid alone decreased by 18.1 mg kg -1 The decrease was 44.8%. The soil available phosphorus content in treatments T2 to 4 with single hydroxyapatite application decreased from 40.4 mg·kg-1 in CK to 29.1, 21.1, and 27.3 mg·kg-1, respectively. -1 , respectively reduced by 30.0%, 36.9%, and 32.4%. The soil available phosphorus content of treatments T1 to 7 with hydroxyapatite and humic acid was reduced by 13.1, 11.4, and 13.4 mg kg-1, respectively, compared with CK, with a decrease of 30.2%, 28.2%, and 33.2%, respectively. Among them, the reduction of soil available phosphorus in treatment T1 with 1% humic acid alone was the largest, and there was no significant difference between other treatments (T0, T2 to T7).

[0086] 6) Effects of hydroxyapatite and humic acid combined with giant fungus grass on field soil organic matter

[0087] The organic matter content in the soil samples of Examples 1 to 3 and Comparative Examples 1 to 6 was measured. The results are as follows: Fig.14 shown.

[0088] Depend on Fig.14 It can be seen that the changes in soil organic matter are exactly opposite to the changes in available phosphorus content. When giant fungus grass is planted, each treatment significantly increases soil organic matter, which is beneficial to improving soil fertility. Among them, the treatment with hydroxyapatite combined with humic acid is the best. The soil organic matter content of each treatment is from high to low as T6>T1>T7>T1>T2>T3>T4>T0>CK. The soil organic matter content of the single giant fungus grass T0 treatment increased from 6.7g·kg-1 in CK to 11g·kg -1 Among all treatments, hydroxyapatite combined with humic acid T1-7 had the best effect on improving soil organic matter. The soil organic matter content of T1-7 treatments was 17.3, 17.7, and 17.2 g·kg -1, which were 2.18, 2.64, and 2.16 times higher than those of CK, respectively. There was no significant difference between T1 and 7 with the increase of addition amount. In addition, the improvement of soil organic matter by single humic acid T1 treatment was better than that by single hydroxyapatite treatment T2 to 4. The soil organic matter content of T1 treatment was 14.3 g kg -1 , an increase of 7.6 g·kg compared to CK -1 The soil organic matter contents of T2-4 treatments were 12.7, 11.7, and 11.1 g·kg-1, respectively, which were 6.0, 1.0, and 4.4 g·kg-1 higher than those of CK. -1 , and under the single hydroxyapatite treatment, the soil organic matter showed a decreasing trend with the increase of the added amount.

[0089] 7) Effects of hydroxyapatite and humic acid on the biomass of giant grass

[0090] The biomass of the giant fungus grass of Examples 1 to 3 and Comparative Examples 1 to 6 was measured, and the results are shown in Table 3.

[0091] Table 3 Changes in biomass of Giant Grass under the action of hydroxyapatite and humic acid

[0092]

[0093]

[0094] As shown in Table 3, different treatments of hydroxyapatite and humic acid are beneficial to increase the biomass of giant fungus grass. Without the application of passivation agent, the fresh weight of the aboveground and underground giant fungus grass were 0.89kg and 0.41kg, respectively. After adding hydroxyapatite T2~T4 treatments, the aboveground biomass of giant fungus grass increased to 1.12, 1.11, and 1.07kg, respectively, which increased by 21.8%, 29.2%, and 20.2% compared with T0; the underground biomass showed a trend of first increasing and then decreasing with the increase of dosage. Compared with T0, T2 and T3 treatments increased by 2.4% and 14.6%, while T4 decreased by 19.1%. Under the treatment of adding humic acid (T1) and its combination with hydroxyapatite (T1-T7), the aboveground biomass of giant fungus grass increased significantly to 1.31, 1.40, 1.37, and 1.33 kg, respectively, which increased by 11.7%, 17.3%, 13.9%, and 49.4% compared with T0; the underground biomass also showed a decreasing trend with the increase of dosage. In general, the order of the size of the giant fungus grass biomass under different treatments is: hydroxyapatite + humic acid = humic acid > hydroxyapatite > no addition. It can be seen that the addition of humic acid has a good effect on the increase of giant fungus grass biomass, and hydroxyapatite is beneficial to the increase of giant fungus grass biomass within a certain range. When added in excess, it will inhibit the root growth of giant fungus grass.

[0095] 8) Effects of hydroxyapatite and humic acid on superoxide dismutase and peroxidase activities in giant grass

[0096] The superoxide dismutase and peroxidase activities of the giant fungus grass of Examples 1 to 3 and Comparative Examples 1 to 6 were measured, and the results are shown in Table 4.

[0097] Table 4 Effects of hydroxyapatite and humic acid on the oxidase activity of giant grass

[0098]

[0099] As shown in Table 4, the increase of superoxide dismutase (SOD) and peroxidase (POD) in plants is usually related to the recovery mechanism of oxidative decomposition under metal stress. The SOD and POD contents in the giant grass decreased to varying degrees, indicating that the hydroxyapatite and humic acid treatments alleviated the toxic effects of heavy metals on the giant grass and reduced the antioxidant stress response of the giant grass. Without the addition of passivation agents, the SOD content in the giant grass was 214 U·g -1 After adding hydroxyapatite T2~T4 treatments, the SOD content in giant fungus grass decreased to 184, 139, and 169 U·g -1 Compared with T0, the decrease of SOD in giant fungus grass was 14%, 31%, and 21% respectively. The treatments of hydroxyapatite and humic acid T1 to T7 showed a more significant decrease in SOD in giant fungus grass, and there was no significant difference with the addition amount, with the values ​​of 142, 110, and 147 U·g -1 ·Fw, which was reduced by 29.9-33.6% compared with T0. The changes in peroxidase (POD) content under the same treatment were slightly different from those of SOD. The POD content of giant fungus grass was also significantly reduced in T1-T7 treatments, from 779U·g in T0 to 1.337U·g in T1-T7. -1 Fw reduced to 621, 661, 662 U g -1 ·Fw, the decrease range was 11.0~19.8%. However, the POD content of giant fungus grass increased in T2~T4 treatments, with the values ​​increasing to 891, 980 and 816 U·g-1·Fw respectively, with the increase range of 10.0~21.8%.

[0100] 9) Effects of hydroxyapatite and humic acid on chlorophyll content in Giant grass

[0101] The chlorophyll content of the giant fungus grass of Examples 1 to 3 and Comparative Examples 1 to 6 was measured, and the results are shown in Table 5.

[0102] Table 5 Changes in chlorophyll content of giant grass under the action of hydroxyapatite and humic acid

[0103]

[0104] As shown in Table 5, chlorophyll is an important component in the photosynthesis process. When lead and cadmium accumulate to a certain amount in plants, it will not only affect the absorption of nutrients and water by the plant roots, but also hinder the synthesis of chlorophyll in plant leaves. Among them, chlorophyll a, chlorophyll b and the total amount of chlorophyll can be affected to varying degrees. Chlorophyll a has the function of capturing light energy, while chlorophyll b has the function of converting light energy. Without the addition of passivation agent, the chlorophyll a, b and total amount of giant fungus grass were 0.881, 1.016 and 2.114 g, respectively. Under the treatment of single hydroxyapatite application, T2 and T3 both reduced the chlorophyll a, b and total content in giant fungus grass and the degree of reduction was the largest among all treatments, while the content of the three chlorophylls under T4 treatment was relatively high and there was no significant difference from T0. The addition of passivation agent inevitably affects the chlorophyll synthesis of giant grass. T0-T6 have a weaker degree of inhibition on the stress of heavy metals. In contrast, the T7 treatment group is more effective in fixing heavy metals, reducing its stress on giant grass, thereby promoting the synthesis of chlorophyll in giant grass. The content of the three chlorophylls was also significantly reduced under the treatment of T1 with 1% humic acid alone, but the degree of reduction was lower than that of T2 and T3. In the treatment of hydroxyapatite and humic acid, the content of the three chlorophylls in giant grass was basically the same as that of T0 in T1 and T6 treatments. In particular, the chlorophyll a, b and total amount of giant grass were significantly increased under T7 treatment, which increased by 0.182, 0.241, and 0.419 g, respectively, compared with T0, with an increase of 20.7%, 19.4%, and 21.7%, respectively. It was observed that the chlorophyll in giant fungus grass showed an increasing trend with the increase of hydroxyapatite single and combined treatments, and high-dose hydroxyapatite single and combined treatments were beneficial to the production of chlorophyll.

[0105] 10) Changes in bacterial α-diversity index under the treatment of hydroxyapatite and humic acid combined with giant fungus grass

[0106] The bacterial alpha diversity index in the soil samples of Example 3 and Comparative Examples 1, 2 and 6 was measured, and the results are shown in Table 6.

[0107] Table 6 Changes in bacterial community diversity index under the treatment of hydroxyapatite and humic acid combined with giant grass

[0108]

[0109] As shown in Table 6, the α diversity index reflects the richness and diversity of species in the soil microbial community. This study used 1 type of α diversity index, Ace, Chao, Simpson, Shannon, and Coverage. Among them, the Simpson index was negatively correlated with species richness and diversity, while the other indices were positively correlated with species richness and diversity. In general, the richness and diversity of soil bacteria species were significantly improved after planting giant fungus grass and its combined treatment with hydroxyapatite and humic acid. The sample sequencing depth index (Coverage) values ​​under different treatments were all above 0.99, indicating that the sequencing results of soil samples were reasonable and sufficient to reflect the diversity contained in the current samples. Under the CK treatment, the bacterial community richness index Ace and Chao values ​​and the diversity index Shannon value were the lowest, and the diversity index Simpson value was the highest. After T0, T4, and T7 treatments, Ace, Chao, and Shannon were significantly higher than CK, and the Shannon values ​​were lower than CK, while there was no significant difference between T0, T4, and T7 treatments. This indicates that planting giant fungus grass is beneficial to increasing the richness and diversity of soil microorganisms, and the application of hydroxyapatite and humic acid has no negative effect on species richness.

[0110] 11) Changes in bacterial species numbers under hydroxyapatite and humic acid combined with giant fungus grass treatment

[0111] The number of bacterial species in the soil samples of Example 3, Comparative Examples 1, 2 and 6 was determined. Fig.15 shown.

[0112] Depend on Fig.15 It can be seen that the number of soil bacterial species increased significantly after planting giant grass and its combined treatment with hydroxyapatite and humic acid. The total number of soil bacterial species under CK treatment was 1460, while the total number of soil bacterial species after T0, T4, and T7 treatments were 2193, 2061, and 2069, respectively. It can be seen that hydroxyapatite and humic acid combined with giant grass treatment is beneficial to increase the number of microorganisms and improve the soil environment. In addition, the number of bacterial species in the four treatments was 1169, the number of unique bacterial species under CK treatment was 21, and the number of unique bacterial species after T0, T4, and T7 treatments were 149, 36, and 49, respectively. Overall, the total number and unique number of OTUs of soil bacterial communities in the treatment of single giant grass planting were the highest.

[0113] 12) Changes in bacterial community composition and abundance under hydroxyapatite and humic acid combined with giant fungus grass treatment

[0114] The bacterial community composition and abundance changes in the soil samples of Example 3, Comparative Examples 1, 2 and 6 were measured. The results are as follows: Fig.16 shown.

[0115] Depend on Fig.16 It can be seen that there are 37 phyla, 97 classes, 233 orders, 314 families, 177 genera and 1012 species of bacteria in the four treatment soils, and each habitat has a high diversity at the phylum classification level. The addition of hydroxyapatite and humic acid combined with the planting of giant fungus grass enriched the bacterial community composition and changed the species abundance. The top five bacterial phyla in relative abundance in the four treatment soils are Actinobacteriota, Chloroflexi, Proteobacteria, Acidobacteriota, and Gemmatimonadota. Among them, the relative abundance of Actinobacteria, Chloroflexi, and Gemmatimonadota in CK soil were 29%, 29%, and 33%, respectively. After T0, T4, and T7 treatments, the relative abundance of the three phyla of bacteria decreased to a certain extent, and the values ​​decreased to 22-21%, 22-26%, and 20-21%, respectively. The relative abundance of Proteobacteria and Acidobacteria in the soil increased after treatment with T0, T4, and T7. Proteobacteria increased from 18% in CK to 27%, 29%, and 21%, respectively; Acidobacteria increased from 20% in CK to 31%, 22%, and 27%, respectively. At the same time, other bacterial communities with a relative abundance of less than 1% accounted for 18% in CK soil, which increased significantly to 28%, 27%, and 27% after treatment with T0, T4, and T7. Overall, the addition of hydroxyapatite and humic acid combined with giant fungus grass enriched the composition of the bacterial community (improved the soil ecosystem to be healthier) (linked to heavy metals and landed in heavy metals).

[0116] In summary, the application of hydroxyapatite alone and in combination with humic acid reduced the percentage content of active Cd, Pb, Cu, and Zn in the soil, and the reduction effect increased with the increase of the addition amount. Except for Zn, the reduction effect of active Cd, Pb, and Cu was best in the treatment of high-dose hydroxyapatite and humic acid, indicating that it has broad application prospects for the treatment of alkaline soil contaminated by heavy metals. The treatment of hydroxyapatite and humic acid combined with giant fungus grass significantly increased soil organic matter and reduced available phosphorus, while having no significant effect on soil pH and conductivity. This shows that under the action of giant fungus grass, the application of hydroxyapatite and humic acid treatment is beneficial to improve soil fertility and will not cause significant changes in the soil microenvironment. At the same time, the exogenous phosphorus in hydroxyapatite does not cause the risk of secondary pollution. Giant fungus grass has a significant absorption effect on Cd, Pb, Cu, and Zn in the soil. The single or combined addition of hydroxyapatite and humic acid inhibited the absorption of heavy metals in the underground part of giant fungus grass to a certain extent, but had little effect on the aboveground part. Overall, the concentration of heavy metals was high, exceeding the National Feed Hygiene Standard (GB 13078-2017). Among the four metals, the transport coefficient of Zn in giant fungus grass was the highest, while the enrichment capacity of Cd was stronger; the addition of hydroxyapatite and humic acid at the same time had no significant effect on the heavy metal transport capacity and enrichment capacity of giant fungus grass. The single or combined addition of hydroxyapatite and humic acid can reduce the toxic effects of heavy metals on giant fungus grass, thereby increasing the biomass of giant fungus grass. In general, the presence of humic acid has a significant effect on the biomass of giant fungus grass, while excessive addition of hydroxyapatite will have a certain inhibitory effect on giant fungus grass; in addition, the combination of hydroxyapatite and humic acid reduces the antioxidant stress response of giant fungus grass, thereby significantly reducing the content of superoxide dismutase and peroxidase in its body, and also increases the content of chlorophyll a, b and total chlorophyll at high doses, which is beneficial to the light energy capture and conversion of giant fungus grass, and promotes the production and development of giant fungus grass. The effect of giant grass increased the number of soil microorganisms and enriched the diversity of microbial communities. Planting giant grass increased the Ace, Chao and Shannon indexes of soil bacteria, while reducing the Simpson index. The number of soil bacterial species increased significantly and the species composition was enriched, indicating that the richness and diversity of bacterial communities increased. At the same time, the addition of hydroxyapatite and humic acid had no significant effect on the microbial effects of giant grass.

[0117] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention rather than all the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A composition for repairing alkaline soil contaminated by heavy metals, characterized in that: It is composed of hydroxyapatite, humic acid and giant fungus grass; The ratio of the mass of the hydroxyapatite, the mass of the humic acid and the number of giant fungus grass plants is (7.2-10.2) kg: (3.6-5.6) kg: (4-20) plants.

2. Use of the composition according to claim 1 in in-situ remediation of heavy metal-contaminated alkaline soil.

3. The use according to claim 2, characterized in that: The heavy metal includes one or more of Cd, Pb, Cu and Zn.

4. A method for repairing heavy metal-contaminated alkaline soil using the composition of claim 1, characterized in that: The following steps are involved: Hydroxyapatite and humic acid are applied to the tillage layer of alkaline soil contaminated by heavy metals, and giant fungus grass is planted on the tillage layer for restoration.

5. The method according to claim 4, characterized in that The depth of the tillage layer is 5 to 30 cm.

6. The method according to claim 4 or 5, characterized in that: The mass of the hydroxyapatite is 0.1-2% of the total mass of the cultivated layer soil.

7. The method according to claim 4 or 5, characterized in that: The mass of the humic acid is 0.1-2% of the total mass of the cultivated layer soil.

8. The method according to claim 4, characterized in that Based on the area of ​​the heavy metal-contaminated alkaline soil, the planting amount of the giant fungus grass is 4 to 20 plants / m 2 .

9. The method according to claim 4, characterized in that The repairing time is 30 to 300 days.

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