Biochar material and method for adsorbing heavy metals in wormcast

Abstract

The invention relates to the technical field of heavy metal pollution treatment, and particularly discloses a biochar material and method for adsorbing heavy metals in wormcast. The biochar material for adsorbing the heavy metals in the wormcast adopts waste green tea residues as a raw material, and after being soaked in a phosphoric acid solution with the mass concentration of 38-42%, the biochar material is subjected to heat treatment at the temperature of 540-560 DEG C to obtain P-BC powder. The P-BC powder is soaked in a metal salt solution with the total metal ion concentration being 0.8-1.2 mol / L, and under the action of a precipitator, the LDH-coated P-BC material is obtained. The LDH-coated P-BC material is mixed with a ferric chloride hexahydrate solution and a NaBH4 aqueous solution for reaction to obtain the biochar material for adsorbing the heavy metals in the wormcast, so that the fixing and stabilizing effects of the biochar material on the heavy metals in the wormcast are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of heavy metal pollution treatment, and in particular to a biochar material for adsorbing heavy metals in earthworm manure and a method. BACKGROUND

[0002] With the rapid development of modern agriculture and intensive farming, the amount of livestock and poultry manure is increasing. Earthworm composting, as an efficient and environmentally friendly biological treatment technology, is widely used in the harmless and resourceful treatment of livestock and poultry manure. Through the digestion of earthworms and the synergistic effect of microorganisms, high-quality organic fertilizer, earthworm manure, can be produced. However, some compost raw materials contain city sludge, kitchen waste and other raw materials that may carry heavy metal elements such as lead and cadmium, which can easily lead to the presence of heavy metals in earthworm manure. In 2020, the Jiangsu Academy of Agricultural Sciences found that 15% of the commercially available earthworm manure samples exceeded the standard for heavy metals, with the highest detection value exceeding 3 times the national organic fertilizer standard. Long-term use of such fertilizers can lead to the accumulation of heavy metals in the soil and enter the food chain through crops. Therefore, developing a technology that can effectively fix and stabilize heavy metals in earthworm manure is a key prerequisite for its safe agricultural use.

[0003] In related technologies, CN114917869A discloses a preparation method of waste green tea biochar for heavy metal preferential adsorption, comprising the following steps: S1, carbonization treatment: carbonizing tea leaf residue to obtain carbonized particles; S2, activation treatment: activating the carbonized particles to obtain an activated product; S3, washing treatment: washing the activated product to obtain carbon particles; S4, mixing treatment: mixing the carbon particles with nano zero-valent iron to obtain green tea biochar.

[0004] However, when the carbon particles and nano zero-valent iron are mixed in the air, the nano zero-valent iron is completely exposed to the air, leading to instantaneous oxidation and failure, generating inactive iron oxides, which makes the prepared biochar have poor function of reducing and fixing heavy metals, and it is difficult to effectively fix and stabilize heavy metals in earthworm manure. SUMMARY

[0005] In order to improve the fixing and stabilizing effect of biochar material on heavy metals in earthworm manure, the present application provides a biochar material for adsorbing heavy metals in earthworm manure and a method.

[0006] In a first aspect, the present application provides a preparation method of a biochar material for adsorbing heavy metals in earthworm manure, which adopts the following technical scheme:

[0007] The preparation method of the biochar material for adsorbing heavy metals in earthworm manure comprises the following steps:

[0008] S1, taking waste green tea residue, drying and crushing, then immersing in a phosphoric acid solution with a mass concentration of 38-42% for 5-6 hours, filtering to obtain filter residue, treating the filter residue at 540-560°C for 58-66 minutes under nitrogen protection, washing to neutral after cooling, drying and grinding to obtain P-BC powder;

[0009] S2, dispersing the P-BC powder in deionized water, adding a metal salt solution with a total metal ion concentration of 0.8-1.2 mol / L, stirring for 55-65 minutes under nitrogen protection, adding a precipitant dropwise, adjusting the pH to 9.5-10.5, heating to 62-68°C, and keeping the temperature for 17.2-18.6 hours, then cooling, filtering, washing and drying to obtain a LDH@P-BC material; the mass-volume ratio of the P-BC powder to the metal salt solution is 0.22-0.28 g / mL, and the molar ratio of Mg 2+ to Al 3+ in the metal salt solution is (1.8-2.2):1;

[0010] S3, dispersing the LDH@P-BC material in deionized water under nitrogen protection and stirring, adding a ferric chloride hexahydrate solution with a concentration of 132-136 g / L, stirring at 36-42°C for 3.5-4.5 hours, adding a NaBH4 aqueous solution with a concentration of 0.6-1.0 mol / L dropwise, and after the addition is completed, separating, washing and drying to obtain a biochar material for adsorbing heavy metals in earthworm manure.

[0011] In a specific implementable embodiment, the precipitant is a NaOH solution with a molar concentration of 1.8-2.2 mol / L.

[0012] In a specific implementable embodiment, the preparation step of the metal salt solution is as follows: dissolving magnesium chloride hexahydrate and aluminum chloride in deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution, mixing the two solutions, and then making up the volume to obtain the metal salt solution.

[0013] In a specific implementable embodiment, in the S3 step, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.15-0.22 g / mL.

[0014] In a specific implementable embodiment, in the S3 step, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.4-0.44 g / mL.

[0015] In a specific implementable embodiment, in the S1 step, after drying and grinding, sieving is performed to obtain P-BC powder with a particle size of 60-160 mesh.

[0016] In a second aspect, the application provides a biochar material for adsorbing heavy metals in earthworm manure, which adopts the following technical scheme:

[0017] The biochar material for adsorbing heavy metals in earthworm manure is prepared by the preparation method of the biochar material for adsorbing heavy metals in earthworm manure.

[0018] In a third aspect, the application provides a treatment method using the biochar material for adsorbing heavy metals in earthworm manure, which adopts the following technical scheme:

[0019] The treatment method using the biochar material for adsorbing heavy metals in earthworm manure includes the following steps:

[0020] The earthworm manure and the biochar material for adsorbing heavy metals in earthworm manure are uniformly mixed, deionized water is added during the mixing process, a mixture with a water content of 50%-60% is obtained, the mixture is placed in a sealed container, and is allowed to stand at 25-35°C, the mixture is stirred every 3-5 days during the standing period, and the standing period is 14-21 days, the mixture is naturally air-dried until the water content is less than 30%, and the stabilized earthworm manure is obtained, and the treatment is completed.

[0021] In summary, the application has the following beneficial effects:

[0022] 1. The application grows LDH in situ on the surface and pores of P-BC, loads nZVI in the pores of LDH@P-BC, and prepares a biochar material for adsorbing heavy metals in earthworm manure, which helps to improve the fixing and stabilizing effect of the biochar material on heavy metals in earthworm manure.

[0023] 2. In the application, the molar concentration of the NaOH solution is preferably 1.8-2.2 mol / L, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.15-0.22 g / mL, and the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.4-0.44 g / mL, which helps to further improve the fixing and stabilizing effect of the biochar material on heavy metals in earthworm manure.

[0024] 3. The treatment method using the biochar material for adsorbing heavy metals in earthworm manure can effectively solidify and stabilize heavy metals in earthworm manure. DETAILED DESCRIPTION

[0025] Unless otherwise specified, the raw materials used in the application are commercially available. Among them, the waste green tea dregs are purchased from Huamo (Shandong) Biotechnology Co., Ltd. The earthworm manure is purchased from Shijiazhuang Yitian Biotechnology Co., Ltd.

[0026] The application will be further described in detail below in combination with examples and comparative examples.

[0027] Example

[0028] Example 1

[0029] This embodiment provides a method for preparing biochar material that adsorbs heavy metals from earthworm castings, comprising the following steps:

[0030] S1. Weigh the waste green tea residue, dry and crush it, add it to a 40% phosphoric acid solution, stir evenly, soak for 5.5 hours, filter to obtain filter residue, place the filter residue in a pyrolysis furnace under nitrogen protection, heat treat at 550℃ for 62 minutes, stop heating, cool naturally to room temperature, wash until neutral, dry, grind, and sieve to obtain P-BC powder with a particle size between 60-160 mesh.

[0031] S2. Disperse P-BC powder in deionized water. While stirring, add a metal salt solution with a total metal ion concentration of 1.0 mol / L at a mass-to-volume ratio of P-BC powder to metal salt solution of 0.25 g / mL. Stir for 60 min under nitrogen protection, then add NaOH solution with a molar concentration of 2 mol / L dropwise to adjust the pH to 10 and maintain it. Then raise the temperature to 65℃ and keep the reaction at this temperature for 18 h. After naturally cooling to room temperature, filter, wash three times with deionized water, and dry to obtain LDH@P-BC material.

[0032] S3. Disperse LDH@P-BC material in deionized water. Under nitrogen protection and stirring, add 134 g / L ferric chloride hexahydrate solution at a mass-to-volume ratio of 0.42 g / mL to LDH@P-BC material and ferric chloride hexahydrate solution. Stir at 39°C for 4 h. Then, add 0.8 mol / L NaBH4 aqueous solution dropwise at a mass-to-volume ratio of 0.19 g / mL to LDH@P-BC material and NaBH4 aqueous solution. After the addition is complete, separate to obtain a solid product. Wash the solid product three times with anhydrous ethanol and dry to obtain biochar material that adsorbs heavy metals from earthworm castings.

[0033] In S2, the preparation steps of the metal salt solution are as follows: Weigh 0.666 mol of magnesium chloride hexahydrate and 0.333 mol of aluminum trichloride, respectively. Dissolve magnesium chloride hexahydrate and aluminum trichloride in 100 mL of deionized water, respectively, to obtain magnesium chloride hexahydrate solution and aluminum trichloride solution. Transfer all of the magnesium chloride hexahydrate solution and aluminum trichloride solution to a 1000 mL volumetric flask, and after dilution to volume, obtain a metal salt solution with a total metal ion concentration of 0.999 mol / L. The Mg in the metal salt solution... 2+ With Al 3 + The molar ratio is 2:1.

[0034] The embodiment also provides a treatment method of applying the biochar material for adsorbing heavy metals in earthworm manure, comprising the following steps:

[0035] The earthworm manure is mixed with the prepared biochar material for adsorbing heavy metals in earthworm manure, and the amount of the biochar material is 3% of the dry weight of the earthworm manure. Deionized water is added during the mixing process to obtain a mixture with a water content of 55%. The mixture is loaded into a container with a cover, sealed, and placed in an environment with a temperature in the range of 25-35°C. The mixture is stirred every 4 days during the standing period, and the standing period is 18 days. The mixture is naturally air-dried until the water content is less than 30% to obtain stabilized earthworm manure, and the treatment is completed.

[0036] Example 2

[0037] The embodiment differs from example 1 only in that the mass concentration of the phosphoric acid solution in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 36%.

[0038] Example 3

[0039] The embodiment differs from example 1 only in that the mass concentration of the phosphoric acid solution in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 38%.

[0040] Example 4

[0041] The embodiment differs from example 1 only in that the mass concentration of the phosphoric acid solution in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 42%.

[0042] Example 5

[0043] The embodiment differs from example 1 only in that the mass concentration of the phosphoric acid solution in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 44%.

[0044] Example 6

[0045] The embodiment differs from example 1 only in that the P-BC powder with a particle size of 20-50 mesh is obtained in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure.

[0046] Example 7

[0047] The embodiment differs from example 1 only in that the P-BC powder with a particle size of 180-220 mesh is obtained in the S1 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure.

[0048] Example 8

[0049] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the molar concentration of the NaOH solution is 1.8 mol / L.

[0050] Example 9

[0051] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the molar concentration of the NaOH solution is 2.2 mol / L.

[0052] Example 10

[0053] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the molar concentration of the NaOH solution is 2.2 mol / L.

[0054] Example 11

[0055] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the total metal ion concentration of the metal salt solution is 0.6 mol / L. The preparation steps of the metal salt solution are as follows: 0.4 mol of magnesium chloride hexahydrate and 0.2 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 0.6 mol / L is obtained. The molar ratio of Mg 2+ and Al 3+ in the metal salt solution is 2:1.

[0056] Example 12

[0057] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the total metal ion concentration of the metal salt solution is 0.801 mol / L. The preparation steps of the metal salt solution are as follows: 0.534 mol of magnesium chloride hexahydrate and 0.267 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 0.801 mol / L is obtained. The molar ratio of Mg 2+ and Al 3+ in the metal salt solution is 2:1.

[0058] Example 13

[0059] The difference between this example and Example 1 is only that the total metal ion concentration of the metal salt solution in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 1.2 mol / L. The preparation steps of the metal salt solution are as follows: 0.8 mol of magnesium chloride hexahydrate and 0.4 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 1.2 mol / L is obtained. The molar ratio of Mg 2+ to Al 3+ in the metal salt solution is 2:1.

[0060] Example 14

[0061] The difference between this example and Example 1 is only that the total metal ion concentration of the metal salt solution in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure is 1.5 mol / L. The preparation steps of the metal salt solution are as follows: 1 mol of magnesium chloride hexahydrate and 0.5 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 1.5 mol / L is obtained. The molar ratio of Mg 2+ to Al 3+ in the metal salt solution is 2:1.

[0062] Example 15

[0063] The difference between this example and Example 1 is only that the preparation steps of the metal salt solution in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure are as follows: 0.642 mol of magnesium chloride hexahydrate and 0.357 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 0.999 mol / L is obtained. The molar ratio of Mg 2+ to Al 3 + in the metal salt solution is 1.8:1.

[0064] Example 16

[0065] The difference between this embodiment and embodiment 1 is only that in the S2 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the preparation step of the metal salt solution is as follows: 0.687 mol of magnesium chloride hexahydrate and 0.312 mol of aluminum chloride are weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride are dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution are all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 0.999 mol / L is obtained. The molar ratio of Mg 2+ The molar ratio of Al 3 + is 2.2:1.

[0066] Example 17

[0067] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.38 g / mL, and the ferric chloride hexahydrate solution with a concentration of 134 g / L is added.

[0068] Example 18

[0069] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.4 g / mL, and the ferric chloride hexahydrate solution with a concentration of 134 g / L is added.

[0070] Example 19

[0071] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.44 g / mL, and the ferric chloride hexahydrate solution with a concentration of 134 g / L is added.

[0072] Example 20

[0073] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution is 0.46 g / mL, and the ferric chloride hexahydrate solution with a concentration of 134 g / L is added.

[0074] Example 21

[0075] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.12 g / mL, and the NaBH4 aqueous solution with a concentration of 0.8 mol / L is added dropwise.

[0076] Embodiment 22

[0077] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.15 g / mL, and the NaBH4 aqueous solution with a concentration of 0.8 mol / L is added dropwise.

[0078] Embodiment 23

[0079] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.22 g / mL, and the NaBH4 aqueous solution with a concentration of 0.8 mol / L is added dropwise.

[0080] Embodiment 24

[0081] The difference between this embodiment and embodiment 1 is only that in the S3 step of the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution is 0.25 g / mL, and the NaBH4 aqueous solution with a concentration of 0.8 mol / L is added dropwise.

[0082] Embodiment 25

[0083] The difference between this embodiment and embodiment 1 is only that the preparation method of the biochar material for adsorbing heavy metals in earthworm manure comprises the following steps:

[0084] S1, weigh the waste green tea residue, dry and crush, then add a phosphoric acid solution with a mass concentration of 40%, stir uniformly, immerse for 5 h, filter, and obtain the filter residue. Under the protection of nitrogen, the filter residue is placed in a pyrolysis furnace, and is subjected to constant temperature heat treatment at 540℃ for 66 min. After stopping heating, it is naturally cooled to room temperature, washed to neutral, dried, ground, and sieved to obtain P-BC powder with a particle size of 60-160 mesh.

[0085] S2, the P-BC powder was dispersed in deionized water, under stirring, the mass-volume ratio of the P-BC powder to the metal salt solution was 0.25 g / mL, and a metal salt solution with a total metal ion concentration of 1.0 mol / L was added; under nitrogen protection, stirring was performed for 55 min, a 2 mol / L NaOH solution was added dropwise, the pH was adjusted to 9.5 and maintained. Then, the temperature was raised to 62°C, and the reaction was maintained for 18.6 h, and then naturally cooled to room temperature. After filtration, the product was washed with deionized water three times and dried to obtain the LDH@P-BC material.

[0086] S3, the LDH@P-BC material was dispersed in deionized water, under nitrogen protection and stirring, the mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution was 0.42 g / mL, and a 132 g / L ferric chloride hexahydrate solution was added, and stirring was performed at 36°C for 4.5 h. Then, the mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution was 0.19 g / mL, and a 0.6 mol / L NaBH4 aqueous solution was added dropwise. After the dropwise addition was completed, the solid product was separated, washed with anhydrous ethanol three times, and dried to obtain the biochar material for adsorbing heavy metals in earthworm manure.

[0087] In S2, the preparation steps of the metal salt solution are as follows: 0.666 mol of magnesium chloride hexahydrate and 0.333 mol of aluminum chloride were weighed respectively. The magnesium chloride hexahydrate and the aluminum chloride were dissolved in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. The magnesium chloride hexahydrate solution and the aluminum chloride solution were all transferred to a 1000 mL volumetric flask, and after constant volume, a metal salt solution with a total metal ion concentration of 0.999 mol / L was obtained. The molar ratio of Mg 2+ to Al 3 + was 2:1.

[0088] The present embodiment also provides a treatment method using the biochar material for adsorbing heavy metals in earthworm manure, which comprises the following steps:

[0089] The earthworm manure and the prepared biochar material for adsorbing heavy metals in earthworm manure were mixed uniformly, and the amount of the biochar material was 3% of the dry weight of the earthworm manure. Deionized water was added during the mixing process to obtain a mixture with a water content of 50%. The mixture was placed in a container with a lid, and after sealing, it was placed in an environment with a temperature in the range of 25-35°C, and was stirred every 3 days during the standing period. After standing for 14 days, the mixture was naturally air-dried until the water content was less than 30% to obtain stabilized earthworm manure, and the treatment was completed.

[0090] Example 26

[0091] The difference between the present embodiment and embodiment 1 is only the preparation method of the biochar material for adsorbing heavy metals in earthworm manure, which comprises the following steps:

[0092] S1, weigh the waste green tea residue, dry and crush, then add a 40% mass concentration phosphoric acid solution, stir evenly, soak for 6 hours, filter, and obtain the filter residue. The filter residue is placed in a pyrolysis furnace under nitrogen protection, and is treated at a constant temperature of 560°C for 58 minutes. After stopping heating, it is naturally cooled to room temperature, washed to neutral, dried, ground, and sieved to obtain P-BC powder with a particle size of 60-160 mesh.

[0093] S2, disperse the P-BC powder in deionized water, and under stirring, add a metal salt solution with a total metal ion concentration of 1.0 mol / L according to a mass-volume ratio of P-BC powder to metal salt solution of 0.25 g / mL. Stir for 65 minutes under nitrogen protection, and dropwise add a 2 mol / L NaOH solution to adjust the pH to 10.5 and maintain. Then, heat to 68°C, and maintain for 17.2 hours. After natural cooling to room temperature, filter, wash with deionized water for 3 times, and dry to obtain the LDH@P-BC material.

[0094] S3, disperse the LDH@P-BC material in deionized water under nitrogen protection and stirring, and add a 136 g / L ferric chloride hexahydrate solution according to a mass-volume ratio of LDH@P-BC material to ferric chloride hexahydrate solution of 0.42 g / mL. Stir at 42°C for 3.5 hours, then dropwise add a 1.0 mol / L NaBH4 aqueous solution according to a mass-volume ratio of LDH@P-BC material to NaBH4 aqueous solution of 0.19 g / mL. After the dropwise addition is completed, separate to obtain a solid product. Wash the solid product with anhydrous ethanol for 3 times, and dry to obtain the biochar material for adsorbing heavy metals in earthworm manure.

[0095] In S2, the preparation steps of the metal salt solution are as follows: weigh 0.666 mol of magnesium chloride hexahydrate and 0.333 mol of aluminum chloride. Dissolve the magnesium chloride hexahydrate and the aluminum chloride in 100 mL of deionized water respectively to obtain a magnesium chloride hexahydrate solution and an aluminum chloride solution. Transfer the magnesium chloride hexahydrate solution and the aluminum chloride solution to a 1000 mL volumetric flask, and after constant volume, obtain a metal salt solution with a total metal ion concentration of 0.999 mol / L. The molar ratio of Mg 2+ to Al 3 in the metal salt solution is 2:1. +

[0096] The present embodiment also provides a treatment method using the biochar material for adsorbing heavy metals in earthworm manure, which comprises the following steps:

[0097] The vermicompost is mixed with the prepared biochar material for adsorbing heavy metals in vermicompost uniformly, and the amount of the biochar material is 3% of the dry weight of the vermicompost. Deionized water is added during the mixing process to obtain a mixture with a water content of 60%. The mixture is loaded into a container with a cover, sealed, and placed in an environment with a temperature of 25-35°C. The mixture is stirred every 5 days during the standing period, and the standing period is 21 days. After standing, the mixture is naturally air-dried to a water content of less than 30% to obtain stabilized vermicompost, and the treatment is completed.

[0098] Comparative Example

[0099] Comparative Example 1

[0100] The difference between this comparative example and Example 1 is only that the S1 step of the preparation method of the biochar material for adsorbing heavy metals in vermicompost is as follows: the waste green tea residue is weighed, dried, and crushed. Then, under nitrogen protection, the waste green tea residue is placed in a pyrolysis furnace and heat-treated at 550°C for 62 min. After stopping heating, the waste green tea residue is naturally cooled to room temperature, washed to neutral, dried, ground, and sieved to obtain BC powder with a particle size of 60-160 mesh.

[0101] Comparative Example 2

[0102] The difference between this comparative example and Example 1 is only that the S2 step of the preparation method of the biochar material for adsorbing heavy metals in vermicompost is as follows: the P-BC powder is dispersed in deionized water, and under stirring, metal salt solution with a total metal ion concentration of 1.0 mol / L is added according to a mass-volume ratio of P-BC powder to metal salt solution of 0.25 g / mL. Then, the temperature is raised to 65°C, and the reaction is kept for 18 h. After natural cooling to room temperature, the mixture is filtered and washed with deionized water three times, and then dried to obtain the LDH@P-BC material.

[0103] Comparative Example 3

[0104] The difference between this comparative example and Example 1 is only that the S3 step of the preparation method of the biochar material for adsorbing heavy metals in vermicompost is as follows: the LDH@P-BC material is dispersed in deionized water, and under nitrogen protection and stirring, iron chloride hexahydrate solution with a concentration of 134 g / L is added according to a mass-volume ratio of LDH@P-BC material to iron chloride hexahydrate solution of 0.42 g / mL. The mixture is stirred at 39°C for 4 h, and then the solid product is separated, washed with anhydrous ethanol three times, and dried to obtain the biochar material for adsorbing heavy metals in vermicompost.

[0105] Performance detection test

[0106] For Examples 1-26 and Comparative Examples 1-3, the following performance detection tests are performed:

[0107] (1) Heavy metal fixation rate test: 10.00 g of raw vermicompost without any treatment and 10.00 g of stabilized vermicompost treated in each example and comparative example were weighed into a 50 mL centrifuge tube, 20.0 mL of DTPA extraction solution (0.005 mol / L DTPA + 0.01 mol / L CaCl2+ 0.1 mol / L TEA, pH = 7.3) was added, and extraction was performed at 25 ± 2°C with 180 r / min oscillation for 2 hours. Filtration was performed using ashless filter paper, and the filtrate was collected in a polyethylene bottle. The concentration of heavy metals Cd and As in the filtrate was determined using inductively coupled plasma mass spectrometry (ICP-MS) or atomic absorption spectrometry (AAS).

[0108] The effective state content of heavy metals was calculated according to ω = (ρ × V) / (m × 1000).

[0109] ω: effective state heavy metal content in the sample, mg / kg;

[0110] ρ: mass concentration of heavy metals in the determination solution, μg / L;

[0111] V: volume of extraction solution, mL;

[0112] m: sample mass, g.

[0113] The fixation rate of heavy metals was calculated according to fixation rate (%) = (effective state content of heavy metals in raw vermicompost - effective state content of heavy metals in examples or comparative examples) / effective state content of heavy metals in raw vermicompost × 100%.

[0114] (2) Heavy metal leaching toxicity test: 10.00 g of raw vermicompost without any treatment and 10.00 g of stabilized vermicompost treated in each example and comparative example were weighed into an extraction bottle, and the vermicompost was added to the extraction bottle with an extraction solution (acetic acid buffer solution with pH = 2.64) at a liquid-solid ratio of 20:1 (L / kg). The extraction bottle was fixed on a reverse oscillation device and oscillated at a speed of 30 ± 2 r / min for 18 ± 2 hours. Filtration was performed using a 0.45 μm or 0.6 μm glass fiber filter membrane under negative pressure, and the filtrate was collected. The total cadmium concentration and total arsenic concentration in the filtrate were determined using ICP-MS or AAS.

[0115] The maximum allowable emission concentration in the "Integrated Wastewater Discharge Standard" (GB 8978-1996) is: total cadmium 0.1 mg / L, total arsenic 0.5 mg / L.

[0116] The test results are shown in Table 1.

[0117] Table 1

[0118]

[0119] It can be seen from the combination of Example 1 and Comparative Examples 1-3 and Table 1 that the Cd fixation rate and the As fixation rate of Comparative Examples 1-3 are less than 60%, the total cadmium concentration in the filtrate is greater than 0.1 mg / L, and the total arsenic concentration in the filtrate is greater than 0.5 mg / L. This shows that the raw material ratio and preparation method of Example 1 can help to improve the fixation and stabilization effect of the biochar material on heavy metals in the earthworm manure, and effectively fix and stabilize the heavy metals in the earthworm manure.

[0120] This may be because phosphoric acid etches biomass at high temperature, creating extremely developed pore structures, providing a large specific surface area and attachment sites for subsequent loading of LDH and nZVI, and also directly adsorbing and fixing heavy metal ions. The oxygen-containing and phosphorus-containing functional groups introduced by phosphoric acid activation can undergo strong surface complexation with heavy metal ions and generate extremely stable metal phosphate precipitates. In S2, the P-BC is immersed in a mixed solution of Mg 2+ and Al 3+ ions, which are adsorbed on the surface. After adding alkali, these ions precipitate in the form of LDH under mild hydrothermal conditions, growing in situ on the surface and in the pores of P-BC, and binding very firmly. LDH has a unique layered structure, with positively charged layers and exchangeable anions between the layers. When encountering anionic heavy metals such as AsO4 3- and CrO4 2- , ion exchange occurs, firmly fixing them between the layers. P-BC is good at fixing cationic heavy metals, while LDH is good at fixing anionic heavy metals. The combination of the two gives the material broad-spectrum adsorption capacity, covering almost all types of toxic heavy metals in earthworm manure. LDH grows in the pores of P-BC, avoiding stacking of its layers and exposing more active sites, improving adsorption efficiency. On the basis of adsorption and precipitation, reduction stabilization is introduced as a more thorough mechanism. In particular for Cr(VI) and As(III), which are difficult to completely solve by adsorption, the reduction of nZVI is crucial. Loading nZVI in the pores of LDH@P-BC can prevent the agglomeration of nZVI nanoparticles, improve their dispersibility and reactivity, and also serve as a protective layer for nZVI, reducing its oxidation failure and making it more durable. All captured heavy metals are ultimately converted into extremely stable forms in the natural environment through various pathways such as formation of phosphate precipitates, fixation between LDH layers, wrapping by iron oxides, or reduction to inert elements, greatly reducing their bioavailability and leaching risk.

[0121] It can be seen from the combination of embodiments 1-26 and table 1 that the Cd fixation rate and the As fixation rate of embodiments 1-26 are both greater than 70%, the total cadmium concentration in the filtrate is significantly less than 0.1 mg / L, and the total arsenic concentration in the filtrate is significantly less than 0.5 mg / L. This shows that using the raw material ratio and preparation method in the range of embodiments 1-26 can help to improve the fixation and stabilization effect of the biochar material on heavy metals in the earthworm manure.

[0122] It can be seen from the comparison of the detection data of embodiments 1-26 that using a NaOH solution with a molar concentration of 1.8-2.2 mol / L, a mass-volume ratio of the LDH@P-BC material to the NaBH4 aqueous solution of 0.15-0.22 g / mL, a mass-volume ratio of the LDH@P-BC material to the ferric chloride hexahydrate solution of 0.4-0.44 g / mL, and P-BC powder with a particle size of 60-160 mesh, can help to further improve the fixation and stabilization effect of the biochar material on heavy metals in the earthworm manure.

[0123] The specific embodiments are only an explanation of the present application, and are not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the present specification, as long as the modifications are within the scope of the claims of the present application.

Claims

1. A method for preparing biochar material that adsorbs heavy metals from earthworm castings, characterized in that, Includes the following steps: S1. Take waste green tea residue, dry and crush it, soak it in a phosphoric acid solution with a mass concentration of 38-42% for 5-6 hours, filter it to obtain filter residue, heat treat the filter residue at 540-560℃ for 58-66 minutes under nitrogen protection, cool it, wash it until neutral, dry it and grind it to obtain P-BC powder. S2. Disperse P-BC powder in deionized water, add a metal salt solution with a total metal ion concentration of 0.8-1.2 mol / L, stir for 55-65 min under nitrogen protection, add a precipitant dropwise, adjust the pH to 9.5-10.5, raise the temperature to 62-68℃, maintain the reaction temperature for 17.2-18.6 h, cool, filter, wash, and dry to obtain LDH@P-BC material; the mass-to-volume ratio of P-BC powder to metal salt solution is 0.22-0.28 g / mL, and the Mg content in the metal salt solution is... 2+ With Al 3+ The molar ratio is (1.8-2.2):1; S3. Disperse LDH@P-BC material in deionized water, add ferric chloride hexahydrate solution with a concentration of 132-136 g / L under nitrogen protection and stirring, stir at 36-42℃ for 3.5-4.5 h, add NaBH4 aqueous solution with a concentration of 0.6-1.0 mol / L dropwise, after the addition is complete, separate, wash and dry to obtain biochar material that adsorbs heavy metals in earthworm castings.

2. The method for preparing biochar material for adsorbing heavy metals in earthworm castings according to claim 1, characterized in that, The precipitant is a NaOH solution with a molar concentration of 1.8-2.2 mol / L.

3. The method for preparing biochar material for adsorbing heavy metals in earthworm castings according to claim 1, characterized in that, The preparation steps of the metal salt solution are as follows: dissolve magnesium chloride hexahydrate and aluminum trichloride in deionized water to obtain magnesium chloride hexahydrate solution and aluminum trichloride solution respectively. Mix the magnesium chloride hexahydrate solution and aluminum trichloride solution and make up to a certain volume to obtain the metal salt solution.

4. The method for preparing biochar material for adsorbing heavy metals in earthworm castings according to claim 1, characterized in that, In step S3, the mass-to-volume ratio of LDH@P-BC material to NaBH4 aqueous solution is 0.15-0.22 g / mL.

5. The method for preparing biochar material for adsorbing heavy metals in earthworm castings according to claim 4, characterized in that, In step S3, the mass-to-volume ratio of LDH@P-BC material to ferric chloride hexahydrate solution is 0.4-0.44 g / mL.

6. The method for preparing biochar material for adsorbing heavy metals in earthworm castings according to claim 1, characterized in that, In step S1, after drying, grinding, and sieving, P-BC powder with a particle size of 60-160 mesh is obtained.

7. A biochar material for adsorbing heavy metals from earthworm castings, characterized in that, It is prepared by the method for preparing biochar material for adsorbing heavy metals in earthworm castings as described in any one of claims 1-6.

8. A treatment method using the biochar material for adsorbing heavy metals in earthworm castings as described in claim 7, characterized in that, Earthworm castings are mixed evenly with biochar material that adsorbs heavy metals from the earthworm castings. Deionized water is added during the mixing process to obtain a mixture with a moisture content of 50%-60%. The mixture is placed in a sealed container and left to stand at 25-35℃. During the standing period, it is stirred every 3-5 days. After standing for 14-21 days, the mixture is allowed to mature and then naturally air-dried until the moisture content is below 30%, resulting in stabilized earthworm castings. The treatment is then complete.

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