Modified biochar adsorbent as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of functional materials, and discloses a modified charcoal adsorbent as well as a preparation method and application thereof. The invention provides a modified biochar adsorbent capable of efficiently adsorbing heavy metals, which is prepared by modifying wheat straw biochar (WB) through Prussian blue (PB), and the preparation method comprises the following steps: 1) pretreating wheat straws; 2) calcining wheat straws to prepare biochar; 3) modifying the biochar with Prussian blue; and 4) preparing the adsorbent. The modified biochar adsorbent has the porous structure and high specific surface area of biochar and the strong adsorption characteristic of Prussian blue on heavy metal ions, shows excellent adsorption performance on Tl in water and soil, can face complex actual use environments, and is suitable for treatment of industrial wastewater and heavy metal contaminated soil.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional materials, and relates to a modified biochar adsorbent, a preparation method thereof and an application thereof. Background Art

[0002] Thallium (Tl) is widely distributed in nature and has been widely used in industrial fields such as electronics, pharmaceuticals, aerospace and high-energy physics. Therefore, it can be widely detected in water and soil. Due to the strong toxicity of Tl, even exposure to a very small amount of Tl will cause serious damage to multiple organ systems of the human body, especially the nervous system. The adult lethal dose of Tl is only 8-10 mg / kg. Therefore, many countries have listed it as a controlled pollutant. However, due to the historical neglect of Tl pollution and the lag of regulatory actions, the pollution problem has been continuously exacerbated.

[0003] Among various existing materials, biochar has received increasing attention due to its unique properties. Research shows that biochar can improve the physical and chemical properties of soil and effectively immobilize heavy metals through mechanisms such as redox, surface adsorption, complexation, precipitation, ion exchange and electrostatic interaction. However, due to differences in raw materials and preparation conditions, the effects of biochar also show great differences. For example, the limited surface area and surface functional groups of biochar usually limit its adsorption capacity and affinity for heavy metals, resulting in low removal rate and poor removal effect. In order to improve the adsorption performance, different modification methods can be used to improve its adsorption capacity for heavy metals and the like.

[0004] Prussian blue (PB) is the first modern synthetic pigment formed by the oxidation of ferric ferrocyanide salts, with the chemical formula Fe4[Fe(CN)6]3. It is insoluble in water and exists in an extremely fine colloidal dispersion state, and its sensitivity depends on the size of the colloidal particles. In addition to being used in coatings, PB is also used as an antidote for Tl(I) due to its strong binding ability with metals. However, the easy aggregation and difficult recovery of PB powder particles limit its application in large-scale environmental remediation.

[0005] In order to overcome the disadvantages of the existing technology, such as the complex preparation method and high cost of thallium pollution remediation materials, low treatment efficiency and unsatisfactory effect on thallium pollution, it is necessary to explore a composite material that can integrate the performance advantages of biochar and Prussian blue, in order to achieve the treatment of Tl pollution in water or soil. Summary of the Invention

[0006] The technical problem to be solved by the present invention is: to provide a composite material for treating Tl pollution in water bodies or soil, which is simple and convenient to prepare, economically feasible and has excellent performance. By loading Prussian blue (PB) onto biochar with a porous structure and utilizing the adsorption characteristics of biochar and the strong binding ability of PB to heavy metals such as Tl, a synergistic treatment effect is achieved. To achieve this technical purpose, the present invention provides the following detailed technical solutions.

[0007] In the first aspect, the present invention provides a preparation method of a modified biochar adsorbent, including:

[0008] 1) Pretreatment of wheat straw;

[0009] 2) Calcination of wheat straw to prepare biochar;

[0010] 3) Modification of biochar with Prussian blue;

[0011] 4) Preparation of the adsorbent.

[0012] Further, in step 1) of the above preparation method, the pretreatment method includes: washing wheat straw with deionized water and absolute ethanol respectively, and drying for later use.

[0013] Further, in step 2) of the above preparation method, the pretreated wheat straw is calcined in an inert gas atmosphere to obtain wheat straw biochar; the inert gas is nitrogen; the heating rate of calcination is 7 - 10 °C / min, the calcination temperature is 450 - 550 °C, calcination is carried out for 2 - 4 h, and then it is kept warm for 1 - 3 h.

[0014] Further, in step 3) of the above preparation method, the biochar prepared in step 2) is ultrasonically oscillated and dispersed with ultrapure water, then Prussian blue is added, continuously stirred and then left to stand, centrifuged, and washed to obtain a solid; the mass ratio of Prussian blue to biochar is 1:1.

[0015] Further, in step 3) of the above preparation method, the continuous stirring time is 15 min, the standing time is 24 h, the centrifugation parameters are 4000 rpm and 5 min, and the washing water is ultrapure water.

[0016] Further, in step 4) of the above preparation method, the solid obtained in step 3) is dried and ground to obtain the modified biochar adsorbent.

[0017] Further, in step 4) of the above preparation method, the drying time is 12 h and the temperature is 40 °C; the grinding particle size is 180 - 250 μm.

[0018] In the second aspect, the present invention provides a modified biochar adsorbent, which is prepared by the above-mentioned preparation method.

[0019] Thirdly, the present invention provides the application of the above-mentioned modified biochar adsorbent, and the modified biochar adsorbent is used for heavy metal pollution treatment.

[0020] Specifically, in the above application, the heavy metal pollution includes thallium pollution; the matrix to be treated includes: water body or soil.

[0021] Compared with the prior art, the "modified biochar adsorbent, its preparation method and application" of the present invention has at least the following beneficial effects:

[0022] 1) The present invention uses common agricultural waste wheat straw (WB) as the raw material, and prepares a modified biochar adsorbent that can be used for the treatment of Tl pollution in water bodies and soils after modification with Prussian blue (PB). Not only is the raw material source rich, but the preparation cost is low, and the technology is easy to promote. At the same time, it also provides a suitable way for the resource utilization of wheat straw, which helps to improve the economic value of wheat straw.

[0023] 2) The specific surface area of the biochar adsorbent prepared by the present invention is increased by 56.75% compared with that of wheat straw biochar (WB), and the pore volume and average pore diameter are increased by 877% and 235% respectively, which is beneficial to the removal of Tl.

[0024] 3) The modified biochar adsorbent prepared by the present invention has excellent removal effect on Tl-containing water bodies. The adsorption capacity of Tl is 2.21 times that of WB, and the highest removal rate reaches 99.3%. It can also maintain a high Tl removal rate (≥95%) in a wide pH value range (2 - 11) and in the presence of various competing cations (Na + 、Mg 2+ ), far superior to the WB material.

[0025] 4) The modified biochar adsorbent prepared by the present invention also has an outstanding passivation effect on Tl in soil. The passivation rate of Tl reaches 87.7%, significantly reducing the bioavailability of Tl in soil and reducing the environmental pollution of Tl around and its enrichment in plants. Description of the Drawings

[0026] Figure 1 Shows the changes in Tl adsorption capacity and removal rate of the material of the present invention and the comparative material under different dosages and different initial pH conditions.

[0027] Figure 2 Shows the changes in Tl adsorption capacity and removal rate of the material of the present invention and the comparative material under different interfering ion concentration conditions.

[0028] Figure 3 Are SEM images of PB@WB (the material of the present invention) and the comparative materials (Fe-OH@WB and WB) before and after Tl adsorption.

[0029] Figure 4 These are the XRD patterns of the material of the present invention and the comparative material before and after Tl adsorption.

[0030] Figure 5 These are the FTIR patterns of the material of the present invention and the comparative material before and after Tl adsorption.

[0031] Figure 6 These are the XPS patterns of the material of the present invention before and after Tl adsorption.

[0032] Figure 7 These are the proportions of Tl species contents in the Tl-containing soil after adding the material of the present invention and the comparative material for 7 days and 15 days respectively.

[0033] Figure 8 These are the proportions of Tl species contents in the Tl-containing soil after adding the material of the present invention and the comparative material for 30 days and 45 days respectively. Detailed implementation manners

[0034] The present invention will be described below in conjunction with embodiments. The technical solutions in the embodiments of the present invention will be clearly and completely described. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without making creative efforts belong to the scope of protection of the present invention.

[0035] The adsorption amount and removal rate of Tl in water are obtained by the following method: An inductively coupled plasma mass spectrometer (ICP-MS, NexION2000, PerkinElmer, USA) is used to measure the remaining concentration of Tl after adsorption.

[0036] The adsorption amount (q t ) and removal rate (R) of Tl are calculated through the formula:

[0037]

[0038] where q t represents the adsorption amount of Tl at time t (μg / g), C0 represents the concentration of Tl at the start of the reaction (μg / L), C t represents the concentration of Tl at time t (μg / L), m represents the mass of the adsorbent added (g), and V represents the volume of the solution (L). R represents the removal rate of Tl (%), and C e represents the concentration of Tl at equilibrium (μg / L).

[0039] The passivation rate of Tl in the soil was obtained by the following method: The thallium in the soil was fractionated by the modified BCR method, and the concentration of Tl was measured using an inductively coupled plasma mass spectrometer (ICP-MS, NexION2000, PerkinElmer, USA). The passivation rate (I) of Tl was calculated by the formula:

[0040]

[0041] where I represents the passivation rate (%), S0 represents the concentration (μg / g) of bioavailable Tl (weak acid exchange form) in the control group soil (without using adsorbent), and S t represents the concentration (μg / g) of bioavailable Tl after adding the adsorbent.

[0042] Example 1

[0043] This example describes the preparation method of the modified biochar adsorbent.

[0044] 1) Pretreatment of wheat straw: The wheat straw was washed with deionized water and absolute ethanol respectively and dried for later use.

[0045] 2) Preparation of biochar by calcining wheat straw: The pretreated wheat straw was calcined in a nitrogen atmosphere. The heating rate of calcination was 8 °C / min, the calcination temperature was 500 °C, and it was calcined for 3 h and then kept warm for 2 h to obtain wheat straw biochar (WB).

[0046] 3) Modification of biochar with Prussian blue (PB): Take 2 g of the WB sample prepared in step 2) and put it into a beaker containing 200 mL of ultrapure water, ultrasonically disperse for 60 min, then add 2 g of PB (the mass ratio of PB to WB is 1:1), continuously stir for 15 min and then let it stand for 24 h to ensure full contact between PB and WB; after standing, centrifuge at 4000 rpm for 5 min and wash with ultrapure water to obtain the solid.

[0047] 4) Preparation of the adsorbent: Dry the solid obtained in step 3) at 40 °C for 12 h and grind it to 180 - 250 μm to obtain the biochar adsorbent modified with Prussian blue, which is denoted as PB@WB.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is as follows: The modification method is different from that of Example 1, and the other raw materials are the same as those in Example 1.

[0050] 1) Pretreatment of wheat straw: The same as in Example 1.

[0051] 2) Preparation of biochar by calcining wheat straw: The same as in Example 1.

[0052] 3) FeCl3-modified biochar: Grind the WB prepared in step 2) to 180 - 250 μm, take 50 g of the ground WB sample and put it into a 0.1 M FeCl3 solution, adjust the pH of the mixture to 8 with NaOH, stir the mixture for 30 min and then let it stand for 24 h.

[0053] 4) Preparation of adsorbent: Dry the standing mixture in an electrothermal blast drying oven at 40 °C until constant weight, grind it again to 180 - 250 μm to obtain the FeCl3-modified biochar adsorbent, denoted as Fe-OH@WB.

[0054] Example 2

[0055] This example describes the treatment effect of the modified biochar adsorbent PB@WB on Tl-polluted water under different Tl concentration conditions.

[0056] 1) Prepare 20 mL of aqueous solutions with initial Tl concentrations of 50, 100, 200, 400, 800, and 1000 μg / L respectively in 50 mL centrifuge tubes, and adjust the initial pH value to 6.0 ± 0.1.

[0057] 2) Add the PB@WB prepared in Example 1 to the 20 mL of the aqueous solution so that its final concentration in the aqueous solution is 1.25 g / L, then place the centrifuge tube on a shaker at 25 °C and 180 rpm for 24 h.

[0058] 3) After the reaction, take samples, filter with a 0.22 μm polyethersulfone membrane, and analyze the Tl content in the filtrate with an inductively coupled plasma mass spectrometer (ICP-MS). The experimental results are shown in Table 1.

[0059] Table 1. Treatment effect of PB@WB on Tl-polluted water with different concentrations

[0060]

[0061] As can be seen from Table 1, in the Tl concentration range of 50 - 1000 μg / L, the treatment effect of PB@WB on Tl-polluted water (expressed as Tl removal rate) reaches over 95%, showing significant results.

[0062] Example 3

[0063] This example describes the treatment effect of PB@WB on Tl-polluted water under different dosages of the modified biochar adsorbent PB@WB.

[0064] 1) Prepare 20 mL of an aqueous solution with an initial Tl concentration of 400 μg / L in a 50 mL centrifuge tube, and adjust the initial pH value to 6.0 ± 0.1.

[0065] 2) Add the PB@WB prepared in Example 1 to 20 mL of the aqueous solution respectively, so that their final concentrations in the aqueous solution are 0.125, 0.25, 0.615, 1.25, 2.5, and 3.75 g / L respectively. Then place the centrifuge tubes on a shaker at 25 °C and 180 rpm and react for 24 h.

[0066] 3) After the reaction, take samples, filter with a 0.22 μm polyethersulfone membrane, and analyze the Tl content in the filtrate with an inductively coupled plasma mass spectrometer (ICP-MS). The experimental results are shown in Table 2.

[0067] Table 2. Treatment effects of Tl-polluted water bodies with different dosages of PB@WB

[0068]

[0069] As can be seen from Table 2, within the range of PB@WB dosages from 0.125 to 3.75 g / L, the treatment effects of PB@WB on Tl-polluted water bodies (expressed by Tl removal rate) are not lower than 93%, and the results are remarkable.

[0070] Example 4

[0071] This example describes the treatment effects of the modified biochar adsorbent PB@WB on Tl-polluted water bodies under different reaction time conditions. The difference between this example and Example 2 is that the reaction time conditions in step 2) are different. The setting of the reaction time and the experimental results are shown in Table 3.

[0072] Table 3. Treatment effects of Tl-polluted water bodies with different reaction times

[0073]

[0074] As can be seen from Table 3, within the time range of 1 to 1440 min, the treatment effects of PB@WB on Tl-polluted water bodies (expressed by Tl removal rate) all reach more than 64%, and the results are remarkable.

[0075] Example 5

[0076] This example describes the treatment effects of the modified biochar adsorbent PB@WB on Tl-polluted water bodies under different solution pH conditions. The difference between this example and Example 2 is that the reaction pH value in step 1) is different. The setting of the pH value and the experimental results are shown in Table 4.

[0077] Table 4. Treatment effects of Tl-polluted water bodies with different reaction pH values

[0078]

[0079] As can be seen from Table 4, in the pH range of 2 - 11, the treatment effect of PB@WB on Tl-polluted water bodies (expressed as the Tl removal rate) reached over 94%, showing significant results.

[0080] Example 6

[0081] This example describes the treatment effect of the modified biochar adsorbent PB@WB on Tl-polluted water bodies under the condition of the presence of interfering ions with different concentrations. The difference between this example and Example 2 is that: the aqueous solution prepared in step 1) also contains other interfering ions (adding NaNO3 that contributes Na + or adding Mg(NO3)2 that contributes Mg 2+ ). The setting conditions of the interfering ions and the experimental results are shown in Table 5.

[0082] Table 5. Influence of interfering ions on the treatment effect of Tl-polluted water bodies

[0083]

[0084]

[0085] As can be seen from Table 5, Na + and Mg 2+ have no obvious influence on the treatment effect of the modified biochar adsorbent PB@WB on Tl-polluted water bodies (expressed as the Tl removal rate). In the presence of interfering ions with a concentration as high as 50 mmol / L, the removal rate remains above 96%, indicating that the modified biochar adsorbent PB@WB can be used for the removal of Tl in complex ion interference environments such as hard water quality.

[0086] Example 7

[0087] This example describes the comparison of the use effects of the modified biochar adsorbent PB@WB, Fe-OH@WB, and WB in Tl-polluted water bodies.

[0088] According to the test results of the foregoing examples, the test conditions of an initial Tl concentration of 400 μg / L, an adsorbent dosage of 1.25 g / L, a reaction time of 24 h, and a reaction pH of 6 were selected to compare the use effects of PB@WB, Fe-OH@WB, and WB. The test method was the same as that in Example 2, and the test results are shown in Table 6.

[0089] Table 6. Use effects of PB@WB, Fe-OH@WB, and WB in Tl-polluted water bodies

[0090] Group Adsorption capacity (μg / g) Tl removal rate (%) WB 146.1 43.11 Fe-OH@WB 139.9 41.28 PB@WB 322.8 95.24

[0091] As can be seen from Table 6, the treatment effects of unmodified wheat straw biochar WB and the adsorbent Fe-OH@WB modified with FeCl3 on Tl-polluted water are both poor, less than 45%; the treatment effect of the modified biochar adsorbent PB@WB on Tl-polluted water (expressed by the Tl removal rate) is the best, reaching 95.24%, indicating that the modified biochar adsorbent prepared by the method of the present invention significantly improves the treatment effect of Tl-containing sewage.

[0092] Analysis results of Examples 5-7: Under different changing conditions, PB@WB has outstanding performance in the adsorption of Tl. Compared with WB and Fe-OH@WB, the removal rates of Tl by PB@WB are all maintained above 95% (see Figure 1 and Table 6). In the face of a wide range of pH conditions and a complex ion interference environment, the removal effect of PB@WB is still leading (see Table 4 and Table 5). Among them, for the extreme solution environments with pH of 2 and 11, PB@WB has high removal rates of 94.5% and 99.0% for Tl ( Figure 1 ); for the situation where there are other interfering ions, the average removal rate of PB@WB reaches 98% ( Figure 2 ), indicating that PB@WB has a wide application range and is more capable of facing complex actual environments.

[0093] Example 8

[0094] This example describes the specific surface area, average pore diameter and pore volume of the modified biochar adsorbent PB@WB, Fe-OH@WB and WB. The specific surface area, average pore diameter and pore volume are measured by the nitrogen adsorption-desorption isotherm measurement method (BET, Micromeritics ASAP 2460, USA), and the results are shown in Table 7.

[0095] Table 7. Specific surface area, average pore diameter and pore volume of PB@WB, Fe-OH@WB and WB

[0096] Group <![CDATA[S BET (m 2 / g)]]> Average pore diameter (nm) <![CDATA[Pore volume (cm 3 / g)]]> WB 34.37 4.83 0.036 Fe-OH@WB 34.25 4.27 0.032 PB@WB 53.87 16.19 0.352

[0097] As can be seen from Table 7, the specific surface area, average pore diameter and pore volume of the modified biochar adsorbent PB@WB prepared by the present invention are significantly increased compared with the other two groups, indicating that PB@WB has a stronger adsorption effect on Tl.

[0098] Example 9

[0099] This example describes the surface characteristics of the modified biochar adsorbent PB@WB, Fe-OH@WB and WB.

[0100] 1) Surface morphology

[0101] The surface morphology and elemental composition of the materials were analyzed using a scanning electron microscope (SEM, TESCAN MIRALMS, Czech Republic) combined with an energy-dispersive spectrometer (EDS). The SEM scanning results of WB, Fe-OH@WB, and PB@WB are as Figure 3 shown. It can be seen from Figure 3 that compared with WB and Fe-OH@WB, PB@WB has a larger specific surface area and richer pores, and these changes enhance the adsorption capacity for Tl.

[0102] 2) Surface mineral composition

[0103] The mineral composition on the surface of the materials was characterized using X-ray diffraction analysis (XRD, Rigaku Ultima IV, Japan). The XRD analysis results of PB@WB, Fe-OH@WB, and WB materials before and after Tl adsorption are as Figure 4 shown. It can be seen from Figure 4 that PB@WB shows new obvious characteristic peaks at 17.4°, 24.7°, 35.2°, 39.5°, 50.6°, 53.9°, and 57.1°, which are consistent with the characteristic peaks of Prussian blue (PB), corresponding to the (200), (210), (211), (220), (310), (311), and (222) crystal planes respectively. The appearance of these characteristic peaks confirms the successful incorporation of PB onto WB, which can strengthen the exchange interaction between thallium ions and PB@WB, providing strong evidence for the high adsorption capacity of PB@WB.

[0104] 3) Surface functional groups

[0105] The surface functional groups of the materials were analyzed using a Fourier transform infrared spectrometer (FTIR, Thermo Fisher Scientific Nicolet iS20, USA). The FTIR analysis results of PB@WB, Fe-OH@WB, and WB materials before and after Tl adsorption are as Figure 5 shown. It can be seen from Figure 5 that compared with WB and Fe-OH@WB, PB@WB has a richer variety and higher intensity of functional groups, so it has a stronger adsorption capacity for Tl.

[0106] 4) Valence analysis

[0107] X-ray photoelectron spectroscopy (XPS, Thermo Scientific K-Alpha+, USA) was used to analyze the surface composition and valence state of the materials with the C1s peak as the internal standard calibration peak. The XPS analysis results of PB@WB before and after Tl adsorption are as Figure 6 shown. It can be seen from Figure 6 that the diffraction peak intensity of Tl is obvious, indicating the successful adsorption of Tl by PB@WB.

[0108] Example 10

[0109] This example describes the application effect of the modified biochar adsorbent PB@WB in the treatment of Tl-containing soil.

[0110] In the soil contaminated with Tl (3.75 mg / kg), 5, 10, 20, and 30 g / kg of PB@WB prepared in Example 1, Fe-OH@WB prepared in Comparative Example 1, and WB were respectively applied. During this period, deionized water was supplemented by the weighing method to keep the soil samples at 60% of the maximum water holding capacity in the field. The treated soil samples were cultured under indoor conditions, and soil samples were collected at 7 d, 15 d, 30 d, and 45 d respectively to measure the concentrations (mg / kg) of four forms of Tl in the soil (including weak acid exchangeable state, reducible state, oxidizable state, and residual state). The soil without adsorbent was used as the blank control group (CK), and the passivation efficiency (%) was calculated. According to the results, the influence of different treatment materials on the passivation effect of Tl was analyzed, and the results are as Figure 7 、 Figure 8 shown.

[0111] As Figure 7 、 Figure 8 can be seen, PB@WB, Fe-OH@WB, and WB can all reduce the content of available Tl in the soil to varying degrees. Among them, the passivation effect of PB@WB is significantly better, so the content of the most difficult-to-extract residual Tl in the soil is also the largest. For example, after treating the Tl-containing soil with 30 g / kg of PB@WB for 30 d, the Tl in the weak acid exchangeable state in the soil decreased from 1.6% in the control group to 0.13%, while the residual Tl increased from 92.16% in the control group to 97.68%. After the treatment time reached 45 d, the passivation rate reached 87.7% and the fluctuation was small. When using the same dose (30 g / kg) of WB and Fe-OH@WB for treatment, after the same passivation time, the Tl in the weak acid exchangeable state was 0.80% and 1.04% respectively. It shows that PB@WB can convert more weak acid exchangeable Tl into residual Tl with low bioavailability, thereby effectively reducing the bioavailability and mobility of Tl in the soil, and the passivation effect is better. This further shows that the modified biochar adsorbent PB@WB prepared by the method described in the present invention also has high-efficiency and stable passivation ability for Tl-containing soil.

[0112] The above-described examples are only a part of the examples of the present invention, rather than all the examples. The detailed description of the examples of the present invention is not intended to limit the scope of the present invention claimed, but only represents the selected examples of the present invention. All other examples obtained by relevant deductions and substitutions made by those of ordinary skill in the art under the premise of not making creative labor according to the concept of the present invention belong to the scope of protection of the present invention.​

Claims

1. A preparation method of a modified biochar adsorbent, characterized in that, Including: 1) Pretreatment of wheat straw; 2) Calcination of wheat straw to prepare biochar; 3) Modification of biochar with Prussian blue; 4) Preparation of adsorbent.

2. The preparation method according to claim 1, wherein In step 1), the pretreatment method includes: washing wheat straw with deionized water and absolute ethanol respectively, and drying for standby.

3. The preparation method according to claim 1, characterized in that, In step 2), the pretreated wheat straw is calcined in an inert gas atmosphere to obtain wheat straw biochar; the inert gas is nitrogen; the heating rate of calcination is 7 - 10 °C / min, the calcination temperature is 450 - 550 °C, calcination is carried out for 2 - 4 h, and then kept warm for 1 - 3 h.

4. The preparation method according to claim 1, characterized in that, In step 3), the biochar prepared in step 2) is ultrasonically oscillated and dispersed with ultrapure water, then Prussian blue is added, continuously stirred and then left to stand, centrifuged, and washed to obtain a solid; the mass ratio of Prussian blue to biochar is 1:

1.

5. The preparation method according to claim 4, wherein, In step 3), the continuous stirring time is 15 min, the standing time is 24 h, the centrifugation parameters are 4000 rpm and 5 min, and the washing water is ultrapure water.

6. The preparation method according to claim 1, characterized in that, In step 4), the solid obtained in step 3) is dried and ground to obtain the modified biochar adsorbent.

7. The preparation method according to claim 6, characterized in that, In step 4), the drying time is 12 h and the temperature is 40 °C; the grinding particle size is 180 - 250 μm.

8. A modified biochar adsorbent, characterized in that, Prepared by the preparation method according to any one of claims 1 - 7.

9. Use of the modified biochar adsorbent according to claim 8, characterized in that, The modified biochar adsorbent is used for heavy metal pollution treatment.

10. The application according to claim 9, wherein The heavy metal pollution includes thallium pollution; the matrix to be treated includes: water body or soil.

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