Preparation method and application of sulfur-modified shrimp shell biochar

Abstract

The application discloses a preparation method of sulfur-modified shrimp shell biochar and application thereof. The preparation method of the sulfur-modified shrimp shell biochar comprises the following steps: taking shrimp shell raw biomass as raw material, and preparing raw biochar through limited oxygen slow pyrolysis; and using a sulfur modification liquid containing dithiodibenzoic acid and KOH to modify the biochar, so as to obtain a sulfur-modified biochar product. The application uses biochar to prepare a cheap, green and efficient sulfur-modified biochar material as an adsorbent, so that cadmium in water can be efficiently removed.

Description

Technical Field

[0001] The invention belongs to the technical field of heavy metal pollution treatment, and in particular relates to a preparation method of sulfur-modified shrimp shell biochar and application thereof. Background Art

[0002] With the development of industrialization and urbanization, heavy metal pollution in water bodies has become a major issue impacting economic development. Cadmium is widely used in electroplating, electronics, light industry, and machinery manufacturing, leading to a rapid increase in cadmium smelting production. Furthermore, the large amount of industrial wastewater generated during cadmium production and smelting has caused serious pollution to soil and water bodies. Once cadmium enters soil and water, it harms and inhibits the growth of plants, animals, and microorganisms, negatively impacting the ecological environment and human health. For example, long-term exposure to cadmium in the environment first causes an increase in urinary cadmium, which can cause permanent kidney damage. It can also cause bone decalcification, leading to osteoporosis, and even lead to "pain syndrome," one of the ten major environmental health hazards. Clinical studies have also shown that patients with chronic cadmium poisoning may also suffer from damage to the nervous system, immune system, and reproductive system, as well as a higher incidence of tumors. Therefore, reducing or eliminating cadmium ions in industrial wastewater is of paramount importance.

[0003] Methods for removing cadmium from water bodies are mainly divided into three categories: biological, chemical, and physical. Chemical methods are further divided into redox methods and chemical co-precipitation methods; physical methods include adsorption, membrane separation technology, and ion exchange methods; biological methods include microbial complexation, flocculation, adsorption, and plant remediation. Although there are many methods, they all have some drawbacks. For example, chemical precipitation requires a large amount of chemicals, which can easily lead to secondary pollution; the combined plant and animal remediation method may not show obvious remediation effects for a long time. Adsorption is the most common method for treating wastewater. It is simple to operate and easy to use.

[0004] Biochar is a carbon-rich, highly aromatic, and stable solid product produced by the slow pyrolysis of carbon-rich biomass feedstock under completely anaerobic or partially anoxic conditions. It features a well-developed internal porosity, a large specific surface area, and abundant surface oxygen-containing functional groups. Biochar can be produced from a wide range of raw materials, primarily agricultural and aquaculture waste, biochar sludge, organic solid waste, and animal manure. In recent years, biochar has garnered significant attention for the remediation of heavy metal contamination in terrestrial and aquatic environments. Biochar's graded porosity and abundant functional groups provide numerous adsorption sites for heavy metal adsorption. Studies have shown that the presence of mineral components in biochar significantly enhances heavy metal adsorption. During pyrolysis, the presence of mineral components alters the biochar's surface functional groups and ion exchange capacity, thereby increasing its ion exchange capacity. Biochar has a significant effect on the remediation of heavy metals in aquatic environments. However, conventional, unmodified biochar typically loses a significant number of surface functional groups at elevated temperatures, significantly reducing its adsorption efficiency. However, the pore structure and specific surface area of ​​biochar produced at lower temperatures are smaller, so its treatment effect is not very significant. Therefore, the researchers turned their research direction to modifying biochar with other materials or treatment methods with special functions to synthesize carbon composite materials with more significant effects.

[0005] Existing sulfur-modified biochar typically uses a sulfur-modified solution prepared by mixing NaOH and CS2 solutions to modify plant biochar. For example, Chinese patent CN112755960A uses a sulfur-modified solution obtained by reacting sulfide containing CS2 with alkali metal hydroxide to modify biochar. This solution is then mixed with alginate to form a gel for removing heavy metals from the solution. Chinese patent CN107236545A uses a sulfur-modified solution mixed with NaOH and CS2 solutions to prepare a sulfur-based biochar precursor. This solution is then modified with an iron solution to produce a sulfur-based-iron composite modified biochar, which is used as a heavy metal cadmium stabilizer. The preparation process is relatively complex. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the purpose of the present invention is to provide a preparation method and application of sulfur-modified biochar, wherein the sulfur-modified shrimp shell biochar has a good adsorption effect on Cd in water and reduces its heavy metal mobility.

[0007] In order to achieve the above invention purpose, the present invention adopts the following technical solutions:

[0008] A method for preparing sulfur-modified shrimp shell biochar comprises the following steps: mixing shrimp shell biochar and a sulfur-modified modification liquid, shaking the mixture to mix evenly, filtering, drying, grinding, and screening to obtain the sulfur-modified biochar; the sulfur-modified modification liquid comprises dithiodibenzoic acid and a KOH solution.

[0009] Preferably, the concentration of the KOH solution is 0.8 mol / L, and the solid-liquid ratio of dithiodibenzoic acid and the KOH solution is 0.5-3 g:10 ml; the preparation method of the sulfur-modified modification liquid is to mix the dithiodibenzoic acid and the KOH solution evenly, magnetically stir at 25° C. for 4 hours, and then continue ultrasonication for 2 hours to obtain the sulfur-modified modification liquid.

[0010] Preferably, the shrimp shell biochar and the sulfur-modified modification liquid are impregnated and mixed at a solid-liquid ratio of 1g:10ml to obtain a suspension, the suspension is magnetically stirred for 16 hours, and shaken at a constant temperature for 4 hours, filtered at room temperature, and dried at 40°C to obtain a solid product, namely the sulfur-modified biochar, which is ground, passed through a 60-mesh sieve, and sealed for storage.

[0011] Preferably, the temperature in the constant temperature shaking box is 25±0.5°C and the rotation speed is 195±5 rpm / min.

[0012] Furthermore, shrimp shell biochar is prepared by a method of slow pyrolysis with oxygen limitation and temperature control. Specifically, crayfish shells are used as raw materials, which are cleaned, dried, crushed, sieved, and dried for later use. The dried shrimp shells are then subjected to slow pyrolysis with oxygen limitation and temperature control to prepare raw biochar.

[0013] Preferably, the shrimp shells are cleaned with deionized water, dried in an oven at not less than 105° C. for at least 48 hours, crushed in a grinder, sieved, packed in a plastic bag and stored in a desiccator for later use.

[0014] Preferably, the pyrolysis conditions are as follows: introducing carrier gas, heating to not less than 130°C, dwelling, then heating to 300-700°C, and carbonizing at a constant temperature for 2 hours; after the pyrolysis time is reached, the program automatically stops heating, continues to introduce carrier gas, and after the temperature naturally cools to room temperature, the pyrolysis product is taken out, which is the original biochar, which is ground after weighing and passed through a 60-mesh sieve, and then sealed and stored for use.

[0015] Furthermore, the carrier gas is N2, and its gas flow rate is not less than 130 mL / min;

[0016] Furthermore, during pre-pyrolysis, the temperature is raised from room temperature to not less than 130°C at a heating rate of not less than 5°C / min and maintained for 30 minutes, so that oxygen in the tubular furnace is exhausted and the biomass is in a dry state.

[0017] Further, heating is performed to 300°C or 700°C at a rate of not less than 5°C / min.

[0018] The present invention also provides an application of the sulfur-modified shrimp shell biochar, wherein the sulfur-modified shrimp shell biochar is used to remove cadmium ions in water.

[0019] Compared with the prior art, the present invention has the following significant features and positive effects:

[0020] 1. The present invention uses crayfish shells as raw materials to prepare biochar. After slow pyrolysis under oxygen-limited temperature control, it is mixed with a sulfur-modified liquid and impregnated. The adsorption effect on cadmium ions shows that the adsorption capacity of the modified shrimp shell biochar for cadmium ions is significantly improved.

[0021] 2. The sulfur-modified modification liquid used in the present invention is obtained by reacting dithiodibenzoic acid and KOH, which is different from the sulfur-modified treatment method of reacting CS2 with NaOH in the prior art. Adsorption experiments show that the sulfur-modified biochar obtained by the former treatment has a more efficient adsorption effect on cadmium ions, which is beneficial for application in environmental fields such as heavy metal wastewater and soil heavy metal remediation.

[0022] 3. The biochar prepared by the method of the present invention also has a good adsorption effect on other heavy metal ions similar to cadmium ions (lead, copper). At the same time, the method is simple, easy to operate, low-cost, green and environmentally friendly and suitable for promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The pseudo-first-order kinetic model diagrams of SBC300 (a) and SBC700 (b) for Cd before and after modification;

[0024] Figure 2 The pseudo-second-order kinetic model diagrams of SBC300 (c) and SBC700 (d) for Cd before and after modification;

[0025] Figure 3 Langmuir fitting model diagrams of SBC300 (e) and SBC700 (f) for Cd before and after modification;

[0026] Figure 4 Freundlich fitting model diagram of SBC300 (g) and SBC700 (h) for Cd before and after modification.

[0027] Figure 5 SEM images of SBC700 biochar before (a) and after (b) modification in Example 11;

[0028] Figure 6 These are the XRD patterns of biochars: SBC300 before modification, SBC700 before modification, sulfur-modified SBC300 in Example 5, and sulfur-modified SBC700 in Example 11. DETAILED DESCRIPTION

[0029] The essential contents and beneficial effects of the present invention are further described in detail below with reference to the examples, which are only used to illustrate the present invention rather than to limit the present invention.

[0030] Example 1

[0031] The method for using a sulfur-modified liquid to modify shrimp shell biochar to adsorb cadmium ions has the following specific steps:

[0032] (1) Clean, dry, crush and pass fresh crayfish shells through a 60-mesh sieve to obtain crayfish shell powder.

[0033] (2) The shrimp shell powder that had passed through a 60-mesh sieve was placed in a rectangular ark and then placed in a tubular electric furnace; N2 was introduced, the temperature was raised to 130°C, maintained for 30 minutes, and then the temperature was raised to 300°C and carbonized at a constant temperature for 2 hours; after the pyrolysis time was reached, the program automatically stopped heating and continued to introduce N2. After the temperature naturally cooled to room temperature, the pyrolysis product was taken out, which was SBC300. After weighing, it was ground and passed through a 60-mesh sieve and sealed for storage.

[0034] (3) Dithiodibenzoic acid and 0.8 mol / L KOH were mixed at a solid-liquid ratio of 0.5:10, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur-modified modification solution; 10 g of the SBC300 prepared in the step (2) was weighed, and the SBC300 and the sulfur-modified modification solution were mixed at a solid-liquid ratio of 1:10, that is, 10 g of the SBC300 prepared in the step (2) was added to 100 ml of the sulfur-modified modification solution, and the suspension was magnetically stirred for 16 hours, and constantly shaken at (25±0.5)°C, 195±5 rpm / min for 4 hours, vacuum filtered at room temperature, and dried at 40°C to obtain the sulfur-modified SBC300, ground, sieved through a 60-mesh sieve, sealed and stored for use.

[0035] (4) The sulfur-modified SBC300 obtained in step (3) was subjected to an adsorption kinetics experiment. 0.1 g of sulfur-modified SBC300 was placed in a 100 mL conical flask and a mass concentration of 170 mg·L was prepared with Cd(NO3)2·4H2O. -1 CD 2+ Solution 50mL, deionized water as background solution, 0.1mol·L -1 The pH of the solution was adjusted to (5.0±0.05) with HNO3 or NaOH. The adsorption system was placed at (25±0.5)℃ and shaken in the dark at 195±5rpm / min after covering. Samples were taken at 0, 5, 20, 40, 60, 90, 150, 240, 480, 720min and 1440min, respectively, and transferred to a 50mL centrifuge tube and centrifuged at 4500r·min. -1 Centrifuge for 10 minutes, take the supernatant and filter it through a 0.45 μm water filter membrane, dilute it with 1% HNO3 and determine the Cd content in the solution using a novAA300 flame atomic absorption spectrometer. 2+ concentration.

[0036] (5) The sulfur-modified SBC300 obtained in step (3) was subjected to an adsorption isotherm experiment. 2+ The stock solution was prepared with initial ρ(Cd 2+ ) is 20~300mg·L -1 50 mL of the solution was placed in a 100 mL conical flask, and 0.1 g of the sulfur-modified SBC300 prepared in (3) was added and shaken for 24 h. The remaining experimental conditions and steps were the same as those of the adsorption kinetics experiment.

[0037] Example 2

[0038] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 1:10.

[0039] Example 3

[0040] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 1.5:10.

[0041] Example 4

[0042] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 2:10.

[0043] Example 5

[0044] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 2.5:10.

[0045] Example 6

[0046] This embodiment is substantially the same as embodiment 1, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 3:10.

[0047] Example 7

[0048] The method for using a sulfur-modified liquid to modify shrimp shell biochar to adsorb cadmium ions has the following specific steps:

[0049] (1) Clean, dry, crush and pass fresh crayfish shells through a 60-mesh sieve to obtain crayfish shell powder.

[0050] (2) The shrimp shell powder that had passed through a 60-mesh sieve was placed in a rectangular ark and then placed in a tubular electric furnace; N2 was introduced, the temperature was raised to 130°C, maintained for 30 minutes, and then the temperature was raised to 700°C and carbonized at a constant temperature for 2 hours; after the pyrolysis time was reached, the program automatically stopped heating and continued to introduce N2. After the temperature naturally cooled to room temperature, the pyrolysis product was taken out, which was SBC700. After weighing, it was ground and passed through a 60-mesh sieve and sealed for storage.

[0051] (3) Dithiodibenzoic acid and 0.8 mol / L KOH were mixed at a solid-liquid ratio of 0.5:10, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur-modified modification solution; 10 g of the SBC700 prepared in the step (2) was weighed, and the SBC700 and the sulfur-modified modification solution were mixed at a solid-liquid ratio of 1:10, that is, 10 g of the SBC700 prepared in the step (2) was added to 100 ml of the sulfur-modified modification solution, and the suspension was magnetically stirred for 16 hours, and constantly shaken at (25±0.5)°C, 195±5 rpm / min for 4 hours, vacuum filtered at room temperature, and dried at 40°C to obtain the sulfur-modified SBC700, ground, sieved through a 60-mesh sieve, sealed and stored for use.

[0052] (4) The sulfur-modified SBC700 obtained in step (3) was subjected to an adsorption kinetics experiment. 0.1 g of sulfur-modified SBC700 was placed in a 100 mL conical flask and a mass concentration of 150 mg·L was prepared with Cd(NO3)2·4H2O. -1 CD 2+ Solution 50mL, deionized water as background solution, 0.1mol·L -1 The pH of the solution was adjusted to (5.0±0.05) with HNO3 or NaOH. The adsorption system was placed at (25±0.5)℃ and shaken in the dark at 195±5rpm / min after covering. Samples were taken at 0, 5, 20, 40, 60, 90, 150, 240, 480, 720min and 1440min, respectively, and transferred to a 50mL centrifuge tube and centrifuged at 4500r·min. -1 Centrifuge for 10 minutes, take the supernatant and filter it through a 0.45 μm water filter membrane, dilute it with 1% HNO3 and determine the Cd content in the solution using a novAA300 flame atomic absorption spectrometer. 2+ concentration.

[0053] In the adsorption kinetics experiment, the experimental conditions were that the solid-liquid ratio of biochar to cadmium ion solution was 1:500, and Cd 2+ The concentration is 150 mg / L, and the pH in the system is preferably (5.0±0.05).

[0054] (5) The sulfur-modified SBC700 obtained in step (3) was subjected to an adsorption isotherm experiment.2+ The stock solution was prepared with initial ρ(Cd 2+ ) is 20~300mg·L -1 50 mL of the solution was placed in a 100 mL conical flask, and 0.1 g of the sulfur-modified SBC700 prepared in (3) was added and shaken for 24 h. The rest of the experimental conditions and steps were the same as those of the adsorption kinetics experiment.

[0055] Example 8

[0056] This embodiment is substantially the same as embodiment 7, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 1:10.

[0057] Example 9

[0058] This embodiment is substantially the same as embodiment 7, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 1.5:10.

[0059] Example 10

[0060] This embodiment is substantially the same as embodiment 7, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 2:10.

[0061] Example 11

[0062] This embodiment is substantially the same as embodiment 7, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 2.5:10.

[0063] Example 12

[0064] This embodiment is substantially the same as embodiment 7, except that in this embodiment, the solid-to-liquid ratio of dithiodibenzoic acid to KOH is 3:10.

[0065] Comparative Example 1

[0066] The preparation of shrimp shell biochar SBC300 before modification was the same as in Example 1.

[0067] Comparative Example 2

[0068] Preparation of sulfur-modified shrimp shell biochar:

[0069] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 1:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 1.

[0070] Comparative Example 3

[0071] Preparation of sulfur-modified shrimp shell biochar:

[0072] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 2:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 1.

[0073] Comparative Example 4

[0074] Preparation of sulfur-modified shrimp shell biochar:

[0075] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 3:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 1.

[0076] Comparative Example 5

[0077] The preparation of shrimp shell biochar SBC700 before modification is the same as in Example 7.

[0078] Comparative Example 6

[0079] Preparation of sulfur-modified shrimp shell biochar:

[0080] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 1:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 7.

[0081] Comparative Example 7

[0082] Preparation of sulfur-modified shrimp shell biochar:

[0083] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 2:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 7.

[0084] Comparative Example 8

[0085] Preparation of sulfur-modified shrimp shell biochar:

[0086] Sulfur modification solution: CS2 and 0.5 mol / L NaOH were mixed in a volume ratio of 3:3, magnetically stirred at 25°C for 4 hours, and then ultrasonicated for 2 hours to obtain a sulfur modification solution. Other steps were the same as in Example 7.

[0087] Analysis of adsorption kinetics model of biochar

[0088] The adsorption kinetic model parameters of SBC300 and SBC700 before and after modification are shown in Table 1, and the model fitting curves are shown in Figures 1 to 4 From the fitting results, we can see that in Cd 2+ The initial concentration was 170 mg·L -1Under the same conditions, the kinetic trend consists of three stages: rapid adsorption, slow adsorption and equilibrium. 2+ The adsorption amount increased rapidly within 1 hour, then gradually slowed down and basically reached adsorption equilibrium within 24 hours. Compared with SBC300, the overall equilibrium time of SBC700 was shorter.

[0089] It can be seen from the figure that the pseudo-first-order kinetic equation can fit the initial stage of adsorption well (t<60min), and gradually deviate from the adsorption process after t>60min. And it can be seen from Table 1 that the model fitting can determine the R 2 (0.828<R 2 <0.975) The quasi-second-order model can determine R 2 Low (0.997<R 2 <0.999), the entire adsorption process cannot be well evaluated. Therefore, liquid film diffusion is not the main cause of Cd 2 + The only factor that affects the adsorption rate during the SBC adsorption process.

[0090] Compared with the pseudo-first-order kinetic model, the pseudo-second-order kinetic equation fitting coefficient of determination R 2 All of them are greater than 0.997, and the linear correlation is significant, which can more accurately fit the entire adsorption process, which means that chemical adsorption is involved in the adsorption process. 2+ The adsorption mechanism on SBC involves physical adsorption and chemical adsorption, among which chemical adsorption dominates the reaction process.

[0091] As can be seen from Table 1, after sulfur modification, the adsorption capacity of SBC is greatly improved compared with that before modification. The increase in the adsorption rate constant k means that the reaction rate in each system has been accelerated to varying degrees, accelerating the formation of the equilibrium system.

[0092] Table 1 Parameters of biochar adsorption kinetic model

[0093]

[0094]

[0095] a Actual adsorption capacity of biochar

[0096] Combined with Table 2 Figure 3-4 It can be seen that the Langnmir model has a better fitting effect on adsorption than the Freundlich model in the adsorption isotherm experiment. 2 is 0.996~0.999, which indicates that SBC has a great influence on Cd 2+The adsorption occurs on a uniform surface, which is similar to monolayer adsorption. The maximum adsorption amount fitted by the Langnmir equation increases with the increase of SBC preparation temperature and modification treatment, and K L The value also showed a gradual increasing trend, indicating that SBC has a great influence on Cd 2+ Affinity gradually increases.

[0097] Table 2 Biochar adsorption isotherm model parameters

[0098]

[0099] according to Figure 5 (a) It can be observed that the pore size of the SBC before modification is circular, the pore structure is not obvious, and a certain degree of irregular small particles are scattered on the surface. This may be due to the fact that proteins and other organic matter are not fully decomposed and remain on the surface of the SBC. Figure 5 (b) The surface of the modified SBC presents a dense honeycomb-like narrow structure with dense pores. The pore structure is fully extended, and organic matter such as protein is fully decomposed, thereby freeing Cd 2+ Provide more adsorption sites.

[0100] Depend on Figure 5 (b) It can be clearly observed that there are traces of S element loading and sulfate precipitation, combined with Figure 6 X-ray diffraction analysis shows that the peak intensity is significantly improved after modification, the peak shape is sharper, and the crystallinity is significantly improved compared with before modification. At the same time, CaSO3 crystals are generated in the phase composition, which can form CdS precipitation with cadmium ions in the adsorption system, thereby improving the cadmium ion removal efficiency in the system.

[0101] The above is a detailed description of the specific implementation methods of the present invention, but the present invention is not limited to the above embodiments. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principles of the technical solutions of the present invention should be regarded as equivalent replacement methods. As long as they do not deviate from the technical principles and invention purposes of the present invention, they should fall within the scope of protection of the present invention.

Claims

1. Application of sulfur-modified shrimp shell biochar in removing cadmium ions from water, characterized in that: The preparation method of the sulfur-modified shrimp shell biochar comprises the following steps: mixing the shrimp shell biochar and a sulfur-modified modification liquid to obtain a suspension, stirring, shaking, filtering, drying, grinding, and sieving to obtain the sulfur-modified shrimp shell biochar; the sulfur-modified modification liquid comprises dithiodibenzoic acid and a KOH solution.

2. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 1, characterized in that: The concentration of the KOH solution is 0.8 mol / L, and the solid-liquid ratio of dithiodibenzoic acid and the KOH solution is 0.5 ~ 3 g:10 mL.

3. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 1, characterized in that: The sulfur-modified modification solution is prepared by uniformly mixing dithiodibenzoic acid and KOH solution, stirring at 25° C. for 3 to 4 hours, and then continuing ultrasonication for 2 to 3 hours to obtain the sulfur-modified modification solution.

4. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 1, characterized in that: The solid-liquid ratio of shrimp shell biochar and sulfur-modified solution was 1 g:10 mL.

5. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 1, characterized in that: The suspension was magnetically stirred for 16 h and shaken at a constant temperature for 4 h, filtered at room temperature, dried at 40°C, ground, and passed through a 60-mesh sieve to obtain sulfur-modified shrimp shell biochar.

6. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 5, characterized in that: The temperature of the constant temperature oscillation is 24.5 ~ 25.5℃, and the rotation speed is 190 ~ 200rpm.

7. The use of sulfur-modified shrimp shell biochar in removing cadmium ions from water according to claim 1, characterized in that: Shrimp shell biochar is produced by oxygen-limited temperature-controlled slow pyrolysis method, the specific steps are as follows: (1) Wash the shrimp shells with deionized water, dry them in an oven at 105-110°C for 48-72 hours, grind them in a grinder, and pass them through a 60-mesh sieve to obtain shrimp shell powder; (2) The shrimp shell powder of step (1) was preheated to 130°C at a heating rate of 5°C / min under a nitrogen atmosphere for 30 minutes, and then continued to heat to 300-700°C and carbonized at a constant temperature for 2 hours; after cooling naturally to room temperature, the powder was taken out and ground through a 60-mesh sieve to obtain shrimp shell biochar.

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