A spherical adsorbing material based on crab shell and a preparation method and application thereof

Abstract

The application provides a spherical adsorbent of a sodium alginate coated diatomite coating assembled waste crab shell and a preparation method and application thereof, and belongs to the adsorption field. The preparation method comprises the following steps: (1) using a citric acid solution as a matrix to prepare a diatomite suspension liquid; (2) mixing the diatomite suspension liquid obtained in the step (1) with crab shell powder, and then sequentially performing standing and calcination to obtain a diatomite single coating assembled crab shell biochar material; (3) mixing the diatomite single coating assembled crab shell biochar material obtained in the step (2) with a sodium alginate solution, and then dropping into a calcium chloride coagulation solution to perform a crosslinking reaction, so as to obtain a sodium alginate coated diatomite coating assembled crab shell biochar spherical adsorbent. The adsorbent provided by the application has the advantages of low cost, easy separation, high adsorption efficiency for lead ions and good adsorption capacity.

Description

Technical Field

[0001] This invention relates to the field of chemical adsorption, and more particularly to a spherical adsorbent for crab shells assembled with sodium alginate-coated diatomaceous earth, its preparation method, and its application. Background Technology

[0002] Lead is widely used in various fields of industrial manufacturing due to its excellent ductility, corrosion resistance, radioactivity resistance, chemical stability, and high recyclability. For example, highly corrosion-resistant plates and pipes, widely used lead-acid batteries (chemical power sources), and radiation shielding in nuclear submarines and aircraft, as well as in nuclear power plants and the storage and transportation of nuclear waste, all utilize lead to isolate radioactive material leaks and protect people from radiation damage. However, the construction of these facilities generates industrial wastewater containing lead. Increased lead concentrations in the environment pollute water bodies, soil, and the atmosphere, ultimately causing adverse health effects through various ingestion routes. Therefore, the adsorption and secondary recycling of lead ions from wastewater has significant social and economic value.

[0003] Crab shells contain various chemical substances, including proteins, calcium carbonate, and chitin. Simply burying or dumping them into the ocean not only causes environmental pollution and hinders effective recycling and utilization, but also represents a waste of resources. Currently, the preparation of biomass and its derivative biochar adsorbents from agricultural waste and their application in water pollution treatment has become a hot topic. However, powdered biochar is difficult to separate from water, easily causing secondary pollution, which limits its large-scale use. Furthermore, existing biochar adsorbent materials suffer from low adsorption capacity, low adsorption efficiency, and high cost.

[0004] Therefore, how to prepare an adsorbent that can stably exist in solution and has high adsorption efficiency and good adsorption capacity for lead ions has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a sodium alginate-coated diatomaceous earth-coated crab shell spherical adsorbent, its preparation method, and its application. The adsorbent prepared by the method of this invention, using a sodium alginate-coated diatomaceous earth-coated crab shell spherical adsorbent, is stable in solution and exhibits high adsorption efficiency and good adsorption capacity for lead ions.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0007] This invention provides a method for preparing a spherical adsorbent made of crab shell coated with sodium alginate and diatomaceous earth, comprising the following steps:

[0008] (1) A diatomaceous earth suspension was prepared using citric acid solution as the matrix;

[0009] (2) The diatomite suspension obtained in step (1) is mixed with crab shell powder and then subjected to static standing and calcination in sequence to obtain crab shell biochar material assembled with diatomite single coating.

[0010] (3) The crab shell biochar material assembled with diatomite single coating obtained in step (2) is mixed with sodium alginate solution and then added dropwise to calcium chloride coagulation solution to carry out cross-linking reaction, so as to obtain crab shell biochar adsorbent assembled with sodium alginate coating diatomite coating.

[0011] Preferably, the particle size of the crab shell powder in step (2) is <0.15mm.

[0012] Preferably, in step (2), the mass ratio of diatomaceous earth suspension to crab shell powder is (240-260):(8-10).

[0013] Preferably, the calcination temperature in step (2) is 400-500℃ and the calcination time is 1-2 hours.

[0014] Preferably, in step (3), the mass ratio of the diatomaceous earth-coated crab shell biochar material to the sodium alginate solution is (0.8-1.2):(0.5-1.5).

[0015] Preferably, the sodium alginate content in the sodium alginate solution in step (3) is (0.015~0.025) g / mL.

[0016] Preferably, the coagulation solution in step (3) is a CaCl2 solution; the concentration of the CaCl2 solution is 0.1 to 0.3 mol / L.

[0017] This invention provides a crab shell biochar adsorbent assembled with a sodium alginate-coated diatomaceous earth coating prepared by the preparation method described above.

[0018] This invention provides the application of the crab shell biochar adsorbent assembled with sodium alginate-coated diatomaceous earth as described above in the adsorption of heavy metal lead.

[0019] This invention provides a method for preparing a crab shell biochar adsorbent assembled with a sodium alginate-coated diatomite coating, comprising the following steps: (1) preparing a diatomite suspension using a citric acid solution as a matrix; (2) mixing the diatomite suspension obtained in step (1) with crab shell powder and then subjecting it to static standing and calcination in sequence to obtain a crab shell biochar material assembled with a single diatomite coating; (3) mixing the crab shell biochar material assembled with a single diatomite coating obtained in step (2) with a sodium alginate solution and then adding it dropwise to a coagulated calcium chloride solution to carry out a crosslinking reaction to obtain a crab shell biochar adsorbent assembled with a sodium alginate-coated diatomite coating. This invention uses crab shells as raw material, preparing them into biochar. The high carbon content and porous nature of biochar, along with the abundance of oxygen-containing functional groups, enhance the adsorption rate of lead ions. Diatomaceous earth's high specific surface area allows it to fully contact and adsorb heavy metal ions or organic matter in water. Sodium alginate molecules contain numerous carboxyl and hydroxyl functional groups, enabling them to form electrostatic interactions with cations in solution. The coating and assembly of crab shell biochar with sodium alginate and diatomaceous earth significantly increases the number of groups capable of binding to lead ions and the specific surface area of ​​the adsorbent, thereby improving the adsorption efficiency and capacity for lead ions and ensuring the adsorbent's stability in solution. Experimental results show that the crab shell biochar adsorbent prepared by the method provided in this invention, with a sodium alginate-coated diatomaceous earth coating, achieves an adsorption rate of 86% for lead ions in wastewater within 8 hours, with a maximum single-layer adsorption capacity of 248 mg / g, exhibiting high adsorption efficiency and good adsorption capacity. Attached Figure Description

[0020] Figure 1 This is a process flow diagram of the preparation of crab shell biochar adsorbent with sodium alginate-coated diatomite coating in an embodiment of the present invention.

[0021] Figure 2 This is a SEM image at 55x magnification of the crab shell biochar adsorbent assembled with sodium alginate-coated diatomite coating prepared in Example 1 of this invention.

[0022] Figure 3 The image shows a crab shell biochar adsorbent assembled with sodium alginate-coated diatomite coating prepared in Example 1 of this invention at a magnification of 20,000.

[0023] Figure 4 The image shows the EDS (Electrode Spectroscopy) of lead adsorbent assembled from crab shell biochar with sodium alginate-coated diatomaceous earth coating prepared in Example 1 of this invention. Detailed Implementation

[0024] This invention provides a method for preparing a crab shell biochar adsorbent assembled with sodium alginate-coated diatomaceous earth, comprising the following steps:

[0025] (1) A diatomaceous earth suspension was prepared using citric acid solution as the matrix;

[0026] (2) The diatomite suspension obtained in step (1) is mixed with crab shell powder and then subjected to static standing and calcination in sequence to obtain crab shell biochar material assembled with diatomite single coating.

[0027] (3) The crab shell biochar material assembled with diatomite single coating obtained in step (2) is mixed with sodium alginate solution and then added dropwise to calcium chloride coagulation solution to carry out cross-linking reaction, so as to obtain crab shell biochar adsorbent assembled with sodium alginate coating diatomite coating.

[0028] This invention uses citric acid solution as a matrix to prepare diatomaceous earth suspension.

[0029] In this invention, the preferred specific operation for preparing the diatomaceous earth suspension using the citric acid solution as the matrix is ​​as follows:

[0030] (a) Mix deionized water and citric acid to obtain a citric acid solution;

[0031] (b) The citric acid solution obtained in step (a) is mixed with diatomaceous earth to obtain a diatomaceous earth suspension.

[0032] The present invention preferably involves mixing water and citric acid to obtain a citric acid solution.

[0033] In this invention, the preferred mass ratio of water to citric acid is (240–260):(18–22), more preferably (245–255):(19–21), and even more preferably 250:20. Limiting the mass ratio of water to citric acid to the above range helps prevent precipitation during the dissolution process.

[0034] In this invention, citric acid solution is preferably mixed with diatomaceous earth to obtain a diatomaceous earth suspension.

[0035] In this invention, the preferred mass ratio of citric acid solution to diatomaceous earth is (240-260):(1.6-2.4), more preferably (245-255):(1.8-2.2), and even more preferably 250:2. Limiting the mass ratio of citric acid solution to diatomaceous earth to the above range ensures the stable formation of the suspension.

[0036] After obtaining the diatomaceous earth suspension, the present invention mixes the diatomaceous earth suspension with crab shell powder and then allows it to stand and calcine in sequence to obtain crab shell biochar material assembled with a single diatomaceous earth coating.

[0037] In this invention, the particle size of the crab shell powder is preferably <0.15 mm. By limiting the particle size of the crab shell powder to the above range, this invention can increase the surface area of ​​biochar, thereby improving the adsorption performance of the adsorbent.

[0038] In this invention, the preferred preparation process of the crab shell powder is as follows: crab shells are washed, dried, crushed and sieved in sequence to obtain crab shell powder.

[0039] In this invention, the solvent used for cleaning is preferably deionized water; the number of cleaning cycles is preferably three. This invention does not impose any special limitations on the cleaning equipment and operations; commonly used cleaning equipment and operations by those skilled in the art can be employed. This invention can remove impurities from the surface of crab shells through cleaning.

[0040] In this invention, the drying temperature is preferably 80°C, and the drying time is preferably 2 days. This invention does not impose any special limitations on the drying equipment; any drying equipment commonly used by those skilled in the art can be used. This invention effectively removes moisture from the crab shells through drying, facilitating subsequent crushing.

[0041] The present invention does not impose any special limitations on the crushing equipment and operation; any equipment and operation known to those skilled in the art can be used.

[0042] In this invention, the sieving is preferably performed through a 100-mesh sieve. This invention allows the particle size of the crab shell powder to be controlled to <0.15mm through sieving.

[0043] In this invention, the preferred mass ratio of diatomaceous earth to crab shell powder is (1-3):(8-12), more preferably (1.5-2.5):(9-11), further preferably (1.8-2.2):(9.5-10.5), and most preferably 2:10. By limiting the mass ratio of diatomaceous earth to crab shell powder to the above range, this invention allows for better coating of diatomaceous earth onto crab shell biochar.

[0044] In this invention, the mixing of diatomaceous earth and crab shell powder is preferably carried out under stirring conditions; the stirring speed is preferably 160-200 r / min, more preferably 170-190 r / min; the stirring time is preferably 11-13 h, more preferably 12 h. Setting the mixing time of diatomaceous earth and crab shell powder within the above range allows the diatomaceous earth to fully coat the surface of the crab shell powder, which is beneficial for the subsequent coating of the crab shell biochar with diatomaceous earth.

[0045] In this invention, the settling time is preferably 11-13 hours, more preferably 12 hours; the settling temperature is preferably 25-30°C. This invention allows the formation of a blocky solid through settling.

[0046] After the settling period, the present invention preferably dries and grinds the blocky solid formed by settling period to obtain a brownish-yellow powder.

[0047] In this invention, the drying temperature is preferably 60–100°C, more preferably 80°C; the drying time is preferably 22–26 hours, more preferably 24 hours. This invention removes moisture from the solid through drying, facilitating grinding.

[0048] This invention does not impose any special limitations on the grinding equipment and operation; it is sufficient to grind the dried gel to a particle size of <0.15mm.

[0049] In this invention, the calcination is preferably carried out in a muffle furnace; the calcination temperature is preferably 350–450°C, more preferably 400°C; and the calcination time is preferably 0.5–1.5 h, more preferably 1 h. Limiting the calcination temperature and time to the above ranges ensures that the biochar has a high porosity and allows silica to be fully coated on the surface of the biochar, thereby improving the adsorption effect of the biochar.

[0050] After calcination, the present invention preferably cools, grinds and sieves the calcined product in sequence to obtain diatomaceous earth-coated crab shell biochar material.

[0051] The present invention does not have any particular limitation on the cooling operation, as long as the calcined product is cooled to room temperature.

[0052] The present invention does not impose any special limitations on the equipment and operation of the grinding process; any operation known to those skilled in the art can be used.

[0053] In this invention, the sieving is preferably performed through a 100-mesh sieve. This sieving process allows the particle size of the diatomaceous earth-coated crab shell biochar material to be less than 0.15 mm, which is beneficial for subsequent sodium alginate coating.

[0054] After obtaining the diatomaceous earth-coated crab shell biochar material, the present invention mixes the diatomaceous earth-coated crab shell biochar material with sodium alginate solution and then adds it dropwise into a coagulation solution to obtain microspheres.

[0055] In this invention, the preferred mass ratio of the diatomaceous earth-coated crab shell biochar material to sodium alginate in the sodium alginate solution is (0.5–1.5):(0.8–1.2), more preferably (0.8–1.2):(0.9–1.1), and even more preferably 1:1. Limiting the mass ratio of the diatomaceous earth-coated crab shell biochar material to sodium alginate within the above range ensures good coating of the diatomaceous earth-coated crab shell biochar material by sodium alginate and successfully prepares microspheres.

[0056] In this invention, the solvent in the sodium alginate solution is preferably deionized water; the sodium alginate content in the sodium alginate solution is preferably (0.015-0.025) g / mL, more preferably (0.018-0.022) g / mL, and even more preferably 0.02 g / mL. Setting the sodium alginate content in the sodium alginate solution within the above range ensures that the sodium alginate is fully dissolved.

[0057] In this invention, the mixing of the diatomaceous earth-coated crab shell biochar material with the sodium alginate solution is preferably carried out under stirring conditions. This invention does not specifically limit the stirring speed; any operation well-known to those skilled in the art can be used to completely disperse the diatomaceous earth-coated crab shell biochar material in the sodium alginate solution.

[0058] In this invention, the coagulation solution is preferably a CaCl2 solution; the concentration of the CaCl2 solution is preferably 0.1–0.3 mol / L, more preferably 0.2 mol / L. By limiting the type and concentration of the coagulation solution to the above ranges, this invention enables the mixture to form microspheres; both excessively high and excessively low concentrations of the CaCl2 solution will prevent the formation of microspheres.

[0059] In this invention, the dropping rate added to the coagulation solution is preferably 0.05 mL / 2 to 3 s; the dropping device is preferably a syringe. Controlling the dropping rate within the above range facilitates the formation of microspheres.

[0060] This invention involves mixing diatomaceous earth-coated crab shell biochar with sodium alginate solution and then adding the mixture dropwise into a coagulation solution. The mixture forms a gel in the coagulation solution because when sodium alginate comes into contact with calcium chloride, the calcium ions in the calcium chloride react with the sodium ions in the sodium alginate, generating water-insoluble calcium alginate. Simultaneously, the calcium ions in the calcium chloride also react with the carboxyl groups in the sodium alginate. These two reactions work together to form a stable three-dimensional network structure between the sodium alginate molecular chains, making it insoluble in calcium chloride. This allows the mixture of diatomaceous earth-coated crab shell biochar and sodium alginate solution to form microspheres in the coagulation solution.

[0061] In this invention, the microspheres are preferably obtained by sequentially allowing the microspheres to stand, sieve, and wash after the addition is completed.

[0062] In this invention, the settling time is preferably 24 hours; the settling temperature is preferably room temperature. This invention allows the microspheres to solidify better through settling.

[0063] The present invention does not impose any special limitations on the equipment and operation of the sieving process, as long as the particle size of the microspheres can be controlled within 800 μm.

[0064] In this invention, the solvent for cleaning is preferably deionized water; this invention does not have a special limitation on the number of cleaning cycles, as long as the pH of the cleaning solution is neutral.

[0065] In this invention, the product of the reaction, gel microspheres, is preferably separated and dried to obtain sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent.

[0066] In this invention, the separation is preferably performed using a sieve spoon.

[0067] In this invention, the drying is preferably performed by air-drying the separated solids in a petri dish.

[0068] This invention uses crab shells as raw material, preparing them into biochar. The high carbon content and porous nature of biochar, along with the abundance of oxygen-containing functional groups, enhance the adsorption rate of lead ions. Diatomaceous earth, with its high specific surface area, allows metal ions to enter the pores for adsorption. Sodium alginate contains numerous functional groups, such as carboxyl and hydroxyl groups, enabling it to form electrostatic interactions with cations in solution. The coating of crab shells with diatomaceous earth and the encapsulation of biochar with sodium alginate significantly increase the number of groups that can bind to lead ions and the specific surface area of ​​the adsorbent, thereby improving the adsorption efficiency and amount of lead ions and ensuring the adsorbent's stable existence in solution.

[0069] The present invention also provides a sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared by the preparation method described in the above technical solution.

[0070] This invention employs diatomaceous earth coating and sodium alginate coating, which greatly increases the number of groups in the adsorbent that can bind to lead ions and the specific surface area of ​​the adsorbent, thereby improving the adsorption efficiency and adsorption capacity of the adsorbent for lead ions.

[0071] The present invention also provides the application of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent described in the above technical solution in the adsorption of heavy metal lead.

[0072] In embodiments of the present invention, such as Figure 1 As shown, the preparation process of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent is as follows:

[0073] After cleaning the waste crab shells, they are dried in an oven at 80℃ to obtain crab shells without impurities. The crab shells without impurities are then crushed and sieved to obtain crab shell powder (crab shell powder biomass basic material).

[0074] A citric acid solution obtained by mixing deionized water and citric acid is then added to diatomaceous earth and crab shell powder (crab shell powder is a basic biomass material) to obtain a brownish-yellow powder. The powder is then calcined in a muffle furnace and ground at room temperature to obtain diatomaceous earth-coated crab shell biochar material (diatomaceous earth-coated crab shell biochar particles).

[0075] After mixing diatomaceous earth-coated crab shell biochar material (diatomaceous earth-coated crab shell biochar particles) with sodium alginate solution (sodium alginate dissolved in deionized water), the mixture was treated with CaCl2 solution to obtain sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent (sodium alginate-coated diatomaceous earth biochar spherical gel adsorbent).

[0076] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0077] Example 1

[0078] A method for preparing a sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent comprises the following steps:

[0079] (1) A diatomaceous earth suspension was prepared using citric acid solution as a matrix;

[0080] (2) The diatomaceous earth suspension obtained in step (1) is mixed with crab shell powder and stirred at 180 r / min for 12 h. After standing for 12 h, it is dried at 80℃ for 12 h. After drying, it is ground and passed through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining a block solid. The obtained block solid is calcined at 400℃ for 1 h and then cooled to room temperature and ground again, passing through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining diatomaceous earth coated crab shell biochar material; the mass ratio of diatomaceous earth to crab shell powder is 2:10.

[0081] (3) The diatomaceous earth-coated crab shell biochar material obtained in step (2) is mixed with sodium alginate solution and then added dropwise to 0.2 mol / L CaCl2 solution at a rate of 0.05 mL / 2 s using a syringe. The mixture is left to stand in CaCl2 solution for 24 h. After standing, the mixture is sieved with a sieve spoon. The sieved microspheres are then rinsed with deionized water until the pH of the washing solution is neutral to obtain microspheres. The solvent in the sodium alginate solution is deionized water. The sodium alginate content in the sodium alginate solution is 0.02 g / mL. The mass ratio of diatomaceous earth-coated crab shell biochar material to sodium alginate is 1:1.

[0082] The preferred specific operation for preparing diatomaceous earth suspension using citric acid solution as a matrix is ​​as follows:

[0083] (a) Mix 250 ml of deionized water and 20 g of citric acid to obtain a citric acid solution;

[0084] (b) Mix 2g of diatomaceous earth with citric acid solution to obtain a diatomaceous earth suspension;

[0085] The preparation process of the crab shell powder is as follows: the crab shells are washed three times with deionized water, dried at 80°C for 2 days, crushed and passed through a 100-mesh sieve to obtain crab shell powder.

[0086] The scanning electron microscope (SEM) image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 at 55x magnification is shown below. Figure 2 As shown, from Figure 2 As can be seen from the above, the prepared sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent is in the form of microspheres.

[0087] The scanning electron microscope (SEM) image of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared in Example 1 at 20,000x magnification is shown below. Figure 3 As shown, from Figure 3 As can be seen, the prepared sodium alginate-coated diatomite-coated crab shell biochar adsorbent has a smooth surface, and the irregular spherical protrusions on the surface of the microspheres are characteristic of diatomite morphology. These spherical protrusions are tightly arranged and coated on the porous surface of the biochar.

[0088] Comparative Example 1

[0089] A method for preparing a sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent comprises the following steps:

[0090] (1) A diatomaceous earth suspension was prepared using citric acid solution as a matrix;

[0091] (2) The diatomaceous earth suspension obtained in step (1) is mixed with crab shell powder and stirred at 180 r / min for 20 min. After standing for 12 h, it is dried at 80℃ for 12 h. After drying, it is ground and passed through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining a block solid. The obtained block solid is calcined at 500℃ for 1 h and then cooled to room temperature and ground again, passing through a 100-mesh sieve to make the particle size of the ground powder <0.15 mm, thus obtaining diatomaceous earth coated crab shell biochar material; the mass ratio of diatomaceous earth to crab shell powder in the diatomaceous earth suspension is 2:10.

[0092] (3) The diatomaceous earth-coated crab shell biochar material obtained in step (2) is mixed with sodium alginate solution and then added dropwise to 0.2 mol / L CaCl2 solution at a rate of 0.05 mL / 2 s using a syringe. The mixture is left to stand in CaCl2 solution for 24 h. After standing, the mixture is sieved with a sieve spoon. The sieved microspheres are then rinsed with deionized water until the pH of the washing solution is neutral to obtain microspheres. The solvent in the sodium alginate solution is deionized water. The sodium alginate content in the sodium alginate solution is 0.02 g / mL. The mass ratio of diatomaceous earth-coated crab shell biochar material to sodium alginate is 1:1.

[0093] The preferred specific operation for preparing diatomaceous earth suspension using citric acid solution as a matrix is ​​as follows:

[0094] (a) Mix 250 mL of deionized water and 20 g of citric acid to obtain a citric acid solution;

[0095] (b) Mix 2g of diatomaceous earth with citric acid solution to obtain a diatomaceous earth suspension;

[0096] The preparation process of the crab shell powder is as follows: the crab shells are washed three times with deionized water, dried at 80°C for 2 days, crushed and passed through a 100-mesh sieve to obtain crab shell powder.

[0097] Application Example 1 and Comparative Application Example 1

[0098] 50 mg of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared in Example 1 and Comparative Example 1 was added to 100 mL of a solution with a lead ion content of 150 mg / L. The solution was placed in a water bath constant temperature shaker and continuously adsorbed at 26 °C and 240 r / min for 16 hours. After filtration with a 0.45 μm filter, the concentration of lead ions in the adsorbed solution was determined by atomic absorption spectrometry.

[0099] The performance of microsphere adsorbents prepared by the two processes in Example 1 and Comparative Example 1 was compared.

[0100] The adsorbent prepared in Example 1 achieved an equilibrium adsorption rate of 86% for a 150 mg / L lead ion solution, while the adsorbent prepared in Comparative Example 1 only achieved an equilibrium adsorption rate of 63% for the same solution. This performance difference stems from the difference in firing temperature. The firing temperature of Comparative Example 1 was insufficient to allow the Si-O-Si bonds in the diatomaceous earth to play a major role in adsorption. Furthermore, the formation of biochar porosity is temperature-dependent; both excessively high and low temperatures negatively impact the adsorption effect. The firing temperature of 500°C in Comparative Example 1 exceeded the optimal firing time for biochar, reducing the number of functional groups. Therefore, the firing temperature in Example 1 was the optimal firing temperature. The proportions, firing time, and temperature in Example 1 represent the optimal conditions for preparing a sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent.

[0101] The EDS spectrum of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared in Example 1 after adsorbing lead ions is shown below. Figure 4 As shown, from Figure 4 As can be seen, there are dense and uniformly distributed lead elements on the surface of the adsorbent, indicating that the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 has a good ability to adsorb metallic lead.

[0102] The adsorption performance of the sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared in Example 1 was tested. The results showed that the lead ion concentrations in the solution before and after adsorption were 150 mg / L and 21 mg / L, respectively. The adsorbent achieved an adsorption rate of 86% for lead ions in wastewater after 8 hours. Compared to other biochar-modified materials, which require 16 hours to achieve good adsorption of lead, the sodium alginate-coated diatomaceous earth-coated crab shell biochar microsphere adsorbent exhibits rapid adsorption efficiency for lead ions. Compared to powdered adsorbents, microsphere adsorbents offer a more convenient and environmentally friendly recovery method, avoiding incomplete recovery and secondary pollution of water bodies. The sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent prepared in Example 1 of this invention achieved a final equilibrium adsorption rate of 86% and a maximum single-layer adsorption capacity of 248 mg / g, demonstrating excellent adsorption capacity for the heavy metal lead.

[0103] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a spherical adsorbent for crab shells assembled with sodium alginate-coated diatomaceous earth, comprising the following steps: (1) A diatomaceous earth suspension was prepared using citric acid solution as the matrix; (2) The diatomaceous earth suspension obtained in step (1) is mixed with crab shell powder and then allowed to stand and calcined in sequence to obtain crab shell biochar material assembled with diatomaceous earth single coating. (3) The crab shell biochar material assembled with diatomite single coating obtained in step (2) is mixed with sodium alginate gel and then added dropwise to the coagulation solution calcium chloride to carry out cross-linking reaction, so as to obtain the crab shell biochar spherical adsorbent assembled with sodium alginate coating diatomite coating.

2. The preparation method according to claim 1, characterized in that: The particle size of the crab shell powder in step (2) is <0.15mm.

3. The preparation method according to claim 1, characterized in that: In step (2), the mass ratio of diatomaceous earth suspension to crab shell powder is (240-260): (8-10).

4. The preparation method according to claim 1, characterized in that: In step (2), the calcination temperature is 350~450℃ and the calcination time is 0.5~1.5h.

5. The preparation method according to claim 1, characterized in that: In step (3), the mass ratio of the crab shell biochar material assembled with diatomite single coating to sodium alginate in sodium alginate solution is (0.8-1.2):(0.5-1.5).

6. The preparation method according to claim 1 or 5, characterized in that: In step (3), the sodium alginate content in the sodium alginate solution is (0.015~0.025) g / mL.

7. The preparation method according to claim 1, characterized in that: The coagulation solution in step (3) is a CaCl2 solution; the concentration of the CaCl2 solution is 0.1~0.3 mol / L.

8. The crab shell biochar adsorbent prepared by the preparation method according to any one of claims 1 to 7, using sodium alginate coated with diatomaceous earth.

9. The application of the crab shell biochar adsorbent with sodium alginate-coated diatomite double-layer assembly as described in claim 8 in the adsorption of heavy metal lead.

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