Novel spherical adsorption material based on crab shells as well as preparation method and application of novel spherical adsorption material

Abstract

The invention provides a spherical adsorbent prepared by assembling waste crab shells with a diatomite coating coated with sodium alginate as well as a preparation method and application of the spherical adsorbent, and belongs to the field of adsorption. The preparation method provided by the invention comprises the following steps: (1) preparing a diatomite suspension by taking a citric acid solution as a matrix; (2) mixing the diatomite suspension obtained in the step (1) with crab shell powder, and sequentially standing and calcining to obtain a diatomite single coating assembled crab shell biochar material; and (3) mixing the diatomite single coating assembled crab shell biochar material obtained in the step (2) with a sodium alginate solution, dropwise adding the mixture into a solidification solution calcium chloride, and carrying out a cross-linking reaction to obtain the sodium alginate coated diatomite coating assembled crab shell biochar spherical adsorbent. The adsorbent provided by the invention is low in cost, easy to separate, high in lead ion adsorption efficiency and good in adsorption capacity.

Description

Technical Field

[0001] The present invention relates to the field of chemisorption, and particularly relates to a spherical adsorbent for crab shells assembled with a sodium alginate-coated diatomite coating, and a preparation method and application thereof. Background Art

[0002] Lead is widely used in various fields of industrial manufacturing due to its excellent ductility, corrosion resistance, radiation resistance, chemical stability, and high recyclability. For example, high-corrosion-resistant plates and pipes, the widely used chemical power source "lead-acid battery", as well as the radiation shielding of nuclear submarines and aircraft, and the storage and transportation of nuclear power plants and nuclear waste all use lead to isolate the leakage of radioactive substances and protect people from radiation damage. However, industrial wastewater containing lead is discharged during the production of these facilities. The increase in lead concentration in the environment will pollute water bodies, soil, and the atmosphere, and ultimately have an adverse impact on people's health through various intake pathways. Therefore, adsorbing lead ions from wastewater and recycling them secondarily has important social significance and economic value.

[0003] Crab shells contain various chemical substances, including proteins, calcium carbonate, chitin, etc. If they are simply landfilled or dumped into the ocean, it will not only cause environmental pollution problems, but also cannot be effectively recycled and utilized, which is also a waste of resources. Currently, the preparation of biomass and its derived biochar adsorbent materials from agricultural waste and their application in water pollution treatment have become a research focus. However, powdered biochar is difficult to separate from water bodies and is prone to secondary pollution, which limits its large-scale use. In addition, the existing biochar adsorbent materials have problems such as small adsorption capacity, low adsorption efficiency, and high cost.

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

[0005] The purpose of the present invention is to provide a spherical adsorbent for crab shells assembled with a sodium alginate-coated diatomite coating, and a preparation method and application thereof. The adsorbent prepared by the preparation method of the spherical adsorbent for crab shells assembled with a sodium alginate-coated diatomite coating provided by the present invention can stably exist in solution, has a high adsorption efficiency for lead ions, and good adsorption capacity.

[0006] To achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a spherical adsorbent for crab shells assembled with a sodium alginate-coated diatomite coating, comprising the following steps:

[0008] (1) Using a citric acid solution as a matrix to prepare a diatomite suspension;

[0009] (2) Mix the diatomite suspension obtained in step (1) with the crab shell powder, and then carry out static settlement and calcination in sequence to obtain a crab shell biochar material assembled with a single diatomite coating.

[0010] (3) Mix the crab shell biochar material assembled with a single diatomite coating obtained in step (2) with a sodium alginate solution, and then drop the mixture into a coagulation solution of calcium chloride for cross-linking reaction to obtain a crab shell biochar adsorbent coated with sodium alginate and assembled with a diatomite coating.

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

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

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

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

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

[0016] Preferably, the coagulation solution in step (3) is CaCl 2 solution; the concentration of the CaCl 2 solution is 0.1 - 0.3 mol / L.

[0017] The present invention provides a crab shell biochar adsorbent coated with sodium alginate and assembled with a diatomite coating prepared by the preparation method described in the above technical solution.

[0018] The present invention provides the application of the crab shell biochar adsorbent coated with sodium alginate and assembled with a diatomite coating described in the above technical solution in adsorbing heavy metal lead.

[0019] The present invention provides a preparation method of a sodium alginate-coated diatomite-coated crab shell biochar adsorbent, 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, followed by standing and calcination in sequence to obtain a diatomite single-coated crab shell biochar material; (3) mixing the diatomite single-coated crab shell biochar material obtained in step (2) with a sodium alginate solution and dropping the mixture into a coagulation solution of calcium chloride for cross-linking reaction to obtain a sodium alginate-coated diatomite-coated crab shell biochar adsorbent. The present invention uses crab shells as raw materials. By preparing crab shells into biochar, the high carbon content and porous characteristics of biochar, as well as the large amount of oxygen-containing functional groups in crab shell biochar, are utilized to improve the adsorption rate of lead ions; the high specific surface area of diatomite enables it to fully contact heavy metal ions or organic substances in water for adsorption; a large number of carboxyl and hydroxyl functional groups are contained on the molecular chain of sodium alginate, enabling it to form electrostatic interactions with cations in the solution; through the coating and assembly of sodium alginate and diatomite on crab shell biochar, the groups capable of binding to metal lead ions contained in the adsorbent and the specific surface area of the adsorbent are greatly increased, improving the adsorption efficiency and adsorption capacity of the adsorbent for metal lead ions and enabling the adsorbent to stably exist in the solution. Experimental results show that the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared by the preparation method provided by the present invention has an adsorption rate of 86% for lead ions in wastewater within 8 hours, and the maximum monolayer adsorption capacity is 248 mg / g, featuring high adsorption efficiency and good adsorption capacity. Description of the Drawings

[0020] Figure 1 It is a process flow chart for preparing a sodium alginate-coated diatomite-coated crab shell biochar adsorbent in an embodiment of the present invention;

[0021] Figure 2 It is an SEM image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 of the present invention at 55 times magnification;

[0022] Figure 3 It is an SEM image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 of the present invention at 20000 times magnification;

[0023] Figure 4 It is an EDS image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 of the present invention after adsorbing lead. Detailed Embodiments

[0024] The present invention provides a preparation method of a sodium alginate-coated diatomite-coated crab shell biochar adsorbent, comprising the following steps:

[0025] (1) Prepare a diatomite suspension using a citric acid solution as the matrix;

[0026] (2) Mix the diatomite suspension obtained in step (1) with crab shell powder, and then carry out static settling and calcination in sequence to obtain a crab shell biochar material assembled with a single diatomite coating;

[0027] (3) Mix the crab shell biochar material assembled with a single diatomite coating obtained in step (2) with a sodium alginate solution, and then drop the mixture into a coagulation solution of calcium chloride for cross-linking reaction to obtain a crab shell biochar adsorbent coated with sodium alginate and assembled with a diatomite coating.

[0028] The present invention uses a citric acid solution as the matrix to prepare a diatomite suspension.

[0029] In the present invention, the specific operation of preparing the diatomite suspension using the citric acid solution as the matrix is preferably as follows:

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

[0031] (b) Mix the citric acid solution obtained in step (a) with diatomite to obtain a diatomite suspension.

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

[0033] In the present invention, the mass ratio of water to citric acid is preferably (240 - 260):(18 - 22), more preferably (245 - 255):(19 - 21), and further preferably 250:20. Limiting the mass ratio of water to citric acid within the above range in the present invention can avoid precipitation during the dissolution process.

[0034] The present invention preferably mixes the citric acid solution with diatomite to obtain a diatomite suspension.

[0035] In the present invention, the mass ratio of the citric acid solution to diatomite is preferably (240 - 260):(1.6 - 2.4), more preferably (245 - 255):(1.8 - 2.2), and further preferably 250:2. Limiting the mass ratio of the citric acid solution to diatomite within the above range in the present invention can ensure the stable formation of the suspension.

[0036] After obtaining the diatomite suspension, the present invention mixes the diatomite suspension with crab shell powder, and then carries out static settling and calcination in sequence to obtain a crab shell biochar material assembled with a single diatomite coating.

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

[0038] In the present invention, the preparation process of the crab shell powder is preferably: the crab shells are sequentially cleaned, dried, crushed and sieved to obtain the crab shell powder.

[0039] In the present invention, the solvent used for the cleaning is preferably deionized water; the number of cleaning times is preferably 3 times. The present invention has no special restrictions on the cleaning equipment and operation, and the cleaning equipment and operation commonly used by those skilled in the art can be used. The present invention can wash away impurities on the surface of the crab shell by cleaning.

[0040] In the present invention, the drying temperature is preferably 80° C., and the drying time is preferably 2 days. The present invention has no special limitation on the drying equipment, and any drying equipment commonly used by those skilled in the art can be used. The present invention can fully remove the moisture in the crab shell by drying, which is beneficial to the subsequent crushing.

[0041] The present invention has no particular limitation on the crushing equipment and operation, and equipment and operations familiar to those skilled in the art may be used.

[0042] In the present invention, the sieving is preferably through a 100 mesh sieve. The particle size of the crab shell powder can be controlled to be less than 0.15 mm by sieving.

[0043] In the present invention, the mass ratio of diatomaceous earth to crab shell powder is preferably (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. The present invention can better coat the diatomaceous earth on the crab shell biochar by limiting the mass ratio of diatomaceous earth to crab shell powder to the above range.

[0044] In the present invention, the mixing of the diatomaceous earth and the crab shell powder is preferably carried out under stirring conditions; the stirring speed is preferably 160 to 200 r / min, more preferably 170 to 190 r / min; the stirring time is preferably 11 to 13 hours, more preferably 12 hours. In the present invention, the mixing time of the diatomaceous earth and the crab shell powder is set within the above range so that the diatomaceous earth can be fully coated on the surface of the crab shell powder, which is conducive to the subsequent coating of the crab shell biochar with the diatomaceous earth.

[0045] In the present invention, the standing time is preferably 11 to 13 hours, more preferably 12 hours; the standing temperature is preferably 25 to 30° C. In the present invention, a block solid can be formed by standing.

[0046] After the static settlement is completed, the present invention preferably dries and grinds the massive solid formed by the static settlement in sequence to obtain a pale yellowish brown powder.

[0047] In the present invention, the temperature of the drying is preferably 60 - 100 °C, more preferably 80 °C; the time of the drying is preferably 22 - 26 h, more preferably 24 h. The present invention removes the moisture in the solid by drying, facilitating the grinding process.

[0048] The present invention has no special limitation on the grinding equipment and operation, and it is only necessary to grind the dried gel to a particle size of <0.15 mm.

[0049] In the present invention, the calcination is preferably carried out in a muffle furnace; the temperature of the calcination is preferably 350 - 450 °C, more preferably 400 °C; the time of the calcination is preferably 0.5 - 1.5 h, more preferably 1 h. The present invention limits the temperature and time of the calcination within the above ranges to ensure that the biochar has a high porosity and enables silica to be fully coated on the surface of the biochar, improving the adsorption effect of the biochar.

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

[0051] The present invention has no special limitation on the cooling operation, and it is only necessary to cool the calcined product to room temperature.

[0052] The present invention has no special limitation on the grinding equipment and operation, and the operations well-known to those skilled in the art can be adopted.

[0053] In the present invention, the sieving is preferably through a 100-mesh sieve. The present invention can make the particle size of the diatomite-coated crab shell biochar material less than 0.15 mm by sieving, which is beneficial to the subsequent coating with sodium alginate.

[0054] After obtaining the diatomite-coated crab shell biochar material, the present invention mixes the diatomite-coated crab shell biochar material with a sodium alginate solution and then drops the mixture into a coagulation solution to obtain microspheres.

[0055] In the present invention, the mass ratio of the diatomite-coated crab shell biochar material to sodium alginate in the sodium alginate solution is preferably (0.5 - 1.5) : (0.8 - 1.2), more preferably (0.8 - 1.2) : (0.9 - 1.1), and further preferably 1 : 1. The present invention limits the mass ratio of the diatomite-coated crab shell biochar material to sodium alginate within the above ranges to ensure a good coating of sodium alginate on the diatomite-coated crab shell biochar material and to successfully prepare microspheres.

[0056] In the present invention, the solvent in the sodium alginate solution is preferably deionized water; the content of sodium alginate in the sodium alginate solution is preferably (0.015 - 0.025) g / mL, more preferably (0.018 - 0.022) g / mL, and further preferably 0.02 g / mL. By setting the content of sodium alginate in the sodium alginate solution within the above range in the present invention, the full dissolution of sodium alginate can be ensured.

[0057] In the present invention, the mixing of the diatomite-coated crab shell biochar material and the sodium alginate solution is preferably carried out under stirring conditions. There is no special limitation on the rotation speed of the stirring in the present invention. By using the operations well-known to those skilled in the art, the diatomite-coated crab shell biochar material can be completely dispersed in the sodium alginate solution.

[0058] In the present invention, the coagulation solution is preferably a CaCl 2 solution; the concentration of the CaCl 2 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 within the above range in the present invention, microspheres can be formed from the mixture. If the concentration of the CaCl 2 solution is too high or too low, microspheres cannot be obtained.

[0059] In the present invention, the dropping speed of the mixture dropped into the coagulation solution is preferably 0.05 mL / 2 - 3 s; the dropping device is preferably a syringe. By controlling the dropping speed within the above range in the present invention, the formation of microspheres can be facilitated.

[0060] In the present invention, after mixing the diatomite-coated crab shell biochar material and the sodium alginate solution, the mixture is dropped into the coagulation solution. The reason why the mixture of the diatomite-coated crab shell biochar material and the sodium alginate solution forms a gel in the coagulation solution is that when sodium alginate contacts calcium chloride, the calcium ions in calcium chloride will undergo a displacement reaction with the sodium ions in sodium alginate to generate calcium alginate that is insoluble in water; at the same time, the calcium ions in calcium chloride will also undergo a cross-linking reaction with the carboxyl groups in sodium alginate; the two reactions work together to form a stable three-dimensional network structure between the sodium alginate molecular chains, making it insoluble in calcium chloride, so that the mixture of the diatomite-coated crab shell biochar material and the sodium alginate solution can form microspheres in the coagulation solution.

[0061] In the present invention, it is preferred to carry out static settlement, sieving, and washing in sequence after the dropping is completed to obtain microspheres.

[0062] In the present invention, the static settlement time is preferably 24 h; the static settlement temperature is preferably room temperature. By static settlement in the present invention, the microspheres can be solidified better.

[0063] The present invention has no special limitation on the sieving equipment and operation, and it is only necessary to control the particle size of the microspheres to 800 μm.

[0064] In the present invention, the cleaning solvent is preferably deionized water; the present invention has no special limitation on the number of cleaning times, and it is only necessary to clean until the pH of the cleaning solution is neutral.

[0065] In the present invention, it is preferred to separate and dry the product gel microspheres of the reaction to obtain the alginate-coated diatomite-coated crab shell biochar adsorbent.

[0066] In the present invention, the separation preferably uses a sieve spoon for separation.

[0067] In the present invention, the drying is preferably to naturally air-dry the separated solid in a petri dish.

[0068] The present invention uses crab shells as raw materials, prepares biochar from crab shells, utilizes the characteristics of high carbon content and porosity of biochar, and the large amount of oxygen-containing functional groups in crab shell biochar to improve the adsorption rate of lead ions; diatomite has a high specific surface area, which enables metal ions to enter the pores for adsorption; there are a large number of functional groups on the alginate molecular chain, such as carboxyl and hydroxyl groups, enabling it to form electrostatic interactions with cations in the solution; by coating diatomite on crab shells and coating biochar with alginate, the groups capable of binding to metal lead ions contained in the adsorbent and the specific surface area of the adsorbent are greatly increased, improving the adsorption efficiency and adsorption capacity of the adsorbent for metal lead ions, and enabling the adsorbent to stably exist in the solution.

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

[0070] The present invention uses diatomite coating and alginate coating, greatly increasing the groups capable of binding to metal lead ions contained in the adsorbent and the specific surface area of the adsorbent, and improving the adsorption efficiency and adsorption capacity of the adsorbent for metal lead ions.

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

[0072] In the examples of the present invention, as Figure 1 shown, the preparation process of the alginate-coated diatomite-coated crab shell biochar adsorbent is as follows:

[0073] After washing the waste crab shells, drying them in an 80 °C oven to obtain impurity-free crab shells, crushing and sieving the impurity-free crab shells to obtain crab shell powder (the basic material of crab shell powder biomass);

[0074] diatomaceous earth and crab shell powder (crab shell powder biomass basic material) are added to a citric acid solution obtained by mixing deionized water and citric acid to obtain a brown-yellow powder, and the powder is placed in a muffle furnace for calcination (firing) and then cooled to room temperature for grinding to obtain a diatomaceous earth-coated crab shell biochar material (diatomaceous earth-coated crab shell biochar particles);

[0075] The diatomite-coated crab shell biochar material (diatomite-coated crab shell biochar particles) was mixed with a sodium alginate solution (sodium alginate dissolved in deionized water) and then treated with CaCl 2 After the solution is treated, a sodium alginate-coated diatomaceous earth-coated crab shell biochar adsorbent (sodium alginate-coated diatomaceous earth biochar spherical gel adsorbent) is obtained.

[0076] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0077] Example 1

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

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

[0080] (2) mixing the diatomaceous earth suspension obtained in step (1) with crab shell powder, stirring at a speed of 180 r / min for 12 h, standing for 12 h, drying at 80° C. for 12 h, grinding after drying and passing through a 100-mesh sieve to make the particle size of the ground powder less than 0.15 mm, and obtaining a block solid; calcining the obtained block solid at 400° C. for 1 h, cooling to room temperature, grinding, passing through a 100-mesh sieve, and making the particle size of the ground powder less than 0.15 mm, and obtaining a diatomaceous earth-coated crab shell biochar material; the mass ratio of the diatomaceous earth to the crab shell powder is 2:10;

[0081] (3) The diatomite-coated crab shell biochar material obtained in step (2) was mixed with the sodium alginate solution and then added dropwise to a 0.2 mol / L CaCl solution at a rate of 0.05 mL / 2 s using a syringe. 2 In solution, in CaCl 2Let it stand in the solution for 24 h, then sieve it with a sieve spoon after standing. Wash the sieved microspheres 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 content of sodium alginate in the sodium alginate solution is 0.02 g / mL; the mass ratio of diatomite-coated crab shell biochar material to sodium alginate is 1:1;

[0082] The specific operation for preparing the diatomite suspension with the citric acid solution as the matrix is preferably 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 2 g of diatomite with the citric acid solution to obtain a diatomite suspension;

[0085] The preparation process of the crab shell powder is as follows: Wash the crab shell three times with deionized water in sequence, dry it at 80 °C for 2 days, crush it, and then sieve it through a 100-mesh sieve to obtain crab shell powder.

[0086] The scanning electron microscope image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 at 55 times is as Figure 2 shown. It can be seen from Figure 2 that the prepared sodium alginate-coated diatomite-coated crab shell biochar adsorbent is microspheres.

[0087] The scanning electron microscope image of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 at 20,000 times is as Figure 3 shown. It can be seen from Figure 3 that the surface of the prepared sodium alginate-coated diatomite-coated crab shell biochar adsorbent is smooth, and the irregular spherical protrusions on the surface of the microspheres are the morphological characteristics of diatomite. These spherical protrusions are closely arranged and coated on the pores formed by the biochar.

[0088] Comparative Example 1

[0089] A preparation method of a sodium alginate-coated diatomite-coated crab shell biochar adsorbent consists of the following steps:

[0090] (1) Prepare a diatomite suspension with the citric acid solution as the matrix;

[0091] (2) mixing the diatomaceous earth suspension obtained in the step (1) with the crab shell powder, stirring at a speed of 180 r / min for 20 min, standing for 12 h, drying at 80° C. for 12 h, grinding after drying and passing through a 100-mesh sieve to make the particle size of the ground powder less than 0.15 mm, and obtaining a block solid; calcining the obtained block solid at 500° C. for 1 h, cooling to room temperature, grinding, passing through a 100-mesh sieve, and making the particle size of the ground powder less than 0.15 mm, and obtaining a diatomaceous earth-coated crab shell biochar material; the mass ratio of diatomaceous earth in the diatomaceous earth suspension to the crab shell powder is 2:10;

[0092] (3) The diatomite-coated crab shell biochar material obtained in step (2) was mixed with the sodium alginate solution and then added dropwise to a 0.2 mol / L CaCl solution at a rate of 0.05 mL / 2 s using a syringe. 2 In solution, in CaCl 2 The solution was allowed to stand for 24 hours, and then sieved with a sieve spoon. The sieved microspheres were rinsed with deionized water until the pH of the washing solution was neutral to obtain microspheres. The solvent in the sodium alginate solution was deionized water. The content of sodium alginate in the sodium alginate solution was 0.02 g / mL. The mass ratio of the diatomite-coated crab shell biochar material to the sodium alginate was 1:1.

[0093] The specific operation of preparing the diatomite suspension using the citric acid solution as a matrix is ​​preferably:

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

[0095] (b) mixing 2 g of diatomaceous earth with the 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 sequentially washed with deionized water three times, dried at 80° C. for 2 days, crushed and sieved through a 100-mesh sieve to obtain the 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 put into 100 mL of a solution with a lead ion content of 150 mg / L, and placed in a water bath constant temperature oscillator for continuous adsorption at 26°C and 240 r / min for 16 hours. After filtering with a 0.45 um filter head, the concentration of the lead ion solution after adsorption was determined by atomic absorption spectrometer.

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

[0100] The equilibrium adsorption rate of the adsorbent prepared in Example 1 for a 150 mg / L lead ion solution reached 86%, while the equilibrium adsorption rate of the adsorbent prepared in Comparative Example 1 for a 150 mg / L lead ion solution only reached 63%. This performance difference is due to the difference in firing temperature. The firing temperature in Comparative Example 1 cannot make the Si-O-Si bonds in diatomite play the main role in adsorption. In addition, the formation of the porosity of biochar has certain requirements for temperature. Too high or too low temperature will affect the adsorption effect of biochar. The firing temperature of 500 °C in Comparative Example 1 exceeds the optimal time point for biochar firing, resulting in a decrease in the number of functional groups of biochar. Therefore, controlling the temperature in Example 1 is the optimal firing temperature. The ratio, firing time, and temperature in Example 1 are all the optimal conditions for preparing the sodium alginate-coated diatomite-coated crab shell biochar adsorbent.

[0101] The EDS energy spectrum of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 after adsorbing lead ions is as Figure 4 shown. It can be seen from Figure 4 that there are dense and evenly 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 good ability to adsorb lead metal.

[0102] Through the test of the adsorption performance of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1, it is obtained that the concentrations of the lead ion solution before and after adsorption by the sodium alginate-coated diatomite-coated crab shell biochar adsorbent are 150 mg / L and 21 mg / L respectively. The adsorption rate of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent for lead ions in wastewater reaches 86% in 8 hours. Compared with other biochar modified materials, which can only achieve good adsorption effect after 16 hours for lead adsorption, the sodium alginate-coated diatomite-coated crab shell biochar microsphere adsorbent has a rapid adsorption efficiency for lead ions. Compared with powder adsorbents, the microsphere adsorbent has a more convenient and green recovery method, and will not cause the situation of incomplete recovery and secondary pollution of water bodies. The final equilibrium adsorption rate of the sodium alginate-coated diatomite-coated crab shell biochar adsorbent prepared in Example 1 of the present invention is 86%, and the maximum monolayer adsorption capacity is 248 mg / g, having excellent ability to adsorb heavy metal lead.

[0103] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a crab shell spherical adsorbent assembled with a sodium alginate-coated diatomaceous earth coating, comprising the following steps: (1) Using citric acid solution as a matrix to prepare a diatomaceous earth suspension; (2) mixing the diatomite suspension obtained in step (1) with crab shell powder, and then sequentially standing and calcining the mixture to obtain a crab shell biochar material assembled with a single diatomite coating; (3) The crab shell biochar material assembled with a single diatomaceous earth coating obtained in step (2) is mixed with sodium alginate gel and then added dropwise to a coagulation solution of calcium chloride for a cross-linking reaction to obtain a crab shell biochar spherical adsorbent assembled with a sodium alginate-coated diatomaceous earth coating.

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

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

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

5. The preparation method according to claim 1, characterized in that: In the step (3), the mass ratio of the crab shell biochar material assembled by the diatomaceous earth single coating to the sodium alginate in the 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: The content of sodium alginate in the sodium alginate solution in step (3) 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 to 0.3 mol / L.

8. The crab shell biochar adsorbent assembled by the sodium alginate-coated diatomaceous earth coating prepared by the preparation method according to claims 1 to 7.

9. Use of the crab shell biochar adsorbent composed of a double layer of sodium alginate-coated diatomaceous earth as described in claim 8 in the adsorption of heavy metal lead.

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