Preparation method of coal-based heavy metal adsorbent

Abstract

The invention relates to the field of heavy metal adsorbents, in particular to a preparation method of a coal-based heavy metal adsorbent, which comprises the following steps: S1, crushing and pickling coal to obtain coal particles; s2, the coal particles and a manganese salt solution are subjected to mixed dipping, drying and pyrolysis, and a pyrolysis product is obtained; s3, adding an adhesive into the pyrolysis product to obtain coal agglomerated particles, namely the coal-based adsorbent; the manganese salt solution is at least one of manganese nitrate and manganese chlorate. According to the method, the coal is subjected to crushing and acid pickling to enlarge the adsorption area of the coal, then the coal is mixed with the manganese salt solution for dipping and pyrolysis, manganese oxide generated by manganese salt decomposition can be dispersed in coal particles in a nano-particle form, and then the binding agent, the heavy metal adsorbent and the cross-linking agent are added, so that the adsorption efficiency is further improved; therefore, the coal-based heavy metal adsorbent with excellent adsorption efficiency is prepared.

Description

Technical Field

[0001] The present application relates to the field of heavy metal adsorbents, and in particular to a method for preparing a coal-based heavy metal adsorbent. Background Art

[0002] Heavy metals (such as lead, mercury, cadmium, chromium, and arsenic) are non-biodegradable in the natural environment. They accumulate over time in water, soil, and organisms (such as fish and plants), entering the human body through the food chain and causing chronic poisoning. Adsorption is considered the most promising water treatment method for heavy metal ion removal, offering advantages such as ease of operation, low energy consumption, and zero secondary pollution. It also features easy recycling of the removed products, aligning with the requirements of a circular economy and sustainable development.

[0003] The Chinese invention patent with the authorization announcement number CN103028379B discloses a method for preparing a coal-based chelated adsorbent, which is to modify coal powder by grafting a chelating group, that is, polyacrylamide reacts with CS2 under alkaline conditions to generate -NHCS2 - The chelating groups of the coal-based chelating adsorbent are adsorbed onto the surface of the coal powder through impregnation, and the pollutants are removed by the chelation between the amino group and the heavy metal ions. The adsorption sites of the coal-based chelating adsorbent depend on the density of the chelating groups.

[0004] Chinese invention patent publication number CN118179450A discloses a preparation method and application of a high-sulfur coal-based heavy metal adsorbent. The sulfur component in the high-sulfur coal is oxidized and activated by pyrolysis to form sulfur-oxygen functional groups and oxygen-containing functional groups to provide adsorption sites for heavy metals. Its adsorption effect mainly depends on the conversion of the high-sulfur coal's own components, the functional groups formed after pyrolysis, and the specific pore structure.

[0005] However, the adsorption effect of the above-mentioned heavy metal adsorbents relies on a single adsorption mechanism and has limited adsorption sites, resulting in unsatisfactory adsorption efficiency and, consequently, unsatisfactory treatment effect on heavy metals in wastewater. Therefore, there is an urgent need for a heavy metal adsorbent with ideal adsorption efficiency. Summary of the Invention

[0006] In order to improve the adsorption efficiency of heavy metal adsorbents, the present application provides a method for preparing a coal-based heavy metal adsorbent.

[0007] The present application provides a method for preparing a coal-based heavy metal adsorbent, which adopts the following technical solution: A method for preparing a coal-based heavy metal adsorbent comprises the following steps: S1: crushing and acid washing the coal to obtain coal particles; S2: mixing and impregnating the coal particles with the manganese salt solution, drying the impregnated coal particles, and pyrolyzing the dried coal particles at 300-500℃ in an inert gas atmosphere to obtain pyrolysis products; S3: adding a binder to the pyrolysis products to obtain coal agglomerated particles, i.e. coal-based heavy metal adsorbents; The manganese salt is at least one of manganese nitrate and manganese chlorate.

[0008] By adopting the above technical solution, the specific surface area of the coal is first expanded by crushing, and the minerals in the coal are then removed by acid pickling, thereby effectively increasing the adsorption sites on the coal for manganese ion adsorption. Then, the manganese ions can be uniformly adsorbed in the pores and on the surface of the coal by impregnation, the manganese salt is fixed in the coal particles by drying, and in the process of pyrolysis, the manganese salt is promoted to generate manganese oxide, and the manganese oxide is dispersed in the form of nanoparticles to provide redox active sites. Through the synergy of the high specific surface area of the manganese oxide and the coal matrix, the adsorption efficiency of the coal-based heavy metal adsorbent is further improved. Finally, the coal particles are agglomerated by a binder to effectively increase the pores between the coal particles and increase the adsorption area of the coal particles, thereby preparing a coal-based heavy metal adsorbent with excellent adsorption efficiency.

[0009] Manganese nitrate and manganese chlorate can decompose to produce manganese dioxide and gas in the process of pyrolysis. The generation of these gases can effectively increase the porosity of the coal and increase the adsorption area of the coal. At the same time, the generated manganese dioxide can be uniformly dispersed in the pores of the coal particles in the form of nanoparticles. The surface of the manganese dioxide is rich in hydroxyl groups, which can form stable surface complexes with heavy metal ions through coordination bonds, or oxidize part of the heavy metals to a higher valence state while being reduced to Mn 2+ or Mn 3+ , forming co-precipitation or stable adsorption, thereby adsorbing heavy metals and improving the adsorption efficiency of the coal-based adsorbent.

[0010] Preferably, the manganese salt is manganese nitrate.

[0011] By adopting the above technical solution, manganese nitrate can be uniformly distributed on the surface of the coal particles during impregnation, and manganese nitrate can be completely converted into manganese dioxide at a relatively low temperature. The generated manganese dioxide can be uniformly attached to the coal particles in the form of nanoparticles. At the same time, NO2 and O2 can be generated in the decomposition process of manganese nitrate. In the process of pyrolysis, NO2 and O2 can react with carbon and organic matter on the surface of the coal to expand the original pores or generate new pores through oxidation etching, effectively expanding the effective adsorption area of the coal particles.

[0012] Preferably, the concentration of the manganese nitrate is 0.2-0.4 mol / L.

[0013] By adopting the above technical solution, when the concentration of manganese nitrate is between 0.2 and 0.4 mol / L, the effective loading and uniform dispersion of manganese ions in coal particles can be guaranteed, and the gas generated by decomposition can etch the pore structure of the coal, thereby increasing the porosity and specific surface area. When the concentration of manganese nitrate is lower than 0.2 mol / L, the content of manganese ions is insufficient, the number of manganese dioxide nanoparticles generated after pyrolysis is small, and the adsorption sites are scarce, resulting in a decrease in the adsorption efficiency of the coal-based heavy metal adsorbent for heavy metals. When the concentration of manganese nitrate is higher than 0.4 mol / L, manganese salts are excessively deposited in the pores and surface of the coal, and are easily agglomerated to form large manganese dioxide particles during pyrolysis, resulting in a decrease in specific surface area and active sites. At the same time, when manganese salts at excessively high concentrations decompose, a large amount of gas is generated, which may destroy the matrix structure of the coal, irregularly increase the pore diameter, and reduce the mechanical strength and adsorption stability of the coal matrix.

[0014] Preferably, the adhesive is at least one of chitosan, tannic acid, and tea polyphenols.

[0015] By adopting the above technical solution, chitosan, tannic acid, tea polyphenols and their mixtures are dissolved in water or weak acid solution to form a solution, which evenly wraps the coal particles and aggregates through hydrogen bonds and van der Waals forces to form particles with a multi-level porous structure. Among them, chitosan contains a large number of amino and hydroxyl groups in its molecular weight. Under neutral or weak acidic conditions, the amino groups are easily protonated to form positively charged -NH3 + After acid washing, the surface of the coal particles is exposed to oxygen-containing functional groups due to the removal of minerals, and the coal particles are negatively charged. The positively charged groups of chitosan are combined with the negatively charged groups on the surface of the coal particles through electrostatic attraction. At the same time, the hydroxyl groups form hydrogen bonds with the hydroxyl groups on the surface of the coal, so that the chitosan molecules are firmly adsorbed on the surface of the coal particles, becoming a bridge between particles, connecting multiple particles through the extension of the molecular chain. In addition, chitosan, as a high molecular polymer, forms long chain molecules after dissolving in water. It can be wrapped around the surface of different coal particles through the steric hindrance effect, and the particles are "bound" together by using the flexibility and viscosity of the molecular chain to achieve the agglomeration of coal particles.

[0016] Tannic acid is a high-molecular polyphenol containing multiple pyrogallol hydroxyl groups. After acid washing, a large number of oxygen-containing functional groups are exposed on the surface of coal, which enables tannic acid to form hydrogen bonds with the polar sites on the surface of coal particles to achieve tight binding, forming a "multi-point anchoring" effect. Tannic acid molecules are firmly adsorbed on the surface of coal particles. At the same time, the aromatic ring structure of tannic acid has good π-π conjugated compatibility with the aromatic carbon structure in the coal matrix. The intermolecular binding force is enhanced through the planar stacking effect between the aromatic rings, and the van der Waals force is generated between the hydrophobic aromatic rings and the carbon skeleton of the coal particles, forming a "hydrogen bond-hydrophobic" composite effect between the particles, realizing the physical agglomeration of coal particles.

[0017] Tea polyphenols mainly contain catechins, which contain multiple phenolic hydroxyl groups in the molecules. The hydroxyl groups of tea polyphenols form a hydrogen bond network with the hydroxyl and carboxyl groups on the surface of coal particles. The agglomeration of coal particles is achieved by bridging the hydroxyl sites on the surfaces of multiple particles. In addition, the aqueous solution of tea polyphenols has a certain viscosity. After dissolution, it can wrap the surface of coal particles and form a sticky film, bonding the particles through physical adhesion.

[0018] Preferably, the adhesive is a mixture of tannic acid and tea polyphenols.

[0019] By adopting the above technical solution, tannic acid forms a three-dimensional network skeleton through intermolecular hydrogen bonds and hydrophobic effects, providing mechanical support and enhancing the physical entanglement between coal particles. Tea polyphenols can fill the gaps in the tannic acid network, and its catechol structure can form hydrogen bonds and π-π conjugation with the oxygen-containing functional groups on the surface of the coal. By penetrating into the micropores of the particles, it strengthens the interfacial adhesion and synergistically improves the agglomeration effect of the coal particles.

[0020] At the same time, the pyrogallol hydroxyl group of tannic acid can react with the Mn 4+ Empty orbitals form coordination bonds, promoting the oxidation of the surface lattice and binding water molecules to generate surface hydroxyl groups. Tea polyphenols can form a stronger bidentate coordination with the MnO2 surface through the catechol group, filling the area covered by tannic acid. The rapid diffusion of small molecules of tea polyphenols combined with the high molecular sustained-release effect of tannic acid forms a "quick start-continuous replenishment" hydroxylation process, which effectively improves the hydroxylation level of the manganese dioxide surface and improves the adsorption efficiency of coal-based heavy metal adsorbents.

[0021] Tannic acid is easily oxidized to produce quinones, which reduces the bonding effect of tannic acid. The gallic acid ester structure of tea polyphenols has strong antioxidant properties and can inhibit the quinones produced by the oxidation of tannic acid. Combining tannic acid and tea polyphenols into an adhesive can effectively improve the bonding effect of the aggregates.

[0022] Preferably, the mixing ratio of the tannic acid and tea polyphenols is 2-3:1.

[0023] By adopting the above technical solution, when the mixing ratio of tannic acid and tea polyphenols is 2-3:1, the adhesive has an ideal agglomeration effect on the coal particles and can effectively promote the hydroxylation of the manganese dioxide surface.

[0024] When the proportion of tannic acid is too high, an overly dense three-dimensional network structure is formed, and the rigidity between the molecular chains is enhanced, resulting in increased brittleness of the coal agglomerates. It may also hinder direct contact between particles, reduce the mechanical meshing force between particles, and weaken the interfacial bonding force. Excessive tannic acid also occupies the catechol chelating sites required by tea polyphenols, preventing the tea polyphenols from inducing lattice oxygen activation through bidentate chelation. It also hinders the diffusion of tea polyphenols to the manganese dioxide surface, resulting in a decrease in the degree of hydroxylation on the manganese dioxide surface.

[0025] When the proportion of tea polyphenols is too high, the bonding network structure of the coal is sparse and the bonding force between the particles is insufficient, resulting in a decrease in the compressive strength of the coal agglomerates. The coal agglomerates also have insufficient water resistance and are prone to fragmentation during the adsorption of heavy metals in wastewater. In addition, the pyrogallol structure in the excessive tea polyphenols is easily catalytically oxidized by manganese dioxide to generate quinone substances, which block the hydroxylation sites on the surface of manganese dioxide.

[0026] Preferably, the added amount of the binder accounts for 8-15% of the mass of the coal particles.

[0027] By adopting the above technical solution, when the amount of adhesive added accounts for 8-15% of the mass of the coal particles, the adhesive can have an ideal bonding effect on the coal particles and can also promote the hydroxylation of the manganese dioxide surface. When the amount of adhesive added is too little, the surface of the coal particles and the manganese dioxide cannot be evenly wrapped, resulting in a weak bonding force between the coal particles and an inability to form a stable agglomerate structure, resulting in low strength and easy breakage of the particles after molding, and insufficient hydroxylation reaction on the surface of the manganese dioxide, and no significant effect on improving the adsorption efficiency of the adsorbent. When the amount of adhesive added is too much, the coal particles are excessively bonded to form agglomerates with excessively large particle sizes, which destroys the porous structure between the particles and affects the adsorption efficiency of the coal-based adsorbent. The surface of the manganese dioxide is covered with an excessively thick adhesive, which hinders the hydroxylation reaction on the surface of the manganese dioxide, resulting in a decrease in the adsorption capacity of manganese dioxide for heavy metals, and excessive tannic acid and tea polyphenols will increase the ash residue and the emission of harmful gases (such as CO and VOCs) during combustion, reducing the clean combustion performance of coal.

[0028] Preferably, in S3, a heavy metal adsorbent is further added, and the heavy metal adsorbent is at least one of polyethyleneimine, sulfonated polystyrene, and lignin.

[0029] By adopting the above technical solution, the addition of heavy metal adsorbents can effectively improve the adsorption effect of coal-based heavy metal adsorbents on heavy metals. The molecular chain of polyethyleneimine contains a high density of primary amine, secondary amine, and tertiary amine groups, which are easily protonated under neutral or acidic conditions. It has the ability of both cationic coordination and complexation and anionic electrostatic adsorption. The lone pair of electrons of the amino group forms a coordination bond with the empty orbital of the heavy metal ion, and has a strong affinity for transition metal ions. The positive charge of the protonated amino group forms electrostatic adsorption with anionic heavy metals. Sulfonated polystyrene contains sulfonic acid groups, which are highly acidic and negatively charged, and can efficiently capture high-valent cationic heavy metals through ion exchange. Lignin contains phenolic hydroxyl groups, carboxyl groups, methoxy groups and aromatic ring structures, and can achieve broad-spectrum adsorption through coordination and complexation, ion exchange, and π-π stacking.

[0030] Preferably, in S3, a cross-linking agent is further added, and the cross-linking agent is at least one of glutaraldehyde, oxidized starch, and divinylbenzene.

[0031] By adopting the above technical solution, the addition of a cross-linking agent can fix the heavy metal adsorbent inside the coal agglomerate particles. Glutaraldehyde contains two aldehyde groups, which can undergo a cross-linking reaction with amino, hydroxyl, and thiol-containing groups, cross-linking the coal agglomerate particles with the active groups in the heavy metal adsorbent to form a three-dimensional network structure, thereby enhancing the mechanical strength of the coal-based heavy metal adsorbent. Oxidized starch, as a natural polymer cross-linking agent, can improve the hydrophilicity and biocompatibility of coal-based heavy metal adsorbents, and the oxidized starch molecules contain polar groups such as carboxyl and aldehyde groups, which can be combined with hydroxyl groups on the surface of coal particles and polar groups in heavy metal adsorbents through ionic bonds, hydrogen bonds, or covalent bonds to achieve cross-linking. At the same time, the carboxyl and other groups contained in the oxidized starch can undergo a complexation reaction with heavy metal ions to assist in improving the adsorption capacity. Divinylbenzene is an aromatic cross-linking agent containing two vinyl groups that can cross-link heavy metal adsorbents and significantly improve the mechanical strength of coal-based heavy metal adsorbents.

[0032] Preferably, in S1, the acid solution used for acid elution is at least one of hydrochloric acid and hydrofluoric acid.

[0033] By adopting the above technical solution, hydrochloric acid can chemically react with some mineral impurities such as carbonates and silicates in the coal, converting them into soluble salts, which can then be removed by water washing, effectively improving the purity of the coal and reducing the impact of impurities on the subsequent adsorbent performance. At the same time, it can increase the surface roughness and porosity, which is beneficial to the subsequent impregnation of manganese salt solution and combination with other substances, thereby improving the adsorption performance of the adsorbent.

[0034] Hydrofluoric acid can react with siliceous impurities (such as quartz) in coal to generate gaseous or water-soluble fluorides, thereby effectively removing siliceous impurities. In addition, hydrofluoric acid treatment can more significantly change the surface structure and chemical properties of coal particles, making their surface have more active sites and a more suitable pore size distribution, which is beneficial to improving the adsorption capacity and selectivity of the adsorbent for heavy metals.

[0035] In summary, this application includes at least one of the following beneficial technical effects: 1. This application increases the specific surface area and adsorption sites of coal by crushing and acid-eluting the coal. The resulting coal particles are then mixed, impregnated, and pyrolyzed with a manganese salt solution (manganese nitrate or manganese chlorate). This allows the manganese oxide produced by the decomposition of the manganese salt to be dispersed in the coal particles in the form of nanoparticles. The high specific surface area of ​​the manganese oxide synergizes with the coal matrix, further improving the adsorption efficiency of the coal-based heavy metal adsorbent. The coal particles are then agglomerated with a binder, effectively increasing the adsorption area of ​​the coal particles. Through the coordination of the above substances, a coal-based heavy metal adsorbent with excellent adsorption efficiency is prepared. 2. In this application, manganese nitrate is selected as the manganese salt for mixing with coal particles for impregnation. Manganese nitrate is easily evenly distributed on the surface of the coal particles during impregnation. Manganese nitrate can decompose at a relatively low temperature and completely convert into manganese dioxide. The decomposed manganese dioxide can be evenly attached to the coal particles in the form of nanoparticles. The large number of hydroxyl groups on the surface of manganese dioxide can form complexes with heavy metals, thereby improving the adsorption efficiency of the coal-based heavy metal adsorbent. 3. This application selects a mixture of tannic acid and tea polyphenols as a binder. Tannic acid forms a three-dimensional network skeleton through intermolecular hydrogen bonds and hydrophobic interactions, providing mechanical support and enhancing the physical entanglement between coal particles. Tea polyphenols can fill the gaps in the tannic acid network and penetrate into the micropores of the particles to strengthen interfacial adhesion and synergistically improve the agglomeration effect of the coal particles. At the same time, tannic acid and tea polyphenols promote the hydroxylation of the manganese dioxide surface, further improving the adsorption efficiency. In addition, tea polyphenols can inhibit the oxidation of tannic acid to generate quinone substances, thereby improving the agglomeration effect of the coal particles. DETAILED DESCRIPTION

[0036] The present application is further described in detail below with reference to the following examples and comparative examples.

[0037] Example 1 A method for preparing a coal-based heavy metal adsorbent comprises the following steps: S1: crushing 200 g of coal and eluting the crushed coal with 500 mL of 4 mol / L hydrochloric acid to obtain coal particles; S2: Mixing coal particles with 1 L of 0.3 mol / L manganese nitrate solution and impregnating the mixture for 2 h, drying the mixture at 60-80° C. and then pyrolyzing the mixture in an inert gas atmosphere to obtain a pyrolysis product; S3: Adding a binder to the pyrolysis product to obtain coal agglomerated particles, which are coal-based heavy metal adsorbents.

[0038] The pyrolysis temperature is 300-500° C., the pyrolysis time is 1.5-2.5 h, the amount of adhesive added is 24 g, the adhesive is a mixture of tannic acid and tea polyphenols, and the mixing ratio of tannic acid to tea polyphenols in the mixture is 2:1.

[0039] Example 2 Example 2 Based on the preparation method of Example 1, 0.3 mol / L manganese nitrate was replaced by 0.3 mol / L manganese chlorate, and other conditions remained unchanged.

[0040] Example 3 Example 3 Based on the preparation method of Example 1, 4 mol / L hydrochloric acid is replaced by 4 mol / L hydrofluoric acid, and other conditions remain unchanged.

[0041] Comparative Example 1 Comparative Example 1: Based on the preparation method of Example 1, the acid washing process of the coal in S1 was removed, and the other processes remained unchanged.

[0042] Comparative Example 2 Comparative Example 2: Based on the preparation method of Example 1, the impregnation and pyrolysis processes of the coal particles and the manganese salt in S2 were removed, and the coal particles obtained in S1 were directly agglomerated, while the other processes remained unchanged.

[0043] Comparative Example 3 Comparative Example 3 is based on the preparation method of Example 1, except that the coal acid elution process in S1 and the impregnation and pyrolysis process of the coal particles with manganese salt in S2 are removed, that is, the crushed coal particles are directly agglomerated, and the other processes remain unchanged.

[0044] Performance testing The coal-based heavy metal adsorbents of Examples 1-3 and Comparative Examples 1-3 were analyzed, and the specific detection method was as follows: Adsorption rate The prepared coal-based heavy gold adsorbent was mixed with the prepared solution containing cadmium or copper ions. The Cd2+ concentration in the cadmium-containing solution was 10 mg / L and the pH value was 6. The Cu2+ concentration in the copper-containing solution was 10 mg / L and the pH value was 6. The amount of adsorbent added was 10 g / L. After adsorption for 2 hours, the mixture was filtered and rinsed with distilled water. The concentrations of Cd2+ and Cu2+ in the aqueous solution were tested.

[0045] According to the above detection method, the test results of Examples 1-3 and Comparative Examples 1-3 were obtained, as shown in Table 1 below.

[0046] Table 1 Performance test table of Examples 1-3 and Comparative Examples 1-3 project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 <![CDATA[Cd 2+ Adsorption rate / %]]> 90.4 89.7 89.5 84.6 81.8 79.1 <![CDATA[Cu 2+ Adsorption rate / %]]> 86.1 85.6 85.3 80.2 78.5 76.4 Referring to Table 1, by comparing Examples 1-3 and Comparative Examples 1-3, it can be seen that the coal-based heavy metal adsorbents obtained in Examples 1-3 have a high adsorption capacity for Cd 2+ and Cu 2+ The adsorption rate of the coal particles is significantly higher than that of the comparative examples 1-3. This may be because the acid elution can effectively remove the minerals in the coal, thereby effectively increasing the adsorption sites on the coal for manganese ion adsorption. Then, by immersing the coal particles in the manganese nitrate solution, the manganese nitrate can be decomposed during pyrolysis to produce gas, which expands the original voids or generates new channels through oxidation etching, effectively expanding the effective adsorption area of ​​the coal particles. At the same time, the manganese dioxide generated is attached to the coal particles in the form of nanoparticles. The high specific surface area of ​​the nano manganese dioxide and the synergy of the coal matrix further improve the coal-based heavy metal adsorbent for Cd 2+ and Cu 2+ adsorption efficiency.

[0047] Examples 4-5 In Example 4-5, based on the preparation method of Example 1, the concentration of manganese nitrate was adjusted. The specific adjustments are shown in Table 2.

[0048] Comparative Examples 4-5 Comparative Example 4-5 is based on the preparation method of Example 1, but the concentration of manganese nitrate is adjusted. The specific adjustments are shown in Table 2.

[0049] The coal-based heavy metal adsorbents obtained in Examples 4-5 and Comparative Examples 4-5 were subjected to the above performance tests, and the test results are shown in Table 2.

[0050] Table 2 Manganese nitrate concentration and performance test table of Example 1, Examples 4-5 and Comparative Examples 4-5 Referring to Table 2, by comparing Example 1, Examples 4-5 and Comparative Examples 4-5, it can be seen that when the concentration of manganese nitrate is 0.2-0.4 mol / L, especially when the concentration of manganese nitrate is 0.3 mol / L, the obtained coal-based heavy metal adsorbent has a high adsorption capacity for Cd 2+ and Cu 2+The adsorption efficiency of the coal-based heavy metal adsorbent is optimal, which can be due to the fact that when the concentration of manganese nitrate is lower than 0.2 mol / L, the content of manganese ions is insufficient, the number of manganese dioxide nanoparticles generated after pyrolysis is small, and the adsorption sites are scarce, resulting in a decrease in the adsorption efficiency of the coal-based heavy metal adsorbent to heavy metals. When the concentration of manganese nitrate is higher than 0.4 mol / L, manganese salt is excessively deposited on the pores and surface of coal, and is prone to agglomeration to form large manganese dioxide particles during pyrolysis, resulting in a decrease in specific surface area and active sites. Meanwhile, a large amount of gas is generated when manganese salt with a high concentration is decomposed, which can damage the matrix structure of coal, increase the irregularity of pore size, and reduce the mechanical strength and adsorption stability of the coal matrix.

[0051] Examples 6-8 Examples 6-8 are based on the preparation method of Example 1, and the types of binders are adjusted, as shown in Table 3.

[0052] Performance detection test The coal-based heavy metal adsorbents of Examples 6-8 are analyzed, and the specific detection method is as follows: Compressive strength A micro-compression tester MCT-510 manufactured by Shimadzu Corporation is used to measure the compressive strength of 20 particles of each heavy metal adsorbent, and the central value is taken as the compressive strength of the heavy metal adsorbent.

[0053] The coal-based heavy metal adsorbents obtained in Examples 6-8 are subjected to the performance detection as described above, and the detection results are shown in Table 3.

[0054] Table 3: Types of binders and performance detection table of Example 1 and Examples 6-8 As shown in Table 3, it can be seen from Comparative Example 1 and Examples 6-8 that when the binder is a mixture of tannic acid and tea polyphenol, the obtained coal-based heavy metal adsorbent has high adsorption efficiency for Cd 2+ and Cu 2+ , and also has ideal compressive strength, which can be due to the fact that tannic acid forms a three-dimensional network skeleton through intermolecular hydrogen bonding and hydrophobic interaction, provides mechanical support, enhances the physical entanglement between coal particles, tea polyphenol can fill the interstitial space of the tannic acid network, penetrate into the micropores of the particles, strengthen the interfacial adhesion, and synergistically improve the agglomeration effect of the coal particles. Meanwhile, the ortho-phenol hydroxyl group of tannic acid can form a complex with the Mn 4+Empty orbitals form coordination bonds, promoting the oxidation of the surface lattice and binding water molecules to generate surface hydroxyl groups. Tea polyphenols can form a stronger bidentate coordination with the MnO2 surface through the catechol group, filling the area covered by tannic acid. Through the rapid diffusion of small molecules of tea polyphenols combined with the high molecular sustained-release effect of tannic acid, a "quick start-continuous replenishment" hydroxylation process is formed, which effectively improves the adsorption effect of coal-based heavy metal adsorbents.

[0055] In addition, the gallate structure of tea polyphenols has strong antioxidant properties, which can inhibit the quinone substances produced by the oxidation of tannic acid. Compounding tannic acid and tea polyphenols into an adhesive can effectively improve the bonding effect of the aggregates. Example 9 Example 9 Based on the preparation method of Example 1, the mixing ratio of tannic acid and tea polyphenols was adjusted, and the specific adjustment is shown in Table 4.

[0056] Comparative Examples 6-7 Comparative Example 6-7 is based on the preparation method of Example 1, but the mixing ratio of tannic acid and tea polyphenols is adjusted. The specific adjustment is shown in Table 4.

[0057] The coal-based heavy metal adsorbents obtained in Example 9 and Comparative Examples 6-7 were subjected to the above performance tests, and the test results are shown in Table 4.

[0058] Table 4 Mixing ratio and performance test table of tannic acid and tea polyphenols in Example 1, Example 9 and Comparative Examples 6-7 Referring to Table 4, by comparing Example 1, Example 9 and Comparative Examples 6-7, it can be seen that when the mixing ratio of tannic acid to tea polyphenols is 2-3:1, especially when the mixing ratio of tannic acid to tea polyphenols is 2:1, the coal-based heavy metal adsorbent has a better adsorption capacity for Cd 2+ and Cu 2+ It has an ideal adsorption rate and excellent compressive strength. This may be because when the proportion of tannic acid is too high, an overly dense three-dimensional network structure will be formed, the rigidity between the molecular chains will be enhanced, and the brittleness of the coal agglomerates will increase. In addition, excessive tannic acid will occupy the catechol chelating sites required by tea polyphenols, resulting in the inability of tea polyphenols to induce lattice oxygen activation through bidentate chelation, which affects the coal-based heavy metal adsorbent for Cd 2+ and Cu 2+ When the proportion of tea polyphenols is too high, the bonding network structure of coal becomes sparse and the bonding force between particles is insufficient, resulting in a decrease in the compressive strength of coal agglomerates.

[0059] Examples 10-11 In Examples 10-11, based on the preparation method of Example 1, the amount of adhesive added was adjusted. The specific adjustments are shown in Table 5.

[0060] Comparative Examples 8-9 In Comparative Examples 8-9, based on the preparation method of Example 1, the amount of binder added was adjusted. The specific adjustments are shown in Table 5.

[0061] The coal-based heavy metal adsorbents obtained in Examples 10-11 and Comparative Examples 8-9 were subjected to the above performance tests, and the test results are shown in Table 5.

[0062] Table 5 Adhesive addition amount and performance test table of Example 1, Examples 10-11 and Comparative Examples 8-9 Referring to Table 5, by comparing Example 1, Examples 10-11 and Comparative Examples 8-9, it can be seen that when the amount of binder added accounts for 8-15% of the mass of the coal particles, especially when the amount of binder added accounts for 12% of the coal particles, the obtained coal-based heavy metal adsorbent has a higher adsorption capacity for Cd 2+ and Cu 2+ The excellent adsorption effect and the ideal compressive strength are achieved at the same time. This may be because when the amount of binder added is too little, the surface of the coal particles and manganese dioxide cannot be evenly wrapped, resulting in weak bonding between the coal particles and failure to form a stable agglomerate structure, resulting in low strength and easy breakage of the formed particles, and insufficient hydroxylation reaction on the surface of manganese dioxide, which has no significant effect on improving the adsorption efficiency of the adsorbent; when the amount of binder added is too much, the coal particles are excessively bonded to form agglomerates with too large a particle size, which destroys the porous structure between the particles and affects the adsorption efficiency of the coal-based adsorbent. In addition, the surface of manganese dioxide is covered with too thick a binder, which hinders the hydroxylation reaction on the surface of manganese dioxide, resulting in manganese dioxide's adsorption of Cd 2+ and Cu 2+ The adsorption capacity decreases.

[0063] Example 12 Example 12 Based on the preparation method of Example 1, 6 g of polyethyleneimine was added to S3 and mixed with coal particles.

[0064] Example 13 Example 13 Based on the preparation method of Example 12, 6g of polyethyleneimine was replaced by 6g of sulfonated polystyrene, and the other conditions remained unchanged.

[0065] Example 14 Example 14 is based on the preparation method of Example 12, except that 6 g of polyethyleneimine is replaced with 6 g of lignin, and the other conditions remain unchanged.

[0066] The coal-based heavy metal adsorbents obtained in Examples 12-14 were subjected to the above performance tests, and the test results are shown in Table 6.

[0067] Table 6 Types and performance test table of heavy metal adsorbents in Example 1 and Examples 12-14 As shown in Table 6, by comparing Example 1 with Examples 12-14, it can be seen that the coal-based heavy metal adsorbent using polyethyleneimine as the heavy metal adsorbent has a better effect on Cd 2+ and Cu 2+ This results in a more ideal adsorption effect, likely due to the fact that the amino groups of polyethyleneimine are easily protonated in aqueous solution, adsorbing negatively charged heavy metal anions through electrostatic interactions or forming stable chelates with heavy metal cations through coordination complexation, resulting in strong and selective adsorption. Furthermore, polyethyleneimine contains a large number of primary and secondary amine groups, which react with the aldehyde groups in the cross-linker glutaraldehyde through a Schiff base reaction, forming a stable covalent bond network. This allows the polyethyleneimine to firmly bind to the surface of coal agglomerates, enhancing the mechanical strength and structural stability of the adsorbent.

[0068] Example 15 Example 15 Based on the preparation method of Example 12, 4 g of glutaraldehyde was added to S3.

[0069] Example 16 Example 16 Based on the preparation method of Example 12, 4 g of glutaraldehyde was replaced by 4 g of oxidized starch, and the other conditions remained unchanged.

[0070] Example 17 Example 17 Based on the preparation method of Example 12, 4g of glutaraldehyde is replaced by 4g of formyl starch, and other conditions remain unchanged.

[0071] The coal-based heavy metal adsorbents obtained in Examples 15-17 were subjected to the above performance tests, and the test results are shown in Table 7.

[0072] Table 7 Types and performance test table of cross-linking agents of Example 12 and Examples 15-17 As shown in Table 7, a comparison between Example 1 and Examples 15-17 shows that the coal-based heavy metal adsorbent using glutaraldehyde as the cross-linking agent has ideal adsorption efficiency and compressive strength. This is probably because glutaraldehyde can react efficiently with the primary / secondary amine groups in polyethyleneimine to form stable covalent bonds. This bifunctional cross-linking agent can simultaneously connect two polyethyleneimine molecules or polyethyleneimine with active groups on the surface of coal agglomerated particles, rapidly constructing a three-dimensional network structure and enhancing the mechanical strength and chemical stability of the adsorbent.

[0073] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A method for preparing a coal-based heavy metal adsorbent, characterized in that: The following steps are involved: S1: crushing and acid washing the coal to obtain coal particles; S2: impregnating the coal particles with the manganese salt solution, drying the impregnated coal particles, and then pyrolyzing them in an inert gas atmosphere at 300-500° C. to obtain pyrolysis products; S3: Adding a binder to the pyrolysis product to obtain coal agglomerated particles, which are coal-based heavy metal adsorbents; The manganese salt is at least one of manganese nitrate and manganese chlorate.

2. The method for preparing a coal-based heavy metal adsorbent according to claim 1, characterized in that: The manganese salt is manganese nitrate.

3. The method for preparing a coal-based heavy metal adsorbent according to claim 2, characterized in that: The concentration of the manganese nitrate is 0.2-0.4 mol / L.

4. The method for preparing a coal-based heavy metal adsorbent according to claim 1, characterized in that: The adhesive is at least one of chitosan, tannic acid and tea polyphenols.

5. The method for preparing a coal-based heavy metal adsorbent according to claim 4, characterized in that: The adhesive is a mixture of tannic acid and tea polyphenols.

6. The method for preparing a coal-based heavy metal adsorbent according to claim 5, characterized in that: The mixing ratio of the tannic acid and tea polyphenols is 2-3:

1.

7. The method for preparing a coal-based heavy metal adsorbent according to claim 4, characterized in that: The added amount of the binder accounts for 8-15% of the mass of the coal particles.

8. The method for preparing a coal-based heavy metal adsorbent according to claim 1, characterized in that: In S3, a heavy metal adsorbent is further added, and the heavy metal adsorbent is at least one of polyethyleneimine, sulfonated polystyrene, and lignin.

9. The method for preparing a coal-based heavy metal adsorbent according to claim 8, characterized in that: In S3, a cross-linking agent is further added, and the cross-linking agent is at least one of glutaraldehyde, oxidized starch, and aldehyde starch.

10. The method for preparing a coal-based heavy metal adsorbent according to claim 1, characterized in that: In S1, the acid solution used for acid elution is at least one of hydrochloric acid and hydrofluoric acid.

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