Calcium silicate hydrate-biochar gel composite material and preparation method and application thereof

Abstract

The application provides a hydrated calcium silicate-biochar gel composite material and a preparation method and application thereof, and belongs to the technical field of environmental engineering materials. Sodium alginate, sodium silicate and biochar material are mixed with water to obtain a sodium alginate-sodium silicate-biochar mixed solution; the sodium alginate-sodium silicate-biochar mixed solution is added into a calcium salt solution for gelation, and then aging and pyrolysis are sequentially performed to obtain the hydrated calcium silicate-biochar gel composite material. The calcium alginate gel method and the hydrated calcium silicate (C-S-H) solution synthesis method are combined to modify the biochar material, and the finally prepared hydrated calcium silicate-biochar gel composite material has excellent adsorption performance on phosphate and also has high mechanical strength.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of environmental engineering materials, and particularly relates to a hydrated calcium silicate-biochar gel composite material, a preparation method and application thereof. BACKGROUND

[0002] Phosphorus, as a non-renewable element, is one of the main causes of water eutrophication. Therefore, research on methods capable of effectively removing and recycling phosphate in water bodies is a key problem in solving water environmental pollution and phosphorus resource shortage.

[0003] Adsorption is a method of using adsorbents with surface active sites to adsorb pollutants. Due to the advantages such as simple operation, biochar, a green and environmentally friendly adsorption material obtained by high-temperature pyrolysis under anaerobic or anoxic conditions, is widely used in water and soil pollution control. However, the surface of biochar is electronegative, and the adsorption performance of inorganic anions is poor, so it is not suitable as a phosphate adsorbent. SUMMARY

[0004] The present application provides a hydrated calcium silicate-biochar gel composite material, a preparation method and application thereof. The hydrated calcium silicate-biochar gel composite material provided by the present application has excellent adsorption performance for phosphate.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a preparation method of a hydrated calcium silicate-biochar gel composite material, comprising the following steps:

[0007] Mixing sodium alginate, sodium silicate and biochar material with water to obtain a sodium alginate-sodium silicate-biochar mixed solution;

[0008] Adding the sodium alginate-sodium silicate-biochar mixed solution to the calcium salt solution for gelation, and then sequentially aging and pyrolyzing to obtain the hydrated calcium silicate-biochar gel composite material.

[0009] Preferably, the preparation method of the biochar material comprises: calcining a biomass raw material to obtain the biochar material.

[0010] Preferably, the biomass raw material comprises one or more of straw, sawdust and sludge; the calcination temperature is 400-600 DEG C, the holding time is 2-4 h, and the temperature rising rate required for the calcination is 5-15 DEG C / min.

[0011] Preferably, the concentration of sodium alginate in the sodium alginate-sodium silicate-biochar mixed solution is 10-40 g / L, the concentration of sodium silicate is 21.96-65.88 g / L, and the concentration of biochar is 5-40 g / L.

[0012] Preferably, the concentration of the calcium salt solution is 3-9wt%; the molar ratio of calcium in the calcium salt solution to silicon in sodium silicate is 0.8-2.0.

[0013] Preferably, the gelation comprises: under stirring, adding the sodium alginate-sodium silicate-biochar mixed solution into the calcium salt solution by using a peristaltic pump and a rubber tube in communication with the peristaltic pump, the rotation speed of the peristaltic pump being 1-1.5rpm, the outlet of the rubber tube being located above the calcium salt solution, and the distance between the outlet of the rubber tube and the liquid surface of the calcium salt solution being 5-8mm.

[0014] Preferably, the aging temperature is 60-80℃, and the aging time is 1-10d.

[0015] Preferably, the pyrolysis temperature is 300-500℃, and the holding time is 2-4h.

[0016] The present application provides a hydrated calcium silicate-biochar gel composite material prepared by the preparation method described in the above technical solution, which comprises biochar material, and calcium alginate nanoparticles and hydrated calcium silicate nanoparticles loaded on the biochar material.

[0017] The present application provides an application of the hydrated calcium silicate-biochar gel composite material described in the above technical solution in preparing a phosphate adsorbent.

[0018] The present application provides a preparation method of a hydrated calcium silicate-biochar gel composite material, which comprises the following steps: mixing sodium alginate, sodium silicate, biochar material and water to obtain a sodium alginate-sodium silicate-biochar mixed solution; adding the sodium alginate-sodium silicate-biochar mixed solution into a calcium salt solution for gelation, and then sequentially aging and pyrolyzing to obtain the hydrated calcium silicate-biochar gel composite material. The present application combines calcium alginate gel method and hydrated calcium silicate (C-S-H) solution synthesis method to modify biochar material, and the finally prepared hydrated calcium silicate-biochar gel composite material has excellent adsorption performance on phosphate and also has high mechanical strength. Specifically, the present application uniformly fixes biochar material and sodium silicate through rapid gelation, generates hydrated calcium silicate through hydration reaction in the aging process, and then pyrolyzes, which can effectively improve the adsorption effect of the composite material on phosphate, and calcium alginate and hydrated calcium silicate provide good support for the mechanical strength of the composite material. The results of the examples show that the adsorption capacity of the hydrated calcium silicate-biochar gel composite material provided by the present application on phosphate is 17.30-36.22mg / g, and the maximum load is 1.27-3.22N. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1A structural schematic diagram of a device required for a gelation step in preparation of a calcium silicate hydrate-biochar gel composite material;

[0020] Figure 2 A test result graph of phosphate removal performance of the calcium silicate hydrate-biochar gel composite material in Test Example 1;

[0021] Figure 3 A test result graph of phosphate removal performance of the calcium silicate hydrate-biochar gel composite material in Test Example 2 and the sodium alginate-biochar gel material in Comparative Example 1;

[0022] Figure 4 A test result graph of maximum load of the calcium silicate hydrate-biochar gel composite material in Test Example 3;

[0023] Figure 5 A deformation process graph of the calcium silicate hydrate-biochar gel composite material in Test Example 3;

[0024] Figure 6 A scanning electron microscope graph of the calcium silicate hydrate-biochar gel composite material and corn straw biochar in Example 1;

[0025] Figure 7 An EDS analysis graph of the calcium silicate hydrate-biochar gel composite material in Example 1;

[0026] Figure 8 An FTIR spectrum of the calcium silicate hydrate-biochar gel composite material in Test Example 3 and the sodium alginate-biochar gel material in Comparative Example 1;

[0027] Figure 9 An XRD spectrum of the calcium silicate hydrate-biochar gel composite material in Test Example 3 and the sodium alginate-biochar gel material in Comparative Example 1;

[0028] Figure 10 A TG-DTG analysis graph of the calcium silicate hydrate-biochar gel composite material in Example 1 and the sodium alginate-biochar gel material in Comparative Example 1. DETAILED DESCRIPTION

[0029] The present application provides a preparation method of a calcium silicate hydrate-biochar gel composite material, comprising the following steps:

[0030] Mixing sodium alginate, sodium silicate and biochar material with water to obtain a sodium alginate-sodium silicate-biochar mixed solution;

[0031] Adding the sodium alginate-sodium silicate-biochar mixed solution to the calcium salt solution for gelation, and then sequentially aging and pyrolyzing to obtain the calcium silicate hydrate-biochar gel composite material.

[0032] In the present application, if not otherwise specified, all raw materials used are commercially available or prepared by methods well known to those skilled in the art.

[0033] The present application first prepares a biochar material, and the preparation method of the biochar material preferably comprises: roasting a biomass raw material to obtain the biochar material.

[0034] In the present application, the biomass raw material preferably comprises one or more of straw, sawdust and sludge, more preferably straw, sawdust or sludge, and further preferably straw; the straw preferably comprises corn straw and / or wheat straw, and more preferably corn straw; the sludge preferably is excess sludge, and more preferably excess sludge generated in a sewage treatment plant. The present application preferably uses waste biomass such as straw, sawdust and sludge as raw material to prepare biochar material, and further prepares hydrated calcium silicate-biochar gel composite material, which can achieve the dual effects of solid waste treatment and pollution control. Before the roasting, the present application preferably sequentially subjects the biomass raw material to crushing and drying; the present application preferably crushes the biomass raw material to a particle size of 60-100 mesh; the temperature of the drying is preferably 60-105°C, and more preferably 95-105°C, and the time is preferably 24-48h, and more preferably 40-48h. In the present application, the temperature of the roasting in a muffle furnace is preferably 400-600°C, more preferably 450-550°C, and further preferably 500°C; the holding time is preferably 2-4h, more preferably 2.5-3.5h, and further preferably 3h; the temperature rising rate to the temperature required for the roasting is preferably 5-15°C / min, more preferably 8-12°C / min, and further preferably 10°C / min; and the roasting is preferably performed in an air atmosphere. In the examples of the present application, the roasting is specifically performed in a muffle furnace. The present application preferably performs the roasting under the above conditions, which can make the biomass raw material have a good carbonization effect, and slow temperature rising and high roasting temperature are conducive to obtaining biochar material with better performance. After the roasting, the present application preferably sequentially subjects the obtained roasted material to washing, drying, grinding and sieving to obtain the biochar material. The present application preferably selects a reagent for washing according to the type of the biomass raw material; specifically, when the biomass raw material is sludge, the present application preferably sequentially uses hydrochloric acid and water to wash the roasted material; the present application removes ash in the roasted material by hydrochloric acid washing, and then washes the roasted material to neutral with water; the concentration of the hydrochloric acid is preferably 1 mol / L, and the water is preferably deionized water; when the biomass raw material is other raw material except sludge, such as straw or sawdust, the present application preferably directly uses water to wash the roasted material to neutral, and the water is preferably deionized water. In the present application, the temperature of the drying is preferably 60-105°C, and more preferably 95-105°C, and the time of the drying is based on ensuring sufficient drying; the grinding is based on ensuring that the obtained biochar material has a desired particle size; and the mesh size of the screen used for the sieving is preferably 100-200 mesh.

[0035] After obtaining the biochar material, the present application mixes sodium alginate, sodium silicate, the biochar material and water to obtain a sodium alginate-sodium silicate-biochar mixed solution. In the present application, the sodium silicate is preferably instant sodium silicate powder, i.e. industrial building material soda ash. The present application preferably uses the low-cost industrial building material soda ash, which is conducive to reducing the production cost. In the present application, the sodium alginate is a by-product of marine product processing, and using it as a raw material is conducive to reducing the production cost. In the present application, the concentration of sodium alginate in the sodium alginate-sodium silicate-biochar mixed solution is preferably 10-40 g / L, more preferably 15-30 g / L, and further preferably 20 g / L; the concentration of sodium silicate is preferably 21.96-65.88 g / L, more preferably 21.96 g / L, 43.92 g / L or 65.88 g / L; and the concentration of biochar is preferably 5-40 g / L, more preferably 10-30 g / L, and further preferably 20 g / L. The present application preferably first stirs and mixes the sodium alginate and water to obtain a sodium alginate solution, then secondly stirs and mixes the sodium alginate solution and the sodium silicate to obtain a sodium alginate-sodium silicate mixed solution, and finally thirdly stirs and mixes the sodium alginate-sodium silicate mixed solution and the biochar material to obtain the sodium alginate-sodium silicate-biochar mixed solution. The present application does not have a special limitation on the time of the first stirring and mixing, as long as the sodium alginate is completely dissolved; the time of the second stirring and mixing is preferably 6-18 h, and more preferably 12 h; and the time of the third stirring and mixing is preferably 0.5-3 h, and more preferably 1 h. The present application preferably ensures that the biochar material quickly gels to form a calcium alginate composite gel through a long time of stirring, and then the sodium silicate and Ca 2+ The hydration reaction is uniform in the gel.

[0036] After obtaining the sodium alginate-sodium silicate-biochar mixed solution, the sodium alginate-sodium silicate-biochar mixed solution is added into the calcium salt solution for gelation, and then aging and pyrolysis are sequentially performed to obtain the calcium silicate hydrate-biochar gel composite material. In the present application, the calcium salt in the calcium salt solution preferably includes calcium chloride, calcium sulfate or calcium nitrate, and more preferably is calcium chloride. In the present application, the concentration of the calcium salt solution is preferably 3-9 wt%, and specifically can be 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt% or 9 wt%; the molar ratio of calcium in the calcium salt solution to silicon in sodium silicate is preferably 0.8-2.0, more preferably 1.0-1.8, and further preferably 1.5. The present application preferably facilitates the generation of type II calcium silicate hydrate (C-S-H (II)) under the condition of a higher Ca / Si molar ratio, which plays a stronger supporting role on the mechanical strength of the material, but a too high Ca / Si molar ratio will lead to the generation of amorphous Ca(OH)2, which is not conducive to the stability of the composite material structure. The present application preferably controls the concentrations and ratios of sodium alginate, sodium silicate and calcium chloride within the above-mentioned ranges, which is conducive to ensuring that the finally obtained composite material has excellent mechanical strength. For example, if the concentration of the calcium salt solution is too low, the internal hydration reaction of the biochar material gel will be insufficient, the calcium silicate hydrate will be less, and the mechanical strength of the composite material will be insufficient.

[0037] In the present application, the gelation preferably includes: under stirring conditions, the sodium alginate-sodium silicate-biochar mixed solution is added dropwise into the calcium salt solution by using a peristaltic pump and a rubber tube in communication with the peristaltic pump. In the present application, the device structure used for gelation is shown in Figure 1 The liquid inlet and the liquid outlet of the peristaltic pump are respectively communicated with the rubber tubes, wherein the sodium alginate-sodium silicate-biochar mixed solution is transported to the peristaltic pump through the rubber tube in communication with the liquid inlet, and then added dropwise into the calcium salt solution through the rubber tube in communication with the liquid outlet. In the present application, the rotation speed of the peristaltic pump is preferably 1-1.5 rpm; the outlet of the rubber tube in communication with the liquid outlet is located above the calcium salt solution, and the distance between the outlet of the rubber tube and the liquid level of the calcium salt solution is preferably 5-8 mm. The present application preferably performs gelation under the above-mentioned rotation speed and distance conditions, which is conducive to ensuring that the sodium alginate-sodium silicate-biochar mixed solution is formed into a relatively regular spherical gel through gelation in the calcium salt solution, and the stirring in the process of gelation is conducive to making the gel fully settle.

[0038] After the gelation is completed (i.e. after the sodium alginate-sodium silicate-biochar mixed solution is added dropwise), the present application ages the obtained material solution to obtain an aged product. In the present application, the temperature of the aging is preferably 60-80℃, more preferably 60-70℃; the time is preferably 1-10d, and can be 1d, 2d, 3d, 4d, 5d, 6d, 7d, 8d, 9d or 10d. The present application preferably ages under the above conditions, which is conducive to ensuring that the hydration reaction is fully carried out. The present application preferably ages in an oven. After the aging is completed, the present application preferably further includes sequentially performing washing and drying, the reagent used for the washing is preferably water, more preferably deionized water; the temperature of the drying is preferably 60-105℃, more preferably 95-105℃, and the time of the drying is sufficient to ensure that the drying is complete.

[0039] After the aged product is obtained, the present application pyrolyzes the aged product to obtain the hydrated calcium silicate-biochar gel composite material. In the present application, the temperature of the pyrolysis is preferably 300-500℃, more preferably 350-450℃, and further preferably 400℃; the holding time is preferably 2-4h, more preferably 2.5-3.5h, and further preferably 3h. The present application preferably pyrolyzes under the above conditions, which is conducive to ensuring that the finally obtained composite material has good adsorption performance for phosphate, specifically, calcium alginate and hydrated calcium silicate begin to decompose at greater than 300℃, which is conducive to the exposure of the adsorption sites of the composite material and the improvement of the adsorption performance. After the pyrolysis is completed, the present application preferably further includes sequentially performing washing and drying, the reagent used for the washing is preferably water, more preferably deionized water; the temperature of the drying is preferably 60-105℃, more preferably 95-105℃, and the time of the drying is sufficient to ensure that the drying is complete.

[0040] The preparation method of the hydrated calcium silicate-biochar gel composite material provided by the present application is simple to operate, requires relatively conventional equipment, and has low production cost, and is suitable for large-scale popularization and application.

[0041] The present application provides a hydrated calcium silicate-biochar gel composite material prepared by the preparation method described in the above technical solution, which comprises biochar material and calcium alginate nanoparticles and hydrated calcium silicate nanoparticles loaded on the biochar material. In the present application, the hydrated calcium silicate-biochar gel composite material as a whole is irregularly spherical in surface, and the particle size is preferably 2-4mm. In the present application, the calcium alginate nanoparticles and the hydrated calcium silicate nanoparticles are specifically loaded in the interstices of the biochar material, and the calcium alginate nanoparticles and the hydrated calcium silicate nanoparticles are in a mutually crosslinked state, and the particle size of the calcium alginate nanoparticles and the hydrated calcium silicate nanoparticles is preferably independently 50-150nm.

[0042] The application provides application of the calcium silicate hydrate-biochar gel composite material in preparation of a phosphate adsorbent. 16 (OH)·4H2O) is the main strength source of the cement-based composite material, and Ca 2+ The existence of Ca and -OH enables the material to have certain adsorption performance on phosphate, and the sodium alginate can be ion-exchanged with Ca 2+ rapidly to generate a hydrogel, and the generated hydrogel has thermal irreversibility, so that the calcium silicate hydrate-biochar gel composite material finally prepared has excellent phosphate adsorption and removal capacity and mechanical strength, and can realize efficient treatment of phosphate in water.

[0043] The technical solutions in the application will be described clearly and completely below with reference to the embodiments in the application. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the application.

[0044] In the following examples, comparative examples and test examples, the materials used are commercially available unless otherwise specified, and the experimental methods used are conventional methods unless otherwise specified.

[0045] Example 1

[0046] (1) Preparation of corn straw biochar: corn straw (from a certain agricultural product processing plant in Lianyungang, Jiangsu) was crushed and sieved, and corn straw particles with a particle size of 60-100 mesh were taken and placed in a 105℃ oven for drying for 48h. The dried corn straw was placed in a muffle furnace, and heated to 500℃ at a heating rate of 10℃ / min. The corn straw was calcined at 500℃ for 3h, and then washed with deionized water until neutral, and dried in a 105℃ oven. After that, the corn straw biochar with a particle size of 100 mesh was obtained by grinding and sieving, and was ready for use.

[0047] (2) Preparation of sodium alginate-sodium silicate-biochar mixture: prepare a sodium alginate solution with a concentration of 20 g / L with deionized water, then add a certain amount of instant sodium silicate powder to make the sodium silicate concentration 21.96 g / L, 43.92 g / L, and 65.88 g / L, respectively, and stir for 12 h to obtain a sodium alginate-sodium silicate solution. Then, add corn straw biochar at a solid-liquid ratio of 1 g:50 mL, and stir for 1 h to obtain a sodium alginate-sodium silicate-biochar mixture;

[0048] (3) Preparation of hydrated calcium silicate-biochar gel composite materials: Calcium chloride solutions with concentrations of 3 wt%, 6 wt%, and 9 wt% were prepared with deionized water, and the mixture was pumped through a peristaltic pump and a hose connected to the peristaltic pump (such as Figure 1 (As shown in the figure), a sodium alginate-sodium silicate-biochar mixture was added dropwise to the calcium chloride solution (the molar ratio of calcium in the calcium chloride solution to silicon in the sodium silicate was 1.5). The peristaltic pump speed was set to 1.0 rpm, the hose outlet was located above the calcium chloride solution, and the distance between the hose outlet and the calcium chloride solution level was 6 mm. Stirring was maintained during the addition to ensure sufficient sedimentation of the biochar gel material. After the addition was completed, the resulting material was placed in a 60°C oven for aging for 5 days. After aging, it was washed with deionized water and dried in a 105°C oven. It was then placed in a muffle furnace and heated to 300°C at a heating rate of 10°C / min. It was pyrolyzed at 300°C for 2 hours. After the pyrolysis was completed, it was washed with deionized water and dried in a 105°C oven to obtain hydrated calcium silicate-biochar gel composite materials with particle sizes of 2 to 4 mm, which were recorded as Sample 1#, Sample 2#, and Sample 3#, respectively. The specific conditions are shown in Table 1.

[0049] Table 1 Operating conditions

[0050] Sample No. Calcium chloride concentration (wt%) Aging time (d) Pyrolysis temperature (°C) 1# 3 5 300 2# 6 5 300 3# 9 5 300

[0051] Example 2

[0052] The method for preparing sample 2# in Example 1 was followed, with the only difference being that the aging time was 1 day and 10 days respectively; the specific conditions are shown in Table 2 (sample 2# in Example 1 is also listed in Table 2).

[0053] Table 2 Operating conditions

[0054] Sample No. Calcium chloride concentration (wt%) Aging time (d) Pyrolysis temperature (°C) 4# 6 1 300 2# 6 5 300 5# 6 10 300

[0055] Example 3

[0056] The method for preparing sample 5# in Example 2 was followed, except that the pyrolysis temperatures were 400°C and 500°C, respectively; the specific conditions are shown in Table 3 (sample 5# in Example 2 is also listed in Table 3).

[0057] Table 3 Operating conditions

[0058] Sample No. Calcium chloride concentration (wt%) Aging time (d) Pyrolysis temperature (°C) 5# 6 10 300 6# 6 10 400 7# 6 10 500

[0059] Example 4

[0060] The procedure for preparing sample 2# in Example 1 was followed, except that corn stalks were replaced by wood chips, and the resulting hydrated calcium silicate-biochar gel composite was designated as sample 8#.

[0061] Example 5

[0062] The procedure for preparing sample 2# in Example 1 was followed, except that corn stalks were replaced by wheat stalks, and the resulting hydrated calcium silicate-biochar gel composite was designated as sample 9#.

[0063] Example 6

[0064] (1) Preparation of sewage sludge char: The residual sludge (from a sewage treatment plant in Hangzhou, Zhejiang) was dried in an oven at 105 °C for 48 h, and the dried residual sludge was placed in a muffle furnace and heated to 600 °C at a heating rate of 10 °C / min, and calcined at 600 °C for 3 h. After calcination, the ash was washed off with 1 mol / L hydrochloric acid, and then washed with deionized water until neutral, and dried in an oven at 105 °C. After grinding and sieving, sewage sludge char with a particle size of 100 mesh was obtained for use;

[0065] (2) The procedure for preparing sample 2# in Example 1 was followed, except that corn stalks biochar was replaced by the sewage sludge char, and the resulting hydrated calcium silicate-biochar gel composite was designated as sample 10#.

[0066] Comparative Example 1

[0067] Preparation of sodium alginate-biochar gel material: a sodium alginate solution with a concentration of 20 g / L was prepared with deionized water, and then biochar material (specifically corn straw biochar prepared in Example 1) was added at a solid-liquid ratio of 1 g: 50 mL, and stirred for 1 h to obtain a sodium alginate-biochar mixture; a calcium chloride solution with a concentration of 6 wt% was prepared with deionized water, and the sodium alginate-biochar mixture was added dropwise into the calcium chloride solution through a peristaltic pump and a rubber tube connected to the peristaltic pump, the rotation speed of the peristaltic pump was set to 1.0 rpm, the outlet of the rubber tube was located above the calcium chloride solution, and the distance between the outlet of the rubber tube and the surface of the calcium chloride solution was 6 mm, and stirring was maintained during the dropping process to ensure the full settlement of the biochar gel material, after the dropping was completed, the obtained material liquid was placed in a 60°C oven and aged for 1 d, 5 d and 10 d respectively, after aging, it was washed with deionized water and dried in a 105°C oven, to obtain sodium alginate-biochar gel material with a particle size of 2-4 mm, which were respectively recorded as sample 11# (aging time 1 d), sample 12# (aging time 5 d) and sample 13# (aging time 10 d). It should be noted that the sample 11#, sample 12# and sample 13# prepared in Comparative Example 1 are not subjected to pyrolysis after aging, because in the absence of calcium silicate hydrate, calcium alginate begins to decompose above 200°C, and cannot maintain stable particle size and mechanical strength.

[0068] Test Example 1

[0069] A phosphate salt simulated water sample with a concentration of 20 mg P / L was prepared with deionized water and potassium dihydrogen phosphate, and the initial pH was adjusted to 7, 25 mL of the phosphate salt simulated water sample was placed in a conical flask with a plug, and then different conditions of the calcium silicate hydrate-biochar gel composite material was added, and the addition amount was 0.5 g / L, and the conical flask was shaken in a constant temperature shaker at a temperature of 25°C and a rotation speed of 180 rpm for 24 h, the supernatant was filtered with a 0.45 μm filter membrane, the residual phosphate salt concentration in the solution was determined, and the adsorption capacity was calculated according to the following formula: adsorption capacity (mg / g) = (c 吸附前 -c 吸附后 ) × V / m bc , wherein V is 25 mL, m bc is 0.0125 g.

[0070] Figure 2 Figure 2 is a graph of the phosphate removal performance test results of the calcium silicate hydrate-biochar gel composite materials (sample 1#-sample 7#) prepared under different conditions, and the specific data are shown in Table 4. Figure 2 As can be seen from Table 4, with the increase of the Ca 2+The phosphate removal performance of the calcium silicate hydrate-biochar gel composite material presents a trend of first increasing and then decreasing and gradually rising with the increase of the concentration, the aging time and the pyrolysis temperature, respectively. The prepared calcium silicate hydrate-biochar gel composite material has the best phosphate adsorption performance under the conditions of the calcium chloride concentration of 6 wt%, the aging time of 5 days and the pyrolysis temperature of 300 ℃, and the phosphate adsorption capacity reaches 36.22 mgP / g. The former may be due to the increase of the contents of the calcium silicate hydrate and the calcium alginate in the composite material, and the phosphate can be combined with the composite material through surface complexation, ion exchange and the like. 2+ The increase of the concentration and the aging time leads to the increase of the contents of the calcium silicate hydrate and the calcium alginate in the composite material, and the phosphate can be combined with the composite material through surface complexation, ion exchange and the like. 2+ The further increase of the concentration and the aging time leads to the increase of the content of the calcium silicate hydrate and the more compact structure of the composite material, and the specific surface area and the adsorption site are reduced. The latter may be due to the gradual decomposition of the calcium silicate hydrate and the calcium alginate with the increase of the pyrolysis temperature, the exposure of the adsorption site in the composite material and the enhancement of the adsorption capacity for the phosphate.

[0071] Table 4 Experimental results

[0072]

[0073]

[0074] Test Example 2

[0075] The performance of the prepared calcium silicate hydrate-biochar gel composite material under different conditions and the sodium alginate-biochar gel material prepared in Comparative Example 1 is tested according to the method of Test Example 1.

[0076] Figure 3 The phosphate removal performance test results of the prepared calcium silicate hydrate-biochar gel composite material under different conditions (sample 2#, sample 8#, sample 9# and sample 10#) and the sodium alginate-biochar gel material (sample 12#) prepared in Comparative Example 1 are shown in the figure, and the specific data is shown in Table 5. It can be seen from Table 5 that the phosphate adsorption capacity of the prepared composite material is 36.22 mg / g, which is the best among the prepared composite materials. Figure 3 As shown in Table 5, the phosphate adsorption performance of the composite material prepared by taking corn straw as the raw material is the best, and the phosphate adsorption capacity is 36.22 mg / g, followed by the composite material prepared by taking the residual sludge, the wheat straw and the wood chips as the raw material. Compared with the traditional biochar gel particle preparation method in Comparative Example 1, the prepared calcium silicate hydrate-biochar gel composite material has better adsorption performance.

[0077] Table 5 Experimental results

[0078]

[0079] Test Example 3

[0080] The mechanical strength of the calcium silicate hydrate-biochar gel composites prepared under different conditions was tested using an Instron 5943 electronic universal testing machine. Particles with a particle size of 2 mm were selected, the speed was set to 1 mm / min, and the maximum deformation was set to 30%. Three to five parallel samples were set for each group of samples, and the average value was taken as the experimental result.

[0081] Figure 4 The maximum load test results of the calcium silicate hydrate-biochar gel composite material (sample 1# to sample 7#) prepared under different conditions are shown in Table 6. Figure 4 As shown in Table 6, with the increase of Ca 2+ With the increase of concentration, aging time and pyrolysis temperature, the maximum load of calcium silicate hydrate-biochar gel composite material showed a trend of gradually increasing, first increasing and then decreasing, and gradually decreasing. Under the conditions of calcium chloride concentration of 9wt%, aging time of 5d and pyrolysis temperature of 300℃, the mechanical properties of calcium silicate hydrate-biochar gel composite material prepared were the best, and its maximum load reached 3.22N. Calcium silicate hydrate is one of the main sources of cement strength. 2+ The increase in concentration and aging time increases the content of calcium silicate hydrate in the composite material, so the maximum load of the composite material increases. As the pyrolysis temperature increases, calcium alginate and calcium silicate hydrate begin to decompose, so the maximum load of the composite material decreases.

[0082] Table 6 Test results

[0083]

[0084] Figure 5 The deformation process diagram of the calcium silicate hydrate-biochar gel composite material (sample 1# to sample 7#) prepared under different conditions. The slope of the curve reflects the rigidity and toughness of the material to a certain extent. The higher the slope, the higher the hardness and the stronger the rigidity of the material. Figure 5 As shown in the figure, under the conditions of calcium chloride concentration of 9 wt%, aging time of 5 d and pyrolysis temperature of 300 °C, the prepared calcium silicate hydrate-biochar gel composite material has the highest hardness and the strongest rigidity.

[0085] Figure 6 The scanning electron microscope images of the calcium silicate hydrate-biochar gel composite material (sample 2#) and corn straw biochar in Example 1 are shown in FIG. Figure 6As shown in the figure, the corn straw biochar presents a regular lamellar structure, and there is no obvious filler in the biochar voids; the overall hydration calcium silicate-biochar gel composite material is irregularly spherical in surface, the biochar voids are filled with particles of 50-150 nm in size formed by calcium alginate and hydration calcium silicate, and obvious connections between the particles can be observed, indicating that the calcium alginate and hydration calcium silicate are crosslinked with each other and attached to the biochar, thereby providing support for the strength of the hydration calcium silicate-biochar gel composite material.

[0086] Figure 7 The EDS analysis diagram of the hydration calcium silicate-biochar gel composite material (sample 2#) in Example 1 is shown in the figure. Figure 7 As shown in the figure, the main constituent elements of the hydration calcium silicate-biochar gel composite material are C, O, Si, Cl and Ca, and the content of Si is relatively high due to the presence of O-Si-O.

[0087] Figure 8 The FTIR spectra of the hydration calcium silicate-biochar gel composite materials (samples 4#, 2# and 5#) prepared under different aging time conditions and the sodium alginate-biochar gel materials (samples 11#, 12# and 13#) in Comparative Example 1 are shown in the figure. Figure 8 As shown in the figure, with the increase of the aging time, the absorption peak of Si-O-Si at 1095 cm -1 increases gradually.

[0088] Figure 9 The XRD spectra of the hydration calcium silicate-biochar gel composite materials (samples 4#, 2# and 5#) prepared under different aging time conditions and the sodium alginate-biochar gel materials (samples 11#, 12# and 13#) in Comparative Example 1 are shown in the figure. Figure 9 As shown in the figure, with the increase of the aging time, the characteristic peak of C-S-H gradually increases.

[0089] Figure 10 The TG-DTG analysis diagram of the hydration calcium silicate-biochar gel composite material (sample 5#) prepared in Example 1 and the sodium alginate-biochar gel material (sample 13#) in Comparative Example 1 is shown in the figure. Figure 10 As shown in the figure, the calcium alginate begins to decompose at about 300°C, and the presence of the hydration calcium silicate effectively alleviates the decomposition of the calcium alginate.

[0090] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing a calcium silicate hydrate-biochar gel composite material, comprising the following steps: mixing sodium alginate, sodium silicate, and biochar material with water to obtain a sodium alginate-sodium silicate-biochar mixture; adding the sodium alginate-sodium silicate-biochar mixture to a calcium salt solution to perform gelation, and then sequentially performing aging and pyrolysis to obtain the calcium silicate hydrate-biochar gel composite material, wherein the calcium silicate hydrate-biochar gel composite material comprises biochar material, calcium alginate nanoparticles, and calcium silicate hydrate nanoparticles supported on the biochar material. The method for preparing the biochar material comprises: roasting a biomass raw material to obtain the biochar material. The biomass raw material comprises one or more of straw, sawdust, and sludge; the roasting temperature is 400-600℃, the holding time is 2-4 h, and the temperature rising rate for rising to the roasting temperature required is 5-15℃ / min.

2. The production method according to claim 1, characterized by, The concentration of sodium alginate in the sodium alginate-sodium silicate-biochar mixture is 10-40 g / L, the concentration of sodium silicate is 21.96-65.88 g / L, and the concentration of biochar is 5-40 g / L.

3. The production method according to claim 2, characterized by, The concentration of the calcium salt solution is 3-9 wt%, and the molar ratio of calcium in the calcium salt solution to silicon in sodium silicate is 0.8-2.

0.

4. The production method according to any one of claims 1 to 3, characterized by, The gelation comprises: under stirring, using a peristaltic pump and a rubber tube in communication with the peristaltic pump to drop the sodium alginate-sodium silicate-biochar mixture into the calcium salt solution, the rotation speed of the peristaltic pump is 1-1.5 rpm, the outlet of the rubber tube is located above the calcium salt solution, and the distance between the outlet of the rubber tube and the liquid surface of the calcium salt solution is 5-8 mm.

5. The preparation method according to claim 4, characterized in that The temperature for the aging is 60-80℃, and the time is 1-10 d.

6. The method of claim 1, wherein, The temperature for the pyrolysis is 300-500℃, and the holding time is 2-4 h.

7. The preparation method according to claim 1, characterized in that 9.The calcium silicate hydrate-biochar gel composite material prepared by the method of any one of claims 1-8.

8. The method of claim 1, wherein, 10.Use of the calcium silicate hydrate-biochar gel composite material of claim 9 in preparing a phosphate adsorbent. ​ ​

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