A method for preparing a functional group-rich gel adsorbent from straw and sludge

Abstract

The present application belongs to the technical field of solid waste resource utilization, and provides a method for preparing a functional group-rich gel adsorbent from straw and sludge. Crop straw and sludge can both undergo decarboxylation in a hydrothermal environment, and the generated functional groups such as hydroxyl groups and carboxyl groups are transferred to the hydrothermal liquid. The hydrothermal liquid is mixed with active matrix units and then solidified into a ball to obtain a modified gel adsorbent rich in functional groups. The modified gel adsorbent has abundant functional groups, thereby significantly enhancing the adsorption capacity. Meanwhile, the hydrothermal liquid contains abundant fiber substances, which can significantly enhance the mechanical stability. The modified gel adsorbent rich in functional groups prepared by the present application can effectively remove heavy metals, organic matter and complex pollutants in water, has a wide range of applications, and has good reusability. In summary, the present application simultaneously realizes the resource utilization of various waste biomasses.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid waste resource utilization, and particularly relates to a method for preparing a functional group-rich gel adsorbent from straw and sludge. BACKGROUND

[0002] With the population growth, urbanization process and river and lake restoration dredging, the sludge production of sewage plants and the total amount of river sludge are increasing. The conventional disposal methods include stable landfill, dry incineration, and resource utilization. Among them, sludge landfill is not sustainable, and dry incineration has the defect of high economic cost. The resource utilization of sludge needs different resource utilization technologies due to the complex composition of sludge, which requires relatively high investment and operating cost, limiting the large-scale application of sludge resource utilization technology.

[0003] On the other hand, crop straw is large in amount and wide in range, and contains rich cellulose and lignin, which has resource value. At present, the mainstream of incineration treatment has been strictly limited due to environmental pollution and fire risk, and the resource and energy utilization methods such as straw returning to field and composting also face the problem of insufficient efficiency, so it is urgent to explore effective resource utilization technology to fully recover the beneficial resources in crop straw.

[0004] The current solid waste resource utilization treatment technology includes heat treatment, bioleaching, chemical extraction and electrodialysis. Among them, the hydrothermal method in heat treatment is a simple and efficient treatment method, which is carried out at relatively low temperature and pressure, and compared with traditional pyrolysis or incineration, it greatly reduces energy consumption and operating cost. In the hydrothermal method, the hydrothermal carbonization technology has more environmental and economic benefits. In the hydrothermal carbonization process, decarboxylation, deamination and condensation reactions occur, and part of the organic carbon in it is humified to form humic-like substances, producing hydrothermal liquid and stable hydrothermal carbon with resource value. At present, the research and application at home and abroad mainly focus on hydrothermal carbon, but the research on modified gel adsorbent by hydrothermal liquid is still lacking. Yang et al. (Resour Conserv Recy 187 (2022) 106630) prepared a sludge-based fiber adsorbent using hydrothermal liquid, which confirmed that the hydrothermal liquid contains functional groups that can adsorb heavy metals, but the adsorption capacity is low (13.8 mg / g). Chinese invention patent (CN 114768772 A) discloses a method for modifying biomass-based gel using hydrothermal carbon, Zhang Junsong et al. (Light Industry Science and Technology. 2023. 38(04): 105-112) and Fang Junhua et al. (Water Treatment Technology, 2021, 47(09): 52-57) all synthesized biochar based on hydrothermal carbonization technology to realize the resource utilization of waste, but they all ignored the hydrothermal liquid with resource value.

[0005] Due to the large proportion of sludge ash, direct hydrothermal carbonization of sludge will increase energy consumption and reduce product quality, which limits the resource treatment of sludge. On the other hand, crop straw has a high carbon content, and can be co-hydrothermally carbonized with sludge to disperse ash and adjust the carbon-nitrogen ratio, thereby achieving the resource utilization of multiple waste biomasses. Therefore, co-hydrothermal carbonization of crop straw and sludge can obtain hydrothermal liquid containing more oxygen-containing functional groups, which can be used to prepare adsorbents, thereby improving the physical and chemical structure and application performance of the adsorbents.

[0006] Biomass polymer-based gel materials are low in cost and rich in availability, have the advantages of porosity and easy exposure of active sites, and have high hydrophilicity and multiple network structures, which can greatly improve their adsorption performance, and have become a new type of adsorbent in water treatment. At the same time, the three-dimensional network structure is highly interconnected, and the hydroxyl groups are highly dense and exposed, which are also easy to modify. At present, there is no case of directly modifying biomass polymer-based gels with hydrothermal liquid. This low-cost modification method can not only realize the resource utilization of waste, but also effectively improve the performance of gel adsorbents. SUMMARY

[0007] At present, hydrothermal liquid is mainly used as a soil conditioner, and there is still a lack of research on the modification of adsorbents with hydrothermal liquid. In the present application, hydrothermal liquid is used instead of water to graft the rich functional groups in the hydrothermal liquid to the adsorbents to improve the adsorption performance. Therefore, the present application provides a method for preparing a functional group-rich gel adsorbent from straw and sludge.

[0008] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions: a method for preparing a functional group-rich gel adsorbent from straw and sludge, comprising the following steps:

[0009] 1) mixing crop straw, sludge, water and alkali, heating, cooling, solid-liquid separation, obtaining hydrothermal liquid, the mass ratio of crop straw to sludge is 0.005-0.1:1, the mass ratio of the total mass of sludge and crop straw to water is 0.5-10:1, the amount of alkali added is to adjust the pH of the hydrothermal liquid to 8-14, the heating temperature in the hydrothermal process is 90-200℃, and the heating time is 5-50h;

[0010] 2) adjusting the pH of the hydrothermal liquid with dilute acid solution, mixing with active matrix units, and then adding to the crosslinking agent to solidify into a ball to obtain a functional group-rich gel adsorbent.

[0011] Further, in step 1), the mass ratio of sludge to crop straw is 0.015-0.05:1; the mass ratio of the total mass of sludge and crop straw to water is 1.5-2.0:1; the amount of alkali added needs to satisfy the pH of the hydrothermal liquid being 8-10; the heating temperature is 90-130℃, and the time is 5-24h.

[0012] Further, in step 1), the crop straw is one or mixture of corn stalks, rice husks and bamboo; the sludge is one or mixture of residual sludge of sewage plant, mixed sludge and river sludge; and the alkali is one or mixture of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate and potassium carbonate.

[0013] Further, in step 2), the pH of the hydrothermal liquid is adjusted to 5-7 by using dilute acid solution; the dilute acid solution is one of hydrochloric acid and sulfuric acid, and the concentration is 0.1-2.0 mmol / L.

[0014] Further, in step 2), the active matrix unit is one or mixture of sodium alginate, chitosan and sodium carboxymethyl cellulose; and the crosslinking agent is one or mixture of calcium chloride solution, glutaraldehyde, epichlorohydrin and sodium hydroxide solution.

[0015] The present application provides a kind of gel adsorbent rich in functional groups prepared from straw and sludge, which is rich in hydroxyl, carboxyl and other oxygen-containing functional groups, and the gel surface is uniformly distributed with fiber layer.

[0016] The present application provides a kind of gel adsorbent rich in functional groups prepared from straw and sludge, which is rich in hydroxyl, carboxyl and other oxygen-containing functional groups, and the gel surface is uniformly distributed with fiber layer.

[0017] The present application provides a kind of gel adsorbent rich in functional groups prepared from straw and sludge, which is rich in hydroxyl, carboxyl and other oxygen-containing functional groups, and the gel surface is uniformly distributed with fiber layer.

[0018] The present application provides a kind of gel adsorbent rich in functional groups prepared from straw and sludge, which is rich in hydroxyl, carboxyl and other oxygen-containing functional groups, and the gel surface is uniformly distributed with fiber layer.

[0019] From the active matrix unit and FTIR diagram, it can be seen that the functional groups of the gel adsorbent in the present application are mainly: hydroxyl, carboxyl and hydrogen bond. The role of hydrothermal liquid is to enrich the number and types of functional groups on the active matrix unit; the modified gel adsorbent can adsorb heavy metal ions through the coordination of these oxygen-containing functional groups, and the heavy metal ions can also play a bridging role in the adsorption process, thereby increasing the adsorption of organic matter.

[0020] The present application has the following advantages:

[0021] (1) The present application uses crop straw and residual sludge as raw materials for co-hydrothermal carbonization, which takes advantage of the high carbon content of crop straw, and the advantages of the two are complementary, ensuring that the hydrothermal liquid has a large number of functional groups; and in the preparation process, the operation is simple and the cost is low.

[0022] (2) The prepared modified gel can remove heavy metals and organic matters in a synergistic manner.

[0023] (3) The present application uses crop straw and residual sludge as raw materials, so that the crop straw and residual sludge can be effectively disposed of, the influence of the crop straw and residual sludge on the environment is avoided, and the resource utilization of the crop straw and residual sludge is realized. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 Scanning electron microscope image of gel C in Example 2.

[0025] Figure 2 Fourier transform infrared spectrum of gels A and C in Example 2. DETAILED DESCRIPTION

[0026] The specific implementation of the present application is further illustrated below in combination with the drawings and examples, but the implementation and protection of the present application are not limited thereto. It should be noted that if the following processes are not specifically and in detail described, they can be implemented or understood by those skilled in the art with reference to the prior art.

[0027] Example 1: Hydrothermal liquid prepared under different raw material ratios and hydrothermal conditions

[0028]

[0029] The city residual sludge, corn straw and alkali were weighed according to the amount ratio in Table 1 in 20 mL pure water, and then added to a 100 mL hydrothermal reactor, heated at different temperatures for a certain time, naturally cooled to room temperature, and then subjected to solid-liquid separation by vacuum filtration, and the hydrothermal liquid was collected.

[0030] Example 2

[0031] The pH of the hydrothermal liquids 1-7 in Example 1 was adjusted to 7 using a dilute HCl solution, and then a 2% mass fraction sodium alginate solution was prepared using the hydrothermal liquid. After mixing uniformly, 1 mL of the solution was slowly added to a 2% mass fraction calcium chloride solution using a 1 mL syringe, and then crosslinked for 3 hours. The gel adsorbent was washed with pure water until the pH of the washing liquid was 7, and then stored for use. The prepared gel adsorbent was labeled as A, B, C, D, E, F and G, respectively.

[0032] The synthesized gel was used to test the adsorption performance:

[0033] Take 0.4g of the wet gel above into a 60mL screw neck glass bottle, add 50mL of Cu(II) and 0.3mmol / L of TC mixed solution with initial concentration of 1.0mmol / L, initial pH value is 5, oscillate in 298K constant temperature oscillator at 160rpm for 24h to make adsorption reach equilibrium, measure the concentration of Cu(II) and TC in solution at initial and equilibrium, calculate the corresponding dry weight adsorption capacity (mmol / g).

[0034] Example 3

[0035] Adjust the pH of No.3 hydrothermal solution in Example 1 to 7 with dilute HCl solution, then use it to prepare 2% acetic acid solution, and then use it to prepare 3% chitosan solution. After mixing, use a 1mL syringe to slowly drop into NaOH solution with pH=13, solidify and crosslink for 3h, then wash with pure water until the pH of the washing solution is 7, and store for later use. The prepared modified gel is marked as gel H.

[0036] Test the adsorption performance using the synthesized gel:

[0037] Take 0.4g of the wet gel above into a 60mL screw neck glass bottle, add 50mL of Cu(II) and 0.3mmol / L of TC mixed solution with initial concentration of 1.0mmol / L, initial pH value is 5, oscillate in 298K constant temperature oscillator at 160rpm for 24h to make adsorption reach equilibrium, measure the concentration of Cu(II) and TC in solution at initial and equilibrium, calculate the corresponding dry weight adsorption capacity (mmol / g).

[0038] Example 4

[0039] Adjust the pH of No.3 hydrothermal solution in Example 1 to 7 with dilute HCl solution, then use it to prepare 4% carboxymethyl cellulose sodium solution, then take 20mL of it and mix with 20mL of 6% polyethyleneimine solution and 0.8mL of epichlorohydrin, mix well, crosslink at 343K for 4h, cut into pieces, then wash with 1mol / L dilute HCl solution, ultrapure water, 1.0mol / L NaOH solution, and then wash several times with ultrapure water, store for later use. The prepared modified gel is marked as gel I.

[0040] Test the adsorption performance using the synthesized gel:

[0041] Take 0.4g of the above wet gel into a 60mL screw glass bottle, and add 50mL of Cu(II) and 0.3mmol / L of TC mixed solution with an initial concentration of 1.0mmol / L, respectively, with an initial pH of 5. Shake in a constant temperature oscillator at 298K with a speed of 160rpm for 24h to reach adsorption equilibrium. Measure the concentrations of Cu(II) and TC in the solution at the initial and equilibrium stages, and calculate the corresponding dry weight adsorption (mmol / g). The results are shown in Table 2.

[0042]

[0043] Example 5: Test the single-component metal adsorption performance using the gel C in Example 2

[0044] Take 0.4g of the above wet gel into a 60mL screw glass bottle, and add 50mL of Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Ni(II), Pb(II), and Zn(II) with an initial concentration of 1.0mmol / L, respectively, with an initial pH of 4. Shake in a constant temperature oscillator at 298K with a speed of 160rpm for 24h to reach adsorption equilibrium. Measure the concentrations of heavy metals in the solution at the initial and equilibrium stages, and calculate the corresponding dry weight adsorption (mmol / g). The results are shown in Table 3.

[0045]

[0046] Example 6: Test the single-component organic matter adsorption performance using the gel C in Example 2

[0047] Take 0.4g of the above wet gel into a 60mL screw glass bottle, and add 50mL of tetracycline hydrochloride, ciprofloxacin, sulfamethoxazole, and ofloxacin with an initial concentration of 0.2mmol / L, respectively, with an initial pH of 5. Shake in a constant temperature oscillator at 298K with a speed of 160rpm for 24h to reach adsorption equilibrium. Measure the concentrations of heavy metals in the solution at the initial and equilibrium stages, and calculate the corresponding dry weight adsorption (mmol / g). The results are shown in Table 4.

[0048]

[0049] Example 7: Component analysis of corn straw and municipal residual sludge

[0050] The main indicators of corn straw and municipal residual sludge were detected by elemental analysis and industrial analysis. The detection results are shown in Table 5.

[0051]

[0052] Example 8: Component analysis of gel A and gel C

[0053] The results of the dry weight adsorption of copper ions and tetracycline hydrochloride by the modified gels prepared in Examples 2 to 4 at pH = 5.0 (Table 3) show that hydrogel C has the best performance. Figure 2 ) The results show that the superposition of the stretching vibration peaks of OH in sodium alginate and NH in hydrothermal solution makes the spectrum of gel C form 3700~3000cm -1 The broad absorption peak at 1695 cm -1 and 1028cm -1 The peak signal at the bottom of the column increases significantly, indicating the beneficial effect of hydrothermal modification.

[0054] Example 9: Regeneration performance of gel

[0055] The regeneration effect of gel C in Example 2 was tested using the following steps:

[0056] 0.4 g of the wet gel was weighed and placed in a 60 mL glass tube. 50 mL of a solution containing 1.0 mmol / L Cu(II) and 0.2 mmol / L TC (with an initial pH of 5) was added. The solution was shaken at 160 rpm at 298 K for 24 h to ensure adsorption equilibrium. The gel, after adsorbing Cu(II), was washed several times and then exposed to 1 mol / L hydrochloric acid, 1 mol / L sulfuric acid, and 0.1 mol / L hydrochloric acid to remove copper ions. The filtered gel was then exposed to 0.1 mol / L sodium hydroxide solution and then to 0.05 mol / L sodium hydroxide solution to remove tetracycline hydrochloride. Each desorption reaction was continued at 160 rpm at 298 K for 24 h to ensure complete desorption. The concentrations of desorbed copper ions and tetracycline hydrochloride were measured, and the recovery efficiency was calculated. The results are listed in Table 6.

[0057]

Claims

1. A method for preparing a functional group-rich gel adsorbent from straw and sludge, comprising the following steps: 1) mixing crop straw, sludge, water, and alkali, then heating, cooling, and solid-liquid separation to obtain a hydrothermal solution, wherein the mass ratio of crop straw to sludge is 0.005-0.1:1, the mass ratio of the total mass of sludge and crop straw to water is 0.5-10:1, the amount of alkali added is such that the pH of the hydrothermal solution is adjusted to 8-14, the heating temperature of the hydrothermal process is 90-200° C., and the heating time is 5-50 hours; 2) The hydrothermal liquid is acidified with a dilute acid solution and then mixed evenly with the active matrix unit, and then added to a crosslinking agent to solidify into balls to obtain a functional group-rich gel adsorbent, wherein the active matrix unit is any one of sodium alginate, chitosan, and sodium carboxymethyl cellulose or a mixture thereof, and the crosslinking agent is any one of calcium chloride solution, glutaraldehyde, epichlorohydrin, and sodium hydroxide solution or a mixture thereof.

2. The method for preparing a functional group-rich gel adsorbent from straw and sludge according to claim 1, characterized in that: The mass ratio of the crop straw to the sludge in step 1) is 0.015-0.05:1, the mass ratio of the total mass of the sludge and the crop straw to water is 1.5-2.0:1, the amount of alkali added is such that the pH of the hydrothermal solution is adjusted to 8-10, the heating temperature of the hydrothermal process is 90-130°C, and the heating time is 5-24h.

3. The method for preparing a functional group-rich gel adsorbent from straw and sludge according to claim 1, characterized in that: In step 1), the crop straw is one of corn straw, rice husk, and bamboo, or a mixture thereof; the sludge is any one of excess sludge from a sewage treatment plant, mixed sludge, and river sludge, or a mixture thereof; and the alkali is any one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, and potassium carbonate, or a mixture thereof.

4. The method for preparing a functional group-rich gel adsorbent from straw and sludge according to claim 1, characterized in that: In step 2), the step of adjusting the acidity of the hydrothermal solution with a dilute acid solution is to adjust the pH of the hydrothermal solution to 5-7 with a dilute acid solution, wherein the dilute acid solution is an aqueous solution of any one of hydrochloric acid and sulfuric acid with a concentration of 0.1-2.0 mmol / L.

5. A functional group-rich gel adsorbent prepared by the method for preparing a functional group-rich gel adsorbent from straw and sludge according to any one of claims 1 to 4, characterized in that: The functional groups of the functional group-rich gel adsorbent are carboxyl, hydroxyl and oxygen-containing functional groups, and the fiber layer is evenly distributed on the surface of the functional group-rich gel adsorbent.

6. A method for water treatment using the functional group-rich gel adsorbent according to claim 5, characterized in that: The functional group-rich gel adsorbent is brought into contact with an aqueous solution of pollutants to adsorb and remove the pollutants, wherein the aqueous solution of pollutants contains any one of heavy metals and organic matter or a mixture thereof.

7. A method for regenerating a functional group-rich gel adsorbent as claimed in claim 5, characterized in that: After the functional group-rich gel adsorbent has adsorbed pollutants, a dilute acid solution and / or a dilute alkali solution with a concentration of 0.1-2.0 mol / L is used as a regeneration agent to elute the adsorbed pollutants and regenerate the functional group-rich gel adsorbent. The pollutant aqueous solution contains any one or a mixture of heavy metals and organic matter.

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