CN117380168A

CN117380168A - Method for preparing functional group-rich gel adsorbent from straw and sludge

Info

Publication number: CN117380168A
Application number: CN202311497525.6A
Authority: CN
Inventors: 刘福强; 张为国; 鲁凌霄; 刘子帆; 李爱民
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2023-11-11
Filing date: 2023-11-11
Publication date: 2024-01-12

Abstract

The invention belongs to the technical field of solid waste recycling. The invention provides a method for preparing a functional group-rich gel adsorbent from straw and sludge. The crop straw and the sludge can be subjected to decarboxylation reaction in a hydrothermal environment, and the generated functional groups such as hydroxyl, carboxyl and the like can be transferred into the hydrothermal solution. The hydrothermal solution and the active matrix unit are uniformly mixed and then solidified into balls, so that the modified gel adsorbent rich in functional groups is prepared, and has rich functional groups, so that the adsorption capacity of the modified gel adsorbent can be remarkably enhanced. Meanwhile, the hydrothermal solution contains abundant fiber substances, so that the mechanical stability of the hydrothermal solution can be remarkably enhanced. The modified gel adsorbent rich in functional groups, which is prepared by the invention, can effectively remove heavy metals, organic matters and composite pollutants in water, and has wide application range and good reproducibility. In conclusion, the invention realizes the recycling of various waste biomasses at the same time.

Description

Method for preparing functional group-rich gel adsorbent from straw and sludge

Technical Field

The invention relates to the technical field of solid waste recycling, in particular to a method for preparing a functional group-rich gel adsorbent from straw and sludge.

Background

Along with population growth, urban process and river and lake restoration dredging, the sludge yield of a sewage plant and the total amount of river sludge are continuously increased, and conventional disposal methods comprise stable landfill, drying incineration and resource utilization, wherein the sludge landfill has no sustainability, and the drying incineration has the defect of high economic cost. And the recycling of the sludge requires different recycling technologies due to complex components of the sludge, and the technologies require higher investment and operation cost, so that the large-scale application of the sludge recycling technology is limited.

On the other hand, the crop straw has wide range, contains abundant cellulose and lignin, and has resource value. At present, the main stream incineration treatment is strictly limited due to environmental pollution, fire risk and the like, and the recycling energy modes such as straw returning and composting utilization are also faced with the problems of insufficient efficiency and the like, so that effective recycling technology is urgently needed to be explored, and the beneficial resources in crop straw are fully recovered.

The current solid waste recycling treatment technology comprises heat treatment, bioleaching, chemical extraction, electrodialysis and the like. 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 greatly reduces energy consumption and operation cost compared with conventional pyrolysis or incineration. In the hydrothermal method, the hydrothermal carbonization technology has more environmental and economic benefits. In the hydrothermal carbonization process, decarboxylation, deamination and condensation reaction can occur, wherein organic carbon can be partially humified to form humic substances, and the hydrothermal liquid with resource value and stable hydrothermal carbon are produced. At present, research and application at home and abroad are mainly focused on hydrothermal carbon, but research on hydrothermal liquid modified gel adsorbents is not yet available. The preparation of sludge-based fiber adsorbent by Yang et al (Resour Conserv Recy 187 (2022) 106630) using hydrothermal solution confirmed that the hydrothermal solution contained functional groups capable of adsorbing heavy metals, but the adsorption amount was low (13.8 mg/g). Chinese patent (CN 114768772A) discloses a method for modifying biomass-based gel by using hydrothermal carbon, zhang Junsong (light industrial report. 2023.38 (04): 105-112) and Fang Junhua (water treatment technology, 2021,47 (09): 52-57) all use the hydrothermal carbonization technology to synthesize biochar to realize recycling of waste, but the hydrothermal solution with resource value is ignored.

Because the ash content of the sludge is large, the sludge is directly subjected to hydro-thermal carbonization, and the recycling treatment of the sludge is limited due to the increase of energy consumption, the reduction of product quality and the like; on the other hand, the crop straw has higher carbon element, and can be subjected to hydrothermal carbonization together with the sludge, so that ash can be dispersed, the carbon-nitrogen ratio can be adjusted, and the recycling of various waste biomasses can be synchronously realized. In conclusion, the crop straw and the sludge are subjected to co-hydrothermal carbonization to obtain the hydrothermal solution containing more oxygen-containing functional groups, and the hydrothermal solution is used for preparing the adsorbent, so that the physical and chemical structure of the adsorbent is improved, and the application performance of the adsorbent is improved.

The biomass polymer-based gel material has the advantages of low cost, rich availability, porous performance and easy exposure of active sites, and the high hydrophilicity and the multiple network structure can greatly improve the adsorption performance of the material, so that the material becomes a novel adsorbent in water treatment. Meanwhile, the modified polyurethane has a highly-interconnected three-dimensional network structure, high density and exposed hydroxyl groups, and is easy to modify. At present, no case of directly modifying biomass polymer-based gel by utilizing hydrothermal solution exists, and the modification method with low cost can effectively improve the performance of the gel adsorbent while realizing recycling of waste.

Disclosure of Invention

In the present invention, hydrothermal solution is used for soil conditioner and research on hydrothermal solution modified adsorbent is not available, and the hydrothermal solution is used for replacing water, so that abundant functional groups in the hydrothermal solution are grafted on the adsorbent to improve the adsorption performance. Thus, the invention provides a method for preparing the functional group-rich gel adsorbent from straw and sludge.

In order to achieve the above object, the present invention provides the following technical solutions: 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, heating, cooling, and performing solid-liquid separation to obtain hydrothermal solution, wherein the mass ratio of the crop straw to the sludge is 0.005-0.1:1, the mass ratio of the total mass of the sludge to the crop straw to the water is 0.5-10:1, the addition amount of the alkali is that the pH value of the hydrothermal solution is adjusted to 8-14, the heating temperature in the hydrothermal process is 90-200 ℃, and the heating time is 5-50 h;

2) Mixing the hydrothermal solution with active matrix unit after regulating acid with dilute acid solution, adding into cross-linking agent, and curing to obtain gel adsorbent with rich functional groups.

Further, the mass ratio of the sludge to the crop straw in the step 1) is 0.015-0.05:1; the mass ratio of the total mass of the sludge and the crop straw to the water is 1.5-2.0:1; the addition amount of the alkali is required to meet the requirement that the pH value of the hydrothermal solution is 8-10; the heating temperature is 90-130 ℃ and the heating time is 5-24 h.

Further, the crop straw in the step 1) is one or a mixture of corn straw, rice husk and bamboo wood; the sludge is any one or a mixture of excess sludge, mixed sludge and river sludge of a sewage plant; the alkali is any one or a mixture of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate and potassium carbonate.

Further, in the acid regulating process in the step 2), the pH value of the hydrothermal solution is regulated to be 5-7 by dilute acid solution; the dilute acid solution can be prepared into aqueous solution by using any one of hydrochloric acid and sulfuric acid, and the concentration is 0.1-2.0 mmol/L.

Further, the active matrix unit in the step 2) is any one or a mixture of sodium alginate, chitosan and sodium carboxymethyl cellulose; the cross-linking agent is any one or a mixture of calcium chloride solution, glutaraldehyde, epichlorohydrin and sodium hydroxide solution.

A gel adsorbent rich in functional groups is prepared from straw and sludge, and contains rich oxygen-containing functional groups such as hydroxyl groups, carboxyl groups and the like, and fiber layers are uniformly distributed on the surface of the gel.

The invention provides an application of preparing a gel adsorbent rich in functional groups from straw and sludge in treating heavy metals, organic matters and composite pollutants in an aqueous solution, which comprises the following specific steps:

the gel adsorbent is contacted with an aqueous solution containing heavy metals, organic matters and composite pollutants, and the reaction is carried out for a period of time, so that the effective removal of the pollutants can be realized.

The invention provides a regeneration method of a gel adsorbent, which comprises the following specific steps: for the modified gel for adsorbing heavy metals, organic matters and composite pollutants, dilute acid solution and dilute alkali solution with the concentration of 0.1-2.0mol/L are sequentially used as a regenerant, so that the effective regeneration of the modified gel adsorbent can be realized.

As can be seen from the active matrix units and FTIR chart, the functional groups of the gel adsorbent in the present invention are mainly: hydroxyl, carboxyl and hydrogen bonds. The hydrothermal solution plays a role in enriching the number and variety of functional groups on the active matrix units; the modified gel adsorbent can adsorb heavy metal ions through coordination of the oxygen-containing functional groups, and the heavy metal ions can also play a bridging role in the adsorption process, so that the adsorption of organic matters is increased.

The invention has the advantages that:

(1) The invention adopts crop straw and excess sludge as raw materials for co-hydrothermal carbonization, utilizes the characteristic of high carbon content of the crop straw, and ensures that the hydrothermal solution has more functional groups due to complementary advantages of the crop straw and the excess sludge; in addition, in the preparation process, the operation is simple, and the cost is low.

(2) The modified gel prepared by the invention can have the synergistic effect of removing heavy metals and organic matters.

(3) The invention adopts the crop straw and the residual sludge as raw materials, so that the crop straw and the residual sludge can be effectively treated, the influence of the crop straw and the residual sludge on the environment is avoided, and the recycling utilization of the crop straw and the residual sludge is realized.

Drawings

FIG. 1 is a scanning electron microscope image of gel C in example 2.

Fig. 2 is a fourier transform infrared spectrum of gels a and C in example 2.

Detailed Description

Specific implementations of the invention are further described below with reference to the drawings and examples, but the implementation and protection of the invention are not limited thereto. It should be noted that the following processes, if not specifically described in detail, can be realized or understood by those skilled in the art with reference to the prior art.

Example 1: different raw material proportions and hydrothermal conditions to prepare the hydrothermal solution

The urban excess sludge, the corn stalks and the alkali are weighed according to the weight ratio in the table 1 and added into 20mL of pure water, then the mixture is added into a 100mL of hydrothermal reaction kettle, the mixture is naturally cooled to room temperature after being heated for a certain time at different temperatures, and the solid-liquid separation is carried out by using vacuum suction filtration to collect hydrothermal solution.

Example 2

And (3) adjusting the pH value of the hydrothermal solution 1-7 in the embodiment 1 to 7 by using a dilute HCl solution, and then preparing a sodium alginate solution with the mass fraction of 2% by using the hydrothermal solution. After the components are uniformly mixed, slowly dripping the components into a calcium chloride solution with the mass fraction of 2% by using a 1mL syringe, solidifying and crosslinking for 3 hours, washing the components by using pure water until the pH value of the washing solution is 7, and preserving the components for later use. The resulting gel adsorbents are each labeled A, B, C, D, E, F, G.

Adsorption performance was tested using synthetic gels:

0.4g of the wet gel was weighed out separately, 50mL of a mixed solution of Cu (II) and TC (TC) having initial concentrations of 1.0mmol/L and 0.3mmol/L were added to a 60mL screw glass bottle, the initial pH values were 5, the mixture was oscillated in a 298K constant temperature oscillator at 160rpm for 24 hours to equilibrate the adsorption, the concentrations of Cu (II) and TC in the solutions at the initial and equilibrated time were measured, and the corresponding dry weight adsorption amounts (mmol/g) were calculated.

Example 3

The pH of the hydrothermal solution No. 3 of example 1 was adjusted to 7 with a dilute HCl solution, followed by preparing a 2% acetic acid solution by mass fraction, and then preparing a 3% chitosan solution therefrom. After mixing uniformly, slowly dropping the mixture into NaOH solution with pH=13 by using a 1mL syringe, solidifying and crosslinking for 3 hours, washing the mixture by pure water until the pH of the washing solution is 7, and preserving the mixture for later use. The modified gel was prepared and labeled as gel H.

Adsorption performance was tested using synthetic gels:

0.4g of the wet gel was weighed, 50mL of a mixed solution of Cu (II) with an initial concentration of 1.0mmol/L and TC with an initial pH of 0.3mmol/L was added to a 60mL screw glass bottle, the mixed solution was oscillated in a 298K constant temperature oscillator at 160rpm for 24 hours to equilibrate the adsorption, the concentrations of Cu (II) and TC in the solution at the initial and equilibrated time were measured, and the corresponding dry weight adsorption amount (mmol/g) was calculated.

Example 4

The pH of the No. 3 hydrothermal solution in the example 1 is regulated to 7 by using a dilute HCl solution, then a sodium carboxymethyl cellulose solution with the mass fraction of 4% is prepared by using the hydrothermal solution, then 20mL of the sodium carboxymethyl cellulose solution, 20mL of a 6% polyethylenimine solution and 0.8mL of epichlorohydrin are taken and uniformly mixed, crosslinked for 4 hours at 343K, and after dicing, the sodium carboxymethyl cellulose solution is washed by using 1mol/L of dilute HCl solution, ultrapure water and 1.0mol/L of NaOH solution in sequence, and then the sodium carboxymethyl cellulose solution is washed by using ultrapure water for a plurality of times and is preserved for standby. The modified gel was prepared and labeled as gel I.

Adsorption performance was tested using synthetic gels:

0.4g of the wet gel was weighed, 50mL of a mixed solution of Cu (II) with an initial concentration of 1.0mmol/L and TC with an initial pH of 0.3mmol/L was added to a 60mL screw glass bottle, the mixed solution was oscillated in a 298K constant temperature oscillator at 160rpm for 24 hours to equilibrate the adsorption, the concentrations of Cu (II) and TC in the solutions at the initial and equilibrated time were measured, and the corresponding dry weight adsorption amounts (mmol/g) were calculated, and the results are shown in Table 2.

Example 5: the single component metal adsorption performance was tested using gel C in example 2

0.4g of the wet gel was weighed, 50mL of Cd (II), co (II), cr (III), cu (II), fe (III), mn (II), ni (II), pb (II) and Zn (II) having an initial concentration of 1.0mmol/L were respectively added to a 60mL screw glass bottle, the initial pH was 4, the mixture was oscillated at 160rpm in a 298K constant temperature oscillator for 24 hours to equilibrate the adsorption, the concentration of heavy metals in the solution at the time of the initial and equilibration was measured, and the corresponding dry weight adsorption amount (mmol/g) was calculated, and the results were shown in Table 3.

Example 6: the single component organic adsorption performance was tested using gel C in example 2

0.4g of the wet gel was weighed, 50mL of tetracycline hydrochloride, ciprofloxacin, sulfamethoxazole and ofloxacin each having an initial concentration of 0.2mmol/L were added to a 60mL screw glass bottle, the initial pH was 5, the adsorption was equilibrated by shaking in a 298K constant temperature shaker at 160rpm for 24 hours, the concentration of heavy metals in the solution at the time of the initial and equilibration was measured, and the corresponding dry weight adsorption amount (mmol/g) was calculated, and the results are shown in Table 4.

Example 7: component analysis of corn stalk and urban excess sludge

The main indexes of the corn stalks and the municipal excess sludge were detected by an elemental analyzer and an industrial analysis method, and the detection results are shown in table 5.

Example 8: component analysis of gel A and gel C

The results of the dry weight adsorption of copper ions and tetracycline hydrochloride at ph=5.0 for the modified gels prepared in examples 2 to 4 (table 3) show that the performance of hydrogel C is relatively optimal. The result of the Fourier infrared spectrum (figure 2) shows that the superposition of the stretching vibration peaks of O-H in sodium alginate and N-H in hydrothermal solution leads the spectrogram of gel C to form 3700-3000 cm ^-1 Broad absorption peak at 16 cm ^-1 And 1028cm ^-1 The peak signal is obviously increased, which indicates the benefit of hydrothermal modification.

Example 9: regeneration performance of gel

The regeneration effect was tested using gel C of example 2, as follows:

0.4g of the wet gel was weighed into a 60mL glass tube, 50mL of Cu (II) having an initial pH of 5 and a solution of TC having an initial concentration of 1.0mmol/L and 0.2mmol/L were added, and reacted in a 298K shaker at 160rpm for 24h to ensure adsorption equilibrium. The gel after adsorbing Cu (II) is washed for a plurality of times, the gel is respectively placed in 1mol/L hydrochloric acid, 1mol/L sulfuric acid and 0.1mol/L hydrochloric acid to remove copper ions, then the gel is filtered and respectively placed in 0.1mol/L sodium hydroxide solution and 0.05mol/L sodium hydroxide solution to remove tetracycline hydrochloride, and each desorption is reacted in a 298K oscillator at a rotating speed of 160rpm for 24h so as to ensure complete desorption. The desorbed copper ion and tetracycline hydrochloride concentrations were measured and recovery efficiency calculated. The results are shown in Table 6.

Claims

1. A method for preparing a functional group-rich gel adsorbent from straw and sludge comprises the following steps:

2. The method for preparing the functional group-rich gel adsorbent from the straw and the sludge according to claim 1, wherein the method comprises the following steps of: in the step 1), the mass ratio of the crop straw to the sludge is 0.015-0.05:1, the mass ratio of the total mass of the sludge to the crop straw to the water is 1.5-2.0:1, the addition amount of the alkali is that the pH value of the hydrothermal solution is adjusted to 8-10, the heating temperature in the hydrothermal process is 90-130 ℃, and the heating time is 5-24 hours.

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

4. The method for preparing the functional group-rich gel adsorbent from the straw and the sludge according to claim 1, wherein the method comprises the following steps of: in the step 2), the diluted acid solution is used for regulating the pH value of the hydrothermal solution to be 5-7, and the diluted acid solution is any one of hydrochloric acid and sulfuric acid, and the concentration is 0.1-2.0 mmol/L.

5. The method for preparing the functional group-rich gel adsorbent from the straw and the sludge according to claim 1, wherein the method comprises the following steps of: the active matrix unit in the step 2) is any one or a mixture of sodium alginate, chitosan and sodium carboxymethyl cellulose, and the cross-linking agent is any one or a mixture of calcium chloride solution, glutaraldehyde, epichlorohydrin and sodium hydroxide solution.

6. The functional group-rich gel adsorbent prepared by the method for preparing the functional group-rich gel adsorbent from straw and sludge according to claim 1-5, which is characterized in that: the functional groups of the functional group-rich gel adsorbent are carboxyl-containing and hydroxyl-containing oxygen functional groups, and fiber layers are uniformly distributed on the surface of the functional group-rich gel adsorbent.

7. A method for water treatment using the functional group-rich gel adsorbent according to claim 1 to 6, characterized in that: and (3) contacting the functional group-rich gel adsorbent with an aqueous solution of pollutants to adsorb and remove the pollutants, wherein the aqueous solution of the pollutants is any one or a mixture of heavy metals and organic matters.

8. A method for regenerating a functional group-rich gel adsorbent according to claim 1 to 6, characterized in that: and eluting the adsorbed pollutant by using dilute acid solution and/or dilute alkali solution with the concentration of 0.1-2.0mol/L as a regenerant to regenerate the functional group-rich gel adsorbent of the attaching agent, wherein the pollutant aqueous solution is any one or a mixture of heavy metals and organic matters.