Preparation method of paper pulp industry sludge-based composite wave-absorbing material

Abstract

The invention relates to the technical field of microwave absorbing materials, in particular to a preparation method of a paper pulp industry sludge-based composite wave absorbing material. The preparation method comprises the following steps: (1) pre-drying paper pulp industrial sludge, ball-milling, and sieving to obtain a sludge carrier; (2) taking a sludge carrier, adding acidizing fluid for activation, and drying for 6-12 hours at the temperature of 70-100 DEG C to obtain a dried product for later use; (3) dropwise adding the transition metal nitrate solution into the tannic acid solution, and adjusting the pH value through ammonia water until stable sol is formed; and (4) dipping the dried product in the step (2) into the sol in the step (3), and oscillating and loading for 12-24 hours in a phosphate buffer environment to obtain the product. According to the method, the pulp industrial sludge is recycled, meanwhile, the preparation is simple, the cost is low, and the prepared composite microwave absorbing material is unique in structure and excellent in performance.

Description

Technical Field

[0001] This invention relates to the field of microwave absorbing materials technology, and in particular to a method for preparing a composite microwave absorbing material based on pulp industry sludge. Background Technology

[0002] With the rapid development of modern electronic information technology, more and more electronic devices have become indispensable tools in our lives and work. They are widely used in military (radar) and civilian (computers, navigation, communication, electrical equipment) fields, making significant contributions to social progress and development. At the same time, people are also facing increasingly serious problems of interference and radiation from electronic devices. Silent, odorless, and colorless electromagnetic waves exist in human living spaces, not only interfering with communications but also seriously endangering human health, making it the fourth largest form of pollution after water pollution, air pollution, and noise pollution. Therefore, electromagnetic pollution has become one of the focal points of concern in human society. To eliminate the harm of electromagnetic pollution, protection is necessary. However, we have noticed that while protection is being implemented, the reflected electromagnetic waves will again generate radiation and interference. This necessitates finding a wave-absorbing material that can absorb and attenuate electromagnetic wave radiation.

[0003] Pulp industry sludge, as a solid waste product of the pulping and papermaking process, poses a serious threat to the ecological environment if not properly treated due to the pollutants in its concentrate and papermaking wastewater. In recent years, with the booming development of the papermaking industry, the output of pulp industry sludge has increased, making its treatment and disposal difficult and costly, thus becoming a bottleneck for the industry's development. Currently, my country's treatment of pulp industry sludge mainly focuses on sanitary landfill, incineration, agricultural use, and filler processing. However, excessive landfilling occupies a large amount of land and causes soil pollution. Furthermore, while incinerating pulp industry sludge recovers some heat energy, heavy metals in the sludge pollute the air with the spread of smoke and dust, and the combustion of large quantities of pulp industry sludge emits significant amounts of CO2 greenhouse gases. Therefore, it is necessary to reduce the proportion of sludge landfill and incineration, and further increase the proportion of sludge treated and disposed of in agriculture, building materials, and other high-value resource utilization applications.

[0004] Considering the compositional characteristics of pulp industry sludge, which contains a large amount of lignin, cellulose, and a small amount of inorganic minerals, the carbon skeleton structure formed after heat treatment has a large specific surface area, making it a highly promising adsorbent material. In recent years, there have been reports on the development and utilization of pulp industry sludge to prepare adsorbent materials, but many problems remain, such as low utilization rate, immature processes, and limited product variety. While the carbon skeleton structure formed after heat treatment of pulp industry sludge possesses characteristics such as large specific surface area, porous structure, certain conductivity, and low cost, its direct application in preparing microwave absorbing materials still suffers from low absorption capacity. Therefore, some studies have shown that loading magnetic particles onto the surface of carbon materials can enhance the magnetic loss of the carbon materials, thereby compensating for the dielectric loss in electromagnetic wave absorption. However, existing methods for preparing microwave absorbing materials doped with magnetic particles are complex, costly, and have low electromagnetic absorption rates, resulting in unstable performance of the obtained microwave absorbing materials.

[0005] Based on this, developing a novel microwave absorbing material that efficiently and rationally utilizes pulp industry sludge can not only effectively alleviate various ecological and environmental pressures caused by the large-scale discharge and accumulation of pulp industry sludge, but also reduce the production cost of microwave absorbing materials, turning waste into treasure and taking into account environmental, economic and social benefits. Summary of the Invention

[0006] This invention provides a method for preparing a composite microwave absorbing material based on pulp industry sludge. While making resource-efficient use of pulp industry sludge, the preparation method is simple and low-cost. The resulting composite microwave absorbing material has a unique structure and excellent performance, thus solving the problems existing in the prior art.

[0007] One of the technical solutions adopted in this invention is: A method for preparing a pulp industry sludge-based composite microwave absorbing material is provided, comprising the following steps: (1) After pre-drying the pulp industry sludge, ball mill it and sieve it through a 100-200 mesh screen to obtain a sludge carrier; (2) Take the sludge carrier from step (1), add acidification solution, react at pH 1.8-2.2 for 1-4 hours, wash away the acid solution, and the pH of the filtrate during the washing process reaches 6.8-7.2, indicating that sufficient acidification has been achieved. After solid-liquid separation, the pretreated sludge carrier is obtained, and dried at 70-100℃ for 6-12 hours to obtain the dried product for later use. (3) Add 0.1-1.0 mol / L transition metal nitrate solution dropwise to 0.01-0.1 mol / L tannic acid solution, and adjust the pH to 4.2-4.8 with ammonia water to form a stable sol, which is used to construct metal complex precursors; (4) The dried product prepared in step (2) is immersed in the sol in step (3), and shaken and loaded in a phosphate buffer environment with pH 7.2-7.8 for 12-24 h, and dried at 60-90℃ to form a precursor; (5) Under an argon flow, the precursor obtained in step (4) is heated to 600-900℃ at 5℃ / min and kept at that temperature for 1-3h for controlled pyrolysis to obtain a magnetic composite microwave absorbing material with a porous carbon skeleton.

[0008] Further, in step (2), the mass-to-volume ratio of sludge carrier to acidification liquid is 1:10; the acidification liquid is 5-20wt% HCl.

[0009] Furthermore, in step (2) acidification washing treatment, dynamic pH control is adopted. When pH>2.5, acidification solution is added to 1.8-2.2 until the reaction is completed. The addition of hydrochloric acid removes calcium carbonate from the sludge, the calcite removal rate is ≥95%, pores are formed to increase the specific surface area of ​​the material, and the oxygen-containing functional groups of papermaking sludge are increased.

[0010] Furthermore, the drying temperature in step (1) is 100-110℃.

[0011] Further, in step (3), the metal nitrate solution is ferric nitrate nonahydrate, cobalt nitrate hexahydrate, or nickel nitrate hexahydrate.

[0012] Furthermore, the molar ratio of tannic acid in the tannic acid solution to the metal ions in the metal nitrate solution is 1.2-3:1.

[0013] Furthermore, in step (5), the temperature range is 700-800℃, and the specific surface area of ​​the obtained magnetic composite absorbing material is 90-251m². 2 / g.

[0014] The beneficial effects of this invention are: 1. The main raw material used in this invention is solid waste sludge from the pulp industry. By effectively recycling and pre-treating it and using it as a carrier for preparing microwave absorbing materials, not only is waste turned into treasure, but the preparation of microwave absorbing materials is also made cheaper.

[0015] 2. The metal complex precursor (tannic acid-metal complex) obtained in the preparation method of this invention can construct a dense network structure on the carrier surface rather than simple adsorption, ensuring that the magnetic metal particles are uniformly dispersed at an ultrafine size of 5-30 nm. This avoids the problem of metal agglomeration that is easily caused by traditional impregnation methods. This complex system can precisely control the loading density, breaking through the bottleneck of nanoscale magnetic phase dispersion technology.

[0016] 3. This invention employs a process of "acid washing and activation + complexation loading + controlled pyrolysis," and by rationally controlling the process conditions and dosage, a mesoporous carbon framework (90-251 μm) is constructed. 2 / g) has a unique structure that embeds 5-30nm magnetic particles.

[0017] 4. The pulp industry sludge used in this invention contains 14.32 wt% biochar. During the calcination process under an inert atmosphere, the biochar can reduce the metal complex precursors loaded on the carrier in situ to form magnetic components such as Fe3O4, Fe, Co, or Ni, which enhances the microwave absorption performance of the composite material. Attached Figure Description

[0018] Figure 1 This is a hysteresis loop diagram of the composite absorbing material of the present invention; Figure 2 The image shows the Raman spectrum of the composite absorbing material of this invention. Figure 3 This is a scanning electron microscope (SEM) image of the composite absorbing material of the present invention; Figure 4 The XRD pattern of the composite absorbing material of this invention is shown below. Figure 5 The microwave absorption performance of the composite microwave absorbing material of the present invention was tested.

[0019] in, Figure 1 , Figure 2 , Figure 3 (a)-(e) correspond to the results of Embodiments 1-5 of the present invention, respectively. Detailed Implementation

[0020] To clearly illustrate the technical features of this solution, the invention will be described in detail below through specific embodiments and in conjunction with the accompanying drawings.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.

[0022] The following embodiments are for illustrative purposes only and are not intended to limit the scope of this application. Experimental methods in the following embodiments that do not specify specific conditions should first refer to the guidelines given in this application, or may be performed according to experimental manuals or conventional conditions in the art, or by referring to experimental methods known in the art. Unless otherwise specified, all methods are conventional methods in the art.

[0023] In the following specific embodiments, unless otherwise specified, slight deviations may exist within the weighing accuracy range for the measurement parameters of the raw material components. For temperature and time parameters, acceptable deviations due to instrument testing accuracy or operational precision are permissible. The equipment and raw materials used are commercially available or commonly used in the art.

[0024] The pulp industry sludge used in the following specific embodiments is sourced from a paper mill in Taiyuan, Shanxi Province. The main components and corresponding weight percentages of the pulp industry sludge used are shown in Table 1.

[0025] Example 1 A method for preparing a pulp industry sludge-based composite microwave absorbing material includes the following steps: (1) The pulp industry sludge was pre-dried at 105℃ and then ball-milled and sieved through a 100-mesh sieve to obtain a sludge carrier; (2) Weigh 10g of the sludge carrier prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (10wt% HCl) to the conical flask and react at pH 1.8 for 2h. Use online pH monitoring to control the acid washing endpoint. After acid washing, wash away the acid solution. During the washing process, the pH of the rinsing filtrate reaches 7.2, indicating that sufficient acidification has been achieved. Terminate the washing and obtain the pretreated sludge carrier after solid-liquid separation. Dry it at 100℃ for 12h for later use. (3) 5 mL of 0.75 mol / L transition metal nonahydrate ferric nitrate solution was added dropwise to 100 mL of 0.05 mol / L tannic acid solution, and the pH was adjusted to 4.2 with ammonia to form a stable sol, which was used to construct the metal complex precursor; (4) The product of step (2) is immersed in the sol of step (3), and shaken and loaded for 12 h in a phosphate buffer environment with pH 7.2, and dried at 90°C to form a precursor; (5) The temperature was increased to 700℃ at 5℃ / min under argon flow and kept at the temperature for 2h for controlled pyrolysis to obtain a porous carbon skeleton composite microwave absorbing material loaded with Fe3O4.

[0026] Example 2 A method for preparing a pulp industry sludge-based composite microwave absorbing material includes the following steps: (1) The pulp industry sludge was pre-dried at 105℃ and then ball-milled and sieved through a 150-mesh screen to obtain a sludge carrier; (2) Weigh 10g of the carrier prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (15wt% HCl) to the conical flask and react at pH 2.2 for 2h. Use online pH monitoring to control the acid washing endpoint. Then wash away the acid solution. Stop washing when the pH of the filtrate reaches 7. After solid-liquid separation, the pretreated sludge carrier is obtained. Dry it at 100℃ for 12h and keep it for later use. (3) 10 mL of 0.5 mol / L transition metal cobalt nitrate hexahydrate solution was added dropwise to 100 mL of 0.1 mol / L tannic acid solution, and the pH was adjusted to 4.0 with ammonia to form a stable sol, which was used to construct the metal complex precursor; (4) The product of step (2) is immersed in the sol of step (3), and shaken and loaded in a phosphate buffer environment of pH 7.0 for 24 h, and dried at 90°C to form a precursor; (5) The temperature was increased to 700℃ at 5℃ / min under argon flow and kept at the temperature for 2h for controlled pyrolysis to obtain a porous carbon skeleton composite microwave absorbing material loaded with elemental metal Co.

[0027] Example 3: A method for preparing a pulp industry sludge-based composite microwave absorbing material includes the following steps: (1) The pulp industry sludge was pre-dried at 105℃ and then ball-milled and sieved through a 200-mesh screen to obtain a sludge carrier; (2) Weigh 10g of the carrier prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (20wt% HCl) to the conical flask and react at pH 2.0 for 4h. Use online pH monitoring to control the acid washing endpoint. Then wash away the acid solution. Stop washing when the pH of the filtrate reaches 7.2. Solid-liquid separation yields the pretreated sludge carrier. Dry it at 100℃ for 12h and reserve it for later use. (3) 10 mL of 0.5 mol / L transition metal nickel nitrate hexahydrate solution was added dropwise to 100 mL of 0.1 mol / L tannic acid solution, and the pH was adjusted to 4.5 with ammonia water to form a stable sol, which was used to construct the metal complex precursor; (4) The product of step (2) is immersed in the sol of step (3), and shaken and loaded in a phosphate buffer environment of pH 7.5 for 20 h, and dried at 80 °C to form a precursor; (5) The temperature was increased to 700℃ at 5℃ / min under argon flow and kept at the temperature for 2h for controlled pyrolysis to obtain a porous carbon skeleton composite microwave absorbing material loaded with Ni.

[0028] Example 4: A method for preparing a pulp industry sludge-based composite microwave absorbing material includes the following steps: (1) The pulp industry sludge was pre-dried at 105℃ and then ball-milled and sieved through a 150-mesh screen to obtain a sludge carrier; (2) Weigh 10g of the carrier prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (10wt% HCl) to the conical flask and react at pH 1.8 for 2h. Use online pH monitoring to control the acid washing endpoint. Then wash away the acid solution. Stop washing when the pH of the filtrate reaches 7. Separate the solid and liquid to obtain the pretreated sludge carrier. Dry it at 80℃ for 12h and keep it for later use. (3) 5 mL of 1.0 mol / L transition metal nonahydrate ferric nitrate solution was added dropwise to 100 mL of 0.1 mol / L tannic acid solution, and the pH was adjusted to 4.2 with ammonia water to form a stable sol, which was used to construct the metal complex precursor; (4) The product of step (2) was immersed in the sol of step (3), and the mixture was shaken and loaded for 24 hours in a phosphate buffer environment at pH 7, and then dried at 90°C to form a precursor. (5) The temperature was increased to 800℃ at 5℃ / min under argon flow and kept at the temperature for 3h for controlled pyrolysis to obtain a porous carbon skeleton composite microwave absorbing material loaded with Fe3O4 / Fe.

[0029] Example 5 A method for preparing a pulp industry sludge-based composite microwave absorbing material includes the following steps: (1) The pulp industry sludge was pre-dried at 105℃ and then ball-milled and sieved through a 200-mesh screen to obtain a sludge carrier; (2) Weigh 10g of the carrier prepared in step (1) and place it in a conical flask. Add 100mL of acidification solution (10wt% HCl) to the conical flask and react at pH 2.0 for 4h. Use online pH monitoring to control the acid washing endpoint. After acid washing, wash away the acid solution. Stop washing when the pH of the filtrate reaches 7. Separate the solid and liquid to obtain the pretreated sludge carrier. Dry it at 100℃ for 12h and keep it for later use. (3) 12 mL of 0.9 mol / L transition metal cobalt nitrate hexahydrate solution was added dropwise to 100 mL of 0.1 mol / L tannic acid solution, and the pH was adjusted to 4.2 with ammonia to form a stable sol, which was used to construct the metal complex precursor; (4) The product of step (2) was immersed in the sol of step (3), and the mixture was shaken and loaded for 24 hours in a phosphate buffer environment at pH 7, and then dried at 90°C to form a precursor. (5) The temperature was increased to 700℃ at 5℃ / min under argon flow and kept at the temperature for 3h for controlled pyrolysis to obtain a porous carbon skeleton composite microwave absorbing material loaded with Ni.

[0030] Performance testing: I. Hysteresis loops of the composite absorbing materials prepared in Examples 1-5. For example... Figure 1 As shown, the hysteresis loops of the composite microwave absorbing materials prepared in Examples 1-5 exhibit typical ferromagnetism, with saturation magnetization intensities of 20.10, 27.47, 23.33, 26.53 and 58.32 emu / g, respectively, indicating that the pulp industry sludge is loaded with a large amount of magnetic components after the carbothermic reduction reaction.

[0031] II. The Raman spectra of the composite absorbing materials obtained in Examples 1-5 are as follows: Figure 2 As shown. The Raman spectra of the composite microwave absorbing materials in Examples 1-5 all exhibit the simultaneous presence of D and G peaks, and I... D / I G The values ​​were 0.78, 0.77, 0.76, 0.85, and 0.75, respectively, indicating that carbon still exists in the pulp industry sludge after the carbothermic reduction reaction, and the carbon is in the form of graphitic carbon.

[0032] III. The scanning electron microscope (SEM) in the above embodiments is as follows: Figure 3 As shown, this indicates that the tannic acid-metal complex (metal complex precursor) forms a dense network structure on the surface of the sludge carrier. See the XRD pattern for reference. Figure 4 .

[0033] IV. Absorption Performance Test The porous composite microwave absorbing materials prepared in Examples 1-5 were tested for minimum reflection loss versus frequency. The results are shown below. Figure 5As shown in the figure, the composite microwave absorbing material prepared in Example 1, with a coating thickness of 2.0 mm, has a minimum reflection loss of -39.5 dB and an effective bandwidth of 4.3 GHz; the composite microwave absorbing material prepared in Example 2, with a coating thickness of 2.0 mm, has a minimum reflection loss of -36.5 dB and an effective bandwidth of 5.6 GHz; the composite microwave absorbing material prepared in Example 3, with a coating thickness of 2.0 mm, has a minimum reflection loss of -33.9 dB and an effective bandwidth of 4.9 GHz; the composite microwave absorbing material prepared in Example 4, with a coating thickness of 2.0 mm, has a minimum reflection loss of -39.5 dB and an effective bandwidth of 5.7 GHz; in contrast, the composite microwave absorbing material prepared in Example 5 has significantly reduced absorption performance, and its poor absorption performance cannot meet the application requirements. Analysis suggests that in Examples 1-4, the graphitization of carbon was well-developed, resulting in excellent electrical conductivity. Furthermore, the microwave absorbing material possessed a certain degree of porosity, achieving a good pore-forming effect and endowing the material with excellent dielectric properties, thus giving it superior microwave absorption performance. In contrast, the poor microwave absorption performance of Example 5 was mainly due to changes in the concentration of the metal nitrate solution and the amount of tannic acid used. This led to an increase in the magnetic components within the sample, consuming a large amount of carbon, disrupting the conductive network within the composite, reducing its conductivity and thus its electromagnetic loss capacity, resulting in poorer microwave absorption performance.

[0034] The above absorption performance test process is as follows: First, the sample is uniformly mixed with 60% paraffin by mass. Then, the mixture is pressed into a cylindrical block with an outer diameter of 7.00 mm and an inner diameter of 3.04 mm. Finally, the relative complex permittivity (εr=ε′-jε″) and permeability (μr=μ′-jμ″) of the sample are measured in the frequency range of 2-18 GHz using a vector network analyzer (VNA, Agilent N5230). The reflection loss value (RL) of the material is simulated and calculated based on transmission line theory.

[0035] The method for preparing composite microwave absorbing materials using pulp industry sludge provided by the present invention has been described in detail above. The specific embodiments described above should not be construed as limiting the scope of protection of the present invention. Any alternative modifications or variations made to the embodiments of the present invention by those skilled in the art will fall within the scope of protection of the present invention.

[0036] Any aspects of this invention not described in detail are well-known to those skilled in the art.

Claims

1. A method for preparing a pulp industry sludge-based composite wave-absorbing material, characterized by, The method comprises the following steps: (1) Pre-drying and ball-milling pulp industrial sludge, and sieving to obtain sludge carrier with 100-200 mesh; (2) Adding acidizing liquid to the sludge carrier in step (1) and reacting for 1-4 h at pH 1.8-2.2, washing away the acidizing liquid, and performing solid-liquid separation to obtain pretreated sludge carrier, which is dried at 70-100 ℃ for 6-12 h to obtain a dried product for standby use; (3) Adding 0.1-1.0 mol / L transition metal nitrate solution dropwise into 0.01-0.1 mol / L tannic acid solution, and adjusting pH to 4.2-4.8 by ammonia water to form a stable sol, which is used for constructing a metal complex precursor; (4) Immersing the dried product prepared in step (2) in the sol in step (3), and oscillating in a phosphate buffer environment at pH 7.2-7.8 for 12-24 h to form a precursor after drying at 60-90 ℃; (5) Under an argon flow, the precursor obtained in step (4) is heated at a rate of 5 ℃ / min to 600-900 ℃, and heat-treated for 1-3 h to obtain a magnetic composite wave-absorbing material with a porous carbon skeleton.

2. The production method according to claim 1, characterized by, In step (2), the mass-volume ratio of the sludge carrier to the acidizing liquid is 1:10; the acidizing liquid is 5-20 wt% HCL.

3. The preparation method according to claim 2, characterized in that, In the acidizing liquid washing treatment in step (2), dynamic pH control is adopted, and the acidizing liquid is supplemented when pH>2.

5.

4. The method of claim 1, wherein, In step (1), the drying temperature is 100-110 ℃.

5. The preparation method according to claim 1, characterized in that, In step (3), the metal nitrate solution is ferric nitrate nine hydrate solution, cobalt nitrate six hydrate solution or nickel nitrate six hydrate solution.

6. The method of claim 1, wherein, In the tannic acid solution, the molar ratio of tannic acid to metal ions in the metal nitrate solution is 1.2-3:

1.

7. The preparation method according to claim 1, characterized in that, In step (5), the heating range is 700-800 ℃.

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