Preparation method of magnetic biochar and method for removing Congo red pollutants

Abstract

The invention discloses a processing method of magnetic biochar. The processing method comprises the following steps: crushing broad bean straws into biomass powder by using a crusher; the biomass powder is sorted and automatically falls into a storage box, the storage box is transported to the position above a mixing box, a preset amount of biomass powder is poured into the mixing box containing the ferric nitrate nonahydrate solution, and then a sodium hydroxide solution is added for dipping; and performing pyrolysis, washing and vacuum freezing to obtain the modified biochar. According to the method, the magnetic biochar is prepared through a dipping pyrolysis method, the magnetic biochar has high surface area and outstanding adsorption capacity on Congo red dye, the biochar material can be separated and recycled by means of an external magnetic field after adsorbing organic pollutants, secondary pollution is avoided, the process is simple, the cost is low, energy consumption is low, and the method is suitable for industrial production. The Congo red adsorbent has high adsorption removal efficiency and can be repeatedly used. The invention also relates to a method for removing Congo red pollutants.

Description

Technical Field

[0001] The invention relates to the technical field of preparation of magnetic biochar, in particular to the technical field of preparation of magnetic biochar from broad bean straw. The invention also relates to a method for removing Congo red pollutants in sewage by using the magnetic biochar prepared from the broad bean straw. Background Art

[0002] At present, the research on biochar from cereal straw, such as corn, wheat, and rice, is relatively concentrated, while there is relatively little research on biochar made from bean straw, especially broad bean straw.

[0003] On the other hand, due to the high toxicity, non-biodegradability and carcinogenicity of dyes, dye wastewater poses a considerable threat to both humans and the ecosystem. Most synthetic dyes are organic compounds that can absorb visible light, and their main components include a chromophore-chromophore conjugated system (electron acceptor), electron resonance (delocalized π electrons of aromatic rings) and auxochromes. The chromophore (aromatic ring of benzene, naphthalene or anthracene) combines with a chromophore (such as azo (-N=N-), methine (-CH=), carbonyl (=C=O), etc.) to form a conjugated system, while the presence of auxochromes (such as amino (-NH2), carboxyl (-COOH), hydroxyl (-OH), etc.) increases the solubility of the dye in water. Most of the Congo red wastewater is composed of unreacted Congo red pigment in industrial production and impurities in dye wastewater, among which the content of Congo red pigment accounts for the majority. So far, many technologies for removing dyes from wastewater have been successfully explored, including adsorption, biodegradation, photocatalytic degradation, ion exchange, coagulation, coprecipitation and membrane filtration. Among them, adsorption is considered the most promising technology for removing dye pollutants from wastewater due to its high efficiency, low cost and easy operation. At present, the existing biochar adsorbents have low efficiency in removing organic pollutants. At the same time, the south is an important textile industry cluster in China, close to the production area of ​​broad beans. How to use broad bean straw as raw material to prepare modified biochar to solve the problem of low efficiency of existing biochar adsorbents in removing organic pollutants and how to achieve industrial processing are topics worth studying. Summary of the invention

[0004] The purpose of the present invention is to provide a method for processing modified biochar using broad bean straw as raw material and realizing industrial processing. The purpose of the present invention is also to provide a method for removing Congo red pollutants in textile wastewater by using broad bean straw biochar.

[0005] To this end, the present invention provides a method for processing magnetic biochar, which includes: using a pulverizer to pulverize broad bean straw into biomass powder; after the biomass powder is discharged from the discharge port of the pulverizer, it is transported to a sorting device via a second conveyor belt, and the sorted biomass powder is sent to a storage box, and the storage box includes an oblique conveyor belt through the conveying device, which is used to transport the storage box to the top of a mixing box and pour a predetermined amount of biomass powder into the mixing box, the mixing box is pre-injected with a nonahydrate ferric nitrate solution, the biomass powder is stirred after being added, and then a sodium hydroxide solution is added for impregnation; after impregnation, the modified biomass is extracted from the storage box and dried; the dried modified biomass is sent to a tubular furnace for pyrolysis; the biochar extracted after pyrolysis is sent to a flushing device for flushing to adjust the pH to neutral, and then sent to a vacuum freeze dryer for freeze drying to obtain modified biochar.

[0006] Furthermore, it also includes a first conveyor belt, an oven and a vibrating screen for preparing broad bean straw biomass powder. The broad bean straw is conveyed to the oven for drying by the first conveyor belt, and then conveyed to the grinder for crushing. After crushing, it enters the vibrating screen through the second conveyor belt. The vibrating screen is arranged obliquely, and the storage box moves to the bottom of the vibrating screen under the drive of the conveying device.

[0007] Furthermore, the conveying device includes a third conveyor belt, the third conveyor belt includes chain links, a retractable clamp is arranged on the chain links, a wing plate cooperating with the retractable clamp is arranged on the lower side of the storage box, a support plate protruding outward is arranged in the middle of the storage box, a guide plate is arranged at the rear of the storage box, and a jacking device cooperating with the support plate is arranged below the vibrating screen. When the storage box is transported to the bottom of the vibrating screen, the jacking device cooperates with the support plate to support the storage box and leave the third conveyor belt. When one storage box runs above the mixing box, the other storage box moves to cooperate with the guide plate of the storage box below the vibrating screen.

[0008] Furthermore, the concentration of the ferric nitrate nonahydrate solution is 0.08-0.10 mol / L, and the concentration of the sodium hydroxide solution is 0.02-0.04 mol / L.

[0009] Furthermore, the modified biomass is placed in a tubular furnace and nitrogen is introduced, and the temperature of the tubular furnace is heated to 700-900° C. and fired for 1-3 hours.

[0010] Further, the washed biochar was transferred into a vacuum sealed bag and dried in a vacuum freeze dryer at a vacuum degree of 0.1 to 0.2 Pa and a temperature of -70°C to -75°C for 10 to 12 h.

[0011] The present invention also includes a method for removing Congo red pollutants using the magnetic broad bean straw biochar, comprising: adjusting the pH value of the sewage treatment pool to 6-10, adding the prepared modified biochar to sewage containing Congo red, reacting for 7-9 hours, and recovering the biochar by magnetic separation.

[0012] Furthermore, the biochar is added into a sewage treatment tank at a solid-liquid ratio of 1 g / L.

[0013] The beneficial technical effects of the present invention are:

[0014] The present invention prepares magnetic biochar by impregnation pyrolysis, which has a high surface area and outstanding adsorption capacity for Congo red dye, and realizes separation and recovery of biochar materials after adsorbing organic pollutants with the help of an external magnetic field, thereby avoiding secondary pollution. The process is relatively simple, the cost is low, the energy consumption is low, the adsorption removal efficiency is high, and the material can be reused. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a graph showing the change of the adsorption effect of magnetic broad bean straw biochar on Congo red dye in water over time;

[0016] Figure 2 The adsorption effect of the prepared magnetic broad bean straw biochar on Congo red dye in water changes with the initial concentration;

[0017] Figure 3 The adsorption effect of the prepared magnetic broad bean straw biochar on Congo red dye in water changes with pH;

[0018] Figure 4 This is the specific surface area (BET) image of the prepared magnetic broad bean straw biochar;

[0019] Figure 5 This is the X-ray powder diffraction (XRD) spectrum of the prepared magnetic broad bean straw biochar;

[0020] Figure 6 This is the magnetic hysteresis loop (VSM) image of the prepared magnetic broad bean straw biochar;

[0021] Figure 7 It is a schematic diagram of the processing equipment;

[0022] Figure 8 is a schematic diagram of the third conveyor belt and the mixing box;

[0023] Fig. 9 A schematic diagram of the storage box below the vibrating screen;

[0024] Fig.10 It is a schematic diagram of a clamping member clamping a tank wing panel.

[0025] Explanation of the reference numerals: 1. first conveyor belt; 2. oven; 3. crusher; 4. second conveyor belt; 5. vibrating screen; 6. storage box; 601. wing plate; 602. support plate; 603. guide plate; 7. third conveyor belt; 8. clamping member; 9. lifting device; 10. mixing box. DETAILED DESCRIPTION

[0026] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0027] Reference Figure 7 As shown, a processing method of magnetic biochar of the present invention comprises: using a pulverizer 3 to pulverize broad bean straw into biomass powder; after the biomass powder is discharged from the discharge port of the pulverizer 3, it is conveyed to a sorting device via a second conveyor belt 4, and the biomass powder after sorting is sent to a storage box 6, and the storage box 6 includes an oblique conveyor belt through the conveying device, which is used to transport the storage box 6 to the top of a mixing box and pour a predetermined amount of biomass powder into the mixing box, and the mixing box is pre-injected with a nonahydrate ferric nitrate solution, and the biomass powder is stirred after being added, and then a sodium hydroxide solution is added for impregnation; after impregnation, the modified biomass is extracted from the storage box 6 and dried; the dried modified biomass is sent to a tubular furnace for pyrolysis; the biochar extracted after pyrolysis is sent to a flushing device for flushing to adjust the pH to neutral, and then sent to a vacuum freeze dryer for freeze drying to obtain modified biochar.

[0028] The processing method of the present invention can be simply divided into the pretreatment, impregnation, pyrolysis and post-treatment steps of broad bean straw, which will be described in detail below in conjunction with an embodiment.

[0029] The pretreatment process of this embodiment may also include pre-treatment of washing and drying the broad bean straw. The first conveyor belt 1 conveys the broad bean straw to the drying oven 2 for drying, reduces the moisture content of the straw to meet the requirements, and the broad bean straw dried in the drying oven 2 is fed into the feed port of the crusher 3 by the first conveyor belt 1. The powder formed after the crushing of the crusher 3 enters the second conveyor belt 4 from the discharge port, and the second conveyor belt 4 feeds it into the inclined vibration screen 5. The biomass powder falls from the sieve hole into the storage box 6 arranged below the vibration screen 5, and the coarse particles are separated along the surface of the vibration screen 5. The coarse particles can be crushed or ground again to improve the utilization rate of the material.

[0030] The main steps of processing modified biochar are impregnation and pyrolysis. Impregnation is used to attach magnetic substances to the surface of biomass powder. The processing method of this embodiment realizes the assembly line and automation of straw pretreatment and impregnation. Figure 7 and Figure 8As shown, specifically, the storage box 6 is arranged on the third conveyor belt 7, and the third conveyor belt 7 includes a section of oblique conveyor belt for lifting the storage box 6 to the top of the mixing box 10. When the storage box 6 is loaded with a predetermined amount of biomass powder, the predetermined amount of biomass powder can be achieved by weight monitoring, such as installing a gravity sensor in the storage box. The third conveyor belt 7 brings the storage box 6 to the top of the mixing box and pours the biomass powder into the mixing box 10 filled with a predetermined amount of 0.08-0.10 mol / L ferric nitrate nonahydrate solution, stir for ten minutes, add 0.08-0.10 mol / L sodium hydroxide solution, and then immerse, transfer the mixing box to the immersion area by rail for 3 to 5 hours, and transfer the mixing box loaded with ferric nitrate nonahydrate solution to a predetermined position. In the prior art, it is generally necessary to increase the impregnation time under heat preservation, and the impregnation time is generally 8 hours. Increasing the impregnation time may cause excessive metal oxides to adhere, so that too much biochar surface is occupied by metal oxides, resulting in reduced adsorption effect. Compared with the prior art, the biomass powder formed after pretreatment in this embodiment has a smaller particle size and a larger specific surface area. More magnetic substances can be attached during impregnation, and the impregnation time is greatly reduced to 3 to 5 hours. Not only does it have a more prominent negative magnetic effect after pyrolysis, but part of the magnetic substances are transferred to the interior of the biochar during the carbonization and polymerization process of the biomass powder, which can avoid excessive oxides from occupying the surface and pores of the biochar, thereby improving the adsorption effect of the biochar. The process of this embodiment also realizes the assembly line processing from broad bean straw pretreatment to impregnation.

[0031] In the process of combining the pretreatment and the impregnation process, the amount of biomass powder processed by the pulverizer 3 and the vibrating screen 5 at a time needs to match the amount of the storage box 6. The biomass powder is transported intermittently by the storage box 6, so the operation of the equipment needs to be matched, resulting in great waste. An improved solution, referring to Fig. 9 and Fig.10 As shown, the third conveyor belt 7 may include a chain link, on which a retractable clamping member 8 is provided, which may be as follows: Fig.10The U-shaped clamping member shown in the figure has a telescopic rod controlled and driven by a motor, and the telescopic rod can also be connected to a spring. At the position corresponding to the clamping position, a guide slope is set on the outside of the conveying device to push the clamping member 8 to retract the wing plate 601 that clamps the storage box 6. The lower side of the storage box 6 is provided with a wing plate 601 that cooperates with the telescopic clamping member 8, and the middle part of the storage box 6 is provided with a support plate 602 protruding outward, and the support plate 602 extends to the outside of the conveying device. A guide plate 603 is provided at the rear of the storage box 6. A lifting device 9 that cooperates with the support plate 602 is set below the vibrating screen 5, and the lifting device 9 is also set on the outside of the conveying device. When a storage box 6 is below the vibrating screen 5, its guide plate 603 cooperates with another storage box 6 at the rear (a matching groove can be set on the wall plate of the corresponding storage box). When the material in the storage box 6 reaches a predetermined amount, the lifting device 9 descends to make the storage box 6 contact with the third conveyor belt 7, and the clamping member 8 clamps the wing plate 601. The third conveyor belt 7 starts to drive the two storage boxes 6 to move forward. At this time, the continuously falling biomass powder will enter the latter storage box from the guide plate 603. When the latter storage box is transferred to the bottom of the vibrating screen 5, the retractable clamping member 8 releases the clamping of its wing plate 601, the conveying device stops, and the lifting device 9 cooperates with the support plate 602 to support the storage box 6 and leave the third conveyor belt 7. The biomass powder falls into the storage box 6, and the third conveyor belt 7 starts again to send the storage box 6 filled with materials to the top of the mixing box. At this time, one storage box runs to the rear of the storage box under the vibrating screen 5 and cooperates with its guide plate 603. This embodiment realizes the continuous operation of the pretreatment and the intermittent operation of the third conveyor belt 7, and the biomass powders all fall into the corresponding storage boxes.

[0032] Pyrolysis is to carbonize biomass to form porous biochar under low oxygen or oxygen-free conditions. This embodiment also completes negative magnetism at the same time. Pyrolysis is one of the main processes for preparing biochar. In this embodiment, biomass is extracted after impregnation and dried in a dryer or oven at a temperature of 90°C. The extraction of biomass can be done by extracting the solution through a pipeline and filtering it. The dried modified biomass is spread flat and transferred to a tubular furnace and nitrogen is introduced for protection. The nitrogen flow rate can be 0.1L / min. The temperature of the tubular furnace is heated to 700-900°C and fired for 1-3h. The temperature of this embodiment is 800°C and the time is 2h. In this embodiment, the obtained biochar is transferred to a flushing device and rinsed to neutrality with distilled water. The flushed biochar is transferred to a vacuum sealed bag and dried in a vacuum freeze dryer to obtain modified biochar. In this embodiment, the vacuum degree of the vacuum freeze dryer is 0.1Pa, the temperature is -72°C, and the drying time is 10-12h.

[0033] The present invention also includes a method for removing Congo red pollutants using the modified biochar, which includes adjusting the pH value of the sewage treatment pool to 6 to 10, adding the prepared modified biochar to the sewage treatment pool containing Congo red at a solid-liquid ratio of 1 g / L, reacting for 7 to 9 hours, and recovering the biochar by magnetic separation.

[0034] The applicant conducted a Congo red pollutant removal test, the details of which are as follows:

[0035] Example 1: At a solid-liquid ratio of 1 g / L, magnetic broad bean straw biochar was added to polyethylene reaction bottles containing a certain concentration of Congo red solution and shaken. Placed in a water bath constant temperature oscillator at 25°C, the oscillation speed was 155 rpm, and taken out at different time intervals (t = 0.083, 0.16, 0.25, 0.5, 1, 2, 4, 6, 8 and 12h). Rapid magnetic separation was performed using a magnet, the supernatant was taken and diluted to an appropriate concentration, and the remaining Congo red content was determined using an ultraviolet spectrophotometer (UV-Vis).

[0036] Calculation of Congo red adsorption of biochar:

[0037] q t is the adsorption amount of Congo red by biochar, C0 is the initial concentration of Congo red in the solution, C e is the adsorption equilibrium concentration of Congo red in the solution, and m is the mass of the adsorbent.

[0038] Effect of adsorbent on Congo red adsorption under different oscillation times Figure 1 As shown in the figure, the adsorption amount increases with the increase of oscillation time. Within 240 minutes, the adsorption amount of Congo red by the adsorbent increases rapidly, and the removal rate of Congo red reaches 60%. After 240 minutes, the increase in the adsorption amount of Congo red begins to slow down, and the adsorption amount reaches equilibrium after 540 minutes.

[0039] Example 2: Add magnetic broad bean straw biochar to polyethylene reaction bottles containing different concentrations of Congo red solution at a solid-liquid ratio of 1g / L and shake well. Place in a water bath constant temperature oscillator at 25°C, with an oscillation speed of 155rpm and an oscillation time of 12h. Use a magnet for rapid magnetic separation, take the supernatant and dilute it to a suitable concentration, and use an ultraviolet spectrophotometer (UV-Vis) to determine the remaining Congo red content. The effect of different concentrations of Congo red adsorption is shown in Figure 2. Figure 2As shown in the figure, when the initial concentration increases from 1000 mg·L-1 to 2000 mg·L-1, the amount of dye adsorbed on the magnetic broad bean straw biochar increases with the increase in the initial concentration of the dye, and finally reaches the maximum adsorption capacity of the adsorbent of 1200 mg·g-1. In the early stage of the reaction, the adsorption rate is high but the adsorption amount is low. This is because there are a large number of adsorption sites on the surface of the magnetic broad bean straw biochar that can be used for a limited number of dye molecules. However, when the concentration of dye molecules in the solution is high enough, the adsorption amount reaches a constant value, and after exceeding this value, the dye is no longer removed from the solution.

[0040] Example 3: Add magnetic broad bean straw biochar to a polyethylene reaction bottle containing a certain concentration of Congo red solution at a solid-liquid ratio of 1g / L, adjust the pH to 2, 4, 6, 7, 8, 10, 12, and shake well. Place in a water bath constant temperature oscillator at 25°C, with an oscillation speed of 155rpm and an oscillation time of 12h. Use a magnet for rapid magnetic separation, take the supernatant and dilute it to an appropriate concentration, and use an ultraviolet spectrophotometer (UV-Vis) to determine the remaining Congo red content. The effect of different pH on the adsorption of Congo red is as follows: Figure 3 As shown in the figure, the surface charge and protonation of the adsorbent are significantly affected by the solution pH. Congo red exists as an anion at alkaline pH (pH greater than 5.5) and as a cation at acidic pH (pH less than 5.5). The removal rate of Congo red by magnetic broad bean straw biochar in the pH range of 6-10 reached 99%.

[0041] Example 4: Structural Characterization of Adsorbents The specific surface area of ​​the materials and their adsorption and desorption curves were measured using a TriStar II 3020 surface area meter (McMerrittick) with nitrogen as the adsorbed gas. The surface morphology of the samples was analyzed using a scanning electron microscope (Nova 200NanoSEM, FEI Co., Ltd., USA). Fourier transform infrared spectra (FTIR) were obtained using a TENSOR27 Fourier transform infrared spectrometer (Zhengzhou Great Wall Technology Industry and Trade Co., Ltd., Zhengzhou, China) with a scanning range of 4000-400 cm-1.

[0042] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for processing magnetic biochar, characterized in that: The processing method comprises: Using a crusher to crush broad bean straw into biomass powder; After being discharged from the discharging port of the pulverizer, the biomass powder is conveyed to the sorting device via a second conveyor belt. After sorting, the biomass powder is conveyed into a storage box. The storage box includes an oblique conveyor belt through the conveying device, which is used to transport the storage box to the top of the mixing box and pour a predetermined amount of biomass powder into the mixing box. The mixing box is pre-injected with a nonahydrate ferric nitrate solution. After the biomass powder is added, it is stirred and then a sodium hydroxide solution is added for impregnation; After impregnation, the modified biomass is extracted from the storage box and dried; the dried modified biomass is sent to a tubular furnace for pyrolysis; the biochar extracted after pyrolysis is sent to a flushing device for flushing to adjust the pH to neutral, and then sent to a vacuum freeze dryer for freeze drying to obtain the modified biochar.

2. The method for preparing magnetic biochar according to claim 1, characterized in that: It also includes a first conveyor belt, an oven and a vibrating screen for preparing broad bean straw biomass powder. The broad bean straw is conveyed to the oven for drying by the first conveyor belt, and then conveyed to the grinder for crushing. After crushing, it enters the vibrating screen through the second conveyor belt. The vibrating screen is arranged obliquely, and the storage box moves to the bottom of the vibrating screen under the drive of the conveying device.

3. The method for preparing magnetic biochar according to claim 2, characterized in that: The conveying device includes a third conveyor belt, and the third conveyor belt includes chain links. A retractable clamp is arranged on the chain links. A wing plate cooperating with the retractable clamp is arranged on the lower side of the storage box. A support plate protruding outward is arranged in the middle of the storage box. A guide plate is arranged at the rear of the storage box. A lifting device cooperating with the support plate is arranged below the vibrating screen. When the storage box is transported to the bottom of the vibrating screen, the lifting device cooperates with the support plate to support the storage box and leave the third conveyor belt. When one storage box runs above the mixing box, the other storage box moves to cooperate with the guide plate of the storage box below the vibrating screen.

4. A method for preparing magnetic biochar according to any one of claims 1 to 3, characterized in that: The concentration of the ferric nitrate nonahydrate solution is 0.08-0.10 mol / L, and the concentration of the sodium hydroxide solution is 0.02-0.04 mol / L.

5. A method for preparing magnetic biochar according to any one of claims 1 to 3, characterized in that: The dried biomass is transferred into a tubular furnace and nitrogen is introduced, and the temperature of the tubular furnace is heated to 700-900° C. and fired for 1-3 hours.

6. A method for preparing magnetic biochar according to any one of claims 1 to 3, characterized in that: The washed biochar was transferred to a vacuum sealed bag and dried in a vacuum freeze dryer at a vacuum degree of 0.1 to 0.2 Pa and a temperature of -70°C to -75°C for 10 to 12 h.

7. A method for removing Congo red pollutants, using the magnetic broad bean straw biochar prepared according to claim 1, characterized in that: The pH value of the sewage treatment pool is adjusted to 6-10, the prepared modified biochar is added to the sewage containing Congo red, and the biochar is recovered by magnetic separation after reacting for 7-9 hours.

8. A method for removing Congo red pollutants according to claim 7, characterized in that: The biochar was added into the sewage treatment tank at a solid-liquid ratio of 1 g / L.

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