Preparation method of modified activated carbon adsorption carrier

Abstract

The invention provides a preparation method of a modified activated carbon adsorption carrier, and relates to the technical field of activated carbon processing. The modified activated carbon adsorption carrier is obtained by activating raw material activated carbon in a KOH aqueous solution, mixing the activated carbon with graphene oxide, performing ultrasonic centrifugation, soaking the activated carbon in a glucoside and starch mixed aqueous solution, performing centrifugation, performing two-stage heat treatment in a nitrogen atmosphere, and finally performing cooling under a certain oxygen concentration. The defects in the prior art are overcome, the prepared modified activated carbon adsorption carrier can quickly adsorb hexavalent chromium in wastewater in various environments, and the removal efficiency of hexavalent chromium is guaranteed.

Description

Technical Field

[0001] The present invention relates to the technical field of activated carbon processing, and in particular to a method for preparing a modified activated carbon adsorption carrier. Background Art

[0002] Chromium is a common heavy metal pollutant, widely found in low-quality cosmetic raw materials and industrial wastewater such as electroplating. It mainly exists in water in the form of hexavalent chromium and trivalent chromium. Hexavalent chromium is a substance that pollutes water bodies.

[0003] Hexavalent chromium changes the taste, odor, and color of water, making it more difficult to digest and absorb. High levels of hexavalent chromium can also cause symptoms such as rhinitis and conjunctivitis, and even acute toxic effects such as severe vomiting and diarrhea. Hexavalent chromium is also a hydrophilic heavy metal. Excessive levels can enter the soil, disrupting the soil ecosystem and affecting its ability to breathe and retain water. There's also the risk of affecting plant growth and even poisoning crops.

[0004] Therefore, how to remove hexavalent chromium from water is crucial. Existing removal methods mainly include chemical reduction, ion exchange, electrolysis, biological methods and adsorption. Among them, the chemical reduction method is to reduce hexavalent chromium to trivalent chromium using chemical reducing agents (such as sodium sulfite, ferrous sulfate, etc.) under acidic conditions, and then adjust the pH value to form chromium hydroxide precipitation for removal. However, this method will produce a large amount of chromium-containing sludge during the reduction process, which is likely to cause secondary pollution and has high treatment costs. The ion exchange method is to use exchangeable ions on ion exchange resins to exchange hexavalent chromium ions in water, thereby removing hexavalent chromium from water. However, the cost of ion exchange equipment and resins is high, and the overall operation is complicated, making it unsuitable for widespread use. The electrolysis method uses an iron plate as an anode. During the electrolysis process, iron dissolves to form ferrous ions. Under acidic conditions, the ferrous ions reduce hexavalent chromium ions to trivalent chromium ions. The trivalent chromium is then removed by adjusting the pH value to form chromium hydroxide precipitation. However, the overall iron plate consumption is relatively high, and the sludge produced is difficult to utilize. The biological method uses the metabolic activities of microorganisms to remove hexavalent chromium from wastewater. For example, some microorganisms can reduce hexavalent chromium to trivalent chromium, reducing its toxicity. However, the overall operational stability is low and it is easy to cause secondary pollution. The adsorption method uses adsorbents (such as activated carbon, zeolite, diatomaceous earth, etc.) to adsorb hexavalent chromium ions in wastewater. However, it can often only be used for hexavalent chromium wastewater with lower concentrations, and the overall adsorption effect is poor.

[0005] Taking into account the cost and subsequent secondary pollution issues, the adsorption of hexavalent chromium by activated carbon is an important research direction. However, generally speaking, activated carbon can only have a good removal effect on hexavalent chromium in wastewater under acidic conditions. How to overcome the current problems of low adsorption efficiency of activated carbon and poor adsorption effect at high pH is the focus of current research. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention provides a method for preparing a modified activated carbon adsorption carrier, which can quickly adsorb hexavalent chromium in wastewater under various environments and ensure the removal efficiency of hexavalent chromium.

[0007] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0008] A method for preparing a modified activated carbon adsorption carrier, the preparation method comprising the following steps:

[0009] S1, ultrasonically clean the raw activated carbon, place it in a KOH aqueous solution for activation treatment, and then dry it to obtain preliminary activated activated carbon;

[0010] S2. Place the preliminarily activated activated carbon in clean water, then add graphene oxide, let it stand for 2-4 hours after ultrasonic vibration, and then centrifuge and filter to obtain activated carbon loaded with graphene oxide;

[0011] S3, adding the activated carbon loaded with graphene oxide to a mixed aqueous solution of glucoside and starch, stirring thoroughly, centrifuging twice, and filtering to obtain loaded activated carbon;

[0012] S4, drying the loaded activated carbon with microwaves and then heat-treating it at 200-220° C. for 1-2 h under a nitrogen atmosphere to obtain a first heat-treated activated carbon;

[0013] S5. Continue heating the first heat-treated activated carbon to 350-400° C. and heat-treating for 30-40 minutes to obtain a second heat-treated activated carbon;

[0014] S6. The heat treatment atmosphere of the second heat-treated activated carbon is adjusted to an oxygen concentration of 30%-40%, and then cooled to room temperature to obtain a modified activated carbon adsorption carrier.

[0015] Preferably, the mass concentration of KOH in the KOH aqueous solution in step S1 is 25%-30%, and the activation time is 1-2 hours.

[0016] Preferably, the drying temperature in step S1 is 110-120° C., and the drying time is 4-6 hours.

[0017] Preferably, in step S2, the mass ratio of graphene oxide to preliminarily activated activated carbon is 1:5-8.

[0018] Preferably, the power of the ultrasonic oscillation in step S2 is 200-300 W, and the oscillation time is 40-60 min.

[0019] Preferably, in the aqueous solution of the mixture of glucoside and starch in step S3, the mass concentration of glucoside is 1%-1.5%, and the mass concentration of starch is 15%-20%.

[0020] Preferably, the heating rate during the heat treatment in step S4 is 10-15°C / min.

[0021] Preferably, the rate of continuing to increase the temperature in step S5 is 5-10° C. / min.

[0022] Preferably, the cooling rate in step S6 is 5-10°C / min.

[0023] The present invention provides a method for preparing a modified activated carbon adsorption carrier, which has the following advantages over the prior art:

[0024] The present invention uses activated carbon as a raw material, loads graphene oxide after KOH activation, and wraps it with glucoside and starch before high-temperature heat treatment. This effectively increases the specific surface area of the activated carbon while improving the physical adsorption efficiency of the activated carbon for hexavalent chromium. At the same time, it ensures that the activated carbon has a good adsorption effect on hexavalent chromium within a wide pH range, thereby comprehensively improving the application range of the material. DETAILED DESCRIPTION

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0026] The following activated carbon raw materials are selected from coconut shell activated carbon AC (specific surface area of about 1363.4m 2 / g, 200 mesh), the specifications of graphene oxide GO are 0.5-3 μm, and the thickness is 0.55-1.2 nm.

[0027] Example 1:

[0028] Preparation of modified activated carbon adsorption carrier:

[0029] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 25% KOH aqueous solution for activation treatment for 2 hours, then washed with distilled water until neutral, and dried at 110°C for 6 hours to obtain preliminarily activated activated carbon;

[0030] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of primary activated carbon to graphene oxide of 5:1. The mixture was then ultrasonically shaken at 200W for 60 minutes, allowed to stand for 2 hours, and then centrifuged at 4200 r / min for 10 minutes. The supernatant was removed to obtain GO-AC.

[0031] (3) preparing an aqueous solution with a glucoside concentration of 1% and a starch concentration of 15%, placing GO-AC in the aqueous solution, stirring it at 200 r / min for 20 min, and then centrifuging it at 4200 r / min for 10 min. The supernatant was removed to obtain loaded activated carbon;

[0032] (4) The loaded activated carbon was dried using a 1000W microwave to a moisture content of ≤6%, and then placed in a calcining furnace. The air in the furnace was replaced with nitrogen. The temperature was then increased to 200°C at a heating rate of 10°C / min and heat treated for 2 hours. The temperature was then increased to 350°C at a heating rate of 5°C / min and heat treated for 40 minutes. The oxygen concentration in the furnace was then adjusted to 30%, and the temperature was cooled to room temperature at a rate of 5°C / min to obtain APG / ST-GO-AC-1.

[0033] Example 2:

[0034] Preparation of modified activated carbon adsorption carrier:

[0035] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 30% KOH aqueous solution for activation treatment for 1 hour, then washed with distilled water until neutral and dried at 120°C for 4 hours to obtain preliminarily activated activated carbon;

[0036] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of 8:1 between the primary activated carbon and graphene oxide. The mixture was then ultrasonically shaken at 300W for 40 minutes, allowed to stand for 4 hours, and then centrifuged at 4200 rpm for 10 minutes. The supernatant was removed to obtain GO-AC.

[0037] (3) preparing an aqueous solution with a glucoside concentration of 1.5% and a starch concentration of 20%, placing GO-AC in the aqueous solution, stirring it at 200 r / min for 20 min, and then centrifuging it at 4200 r / min for 10 min. The supernatant was removed to obtain loaded activated carbon;

[0038] (4) The loaded activated carbon was dried using a 1000W microwave to a moisture content of ≤6%, and then placed in a calcining furnace. The air in the furnace was replaced with nitrogen. The temperature was then increased to 220°C at a heating rate of 15°C / min and heat treated for 1 hour. The temperature was then increased to 400°C at a heating rate of 10°C / min and heat treated for 30 minutes. The oxygen concentration in the furnace was then adjusted to 40%, and the temperature was cooled to room temperature at a rate of 10°C / min to obtain APG / ST-GO-AC-2.

[0039] Comparative Example 1:

[0040] Preparation of modified activated carbon adsorption carrier:

[0041] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 25% KOH aqueous solution for activation treatment for 2 hours, then washed with distilled water until neutral, and dried at 110°C for 6 hours to obtain preliminarily activated activated carbon;

[0042] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of primary activated carbon to graphene oxide of 5:1. The mixture was then ultrasonically shaken at 200W for 60 minutes, allowed to stand for 2 hours, and then centrifuged at 4200 r / min for 10 minutes. The supernatant was removed to obtain GO-AC.

[0043] (3) preparing an aqueous solution with a glycoside mass concentration of 1% and a starch concentration of 15%, placing GO-AC in the aqueous solution, stirring it at a speed of 200 r / min for 20 min, and then centrifuging it at a speed of 4200 r / min for 10 min. The supernatant was removed to obtain loaded activated carbon;

[0044] (4) The loaded activated carbon was dried using a 1000W microwave to a moisture content of ≤6%, and then placed in a calcining furnace with air as the atmosphere. The temperature was raised to 200°C at a heating rate of 10°C / min and heat treated for 2 h. The temperature was then raised to 350°C at a heating rate of 5°C / min, and the heat treatment was continued for 40 min. The temperature was then cooled to room temperature at a rate of 5°C / min to obtain APG / ST-GO-AC-3.

[0045] Comparative Example 2:

[0046] Preparation of modified activated carbon adsorption carrier:

[0047] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 25% KOH aqueous solution for activation treatment for 2 hours, then washed with distilled water until neutral, and dried at 110°C for 6 hours to obtain preliminarily activated activated carbon;

[0048] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of primary activated carbon to graphene oxide of 5:1. The mixture was then ultrasonically shaken at 200W for 60 minutes, allowed to stand for 2 hours, and then centrifuged at 4200 r / min for 10 minutes. The supernatant was removed to obtain GO-AC.

[0049] (3) preparing an aqueous solution with a starch concentration of 15%, placing GO-AC in the aqueous solution, stirring it at 200 r / min for 20 min, and then centrifuging it at 4200 r / min for 10 min. The supernatant was removed to obtain loaded activated carbon;

[0050] (4) The loaded activated carbon was dried using a 1000W microwave to a moisture content of ≤6%, and then placed in a calcining furnace. The air in the furnace was replaced with nitrogen. The temperature was then increased to 200°C at a heating rate of 10°C / min and heat treated for 2 h. The temperature was then increased to 350°C at a heating rate of 5°C / min and heat treated for 40 min. The oxygen concentration in the furnace was then adjusted to 30%, and the temperature was cooled to room temperature at a rate of 5°C / min to obtain ST-GO-AC.

[0051] Comparative Example 3:

[0052] Preparation of modified activated carbon adsorption carrier:

[0053] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 25% KOH aqueous solution for activation treatment for 2 hours, then washed with distilled water until neutral, and dried at 110°C for 6 hours to obtain preliminarily activated activated carbon;

[0054] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of primary activated carbon to graphene oxide of 5:1. The mixture was then ultrasonically shaken at 200W for 60 minutes, allowed to stand for 2 hours, and then centrifuged at 4200 r / min for 10 minutes. The supernatant was removed to obtain GO-AC.

[0055] (3) preparing an aqueous solution with a glucoside concentration of 1%, placing GO-AC in the aqueous solution, stirring it at 200 r / min for 20 min, and then centrifuging it at 4200 r / min for 10 min. The supernatant was removed to obtain loaded activated carbon;

[0056] (4) The loaded activated carbon was dried using a 1000W microwave to a moisture content of ≤6%, and then placed in a calcining furnace. The air in the furnace was replaced with nitrogen. The temperature was then increased to 200°C at a heating rate of 10°C / min and heat treated for 2 hours. The temperature was then increased to 350°C at a heating rate of 5°C / min and heat treated for 40 minutes. The oxygen concentration in the furnace was then adjusted to 30%, and the temperature was cooled to room temperature at a rate of 5°C / min to obtain APG-GO-AC.

[0057] Comparative Example 4:

[0058] Preparation of modified activated carbon adsorption carrier:

[0059] (1) AC was cleaned with clean water under 400W ultrasound for 20 minutes, then removed and placed in a 25% KOH aqueous solution for activation treatment for 2 hours, then washed with distilled water until neutral, and dried at 110°C for 6 hours to obtain preliminarily activated activated carbon;

[0060] (2) The primary activated carbon was placed in clean water, and graphene oxide was added to the clean water at a mass ratio of primary activated carbon to graphene oxide of 5:1. The mixture was then ultrasonically shaken at 200W for 60 minutes, allowed to stand for 2 hours, and then centrifuged at 4200 r / min for 10 minutes. The supernatant was removed to obtain GO-AC.

[0061] (3) The GO-AC was dried using a 1000W microwave to a moisture content of ≤6%, then placed in a calcining furnace, the air in the furnace was replaced with nitrogen, and then heated to 200°C at a heating rate of 10°C / min for heat treatment for 2 h, then heated to 350°C at a heating rate of 5°C / min, and continued to heat treat for 40 min. The oxygen concentration in the furnace was then adjusted to 30%, and the temperature was cooled to room temperature at a rate of 5°C / min to obtain GO-AC-1.

[0062] Detection:

[0063] Prepare a chromium solution with a hexavalent chromium concentration of 250 mg / L for later use;

[0064] 1. Detect the adsorption effect of each group of modified activated carbon adsorption carriers on hexavalent chromium at different times: 0.2g of modified activated carbon adsorption carrier was placed in a 100mL conical flask, and then 50mL of chromium solution was poured in. The pH was adjusted to 4, and the solution was allowed to stand for 5min, 20min, 40min, and 60min respectively. The concentration of hexavalent chromium in the solution was filtered and the removal rate was calculated. The specific results are shown in Table 1 below:

[0065] Table 1

[0066]

[0067] It can be seen from the above table that APG / ST-GO-AC-1 and APG / ST-GO-AC-2 can achieve good hexavalent chromium removal effects in a relatively short time. Although APG / ST-GO-AC-3 also has a high removal rate in the end after 20 hours, its removal efficiency in the early stage is relatively slow. ST-GO-AC, APG-GO-AC and GO-AC-1 are worse than APG / ST-GO-AC-1 and APG / ST-GO-AC-2 in terms of hexavalent chromium removal efficiency and final removal rate.

[0068] 2. Detect the adsorption effect of each group of modified activated carbon adsorption carriers on hexavalent chromium under different pH conditions: 0.2g of modified activated carbon adsorption carrier was placed in a 100mL conical flask, and then 50mL of chromium solution was poured in. The pH was adjusted to 3, 4, 6, and 8 respectively. After standing for 40 minutes, the concentration of hexavalent chromium in the solution was filtered and the removal rate was calculated. The specific results are shown in Table 2 below:

[0069] Table 2

[0070]

[0071]

[0072] It can be seen from the above table that APG / ST-GO-AC-1, APG / ST-GO-AC-2 and APG / ST-GO-AC-3 are less affected by pH, while the removal rates of hexavalent chromium by ST-GO-AC, APG-GO-AC and GO-AC-1 decrease significantly at higher pH.

[0073] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a modified activated carbon adsorption carrier, characterized in that: The preparation method comprises the following steps: S1, ultrasonically clean the raw activated carbon, place it in a KOH aqueous solution for activation treatment, and then dry it to obtain preliminary activated activated carbon; S2. Place the preliminarily activated activated carbon in clean water, then add graphene oxide, let it stand for 2-4 hours after ultrasonic vibration, and then centrifuge and filter to obtain activated carbon loaded with graphene oxide; S3, adding the activated carbon loaded with graphene oxide to a mixed aqueous solution of glucoside and starch, stirring thoroughly, centrifuging twice, and filtering to obtain loaded activated carbon; S4, drying the loaded activated carbon with microwaves and then heat-treating it at 200-220° C. for 1-2 h under a nitrogen atmosphere to obtain a first heat-treated activated carbon; S5. Continue heating the first heat-treated activated carbon to 350-400° C. and heat-treating for 30-40 minutes to obtain a second heat-treated activated carbon; S6. The heat treatment atmosphere of the second heat-treated activated carbon is adjusted to an oxygen concentration of 30%-40%, and then cooled to room temperature to obtain a modified activated carbon adsorption carrier.

2. The preparation method according to claim 1, wherein: The mass concentration of KOH in the KOH aqueous solution in step S1 is 25%-30%, and the activation time is 1-2 hours.

3. The preparation method according to claim 1, wherein: The drying temperature in step S1 is 110-120° C., and the drying time is 4-6 hours.

4. The preparation method according to claim 1, wherein: In step S2, the mass ratio of graphene oxide to preliminarily activated activated carbon is 1:5-8.

5. The preparation method according to claim 1, wherein: The power of the ultrasonic oscillation in step S2 is 200-300W, and the oscillation time is 40-60 minutes.

6. The preparation method according to claim 1, wherein: In the aqueous solution of the mixture of glucoside and starch in step S3, the mass concentration of glucoside is 1%-1.5%, and the mass concentration of starch is 15%-20%.

7. The preparation method according to claim 1, wherein: The heating rate during the heat treatment in step S4 is 10-15°C / min.

8. The preparation method according to claim 1, wherein: The rate of continuing to heat up in step S5 is 5-10°C / min.

9. The preparation method according to claim 1, wherein: The cooling rate in step S6 is 5-10°C / min.

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