Method for recycling waste activated carbon after water purification treatment

Abstract

The application discloses a method for recycling waste activated carbon after water purification treatment, and belongs to the field of waste activated carbon recycling, which comprises the steps of metal ion desorption, organic matter desorption and recovery of pre-product activation. In the process of organic matter desorption, trimethylol aminomethyl methane, disodium hydrogen phosphate, sodium hydroxide, ethylene carbonate and triethanolamine are configured into an electrolyte, and the modified titanium-copper composite electric negative plate is used to regenerate the waste activated carbon, so that the regeneration efficiency of the waste activated carbon can reach 93.4%, and the adsorption activity of the recovered activated carbon is equivalent to that of the purchased activated carbon powder. The modified titanium-copper composite electric negative plate is obtained by uniformly mixing ethylene carbonate and stearic acid, adding tetraethyl orthosilicate at 100-120 DEG C, immersing the titanium-copper composite electric negative plate into the mixture, and then drying to form an alkali-resistant film.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of activated carbon recycling, in particular to a method for recycling waste activated carbon after water purification treatment. BACKGROUND

[0002] Industrial wastewater purification treatment and secondary utilization have become a necessary link for many enterprises and local industrial production. If wastewater purification cannot be correctly and comprehensively carried out, harmful substances in the wastewater will cause certain pollution to the environment. Activated carbon not only has good chemical stability, is convenient to regenerate, and has rich pore structure and high specific surface area, but also has strong adsorption. Therefore, activated carbon can be used as a high-activity adsorbent, which can be used not only in industrial production fields such as solvent, gas removal, removal of toxic substances, solution decolorization and wastewater, but also widely used in industrial wastewater purification treatment. However, the service life of activated carbon is short and the manufacturing cost is high, the adsorption performance has certain limit, and after saturation, it is easy to release again in a high-temperature environment to form secondary pollution, which limits the use of activated carbon in various fields.

[0003] In order to reuse activated carbon in order to save resources, the activated carbon is usually recycled. Common recycling methods include thermal regeneration, solution regeneration, biological regeneration and electrochemical regeneration. As the most mature method, the thermal regeneration method has the problems of large loss of carbon in the regeneration process, strict requirements for equipment and high operating cost. The solution regeneration method is specific and cannot handle industrial wastewater with complex components. The biological regeneration method needs to specially cultivate microorganisms and has a long regeneration time. The electrochemical regeneration method as a new activated carbon regeneration method has the advantages of high regeneration efficiency, small pollution, simple operation and small decrease in adsorption of activated carbon after multiple recycling. Its principle is to fill the waste activated carbon between two main electrodes, pass a direct current through the electrolyte, and under the action of the electric field, the two ends of the activated carbon show opposite polarity, chemical reaction occurs, and the pollutants adsorbed on the surface of the activated carbon are directly desorbed after decomposition. However, the regeneration efficiency is reduced due to the conductivity of the electrolyte and the change of the pH value of the electrolyte in the waste activated carbon recovery process, which leads to the inability to realize the large-scale treatment of waste activated carbon by the electrochemical regeneration method. Therefore, there is an urgent need for a method for treating waste activated carbon after water purification treatment by controlling the conductivity and pH of the electrolyte in the electrochemical regeneration process to realize large-scale recycling of waste activated carbon. SUMMARY

[0004] Therefore, the purpose of the present application is to provide a method for recycling waste activated carbon after water purification treatment, which solves the problem of low regeneration efficiency in the waste activated carbon recovery process by improving the conductivity of the electrolyte and controlling the change of the pH value of the electrolyte in the waste activated carbon recovery process.

[0005] The present application solves the above technical problems by providing a method for recycling waste activated carbon after water purification treatment, specifically as follows:

[0006] S1. Metal ion desorption: pour the waste activated carbon into the reaction tank, add acid washing solution and stir for 10-15 min, remove the supernatant after standing and layering, then add alkaline washing solution and continue stirring for 5-10 min, remove the supernatant after standing and layering to obtain metal ion-removed activated carbon;

[0007] S2. Organic matter desorption: add the metal ion-removed activated carbon into the electrolytic cell, pass in the electrolyte, insert the electrode plate and pass in 0.8-1.2 A direct current, take out the activated carbon after passing electricity for 20-30 min, and dry to obtain the recycled pre-product;

[0008] S3. Activation of the recycled pre-product: calcine the recycled pre-product at 300-400℃ for 30-40 min under nitrogen protection to obtain the recycled activated carbon.

[0009] Further, the waste activated carbon in step S1 is waste activated carbon generated after industrial dye wastewater treatment.

[0010] Further, the acid washing solution in step S1 is dilute hydrochloric acid with pH=5-6, and the alkaline washing solution is sodium hydroxide solution with pH=11-12.

[0011] Further, the preparation raw materials of the electrolyte in step S2 include: tris-hydroxymethyl aminomethane, ethylene carbonate, triethanolamine, disodium hydrogen phosphate, and sodium hydroxide.

[0012] Further, the preparation method of the electrolyte is as follows:

[0013] Mix ethylene carbonate and triethanolamine uniformly, heat to 60-80℃, stir for 10-20 min, then keep constant temperature, add tris-hydroxymethyl aminomethane, disodium hydrogen phosphate, and sodium hydroxide in sequence while stirring, fully dissolve, then cool to room temperature to obtain the electrolyte.

[0014] Further, the mass-volume ratio of tris-hydroxymethyl aminomethane, disodium hydrogen phosphate, sodium hydroxide, ethylene carbonate, and triethanolamine is (1-3) g:(2-3) g:(1-2) g:(10-12) L:(0.8-1.2) L.

[0015] Further, the electrode plate in step S2 includes modified titanium-copper composite cathode plate and graphite anode plate.

[0016] Further, the preparation raw materials of the modified titanium-copper composite cathode plate include: titanium-copper composite cathode plate, tetraethyl orthosilicate, ethylene carbonate, and stearic acid.

[0017] Further, the preparation method of the modified metal electric negative plate is as follows:

[0018] The ethylene carbonate and stearic acid are mixed uniformly, and then the mixture is heated to 100-120 DEG C, and then the tetraethyl orthosilicate is added while hot, and then the mixture is stirred and mixed uniformly, and then the titanium-copper composite electric negative plate is immersed in the mixture for 3-5s, and then taken out quickly, and then dried to obtain the modified metal electric negative plate.

[0019] Further, the volume ratio of the tetraethyl orthosilicate, the ethylene carbonate and the stearic acid is (1-2)L:(8-12)L:(1-2)L.

[0020] The industrial dye wastewater is purified and treated, and then the waste activated carbon is discarded mainly because a large amount of metal ions and organic substances are adsorbed, so that the activated carbon does not have the adsorption performance any more. The metal ions are resolved from the waste activated carbon by the pickling and alkali cleaning method, so that the metal ions do not corrode the electrode during the subsequent desorption of various organic dyes, and the desorption effect is affected.

[0021] The metal ion-removed activated carbon is placed in an electrolytic cell, and then a recovery product is obtained through electrolysis. The ordinary inorganic electrolyte has good conductivity, but because the production rate of hydrogen ions in the electrolysis process is twice that of hydroxyl ions, the pH value of the electrolyte is gradually reduced, and the efficiency of electrolytic desorption of organic matters is gradually reduced. The commonly used organic electrolyte has poor conductivity and neutral pH value, so that the desorption rate of organic matters in the activated carbon is low. Therefore, the ethylene carbonate is used as the electrolyte, and the trihydroxymethyl aminomethane, the disodium hydrogen phosphate, the sodium hydroxide and the triethanolamine are added to improve the pH value and the conductivity of the electrolyte, and at the same time, a buffer system is formed to keep the electrolysis process in an alkaline environment, so that the pyrolysis reaction in the electrolysis process is effectively reduced, and the recovery efficiency of the activated carbon is improved.

[0022] Because the electrolyte used in the present application is a special organic-inorganic mixed alkali electrolyte, the electrode is easily aged, especially the metal electrode, so that the titanium-copper composite electric negative plate is placed in the mixed liquid of the ethylene carbonate, the stearic acid and the tetraethyl orthosilicate under high temperature conditions before use, and then an alkali-resistant film is formed on the surface of the titanium-copper composite electric negative plate after cooling to room temperature, and the porous silicon dioxide is formed in the gap of the film to maintain the conductivity of the titanium-copper composite electric negative plate. The corrosion resistance of the titanium-copper composite electric negative plate is improved, and at the same time, the production rate of hydrogen ions in the cathode is slowed down, and the pH value of the electrolyte system is further slowed down. The modified metal electric negative plate is used in cooperation with the electrolyte, so that the organic matters adsorbed in the waste activated carbon can be efficiently removed, the consumption rate of the activated carbon is reduced, and the utilization rate of the waste activated carbon is improved. The activated carbon after desorption of the metal ions and the organic matters is calcined and activated under nitrogen protection to obtain the recovered activated carbon, and the loss rate is low and the regeneration efficiency is high in the process.

[0023] Advantages:

[0024] 1、The waste activated carbon is recovered by metal ions and metal ion desorption after high temperature activation, the whole process has low activated carbon loss rate, high regeneration efficiency, and the recovered activated carbon has high activity.

[0025] 2、The buffer system is formed by trihydroxymethyl aminomethane, disodium hydrogen phosphate, sodium hydroxide and triethanolamine in ethylene carbonate, the electrolyte conductivity is improved, the electrolysis system is effectively controlled in an alkaline environment, the desorption of organic matter is accelerated, the desorption efficiency is improved, and the regeneration efficiency of activated carbon is improved.

[0026] 3、The modified metal electric negative plate and graphite electric positive plate can ensure the desorption efficiency of organic matter while the electrolyte corrosion is small, and can be used continuously, so that the regeneration efficiency in the activated carbon recovery process is ensured. DETAILED DESCRIPTION

[0027] The application will be described in detail below with reference to the examples:

[0028] The waste activated carbon used in the application is waste activated carbon produced after industrial dye wastewater treatment.

[0029] I. Preparation of electrolyte

[0030] The application provides a preparation method of electrolyte, and the specific amount of raw materials for preparing the electrolyte is shown in Table 1:

[0031] Table 1

[0032]

[0033] The preparation steps of each example and comparative example are as follows:

[0034] Example 1:

[0035] The ethylene carbonate and triethanolamine were weighed and mixed uniformly, heated to 70℃ and stirred for 15min, then the trihydroxymethyl aminomethane, disodium hydrogen phosphate and sodium hydroxide were added in sequence while stirring, and the mixture was cooled to room temperature after complete dissolution to obtain the electrolyte.

[0036] Example 2:

[0037] The ethylene carbonate and triethanolamine were weighed and mixed uniformly, heated to 80℃ and stirred for 10min, then the trihydroxymethyl aminomethane, disodium hydrogen phosphate and sodium hydroxide were added in sequence while stirring, and the mixture was cooled to room temperature after complete dissolution to obtain the electrolyte.

[0038] Example 3:

[0039] Take ethylene carbonate and triethanolamine respectively, mix uniformly, heat to 60℃, stir for 20min, then continue to stir at constant temperature, and then add trihydroxymethyl aminomethane, disodium hydrogen phosphate and sodium hydroxide in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0040] Comparative example 1:

[0041] Take ethylene carbonate and triethanolamine respectively, mix uniformly, heat to 70℃, stir for 15min, then continue to stir at constant temperature, and then add trihydroxymethyl aminomethane, disodium hydrogen phosphate and sodium hydroxide in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0042] Comparative example 2:

[0043] Take ethylene carbonate and triethanolamine respectively, mix uniformly, heat to 70℃, stir for 15min, then continue to stir at constant temperature, and then add disodium hydrogen phosphate and sodium hydroxide in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0044] Comparative example 3:

[0045] Take ethylene carbonate and triethanolamine respectively, mix uniformly, heat to 70℃, stir for 15min, then continue to stir at constant temperature, and then add trihydroxymethyl aminomethane and sodium hydroxide in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0046] Comparative example 4:

[0047] Take ethylene carbonate, heat to 70℃, stir for 15min, then continue to stir at constant temperature, and then add trihydroxymethyl aminomethane, disodium hydrogen phosphate and sodium hydroxide in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0048] Comparative example 5:

[0049] Take triethanolamine, heat to 70℃, stir for 15min, then continue to stir at constant temperature, and then add trihydroxymethyl aminomethane and disodium hydrogen phosphate in sequence until completely dissolved, cool to room temperature to obtain electrolyte.

[0050] II. Preparation of modified titanium-copper composite electric negative plate

[0051] The application provides a preparation method of a modified titanium-copper composite electric negative plate, and specific dosages of raw materials for preparing the modified titanium-copper composite electric negative plate are shown in Table 2.

[0052] Table 2

[0053]

[0054]

[0055] Preparation steps of each example and comparative example are as follows:

[0056] Example 4:

[0057] The ethylene carbonate and stearic acid were measured and mixed, and then heated to 110°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 4s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0058] Example 5:

[0059] The ethylene carbonate and stearic acid were measured and mixed, and then heated to 100°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 5s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0060] Example 6:

[0061] The ethylene carbonate and stearic acid were measured and mixed, and then heated to 20°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 3s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0062] Comparative Example 6:

[0063] The ethylene carbonate and stearic acid were measured and mixed, and then heated to 20°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 3s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0064] Comparative Example 7:

[0065] The stearic acid was measured and heated to 110°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 4s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0066] Comparative Example 8:

[0067] The ethylene carbonate was measured and heated to 110°C. Tetraethyl orthosilicate was added while stirring, and the mixture was uniformly mixed. The titanium-copper composite cathode plate was immersed for 4s and then quickly removed. After drying, the modified metal cathode plate was obtained.

[0068] III. Recycling of waste activated carbon

[0069] The specific steps are as follows:

[0070] Example 7:

[0071] In this example, the electrolyte prepared in Example 1 and the titanium-copper composite cathode plate prepared in Example 4 were used for the experiment.

[0072] S1. Metal ion desorption: 5 kg of waste activated carbon after water purification treatment was poured into the reaction tank, 6 L of dilute hydrochloric acid with pH = 5.5 was added, stirring for 12 min, and then standing and removing the supernatant to obtain metal ion-removed activated carbon;

[0073] S2. Organic matter desorption: The metal ion-removed activated carbon was added into the electrolytic cell, 8 L of electrolyte was poured, the modified titanium-copper composite electric negative plate and the graphite electric positive plate were inserted, 1 A of direct current was introduced for 25 min, and then standing and removing the supernatant to obtain the recovered pre-product;

[0074] S3. Activation of the recovered pre-product: The recovered pre-product was calcined at 350℃ for 35 min under nitrogen protection to obtain the recovered activated carbon.

[0075] Experiment one: waste activated carbon recovery and regeneration efficiency experiment

[0076] The specific selection of the electrolyte and the modified metal electric negative plate in the electrolytic cell is as follows:

[0077] Experimental group:

[0078] The electrolyte was the electrolyte prepared in Example 1, and the modified metal electric negative plate was the modified metal electric negative plate prepared in Example 4.

[0079] Control group:

[0080] Control group 1-5, the electrolyte was the electrolyte prepared in Comparative Examples 1-5, and the modified metal electric negative plate was the modified metal electric negative plate prepared in Example 4.

[0081] Control group 6-8, the electrolyte was the electrolyte prepared in Example 1, and the modified metal electric negative plate was the modified metal electric negative plate prepared in Comparative Examples 6-8.

[0082] The electrolyte and the modified metal electric negative plate prepared in the experimental group and control groups 1-8 were used to recover and regenerate the waste activated carbon according to the method of Example 7. The weight of the recovered activated carbon was recorded as the recovery mass, and the recovery rate was calculated;

[0083] The recovery rate = (recovery mass / 5 kg) x 100%; the results are shown in Table 3.

[0084] Table 3

[0085]

[0086]

[0087] Experiment two: activated carbon adsorption experiment after recovery

[0088] Take 10 mg of activated carbon recovered in the experimental group and commercially available activated carbon powder, respectively, and add them to 50 mL of rhodamine B solution with an initial concentration of 500 mg / L. Stir for 2 h to reach the adsorption saturation state, then centrifugal separation, and analyze the concentration of the adsorbed rhodamine B solution by ultraviolet spectrophotometry, which is recorded as the post-adsorption concentration. Calculate the adsorption rate as follows:

[0089] Adsorption rate = ((initial concentration - post-adsorption concentration) / initial concentration) x 100%.

[0090] Table 4

[0091] concentration after adsorption adsorption rate recovered activated carbon 5.18 98.96 purchased activated carbon powder 4.38 99.12

[0092] Data analysis:

[0093] As can be seen from the data in Table 3, the recovered mass of 5 kg of waste activated carbon can reach 4.67 kg, and the recovery rate can reach 93.4% within the scope of the present application. As can be seen from the data in Table 4, the adsorption rate of the recovered activated carbon for rhodamine B can reach 98.96%, which is comparable to the adsorption capacity of the purchased activated carbon powder.

[0094] Comparing the results of the experimental group and the control groups 1-5 in Table 3, it can be seen that the electrolyte prepared without adding Tris, disodium hydrogen phosphate, sodium hydroxide, ethylene carbonate, and triethanolamine in the control groups 1-5 is used for recovering waste activated carbon, and the efficiency of waste activated carbon recovery and regeneration is reduced. This is mainly because Tris, disodium hydrogen phosphate, sodium hydroxide, ethylene carbonate, and triethanolamine together form a stable alkaline environment, and the lack of one of them will cause the pH value to drop or not form a buffer system, resulting in a decrease in the recovery rate of waste activated carbon.

[0095] Comparing the results of the experimental group and the control groups 6-8 in Table 3, it can be seen that the modified titanium-copper composite cathode prepared without adding tetraethyl orthosilicate, ethylene carbonate, and stearic acid in the control groups 6-8 is used for recovering waste activated carbon, and the efficiency of waste activated carbon recovery and regeneration is reduced. This is mainly because the prepared electrolyte is a special organic-inorganic mixed alkaline electrolyte, which can easily cause the electrode to age prematurely, especially the metal electrode. Therefore, a layer of alkali-resistant film needs to be prepared and attached to the surface of the titanium-copper composite cathode, but the absence of tetraethyl orthosilicate, ethylene carbonate, and stearic acid will affect the formation of the alkali-resistant film, causing the titanium-copper composite cathode to age prematurely, and thus affecting the efficiency of waste activated carbon recovery and reuse.

[0096] The pH value of the configured electrolyte is stable and unchanged in the waste activated carbon recovery process, and an alkaline environment is maintained, thereby improving the recovery efficiency of the waste activated carbon. The corrosion resistance of the modified metal electric negative plate is effectively improved compared with the titanium-copper composite electric negative plate, and the electrolyte is synergistically combined to efficiently remove the organic matter adsorbed in the waste activated carbon, thereby improving the utilization rate of the waste activated carbon and protecting the titanium-copper composite electric negative plate from premature aging. The activated carbon after desorption of metal ions and organic matter is calcined and activated under nitrogen protection to obtain the recovered activated carbon, which has an adsorption performance equivalent to that of the high-efficiency activated carbon in life, and has a low loss rate and a high regeneration efficiency in the process.

[0097] The above examples are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present application, and all should be covered in the scope of the claims of the present application. The technical, shape and structure parts not described in detail in the present application are well-known technologies.

Claims

1. A method for recycling and reusing waste activated carbon after water purification treatment, characterized in that, The specific method for recycling and reusing waste activated carbon after water purification treatment is as follows: S1. Metal ion desorption: Pour the waste activated carbon into the reaction tank, add acidic washing solution and stir for 10-15 minutes. After standing and separating the layers, remove the supernatant. Then add alkaline washing solution and continue stirring for 5-10 minutes. After standing and separating the layers, remove the supernatant to obtain metal ion-removed activated carbon. S2. Desorption of organic matter: Add metal ion-removing activated carbon to the electrolytic cell, pass in the electrolyte, insert the electrode plate and pass in direct current for 20-30 minutes, then take out the activated carbon, dry it to obtain the recovery pre-product; S3. Activation of recovered preproducts: The recovered preproducts are calcined at 300-400℃ for 30-40 min under nitrogen protection to obtain recovered activated carbon; The raw materials for preparing the electrolyte in step S2 include: tris(hydroxymethyl)aminomethane, ethylene carbonate, triethanolamine, disodium hydrogen phosphate, and sodium hydroxide. The electrode plate in step S2 includes a modified titanium-copper composite cathode plate and a graphite anode plate. The raw materials for preparing the modified titanium-copper composite electrode include: titanium-copper composite electrode, tetraethyl orthosilicate, ethylene carbonate, and stearic acid.

2. The method for recycling and reusing waste activated carbon after water purification treatment according to claim 1, characterized in that, The waste activated carbon in step S1 is waste activated carbon generated after the treatment of industrial dye wastewater.

3. The method for recycling and reusing waste activated carbon after water purification treatment according to claim 1, characterized in that, In step S1, the acidic washing solution is dilute hydrochloric acid with a pH of 5-6, and the alkaline washing solution is sodium hydroxide solution with a pH of 11-12.

4. The method for recycling and reusing waste activated carbon after water purification treatment according to claim 3, characterized in that, The electrolyte is prepared as follows: Ethylene carbonate and triethanolamine are mixed evenly, heated to 60-80℃ and stirred for 10-20 minutes, then kept at a constant temperature. While stirring, tris(hydroxymethyl)aminomethane, disodium hydrogen phosphate and sodium hydroxide are added in sequence until fully dissolved. The mixture is then cooled to room temperature to obtain the electrolyte.

5. A method for recycling and reusing waste activated carbon after water purification treatment according to claim 4, characterized in that, The mass-to-volume ratio of the tris(hydroxymethyl)aminomethane, disodium hydrogen phosphate, sodium hydroxide, ethylene carbonate, and triethanolamine is (1-3) g: (2-3) g: (1-2) g: (10-12) L: (0.8-1.2) L.

6. The method for recycling and reusing waste activated carbon after water purification treatment according to claim 5, characterized in that, The preparation method of the modified titanium-copper composite electrode is as follows: Ethylene carbonate and stearic acid are mixed evenly, and after heating to 100-120℃, ethyl orthosilicate is added while hot. After stirring and mixing evenly, the titanium-copper composite electrode is immersed for 3-5 seconds and then quickly removed and dried to obtain the modified titanium-copper composite electrode.

7. A method for recycling and reusing waste activated carbon after water purification treatment according to claim 6, characterized in that, The volume ratio of the tetraethyl orthosilicate, ethylene carbonate and stearic acid is (1-2) L: (8-12) L: (1-2) L.

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