Spherical activated carbon and method for preparing spherical activated carbon using maackia seed

Abstract

The application discloses a kind of spherical activated carbon and the method for preparing spherical activated carbon using korean pine seed, which comprises the following steps: (1) vacuum heating treatment is carried out on korean pine seed at not higher than 300 DEG C, so as to remove light components in korean pine seed;(2) the sphere obtained in step (1) is treated at 300-325 DEG C under air atmosphere;(3) the sphere obtained in step (2) is carbonized under argon atmosphere;(4) the carbonized sphere obtained in step (3) is activated;(5) the activated sphere obtained in step (4) is cooled to room temperature under argon atmosphere, then washed and dried after mixing with dilute hydrochloric acid, so as to obtain spherical activated carbon. By using the method, spherical activated carbon with large diameter and large specific surface area can be prepared, and the method does not need spherical granulation process.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry, and particularly relates to spherical activated carbon and a method for preparing the spherical activated carbon by using Koelreuteria paniculata seeds. Background Art

[0002] Spherical activated carbon is a high-value-added activated carbon product, and its production steps mainly include: spherical granulation, high-temperature heat treatment and physical activation. At present, the spherical granulation processes used in the production of spherical activated carbon mainly include disc rolling granulation method and suspension granulation method. The disc rolling granulation method adopts a non-integrated granulation process and requires the use of a powder bonding process for granulation. Although large-diameter spherical activated carbon products can be prepared, the use of the bonding process makes the surface of the finished product rough and easy to fall off, which limits its application. The spheres produced by the suspension granulation method have a relatively smooth surface, but due to the application of the integrated granulation process, the internal structure of the spheres is relatively compact. During activation, it is not easy for the activator to enter the interior of the large-diameter spheres from the surface, thereby affecting the formation of pores inside the spheres, and then resulting in the large-diameter particles. The product has a small specific surface area and is difficult to meet the use requirements. Therefore, the spherical activated carbon products produced by the suspension granulation method generally do not exceed 2mm in diameter. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to propose a spherical activated carbon and a method for preparing spherical activated carbon using Koelreuteria paniculata seeds. This method can prepare spherical activated carbon with a large diameter and a large specific surface area, and the method does not require a spherical granulation process.

[0004] In one aspect of the present invention, a method for preparing spherical activated carbon using Koelreuteria paniculata seeds is provided. According to an embodiment of the present invention, the method comprises: (1) vacuum heating the Koelreuteria paniculata seeds at a temperature not higher than 300°C to remove light components in the Koelreuteria paniculata seeds; (2) treating the spheres obtained in step (1) at 300-325°C in an air atmosphere; (3) carbonizing the spheres obtained in step (2) in an argon atmosphere; (4) activating the carbonized spheres obtained in step (3); and (5) cooling the activated spheres obtained in step (4) to room temperature in an argon atmosphere, and then washing and drying the activated spheres obtained in step (4) to obtain spherical activated carbon.

[0005] In a second aspect of the present invention, the present invention provides a spherical activated carbon. According to an embodiment of the present invention, the spherical activated carbon is prepared by the above-mentioned method.

[0006] Preferably, in step (1), the absolute pressure of the vacuum heating treatment is 0.5-1.5 kPa, the heating rate is 1.5-2° C. / min, and the holding time is 1.5-2 h.

[0007] Preferably, in step (2), the heating rate is 0.5-1°C / min and the holding time is 1-2h.

[0008] Preferably, in step (3), the carbonization treatment comprises: heating from 325°C to 400°C at a heating rate of 0.5-1°C / min, then heating to 800-900°C at a heating rate of 5-10°C / min and keeping the temperature for 1-1.5h.

[0009] Preferably, in step (4), the activation treatment conditions include: cooling the carbonized spheres obtained in step (3) to 700-800° C., then keeping the temperature and introducing water vapor to react for 0.5-5 hours.

[0010] Preferably, in step (5), the mass concentration of the dilute hydrochloric acid is 18-19%.

[0011] Preferably, in step (5), the activated spheres and the dilute hydrochloric acid are mixed at a mass ratio of 1:(10-12).

[0012] Preferably, in step (5), the temperature of mixing the activated spheres and the dilute hydrochloric acid is 45-50°C.

[0013] Compared with the prior art, the method for preparing spherical activated carbon using Koelreuteria paniculata seeds of the present invention uses Koelreuteria paniculata seeds as raw materials for preparing spherical activated carbon, the average diameter of the Koelreuteria paniculata seeds is 4-6 mm, and the Koelreuteria paniculata seeds are vacuum-heated at no more than 300°C to remove light components in the Koelreuteria paniculata seeds, which can not only prevent the light components from overflowing and bursting the spheres in the subsequent process, but also avoid the combustion of the light components in the subsequent air treatment process, and then treat the spheres with the light components removed at 300-325°C in an air atmosphere, so that other components in the spheres are cross-linked, extending the molecular chain, thereby improving the high-temperature resistance of the spheres; then, the obtained spheres are carbonized in an argon atmosphere. During the carbonization process, high temperature promotes the reduction of structural defects of carbonaceous materials and the increase of molecular cross-linking, which is beneficial to the conversion of toxic organic matter in the sphere into non-toxic amorphous carbon material and the extension and growth of carbon-based pore walls. These pore walls form initial pores, which give the activator more opportunities to diffuse from the surface of the sphere into the interior of the sphere during the activation process, thereby achieving uniform activation and preventing the pore collapse or pore ablation caused by excessive activation in local areas, which may cause the sphere to crack easily. Finally, the activated sphere is cooled to room temperature in an argon atmosphere and then mixed with dilute hydrochloric acid for washing, which can effectively remove calcium and magnesium impurities. After drying, spherical activated carbon with a large diameter and high specific surface area can be obtained. DETAILED DESCRIPTION

[0014] The present invention will be further described in detail below with reference to the following examples. The following examples are merely illustrative and non-limiting, and the scope of protection of the present invention cannot be limited thereto.

[0015] In one aspect of the present invention, a method for preparing spherical activated carbon using Koelreuteria paniculata seeds is provided. According to an embodiment of the present invention, the method comprises:

[0016] S1: vacuum heat treatment of Koelreuteria paniculata seeds at a temperature not exceeding 300°C

[0017] Specifically, the present application selects Luan wood seeds as the raw material for preparing spherical activated carbon. The raw material itself has a spherical shape and does not require a spherical granulation process. The particle size is large (the average diameter is 4-6 mm, and the average diameter of each Luan wood seed can be understood as the average of the maximum diameter and the minimum diameter in the seed) and the structure is not compact (due to the needs of seed respiration and other functions, the seed itself has a tiny fluid flow channel), which makes it easy for the activator to diffuse into the interior; in addition, the surface of Luan wood seeds is smooth, the seed coat is hard, and it is not easy to crack when heated at high temperatures, but its own heat-resistant non-cracking temperature is about 300 ° C, and the carbonization temperature for producing spherical activated carbon is often high. At this carbonization temperature, the sphere will break, making it impossible to maintain a spherical shape. Therefore, the present application controls the Luan wood seeds to be vacuum heated at no more than 300 ° C, which can remove the light components in the Luan wood seeds, not only preventing the light components from overflowing and bursting the sphere in the subsequent process, but also avoiding the combustion of the light components in the subsequent air treatment process.

[0018] Furthermore, the vacuum heating treatment is performed under an absolute pressure of 0.5-1.5 kPa, a heating rate of 1.5-2°C / min, and a holding time of 1.5-2 hours. Thus, under these heating conditions, the removal rate of light components in the Koelreuteria seeds can be increased, thereby maintaining the spherical shape.

[0019] S2: Treat the spheres obtained in step S1 at 300-325°C in an air atmosphere.

[0020] In this step, the spheres obtained in step S1 are treated at 300-325° C. in an air atmosphere, so that other components in the spheres (remaining components after the light components are removed) are cross-linked, extending the molecular chains, thereby improving the high temperature resistance of the spheres.

[0021] Furthermore, during this process, the heating rate is 0.5-1°C / min and the holding time is 1-2 hours. Thus, adopting this heating rate and holding time allows the cross-linking reaction of other components to be relatively moderate and sufficient, thereby significantly improving the high-temperature resistance of the sphere.

[0022] S3: Carbonize the spheres obtained in step S2 under argon atmosphere

[0023] In this step, the obtained spheres are carbonized under an argon atmosphere. The high temperature during the carbonization process promotes the reduction of structural defects in the carbonaceous material and the increase of the degree of molecular cross-linking, which is beneficial to the conversion of toxic organic matter in the spheres into non-toxic amorphous carbon materials and the extension and growth of carbon-based pore walls. These pore walls form initial pores, which give the activator more opportunities to diffuse from the surface of the sphere into the interior of the sphere during the activation treatment, thereby achieving uniform activation and preventing the pore collapse or pore ablation caused by excessive activation at local locations, which may cause the spheres to crack easily.

[0024] Furthermore, the carbonization treatment includes: heating from 325°C to 400°C at a heating rate of 0.5-1°C / min, then heating to 800-900°C at 5-10°C / min and keeping warm for 1-1.5h. That is, the present application adopts low-temperature carbonization (325-400°C) and high-temperature carbonization process (800-900°C). The low-temperature carbonization process adopts a relatively low heating rate to further prevent the cracking of the sphere caused by excessive structural evolution (thermal polycondensation reaction, etc.), while the high temperature in the high-temperature carbonization process promotes the reduction of structural defects of the carbonaceous material and the increase of the degree of molecular cross-linking, which is conducive to the conversion of toxic organic matter in the sphere into non-toxic amorphous carbon material and the extension and growth of carbon-based pore walls. These pore walls form initial pores, so that the activator has more opportunities to diffuse from the surface of the sphere into the interior of the sphere during the activation process, thereby achieving uniform activation and preventing the pore collapse or pore ablation caused by excessive activation in local positions, which makes the sphere easy to crack.

[0025] S4: Activate the carbonized spheres obtained in step S3

[0026] In this step, the carbonized spheres are cooled to 700-800°C, then kept warm and steamed for 0.5-5 hours. During this stage, the steam diffuses to the surface and interior of the spheres. It also reacts with the carbon atoms in the spheres, generating gases like carbon monoxide and carbon dioxide. This creates carbon cavities within the spheres' carbonaceous structure, which then grow and develop, ultimately forming a rich, porous structure. This post-cooling reactivation process moderately reduces the reaction rate, allowing the steam more opportunities to diffuse into the spheres rather than being rapidly consumed upon reaching the surface, resulting in a low degree of activation within the spheres.

[0027] S5: Cool the activated spheres obtained in step S4 to room temperature in an argon atmosphere, then mix with dilute hydrochloric acid and wash and dry.

[0028] In this step, the activated spheres obtained above are mixed with dilute hydrochloric acid (mass concentration is 18-19%, the mass ratio of the activated spheres to the dilute hydrochloric acid is 1:10-12, and the temperature of the mixed material is controlled to be 45-50°C) to dissolve and remove carbonates such as calcium and magnesium in the activated spheres, and then filter. Thereafter, deionized water is used for multiple washing and filtration to remove residual hydrochloric acid and magnesium chloride, calcium chloride (generated by the reaction of calcium, magnesium and other carbonates with hydrochloric acid) and other substances. After washing until the system is neutral, it is filtered and finally dried to obtain spherical activated carbon.

[0029] Therefore, the method of the present invention can be used to prepare spherical activated carbon with a large diameter and a large specific surface area, and the method does not require a spherical granulation process.

[0030] In a second aspect of the present invention, the present invention provides a spherical activated carbon. According to an embodiment of the present invention, the spherical activated carbon is prepared by the above-mentioned method.

[0031] The present invention is described below with reference to specific examples. It should be noted that these examples are merely illustrative and should not limit the present invention in any way.

[0032] Example 1

[0033] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 2 °C / min and maintain for 2 h;

[0034] (2) introducing air into the tube furnace in step (1) at a temperature range of 300-325°C at a heating rate of 0.5°C / min and maintaining the temperature at 325°C for 1 hour;

[0035] (3) replacing the atmosphere in the tube furnace in step (2) with argon, then heating from 325°C to 400°C (heating rate 0.5°C / min), then heating to 900°C at a heating rate of 5°C / min and holding the temperature for 1 h;

[0036] (4) The tubular furnace in step (3) was naturally cooled to 800°C, and water vapor was introduced into the furnace for reaction for 0.5 h;

[0037] (5) The atmosphere in the tubular furnace in step (4) was replaced with argon, and after the temperature naturally dropped to room temperature, the activated Koelreuteria seeds were taken out, and then diluted hydrochloric acid (mass concentration 18-19%) 10 times the mass of the activated seeds was used to dissolve and remove carbonates such as calcium and magnesium at 50°C, and filtered. Thereafter, deionized water was used to wash and filter several times to remove residual hydrochloric acid and substances such as magnesium chloride and calcium chloride. After washing until the system was neutral, it was filtered and dried to obtain spherical activated carbon. The BET specific surface area of ​​the spherical activated carbon was 718m 2 / g, with an average diameter of 3.8-5.6mm.

[0038] Example 2

[0039] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 1.5 °C / min and maintain for 1.5 h;

[0040] (2) introducing air into the tube furnace in step (1) at a temperature range of 300-325°C at a heating rate of 0.75°C / min and maintaining the temperature at 325°C for 1.5 hours;

[0041] (3) replacing the atmosphere in the tube furnace in step (2) with argon, then heating from 325°C to 400°C (heating rate 0.5°C / min), then heating to 800°C at a heating rate of 7°C / min and holding the temperature for 1.5 h;

[0042] (4) The tube furnace in step (3) was naturally cooled to 700°C, water vapor was introduced into the furnace, and the reaction was carried out for 5 hours;

[0043] (5) The atmosphere in the tubular furnace in step (4) was replaced with argon, and after naturally cooling to room temperature, the activated Koelreuteria seeds were taken out, and then diluted hydrochloric acid (mass concentration 18-19%) 10 times the mass of the activated seeds was used to dissolve and remove carbonates such as calcium and magnesium at 50°C, and filtered. Thereafter, deionized water was used to wash and filter several times to remove residual hydrochloric acid and substances such as magnesium chloride and calcium chloride. After washing until the system was neutral, it was filtered and dried to obtain spherical activated carbon. The BET specific surface area of ​​the spherical activated carbon was 858m 2 / g, with an average diameter of 3.8-5.6mm.

[0044] Example 3

[0045] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 2 °C / min and maintain for 2 h;

[0046] (2) introducing air into the tube furnace in step (1) within a temperature range of 300-325°C at a heating rate of 1°C / min and maintaining the temperature at 325°C for 2 h;

[0047] (3) replacing the atmosphere in the tube furnace in step (2) with argon, then heating from 325°C to 400°C (heating rate 0.5°C / min), then heating to 850°C at a heating rate of 5°C / min and holding the temperature for 1 h;

[0048] (4) The tube furnace in step (3) was naturally cooled to 750°C, water vapor was introduced into the furnace, and the reaction was carried out for 3 hours;

[0049] (5) The atmosphere in the tubular furnace in step (4) was replaced with argon, and after the temperature naturally dropped to room temperature, the activated Koelreuteria seeds were taken out, and then diluted hydrochloric acid (mass concentration 18-19%) 12 times the mass of the activated seeds was used to dissolve and remove carbonates such as calcium and magnesium at 45°C, and filtered. Thereafter, deionized water was used to wash and filter several times to remove residual hydrochloric acid and substances such as magnesium chloride and calcium chloride. After washing until the system was neutral, it was filtered and dried to obtain spherical activated carbon. The BET specific surface area of ​​the spherical activated carbon was 773m 2 / g, with an average diameter of 3.8-5.6mm.

[0050] Example 4

[0051] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 1.5 °C / min and maintain for 1.5 h;

[0052] (2) introducing air into the tube furnace in step (1) at a temperature range of 300-325°C at a heating rate of 0.5°C / min and maintaining the temperature at 325°C for 2 h;

[0053] (3) replacing the atmosphere in the tube furnace in step (2) with argon, then heating from 325°C to 400°C (heating rate 1°C / min), then heating to 800°C at a heating rate of 10°C / min and holding the temperature for 1.5 h;

[0054] (4) The tube furnace in step (3) was naturally cooled to 750°C, and water vapor was introduced into the furnace for reaction for 3.5 hours;

[0055] (5) The atmosphere in the tubular furnace in step (4) was replaced with argon, and after the temperature naturally dropped to room temperature, the activated Koelreuteria seeds were taken out, and then diluted hydrochloric acid (mass concentration 18-19%) 10 times the mass of the activated seeds was used to dissolve and remove carbonates such as calcium and magnesium at 50°C, and filtered. Thereafter, deionized water was used to wash and filter several times to remove residual hydrochloric acid and substances such as magnesium chloride and calcium chloride. After washing until the system was neutral, it was filtered and dried to obtain spherical activated carbon. The BET specific surface area of ​​the spherical activated carbon was 823m 2 / g, with an average diameter of 3.8-5.6mm.

[0056] Example 5

[0057] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 2 °C / min and maintain for 2 h;

[0058] (2) introducing air into the tube furnace in step (1) at a temperature range of 300-325°C, heating at a rate of 1°C / min, and maintaining the temperature at 325°C for 1 hour;

[0059] (3) replacing the atmosphere in the tube furnace in step (2) with argon, then heating from 325°C to 400°C (heating rate 0.5°C / min), then heating to 900°C at a heating rate of 10°C / min and holding the temperature for 1 h;

[0060] (4) The tube furnace in step (3) was naturally cooled to 775°C, and water vapor was introduced into the furnace for reaction for 1 hour;

[0061] (5) The atmosphere in the tubular furnace in step (4) was replaced with argon, and after the temperature naturally dropped to room temperature, the activated Koelreuteria seeds were taken out, and then diluted hydrochloric acid (mass concentration 18-19%) 10 times the mass of the activated seeds was used to dissolve and remove carbonates such as calcium and magnesium at 50°C, and filtered. Thereafter, deionized water was used to wash and filter several times to remove residual hydrochloric acid and substances such as magnesium chloride and calcium chloride. After washing until the system was neutral, it was filtered and dried to obtain spherical activated carbon. The BET specific surface area of ​​the spherical activated carbon was 726m 2 / g, with an average diameter of 3.8-5.6mm.

[0062] Comparative Example 1

[0063] Koelreuteria paniculata seeds (average diameter 4-6 mm) were placed in a tube furnace, and air was introduced into the tube furnace. The temperature was raised from room temperature to 325°C at a rate of 0.75°C / min and maintained at 325°C for 1.5 h.

[0064] Because the Koelreuteria paniculata seeds were not vacuum-treated to remove light components before being placed in an air atmosphere in a tubular furnace, after the Koelreuteria paniculata seeds were heated to 300°C in the tubular furnace, the light components of the spheres began to overflow in large quantities, the internal pressure of the spheres increased, the spheres broke significantly, the spherical shape was difficult to maintain, and the spheres lost their value for further processing.

[0065] Comparative Example 2

[0066] (1) Koelreuteria paniculata seeds (average diameter 4-6 mm) were placed in a tube furnace, evacuated to an absolute pressure of 0.5-1.5 kPa, and heated from room temperature to 325 °C at a rate of 2 °C / min and maintained for 2 h;

[0067] (2) At a temperature of 325° C., air was introduced into the tube furnace in step (1), and the temperature was maintained at 325° C. for 1 hour;

[0068] (3) The atmosphere in the tube furnace in step (2) was replaced with argon, and then the temperature was increased from 325°C to 400°C (heating rate 0.5°C / min), and then the temperature was increased to 900°C at a heating rate of 5°C / min and kept constant for 1 h.

[0069] Since the processing temperature of the Koelreuteria paniculata seeds is too high in step (1), and there is no air treatment process from low temperature to high temperature in step (2), the air reacts quickly after reaching the surface of the sphere, and has little chance of diffusing into the interior of the sphere, resulting in insufficient cross-linking reaction inside the sphere and low high temperature resistance. In step (3), the sphere is obviously broken, the spherical shape is difficult to maintain, and it loses the value of further processing.

[0070] Comparative Example 3

[0071] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 2 °C / min and maintain for 2 h;

[0072] (2) The atmosphere in the tube furnace in step (1) was replaced with argon, and then the temperature was increased from 300°C to 400°C (heating rate 0.5°C / min), and then the temperature was increased to 900°C at a heating rate of 5°C / min and kept constant for 1 h.

[0073] Since the vacuum-treated Koelreuteria seeds were not subjected to air heat treatment before carbonization, the spheres had poor high-temperature resistance. Therefore, in step (2), the spheres were obviously broken, the spherical shape was difficult to maintain, and the spheres lost their value for further processing.

[0074] Comparative Example 4

[0075] (1) Place Koelreuteria paniculata seeds (average diameter 4-6 mm) in a tube furnace, evacuate to an absolute pressure of 0.5-1.5 kPa, and heat from room temperature to 300 °C at a rate of 2 °C / min and maintain for 2 h;

[0076] (2) In the temperature range of 300-350°C, air is introduced into the tubular furnace in step (1) at a heating rate of 0.5°C / min, and the temperature is maintained at 350°C for 1 hour.

[0077] Since the air treatment temperature in step (2) is higher than 325° C., the air not only causes a cross-linking reaction in the spheres, but also causes significant oxidation and ablation, resulting in a rough surface of the spheres and loss of further processing value.

[0078] Comparative Example 5

[0079] Koelreuteria seeds (average diameter of 4-6 mm) were placed in a tube furnace, and the atmosphere in the tube furnace was replaced with argon. The temperature was then raised from room temperature to 400°C (heating rate 0.5°C / min), and then raised to 900°C at a heating rate of 5°C / min and kept constant for 1 h.

[0080] Since the spheres have not undergone vacuum light component removal treatment and air heat treatment, they cannot withstand high-temperature heat treatment. Therefore, a large number of spheres are broken during the carbonization process, the spherical shape is difficult to maintain, and they lose the value of further processing.

[0081] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing spherical activated carbon using Koelreuteria paniculata seeds, characterized in that: include: (1) vacuum heating the Koelreuteria koelreuteria seeds at a temperature not higher than 300° C. to remove light components from the Koelreuteria koelreuteria seeds; (2) treating the spheres obtained in step (1) at 300-325° C. in an air atmosphere; (3) carbonizing the spheres obtained in step (2) under an argon atmosphere; (4) activating the carbonized spheres obtained in step (3); (5) cooling the activated spheres obtained in step (4) to room temperature in an argon atmosphere, then mixing with dilute hydrochloric acid, washing, and drying to obtain spherical activated carbon. Wherein, in step (2), the heating rate is 0.5-1°C / min, and the holding time is 1-2h. In step (3), the carbonization treatment includes: heating from 325°C to 400°C at a heating rate of 0.5-1°C / min, then heating to 800-900°C at a heating rate of 5-10°C / min and keeping the temperature for 1-1.5h.

2. The method according to claim 1, characterized in that In step (1), the absolute pressure of the vacuum heating treatment is 0.5-1.5 kPa, the heating rate is 1.5-2°C / min, and the holding time is 1.5-2 h.

3. The method according to claim 1, characterized in that In step (4), the activation treatment conditions include: cooling the carbonized spheres obtained in step (3) to 700-800° C., then keeping the temperature and introducing water vapor for reaction for 0.5-5 hours.

4. The method according to claim 1, wherein In step (5), the mass concentration of the dilute hydrochloric acid is 18-19%.

5. The method according to claim 1, wherein In step (5), the activated spheres and the dilute hydrochloric acid are mixed in a mass ratio of 1:(10-12).

6. The method according to claim 1, characterized in that In step (5), the activated spheres and the dilute hydrochloric acid are mixed at a temperature of 45-50°C.