Preparation method of high gold adsorption capacity activated carbon, and product and application thereof

Abstract

The application discloses a preparation method of high gold adsorption capacity activated carbon and application of the activated carbon, and belongs to the technical field of activated carbon preparation. The method uses shell powder as raw material, impregnates the shell powder with an activating agent, heats and activates the shell powder in a pressurized protective atmosphere, and then performs acid pickling, water washing, drying and kneading forming to obtain the activated carbon. In the activation stage, the pressurized protective atmosphere is used to improve the gas phase partial pressure and diffusion driving force of pyrolysis small molecule volatile components and other self-activating agents, promote the deep penetration of the self-activating agents from the surface layer of particles to the inside, eliminate the defects of uneven activation inside and outside, delay the thermal collapse of micropore walls, and build a uniform and connected multi-level pore structure. Meanwhile, the method inhibits the escape of pyrolysis volatile components, enables active oxygen-containing intermediates to continuously participate in in-situ surface oxidation modification, and directionally enriches polar oxygen-containing functional groups. The saturated adsorption capacity of the activated carbon prepared by the method to gold cyanide complexes can reach more than 700 mg / g, is significantly better than that of a product activated under normal pressure, and has a wide application prospect in the field of gold hydrometallurgy.

Description

Technical Field

[0001] This invention belongs to the field of activated carbon preparation and precious metal recycling technology, specifically relating to an activated carbon with high gold adsorption capacity and its preparation method, as well as the application of the activated carbon in gold adsorption. Background Technology

[0002] Activated carbon, due to its high specific surface area, well-developed pore structure, and abundant surface functional groups, is widely used as an adsorbent in the hydrometallurgical process for gold, especially in carbon-in-pulp and carbon-leaching processes, for the efficient adsorption of gold-cyanide complexes in solutions. Traditional activated carbon is mostly prepared from coconut shells, coal, etc., but these resources are costly and have long or non-renewable regeneration cycles, necessitating the search for alternative raw materials. Fruit shells, as a major byproduct of agricultural product processing, have a huge annual output and high lignin content, making them a potential high-quality precursor for activated carbon.

[0003] In existing technologies, chemical activation methods mainly include two steps: carbonization and activation. The activation step is crucial in determining the pore structure of activated carbon, and potassium hydroxide (KOH) is often used as the activating agent, with high-temperature treatment under atmospheric pressure and inert gas protection. However, during atmospheric pressure activation, the gas phase partial pressure of the small volatile molecules from the pyrolysis of the raw material is low, and the diffusion driving force is insufficient. This causes the reaction to occur only on the surface of the carbon particles, making it difficult to penetrate deep into the internal pores. This results in non-uniform defects such as excessive surface etching and insufficient internal activation, accompanied by poor pore connectivity and low pore utilization, thus limiting the adsorption capacity of activated carbon for gold cyanide complexes. Therefore, developing a method to control the uniformity of the pore structure of activated carbon and prepare activated carbon with high gold adsorption capacity using fruit shells has significant industrial value. Summary of the Invention

[0004] To address the shortcomings of the prior art, this invention provides a method for preparing activated carbon with high gold adsorption capacity using fruit shells as raw materials. The method achieves regulation of the pore structure of activated carbon through high-pressure activation, thereby enhancing its adsorption capacity for gold cyanide complexes.

[0005] To achieve the above objectives, the technical solution of this invention is as follows: A method for preparing activated carbon with high gold absorption capacity includes the following steps: S1, mix and impregnate the fruit shell powder with the activator according to the mass ratio, stir thoroughly and then dry to obtain the activated precursor; S2, The activated precursor obtained in step S1 is placed in a high-pressure reactor, heated to the activation temperature under a pressurized protective atmosphere and kept at that temperature to obtain the activated product; S3. The activated product obtained in step S2 is washed sequentially with dilute acid and deionized water until the filtrate is neutral. After drying, it is kneaded with a binder to form a high gold absorption capacity activated carbon.

[0006] Preferably, in step S1, the fruit shell powder is obtained by washing, drying, crushing and sieving fruit shells, and the particle size of the fruit shell powder is less than 0.25 mm. The fruit shell is at least one of peanut shells, almond shells, camellia shells, sunflower seed shells, pistachio shells and hazelnut shells.

[0007] Preferably, in step S1, the activator is at least one of potassium carbonate, potassium hydroxide, potassium citrate, and potassium oxalate, and the mass ratio of the activator to the fruit shell powder is (2-5):1.

[0008] Preferably, in step S1, the stirring time is 1 to 3 hours, the drying temperature is 100 to 140°C, and the drying time is 12 to 24 hours.

[0009] Preferably, in step S2, the protective atmosphere is at least one of nitrogen, argon, and helium, with a pressure of 2 to 8 bar, the activation temperature is 700 to 1000°C, the heating rate is 5 to 15°C / min, and the holding time is 1 to 2 hours.

[0010] Preferably, in step S3, the dilute acid is any one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid, with a concentration of 1 to 5 mol / L, the drying temperature is 60 to 120°C, and the drying time is 12 to 24 hours.

[0011] Preferably, in step S3, the kneading pressure is 15-40 MPa and the kneading time is 0.5-2 h.

[0012] The present invention also provides activated carbon with high gold absorption capacity prepared by the above preparation method.

[0013] Preferably, the high gold-absorbing activated carbon is effective against the gold-cyanide complex Au(CN)2. - The saturated adsorption capacity is not less than 700 mg / g.

[0014] The present invention also provides the application of the above-mentioned high gold adsorption capacity activated carbon in the adsorption and recovery of gold from gold-containing cyanide solutions.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By using a pressurized protective atmosphere (such as nitrogen) during the activation stage, this invention effectively enhances the gas phase partial pressure and molecular diffusion driving force of self-activating agents such as small molecule volatiles from pyrolysis of fruit shells, promoting their deep penetration from the surface of carbon particles into the internal pores. This eliminates the non-uniform defects of excessive surface etching and insufficient internal activation present in atmospheric pressure activation, making the pores of activated carbon uniform inside and out, significantly improving the pore connectivity, greatly increasing the pore utilization rate, delaying the thermal collapse of the micropore wall at high temperature, stably generating a large number of effective micropores with concentrated pore size, and promoting the orderly growth of micropores and secondary mesopores, constructing a multi-level pore structure with distinct layers and excellent connectivity, greatly improving the pore utilization rate and adsorption mass transfer efficiency; inhibiting the rapid escape of pyrolysis small molecule volatiles, allowing active oxygen-containing intermediates in the system to continuously participate in the in-situ surface oxidation modification, and directionally enriching polar oxygen-containing functional groups without destroying the pore structure; (2) The activator of the present invention is a composite activator. The multi-component potassium salt undergoes stepwise pyrolysis and stepwise reaction, which can continuously release oxygen-containing active gaseous intermediates and fully react with unsaturated carbon sites on the carbon matrix surface. Compared with a single activation system, it can significantly increase the total content of multiple oxygen-containing functional groups such as hydroxyl, carboxyl, carbonyl, and lactone groups on the activated carbon surface, thereby controlling the total amount of oxygen-containing functional groups on the surface and the ratio of carboxyl to phenolic hydroxyl groups. (3) By adjusting the amount of activator and the activation temperature, the strong activating component can deeply etch the carbon matrix, generating abundant initial micropore nuclei inside the carbon skeleton, which greatly increases the specific surface area and total micropore volume of activated carbon; the mild activating component can moderately buffer the excessive etching effect of strong potassium salt, inhibit the collapse of micropore walls and disordered expansion of macropores, and induce some micropores to expand and connect, significantly improving the pore order and pore volume utilization, thereby synergistically controlling the specific surface area and mesopore rate of activated carbon. (4) By systematically adjusting the multidimensional variables of “activator type-dosage-temperature-pressure”, the present invention can synergistically regulate the pore structure (mesopore / micropore ratio), pore size distribution (concentrated in 1-5 nm) and surface properties (oxygen-containing functional group type and quantity) of activated carbon, thus overcoming the limitations of single index optimization; and by utilizing low-cost, renewable fruit shell waste, resource utilization can be achieved, thereby reducing the production cost of activated carbon. (5) The saturated adsorption capacity of the coconut shell-based activated carbon prepared by the method of the present invention for gold cyanide complex can reach more than 700 mg / g. The optimized activated carbon has well-developed mesopores, which is beneficial to [Au(CN)2] - It diffuses rapidly and is rich in polar functional groups such as carboxyl groups on its surface, which enhances the electrostatic adsorption of anionic gold cyanide complexes. Its gold adsorption capacity is 30%-50% higher than that of commercially available coconut shell activated carbon. Attached Figure Description

[0016] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0017] Figure 1 This is a schematic flowchart of the preparation method of the present invention; Figure 2 This is a morphological image of Embodiment 1 of the present invention before gold absorption; Figure 3 This is a morphological image of Embodiment 1 of the present invention before gold absorption. Detailed Implementation

[0018] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0019] The protective atmosphere gas used in this invention is at least one of nitrogen, argon, and helium, and nitrogen is used as an example in the following embodiments; the dilute acid used for pickling in this invention can be at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid, and hydrochloric acid is used as an example in the following embodiments.

[0020] Example 1

[0021] This embodiment provides a method for preparing gold-absorbing activated carbon, including the following steps: 10 g of peanut shells were crushed and sieved to below 0.25 mm, then soaked in an alkaline solution of 20 g potassium hydroxide and 10 g potassium carbonate for 2 h. After drying at 110 ℃ for 12 h, the shells were placed in a nitrogen atmosphere at 7 bar and heated from room temperature to 800 ℃ at a rate of 10 ℃ / min for 1 h. The shells were then washed with 3 M hydrochloric acid and water until neutral. After solid-liquid separation, the shells were transferred to a dry place at 100 ℃ for 20 h and then kneaded at 30 MPa for 1 h to obtain gold-absorbing activated carbon.

[0022] Example 2

[0023] This embodiment provides a method for preparing gold-absorbing activated carbon, including the following steps: 10 g of camellia shells were crushed and sieved to below 0.15 mm, then soaked in an alkaline solution of 10 g potassium hydroxide and 30 g potassium citrate for 1 h. After drying at 120 ℃ for 16 h, the shells were placed in a nitrogen atmosphere at 2 bar and heated from room temperature to 900 ℃ at a rate of 5 ℃ / min for 1.5 h. The shells were then washed with 2 M hydrochloric acid and water until neutral. After solid-liquid separation, the shells were transferred to a dryer at 120 ℃ for 15 h and then kneaded at 25 MPa for 1.5 h to obtain gold-absorbing activated carbon.

[0024] Example 3

[0025] This embodiment provides a method for preparing gold-absorbing activated carbon, including the following steps: 10 g of pistachio shells were crushed and sieved to below 0.20 mm, then soaked in an alkaline solution of 15 g potassium carbonate and 10 g potassium oxalate for 1.5 h. After drying at 140 ℃ for 14 h, the shells were placed in a nitrogen atmosphere at 5 bar and heated from room temperature to 1000 ℃ at a rate of 15 ℃ / min for 2 h. After washing with 4 M hydrochloric acid and water until neutral, the shells were separated into solid and liquid phases, transferred to 80 ℃ for drying for 24 h, and then kneaded at 20 MPa for 2 h to obtain gold-absorbing activated carbon.

[0026] Example 4

[0027] This embodiment provides a method for preparing gold-absorbing activated carbon. The difference between this method and Example 1 is that the amount of activator added is adjusted so that the mass ratio of activator to peanut shell powder is 1:1.

[0028] Example 5

[0029] This embodiment provides a method for preparing gold-absorbing activated carbon. The difference between this method and Example 1 is that the amount of activator added is adjusted so that the mass ratio of activator to peanut shell powder is 7:1.

[0030] Example 6

[0031] This embodiment provides a method for preparing gold-absorbing activated carbon. The only difference between this method and that of Example 1 is that the activation temperature is adjusted to 500 °C.

[0032] Example 7

[0033] This embodiment provides a method for preparing gold-absorbing activated carbon. The only difference between this method and that of Example 1 is that the activation temperature is adjusted to 1200 °C.

[0034] Example 8

[0035] This embodiment provides a method for preparing gold-absorbing activated carbon. The only difference between this method and that of Example 1 is that the nitrogen pressure is adjusted to atmospheric pressure.

[0036] Example 9

[0037] This embodiment provides a method for preparing gold-absorbing activated carbon. The only difference between this method and Example 1 is that the nitrogen pressure is adjusted to 10 bar.

[0038] Comparative Example 1 Commercially available coconut shell activated carbon.

[0039] Comparative Example 2 Commercially available coal-based activated carbon.

[0040] Examples 1-9 and Comparative Examples 1-2 were tested for their gold adsorption performance. Their specific surface area and micro-mesopore ratio were tested by nitrogen adsorption, and their surface oxygen-containing functional groups were tested by Boehm titration. The experimental results are shown in Table 1.

[0041] Table 1 Experimental Results

[0042] The following points can be observed from the data in Table 1: (1) As can be seen from the data in 1-3, under better conditions, the preparation method provided by the present invention can obtain gold-adsorbing porous carbon with rich pore structure, suitable micro-mesopore ratio and more oxygen-containing functional groups. The gold adsorption capacity can reach more than 755 mg / g, which has good adsorption performance.

[0043] (2) A comprehensive comparison of the data from Example 1 and Examples 4-5 shows that the only difference between Example 4-5 and Example 1 is that the amount of activator added is not within the preferred range of the present invention. The gold adsorption capacity in Example 1 is significantly better than that in Example 4-5. Therefore, it can be seen that the present invention can further control the gold adsorption capacity of gold-absorbing activated carbon by preferably controlling the amount of activator added.

[0044] (3) A comprehensive comparison of the data from Example 1 and Example 6-7 shows that the only difference between Example 6-7 and Example 1 is that the activation temperature is not within the preferred range of the present invention. The gold adsorption capacity in Example 1 is significantly better than that in Example 6-7. Therefore, it can be seen that the present invention can further control the gold adsorption capacity of the gold-adsorbing activated carbon by controlling the activation temperature.

[0045] (4) A comprehensive comparison of the data from Example 1 and Examples 8-9 shows that the only difference between Examples 8-9 and Example 1 is that the activation pressure (nitrogen pressure) is not within the preferred range of the present invention. The gold adsorption capacity in Example 1 is significantly better than that in Examples 8-9. Therefore, it can be seen that the present invention preferably controls the activation pressure (nitrogen pressure) to further control the gold adsorption capacity of the gold-adsorbing activated carbon.

[0046] (5) A comprehensive comparison of the data from Example 1 and Comparative Examples 1-2 shows that the gold adsorption capacity in Example 1 is significantly better than that in Comparative Examples 1-2, indicating that the performance of the gold-adsorbing activated carbon obtained by the present invention is better than that of similar products on the market.

[0047] In summary, this invention combines pressure activation with potassium salt compounding processes. By systematically adjusting multiple variables such as "activator type, dosage, temperature, and pressure," it can synergistically control the pore structure (mesopore / micropore ratio), pore size distribution (concentrated in the 1-5 nm range), and surface properties (type and number of oxygen-containing functional groups) of activated carbon. This overcomes the limitations of optimizing a single indicator. The resulting activated carbon possesses a stable pore structure and suitable oxygen-containing functional groups, thus achieving a high gold adsorption capacity. The saturated adsorption capacity of the shell-based activated carbon prepared by this invention for gold cyanide complexes can reach over 700 mg / g. The optimized activated carbon has well-developed mesopores, which is beneficial for [Au(CN)2]. - It diffuses rapidly and is rich in polar functional groups such as carboxyl groups on its surface, which enhances the electrostatic adsorption of anionic gold cyanide complexes. Its gold adsorption capacity is 30%-50% higher than that of commercially available coconut shell activated carbon.

[0048] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing activated carbon with high gold absorption capacity, characterized in that, Includes the following steps: S1, mix and impregnate the fruit shell powder with the activator according to the mass ratio, stir thoroughly and then dry to obtain the activated precursor; S2, The activated precursor obtained in step S1 is placed in a high-pressure reactor, heated to the activation temperature under a pressurized protective atmosphere and kept at that temperature to obtain the activated product; S3. The activated product obtained in step S2 is washed sequentially with dilute acid and deionized water until the filtrate is neutral. After drying, it is kneaded with a binder to form a high gold absorption capacity activated carbon.

2. The method for preparing high gold absorption capacity activated carbon as described in claim 1, characterized in that: In step S1, the fruit shell powder is obtained by washing, drying, crushing and sieving fruit shells. The particle size of the fruit shell powder is less than 0.25 mm. The fruit shell is at least one of peanut shells, almond shells, camellia shells, sunflower seed shells, pistachio shells and hazelnut shells.

3. The method for preparing activated carbon with high gold absorption capacity as described in claim 1, characterized in that: In step S1, the activator is at least one of potassium carbonate, potassium hydroxide, potassium citrate, and potassium oxalate, and the mass ratio of the activator to the fruit shell powder is (2-5):

1.

4. The method for preparing activated carbon with high gold absorption capacity as described in claim 1, characterized in that: In step S1, the stirring time is 1 to 3 hours, the drying temperature is 100 to 140°C, and the drying time is 12 to 24 hours.

5. The method for preparing activated carbon with high gold absorption capacity as described in claim 1, characterized in that: In step S2, the protective atmosphere is at least one of nitrogen, argon, and helium, with a pressure of 2 to 8 bar, an activation temperature of 700 to 1000°C, a heating rate of 5 to 15°C / min, and a holding time of 1 to 2 hours.

6. The method for preparing activated carbon with high gold absorption capacity as described in claim 1, characterized in that: In step S3, the dilute acid is at least one of dilute hydrochloric acid, dilute sulfuric acid, and dilute nitric acid, with a concentration of 1–5 mol / L. The drying temperature is 60–120°C, and the drying time is 12–24 h.

7. The method for preparing activated carbon with high gold absorption capacity as described in claim 1, characterized in that: In step S3, the kneading pressure is 15-40 MPa and the kneading time is 0.5-2 h.

8. A high gold absorption capacity activated carbon, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 7.

9. The activated carbon with high gold absorption capacity as described in claim 8, characterized in that: The high gold absorption capacity activated carbon is effective against gold cyanide complex Au(CN)2. - The saturated adsorption capacity is not less than 700 mg / g.

10. The application of the high gold adsorption capacity activated carbon as described in claim 8 or 9 in the adsorption and recovery of gold from a gold-containing cyanide solution.

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