Cobalt extraction bamboo activated carbon and preparation method thereof

Abstract

The application belongs to the field of adsorption materials, and particularly relates to a cobalt-extracting bamboo active carbon and a preparation method thereof. The method comprises the following steps: 1) mixing and grinding bamboo powder with an alkaline activator, and then performing alkaline thermal activation and surface oxidation functionalization treatment in a protective atmosphere to obtain activated carbon powder; 2) mixing bamboo powder with a calcium source and lignosulfonate, adding water to prepare a crude blank, crushing the crude blank to obtain bamboo coarse powder, mixing the bamboo coarse powder with the activated carbon powder, and adding water to prepare a composite blank; 3) immersing the composite blank in a phosphoric acid solution to perform immersion thermal activation and crushing to obtain activated particles, immersing the activated particles in an iron salt solution to perform metal doping treatment, and then calcining to obtain the cobalt-extracting bamboo active carbon. The application improves the adsorption capacity and adsorption stability of the bamboo active carbon through multi-effect synergistic effect, and simultaneously has a certain cobalt ion selective adsorption capacity, so that the bamboo active carbon can be more effectively used for the treatment of cobalt-containing wastewater and the enrichment and recovery of cobalt.

Description

Technical Field

[0001] This invention belongs to the field of adsorption materials, and particularly relates to a cobalt-extractable bamboo activated carbon and its preparation method. Background Technology

[0002] Activated carbon is a very common and widely used adsorbent and pollution treatment agent, with extensive applications in wastewater treatment and adsorption. However, although activated carbon generally has good adsorption capacity, it typically achieves physical adsorption of the substances to be adsorbed through its high specific surface area and well-developed pore structure, which leads to poor selectivity and poor adsorption stability.

[0003] Especially for cobalt, the adsorption capacity of common activated carbon is very limited, and its adsorption stability is poor. Other metal ions in the system to be adsorbed can easily interfere, resulting in poor adsorption and extraction efficiency for cobalt. While existing modified activated carbon, modified by physical and / or chemical methods, may achieve stronger adsorption effects and stability, its overall adsorption capacity is still relatively limited, and the regeneration of cobalt after adsorption is relatively difficult.

[0004] However, as a heavy metal pollutant and a potential radioactive pollutant (such as the isotope Co-60), cobalt typically requires more stringent treatment. Many industrial and medical wastewaters, such as industrial tracer wastewater and medical treatment wastewater, require priority treatment for cobalt extraction and adsorption to ensure the effective separation of potential radioactive pollutants. Therefore, developing activated carbon with selective cobalt adsorption capabilities is of extremely high industrial value. Summary of the Invention

[0005] To address the limitations of existing activated carbon in terms of adsorption capacity and stability, as well as the difficulty in effectively and selectively extracting and adsorbing cobalt, this invention provides a method for preparing cobalt-extracting bamboo-based activated carbon.

[0006] The main objective of this invention is to: 1. significantly improve the adsorption performance of bamboo activated carbon.

[0007] Second, it has the ability to selectively adsorb cobalt.

[0008] Third, it has regenerative capabilities.

[0009] To achieve the above objectives, the present invention adopts the following technical solution.

[0010] A method for preparing cobalt-extracted bamboo activated carbon, the method comprising: 1) mixing and grinding bamboo powder with an alkaline activator and then performing alkaline thermal activation in a protective atmosphere; after alkaline thermal activation, placing the mixture in an oxidizing solution for surface oxidation functionalization treatment to obtain activated carbon powder.

[0011] 2) Mix bamboo powder with calcium source and lignin sulfonate, add water to make slurry, press and dry to make rough blank, crush and pulverize the rough blank to obtain bamboo coarse powder, mix bamboo coarse powder with activated carbon powder, add water to make slurry, press and dry to obtain composite material.

[0012] 3) The composite material is impregnated in a phosphoric acid solution for impregnation and thermal activation, then crushed to obtain activated particles. The activated particles are placed in an iron salt solution for metal doping treatment, then filtered, dried and calcined to obtain cobalt-extracted bamboo activated carbon.

[0013] Preferably, the alkaline activator in step 1) is potassium hydroxide; the bamboo powder and alkaline activator in step 1) are mixed and ground in a mass ratio of 1:(3.5-4.5) to a mesh size ≥120 mesh, and then heated to 750-850 ℃ and kept at that temperature for 2-3 h in a protective atmosphere for alkaline thermal activation.

[0014] Preferably, the oxidizing solution in step 1) is a 3-5 mol / L nitric acid aqueous solution, and the amount of the nitric acid aqueous solution is (25-35) mL / g bamboo powder; the surface oxidation functionalization treatment in step 1) is carried out by stirring the reaction in a water bath at 70-90 ℃ for 3-5 h.

[0015] Preferably, the bamboo powder in step 2) is bamboo powder with a mesh size of 40-60; the calcium source in step 2) is calcium carbonate; the lignin sulfonate in step 2) is sodium lignin sulfonate with a medium molecular weight of 20,000-30,000; the bamboo powder, calcium source and lignin sulfonate in step 2) are mixed in a mass ratio of 100:(12-18):(8-10), and water is added to form a slurry with a solid content of 55-65 wt%, which is then pressed at 25-35 MPa and subsequently dried to obtain a rough blank.

[0016] Preferably, in step 3), the coarse blank is crushed and pulverized to obtain bamboo coarse powder with a particle size of 0.5 to 2.0 mm; in step 2), the bamboo coarse powder and activated carbon powder are mixed evenly at a mass ratio of 1:(0.25 to 0.35), water is added to form a slurry with a solid content of 60 to 70 wt%, and the slurry is pressed and molded under a pressure of 15 to 25 MPa and then dried to obtain a composite blank.

[0017] Preferably, the phosphoric acid solution in step 3) is a 35-45 wt% aqueous phosphoric acid solution; after the composite material in step 3) is completely immersed in the aqueous phosphoric acid solution, it is heated to 80 ℃ and kept at a constant temperature for 24 h, then filtered and immediately transferred to a protective atmosphere and heated to 490-520 ℃ for 1.5-2.5 h to complete the impregnation thermal activation; the crushing in step 3) is to crush the product after impregnation thermal activation into particles with a particle size of 1.0-3.0 mm to obtain activated particles.

[0018] Preferably, the iron salt solution in step 3) is an aqueous solution of iron salt with a ferric ion concentration of 0.18–0.25 mol / L; the ratio of the amount of activated particles to the iron salt solution in step 3) is (25–35) g activated particles: 100 mL iron salt solution.

[0019] Preferably, the metal doping treatment in step 3) involves adding the activated particles to an iron salt solution and then hot-stirring at 40–60 °C for 6–10 h; the calcination in step 3) involves calcining at 300–320 °C for 1.5–3.0 h in a protective atmosphere to obtain cobalt-extracted bamboo activated carbon.

[0020] A cobalt-extracting bamboo-based activated carbon, wherein the cobalt-extracting bamboo-based activated carbon has a multi-level pore structure and the ability to selectively adsorb cobalt ions, and is suitable for the treatment of acidic metal ion wastewater with a pH value of 3.5 to 5.5 or for use in industrial cobalt purification processes.

[0021] The technical solution of this invention essentially achieves specific and efficient adsorption of cobalt ions through the construction of multi-level micro-nano structures combined with the construction of multiple active sites to create a multi-effect synergistic effect.

[0022] One key aspect is the iron-induced formation of ferro-oxygen nanoclusters, specifically nanoclusters composed of multiple components such as phosphates, Fe2O3, Fe3O4, and FeOOH bonded to a carbon framework. These nanoclusters can induce specific complexation at the Co-Fe oxide interface. Generally, the adsorption affinity for metal ions follows the Irving-Williams sequence, meaning that among common interfering ions, zinc, copper, and nickel are adsorbed earlier than Co ions. This makes these interfering ions important components for achieving specific Co adsorption in this invention. The ferro-oxygen nanoclusters and phosphates constructed in this invention can first coordinate with Co ions through surface hydroxyl groups. Based on this coordination complexation, efficient redox-driven processes and the isomorphic effect of iron and cobalt enable better selective adsorption and fixation of cobalt, and partial conversion of divalent cobalt to trivalent cobalt, thereby achieving irreversible surface fixation and forming a cobalt oxide precipitate with a composite valence state. However, this process relies heavily on high-valence iron ions (ferric iron) and ferric hydroxide. Therefore, if the calcination temperature in step 3) is too high or the calcination time is too long, the adsorption capacity and adsorption stability of the activated carbon will decrease. At the same time, this process depends on the control of the pH value of the system. If the pH value is too low, the process will become more difficult. Firstly, the stability of trivalent cobalt will deteriorate, resulting in a decrease in fixation efficiency. Secondly, a low pH value will also lead to severe loss of ferric oxygen nanoclusters. Especially when the pH value is ≤2.0, the ferric oxygen nanoclusters will be dissolved and lost. But most importantly, under strongly acidic conditions, the adsorption of cobalt will compete with hydrogen ions under acidic conditions, which will lead to a sharp decrease in its adsorption capacity. In fact, if there are enough hydrogen ions, they will reverse the exchange and elute the already adsorbed cobalt ions. Therefore, the elution and regeneration process of activated carbon after adsorption in this invention is actually carried out under acidic conditions. On the other hand, although the technical solution of this invention has achieved the fixation of nanoclusters and phosphates through methods such as carbon framework fixation, irreversible adsorption capacity loss is easily generated in an excessively acidic environment, and the adsorption effect will also decrease significantly. However, according to market research, most cobalt-containing wastewater can still meet the optimal pH environment for the activated carbon of this invention, that is, the pH range of 3.5 to 5.5.

[0023] Secondly, this invention also forms a unique P-Co chelate bag by activating with phosphoric acid in conjunction with the micro-nano pore structure previously constructed. In step 3), this invention first performs phosphoric acid impregnation activation, which is not only for the subsequent construction of iron nanoclusters, but also to effectively introduce phosphoric acid groups and pyrophosphate groups on the carbon skeleton, enabling it to form multi-ring chelates with cobalt ions and achieve effective fixation of cobalt ions.

[0024] Most importantly, this invention achieves ion sieving through the hierarchical construction of micro- and nano-pores. For example, through the synergistic effect of alkaline activation in step 1) and phosphoric acid activation in step 3), this invention can construct narrow micropores with sieving function, which can effectively separate and reduce interference from larger diameter metal ions / hydrated ions, thereby achieving enhanced selectivity.

[0025] Therefore, in addition to the common dual adsorption mechanism of hydroxyl exchange adsorption and hydrogen ion exchange adsorption, the activated carbon of this invention also enhances the selectivity of cobalt ion adsorption through the redox-driven and sieve chelation effects of channels, nanoclusters and phosphates, enabling the activated carbon of this invention to more effectively achieve selective adsorption of cobalt ions.

[0026] To address this, the present invention first achieves the separate preparation of activated carbon powder through alkaline activation and surface oxidation treatment. This part serves two purposes: firstly, to construct hierarchical channels in conjunction with subsequent phosphoric acid activation; and secondly, to first construct a large cavity with a large specific surface area that can act as a "bag" to increase adsorption efficiency and adsorption capacity. Subsequently, the present invention introduces and effectively fixes calcium through calcium salt and lignin sulfonate in step 2), which forms the basis for subsequent carbon dioxide pore expansion and preferential site occupancy to enhance the fixation of iron ions through ion exchange. In the overall process of step 2, the coarse powder of the preform is actually used to construct a microscopic synergistic unit of short-range alternating adsorption-ion transport-ion fixation and storage by cooperating with activated carbon powder. During the phosphoric acid activation treatment, carbon dioxide is generated to form a pore expansion effect, and the carbon skeleton is stabilized during calcination. Finally, slow ion exchange conversion is achieved in the iron salt solution treatment to obtain the final product, cobalt-extractable bamboo activated carbon.

[0027] The beneficial effects of this invention are: this invention improves the adsorption capacity and adsorption stability of bamboo activated carbon through multi-effect synergy, and at the same time has a certain selective adsorption capacity for cobalt ions, which can be used more effectively for the treatment of cobalt-containing wastewater and the enrichment and recovery of cobalt. Attached Figure Description

[0028] Figure 1 Microscopic morphology characterization of the sample in Example 1 of this invention Figure 1 .

[0029] Figure 2 Microscopic morphology characterization of the sample in Example 1 of this invention Figure 2 . Detailed Implementation

[0030] The present invention will be further described clearly and in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0031] Unless otherwise specified, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

[0032] Unless otherwise specified, the bamboo powder used in the embodiments of this invention is all moso bamboo powder.

[0033] Example 1: A cobalt-extracted bamboo activated carbon, which is prepared by the following method: 1) Bamboo powder and potassium hydroxide are mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder is placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, the alkaline thermal activation product is placed in a 3.0 mol / L nitric acid aqueous solution at a ratio of 30 mL per 1 g of bamboo powder raw material, heated in an 80 ℃ water bath and stirred for 4 h, then filtered and dried at 60 ℃ to obtain activated carbon powder.

[0034] 2) Take bamboo powder, calcium carbonate and sodium lignosulfonate with a molecular weight of 22000 and mix them in a mass ratio of 100:15:8. Add water to make a slurry with a solid content of 60 wt%. Press the slurry at 30 MPa and dry it at 60 ℃ to obtain a rough blank. Crush the rough blank into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. Mix the bamboo coarse powder with activated carbon powder in a mass ratio of 1:0.3 and add water to make a slurry with a solid content of 65 wt%. Press the slurry at 20 MPa and dry it at 60 ℃ to obtain a composite blank.

[0035] 3) The composite material was completely immersed in a 40 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 300 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0036] Characterization and performance testing were performed on the cobalt-extracted bamboo activated carbon in this case.

[0037] Characterization testing includes microscopic morphology characterization testing, and the characterization results are as follows: Figures 1-2 As shown. From Figure 1 and Figure 2 As can be clearly seen, the activated carbon of this invention effectively constructs a multi-level, multi-size pore structure, which includes micron-level pores and cavities, as well as nanoparticle clusters and nanoscale pore structures, thus achieving effective construction of the target structure.

[0038] A 50 g / L cobalt chloride hexahydrate aqueous solution was prepared as the standard test solution (initial pH 4.9). The saturated adsorption capacity of bamboo activated carbon for cobalt extraction in this example was calculated by determining the remaining cobalt content before and after adsorption using a ratio of 2 g activated carbon to 1 L standard test solution. The limiting adsorption threshold was demonstrated by determining the cobalt content after adsorption using a ratio of 600 g activated carbon to 1 L standard test solution. In all adsorption processes, activated carbon was added to the standard test solution, stirred at 35 ℃ for 15 min, and then filtered to separate the activated carbon.

[0039] In addition, cobalt-containing industrial heavy metal wastewater (containing important interfering ions Zn, Cu and Ni, with an initial pH of approximately 4.3) was used, and the same adsorption operation as described above was performed with a ratio of 100 g activated carbon to 1 L standard test solution. The contents of important ions such as Co, Zn, Cu and Ni before and after adsorption were measured to characterize and calculate selectivity.

[0040] The performance characterization results are shown in Table 1 below.

[0041] Table 1: Characterization results of adsorption performance of activated carbon sample in Example 1:

[0042]

[0043] As can be seen from the characterization results in Table 1 above, the activated carbon of this invention exhibits excellent adsorption performance. Regarding saturated adsorption capacity, this invention demonstrates a significantly higher capacity than conventional activated carbon. Conventional activated carbon typically has an adsorption capacity of around 50–70 mg / L for cobalt, and this capacity may decrease further under continuous stirring. However, the coated adsorption capacity of the activated carbon of this invention is almost twice that of conventional activated carbon. This is attributed to the multi-level structure of this invention, which combines highly efficient and stable adsorption capacity with a large adsorption space. Furthermore, regarding the limiting adsorption threshold, the activated carbon of this invention also demonstrates a significantly superior performance compared to conventional activated carbon. Conventional activated carbon typically relies on physical adsorption, resulting in poor adsorption stability. As the cobalt concentration decreases, it reaches a dynamic equilibrium, making it difficult to reduce the cobalt content to the limiting adsorption threshold (i.e., a solid content < 50 μg / L) through adsorption treatment. In contrast, this invention achieves deep adsorption and extraction of cobalt through multi-effect synergy and multi-pathway action. This is of great significance for the deep treatment of heavy metal cobalt in industrial wastewater and for the enrichment of cobalt in some cobalt industries.

[0044] In terms of adsorption selectivity, it is also evident that Zn, Cu, and Ni, as important interfering elements, do indeed interfere with the adsorption process of cobalt by the activated carbon of this invention. However, even so, the selective adsorption capacity of the activated carbon for cobalt in this example reaches nearly 80%, demonstrating a clear selective preference for cobalt. It can be effectively used as a medium for deep cleaning treatment of cobalt pollution and deep enrichment of cobalt extraction.

[0045] Example 2: A cobalt-extracted bamboo activated carbon, which is prepared by the following method: 1) Bamboo powder and potassium hydroxide are mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder is placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, the alkaline thermal activation product is placed in a 3.0 mol / L nitric acid aqueous solution at a ratio of 30 mL per 1 g of bamboo powder raw material, heated in an 80 ℃ water bath and stirred for 4 h, then filtered and dried at 60 ℃ to obtain activated carbon powder.

[0046] 2) Take bamboo powder, calcium carbonate and sodium lignosulfonate with a molecular weight of 22000 and mix them in a mass ratio of 100:18:8. Add water to make a slurry with a solid content of 60 wt%. Press the slurry at 30 MPa and dry it at 60 ℃ to obtain a rough blank. Crush the rough blank into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. Mix the bamboo coarse powder with activated carbon powder in a mass ratio of 1:0.3 and add water to make a slurry with a solid content of 65 wt%. Press the slurry at 20 MPa and dry it at 60 ℃ to obtain a composite blank.

[0047] 3) The composite material was completely immersed in a 45 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 300 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0048] The cobalt-extracted bamboo activated carbon in this example was subjected to the same performance characterization tests as in Example 1.

[0049] The performance characterization results are shown in Table 2 below.

[0050] Table 2: Characterization results of adsorption performance of activated carbon samples in Example 2:

[0051]

[0052] Based on the characterization results in Table 2 above, this example shows that the amount of calcium carbonate and phosphoric acid was slightly increased, which slightly increased the overall saturated adsorption capacity and adsorption selectivity of the activated carbon.

[0053] Example 3: A cobalt-extracted bamboo activated carbon, which is prepared by the following method: 1) Bamboo powder and potassium hydroxide are mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder is placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, the alkaline thermal activation product is placed in a 3.0 mol / L nitric acid aqueous solution at a ratio of 30 mL per 1 g of bamboo powder raw material. The mixture is heated in an 80 ℃ water bath and stirred for 4 h. Then it is filtered and dried at 60 ℃ to obtain activated carbon powder.

[0054] 2) Bamboo powder, calcium carbonate, and sodium lignosulfonate with a molecular weight of 22,000 are mixed in a mass ratio of 100:12:8, and water is added to make a slurry with a solid content of 60 wt%. The slurry is pressed at 30 MPa and dried at 60 ℃ to obtain a rough blank. The rough blank is crushed into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. The bamboo coarse powder is mixed with activated carbon powder in a mass ratio of 1:0.3 and water is added to make a slurry with a solid content of 65 wt%. The slurry is pressed at 20 MPa and dried at 60 ℃ to obtain a composite blank.

[0055] 3) The composite material was completely immersed in a 35 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 300 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0056] The cobalt-extracted bamboo activated carbon in this example was subjected to the same performance characterization tests as in Example 1.

[0057] The performance characterization results are shown in Table 3 below.

[0058] Table 3: Characterization results of adsorption performance of activated carbon sample in Example 3:

[0059]

[0060] From the characterization results in Table 3 above, this example shows a slight reduction in the amount of calcium carbonate and phosphoric acid, resulting in a slight decrease in the overall saturated adsorption capacity and adsorption selectivity of the activated carbon. However, considering Examples 1-3, in terms of adsorption selectivity, the pre-fixation amount of calcium and the amount of phosphoric acid mainly affect the capacity of the sample, with a relatively small impact on selectivity. It can be seen that the combination of the two mainly affects the final selectivity of iron phosphate and the P-Co chelation selectivity. However, from the data, the change in Ni selectivity is quite special. There seems to be a certain positive correlation between the adsorption selectivity of Co and Ni. It is evident that nickel may be the biggest interfering factor for the selective adsorption of cobalt, and future research can focus on this aspect.

[0061] In the remaining unshown experimental groups, insufficient amounts of calcium carbonate and phosphoric acid resulted in a significant decrease in capacity and adsorption selectivity. Excessive amounts, while not significantly improving adsorption selectivity, did lead to a significant decrease in saturation adsorption capacity and limiting adsorption threshold. This is primarily due to their impact on the sample microstructure. Excessive amounts of calcium carbonate and phosphoric acid may have caused the collapse of the microstructure.

[0062] Comparative Example 1: A cobalt-extracted bamboo activated carbon was prepared by the following method: 1) Bamboo powder and potassium hydroxide were mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder was placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, the alkaline thermal activation product was placed in a 3.0 mol / L nitric acid aqueous solution at a ratio of 30 mL per 1 g of bamboo powder raw material, heated in an 80 ℃ water bath and stirred for 4 h, then filtered and dried at 60 ℃ to obtain activated carbon powder.

[0063] 2) Take bamboo powder, calcium carbonate and sodium lignosulfonate with a molecular weight of 45,000 and mix them in a mass ratio of 100:15:8. Add water to make a slurry with a solid content of 60 wt%. Press the slurry at 30 MPa and dry it at 60 ℃ to obtain a rough blank. Crush the rough blank into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. Mix the bamboo coarse powder with activated carbon powder in a mass ratio of 1:0.3 and add water to make a slurry with a solid content of 65 wt%. Press the slurry at 20 MPa and dry it at 60 ℃ to obtain a composite blank.

[0064] 3) The composite material was completely immersed in a 40 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 300 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0065] The cobalt-extracted bamboo activated carbon in this example was subjected to the same performance characterization tests as in Example 1.

[0066] The performance characterization results are shown in Table 4 below.

[0067] Table 4: Adsorption performance characterization results of activated carbon sample in Comparative Example 1:

[0068]

[0069] As can be seen from the characterization results in Table 4 above, this example only changed the molecular weight of the sodium lignosulfonate used, selecting a commercially available sodium lignosulfonate product with a larger scalar molecular weight for the preparation of activated carbon, which resulted in a significant difference in performance. This is mainly because sodium lignosulfonate plays a role in the initial fixation of calcium. When using sodium lignosulfonate with an excessively large molecular weight, it easily leads to molecular entanglement and site shielding, reducing the effective amount of calcium fixation and subsequent Ca-Fe exchange capacity. Furthermore, the reduced amount of calcium fixation also weakens the pore-expanding effect of carbon dioxide, leading to a decrease in saturated adsorption capacity, and may also result in a decrease in the ability to deeply process cobalt. The decreased cobalt selectivity, increased zinc and copper selectivity, and decreased nickel selectivity also confirm the viewpoint of Example 3 above. If the selectivity of the activated carbon of this invention for cobalt can be further effectively shielded from the effect on nickel, a further leap in performance can be achieved.

[0070] In addition, the cross-sectional control group in this case also used sodium lignosulfonate with a calibrated molecular weight of 8000 Da (labeled as the low molecular weight group), and the effect was significantly weakened after use, which was mainly reflected in the regeneration performance of activated carbon. While the saturated adsorption capacity, limiting adsorption threshold, and adsorption selectivity decreased slightly, they remained relatively controllable. For example, the saturated capacity remained at 106.7 mg / g. However, in terms of regeneration performance, the activated carbon of this invention is suitable for ultrasonic acid washing and regeneration in acidic solutions with a pH of 2.5–2.8. The saturated adsorption activated carbon sample was ultrasonically treated in a hydrogen chloride aqueous solution with a pH of approximately 2.6 for 20 min, and this process was repeated twice. After washing and drying, the regeneration process was completed. In Examples 1–3, after five saturated adsorption cycles and five regeneration cycles, the saturated adsorption capacity in the sixth cycle remained at 99.7 mg / g, 102.1 mg / g, and 99.6 mg / g, respectively, with capacity retention rates of approximately 88.1%, 88.0%, and 89.3%, respectively, demonstrating good regenerability. However, in the low molecular weight group, after three saturated adsorption cycles and three regeneration cycles, the saturated adsorption capacity in the fourth cycle decreased significantly, with a capacity retention rate of only 86.2%.

[0071] As can be seen, although some groups in sodium lignosulfonate are decomposed during heat treatment, thus making it not the main functional raw material for adsorption, it has a significant impact on the initial fixation of calcium and subsequent ion conversion processes. Therefore, it is necessary to select sodium lignosulfonate with an appropriate molecular weight for use.

[0072] Comparative Example 2: A cobalt-extracted bamboo activated carbon was prepared by the following method: 1) Bamboo powder and potassium hydroxide were mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder was placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, the alkaline thermal activation product was placed in a 3.0 mol / L nitric acid aqueous solution at a ratio of 30 mL per 1 g of bamboo powder raw material, heated in an 80 ℃ water bath and stirred for 4 h, then filtered and dried at 60 ℃ to obtain activated carbon powder.

[0073] 2) Take bamboo powder, calcium carbonate and sodium lignosulfonate with a molecular weight of 22000 and mix them in a mass ratio of 100:15:8. Add water to make a slurry with a solid content of 60 wt%. Press the slurry at 30 MPa and dry it at 60 ℃ to obtain a rough blank. Crush the rough blank into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. Mix the bamboo coarse powder with activated carbon powder in a mass ratio of 1:0.5 and add water to make a slurry with a solid content of 65 wt%. Press the slurry at 20 MPa and dry it at 60 ℃ to obtain a composite blank.

[0074] 3) The composite material was completely immersed in a 40 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 300 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0075] The cobalt-extracted bamboo activated carbon in this example was subjected to the same performance characterization tests as in Example 1.

[0076] The performance characterization results are shown in Table 5 below.

[0077] Table 5: Characterization results of adsorption performance of activated carbon sample in Comparative Example 2:

[0078]

[0079] As shown in Table 5 above, this example used more activated carbon powder during the mixing of bamboo coarse powder and activated carbon powder. This resulted in a higher saturated adsorption capacity for the sample, with almost no significant change in adsorption selectivity. A noticeable increase was observed in the adsorption of zinc, and the limiting adsorption threshold also decreased significantly. This indicates that for the technical solution of this invention, the important factors are not only the construction of the microstructure, but more importantly, the synergy between the microstructure, adsorption sites, and adsorption mechanism. Using more activated carbon powder leads to a greater shift in the adsorption mechanism towards physical adsorption characteristics and a weakening of the pore sieving effect. This is advantageous for zinc ions with larger ionic radii, resulting in a significant increase in the adsorption ratio of zinc ions. Although a higher saturated adsorption capacity was achieved, the deep processing capability for cobalt was significantly reduced.

[0080] On the other hand, a comparative experiment was also set up in this case, in which bamboo coarse powder and activated carbon powder were mixed at a mass ratio of 1:0.2. In this comparative experimental group, a sharp decrease in saturated adsorption capacity and a sharp decrease in regeneration performance were observed. The researchers believe that this is mainly because the activated carbon powder has a positive effect on building a larger internal cobalt storage space, and it also has a certain "binding" effect. This is because during the regeneration process, the sample in the comparative experimental group clearly showed pulverization during ultrasonic acid washing, indicating poor stability.

[0081] Comparative Example 3: A cobalt-extracted bamboo activated carbon, which is prepared by the following method: 1) Bamboo powder and potassium hydroxide are mixed and ground in a mass ratio of 1:4 and passed through a 120-mesh sieve to obtain a mixed powder with a mesh size ≥120 mesh. The mixed powder is placed in a nitrogen atmosphere for alkaline thermal activation at 800 ℃ for 2 h. After alkaline thermal activation, 30 mL of nitric acid aqueous solution is taken for every 1 g of bamboo powder raw material. The alkaline thermal activation product is placed in a 3.0 mol / L nitric acid aqueous solution, heated in an 80 ℃ water bath and stirred for 4 h. Then, it is filtered and dried at 60 ℃ to obtain activated carbon powder.

[0082] 2) Take bamboo powder, calcium carbonate and sodium lignosulfonate with a molecular weight of 22000 and mix them in a mass ratio of 100:15:8. Add water to make a slurry with a solid content of 60 wt%. Press the slurry at 30 MPa and dry it at 60 ℃ to obtain a rough blank. Crush the rough blank into bamboo coarse powder with a particle size of about 0.5 to 2.0 mm. Mix the bamboo coarse powder with activated carbon powder in a mass ratio of 1:0.3 and add water to make a slurry with a solid content of 65 wt%. Press the slurry at 20 MPa and dry it at 60 ℃ to obtain a composite blank.

[0083] 3) The composite material was completely immersed in a 40 wt% phosphoric acid solution at 80 ℃ for 24 h. After immersion, it was filtered and immediately transferred to a nitrogen furnace and heated to 500 ℃ for 2 h to complete the thermal activation. Then, it was crushed to obtain activated particles with a particle size of 1.0-3.0 mm. The activated particles were placed in a 0.2 mol / L ferric chloride aqueous solution and hot-stirred at 55 ℃ for 8 h for metal doping treatment. After filtration and drying at 60 ℃, it was calcined at 450 ℃ for 2 h to obtain cobalt-extracted bamboo activated carbon.

[0084] The cobalt-extracted bamboo activated carbon in this example was subjected to the same performance characterization tests as in Example 1.

[0085] The performance characterization results are shown in Table 6 below.

[0086] Table 6: Adsorption performance characterization results of activated carbon sample in Comparative Example 3:

[0087]

[0088] As shown in Table 6 above, the higher calcination temperature used in this example resulted in a decrease in both the saturated adsorption capacity and the limiting adsorption threshold, as expected. Although some selectivity was still observed, it was significantly reduced, especially with a sharp increase in the content of other adsorbates. This is because the iron compounds underwent an irreversible transformation, which may have damaged the cobalt storage space and altered the micro- and nano-pores, leading to changes in both the adsorption mechanism and adsorption capacity. Consequently, the overall targeted deep cobalt treatment effect was significantly reduced.

Claims

1. A method for preparing cobalt-extracted bamboo activated carbon, characterized in that, The method includes: 1) Bamboo powder is mixed and ground with an alkaline activator and then subjected to alkaline thermal activation in a protective atmosphere. After alkaline thermal activation, it is placed in an oxidizing solution for surface oxidation functionalization treatment to obtain activated carbon powder. 2) Take bamboo powder, calcium source and lignin sulfonate, mix them with water to make slurry, press and dry them into rough blanks, crush and pulverize the rough blanks to obtain bamboo coarse powder, mix the bamboo coarse powder with activated carbon powder, add water to make slurry, press and dry them to obtain composite blanks. 3) The composite material is impregnated in a phosphoric acid solution for impregnation and thermal activation, then crushed to obtain activated particles. The activated particles are placed in an iron salt solution for metal doping treatment, then filtered, dried and calcined to obtain cobalt-extracted bamboo activated carbon. Step 2) The lignin sulfonate is a medium molecular weight sodium lignin sulfonate with a molecular weight of 20,000 to 30,000; Step 2) The bamboo powder, calcium source and lignin sulfonate are mixed in a mass ratio of 100:(12-18):(8-10); Step 3) The calcination is carried out in a protective atmosphere at 300-320 °C for 1.5-3.0 h to obtain cobalt-extracted bamboo activated carbon.

2. The method for preparing cobalt-extracted bamboo activated carbon according to claim 1, characterized in that, The alkaline activator in step 1) is potassium hydroxide; Step 1) The bamboo powder and alkaline activator are mixed and ground to a mesh size ≥120 mesh at a mass ratio of 1:(3.5~4.5). Then, alkaline thermal activation is carried out by heating to 750~850 ℃ and holding for 2~3 h in a protective atmosphere.

3. The method for preparing cobalt-extracted bamboo activated carbon according to claim 1 or 2, characterized in that, Step 1) The oxidizing solution is a 3-5 mol / L nitric acid aqueous solution, and the amount of the nitric acid aqueous solution used is (25-35) mL / g bamboo powder; Step 1) The surface oxidation functionalization treatment is carried out by stirring the reaction in a water bath at 70-90 ℃ for 3-5 h.

4. The method for preparing cobalt-extracted bamboo activated carbon according to claim 1, characterized in that, Step 2) The bamboo powder mentioned is bamboo powder with a mesh size of 40-60. Step 2) The calcium source is calcium carbonate; Step 2) The bamboo powder, calcium source and lignin sulfonate are then mixed with water to form a slurry with a solid content of 55-65 wt%, which is then pressed at 25-35 MPa and subsequently dried to obtain a rough blank.

5. A method for preparing cobalt-extracted bamboo activated carbon according to claim 1 or 4, characterized in that, Step 3) involves crushing and pulverizing the rough blank to obtain bamboo coarse powder with a particle size of 0.5–2.0 mm; Step 2) The bamboo coarse powder and activated carbon powder are mixed evenly at a mass ratio of 1:(0.25~0.35), and water is added to form a slurry with a solid content of 60~70 wt%. The slurry is then pressed and molded under a pressure of 15~25 MPa and dried to obtain a composite preform.

6. The method for preparing cobalt-extracted bamboo activated carbon according to claim 1, characterized in that, Step 3) The phosphoric acid solution is a 35-45 wt% aqueous phosphoric acid solution; Step 3) After the composite preform is completely immersed in the phosphoric acid aqueous solution, it is heated to 80 ℃ and kept at a constant temperature for 24 h. After filtration, it is immediately transferred to a protective atmosphere and heated to 490~520 ℃ for 1.5~2.5 h to complete the impregnation thermal activation. Step 3) The crushing process involves crushing the product after impregnation and thermal activation into particles with a particle size of 1.0 to 3.0 mm to obtain activated particles.

7. The method for preparing cobalt-extracted bamboo activated carbon according to claim 1, characterized in that, Step 3) The iron salt solution is an aqueous solution of iron salt with a ferric ion concentration of 0.18–0.25 mol / L; Step 3) The ratio of activated particles to iron salt solution is (25-35) g activated particles: 100 mL iron salt solution.

8. A method for preparing cobalt-extracted bamboo activated carbon according to claim 1 or 7, characterized in that, Step 3) The metal doping treatment involves adding the activated particles to the iron salt solution and then hot-stirring it at 40–60 °C for 6–10 h.

9. A cobalt-extracting bamboo activated carbon prepared by any one of claims 1 to 8.

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