Cationic chitosan fibers, methods of making and using the same

Abstract

This invention belongs to the field of resource recycling and water treatment agent technology, and more specifically, relates to a cationic chitosan fiber, its preparation method, and its application. The present invention provides a cationic chitosan fiber with a cross-sectional size in the micrometer range. First, chitosan fibers are mixed with a cross-linking agent to undergo a cross-linking reaction, transforming the linear chitosan molecular structure in the chitosan fibers into a three-dimensional network structure of cross-linked chitosan fibers. Then, the cross-linked chitosan fibers are mixed with a quaternary ammonium salt cationic modifier for modification, so that the quaternary ammonium groups are fixed on the cross-linked chitosan fibers, thus preparing the cationic chitosan fiber. The quaternized cationic chitosan fiber prepared by this invention has a positive effect on Au(CN)2. ‑ The adsorption rate is extremely fast. Furthermore, the quaternized cationic chitosan fibers prepared in this invention exhibit excellent adsorption of Au(CN)₂ in an alkaline environment. ‑ Its adsorption capacity can reach up to 669.8±47.2 mg / g, which is much higher than that of the adsorbents reported so far.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling and water treatment agent technology, and more specifically, relates to a cationic chitosan fiber, its preparation method and application. Background Technology

[0002] Gold is widely used in chemical, electronic, and aerospace industries due to its high stability, excellent thermal conductivity, and good catalytic activity. However, the increasing scarcity of high-quality gold ore resources has led to a growing imbalance between supply and demand for gold. Therefore, the recovery of gold from electronic waste and decommissioned gold-bearing catalysts has attracted widespread attention.

[0003] Gold recovery from electronic waste mainly involves two steps: leaching and extraction. Among these, cyanide leaching (Equation 1) has become the mainstream gold leaching technology for nearly a century due to its advantages such as low cost and high efficiency. However, to avoid the health effects of highly toxic hydrogen cyanide gas volatilization, cyanide gold leaching technology must be carried out in an alkaline environment (pKa). HCN =9.21). OH- is abundant in alkaline environments. - Ions and gold cyanide anions (Au(CN)2) - The competitive effect of ) makes Au(CN)2 in the leachate... - Although the recovery is quite challenging, it is of great research value.

[0004]

[0005] Among numerous gold recovery technologies, adsorption has garnered widespread attention due to its simple operation and low operating costs. The core of adsorption technology lies in the research and development and preparation of high-performance adsorption materials. However, due to the high pH characteristics of cyanide leachates, most adsorption materials reported in recent years exhibit poor adsorption performance. For instance, it has been reported that GRC-22 commercial activated carbon powder and coconut shell activated carbon show poor adsorption performance for Au(CN)₂ at pH = 10.5 and pH = 11. - The maximum adsorption capacities were 56.17 mg(Au) / g and 1.79 mg(Au) / g, respectively. Furthermore, the inherent difficulty in solid-liquid separation of powdered adsorbents also limited their gold recovery from actual leachates. Literature has prepared graphene oxide-polyethyleneimine composite hydrogels for the adsorption of Au(CN)₂. - It exhibits good adsorption performance, with a maximum adsorption capacity of 252.88 mg / g at pH=9; however, its slow adsorption rate still limits its application. Therefore, for Au(CN)2 in alkaline environments... - The development of high-performance, rapidly recoverable, and easily solid-liquid separated adsorbents has a promising application prospect. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a cationic chitosan fiber, its preparation method, and its application in the recovery of gold cyanide in alkaline environments and the removal of anionic pollutants in neutral-alkaline environments. This addresses the technical problems that limit the widespread application of existing technologies for the adsorption and recovery of gold cyanide in neutral-alkaline environments, such as low adsorption capacity and slow adsorption rate.

[0007] To achieve the above objectives, the present invention provides a method for preparing cationic chitosan fibers, comprising the following steps:

[0008] (1) Dissolve chitosan in an aqueous solution of acetic acid to obtain chitosan gel;

[0009] (2) The chitosan gel described in step (1) is extruded into an alkaline aqueous solution to obtain chitosan fibers with a cross-sectional size in the micrometer range;

[0010] (3) Mix the chitosan fiber described in step (2) with an aqueous solution of a crosslinking agent to cause a crosslinking reaction to change the linear structure of the chitosan molecule and obtain crosslinked chitosan fiber.

[0011] (4) The cross-linked chitosan fiber described in step (3) is mixed with an aqueous solution of a quaternary ammonium salt cationic modifier to react, so that the quaternary ammonium group of the quaternary ammonium salt cationic modifier is fixed on the cross-linked chitosan fiber. After washing and drying, cationic chitosan fiber is obtained.

[0012] Preferably, the concentration of acetic acid in the aqueous solution of acetic acid in step (1) is 2 vol% to 5 vol%.

[0013] Preferably, the crosslinking agent in step (3) is one or more of epichlorohydrin, ethylene glycol diglycidyl ether and glutaraldehyde; the concentration of the crosslinking agent in the aqueous solution of the crosslinking agent is 0.02 vol% to 1 vol%; each gram of chitosan fiber is mixed with 50 to 200 mL of the aqueous solution of the crosslinking agent.

[0014] Preferably, the aqueous solution of the crosslinking agent in step (3) has a pH of 7 to 12; and the crosslinking reaction takes 8 to 20 hours.

[0015] Preferably, the quaternary ammonium salt cationic modifier in step (4) is (3-chloro-2-hydroxypropyl)trimethylammonium chloride and / or glycidyltrimethylammonium chloride (2,3-epoxypropyltrimethylammonium chloride); the concentration of the quaternary ammonium salt cationic modifier in the aqueous solution is less than or equal to 20 vol%, preferably 5 to 18 vol%; the pH of the aqueous solution of the quaternary ammonium salt cationic modifier is 7 to 12.

[0016] Preferably, the reaction temperature in step (4) is 25–85°C and the reaction time is 8–20 hours.

[0017] Preferably, the mass-to-volume ratio of the cross-linked chitosan fiber to the aqueous solution of the quaternary ammonium salt cationic modifier in step (4) is 1 g: (50-200) mL.

[0018] According to another aspect of the present invention, a cationic chitosan fiber prepared by the preparation method described above is provided.

[0019] According to another aspect of the invention, an application is provided for the cationic chitosan fiber described above in recovering gold cyanide from water samples in alkaline environments and / or removing anionic contaminants from water samples in neutral-alkaline environments; preferably, the anionic contaminants in the water samples in neutral or alkaline environments are sodium dichlorophenate, phosphate, glyphosate, As(V), Cr(VI), or RBV-5R dye.

[0020] In some embodiments, the cationic chitosan fiber is used as an adsorbent to adsorb and recover gold cyanide from alkaline water samples and / or remove anionic pollutants from water samples in neutral or alkaline environments. The adsorbed chitosan fiber is then regenerated using sodium hydroxide or sodium chloride solution.

[0021] In summary, compared with the prior art, the above-described technical solutions conceived by this invention have the following advantages:

[0022] Beneficial effects:

[0023] (1) The present invention provides a cationic chitosan fiber with a cross-sectional size in the micrometer range. First, chitosan fibers are mixed with a cross-linking agent to undergo a cross-linking reaction, transforming the linear chitosan molecular structure in the chitosan fibers into a three-dimensional network structure of cross-linked chitosan fibers. Then, the cross-linked chitosan fibers are mixed with a quaternary ammonium salt cationic modifier to modify them, thereby fixing the quaternary ammonium groups onto the cross-linked chitosan fibers, thus preparing the cationic chitosan fiber of the present invention. In a preferred embodiment, the cationic chitosan fiber of the present invention is used to adsorb and recover Au(CN)₂ from an alkaline aqueous solution. - Anions were found in the experiments to have an effect on Au(CN)2. - The adsorption rate is extremely fast, and the adsorption process reaches equilibrium within 10 minutes; simultaneously, at pH 9.5, 10.5, and 11.5, the adsorption of Au(CN)₂... - The maximum adsorption capacities of Au in the simulated leachate were 669.8±47.2, 613.3±45.0 and 592.2±55.9 mg / g, respectively, which are much higher than all the adsorbents reported to date.

[0024] (2) The method for preparing cationic chitosan fiber of the present invention is simple, mild and easy to scale up.

[0025] (3) The cationic chitosan fiber of the present invention is very easy to separate from the solution after adsorption, and it has great potential in practical engineering applications.

[0026] (4) The cationic chitosan fiber of the present invention can be rapidly desorbed and regenerated by sodium hydroxide or sodium chloride solution, which facilitates the recycling of adsorbent.

[0027] (5) The cationic chitosan fiber of the present invention also has good removal performance for many other anionic pollutants in aqueous solution (sodium dichlorophenate, phosphate, glyphosate, As(V), Cr(VI) or RBV-5R dye, etc.). Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the process for preparing quaternary ammonium salt cationic chitosan fibers in an embodiment of the present invention.

[0029] Figure 2 FE-SEM / EDX analysis of the chitosan fibers, cross-linked chitosan fibers, and quaternary ammonium salt cationic chitosan fiber materials prepared in Example 1.

[0030] Figure 3 The chitosan fibers, cross-linked chitosan fibers, and quaternary ammonium salt cationic chitosan fibers prepared in Example 1 were characterized by FT-IR and XRS.

[0031] Figure 4 The quaternary ammonium salt cationic chitosan fibers prepared in Example 1 showed the effect of Au(CN)2 in alkaline solution. - Adsorption performance evaluation.

[0032] Figure 5 Evaluation of the regeneration performance of the quaternary ammonium salt cationic chitosan fiber prepared in Example 1.

[0033] Figure 6 This study investigates the removal of other anionic pollutants by the quaternary ammonium salt cationic chitosan fibers prepared in Example 1 in a neutral-alkaline environment. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0035] The present invention provides a method for preparing cationic chitosan fibers, comprising the following steps:

[0036] (1) Dissolve chitosan in an aqueous solution of acetic acid to obtain chitosan gel;

[0037] (2) The chitosan gel described in step (1) is extruded into an alkaline aqueous solution to obtain chitosan fibers with a cross-sectional size in the micrometer range;

[0038] (3) Mix the chitosan fiber described in step (2) with an aqueous solution of a crosslinking agent to allow it to undergo a crosslinking reaction to change the linear structure of the chitosan molecule and obtain crosslinked chitosan fiber to improve the physicochemical stability of the chitosan fiber.

[0039] (4) The cross-linked chitosan fiber described in step (3) is mixed with an aqueous solution of a quaternary ammonium salt cationic modifier to react, so that the quaternary ammonium group of the quaternary ammonium salt cationic modifier is fixed on the cross-linked chitosan fiber. After washing and drying, cationic chitosan fiber is obtained.

[0040] In some embodiments, the concentration of acetic acid in the aqueous solution of acetic acid in step (1) is 2 vol% to 5 vol%. Chitosan can be in various forms, including but not limited to powder, granules, etc. The mass ratio of chitosan to the aqueous solution of acetic acid is 1:(30 to 60).

[0041] In some embodiments, step (2) involves extruding the chitosan gel into an alkaline aqueous solution using a pressure injection container, such as a dispensing syringe connected to an air pump. The cross-sectional size (i.e., the diameter of the fiber cross-section) of the extruded chitosan fiber can be controlled by adjusting the size of the dispensing syringe. The alkaline aqueous solution is a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution with a concentration of 0.5–3 mol / L. The cross-sectional size of the chitosan fiber prepared in step (2) is preferably 50–500 micrometers, and more preferably 50–200 micrometers. In the experiment, chitosan fibers with a cross-sectional size of 1–2 mm were prepared, and then cationic chitosan fibers with a cross-sectional size of 1–2 mm were obtained using the same modification method. The experiment found that when the cross-sectional size is larger, although it can also be used to adsorb and recover gold cyanide anions (Au(CN)2) in the water sample, the cross-sectional size is still relatively small. - However, the adsorption rate is relatively slow.

[0042] In some embodiments, the crosslinking agent in step (3) is one or more of epichlorohydrin, ethylene glycol diglycidyl ether, and glutaraldehyde; the concentration of the crosslinking agent in the aqueous solution is 0.02 vol% to 1 vol%; each gram of chitosan fiber is mixed with 50 to 200 mL of the aqueous solution of the crosslinking agent. The pH of the aqueous solution of the crosslinking agent in step (3) is 7 to 12; the crosslinking reaction time is 8 to 20 hours.

[0043] In some embodiments, the quaternary ammonium salt cationic modifier in step (4) is (3-chloro-2-hydroxypropyl)trimethylammonium chloride and / or glycidyltrimethylammonium chloride (2,3-epoxypropyltrimethylammonium chloride); the concentration of the quaternary ammonium salt cationic modifier in the aqueous solution is less than or equal to 20 vol%, preferably 5-18 vol%; the pH of the aqueous solution of the quaternary ammonium salt cationic modifier is 7-12. When the quaternary ammonium salt cationic modifier in step (4) is (3-chloro-2-hydroxypropyl)trimethylammonium chloride, the modifier first undergoes dehydration condensation in an alkaline environment to form epoxy groups, and the epoxy groups undergo organic covalent reactions with the amino and hydroxyl groups on the cross-linked chitosan fibers, so that the quaternary ammonium groups are fixed on the cross-linked chitosan fibers. When the quaternary ammonium salt cationic modifier is glycidyltrimethylammonium chloride (or 2,3-epoxypropyltrimethylammonium chloride), the epoxy groups in the modifier directly react with the amino and hydroxyl groups on the cross-linked chitosan fibers in an organic covalent reaction, so that the quaternary ammonium groups are fixed on the cross-linked chitosan fibers.

[0044] In some embodiments, the reaction temperature in step (4) is 25–85°C, and the reaction time is 8–20 hours. The mass-to-volume ratio of the cross-linked chitosan fiber to the aqueous solution of the quaternary ammonium salt cationic modifier in step (4) is 1 g: (50–200) mL.

[0045] The cationic chitosan fibers with a cross-sectional size in the micrometer range prepared by this invention can be used to recover gold cyanide from alkaline water samples and to remove anionic contaminants from neutral to alkaline water samples. In some embodiments, the alkaline water samples are gold ore cyanide leaching solutions, waste circuit board gold cyanide leaching solutions, etc. The anionic contaminants in the neutral or alkaline water samples are sodium dichlorophenate, phosphates, glyphosate, As(V), Cr(VI), or RBV-5R dyes, etc.

[0046] In some embodiments, the cationic chitosan fiber described in this invention is used as an adsorbent to adsorb and recover gold cyanide from alkaline water samples and / or remove anionic pollutants from water samples in neutral or alkaline environments. The adsorbed chitosan fiber is then regenerated using sodium hydroxide or sodium chloride solution.

[0047] This invention discloses a gold cyanide anion (Au(CN)2) suitable for alkaline water environments. -This invention discloses a method for preparing quaternized cationic chitosan fibers. In some embodiments, chitosan fibers are obtained by extruding chitosan gel into a sodium hydroxide solution; the chitosan fibers are then immersed in a 0.02–1% (v / v) epichlorohydrin solution, stirred for 12 h at pH 7–12 and room temperature, separated, washed with deionized water, and dried to obtain cross-linked chitosan fibers; the cross-linked chitosan fibers are then immersed in a (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution, stirred for 12 h at pH 7–12 and temperature 25–85°C, separated, washed with deionized water, and dried to obtain quaternized cationic chitosan fibers. The quaternized cationic chitosan fibers prepared by this invention have a positive effect on Au(CN)2. - The adsorption rate is extremely fast. Furthermore, the quaternized cationic chitosan fibers prepared in this invention exhibit excellent adsorption properties for Au(CN)₂ in an alkaline environment. - The adsorption capacity can reach as high as 669.8±47.2 mg / g, which is far higher than that of currently reported adsorbents. Furthermore, the quaternized cationic chitosan fiber prepared in this invention also exhibits outstanding removal performance for numerous anionic pollutants in water.

[0048] The modifiers used in the following examples were commercially available. Among them, (3-chloro-2-hydroxypropyl)trimethylammonium chloride was a 60% aqueous solution of (3-chloro-2-hydroxypropyl)trimethylammonium chloride, with CAS number 3327-22-8; glycidyltrimethylammonium chloride (2,3-epoxypropyltrimethylammonium chloride) was also a liquid reagent, with CAS number 3033-77-0.

[0049] The following is an example:

[0050] Example 1

[0051] A method for preparing cationic chitosan fibers, such as... Figure 1 As shown, proceed as follows:

[0052] (1) Mix 2 g of chitosan powder with 98 mL of 2 vol% acetic acid aqueous solution to obtain chitosan gel.

[0053] (2) The chitosan gel prepared in step (1) is loaded into a dispensing syringe with a dispensing needle size of 30G. The syringe is connected to an air pump and the chitosan gel is squeezed into a 1M sodium hydroxide solution under pressure. After separation, the gel is washed with deionized water and freeze-dried to obtain chitosan fibers with a cross-sectional size of about 90 micrometers (read from electron microscope images).

[0054] (3) Mix 1g of chitosan fiber with 100mL of 0.02vol% (volume percentage concentration) epichlorohydrin aqueous solution at pH=11. Allow it to undergo a crosslinking reaction for 12 hours, wash with water and freeze-dry to obtain epichlorohydrin crosslinked chitosan fiber.

[0055] (4) 1g of epichlorohydrin-crosslinked chitosan fiber was soaked in 100mL of (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution with pH 11 and a concentration of 17.1 vol% and reacted at 85°C for 12 hours. After washing with water until neutral, it was placed in a freeze dryer and vacuumed when the temperature dropped below -50°C. After freeze drying at -50°C, cationic chitosan fiber was obtained.

[0056] Example 2

[0057] A method for preparing cationic chitosan fibers, comprising the following steps:

[0058] (1) Mix 2 g of chitosan powder with 98 mL of 2 vol% acetic acid aqueous solution to obtain chitosan gel.

[0059] (2) The chitosan gel prepared in step (1) is loaded into a dispensing syringe with a dispensing needle size of 30G. The syringe is connected to an air pump and the chitosan gel is extruded into a 1M sodium hydroxide solution under pressure. After washing with deionized water and freeze-drying, chitosan fibers with a cross-sectional size of about 90 micrometers are obtained (read from electron microscope images).

[0060] (3) Mix 1g of chitosan fiber with 100mL of 1vol% epichlorohydrin aqueous solution with pH=11. Allow it to undergo a cross-linking reaction for 12 hours, wash with water and freeze dry to obtain epichlorohydrin cross-linked chitosan fiber.

[0061] (4) 1g of epichlorohydrin-crosslinked chitosan fiber was soaked in 100mL of (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution with pH 11 and a concentration of 17.1 vol% and reacted at 85 degrees Celsius for 12 hours. After washing with water until neutral, the cationic chitosan fiber was prepared by freeze drying at -50°C.

[0062] Example 3

[0063] A method for preparing cationic chitosan fibers, comprising the following steps:

[0064] (1) Mix 2 g of chitosan powder with 98 mL of 2% acetic acid aqueous solution to obtain chitosan gel.

[0065] (2) The chitosan gel prepared in step (1) is loaded into a dispensing syringe with a dispensing needle size of 30G. The syringe is connected to an air pump and the chitosan gel is extruded into a 1M sodium hydroxide solution under pressure. After washing with deionized water and freeze-drying, chitosan fibers with a cross-sectional size of about 90 micrometers are obtained (read from electron microscope images).

[0066] (3) Mix 1g of chitosan fiber with 100mL of 0.02vol% epichlorohydrin aqueous solution with pH=11. Allow it to undergo a cross-linking reaction for 12 hours, wash with water and freeze-dry to obtain epichlorohydrin cross-linked chitosan fiber.

[0067] (4) 1g of epichlorohydrin-crosslinked chitosan fiber was soaked in 100mL of (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution with pH 7 and concentration of 17.1% and reacted at 85°C for 12 hours. After washing with water until neutral, the cationic chitosan fiber was prepared by freeze drying at -50°C.

[0068] Example 4

[0069] A method for preparing cationic chitosan fibers, comprising the following steps:

[0070] (1) Mix 2 g of chitosan powder with 98 mL of 2 vol% acetic acid aqueous solution to obtain chitosan gel.

[0071] (2) The chitosan gel prepared in step (1) is loaded into a dispensing syringe with a dispensing needle size of 30G. The syringe is connected to an air pump and the chitosan gel is extruded into a 1M sodium hydroxide solution under pressure. After washing with deionized water and freeze-drying, chitosan fibers with a cross-sectional size of about 90 micrometers are obtained (read from electron microscope images).

[0072] (3) Mix 1g of chitosan fiber with 100mL of 0.02% epichlorohydrin aqueous solution at pH=11. Allow it to undergo a cross-linking reaction for 12 hours, wash with water and freeze-dry to obtain epichlorohydrin cross-linked chitosan fiber.

[0073] (4) 1g of epichlorohydrin-crosslinked chitosan fiber was soaked in 100mL of (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution with pH 11 and concentration of 6vol% and reacted at 25 degrees Celsius for 12 hours. After washing with water until neutral, the cationic chitosan fiber was prepared by freeze drying.

[0074] Example 5

[0075] Other conditions are the same as in Example 1, except that epichlorohydrin in Example 1 is replaced with glutaraldehyde.

[0076] Example 6

[0077] Other conditions are the same as in Example 1, except that the crosslinking agent epichlorohydrin in Example 1 is replaced with ethylene glycol diglycidyl ether.

[0078] Comparative Example 1

[0079] A method for preparing cationic chitosan fibers, comprising the following steps:

[0080] (1) Mix 2 g of chitosan powder with 98 mL of 2% acetic acid aqueous solution to obtain chitosan gel.

[0081] (2) The chitosan gel prepared in step (1) is loaded into a dispensing syringe with a dispensing needle size of 30G. The syringe is connected to an air pump and the chitosan gel is extruded into a 1M sodium hydroxide solution under pressure. After washing with deionized water and freeze-drying, chitosan fibers with a cross-sectional size of about 90 micrometers are obtained (read from electron microscope images).

[0082] (3) Mix 1g of chitosan fiber with 100mL of 0.02% epichlorohydrin aqueous solution at pH=11. Allow it to undergo a cross-linking reaction for 12 hours, wash with water and freeze-dry to obtain epichlorohydrin cross-linked chitosan fiber.

[0083] (4) 1g of epichlorohydrin-crosslinked chitosan fiber was soaked in 100mL of (3-chloro-2-hydroxypropyl)trimethylammonium chloride aqueous solution with pH 11 and concentration 0% and reacted at 85°C for 12 hours. After washing with water until neutral, cationic chitosan fiber was prepared by freeze drying at -50°C.

[0084] The cationic chitosan fibers obtained in Examples 1-6 and Comparative Example 1 were used in an alkaline solution containing Au(CN)2. - The recovery and adsorption conditions were as follows: initial Au ion solution concentration was approximately 500 mg / L, solution volume was 10 mL, adsorbent dosage was 10 mg, temperature was 25℃, pH = 9.5, and adsorption time was 12 h. After adsorption, the residual Au ion concentration was detected using inductively coupled plasma atomic emission spectrometry (ICP-AES). The prepared adsorbent was then used to analyze the Au(CN)₂ content. - The adsorption performance was measured, and the test results are shown in Table 1.

[0085] Table 1. Au(CN)2 in the alkaline solution of cationic chitosan fibers prepared in Examples 1-6 and Comparative Example 1 - Adsorption performance

[0086] Au adsorption capacity (mg / g) Example 1 387.4±19.7 Example 2 193.1±10.32 Example 3 213.9±3.12 Example 4 205.6±13.31 Example 5 390.5±13.1 Example 6 411.9±14.6 Comparative Example 1 12.1±9.05

[0087] Figure 2The images show SEM images of cationic chitosan fibers, epichlorohydrin crosslinked chitosan fibers, and quaternary ammonium salt cationic chitosan fibers prepared in Example 1 (contents a and d are SEM images of chitosan fibers obtained in step (1) of Example 1, contents b and e are SEM images of epichlorohydrin crosslinked chitosan fibers obtained in step (3), and contents c and f are SEM images of quaternary ammonium salt cationic chitosan fibers obtained in step (4). It can be seen that the adsorbent maintains a good fiber shape throughout the preparation process. Figure 3 XPS images of chitosan fibers and cationic chitosan fibers prepared in Example 1 are shown (content a is the FT-IR spectrum of chitosan fibers at different stages, and content b is the N1s XPS spectrum of chitosan fibers at different stages). It can be seen that compared with the FT-IR and N1s XPS spectra of chitosan fibers and cross-linked chitosan fibers, cationic chitosan fibers show obvious quaternary ammonium functional groups on their surface. This result indicates that cationic chitosan fibers were successfully prepared.

[0088] Example 7

[0089] 0.1 g of the cationic chitosan fiber prepared in Example 1 was added to 100 mL of Au(CN)2. - In simulated leachate, its effect on Au(CN)2 was investigated. - The recovery kinetics were studied under the following adsorption conditions: initial Au ion solution concentration of approximately 500 mg / L, solution volume of 100 mL, adsorbent dosage of 0.1 g, temperature of 25 °C, and pH of 9.5. 0.01 g of the cationic chitosan fiber prepared in Example 1 was added to 10 mL of Au(CN)₂. - Investigating its effect on Au(CN)2 in simulated leachate - The isothermal adsorption study was conducted under the following conditions: initial concentration of Au ion solution was approximately 100-1000 mg / L, solution volume was 10 mL, adsorbent dosage was 0.01 g, temperature was 25 °C, pH was 9.5, 10.5 or 11.5, and adsorption time was 12 h.

[0090] Figure 4 The cationic chitosan fibers prepared in Example 1 are used to prepare Au(CN)2. - Study on Au recovery kinetics and isothermal adsorption in simulated leachate Figure 4 (As shown in content a and content b). Kinetic studies indicate that cationic chitosan fibers have an effect on Au(CN)2. - The adsorption rate is extremely fast. Under the conditions of an initial Au ion solution concentration of approximately 500 mg / L, a solution volume of 100 mL, an adsorbent dosage of 100 mg, a temperature of 25 °C, and a pH of 9.5, 60.34% q e Au(CN)2 -It was adsorbed within 0.5 minutes, 95.42% q. e Au(CN)2 - It was adsorbed within 5 minutes, and the entire adsorption process reached adsorption equilibrium within 10 minutes. Adsorption isotherms showed that Au(CN)₂ was effectively adsorbed at pH 9.5, 10.5, and 11.5. - The maximum adsorption capacities of Au in the simulated leachate were 669.8±47.2, 613.3±45.0, and 592.2±55.9 mg / g, respectively. Table 2 shows that the prepared cationic chitosan fibers exhibited high adsorption capacity for Au(CN)2 in an alkaline environment. - Its adsorption capacity is far higher than that of any adsorbent reported to date.

[0091] Table 2. Comparison of adsorption capacity of different materials for gold cyanide in alkaline environment

[0092]

[0093]

[0094] [1] E. Vences-Alvarez, E. Razo-Flores, I. Lázaro, R. Briones-Gallardo, G. Velasco-Martínez, R. Rangel-Mendez, Gold recovery from very dilute solutions from a mine in closing process: Adsorption-desorption onto carbon materials, Journal of Molecular Liquids, 240 (2017) 549-555.

[0095] [2] R.Khosravi, A.Azizi, R.Ghaedrahmati, VKGupta, S.Agarwal, Adsorption of gold from cyanide leaching solution onto activated carbon originating from coconut shell—Optimization, kinetics and equilibrium studies, Journal of Industrial and Engineering Chemistry, 54 (2017) 464-471.

[0096] [3]D.Swantomo,I.R.Faturrahman,K.T.Basuki,D.Wongsawaeng,Chitosan-polyacrylamide graft copolymers prepared with gamma irradiation for goldcyanide adsorption,Polymer-Plastics Technology and Materials,59(2020)1284-1291.

[0097] [4]R.Tsolele,F.M.Mtunzi,M.J.Klink,V.E.Pakade,An alternative low-costadsorbent for gold recovery from cyanide-leached liquors:Adsorption isothermand kinetic studies,Adsorption Science&Technology,37(2019)3-23.

[0098] [5]K.Ramírez- S.Song,S.Berber-Mendoza,S.Tong,Adsorption of thecomplex ion Au(CN)2-onto sulfur-impregnated activated carbon in aqueoussolutions,Journal of colloid and interface science,349(2010)602-606.

[0099] [6]K.Sun,W.Peng,H.Li,S.Song,Recovery of Au(CN)2-with magnetic reducedgraphene oxide hydrogel in aqueous leach solution,Hydrometallurgy,176(2018)208-215.

[0100] [7] L. Yang, F. Jia, S. Song, Recovery of [Au(CN)2]-from gold cyanidation with graphene oxide as adsorbent, Sep. Purif. Technol., 186 (2017) 63-69.

[0101] [8]L.Yang,F.Jia,B.Yang,S.Song,Efficient adsorption of Au(CN)2-fromgold cyanidation with graphene oxide-polyethylenimine hydrogel as adsorbent,Results in physics,7(2017)4089-4095.

[0102] Example 8

[0103] The cationic chitosan fibers saturated with adsorption in Example 7 were immersed in sodium hydroxide or sodium chloride solution to investigate Au(CN)2. - Results of the regeneration performance of cationic chitosan fibers are as follows: Figure 5 As shown, content a represents the desorption rate of the adsorption-saturated cationic chitosan fibers in 1M sodium hydroxide and 1M sodium chloride solutions in Example 7; content b represents the desorption rate and time curve of the adsorption-saturated cationic chitosan fibers in 1M sodium chloride solution in Example 7; content c represents the change in gold adsorption capacity of the adsorption-saturated cationic chitosan fibers in Example 7 after multiple adsorption-desorption cycles; the experiment found that Au(CN)₂ - Cationic chitosan fibers can be rapidly regenerated using sodium hydroxide or sodium chloride solutions. After five adsorption-desorption cycles, the Au(CN)2 content of the cationic chitosan fibers is [data missing]. - The adsorption performance did not decrease significantly.

[0104] Example 9

[0105] The cationic chitosan fiber prepared in Example 1 was used to conduct adsorption experiments on simulated diclofenac sodium (DCF), As(V), Cr(VI), phosphate, glyphosate, and reactive purple violet 5 (RBV-5) pollutants. The adsorption conditions were: solution volume 10 mL, adsorbent amount 0.01 g, temperature 25 °C, pH = 7, and adsorption time = 12 h. The experimental results are as follows. Figure 6 As shown, the results indicate that the prepared cationic chitosan fiber also has good application prospects for the removal of other anionic pollutants.

[0106] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for producing cationic chitosan fibers, characterized by, Includes the following steps: (1) Chitosan was dissolved in an aqueous solution of acetic acid to obtain chitosan gel; (2) The chitosan gel obtained in step (1) is extruded into an alkaline aqueous solution, taken out and separated, washed with deionized water, and freeze-dried to obtain chitosan fibers with a cross-sectional size in the micrometer range; the cross-sectional size of the chitosan fibers is 50 to 500 micrometers. (3) The chitosan fiber described in step (2) is mixed with an aqueous solution of a crosslinking agent to induce a crosslinking reaction and change the linear structure of the chitosan molecules to obtain crosslinked chitosan fiber; the crosslinking agent is one or more of epichlorohydrin, ethylene glycol diglycidyl ether and glutaraldehyde; the concentration of the crosslinking agent in the aqueous solution is 0.02 vol%; each gram of chitosan fiber is mixed with 50 to 200 mL of the aqueous solution of the crosslinking agent; the pH of the aqueous solution of the crosslinking agent is 7 to 12; (4) The cross-linked chitosan fibers described in step (3) are mixed with an aqueous solution of a quaternary ammonium salt cationic modifier to react, so that the quaternary ammonium groups of the quaternary ammonium salt cationic modifier are fixed on the cross-linked chitosan fibers. After washing and drying, cationic chitosan fibers are obtained. The quaternary ammonium salt cationic modifier is (3-chloro-2-hydroxypropyl)trimethylammonium chloride and / or glycidyltrimethylammonium chloride. The concentration of the aqueous solution of the quaternary ammonium salt cationic modifier is less than or equal to 20 vol%. The pH of the aqueous solution of the quaternary ammonium salt cationic modifier is 7 to 12. The reaction temperature is 25 to 85°C and the reaction time is 8 to 20 hours.

2. The production method according to claim 1, wherein In step (1), the concentration of acetic acid in the aqueous solution of acetic acid is 2 vol% to 5 vol.

3. The production method according to claim 1, wherein The cross-linking reaction in step (3) takes 8 to 20 hours.

4. The production method according to claim 1, wherein In step (4), the mass-to-volume ratio of the cross-linked chitosan fiber to the aqueous solution of the quaternary ammonium salt cationic modifier is 1 g: (50-200) mL.

5. Cationic chitosan fibers prepared by the preparation method according to any one of claims 1 to 4.

6. The application of the cationic chitosan fiber as described in claim 5 in the recovery of gold cyanide from alkaline water samples and / or the removal of anionic contaminants from neutral-alkaline water samples.

7. Use according to claim 6, wherein The anionic contaminants in the water samples from the neutral or alkaline environment are sodium dichlorophenate, phosphate, glyphosate, As(V), Cr(VI), or RBV-5R dye.

8. The use according to claim 6, wherein Using the cationic chitosan fiber described in claim 5 as an adsorbent, gold cyanide in alkaline water samples is adsorbed and recovered, and / or anionic pollutants in neutral or alkaline water samples are adsorbed and removed. The adsorbed cationic chitosan fiber is regenerated using sodium hydroxide or sodium chloride solution.

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