Amidoxime-modified lignin-based adsorbents, methods of making and applications

Abstract

This invention relates to the field of polymer materials technology, and discloses a lignin-based adsorbent modified with a methylamine oxime, its preparation method, and its application. The invention uses lignin enzymatically hydrolyzed solid waste from industrial ethanol production as raw material. Utilizing the phenolic hydroxyl activity of lignin, methylamine oxime functional groups are chemically grafted onto the lignin structure to obtain a lignin-based adsorbent modified with a methylamine oxime. This adsorbent has the advantages of strong stability, high adsorption activity, low cost, and recyclability, enabling the high-value utilization of waste enzymatically hydrolyzed lignin. When the above-mentioned lignin-based adsorbent is used in the treatment of highly acidic uranium-containing nuclear wastewater, the uranium adsorption rate can reach up to 99.9%, which is beneficial for the promotion of lignin-based materials in the industrial application of treating highly acidic nuclear wastewater.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a lignin-based adsorbent modified with a methylamine oxime, its preparation method, and its application. Background Technology

[0002] Uranium is the primary source of nuclear fuel. Large quantities of uranium-containing nuclear wastewater are generated during uranium mining and processing, nuclear fuel manufacturing, reactor operation and reprocessing, and the production of radioactive isotopes. Factories and research institutions in related fields also discharge uranium-containing nuclear wastewater due to the use of radioactive isotopes, leading to an increasingly complex and diverse range of types and compositions of uranium-containing nuclear wastewater. Enriching and recovering uranium from uranium-containing nuclear wastewater can not only reduce the damage of radioactive substances to humans and the environment, but also allow for the recycling of uranium from the wastewater as an alternative resource, thus promoting resource recycling.

[0003] For the extraction, recovery, and removal of uranium from uranium-containing nuclear wastewater, reported methods include coordination precipitation, evaporation, extraction, ion exchange, membrane separation, adsorption, and bioengineering. Adsorption is considered one of the most promising and easily implemented methods for treating uranium-containing nuclear wastewater due to its simplicity, low cost, large processing capacity, and versatility of materials. However, the nuclear industry often uses strong inorganic acids such as sulfuric acid and nitric acid to dissolve uranium ore and fuel, resulting in extremely acidic environments in the nuclear wastewater. Uranium in these acidic environments exists as UO₂. 22+ In the presence of ions, the adsorption capacity of adsorbents for uranium is significantly suppressed under acidic conditions. Most adsorbents can only be used in the pH range of 5-7, making them difficult to apply in practical high-acid environments.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] To address the aforementioned problems, the primary objective of this invention is to provide a method for preparing a lignin-based adsorbent modified with a methylamine oxime, using lignin enzymatically hydrolyzed from solid waste from industrial ethanol production as raw material, and grafting methylamine oxime groups onto the lignin structure.

[0006] The second objective of this invention is to provide a lignin-based adsorbent modified with a methylamine oxime by the above method, which has a large specific surface area, many active sites, and high adsorption activity.

[0007] A third objective of this invention is to provide the application of the above-mentioned lignin-based adsorbent modified with a methylamine oxime in the treatment of highly acidic uranium-containing nuclear wastewater.

[0008] To achieve the above-mentioned objectives of the present invention, the first technical solution of the present invention provides a method for preparing a lignin-based adsorbent modified with a methylamine oxime, comprising the following steps:

[0009] Enzymatic hydrolysis of lignin is carried out with a cross-linking agent to obtain a mixed solution of enzymatically hydrolyzed lignin.

[0010] Under a nitrogen atmosphere, an initiator was added to the above-mentioned enzymatically hydrolyzed lignin mixture to carry out the first reaction, followed by the addition of acrylonitrile to carry out the second reaction, and the addition of hydroxylamine hydrochloride to carry out the third reaction.

[0011] Furthermore, the amounts of each reactive component added, by weight, are as follows:

[0012] Enzymatic hydrolysis of lignin: 1-5 parts

[0013] 1-3 parts of crosslinking agent

[0014] Initiator 1-5 parts,

[0015] 1-5 parts acrylonitrile

[0016] Hydroxylamine hydrochloride 1-5 parts.

[0017] Furthermore, the crosslinking reaction is carried out at a temperature of 40 °C for 1 h.

[0018] Furthermore, the first reaction temperature is 35-40 °C, and the reaction time is 2-6 h.

[0019] Furthermore, the second reaction temperature is 60-80 ℃, and the reaction time is 2-6 h.

[0020] Furthermore, the third reaction temperature is 60-80 ℃, and the reaction time is 2-6 h.

[0021] The second technical solution of the present invention provides a lignin-based adsorbent modified with a methylamine oxime according to the above preparation method.

[0022] The third technical method of the present invention provides the application of the above-mentioned lignin-based adsorbent modified with amine oxime in the treatment of uranium-containing nuclear wastewater.

[0023] Furthermore, the initial pH of the nuclear wastewater is 1-11.

[0024] Furthermore, the dosage of the lignin-based adsorbent modified with the amine oxime is 0.05-0.5 g / L.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] (1) The present invention uses enzymatic hydrolysis of lignin from solid waste of industrial ethanol production as raw material to prepare a lignin-based adsorbent modified with a lignin-amine oxime. The phenolic hydroxyl group in lignin with high reactivity is used as the active site. The lignin-amine oxime group is grafted onto the lignin. The grafted lignin-amine oxime group is chemically bonded to the phenolic hydroxyl group and is stably fixed on the lignin, which does not easily cause the adsorbent to deactivate.

[0027] (2) The lignin-based adsorbent modified with amine oxime prepared in this invention has a large specific surface area, many active sites, high adsorption activity, and is easy to recycle and reuse, with low cost and good recyclability.

[0028] (3) The lignin-based adsorbent modified with amine oxime prepared in this invention is used in the treatment of uranium-containing nuclear wastewater. It adsorbs uranium under extremely acidic conditions and still has a high adsorption rate and adsorption capacity, which solves the problem that uranium in nuclear wastewater is difficult to recover and utilize under high acid conditions. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0030] Figure 1 This is a comparison chart showing the adsorption performance of the sample from Example 1 of the present invention and the comparative sample on uranium in nuclear wastewater at pH 7.

[0031] Figure 2 This is a diagram showing the effect of uranium recovery and utilization under different pH conditions in Example 1 of the present invention. Detailed Implementation

[0032] To better understand the technical solution of the present invention, the technical solution of the present invention will be further described below in conjunction with the accompanying drawings and embodiments. The ways to implement the present invention include, but are not limited to, the following embodiments. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art. Unless otherwise specified, the test methods in the following embodiments are conventional methods.

[0033] In the embodiments of the present invention, "parts" refers to the mass parts of the corresponding substance, such as "20 parts" indicating that its mass parts are 20 parts.

[0034] The first embodiment of the present invention provides a method for preparing a lignin-based adsorbent modified with a methylamine oxime, comprising the following steps:

[0035] Enzymatic hydrolysis of lignin is carried out with a cross-linking agent to obtain a mixed solution of enzymatically hydrolyzed lignin.

[0036] Under a nitrogen atmosphere, an initiator was added to the above-mentioned enzymatically hydrolyzed lignin mixture to carry out the first reaction, followed by the addition of acrylonitrile to carry out the second reaction, and the addition of hydroxylamine hydrochloride to carry out the third reaction.

[0037] In a specific implementation, to ensure complete reaction at each stage, the crosslinking agent is added in 1-3 parts by weight, and the enzymatic hydrolysate, initiator, acrylonitrile, and hydroxylamine hydrochloride are all added in 1-5 parts.

[0038] It should be noted that the enzymatically hydrolyzed lignin used in this invention is a waste product from the straw-to-ethanol industry, which is difficult to recycle and is mostly directly incinerated or discharged into the environment, wasting resources and causing environmental pollution. However, the enzymatically hydrolyzed lignin structure contains various functional groups such as phenolic hydroxyl, methoxy, carboxyl, and unsaturated double bonds, which can be easily introduced into diverse functional groups through reactions such as methylation, amination, and nitration, thereby improving the selectivity and treatment capacity for various pollutants and showing excellent application prospects in the field of wastewater treatment. On the other hand, the metallo-oxime group is currently the most widely used functional group among adsorbents for uranyl ions, exhibiting high adsorption capacity and excellent selectivity for uranyl ions. However, the metallo-oxime group is prone to protonation under acidic conditions, transforming into a strongly positively charged group and thus losing its adsorption activity. Therefore, this invention utilizes the highly reactive phenolic hydroxyl groups in enzymatically hydrolyzed lignin as active sites, grafting a methylamine oxime group onto the phenolic hydroxyl groups of lignin. The grafted methylamine oxime group is chemically bonded to the phenolic hydroxyl groups and stably fixed on the lignin, making it less prone to deactivation in acidic solutions.

[0039] Understandably, the present invention uses enzymatic hydrolysis of lignin to crosslink with a crosslinking agent to obtain an enzymatic hydrolyzed lignin mixture. The purpose of this invention is to improve the crosslinking property of the enzymatic hydrolyzed lignin, so that the enzymatic hydrolyzed lignin maintains high reactivity in subsequent reactions.

[0040] In a specific embodiment, the crosslinking agent is glutaraldehyde.

[0041] Specifically, the crosslinking reaction is carried out at a temperature of 40 °C for 1 h.

[0042] Furthermore, it is understood that an initiator is first added to the enzymatic hydrolysis lignin mixture of the present invention to carry out the first reaction, the purpose of which is to generate active groups on the phenolic hydroxyl groups on the enzymatic hydrolyzed lignin, which is more conducive to the modification of the lignin by amine oxime.

[0043] In a specific embodiment, the initiator is cerium ammonium nitrate.

[0044] Specifically, the first reaction temperature is 35-40 ℃, and the reaction time is 2-6 h.

[0045] In a further embodiment, the second and third reactions are processes for modifying lignin with amine oxime.

[0046] Specifically, the second reaction temperature is 60-80 ℃, and the reaction time is 2-6 h.

[0047] Specifically, the third reaction temperature is 60-80 ℃, and the reaction time is 2-6 h.

[0048] In a specific implementation, the third reaction is followed by washing and drying, where washing removes reagents from the adsorbent and drying removes moisture from the surface of the adsorbent.

[0049] The second embodiment of the present invention provides a lignin-based adsorbent modified with a methylamine oxime according to the above preparation method. In this adsorbent, the methylamine oxime groups are stably fixed on the lignin, resulting in a large specific surface area and many active sites. It still has high adsorption activity even in a high acid environment, and also has good recyclability and low cost.

[0050] The third embodiment of the present invention provides the application of the above-mentioned lignin-based adsorbent modified with amine oxime in the treatment of uranium-containing nuclear wastewater.

[0051] In a specific implementation, the initial pH of the nuclear wastewater is 1-11.

[0052] It should be noted that when using adsorbents to adsorb uranium from highly acidic nuclear wastewater, uranium exists as UO under acidic conditions. 22+ The presence of ions significantly inhibits the adsorption capacity of adsorbents, limiting their use to acidic solutions with a pH range of 5-7. This invention, a lignin-based adsorbent modified with a methylamine oxime, stabilizes the methylamine oxime group on the lignin phenolic hydroxyl group, ensuring its activity under acidic conditions. This allows the adsorbent to maintain high adsorption rate and capacity for uranium even under extremely acidic conditions (initial pH of nuclear wastewater is 1), solving the problem of difficult uranium recovery in acidic environments, especially highly acidic ones.

[0053] Furthermore, it should be noted that the treatment conditions for uranium recovery from nuclear wastewater using the amine oxime-modified lignin-based adsorbent described in this invention can be reasonably adjusted by those skilled in the art based on the concentration of uranium in the nuclear wastewater. This invention does not impose any special limitations, but only provides some preferred embodiments.

[0054] In a preferred embodiment, the uranium concentration in the nuclear wastewater is 10-50 mg / L.

[0055] Furthermore, the dosage of the lignin-based adsorbent modified with the amine oxime is 0.05-0.5 g / L.

[0056] Furthermore, the processing conditions are: atmospheric pressure, reaction temperature 10-60℃, reaction time 60-240 min, and rotation speed 150-250 rpm.

[0057] To make the present invention clearer, specific embodiments and comparative examples are provided below for further illustration. However, it should be understood that these embodiments are merely for more detailed illustration and should not be construed as limiting the present invention in any way.

[0058] Example 1

[0059] Dissolve 2 parts of glutaraldehyde in 200 mL of deionized water, add 3 parts of enzymatically hydrolyzed lignin while stirring, and crosslink at 40 °C for 1 h to obtain a crosslinked enzymatically hydrolyzed lignin mixture.

[0060] Under a nitrogen atmosphere, 3 parts of cerium ammonium nitrate were added to the enzymatic hydrolysis lignin mixture, and the first reaction was carried out at 38 °C for 4 h; then 3 parts of acrylonitrile were added and the second reaction was carried out at 70 °C for 4 h; then 3 parts of hydroxylamine hydrochloride were added and the third reaction was carried out at 70 °C for 4 h. After washing and drying, the lignin-based adsorbent modified with amine oxime was obtained.

[0061] Example 2

[0062] Dissolve 1 part of glutaraldehyde in 50 mL of deionized water, add 1 part of enzymatically hydrolyzed lignin while stirring, and crosslink at 40 °C for 1 h to obtain a crosslinked enzymatically hydrolyzed lignin mixture.

[0063] Under a nitrogen atmosphere, 1 part of cerium ammonium nitrate was added to the enzymatic hydrolysis lignin mixture, and the first reaction was carried out at 35 °C for 6 h; then 1 part of acrylonitrile was added and the second reaction was carried out at 60 °C for 6 h; then 1 part of hydroxylamine hydrochloride was added and the third reaction was carried out at 60 °C for 6 h. After washing and drying, the lignin-based adsorbent modified with amine oxime was obtained.

[0064] Example 3

[0065] Dissolve 3 parts of glutaraldehyde in 300 mL of deionized water, add 5 parts of enzymatically hydrolyzed lignin while stirring, and crosslink at 40 °C for 1 h to obtain a crosslinked enzymatically hydrolyzed lignin mixture.

[0066] Under a nitrogen atmosphere, 5 parts of cerium ammonium nitrate were added to the enzymatic hydrolysis lignin mixture, and the first reaction was carried out at 40 °C for 2 h; then 5 parts of acrylonitrile were added and the second reaction was carried out at 80 °C for 2 h; then 5 parts of hydroxylamine hydrochloride were added and the third reaction was carried out at 80 °C for 2 h. After washing and drying, the lignin-based adsorbent modified with amine oxime was obtained.

[0067] Comparative Example

[0068] The enzymatic hydrolysis of lignin from industrial ethanol solid waste was provided by Nanjing Yihuan Technology Co., Ltd.

[0069] Experimental Example 1

[0070] At a dosage of 0.1 g / L, the samples from Example 1 and the comparative example were respectively added to uranium-containing nuclear wastewater with an initial uranium concentration of 20 mg / L and a pH value of 7. After reacting at 25 °C for 60 min, the adsorption effect of the two samples on uranium was measured.

[0071] Measurement method: The uranium concentration in the solution was measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES), and then the adsorption capacity and adsorption rate were calculated using the following formulas:

[0072] ,

[0073] ,

[0074] In the formula: Q e —Adsorption capacity at equilibrium (mg / g)

[0075] R—Adsorption rate at equilibrium (%)

[0076] C e —Uranium concentration in the solution at equilibrium (mg / L)

[0077] C0 — Initial uranium concentration in the solution (mg / L)

[0078] m — mass of adsorbent (mg)

[0079] V — Volume of uranium (mL).

[0080] The measurement results are as follows Figure 1 As shown, EHL-PNC is the sample of Example 1, and EHL is the comparative sample.

[0081] Depend on Figure 1 The experimental results show that the adsorption rate and adsorption capacity of the lignin-based adsorbent modified with amine oxime in Example 1 for uranium were 99.88% and 15.28 mg / g, respectively; while the adsorption rate and adsorption capacity of the comparative sample for uranium were 0% and 0 mg / g, respectively.

[0082] Experimental Example 2

[0083] The sample from Example 1 was added to uranium-containing nuclear wastewater with an initial uranium concentration of 20 mg / L and a pH of 1 at a dosage of 0.1 g / L. The reaction was carried out at 25 °C for 60 min. The pH of the nuclear wastewater was then gradually adjusted to 11, and the adsorption performance of the sample on uranium at different pH values ​​was measured.

[0084] The measurement method is the same as in Experiment 1.

[0085] The measurement results are as follows Figure 2 As shown.

[0086] according to Figure 2The experimental results show that the sample of Example 1 of this invention exhibits a uranium adsorption rate as high as 99.9% and an adsorption capacity of 2.41 mg / g under extremely acidic conditions (pH = 1), indicating that the amylopectin-modified lignin adsorbent prepared in this embodiment can effectively recover and utilize uranium under extreme nuclear wastewater conditions. However, as the pH value of the nuclear wastewater is adjusted, with an increase in pH and a decrease in uranium concentration, the adsorption effect of the adsorbent on uranium gradually decreases.

[0087] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. Use of a modified amine-oxime lignin-based adsorbent in the treatment of nuclear waste water containing uranium, characterized in that, The initial pH of the nuclear waste water is 1-3; The preparation of the amidoxime-modified lignin-based adsorbent comprises the following steps: The enzymatic hydrolysis lignin and glutaraldehyde are cross-linked at 40 DEG C for 1 h to obtain an enzymatic hydrolysis lignin mixture; Under a nitrogen atmosphere, cerium nitrate is added to the above-mentioned enzymatic hydrolysis lignin mixture to perform a first reaction, then acrylonitrile is added to perform a second reaction, and hydroxylamine hydrochloride is added to perform a third reaction.

2. Use according to claim 1, characterized in that, The amount of each reaction component is as follows in terms of weight parts: Enzymatic hydrolysis lignin 1-5 parts, Glutaraldehyde 1-3 parts, Cerium nitrate 1-5 parts, Acrylonitrile 1-5 parts, Hydroxylamine hydrochloride 1-5 parts.

3. Use according to claim 1, characterized in that, The first reaction temperature is 35-40 DEG C, and the reaction time is 2-6 h.

4. Use according to claim 1, characterized in that, The second reaction temperature is 60-80 DEG C, and the reaction time is 2-6 h.

5. The use according to claim 1, characterized in that, The third reaction temperature is 60-80 DEG C, and the reaction time is 2-6 h.

6. The use according to claim 1, characterized in that, The dosage of the amidoxime-modified lignin-based adsorbent is 0.05-0.5 g / L.

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