A lignin-based flocculant, and a preparation method and application thereof

Abstract

The application belongs to the field of electrolytic manganese dioxide preparation, and particularly relates to a lignin-based flocculant as well as a preparation method and application thereof. The method comprises the following steps: (1) uniformly mixing lignin and a crosslinking agent according to a proportion to prepare a precursor; and (2) uniformly mixing the precursor and a vulcanizing agent according to a proportion, reacting under alkaline conditions, and purifying and drying to prepare the lignin-based flocculant. The lignin-based flocculant has good selectivity, can effectively remove metal ion impurities in electrolyte stock solution, and has high ion sensitivity, that is, even if the impurity concentration is low, the removal can be effectively achieved.

Description

Technical Field

[0001] This invention belongs to the field of electrolytic manganese dioxide preparation, and particularly relates to a lignin-based flocculant, its preparation method, and its application. Background Technology

[0002] The primary industrial application of electrolytic manganese dioxide is in the battery sector, with additional applications in ceramics, glass, and steelmaking. Downstream primary battery manufacturers are experiencing strong production demand, and with the increasing demand for lithium manganese oxide batteries in electric bicycles and power tools, the electrolytic manganese dioxide industry is facing a supply shortage, driving up market prices. Therefore, the implementation of this project can maximize the stimulation of the entire manganese-related industrial chain in Guangxi, which is of great significance to the coordinated development of industries across the region.

[0003] The main global production regions of electrolytic manganese dioxide (EMD) include the United States, Japan, Europe, and China. Electrolytic manganese dioxide was first produced and used by the Burgess Battery Company in the United States in the late 1930s. Japan's electrolytic manganese dioxide industry also developed relatively early, around the mid-1940s. In addition, Australia, South Africa, India, Brazil, and other countries also produce a certain amount of electrolytic manganese dioxide. The electrolytic preparation of manganese dioxide using a manganese sulfate + sulfuric acid system is currently the mainstream method for producing EMD worldwide, but it still suffers from problems such as low current density, low production efficiency, and impure crystal form of the obtained EMD product, as well as insufficient discharge capacity and reversibility.

[0004] Although my country has a large-scale electrolytic manganese dioxide production capacity, the quality of electrolytic manganese dioxide produced by the current electrolysis technology still has some shortcomings. The most critical issue is the difficulty in adopting effective impurity removal processes and process intensification measures to thoroughly purify the sulfuric acid leaching solution of manganese dioxide before electrolysis preparation. This results in a high content of metal ion impurities in the final product, affecting product quality and severely reducing the product's discharge performance. Summary of the Invention

[0005] This invention addresses the technical challenges of complex processes, severe pollution, and difficulty in effectively removing metal ion impurities in traditional electrolytic manganese dioxide production. It provides a lignin-based flocculant, its preparation method, and its application.

[0006] The main objective of this invention is:

[0007] 1) It can effectively and deeply remove conventional metal ion impurities from the electrolyte stock solution;

[0008] 2) It can remove conventional metal ion impurities while retaining manganese ions to a certain extent, thus exhibiting selectivity.

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

[0010] A method for preparing a lignin-based flocculant.

[0011] The method includes:

[0012] (1) Mix lignin and crosslinking agent evenly in proportion to prepare a precursor;

[0013] (2) Mix the precursor and the sulfurizing agent in proportion, react under alkaline conditions, purify and dry to prepare lignin-based flocculant.

[0014] As a preferred option

[0015] The lignin mentioned in step (1) is alkali lignin;

[0016] The crosslinking agent in step (1) is epichlorohydrin;

[0017] The lignin and crosslinking agent in step (1) are mixed evenly at a mass ratio of 1:(4.8~5.2).

[0018] As a preferred option

[0019] The preparation of the precursor in step (1) is carried out in a protective atmosphere at a temperature of 40–60 °C and a pH of 11–13 for 120–180 min.

[0020] As a preferred option

[0021] The sulfiding agent in step (2) is a mixture of ammonium sulfide and carbon disulfide, wherein the ammonium sulfide and carbon disulfide are mixed evenly in a mass ratio of 1:(8-12);

[0022] The precursor and vulcanizing agent in step (2) are mixed evenly at a mass ratio of 1:(2.3~2.7).

[0023] As a preferred option

[0024] The alkaline conditions described in step (2) have a pH of 11 to 13.

[0025] As a preferred option

[0026] The reaction described in step (2) is carried out in a protective atmosphere at a temperature of 30–50 °C for 240–300 min.

[0027] As a preferred option

[0028] The purification step (2) involves adjusting the pH to 7-8 with 1 mol / L hydrochloric acid, followed by adding excess anhydrous ethanol after the reaction.

[0029] The amount of anhydrous ethanol used is at least 300% VOL of the reaction system after the reaction;

[0030] The purification process is repeated 3 to 5 times.

[0031] As a preferred option

[0032] The drying in step (2) is carried out in an environment with a temperature of -30 to -50 ℃ and a pressure of 1.0 to 3.0 Pa for 120 to 180 minutes.

[0033] A lignin-based flocculant.

[0034] Application of a lignin-based flocculant

[0035] The lignin-based flocculant is used to remove ionic impurities from the manganese dioxide electrolyte stock solution.

[0036] Lignin, as a renewable natural polymer material, is widely available, possesses good biocompatibility, and is environmentally friendly, making it one of the most promising functional polymer materials. However, due to its complex structure and high resistance, lignin is not fully utilized. Furthermore, processed and extracted lignin easily loses its biological activity, reducing its flocculation ability for metal ion impurities and exhibiting non-specific selection for certain heavy metal ions, thus failing to meet practical application requirements. The technical solution of this invention is based on the chemical modification and material composite of alkali lignin to prepare a lignin-based flocculant. This flocculant possesses a unique functional principle of flocculation followed by adsorption, enabling selective adsorption of specific ions, including heavy metals and highly soluble stubborn metals. When the flocculant of this invention is placed in water, it first undergoes hydrolysis of the support medium, like ordinary flocculants, to complex and fix specific metal ion suspensions and colloids, producing a flocculation effect. Subsequently, lignin organic macromolecules are released from the complexed flocs as the center, adsorbing heavy metal ions in the surrounding space, reducing the local concentration and creating a concentration gradient, thereby inducing ion aggregation and achieving further removal of soluble heavy metal ion impurities.

[0037] To achieve the above objectives, lignin is modified to acquire specific physicochemical properties. Modifiers containing free electrons, oxygen-containing groups, nitrogen-containing groups, and sulfur-containing groups are used. Through chemical methods, active hydrogen atoms at the primary phenolic hydroxyl group and near, para- and ortho-positions of phenolic groups, as well as the reactivity of alcoholic hydroxyl groups and side chains, are used to modify lignin. Polar groups with strong adsorption and flocculation effects are grafted onto the active sites of lignin. lignin is modified and altered to target the flocculation of different metal ion impurities.

[0038] Through the inventors' practical experience and research on the process of preparing electrolytic manganese dioxide using "two minerals plus acid," it was found that the content of metal ions such as potassium, sodium, and iron in the electrolyte was too high. Furthermore, these impurities would be incorporated into the positive electrode during manganese dioxide electrolysis, significantly reducing the purity of manganese dioxide. Additionally, the energy level transitions and valence state transformations of iron and low-valence sulfur would hinder the precipitation of manganese dioxide at the positive electrode. Modified lignin molecules possess numerous different types of active functional groups, exhibiting adsorption properties for metal ions in the solution. In the process of preparing electrolytic manganese dioxide using "two minerals plus acid," the impurities in the electrolyte have a significant impact on the formation and quality indicators of electrolytic manganese dioxide. Therefore, removing impurity metal ions is a crucial step in the electrolytic production of manganese dioxide. The inventors' research and observation revealed that the types of impurity metal ions in the electrolyte typically include Ni. 2+ Co 2+ Cu 2+ Pb 2+ Fe 3+ and Zn 2+ In the present invention, the lignin flocculant has an adsorption effect on impurity metal ions. The binding mode of different metal ions with the flocculant varies with the type and concentration of the ions and is closely related to the ion adsorption affinity.

[0039] In this invention, the lignin-based flocculant removes metal ions by chelating them. During the electrolytic production of manganese dioxide, modified lignin in an aqueous solution forms insoluble chelates with metal ions, which are then precipitated and removed. Firstly, because Mn in the solution... 2+ High concentration, modified lignin and Mn 2+ A sparingly soluble chelate precipitate is formed, and then, through an ion exchange reaction, the impurity heavy metal ions in the solution replace Mn. 2+ This leads to the formation of more poorly soluble chelate precipitates. The stability of impurity metal ion chelates relative to Mn is... 2+ The greater the difference in chelates, the easier it is to remove impurity metal ions.

[0040] Various metal ions in a high-concentration manganese ion electrolyte can form different types of chelates under the action of the lignin flocculant of this invention, among which Fe... 3+ The stability of the chelate is much higher than that of Mn. 2+ The stability of other metal chelates decreases in the following order: Hg 2+ Ag + Cu 2+ Ni 2+ Co 2+ Pb 2+ Zn 2+ Mn 2+ From this sorting result, it can be seen that Fe 3+ Hg2+ Ni 2+ Co 2+ The chelate formed is more than that formed by Mn 2+ The resulting chelate is much more stable. When the lignin-based flocculant provided by this invention is added to a manganese sulfate solution, due to the Mn... 2+ At high concentrations, it first interacts with Mn. 2+ A sparingly soluble chelate is formed, and then Fe is removed through ion exchange. 3+ Hg 2+ Ni 2+ Co 2+ The stability of various metal chelates is ranked in the order of Mn 2+ The preceding metal substitutes Mn 2+ The formation of more insoluble chelates removes Ni from the manganese sulfate solution. 2+ Co 2+ The present invention can effectively remove metal impurities present in electrolytic manganese dioxide and obtain stable flocculent precipitates without causing secondary pollution to the environment.

[0041] The beneficial effects of this invention are:

[0042] The lignin-based flocculant of this invention has good selectivity and can effectively remove metal ion impurities in the electrolyte stock solution. It is also highly sensitive to ions and can effectively remove impurities even at low concentrations. Detailed Implementation

[0043] The present invention will be further described clearly and in detail below with reference to specific embodiments. 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.

[0044] 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.

[0045] Example 1

[0046] A method for preparing a lignin-based flocculant.

[0047] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:4.8 and reacted for 180 min at a temperature of 40 °C, a nitrogen atmosphere and a pH of 11 to prepare a precursor.

[0048] (2) The precursor and the sulfurizing agent were mixed evenly at a mass ratio of 1:2.3. The pH value was adjusted to 11 with ammonia water, the temperature was 30℃, and the reaction was carried out for 300 min under a nitrogen atmosphere. After adjusting the pH to 7 with 1 mol / L hydrochloric acid, the product was added to anhydrous ethanol of 300% VOL and purified repeatedly 3 times. The product was purified by rotary evaporation and dried for 180 min under an environment of -30℃ and 1.0 Pa to prepare lignin-based flocculant. The sulfurizing agent was ammonium sulfide and carbon disulfide mixed evenly at a mass ratio of 1:8.

[0049] The polymeric flocculant prepared in the examples was tested, and the specific operation and characterization results are as follows:

[0050] Manganese dioxide sulfuric acid leaching solution from soft manganese ore rhodochrosite was collected as an industrial sample solution. A 0.5 mol / L manganese sulfate solution was prepared, and 0.5 g ferric sulfate, 0.5 g nickel chloride, 0.3 g copper sulfate, 0.3 g zinc chloride, and 1.0 g calcium nitrate were added to the solution to prepare a laboratory sample solution. The polymeric flocculant and sample solution were mixed at a mass ratio of 3:97 and stirred for 20 min, followed by filtration. The ion concentration and average particle size of the filter residue in the solution system before and after treatment were measured. The removal rate of impurity metal ions, the retention rate of manganese ions, and the average particle size of agglomerated particles were characterized. The characterization results are as follows.

[0051]

[0052] Prepare solutions containing different impurity ions (Fe) using 0.5 mol / L manganese sulfate solution as the base solution. 3+ Gradient experiments were conducted on laboratory sample solutions of [specific substance] to test the concentration threshold for impurity removal and to characterize impurity ions (Fe). 3+ The removal rate and corresponding manganese ion retention rate at different concentrations are characterized as follows.

[0053]

[0054] In addition, the sample solution of the present invention was mixed with a suspension (the suspended matter being fine sand with a particle size of about 120 mesh) at a mass ratio of 3:97, stirred for 20 min and then filtered. The removal rate of solid particles in the suspension was characterized and calculated. The filter residue obtained by filtration was characterized and its average particle size was detected. The characterization results are as follows.

[0055]

[0056] Example 2

[0057] A method for preparing a lignin-based flocculant.

[0058] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:5 and reacted for 150 min at a temperature of 50 ℃, a nitrogen atmosphere and a pH of 12 to prepare a precursor.

[0059] (2) The precursor and the sulfiding agent were mixed evenly at a mass ratio of 1:2.5. The pH value was adjusted to 11.2 with ammonia water, and the reaction was carried out for 270 min at a temperature of 40 ℃ and a nitrogen atmosphere. The pH value was adjusted to 7.5 with 1 mol / L hydrochloric acid. The product was then purified by adding 350% VOL of anhydrous ethanol and repeated 4 times. The product was purified by rotary evaporation and dried for 150 min at a temperature of -40 ℃ and a Pa of 2.0. The lignin-based flocculant was prepared, wherein the sulfiding agent was ammonium sulfide and carbon disulfide mixed evenly at a mass ratio of 1:10.

[0060] The polymeric flocculant prepared in the examples was tested, and the specific operation and characterization results are as follows:

[0061] Manganese dioxide sulfuric acid leaching solution from soft manganese ore rhodochrosite was collected as an industrial sample solution. A 0.5 mol / L manganese sulfate solution was prepared, and 0.5 g ferric sulfate, 0.5 g nickel chloride, 0.3 g copper sulfate, 0.3 g zinc chloride, and 1.0 g calcium nitrate were added to the solution to prepare a laboratory sample solution. The polymeric flocculant and sample solution were mixed at a mass ratio of 3:97 and stirred for 20 min, followed by filtration. The ion concentration and average particle size of the filter residue in the solution system before and after treatment were measured. The removal rate of impurity metal ions, the retention rate of manganese ions, and the average particle size of agglomerated particles were characterized. The characterization results are as follows.

[0062]

[0063] Prepare solutions containing different impurity ions (Fe) using 0.5 mol / L manganese sulfate solution as the base solution. 3+ Gradient experiments were conducted on laboratory sample solutions of [specific substance] to test the concentration threshold for impurity removal and to characterize impurity ions (Fe). 3+ The removal rate and corresponding manganese ion retention rate at different concentrations are characterized as follows.

[0064]

[0065] In addition, the sample solution of the present invention was mixed with a suspension (the suspended matter being fine sand with a particle size of about 120 mesh) at a mass ratio of 3:97, stirred for 20 min and then filtered. The removal rate of solid particles in the suspension was characterized and calculated. The filter residue obtained by filtration was characterized and its average particle size was detected. The characterization results are as follows.

[0066]

[0067] Example 3

[0068] A method for preparing a lignin-based flocculant.

[0069] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:5.2 and reacted for 120 min at a temperature of 60 °C, a nitrogen atmosphere and a pH of 13 to prepare a precursor.

[0070] (2) The precursor and the sulfurizing agent were mixed evenly at a mass ratio of 1:2.7. The pH value was adjusted to 11.5 with ammonia water, and the reaction was carried out for 240 min at a temperature of 50 ℃ and a nitrogen atmosphere. After adjusting the pH to 8 with 1 mol / L hydrochloric acid, the product was added to anhydrous ethanol of 400% VOL and purified repeatedly 5 times. The product was purified by rotary evaporation and dried for 120 min at a temperature of -50 ℃ and a Pa of 3.0 to prepare lignin-based flocculant. The sulfurizing agent was ammonium sulfide and carbon disulfide mixed evenly at a mass ratio of 1:12.

[0071] The polymeric flocculant prepared in the examples was tested, and the specific operation and characterization results are as follows:

[0072] Manganese dioxide sulfuric acid leaching solution from soft manganese ore rhodochrosite was collected as an industrial sample solution. A 0.5 mol / L manganese sulfate solution was prepared, and 0.5 g ferric sulfate, 0.5 g nickel chloride, 0.3 g copper sulfate, 0.3 g zinc chloride, and 1.0 g calcium nitrate were added to the solution to prepare a laboratory sample solution. The polymeric flocculant and sample solution were mixed at a mass ratio of 3:97 and stirred for 20 min, followed by filtration. The ion concentration and average particle size of the filter residue in the solution system before and after treatment were measured. The removal rate of impurity metal ions, the retention rate of manganese ions, and the average particle size of agglomerated particles were characterized. The characterization results are as follows.

[0073]

[0074] Prepare solutions containing different impurity ions (Fe) using 0.5 mol / L manganese sulfate solution as the base solution. 3+ Gradient experiments were conducted on laboratory sample solutions of [specific substance] to test the concentration threshold for impurity removal and to characterize impurity ions (Fe). 3+ The removal rate and corresponding manganese ion retention rate at different concentrations are characterized as follows.

[0075]

[0076] In addition, the sample solution of the present invention was mixed with a suspension (the suspended matter being fine sand with a particle size of about 120 mesh) at a mass ratio of 3:97, stirred for 20 min and then filtered. The removal rate of solid particles in the suspension was characterized and calculated. The filter residue obtained by filtration was characterized and its average particle size was detected. The characterization results are as follows.

[0077]

[0078] Comparative Example 1

[0079] A method for preparing a lignin-based flocculant, the specific preparation method of which is the same as in Example 2, except that the proportion of the precursor component unique to this invention is changed, and the lignin-based flocculant is prepared by means of the following steps:

[0080] A method for preparing a lignin-based flocculant.

[0081] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:8 and reacted for 150 min at a temperature of 50 ℃, a nitrogen atmosphere and a pH of 12 to prepare a precursor.

[0082] (2) The precursor and the sulfiding agent were mixed evenly at a mass ratio of 1:2.5. The pH value was adjusted to 11.2 with ammonia water, and the reaction was carried out for 270 min at a temperature of 40 ℃ and a nitrogen atmosphere. The pH value was adjusted to 7.5 with 1 mol / L hydrochloric acid. The product was then purified by adding 350% VOL of anhydrous ethanol and repeated 4 times. The product was purified by rotary evaporation and dried for 150 min at a temperature of -40 ℃ and a Pa of 2.0. The lignin-based flocculant was prepared, wherein the sulfiding agent was ammonium sulfide and carbon disulfide mixed evenly at a mass ratio of 1:10.

[0083] The prepared polymeric flocculant was characterized in the same way as in Example 2, and the specific characterization results are as follows.

[0084]

[0085] A comparison of the characterization results with those of Example 2 revealed that the flocculant prepared in the comparative example exhibited reduced removal rates of suspended solids and metal ions. The inventors' research found that due to the complex spatial structure and resistance of alkali lignin, the chemical modification of alkali lignin requires strict control of the precursor component ratio to maintain its biological activity. This improves the flocculation ability of the modified lignin-based flocculant against metal ion impurities, giving it a unique functional principle of flocculation followed by adsorption, enabling selective adsorption of specific ions, including heavy metals and highly soluble stubborn metals. However, excessive modification can weaken the selectivity of lignin and limit its adsorption capacity. Particularly regarding the removal capacity of ferric ions and the threshold for low-concentration ionic impurities, excessive treatment reduces the ion sensitivity of the flocculant, resulting in a significant decrease in its removal rate at low concentrations.

[0086] Comparative Example 2

[0087] A method for preparing a lignin-based flocculant, the specific preparation method of which is the same as in Example 2, except that the sulfurizing agent unique to this invention is not used, and an equal amount of carbon disulfide is used to replace ammonium sulfide to prepare the polymeric flocculant. The specific operation is as follows:

[0088] A method for preparing a lignin-based flocculant.

[0089] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:5 and reacted for 150 min at a temperature of 50 ℃, a nitrogen atmosphere and a pH of 12 to prepare a precursor.

[0090] (2) The precursor and carbon disulfide were mixed evenly at a mass ratio of 1:2.5. The pH was adjusted to 11.2 with ammonia water, and the reaction was carried out for 270 min at a temperature of 40 ℃ and a nitrogen atmosphere. The pH was adjusted to 7.5 with 1 mol / L hydrochloric acid. The product was then purified by adding 350% VOL of anhydrous ethanol and repeated 4 times. The product was purified by rotary evaporation and dried for 150 min at a temperature of -40 ℃ and a Pa of 2.0 to prepare lignin-based flocculant.

[0091] The prepared polymeric flocculant was characterized in the same way as in Example 2, and the specific characterization results are as follows.

[0092]

[0093] Comparing the characterization results above with those of Example 2, it was found that the flocculant prepared in the comparative example had reduced intrinsic viscosity, suspended solids, and metal removal rates. The flocculant also exhibited lower diffusion in the water system, resulting in poorer flocculation. The inventors discovered that the higher the molecular weight of the polymer in the present invention, the better the flocculation performance. The lignin-based flocculant carries an electric charge, which is removed from the water system through a neutralization mechanism and ion complexation. The flocculant prepared by the present invention has a large number of active sites, providing more chelation sites, increasing the molecular weight of the polymer, inducing metal ion flocculation, and improving the water sedimentation process.

[0094] Comparative Example 3

[0095] A method for preparing a lignin-based flocculant, the specific preparation method of which is the same as in Example 2, except that the drying process unique to this invention is modified to prepare the polymeric flocculant. The specific operation is as follows:

[0096] A method for preparing a lignin-based flocculant.

[0097] (1) Alkali lignin and epichlorohydrin were mixed evenly at a mass ratio of 1:5 and reacted for 150 min at a temperature of 50 ℃, a nitrogen atmosphere and a pH of 12 to prepare a precursor.

[0098] (2) The precursor and the sulfiding agent were mixed evenly at a mass ratio of 1:2.5. The pH value was adjusted to 11.2 with ammonia water, and the reaction was carried out for 270 min at a temperature of 40 ℃ and a nitrogen atmosphere. After adjusting the pH to 7.5 with 1 mol / L hydrochloric acid, the product was added to anhydrous ethanol of 350% VOL and purified repeatedly 4 times. The product was purified by rotary evaporation and dried for 150 min at a temperature of 90 ℃ and an environment of 101.325 kPa to prepare lignin-based flocculant. The sulfiding agent was ammonium sulfide and carbon disulfide mixed evenly at a mass ratio of 1:10.

[0099] The prepared polymeric flocculant was characterized in the same way as in Example 2, and the specific characterization results are as follows.

[0100]

[0101] Comparing the characterization results above with those of Example 2, it was found that the turbidity removal rate of the flocculant prepared in the comparative example was significantly reduced. According to the inventors' research and observation, the flocculant of the present invention, after low-temperature drying, can maintain the activity of the modified lignin and ensure the existence of the charge effect at the active sites. In the production of electrolytic manganese dioxide in a sulfuric acid system, if the spatial structure of the flocculant changes too much, it will cause Mn... 2+ Mn was not fully generated 4+ Mn appears in some parts 3+ This situation will lead to a decrease in current efficiency and distortion of the generated γ-MnO2 lattice, resulting in a decrease in the purity of electrolyzed manganese dioxide. Therefore, although the flocculant prepared in this example maintains a high manganese ion retention rate and a high metal ion impurity removal rate, it will actually lead to a deterioration in the subsequent electrolytic preparation effect and poor practical application results.

[0102] Comparative Example 4

[0103] A commercially available flocculant was characterized using the same performance methods as in Example 2. The specific characterization results are as follows.

[0104]

[0105] Analysis of the above characterization results clearly shows that commercially available flocculants can remove more suspended solid particles and effectively remove impurity metal ions. However, they cannot retain manganese ions in the solution, significantly reducing the manganese ion content and lacking metal ion selectivity. Therefore, they cannot be used as the electrolyte stock solution for the electrolysis of manganese dioxide. Through research and testing by the inventors, it has been found that the lignin-based flocculant in this invention, during the electrolytic production of manganese dioxide, first modifies lignin and Mn... 2+ A sparingly soluble chelate precipitate is formed, and then, through an ion exchange reaction, impurity heavy metal ions in the solution replace Mn.2+ The formation of more insoluble chelate precipitates can effectively remove metallic impurities present in electrolytic manganese dioxide, and also produce stable flocculent precipitates without causing secondary pollution, and can selectively precipitate metal ions.

Claims

1. A method for preparing a lignin-based flocculant, characterized in that, The method includes: (1) Mix lignin and crosslinking agent evenly in proportion to prepare a precursor; (2) Mix the precursor and the sulfurizing agent in proportion, react under alkaline conditions, purify and dry to prepare lignin-based flocculant; The lignin mentioned in step (1) is alkali lignin; The crosslinking agent in step (1) is epichlorohydrin; In step (1), the lignin and crosslinking agent are mixed evenly at a mass ratio of 1:(4.8-5.2); The sulfiding agent in step (2) is a mixture of ammonium sulfide and carbon disulfide, wherein the ammonium sulfide and carbon disulfide are mixed evenly in a mass ratio of 1:(8-12); In step (2), the precursor and the vulcanizing agent are mixed evenly at a mass ratio of 1:(2.3~2.7); The alkaline conditions described in step (2) have a pH of 11 to 13; The reaction described in step (2) is carried out in a protective atmosphere at a temperature of 30–50 °C for 240–300 min; The drying in step (2) is carried out in an environment with a temperature of -30 to -50 ℃ and a pressure of 1.0 to 3.0 Pa for 120 to 180 min.

2. The method for preparing a lignin-based flocculant according to claim 1, characterized in that, The preparation of the precursor in step (1) is carried out in a protective atmosphere at a temperature of 40–60 °C and a pH of 11–13 for 120–180 min.

3. The method for preparing a lignin-based flocculant according to claim 1, characterized in that, The purification step (2) involves adjusting the pH to 7-8 with 1 mol / L hydrochloric acid, followed by adding excess anhydrous ethanol after the reaction. The amount of anhydrous ethanol used is at least 300% VOL of the reaction system after the reaction; The purification process is repeated 3 to 5 times.

4. A lignin-based flocculant prepared by any one of the methods described in claims 1 to 3.

5. An application of the lignin-based flocculant as described in claim 4 in the removal of ionic impurities, characterized in that, The lignin-based flocculant is used to remove ionic impurities from the manganese dioxide electrolyte stock solution.

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