Nano lignin-based flotation desulfurization collecting agent as well as preparation method and application thereof

Abstract

The invention relates to a nano lignin-based flotation desulfurization collecting agent and a preparation method and application thereof, and belongs to the technical field of mineral flotation. The collecting agent comprises a nanoscale lignin core, alkyl chains and sulfydryl collecting functional groups, wherein the alkyl chains and the sulfydryl collecting functional groups are grafted to the surface of the core. The sulfydryl collecting functional group realizes selective recognition and collection by utilizing the specific chemical affinity of sulfur atoms and iron ions on the surface of the pyrite. The nanoscale lignin core has a particle form and a high specific surface area, after the collecting agent is adsorbed to the surface of pyrite through a sulfydryl functional group, the core can be firmly anchored to minerals, and the binding force of the collecting agent and the minerals is enhanced. Meanwhile, the surface of the pyrite is hydrophobic through the grafted alkyl chain, and the pyrite is promoted to be attached to bubbles and float upwards. In addition, the nanoscale lignin core has no affinity to diaspore, and can inhibit floating of aluminum minerals. Through the synergistic effect, the collecting agent achieves efficient separation of pyrite and diaspore.

Description

Technical Field

[0001] This application relates to the field of mineral flotation technology, and in particular to a nano-lignin-based flotation desulfurization collector, its preparation method, and its application. Background Technology

[0002] In the field of mineral processing, flotation collectors are key reagents that determine separation efficiency. While traditional collectors and synthetic small-molecule collectors (such as xanthates) have some ability to collect sulfide minerals, they suffer from high costs and environmental inefficiencies. Developing novel, green collectors utilizing renewable biomass resources has become a research hotspot.

[0003] Lignin is considered a promising raw material for modifying flotation reagents due to its wide availability, low price, and the presence of various active functional groups. However, ordinary lignin has a large molecular weight, poor water solubility, and low accessibility of reactive sites. When directly used for modification to prepare collectors, the resulting products fail to meet industrial requirements in terms of collection efficiency and selectivity for the target minerals, thus limiting the application of lignin in the field of flotation reagents. Summary of the Invention

[0004] This application provides a nano-lignin-based flotation desulfurization collector, its preparation method, and its application, in order to solve the following technical problem: how to develop a highly efficient and green flotation desulfurization collector that combines the characteristics of nanomaterials with strong collecting selectivity.

[0005] In a first aspect, embodiments of this application provide a nano-lignin-based flotation desulfurization collector, the collector comprising a nano-sized lignin core, and alkyl chains and mercapto-based collecting functional groups grafted onto the surface of the core.

[0006] Optionally, the thiol-based collecting functional group is derived from at least one of butyl xanthate, isobutyl xanthate, pentyl xanthate, isopentyl xanthate, and ethyl thiocyanate.

[0007] Optionally, the average hydrated particle size of the nanoscale lignin core is 100nm~300nm, and the polydispersity index (PDI) is ≤0.2.

[0008] In a second aspect, embodiments of this application provide a method for preparing the nano-lignin-based flotation desulfurization collector described in the first aspect, the method comprising: grafting a nano-sized lignin dispersion, a quaternary ammonium salt surfactant, and a thiol-based collector into a copolymerization reaction in the presence of an inert atmosphere and a free radical initiator; The nano-sized lignin solid in the nano-sized lignin dispersion has a mass ratio of 1:(5~10) to the mercapto-based collector, and the mass of the free radical initiator is 10%~30% of the mass of the mercapto-based collector; the graft copolymerization reaction temperature is 50~90℃, and the graft copolymerization reaction time is 20 hours~30 hours.

[0009] Optionally, the quaternary ammonium salt surfactant is at least one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0010] Optionally, the free radical initiator is one of ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride.

[0011] Optionally, the preparation method of the nanoscale lignin dispersion includes: Pretreated lignin was dissolved in an organic solvent and stirred to obtain a lignin organic solution. Deionized water was added to the lignin organic solution to dilute and induce self-assembly, causing lignin to precipitate and form nanoparticles, thus obtaining a nano-lignin suspension. The nano-lignin suspension was transferred into a pretreated dialysis bag for dialysis purification to remove the organic solvent and small molecule impurities, thereby obtaining a nano-sized lignin dispersion. The pretreatment of the dialysis bag includes: boiling the dialysis tube in deionized water containing sodium bicarbonate and disodium EDTA, rinsing it, boiling it again in deionized water containing disodium EDTA, rinsing it, and then soaking it in an ethanol aqueous solution for later use.

[0012] Optionally, the organic solvent is at least one selected from methanol, anhydrous ethanol, isopropanol, acetone, tetrahydrofuran, and N,N-dimethylformamide.

[0013] Optionally, the pretreated lignin is one of alkali lignin, lignin sulfonate, enzymatically hydrolyzed lignin, or organic solvent lignin.

[0014] Optionally, the lignin in the lignin organic solution has a mass concentration of 1 mg / mL to 50 mg / mL.

[0015] Optionally, in the dilution-induced self-assembly treatment, the volume ratio of the deionized water to the lignin organic solution is (3~50):1.

[0016] Optionally, in the dialysis purification process, the deionized water is replaced every 8 to 12 hours, the molecular weight cutoff of the dialysis bag is ≥3500 Da, and the dialysis time is ≥48 hours.

[0017] Thirdly, embodiments of this application provide an application of the nano-lignin-based flotation desulfurization collector described in the first aspect in mineral flotation. In bauxite reverse flotation desulfurization operations, the nano-lignin-based flotation desulfurization collector is used for selective flotation to remove pyrite.

[0018] Optionally, in the selective flotation process for removing pyrite, the total amount of collector used is 400 g / t raw ore to 700 g / t raw ore, and the pH value of the flotation pulp is 4.0 to 9.0.

[0019] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a nano-lignin-based flotation desulfurization collector, comprising a nano-sized lignin core and alkyl chains and mercapto-based collecting functional groups grafted onto the surface of the core. The mercapto-based collecting functional groups grafted onto the surface of the nano-sized lignin core exhibit a strong chemical affinity for metal ions on the surface of pyrite. The sulfur atoms in the mercapto-based collecting functional groups possess lone pairs of electrons, enabling them to form coordination bonds or undergo chemisorption with iron ions on the pyrite surface, thereby selectively binding the nano-lignin-based flotation desulfurization collector to the pyrite surface. By utilizing the specific interaction between the mercapto-based collecting functional groups and pyrite, selective recognition and collection of pyrite are achieved, solving the problem of insufficient selectivity in traditional collectors. Nanoscale lignin cores possess a granular morphology and a large specific surface area. When the nanoscale lignin-based flotation desulfurization collector is adsorbed onto the surface of pyrite via mercapto-based collecting functional groups, the nanoscale lignin cores can be stably anchored to the mineral surface, enhancing the binding force between the nanoscale lignin-based flotation desulfurization collector and the mineral and preventing it from detaching during flotation. The alkyl chains grafted onto the surface of the nanoscale lignin cores are hydrophobic, forming a hydrophobic film on the pyrite surface, enhancing the hydrophobicity of the pyrite surface, promoting the adhesion of pyrite particles to air bubbles, and achieving flotation separation. Simultaneously, the nanoscale lignin cores themselves have no significant affinity for the surface of aluminum minerals such as gibbsite, and the hydrophilic groups of the lignin molecules help inhibit the flotation of aluminum minerals. Through the hydrophobic enhancement effect of the alkyl chains and the lack of affinity of the nanoscale lignin cores for gibbsite, efficient separation of pyrite and gibbsite is achieved, solving the problem of low desulfurization efficiency in bauxite reverse flotation. Attached Figure Description

[0020] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A transmission electron microscope image of the nanoscale lignin dispersion provided in Example 1 of this application; Figure 2 This is a transmission electron microscope image of the nano-lignin-based flotation desulfurization collector provided in Example 1 of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] The range descriptions used herein, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "including" and "contains" as used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships mentioned herein, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained through commercial purchase or prepared using existing methods.

[0025] In a first aspect, embodiments of this application provide a nano-lignin-based flotation desulfurization collector, the collector comprising a nano-sized lignin core, and alkyl chains and mercapto-based collecting functional groups grafted onto the surface of the core.

[0026] The thiol-based collecting functional groups grafted onto the surface of nanoscale lignin cores exhibit a strong chemical affinity for metal ions on the pyrite surface. The sulfur atoms in these thiol-based collecting functional groups possess lone pairs of electrons, enabling them to form coordination bonds or undergo chemisorption with iron ions on the pyrite surface. This allows the nanoscale lignin-based flotation desulfurization collector to selectively bind to the pyrite surface. Utilizing the specific interaction between the thiol-based collecting functional groups and pyrite, selective recognition and collection of pyrite are achieved, overcoming the problem of insufficient selectivity in traditional collectors. The nanoscale lignin cores possess a particle morphology and a large specific surface area. After the nanoscale lignin-based flotation desulfurization collector is adsorbed onto the pyrite surface via the thiol-based collecting functional groups, the nanoscale lignin cores can be stably anchored to the mineral surface, enhancing the binding force between the nanoscale lignin-based flotation desulfurization collector and the mineral, preventing it from detaching during the flotation process. The alkyl chains grafted onto the surface of the nanoscale lignin core are hydrophobic, forming a hydrophobic film on the pyrite surface, enhancing its hydrophobicity, and promoting the adhesion of pyrite particles to air bubbles, thus achieving flotation separation. Simultaneously, the nanoscale lignin core itself has no significant affinity for the surface of aluminum minerals such as gibbsite, and the hydrophilic groups of the lignin molecules help inhibit the flotation of aluminum minerals. Through the hydrophobic enhancement effect of the alkyl chains and the lack of affinity of the nanoscale lignin core for gibbsite, highly efficient separation of pyrite and gibbsite is achieved, solving the problem of low desulfurization efficiency in bauxite reverse flotation.

[0027] In some embodiments, the thiol-based collecting functional group is derived from at least one of butyl xanthate, isobutyl xanthate, pentyl xanthate, isopentyl xanthate, and ethyl thiocyanate.

[0028] Thiol-based collecting functional groups refer to the chemical groups in the final nanoscale lignin-based flotation desulfurization collector molecule responsible for selectively interacting with the surface of target minerals (such as pyrite). These functional groups are not generated out of thin air but introduced through a chemical reaction. Butyl xanthate, isobutyl xanthate, pentyl xanthate, isopentyl xanthate, and ethyl thiocyanate all belong to the thiol class of compounds and contain sulfur atoms that can chemically adsorb metal ions on the mineral surface, thus exhibiting natural selective collecting ability for sulfide minerals such as pyrite.

[0029] Substances from different sources (such as butyl xanthate and pentyl xanthate) may produce slightly different final synthesized nanoscale lignin-based flotation desulfurization collectors in terms of hydrophobicity, steric hindrance, and selectivity for specific minerals due to differences in alkyl chain length or structure. Therefore, one or more of the above-mentioned substances can be selected and used in combination, depending on the characteristics of the ore to be treated (such as the dissemination characteristics of pyrite in bauxite), to achieve the best flotation desulfurization effect.

[0030] In some embodiments, the average hydrated particle size of the nanoscale lignin core is 100nm~300nm, and the polydispersity index (PDI) is ≤0.2.

[0031] The average hydrated particle size refers to the average hydrodynamic diameter of nano-sized lignin particles in an aqueous medium, measured by dynamic light scattering, and is expressed in nanometers (nm). This parameter reflects the actual size of nanoparticles in an aqueously dispersed state and is a core indicator for evaluating the particle size of nanomaterials. The polydispersity index (PDI) is the particle size distribution width index measured by dynamic light scattering, with a value ranging from 0 to 1. A smaller PDI value indicates a narrower and more uniform particle size distribution; a larger PDI value indicates a wider particle size distribution and less uniform particle size. In the embodiments of this application, a PDI ≤ 0.2 indicates a highly uniform particle size distribution of the nano-sized lignin particles.

[0032] In a second aspect, embodiments of this application provide a method for preparing the nano-lignin-based flotation desulfurization collector described in the first aspect, the method comprising: grafting a nano-sized lignin dispersion, a quaternary ammonium salt surfactant, and a thiol-based collector into a copolymerization reaction in the presence of an inert atmosphere and a free radical initiator; The nano-sized lignin solid in the nano-sized lignin dispersion has a mass ratio of 1:(5~10) to the mercapto-based collector, and the mass of the free radical initiator is 10%~30% of the mass of the mercapto-based collector; the graft copolymerization reaction temperature is 50~90℃, and the graft copolymerization reaction time is 20 hours~30 hours.

[0033] In the graft copolymerization reaction, the mass ratio of the added nanoscale lignin solid to the added mercapto-based collector is 1:5 to 1:10. For example, when using 1 gram of nanoscale lignin solid, 5 to 10 grams of mercapto-based collector must be used simultaneously. This ratio range ensures that a sufficient number of mercapto-based collector molecules can be grafted onto the surface of the nanoscale lignin solid, thereby endowing the final product, a nanoscale lignin-based flotation desulfurization collector, with sufficiently strong collecting ability.

[0034] The mass of the free radical initiator used must be 10% to 30% of the mass of the thiol-based collector used. This ratio ensures that an appropriate amount of free radicals are generated in the reaction system to effectively initiate the graft copolymerization reaction between nanoscale lignin solids and the thiol-based collector. Too little free radical initiator (below 10%) may lead to incomplete reaction, while too much free radical (above 30%) may trigger side reactions or result in uneven molecular weight distribution of the product.

[0035] The graft copolymerization reaction temperature is 50–90°C, which defines the temperature range that the reaction system must maintain. Within this temperature range, the free radical initiator can decompose at a suitable rate to generate free radicals, thereby driving the graft copolymerization reaction at a controllable rate. The graft copolymerization reaction time is 20–30 hours, which defines the reaction duration. This time range ensures that the graft copolymerization reaction between nano-sized lignin solids and thiol-based collectors can proceed fully under the temperature conditions of 50–90°C, achieving the expected conversion rate and grafting rate.

[0036] In some embodiments, the quaternary ammonium salt surfactant is at least one selected from dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0037] Dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide are four specific quaternary ammonium salt surfactant compounds. These four compounds share common molecular structural features: they all contain a quaternary ammonium cationic head group, a bromide counterion, and an alkyl group with different carbon chain lengths (dodecyl, tetradecyl, hexadecyl, and octadecyl, respectively). With increasing alkyl carbon chain length, the hydrophobicity and arrangement behavior at the oil-water interface of quaternary ammonium salt surfactants exhibit a regular change, but their basic properties and functions as quaternary ammonium salt surfactants remain similar.

[0038] In the reaction system of this application embodiment, the above-mentioned quaternary ammonium salt surfactant can be adsorbed on the surface of the nanoscale lignin core through electrostatic interaction and hydrophobic interaction, improve the dispersion state of the nanoscale lignin core in the aqueous phase, increase the accessibility of the reaction site, and thus promote the graft copolymerization reaction between the nanoscale lignin core and the mercapto collector.

[0039] In some embodiments, the free radical initiator is one of ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride.

[0040] Free radical initiators are compounds that can decompose to generate free radicals under graft copolymerization conditions, thereby initiating a graft copolymerization reaction between nanoscale lignin cores and thiol-based collectors. The free radical initiators used in the embodiments of this application are all water-soluble free radical initiators, suitable for the aqueous reaction system of this application. Ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride are three specific water-soluble free radical initiator compounds. Among them, ammonium persulfate and potassium persulfate belong to inorganic persulfate initiators, while azobisisobutyramidine hydrochloride belongs to water-soluble azo initiators. These three initiators differ in chemical structure, but all possess the ability to decompose and generate free radicals under heating conditions, and the decomposition temperature range of these three initiators matches the graft copolymerization reaction temperature (50~90℃) defined in the embodiments of this application.

[0041] In some embodiments, the preparation method of the nanoscale lignin dispersion includes: Pretreated lignin was dissolved in an organic solvent and stirred to obtain a lignin organic solution. Deionized water was added to the lignin organic solution to dilute and induce self-assembly, causing lignin to precipitate and form nanoparticles, thus obtaining a nano-lignin suspension. The nano-lignin suspension was transferred into a pretreated dialysis bag for dialysis purification to remove the organic solvent and small molecule impurities, thereby obtaining a nano-sized lignin dispersion. The pretreatment of the dialysis bag includes: boiling the dialysis tube in deionized water containing sodium bicarbonate and disodium EDTA, rinsing it, boiling it again in deionized water containing disodium EDTA, rinsing it, and then soaking it in an ethanol aqueous solution for later use.

[0042] The preparation method of the nanoscale lignin dispersion is a preparatory step specifically designed to provide the core raw material for the synthesis of nanoscale lignin-based flotation desulfurization collectors. The dissolution treatment provides the molecular-level dispersion basis for the dilution-induced self-assembly process; only when lignin is fully dissolved in the organic solvent can it form uniform nanoparticles through self-assembly upon subsequent water addition. The dilution-induced self-assembly process provides a suspension of nanoparticles to be purified for the dialysis purification process; the size and distribution of the nanoparticles formed in this step directly affect the quality of the final product. The dialysis purification process removes the organic solvent and small molecule impurities, obtaining a pure nanoscale lignin dispersion that can be directly used in the method described in the second aspect.

[0043] In some embodiments, the organic solvent is at least one selected from methanol, anhydrous ethanol, isopropanol, acetone, tetrahydrofuran, and N,N-dimethylformamide.

[0044] Organic solvents are organic liquid media used to dissolve pretreated lignin and form lignin organic solutions. Methanol, anhydrous ethanol, and isopropanol are alcohol solvents; acetone is a ketone solvent; tetrahydrofuran is an ether solvent; and N,N-dimethylformamide is an amide solvent. Although these six solvents belong to different chemical categories, they can all effectively dissolve various types of lignin (including alkali lignin, lignin sulfonate, enzymatically hydrolyzed lignin, and organic solvent lignin) to form homogeneous and stable lignin organic solutions.

[0045] Meanwhile, all six solvents mentioned above are completely miscible with water. This characteristic is crucial to the method of this application: when deionized water is added to the lignin organic solution, the addition of water changes the composition of the solvent, reduces the solubility of lignin, and thus induces lignin molecules to precipitate and form nanoparticles through self-assembly. If the solvent is immiscible with water or has poor miscibility, a uniform dilution-induced self-assembly process cannot be achieved.

[0046] In some embodiments, the pretreated lignin is one of alkali lignin, lignin sulfonate, enzymatically hydrolyzed lignin, or organic solvent lignin.

[0047] Pretreated lignin refers to lignin raw materials separated and extracted from plant fiber raw materials that have not undergone the nano-processing steps described in this application. In the context of this application, "pretreatment" does not refer to a specific step in this method, but rather distinguishes the lignin treated by this method from commercially available or industrially produced lignin products that have undergone industrial separation processes and are directly obtainable, rather than untreated natural wood fiber raw materials found in nature. Alkali lignin refers to lignin products extracted from black liquor using alkaline pulping processes (such as the sulfate process or caustic soda process). Lignin sulfonate refers to lignin derivatives containing sulfonic acid groups produced using sulfite pulping processes. Enzymatically hydrolyzed lignin refers to lignin extracted from the residue remaining after biomass has been hydrolyzed and saccharified using enzymes such as cellulase. Organic solvent lignin refers to lignin products extracted from plant raw materials using organic solvent methods (such as the ethanol method or acetic acid method). Although alkali lignin, lignin sulfonate, enzymatically hydrolyzed lignin, and organic solvent lignin differ in their sources and extraction processes, they all belong to the lignin family. Lignin is a naturally abundant and renewable aromatic polymer, and its molecular structure contains abundant active functional groups such as phenolic hydroxyl groups, alcoholic hydroxyl groups, and carboxyl groups. These functional groups provide reactive sites for subsequent graft copolymerization reactions. Furthermore, all four types of lignin possess amphiphilic molecular structures. Under conditions of dissolution in organic solvents followed by dilution with water, they can all undergo self-assembly through hydrophobic interactions and π-π stacking, precipitating out nanoscale particles. Although the molecular weight and functional group content of lignin from different sources vary, potentially leading to slight differences in the particle size and distribution of the formed nanoparticles, the fundamental characteristics of self-assembly forming nanoparticles are consistent.

[0048] In some embodiments, the lignin organic solution has a lignin concentration of 1 mg / mL to 50 mg / mL.

[0049] The mass concentration of lignin refers to the mass of pretreated lignin contained in a unit volume of lignin organic solution, expressed in milligrams per milliliter (mg / mL). This mass concentration parameter is a key variable controlling the subsequent dilution-induced self-assembly process and the final particle size and distribution of nanoscale lignin particles. When deionized water is added to the lignin organic solution, the solvent system's ability to dissolve lignin decreases rapidly, causing lignin molecular chains to aggregate and precipitate due to supersaturation, forming nanoparticles. If the lignin mass concentration is below 1 mg / mL, the number of lignin molecules per unit volume of solution is too small. During dilution with water, the probability of intermolecular collisions and aggregation into nuclei is significantly reduced, potentially leading to low nanoparticle yield or particles that are too small and unstable. If the lignin mass concentration is above 50 mg / mL, the solution viscosity is too high, and the lignin molecular chains are in a highly entangled state. During dilution with water, local supersaturation becomes extremely high, causing lignin molecules to aggregate rapidly and disorderly, easily forming aggregates with wide particle size distributions, excessively large sizes, or even micrometer-sized aggregates, making it impossible to obtain nanoscale lignin with uniform particle size.

[0050] In some embodiments, in the dilution-induced self-assembly treatment, the volume ratio of the deionized water to the lignin organic solution is (3~50):1.

[0051] In this embodiment, the dilution-induced self-assembly treatment refers to the process of adding deionized water to the obtained lignin organic solution to induce the self-assembly of lignin molecules into nanoparticles by changing the solvent polarity. Deionized water is an aqueous medium used in the dilution-induced self-assembly treatment, which reduces the solvent polarity, decreases the solubility of lignin, and causes precipitation and self-assembly. If the volume ratio of deionized water to lignin organic solution is less than 3:1, it means that the amount of water added is insufficient. At this time, the proportion of organic solvent in the mixed solvent system is still relatively high, and the solubility of lignin is still strong. This will lead to a low supersaturation of lignin, insufficient precipitation driving force, and only a small amount of lignin may form particles, or the formed particles may be too large and unevenly distributed, or even unable to effectively form stable nanoscale particles, resulting in low yield. If the volume ratio of deionized water to lignin organic solution is greater than 50:1, it means that a large amount of water has been added. At this time, the mixed solvent system instantly becomes a water-dominated unfavorable solvent environment, and the supersaturation of lignin increases sharply. This leads to explosive nucleation of lignin molecules in a very short time, making it difficult to control the particle growth process. It easily forms a system with a very wide particle size distribution, containing a large number of fine particles and large aggregates, and it is also impossible to obtain nanoscale lignin with uniform particle size.

[0052] In some embodiments, during the dialysis purification process, the deionized water is replaced every 8 to 12 hours, the molecular weight cutoff of the dialysis bag is ≥3500 Da, and the dialysis time is ≥48 hours.

[0053] Dialysis purification involves transferring the obtained nano-lignin suspension into a dialysis bag and using the selective permeation principle of a semi-permeable membrane to remove organic solvents, inorganic salts, and small molecule impurities from the suspension, thereby obtaining a pure nano-sized lignin dispersion. During the dialysis purification process, the deionized water outside the dialysis bag is periodically replaced with fresh deionized water at 8- to 12-hour intervals. This operation aims to maintain the concentration gradient of organic solvents and small molecule impurities inside and outside the dialysis bag, ensuring the continuous progress of the dialysis process.

[0054] A dialysis bag with a molecular weight cutoff of ≥3500 Da means that the bag can retain molecules with a molecular weight of ≥3500 Daltons, while allowing molecules with a molecular weight of ≥3500 Daltons to pass freely. This parameter determines the selective permeation performance of the dialysis bag. This specification of dialysis bag allows organic solvent molecules, inorganic salt ions, and small oligomers generated from lignin degradation with a molecular weight below 3500 Da to diffuse freely through the membrane pores into the external liquid, while effectively retaining lignin nanoparticles with a molecular weight of ≥3500 Da within the bag. Under these molecular weight cutoff conditions, a dialysis process of more than 48 hours is required to reduce the concentration of organic solvents, inorganic salts, and small molecule impurities in the nano-lignin suspension to a negligible level through repeated concentration gradient diffusion, thereby obtaining a pure nano-sized lignin dispersion.

[0055] Thirdly, embodiments of this application provide an application of the nano-lignin-based flotation desulfurization collector described in the first aspect in mineral flotation. In bauxite reverse flotation desulfurization operations, the nano-lignin-based flotation desulfurization collector is used for selective flotation to remove pyrite.

[0056] Bauxite reverse flotation desulfurization refers to a specific separation process using bauxite as the raw ore. Sulfur-containing minerals (mainly pyrite) are scraped off as a froth product through flotation, while aluminum minerals (mainly gibbsite) are enriched in the product within the flotation tank. Pyrite is the main sulfur-containing mineral in bauxite and is the target mineral selectively removed by nano-lignin-based flotation desulfurization collectors in bauxite reverse flotation desulfurization. This application is based on the molecular structure characteristics of the nano-lignin-based flotation desulfurization collector: thiol-based collecting functional groups grafted onto the surface of nano-sized lignin cores have a specific chemical affinity for the pyrite surface. In the flotation pulp, these functional groups preferentially recognize and interact with metal ions (such as iron ions) on the pyrite surface, thereby causing the collector molecules to firmly adsorb onto the surface of the pyrite particles. The collector molecules adsorbed on the pyrite surface have alkyl chains facing the aqueous phase, imparting hydrophobicity to the originally hydrophilic pyrite particles. Hydrophobic pyrite particles readily adhere to air bubbles in the slurry and rise to the surface, forming a foam product that is scraped off, thus removing the bauxite. In this process, the nano-sized lignin core not only acts as a carrier for thiol-based collecting functional groups and alkyl chains, but its own nano-size effect and high specific surface area also enhance the dispersibility of the collector in the slurry and the probability of collision with mineral particles, further improving the collection efficiency.

[0057] In some embodiments, during the selective flotation process for removing pyrite, the total amount of collector used is 400 g / t raw ore to 700 g / t raw ore, and the pH value of the flotation pulp is 4.0 to 9.0.

[0058] The total collector dosage refers to the total mass of nano-lignin-based flotation desulfurization collector added to a unit mass of raw ore in a complete flotation operation (including roughing and multiple cleaning processes), expressed in grams per ton of raw ore (g / t). If the total collector dosage is less than 400 g / t of raw ore, the mercapto-based collecting functional groups of the collector may not be sufficient to fully activate all pyrite surfaces, resulting in some pyrite remaining in the concentrate and causing the sulfur content of the aluminum concentrate to exceed the standard. If the total collector dosage is greater than 700 g / t of raw ore, on the one hand, it will increase reagent costs and reduce the economic efficiency of the process; on the other hand, excessive collector may cause non-selective adsorption due to the hydrophobic alkyl chains in its molecular structure, starting to collect target minerals (such as gibbsite), leading to the loss of target minerals and a significant decrease in aluminum concentrate yield. At the same time, excessive reagent may also form micelles in the pulp, consuming bubbles and disrupting the flotation process.

[0059] Flotation pulp refers to a solid-liquid two-phase system formed by mixing raw ore with water after grinding, used for flotation separation. The pH of flotation pulp ranges from 4.0 to 9.0, covering a broad range from neutral (pH 7.0) to weakly alkaline (pH 9.0) and weakly acidic (pH 4.0). Within this range, the nano-sized lignin core and grafted thiol-based collecting functional groups of the nano-sized lignin-based flotation desulfurization collector maintain stable chemical structures and dispersion states. Below pH 4.0, the strongly acidic environment may cause the decomposition of thiol-based collecting functional groups or acid-catalyzed condensation of the nano-sized lignin core, destroying the collector structure. Above pH 9.0, the strongly alkaline environment may inhibit the adsorption of thiol-based collecting functional groups on the pyrite surface or cause the formation of a hydrophilic iron hydroxide film on the pyrite surface, reducing its floatability.

[0060] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0061] Example 1 Preparation of nanoscale lignin dispersion: 0.4 g of alkali lignin was dissolved in 25 mL of anhydrous ethanol and magnetically stirred for 2 hours until completely dissolved, preparing a lignin ethanol solution. 75 mL of deionized water was slowly added to this lignin ethanol solution, and the mixture was magnetically stirred for 2 hours until it became a milky white suspension, yielding a nano-lignin suspension. The entire suspension was transferred to a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed with deionized water for 72 hours, changing the deionized water every 12 hours to remove ethanol and small molecule impurities, resulting in a nano-sized lignin dispersion. Dynamic light scattering analysis showed that the average hydrated particle size of the obtained nano-sized lignin was 156 nm, and the polydispersity index (PDI) was 0.12.

[0062] Preparation of nano-lignin-based flotation desulfurization collector: Add 100 mL of deionized water to a 500 mL three-necked flask. Weigh 1.0 g of hexadecyltrimethylammonium bromide (a quaternary ammonium salt surfactant) and 35 g of the nano-sized lignin dispersion prepared above into the flask. Purge air with nitrogen, turn on magnetic stirring (450 rpm), and heat to 70 °C for a pre-reaction of 30 minutes. Weigh 0.5 g of ammonium persulfate (a free radical initiator) and dissolve it in 10 mL of deionized water. Add the solution to the reaction system over 5 minutes using a constant-pressure dropping funnel, and continue the reaction at 70 °C for 15 minutes. Weigh 50 g of the nano-sized lignin dispersion prepared above and dissolve 2.0 g of butyl xanthate (a mercapto collector) in 40 mL of deionized water. Place the mixture in a constant-pressure dropping funnel and slowly and evenly add it dropwise to the reaction system over 6 hours. After the addition is complete, continue the reaction at 70 °C for 20 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain the nano-lignin-based flotation desulfurization collector product, denoted as NL-1.

[0063] Example 2 The operation steps are the same as in Example 1, except that: In the preparation of the nano-sized lignin dispersion, 1.0 g of alkali lignin was weighed and dissolved in 25 mL of anhydrous ethanol, and then 75 mL of deionized water was added to obtain a nano-sized lignin suspension. After dialyzing, a nano-sized lignin dispersion was obtained with an average hydrated particle size of 215 nm and a PDI of 0.11.

[0064] In the preparation of the nano-lignin-based flotation desulfurization collector, the amount of ammonium persulfate was changed to 1.2 g, and the total amount of nano-lignin dispersion added was 100 g (achieved by adding the nano-lignin dispersion twice). 6.0 g of pentyl xanthate was selected as the mercapto-based collector. The resulting nano-lignin-based flotation desulfurization collector product is designated NL-2.

[0065] Example 3 The operation steps are the same as in Example 1, except that: In the preparation of the nanoscale lignin dispersion, 0.4 g of enzymatically hydrolyzed lignin was weighed and dissolved in 25 mL of anhydrous ethanol, and then 250 mL of deionized water was added to obtain a nanoscale lignin suspension. After dialyzing, a nanoscale lignin dispersion was obtained with an average hydrated particle size of 128 nm and a PDI of 0.09.

[0066] In the preparation of the nano-lignin-based flotation desulfurization collector, 0.9 g of potassium persulfate was used as the free radical initiator, the total amount of nano-lignin dispersion added was 80 g (achieved by adding the nano-lignin dispersion twice), and 4.0 g of isobutyl xanthate was used as the mercapto collector. The resulting nano-lignin-based flotation desulfurization collector product is designated as NL-3.

[0067] Comparative Example 1 The operating steps are exactly the same as in Example 1, except that the nano-sized lignin dispersion used in the steps is replaced with an equal amount of ordinary alkali lignin aqueous slurry with a solid content (0.4 g of ordinary alkali lignin powder is directly dispersed in 100 mL of water and stirred for 2 hours). The resulting product is designated as CL-1.

[0068] The collectors obtained in Examples 1-3 and Comparative Example 1 were used in a reverse flotation desulfurization experiment of high-sulfur bauxite in a certain area of ​​Guangxi. The sulfur content of the raw ore was 6.1% (in the form of pyrite), and the main aluminum mineral was gibbsite. The flotation process consisted of one roughing and three cleaning stages, with the pulp pH adjusted to 7.5. The flotation results are shown in Table 1.

[0069] Table 1 Summary of flotation test results

[0070] Appendix Figure 1-2 Detailed explanation: Figure 1 This is a transmission electron microscope image of the nanoscale lignin dispersion provided in Example 1 of this application; as shown. Figure 1 As shown, the nano-sized lignin particles are spherical, with uniform particle size distribution and good dispersibility.

[0071] Figure 2 This is a transmission electron microscope image of the nano-lignin-based flotation desulfurization collector provided in Example 1 of this application; as shown. Figure 2 As shown, the nano-lignin-based flotation desulfurization collector particles are spherical with a uniform particle size distribution.

[0072] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: Environmentally friendly and in line with sustainable development requirements: This invention uses renewable industrial lignin (such as alkali lignin, enzymatically hydrolyzed lignin, etc.) as the main raw material, which is widely available and inexpensive; the preparation process is mild and does not require high temperature and high pressure; the organic solvent can be recovered through dialysis purification, reducing environmental pollution. This transforms industrial lignin from low-value combustion utilization into high-value flotation reagent products, opening up new avenues for the high-value utilization of lignin.

[0073] The process is simple and easy to industrialize: The method for preparing nano-sized lignin and the method for synthesizing nano-lignin-based flotation desulfurization collectors in the embodiments of the present invention are simple to operate, have low equipment requirements, and the process parameters are easy to control, and have good prospects for industrial application.

[0074] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A nano-lignin-based flotation desulfurization collector, characterized in that, The collector comprises a nanoscale lignin core, and alkyl chains and mercapto-based collecting functional groups grafted onto the surface of the core.

2. The collector according to claim 1, characterized in that, The thiol-based collecting functional group is derived from at least one of butyl xanthate, isobutyl xanthate, pentyl xanthate, isopentyl xanthate, and ethyl thiocyanate.

3. The collector according to claim 1 or 2, characterized in that, The average hydrated particle size of the nanoscale lignin core is 100nm~300nm, and the polydispersity index (PDI) is ≤0.

2.

4. A method for preparing the nano-lignin-based flotation desulfurization collector according to any one of claims 1 to 3, characterized in that, The method includes: grafting a nano-sized lignin dispersion, a quaternary ammonium salt surfactant, and a thiol-based collector into a copolymer in the presence of an inert atmosphere and a free radical initiator; The nano-sized lignin solid in the nano-sized lignin dispersion has a mass ratio of 1:(5~10) to the mercapto-based collector, and the mass of the free radical initiator is 10%~30% of the mass of the mercapto-based collector; the graft copolymerization reaction temperature is 50~90℃, and the graft copolymerization reaction time is 20 hours~30 hours.

5. The method according to claim 4, characterized in that, The quaternary ammonium salt surfactant is at least one selected from dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide; and / or, The free radical initiator is one of ammonium persulfate, potassium persulfate, or azobisisobutyramidine hydrochloride.

6. The method according to claim 4, characterized in that, The preparation method of the nanoscale lignin dispersion includes: Pretreated lignin was dissolved in an organic solvent and stirred to obtain a lignin organic solution. Deionized water was added to the lignin organic solution to dilute and induce self-assembly, causing lignin to precipitate and form nanoparticles, thus obtaining a nano-lignin suspension. The nano-lignin suspension was transferred into a pretreated dialysis bag for dialysis purification to remove organic solvents and small molecule impurities from the nano-lignin suspension, thereby obtaining a nano-sized lignin dispersion. The pretreatment of the dialysis bag includes: boiling the dialysis tube in deionized water containing sodium bicarbonate and disodium EDTA, rinsing it, boiling it again in deionized water containing disodium EDTA, rinsing it, and then soaking it in an ethanol aqueous solution for later use.

7. The method according to claim 6, characterized in that, The organic solvent is at least one selected from methanol, anhydrous ethanol, isopropanol, acetone, tetrahydrofuran, and N,N-dimethylformamide; and / or, The pretreated lignin is one of alkali lignin, lignin sulfonate, enzymatically hydrolyzed lignin, or organic solvent lignin; and / or... The lignin organic solution contains lignin at a concentration of 1 mg / mL to 50 mg / mL.

8. The method according to claim 6, characterized in that, In the dilution-induced self-assembly treatment, the volume ratio of deionized water to the lignin organic solution is (3~50):1; and / or, In the dialysis purification process, the deionized water is replaced every 8 to 12 hours, the molecular weight cutoff of the dialysis bag is ≥3500 Da, and the dialysis time is more than 48 hours.

9. The application of the nano-lignin-based flotation desulfurization collector according to any one of claims 1 to 3 in mineral flotation, characterized in that, In bauxite reverse flotation desulfurization operations, the nano-lignin-based flotation desulfurization collector is used for selective flotation removal of pyrite.

10. The application according to claim 9, characterized in that, In the selective flotation process for removing pyrite, the total amount of collector used is 400 g / t raw ore to 700 g / t raw ore, and the pH value of the flotation pulp is 4.0 to 9.0.

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