Nanometer lignin-based direct flotation desilicication collecting agent and preparation method and application thereof

Abstract

The invention relates to a nanometer lignin-based direct flotation desilicication collecting agent and a preparation method and application thereof, and belongs to the technical field of mineral flotation. The novel collecting agent with excellent selectivity and efficient collecting capacity is successfully prepared by loading high-selectivity carboxyl / hydroximic acid functional groups on the surfaces of nano lignin particles in a chemical grafting manner and assisting with a stable and controllable synthesis process. The collecting agent can accurately capture diaspore through selective chemical adsorption of functional groups in the low-grade bauxite direct flotation desilicication operation, diaspore is effectively floated out through the hydrophobic effect of the nano-carrier, meanwhile, entrainment of silicon-containing gangue minerals is reduced, and therefore the aluminum-silicon separation efficiency is remarkably improved, and the collecting agent has the advantages of being simple in process, low in cost and good in application prospect in the direct flotation desilicication operation of the low-grade bauxite. The problems that in the prior art, selectivity is poor, and adaptability to micro-fine ore is poor are effectively solved.

Description

Technical Field

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

[0002] Bauxite is the main raw material for alumina production. With the increasing depletion of high-quality bauxite resources, the efficient utilization of low-grade bauxite has become a focus of industry attention. Direct flotation desilication is one of the important methods for processing low-grade bauxite. Its core lies in selectively flotating and enriching aluminum-bearing minerals (mainly gibbsite) by adding collectors, while suppressing silicon-bearing minerals (such as kaolinite and illite) in the pulp, thereby achieving aluminum-silicon separation and improving concentrate quality.

[0003] Currently, the collectors commonly used in bauxite direct flotation desilication mainly include fatty acids and their derivatives. These collectors are widely available and relatively inexpensive, and have a certain collecting ability for oxide ores. However, fatty acid collectors have poor selectivity. While collecting gibbsite, they also tend to undergo non-specific adsorption with metal ions on the surface of silicon-containing minerals, resulting in a high silicon content in the concentrate and limited improvement in the aluminum-silicon ratio. Furthermore, for low-grade bauxite with fine-grained dispersibility and high liberation requirements, the collecting capacity and selectivity of fatty acid collectors often fail to meet the process requirements for efficient desilication. Summary of the Invention

[0004] This application provides a nano-lignin-based positive flotation desilication collector, its preparation method, and its application, in order to solve the following technical problem: how to develop a novel desilication collector.

[0005] In a first aspect, embodiments of this application provide a method for preparing a nano-lignin-based positive flotation desilication collector, the method comprising: The first part of the nano-lignin dispersion, the quaternary ammonium salt surfactant and deionized water are mixed to obtain the first mixture. Under an inert atmosphere, the first mixture is heated to 50°C to 80°C and stirred for the first time at a speed of 300 rpm to 600 rpm to form a pre-dispersed system. An aqueous solution of a water-soluble free radical initiator is mixed with the pre-dispersed system for a second initiation reaction to obtain an activated reaction system; Dissolve carboxyl and / or hydroxamic acid functional group agents in an alkaline aqueous solution to obtain a saponified functional group solution; The second part of the nano-sized lignin dispersion is mixed with the saponified functional group solution in a third mixing process to obtain a functionalized mixture. The functionalized mixture is added dropwise to the activation reaction system over a period of 2 to 6 hours, and the reaction continues for 12 to 24 hours after the addition is complete, so as to achieve the grafting of carboxylic acid and / or hydroxamic acid functional groups on the surface of nano-lignin, thereby obtaining a nano-lignin-based positive flotation desilication collector.

[0006] Optionally, both the first and second parts of the nanoscale lignin dispersion meet the following requirements: the average particle size of the nanoparticles is 50nm~200nm, and the mass fraction of lignin contained is 0.05%~5%.

[0007] Optionally, the mass ratio of the first part of the nano-lignin dispersion to the second part of the nano-lignin dispersion is 1:(1~5).

[0008] Optionally, the temperature for initiating the reaction is 50°C to 80°C, and the reaction time is 20 minutes to 80 minutes.

[0009] Optionally, by mass parts, the first mixture comprises: 20 to 40 parts of nano-lignin dispersion, 0.5 to 2 parts of quaternary ammonium salt surfactant, and 90 to 110 parts of deionized water.

[0010] Optionally, the alkaline aqueous solution is prepared from sodium hydroxide or potassium hydroxide, the pH value of the alkaline aqueous solution is 9-12, and the temperature of the alkaline aqueous solution is 50℃-90℃.

[0011] Optionally, the quaternary ammonium salt surfactant is at least one of dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0012] Optionally, the water-soluble free radical initiator is one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride, and the mass concentration of the aqueous solution of the water-soluble free radical initiator is 5% to 20%.

[0013] Optionally, the carboxyl and / or hydroxamic acid functional group agent is at least one selected from oleic acid, tal oil, oxidized paraffin soap, salicylic acid, benzoic acid, and C5-C9 alkyl hydroxamic acid, and the mass ratio of the carboxyl and / or hydroxamic acid functional group agent to the total solid content of the nano-lignin dispersion is 9-15.

[0014] Secondly, embodiments of this application provide a nano-lignin-based positive flotation desilication collector, which is prepared by the method described in the first aspect.

[0015] Optionally, the collector is a nanoparticle with carboxylic acid and / or hydroxamic acid functional groups grafted onto its surface, and the average particle size of the nanoparticle is 50 nm to 300 nm.

[0016] Thirdly, embodiments of this application provide an application of the nano-lignin-based positive flotation desilication collector described in the second aspect in mineral flotation. In the positive flotation desilication operation of low-grade bauxite, the nano-lignin-based positive flotation desilication collector is used for selective flotation enrichment of gibbsite.

[0017] Optionally, in the selective flotation enrichment of gibbsite, the total amount of collector used is 1000 g / t raw ore to 1300 g / t raw ore, and the pH value of the flotation pulp is 8.0 to 9.5.

[0018] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing a nano-lignin-based positive flotation desilication collector. The method includes: firstly mixing a first portion of nano-lignin dispersion, a quaternary ammonium salt surfactant, and deionized water to obtain a first mixture; heating the first mixture to 50°C~80°C under an inert atmosphere and stirring it at a speed of 300 rpm~600 rpm to form a pre-dispersion system; and secondly mixing an aqueous solution of a water-soluble free radical initiator with the pre-dispersion system to initiate a reaction. An activation reaction system is obtained; carboxyl and / or hydroxamic acid functional group reagents are dissolved in an alkaline aqueous solution to obtain a saponified functional group solution; a second part of the nanoscale lignin dispersion is mixed with the saponified functional group solution to obtain a functionalized mixture; the functionalized mixture is added dropwise to the activation reaction system over 2 to 6 hours, and the reaction continues for 12 to 24 hours after the addition is complete to achieve grafting of carboxylic acid and / or hydroxamic acid functional groups onto the surface of nano-lignin, thereby obtaining a nano-lignin-based positive flotation desilication collector. This application, by dissolving carboxylic acid and / or hydroxamic acid functional group reagents in an alkaline solution for saponification, endows the reagents with water solubility and reactivity. These functional groups have a strong selective chelating ability for aluminum ions on the surface of gibbsite monohydrate, forming stable chemical adsorption, fundamentally achieving precise identification of target minerals. Secondly, by using a nano-lignin dispersion as a carrier, the large specific surface area of ​​nano-lignin provides ample grafting sites for the aforementioned functional groups. The grafted nano-lignin particles not only exhibit multi-site, high-intensity adsorption with gibbsite through their dense functional groups, but the nanoparticles themselves also provide the necessary hydrophobic surface for the captured mineral particles. This characteristic significantly enhances the collection ability and flotation efficiency for fine-grained minerals. In summary, this technical solution prepares a novel, structurally stable collector by firmly loading highly selective functional groups onto the surface of nano-lignin. This collector can accurately capture and effectively float gibbsite during flotation, while significantly reducing the entrainment of silica-containing gangue minerals, thereby greatly improving the aluminum-silicon separation efficiency and solving the pain points of poor selectivity and difficulty in recovering fine particles in existing technologies. Attached Figure Description

[0019] 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.

[0020] 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.

[0021] Figure 1 This is a schematic flowchart illustrating a method for preparing a nano-lignin-based positive flotation desilication collector, as provided in an embodiment of this application. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] Figure 1 This is a schematic flowchart illustrating a method for preparing a nano-lignin-based positive flotation desilication collector, as provided in an embodiment of this application.

[0025] Please see Figure 1 In a first aspect, embodiments of this application provide a method for preparing a nano-lignin-based positive flotation desilication collector, the method comprising: S1. The first part of the nano-lignin dispersion, the quaternary ammonium salt surfactant and deionized water are mixed to obtain the first mixture; S2. Under an inert atmosphere, the first mixture is heated to 50°C to 80°C and stirred for the first time at a speed of 300 rpm to 600 rpm to form a pre-dispersed system. S3. The aqueous solution of the water-soluble free radical initiator is mixed with the pre-dispersion system for a second initiation reaction to obtain an activated reaction system; S4. Dissolve carboxyl and / or hydroxamic acid functional group agents in an alkaline aqueous solution to obtain a saponified functional group solution; S5. The second part of the nano-sized lignin dispersion is mixed with the saponified functional group solution to obtain a functionalized mixture. S6. The functionalized mixture is added dropwise to the activation reaction system over 2 to 6 hours, and the reaction continues for 12 to 24 hours after the addition is complete, so as to achieve the grafting of carboxylic acid and / or hydroxamic acid functional groups on the surface of nano-lignin, thereby obtaining a nano-lignin-based positive flotation desilication collector.

[0026] The preparation method of this application first uses a first part of nano-lignin as the initiating core, generating active sites through free radical activation. Then, a second part of nano-lignin is mixed with a functional group agent and added to the reaction slowly dropwise. This stepwise addition design maximizes the utilization of free radicals, achieving uniform and efficient grafting of the functional group agent onto the surface of a large number of nano-lignin particles, thereby preparing a nano-collector with stable structure and excellent collecting performance.

[0027] In some embodiments, both the first and second portions of the nanoscale lignin dispersion satisfy the following conditions: the average particle size of the nanoparticles is 50 nm to 200 nm, and the mass fraction of lignin contained is 0.05% to 5%.

[0028] In both Part I and Part II of the nanoscale lignin dispersion, the average particle size of the nanoparticles ranges from 50 nm to 200 nm. This parameter defines the size range of the nanoparticles used to synthesize nano-lignin-based positive flotation desilication collectors. Within the particle size range of 50 nm to 200 nm, the nano-lignin particles exhibit a significant small size effect and high specific surface area, providing ample attachment sites and reaction surfaces for subsequent grafting of carboxyl and / or hydroxyxamic acid functional group agents.

[0029] In this embodiment, the lignin mass fraction of both the first and second part of the nano-lignin dispersion is 0.05%~5%, which enables the nano-lignin dispersion to have good fluidity and stability, facilitates accurate measurement and uniform addition, and ensures the establishment of a suitable reactant concentration in the reaction system.

[0030] In some embodiments, the mass ratio of the first portion of nano-lignin dispersion to the second portion of nano-lignin dispersion is 1:(1~5).

[0031] The mass ratio of the first part of the nano-lignin dispersion to the second part of the nano-lignin dispersion is 1:(1~5). This parameter defines the distribution ratio of the same batch of nano-lignin dispersion in the two-step addition step of the synthesis method of the nano-lignin-based positive flotation desilication collector. The role of the first part of the nano-lignin dispersion is to be preferentially activated in the initiation reaction stage, becoming the active core and initiation site for the entire graft copolymerization reaction. The role of the second part of the nano-lignin dispersion is to serve as the main material for the subsequent grafting reaction. After being pre-mixed with carboxyl and / or hydroxamic acid functional group agents, it enters the reaction system containing active cores together to participate in the graft copolymerization reaction. The mass ratio of the first part of the nano-lignin dispersion to the second part of the nano-lignin dispersion is limited to 1:(1~5). The amount of the first part of the nano-lignin dispersion is moderate, which can generate a sufficient number and uniformly distributed active cores in the initiation reaction stage, providing sufficient initiation sites for the subsequent grafting reaction, while avoiding cross-linking between particles due to excessively dense active sites. The second part, a nano-lignin dispersion, constitutes a relatively large proportion, ensuring sufficient yield of active ingredients in the final product. When the functionalized mixture containing the second part of the nano-lignin dispersion and carboxyl and / or hydroxamic acid functional group agents is slowly added dropwise over 2 to 6 hours, the newly added nano-lignin particles can be activated by the existing active core or by the low concentration of free radicals continuously present in the system during the dropwise addition process. This achieves uniform and efficient grafting of carboxyl and / or hydroxamic acid functional group agents onto the surface of all nano-lignin particles.

[0032] In some embodiments, the temperature for initiating the reaction is 50°C to 80°C, and the reaction time is 20 minutes to 80 minutes.

[0033] The initiation reaction refers to the process of mixing an aqueous solution of a water-soluble free radical initiator with a pre-dispersion system, and then maintaining the mixture at a set temperature for a specified period of time. This allows the initiator to decompose thermally, generating sufficient free radicals that act on the surface of the nano-lignin particles, forming active sites capable of grafting and copolymerizing with subsequent functional group reagents. Controlling the initiation reaction temperature to 50℃~80℃ and the reaction time to 20 minutes~80 minutes ensures that the free radical initiator decomposes at a stable and sufficient rate, generating an appropriate amount of free radicals. This effectively activates the surface of the nano-lignin particles, creating an optimal active center state and reaction starting point for the subsequent slow addition of carboxyl and / or hydroxamic acid functional group reagents to the activation reaction system over 2 hours~6 hours, followed by a 12-24 hour reaction period to achieve grafting of carboxyl and / or hydroxamic acid functional groups onto the nano-lignin surface. This fundamentally ensures that the final synthesized nano-lignin-based positive flotation desilication collector possesses the designed chemical structure and stable collecting performance.

[0034] In some embodiments, the first mixture comprises, by mass parts: 20 to 40 parts of nano-lignin dispersion, 0.5 to 2 parts of quaternary ammonium salt surfactant, and 90 to 110 parts of deionized water.

[0035] The first mixture refers to the system formed by first mixing the first part of the nano-lignin dispersion, the quaternary ammonium salt surfactant and deionized water.

[0036] The amount of nano-lignin dispersion is limited to 20-40 parts, which serves to provide sufficient and appropriately concentrated reaction nuclei for the entire reaction system. The nano-lignin particles in the nano-lignin dispersion are the solid carriers for the grafting reaction, and the amount of nano-lignin dispersion directly determines the final yield of the collector and the total amount of active sites available for grafting in the reaction system.

[0037] The amount of quaternary ammonium salt surfactant is limited to 0.5 to 2 parts. Its function is to improve the dispersion state of nano-lignin particles in the aqueous phase and may form a microenvironment on the particle surface that is conducive to the action of free radical initiators. Quaternary ammonium salt surfactant is a type of cationic surfactant that can adsorb onto the surface of nano-lignin particles and prevent particle aggregation through electrostatic repulsion and steric hindrance, thus ensuring the stability of the pre-dispersion system.

[0038] The amount of deionized water is limited to 90-110 parts to provide a sufficient liquid-phase reaction medium. As a continuous phase, deionized water dissolves the quaternary ammonium salt surfactant and disperses the nano-lignin particles, providing the necessary fluid environment for the entire reaction and ensuring good flowability and heat and mass transfer properties of the system. The proportion of deionized water is matched with the proportions of the nano-lignin dispersion and the quaternary ammonium salt surfactant, jointly determining the total volume of the first mixture and the concentration of each component therein.

[0039] In some embodiments, the alkaline aqueous solution is prepared from sodium hydroxide or potassium hydroxide, the pH value of the alkaline aqueous solution is 9-12, and the temperature of the alkaline aqueous solution is 50°C-90°C.

[0040] The role of alkaline aqueous solutions is to convert carboxyl and / or hydroxamic acid functional group agents into water-soluble saponifiable forms, enabling these agents to be uniformly dispersed in the aqueous reaction system and to undergo effective graft copolymerization with nano-lignin particles activated by free radical initiators. The alkaline aqueous solutions are prepared using sodium hydroxide or potassium hydroxide because they are strong bases that can react with carboxylic acid functional group agents such as oleic acid, talc oil, and oxidized paraffin soap to form carboxylates, and can also react with hydroxamic acid functional group agents such as salicylic acid, benzoic acid, and C5-C9 alkyl hydroxamic acids to form hydroxamic acid salts. The salt form generated through saponification has better water solubility, ensuring that hydrophobic carboxyl and / or hydroxamic acid functional group agents can be transformed from an organic phase or pure substance state into a form that can be uniformly dispersed and transported in the aqueous phase. This is a prerequisite for subsequent aqueous graft copolymerization. Limiting the pH of the alkaline aqueous solution to 9-12 ensures sufficient saponification and dissolution of the carboxyl and / or hydroxamic acid functional group agents while maintaining the integrity of their molecular structure and providing a suitable weakly alkaline to alkaline environment for the grafting reaction. Controlling the temperature of the alkaline aqueous solution between 50℃ and 90℃ accelerates the saponification process, ensuring that the carboxyl and / or hydroxamic acid functional group agents completely dissolve and form a homogeneous saponified functional group solution within a short time. This temperature range matches the main reaction temperature of the subsequent graft copolymerization reaction, avoiding thermal shock to the reaction system caused by excessive temperature differences.

[0041] In some embodiments, the quaternary ammonium salt surfactant is at least one selected from dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0042] Dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide all belong to the alkyltrimethylammonium bromide series of cationic surfactants. The molecular structure of these four substances consists of a hydrophobic long-chain alkyl group, a positively charged hydrophilic quaternary ammonium salt head group, and a bromide ion as a counterion.

[0043] In the synthesis method of the nano-lignin-based positive flotation desilication collector, the core function of the quaternary ammonium salt surfactant is to physically adsorb onto the surface of the nano-lignin particles in the first part of the nano-lignin dispersion. Since nano-lignin particles typically carry a negative charge in the aqueous medium, while the hydrophilic head group of the quaternary ammonium salt surfactant carries a positive charge, the two can achieve a strong bond through strong electrostatic attraction. After bonding, the hydrophobic alkyl chain of the quaternary ammonium salt surfactant extends into the aqueous phase, forming a steric barrier around the nano-lignin particles. This barrier effectively prevents the nano-lignin particles from approaching each other, thus preventing their aggregation or sedimentation in the aqueous phase. This dispersion stabilization effect ensures that the pre-dispersion system containing the first part of the nano-lignin dispersion maintains a uniform and stable state throughout the subsequent heating, stirring, and initiation reaction with the addition of a water-soluble free radical initiator, avoiding problems such as reduced reactive sites or inhomogeneity of the reaction system caused by nano-lignin particle aggregation.

[0044] In some embodiments, the water-soluble free radical initiator is one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride, and the mass concentration of the aqueous solution of the water-soluble free radical initiator is 5% to 20%.

[0045] Ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride are all water-soluble free radical initiators. Under heating conditions, ammonium persulfate and potassium persulfate can generate sulfate radicals through thermal decomposition, while azobisisobutyramidine hydrochloride can generate cationic radicals through thermal decomposition. These free radicals can attack the active sites in the molecular structure of nano-lignin and the unsaturated bonds or active groups in carboxyl and / or hydroxyxamic acid functional group agents, thereby initiating and maintaining the graft copolymerization reaction and achieving chemical bonding of functional group agents on the surface of nano-lignin.

[0046] Preparing the water-soluble free radical initiator into an aqueous solution with a mass concentration of 5%–20% and adding it to the reaction system is based on a balance between initiation efficiency and reaction controllability. If the mass concentration of the aqueous solution is less than 5%, the amount of initiator added to the reaction system is relatively insufficient, resulting in a smaller number of free radicals generated. This may not be enough to fully activate the nano-lignin and functional group agents, leading to incomplete grafting reactions and low functional group grafting density on the surface of the resulting collector, affecting its collection performance on gibbsite. If the mass concentration of the aqueous solution is greater than 20%, the local concentration of the initiator is too high, which may generate a large number of free radicals upon addition, causing the initiation reaction rate to be too fast. This can easily lead to homopolymerization or cross-linking between functional group agents, or local overheating of the reaction system, which would reduce grafting efficiency and may affect the dispersion stability of the nano-lignin particles.

[0047] In some embodiments, the carboxyl and / or hydroxamic acid functional group agent is at least one selected from oleic acid, tal oil, oxidized paraffin soap, salicylic acid, benzoic acid, and C5-C9 alkyl hydroxamic acid, and the mass ratio of the carboxyl and / or hydroxamic acid functional group agent to the total solid content of the nano-lignin dispersion is 9-15.

[0048] Oleic acid, talc oil, and oxidized paraffin soap belong to the carboxylic acid functional group class of reagents, containing carboxyl groups in their molecular structure; salicylic acid, benzoic acid, and C5-C9 alkyl hydroxyoxime acids belong to the hydroxyoxime acid functional group class of reagents, containing hydroxyoxime acid groups in their molecular structure. These reagents, after saponification in alkaline aqueous solutions, can form reactive forms that can undergo graft copolymerization reactions with active sites on the surface of nano-lignin under the action of free radical initiators, thereby introducing carboxyl or hydroxyoxime acid functional groups onto the surface of nano-lignin particles. Carboxyl and hydroxyoxime acid groups are characteristic functional groups in flotation collectors that exhibit strong selective chelation effects on oxidized minerals such as gibbsite in bauxite, and can chemically adsorb metal ions on the mineral surface, achieving efficient collection of the target mineral. Oleic acid, talc oil, and oxidized paraffin soaps are commonly used carboxylic acid reagents in industry, which are widely available and inexpensive. Hydroxyxamic acid reagents, such as salicylic acid, benzoic acid, and C5-C9 alkyl hydroxyxamic acids, exhibit stronger selective collection capabilities for gibbsite monohydrate. The limitation to at least one reagent means that in actual synthesis, depending on the characteristics of the target mineral and the requirements of the flotation process, a single carboxylic acid or a single hydroxyxamic acid reagent can be used, or a combination of carboxylic acid and hydroxyxamic acid reagents can be used to achieve synergistic optimization of collection performance and selectivity.

[0049] The mass ratio of carboxyl and / or hydroxyxamic acid functional group reagents to the total solid content of the nano-lignin dispersion is 9-15. This ratio refers to the ratio between the mass of carboxyl and / or hydroxyxamic acid functional group reagents added to the reaction system used to synthesize the nano-lignin-based positive flotation desilication collector and the total mass of solid lignin contained in all nano-lignin dispersions used in the reaction process. The total solid content of the nano-lignin dispersion consists of two parts: the sum of the masses of solid lignin in the first part of the nano-lignin dispersion and the second part of the nano-lignin dispersion. The mass ratio of carboxyl and / or hydroxamic acid functional group agents to the total solid content of the nano-lignin dispersion is controlled within the range of 9 to 15. This ensures that in the graft copolymerization reaction initiated by the free radical initiator, a sufficient amount of carboxyl and / or hydroxamic acid functional group agents are effectively grafted onto the active sites on the surface of the nano-lignin, thereby introducing a sufficient density of carboxyl and / or hydroxamic acid collecting functional groups on the surface of the nano-lignin particles.

[0050] Secondly, embodiments of this application provide a nano-lignin-based positive flotation desilication collector, which is prepared by the method described in the first aspect.

[0051] The nano-lignin-based positive flotation desilication collector provided in this application is characterized by the method described in the first aspect. This collector is a direct product obtained after implementing the method described in the first aspect, and its composition, structure, and properties are determined by the raw material ratio and process conditions of the method.

[0052] In some embodiments, the collector is a nanoparticle with carboxylic acid and / or hydroxamic acid functional groups grafted onto its surface, and the average particle size of the nanoparticle is 50 nm to 300 nm.

[0053] The nano-lignin-based positive flotation desilication collector prepared by the method in the first aspect is in the form of nanoparticles with carboxylic acid and / or hydroxamic acid functional groups grafted onto their surface. The average particle size of these nanoparticles is 50 nm to 300 nm. This collector combines the anchoring effect and steric effect provided by the nano-lignin core with the strong collecting ability provided by the surface-grafted carboxylic acid and / or hydroxamic acid functional groups.

[0054] Thirdly, embodiments of this application provide an application of the nano-lignin-based positive flotation desilication collector described in the second aspect in mineral flotation. In the positive flotation desilication operation of low-grade bauxite, the nano-lignin-based positive flotation desilication collector is used for selective flotation enrichment of gibbsite.

[0055] In the bauxite direct flotation desilication process, the goal is to concentrate aluminum-containing minerals (mainly gibbsite) in the froth product while suppressing silicon-containing minerals in the in-cell product, thereby achieving the separation of aluminum and silicon. This application presents a nano-lignin-based direct flotation desilication collector in the form of nanoparticles with surface grafted carboxylic acid and / or hydroxamic acid functional groups. Carboxylic acid and hydroxamic acid functional groups have a strong selective chelating effect on oxide minerals such as gibbsite, and can chemically adsorb aluminum ions on the surface of gibbsite to form stable surface complexes. The nano-lignin particles in the nano-lignin-based direct flotation desilication collector provide a hydrophobic framework, which provides the necessary hydrophobic surface for the gibbsite particles, enabling them to stably adhere to the bubbles. Therefore, in the desilication of low-grade bauxite by direct flotation, the nano-lignin-based direct flotation desilication collector can accurately capture diaspore particles through the selective chemical adsorption of the functional groups on the surface of the nano-lignin-based direct flotation desilication collector. Furthermore, through the hydrophobic effect of the nanoparticles of the nano-lignin-based direct flotation desilication collector, the diaspore particles are effectively transported to the froth layer, achieving selective flotation enrichment.

[0056] In some embodiments, during the selective flotation enrichment of gibbsite, the total amount of collector used is 1000 g / t raw ore to 1300 g / t raw ore, and the pH value of the flotation pulp is 8.0 to 9.5.

[0057] When using nano-lignin-based direct flotation desilication collectors to selectively enrich monohydrate gibbsite in low-grade bauxite through direct flotation desilication, the total amount of nano-lignin-based direct flotation desilication collectors and the pH of the flotation pulp must be controlled within specific process parameter ranges. The total amount of nano-lignin-based direct flotation desilication collectors refers to the total mass of nano-lignin-based direct flotation desilication collectors added per ton of raw ore throughout the entire flotation process (including roughing, cleaning, and scavenging operations), and the total amount is limited to 1000 grams to 1300 grams. The pH of the flotation pulp refers to the acidity or alkalinity of the pulp during flotation separation, and the pH range is limited to 8.0 to 9.5.

[0058] 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.

[0059] Example 1 A nano-lignin dispersion with a solid content of 1% and an average particle size of 100 nm was divided into two parts at a mass ratio of 1:2. 20 parts (by mass) of the first part of the nano-lignin dispersion, 1 part of hexadecyltrimethylammonium bromide, and 100 parts of deionized water were weighed and mixed to obtain a first mixture. Under a nitrogen atmosphere, the first mixture was heated to 65°C and stirred at 450 rpm for 30 minutes to form a stable pre-dispersion system. A 10% ammonium persulfate aqueous solution was prepared. This ammonium persulfate aqueous solution was added to the pre-dispersion system, and an initiation reaction was carried out at 65°C for 40 minutes to obtain an activated reaction system. Oleic acid was used as a carboxylic acid functional group reagent. An alkaline sodium hydroxide aqueous solution with pH=10 and a temperature of 70°C was prepared, and oleic acid was dissolved in it to obtain a saponified functional group solution. The mass ratio of oleic acid to the total solid content of the nano-lignin dispersion was 12:1. The second part of the nano-lignin dispersion was mixed with the obtained saponified functional group solution to obtain a functionalized mixture. The obtained functionalized mixture was added dropwise to the obtained activation reaction system at a uniform rate over 4 hours. After the addition was complete, the reaction was continued at 65℃ for 18 hours. After the reaction was completed, the material was cooled and discharged to obtain a nano-lignin-based positive flotation desilication collector. Analysis showed that the obtained product consisted of nanoparticles with carboxylic acid groups grafted onto their surface, with an average particle size of 180 nm. This product was designated NS-1.

[0060] Example 2 This embodiment is basically the same as Embodiment 1, except that: The functional group reagent used was salicylic acid (a type of hydroxamic acid), and the alkaline aqueous solution was a potassium hydroxide solution with a pH of 11. The saponification temperature was 80℃. The resulting nano-lignin-based positive flotation desilication collector had hydroxamic acid groups grafted onto its surface, with an average particle size of 175 nm. It was designated NS-2.

[0061] Example 3 This embodiment is basically the same as Embodiment 1, except that: The average particle size of the nano-lignin dispersion was 50 nm, and the solid content was 0.5%. The first mixture was heated to 50°C and stirred for 30 minutes at 300 rpm to form a stable pre-dispersion system. In step (3), the heating temperature was 50°C, and the stirring speed was 300 rpm. The initiation reaction time was 80 minutes. The functional group reagent was C7 alkyl hydroxyxamic acid, the alkaline aqueous solution had a pH of 9, the temperature was 90°C, and the mass ratio of the amount of functional group reagent to the total solid content of nano-lignin was 9:1. The functionalized mixture was added dropwise to the obtained activation reaction system over 6 hours, and the reaction was carried out for 24 hours after the addition was completed. The average particle size of the obtained nano-lignin-based positive flotation desilication collector was 120 nm. It was designated as NS-3.

[0062] Comparative Example 1 This comparative example provides a method for synthesizing a common lignin-based collector. The steps are basically the same as in Example 1, except that the nano-sized lignin dispersion is replaced with a common alkali lignin aqueous slurry with equal solids content. The resulting product is designated as CS-1.

[0063] The collectors obtained in Examples 1-3 and Comparative Example 1 were used to conduct direct flotation desilication tests on low-grade bauxite from a certain location in Shanxi Province. The raw ore had an alumina content of 54.60% and an aluminum-to-silicon ratio of 2.05. After processing the raw ore through a one-roughing, two-cleaning, one-scavenging direct flotation desilication process, aluminum concentrate and tailings were obtained. The pH value of the flotation pulp was 9.0 ± 0.2.

[0064] The flotation results are shown in Table 1.

[0065] Table 1 Summary of flotation test results

[0066] Furthermore, one or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages: The nano-lignin-based positive flotation desilication collector provided in this invention achieves precise capture of the target mineral (diaspore) by chemically grafting carboxylic acid / hydroxyoxime functional groups with strong selective chelating effect on diaspore onto the surface of nano-lignin, while significantly reducing non-specific adsorption of silica gangue minerals (such as kaolinite and illite).

[0067] The embodiments of this invention use lignin, a renewable biomass resource, as raw material. The preparation process and the application of the collector are environmentally friendly and meet the requirements of sustainable development.

[0068] 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 method for preparing a nano-lignin-based positive flotation desilication collector, characterized in that, The method includes: The first part of the nano-lignin dispersion, the quaternary ammonium salt surfactant and deionized water are mixed to obtain the first mixture. Under an inert atmosphere, the first mixture is heated to 50°C to 80°C and stirred for the first time at a speed of 300 rpm to 600 rpm to form a pre-dispersed system. An aqueous solution of a water-soluble free radical initiator is mixed with the pre-dispersed system for a second initiation reaction to obtain an activated reaction system; Dissolve carboxyl and / or hydroxamic acid functional group agents in an alkaline aqueous solution to obtain a saponified functional group solution; The second part of the nano-sized lignin dispersion is mixed with the saponified functional group solution in a third mixing process to obtain a functionalized mixture. The functionalized mixture is added dropwise to the activation reaction system over a period of 2 to 6 hours, and the reaction continues for 12 to 24 hours after the addition is complete, so as to achieve the grafting of carboxylic acid and / or hydroxamic acid functional groups on the surface of nano-lignin, thereby obtaining a nano-lignin-based positive flotation desilication collector.

2. The method according to claim 1, characterized in that, Both the first and second parts of the nanoscale lignin dispersion meet the following requirements: the average particle size of the nanoparticles is 50 nm to 200 nm, and the lignin mass fraction is 0.05% to 5%; and / or, The mass ratio of the first part of the nano-lignin dispersion to the second part of the nano-lignin dispersion is 1:(1~5).

3. The method according to claim 1, characterized in that, The initiation reaction temperature is 50℃~80℃, and the initiation reaction time is 20 minutes~80 minutes.

4. The method according to claim 1, characterized in that, The first mixture comprises, by mass parts: 20 to 40 parts of nano-lignin dispersion, 0.5 to 2 parts of quaternary ammonium salt surfactant, and 90 to 110 parts of deionized water.

5. The method according to claim 1, characterized in that, The alkaline aqueous solution is prepared from sodium hydroxide or potassium hydroxide, the pH value of the alkaline aqueous solution is 9~12, and the temperature of the alkaline aqueous solution is 50℃~90℃.

6. The method according to claim 1, 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 water-soluble free radical initiator is one of ammonium persulfate, potassium persulfate, and azobisisobutyramidine hydrochloride, and the aqueous solution of the water-soluble free radical initiator has a mass concentration of 5% to 20%; and / or, The carboxyl and / or hydroxamic acid functional group agent is at least one selected from oleic acid, tal oil, oxidized paraffin soap, salicylic acid, benzoic acid, and C5-C9 alkyl hydroxamic acid, and the mass ratio of the carboxyl and / or hydroxamic acid functional group agent to the total solid content of the nano-lignin dispersion is 9-15.

7. A nano-lignin-based positive flotation desilication collector, characterized in that, The collector is prepared by the method according to any one of claims 1 to 6.

8. The collector according to claim 7, characterized in that, The collector is a nanoparticle with carboxylic acid and / or hydroxamic acid functional groups grafted onto its surface, and the average particle size of the nanoparticle is 50 nm to 300 nm.

9. The application of the nano-lignin-based positive flotation desilication collector according to claim 7 or 8 in mineral flotation, characterized in that, In the positive flotation desilication operation of low-grade bauxite, the nano-lignin-based positive flotation desilication collector is used for selective flotation enrichment of gibbsite.

10. The application according to claim 9, characterized in that, In the selective flotation enrichment of gibbsite, the total amount of collector used is 1000 g / t raw ore to 1300 g / t raw ore, and the pH value of the flotation pulp is 8.0 to 9.5.

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