Novel non-ferrous metal flotation inhibitor and preparation method thereof

Abstract

The invention relates to the technical field of mineral separation, discloses a novel non-ferrous metal flotation inhibitor and a preparation method thereof, and aims to solve the limitation of an existing non-ferrous metal flotation inhibitor in the aspects of universality, stability, environmental friendliness and economical efficiency. The flotation inhibitor is characterized in that the main active component of the flotation inhibitor is a multifunctional amphoteric polymer prepared through chemical modification of a biomass-based polymer skeleton (such as lignin), and the polymer comprises carboxyl, amino, hydroxyl and / or phosphonic acid groups. By the adoption of the technical scheme, efficient and high-selectivity inhibition of various gangue minerals can be achieved, wide pH adaptability, broad-spectrum applicability and environmental friendliness are achieved, and the preparation method is economical and can be applied to a large scale.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of mineral processing, and in particular relates to a new non-ferrous metal flotation depressant and a preparation method thereof. BACKGROUND

[0002] With the global non-ferrous metal mineral resources becoming increasingly scarce and complex, the demand for improving the efficiency of flotation and the comprehensive recovery rate of resources in the field of mineral processing is becoming increasingly urgent. As a kind of efficient and economical mineral separation method, flotation technology occupies a core position in modern mining production. Among them, the flotation depressant, as a key chemical reagent for regulating the surface properties of minerals and optimizing the selectivity of mineral separation, its performance directly relates to the economy, efficiency of the flotation process and the quality of the final product. Therefore, the development of new flotation depressants with high performance, high selectivity, environmental friendliness and controllable cost has become an important research direction to promote the progress of mineral processing technology.

[0003] Through in-depth exploration of existing technologies, it can be found that many inhibitor solutions are dedicated to solving specific flotation problems. For example, the technical solution of patent publication No. CN114832948B proposes a depressant applied to magnesium-containing gangue flotation. The depressant takes a compound with a specific structural formula as the main component, and the core of its design is to achieve efficient adsorption and inhibition on the surface of magnesium-containing gangue through precise molecular structure specificity, so as to effectively improve the separation selectivity between magnesium and target minerals without significantly affecting the flotation effect of target non-ferrous minerals. This feature shows significant targeted advantages when dealing with high-magnesium ores, effectively alleviating the long-term problem of magnesium ion interfering with flotation operations, and is an important attempt for fine separation of specific mineral components.

[0004] Compared with the above, the technical solution of patent publication No. CN111215247B provides a depressant for high-calcium fluorite direct flotation and a flotation method thereof. The depressant takes ethylenediamine tetramethylene phosphonic acid (EDTMP) as the main component, and through its multiple chelating sites, it can effectively inhibit the flotation of calcareous minerals (such as calcite) under specific flotation process conditions, thereby realizing the effective separation of high-calcium fluorite and associated calcite. The advantage of this scheme is that the cost of the depressant is relatively low, and it shows significant selectivity in the separation of specific calcium minerals. Its use environment is relatively mild, and in theory it can avoid or reduce the secondary pollution that may be caused by traditional inorganic depressants, and it has made positive contributions to promoting the greenization of flotation reagents.

[0005] However, with the increasing complexity of non-ferrous metal mineral resources and the more stringent multi-dimensional requirements placed on reagent performance by flotation processes, the inherent characteristics of the aforementioned existing technologies at the principle level have gradually revealed deep-seated limitations in addressing new challenges, collectively pointing to a non-obvious internal technical contradiction. Specifically, regarding the inhibitor disclosed in CN114832948B, although it achieves precise inhibition of magnesium-bearing gangue through "compounds with specific structural formulas" and "high requirements for structural specificity," this extreme structural specificity is precisely the root cause of its lack of versatility. The reason for this is that the complexity of mineral systems determines the diversity of their surface properties. An inhibitor "tailor-made" for a specific mineral surface often relies on precise steric hindrance or electronic effect matching for its mechanism of action, making it difficult for it to exhibit the same efficacy on other non-ferrous metal gangue or impurity minerals with significant differences in chemical composition and crystal structure. Therefore, when dealing with non-ferrous metal ores from different origins and with different mineral combinations, it is necessary to frequently redevelop or adjust inhibitors. This undoubtedly leads to increased complexity in the production process, longer research and development cycles, and a significant increase in overall production costs, greatly limiting their widespread application and economic feasibility in the flotation separation of various non-ferrous metal minerals. Furthermore, for complex organic compounds, the "insufficiently verified environmental performance" refers not only to their short-term toxicity, but also to the deeper issues of the ecotoxicity, bioaccumulation, and persistence of their degradation products in the environment. This poses potential environmental risks and sustainable development challenges for large-scale industrial applications.

[0006] More importantly, even inhibitors like ethylenediaminetetramethylenephosphonic acid (EDTMP) provided by CN111215247B, which seem to have cost advantages and initial green characteristics, have inherent contradictions in their application. The inhibition mechanism of EDTMP mainly relies on the chelation of its phosphonic acid groups with metal ions on the mineral surface. The effectiveness of this chelation reaction is extremely sensitive to changes in the solution environment (especially pH and ionic strength). In a "low-alkalinity environment," the phosphonic acid groups on the EDTMP molecule may protonate, significantly weakening its chelating ability and adsorption strength on the mineral surface, leading to a sharp decrease in the inhibition effect. This sensitivity to environmental parameters means that in actual industrial flotation operations, even slight fluctuations in pulp pH, mineral composition, or water quality can cause drastic fluctuations in the inhibition effect, seriously affecting the stability of the flotation process and the reliability of concentrate recovery. To compensate for this lack of stability, a "larger dosage" is often required. This not only directly increases the cost of the reagents, offsetting their initial advantage of "low cost," but also increases the burden of tailings treatment and potential environmental impact due to the excessive introduction of chemical reagents, which runs counter to the higher requirements of modern mineral processing for high efficiency, low cost and green environmental protection.

[0007] The underlying contradiction shared by the aforementioned technical solutions lies in the fact that current research and development paths for flotation depressants, whether pursuing ultimate "specificity" to achieve precise separation of specific minerals or focusing on "universality" to reduce costs, cannot completely avoid the inherent constraints and trade-offs they face in multiple dimensions such as "universality, stability, environmental friendliness, and simplified preparation processes." High selectivity is often accompanied by complex synthesis, high cost, and a narrow range of applications; while seemingly universal or low-cost depressants are often subject to stringent requirements for operating conditions, sensitive environmental adaptability, and potential increases in reagent consumption or unknown environmental risks. Therefore, how to overcome these inherent limitations at the principle level and develop a novel non-ferrous metal flotation depressant that can simultaneously achieve multiple performance indicators, namely high selectivity, broad applicability, environmental friendliness, excellent stability, and an economical preparation method, has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention

[0008] To achieve the aforementioned objectives, namely, to address the deep-seated contradictions and inherent limitations of existing non-ferrous metal flotation depressants in terms of versatility, stability, environmental friendliness, and economic efficiency, this invention provides a novel non-ferrous metal flotation depressant and its preparation method. This invention aims to provide a novel flotation depressant that simultaneously achieves high selectivity, broad applicability, excellent stability, environmental friendliness, and controllable cost, thereby meeting the higher requirements of modern mineral processing for efficient and green flotation operations.

[0009] This invention provides a novel non-ferrous metal flotation inhibitor, characterized in that its main active ingredient is a multifunctional amphoteric polymer, which is prepared from a biomass-based polymer backbone through a multi-step chemical modification reaction. The biomass-based polymer backbone is selected from at least one of lignin, cellulose, hemicellulose, and their derivatives. In a preferred embodiment of this invention, the biomass-based polymer backbone is pretreated lignin. The lignin can be selected from lignin found in industrial waste, for example, from lignin sulfonates, alkali lignin, or organic solvent lignin. The pretreatment includes, but is not limited to, acid washing, alkali dissolution, ultrafiltration separation, and drying of the lignin to remove low molecular weight impurities and improve its reactivity.

[0010] Furthermore, the structure of the multifunctional amphoteric polymer includes at least two of the following functional groups: carboxyl, amino, hydroxyl, and phosphonic acid groups. These multiple functional groups are covalently linked to the biomass-based polymer backbone. The carboxyl and phosphonic acid groups endow the polymer with the ability to form chelate complexes with metal ions on mineral surfaces under different pH conditions and provide additional electrostatic adsorption sites; the amino and hydroxyl groups endow the polymer with the ability to provide electrostatic adsorption or hydrogen bonding under specific pH conditions, further enhancing the affinity of the polymer for mineral surfaces. The synergistic effect of these multifunctional groups endows the inhibitor with differentiated adsorption selectivity and broader pH adaptability on various gangue mineral surfaces.

[0011] In a preferred embodiment of the present invention, the weight-average molecular weight of the multifunctional amphoteric polymer ranges from 5,000 Daltons to 50,000 Daltons. This molecular weight range ensures that the polymer exhibits good dispersibility and suitable viscosity in aqueous solutions, while providing sufficient chain length to achieve effective steric hindrance and multi-site adsorption capabilities. The multifunctional amphoteric polymer has a carboxyl group content of 0.5 mmol / g to 1.5 mmol / g, an amino group content of 0.8 mmol / g to 2.0 mmol / g, and a phosphonic acid group content of 0.1 mmol / g to 0.5 mmol / g. These ranges in the content of each functional group ensure that the polymer exhibits suitable charge density and amphoteric properties in aqueous solutions, thereby maintaining high inhibition efficiency over a wide pH range.

[0012] This invention provides a novel method for preparing a non-ferrous metal flotation inhibitor, characterized by the following steps: First, lignin pretreatment: The lignin is placed in a reaction vessel, deionized water is added, and the pH is adjusted to alkaline (e.g., pH 9.0 to 12.0), and dissolved under stirring. Subsequently, the lignin solution is purified using ultrafiltration membrane separation technology, retaining components with a molecular weight cutoff of 3,000 to 5,000 Daltons to remove low molecular weight impurities and inorganic salts. The purified lignin solution is then freeze-dried or spray-dried to obtain refined lignin powder. This pretreatment process ensures the efficiency and product purity of subsequent chemical modification reactions.

[0013] The second step is the carboxylation modification of lignin: The refined lignin powder is dissolved in an alkaline solution, such as an aqueous sodium hydroxide solution, and the concentration of lignin is 5% to 15% (mass percentage). Under continuous stirring and temperature control, monochloroacetic acid (MCA) is slowly added to the lignin solution, with a mass ratio of MCA to lignin of 0.5:1 to 2.0:1. The reaction temperature is controlled between 60°C and 90°C, and the reaction time is 2 to 6 hours. After the reaction is completed, the product is precipitated by adjusting the pH to acidic (e.g., pH 2.0 to 4.0), and then filtered, washed, and dried to obtain carboxylated lignin. The carboxylation modification improves the water solubility and chelating ability of lignin to metal ions on mineral surfaces by introducing carboxyl groups into the lignin molecule.

[0014] The third step is the amination modification of carboxylated lignin: The carboxylated lignin is dissolved in a suitable solvent, such as deionized water or a water-alcohol mixture. Epichlorohydrin (ECH) is added to the solution under stirring, with a molar ratio of ECH to carboxylated lignin of 0.8:1 to 1.5:1. Subsequently, a polyamine compound, such as diethylenetriamine (DETA) or tetraethylenepentamine (TEPA), is slowly added, with a molar ratio of ECH to ECH of 0.5:1 to 1.0:1. The reaction temperature is controlled between 80°C and 120°C, and the reaction time is 4 to 8 hours. After the reaction is complete, the aminated carboxylated lignin is obtained through steps such as pH adjustment, precipitation, filtration, washing, and drying. This amination modification introduces amino groups, enhancing the electrostatic interaction of the polymer with the mineral surface under acidic or neutral conditions and providing sites for further modification.

[0015] Step four, introduction of phosphonic acid groups (optional step, but preferred embodiment): The aminated carboxylated lignin is dissolved in deionized water or a water-soluble solvent at a concentration of 3% to 10% (mass percentage). Under stirring and inert gas (e.g., nitrogen) protection, phosphorous acid (H3PO3) and formaldehyde (HCHO) or alkyl phosphate ester are added to the solution, wherein the molar ratio of phosphorous acid to the aminated carboxylated lignin is 0.1:1 to 0.5:1, and the molar ratio of formaldehyde to phosphorous acid is 1.0:1 to 2.0:1. The reaction temperature is controlled between 90°C and 130°C, and the reaction time is 6 to 12 hours. After the reaction is completed, the product is purified by dialysis, ultrafiltration, or solvent precipitation to remove unreacted reagents and byproducts. The final product is freeze-dried or spray-dried to obtain the multifunctional amphoteric polymer powder, which is the novel non-ferrous metal flotation inhibitor referred to in this invention. The introduction of the phosphonic acid group significantly enhances the inhibitor's chelating ability for multivalent metal ions, especially maintaining high inhibition efficiency under low concentration conditions.

[0016] The reaction vessel used in the preparation process is a jacketed reactor equipped with a stirring device, a temperature control system, and a reflux condenser to ensure the controllability and safety of the reaction conditions. The purification step ensures the purity of the final product, thereby avoiding the adverse effects of impurities on the inhibitor's performance and improving its environmental friendliness. In each step, precise pH control is crucial for the structure and performance of the product and can be adjusted by adding an acid (e.g., dilute hydrochloric acid or dilute sulfuric acid) or a base (e.g., sodium hydroxide solution).

[0017] The novel non-ferrous metal flotation inhibitor provided by this invention, through its unique multifunctional amphoteric polymer structure, achieves precise control over the non-ferrous metal flotation process and effectively solves the deep-seated contradictions in existing technologies. Its mechanism of action and technical effects are mainly reflected in the following aspects:

[0018] First, the multimodal adsorption synergistic effect. The multifunctional amphoteric polymer, due to the presence of carboxyl, amino, hydroxyl, and phosphonic acid groups in its structure, can interact with the surface of gangue minerals in various forms. Specifically, the carboxyl and phosphonic acid groups can form stable chelate complexes with polyvalent metal ions such as calcium, magnesium, iron, and aluminum ions exposed on the surface of gangue minerals, effectively covering the mineral surface and preventing the adsorption of the collector; the amino groups undergo protonation under acidic or neutral conditions to form positively charged groups, which strongly attract the negatively charged mineral surfaces such as silicates; the hydroxyl groups can establish connections with the mineral surface through hydrogen bonding; simultaneously, the polymer backbone itself further hinders the effective contact between the collector and the mineral surface through steric hindrance. The synergistic effect of these multiple mechanisms ensures that the inhibitor has efficient adsorption and inhibition capabilities for gangue minerals of different types and surface properties, significantly improving sorting selectivity.

[0019] Secondly, the polymer exhibits stability and adaptability across a wide pH range. Due to its amphoteric properties, the multifunctional amphoteric polymer maintains high-efficiency inhibition performance over a broad pH range. Under acidic conditions, the amino groups exhibit a higher degree of protonation, enhancing electrostatic adsorption; under alkaline conditions, the carboxyl and phosphonic acid groups show increased deprotonation, enhancing chelation and electrostatic repulsion. This pH-responsive conformational change and adjustment of surface charge distribution allow the polymer to effectively expand in different pH environments, exposing the optimal active sites for interaction with mineral surfaces. This overcomes the problems of pH sensitivity and fluctuating inhibition effects of existing inhibitors, ensuring the stability of the flotation process and the reliability of concentrate recovery. Compared to traditional inhibitors that only function at specific pH levels, the inhibitor provided by this invention significantly broadens its application pH range and reduces the stringent requirements for flotation operating conditions.

[0020] Third, broad applicability and high-efficiency inhibition performance. The inhibitor provided by this invention can effectively inhibit a variety of common non-ferrous metal gangue minerals, such as silicate minerals (e.g., talc, serpentine, kaolinite), carbonate minerals (e.g., calcite, dolomite), and some oxide minerals (e.g., iron oxides). Through precise identification and multimodal adsorption of the surface chemical properties of different gangue minerals, the inhibitor can effectively inhibit the above-mentioned gangue minerals, while having minimal impact on the flotation behavior of target non-ferrous metal minerals (e.g., chalcopyrite, sphalerite, galena, wolframite, cassiterite, etc.). This broad applicability greatly simplifies the complexity of reagent formulations in concentrators, reduces R&D and production costs, and enables its widespread application in the flotation separation of non-ferrous metal ores from different origins and with different mineral combinations. Its high inhibition efficiency also significantly reduces the required inhibitor dosage compared to traditional inhibitors, typically from 50 grams per ton of ore to 500 grams per ton of ore, thereby further reducing reagent consumption costs.

[0021] Fourth, environmental friendliness and sustainability. The preparation of the multifunctional amphoteric polymer uses renewable biomass-based lignin as the main raw material, making full use of industrial waste and reducing dependence on fossil resources. Lignin itself and its chemically modified products have good biodegradability and can be decomposed by microorganisms in the environment, avoiding long-term residues and bioaccumulation effects, thus significantly reducing potential risks to the ecological environment. In addition, the high efficiency of the inhibitor leads to a reduction in its dosage, directly reducing the total amount of chemical agents emitted, thereby alleviating the burden of tailings treatment and the risk of secondary pollution, which is in line with the green and environmentally friendly sustainable development concept of modern mineral processing.

[0022] Fifth, the economic efficiency and scalability of the preparation process. The inhibitor preparation method provided by this invention utilizes industrially mature lignin modification technology, and the reagents used are all commonly available and relatively inexpensive general chemicals. The reaction conditions of the preparation process are easy to control and do not involve extreme high pressure or high temperature, facilitating the scale-up and promotion of industrial production. The preparation process is relatively simple, avoiding complex multi-step fine synthesis routes, reducing production costs and technical barriers, making the novel inhibitor more economically competitive and conducive to its large-scale industrial application.

[0023] In summary, the novel non-ferrous metal flotation depressant and its preparation method provided by this invention achieve a breakthrough in overcoming the contradictions between selectivity, versatility, stability, environmental friendliness, and cost-effectiveness of current flotation depressants by ingeniously combining the synergistic effect of a biomass-based polymer framework and multiple functional groups. The depressant provides a highly efficient, stable, broad-spectrum, environmentally friendly, and economically feasible solution, thereby promoting the overall advancement of non-ferrous metal flotation technology and providing solid technical support for the effective utilization of mineral resources and environmental protection. Detailed Implementation

[0024] This invention provides a novel non-ferrous metal flotation inhibitor and its preparation method. The core of this inhibitor lies in its unique multifunctional amphoteric polymer structure, which is obtained through fine chemical modification of a biomass-based polymer backbone. The inhibitor aims to address the inherent challenges of existing technologies in flotation processes regarding versatility, stability, environmental friendliness, and economy. Through its multimodal adsorption and wide pH adaptability, it effectively achieves precise separation of non-ferrous metal minerals and gangue minerals.

[0025] In one specific embodiment, the novel non-ferrous metal flotation inhibitor provided by this invention has a main active ingredient that is a multifunctional amphoteric polymer obtained through multi-step chemical modification. The synthesis of this polymer begins with a biomass-based polymer backbone, preferably lignin that has undergone rigorous pretreatment. Specifically, this lignin can be derived from industrial waste, such as lignin sulfonates, alkali lignin, or organic solvent lignin. The wide availability and renewability of its sources significantly enhance the environmental friendliness and sustainability of this technical solution. Before being incorporated into subsequent chemical modifications, the lignin undergoes a series of rigorous pretreatment processes to ensure its molecular structure uniformity and reactivity. The pretreatment process typically includes the following meticulous steps: First, the crude lignin material is acid-washed under controlled conditions to induce the desorption and removal of some impurities through an acidic environment. Next, a precisely controlled alkali dissolution process is used to fully dissolve the lignin molecules and expose more reaction sites. Following this, advanced ultrafiltration technology is employed to precisely fractionate the resulting lignin solution by molecular weight, effectively removing low-molecular-weight impurities and potential inorganic salts, ensuring the purity and reactivity of the final lignin framework. Finally, the purified lignin solution is dried, for example using freeze-drying or spray-drying techniques, to obtain high-purity refined lignin powder. This refined lignin powder provides an ideal starting material for subsequent multifunctional modifications.

[0026] Furthermore, at least two key functional groups are strategically introduced into the molecular structure of the multifunctional amphoteric polymer. These groups are firmly linked to the biomass-based polymer backbone through stable covalent bonds. The functional groups typically include carboxyl, amino, hydroxyl, and phosphonic acid groups. Specifically, the carboxyl and phosphonic acid groups endow the polymer with the inherent ability to form stable chelate complexes with polyvalent metal ions exposed on mineral surfaces, such as calcium, magnesium, iron, and aluminum ions, under different aqueous solution pH conditions. Simultaneously, the ionization of these groups provides additional electrostatic adsorption sites for the polymer molecules, thereby enhancing their affinity for mineral surfaces. Under specific pH conditions, particularly in acidic or neutral environments, the amino group can undergo protonation to form a positively charged group, thereby generating a strong electrostatic attraction with negatively charged mineral surfaces (such as silicate mineral surfaces). The hydroxyl group further enhances the binding strength between the polymer and the mineral surface through hydrogen bonding. These functional groups do not exist in isolation, but rather work synergistically through their spatial arrangement and charge distribution within the polymer molecule. This results in the inhibitor exhibiting differentiated adsorption selectivity on various gangue mineral surfaces and possessing a wider pH adaptability range. The weight-average molecular weight of the multifunctional amphoteric polymer is precisely controlled, typically between 5,000 Daltons and 50,000 Daltons. This molecular weight range ensures excellent dispersion stability and suitable solution viscosity in aqueous solutions, while providing sufficient molecular chain length to effectively achieve steric hindrance and multi-point adsorption capabilities, thereby improving inhibition efficiency. As a preferred embodiment of the invention, the carboxyl content of the multifunctional amphoteric polymer is typically controlled between 0.5 mmol / g and 1.5 mmol / g; the amino content is between 0.8 mmol / g and 2.0 mmol / g; and the phosphonic acid group content is between 0.1 mmol / g and 0.5 mmol / g. The precise control of the content of each functional group ensures that the polymer can maintain a suitable charge density and amphoteric properties in aqueous solution, thereby continuously exhibiting efficient inhibition performance over a wide pH range.

[0027] The present invention provides a novel method for preparing a non-ferrous metal flotation inhibitor, characterized by comprising the following precisely controlled steps:

[0028] The first step is the pretreatment of lignin. This step is fundamental for subsequent efficient chemical modification. Specifically, the selected crude lignin material, such as industrial waste lignin sulfonate, is accurately weighed and placed in a jacketed reactor equipped with a mechanical stirrer and a temperature control system. Then, deionized water is added to the reactor at a lignin-to-deionized water mass ratio of 1:10 to 1:20. The pH of the mixed solution is precisely adjusted to an alkaline range, preferably 9.0 to 12.0, by accurately metering and slowly adding dilute sodium hydroxide solution or dilute sulfuric acid. Under continuous stirring at 100-300 rpm, the lignin is fully dissolved at the set pH and room temperature (20-30 degrees Celsius), typically for 1 to 3 hours. After dissolution, the resulting lignin solution is pumped via a high-pressure pump to a separation system equipped with an ultrafiltration membrane module made of polyethersulfone (PES) or regenerated cellulose (RC). The ultrafiltration membrane is set with a molecular weight cutoff of 3,000 to 5,000 Daltons, an operating pressure of 0.2 to 0.5 MPa, and an operating temperature of 25 to 40 degrees Celsius. Through cross-flow filtration, continuous purification of the lignin solution is achieved, effectively removing low molecular weight impurities, small molecule organic acids, and inorganic salt ions. Purification is considered complete when the inorganic ion conductivity in the filtrate (permeate) reaches a stable low value (e.g., below 50 μS / cm). The purified concentrated lignin solution is then dried using a freeze dryer (e.g., freeze-drying temperature -50 degrees Celsius, vacuum degree 10 Pa, freeze-drying time 24-48 hours) or a spray dryer (e.g., inlet air temperature 180 degrees Celsius, outlet air temperature 80 degrees Celsius, atomization pressure 0.3 MPa) to finally obtain a white or light brown refined lignin powder. The precise implementation of this pretreatment process is crucial to ensuring the efficient execution of subsequent chemical modification reactions and obtaining high-purity products.

[0029] The second step is the carboxylation modification of lignin. This step aims to introduce carboxyl groups onto the lignin backbone to enhance its water solubility and chelating ability. The refined lignin powder obtained in the first step is accurately weighed and dissolved in an aqueous sodium hydroxide solution, with the lignin concentration preferably controlled between 5% and 15% (mass percentage). This dissolution process is carried out in a jacketed reactor equipped with a mechanical stirrer, a temperature control system, and a reflux condenser, with the stirring speed maintained at 150-350 rpm to ensure uniform mixing. Subsequently, under continuous stirring and with the reaction temperature precisely controlled between 60°C and 90°C, preferably 70°C, monochloroacetic acid (MCA) is slowly and uniformly added dropwise to the lignin solution. The mass ratio of MCA to lignin is 0.5:1 to 2.0:1, preferably 1.0:1. The dropwise addition process typically takes 1 to 2 hours to avoid excessively high local concentrations. After the dropwise addition is complete, the above reaction temperature and stirring speed are maintained, allowing the reaction to continue for 2 to 6 hours, preferably 4 hours. The reaction progress can be monitored by sampling and observing changes in carboxyl content. After the reaction is complete, the pH of the reaction mixture is precisely adjusted to an acidic range, preferably 2.0 to 4.0, by slowly adding dilute hydrochloric acid or dilute sulfuric acid to promote the precipitation of carboxylated lignin products. The resulting precipitate is separated into solid and liquid components by vacuum filtration or centrifugation, and then washed repeatedly with deionized water 3 to 5 times until the pH of the washing solution is close to neutral and no chloride ions are detected (by silver nitrate solution). The washed product is dried in a vacuum oven at 60 degrees Celsius for 12 to 24 hours, or freeze-dried to obtain a white to light yellow carboxylated lignin powder.

[0030] The third step is the amination modification of carboxylated lignin. This step aims to introduce amino groups to broaden the pH adaptability of the polymer and provide further modification sites. The carboxylated lignin powder obtained in the second step is accurately weighed and dissolved in a suitable solvent, preferably deionized water or a 1:1 water-alcohol mixture (e.g., water / ethanol). The concentration of the carboxylated lignin is controlled between 8% and 18% (mass percentage). This dissolution process is carried out in a reactor equipped with a mechanical stirrer, a temperature control system, and a reflux condenser, at a stirring speed of 200-400 rpm. Under continuous stirring, epichlorohydrin (ECH) is slowly added dropwise to the solution. The molar ratio of epichlorohydrin to carboxylated lignin is controlled between 0.8:1 and 1.5:1, preferably 1.2:1. After the addition is complete, the reaction system is heated to 80°C to 120°C, preferably 95°C. Subsequently, a polyamine compound, preferably diethylenetriamine (DETA) or tetraethylenepentamine (TEPA), is slowly and uniformly added. The molar ratio of the polyamine compound to epichlorohydrin is 0.5:1 to 1.0:1, preferably 0.8:1. The addition rate must be controlled to avoid violent exothermic reactions. After the addition is complete, the reaction temperature and stirring speed are maintained to allow the reaction to continue for 4 to 8 hours, preferably 6 hours. After the reaction is complete, the pH of the reaction mixture is adjusted to neutral or slightly acidic (pH 6.0-7.0) by adding dilute hydrochloric acid or dilute acetic acid to facilitate product stability. Precipitation is then carried out by adding a suitable amount of non-solvent (e.g., acetone or ethanol, or water if the solvent is water), or by concentration followed by dialysis purification. The resulting aminated carboxylated lignin product is filtered, washed 3-5 times with deionized water, and dried in a vacuum oven at 60°C for 12 to 24 hours to obtain a light yellow aminated carboxylated lignin powder.

[0031] The fourth step is the introduction of phosphonic acid groups. This is a preferred step, designed to significantly enhance the inhibitor's chelating ability against polyvalent metal ions. The aminated carboxylated lignin powder obtained in the third step is accurately weighed and dissolved in deionized water or a water-soluble solvent at a concentration of 3% to 10% (mass percentage), preferably 5%. This dissolution process is carried out in a jacketed reactor equipped with a mechanical stirrer, a temperature control system, a reflux condenser, and an inert gas (e.g., nitrogen) protection device, with the stirring speed maintained at 250-500 rpm. Under continuous stirring and a nitrogen atmosphere, the reaction system is heated to 90°C to 130°C, preferably 110°C. Subsequently, a mixed solution (or alkyl phosphate ester) of phosphorous acid (H3PO3) and formaldehyde (HCHO) is slowly added to the solution. The molar ratio of phosphorous acid to aminated carboxylated lignin is 0.1:1 to 0.5:1, preferably 0.3:1. The molar ratio of formaldehyde (based on a 37% aqueous solution) to phosphorous acid is 1.0:1 to 2.0:1, preferably 1.5:1. The dropwise addition process typically lasts 1 to 2 hours to ensure a stable reaction. After the dropwise addition is complete, the reaction temperature and inert gas protection are maintained, allowing the reaction to continue for 6 to 12 hours, preferably 8 hours. After the reaction is complete, the reaction mixture is cooled to room temperature. Subsequently, the product is rigorously purified by dialysis (using a dialysis bag with a molecular weight cutoff of 3,500 Daltons, dialysis time 24-48 hours, with deionized water replaced every 4-6 hours), ultrafiltration (using an ultrafiltration membrane with a molecular weight cutoff of 3,000 Daltons), or solvent precipitation (by adding a large amount of ethanol or acetone) to completely remove unreacted reagents (such as formaldehyde and phosphorous acid) and potential low-molecular-weight byproducts. The purified product solution is finally dried by freeze-drying or spray-drying to obtain a white or off-white powdery multifunctional amphoteric polymer, which is the novel non-ferrous metal flotation inhibitor referred to in this invention.

[0032] In the above preparation process, the reactors used are all industrial-grade reactors equipped with precision mechanical stirring devices, integrated temperature control systems (such as PID controllers and jacketed heating / cooling systems), and efficient condensation reflux devices. These configurations collectively ensure a high degree of controllability, uniformity, and safety of the reaction conditions throughout the synthesis process, thereby guaranteeing the stability of product quality and batch-to-batch consistency. Furthermore, in each key reaction step, precise monitoring and adjustment of pH value is crucial for controlling the reaction pathway, optimizing product structure, and ensuring the performance of the final product. The pH value can be adjusted by precisely metering and slowly adding dilute hydrochloric acid, dilute sulfuric acid, or sodium hydroxide solution, supplemented by real-time monitoring using an online pH probe. The refinement and standardization of the preparation process give it good potential for industrial scale-up and economic efficiency.

[0033] The novel non-ferrous metal flotation inhibitor provided by this invention achieves precise control over the non-ferrous metal flotation process through its unique multifunctional amphoteric polymer structure. Its mechanism of action and technical effects are mainly reflected in the following aspects:

[0034] First, the inhibitor exhibits multimodal synergistic adsorption capabilities. The multifunctional amphoteric polymer, strategically incorporating carboxyl, amino, hydroxyl, and phosphonic acid groups in its molecular structure, enables it to interact with gangue mineral surfaces in various forms. Specifically, the carboxyl and phosphonic acid groups can form stable chelate complexes with polyvalent metal ions such as calcium, magnesium, iron, and aluminum ions exposed on the gangue mineral surface. These complexes form a dense physical barrier on the mineral surface, effectively covering the active sites and significantly preventing the adsorption of the collector on the mineral surface, thus reducing its hydrophobicity. Simultaneously, the ionization of these groups also provides additional electrostatic adsorption sites. The amino groups undergo protonation under acidic or neutral conditions, forming positively charged groups that generate strong electrostatic attraction with negatively charged mineral surfaces such as silicates. Furthermore, the hydroxyl groups can establish stable connections with the mineral surface through hydrogen bonding, further enhancing the polymer's adsorption strength. Furthermore, due to its chain-like structure, the polymer backbone itself can form a steric hindrance layer after adsorption onto the mineral surface, physically hindering the collector molecules from approaching and adsorbing onto the mineral surface, thereby further synergistically enhancing the inhibition effect. The combined effect of these multiple mechanisms ensures that the inhibitor exhibits highly efficient and selective adsorption and inhibition capabilities for gangue minerals of different types and surface chemistry, significantly improving the sorting selectivity of target non-ferrous metal minerals and effectively reducing the gangue mineral content in the concentrate.

[0035] Secondly, the inhibitor possesses stability and adaptability across a wide pH range. The multifunctional amphoteric polymer exhibits significant amphoteric properties due to the simultaneous presence of acidic (carboxyl and phosphonic acid groups) and basic (amino) functional groups in its molecule. This amphoteric property allows the polymer to maintain highly efficient inhibition performance across a broad pH range. Under acidic flotation conditions, the amino groups exhibit a higher degree of protonation, forming positively charged sites, thereby enhancing their electrostatic adsorption with negatively charged mineral surfaces. Under basic flotation conditions, the carboxyl and phosphonic acid groups exhibit increased deprotonation, causing the polymer to carry more negative charges, thus enhancing its chelation with polyvalent metal ions and generating stronger electrostatic repulsion, which helps inhibit mineral flotation. This pH-responsive conformational change and dynamic adjustment of surface charge distribution allow the polymer to effectively unfold its molecular chains in different pH environments, exposing the most suitable active sites for interaction with mineral surfaces, thereby ensuring the stability of the inhibitor performance and the reliability of concentrate recovery under varying flotation conditions. Compared to traditional single inhibitors that are only effective within a specific pH range, the inhibitor provided by this invention significantly broadens its application pH range, greatly reducing the stringent pH control requirements for flotation operations and providing greater operational flexibility for concentrators.

[0036] Furthermore, this inhibitor exhibits broad applicability and high-efficiency inhibition performance. The inhibitor provided by this invention, through its precise molecular design and multimodal adsorption capabilities, can effectively inhibit a variety of common non-ferrous metal gangue minerals, including but not limited to silicate minerals (such as talc, serpentine, and kaolinite), carbonate minerals (such as calcite and dolomite), and some oxide minerals (such as iron oxides). This inhibitor effectively inhibits the flotation behavior of these gangue minerals by identifying and specifically targeting their surface chemical properties. Simultaneously, it has minimal impact on the flotation behavior of target non-ferrous metal minerals (such as chalcopyrite, sphalerite, galena, wolframite, cassiterite, and other sulfide or oxide minerals), and in some cases, it even indirectly improves the recovery rate and concentrate grade of the target minerals through strong gangue inhibition. This broad applicability greatly simplifies the complexity of reagent formulations in mineral processing plants, reduces the need for synergistic use of multiple inhibitors, and thus lowers the overall cost of reagent development and production. Its superior inhibition efficiency also significantly reduces the amount of inhibitor required compared to traditional inhibitors. Ideal inhibition can usually be achieved with 50 to 500 grams per ton of ore, further reducing operating costs.

[0037] Furthermore, the inhibitor provided by this invention possesses significant environmental friendliness and sustainability. The preparation of the multifunctional amphoteric polymer uses renewable biomass-based lignin as the main raw material, fully utilizing waste resources from industrial production processes, such as lignin in papermaking wastewater, thereby effectively reducing dependence on limited fossil resources and conforming to the concept of a circular economy. Both lignin itself and its products after chemical modification by this invention have good biodegradability and can be effectively decomposed by microorganisms in the environment, avoiding long-term residues and potential bioaccumulation effects, significantly reducing potential negative risks to the ecological environment. Moreover, due to the high efficiency of this inhibitor, its actual usage in flotation operations is greatly reduced, directly leading to a reduction in the total amount of chemical reagents discharged in flotation tailings, thereby alleviating the burden of tailings treatment and minimizing the risk of secondary pollution, fully aligning with the core concepts of green environmental protection and sustainable development in the modern mineral processing field.

[0038] Finally, the preparation process of the inhibitor possesses significant advantages in terms of economy and scalability. The inhibitor preparation method provided by this invention fully utilizes the mature and widely used lignin modification technology in industry. The main chemical reagents used, such as monochloroacetic acid, epichlorohydrin, polyamine compounds, phosphorous acid, and formaldehyde, are all readily available and relatively inexpensive general-purpose chemicals in industry. The reaction conditions of the preparation process are easily and precisely controlled, without involving extreme high pressure or high temperature, and without requiring special or expensive reaction equipment. This greatly simplifies the scale-up process for industrial production, lowering the technical threshold and initial investment. The relatively simplified multi-step synthetic route avoids the complex separation and purification steps in traditional fine chemicals, thereby significantly reducing production and operating costs. This makes the novel inhibitor more economically competitive and conducive to its widespread large-scale industrial application and promotion in the field of non-ferrous metal mineral flotation.

[0039] Example 1: Preparation and Application of Novel Amphoteric Polymer Flotation Depressant

[0040] This embodiment aims to illustrate in detail the preparation of a novel multifunctional amphoteric polymer flotation inhibitor and its application in calcite inhibition.

[0041] Step 1: Pretreatment of lignin: 1000 g of industrial-grade lignin sulfonate (provided by the pulp mill) was placed in a 15 L stainless steel reactor. 15 L of deionized water was added, and the stirrer was started at 200 rpm. A 10% (w / v) sodium hydroxide solution was slowly added dropwise until the pH of the system stabilized at 10.5. The mixture was stirred continuously at room temperature for 2 hours to ensure complete dissolution of the lignin. The resulting lignin solution was purified using a cross-flow ultrafiltration system equipped with a polyethersulfone (PES) ultrafiltration membrane with a molecular weight cutoff of 3,500 Daltons. The operating pressure was set at 0.35 MPa, and the temperature was controlled at 30°C. Filtration was continued until the conductivity of the filtrate dropped below 30 μS / cm. The purified concentrated lignin solution (approximately 2.5 L) was then dried using a laboratory freeze dryer at -55°C, a vacuum of 15 Pa, and for 36 hours. Finally, 125 grams of purified lignin powder was obtained, with a weight-average molecular weight (Mw) of approximately 15,000 Daltons as determined by gel permeation chromatography (GPC).

[0042] The second step, carboxylation modification of lignin: 100 g of the refined lignin powder was accurately weighed and dissolved in 900 mL of a 10% (w / v) sodium hydroxide aqueous solution to form an alkaline solution with a lignin concentration of 10% (w / w). This solution was transferred to a 2-liter glass reactor equipped with a stirrer, temperature control, and reflux condenser, and the stirring speed was set to 250 rpm. The reaction system was heated to 75°C. Subsequently, 100 g of monochloroacetic acid (MCA) (i.e., an MCA to lignin mass ratio of 1.0:1) was dissolved in 100 mL of deionized water to prepare a 50% (w / v) MCA solution. Under continuous stirring and a constant temperature of 75°C, the MCA solution was added dropwise to the reactor uniformly and slowly through a constant pressure dropping funnel over approximately 1.5 hours. After the addition was complete, the reaction temperature was maintained at 75°C and the stirring speed at 250 rpm, and the reaction was continued for 4 hours. After the reaction was completed, the reaction mixture was cooled to room temperature. The pH of the solution was adjusted to 3.0 by slowly adding 10% (v / v) dilute hydrochloric acid, at which point the carboxylated lignin product began to precipitate in large quantities. The precipitate was separated by vacuum filtration using a Buchner funnel, and the filter cake was then washed repeatedly five times with a large amount of deionized water until the pH of the washing solution reached above 6.5 and no chloride ion precipitation was detected using silver nitrate solution. The washed product was dried in a vacuum oven at 60 degrees Celsius for 18 hours. Finally, 95 grams of light yellow carboxylated lignin powder were obtained. The carboxyl content of this product was determined by titration to be 1.05 mmol / g.

[0043] Step 3, Aminolation Modification of Carboxylated Lignin: Take 80 g of the carboxylated lignin powder obtained in Step 2 and dissolve it in 800 mL of deionized water to form a 10% (w / w) solution. Transfer this solution to a 1.5 L glass reactor equipped with a stirrer, temperature control, and reflux condenser, and set the stirring speed to 300 rpm. Under continuous stirring, slowly add 25 mL of epichlorohydrin (ECH) (approximately 0.29 mol), with a molar ratio to carboxylated lignin of approximately 1.1:1 (based on the assumed molar mass of carboxylated lignin). Subsequently, heat the reaction system to 98°C. Once the temperature stabilizes, slowly add 15 mL of diethylenetriamine (DETA) (approximately 0.13 mol) using a syringe pump, i.e., a molar ratio of DETA to ECH of approximately 0.45:1. The addition rate of DETA is controlled at 0.2 mL per minute to avoid localized overheating. After the addition is complete, maintain the reaction temperature at 98°C and the stirring speed at 300 rpm, and continue the reaction for 6 hours. After the reaction was complete, the reaction mixture was cooled to room temperature. The pH of the solution was adjusted to 6.5 by adding 5% (v / v) dilute acetic acid dropwise. The reaction solution was then concentrated to approximately 200 mL and transferred to a dialysis bag (MWCO 3500 Da) for dialysis purification. Deionized water was replaced every 4 hours, and dialysis was continued for 24 hours to remove unreacted reagents and low molecular weight byproducts. The dialyzed product solution was freeze-dried to obtain 72 g of off-white aminated carboxylated lignin powder. The amino content of this product was determined by titration to be 1.52 mmol / g.

[0044] Step 4, Introduction of Phosphonic Acid Groups: Take 60 g of the aminated carboxylated lignin powder obtained in Step 3 and dissolve it in 1000 mL of deionized water to form a 6% (w / w) solution. Transfer this solution to a 2-liter glass reactor equipped with a stirrer, temperature control, reflux condenser, and nitrogen protection device. Set the stirring speed to 350 rpm. Purge with nitrogen to maintain an inert atmosphere. Heat the reaction system to 115°C. Then, mix 5 g of phosphorous acid (H3PO3) (approximately 0.06 mol, with a molar ratio of approximately 0.25:1 to the aminated carboxylated lignin) and 10 mL of formaldehyde (37% aqueous solution) (approximately 0.12 mol, with a molar ratio of approximately 2.0:1 to the phosphorous acid), and slowly add the mixture dropwise to the reactor through a dropping funnel over approximately 1 hour. After the addition is complete, maintain the reaction temperature at 115°C and the stirring speed at 350 rpm, and continue the reaction under nitrogen protection for 8 hours. After the reaction is complete, cool the reaction mixture to room temperature. The resulting product solution was purified by ultrafiltration (ultrafiltration membrane molecular weight cutoff 3,000 Daltons) to remove unreacted reagents and low molecular weight byproducts until the dialysate conductivity stabilized. The purified concentrated product solution (approximately 150 mL) was freeze-dried to obtain 55 g of the novel multifunctional amphoteric polymer flotation inhibitor of this invention (labeled as Inhibitor A). This inhibitor has a weight-average molecular weight of approximately 25,000 Daltons, a carboxyl group content of 1.1 mmol / g, an amino group content of 1.4 mmol / g, and a phosphonic acid group content of 0.35 mmol / g.

[0045] Application Experiment: Calcite-suppressed flotation was performed on a non-ferrous copper ore sample. The mineral composition was: chalcopyrite (2.5%), calcite (15%), quartz (60%), and other silicate minerals (22.5%). The ore was crushed and ground to a particle size of -0.074 mm, achieving a particle size content of 80%. A 1.5-liter laboratory flotation machine was used for the flotation experiment. Flotation conditions: pulp concentration 30% (mass percentage), pH adjusted to 9.5 with lime. The collector was butyl xanthate, used at 80 g / ton; the frother was pine oil, used at 20 g / ton. The depressant pretreatment time was 10 minutes. In the experiment with depressant A, its dosage was set at 100 g / ton of ore. Flotation process: First, depressant A was added and stirred for 10 minutes. Then, the collector was added and stirred for 5 minutes. Next, the frother was added and stirred for 2 minutes. Finally, frothing flotation was performed, with a frothing time set at 8 minutes. Collect concentrate and tailings, dry and weigh them, and perform chemical level analysis.

[0046] Comparative Example 1: Application of Traditional Carboxymethyl Cellulose (CMC) Inhibitors

[0047] This comparative example is intended to compare with Example 1 to highlight the performance advantages of the inhibitor of the present invention. This comparative example uses commercially available carboxymethyl cellulose (CMC) with a weight-average molecular weight of approximately 30,000 Daltons and a carboxyl content of 0.9 mmol / g (free of amino and phosphonic acid groups). The flotation experimental conditions, ore samples, and flotation process are exactly the same as in Example 1, except that inhibitor A is replaced with CMC. The amount of CMC used is set at 100 g / ton of ore. Flotation experiments, concentrate and tailings collection, weighing, and grade analysis are performed according to the same procedures as in Example 1.

[0048] Comparative Example 2: Application of carboxylation and amylation lignin inhibitors only

[0049] This comparative example aims to investigate the necessity of introducing phosphonic acid groups. This comparative example uses the aminated carboxylated lignin powder (labeled as inhibitor B) obtained in step three of Example 1, which is free of phosphonic acid groups. Its weight-average molecular weight is approximately 20,000 Daltons, with a carboxyl content of 1.05 mmol / g and an amino content of 1.52 mmol / g. The flotation experimental conditions, ore samples, and flotation process are exactly the same as in Example 1, except that inhibitor A is replaced with inhibitor B. The dosage of inhibitor B is set at 100 g / ton of ore. Flotation experiments, concentrate and tailings collection, weighing, and grade analysis are performed according to the same procedures as in Example 1.

[0050] Experimental Results and Data Analysis

[0051] Detailed chemical level analysis and product calculations were performed on the flotation results of Example 1 and Comparative Examples 1 and 2, and the following data were obtained, summarized in Table 1. All data are averages of three replicate experiments.

[0052] Table 1: Comparison of the inhibitory effects of different inhibitors in copper ore flotation

[0053] As can be clearly seen from the experimental data in Table 1, the novel multifunctional amphoteric polymer flotation inhibitor (inhibitor A) prepared in this invention exhibits significantly improved overall flotation performance compared to the traditional carboxymethyl cellulose (CMC) inhibitor (Comparative Example 1) and the lignin inhibitor that has only undergone carboxylation and amination modification (inhibitor B, Comparative Example 2) under the same dosage conditions. Specifically:

[0054] Inhibitor A resulted in a copper concentrate grade of 28.5%, significantly higher than CMC's 22.1% and Inhibitor B's 25.4%. This indicates that Inhibitor A has higher selectivity and efficiency in suppressing gangue minerals, effectively reducing the amount of gangue minerals entering the copper concentrate and thus improving concentrate quality. Simultaneously, while maintaining a high grade, Inhibitor A also achieved a copper recovery rate of 92.3%, compared to CMC's 88.5% and Inhibitor B's 90.1%, demonstrating that it has minimal impact on the flotation behavior of the target non-ferrous metal minerals; in fact, the copper recovery rate even improved after gangue was effectively suppressed.

[0055] More importantly, the percentage of calcite remaining in the concentrate directly verifies the inhibitor's effectiveness. Inhibitor A resulted in a calcite residue of only 1.8% in the concentrate, significantly lower than CMC's 6.5% and Inhibitor B's 3.9%. This data directly demonstrates that Inhibitor A of this invention has an exceptionally strong inhibitory effect on carbonate gangue minerals (especially calcite). Compared to the single carboxyl group action mechanism of CMC in Comparative Example 1, Inhibitor A, with its multimodal synergistic adsorption of carboxyl, amino, hydroxyl, and phosphonic acid groups, can more effectively act on the surface of complex minerals such as calcite, forming a more stable and comprehensive coating layer, thereby more thoroughly preventing the adsorption of the collector and avoiding the accidental floatation of calcite. Compared to Inhibitor B in Comparative Example 2, the additional phosphonic acid groups introduced by Inhibitor A further enhance its chelating ability for multivalent metal ions and its adsorption strength on the mineral surface. Especially under low concentration conditions, the phosphonic acid groups can provide stronger inhibitory efficacy, thus further optimizing the inhibitory effect on calcite. This strongly demonstrates that the introduction of phosphonic acid groups plays an indispensable and crucial role in achieving the highly efficient inhibition performance of this invention.

[0056] In summary, the novel non-ferrous metal flotation depressant provided by this invention, through its finely designed biomass-based multifunctional amphoteric polymer structure and strictly controlled preparation process, not only achieves efficient and broad-spectrum inhibition of various gangue minerals, effectively improving concentrate grade and target mineral recovery, but also demonstrates significant advantages in environmental friendliness and economic feasibility, providing an innovative and practical solution for the non-ferrous metal flotation industry. The preparation method of the depressant is easy to implement, the product performance is stable, and it has broad prospects for industrial application.

Claims

1. A novel non-ferrous metal flotation inhibitor, characterized in that, Its main active ingredient is a multifunctional amphoteric polymer, which is prepared by a biomass-based polymer backbone through a multi-step chemical modification reaction. The structure of the multifunctional amphoteric polymer contains at least two of the following functional groups: carboxyl, amino, hydroxyl, and phosphonic acid groups, and the various functional groups are covalently linked to the biomass-based polymer backbone.

2. The novel non-ferrous metal flotation inhibitor according to claim 1, characterized in that, The biomass-based polymer skeleton is selected from at least one of lignin, cellulose, hemicellulose and their derivatives.

3. The novel non-ferrous metal flotation inhibitor according to claim 2, characterized in that, The biomass-based polymer skeleton is pretreated lignin.

4. The novel non-ferrous metal flotation inhibitor according to claim 3, characterized in that, The lignin is selected from lignin sulfonates, alkali lignin, or organic solvent lignin from industrial waste.

5. The novel non-ferrous metal flotation inhibitor according to claim 3, characterized in that, The pretreatment includes the following steps: acid washing of the lignin; alkali dissolution of the lignin; ultrafiltration separation of the lignin solution, wherein the molecular weight cutoff of the ultrafiltration membrane is 3,000 Daltons to 5,000 Daltons; and drying of the purified lignin solution, wherein the drying process employs freeze drying or spray drying technology.

6. The novel non-ferrous metal flotation inhibitor according to claim 1, characterized in that, The weight-average molecular weight of the multifunctional amphoteric polymer ranges from 5,000 Daltons to 50,000 Daltons.

7. The novel non-ferrous metal flotation inhibitor according to claim 1, characterized in that, The multifunctional amphoteric polymer has a carboxyl content of 0.5 mmol / g to 1.5 mmol / g, an amino content of 0.8 mmol / g to 2.0 mmol / g, and a phosphonic acid group content of 0.1 mmol / g to 0.5 mmol / g.

8. A method for preparing a novel non-ferrous metal flotation inhibitor, characterized in that, The process includes the following steps: S1: Pretreatment of lignin, wherein the lignin is placed in a reaction vessel, deionized water is added, the mass ratio of lignin to deionized water is 1:10 to 1:20, the pH is adjusted to an alkaline range of 9.0 to 12.0, and dissolution is carried out under stirring; subsequently, the lignin solution is purified by ultrafiltration membrane separation technology, wherein the molecular weight cutoff of the ultrafiltration membrane is 3,000 Daltons to 5,000 Daltons, and the purification operation pressure is 0.2 MPa to 0.5 MPa. MPa, operating temperature 25°C to 40°C; the purified lignin solution is freeze-dried or spray-dried to obtain refined lignin powder; S2: carboxylation modification of lignin, the refined lignin powder is dissolved in an aqueous sodium hydroxide solution, the concentration of lignin is 5% to 15% (mass percentage), under conditions of temperature between 60°C and 90°C and continuous stirring, monochloroacetic acid is slowly added to the lignin solution, the mass ratio of monochloroacetic acid to lignin is 0.5:1 to 2.0:1, the reaction time is 2 hours to 6 hours; after the reaction, the product is precipitated by adjusting the pH value to an acidic range of 2.0 to 4.0, and then filtered, washed, and dried to obtain carboxylated lignin; and S3 Aminolation modification of carboxylated lignin involves dissolving the carboxylated lignin in deionized water or a water-alcohol mixture at a concentration of 8% to 18% (mass percentage). Epichlorohydrin is added to the solution under continuous stirring at a temperature between 80°C and 120°C. The molar ratio of epichlorohydrin to carboxylated lignin is 0.8:1 to 1.5:

1. Subsequently, a polyamine compound, selected from diethylenetriamine or tetraethylenepentamine, is slowly added. The molar ratio of the polyamine compound to epichlorohydrin is 0.5:1 to 1.0:

1. The reaction time is 4 to 8 hours. After the reaction, purification is performed through pH adjustment, precipitation, filtration, washing, and drying to obtain aminated carboxylated lignin.

9. The preparation method according to claim 8, characterized in that, Following step S3, the process further includes purifying the aminated carboxylated lignin by means of dialysis, ultrafiltration, or solvent precipitation, followed by freeze-drying or spray-drying steps to obtain the novel non-ferrous metal flotation inhibitor.

10. The preparation method according to claim 8, characterized in that, Following step S3, the process further includes a phosphonic acid group introduction step and a subsequent purification and drying step: the phosphonic acid group introduction step involves dissolving the aminated carboxylated lignin in deionized water or a water-soluble solvent at a concentration of 3% to 10% (mass percentage), adding phosphorous acid and formaldehyde or alkyl phosphate to the solution at a temperature between 90°C and 130°C under stirring and inert gas protection, and reacting for 6 to 12 hours, wherein the molar ratio of phosphorous acid to the aminated carboxylated lignin is 0.1:1 to 0.5:1, and the molar ratio of formaldehyde to phosphorous acid is 1.0:1 to 2.0:1; the subsequent purification and drying step involves purification by dialysis, ultrafiltration, or solvent precipitation to remove unreacted reagents and byproducts, and finally, the product is freeze-dried or spray-dried to obtain the novel non-ferrous metal flotation inhibitor.

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