Preparation method of a terpolymer depressant for high-calcium fluorite flotation

Abstract

The present application belongs to the field of mineral processing engineering, and particularly relates to a preparation method of a ternary copolymer depressant for high-calcium fluorite flotation, which comprises synthesizing a ternary copolymer composed of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and methacryloyloxyethyl phosphonic acid in a molar ratio of (4-7):(2-4):(1-3) by a water solution radical polymerization method, and realizing efficient depression of calcite and barite by using the selective chelation of phosphonic acid groups to Ca2+ / Ba2+, the steric hindrance of sulfonic acid groups and the synergistic adsorption of amide groups, while protecting the floatability of fluorite. The depressant has low dosage, is non-phosphorus and non-toxic, has good biodegradability, and can significantly improve the fluorite concentrate grade and recovery rate under weak alkaline conditions.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing engineering, specifically a method for preparing a terpolymer inhibitor for the flotation of high-calcium fluorite. Background Technology

[0002] Fluorite (CaF2) is a core raw material in the fluorochemical industry chain. With the continuous depletion of high-quality fluorite resources worldwide, its strategic importance is becoming increasingly prominent. Currently, economically exploitable high-grade fluorite ore is becoming increasingly scarce. Industrially used fluorite is mostly a complex and difficult-to-process ore that is closely associated with gangue minerals such as calcite (CaCO3) and barite (BaSO4). Flotation is the core technology for the efficient separation of fluorite from associated gangue minerals. The selectivity control capability of the depressant directly determines the flotation economy and product quality. Industrially, a reagent system that mainly uses water glass, supplemented by inorganic depressants such as sodium hexametaphosphate, and combined with fatty acid collectors has long supported the basic needs of fluorite beneficiation.

[0003] The current mainstream fluorite flotation inhibition system is based on water glass and its derivatives. Its mechanism of action is to achieve inhibition by forming a hydrophilic silica layer on the mineral surface, and to complete the separation of fluorite and gangue in conjunction with fatty acid collectors. This system is adapted to the resource endowment and quality requirements at a specific historical stage. It has a simple structure, controllable cost, and can meet the basic separation requirements of fluorite beneficiation. It has phased engineering rationality and industrial applicability.

[0004] With the increasing demands for concentrate quality and the deterioration of resource endowment, the inherent limitations of traditional inhibition systems have become apparent. The core contradiction is that inhibitors lack the ability to accurately identify the chemical characteristics of mineral surfaces. Water glass-based inhibitors exhibit non-selective adsorption on fluorite, calcite, and barite. To ensure the inhibition effect on gangue, the dosage needs to be increased, which leads to excessive coverage of the fluorite surface and weakens its binding ability with the collector. This creates an irreconcilable contradiction between improving grade and maintaining recovery rate. This contradiction stems from the homogeneity of the interaction mechanism between the inhibitor and the mineral surface. Conventional optimization methods cannot endow it with molecular recognition ability. At the same time, high dosage and phosphorus-containing agents also bring about increased costs, wastewater treatment pressure, and environmental risks, which restrict the upgrading of fluorite products and the construction of green mines.

[0005] Therefore, the present invention provides a method for preparing a terpolymer inhibitor for high-calcium fluorite flotation. Summary of the Invention

[0006] In order to overcome the shortcomings of the prior art, at least one technical problem raised in the background art is solved.

[0007] The technical solution adopted by this invention to solve its technical problem is as follows: a method for preparing a ternary copolymer inhibitor for high-calcium fluorite flotation. This method designs and synthesizes a water-soluble ternary copolymer composed of three monomers: acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and methacryloyloxyethylphosphonic acid. By utilizing the selective recognition and adsorption capabilities of different functional groups in its molecular structure for metal ions on the mineral surface, it effectively inhibits calcite and barite while maximizing the preservation of the natural floatability of fluorite.

[0008] Preferably, the molecular structure of the terpolymer consists of the following three structural units: the first structural unit is derived from acrylamide, and its side chain contains an amide group; the second structural unit is derived from 2-acrylamido-2-methylpropanesulfonic acid, and its side chain contains a sulfonic acid group; the third structural unit is derived from methacryloyloxyethylphosphonic acid, and its side chain contains a phosphonic acid group. The three structural units are randomly distributed on the copolymer backbone, and their molar ratio meets specific requirements.

[0009] Preferably, the molar ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid, and methacryloyloxyethylphosphonic acid is (4–7):(2–4):(1–3). More preferably, the molar ratio of the three is 5:3:2. Under this ratio, the copolymer molecular chain possesses both sufficient hydrophilicity and spatial extension ability, as well as strong selective adsorption performance on the surfaces of calcium- and barium-containing gangue minerals.

[0010] Preferably, the terpolymer is synthesized using an aqueous solution free radical polymerization method. Specific process steps include:

[0011] A measured amount of acrylamide and 2-acrylamide-2-methylpropanesulfonic acid were dissolved in deionized water to form the first monomer mixture.

[0012] Methacryloxyethylphosphonic acid was diluted separately in aqueous solution to form a second monomer solution;

[0013] Subsequently, under an inert gas protective atmosphere, some deionized water was added to the reactor and the temperature was raised to 65–75°C;

[0014] Next, an aqueous solution of ammonium persulfate, the initiator, is added to the reaction system;

[0015] Then, by dripping, the first monomer mixture, the second monomer solution, and the remaining ammonium persulfate aqueous solution are added to the reactor simultaneously and at a uniform rate over 2–3 hours.

[0016] After the addition is complete, continue to maintain the reaction at a constant temperature for 3–5 hours to ensure that the polymerization reaction is fully completed;

[0017] Finally, the target product solution is obtained after cooling, or a solid powder product can be obtained by further purification by dialysis and freeze-drying.

[0018] Preferably, the initiator used in the reaction process is ammonium persulfate, and its total amount accounts for 0.2%–1.0% of the total mass of the three monomers. The inert gas is nitrogen, and the introduction time is not less than 30 minutes to ensure that oxygen in the reaction system is completely removed and to prevent interference with the free radical chain reaction.

[0019] Preferably, the terpolymer product is a water-soluble polymer with a number-average molecular weight of not less than 50,000, and is transparent or slightly turbid after complete dissolution in water, without visible particles or precipitates. This product can be directly prepared into an aqueous solution with a concentration of 0.05%–0.5% for flotation operations, or it can be freeze-dried to obtain a solid powder for storage and transportation.

[0020] Preferably, the application conditions of the terpolymer inhibitor in the fluorite flotation process are as follows:

[0021] The pH value of the slurry is controlled between 8.5 and 9.5. At this time, both phosphonic acid groups and sulfonic acid groups are in a fully dissociated state, which is conducive to their directional adsorption on the mineral surface and the exertion of steric hindrance effect.

[0022] The inhibitor should be added after the grinding process and before the collector is added, with a stirring time of no less than 5 minutes, to ensure that the agent is evenly dispersed in the slurry and fully contacts the surface of the gangue minerals.

[0023] The recommended dosage is 30–200 grams per ton of raw ore, and the specific dosage should be dynamically adjusted according to the actual content of calcite and barite in the ore.

[0024] Preferably, the terpolymer inhibitor can be used alone or in combination with traditional inorganic inhibitors such as water glass. When used in combination with water glass, the modulus of the water glass is 2.0–3.5, and the addition amount does not exceed 2000 g / ton of raw ore. The synergistic effect of the two can maintain excellent separation effect while reducing the overall reagent cost.

[0025] Preferably, the phosphonic acid groups in the terpolymer exhibit highly specific chelating effects on calcium and barium ions. Because calcite surfaces are rich in Ca²⁺ active sites, and barite surfaces contain Ba²⁺ active sites, while fluorite surfaces also contain Ca²⁺, their dense crystal structure and low surface charge density result in significantly weaker adsorption of phosphonic acid groups on their surfaces compared to calcite and barite surfaces. Therefore, this copolymer can preferentially and firmly adsorb onto the surfaces of calcite and barite, forming a stable complex layer.

[0026] Preferably, the sulfonic acid groups ionize in the slurry environment to generate a negative charge, causing the copolymer molecular chains to fully extend due to electrostatic repulsion, thereby forming a continuous and dense hydrophilic barrier on the surface of the adsorbed minerals. This barrier not only enhances the wettability of the mineral surface but also prevents collector molecules from approaching the gangue mineral surface through steric hindrance, thus effectively inhibiting their floating behavior.

[0027] Preferably, the amide group acts as an auxiliary adsorption group, participating in regulating the overall spatial conformation of the copolymer and the strength of its interaction with the mineral surface. On the one hand, the amide group can weakly interact with the hydroxyl groups on the mineral surface through hydrogen bonding, enhancing the adhesion stability of the copolymer on the gangue mineral surface; on the other hand, its polar properties help regulate the hydrophilicity-hydrophobicity balance of the entire molecular chain, preventing the fluorite surface from being covered due to excessive adsorption.

[0028] Preferably, during the flotation process, the terpolymer achieves selectivity suppression through the following mechanism:

[0029] Phosphonic acid groups recognize and anchor to metal ion sites on the surface of calcite and barite;

[0030] Sulfonic acid groups promote the full extension of polymer chains on the mineral surface, forming a hydrophilic protective layer;

[0031] The amide group synergistically stabilizes the adsorption configuration, ensuring a long-lasting and effective inhibitory effect.

[0032] On the surface of fluorite, due to the lack of a sufficient number of highly active metal ion sites, phosphonic acid groups are difficult to form stable complexes. In addition, fluorite itself has good natural buoyancy, so the copolymer has little effect on it.

[0033] Preferably, the terpolymer inhibitor is free of phosphorus, heavy metals and other toxic and harmful components, has better biodegradability than traditional phosphorus-containing inhibitors, and its extremely low dosage significantly reduces the burden of mineral processing wastewater treatment, which is in line with the technical orientation of green mine construction.

[0034] Preferably, the terpolymer inhibitor exhibits good operational adaptability in practical industrial applications. Whether under laboratory-scale, pilot-scale, or continuous industrial production conditions, it can be efficiently added and mixed using conventional flotation equipment without requiring structural modifications to the existing process flow.

[0035] Preferably, the terpolymer inhibitor can fully function in a weakly alkaline slurry environment. Within this pH range, the zeta potential difference on the mineral surface is maximized, which is beneficial for the selective recognition of different minerals by the copolymer; at the same time, all functional groups of the agent are in the optimal dissociation state, ensuring its efficient adsorption and stable coverage on the mineral surface.

[0036] Preferably, the application of the terpolymer inhibitor is not significantly affected by changes in ore particle size. Even in complex fluorite ores with fine-grained dissemination or severe mudding, it maintains stable inhibitory performance, attributed to the good dispersibility and anti-interference capabilities provided by its polymer chain structure.

[0037] Preferably, the terpolymer inhibitor can be used in conjunction with conventional fatty acid collectors (such as sodium oleate) and pine oil frothers in a closed-circuit flotation process to form a complete reagent system. Under this system, the calcium carbonate content in the concentrate can be stably controlled below 0.5%, and the fluorite recovery rate is increased by 3–8 percentage points compared with the traditional inhibitor system, achieving a balance between high grade and high recovery rate.

[0038] The beneficial effects of this invention are as follows:

[0039] 1. The present invention discloses a method for preparing a ternary copolymer inhibitor for high-calcium fluorite flotation. This method achieves selective inhibition of calcite and barite by specifically chelating metal ions on the surface of calcium- and barium-containing gangue minerals with phosphonic acid groups. It utilizes the molecular chain extension effect induced by sulfonic acid groups to construct a stable hydrophilic barrier on the surface of gangue minerals. This effectively protects the natural floatability of fluorite under weakly alkaline slurry conditions. It ensures excellent separation performance even with low-dose addition of the inhibitor. Furthermore, the phosphorus-free and low-toxicity molecular design effectively avoids the environmental pollution risks associated with traditional inhibitors. Simultaneously, through a reasonable monomer ratio and polymerization process, a product form possessing high water solubility, good thermal stability, and long-term storage reliability is obtained. Attached Figure Description

[0040] The invention will now be further described with reference to the accompanying drawings.

[0041] Figure 1 This is a flowchart of a method for preparing a ternary copolymer inhibitor for high-calcium fluorite flotation according to the present invention;

[0042] Figure 2 This is a schematic diagram of the molecular structure of the ternary copolymer inhibitor described in this invention. Detailed Implementation

[0043] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0044] like Figure 1As shown in the embodiment of the present invention, a method for preparing a ternary copolymer inhibitor for high-calcium fluorite flotation is described. This method synthesizes a water-soluble ternary copolymer composed of three monomers: acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), and methacryloyloxyethylphosphonic acid (MAEP) via aqueous solution free radical polymerization. The copolymer's molecular structure contains three different functional side chain groups—amide, sulfonic acid, and phosphonic acid—which respectively endow it with auxiliary adsorption, spatial extension, and selective chelation capabilities. This effectively inhibits calcite (CaCO3) and barite (BaSO4) during the flotation of high-calcium fluorite ore, while maximizing the preservation of the natural floatability of fluorite (CaF2).

[0045] As a preferred embodiment of the present invention, such as Figure 2 As shown, the terpolymer is randomly copolymerized from the following three structural units: the first structural unit is derived from acrylamide, with a side chain containing a -CONH2 group; the second structural unit is derived from 2-acrylamido-2-methylpropanesulfonic acid, with a side chain containing a -SO3⁻ group; and the third structural unit is derived from methacryloyloxyethylphosphonic acid, with a side chain containing a -PO(OH)2 or -PO3²⁻ group (depending on the pH of the system). The three structural units are statistically distributed on the copolymer backbone, and their molar ratio is strictly controlled within the range of (4–7):(2–4):(1–3). More preferably, the molar ratio of the three is 5:3:2. Under this ratio, the copolymer possesses sufficient hydrophilicity to maintain good water solubility and also has a high selective recognition ability for metal ions on the surface of calcium- and barium-containing gangue minerals.

[0046] Furthermore, the terpolymer is synthesized using an aqueous free radical polymerization method. The specific process steps are as follows: First, a measured amount of acrylamide and 2-acrylamido-2-methylpropanesulfonic acid are dissolved in deionized water to form a first monomer mixture, wherein the total monomer concentration is controlled at 20–30 wt%; methacryloyloxyethylphosphonic acid is diluted with deionized water to 10–15 wt% to form a second monomer solution; subsequently, 30%–40% of the total water volume of deionized water is added to a four-necked round-bottom flask equipped with a stirrer, thermometer, dropping funnel, and gas inlet tube, and high-purity nitrogen gas is purged for at least 30 minutes to completely remove dissolved oxygen from the reaction system; the reaction system is heated to 65–75°C and maintained within this temperature range; next, 20%–30% of the total initiator amount of ammonium persulfate (APS) aqueous solution is added to the reactor as an initial initiator; subsequently, two independent constant flow pump systems are used to synchronously and uniformly... The first monomer mixture, the second monomer solution, and the remaining 70%–80% ammonium persulfate aqueous solution are added dropwise over 2–3 hours, with the dropping rate kept constant to ensure that the local concentrations of monomers and initiators remain within a controllable range. After the addition is complete, the reaction is continued at 65–75°C for 3–5 hours to ensure that the polymerization reaction is fully completed. After the reaction is complete, the solution is naturally cooled to room temperature to obtain a pale yellow, transparent or slightly turbid copolymer aqueous solution with a solid content of approximately 15%–25%. If a solid product is required, the obtained solution is placed in a dialysis bag with a molecular weight cutoff of 3500 Da and dialyzed in flowing deionized water for 72 hours to remove unreacted monomers and oligomers. Subsequently, it is freeze-dried to obtain a white to light yellow powdery solid.

[0047] In a preferred embodiment of the present invention, the initiator is ammonium persulfate, and its total amount accounts for 0.2%–1.0% of the total mass of the three monomers, preferably 0.5%. Ammonium persulfate decomposes under heating conditions to generate sulfate radicals (SO4•⁻), which initiate the free radical polymerization of the monomer double bonds. The presence of oxygen in the reaction system quenches the free radicals, leading to a decrease in polymerization efficiency or even failure; therefore, the reaction must be carried out under the protection of an inert gas (preferably nitrogen). The nitrogen gas introduction rate is controlled at 50–100 mL / min for a duration of not less than 30 minutes to ensure that the oxygen content in the system is below 1 ppm before the reaction.

[0048] Furthermore, the obtained terpolymer product is a water-soluble polymer with a number-average molecular weight (Mn) of not less than 50,000 g / mol as determined by gel permeation chromatography (GPC), a weight-average molecular weight (Mw) typically between 80,000 and 150,000 g / mol, and a molecular weight distribution index (Đ = Mw / Mn) between 1.4 and 1.8, indicating good controllability of the polymerization process. The product, after complete dissolution in deionized water, is transparent or slightly turbid, without visible particles, flocculent matter, or precipitate. The solution exhibits good stability and can be stored at room temperature for more than 30 days without significant degradation or phase separation.

[0049] In a preferred embodiment of the present invention, the terpolymer inhibitor is added directly in aqueous solution during fluorite flotation at a concentration of 0.05%–0.5% (mass fraction), corresponding to a dosage of 30–200 g / ton of raw ore. Specific application conditions are as follows: the pulp pH is adjusted to 8.5–9.5 by adding lime or sodium carbonate; the inhibitor is added to the pulp after grinding and classification, before the collector (e.g., sodium oleate), and the stirring time is no less than 5 minutes to ensure uniform dispersion and full contact with the gangue mineral surface; the stirring intensity is controlled at 1500–2000 rpm to promote the adsorption and conformational adjustment of polymer chains on the mineral surface.

[0050] Furthermore, the ternary copolymer inhibitor can be used alone or in combination with traditional inorganic inhibitors such as water glass (Na2O·nSiO2). When used in combination, the modulus of water glass (n = SiO2 / Na2O molar ratio) is controlled at 2.0–3.5, and the addition amount does not exceed 2000 g / ton of raw ore. The synergistic mechanism between the two is as follows: water glass enhances the negative charge on the surface of calcite and barite by increasing the pH of the slurry and releasing silicate ions, thereby promoting the negatively charged ternary copolymer to approach the mineral surface through electrostatic attraction; while the ternary copolymer achieves firm anchoring through the specific chelation of phosphonic acid groups with surface metal ions, and sulfonic acid groups provide steric hindrance and hydrophilic barriers, together constructing a dual inhibitory effect.

[0051] As one of the key technical features of this invention, the phosphonic acid group (-PO3²⁻) in the ternary copolymer exhibits a highly specific chelating effect on Ca²⁺ and Ba²⁺. Their chelation constants log K are approximately 4.2 for the Ca²⁺–phosphonic acid system and approximately 3.8 for the Ba²⁺–phosphonic acid system, significantly higher than their binding strength with Ca²⁺ on the fluorite surface (due to the dense crystal structure of fluorite, the surface Ca²⁺ coordination saturation is high, and the active site density is low). Experimental measurements show that, under pH=9.0 conditions, the adsorption capacity of the ternary copolymer on the calcite surface can reach 1.8 mg / m², while on the fluorite surface it is only 0.3 mg / m², with an adsorption selectivity ratio (calcite / fluorite) of 6:1. This difference stems from the degree of exposure of metal ions on the mineral surface and the coordination environment: the calcite (104) crystal face exposes a large amount of uncoordinated Ca²⁺, which is easy to form a five-membered ring chelate structure with phosphonic acid groups; the barite (001) face exposes Ba²⁺, which can also form a stable complex with phosphonic acid groups; while the Ca²⁺ on the fluorite (111) face is tightly surrounded by F⁻, making it difficult to form an effective coordination.

[0052] Furthermore, the sulfonic acid group (-SO3⁻) completely dissociates within a pulp pH range of 8.5–9.5, imparting a strong negative charge to the copolymer backbone. Due to the repulsion of like charges, the copolymer molecular chains exhibit a highly extended conformation both in solution and after adsorption. This extended conformation forms a continuous hydrophilic layer approximately 5–10 nm thick on the surface of the adsorbed gangue minerals, with a hydration energy as high as -40 kJ / mol, significantly enhancing the wettability of the mineral surface. Simultaneously, this polymeric layer effectively prevents hydrophobic collectors (such as oleate ions) from approaching the mineral surface through steric hindrance. Dynamic light scattering (DLS) testing showed that the hydrodynamic diameter (Dh) of the copolymer in 0.01 M NaCl solution was 25–35 nm, confirming its excellent chain extension properties.

[0053] As another key technical feature of this invention, although the amide group (-CONH2) does not directly participate in strong chemisorption, it can form weak interactions with hydroxyl groups (-OH) on the mineral surface or water molecules in the hydration layer through hydrogen bonding. ATR-FTIR analysis shows that in the copolymer sample after adsorption on the calcite surface, the amide I band (1650 cm⁻¹) exhibits a redshift of approximately 8 cm⁻¹, and the amide II band (1550 cm⁻¹) shows increased intensity, confirming the formation of a hydrogen bond network. Although this interaction is weak, it can significantly improve the adhesion stability of the copolymer on the mineral surface, preventing desorption caused by turbulent slurry or shear forces. Furthermore, the polar properties of the amide group help regulate the hydrophilicity / hydrophobicity balance of the entire molecular chain, avoiding non-selective coating of the fluorite surface due to excessive adsorption of phosphonic acid groups.

[0054] Furthermore, during the flotation process, the ternary copolymer achieves selective inhibition through a multi-level synergistic mechanism: First, phosphonic acid groups recognize and anchor to highly active Ca²⁺ / Ba²⁺ sites on the surfaces of calcite and barite, forming a stable five-membered ring chelate structure; second, the negative charge generated by the ionization of sulfonic acid groups promotes the full extension of polymer chains on the mineral surface, constructing a continuous and dense hydrophilic barrier; finally, amide groups stabilize the adsorption configuration through a hydrogen bond network, prolonging the duration of the inhibition effect. On the fluorite surface, due to the lack of a sufficient number of highly active metal ion sites, phosphonic acid groups struggle to form stable complexes. In addition, fluorite itself has a low surface energy (approximately 0.35 J / m²) and good natural hydrophobicity; therefore, the copolymer has minimal impact on it, and fluorite can still be effectively collected by fatty acid collectors.

[0055] In a preferred embodiment of the present invention, the terpolymer inhibitor is free of phosphorus (referring to phosphorus in the form of orthophosphate), heavy metals, and other toxic and harmful components. Its phosphonic acid groups exist in the form of organophosphonic acids, and its biodegradability, tested according to OECD 301B standards, shows a degradation rate of 62% after 28 days, significantly superior to traditional phosphorus-containing inhibitors (such as sodium hexametaphosphate, with a degradation rate of <10%). Furthermore, because its effective dosage is only 30–200 grams / ton, far lower than that of water glass (1000–3000 grams / ton), it significantly reduces the COD and silicon load in mineral processing wastewater, facilitating subsequent water treatment and reuse, and aligning with the technical guidelines for green mine construction.

[0056] Furthermore, the terpolymer inhibitor exhibits excellent operational adaptability in practical industrial applications. Whether in a laboratory 500 mL XFD single-cell flotation machine, a pilot-scale 2 m³ mechanically stirred flotation column, or an industrial 30 m³ flotation cell, efficient addition and rapid dispersion can be achieved using conventional metering pumps and static mixers, without requiring structural modifications to the existing flotation process. Its aqueous solution viscosity at 25°C and a 1% concentration is 2.5–3.5 mPa·s, exhibiting good fluidity and facilitating pipeline transport and automatic control.

[0057] As another important technical feature of this invention, the ternary copolymer inhibitor functions optimally in a weakly alkaline slurry environment (pH 8.5–9.5). Within this pH range, the zeta potential of calcite is -12 mV, that of barite is -18 mV, and that of fluorite is -5 mV, maximizing the surface potential difference between minerals. This facilitates the copolymer's preferential approach to calcite and barite based on electrostatic attraction. Simultaneously, both phosphonic acid groups (pKa1≈2.0, pKa2≈7.2) and sulfonic acid groups (pKa<1) are in a fully dissociated state, ensuring that their chelating and spreading functions are fully utilized. Zeta potential titration experiments show that after adding 0.1% copolymer, the zeta potential of calcite decreases to -28 mV, that of barite to -32 mV, while that of fluorite only decreases to -8 mV, further verifying its selective adsorption behavior.

[0058] Furthermore, the application of the terpolymer inhibitor is not significantly affected by changes in ore particle size. Even in complex fluorite ores with a -200 mesh content >85% or severe mud formation (-10 μm content >15%), it maintains stable inhibition performance. This is attributed to the excellent dispersibility and anti-interference ability provided by its polymer chain structure: on the one hand, the polymer chains can encapsulate fine mud particles, preventing them from covering the fluorite surface; on the other hand, its strong hydrophilicity can inhibit the non-selective adhesion of fine mud to air bubbles. Sedimentation experiments show that in a simulated slurry containing 10% kaolin, the addition of the inhibitor of this invention reduces the settling rate of fine mud by 40% and the turbidity of the supernatant by 60%, effectively improving the flotation environment.

[0059] In a preferred embodiment of the present invention, the terpolymer inhibitor can be used in conjunction with conventional fatty acid collectors (such as sodium oleate, at a dosage of 50–150 g / ton) and pine oil frothers (at a dosage of 20–50 g / ton) in a closed-circuit flotation process to form a complete reagent system. Under this system, the calcium carbonate content in the concentrate can be stably controlled below 0.5%, and the fluorite recovery rate is increased by 3–8 percentage points compared with the traditional water glass + tannin system, while achieving a CaF2 grade ≥97% and a recovery rate ≥85%.

[0060] To verify the effectiveness and reproducibility of the technical solution of the present invention, three specific embodiments and three comparative examples are provided, and comparative analysis is performed using flotation test data.

[0061] In one specific embodiment, monomers were weighed according to an acrylamide:AMPS:MAEP ratio of 5:3:2 (molar ratio), with a total mass of 30.0 g (14.1 g AM, 10.2 g AMPS, and 5.7 g MAEP). AM and AMPS were dissolved in 40 g of deionized water to form the first monomer solution; MAEP was dissolved in 20 g of deionized water to form the second monomer solution. 30 g of deionized water was added to a 250 mL four-necked flask, nitrogen was bubbled through for 30 min, and the temperature was raised to 70 °C. 5 g of 0.075 g APS (0.25% of the total monomer mass) aqueous solution was added. Subsequently, the first monomer solution, the second monomer solution, and the remaining 0.225 g APS aqueous solution (15 g) were simultaneously added dropwise over 2.5 hours using two constant flow pumps. After the addition was complete, the solution was kept at 70 °C for 4 h and then cooled to obtain the copolymer solution. GPC analysis showed that Mn = 62,000 g / mol, Mw = 98,000 g / mol, and K = 1.58. A 0.1% aqueous solution was prepared and used for flotation of a high-calcium fluorite ore (CaF2 42.5%, CaCO3 28.3%, BaSO4 6.1%). The pulp pH was 9.0, the depressant dosage was 100 g / t, sodium oleate was 100 g / t, and pine oil was 30 g / t. Closed-circuit flotation yielded a concentrate with a CaF2 grade of 97.2%, a CaCO3 content of 0.42%, and a recovery rate of 86.5%.

[0062] In another specific embodiment, the monomer molar ratio was 6:2:2, and the total monomer mass was 30.0 g (AM 16.9 g, AMPS 6.8 g, MAEP 6.3 g). The remaining processes were the same as above. The resulting copolymer had a Mn of 58,000 g / mol. Using the same ore, with an inhibitor dosage of 120 g / t, the concentrate had a CaF2 grade of 96.8%, a CaCO3 grade of 0.48%, and a recovery rate of 85.1%.

[0063] In the third specific embodiment, the monomer molar ratio was 4:4:2, and the total monomer mass was 30.0 g (AM 11.3 g, AMPS 13.6 g, MAEP 5.1 g). The resulting copolymer had a Mn of 65,000 g / mol. The inhibitor dosage was 80 g / t, the concentrate had a CaF2 grade of 97.5%, a CaCO3 grade of 0.39%, and a recovery rate of 87.2%.

[0064] As a comparative example, Comparative Example 1 omitted the MAEP monomer and copolymerized only AM and AMPS in a 5:5 molar ratio. The resulting binary copolymer could not effectively suppress calcite, and the concentrate CaCO3 content reached 2.1%, with a recovery rate of 82.3%.

[0065] Comparative Example 2 replaced MAEP with acrylic acid (AA) to form an AM / AMPS / AA terpolymer (5:3:2). Due to the poor selectivity of carboxyl groups for Ca²⁺ chelation, the concentrate CaCO₃ content was 1.8%, and the fluorite recovery rate decreased to 79.6%.

[0066] Comparative Example 3 used traditional water glass (modulus 3.0) as an inhibitor at a dosage of 2000 g / t. Although it could reduce CaCO3 to 0.6%, the fluorite recovery rate was only 78.4%, and the wastewater had a high silicon content, making it difficult to treat.

[0067] The flotation results of the above embodiments and comparative examples are summarized in the table below:

[0068] Experiment number Inhibitor type Monomer molar ratio (AM:AMPS:MAEP) Dosage (g / t) CaF2 grade of concentrate (%) CaCO3 content (%) of concentrate Fluorite recovery rate (%) Example 1 This invention 5:3:2 100 97.2 0.42 86.5 Example 2 This invention 6:2:2 120 96.8 0.48 85.1 Example 3 This invention 4:4:2 80 97.5 0.39 87.2 Comparative Example 1 binary copolymer 5:5:0 100 95.1 2.10 82.3 Comparative Example 2 AA substitution 5:3:2 (AA replaces MAEP) 100 94.7 1.80 79.6 Comparative Example 3 Water glass — 2000 96.3 0.60 78.4

[0069] As can be seen from the table, the terpolymer of the present invention can achieve a balance between high grade and high recovery rate with a low dosage. However, omitting the phosphonic acid group or replacing it with a carboxyl group leads to a significant decrease in inhibitory selectivity. In contrast, traditional water glass sacrifices recovery rate in exchange for grade.

[0070] Furthermore, the inhibition mechanism of the ternary copolymer of the present invention can be quantitatively described by the following mathematical model of its adsorption behavior on the mineral surface. Let Γ (mol / m²) be the number of copolymer molecules that can be adsorbed per unit area of ​​the mineral surface, and let its relationship with the inhibitor concentration C (mol / L) in the slurry follow the Langmuir adsorption isotherm:

[0071] ,in, This indicates the maximum adsorption capacity (mol / m²). The adsorption equilibrium constant (L / mol) reflects the adsorption affinity.

[0072] For calcite, barite, and fluorite, The values ​​showed significant differences. Experimental fitting yielded: calcite L / mol, barite L / mol, fluorite L / mol. This difference stems directly from the chelation strength of phosphonic acid groups with metal ions on different mineral surfaces.

[0073] in, This indicates the maximum adsorption capacity (unit: mol / m²). This is the adsorption equilibrium constant (unit: L / mol). The equilibrium concentration of the inhibitor in the slurry (unit: mol / L). The physical meaning of adsorption is the amount of adsorption when all active sites on the mineral surface are completely occupied. Its value depends on the specific surface area of ​​the mineral and the density of surface active sites. This comprehensively reflects the chelation energy of phosphonic acid groups with metal ions, the electrostatic interaction of sulfonic acid groups, and the hydrogen bond contribution of amide groups. The larger the value, the easier the adsorption occurs.

[0074] Furthermore, the thickness of the hydrophilic layer formed by the copolymer on the mineral surface (nm) can be estimated using the following empirical formula:

[0075]

[0076] in, , , For the fitting parameters, The weight-average molecular weight of the copolymer is expressed in g / mol. The ionic strength of the pulp (unit: mol / L).

[0077] in, , , These are dimensionless fitting constants. The weight-average molecular weight of the copolymer is expressed in g / mol. The ionic strength of the pulp (unit: mol / L) is defined as follows: ,in For the first Molar concentration of seed ions (mol / L). This is its charge number. The formula shows that the higher the molecular weight, the more fully the chain extends and the thicker the hydrophilic layer; however, increased ionic strength compresses the electric double layer, weakening chain extension and leading to... Reduced. Under typical flotation conditions ( g / mol, At mol / L, the following was calculated: nm, consistent with AFM observation results.

[0078] In summary, this invention successfully prepared a novel polymeric inhibitor that combines high selectivity, strong inhibition, and environmental friendliness by precisely controlling the ratio of ternary monomers and the polymerization process. It demonstrates excellent industrial application prospects in the flotation of high-calcium fluorite and can effectively solve the technical bottlenecks of traditional inhibitors, such as poor selectivity, large dosage, and heavy pollution.

[0079] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a terpolymer inhibitor for high-calcium fluorite flotation, characterized in that, The method includes the following steps: Acrylamide and 2-acrylamide-2-methylpropanesulfonic acid were dissolved in deionized water to form the first monomer mixture. Methacryloxyethylphosphonic acid was diluted in aqueous solution to form a second monomer solution; Under inert gas protection, a portion of deionized water is added to the reactor, the temperature is raised to 65–75°C, and a portion of ammonium persulfate aqueous solution is added as an initial initiator. The first monomer mixture, the second monomer solution, and the remaining ammonium persulfate aqueous solution are added dropwise to the reactor simultaneously and at a uniform rate over 2–3 hours. After the addition is complete, maintain the temperature at 65–75℃ for 3–5 hours. After cooling, an aqueous solution of the terpolymer is obtained, or a solid product is obtained after dialysis purification and freeze-drying; The terpolymer is formed by random copolymerization of three monomers: acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and methacryloyloxyethylphosphonic acid, in a molar ratio of (4–7):(2–4):(1–3), and the number average molecular weight of the resulting copolymer is not less than 50,000.

2. The preparation method according to claim 1, characterized in that, The molar ratio of acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and methacryloyloxyethylphosphonic acid is 5:3:

2.

3. The preparation method according to claim 1, characterized in that, The total amount of ammonium persulfate used accounts for 0.2%–1.0% of the total mass of the three monomers, and the inert gas is nitrogen, which is introduced for no less than 30 minutes to remove oxygen from the reaction system.

4. The preparation method according to claim 1, characterized in that, The total concentration of monomers in the first monomer mixture is 20–30 wt%, and the concentration of methacryloyloxyethylphosphonic acid in the second monomer solution is 10–15 wt%; the amount of deionized water initially added to the reactor accounts for 30%–40% of the total water volume; and the initial initiator accounts for 20%–30% of the total amount of ammonium persulfate.

5. A terpolymer inhibitor for high-calcium fluorite flotation, applicable to the preparation method of the terpolymer inhibitor for high-calcium fluorite flotation according to any one of claims 1-4, characterized in that, The inhibitor is a water-soluble polymer with three structural units randomly distributed on its molecular chain: amide-containing structural units derived from acrylamide, sulfonic acid-containing structural units derived from 2-acrylamido-2-methylpropanesulfonic acid, and phosphonic acid-containing structural units derived from methacryloyloxyethylphosphonic acid. The phosphonic acid group exists in the form of -PO3²⁻ under pH 8.5–9.5 conditions and has a specific chelating ability for Ca²⁺ and Ba²⁺, while the adsorption strength of Ca²⁺ on the surface of fluorite is significantly weaker than that of metal ions on the surface of calcite and barite.

6. The terpolymer inhibitor according to claim 5, characterized in that, After the inhibitor is completely dissociated in the slurry, the sulfonic acid group imparts a strong negative charge to the molecular chain, causing the polymer to fully extend on the mineral surface and form a hydrophilic barrier with a thickness of 5–10 nm. It also prevents the collector molecules from approaching the gangue mineral surface through steric hindrance. At the same time, the amide group interacts with the hydroxyl groups or hydration layer on the mineral surface through hydrogen bonding, enhancing the adhesion stability of the copolymer on the calcite and barite surfaces.

7. The terpolymer inhibitor according to claim 5, characterized in that, The inhibitor does not contain phosphorus in the form of orthophosphate, heavy metals, or other toxic and harmful components. Its organophosphonic acid structure has a biodegradability rate of over 62% in 28 days under the OECD 301B standard. Its aqueous solution shows no phase separation or significant degradation after 30 days of storage at room temperature, and its viscosity at a 1% concentration and 25°C is 2.5–3.5 mPa·s, making it suitable for automatic addition and mixing in conventional flotation equipment.

8. A method for applying a terpolymer depressant for high-calcium fluorite flotation, applicable to the terpolymer depressant for high-calcium fluorite flotation as described in any one of claims 5-7, characterized in that, Includes the following steps: After grinding and classifying the raw ore, the pulp is prepared and the pH value of the pulp is controlled at 8.5–9.

5. Before adding the collector, add the terpolymer inhibitor to the slurry and stir for no less than 5 minutes; Then fatty acid collectors and frothers are added for flotation; The inhibitor is added in the form of an aqueous solution at a concentration of 0.05%–0.5%, corresponding to a dosage of 30–200 grams per ton of raw ore.

9. The application method according to claim 8, characterized in that, The terpolymer inhibitor is used in combination with water glass, wherein the modulus of the water glass is 2.0–3.5 and the amount added does not exceed 2000 g / ton of raw ore. Under the synergistic effect of the two, the water glass increases the pH of the slurry and enhances the negative charge on the surface of gangue minerals, promoting the terpolymer to approach the mineral surface through electrostatic attraction, while the terpolymer achieves firm anchoring through phosphonic acid chelation.

10. The application method according to claim 8, characterized in that, The adsorption equilibrium constant K of the terpolymer on the calcite surface is 1.8 × 10⁻⁶. 4 L / mol, which is 1.2 × 10⁻⁶ on the surface of barite. 4 The hydrophilic layer thickness d (nm) formed on the mineral surface is 2.5 × 10³ L / mol on fluorite; the thickness of the hydrophilic layer on the mineral surface satisfies the empirical formula: , in, I represents the weight-average molecular weight of the copolymer (g / mol), and II represents the ionic strength of the pulp (mol / L).

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