Amidoxime collector and preparation method and application thereof, and method for flotation separation of fluorcarbonate cerium ore and calcium-containing gangue minerals

Abstract

The application belongs to the technical field of mineral processing, and particularly relates to an amido benzhydroxamic acid collector, a preparation method and application thereof, and a method for flotation separation of fluorcarbonate cerium ore and calcium-containing gangue minerals. The amido benzhydroxamic acid collector has the following structure:. The amido benzhydroxamic acid collector in the application can realize high-selectivity separation of fluorcarbonate cerium ore at normal temperature and in a wide pH range.

Description

Technical Field

[0001] This invention belongs to the field of mineral processing technology, specifically relating to an amide-based benzyl hydroxamic acid collector, its preparation method and application, and a method for flotation separation of bastnaesite and calcium-bearing gangue minerals. Background Technology

[0002] Rare earth resources are core raw materials supporting modern high-end manufacturing and strategic emerging industries, holding an irreplaceable position in permanent magnet materials, catalysts, fluorescent materials, precision optics, and national defense high-tech fields. Fluorocarbonate cerium ore is one of the main carrier minerals of my country's light rare earth resources, and its flotation enrichment is a key process in rare earth production. During the flotation process, the ore often contains a large number of calcium-bearing gangue minerals such as fluorite, dolomite, and calcite, which have similar surface chemical properties to rare earth minerals, making it difficult for traditional collectors to achieve high selectivity between the two.

[0003] Hydroxime acids are classic collectors for rare earth mineral flotation. Their hydroxime groups (-CONHOH) can form five-membered chelate rings with rare earth cations, exhibiting strong collecting ability. However, conventional hydroxime acid collectors (such as benzohydroxyxamic acid) lack effective spatial recognition and electronic regulation mechanisms for calcium-bearing gangue minerals, leading to significant non-selective adsorption of gangue minerals such as fluorite and dolomite, making it difficult to guarantee the grade of the flotation concentrate. Furthermore, these collectors are typically highly temperature-dependent, requiring temperatures above 40–50°C to achieve effective collection, resulting in high energy consumption and operating costs. Additionally, these reagents have a narrow applicable pH range and are sensitive to fluctuations in pulp pH, making it difficult to maintain stable and efficient separation parameters in industrial settings. In recent years, research on improving collector selectivity by introducing functional substituents into the benzohydroxyxamic acid skeleton has received widespread attention. Introducing amide functional groups can provide additional hydrogen bond donor / acceptor sites for benzyl hydroxamic acid molecules, and the electron cloud density of the benzene ring can be adjusted through the resonance and steric effects of the amide group, thereby affecting the coordination ability of the hydroxamic acid group and its adsorption selectivity on mineral surfaces. However, in existing technologies, the amide substitution mode is singular and the matching between the alkyl chain and the acyl chain is insufficient. Most modified hydroxamic acids still suffer from problems such as insufficient activity at room temperature, limited improvement in selectivity, complex synthetic routes, and low yield, and cannot simultaneously meet the multiple requirements of high selectivity, low reagent consumption, room temperature flotation, wide pH adaptability, and easy industrial production.

[0004] Therefore, there is an urgent need to design an amide-substituted hydroxamic acid collector with novel structure, outstanding selectivity, high efficiency at room temperature, wide pH adaptability, and simple synthesis, in order to solve the problems of poor selectivity, need for heating, narrow applicability and low separation efficiency of traditional collectors, and achieve efficient flotation separation of bastnaesite and calcium gangue minerals. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides an amide-based benzyl hydroxamic acid collector, its preparation method and application, and a method for flotation separation of bastnaesite and calcium-bearing gangue minerals. This amide-based benzyl hydroxamic acid collector can achieve highly selective separation of bastnaesite at room temperature and over a wide pH range.

[0006] In a first aspect, the present invention provides an amide-based benzyl hydroxamic acid collector having the following structure: .

[0007] In this invention, the N-propylbutyramide group and the hydroxamic acid group on the benzene ring of the amide-based benzoyl hydroxamic acid collector are in a para-disubstituted relationship. Specifically, in the N-propylbutyramide group, the carbonyl group of the butyryl group can finely regulate the electron cloud density of the benzene ring through resonance effect and electron-withdrawing induction, thereby enhancing the acidity of the hydroxamic acid group and improving its chelation coordination ability with rare earth ions; the N-propyl chain and the butyryl carbon chain can provide the molecule with appropriate hydrophobicity, which helps to improve the spread and adsorption strength of the collector at the pulp interface and improve the interfacial activity; furthermore, the lone pair electrons on the nitrogen atom of the amide can directly participate in the construction of the hydrogen bond network on the surface of bastnaesite, endowing the molecule with specific recognition ability and targeted adsorption ability on the surface of bastnaesite; and the steric hindrance effect formed by the propyl and butyryl groups can significantly inhibit the non-specific adsorption of the collector on the surface of calcium-bearing gangue minerals such as fluorite, dolomite, and calcite, greatly improving the flotation selectivity.

[0008] Secondly, the present invention provides a method for preparing an amide-based hydroxyxamic acid collector, comprising the following steps: (1) In the presence of a first solvent and an inorganic base, methyl p-aminobenzoate was subjected to an N-alkylation reaction with 1-bromopropane, followed by a first purification to obtain the alkylation intermediate (methyl N-propyl p-aminobenzoate). (2) In the presence of a second solvent and an acid-binding agent, the alkylation intermediate undergoes an N-acylation reaction with butyryl chloride, followed by a second purification to obtain the acylation intermediate (methyl N-propyl-N-butyryl p-aminobenzoate). (3) In the presence of a third solvent and an alkaline source, the acylation intermediate is subjected to alkaline hydrolysis, then acidified with dilute hydrochloric acid to pH=2~3, and finally purified to obtain the carboxylic acid intermediate (4-(N-propylbutamido)benzoic acid). (4) In the presence of a fourth solvent and triethylamine, the carboxylic acid intermediate undergoes a hydroxamic acidification reaction with hydroxylamine hydrochloride, then the pH is adjusted to neutral, and finally a fourth purification is performed to obtain the amide-based benzoyl hydroxamic acid collector (4-(N-propylbutamido)benzoyl hydroxamic acid).

[0009] In the preparation method of this invention, N-propylbutyramide is introduced into the para position of benzyl hydroxamic acid. Through the resonance effect of amide carbonyl, the synergistic effect of N-propyl hydrophobic chain and butyryl chain, while maintaining the high collection capacity of bastnaesite, the non-selective adsorption of calcium gangue minerals is effectively suppressed, and the efficient and selective separation of bastnaesite from fluorite, dolomite and calcite is achieved. The recovery rate of bastnaesite is over 85%, and the recovery rate of gangue minerals is less than 42%.

[0010] In addition, the synthesis adopts a four-step tandem reaction of N-alkylation, N-acylation, alkaline hydrolysis and hydroxamic acidification. The reaction conditions of each step are mild, the operation is safe, and the raw material cost is moderate, making it suitable for laboratory preparation and industrial scale-up production.

[0011] Preferably, the first solvent is selected from polar aprotic solvents. More preferably, the polar aprotic solvent is selected from at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), and acetonitrile (CH3CN), with N,N-dimethylformamide (DMF) being the most preferred.

[0012] Preferably, the inorganic base is selected from at least one of potassium carbonate, sodium carbonate, and cesium carbonate, with potassium carbonate being the most preferred. To avoid the influence of water on the N-alkylation reaction, the inorganic base is preferably anhydrous potassium carbonate.

[0013] Preferably, in step (1), the molar ratio of methyl para-aminobenzoate to 1-bromopropane is 1:(1.5~3), more preferably 1:2.

[0014] Preferably, in step (1), the amount of inorganic base used is 1.5 to 3 equivalents (eq), preferably 2 equivalents (eq), based on the molar amount of methyl para-aminobenzoate.

[0015] Preferably, in step (1), the amount of the first solvent used is 5 to 15 mL / mmol, based on the molar amount of the methyl para-aminobenzoate.

[0016] Preferably, in step (1), the conditions for the N-alkylation reaction include: reflux reaction for 4 to 6 hours. The reflux reaction temperature is related to the boiling point of the first solvent. For example, when the first solvent is DMF, the temperature is about 153°C. During the reaction, the reaction progress can be monitored using TLC. Specifically, petroleum ether and ethyl acetate with a volume ratio of 3:1 are used as the developing solvent. The reaction is terminated after the spots (with a small Rf) of methyl paraben have completely disappeared, as observed by TLC monitoring.

[0017] Specifically, in step (1), the first solvent can be added to the reaction vessel first, and methyl p-aminobenzoate can be added under stirring. After dissolving, an inorganic base can be added and stirred and dispersed for 5 to 20 minutes. Then, 1-bromopropane can be slowly added and stirred to mix. The mixture can be heated in an oil bath until the first solvent is refluxed. The reaction can be stirred and the reaction can be monitored by TLC until the methyl p-aminobenzoate reaction is complete. Then, the first purification process can be carried out.

[0018] The purpose of the first purification process is to remove N. Unreacted raw materials, inorganic bases, salt impurities, byproducts, and solvent residues in the alkylation reaction system ensure sufficient purity of the alkylation intermediate, preventing impurities from affecting subsequent N-phase reactions. Acylation reactions can cause interference, improving the selectivity and conversion rate of subsequent reactions while ensuring the structural purity and stable flotation performance of the final product. Preferably, the first purification process includes: cooling the reaction solution to room temperature and quenching it by stirring in ice water; extracting with ethyl acetate and combining the organic phases; washing the organic phase with saturated brine, drying with anhydrous sodium sulfate, filtering, and concentrating under reduced pressure to obtain a crude product; purifying the crude product by gradient elution using silica gel column chromatography; collecting the target fraction, concentrating it, and drying it to constant weight to obtain the alkylation intermediate. Preferably, ice water is added at a reaction liquid volume: ice water volume ratio of 1:(1~5), and quenching is completed by stirring for 5~20 min; preferably, ethyl acetate is used as the extractant, and the number of extractions is 2~4 times, with the volume of ethyl acetate in each extraction being 1 / 3 to 1 times the volume of ice water; preferably, the organic phase is washed with saturated brine 1~3 times, with the volume of saturated brine in each wash being 1 / 4 to 1 / 2 of the volume of the organic phase; drying can be done using anhydrous sodium sulfate or anhydrous magnesium sulfate as the drying agent, and the drying time is generally 10~30 min; preferably, the vacuum concentration conditions include: vacuum concentration at 30~50℃ to constant weight to obtain the crude product; preferably, the gradient elution system is: first elution with petroleum ether and ethyl acetate at a volume ratio of 5:1, and then elution with petroleum ether and ethyl acetate at a volume ratio of 3:1, specifically, first eluting weakly polar impurities with a 5:1 ratio, and then increasing the polarity to 3:1 to elute the target product, which can be tracked and collected using TLC. The alkylation intermediate of the target product obtained is methyl N-propylparaaminobenzoate.

[0019] Preferably, the second solvent is selected from anhydrous ether solvents, and more preferably, the anhydrous ether solvent is selected from at least one of anhydrous tetrahydrofuran (THF), anhydrous diethyl ether, and anhydrous methyl tetrahydrofuran, and more preferably anhydrous tetrahydrofuran (THF).

[0020] Preferably, the acid-binding agent is selected from organic tertiary amines, specifically triethylamine, pyridine, N,N At least one of diisopropylethylamine, preferably triethylamine.

[0021] Preferably, in step (2), the molar ratio of the alkylation intermediate to butyryl chloride is 1:(1.2~2), more preferably 1:1.5.

[0022] Preferably, in step (2), the amount of acid-binding agent used is 1.5 to 2.5 equivalents (eq), preferably 2 equivalents (eq), based on the molar amount of the alkylation intermediate.

[0023] Preferably, in step (2), the amount of the second solvent used is 5 to 15 mL / mmol, based on the molar amount of the alkylation intermediate.

[0024] Preferably, in step (2), the N The acylation reaction conditions included: adding butyryl chloride dropwise in an ice bath at 0–5°C, then raising the temperature to room temperature and continuing to stir for 2–3 hours; the reaction was monitored by TLC, with petroleum ether / ethyl acetate (volume ratio 4:1) as the developing solvent, and the reaction was stopped when the alkylation intermediate spots completely disappeared.

[0025] In this invention, unless otherwise specified, room temperature refers to 20~25℃.

[0026] Specifically, in step (2), a second solvent can be added first to dissolve the alkylation intermediate, an acid-binding agent can be added and stirred evenly, the temperature can be lowered to 0-5°C in an ice bath, butyryl chloride can be slowly added dropwise, and the system temperature can be kept below 5°C; after the dropwise addition is complete, the ice bath can be removed, the reaction can be stirred at room temperature, and the second purification process can be carried out after the reaction is monitored by TLC.

[0027] The purpose of the second purification process is to remove unreacted butyryl chloride, acid-binding agents, salts, byproducts, and solvent residues to obtain a high-purity acylation intermediate, avoid impurities interfering with subsequent hydrolysis reactions, and ensure the selectivity, yield, and purity of the final product along the entire route. Preferably, in step (2), the second purification process includes: quenching the reaction solution with a saturated ammonium chloride aqueous solution; extraction with ethyl acetate and combining the organic phases; washing with saturated brine, drying with anhydrous sodium sulfate, filtering, and concentrating under reduced pressure to obtain a crude product; purifying the crude product by gradient elution using silica gel column chromatography, collecting the target fraction, concentrating and drying to constant weight to obtain the acylation intermediate. Preferably, the quencher is added at a ratio of 1:(1~3) of the reaction liquid volume to the volume of saturated ammonium chloride aqueous solution to neutralize TEA hydrochloride and quench excess acyl chloride compounds, and stirred for 5~15 min; preferably, ethyl acetate is extracted 2~4 times, each time with a volume of 1 / 3~1 times the quencher liquid volume; when drying with anhydrous sodium sulfate, the drying time can be 10~30 min; preferably, the conditions for vacuum concentration can include: concentrating to constant weight at 30~50℃; preferably, the gradient elution system can be: first eluting with petroleum ether and ethyl acetate at a volume ratio of 6:1, and then eluting with petroleum ether and ethyl acetate at a volume ratio of 4:1. The target fraction can be collected by TLC tracking, and the target product acylation intermediate can be obtained as methyl N-propyl-N-butyryl p-aminobenzoate.

[0028] Preferably, the third solvent is a mixture of an ether solvent and water, more preferably a mixture of tetrahydrofuran and water, or 1,4 A mixture of dioxane and water is preferably tetrahydrofuran and water in a volume ratio of (4~6):1.

[0029] This invention demonstrates through experiments that using tetrahydrofuran and water in a volume ratio of (4-6):1 as the third solvent can ensure the structural purity, flotation activity, and high selectivity of the amide-based hydroxyxamic acid collector. This is likely because the (4-6):1 volume ratio of tetrahydrofuran and water forms a homogeneous reaction system that can fully dissolve both the hydrophobic acylation intermediate and the base source, thereby significantly improving the hydrolysis rate and reaction completeness. Simultaneously, the moderate polarity of this mixed solvent, coupled with the presence of tetrahydrofuran, appropriately desensitizes the nucleophilic attack capability of the base, allowing the base to preferentially and selectively attack the more reactive methyl ester group while protecting the resonantly stable amide group. This effectively inhibits the breaking of the amide bond while ensuring complete hydrolysis of the methyl ester, ultimately yielding a high-purity carboxylic acid intermediate in high yield.

[0030] Preferably, the alkali source is selected from at least one of lithium hydroxide monohydrate, sodium hydroxide, and potassium hydroxide, and is more preferably lithium hydroxide monohydrate (LiOH·H2O).

[0031] The use of lithium hydroxide monohydrate as an alkaline source in this invention can improve the overall yield of the final collector. This may be because lithium ions have a small ionic radius and a high charge density, which leads to strong hydration in water. This makes the alkalinity of lithium hydroxide monohydrate in a mixed solvent of tetrahydrofuran and water relatively mild and controllable, effectively avoiding side reactions.

[0032] Preferably, in step (3), the amount of the alkali source is 1 to 1.5 equivalents (eq), preferably 1.2 equivalents (eq), based on the molar amount of the acylation intermediate.

[0033] Preferably, in step (3), the amount of the third solvent is 8 to 20 mL / mmol, based on the molar amount of the acylation intermediate.

[0034] The molar concentration of the above-mentioned dilute hydrochloric acid is 0.5~1.2 M.

[0035] Preferably, in step (3), the alkaline hydrolysis conditions include: stirring at room temperature to 40°C for 2 to 4 hours; monitoring with TLC, using ethyl acetate / petroleum ether as the developing solvent (volume ratio 2:1), and ending the reaction after the acylation intermediate spots have completely disappeared.

[0036] Specifically, the acylation intermediate is dissolved in a third solvent, an alkali source is added and stirred until homogeneous, and the reaction is carried out at room temperature. After complete hydrolysis is monitored by TLC, the solution is acidified with dilute hydrochloric acid to pH 2-3, and then a third purification process is performed.

[0037] The purpose of the third purification process is to remove alkali sources, salts, unhydrolyzed raw materials, and byproducts to obtain a high-purity carboxylic acid intermediate, ensuring the efficiency and purity of the subsequent hydroxyoxime acidification reaction. Preferably, the third purification process includes: extraction with ethyl acetate after acidification; combining the organic phases, washing with saturated brine, drying, filtering, and concentrating under reduced pressure to obtain a crude product; the crude product can be further purified by recrystallization or column chromatography. Preferably, ethyl acetate is used as the extractant, and the number of extractions is 2 to 4, with the volume of ethyl acetate extracted each time being 1 / 2 to 1 times the volume of the aqueous phase; preferably, the organic phase is washed with saturated brine 1 to 3 times, with the volume of saturated brine each time being 1 / 4 to 1 / 2 of the volume of the organic phase; drying can be done using anhydrous sodium sulfate or anhydrous magnesium sulfate as the drying agent, and the drying time is generally 10 to 30 minutes; preferably, the conditions for reduced pressure concentration include: concentration under reduced pressure at 30 to 50°C to constant weight to obtain the crude product. The preferred recrystallization conditions are: recrystallization at 60–70°C in a mixed solvent of ethyl acetate and petroleum ether (volume ratio 1:3), followed by filtration and drying to constant weight. The resulting carboxylic acid intermediate is 4-(N-propylbutamido)benzoic acid.

[0038] Preferably, the fourth solvent is selected from anhydrous alcohol solvents, and more preferably, the anhydrous alcohol solvent is selected from at least one of anhydrous methanol, anhydrous ethanol, and anhydrous isopropanol, with anhydrous ethanol being the most preferred.

[0039] The use of anhydrous ethanol as the fourth solvent in this invention can better increase the selectivity of the final target product, amide-benzyl hydroxyxamic acid, as a collector. This is presumably because anhydrous ethanol has moderate polarity and protonicity, which can better dissolve highly polar carboxylic acid substrates and hydroxylamine hydrochloride. It can also synergistically activate carboxylic acid groups with triethylamine, promoting the condensation conversion of carboxylic acid and hydroxylamine, resulting in a higher yield of the target product.

[0040] Preferably, in step (4), the molar ratio of the carboxylic acid intermediate to hydroxylamine hydrochloride is 1:(1.5~2.5), more preferably 1:2.

[0041] Preferably, in step (4), the amount of triethylamine used is 1.5 to 2.5 equivalents (eq), preferably 2.0 equivalents (eq), based on the molar amount of the carboxylic acid intermediate.

[0042] Preferably, in step (4), the amount of the fourth solvent used is 8 to 20 mL / mmol, based on the molar amount of the carboxylic acid intermediate.

[0043] Preferably, in step (4), the conditions for the hydroxamic acidification reaction include: heating under reflux for 1 to 2 hours; for example, the reflux temperature is about 78°C (boiling point of ethanol); TLC monitoring, the developing solvent is dichloromethane and methanol with a volume ratio of 10:1, and the reaction ends when the carboxylic acid intermediate spots completely disappear.

[0044] Specifically, the carboxylic acid intermediate is dissolved in a fourth solvent, hydroxylamine hydrochloride and triethylamine are added, the mixture is stirred until homogeneous, and then heated to reflux. After the reaction is complete, it is cooled to room temperature, the pH is adjusted to neutral, and a fourth purification process is performed. The pH can be adjusted to neutral using 1 M dilute hydrochloric acid.

[0045] The purpose of the fourth purification process is to remove unreacted hydroxylamine hydrochloride, triethylamine, byproducts, and solvent residues to obtain a high-purity final collector product, ensuring its selectivity and stability in flotation applications. Preferably, the fourth purification process includes: vacuum concentration to remove the fourth solvent, dilution with water, and extraction with ethyl acetate; washing, drying, and concentrating the organic phase to obtain a crude product; purifying the crude product by gradient elution using silica gel column chromatography, collecting the target fraction, concentrating and drying to constant weight to obtain the final amide-benzyl hydroxyxamic acid collector. Preferred conditions for vacuum concentration include: concentration to constant weight at 30–50°C; preferably using ethyl acetate as the extractant, with 2–4 extractions, each extraction using ethyl acetate at a volume of 1 / 2 to 1 times the volume of the aqueous phase; preferably washing the organic phase with saturated brine 1–3 times, each wash using saturated brine at a volume of 1 / 4 to 1 / 2 the volume of the organic phase; preferably using anhydrous sodium sulfate or anhydrous magnesium sulfate as the drying agent, with a drying time generally 10–30 min; preferably using a gradient elution system: first eluting with dichloromethane and methanol at a volume ratio of 12:1, followed by elution with dichloromethane and methanol at a volume ratio of 8:1. Specifically, weakly polar impurities are eluted first at a 12:1 ratio, then the polarity is increased to 8:1 to elute the target product, which can be collected using TLC. The obtained product is the amide-based benzoylhydroxyxamic acid collector, namely 4-(N-propylbutyramido)benzoylhydroxyxamic acid.

[0046] Thirdly, the present invention provides an application of an amide-based benzoxime acid collector in the flotation separation of bastnaesite and calcium-bearing gangue minerals, wherein the amide-based benzoxime acid collector is the amide-based benzoxime acid collector described in the first aspect of the present invention, or the amide-based benzoxime acid collector prepared by the preparation method of the amide-based benzoxime acid collector described in the second aspect of the present invention.

[0047] Preferably, the calcium-bearing gangue mineral includes at least one of fluorite, dolomite, and calcite.

[0048] Fourthly, the present invention provides a method for flotation separation of bastnaesite and calcium-bearing gangue minerals. The method includes: crushing and grinding ore containing bastnaesite and calcium-bearing gangue minerals, adding water to prepare a slurry, adjusting the pH value to 5-9, adding water glass and stirring to adjust the slurry, adding an amide-based benzoyl hydroxamic acid collector and stirring, and then performing flotation to collect the froth product to obtain bastnaesite concentrate; wherein the amide-based benzoyl hydroxamic acid collector is the amide-based benzoyl hydroxamic acid collector described in the first aspect of the present invention, or the amide-based benzoyl hydroxamic acid collector prepared by the preparation method of the amide-based benzoyl hydroxamic acid collector described in the second aspect of the present invention.

[0049] The above crushing and grinding are conventional operating methods in this field. Generally, grinding is sufficient to achieve a particle size of less than or equal to 74μm.

[0050] The water mentioned above can be deionized water, and the amount of water used is 10~20 g / mL, based on the mass of the ore containing bastnaesite and calcium gangue minerals.

[0051] The pH value can be adjusted to 5-9 using NaOH or HCl, preferably to 7-8.

[0052] Preferably, the modulus of the water glass is 1.5 to 3.5, and more preferably 2.4.

[0053] Preferably, the amount of water glass used is 400–500 mg / L.

[0054] Preferably, the amount of the amide-based hydroxyoxime acid collector is 15–25 mg / L.

[0055] The above-mentioned amide-based hydroxyoxime acid collector can be prepared into an aqueous solution with a mass concentration of 0.5% to 1.5% before being added.

[0056] Preferably, the flotation conditions include: an aeration rate of 0.1~0.3 L / min, a flotation time of 3~10 min, and a flotation temperature of 20±2℃.

[0057] Specifically, the process flow for the flotation separation of bastnaesite and calcium-bearing gangue minerals is as follows: Figure 2 As shown, the method includes: conducting the flotation in an XFG5-35 type hanging-tank flotation machine (tank volume 35 mL, impeller speed 1992 r / min), adding deionized water and stirring for 2 min to prepare the slurry, adjusting the pH of the slurry to the set value with NaOH or HCl solution, adding water glass and stirring for 3 min, then adding amide-based hydroxyxamic acid collector and stirring for 3 min, followed by aeration flotation at an aeration rate of 0.1~0.3 L / min, a flotation time of 3~10 min, and a flotation temperature of 20±2℃ (room temperature, unheated). After flotation, the froth product and the product in the tank are collected separately. Further, after filtration, drying, and weighing, the content of elements such as Ce, Ca, F, and Mg is analyzed by ICP-OES to calculate the recovery rate of each mineral. The separation efficiency (SI) is defined as the difference between the recovery rate of bastnaesite (concentrate) and the recovery rate of gangue minerals (tailings).

[0058] Compared with the prior art, the present invention has the following beneficial effects: 1. Significantly Improved Selectivity: The amide-based benzohydroxyxamic acid collector provided in this invention introduces an N-propylbutyramide group at the para-position of benzohydroxyxamic acid and utilizes the electron-withdrawing resonance effect of the amide carbonyl group to enhance the coordination ability of the hydroxyxamic acid group. At the same time, the N-propyl and butyryl chains can provide suitable hydrophobicity and steric hindrance, achieving highly efficient and selective collection of bastnaesite and effective inhibition of calcium-bearing gangue minerals. Compared with traditional benzohydroxyxamic acid, its separation efficiency can be improved by more than 30 percentage points.

[0059] 2. Mild operating conditions: The amide-based benzohydroxyxamic acid collector provided in this invention can achieve stable collection and separation effects at room temperature of 20±2℃. Compared with traditional benzohydroxyxamic acid, which requires operation at temperatures above 50℃, this saves heating energy and helps reduce production costs.

[0060] 3. Wide pH adaptability: The amide-based benzoxime acid collector provided in this invention has stable collection performance in the pH range of 7.0 to 8.0, low sensitivity to pulp pH fluctuations, and relatively flexible operation control.

[0061] 4. Low dosage: The dosage of the amide-based hydroxyxamic acid collector in this invention is only 15-25 mg / L, which is much lower than that of traditional hydroxyxamic acid agents, making it green and economical. Attached Figure Description

[0062] Figure 1 The 1H NMR spectrum of the amide-benzyl hydroxamic acid collector in Preparation Example 1.

[0063] Figure 2 This is a flowchart of a method for flotation separation of bastnaesite and calcium-bearing gangue minerals in some embodiments. Detailed Implementation

[0064] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] Preparation Example The following preparation examples illustrate the preparation of amide-based benzoyl hydroxamic acid collectors.

[0066] Preparation Example 1 Preparation of amide-based hydroxyxamic acid collector: (1) Preparation of alkylation intermediates Add 10 mL of anhydrous DMF to a 50 mL round-bottom flask, and add methyl para-aminobenzoate (1.0 eq, 1 mmol) while stirring. After dissolving, add anhydrous K₂CO₃ (2.0 eq, 2 mmol) and stir to disperse for 10 min. Slowly add 1-bromopropane (2.0 eq, 2 mmol) and stir to mix. Heat in an oil bath to reflux DMF (approximately 153 °C), stir the reaction, and monitor by TLC (developing solvent: petroleum ether and ethyl acetate in a 3:1 volume ratio). Stop the reaction after the spots of methyl para-aminobenzoate (with small Rf values) have completely disappeared, approximately 4.5 hours. The reaction solution was then cooled to room temperature and slowly poured into 20 mL of ice water, stirred for 10 min. Extraction was performed with ethyl acetate (15 mL × 3), and the organic phases were combined. The organic phase was washed with saturated brine (10 mL × 2), dried over anhydrous Na₂SO₄ for 15 min, filtered, and concentrated under reduced pressure (40 °C, high vacuum to remove residual DMF) to obtain a crude product. This crude product was then subjected to silica gel column chromatography (eluting first with petroleum ether and ethyl acetate in a 5:1 volume ratio, followed by elution with petroleum ether and ethyl acetate in a 3:1 volume ratio). The target fraction was collected, concentrated, and dried to constant weight to obtain a pure alkylation intermediate (methyl N-propylpara-aminobenzoate), a pale yellow oily liquid, with a single-step yield of 88%.

[0067] (2) Preparation of acylation intermediates Add the alkylation intermediate (1.0 eq, 1 mmol) to a 50 mL dry flask and dissolve it in anhydrous THF (8 mL). Add triethylamine (TEA, 2.0 eq, 2 mmol) and cool to 0°C in an ice bath. Slowly add butyryl chloride (1.5 eq, 1.5 mmol) dropwise through a constant pressure dropping funnel, keeping the system temperature below 5°C. After the addition is complete, remove the ice bath and stir the reaction at room temperature. Monitor the reaction by TLC (developing solvent: petroleum ether / ethyl acetate (v / v)). The reaction is stopped after the spots of the alkylation intermediate have completely disappeared, approximately 2.5 hours later.

[0068] Slowly add 10 mL of saturated NH4Cl aqueous solution to the reaction solution, stir for 10 min, extract with ethyl acetate (15 mL × 3), and combine the organic phases; then wash with saturated brine (10 mL × 2), dry with anhydrous Na2SO4, filter, concentrate under reduced pressure to obtain crude product, then perform silica gel column chromatography (eluting first with petroleum ether and ethyl acetate in a volume ratio of 6:1, then with petroleum ether and ethyl acetate in a volume ratio of 4:1), collect the product fraction, concentrate, and dry to constant weight to obtain acylated intermediate (methyl N-propyl-N-butyryl p-aminobenzoate), which is a colorless to pale yellow liquid with a single-step yield of 90%.

[0069] (3) Preparation of carboxylic acid intermediates Add the acylation intermediate (1.0 eq, 1 mmol) to the flask and dissolve it in a THF / H2O mixed solvent (8 mL of THF and 2 mL of H2O); add LiOH·H2O (1.2 eq, 1.2 mmol), stir to mix, and stir the reaction at room temperature. Monitor the reaction by TLC (econometrics: ethyl acetate / petroleum ether, volume ratio 2:1). Stop the reaction after the spots of the acylation intermediate have completely disappeared, about 3 hours later.

[0070] The reaction solution was acidified to pH 2.5 with 1 M dilute hydrochloric acid, then extracted with ethyl acetate (15 mL × 3), and the organic phases were combined. The mixture was washed with saturated brine (10 mL × 2), dried over anhydrous Na2SO4, filtered, concentrated under reduced pressure, and then recrystallized from ethyl acetate and petroleum ether in a volume ratio of 1:3 at 65 °C. After filtration, the mixture was dried to constant weight to give pure carboxylic acid intermediate (4-(N-propylbutamido)benzoic acid), a white to pale yellow solid, with a single-step yield of 92%.

[0071] (4) Preparation of amide-based benzoyl hydroxamic acid collector Add the carboxylic acid intermediate (1.0 eq, 1 mmol) to the flask and dissolve it in anhydrous ethanol (10 mL); add hydroxylamine hydrochloride (NH2OH·HCl, 2.0 eq, 2 mmol) and triethylamine (TEA, 2.0 eq, 2 mmol), stir to mix well, heat in an oil bath to reflux with anhydrous ethanol (about 78 °C), monitor by TLC (developing solvent is dichloromethane and methanol in a volume ratio of 10:1), the spots of the carboxylic acid intermediate completely disappear after about 1.5 hours.

[0072] After cooling to room temperature, the pH was adjusted to neutral with 1 M dilute hydrochloric acid, and the ethanol was removed by concentration under reduced pressure. The residue was then added to 5 mL of water and extracted with ethyl acetate (15 mL × 3). The organic phase was washed with saturated brine, dried over anhydrous Na₂SO₄, filtered, and concentrated to obtain the crude product. The target fraction was collected by silica gel column chromatography (eluting first with dichloromethane and methanol at a volume ratio of 12:1, followed by elution with dichloromethane and methanol at a volume ratio of 8:1). The fraction was concentrated and dried to constant weight to obtain a white to off-white solid, which was the collector for the target product, amide-benzoyl hydroxamic acid, with a single-step yield of 82%.

[0073] 1H NMR spectrum of amide-benzylhydroxamic acid collector ( 1 H NMR) such as Figure 1 As shown, it can be obtained as 4-(N-propylbutyramido)benzylhydroxyxamic acid, with the following structure: .

[0074] The overall yield of the amide-based hydroxyxamic acid collector in the above four steps was 62.5%.

[0075] Preparation Example 2 Preparation of amide-based hydroxyxamic acid collector: (1) Preparation of alkylation intermediates Same as preparation example 1.

[0076] (2) Preparation of acylation intermediates Same as preparation example 1.

[0077] (3) Preparation of carboxylic acid intermediates The method of Preparation Example 1 was followed, except that the THF / H2O mixed solvent was replaced with 1,4-dioxane / water (6 mL of 1,4-dioxane and 4 mL of water); and LiOH·H2O was replaced with an equimolar amount of sodium hydroxide; and the carboxylic acid intermediate (4-(N-propylbutamido)benzoic acid) was finally obtained with a single-step yield of 88%.

[0078] (4) Preparation of amide-based benzoyl hydroxamic acid collector Using the above-mentioned carboxylic acid intermediate, the method of Preparation Example 1 was followed to obtain the target product, amide-benzyl hydroxamic acid collector, with a single-step yield of 82%.

[0079] The overall yield of the amide-based hydroxyxamic acid collector in the above four steps was 57.1%.

[0080] Preparation Example 3 Preparation of amide-based hydroxyxamic acid collector: (1) Preparation of alkylation intermediates Same as preparation example 1.

[0081] (2) Preparation of acylation intermediates Same as preparation example 1.

[0082] (3) Preparation of carboxylic acid intermediates Same as preparation example 1.

[0083] (4) Preparation of amide-based benzoyl hydroxamic acid collector The method of Preparation Example 1 was followed, except that anhydrous ethanol was replaced with anhydrous acetone, and the mixture was heated in an oil bath until the anhydrous acetone was refluxed to obtain the target product, amide-benzoyl hydroxamic acid collector, with a single-step yield of 75%.

[0084] The overall yield of the amide-based hydroxyxamic acid collector in the above four steps was 54.7%.

[0085] Example All the following examples employed a flotation test scheme involving artificially mixed pure minerals to evaluate the selectivity of the amide-benzyl hydroxamic acid collector in Preparation Example 1 for separating bastnaesite from calcium-bearing gangue minerals. The pure minerals (bastnaesite, fluorite, dolomite, and calcite) were all manually selected, crushed, ground, and sieved to obtain particles smaller than or equal to 74 μm for later use. The purity of each mineral was confirmed to be greater than 95% by XRD and chemical analysis.

[0086] Flotation tests were conducted in an XFG5-35 hanging-tank flotation machine (tank volume 35 mL, impeller speed 1992 r / min). For each test, 1.0 g each of bastnaesite and gangue minerals, totaling 2.0 g, were weighed and added to deionized water to prepare the pulp. The pH of the pulp was adjusted to the set value using NaOH or HCl solution. Water glass (modulus M=2.4) was added and the pulp was stirred for 3 min. Then, amide-benzyl hydroxamic acid collector was added and stirred for 2 min before aeration flotation. The aeration rate was 0.2 L / min, the flotation time was 5 min, and the flotation temperature was 20±2℃ (room temperature, no heating). After flotation, the froth product and the product in the tank were collected separately, filtered, dried, and weighed. The content of elements such as Ce, Ca, F, and Mg was analyzed by ICP-OES, and the recovery rate of each mineral was calculated. The separation efficiency (SI) was defined as the difference between the recovery rate of bastnaesite and the recovery rate of gangue minerals.

[0087] Example 1 Flotation separation of bastnaesite-fluorite artificial mixed ore (pH 7.0, collector dosage 15 mg / L) Weigh 1.0 g of pure bastnaesite and 1.0 g of fluorite (both with a particle size of less than or equal to 74 μm), add 35 mL of deionized water to prepare a mixed slurry, and adjust the pH to 7.0 with NaOH solution. First, add 400 mg / L of water glass and stir to adjust the slurry for 3 min; then add 15 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1 (prepared as a 1 wt% aqueous solution), stir for 2 min, and then perform aeration flotation at an aeration rate of 0.2 L / min for 5 min at a temperature of 20 ± 2℃.

[0088] After flotation, the froth product and the product in the tank are filtered, dried and weighed, and the Ce, Ca and F contents are determined by ICP-OES to calculate the recovery rate of each mineral.

[0089] Flotation results: The recovery rate of bastnaesite was 88.3%, the recovery rate of fluorite was 38.7%, and the separation efficiency (SI) was 49.6 percentage points. The results indicate that, under conditions of pH 7.0 and room temperature, the amide-based benzohydroxyxamic acid collector of this invention exhibits significant selective collecting ability for bastnaesite, while the recovery rate of fluorite is relatively low, and the two can be effectively separated.

[0090] Example 2 The purity requirements for the test ore sample were the same as in Example 1. The difference was that the pH of the slurry was adjusted to 8.0, 500 mg / L of water glass was added, and the slurry was stirred for 3 min. Then, 25 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1 was added, and after stirring for 2 min, the slurry was aerated for flotation. The remaining operating conditions were the same as in Example 1.

[0091] Flotation results: The recovery rate of bastnaesite was 86.9%, the recovery rate of fluorite was 41.2%, and the separation efficiency (SI) was 45.7 percentage points. At pH 8.0, the selectivity of the amide-based benzoxime acid collector of this invention for bastnaesite was maintained, the fluorite recovery rate increased slightly, and the separation efficiency decreased slightly compared to pH 7.0, but overall, good flotation separation performance was still maintained.

[0092] Example 3 Weigh 1.0 g of pure bastnaesite and 1.0 g of dolomite (both with a particle size of ≤74 μm), add 35 mL of deionized water to prepare a mixed slurry, and adjust the pH to 7.0 with NaOH solution. Add 400 mg / L of water glass and stir for 3 min to adjust the slurry; then add 15 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1, stir for 2 min, and then perform aeration flotation. The remaining operating conditions are the same as in Example 1.

[0093] Flotation results: Ce, Ca, and Mg contents were determined by ICP-OES, and the recoveries of each mineral were calculated. The recovery rate of bastnaesite was 87.6%, and that of dolomite was 36.4%, with a separation efficiency (SI) of 51.2 percentage points. A comparison between Examples 1 and 3 shows that the amide-based benzoxime acid collector has slightly better selectivity for the bastnaesite-dolomite system than for the bastnaesite-fluorite system, indicating that the amide group has a more effective inhibitory effect on dolomite.

[0094] Example 4 The purity requirements for the test ore samples were the same as in Example 3. The pH of the slurry was adjusted to 8.0, 500 mg / L of water glass was added, and the slurry was stirred for 3 min. Then, 25 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1 was added, and the mixture was stirred for 2 min before aeration and flotation. The remaining operating conditions were the same as in Example 1.

[0095] Flotation results: The recovery rate of bastnaesite was 85.8%, and the recovery rate of dolomite was 38.1%, with a separation efficiency (SI) of 47.7 percentage points. Compared with pH 7.0, the separation efficiency decreased slightly under pH 8.0 conditions, but the recovery rate of bastnaesite remained above 85%, while the recovery rate of dolomite was below 40%, and the separation effect still met the flotation selectivity requirements.

[0096] Example 5 Weigh 1.0 g of pure bastnaesite and 1.0 g of calcite (both with a particle size of less than or equal to 74 μm), add 35 mL of deionized water to prepare a mixed slurry, and adjust the pH to 7.0 with NaOH solution. Add 400 mg / L of water glass and stir for 3 min to adjust the slurry; then add 15 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1, stir for 2 min, and then perform aeration flotation. The remaining operating conditions are the same as in Example 1.

[0097] Flotation results: Ce and Ca contents were determined by ICP-OES, and the recoveries of each mineral were calculated. The recovery rate of bastnaesite was 89.1%, the recovery rate of calcite was 35.2%, and the separation efficiency (SI) was 53.9 percentage points.

[0098] Example 6 The purity requirements for the test ore samples were the same as in Example 5. The pH of the slurry was adjusted to 8.0, 500 mg / L of water glass was added, and the slurry was stirred for 3 min. Then, 25 mg / L of the amide-benzyl hydroxamic acid collector obtained in Preparation Example 1 was added, and the mixture was stirred for 2 min before aeration and flotation. The remaining operating conditions were the same as in Example 1.

[0099] Flotation results: The recovery rate of bastnaesite was 87.4%, the recovery rate of calcite was 37.3%, and the separation efficiency (SI) was 50.1 percentage points. Combined with Examples 5 and 6, it can be seen that the collector of the present invention maintains stable high selectivity for the bastnaesite-calcite system within the pH range of 7.0–8.0, with bastnaesite recovery rates all above 87% and calcite recovery rates below 38%, demonstrating good separation performance.

[0100] Comparative Example 1 The method of Example 1 is followed, except that the amide-based benzoxime acid collector is replaced with benzoxime acid (BHA, molecular weight 137.14 g / mol, purity ≥95%, commercial reagent), and the amount used is 100 mg / L. The pH is adjusted to 8.5 with NaOH solution (the alkaline pH range suitable for traditional benzoxime acid). The flotation temperature is 50±2℃ (water bath heating as required by traditional process). The rest of the operation process is the same as in Example 1.

[0101] Flotation results: The recovery rate of bastnaesite was 71.3%, and the recovery rate of fluorite was 58.6%, with a separation efficiency (SI) of only 12.7 percentage points. Benzyl hydroxamic acid showed insufficient selective inhibition of fluorite, resulting in a large amount of fluorite floating to the surface with the froth and poor separation. Compared with Examples 1 (SI=49.6%) and 2 (SI=45.7%), the collector of this invention, even at lower dosages (15–30 mg / L) and at room temperature, still exhibited a separation efficiency 33–37 percentage points higher than that of benzoyl hydroxamic acid at 50°C, demonstrating a significant selectivity advantage.

[0102] Comparative Example 2 The method of Example 3 is the same, except that the amide-based benzoyl hydroxamic acid collector is replaced with benzoyl hydroxamic acid (BHA, molecular weight 137.14 g / mol, purity above 95%, commercial reagent), and the amount used is 80 mg / L. The pH is adjusted to 8.5 with NaOH solution (the alkaline pH range suitable for conventional hydroxamic acid). The flotation temperature is 50±2℃ (water bath heating as required by conventional process). The rest of the operation process is the same as in Example 3.

[0103] Flotation results: The recovery rate of bastnaesite was 69.8%, and the recovery rate of dolomite was 55.9%, with a separation efficiency (SI) of only 13.9 percentage points. A large amount of dolomite floated to the surface with the froth, severely affecting selectivity, and the entire process required maintaining a temperature of 50°C. Compared with Examples 3 (SI=51.2%) and 4 (SI=47.7%), the collector of this invention improves the separation efficiency by approximately 34–37 percentage points under ambient temperature and pressure conditions.

[0104] Comparative Example 3 The method of Example 5 is followed, except that the amide-based benzoyl hydroxamic acid collector is replaced with benzoyl hydroxamic acid (BHA, molecular weight 137.14 g / mol, purity ≥95%, commercial reagent), and the amount used is 120 mg / L. The pH is adjusted to 8.5 with NaOH solution (the alkaline pH range suitable for conventional hydroxamic acid). The flotation temperature is 50±2℃ (water bath heating as required by conventional processes). The rest of the operation process is the same as in Example 5.

[0105] Flotation results: The recovery rate of bastnaesite was 67.5%, and the recovery rate of calcite was 53.8%, with a separation efficiency (SI) of only 13.7 percentage points, indicating poor flotation performance. Compared with the collector of this invention (Example 5, SI=53.9%; Example 6, SI=50.1%), the separation efficiency of benzyl hydroxamic acid was still about 36-40 percentage points lower, even under higher temperature conditions.

[0106] Comparative Example 4 The method of Example 1 is followed, except that the amide-benzyl hydroxamic acid collector is replaced with the acylation intermediate in Preparation Example 1; the rest of the operation process is the same as in Example 1.

[0107] Flotation results: The recovery rate of bastnaesite was 51.2%, the recovery rate of fluorite was 22.6%, and the separation efficiency (SI) was 28.6 percentage points. The recovery rate of bastnaesite was about 37 percentage points lower than that of the collector of this invention (Example 1, 88.3%), indicating that the hydroxamic acid group is the core functional group for achieving efficient collection and is indispensable.

[0108] Comparative Example 5 The method of Example 1 is the same as in Example 1, except that the amide-based benzoyl hydroxamic acid collector is replaced with paraben hydroxamic acid; the rest of the operation is the same as in Example 1.

[0109] Flotation results: The recovery rate of bastnaesite was 76.5%, the recovery rate of fluorite was 51.3%, and the separation efficiency (SI) was 25.2 percentage points. The separation efficiency (25.2%) is much lower than that of the collector of this invention (Example 1, SI=49.6%), indicating that the introduction of N-propylbutyramide groups has an irreplaceable structural contribution to improving selectivity.

[0110] The above experimental results further demonstrate the importance of the technical solution defined in this invention to its technical effect.

[0111] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An amide-based benzohydroxyxamic acid collector, characterized in that, It has the following structure: 。 2. A method for preparing an amide-based benzohydroxyoxime acid collector, characterized in that, Includes the following steps: (1) In the presence of a first solvent and an inorganic base, methyl p-aminobenzoate was subjected to an N-alkylation reaction with 1-bromopropane, followed by a first purification to obtain an alkylation intermediate; (2) In the presence of a second solvent and an acid-binding agent, the alkylation intermediate undergoes an N-acylation reaction with butyryl chloride, followed by a second purification to obtain the acylated intermediate; (3) In the presence of a third solvent and an alkaline source, the acylation intermediate is subjected to alkaline hydrolysis, then acidified with dilute hydrochloric acid to pH=2~3, and finally purified to obtain the carboxylic acid intermediate; (4) In the presence of a fourth solvent and triethylamine, the carboxylic acid intermediate undergoes a hydroxamic acidification reaction with hydroxylamine hydrochloride, then the pH is adjusted to neutral, and finally a fourth purification is performed to obtain an amide-benzyl hydroxamic acid collector.

3. The method for preparing the amide-based hydroxyxamic acid collector according to claim 2, characterized in that, The first solvent is selected from polar aprotic solvents, and the polar aprotic solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and acetonitrile; the inorganic base is selected from at least one of potassium carbonate, sodium carbonate, and cesium carbonate; the molar ratio of methyl para-aminobenzoate to 1-bromopropane is 1:(1.5~3); in step (1), based on the molar amount of methyl para-aminobenzoate, the amount of inorganic base used is 1.5~3 equivalents; in step (1), based on the molar amount of methyl para-aminobenzoate, the amount of the first solvent used is 5~15 mL / mmol.

4. The method for preparing the amide-based hydroxyxamic acid collector according to claim 2, characterized in that, The second solvent is selected from anhydrous ether solvents; the anhydrous ether solvent is selected from at least one of anhydrous tetrahydrofuran, anhydrous diethyl ether, and anhydrous methyltetrahydrofuran; the acid-binding agent is selected from organic tertiary amines, wherein the organic tertiary amine is triethylamine, pyridine, or N,N At least one of diisopropylethylamine; in step (2), the molar ratio of the alkylation intermediate to butyryl chloride is 1:(1.2~2); in step (2), the amount of the acid-binding agent is 1.5~2.5 equivalents based on the molar amount of the alkylation intermediate; in step (2), the amount of the second solvent is 5~15 mL / mmol based on the molar amount of the alkylation intermediate.

5. The method for preparing the amide-based hydroxyxamic acid collector according to claim 2, characterized in that, The third solvent is a mixture of ether solvent and water; the alkali source is selected from at least one of lithium hydroxide monohydrate, sodium hydroxide, and potassium hydroxide; in step (3), the amount of the alkali source is 1 to 1.5 equivalents based on the molar amount of the acylation intermediate; in step (3), the amount of the third solvent is 8 to 20 mL / mmol based on the molar amount of the acylation intermediate.

6. The method for preparing the amide-based benzyl hydroxamic acid collector according to claim 2, characterized in that, The fourth solvent is selected from anhydrous alcohol solvents; in step (4), the molar ratio of the carboxylic acid intermediate to hydroxylamine hydrochloride is 1:(1.5~2.5); in step (4), based on the molar amount of the carboxylic acid intermediate, the amount of triethylamine used is 1.5~2.5 equivalents; in step (4), based on the molar amount of the carboxylic acid intermediate, the amount of the fourth solvent used is 8~20 mL / mmol.

7. The method for preparing the amide-based hydroxyxamic acid collector according to any one of claims 2 to 6, characterized in that, In step (1), the conditions for the N-alkylation reaction include: reflux reaction for 4 to 6 hours; in step (2), the N... The acylation reaction conditions include: adding butyryl chloride dropwise under an ice bath at 0-5℃, raising the temperature to room temperature after the addition is complete, and continuing to stir the reaction for 2-3 hours; in step (3), the alkaline hydrolysis conditions include: stirring the reaction at room temperature to 40℃ for 2-4 hours; in step (4), the hydroxyoxime acidification reaction conditions include: heating under reflux for 1-2 hours.

8. The application of an amide-based benzyl hydroxamic acid collector in the flotation separation of bastnaesite and calcium-bearing gangue minerals, characterized in that, The amide-based benzoyl hydroxamic acid collector is the amide-based benzoyl hydroxamic acid collector according to claim 1, or the amide-based benzoyl hydroxamic acid collector prepared by the preparation method of the amide-based benzoyl hydroxamic acid collector according to claims 2 to 7.

9. A method for flotation separation of bastnaesite and calcium-bearing gangue minerals, characterized in that, The method includes: crushing and grinding ore containing bastnaesite and calcium gangue minerals, adding water to prepare a slurry, adjusting the pH value to 5-9, adding water glass and stirring to adjust the slurry, adding amide-based benzoyl hydroxyxamic acid collector and stirring, and then carrying out flotation to collect the froth product to obtain bastnaesite concentrate. The amide-based benzoyl hydroxamic acid collector is the amide-based benzoyl hydroxamic acid collector according to claim 1, or the amide-based benzoyl hydroxamic acid collector prepared by the preparation method of the amide-based benzoyl hydroxamic acid collector according to claims 2 to 7.

10. The method for flotation separation of bastnaesite and calcium-bearing gangue minerals according to claim 9, characterized in that, The amount of water glass used is 400-500 mg / L, and the amount of amide-based hydroxyxamic acid collector used is 15-25 mg / L; the flotation conditions include: an aeration rate of 0.1-0.3 L / min, a flotation time of 3-10 min, and a flotation temperature of 20±2℃.

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