1H-indole-7-hydroxamic acid flotation collector as well as preparation method and application thereof

Abstract

The invention discloses a 1H-indole-7-hydroxamic acid flotation collector as well as a preparation method and application thereof, and belongs to the technical field of mineral separation. The 1H-indole-7-hydroxamic acid flotation collecting agent has the following molecular structure: # imgabs0 #, shows higher collecting capacity and selectivity compared with an existing conventional benzohydroxamic acid collecting agent, can be widely applied to flotation enrichment and recovery of minerals including tungsten, tin, titanium, iron, copper, lead, rare earth and the like, and remarkably improves the flotation recovery rate of valuable metal ores.

Description

Technical Field

[0001] The invention relates to a 1H-indole-7-hydroxamic acid flotation collector, and also relates to a preparation method and application of the 1H-indole-7-hydroxamic acid flotation collector, belonging to the technical field of mineral flotation. Background Art

[0002] Hydroximic acid and its salts refer to chemical substances with the structure -C(=O)-N=OM (M is hydrogen or metal ion), which belong to a type of chelating collector. The lone pair electrons carried by nitrogen and oxygen atoms in the hydroximic acid molecule can bind to Ca on the surface of minerals. 2+ , Pb 2+ , Cu 2+ 、Ti 4+ The empty electron orbitals of isotropic metal ions are combined through coordination bonds to form stable four-membered or five-membered ring chelates. This chelate is more stable than general complexes and has better selectivity than traditional anion collectors such as fatty acids. It is widely used in the flotation of various oxide ores and rare earth minerals such as scheelite, cassiterite, ilmenite, and rutile.

[0003] At present, the most commonly used hydroxamic acid collectors in industry mainly include benzohydroxamic acid, salicylic hydroxamic acid, C7-C9 alkyl hydroxamic acid and H 205 etc. Although hydroxamic acid collectors have better selectivity, their raw material cost is high and the synthesis route is relatively complex. Compared with anionic surfactants with long carbon chain structures such as sodium oleate, sodium linoleate, and sodium dodecyl sulfate, hydroxamic acid collectors containing benzene rings such as benzohydroxamic acid have weak foaming ability because their benzene rings are non-polar groups. In production practice, they often require higher dosages and sometimes need to be activated with metal ions such as lead ions and iron ions, which also leads to higher reagent prices and higher use costs. Therefore, researchers have carried out many design and modification studies on the molecular structure of hydroxamic acid collectors to improve their flotation efficiency.

[0004] Flotation collectors should have at least two abilities: one is solid affinity, that is, the ability to attach to the surface of minerals; the other is hydrophobicity, that is, the ability to increase the hydrophobicity of the mineral surface after attaching to the mineral surface. Therefore, existing research is mostly carried out from the optimization of polar groups and non-polar groups of hydroxamic acid molecules to enhance their collection ability and hydrophobic properties respectively. Literature ("Investigation on flotation separation ofbastnaesite fromcalcite andbaritewith a novel surfactant:Octylamino-bis-(butanohydroxamic acid)", HAO DUAN, et al. Separation and Purification Technology, 2021256:117792), Chinese patents (publication numbers: CN106423574A, CN108906331A), etc., have developed new flotation collectors with polyhydroxamic acid groups, which can increase the adsorption density of the collector on the mineral surface, form a more stable metal chelate ring, and thus enhance its collection ability. The literature ("A novel surfactant 2-amino-6-decanamidohexanoic acid: Flotation performance and adsorption mechanism to diaspore", Minerals Engineering, LANQING DENG, et al. 201693: 16-23) introduces amide groups into hydroxamic acid molecules. There is a hydrogen bond between the hydrogen and oxygen atoms in the amide groups of different molecules. This effect makes the molecules more closely arranged on the mineral surface, increases the density of the reagent adsorbed on the mineral surface, and is conducive to the flotation separation of diaspore and gangue minerals such as kaolinite and pyrophyllite. Chinese patents (publication numbers: CN104888969A, CN110947522A, CN114057614A) disclose that bipolar collectors have been developed by introducing functional groups such as thiol, sulfur-nitrogen, and sulfonic acid groups into the molecular structure of hydroxamic acid, which can simultaneously achieve efficient flotation recovery of oxide ores such as scheelite and cassiterite and sulfide ores such as chalcopyrite and galena.Literature ("Flotation performance of anisic hydroxamic acid as new collector for tungsten and tin minerals". GANG ZHAO, et al. Journal of Central South University, 2022, 29(11): 3645-3655) and Chinese patent (publication number: CN115228618A) introduce hydrophobic groups such as allyl and alkoxy into the hydroxamic acid molecule to enhance the foaming ability of the non-polar group of the collector, thereby improving the hydrophobicity difference of the mineral surface and the quality of the flotation foam, thereby showing better flotation performance. Literature ("Preparation of cinnamic hydroxamic acid collector and study on flotation characteristics and mechanism of scheelite", XIANG YAO, et al. Minerals Engineering, 2023, 33 (6): 773-781.), literature ("Enhanced electronic effect improves the collecting efficiency of benzohydroxamic acid for scheelite flotation", ZHAO WEI, et al. Minerals Engineering, 2020, 152: 106308) and Chinese patent (publication number: CN104016883A) further enhance the chelating ability of oxygen atoms by introducing double bonds into the molecular structure of hydroxamic acid to form a larger conjugated system and introducing the inductive effect of the electron-donating group methyl at the para position of the benzene ring, which can achieve effective flotation recovery of scheelite at a lower dosage. Although a variety of modified hydroxamic acid collectors have been successfully developed and used in actual industrial production in the prior art, there are still defects such as high cost and relatively poor flotation performance. Summary of the invention

[0005] In view of the shortcomings of the prior art, the first object of the present invention is to provide a 1H-indole-7-hydroxamic acid flotation collector, which has a special molecular structure, comprises a large polar conjugated system, has a large degree of electron delocalization, and the hydroxyl oxygen and oxime oxygen on the conjugated system have a stronger ability to chelate the active sites of metal ions on the surface of minerals. At the same time, the nitrogen heteroatom in the pyrrole structure is an excellent hydrogen bond donor, which can enhance the selectivity of its adsorption by the difference in hydrogen bond strength formed with the anions on the surface of the mineral, so that the 1H-indole-7-hydroxamic acid compounds show stronger collection ability and selectivity than conventional hydroxamic acid collectors.

[0006] The second object of the present invention is to provide a method for preparing a 1H-indole-7-hydroxamic acid flotation collector, which has the advantages of low cost, simple operation, mild conditions, etc. and can be produced on a large scale.

[0007] The third object of the present invention is to provide an application of a 1H-indole-7-hydroxamic acid flotation collector, which is used for the flotation of metal oxide ores or rare earth ores, and can better effectively recover valuable metal minerals from oxide ores containing elements such as tungsten, tin, titanium, iron, copper, lead, and rare earths.

[0008] In order to achieve the above technical objectives, the present invention provides a 1H-indole-7-hydroxamic acid flotation collector having a molecular structure shown in Formula 1:

[0009]

[0010] Wherein, M is a +1 valent cation.

[0011] Compared with the existing conventional benzohydroxamic acid collector, the 1H-indole-7-hydroxamic acid flotation collector provided by the present invention has a polar pyrrole ring introduced into the benzene ring. On the one hand, a larger delocalized π bond is formed, and the degree of electron delocalization is large, so that the hydroxyl oxygen and oxime oxygen in the hydroxamic acid group have stronger ability to chelate metal ions, thereby enhancing the adsorption capacity of the active sites of metal ions on the surface of the mineral. On the other hand, the nitrogen atom in the pyrrole ring is an excellent hydrogen bond donor, and the presence of the nitrogen atom can improve the adsorption selectivity through the difference in hydrogen bond strength formed between the nitrogen atom and the anion on the surface of the mineral, thereby strengthening the hydrophilicity and hydrophobicity of the target mineral and the gangue mineral to improve the flotation selectivity.

[0012] As a preferred solution, in the molecular structure shown in Formula 1, M is H + , K + 、Na + or NH4 + .

[0013] The present invention also provides a method for preparing a 1H-indole-7-hydroxamic acid flotation collector, which comprises subjecting 1H-indole-7-carboxylate and hydroxylamine to a hydroxamic reaction under the action of an alkali reagent to obtain 1H-indole-7-hydroxamic acid salt; and acidifying the 1H-indole-7-hydroxamic acid salt to obtain 1H-indole-7-hydroxamic acid.

[0014] The preparation method of the 1H-indole-7-hydroxamic acid flotation collector of the present invention has the characteristics of low raw material cost, simple operation, mild reaction conditions, high reaction yield, few by-products, etc. The preparation process of the 1H-indole-7-hydroxamic acid flotation collector of the present invention is completed by a "one-pot method".

[0015] The 1H-indole-7-carboxylate of the present invention has a structure shown in the following formula 2:

[0016]

[0017] Wherein, R is a short-chain alkyl group, such as methyl, ethyl, etc.

[0018] The reaction principle of the invention is: 1H-indole-7-carboxylate is used as a substrate, and hydroxylamine is used as a nucleophilic reagent to undergo a nucleophilic addition reaction with the carbon group of 1H-indole-7-carboxylate under alkaline conditions to form an intermediate, and the intermediate undergoes intramolecular elimination to remove alcohol small molecules to generate 1H-indole-7-hydroxamate.

[0019] As a preferred embodiment, the molar ratio of 1H-indole-7-carboxylate to hydroxylamine is 1:(0.5-4). The molar ratio of 1H-indole-7-carboxylate to hydroxylamine is more preferably 1:(1-2).

[0020] As a preferred solution, the alkaline agent is used to adjust the pH of the system to 8.0-13.0. The alkaline agent can be sodium hydroxide, potassium hydroxide or ammonia. The alkaline agent mainly maintains the pH environment of the reaction system, helps to promote the smooth progress of the nucleophilic substitution reaction, and the presence of hydroxide anions can activate the reactants and stabilize the reaction intermediates.

[0021] As a preferred solution, the conditions of the hydroxamination reaction are: temperature of 20 to 80° C. and time of 0.5 to 12 h.

[0022] As a preferred solution, the hydroxamination reaction uses methanol as a solvent. The amount of methanol used relative to the amount of 1H-indole-7-carboxylate is (1-100) mL:1 g. Methanol is used as a solvent, which has the advantages of good solubility, low cost and relatively high safety, can maintain the stability of the reaction system, and helps to accelerate the reaction rate and improve the yield.

[0023] The present invention also provides an application of a 1H-indole-7-hydroxamic acid flotation collector, which is applied to the flotation of metal oxide ores. Compared with the existing benzohydroxamic acid collector, it has the characteristics of strong collecting ability and high selectivity.

[0024] As a preferred embodiment, the metal oxide ore is a metal oxide ore containing at least one of tungsten, tin, titanium, iron, copper, lead and rare earth.

[0025] The working principle of the 1H-indole-7-hydroxamic acid flotation collector in the flotation process is that the hydroxamic acid group is used to chelate with the metal ion active site on the surface of the mineral to form a stable "N, O four-membered ring and / or O, O five-membered ring" structure, which is chemically adsorbed on the mineral surface, and the nitrogen heteroatoms in the pyrrole ring act on the anionic groups on the surface of the mineral through hydrogen bonds. After the 1H-indole-7-hydroxamic acid is adsorbed on the mineral surface, the hydrophobic effect of the indole group can be used to improve the hydrophobicity of the mineral surface, thereby strengthening the difference in hydrophilicity and hydrophobicity between the mineral surface and the surfaces of other gangue minerals, thereby realizing the flotation separation of different minerals.

[0026] The process of using the 1H-indole-7-hydroxamic acid flotation collector of the present invention for mineral flotation is as follows: after crushing, grinding and slurrying of metal minerals, a flotation agent including the 1H-indole-7-hydroxamic acid compound is added for flotation to obtain a concentrate product and an in-tank product.

[0027] As a preferred solution, the dosage of the 1H-indole-7-hydroxamic acid compound is 1 to 1000 g / t relative to the mass of the original ore. The 1H-indole-7-hydroxamic acid compound provided by the present invention is used as a collector, with low dosage, high flotation efficiency, wide adaptability, and simple operation.

[0028] As a preferred solution, the flotation pH range suitable for the 1H-indole-7-hydroxamic acid compound is preferably 6-10, and the further preferred pH range is 7-9.

[0029] Compared with the prior art, the beneficial technical effects brought by the present invention are as follows:

[0030] (1) The preparation process of the 1H-indole-7-hydroxamic acid flotation collector of the present invention is completed by an oximation reaction between 1H-indole-7-carboxylic acid methyl ester and hydroxylamine through a one-pot process, which has the characteristics of high yield, few by-products, simple operation, mild conditions, etc.

[0031] (2) The 1H-indole-7-hydroxamic acid flotation collector of the present invention can be used for the flotation enrichment of oxidized metal minerals containing valuable metals such as tungsten, tin, titanium, iron, copper, lead and rare earth. Compared with benzohydroxamic acid, which is the most commonly used in industry at this stage, the conjugated system formed in the molecular structure of the 1H-indole-7-hydroxamic acid collector of the present invention is larger. Based on the combined effects of inductive effect, conjugation effect and field effect, it exhibits a strong electron donating effect, so that the hydroxyl oxygen and oxime oxygen in the hydroxamic acid molecule have stronger chelating ability, and the nitrogen heteroatom in the pyrrole structure can significantly improve the selectivity of the agent as a potential hydrogen bond donor, so that the 1H-indole-7-hydroxamic acid flotation collector can achieve efficient flotation recovery of valuable metal minerals such as tungsten, tin, titanium, iron, copper, lead and rare earth at a lower dosage. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the hydrogen nuclear magnetic resonance spectrum of 1H-indole-7-hydroxamic acid of the present invention.

[0033] Figure 2 It is the carbon nuclear magnetic resonance spectrum of 1H-indole-7-hydroxamic acid of the present invention.

[0034] Figure 3 The present invention is a flotation test flow chart of 1H-indole-7-hydroxamic acid and benzohydroxamic acid.

[0035] Figure 4 The results are the results of the flotation test of wolframite using 1H-indole-7-hydroxamic acid of the present invention. DETAILED DESCRIPTION

[0036] The following examples are further detailed descriptions of the present invention, but are not intended to limit the scope of protection of the claims of the present invention. All other examples obtained by professionals in this field without creative work are still within the scope of protection of the present invention.

[0037] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0038] Example 1

[0039] Synthesis of 1H-indole-7-hydroxamic acid:

[0040] Under stirring conditions, 3.5g of 97% pure 1H-indole-7-carboxylic acid methyl ester (0.02mol), 50ml of methanol and 7.927g of 10wt.% hydroxylamine solution (0.024mol) were added to a three-necked flask in sequence. After the 1H-indole-7-carboxylic acid methyl ester was dissolved, a total of 0.8g of 99% pure sodium hydroxide solid (0.02mol) (0.2g, 0.2g, 0.2g, 0.2g) was added in batches. After the sodium hydroxide was added, the mixture was stirred at a constant temperature of 50℃ for 4h. After the reaction was completed, hydrochloric acid with a mass concentration of 10wt.% was added dropwise to the reaction system while stirring at below 20℃ to adjust the pH of the system to 4.0-5.0. After the addition was completed, the reaction was stirred for 1 hour, the residue was removed by filtration, and the filtrate was distilled under reduced pressure to obtain a purple solid, i.e., a crude product of 1H-indole-7-hydroxamic acid, with a yield of 94.5%. It can be further purified by multiple recrystallizations using ethanol and water as solvents. Its nuclear magnetic resonance 1H NMR and 13C NMR were shown as Figure 1 and Figure 2 .

[0041] Example 2

[0042] Under stirring conditions, 9.461g of 97% pure 1H-indole-7-carboxylic acid ethyl ester (0.05mol), 100ml of methanol and 3.9636g of 50wt.% hydroxylamine solution (0.06mol) were added to a three-necked flask in sequence. After the 1H-indole-7-carboxylic acid ethyl ester was dissolved, a total of 2g of 99% pure sodium hydroxide solid (0.05mol) (0.5g, 0.5g, 0.5g, 0.5g) were added in batches. After the sodium hydroxide was added, the mixture was stirred at a constant temperature of 55°C for 3.5h. After the reaction was completed, hydrochloric acid with a mass concentration of 10wt.% was added dropwise to the reaction system while stirring at room temperature to adjust the pH of the system to 4.0-5.0. After the addition was completed, the reaction was stirred for 1.5 hours, the residue was removed by filtration, and the filtrate was distilled under reduced pressure to obtain a purple solid, i.e., a crude product of 1H-indole-7-hydroxamic acid, with a yield of 90.1%. Other compounds of the same type can be synthesized by this method.

[0043] Use Figure 3 The flotation test flow chart shown is used to carry out the application implementation and control test of the present invention.

[0044] The flotation efficiency of bastnaesite, wolframite and cassiterite and the separation efficiency of scheelite and calcite using conventional benzohydroxamic acid as a collector were used as controls to evaluate the superiority of the flotation performance of the novel 1H-indole-7-hydroxamic acid collector prepared in Example 1. The specific control examples are as follows:

[0045] Application Example 1

[0046] Flotation of bastnaesite with benzohydroxamic acid:

[0047] The amount of benzohydroxamic acid collector added was 1.5×10 -4 mol / L, the pH value of the flotation pulp is 7, the dosage of the frother methyl isobutyl carbinol (MIBC) is 0.5 μL / L, the speed of the flotation machine is 1600 r / min, and the fluorocarbon cerium ore with a particle size of 200-400 mesh is floated for 3 minutes. At this time, the flotation recovery rate of the fluorocarbon cerium ore is 68.1%.

[0048] Application Example 2

[0049] Benzohydroxamic acid flotation of wolframite:

[0050] The amount of benzohydroxamic acid collector added was 2.0×10 -4 mol / L, the dosage of methyl isobutyl carbinol (MIBC) was 12.5μL / L, the speed of the flotation machine was 1800r / min, and wolframite with a particle size of 200-400 mesh was floated for 3 minutes under different pH conditions. The flotation test results are as follows Figure 4 As shown in the figure, it can be seen that the flotation recovery rate of wolframite with benzohydroxamic acid as collector does not exceed 20%, and the highest is only 15.6%, which also shows that the collection ability of benzohydroxamic acid for wolframite is relatively weak.

[0051] Application Example 3

[0052] Flotation of cassiterite with benzohydroxamic acid:

[0053] The amount of benzohydroxamic acid collector added was 3.0×10 -4 mol / L, the pH value of the flotation pulp is 9, the dosage of the foaming agent methyl isobutyl carbinol (MIBC) is 12.5 μL / L, the speed of the flotation machine is 1800 r / min, and the cassiterite with a particle size of -400 mesh is floated for 3 minutes. At this time, the flotation recovery rate of cassiterite is 22.5%.

[0054] Application Example 4

[0055] Flotation separation of scheelite and calcite by benzohydroxamic acid:

[0056] The amount of benzohydroxamic acid collector added was 3.0×10 -4 mol / L, the pH value of the flotation pulp was 9, the dosage of the frother methyl isobutyl carbinol (MIBC) was 10.0μL / L, the speed of the flotation machine was 1600r / min, and the artificial mixed ore with a particle size of 200-400 mesh (the mass ratio of scheelite and calcite was 1:1) was floated for 3 minutes. At this time, the WO3 grade of the concentrate product was 20.8%, and the flotation recovery rate was 40.9%.

[0057] The novel 1H-indole-7-hydroxamic acid compound was used as a collector instead of benzohydroxamic acid, and flotation operation was carried out at the same dosage of the reagent to evaluate the advantages of the flotation efficiency of the novel 1H-indole-7-hydroxamic acid collector. The specific examples are as follows:

[0058] Application Example 1

[0059] 1H-indole-7-hydroxamic acid flotation of bastnaesite:

[0060] The amount of 1H-indole-7-hydroxamic acid collector added was 1.5×10 -4 mol / L, the pH value of the flotation pulp is 7, the dosage of the frother methyl isobutyl carbinol (MIBC) is 0.5 μL / L, the speed of the flotation machine is 1600 r / min, and the fluorocarbon cerium ore with a particle size of 200-400 mesh is floated for 3 minutes. At this time, the flotation recovery rate of the fluorocarbon cerium ore is 98.1%.

[0061] Application Example 2

[0062] 1H-indole-7-hydroxamic acid flotation of wolframite:

[0063] The amount of 1H-indole-7-hydroxamic acid collector added was 2.0×10 -4 mol / L, the dosage of methyl isobutyl carbinol (MIBC) was 12.5μL / L, the speed of the flotation machine was 1800r / min, and wolframite with a particle size of 200-400 mesh was floated for 3 minutes under different pH conditions. The flotation test results are as follows Figure 4 As shown in the figure, it can be seen that under the same dosage, the flotation recovery rate of wolframite with 1H-indole-7-hydroxamic acid as collector is much higher than that with benzohydroxamic acid, and reaches 94.3% when the pH value of the flotation pulp is 9.

[0064] Application Example 3

[0065] 1H-indole-7-hydroxamic acid flotation of cassiterite:

[0066] The amount of 1H-indole-7-hydroxamic acid collector added was 3.0×10 -4 mol / L, the pH value of the flotation pulp is 9, the dosage of the foaming agent methyl isobutyl carbinol (MIBC) is 12.5 μL / L, the speed of the flotation machine is 1800 r / min, and the cassiterite with a particle size of -400 mesh is floated for 3 minutes. At this time, the flotation recovery rate of cassiterite is 99.5%.

[0067] The novel 1H-indole-7-hydroxamic acid compound was used as a collector instead of benzohydroxamic acid, and the flotation separation of scheelite and calcite was carried out at the same dosage of the reagent to evaluate the selectivity advantage of the novel 1H-indole-7-hydroxamic acid collector. The specific examples are as follows:

[0068] Application Example 4

[0069] 1H-indole-7-hydroxamic acid flotation separation of scheelite and calcite:

[0070] The amount of 1H-indole-7-hydroxamic acid collector added was 3.0×10 -4 mol / L, the pH value of the flotation pulp was 9, the dosage of the frother methyl isobutyl carbinol (MIBC) was 10.0μL / L, the speed of the flotation machine was 1600r / min, and the artificial mixed ore with a particle size of 200-400 mesh (the mass ratio of scheelite and calcite was 1:1) was floated for 3 minutes. At this time, the WO3 grade of the concentrate product was 60.2%, and the flotation recovery rate was 85.3%.

Claims

1. A 1H-indole-7-hydroxamic acid flotation collector, characterized in that: It has a molecular structure shown in Formula 1: Wherein, M is a +1 valent cation.

2. A 1H-indole-7-hydroxamic acid flotation collector according to claim 1, characterized in that: M is H + , K + 、Na + or NH4 + .

3. A method for preparing a 1H-indole-7-hydroxamic acid flotation collector according to claim 1 or 2, characterized in that: 1H-indole-7-carboxylate and hydroxylamine undergo hydroxamination reaction under the action of an alkali reagent to obtain 1H-indole-7-hydroxamate; the 1H-indole-7-hydroxamate is acidified to obtain 1H-indole-7-hydroxamic acid.

4. The method for preparing a 1H-indole-7-hydroxamic acid flotation collector according to claim 3, characterized in that: The molar ratio of the 1H-indole-7-carboxylate to hydroxylamine is 1:(0.5-4).

5. The method for preparing a 1H-indole-7-hydroxamic acid flotation collector according to claim 3, characterized in that: The alkaline agent is used to adjust the pH of the system to 8.0-13.

0.

6. A method for preparing a 1H-indole-7-hydroxamic acid flotation collector according to any one of claims 3 to 5, characterized in that: The conditions of the hydroxamination reaction are: temperature of 20 to 80° C. and time of 0.5 to 12 h.

7. The method for preparing a 1H-indole-7-hydroxamic acid flotation collector according to claim 6, characterized in that: The hydroxamination reaction uses methanol as solvent.

8. The use of a 1H-indole-7-hydroxamic acid flotation collector according to claim 1 or 2, characterized in that: Used in flotation of metal oxide ores.

9. The use of a 1H-indole-7-hydroxamic acid flotation collector according to claim 8, characterized in that: The metal oxide ore is a metal oxide ore containing at least one of tungsten, tin, titanium, iron, copper, lead and rare earth.

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