A 1H-indole-7-hydroxamic acid flotation collector and its preparation method and application

Abstract

The present invention discloses a 1H-indole-7-hydroxamic acid flotation collector, its preparation method, and its application, belonging to the field of mineral processing technology. The 1H-indole-7-hydroxamic acid flotation collector has the following molecular structure: #imgabs0#. Compared with conventional benzohydroxamic acid collectors, it exhibits stronger collection capacity and selectivity. It can be widely used in the flotation enrichment and recovery of minerals such as tungsten, tin, titanium, iron, copper, lead, and rare earth elements, significantly improving 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 are chemical substances with the structure -C(=O)-N=OM (M is hydrogen or metal ion), belonging to a class of chelating collectors. The lone pair electrons carried by nitrogen and oxygen atoms in the hydroximic acid molecule can react with Ca on the mineral surface. 2+ , Pb 2+ 、Cu 2+ 、Ti 4+ The empty electron orbitals of isostatic 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 anionic 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 Although hydroxamic acid collectors have better selectivity, their raw material costs are high and the synthesis route is relatively complex. In addition, compared with anionic surfactants with long carbon chain structures such as sodium oleate, sodium linoleate, and sodium lauryl 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. This also leads to higher reagent prices and higher usage costs. Therefore, researchers have conducted numerous design and modification studies on the molecular structure of hydroxamic acid collectors to improve their flotation efficiency.

[0004] Flotation collectors should possess at least two abilities: one is solid affinity, which means they can adhere to the mineral surface; the other is hydrophobicity, which means they can increase the hydrophobicity of the mineral surface after attaching to the mineral surface. Therefore, existing research has mostly focused on optimizing the polar and non-polar groups of hydroxamic acid molecules to enhance their capture ability and hydrophobic properties, respectively. Literature ("Investigation on flotation separation of bastnaesite from calcite and barite with a novel surfactant: Octylamino-bis-(butanohydroxamic acid)", HAO DUAN, et al. Separation and Purification Technology, 2021256:117792) and Chinese patents (publication numbers: CN106423574A, CN108906331A) have developed novel flotation collectors with polyhydroxamic acid groups. These can increase the adsorption density of the collector on the mineral surface, form more stable metal chelate rings, and thus enhance their capture 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. Hydrogen bonds exist between the hydrogen and oxygen atoms in the amide groups of different molecules. This interaction makes the molecules more densely 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 the development of bipolar collectors 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". GANGZHAO, 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 flotation foam quality, 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 a double bond 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 response to the shortcomings of the prior art, the first object of the present invention is to provide a 1H-indole-7-hydroxamic acid flotation collector. The flotation collector has a special molecular structure, which contains a large polar conjugated system with a large degree of electron delocalization. The hydroxyl oxygen and oxime oxygen on the conjugated system have a stronger ability to chelate the active sites of metal ions on the mineral surface. At the same time, the nitrogen heteroatom in the pyrrole structure is an excellent hydrogen bond donor, which can enhance its adsorption selectivity by the difference in hydrogen bond strength formed with the anions on the mineral surface. Therefore, 1H-indole-7-hydroxamic acid compounds exhibit stronger capture 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 can be used for the flotation of metal oxide ores or rare earth ores to effectively recover valuable metal minerals from oxide ores containing elements such as tungsten, tin, titanium, iron, copper, lead, and rare earth elements.

[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] The 1H-indole-7-hydroxamic acid flotation collector provided by the present invention is superior to conventional benzohydroxamic acid collectors in that a polar pyrrole ring is 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 a stronger ability to chelate metal ions, thereby enhancing the adsorption capacity of the active sites of metal ions on the mineral surface. On the other hand, the nitrogen atom in the pyrrole ring is an excellent hydrogen bond donor. The presence of the nitrogen atom can improve the adsorption selectivity by the difference in hydrogen bond strength formed between the nitrogen atom and the anion on the mineral surface, 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. The method comprises the following steps: subjecting 1H-indole-7-carboxylate and hydroxylamine to a hydroximation reaction under the action of an alkaline reagent to obtain 1H-indole-7-hydroxamate; and acidifying the 1H-indole-7-hydroxamate to obtain 1H-indole-7-hydroxamic acid.

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

[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 present invention is as follows: 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, which undergoes intramolecular elimination to remove the alcohol small molecule 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 embodiment, 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 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 for the hydroximation reaction are: temperature of 20 to 80° C., and time of 0.5 to 12 h.

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

[0023] The present invention also provides a 1H-indole-7-hydroxamic acid flotation collector for use in metal oxide ore flotation. Compared with existing benzohydroxamic acid collectors, the 1H-indole-7-hydroxamic acid collector exhibits strong collecting capacity and high selectivity.

[0024] As a preferred solution, 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 of the present invention in the flotation process is as follows: the hydroxamic acid group is used to chelate with the metal ion active sites on the mineral surface 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, while the nitrogen heteroatoms in the pyrrole ring act on the anionic groups on the mineral surface 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 hydrophilicity difference between the mineral surface and the surfaces of other gangue minerals, thereby achieving flotation separation between different minerals.

[0026] The 1H-indole-7-hydroxamic acid flotation collector of the present invention is used for mineral flotation. The process comprises: crushing, grinding and slurrying the metal ore, adding a flotation agent comprising the 1H-indole-7-hydroxamic acid compound, and performing 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. Using the 1H-indole-7-hydroxamic acid compound provided by the present invention as a collector reduces the dosage of the agent, improves flotation efficiency, has a wide range of applications, and is simple to operate.

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

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] (1) The preparation process of the 1H-indole-7-hydroxamic acid flotation collector of the present invention is completed by the 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-hydroxyoxime 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 the most commonly used benzohydroxamic acid in industry at this stage, the conjugated system formed in the molecular structure of the 1H-indole-7-hydroxyoxime collector of the present invention is larger. Based on the combined effects of the inductive effect, conjugated effect and field effect, it exhibits a stronger 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-hydroxyoxime 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 The hydrogen nuclear magnetic resonance spectrum of 1H-indole-7-hydroxamic acid of the present invention is shown in FIG.

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

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

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

[0036] The following examples further illustrate the present invention and are not intended to limit the scope of the present invention. All other embodiments 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] To a three-necked flask, 3.5 g of 97% pure 1H-indole-7-carboxylic acid methyl ester (0.02 mol), 50 ml of methanol, and 7.927 g of a 10 wt.% hydroxylamine solution (0.024 mol) were added sequentially with stirring. After the 1H-indole-7-carboxylic acid methyl ester dissolved, 0.8 g of 99% pure sodium hydroxide solid (0.02 mol) was added in batches (0.2 g, 0.2 g, 0.2 g, 0.2 g). After the sodium hydroxide was added, the mixture was stirred at 50°C for 4 hours. After the reaction was complete, 10 wt.% hydrochloric acid was added dropwise to the reaction system while stirring at below 20°C to adjust the pH to 4.0-5.0. After the addition was complete, 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 was further purified by multiple recrystallizations using ethanol and water as solvents. Its nuclear magnetic resonance 1H NMR and 13C NMR were respectively Figure 1 and Figure 2 .

[0041] Example 2

[0042] To a three-necked flask, 9.461 g of 97% pure 1H-indole-7-carboxylic acid ethyl ester (0.05 mol), 100 ml of methanol, and 3.9636 g of a 50 wt.% hydroxylamine solution (0.06 mol) were added sequentially with stirring. After the 1H-indole-7-carboxylic acid ethyl ester dissolved, 2 g of 99% pure sodium hydroxide solid (0.05 mol) was added in batches (0.5 g, 0.5 g, 0.5 g, 0.5 g). After the sodium hydroxide was added, the mixture was stirred at 55°C for 3.5 hours. After the reaction was complete, 10 wt.% hydrochloric acid was added dropwise to the reaction system while stirring at room temperature to adjust the pH to 4.0-5.0. After the addition was complete, 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, namely the crude product of 1H-indole-7-hydroxamic acid, with a yield of 90.1%. Other compounds of the same type can be synthesized using this method.

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

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

[0045] Application control 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 foaming agent methyl isobutyl carbinol (MIBC) is 0.5 μL / L, the flotation machine speed 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 control example 2

[0049] Flotation of wolframite with benzohydroxamic acid:

[0050] The amount of benzohydroxamic acid collector added was 2.0×10 -4 mol / L, the dosage of methyl isobutyl carbinol (MIBC) as the foaming agent is 12.5μL / L, the speed of the flotation machine is 1800r / min, and wolframite with a particle size of 200-400 mesh is 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 using 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 control 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 flotation machine speed 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 the cassiterite is 22.5%.

[0054] Application control example 4

[0055] Flotation separation of scheelite and calcite using 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 10.0 μL / L, the flotation machine speed was 1600 r / 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] A novel 1H-indole-7-hydroxamic acid compound was used as a collector instead of benzohydroxamic acid. Flotation operations were performed at the same dosage of the reagent to evaluate the advantages of the novel 1H-indole-7-hydroxamic acid collector in flotation efficiency. Specific examples are as follows:

[0058] Application Example 1

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

[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 foaming agent methyl isobutyl carbinol (MIBC) is 0.5 μL / L, the flotation machine speed 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) as the foaming agent is 12.5μL / L, the speed of the flotation machine is 1800r / min, and wolframite with a particle size of 200-400 mesh is floated for 3 minutes under different pH conditions. The flotation test results are as follows Figure 4 As shown in the figure, under the same dosage, the wolframite flotation recovery rate of 1H-indole-7-hydroxamic acid as collector is much higher than that of benzohydroxamic acid, and reaches 94.3% when the pH 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 was 9, the dosage of the foaming agent methyl isobutyl carbinol (MIBC) was 12.5 μL / L, the flotation machine speed was 1800 r / min, and the cassiterite with a particle size of -400 mesh was floated for 3 minutes. At this time, the flotation recovery rate of the cassiterite was 99.5%.

[0067] The novel 1H-indole-7-hydroxamic acid compound was used as a collector instead of benzohydroxamic acid. The flotation separation of scheelite and calcite was carried out at the same reagent dosage 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 10.0 μL / L, the flotation machine speed was 1600 r / 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 the 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. The 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 a hydroxamination reaction under the action of an alkaline 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, wherein: 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 reagent is used to adjust the pH of the system to 8.0-13.

0.

6. The 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 hydroximation 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 hydroximation reaction uses methanol as solvent.

8. 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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