Isohydroxamic acid, also known as hydroxamic acid, has two tautomers. The structural formula of hydroxamic acid is RCONHOH. In recent years, hydroxamic acid has been used as an anti-inflammatory and analgesic in the fields of biology and medicine. Hydroxamic acid can form stable metal chelates with metal ions such as Ti4+, La3+, Al3+, Fe3+ and Cu2+, so it is more used as an efficient flotation collector in flotation industry. At present, the domestic production of hydroxamic acid mainly includes H2O 2(3- hydroxy -2- naphthyl hydroxamic acid), naphthenic hydroxamic acid, salicylic acid hydroxamic acid, phenyl hydroxamic acid, C5-9 hydroxamic acid and so on. However, the high price is the biggest disadvantage of this kind of flotation surfactants, which seriously hinders the industrial popularization and application of hydroxamic acid collectors.
Therefore, the synthesis of low-cost hydroxamic acid is an urgent problem at present. There are many methods to synthesize hydroxamic acid at home and abroad, among which hydroxylamine method is the most mature and has been industrialized. Hydroxylamine method includes hydroxylamine-fatty acid ester synthesis method and hydroxylamine-acyl chloride synthesis method. In this method, fatty acids with suitable hydrocarbon chain length are usually esterified or acylated first, and then oximated with hydroxylamine (hydroxylamine hydrochloride or hydroxylamine sulfate) under alkaline conditions.
At present, the main problem of this process is that toxic raw materials such as methanol and concentrated sulfuric acid are used in fatty acid esterification, which not only increases the synthesis cost, but also is not friendly to the environment. However, in the process of acyl chlorination, the requirements of reaction conditions are high, and the fluidity of products after acyl chlorination is poor, resulting in a large number of acid gases, which leads to great environmental pollution, high cost of subsequent environmental treatment and high cost of product disposal, which does not meet the existing requirements of energy conservation and emission reduction. Because hydroxylamine is expensive, the cost of synthesizing hydroxamic acid can be greatly reduced by simplifying the operation process and selecting suitable cheap raw materials.
Application [2][3][4]
In recent years, a lot of research work has been carried out on hydroxamic acid collectors. As a flotation collector, hydroxamic acid has been used in the flotation of rare earth, cassiterite, copper oxide, wolframite and ilmenite, with excellent selectivity and collecting ability. Using hydroxamic acid as collector of oxidized minerals such as ilmenite has achieved good flotation application effect and broad development prospect. At present, the long-chain alkyl hydroxamic acid commonly used in industry is a mixed high-chain hydroxamic acid mainly composed of octyl hydroxamic acid, in which a certain amount of decyl hydroxamic acid and lauric acid are mixed.
The flotation performance of n-decyl hydroxamic acid and n-octyl hydroxamic acid on ilmenite was studied experimentally, and the interaction mechanism between n-decyl hydroxamic acid and ilmenite was studied by adsorption capacity determination, Zeta potential determination, infrared spectrum analysis and XPS analysis, and the following conclusions were drawn:
1) The optimum pH value of N-decyl hydroxamic acid and N-octyl hydroxamic acid for ilmenite flotation is about 7, and the collecting ability of N-decyl hydroxamic acid for ilmenite is stronger than that of N-octyl hydroxamic acid; When the pulp pH is 7 and the collector dosage is 200 mg /L, 90.32% of ilmenite can be recovered by n-decyl hydroxamic acid, while only 85.2% can be recovered by octyl hydroxamic acid.
2) After N-decyl hydroxamic acid reacts with ilmenite, when the pH value of the solution is higher than the zero pH value of ilmenite, the zeta potential of ilmenite decreases; The peak of dechydroxamic acid shifted in infrared spectrum. The changes of electron binding energy of N, O, Fe and Ti active sites in XPS analysis show that n-decyl hydroxamic acid has been chemically adsorbed on the surface of ilmenite.
XPS analysis also showed that decyl hydroxamic acid was physically adsorbed on the surface of ilmenite. In addition, alkyl hydroxamic acid was applied to the flotation of a phosphate rock in Hubei. At 35℃, the grade of concentrate P2O5 is 30. 5 1%, and the recovery rate is 79. The grade of P2O5 tailings is 6.89%. Flotation of low-grade collophanite with this reagent can simplify the flotation process, reduce the flotation temperature and beneficiation cost, and has good popularization and application prospects.
In addition, it can also be used as a collector for rare metals. The study on the mechanism of the reagent shows that in weak acidic medium, alkyl fatty acids with medium carbon chain (C7~ C9) (HM-50 for short) can form stable complexes with Ti, Sr, Nb, Ta, Zr, Th, Fe 2+, Fe3+ and rare earth cations, and this hydroxamic acid is generated with the cations of floatable minerals. Therefore, hydroxamic acid salt can be easily washed off the mineral surface.
Compared with common fatty acids, hydroxamic acid has weak collecting ability and strong selectivity, and is an effective collector for rare metal ores. Some researchers invented HM-50 and did a lot of research. The research shows that it can effectively flotation jamesonite, olivine, perovskite, sodium titanate and rare earth minerals. In recent years, alkyl hydroxamic acid has been used more and more as a collector not only in laboratory research, but also in flotation industry practice. In many cases, the use of alkyl hydroxamic acid can solve the complex problems in the flotation of rare metal ores and their gravity separation products.
Preparatory work [1]
Alkyl hydroxamic acids with chain lengths of C 12 and C 14 were directly synthesized by hydroxylamine-coconut oil synthesis method. In this method, coconut oil directly reacts with hydroxylamine for oximation, which saves the step of methanol esterification. The process conditions are simple and environmentally friendly. Under the optimized synthesis conditions, the mass fraction of hydroxamic acid in the product reached 77. The quality is higher than that of the first-class industrial grade product (the mass fraction of hydroxamic acid is more than or equal to 65%), and the synthesis cost is reduced. The synthesized alkyl hydroxamic acid was applied to one-step flotation of low-grade collophane, and good flotation indexes were obtained.
The synthesis method is as follows: Coconut oil is a fatty acid glyceride compound, in which coconut oil is rich in fatty acids with 12 carbon chain length and 14 carbon chain length, and also has 16 carbon chain length. At room temperature, coconut oil, hydroxylamine hydrochloride aqueous solution and emulsifier are directly added into a three-necked flask and mixed evenly; Then, putting the three-necked flask into a water bath pot, keeping the constant temperature at 27-28 DEG C, and keeping the temperature below 30 DEG C, and starting to stir with an electric stirrer; Then pour a certain concentration of sodium hydroxide solution into a constant pressure burette (control the dropping speed), and when the pH of the mixture in the flask is 7, add a small amount of sodium sulfide solution; Dropwise adding sodium hydroxide solution, and keeping the temperature and stirring for a certain time. The product after oximation is acidified with excessive sulfuric acid, filtered and dried to obtain the product. The synthetic process flow is shown in the figure.
Main reference materials
[1] Ge, Hou,, et al. Direct synthesis of alkyl hydroxamic acid from coconut oil and its application [J]. Fine Chemical Industry, 201,28 (8): 75 1-754.
Qi Cheng, Hong Zhong, Wang Shuai, et al. Study on flotation performance and mechanism of long-chain alkyl hydroxamic acid for ilmenite [J]. Applied Chemical Industry, 2016,45 (8):1407-141.
Ge, Ceng Liming, Hou, et al. Study on flotation performance of alkyl hydroxamic acid for collophanite and dolomite [J]. Chemical minerals and processing, 2012,41(9):1-4.
[4] Application of alkyl hydroxamic acid in mineral processing of rare metals abroad