Organophosphorus extracting agent widely used in hydrometallurgical, atomic energy industry and environmental science, occupies an important position in terms of metal extraction. The organic phosphorus extractant is divided into a neutral phosphorus extractant and an acidic phosphorus extractant, which have the advantages of good extraction performance, high selectivity, small water solubility and easy back extraction, and have been extensively studied in separating and purifying metals: , bis(2,4,4-trimethylpentyl)phosphonic acid (Cyanex 272) has a high separation factor for the extraction of nickel and cobalt ; bis(2,4,4-trimethylpentyl) thiophosphine Acid (Cyanex302) can directly recover zinc from waste liquid containing Fe 2+ and Ca 2+ to achieve effective separation of ZnFe and Zn/Ca; tributyl phosphate (TBP) has strong extraction ability for uranium and can be used for Uranium is recovered from ore and uranium fuel aftertreatment. With the rapid development of hydrometallurgy and the enhancement of people's environmental awareness, the synthesis of high-quality organic phosphorus extractant and its clean production process have also developed rapidly, and many important achievements have been made in recent years.
I. Classification and structure of organic phosphorus extractants
According to the presence or absence of a hydroxyl group in the structure, the organic phosphorus extractant can be classified into an acidic phosphorus extractant and a neutral phosphorus extractant. The former can be regarded as a product in which two hydroxyl groups in the H 3 PO 4 molecule are substituted by an alkoxy group or an alkyl group, and the latter can be regarded as three hydroxyl groups in the H 3 PO 4 molecule completely by an alkoxy group or an alkyl group. Substituted product. The oxygen in the common organic phosphate extractant molecules can also be replaced by sulfur one by one to form a thiophosphorus extractant.
(1) Structure of organic phosphoric acid
The organic phosphoric acid mainly includes a dialkyl phosphate, a monoalkyl phosphonic acid monoalkyl ester, and a dialkyl phosphonic acid. Their molecular structure is as follows:
Typical representatives of organic phosphoric acid are di(2-ethylhexyl)phosphoric acid (D2EHPA or P204), 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A or P507), and di(2,4,4). - Trimethyl amyl) phosphonic acid (Cyanex 272). The thiophosphoric acid is mainly composed of a thiophosphonic acid and a dithiophosphonic acid. For example, one or two O in Cyanex 272 are substituted by S, and their trade names are Cyanex 302 and Cyanex 301, respectively, and the structural formula is as follows:
(2) Structure of neutral phosphorus extractant
The phosphorus-oxygen neutral extracting agent mainly comprises a phosphate ester, a monoalkylphosphonic acid diester, a dialkylphosphonic acid monoester, and a trialkylphosphine oxide. Typical representatives are tributyl phosphate (TBP), dimethyl heptyl methylphosphonate (P350), octyl dioctylphosphonate, and trioctylphosphine oxide (TOPO). Their structural formulas are as follows:
Second, the synthesis of organic phosphoric acid extractant
Synthesis of (a) bis(2-ethylhexyl)phosphoric acid (D2EHPA or P204)
There are two kinds of synthetic methods of P204: phosphorus oxychloride method and phosphorus trichloride method. At present, the phosphorus oxychloride method, namely 2-ethylhexanol (isooctyl alcohol) and phosphorus oxychloride, is used to obtain diisooctylphosphoryl chloride (esterification), followed by alkali hydrolysis, acidification, water washing and distillation. The process gets P204. The synthetic route is as follows:
The P204 synthesized by this method contains about 5% of monoesters and triesters, and their presence sometimes affects the extraction behavior of P204.
Zhang Lingyun has improved the process. In the process of synthesizing di(2-ethylhexyl)phosphoric acid, a small amount of anhydrous AlCl 3 is added in advance to treat 2-ethylhexyl alcohol, and the water is removed to prevent hydrolysis of phosphorus oxychloride, and phosphorus oxychloride is avoided. - The amount ratio of ethylhexyl alcohol material changes, reducing the formation of monoester or triester; while strictly controlling the reaction temperature, enhancing the absorption of HCl gas, making the reaction proceed more thoroughly, increasing the di(2-ethyl group) The yield and purity of hexyl phosphate.
Cao Ruzhen et al used the reaction of isooctanol and phosphorus trichloride, continued to chlorinate, hydrolyze and acidify without separation, and finally obtained P204 by steam distillation. The synthetic route is shown in the figure. In this process, the reaction conditions of the steam distillation purification product step are difficult to control, and in order to completely evaporate the chloroisooctane, the heating time is prolonged, which easily decomposes P204 to form a monoalkyl phosphate; Without steam distillation, the use of vacuum distillation to remove chloroisooctane is not satisfactory, because P204 has poor thermal stability, while chloroisooctane has a higher boiling point. .
In this regard, the process was improved: after the reaction of isooctanol with phosphorus trichloride, the chloroisooctane was distilled off under reduced pressure. Compound I is very stable and does not decompose during the distillation of chloroisooctane. Then, it is slowly chlorinated at a low temperature, and then hydrolyzed and acidified in the presence of an organic solvent, and finally the organic solvent is distilled off under reduced pressure, and the residue is P204. Since the solvent removal takes a short time, the temperature is low, and it is carried out under anhydrous conditions, the purity and yield of the product can be ensured.
(II) Synthesis of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A or P507)
Cao Ruzhen and others studied the synthesis method of P507, which is also the current general method of P507 production. First preparing 2-ethylhexylphosphonite with 2-ethylhexyl alcohol and phosphorus trichloride; then adding chloro 2-ethylhexane to the product and treating with sodium ethoxide to obtain 2-ethylhexylphosphonic acid Mono-2-ethylhexyl ester, P507. The synthetic route is:
The P507 synthesized by the method has a purity of about 90%, and contains a small amount of mono(2-ethylhexyl)phosphate, mono(2-ethylhexyl)phosphonate, pyrophosphate vinegar, 2-ethylhexyl alcohol, and polyphosphorus. Compounds and other organic impurities and the like. The presence of these impurities has a significant effect on the extraction behavior of P507. Huang Kelong et al. studied the purification of industrially produced P507 by cobalt salt precipitation method. The purified product contained about 99.63% of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester in a yield of 86%.
(iii) bis(2,4,4-methylpentyl)phosphonic acid (Cyanex 272)
Cyanex272 is a cobalt-nickel separation special effect extracting agent invented by Cytec Industries Inc., which mainly has the following steps: using azobisisobutyronitrile as a free radical initiator to make diisobutylene and PH 3 A free radical addition reaction occurs at a certain temperature and pressure to obtain bis(2,4,4-trimethylpentyl)phosphine, which is oxidized and hydrolyzed under acidic conditions with H 2 O 2 to obtain a product. It contains about 85% bis(2,4,4-trimethylpentyl)phosphonic acid. There are many steps in this method, the raw material PH 3 is highly toxic, and the reaction needs to be carried out under several tens of atmospheric pressures, which is very demanding on equipment, and it is difficult for the general extractant factory to meet such requirements. The product synthesized by the method contains a certain amount of bis(2,4,4-trimethylpentyl)phosphine oxide, tris(2,4,4-trimethylpentyl)phosphine oxide and several other different times. phosphonic acids and phosphonates, these impurities significantly affect the properties of the product was extracted, the copper salt can be purified by crystallization.
Wo Shiming et al. successfully prepared high-purity Cyanex 272 by radical addition reaction of hypophosphorous acid with olefin. Under the action of a free radical initiator, two phosphorous hydrogen bonds in the hypophosphorous acid molecule are cleaved to produce a phosphorus-containing radical which is added to the double bond of the olefin to form a dialkylphosphinic acid. The key to this reaction is the free radical initiator and reaction temperature. A small amount of the monoalkylphosphinic acid in the product can be washed away with a dilute base. The advantage of this method is that the use of highly toxic phosphine gas is avoided, and only at a lower pressure, the synthesis reaction can be completed in one step, and the product yield and purity are high.
(4) Synthesis of dithiophosphonic acid
Currently, commercial thiophosphoric acids are mainly bis(2,4,4-trimethylpentyl)dithiophosphinic acid (the main active ingredient of Cyanex 301) and bis(2,4,4-trimethylpentyl). Monothiophosphoric acid (the main active ingredient of Cyanex302), produced by the American Cytec Company, has not been reported by the company. Yu Fengxian and other phosphorus dichloride (PSCl 3 ) and halogenated alkane were used as raw materials to synthesize four dialkyldithiophosphonic acids by Grignard reaction, sulfurization and acidification. The synthetic route is as follows:
Due to the many synthetic steps, the final yield is low, only 21.9% to 47.1%, and the practical application is of little significance.
Liu Leo Zhaoqing et al. reported a patent for the synthesis of dialkyldithiophosphonic acid and dialkylmonothiophosphonic acid. A certain amount of bis(2,4,4-trimethylpentyl)phosphonic acid, a small amount of concentrated sulfuric acid and a certain amount of phosphorus disulfide are mixed, heated to 160 ° C under nitrogen protection, kept for 7 h, and after a series of post-treatment, 90% pure bis(2,4,4-trimethylpentyl)monothiophosphonic acid; a certain amount of bis(2,4,4-trimethylpentyl)phosphonic acid and protected under inert gas Under mixing and heating to 120 ° C, heat for 3h, then add a certain amount of phosphorus pentasulfide, heat to 140 ° C, heat for 3 ~ 4h, cooling, after acidification, water washing and other post-treatment, to obtain a higher purity of two (2, 4 , 4-trimethylpentyl) thiophosphoryl chloride; a certain amount of bis(2,4,4-trimethylpentyl)thiophosphoryl chloride and sodium hydrosulfide solution are stirred at 20-30 ° C for several hours. After a series of work-ups, bis(2,4,4-trimethylpentyl)dithiophosphinic acid having a purity of about 88% was obtained. The synthetic route is as follows:
Third, neutral phosphine extractant
(a) Synthesis of tributyl phosphate
Tributyl phosphate can extract a variety of metals, organic acids and inorganic acids, and is widely used. Lu Jingzhong et al. reported the production of high-purity tributyl phosphate. 9%。 The purity of the product obtained by the esterification reaction of n-butanol and phosphorus oxychloride at room temperature, after alkali washing, alcohol removal, water washing, distillation under reduced pressure, etc., the purity of the product is greater than 99.9%. The method changes the conventional feeding sequence, and n-butanol is added to the phosphorus oxychloride. The hydrogen chloride generated during the reaction is insoluble in the reaction system and is eliminated, thereby reducing the occurrence of side reactions in the esterification reaction, which is favorable for the reaction tendency. Perfect, so that the yield and purity of the product can be improved. Its synthetic route is:
Abdreimova, RR, etc., reacted with n-butanol and white phosphorus, using CCl 4 and PhMe as solvents, and Culcata catalyzed to obtain tributyl phosphate, the yield was close to 100%. Its synthetic route is:
(II) Synthesis of dimethyl heptyl methylphosphonate (P350)
Dimethyl heptyl methylphosphonate is a precious metal extractant. Gupta, Hemendra K et al. reported their synthesis. Heptanol and methylphosphoric acid were loaded on a thin layer chromatography plate of silica gel, and heated under microwave heating to obtain a highly pure methyl dimethyl phosphonate. Its synthetic route is:
(III) Synthesis of Trialkylphosphine oxide (TRPO)
Trialkylphosphine oxide (TRPO) is a typical neutral phosphine extractant. The synthesis methods mainly include olefin-phosphine method, Grignard reagent-phosphorus oxychloride method and alkyl iodide phosphorus complex hydrolysis method. Han Lei et al. carried out the synthesis of trialkyl phosphine oxide by alkyl iodide complex hydrolysis method. The process includes the preparation, hydrolysis and purification of iodinated, alkyl iodide-phosphorus complexes, and the synthetic route is:
The synthesis route of the method is simple, and the purity of the product is high. The starting alcohol may be an alcohol or a mixture of several alcohols, and the product is a single or mixed trialkylphosphine oxide. In general, long straight chain TRPO is easier to synthesize, and its synthesis segment yield is also higher. Commercially available Cyanex 921 (trioctylphosphine oxide, TOPO), Cyanex 923 (R3PO, R2R'PO, a mixture of RR'2PO), and Cyanex 925 (a mixture of R3PO and R2R'PO) can be synthesized by the above method.
Hoye Peter Albert Theodore et al. used 2,2'-azobis(2,4-dimethylvaleronitrile) as initiator to generate free radical addition of olefin and phosphine at room temperature under 365 nm ultraviolet excitation. The reaction produces a trialkylphosphine, which is then oxidized with 30% H 2 O 2 to give a trialkylphosphine oxide. The method has simple synthesis route and easy availability of raw materials, but there are some olefin polymers and impurities such as dialkylphosphonic acid in the product. The synthetic route is (taking trioctylphosphine oxide as an example):
Nikolotova ZI and the like are reacted with a Grignard reagent and phosphorus oxychloride to obtain a trialkylphosphine oxide. The advantage of this method is that the purity of the product is high, and the disadvantage is that the preparation conditions of the Grignard reagent are harsh, resulting in a low overall yield. The synthetic route is as follows:
Fourth, the development trend of phosphorus-containing extractants
Since the coordination number of the P atom in the molecule of the organophosphorus extractant is larger and the polarity of the P=O bond is stronger, the steric hindrance effect and the electronic effect are more adjustable, so that organic phosphorus with different structures can be designed. Extractant to meet the extraction and separation requirements of different metal ions. In recent decades, a large number of in-depth studies have been carried out on various organic phosphoric acid extractants and neutral phosphorus extractants and are widely used in the fields of hydrometallurgy, atomic energy industry and environmental science. Most of the non-polar groups in these organophosphorus extractant molecules are 2 or 3 identical chain alkyl groups, and there are no substituents on the alkyl chain. These structural features limit the organic phosphorus extractant in The electronic effects and steric effects in its molecules are regulated over a wide range. For example, for lanthanides with small differences in radius, the various organic phosphorus extractants currently commercialized have little extraction separation coefficient. Therefore, organic phosphorus extractants with novel structures, such as asymmetry, are designed and synthesized. Different non-polar groups in the molecule, cyclic (cyclic substituents or two substituents on P are linked to form a ring), hydroxyl groups on the alkyl chain, halogens and other substituents, may become the main future Direction of development.
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