| Platinum metal is an important material in modern industry and the building up of national defense because of it has high melting point, electrical conductivity, corrosion-resistance, high temperature stability and strength and high temperature resisting creep ability, which is regarded as"vitamin"and"modern new metal"of modern industry. Palladium is an indispensable critical material in aerospace, aviation, maritime, weapons and nuclear power and other high-tech areas and automobile industry. Physical and chemical properties of platinum metal are very similar and its valence is changeable. Because of these, how to separate platinum metal effectively is a difficult problem. In recent years, solvent extraction is widely used in separation and purification of platinum metal, which has fast reaction rate and better separation effect and has become the major means of separating platinum metal.The development of novel extractants and the scientific design of extraction process are important factors for solvent extraction. Therefore, exploring novel extractants and suitable extraction condition have important significance on extraction chemistry. Sulfur-containing neutral extractants have good extraction capacity especially for palladium in platinum metal. However, the corresponding extraction chemistry and the separation behavior are not considered comprehensively. In this paper, three kinds of disulfide ether amide podands extractants and two kinds of disulfoxide amide podands extractants have been synthesized, and the extraction capacity has been studied in detail. The main results are concluded as follows:(1) Three kinds of disulfide ether extractants have been synthesized: 2,2'-dithiophenyl ethyl ether(DTPEE), 2,2'-di[(p-methyl)thiophenyl]ethyl ether(DMTPEE), 2,2'-di[(n-octyl)sulfenyl]ethyl ether(DOSEE), 2,2'-di[(phenyl)sulfinyl]ethyl ether(DPSEE), 2,2'-di[(p-methylphenyl)sulfinyl]ethyl ether (DMPSEE), and characterized by infrared spectrum, nuclear magnetic resonance and elemental analysis.(2)The extraction capacity of Pd2+ and reaction mechanism were studied for five extractants in hydrochloric acid. The influence of the concentration of hydrochloric acid, H+, extractant and the temperature on the extraction distribution ratio have been investigated. The primary extraction mechanism is coordination replace mechanism. The results indicated that the coordination number of extractant with Pd2+ is different, which were measured in different hydrochloric acid concentration of research scope and were diluted with chloroform. DTPEE, DMTPEE, DOSEE coordinate with Pd2+ in hydrochloric acid concentration of 0.1 mol·dm-3-0.7 mol·dm-3. The structures of complexes is concluded as follows: PdCl2·4DTPEE; PdCl2·3DMTPEE; PdCl2·4DOSEE; The order of extraction ability of Pd2+ with different disulfide ether amide podands extractants is as follows: DOSEE>DTPEE>DMTPEE. DPSEE, DMPSEE coordinate with Pd2+ in hydrochloric acid concentration of 0.1 mol·dm-3-1.0 mol·dm-3. The structures of complexes is concluded as follows: PdCl2·2DPSEE; PdCl2·2DMPSEE. The order of extraction ability of Pd2+ with different disulfoxide amide podands extractants is as follows: DPSEE>DMPSEE. The reason to different extraction mechanism and coordination number is hydrochloric acid concentration and different structure of extractants. In the same condition, the extraction effect of Pd2+ with disulfide ether amide podands extractants is superior to disulfoxide amide podands extractants.(3) The extraction performance and mechanism of Pd2+ with DTPEE in diluents including CHCl3, CH2Cl2, Benzene, Toluene from hydrochloric acid solution were studied. The extraction effect in different factors was studied. The order of extraction ability of Pd2+ with DTPEE in various diluents is as follows: CHCl3> CH2Cl2> Benzene> Toluene. The structures of complex is PdCl2·4DTPEE with CHCl3 as diluent in hydrochloric acid concentration of 0.1 mol·dm-3-0.6 mol·dm-3. The structures of complex is PdCl2·3DTPEE with other diluents. The results indicated diluents have a certain impact to the structures of complexes and the extraction efficiency of extractants.(4) The extraction distribution ratio of Pd2+ for disulfide ether amide podands extractants decreases and then increase with the increase of hydrochloric acid concentration with CHCl3 as diluent in experimental acidity. While the extraction distribution ratio of Pd2+ for disulfoxide amide podands extractants decreases with the increase of hydrochloric acid concentration with CHCl3 as diluent in experimental acidity. The extraction distribution ratio of Pd2+ for DTPEE decreases with the increase of hydrochloric acid concentration with CHCl3 as diluent in experimental acidity. The extraction distribution ratio of Pd2+ for five extractants increases with the increase in the concentration of extractants. The distribution ratio decreases with the increase in the temperature and the extraction reactions are exothermic. The thermal physical constant have been calculated. The IR spectra results of the extracted species indicate that sulfide bond and ether oxygen of disulfide ether amide podands extractants are coordinated with Pd2+ and sulfide bond, oxygen atom and sulfur atom in sulfoxide group of disulfoxide amide podands extractants are coordinated with Pd2+. In the same condition, the extraction effect of Pd2+ with disulfide ether and disulfoxide amide podands extractants is superior to sulfide ether and sulfoxide extractants.
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