Liquid-Liquid Extraction of Palladium(II) from Hydrobromic Acid Media by Hexadecylpyridinium Bromide

Abstract

Liquid-liquid extraction is one of the most efficient methods used to separate, concentrate and purify metal ions and organic compounds. [1][2][3][4][5] Extraction has become a technique used to recover and separate noble metals, including palladium(II). [6][7][8][9] Several reagents have been proposed, including hydroxyoximes, alkyl derivatives of 8-hydroxyquinoline and hydrophobic amines. Some of them are used in industry. However the extraction occurs very slowly; this is caused by the nature of the hydrophobic extractant and the symmetrical palladium chlorocomplex. The drawback can be overcome by the addition of thiocyanide ions, which disturb the symmetry of palladium(II) chlorocomplex, 10,11 the use of asymmetric dialkylsulfides containing a hydrophilic group 12,13 or the use of a phase transfer catalyst.14-16 A similar effect is observed when other hydrophobic extractants are used; e.g. 2-hydroxy-5-nonylbenzophenone oxime and 1-(2-pyridylazo)-2-naphtol (PAN). 10,17 Surfactants have been employed with great success in photometric, 18 fluorometric 19 and phosphorimetric 20 determinations because they tend to enhance the solubility and detection sensitivity of analytes. Surfactants also play an important role in separation science. For example, aqueous micellar solutions are used as the mobile phase in micellar liquid chromatography 21 as well as in the electrolytic mobile phase of micellar electrokinetic capillary chromatography.22 A well-known phase separation method, namely, the cloud point extraction, 23,24 has been successfully used in the extractive preconcentration, separation and purification of various species, ranging from metal chelates, organic compounds of environment concern as well as a number of proteins and related biochemicals. Many investigators have studied the separation of metals by liquid surfactant membranes. [25][26][27][28] In recent years, we have studied the influence of different conditions on the micellization of hexadecylpyridinium bromide (HDPB) using a membrane electrode selective to the surfactant 29-32 and conductometric method. 33In the present study, we found the stoichiometry and extraction mechanism of palladium(II) with HDPB in chloroform by a spectrophotometric method and separation of palladium from hydrobromic acid media. Experimental Reagents and chemicalsHexadecylpyridinium bromide (HDPB) and other reagents were purchased from Merck Chemical Company and were used as received. Reagent grade chloroform (Fluka) was used as the organic phase. A stock solution of 0.01 M palladium(II) was prepared by dissolving PdCl2 (Merck) in 0.1 M hydrobromic acid. The solution was standardized gravimetrically with dimethylglyoxime. 34 ApparatusA Shimadzu UV-VIS 2100 spectrophotometer and a Shimadzu AA-670 atomic absorption spectrophotometer (acetylene-air flame) were used to determine metal ion concentrations in aqueous phases. The pH measurements were made with a Metrohm 692 pH/ion meter using a combined glass electrode. X-Ray studies were made with a Philips WDXRF Spectrometer Mod...

Comparison of the Extractabilities of Tetrachloro- and Tetrabromopalladate(II) Ions with a Thiodiglycolamide Compound

“…2 In contrast, there have been few studies of PGM extraction from acidic bromide media. [3][4][5][6][7][8][9] The replacement of chloride ions by bromide ions in PGM complexes frequently enhances the extractability, and this phenomenon has been explained by the fact that bromo-PGM complexes are more hydrophobic than the corresponding chloro-PGM complexes. 5,6 Because tetrachloropalladate(II), [PdCl4] 2-, is substantially more extractable than other PGM ions, 1 Pd(II) can be extracted in two different modes: via the formation of a coordination complex or via the formation of an ion-pair complex.…”

New cyclopentadiene derivatives as novel pH indicators

“…In this work, three derivatives of (triphenylphosphoranylidene)cyclopenta-1,3-dienes, that are recently synthesized [5,6], are used as pH indicators in the pH range 10e12. For these compounds color change in the pH range 10e12 was extremely sharp and clear (Table 1).…”