2-Hydroxy-4-n-octyloxybenzophenone oxime (HOBO) was recently synthesized to develop a selective extractant for copper(II). HOBO exhibited a high selectivity for only copper(II) over other base metals such as nickel(II) and cobalt(II) which are typically extracted with LIX series hydroxyoxime reagents in the high pH region from 1 M aqueous ammonium nitrate solution. This is due to the introduction of an alkoxyl group to the phenyl group of hydroxyoximes, which causes a lowering of the dissociation constant of phenol. Copper(II) was extracted as a 1:2 complex with HOBO (= ) according to the following reaction:  Cu2+ + 2 ⇔ + 2H +; K ex. The extraction equilibrium constant, K ex = 1.1 × 10-1, was obtained at 303 K. The extraction rate of copper(II) was measured using a Lewis-type transfer cell at 303 K. The extraction reaction of copper(II) with HOBO is interpreted as an interfacial reaction where the elementary reaction step between the intermediate complex adsorbed at the interface and free extractant in the aqueous phase is rate-determining. The reason this step is rate-determining was inferred.

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In this study, we synthesized a polymer extractant and its monomer analogue, and the multifunctional effect was investigated by comparing their extraction behavior for Au(III). To increase the affinity for gold ions, we introduced a sulfur atom into the molecular structure of the extractant as a soft donor. The extraction ability of the new extractants for gold ions was influenced by the HCl concentration in the aqueous feed solution. The multifunctional effect appeared when using the polymer extractant in the liquid-liquid extraction of gold ions. Selectivity of the extractants toward Au(III) was evaluated using a model solution generated from leaching of waste cellphones. Selectivity for Au(III) was found to be enhanced by the multifunctional effect of the polymer extractant.

The precious metals such as silver, gold, palladium and platinum are important metals in industries such as catalyst, battery and electronics. These metals have stimulated the investigation of separation and purification by solvent extraction techniques because very high purity of these metals is required in these industries. [1][2][3][4] Solvent extraction of metal ions with chelate agents such as LIX series reagents has recently attracted interest through hydrometallurgical and waste-water treatment processes. [5][6][7][8][9] An extractant containing sulfur as a donor atom has a high selectivity for platinum metals. Few works on the extraction reactions with such an extractant have been carried out. 10,11 Baba and Inoue 12,13 studied the mechanism of palladium extraction with dihexyl sulfide, concluding that the ratedetermining step was the reaction between the intermediate of trichloropalladium-extractant complex adsorbed at the interface and the extractant dissolved in the aqueous phase. In the case of 1,2-bis(tert-hexylthio)ethane, the rate-determining step was the reaction of the extractant dissolved in the aqueous phase with PdCl3 -and PdCl4 2-in the aqueous phase, because 1,2-bis(terthexylthio)ethane had no interfacial activity and its aqueous solubility was relatively high.A previous paper 14 reported that t-hexadecylthiomethylpyridine (DTMP) including nitrogen and sulfur atoms has a high affinity for palladium, platinum and silver from an ammonium nitrate solution. In this study, the extraction rate of palladium with 2-dodecylthiomethylpyridine (DTP) from hydrochloric acid was examined using a stirred transfer cell. Measurements of palladium-loading capacity and aqueous solubility of extractant were also examined in order to elucidate the extraction mechanism. ExperimentalReagents 2-Dodecylthiomethylpyridine (DTP) was synthesized from ndodecylthiol and 2-chloromethylpyridine according to a conventional method. 14 The reaction mixture was evaporated. Water and chloroform were added to the reaction mixture and then the two phases were separated with a separatory funnel. Chloroform phase was successively washed using 0.1 mol dm -3 hydrochloric acid mixed with sodium chloride as a salting out reagent, 1.0 mol dm -3 aqueous sodium hydroxide and distilled water. The final product was a viscous brownish liquid. Identification of the purified product was carried out using 1 H-NMR, 13 C-NMR and FT-IR spectra. The product was identified as DTP and its purity was 97% as measured by gas chromatography. Selectivity of DTP for metal ionsThe aqueous phase was prepared by dissolving metal chloride into hydrochloric acid. The organic phase was prepared by dissolving with chloroform gravimetrically. Selectivity of metal ions was measured by a batchwise-method at 303 K for 24 h. 2-Dodecylthiomethylpyridine (DTP) was newly synthesized to study its extraction properties for precious metals. DTP was a selective extractant for palladium(II) and gold(III) over base metals. The loading test for palladium(II) showed that one pa...

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