Takahiko Kakoi

Extraction of rare-earth metals by liquid surfactant membranes containing a novel cyclic carrier

Abstract Extraction behavior of three rare-earth metals (Ho, Er and Y), was systematically studied by liquid surfactant membranes (LSMs) containing a novel host compound, a calixarene carboxyl derivative, which is a cyclic compound connected to some phenol rings, as a mobile carrier in a stirred cell. Using the host compound, the extraction equilibrium of the metals in liquid-liquid extraction was also investigated in order to elucidate the complexation mechanism between the metal ions and the cyclic compound. The calixarene carboxyl derivative showed a high extractability for all rare-earth metal ions compared with the analog monomer compound. The extractability for the rare-earth metals was found to increase in the following order: monomer

SOLVENT EXTRACTION OF PALLADIUM WITH BIS(2,4,4,-TRIMETHYLPENTYL)DITHIOPHOSPHINIC ACID AND BIS(2,4,4,-TRIMETHYLPENTYL)MONOTHIOPHOSPHINIC ACID

ABSTRACT Solvent extraction of palladiura(0) with bis(2,4,4,-trimethylpentyl) dithiophosphinic acid (CYANEX 301) and bis(2,4,4,-trimethylpentyl) monothiophosphinic acid (CYANEX 302) in n-heptane diluent was carried out. Measurement of palladium-loading capacity and stripping of palladium extracted by these extractants was also investigated. It was found that both CYANEX 301 and 302 have a high ability of palladium extraction and form the complexes of (palladium) 1 : (CYANEX 301) 1 or (palladium) 1 : (CYANEX 302) 2, individually. The stripping of palladium extracted was very difficult. But when thiourea was used as a stripping reagent, the stripping of these palladium complexes was completely performed.

Separation of platinum and palladium by liquid surfactant membranes utilizing a novel bi-functional surfactant

Abstract Using a bi-functional surfactant which has abilities both as an emulsifier and a carrier, the separation of platinum and palladium by liquid surfactant membranes (LSMs) has been conducted in a stirred tank. The effects of several operational conditions on the behavior of metal extraction and the emulsion stability in LSMs were systematically studied. The bi-functional surfactant not only stabilized a W / O emulsion in a relatively low concentration but also showed a high extraction ability for platinum. Using the bi-functional surfactant, platinum was extracted quickly and concentrated effectively from an external feed solution into an internal recovery phase of W / O emulsions through a thin liquid membrane. Further, the extraction kinetics of the metals by LSMs containing the bi-functional surfactant was examined. The hydrophobic structure of the surfactants was found to be one of the important factors in ensuring a high extraction rate of metal ions by LSMs. An interfacial reaction model which takes into account the adsorption of the surfactant at the interface has been proposed to evaluate the permeation rate of metals by LSMs. The newly developed surfactant appears to be one of the best surfactants currently available for platinum-group metal extraction by liquid surfactant membranes.

Selective recovery of palladium from a simulated industrial waste water by liquid surfactant membrane process

The selective recovery of palladium from an acidic solution of high iron concentration with liquid surfactant membranes (LSMs) containing di-2-ethylhexyl monothiophosphoric acid (commercial name MSP-8) as a carrier has been conducted in a batch and a continuous system using a mixer-settler. In the batch operation, the effects of several chemical species and their concentrations on the recovery of palladium were discussed. Using a relatively low concentration of PX100, stable emulsions were obtained and a high degree of palladium recovery was performed by a LSM technique. The concentration of thiourea employed as a stripping agent greatly affected the efficiency of palladium recovery. Under optimum conditions, palladium ions were separated from a large amount of iron ions and they were concentrated from the external feed aqueous solution into the inner receiving phase of W/O emulsions. Furthermore, an effective recovery of palladium could be achieved in a continuous operation using a mixer-settler under the optimum conditions for the batch system.

Extraction of palladium by liquid surfactant membranes using new surfactants

Abstract Using novel synthetic surfactants, the extraction of palladium(II) by liquid surfactant membranes (LSM) containing didodecylmonothiophosphoric acid as a carrier was conducted in a stirred cell. The role of the surfactants on the extraction behavior of palladium by the LSMs was systematically studied. It was found that the stability of the emulsion and the permeation rate of palladium are strongly influenced by the surfactants used. The effects of the surfactant, extractant, internal hydrogen ion and thiourea (stripping reagent) concentrations on the palladium extraction are discussed. The presence of thiourea in the internal aqueous phase is a key factor in palladium extraction with an LSM. Extraction of more than 95% could be attained in a few minutes under optimum surfactant and carrier concentrations.

Effect of sodium ions on the extraction of rare earth metals by liquid surfactant membranes containing a calix[4]arene carboxyl derivative

A novel host compound calixarene has been applied as a mobile carrier for the separation and concentration of rare earth metals by liquid surfactant membranes (LSMs). Using the novel carrier, extraction of rare earth metals (Ho, Er and Y) by LSMs was systematically studied in a stirred cell. Extraction behavior of rare earth metals by the carboxyl derivative of calix[4]arene was found to be extremely sensitive to coexisting sodium ions in the feed solution. The extractability of rare earth metals was remarkably enhanced by the addition of sodium ions. The permeation rate of rare earth metals through the LSMs in the presence of sodium ions was 100-fold higher than that without sodium ions. This enhancement of the permeation rate is attributed to the preferential conformation change in the host compound of calixarene initiated by sodium ions. The permeation mechanism of rare earth metals by LSMs is elucidated by an interfacial reaction model.

EXTRACTION MECHANISM OF PALLADIUM WITH DIDODECYLMONOTHIOPHOSPHORIC ACID IN HEPTANE DILUENT

ABSTRACT Kinetic study of the extraction of palladium(D) with didodecylmonothiophosphoric acid in n-heptane diluent was carried out using a stirred transfer cell to clarify the extraction mechanism. The effect of surfactants on the kinetics of palladium extraction was also investigated, to elucidate the role of surfactants used in liquid surfactant membranes. Moreover, the interfacial tension between the organic and aqueous phases was measured to elucidate the adsorption equilibrium of the surfactants. It was found that the interfacial activity of each surfactant is higher than that of the extractant. In the kinetic study of palladium extraction, the experimental results of the extraction rate was analyzed by the interfacial reaction model, taking into account of the adsorption of the surfactant and extractant. The rate-determining step of palladium extraction was the complex formation between four chloro-palladium complexes and the extractant at the interface, and the extraction rate constants of each pa...

Permeation behavior of rare earth metals with a calix[4]arene carboxyl derivative in a hollow-fiber membrane

Abstract Extraction of three rare earth metals (Er, Ho and Y) was performed by a microporous hydrophobic hollow-fiber membrane extractor using a novel calix[4]arene carboxyl derivative in toluene. It was found that the permeation rate through the membrane of metal ions with calix[4]arene carboxyl derivative was relatively slow, while the addition of a small amount of sodium ion into the aqueous solution drastically accelerated the permeation rate and also enhanced the selectivity between heavy rare earth metals (Er and Ho) and Y. The experimental results obtained under a variety of conditions were analyzed by a diffusion model which combined with the complexation reaction at the aqueous-organic interface, taking account of the velocity distribution of the aqueous and organic solutions through the inner and outer sides, respectively, of the hollow-fiber membrane extractor. The model well explained the permeation behavior of the rare earth metals through the membrane and the role of sodium ion on the acceleration effect of the permeation rate.

Recovery of Palladium from an Industrial Wastewater Using Liquid Surfactant Membranes

Abstract Selective recovery of palladium from an industrial wastewater including a large amount of iron was studied by liquid surfactant membranes (LSMs) prepared with a sulfur-containing extractant as a carrier in a stirred cell. The extraction behavior of palladium and iron ions in liquid-liquid extraction was also investigated in order to choose an appropriate carrier for the LSM operations. Palladium ions were found to be extracted selectively over iron ions by using the sulfur-containing extractant from an acidic aqueous solution. The effects of several chemical species and operation factors on the recovery of palladium by LSMs were systematically examined with several kinds of sulfur-containing carriers and thiourea as a stripping reagent. The selection of carrier is a key factor for designing an efficient recovery process of palladium with an LSM technique. Di-2-ethylhexyl monothio-phosphoric acid (commercial name MSP-8) appears to be one of the best carriers currently available for palladium recov...

Separation of Cobalt and Nickel by Liquid Surfactant Membranes Containing a Synthesized Cationic Surfactant

ABSTRACT Separation of cobalt(II) and nickel(II) by using a hydroxyoxime extractant has been investigated both in liquid-liquid extraction and in a liquid surfactant membrane(LSM) system. In the liquid-liquid equilibrium extraction studies, hydroxyoximes showed significant extractability for nickel ions, although LIX 84 was found to have exceptional chelating affinity for nickel ions. In the LSM system functionalized by hydroxyoxime, the cobalt ions were efficiently separated from nickel ions as a result of slower permeation of nickel chelates across the emulsion membrane. More complete cobalt recovery was achieved in the LSMs dosed with LIX 860 than when the same carrier was applied to the liquid-liquid extraction system. Furthermore, cobalt permeation rate was enhanced threefold when a quaternary ammonium type of cationic surfactant was used as an emulsifier due to carrier interaction with surfactant at the reaction interface. The permeation mechanism of ions in LSMs was elucidated by an interfacial rea...