INFLUENCE OF THE AMINE NATURE ON THE COMPOSITION OF PALLADIUM COMPLEXES IN SOLVENT EXTRACTION SYSTEMS

ABSTRACT

The extraction of palladium chloro complexes by di-n-octylamine and diamines of various structure as function of the composition of the aqueous and organic phases has been studied. The compositions of the extracted species are indicated and the mechanisms of their distribution are described. It was shown that from 1 to 3 M HC1 solutions. complexes such as (R₂NH₂)₂PdCl₄ solvated by molecules of dioctvlamine chloride are extracted. With increasing the initial concentrations of palladium or decreasing acidity of the aqueous phase, a direct coordination takes place, first of one and then two molecules of amine to atom of palladium with the formation of extracted compounds such as HC1 solutions by salts of amines, diamines and QAB ionic associates such as (AmH)₂PdCl₄, (AmH)₂)PdCl₄ and (R₄N)₂PdCl₄, respectively, are recovered into the organic phase. In systems containing trioctylamine, tetraoctylalkylenediamines (n = 4, 6) and QAB. ionic associates containing the dimeric complex anion, Pd₂Cl₆ ^2-, are also formed. When primary (n-octylaniline - OA) and secondary amines are used as extractants the formation of dimeric species in the organic phase is not observed.

The extraction of palladium from weakly acidic and neutral solutions can proceed through a combination of anion-exchange and coordination mechanisms with the formation of (AmH)[Pd(Am)Cl₃] in systems with primary and secondary amines, and through a coordination mechanism with the formation of complexes such as Pd(Am)₂Cl₂ in systems with primary, secondary and tertiary amines. When palladium is extracted by diamines with a short hydrocarbon chain (n=2) the formation of coordination compounds also takes place.     

EQUILIBRIUM OF PALLADIUM(II) EXTRACTION WITH 1-OCTYLTHEOBROMINE

ABSTRACT

1-Octyltheobromine was synthesized to study extraction equiliburium of palladium(II). To evaluate its efficiency as an extractant, the extraction of palladium(II) from acidic chloride media was studied at 303K using toluene. The extraction of palladium(II) from hydrochloric acid media by 1-octyltheobromine exhibited high selectivity for palladium(II) over the platinum group metals. The stoichiometrics of the extraction of palladium(II) with 1-octyltheobromine was elucidated by examining the effects of hydrochloric acid, chloride ion, hydrogen ion, extractant and metal ion concentrations on its extractability. Palladium(II) was found to be extracted as two molecules of 1-octyltheobromine reacted with PdCl₂ as follows: PdCl₂ +{2}¯RN ? ¯PdCl₂(RN)₂. The extraction equilibrium constant was K=2.72?×?10⁸(mol?dm^?3)^?2. The complex of 1-octyltheobromine with PdCl₂ was confirmed by mass spectrometric analysis. The stripping of palladium(II) was performed over 60% by a single batchwise treatment with an aqueous solution of thiourea or ammonia.     

SOLVENT EXTRACTION OF PALLADIUM(II) WITH A SULFUR-CONTAINING CARBOXYLIC ACID

The mechanism of solvent extraction of palladium (II) from aqueous ammonium chloride solution with α-butylthiolauric acid( α-BTLA = S) in toluene was investigated in terms of extraction equilibrium and kinetics at 303 K. From the results of extraction equilibrium, it was found that α-BTLA behaves as a solvating extractant for palladium(II) and that the extracted species is a 1:2 metal:reagent complex, PdCl₂S₂ The extraction rate of palladium(II) was measured in a batch-type vigorously stirred cell. The effects of the concentrations of palladium(I I), hydrogen ion, chloride ion and extractant on the extraction rate were quantitatively interpreted by a reaction mechanism where the parallel reactions of α-BTLA with PdCl₃(H₂0)- and PdCl₄ ^2- are the rate-determining steps.     

Liquid–liquid extraction of Hg(II) from acidic chloride solutions using bis‐2‐ethylhexyl sulfoxide

The liquid–liquid extraction of Hg(II) from acidic chloride solutions has been studied using bis‐2‐ethylhexyl sulfoxide (B2EHSO) as an extractant. For comparison, extraction studies have also been carried out using di‐n‐octyl sulfoxide (DOSO) and diphenyl sulfoxide (DPhSO). The extraction data have been analysed by both graphical and theoretical methods taking into account aqueous phase speciation and all plausible complexes extracted into the organic phase. These results demonstrate that Hg(II) is extracted into xylene as HgCl₂.3R₂SO (where R₂SO represents the sulfoxide). The equilibrium constant of the extracted complex has been deduced by non‐linear regression analysis. The developed liquid–liquid extraction procedure has been applied for the recovery of mercury from the brine‐sludge of a Chlor‐Alkali plant. © 2001 Society of Chemical Industry     

Palladium(II) complexes with polyphosphazene

An allylphenoxy-substituted polyphosphazene has been modified via inorganic chemical concepts. The transition metal salt is bis(acetonitrile)dichloropalladium(II). The coordination complexes have been characterized using acid-base solution chemistry, sol-gel phase transitions, thermomechanical property measurements and infrared spectroscopy. Solid complexes of polyphosphazene and PdCl₂ cannot be dissolved in the original solvent (i.e., tetrahydrofuran) used during sample preparation. These polymeric palladium complexes also cannot be disrupted by a stronger base, like triphenylphosphine. There is a monotonic increase in the glass transition temperature at higher concentrations of palladium chloride. T_g of the pure polymer increases by 21°C in the presence of 10 mol% palladium chloride. The increase in high-strain mechanical properties cannot be explained solely by a “filler effect.” At higher PdCl₂ concentrations, there is a direct correlation between the enhancement in T_g, higher mechanical fracture stress, and increased infrared absorbance @ 1092 cm^?1 because of the formation of a palladium-π-complex with allylic substituents in the phenoxy sidegroup. Palladium chloride relinquishes its acetonitrile ligands after dissolution in THF, and the vacant sites in the first-shell coordination sphere of the transition metal are occupied by these allylic substituents in the sidegroup. This produces interchain coordination crosslinks, which modify the thermomechanical properties of polyphosphazene/ PdCl₂ complexes.     

SOLVENT EXTRACTION OF PALLADIUM(II) WITH A SCHIFF BASE AND SEPARATION OF PALLADIUM FROM Pd(II)-Pt(VI) MIXTURE

ABSTRACT

A new Schiff base extractant, N,N'-bis[l-phenyl-3-methyl-5-hydroxy-pyrazole-4-benzylidenyl]-l,3-propylene diamine (H₂A) was synthesized and characterized. The extraction mechanism of palladium(II) from HNO₃ or HClO₄ medium with H₂A in chloroform or toluene was investigated. The influences of the Schiff base concentration in the organic phase, the concentration of palladium, the pH and anions (Cl^?, S0₄ ^?, NO₃ ^?, ClO₄ ^?) in the aqueous phase and the temperature on the distribution ratio for palladium (II) have been examined. The extracted complex has been confirmed by chemical analysis, thermoanalyses and IR spectroscopy. It was found that palladium is extracted according to the following extraction reaction:

The extraction equilibrium constants of palladium(II) were 8·4 and 21·3 in chloroform and toluene diluents, respectively. The values for the enthalpy and standard free energy of extraction were also obtained. The separation of Pd(II) from the mixed solution of Pd(II)-Pt(IV) was achieved by adjusting the pH.     

Fatty Imidazolines: A Novel Extractant for the Recovery of Palladium(II) from Hydrochloric Acid Solutions

The extraction of palladium(II) from hydrochloric acid solutions with a novel highly basic extractant, a mixture of homologous 1-[2-(alkanoylamino)ethyl]-2-alkyl-2-imidazolines (AAI) in toluene with 15% (v/v) of n-octanol was studied. Palladium(II) is rapidly and most effectively extracted with AAI hydrochloride at the low hydrochloric acid (chloride ions) concentration (up to 1 M) and can be completely separated from Fe(III), Cu(II), and Co(II). The palladium(II) extraction at the optimum acidity occurs via an anion-exchange mechanism with the formation of ionic associates (LH)₂PdCl₄ (K _ex = (1.5 ± 0.2) · 10⁴ at 0.5 M HCl) and is accompanied by the dimerization of palladium(II) in the organic phase with the formation of ionic associates (LH)₂Pd₂Cl₆ (K _dim = (3.9 ± 0.4) · 10^?4 at 0.5 M HCl). The anion-exchange extraction of palladium(II) at the acidity of 0.5 M HCl is temperature independent in the range 20–49°C. Complete stripping of palladium(II) can be performed using a 5% solution of thiourea in 0.1 M HCl.     

SELECTIVE EXTRACTION OF PALLADIUM(II) FROM CHLORIDE SOLUTIONS WITH NONYLTHIOUREA DISSOLVED IN CHLOROFORM

ABSTRACT

The extraction of Palladium(II) [Pd(II)] from hydrochloric acid solutions with nonylthiourea (NTH) dissolved in chloroform at a constant ionic strength of 1.0?M has been studied. The extraction of Pd(II) has been investigated as a function of the concentration of the extractant, chloride ion, and proton concentrations as well as extraction temperature. The distribution data have been treated graphically and numerically. The analysis of the experimental data has shown that Pd(II) is extracted as PdCl₂·(NTH) and PdCl₂·(NTH)₂ species with the respective extraction constants of log?K ₁₁=5.0±0.1 and log?K ₁₂=9.1±0.1. The back-extraction of Pd(II) from the organic phase using different stripping reagents has been examined. The selectivity of NTH for Pd(II) against Pt(IV), Rh(III), Cu(II), Fe(III), and Zn(II) has also been investigated.     

The extraction of anionic complexes of divalent manganese,cobalt, nickel and copper from aqueous thiocyanate solutions by tricaprylmethylammonium chloride

The extraction of divalent manganese, cobalt, nickel and copper-thiocyanato anionic species from aqueous solutions by tricaprylmethylammonium chloride (R₃R′NCl) in benzene has been investigated under different conditions. Both the aqueous and organic phases have been examined by spectrophotometry. Infrared spectro-photometry and measurements of water content, apparent molecular weight and magnetic moment have been applied to the organic extracts, and electron spin resonance experiments to the organic manganese(II)- and copper(II)-complexes. The mechanism of the extractions and the structures of the extracted complexes are discussed on the basis of the results obtained. As a result, it is found that although the extraction efficiency follows the order Co > Cu > Mn > Ni, the extraction of divalent transition metals is expressed as [M(NCS)₄]²-(aq) + 2R₃R′NNCS(org)→(R₃R′N)₂-[M(NCS)₄](org) + 2NCS-(aq) in which M = Mn, Co, Ni and Cu. The extracted species of divalent manganese, cobalt and nickel give a tetrahedral T_d symmetry, and the copper(II) species is in a distorted tetrahedron (point group D_2d symmetry). In addition the species of nickel (II) extracted at low aqueous concentration exists as a complex (R₃R′N)₂[Ni(NCS)₄(H₂O)₂] in an octahedral arrangement.     

Effect of Br− on the Adsorption Rate of Palladium(II) Ions onto Condensed-Tannin Gel in Chloride Media

Abstract

In chloride media, chloropalladium(II) species are adsorbed onto tannin gel particles through an inner-sphere redox reaction mechanism containing the intermediate step, formation of a ligand-substituted Pd(II)-tannin complex. In this Pd(II) adsorption process, it was observed that the adsorption rate can be increased by introducing Br^?, a softer ligand than Cl^?, into the aqueous chloride solution. The formation of mixed-ligand palladium(II) complexes accelerates the rate of ligand-substitution reactions with the hydroxyl groups of tannin gel by the trans effect. The adsorption condition can be optimized by controlling the [Br_tot]/[Cl_tot] ratio, in which the predominant Pd(II) species are bromo-chloro palladium(II) complexes, the favorable species for the trans effect.     

Extraction of platinum and palladium from hydrochloric solutions by trioctymethylammonium dinonylnaphthalenesulfonate

We investigated the phase distribution of chloride complex platinum and palladium acids in the presence of the binary extracting agent trioctylmethylammonium dinonylnaphthalenesulfonate. During the extraction of H₂PtCl₆ and H₂PdCl₄, the distribution coefficients were found to decrease as long as the pH value was growing, in full accordance with the known general trend of binary extraction. In contrast to the extraction variant using quaternary ammonium bases with inorganic counterions, a binary system, which was based on dinonylnaphthalenesulfonic acid, could be used for the further aqueous reextraction of platinum metals from the organic phase because of the higher thermodynamic stability of the binary reagent in the two-phase system.     

NEW XANTHIC ACID DERIVATIVES AS POTENTIAL REAGENTS IN THE SOLVENT EXTRACTION OF PRECIOUS METAL IONS: EXTRACTION OF PALLADIUM(II) WITH 13-BIS(0-BUTYLXANTHATO)PROPANE

ABSTRACT

Two series of new xanthic acid derivatives namely, the bis (O-butylxanthato) alkanes ( abbreviated as BBXAs or simply as bis-xanthates in this paper) have been synthesized in connection with the solvent extraction of precious metal ions. From an aqueous medium containing 0.1 M NaC10₄ (1 M=l mol dm^-3), these compounds exhibited high selectivity for extraction of Pd(II) and Ag(I) in dichloroethane, over most of the base metals as well as Pt(IV) and Au(III) ions. Towards Pd(II) and Ag(I) ions, the bis compounds act as SS chelating agents where the stabilities of the extractable complexes are determined by the length of the alkylene chain existing between the donor atoms. Pd(II) extraction has been studied in detail taking 13-bis(O-n-butylxanthato)propane (BnBXP) as the representative member of the series of bis-xanthates synthesized in this work. The extraction of palladium(II) was found to be quite slow in pure chloride medium. But, a mixed acid medium containing H₂SO₄ or HNO₃ in the presence of smaller amount of chloride ion provided optimum reversible extraction of palladium in dichloroethane, where Pd(II) forms 1:1 extractabic complexes with BnBXP. Pd(II) extraction is described in terms of the aqueous phase compositions, extraction and back-extraction data, extraction equilibrium, selectivity considerations and probable mechanisms of extraction.     

A new route to preparation of palladium catalysts for VOC combustion

Methyltheophylline is known to be effective and highly selective extractant for Pd in the solvent extraction process. The high selectivity for Pd extraction might be due to the formation of chelate complex of Pd and methyltheophylline. The chelate complexes made insoluble precipitate in organic solvent when it became a certain condition. Partially-oxidized Pd nanoparticles below 100 nm were obtained by calcination of the precipitate. Pd/γ-Al₂O₃ and Pd/cordierite honeycomb catalysts were prepared by conventional impregnation method using the organic solvent containing Pd extracted from aqueous solution, and their catalytic activities for toluene combustion were compared with that of the Pd catalysts prepared from PdCl₂ aqueous solution. Consequently, the Pd catalyst prepared by using Pd extracted organic solvent showed remarkably higher activity for toluene combustion than that prepared from PdCl₂ aqueous solution.     

Transport of Iron and Cobalt Complex Ions through Liquid Membrane Mediated by Methyltrioctylammonium Ion with the Aid of Redox Reaction

Abstract

A new type of carrier-mediated metal transport through liquid membrane is presented. The system involves redox reactions rather than acid-base reactions which have often been utilized in metal transport systems. Iron ion was selectively transported and concentrated through the membrane via a chloride complex by use of a lipophilic quaternary ammonium ion, methyltrioctylammonium (MTOA, Q⁺), as a carrier. The two aqueous solutions of different redox potentials were separated by a polymer-supported liquid membrane in which MTOA · chloride (Q⁺·CI^?) was dissolved as the carrier. Iron(III) ion in hydrochloric acid media formed a FeCl₄ ^? type complex which was readily extracted to the organic membrane phase as an ion-pair complex Q⁺·FeCl₄ ^?. On contact with a reducing agent on the other side of the membrane, iron(III) was reduced to iron(II) and liberated into aqueous solution; the chloride complexes of iron(II) are too hydrophilic to stay in the membrane phase. On the other hand, cobalt ion was transported via nitrilotriacetic acid (NTA) complex by MTOA carrier in a similar manner to the iron transport. The nature of the transport reactions was studied under various operational conditions (redox agents, carrier and ligand concentration, pH, coexisting metals, etc.). The extension of these transport reactions to a water-in-oil-in-water type emulsion system as well as to a photoassisted transport system was studied.     

Extraction of Palladium(II) from Nitric Acid Solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea

The extraction of palladium (II) from HNO₃ solutions with 1‐Benzoyl‐3‐[6‐(3‐benzoyl‐thioureido)‐hexyl]‐thiourea (Ia) and several monodentate thiourea derivatives in 1,2‐dichloroethane has been studied. The effect of HNO₃ concentration in the aqueous phase and that of the extractant in the organic phase on the Pd(II) extraction is considered. The stoichiometry of the extracted complexes has been determined. The increasing number of thioamide groups in the molecule of Ia increases its extraction efficiency towards Pd(II). The potentialities of a polymeric resin impregnated with compound Ia for selective extraction of Pd(II) from nitric acid solutions are demonstrated.     

Extraction of Lanthanides(III) from HClO4 Solutions with Bis(diphenylphosphorylmethylcarbamoyl)alkanes

Abstract

Novel polyfunctional neutral organophosphorus compounds, namely bis(diphenylphosphoryl-methylcarbamoyl)alkanes of general formula [Ph₂P(O)CH₂C(O)NH]₂(CH₂)_n (I-III; n = 3, 5, 8), were synthesized and studied as extractants for La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y from perchloric acid solutions. The influence of both of HClO₄ concentration in the aqueous phase and that of the extractant in the organic phase on the extraction of metal ions is considered. The stoichiometry of the extracted complexes has been determined. Bis(diphenylphosphorylmethylcarbamoyl)alkanes II and III possess a higher extraction efficiency towards Ln(III) than their monoanalogue Ph₂P(O)CH₂C(O)NHC₉H₁₉. The potentialities of polymeric resin impregnated with bis(diphenylphosphorylmethylcarbamoyl)pentane II for the preconcentration of lanthanides(III) from perchloric acid solutions are demonstrated.     

Search for Optimum Conditions of Extraction of Transition Metal Complexes with Alkylimidazoles. I. Extraction of the Co(II), Ni(II), and Zn(II) Complexes of 1-Methylimidazole and of the Co(II) and Zn(II) Complexes of 2-Methylimidazole

Abstract

It has been shown that for the Co(II), Zn(II), and Ni(II) complexes of 1-methylimidazole and for the Co(II) and Zn(II) complexes of 2-methylimidazole, the partition coefficient D between the aqueous and organic phases is proportional to the degree of formation α _n of a definite complex. Tetrahedral species have been found to be extracted with the Co(II) and Zn(II) complexes of 2-methylimidazole and with the Zn(II) complexes of 1-methylimidazole.     

The Influence of the Alkyl Chain Length on Extraction Equilibrium of Cu(II) Complexes with 1‐Alkylimidazoles in Aqueous Solution/Organic Solvent Systems

Abstract

The partition of Cu(II) complexes with 1‐alkylimidazoles (with alkyl ranging from 1‐n‐butyl through 1‐n‐hexadecyl) between the aqueous ((0.5HL, K)NO₃) and organic phase has been studied at 25°C. The organic solvents used were toluene, p‐xylene, tetrahydronaphthalene, dichloromethane, 2‐ethyl‐1‐hexanol, and others. Extraction curves have been shown to be displaced towards lower pH values with increasing alkyl chain length of the alkyl substituent. Stability constants of the Cu(II) complexes with the 1‐alkylimidazoles have been determined in the aqueous phase as well as the number of compounds extractable into the organic solvent, and their partition ratios. Stability constants of the complexes did not depend on the alkyl chain length. One or two complexes were transferred to the organic phase. Partition ratios of these complexes, P ₁ and P ₂, increased rapidly with increasing alkyl chain length. They were higher in magnitude than those of their Co(II), Ni(II), and Zn(II) counterparts.     

The Extraction of Divalent Manganese,Cobalt, Copper,Zinc, and Cadmium from Hydrochloric Acid Solutions by Tri-n-octylamine

Abstract

The distribution of divalent manganese, cobalt, copper, zinc, and cadmium between hydrochloric acid solutions and solutions of tri-n-octylamine (TOA, R₃N) in benzene has been investigated under different conditions. It is found that the extraction of these divalent metals by TOA proceeds as MCl₂(aq) + 2R₃NHCl(org) ? (R₃NH)₂MCl₄(org). The electronic, electron spin resonance, and infrared spectral results indicate that all the complexes formed in the organic phases are in a tetrahedral arrangement. Further, the stability constants of the aqueous chloro complexes of divalent manganese, cobalt, copper, and zinc are determined on the basis of the equilibrium equation.     

CeO2 Nanocrystalline-Supported Palladium Chloride: An Effective Catalyst for Selective Oxidation of Alcohols by Oxygen

The present paper reports on the use of CeO₂ materials supported palladium chloride catalyst for selectively oxidising organic alcohols into aldehydes. Spherical, microsized rod-shaped and spindle-like CeO₂ particles are synthesised and characterised by SEM. The catalysts are prepared by loading palladium chloride onto the CeO₂ support matrix. A complete characterization of the catalysts is performed. The activity of catalysts is studied by the selective oxidation of various alcohols. The results show that (1) the catalytic activities prepared by spherical cerium are superior to the catalysts prepared by spindle-like or rod-shaped cerium and (2) the catalyst PdCl₂/CeO₂ (nanospheres) show good activity, high yield, and good stability.