SORPTION OF PLATINUM GROUP METALS AND GOLD CHLOROCOMPLEXES BY AMINE POLYMERIC SORBENTS

ABSTRACT

The results of an investigation on the sorption of platinum group metals and gold chlorocomplexes by anion-exchangers and complexing sorbents containing amine groups from HC1 solutions are reported. The sorption mechanism is discussed on the base of the obtained extraction data. The complexformation of ruthenium(III) with the amine groups in the sorbent phase was studied by EPR method.     

Extraction of Rhodium Chlorocomplexes and Acid through a Supported Liquid Membrane of Kelex 100

Abstract

The supported liquid membrane (SLM) technique was employed to effect the separation of Rh Chlorocomplexes from hydrochloric acid solutions. The liquid membrane consisted of an alkylated 8-hydroxyquinoline extractant (Kelex 100), tridecanol, and kerosene. The nonaquated Rh complexes were transported through the membrane upon ion-pair formation with protonated Kelex 100 molecules. The ion-pair was then dissociated at the strip side of the membrane, releasing the Rh values. The main driving force for this transport process was the acid activity gradient across the membrane. The permeation of acid and water, which were cotransported with the Rh complexes, was partially prevented upon addition of NaCl to the strip phase. However, the accumulation of Cl^? ions in the strip phase, in turn, slowed down the extraction of Rh. Optimum Rh extraction performance was obtained when a feed of 2.5 M HC1 and a strip solution of pH 1 were used. Under these conditions the membrane was found to be very stable for at least a period of 72 hours (maximum period tested) while the rate of extraction was found to be 2.8 × 10^?6 mol·s^?1·m^?2.     

Effect of composition and ageing of chloride solutions on extraction of Rh(III) and Ru(III) with phosphonium ionic liquids Cyphos IL 101 and IL 104

ABSTRACT

Rhodium(III) and ruthenium(III) were extracted from chloride solutions with phosphonium ionic liquids trihexyl(tetradecyl)phosphonium chloride or trihexyl(tetradecyl)phosphonium bis(2,4,4-trimethylpentyl)phosphinate in toluene. Influence of HCl and NaCl presence in the feed and IL concentration in the organic phase were determined. Rh(III) transport appeared to be inefficient, while over 70% of Ru(III) was extracted from 3 M HCl. Ru(III) extraction was affected by the feed acidity and the type of extractant used. The spectra of the extracts indicated some changes in the structure of Rh(III) and Ru(III) complexes in the organic phase. Also, ageing of feed solutions on the extraction of Ru(III) and Rh(III) was studied.     

Extraction separation of Ir(III) and Rh(III) with Cyanex 923 from chloride media: a possible recovery from spent autocatalysts

Liquid–liquid extraction of Ir(III) and Rh(III) with Cyanex 923 from aqueous hydrochloric acid media has been studied. Quantitative extraction of Ir(III) was observed in the range of 5.0–8.0 mol dm^?3 HCl with 0.1 mol dm^?3 Cyanex 923, while Rh(III) was extracted quantitatively in the range of 1.0–2.0 mol dm^?3 HCl with 0.05 mol dm^?3 Cyanex 923 in toluene along with 0.2 mol dm^?3 SnCl₂. The Ir(III) was back extracted with 4.0 mol dm^?3 HNO₃ quantitatively from the organic phase while Rh(III) was stripped with 3.0 mol dm^?3 HNO₃. The extraction of Rh(III) with Cyanex 923 was not quantitative without use of SnCl₂. However in the extraction of Ir(III) a negative trend was observed in the presence of SnCl₂. Varying the temperature of extraction showed that the extraction reactions of both the metal ions are exothermic in nature, and the stoichiometric ratio of Ir(III)/Rh(III) to Cyanex 923 in organic phase was found to be 1:3. The methods developed were applied to the recovery of these metal ions from a synthetic solution of similar composition to that from leaching of spent autocatalysts in 6.0 mol dm^?3 HCl. © 2002 Society of Chemical Industry     

Study of the Sorption and Separation Abilities of Commercial Solid‐Phase Extraction (SPE) Cartridge Oasis MAX Towards Au(III), Pd(II), Pt(IV), and Rh(III)

Abstract

This paper presents a new, simple, and rapid procedure for the separation and preconcentration of Au, Pt, Pd, and Rh based on the adsorption of the metals on a commercial solid‐phase extraction (SPE) cartridge, Oasis MAX, which contains a polymeric resin with quaternary ammonium substituents. Adsorption studies revealed that the metal affinity towards the adsorbent ranked according to Au?Pd>Pt whereas Rh was not retained. The elution of the metals was accomplished by using 0.5 M thiourea in 1 M HCl solution. This sorbent effectively recovered Pd and Pt from a spent car catalyst sample containing large amounts of metals such as Al, Fe, and Ce.     

Comparison of separation behavior of Ir(IV) and Rh(III) between tin(II) chloride and ascorbic acid as a reducing agent in the extraction with Cyanex 921 and Cyanex 301

In order to compare the separation of Ir(IV) and Rh(III) between SnCl₂ and ascorbic acid as a reducing agent, solvent extraction with Cyanex 921 and Cyanex 301 was investigated in the HCl concentration range from 1 M to 9 M. Addition of both SnCl₂ and ascorbic acid led to the selective extraction of rhodium by the two extractants, leaving Ir(III) in the raffinate. Since tin was selectively extracted over Rh(I) in the presence of SnCl₂, it is necessary to separate Rh(I) and tin by selective stripping from the organic phase. In the presence of ascorbic acid, the extraction percentage of rhodium by Cyanex 921 was much smaller than that in the presence of SnCl₂. UV spectra was analyzed to verify the reduction reaction of both metal ions. FT-IR was analyzed between fresh and loaded organic solution. The reduction of Ir(IV) and Rh(III) in the presence of ascorbic acid was explained. Selective stripping of Rh(I) over tin from the loaded Cyanex 921 was obtained by the mixture of HCl and (NH₂)₂CS.     

RECOVERY AND SEPARATION OF PLATINUM GROUP METALS USING IMPREGNATED RESINS CONTAINING ALAMINE 336

ABSTRACT

The kinetics and equilibrium extraction of pd(II) pt(IV) and RH (III) from hydrochloric acid media using impregnated resins containing Alamine 336 impregnated onto Amberlite XAD2 were studied and compared. While Rh( III) was hardly extracted, Pd( II) and Pt( IV) extraction could be explained by the formation of ( R₃ NH⁺ )₂ MCL_n ^{? 2} complexes: n= 4 for Pd( H) and n= 6 for Pt( TV) Stripping and concentration of the extracted PGMs were assayed with HC1, HC10₄ and thiourea. Straightforward metal separations were designed on the basis of the results obtained in the single metal experiments, and selective co-extraction of Pd( II) and Pt( TV) from Rh( III)at low HC1 concentrations, as well as partial separation between Pd( ll) and Pt( IV) at high acid concentrations, were achieved.     

IMPREGNATED RESINS CONTAINING DI-(2-ETHYLHEXYL) THIOPHOSPHORIC ACID FOR THE EXTRACTION OF PALLADIUM(H). II. SELECTIVE PALLADIUM(II) RECOVERY FROM HYDROCHLORIC ACID SOLUTIONS

ABSTRACT

The extraction of Pd(II) from HC1 solutions by impregnated resins containing di-(2-ethylhexyl) thiophosphoric acid (DEHTPA or HL) on the Amberlite XAD2 polymeric support has been studied. Graphical and computer analysis with the program LETAGROP-DISTR demonstrated that the Pd(II) extraction can be explained by the formation of metal complexes in the resin phase having the composition PdL₂(HL)₂. DEHTPA/XAD2 resins extracted Pd(II) in the presence of other metals: Pt(IV), Rh(III), Cu(II), Fe(III) as well as Zn(II). The stripping of Pd(II) loaded on the organic phase and the lifetime of the resins were also investigated.     

Extraction and separation of HCl and Rh(III) with trioctylamine

In this paper the use of trioctylamine (TOA) to extract HCl from Rh(III)-containing solutions generated by a supported liquid membrane (SLM) process is investigated. TOA was found to extract HCl readily (in a single contact of 3 min duration) at a molar ratio [HCl]/[TOA] equal to one. For each mole of HCl extracted an equivalent amount of H₂O was found to be extracted as well. As far as Rh(III) extraction of TOA is concerned this was found to depend on the age of the solution and the Cl⁻ concentration. Prolonged aging (accelerated by heating) or [Cl⁻]⩾3 M was found to completely suppress the extraction of Rh(III) by TOA. The chloride ion concentration effect was attrib-uted to Le Chatelier's principle while the aging effect was attributed to the aquation/conversion of the extractable RhCl₆³⁻ complexes to RhCl₅(H₂O)²⁻. The aquation reaction was studied with UV–Visible spectroscopy in an effort to substantiate the solvent extraction (SX) results. On the basis of the findings of this work a combined SLM/SX process flowsheet is proposed according to which the Rh(III) and HCl co-transported through the supported liquid membrane are co-extracted by TOA and subsequently separated by differential stripping; Rh(III) with 0·5 M HCl/3 M Cl⁻ medium and HCl with NAOH.     

Comparative Studies on the Extraction of Protactinium Using Different Kinds of Organic Extractants

Abstract

The extraction behavior of Pa(V) from various aqueous solutions was studied using different extractants, namely Amberlite-LA-2 (Amb-LA2), diethylhexyl phosphoric acid (HDEHP), tributylphosphate (TBP) and Tricaprylylmethyl ammonium chloride (TCMA) in toluene. The extraction was carried out from slightly acidic as well as strong acidic solutions of HCl, HBr, and HI, at various temperatures. The extracted species in every case were postulated. Extraction chromatography behavior of Pa(V), its homologue Nb(V), and the chemically similar elements Zr(IV) and Hf(IV) were also studied in the case of TCMA. Radioactive isotopes were used for tracing the corresponding elements. Some separation alternatives were achieved.     

Synergistic Extraction of Rhodium(III) from Hydrochloric Acid Solution with Tri-n-octylamine and Sulfide-type Extractants

Synergistic extraction of Rh(III) from relatively concentrated HCl solution was studied using two mixed solvents (di-n-hexyl sulfide (DHS)–tri-n-octylamine (TOA) and N,N′-dimethyl-N,N′-di-n-octyl-thiodiglycolamide (TDGA)–TOA) in chloroform. The Rh(III) extraction efficiency is poor when 0.5 M TOA, DHS, or TDGA is used independently. In contrast, the 0.5 M TDGA–0.5 M TOA and 0.5 M DHS–0.5 M TOA mixed solvents extract ?90% and ?70% of Rh(III), respectively, at maximum. Slope analyses and Job’s plots for the distribution ratios of Rh(III) at 2 M HCl show that the apparent stoichiometry of Rh(III):TOA:(DHS or TDGA) in the extracted complex is 1:2:1.     

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.     

Highly Efficient Extraction of Rhodium(III) from Hydrochloric Acid Solution with Amide-Containing Tertiary Amine Compounds

Extraction of Rh(III) from a HCl solution with N,N-disubstituted amide–containing tertiary amine (ACTA) compounds (N,N-di-n-hexyl(N-methyl-N-n-octyl-ethylamide)amine (MonoAA), N-n-hexyl-bis(N-methyl-N-n-octyl-ethylamide)amine (BisAA), and tris(N-methyl-N-n-octyl-ethylamide)amine (TrisAA)) was investigated. The ACTAs extract Rh(III) more efficiently than tri-n-octylamine (TOA), and the extraction efficiency increases with increasing number of amide groups: TrisAA > BisAA > MonoAA ? TOA. For all ACTAs, the predominant Rh(III) complex extracted from 2 M HCl is probably {[RhCl₅(H₂O)]·(ACTA·H)₂}. The apparent basicity of the ACTAs and TOA varies in the opposite order from that observed for the Rh(III) extraction efficiency. Rh(III) can be readily back-extracted using 10 M HCl solution possessing a high selectivity over similarly loaded Pd(II) and Pt(IV).     

Recovery of Nonradioactive Palladium and Rhodium from Radioactive Waste

Abstract

The U.S. production of palladium has not exceeded 1000 kg per year while consumption has reached 46,000 kg per year. At the Oak Ridge National Laboratory, we have demonstrated the technical feasibility of a process that could be used to recover over 2000 kg per year of nonradioactive palladium and rhodium each from radioactive nuclear waste. The method is based on an essentially complete removal of ruthenium (the precursor of nonradioactive Pd and Rh) from the radioactive palladium and rhodium. Decay of 368-d ¹⁰⁶Ru and its 30-s ¹⁰⁶Rh daughter produces nonradioactive ¹⁰⁶Pd while decay of 40-d ¹⁰³Ru yields nonradioactive ¹⁰³Rh. After an appropriate waiting period for the decay, separation of this nonradioactive palladium and rhodium from the remaining ¹⁰⁶Ru gives a product suitable for unrestricted commercial use. Several liquid metal extraction and partitioning systems have been investigated which give the required ruthenium-palladium-rhodium separation. For example, when molten magnesium containing 0.1 at. % each of palladium and ruthenium was equilibrated with molten uranium-5 wt % chromium eutectic at 900°C, the ruthenium extracted into the uranium-chromium solution while the palladium remained in the magnesium. Separation factors of greater than 10⁶ were obtained.     

Formation and extraction of Rh–Sn–Cl complexes with an alkylated 8-hydroxyquinoline

The work presented here focuses on the solution pretreatment and extraction stages of a solvent extraction system for rhodium from aqueous chloride solutions. The feed solution pretreatment stage involves a complexation reaction between the aqueous rhodium chloride complexes, [RhCl_6-x(H₂O)_x]^(3-x)− and stannous chloride. Depending on the amount of stannous chloride used, at least two different Rh–Sn complexes are formed, either [Rh(SnCl₃)₅)]⁴⁻ or [RhCl₃(SnCl₃)₃]³⁻. Both of these respond well to extraction with Kelex 100, the extractant investigated in this work. The extraction stage was found to be quantitative for rhodium and it was also found to be very rapid, with contact times of less than 5 min sufficient for rhodium extraction. The extraction mechanism was determined to be ion-pair formation with the protonated Kelex 100 molecules at a stoichiometry such that the overall charge in the organic phase is neutral, i.e. three Kelex 100 molecules for [RhCl₃(SnCl₃)₃]³⁻ and four for [Rh(SnCl₃)₅]⁴⁻. © 1998 SCI     

Electrochemical study of β-diketonatobis(triphenylphosphite)rhodium(I) complexes

The electrochemical behaviour of the series of ten [Rh(RCOCHCOR′)(P(OPh)₃)₂] complexes with R, R′ = CF₃, CF₃ (1), CF₃, CH₃ (2), CF₃, Ph (C₆H₅) (3), CF₃, Fc (ferrocenyl = (C₅H₅)Fe(C₅H₄)) (4), CH₃, Ph (5), CH₃, CH₃ (6), Ph, Ph (7), Fc, CH₃ (8), Fc, Ph (9) and Fc, Fc (10) were studied in acetonitrile containing 0.100 mol dm⁻³ tetra-n-butylammonium hexafluorophosphate as supporting electrolyte utilizing a glassy carbon working electrode. Results are consistent with Rh(I) being first oxidized in an electrochemically irreversible two-electron transfer process at peak anodic potentials ranging E_pa(Rh) = 0.124–0.881 V vs. Fc/Fc⁺. For the ferrocene-containing complexes (4), and (8)–(10) the rhodium oxidation was followed by the electrochemically reversible oxidation of the ferrocenyl group in a one-electron transfer process at a slightly more positive potential. Relationships were established between the electrochemical quantity E_pa(Rh) and kinetic parameter log k₂ as well the sum of experimental group electronegativities (Gordy Scale) of the R and R′ groups (χ_R + χ_R′), the Hammett σ values (σ_R + σ_R′) and the Lever ligand parameter E_L for the [Rh(RCOCHCOR′)(P(OPh)₃)₂] complexes: E_pa(Rh) (vs. Fc/Fc⁺/V) = 0.31 (χ_R + χ_R′)–1.09 = 0.56 (σ_R + σ_R′) + 0.28 = S_M (ΣE_L) + (I_M − 0.66 V) = −0.23 log k₂ − 0.03 (k₂ = second order rate constant for the oxidative addition of methyl iodide to rhodium). A profound shift of E_pa(Rh) to a more positive potential was observed for Rh(I) substrates containing β-diketonato ligands with increasing electronegative substituents R and R′. An exponential dependence of E_pa(Rh) on the pK_a of the β-diketone was obtained.     

Characterization of extracted complexes in liquid–liquid extraction of rhodium with Kelex 100 in the presence of SnCl2

Mixed Rh? Sn complexes found in aqueous and organic solutions involved in the liquid–liquid extraction of Rh(III) from chloride solutions, also containing SnCl₂, with 7-(4-ethyl-1-methyloctyl)-8-hydroxyquinoline (Kelex 100) were characterized through ¹¹⁹Sn NMR and Raman spectroscopy. At Sn: Rh molar ratios of 3:1 and 12:1, it was found that [Rh^IIICl₃(SnCl₃)₃]^3? and [Rh^I(SnCl₃)₅]^4?, respectively, are the dominant complexes in both the aqueous and organic solutions. These complexes can be quantitatively extracted from the aqueous solutions in less than 1 min contact time via ion-pair formation with the protonated 7-substituted 8-hydroxyquinoline reagent such that for both Sn:Rh ratios, the same Rh? Sn complex is found in the aqueous feed and in the fully loaded organic. In addition, it was found that [Rh^I(SnCl₃)₅]^4? is preferentially extracted over excess free Sn(II). Preliminary characterization of the complex stripped from the 12:1 loaded organic using 1·7 M H₂SO₄ shows an Rh? Sn complex having a ratio of 5:1 Sn:Rh.     

Extraction of lanthanides(III) from Perchlorate Solutions with Carbamoyl- and Phosphorylmethoxymethylphosphine Oxides and Tetrabutyldiglycolamide

The solvent extraction of Ln(III) ions from perchlorate aqueous solutions into an organic phase containing neutral polyfunctional organophosphorus ligands R₂P(O)CH₂OCH₂C(O)NBu₂ R = Bu (I), R = Ph (II) and R₂P(O)CH₂OCH₂P(O)R¹₂ R = R¹ = Bu (III); R = Bu, R¹ = Ph (IV); R = R¹ = Ph(V) has been studied. Their extraction behavior was compared with that of tetrabutyldiglycolamide (TBDGA), tetrabutylmethylenediphosphine dioxide (VI), P,P-dibutyl-P’P’-diphenylmethylenediphosphine dioxide (VII), tetraphenylmethylenediphosphine dioxide (VIII), dibutyl-N,N-dibutylcarbamoylmethylphosphine oxide (IX) and diphenyl-N,N-dibutylcarbamoylmethylphosphine oxide (X). The extraction equilibrium was investigated, and the equilibrium constants were calculated. It was found that the lanthanide(III) ions are extracted with the studied extractants from perchlorate solutions as LnL₃(ClO₄)₃ complexes. In the NaClO₄ media, TBDGA was found to possess a higher extraction efficiency towards Ln(III) ions than other neutral donor ligands studied. A successive replacement of the C(O)NBu₂ groups in the diglycolamide extractant molecule by phosphoryl ones leads to a decrease in the extraction efficiency of Ln(III) ions. In the NaClO₄ media, compounds II, IV and V with phenyl radicals at the P(O) group demonstrate a lower extraction efficiency towards Ln(III) ions than their butyl-substituted analogs. In contrast, phenyl-substituted diphosphine dioxides VIII, VII and carbamoylmethylphosphine oxide (X) extract Ln(III) ions more effectively than their butyl-substituted analogs VI and IX. The extraction of Ln(III) ions from HClO₄ solutions is accompanied by HClO₄ interaction with neutral donor extractants, which leads to a decrease of the free extractant concentration in the organic phase. By this reason, an increase in the HClO₄ concentration higher than 0.1 M is accompanied by a decrease of the Ln(III) extraction with TBDGA. In the 3 M HClO₄ system, diphosphine dioxide VIII outperforms TBDGA at the Ln(III) extraction.     

EXTRACTION OF RARE EARTH METALS WITH 2-ETHYLHEXYL PHOSPHONIC ACID MONO-2-ETHYLHEXYL ESTER IN THE PRESENCE OF DIETHYLENETRIAMINEPENTAACETIC ACID IN AQUEOUS PHASE

Abstract

The extraction equilibria of rare earth metals with 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester (commercial name, PC-88A, henceforth abbreviated as HR) dissolved in n-heptane were measured at 303 K. It was found that rare earth metals are extracted with the dimer of the extractant, (HR)₂, as follows.

The extraction equilibrium constants of metals were obtained and compared with the extraction equilibrium constants obtained by di(2-ethylhexyl)phosphoric acid (henceforth D2EHPA).

Furthermore, the extraction equilibria of rare earth metals with PC-88A in the presence of diethylenetriaminepentaacetic acid (henceforth DTPA) in an aqueous phase were also measured to discuss the effect of DTPA on the extraction of rare earth metals.     

SANS STUDY OF AGGREGATION OF THE COMPLEXES FORMED BY SELECTED METAL CATIONS AND P,P'-DI(2-ETHYLHEXYL) ETHANE- AND BUTANE-DIPHOSPHONIC ACIDS∗

ABSTRACT

The aggregation of several metal complexes formed during solvent extraction with P,P'-di(2-ethylhexyl) ethanediphosphonic acid, H₂DEH[EDP], and by P,P'-di(2-ethylhexyl) butanediphosphorac acid, H₂DEH[BuDP], in deuterated toluene, has been investigated by small angle neutron scattering (SANS). With H₂DEH[EDP], the extraction of Ca(II), La(IH) and U(VT) does not disrupt the cyclic hexameric structure of the ligand in solution. Fe(III) and Th(IV) complexes of H₂DEH[EDP], on the other hand, exhibit a very modest tendency to aggregate but only at very high metal loading in the organic phase. With H₂DEH[BuDP], the extraction of Ca(H), La(III), U(VI) and Th(IV) is not accompanied by significant aggregation of the metal complexes The Fe(HI)-H₂DEH[BuDP] complexes, however, form long cylindrical aggregates similar to those previously observed with P,P'di(2-ethylhexyl) methanediphosphonic acid, H₂DEH[MDP]. The aggregation behavior of the various metal-extractant species is discussed in light of the information obtained from earlier solvent extraction, vapor pressure osmometry, and infrared spectroscopy studies.