Separation of Precious Metals through a Trioctylamine Liquid Membrane

Abstract

The extraction behavior of precious metals (PMs) from HCl media has been studied using trioctylamine (TOA) in kerosene. The extraction sequence of PMs was found to be Au(III) > Pd(II), Pt(IV), Ir(IV) > Ir(III). Ru. Transport of PMs was performed through a supported liquid membrane (SLM) impregnated with TOA as a mobile carrier from the HCl feed solution into the HClO₄ or HNO₃ product solution. Selective transport; and recovery of PMs from certain mixtures were accomplished across the TOA-SLM on the basis of differences in extraction equilibria and kinetics.     

Transport of Palladium(II) through Trioctylamine Liquid Membrane

Abstract

The permeation behavior of palladium(II) through a supported liquid membrane (SLM) impregnated with trioctylamine (TOA) in kerosene has been investigated. By selecting perchloric or nitric acid as a stripping agent, Pd(II) was transported through the SLM containing 0.5 M TOA and 20% 1-octanol without remaining in the liquid membrane. The permeation rate (k _{f. obs}) of Pd(II) for HNO₃ was faster than that for HClO₄. Palladium(II) was concentrated across the SLM from the 0.5 M CHI solution into the HClO₄ or HNO₃ solution.     

Column Sorption of Citric Acid from Aqueous Solutions Using Tri-n-octylamine-Impregnated Macroporous Resins

Abstract

Column sorption of citric acid from aqueous solutions using tri-n-octylamine (TOA)-impregnated macroporous resins was studied at 298 K. The breakthrough curves were measured as a function of the feed flow rate, citric acid concentration in the feed solution, TOA concentration in the resin phase, and type of resin. It was found that the type of resin played a most important role in determining the saturated capacity under comparable conditions. The desorption of citric acid from loaded resins was also evaluated with various eluants, including HCl, HNO³, H²SO⁴, and Na²CO³     

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     

Transport of Europium through Supported Liquid Membrane Containing Dihexyl-N,N-diethylcarbamoylmethylphosphonate

Abstract

The transport of europium has been studied through a supported liquid membrane (SLM) impregnated with dihexy-N,N-diethylcarbamoylmethylphosphonate (CMP). Europium was effectively extracted from the perchlorate solution into SLM, but was insufficiently stripped to a dilute acid solution. The addition of 1-decanol improved the stripping process, and quantitative transport of europium was achieved. By the combination of two SLM systems consisting of diiso-decylphosphoric acid and CMP, europium was transported from the feed solution (0.1 M HNO₃) through the intermediate solution (1 M HclO₄ + 4 M NaClO₄) to the product solution (0.1 M HNO₃) and effectively concentrated by a factor of about 20.     

Third Phase Formation in the Solvent Extraction System Ir(IV)—Cyanex 923

Abstract

The splitting of a system from biphasic to triphasic was studied in the liquid‐liquid extraction of Ir(IV) and HCl using Cyanex 923 (C923). The limiting organic concentrations (LOC) of Ir(IV), which are the maximum possible concentrations of Ir(IV) in the organic phase without the formation of a third phase, were determined under different experimental conditions. The experimental conditions investigated were: concentrations of HCl and NaCl in the aqueous phase, concentrations of C923 and a modifier (tributyl phosphate (TBP) or decanol) in the organic phase, and an organic phase made with different diluents such as n‐octane, n‐nonane, n‐dodecane, kerosene, cyclohexane, toluene, and xylene. The formation of a third phase depends on the concentration of Ir(IV) and HCl in the aqueous phase, as well as on the other experimental conditions. The third phase appeared without Ir(IV) when the concentration of HCl in the equilibrated aqueous phase was 3.5 M and the organic phase contained 10% (v/v) C923/kerosene. The maximum LOC of Ir(IV) was obtained when the initial concentration of HCl in the aqueous phase was 2 M. The LOC of Ir(IV) can be increased though the addition of typical solvent modifiers (such as TBP or decanol) in the organic phase. The LOC of Ir(IV) varied significantly when it was extracted from an aqueous solution containing different concentrations of NaCl. The values obtained for the LOC using different diluents were in the following decreasing order: toluene ≈ xylene>cyclohexane>n‐octane>n‐nonane>kerosene>n‐dodecane. No third phase was detected when toluene and xylene were used as diluents. In the case of cyclohexane, no third phase was observed when the aqueous phase contained 4 M HCl. Spectral studies were performed to investigate the chemical composition of the third phase obtained with Ir(IV)‐HCl‐C923.     

Supported Liquid Membrane Extraction Study of (MoO4)2- Ions using Tri-n-octylamine as Carrier

Abstract

The transport of (MoO₄)^2- ions across a tri-n-octylamine (TOA) xylene-based supported liquid membrane has been studied at various HCl concentrations in the feed, TOA concentrations in the membrane, and NaOH concentrations in the strip solution. The distribution coefficient and flux of the Mo(VI) ion species vary with the HCl concentration, indicating that different polymeric species of this metal ion are present in the aqueous solution. A TOA concentration increase of up to 1.308 mol/dm³ enhances flux and permeability of this metal ion, which beyond this concentration is reduced due to an increase in carrier liquid viscosity. An increase in NaOH solution concentration has been found to increase flux and permeability values. The continuous increase in pH of the feed with the transport of metal ions indicates that the (MoO₄)^2- transport does not involve a decrease or increase in concentration as a result of association of lower to higher or decomposition of higher to lower metal ions polymeric species. The optimum conditions of transport of Mo(VI) metal ions across these membranes have been found to be HCl = 0.01, [NaOH] = 1, and [TOA] = 1.308, furnishing flux and permeability values of the order of 2.49 × 10^?4 mol·m^?2·s^?1 and 2.32 × 10^?10 m²·s^?1, respectively.     

Carrier-Mediated Transport of Molybdenum(VI) through Supported Liquid Membranes

Abstract

The liquid membrane transport of Mo(VI) from an acidic solution into an alkaline stripping solution was carried out by using a mobile carrier, 5,8-diethyl-7-hydroxy-dodecan-6-one oxime (LIX 63). Further transport of MoO₄ ^2? from the alkaline solution was performed by using another carrier, trioctylmethylammonium chloride (TOMAC). Molybdenum(VI) was effectively transported through double membranes composed of LIX 63/dilute NaOH solution/TOMAC from a feed solution (10^?3 M HNO₃) into a product solution (1 M NaOH). Molybdenum(VI) was concentrated with high recovery into a small volume of product solution. The separation of Mo(VI) from several ions was performed by means of the double membranes.     

Extraction and Separation of Germanium Using Cyanex 301/Cyanex 923. Its Recovery from Transistor Waste

Abstract

The extraction of Ge(IV) from HCl, HNO₃ and H₂SO₄ media in toluene solution of Cyanex 301 and Cyanex 923 is investigated. It is almost quantitatively extracted (～95%) in Cyanex 301 and Cyanex 923 at 8 molL^?1 HCl but the extractions from H₂SO₄ and HNO₃ are poor in the entire investigated range of acid molarity. Detailed investigations were carried out from HCl medium. Based on the slope analysis data the extracting species is identified as GeCl₄·2R (R=Cyanex 301/Cyanex 923). The extraction of Ge(IV) is higher and comparable in diluents like toluene, n‐hexane and kerosene (160–200°C) and there is no correlation between the dielectric constant and the percent extraction. The extractants are stable towards prolonged acid contact and there is negligible loss in their extraction efficiency even after recycling them for several cycles. The extraction behavior of commonly associated metal ions namely As(V)/(III), Sn(IV), Tl(III), In(III), Ga(III), Fe(III), Al(III), Hg(II), and Cu(II) has also been investigated. Based on the partition data conditions for attaining some binary and ternary separations involving Ge(IV) have been optimized. The separation data have been fused to develop a scheme for the recovery (93%) of pure germanium (～99%) from semi conductor waste.     

Spectroscopic,transport, and morphological studies of polyaniline doped with inorganic acids

A conducting polymer, polyaniline, was synthesized by chemical polymerization using different inorganic acids, such as HCl, H₂SO₄, HClO₄, HNO₃, and H₃PO₄, as protonic acid media. The synthesized polymers were characterized using UV‐visible and FT‐IR spectroscopy. A granular type of morphology was observed under SEM for HCl, HNO₃, and H₃PO₄ doped polyanilines. However, HClO₄ doped polyaniline shows the folded lamellar structure derived from the fibers. The thermal stability of these polymers was investigated with the help of thermogravimetric (TG/SDTA) analysis. The formation of a greater fraction of the conducting emeraldine salt phase is observed in HClO₄ as a protonic acid media. The thermal stability of H₃PO₄ doped material is found to be better as compared with other acids. An increase in conductivity with an increase in temperature was observed in all the samples except for HClO₄ doped polyaniline. Polym. Eng. Sci. 44:1676–1681, 2004. © 2004 Society of Plastics Engineers.     

Third Phase Formation in the Extraction of Inorganic Acids by TBP in n‐Octane

Abstract

The extraction of HNO₃, HClO₄, H₂SO₄ and H₃PO₄ by 20% (v/v) TBP (0.73 M) in n‐octane was measured under identical conditions up to and beyond the critical point of third phase formation (Limiting Organic Concentration, or LOC condition). The data, together with those obtained previously for HCl, allowed us to establish the following lyotropic series of effectiveness with respect to third phase formation in the extraction of acids by TBP: HClO₄>H₂SO₄>HCl>H₃PO₄>HNO₃. This series correlates with the amount of water present into the organic phase at the point of phase splitting. This result reinforces the validity of the reverse micellar model developed previously for the extraction of metal salts by TBP. The measurements of LOC values as a function of temperature revealed major differences among the acid‐TBP systems investigated. For HClO₄, the strong increase of the LOC value with increasing temperatures is accompanied by a large favorable entropy change. The opposite is true for HCl, while H₂SO₄ and H₃PO₄ represent intermediate cases. Measurements of the LOC values for the extraction of HClO₄ by TBP dissolved in a series of diluents confirmed that topological parameters, such as the Connectivity Index, CI, are useful for predicting the critical condition for phase splitting in different diluents. Based on the linear correlation between LOC values for HClO₄ and CI values of diluents, the effective Connectivity Index of the French nuclear reprocessing diluent, HTP, a complex mixture of highly branched alkanes, was determined.     

Graft copolymerization onto cellulose by ceric ion initiator system: Effects of kind of acid and irradiation with ultraviolet light

The effects of kind of acid and irradiation of ultraviolet light on the graft copolymerization of methyl methacrylate onto cellulose with adsorbed ceric ion were investigated. Irrespective of ultraviolet light irradiation, the amount of reduced ceric ion in the reaction systems was increased in the order HCl > HClO₄ > HNO₃ > H₂SO₄, and the number of grafts formed was increased in the order HClO₄ > HNO₃ > HCl > H₂SO₄. Thus, it was definitely observed that the graft copolymerization is affected by the kind of acid. Ultraviolet light remarkably accelerated the reduction of ceric ion adsorbed on cellulose in the various acid mediums, but decreased the efficiency of graft formation. The most favorable results for the formation of grafts were obtained in the system in which HClO₄ and ultraviolet irradiation was employed. A combination of H₂SO₄ and ultraviolet irradiation resulted in the lowest per cent grafting and average molecular weight of grafts. It was found that H₂SO₄ characteristically dissolves out ceric ion adsorbed into an aqueous solution and accelerates the formation of homopolymer.     

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.     

Strong effects of counterions on the electrochemistry of poly(N‐methylaniline) thin films

Poly(N‐methylaniline) thin films show different cyclic voltammetric behaviour when cycled in HClO₄, HBF₄, HCl or HNO₃. While in the first two acids the film shows profiles peak potentials similar to those of polyaniline, profiles in HCl and HNO₃ show higher peak potentials for oxidation and a different shape. The free energy for the process, calculated from the oxidation peak potential, shows a linear correlation with the free energy of hydration of the anions present in the test solution. An energy cycle for the oxidation process is proposed to explain the results. The reaction mechanism assumes that anions have to lose their hydration shell to form the polymer salt during electrochemical oxidation of the films. Electropolymerization also depends on the anion present in the solution. While this is possible with low hydration energy anions (ClO₄^?, BF₄^?), it is difficult or impossible when the electrolyte solution contains other anions (Cl^?, NO₃^?) where a higher oxidation potential of the preformed polymer is observed. © 2002 Society of Chemical Industry     

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.     

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).     

Supported Liquid Membranes Extraction of W(VI) Ions from HCL Solutions Containing Tartaric Acid

Abstract

A transport study of W(VI) ions across tri-n-octylamine (TOA) xylene-based supported liquid membranes from aqueous solutions containing tartaric acid (TA) has been carried out. TA complexes with W(VI) ions to keep them in solution and enhance flux. The optimum conditions of transport found are 0.132 M TA and 0.001 M HCl in the feed, 3.7 M NaOH in the strip, and 0.66 M TOA in the membrane. Beyond these TA and TOA concentrations, there is a decrease in flux and permeability values which are 4.76 × 10^?5 mol/m²/s and 9.15 × 10^?10 m²/s, respectively. NaOH is a better stripping agent than NH₄OH for these metal ions. Increases in membrane phase viscosity and temperature reduce the values of these transport parameters.     

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.     

Sorption of Rare-Earth Elements and Ac on UTEVA Resin in Different Acid Solutions

The distribution of some rare-earth elements (REEs) on Uranium and TEtraValent Actinides (UTEVA) resin was determined from different concentrations of inorganic (HCl, HNO₃, HClO₄, HPF₆) and one organic acid – CCl₃COOH. Low sorption of all REEs in the range of 1 M–5 M HNO₃ was observed. In more concentrated HNO₃, a rapid increase of the distribution coefficients (K_d) was noticed with an increase in the atomic number of the lanthanides as well as in Y and Sc. The system UTEVA–CCl₃COOH showed a higher selectivity for Eu(III). Chromatographic elution profiles were checked in order to confirm the obtained K_d values.     

Effects of Ta,La and Nd additions on the corrosion behaviour of aluminium bronze in mineral acids

Corrosion studies of aluminium bronze with and without additions of Ta, La and Nd were carried out in HCl, HNO₃ and H₂SO₄ solutions, using weight loss, polarization and impedance measurements. The study showed that the addition of each of Ta, La and Nd in small quantities effectively inhibited the corrosion of the alloy in HCl solution, the inhibition effect being greatest with low content of the alloying element. The inhibition of corrosion due to alloying additions was observed to be small in H₂SO₄ solution. In HNO₃ medium, these alloying elements at low level showed slightly beneficial effects while they had adverse effects at higher concentrations.