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     

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 ALUMINUM FROM A PICKLING BATH WITH SUPPORTED LIQUID MEMBRANE EXTRACTION

ABSTRACT

Large amounts of waste are produced yearly in the galvanic and chemical surface treatment industry. Bath liquids used in the various processes lose their function due to contamination. The spent bath liquids have to be replaced and treated prior to disposal, leading to high costs and a high environmental burden. In this paper, a proposed solution to the problem is investigated: the selective removal of the contaminant with supported liquid membrane extraction. The extraction of aluminum, a contaminant at high concentrations, from a pickling bath liquid with hydrofluoric acid and phosphoric acid as its main components has been carried out with the basic extractants Alamine 308 and Alamine 336 in a flat sheet-supported liquid membrane setup. Aluminum transport rates were obtained in the order of 10^?6?10^?5mol/(M²·s), which are normal values for this technique. The extraction was not completely selective as dissolved phosphorus was coextracted. In all experiments, precipitation took place on the surface of the liquid membrane and in the bulk of the strip phase. Increasing the stripping alkalinity from pH = 8 to pH = 13 reduced the amount of precipitation in the bulk of the strip phase but caused a substantial decrease in the aluminum flux. The precipitation prevents industrial application of the systems investigated.     

THE CONVERSION OF Rh(m) CHLOROCOMPLEXES TO BROMOCOMPLEXES AND THEIR SOLVENT EXTRACTION BEHAVIOUR

ABSTRACT

This paper details investigations on the conversion of Rh(HI) chlorocomplexes to bromocomplexes, followed by the extraction of the tatter with an alkylated 8-hydroxyquinoline and their subsequent stripping with hydrobromic acid. It was found that in contrast to Rh(III) chlorocomplexes, the analogous bromocomplexes underwent significantly less aquation, thus rendering themselves to qualitative solvent extraction. Of the extractants tested, Kelex 100 proved to give the best performance. On the other hand, stripping was problematic. It was apparent that complex transformation of the extracted Rh(HI) occurred in the organic phase upon aging, which resulted in metal lock up.     

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.     

Homogeneous Liquid-Liquid Extraction of Metal Ion Utilizing Upper Critical Solution Temperature of Propylene Carbonate

ABSTRACT

This study was undertaken to investigate the extraction of In³⁺ and Ga³⁺ by 7-(4-ethyl-1-methyloctyl)-8-hydroxy-quinoline (Kelex100), which has been found to be a slow extraction process. Homogeneous liquid-liquid extraction utilizing upper critical solution temperature of 4-methyl-1,3-dioxolan-2-one (propylene carbonate, abbreviated as PC) was used to eliminate the interface and speed up the extraction, since distribution between two phases was thought to be the rate-determining step. The effect of contact time on the percentage of metal extraction was examined at 80ºC using Kelex100 dissolved in toluene and PC solutions and the difference between two solvents was evaluated. The results clearly show that the use of homogeneous liquid-liquid extraction using PC with Kelex100 is faster than traditional two phase extraction.     

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     

Solvent Extraction of Au(III) by the Chloride Salt of the Amine Alamine 304 and Its Application to a Solid Supported Liquid Membrane System

Abstract

The extraction of Au(III) by the chloride salt of the amine Alamine 304 (R₃NH⁺Cl^?) in xylene from hydrochloric acid solutions has been investigated. The analysis of metal distribution data by numerical calculations suggested the formation of the species R₃NH⁺AuCl₄ ^? in the organic phase with formation constant log K _ext = 5.44. The results obtained on Au(III) distribution have been implemented in a solid‐supported liquid membrane system, where in NaSCN solutions were found to be the most effective to strip the metal from the organic solution. Influence of membrane composition, metal concentration on gold transport, and the selectivity of the system have also been studied.     

Transition Metal Complexes with 8-Hydroxyquinoline and Kelex 100 in Micellar Systems. Stoichiometry of the Complexes and Kinetics of Dissociation in Acid Media

Abstract

Complexation of metal ions by micelle-solubilized extractants can be used for the development of new extraction processes. Metal extraction in micellar systems is in many respects analogous to solvent extraction if one considers the use of ultrafiltration as a means to separate the micellar pseudophase from the continuous aqueous phase. The present paper is intended to further characterize the nature of the complexes obtained in micellar systems (especially their stoichiometry and their stability as a function of pH) and to compare the results with those previously obtained in classical biphasic systems. The extractant molecules considered in this work were 8-hydroxyquinoline (HQ) and its alkylated analogue (C₁₁-HQ) derived from Kelex 100. Their complexes with Ni²⁺, Co²⁺, and Cu²⁺ have been investigated in micellar solutions made of cetyltrimethylammonium bromide (CTAB), 1-butanol, and water. The stoichiometry of the complexes was determined using Job's continuous variation method, and their kinetics of dissociation was investigated with the stopped-flow technique. Practical selective recovery of the different metal ions from their complexes in micelles was shown to be possible using ultrafiltration.     

Liquid Emulsion Membrane (LEM) Process for Vanadium (IV) Enrichment: Process Intensification

Abstract

A liquid emulsion membrane (LEM) system for vanadium (IV) transport has been designed using di‐2‐ethylhexyl phosphoric acid (D2EHPA), dissolved in n‐dodecane as carrier. The selection of extractant, D2EHPA, was made on the basis of conventional liquid‐liquid extraction studies. The work has been undertaken by first carrying out liquid‐liquid extraction studies for vanadium (IV) to get stoichiometric constant (n), and equilibrium constant (K_ex), which are important for process design.

Transport experiments were carried out at low vanadium (IV) concentration (ppm level). The studies on liquid emulsion membrane included i) the influence of process parameters i.e. feed phase pH, speed of agitation, treat ratio, residence time and ii) emulsion preparation study i.e., organic solvent, extractant concentration, surfactant concentration, internal strip phase concentration. When the strip phase concentration was 2 mol/dm³ (H₂SO₄) and feed phase pH 3 better extraction of vanadium was obtained. Higher V_m/V₁ gave higher extraction of vanadium (IV). A simplified, design engineer friendly model was developed.     

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.     

Separation of Zinc Ions from an Acidic Mine Drainage using a Stirred Transfer Cell–Type Emulsion Liquid Membrane Contactor

Abstract

This is a report on the separation and recovery of zinc ions from an acidic mine drainage using a stirred transfer cell‐type emulsion liquid membrane contactor. Di(2‐ethylhexyl) phosphoric acid was used as a highly selective carrier for the transport of zinc ions through the emulsified liquid membrane. A study was made of the effect on the extraction extent and initial extraction rate of the following variables: pH and initial metal concentration of the feed phase, carrier content in the organic solution, a stripping agent concentration in the receiving phase, and stirring speed in the transfer cell. The content of sulfuric acid as a stripping agent did not show in the studied range any significant influence on metal permeation through the SLM, although a minimum hydrogen ion concentration of 100 g/L is suggested in the internal aqueous solution to ensure an acidity gradient between both aqueous phases to promote the permeation of metal ions toward the strip liquor. Results show that using a pH of 4.0 in the feed acid solution, a concentration of 3% w/w_o of phosphoric carrier in the organic phase and a H₂SO₄ content of 100 g/L in the strip liquor, the extent and rate of extraction through the liquid membrane can be highly favored, pointing to the potential of this method for extracting heavy metals from many kinds of dilute aqueous solutions.     

Extraction rates of amino acids by an emulsion liquid membrane with tri-n-octylmethylammonium chloride

The extraction rates of amino acids from alkaline aqueous solution into an emulsion liquid membrane containing tri-n-octylmethylammonium chloride as a carrier and Paranox 100 as an emulsifier were measured using a stirred transfer cell. The effects of agitation speed (0·33–0·66 rev s⁻¹), amino acid concentrations (0·5–50 mol m⁻³) and temperature (10–45°C) on the extraction rates were examined. The results were analyzed by a double-film model. The mass transfer coefficients of amino acids (0·26–1·58×10⁻⁵ m s⁻¹) and their complexes (0·60–1·72×10⁻⁵ m s⁻¹) were found to correlate well with the hydrophobicities of the amino acids. It was found that the surfactant layer influenced the mass transfer processes of both amino acids in the aqueous film and their complexes in the organic film. The permeation of amino acids with a large hydrophobicity through the emulsion liquid membrane was promoted by both high distribution and larger mass transfer rates. © 1998 Society of Chemical Industry     

Transport of Co(II) Ions through Di(2-ethylhexyl) Phosphoric Acid-CCl4 Supported Liquid Membranes

Abstract

A liquid membrane transport study of Co(II) using di(2-ethylhexyl) phosphoric acid (D2EPHA) as carrier and CCl₄, as diluent supported on polypropylene microporous film has been carried out. The carrier concentration in the membrane and HCl concentration in the stripping phase have been varied to see the effect on transport of Co(II) ions across the membrane. Maximum flux and permeability values of 1.23 × 10^?5 mol · m^?2 · s^?1 and 7.66 × 10^?11 m²/s, respectively, at a 0.87 mol/dm³ carrier concentration in the membrane have been found. At 1 mol/dm³ HCl concentration in the stripping phase the flux and permeability have maximum values of 1.4 mol · m^?2 · s^?1 and 5.27 × 10^?11 m²/s, respectively. The distribution coefficient of Co(II) ions into organic phase has been found to increase with increasing carrier concentration. The diffusion coefficient determined varies from 13.73 × 10^?11 to 0.83 × 10^?11 m²/s, which is the reverse order of the values of the distribution coefficient and explains the permeability of the Co(II) D2EPHA complex through the membrane.     

Process Intensification via Liquid Emulsion Membrane Technique in Extraction and Enrichment of Rhodium (III) from Chloride Media

A liquid emulsion membrane (LEM) system as a tool for process intensification has been studied for rhodium recovery using di-2-ethylhexylphosphoric acid (D2EHPA) as a metal carrier and Monemul 80 as a surfactant, dissolved in liquid paraffin. The various process parameters affecting the LEM process, such as extractant, surfactant, and strip phase concentrations, the speed of agitation, the batch contact time, and the treat ratio have been experimentally investigated to get better insight into the process. Perchloric acid was found to be a better stripping agent in the LEM process. It was observed that the extraction of Rh (III) can be significantly more in the absence of a water repelling agent. The maximum enrichment of Rh (III) in the internal phase obtained was 4.3 times with feed phase pH adjusted to 6, perchloric acid (1.5 mol/dm³), and contact time of 15 min. A mass transfer model to predict the performance of the LEM system was used and found to fit well with the experimental data.     

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.     

Coupled Transport of Zr(IV) through Tri-n-butylphosphate-Xylene-Based Supported Liquid Membranes

Abstract

The transport of Zr(IV) through tri-n-butylphosphate-xylene-based liquid membranes, supported in a polypropylene hydrophobic microporous film, has been studied. The concentration of HNO₃ in the feed solution and tri-n-butylphosphate (TBP) carrier in the membrane were varied, and the flux and permeability coefficients were determined. The optimum conditions found for maximum flux were determined to be 10 mol/dm³ HNO₃ and 2.93 mol/dm³ TBP with a flux value of 12.9 × 10^?6 mol · m^?2 · s^?1. The solvent extraction study revealed that 1.25 to 3.5 protons are involved in zirconium transport, and that two molecules of TBP are involved in the complex formation. The value of protons involved varies with acid concentration. The zirconium ion transport is coupled with nitrate ions transport.     

Non-dispersive selective extraction of germanium from fly ash leachates using membrane-based processes

ABSTRACT

Non-dispersive selective extraction of Ge(IV) tartrates was carried out from simulated fly ash solutions containing heavy metals through supported liquid membranes (SLM). The optimum transport was obtained using a PTFE membrane containing Alamine 336 5%v/v in the condition of tartaric acid 2.76 mmol/L and HCl 1 mol/L in feed and strip phases, respectively. Under this condition, a hollow fiber (HF) SLM experiment was conducted. The results showed that this system could transport germanium from the feed to the strip phase so much faster than the flat sheet (FS) SLM system. The rate of transport through HFSLMs is comparable to dispersive extractions.

Abbreviation: A: Effective area of the membrane (cm²); BDL: Below detection limit; C_f,: Feed concentration (mg/L); C_t,: Initial concentration (mg/L); D: Distribution coefficient; ELM: Emulasion liquid membranes; FSSLM: Flat sheet supported liquid membrane; HF: Hollow fiber; LLX: Liquid-liquid extraction; P: Permeation coefficient (m/h); PTFE: Poly tetra fluoro ethylene; PVDF: Polyvinylidene difluoride; T: Tartrate species (C₄H₄O₆); T: Temperature (K); %T:Germanium transport effeciency; V: Volume of feed solution (cm³); t: time (h); η: Viscosity (P.s (c.P)); κ: Boltzmann constant; r: Ionic radius of species; τ: Tortuosity of the membrane; ρ: Porosity; α: Separation factor.     

Liquid–liquid extraction of cadmium(II) by Cyanex 923 and its application to a solid‐supported liquid membrane system

The extraction of cadmium(II) by Cyanex 923 (a mixture of alkylphosphine oxides) in Solvesso 100 from hydrochloric acid solution has been investigated. The extraction reaction is exothermic. The numerical analysis of metal distribution data suggests the formation of CdCl₂.2L, HCdCl₃.2L and H₂CdCl₄.2L (L = ligand) in the organic phase. The results obtained for cadmium(II) distribution have been implemented in a solid‐supported liquid membrane system. The influences of feed phase stirring speed (400–1400 min^?1), membrane composition (carrier concentration: 0.06–1 mol dm^?3) and metal concentration (0.01–0.08 g dm^?3) on cadmium transport have been investigated. Copyright © 2005 Society of Chemical Industry     

Solvent extraction of Zn(II) by Cyanex 923 and its application to a solid‐supported liquid membrane system

The extraction of zinc(II) by Cyanex 923 (phosphine oxides mixture) in Solvesso 100 from hydrochloric acid solution has been investigated. The extraction reaction is exothermic. The numerical analysis of metal distribution data suggests the formation of ZnCl₂·L₂,HZnCl₃·2L and H₂ZnCl₄·2L(L = ligand) in the organic phase with formation constants K_ext = 4.1,5.6 × 10⁹ and 6.7 × 10⁹, respectively. The results obtained for zinc(II) distribution have been implemented in a solid‐supported liquid membrane system. The influence of source phase stirring speed, membrane composition and metal concentration on zinc transport have been investigated. © 2001 Society of Chemical Industry