Integrated Ion Exchange and Liquid-Liquid Extraction Process for the Separation of Platinum Group Metals (PGM)

A process for concentration and separation of platinum group metals (PGM) by a combination of ion exchange and liquid-liquid extraction is presented. First the PGM metals are dissolved by HC1/C1₁ and then passed through an isothiouronium anion exchange resin, where specific absorption occurs. The thiourea eluate from the resin is converted to the chloride complexes. Further hydrolysis (conditioning) yields an aqueous feed to a liquid-liquid extraction step, with Alamine-336. Platinum and palladium are very well extracted, while most of the other PGM are rejected in the aqueous phase. The liquid-liquid extraction can be used by itself, if the level of the base metals does not exceed the concentration of the PGM ions.

Platinum and palladium are now separated from each other by the selective stripping of palladium with thiourea, and platinum with thiocyanate.

The paper discusses the extraction chemistry of all the steps, and provides also experimental pilot-plant results.     

Extractive spectrophotometric determination of palladium(II) and platinum(II) with 2-allylthiourea and thiocyanate in the presence of EDTA

Palladium(II) and platinum(II) react with 2-allylthiourea and thiocyanate to form colored complexes stable in the presence of EDTA and extractable into isoamyl alcohol. Based on these properties a method was worked out for the extractive spectrophotometric determination of palladium(II) and platinum(II) in the presence of several cations.     

Flotation-spectrophotometric determination of osmium (ruthenium) with thiocyanate and Capri blue

A sensitive flotation-spectrophotometric method for the determination of osmium, based on the ion associate formed by the anionic thiocyanate osmium complex with oxazine basic dye, Capri blue (CB), has been developed. The ion associate is separated by shaking the aqueous solution (pH 2–3) with diisopropyl ether, washing the precipitate with water, and dissolving it in methanol. Molar absorptivity in this method amounts to 2.7 × 10⁵ liters mol⁻¹ cm⁻¹ at 630 nm. The molar ratio Os:SCN:CB in the separated associate is 1:8:5. Under the conditions of the determination of osmium, ruthenium can be determined as well. Metals that form anionic thiocyanate complexes, including other platinum metals, interfere. The method becomes highly selective for osmium and ruthenium after their separation by distillation as tetroxides. Osmium and ruthenium were determined with Capri blue after their extractive separation as thiocyanate complexes.     

Simultaneous determination of palladium, platinum, rhodium and gold by on-line solid phase extraction and high performance liquid chromatography with 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine as pre-column derivatization regents

In this paper, 5-(2-hydroxy-5-nitrophenylazo)thiorhodanine (HNATR) was synthesized. A new method for the simultaneous determination of palladium, platinum, rhodium and gold ions as metal-HNATR chelates was developed using a rapid analysis column high performance liquid chromatography equipped with on-line solid phase extraction technique. The samples (Water, human urine, geological samples and soil) were digested by microwave acid-digestion. The palladium, platinum, rhodium and gold ions in the digested samples were pre-column derivatized with HNATR to form colored chelates. The Pd-HNATR, Pt-HNATR, Rh-HNATR and Au-HNATR chelates can be absorbed onto the front of the enrichment column when they were injected into the injector and sent to the enrichment column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] with a buffer solution of 0.05 mol L(-1) phosphoric acid as mobile phase. After the enrichment had finished, by switching the six ports switching valve, the retained chelates were back-flushed by mobile phase and travelling towards the analytical column. These chelates separation on the analytical column [Zorbax Stable Bound, 10 mm x 4.6 mm, 1.8 microm] was satisfactory with 72% acetonitrile (containing 0.05 mol L(-1) of phosphoric acid and 0.1% of Triton X-100) as mobile phase. The palladium, platinum, rhodium and gold chelates were separated completely within 2.5 min. Compared to the routine chromatographic method, more then 80% of separation time was shortened. By on-line solid phase extraction system, a large volume of sample (10 mL) can be injected, and the sensitivity of the method was greatly improved. The detection limits (S/N=3, the sample injection volume is 10 mL) of palladium, platinum, rhodium and gold in the original samples reaches 1.4, 1.8, 2.0 and 1.2 ng L(-1), respectively. The relative standard deviations for five replicate samples were 2.4-3.6%. The standard recoveries were 88-95%. This method was applied to the determination of palladium, platinum, rhodium and gold in human urine, water and geological samples with good results.     

Surfactant gel adsorption of platinum(II), (IV) and palladium(II) as chloro-complexes and kinetic separation of palladium from platinum using EDTA.

A micellar solution of cetylpyridinium chloride (CPC) can separate into two phases due to a temperature change or to the addition of salts. Platinum(II), (IV) and palladium(II) reacted with chloride ions to form stable anionic complexes of PtCl4(2-), PtCl6(2-) and PdCl4(2-), respectively, and were adsorbed onto the CPC gel phase. The CPC phase plays the role of an ion-exchange adsorbent for the anionic complexes. By such a procedure, the precious metals of platinum and palladium could be separated from base metals such as copper, zinc and iron. The kinetic separation was performed by a ligand exchange reaction of the palladium(II) chloro-complex with EDTA at 60 degrees C. The anionic palladium(II)-EDTA complex could not bind the opposite charged CP+ and was desorbed from the CPC phase. In the aqueous phase, the recovery of palladium(II) by the double-desorption was 101.1 +/- 1.2%. The platinum(II) and (IV) chloro-complexes were stable for at least 30 min and remained in the CPC phase.     

Propiconazole and Penconazole as Effective Extractants for Selective recovery and concentration of platinum(IV) and palladium(II) from hydrochloric acid solutions formed in leaching of spent aluminoplatinum and aluminopalladium catalysts

Selective recovery and concentration of platinum(IV) and palladium(II) from hydrochloric acid solutions of varied composition was studied using commercial reagents propiconazole and penconazole as extractants. The ranges of hydrochloric acid concentrations for effective extraction and highly selective separation of platinum metals from Al(III) and Ni(II) with propiconazole (toluene with 15 vol % n-decanol as deluent) and penconazole (chloroform) were determined. The conditions for 10-fold selective concentration of platinum metals with recovery of more than 99.9% of metal ions into the organic phase were found. The conditions for quantitative (>99%) stripping of platinum(IV) with a hydrochloric acid solution of thiourea and palladium(II) with ammonia solution were determined. The results obtained can be used for optimizing the modes of selective recovery of platinum(IV) and palladium(II) from hydrochloric acid solutions formed in leaching of alumina-supported platinum-rhenium, platinum-nickel, and palladium catalysts.     

Separation of gold, palladium and platinum from metallurgical samples using an amberlite XAD-7 resin column prior to their atomic absorption spectrometric determinations.

A simple and sensitive method for the separation and preconcentration of gold, palladium and platinum has been established prior to their atomic absorption spectrometric determinations. Analytes from 0.5 mol dm(-3) KI in a 2 mol dm(-3) HCl solution were recovered using an Amberlite XAD-7 column as halogeno complexes. The effects of some analytical parameters, including reagent amounts, sample volume and flow rates, on the quantitative recoveries of gold, palladium and platinum were investigated. The influences of some diverse ions were also studied. The proposed method has been applied for the preconcentration and separation of analytes from pure copper and anodic slime samples with satisfactory results (recoveries > 95%, relative standard deviations < 9.0%, relative error < or = 5%).     

Extraction of Palladium(II), Platinum(II), and Platinum(IV) by Bisacylated Diethylenetriamine from Hydrochloric Acid Solutions

The extraction properties of bisacylated diethylenetriamine are studied in the extraction of palladium(II), platinum(II), and platinum(IV) from hydrochloric acid solutions. Optimum extraction parameters are determined. The extraction of metal ions at these parameters follows an ion-associative mechanism. The concentration constants and thermodynamic parameters of extraction reactions are calculated. The feasibility of the extraction separation of palladium and platinum from base metals is verified.     

Flow-Injection Study and Analytical Applications of the Reactions of Palladium(II) and Platinum(IV) with Tin(II) Chloride in Hydrochloric Acid Solutions

The interaction of palladium(II) and platinum(II) with tin(II) chloride in hydrochloric acid solutions was studied by flow-injection (FI) spectrophotometry. It was found using kinetic measurements in the stopped flow mode that the composition of detected products and the rate of their formation depend on the concentrations of tin(II) and chloride ions in the reaction zone and on the acidity of the solution. Optimal FI conditions were found, and the selectivity of interaction of palladium(II) with tin(II) chloride was estimated for the detection of the signal at 407 nm (yellow form) and 646 nm (green form). It was demonstrated that the reaction of the formation of yellow platinum(IV) complexes is slower than that for palladium(II), especially at rather low concentrations of hydrochloric acid in the reaction flow. Based on the detection of green complexes of palladium(II) with tin(II) chloride, a flow injection method was proposed for the selective spectrophotometric determination of palladium(II) in the presence of other platinum-group metals. The height of the recorded peak is directly proportional to the concentration of palladium(II) in the injected solution in the range of 0.028–0.300 mM. The method was used for the analysis of pharmaceuticals and industrial catalysts.     

Extractive separation of platinum from macroamounts of palladium using triphenylphosphine oxide and its successive spectrophotometric determination by the stannous chloride method

Trialkylphosphine oxides extract more effectively chloride complexes of platinum than of palladium(II). Of the examined tributylphosphine (TBPO), trioctylphosphine (TOPO), and triphenylphosphine (TPPO) oxides the latter one makes possible best separation of these metals.The extraction of platinum with TPPO from solutions containing platinum and palladium unfavorably decreases with increasing palladium concentration. Using 0.1 M TPPO solution in dichloroethane, at HCl concentration 7.5 M, it is possible to separate 2–200 μg Pt/ml at a palladium concentration not higher than 10 mg/ml.Separation of platinum from macroamounts of palladium has been combined with spectrophotometric determination of platinum by means of stannous chloride. The method has been applied to the analysis of palladium for platinum content.     

The rapid isolation and determination of iridium after simultaneous liquid-liquid extraction and determination of platinum,palladium, rhodium and gold

The proposed method provides a rapid isolation of iridium form the other noble metals, as well as from Ni, Cu, Fe, Cr, Co and Na. The scheme comprises an initial removal of ruthenium and osmium by volatilization of their tetroxides followed by the simultaneous extraction of platinum, palladium, rhodium and gold as their 2-mercaptobenzothiazole—tin(II) chloride complexes into chloroform. Iridium in the raffinate is complexed by the same reagent system, after boiling, and extracted into chloroform. The extracts after evaporation of the solvent are converted to hydrochloric acid solutions and the noble metals are determined by atomic absorption spectrometry. Satisfactory results are obtained for various noble metal solutions, and for a solid platiniferous sample.     

Ion-Exchange Preconcentration and Separation of Trace mounts of Platinum and Palladium

ABSTRACT

The preconcentration and separation of platinum and palladium from weakly acidic solution (pH=4) were done on microcolumn packed with Cellex-T resin. Selective platinum elution from the column was performed with 0.01 mol/l glycine solution at pH=12, while for palladium elution 1.2 mol/l thiourea (pH=0.5) or 4.0 mol/l potassium thiocyanate (pH=1) may be used. As the detection technique was used either FAAS or GFAAS, depending on the concentration of studied metals in the eluate.     

Use of dicyclohexano-18-crown-6 to separate traces of silver(I) from potassium thiocyanate in hydrochloric acid media,and determination of the silver by atomic absorption spectrometry

Solvent extraction with 0.05 mol L(-1) dicyclohexano-18-crown-6 (DC18C6) in 1,2-dichloroethane, coupled with flame atomic absorption spectrometry (AAS), has been investigated as a new method for separation of trace amounts of silver(I) from 0.05 mol L(-1) potassium thiocyanate in 1.0 mol L(-1) hydrochloric acid media and quantification of the amount of silver present. The method is based on the formation of an extractable ion-association product, [DC18C6.K](+)[Ag(SCN)(2)](-), with a metal-to-crown ether ratio of 1:1 (as derived from slope analysis data). Stripping of the extracted silver(I) in the 1,2-dichloroethane phase was achieved within 5 min by use of 3.0 mol L(-1) potassium thiocyanate. Reducing the concentration of acid in the sample solution to 0.1 mol L(-1) improved the preconcentration factor severalfold. Excellent tolerance of the proposed method to the presence of foreign ions in solution with silver(I) was demonstrated. A detection limit of 13 ng mL(-1) was derived from the mean value of the blank plus three times its standard deviation. The method was used to determine traces of silver(I) after separation from gold(III), platinum(IV), and palladium(II) matrices on the basis of extractability differences with 18-membered crown ethers under specified conditions. The efficiency of the adopted ion-association mechanism for silver(I) extraction was apparent from the average recovery of 96% for spiked standards by use of the back-washing technique. The proposed extraction procedure was applied to the determination of traces of silver(I) in a selection of chemical reagents.     

Ion Exchange Separation of Platinum and Palladium by Nucleophilic Displacement With Thiocyanate or Thiourea1,2

The separation of platinum and palladium, by adsorption onto weak base anion exchange resins, Amberlite XE 299, or ionex (derived from Amberlite XE-305) from 1M hydrochloric acid, followed by ligand substitution with sulfur nucleophiles is described.

In the thiourea system, cationic thiourea complexes are produced, which cannot be readsorbed into the resin. In the thiocyanate system the formation of Pd(SCN)₄ ^2- is favored in both solution and polymer phases. The Pd(SCN)₄ ^2-. readsorption into the anion exchange resin is the basis for the separation of platinum from palladium.     

Analysis of Sub-Microgram Levels of Palladium (II) in Environmental Samples by Selective Extraction and Spectrophotometric Determination with N-p-Methoxyphenyl-2-Furylacrylohydroxamic Acid and 5-(Diethylamino)-2-(2-Pyridylazo) Phenol

Abstract

Nine new hydroxamic acids in conjunction with four pyridylazo reagents were explored for extractive separation and spectrophotometric determination of palladium in environmental samples. It was found that maximum sensitivity and selectivity was achieved by employing N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) and 5-(diethylamino)-2-(2-pyridylazo) phenol (DEPAP). Palladium was first selectively extracted with MFHA in isoamyl alcohol at pH 2.7-3.5 and the extract was equilibrated with a mixture of 5 M HCl and 10^{? 3} M solution of DEPAP in ethanol. The resulting intensely green ternary complex was measured at 560 nm (σ 5.1 × 10⁴ l mole^?1 cm^?1). The extraction system is suitable for enrichment of palladium over 15 times without loss in recovery and enables determination of palladium at levels as low as 10^?4 ppm (0.1 ppb). The method tolerates the presence of a large number of diverse ions normally associated with palladium, including platinum metals, and was employed for the determination of palladium in standard catalysts, biological materials, and freshwaters.     

The separation of platinum, palladium and gold from silicate rocks by the anion exchange separation of chloro complexes after a sodium peroxide fusion: an investigation of low recoveries

A series of experiments was undertaken to measure the recovery efficiency of platinum, palladium and gold from silicate rocks using a sodium peroxide fusion followed by anion exchange separation of the analytes as chloro complexes. Results obtained by graphite furnace atomic absorption spectrometric analysis of standard solutions prepared in dilute HCl or HCl-acidified sodium peroxide solution showed that recoveries were near quantitative. However, when standard solutions were added to an alkaline sodium peroxide solution, which was then acidified, low results were obtained for platinum and gold (46% and 76% respectively). Low and variable results were also obtained when standard solutions were added to a peridotite sample that had been dissolved by the state procedure, and in the analysis of the South African Bureau of Standards certified reference material, SARM 7. Various experiments were undertaken to investigate these low recoveries, but the reason proposed here is the formation of hydroxychloro compounds in alkaline solution which are not, on acidification with HCl, converted quantitatively to the chloro complex necessary for quantitative anion exchange separation. It is concluded that a sodium peroxide fusion followed by an anion-exchange separation does not appear to form the basis of a successful technique for the determination of platinum, palladium and gold in silicate rocks.     

The separation of gold by selective extraction of HAuBr(4) using a poly(tetramethylene) ether glycol impregnated filter

The separation of gold(III) by selective extraction on an organic- impregnated filter (OIF) was studied. Gold was found to be rapidly extracted into the active polytetramethylene ether glycol (polyTHF) layer of the filter from strongly acidic solutions of HBr, as the HAuBr(4) complex. Quantitative extraction of gold from solution was obtained with flow rates up to 600 ml min(-1) through the 10.75 cm(2) OIF and at ng ml(-1) concentration levels. The extraction is shown to be dependent on the solution flow rate and HBr concentration as well as the filter pore size, thickness and porosity. Gold can be eluted from the filter by converting it into the AuBr(4)(-) complex using a KBr solution. The separation of gold is demonstrated from simple binary metal mixtures involving iron and cadmium, as well as from a more complicated matrix, gold ore solution.     

Extraction-spectrophotometric determination of palladium with triphenylphosphine (TPP)

Palladium is extracted with triphenylphosphine (TPP) solution in benzene from hydrochloric acid medium as the PdCl₂ · 2TPP complex showing maximum absorption at 346 nm and a molar absorptivity of ? = 2.26 × 10⁴.The conditions of palladium extraction have been examined and the composition of the extracted species has been found to be PdCl₂ · 2TPP.A 20-fold excess of other platinum and transition metals has no effect on the palladium extraction. Palladium can be determined at platinum concentrations up to 5 mg/ml provided that the result is corrected for the blank. The elaborated method has been applied to the analysis of platinum samples containing not less than 10^?3% of palladium.     

Simultaneous determination of platinum(II) and palladium(II) by reversed phase high-performance liquid chromatography with spectrophotometric detection after collection on and elution from resin coated with dimethylglyoxal bis(4-phenyl-3-thisomicarbazone)

Amberlite XAD-7 resin coated with dimethylglyoxal bis(4-phenyl-3-thiosemicarbazone) (DMBS) was prepared and applied to the preconcentration of platinum(II) and palladium(II) from aqueous solution. Platinum(II) and palladium(II) were collected quantitatively on resin coated with the reagent (DMBS-XAD-7) from acidic solution in the presence of iodide ion by a bach method. The metal ions were then easily eluted from DMBS-XAD-7 as their DMBS chelates with a small volume of N,N-dimethylformamide. This collection and elution method was applied to the simultaneous determination of platinum(II) and palladium(II) by reversed-phase high-performance liquid chromatography with spectrophotometric detection using an ODS column and acetone-water as the mobile phase. The proposed method was applied to the determination of the metals in commercially available samples.     

Extraction of Palladium(II) and Platinum(IV) from Hydrogen Chloride Solutions with 3,7-Dimethyl-5-thianonane-2,8-dione and Complexation of This Reagent with the Platinum Metals

Extraction of palladium(II) and platinum(IV) from acidic chloride solutions with solutions of 3,7-dimethyl-5-thianonane-2,8-dione in toluene and chloroform and complexation of this reagent with platinum metals in aqueous acetone were studied by ^1Hand ^13C NMR and IR spectroscopy. The possibility of extractive separation of palladium(II) from platinum(IV) and their separation from Cu(II), Ni(II), Co(II), Mn(II) and Fe(III) with solutions of 3,7-dimethyl-5-thianonane-2,8-dione in organic solvents was studied. The apparent concentration constants of extraction of palladium(II) and platinum(VI) with 3,7-dimethyl-5-thianonane-2,8-dione and the corresponding thermodynamic parameters were determined.