Preconcentration of gold,silver, palladium,platinum, and ruthenium with organophosphorus extractants

Extraction of noble metals in acid media with new tertiary phosphines and phosphine chalcogenides was examined. Tristyrylphosphine, tristyrylphosphine sulfide tris(2-phenylethyl)phosphine oxide, tris-(2-phenylethyl)phosphine sulfide, bis(2-phenylethyl)[2-(propylthio)ethyl]phosphine oxide, bis(2-phenylethyl)-[2-(butylthio)ethyl]phosphine oxide, and tris[2-(butylthio)ethyl]phosphine oxide were used as extractants. The suitability of the extractants for determination of Au, Ag, and Pd in rock and ore samples was elucidated.     

Determination of platinum, palladium, and gold in a silver assay bead by atomic absorption spectrophotometry

Summary A procedure is given for the atomic absorption determination of platinum, palladium and gold in silver beads. Interferences by coexisting ions usually found in the parting solution could be eliminated by addition of 1% of lanthanum. The lowest working ranges in which it is possible to obtain results comparable in accuracy to those from a good spectrophotometric determination are estimated for each metal. (1 ppm Pd, 1 ppm Au, 5 ppm Pt). The results of several determinations using the proposed procedure to analyse silver assay beads are given.

---

Bestimmung von Platin, Palladium und Gold in dokimastischen Silberperlen durch Atomabsorptions-Spektrophotometrie

Zusammenfassung Störungen durch in der Scheidelösung vorhandene Begleitionen konnten durch Zusatz von 1% Lanthan verhindert werden. Die unteren Grenzen für eine genaue Bestimmbarkeit wurden festgelegt (1 ppm Pd, 1 ppm Au, 5 ppm Pt) und Ergebnisse mehrerer Beleganalysen mitgeteilt.

     

The separation of palladium and platinum by ion flotation

Differences in the ion flotation properties of palladium(II) and platinum(IV) chloro complexes in aqueous solutions are used to achieve separations of these metals. The anionic chloro complex PtCl^2-₆ is floated selectively with cationic surfactants of the type, RNR'₃Br, from solutions of PdCl^2-₄ and various concentrations of hydrochloric acid. The palladium(II) does not float from solutions of ? 3.0 M HCl and the platinum(IV) floated from these solutions can be recovered free of palladium. However, the separation is incomplete as much of the platinum(IV) is also unfloated from these solutions. Quantitative separations are obtained by conversion of the palladium(II) to the cationic ammine, Pd(NH₃)₄²⁺ with aqueous ammonia prior to flotation. The anionic chloro complex of platinum(IV) is unaffected by the presence of ammonia and is floated quantitatively with the surfactant n-hexadecyltri-n-propylammonium bromide from 0.01 M ammonia solutions.     

Halo-carbonyl complexes of palladium,platinum and gold

In this review we summarize some recent literature data concerning synthetic procedures, properties, structure, reactivity and applications of halo-carbonyl complexes of palladium, platinum and gold, taking into consideration that the organometallic chemistry of these metals, with a particular attention to the halo-carbonyls, has been reviewed 20 years ago [F. Calderazzo, J. Organomet. Chem. 400 (1990) 303]. A brief overview of the early studies is provided.     

Determination of palladium, platinum and gold by first derivative spectrophotometry

Summary The application of first-derivative spectrometry to the simultaneous determination of palladium(II), platinum(IV) and gold(III) is described. Light absorption of stable chlorocomplexes formed in 1 mol/l hydrochloric acid provides the basis of their determinations. A difference in the derivative amplitudes between two first-derivative zero crossing points of one metal A is read, corrected for the contribution of metal B and used for quantitation of metal C. Palladium (0.48–20 g ml^–1), platinum (0.16–24 g ml^–1) and gold (0.32–24 g ml^–1) have been determined with good precision and accuracy without any separations. Results are also presented for the simultaneous determination of the three precious metals in the presence of several major constituents.     

Determination of trace amounts of palladium by radiochemical displacement

A method has been developed for the determination of trace amounts of palladium using radioactive mercury dithizonate as the reagent. Experimental conditions for the quantitative displacement of mercury from the reagent, calibration graph and the interfering effects of various ions have been studied. The method is sensitive down to 2 g of palladium present in 10 ml of the aqueous solution.     

Electrochemical behaviour of gold, silver, platinum and palladium on the glassy carbon electrode modified by chitosan and its application

The chitosan-modified glassy carbon electrode can be used as a working electrode for the determination of precious metal elements: Au, Ag, Pt, Pd. In low pH medium, the complex anions of these precious elements combine with the protonated group ---NH₃⁺ in the chitosan molecule in the form of an ion-association complex. These metal ions were selectively enriched and we got sensitive anodic stripping current. These elements content in ore, welding material have been determined by this method. The results were consistent with those from standard sample and ICP atomic emission spectrometry method. The possible mechanism of electrochemical reaction has been proposed by the study of CV, UV and FT-Raman spectrometry.     

Structure of supported palladium,silver and gold clusters

Clusters nucleated by inert gas aggregation have been studied by HREM. The clusters were supported by amorphous carbon films and by crystalline graphite fibres. Multiply twinned particles with 5-fold axes of symmetry were observed whose structures and orientations are discussed. It is also demonstrated that crystalline graphite substrates can be used to calibrate lattice distances and to improve the image processing. With the help of computer simulations complex structures were resolved.     

Neutron activation analysis of high purity noble metals (palladium,platinum, rhodium,gold and silver)

Methods of neutron activation analysis of high purity noble metals have been developed based on the selective extraction procedures for matrix activities separation. These procedures are shown to provide purification coefficients from matrix of about 10⁶–10⁸. High-resolution gamma-spectrometry makes possible the determination of 25–30 elements simultaneously in aqueous phases remained after matrix separation. Complex standard for NA analysis of pure materials has been described.     

Flame atomic absorption spectrometric determination of trace amounts of palladium,gold and nickel after cloud point extraction

In this article, a sensitive cloud point extraction procedure for the preconcentration of trace amounts of palladium, gold and nickel prior to their determination by flame atomic absorption spectrometry has been developed. The cloud point extraction method is based on the complexation of Pd(II), Au(II), and Ni(II) ions with 1-(2-pyridylazo)-2-naphthol and entrapping in non-ionic surfactant Triton X-114. The main factors affecting cloud point extraction efficiency, such as pH of sample solution, concentration of 1-(2-pyridylazo)-2-naphthol and Triton X-114, equilibration temperature and time, were investigated in detail. Under the optimized conditions, calibration curves were constructed for the determination of palladium, gold and nickel according to the general procedure. Linearity was maintained from 0.01 to 1.0 μg/mL for palladium, 10.0 μg/mL to 1.5 μg/mL for gold, and 10.0 μg/mL to 0.5 μg/mL for nickel. Detection limits based on three times the standard deviation of the blank divided by the slope of analytical curve (3Sb/m) for Pd(II), Au(III), and Ni(11) ions were 3.4, 3.9, and 2.4 μg/mL, respectively. Seven replicate determination of a mixture of 0.5 μg/mL palladium and gold and 0.2 μg/mL nickel gave a mean absorbance of 0.174, 0.150, and 0.201 with relative standard deviation ±1.5, ±1.3, and ±1.8%, respectively. The high efficiency of cloud point extraction to carry out the determination of analytes in complex matrices was demonstrated. The proposed method has been applied for determination of trace amount of palladium, gold and nickel in certified reference material and water samples with satisfactory results.     

Improved recovery of trace amounts of gold (III), palladium (II) and platinum (IV) from large amounts of associated base metals using anion-exchange resins

The adsorption and desorption behaviors of gold (III), palladium (II) and platinum (IV) were surveyed in column chromatographic systems consisting of one of the conventional anion-exchange resins of large ion-exchange capacity and dilute thiourea solutions. The noble metals were strongly adsorbed on the anion-exchange resins from dilute hydrochloric acid, while most base metals did not show any marked adsorbability. These facts made it possible to separate the noble metals from a large quantity of base metals such as Ag (I), Al (III), Co (II), Cu (II), ¶Fe (III), Mn (II), Ni (II), Pb (II), and Zn (II). Although it used to be very difficult to desorb the noble metals from the resins used, the difficulty was easily overcome by use of dilute thiourea solutions as an eluant. In the present study, as little as 1.00 μg of the respective noble metals was quantitatively separated and recovered from as much as ca. 10 mg of a number of metals on a small column by elution with a small amount of dilute thiourea solution. The present systems should be applicable to the separation, concentration and recovery of traces of the noble metals from a number of base metals coexisting in a more extended range of amounts and ratios.     

Improved recovery of trace amounts of gold (III), palladium (II) and platinum (IV) from large amounts of associated base metals using anion-exchange resins

The adsorption and desorption behaviors of gold (III), palladium (II) and platinum (IV) were surveyed in column chromatographic systems consisting of one of the conventional anion-exchange resins of large ion-exchange capacity and dilute thiourea solutions. The noble metals were strongly adsorbed on the anion-exchange resins from dilute hydrochloric acid, while most base metals did not show any marked adsorbability. These facts made it possible to separate the noble metals from a large quantity of base metals such as Ag (I), Al (III), Co (II), Cu (II), Fe (III), Mn (II), Ni (II), Pb (II), and Zn (II). Although it used to be very difficult to desorb the noble metals from the resins used, the difficulty was easily overcome by use of dilute thiourea solutions as an eluant. In the present study, as little as 1.00 microg of the respective noble metals was quantitatively separated and recovered from as much as ca. 10 mg of a number of metals on a small column by elution with a small amount of dilute thiourea solution. The present systems should be applicable to the separation, concentration and recovery of traces of the noble metals from a number of base metals coexisting in a more extended range of amounts and ratios.     

Separation and determination of small amounts of palladium and platinum

Summary A procedure is described for the separation of 20 to 100g of Pd(II) from 100 to 300g of Pt(IV) in a mixture. The method is based on the selective separation of Pd(II) on silica gel, leaving Pt(IV) in the solution phase. Complete recovery of Pt(IV) in the supernate has been checked with¹⁹⁷Pt as the radioactive indicator. The deposited palladium is extracted with dil. HCl, and the separated components are determined spectrophotometrically. A possible mechanism has been suggested.

---

Zusammenfassung Die Trennung eines Gemisches aus 20 bis 100g Pd(II) und 100 bis 300g Pt(IV) wurde beschrieben. Sie beruht auf der selektiven Adsorption von Pd(II) an Kieselgel. Das vollständige Verbleiben von Pt(IV) in der Lösung wurde mit¹⁹⁷Pt radiochemisch erwiesen. Das adsorbierte Pd wird mit verd. HCl extrahiert und spektrophotometrisch gemessen. Eine mögliche Interpretation des Adsorptionsvorganges wird angeführt.

     

Neutron activation analysis for iridium,palladium and silver in platinum

A sensitive procedure for the simultaneous determination of trace levels of iridium, palladium and silver in a platinum stock, by thermal-neutron activation analysis utilizing gamma-ray spectrometry, was developed. The radiochemical-separation scheme involved an elution of the chloro complexes of iridium and silver, and subsequently palladium, through a strongly-basic anion-exchange resin, followed by further chemical-separation methods. The ion-exchange method served to greatly reduce the hazard from radiations emitted by the bulk of the activities in the matrix. Activities of 13.5-hr¹⁰⁹Pd, 74.2-d¹⁹²Ir and 255-d^110m Ag were monitored by accumulation of pulses from a 3-in diam. NaI(T1) crystal detector. Further discrimination was attained by resolution of decay curves. The procedure provided analyses for a platinum stock of 0.015±0.0021 ppm Ir; 0.028±0.0043 ppm Pd and 2.4±0.27 ppm Ag.     

Mutual interference of gold, platinum and palladium in atomic-absorption spectroscopy

It is shown that the mutual interference between the chlorides of Au, Pt and Pd in AAS using aqueous solutions nebulized into an air-acetylene flame, can be eliminated by using the dithizonates of these metals. This releasing action is ascribed to the formation of noble metal dithizonates. It is further shown that complex formation with dithizone favours the atomization of Au and that such an effect should be considered as due to complexation rather than to some bulk effect of the organic matrix.     

Determination of silver, gold and palladium by a combined fire-assay atomic-absorption procedure

A method is described which combines the best features of the fire-assay procedure with an atomic-absorption technique. The precious-metal bead resulting from the fire-assay concentration step is dissolved in acids, the solution evaporated to dryness and the residue dissolved in b measured quantity of cyanide solution. The atomicabsorption measurement of this solution allows the determination of as little as 0.017 ppm of silver, 0.08 ppm of gold, and/or 0.08 ppm of palladium in various precious-metat-bearing materials with a precision of +/- 1%.     

Solid-phase extraction in the determination of gold, palladium, and platinum

A simple classification of various sorbents and solid-phase extraction procedures used for preconcentration of trace levels of Au, Pd, and Pt from different sample types is proposed in this review article. The large variety of available sorbents/procedures has been organized according to expected mechanisms of sorption process (complex formation; ion exchange; adsorption; ion-imprinted or molecularly imprinted polymers); according to the kind of monomeric units of the polymer matrix as well as on the basis of the kind of functional group responsible for main performance characteristics (selectivity, capacity) of the sorbent. Advantages of chemically modified sorbents, sulfur-containing sorbent extractants, and ion-imprinted polymers, together with rational pretreatment by means of microwave treatments, scaling down of enrichment, and quantification by means of flow and flow injection approaches are given. Preferred instrumental techniques for quantification of ppb levels of Au, Pd, and Pt in prepared concentrates/column eluates are multielement instrumental techniques: inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICPMS). Excellent limits of detection at picogram levels of these analytes are provided by electrothermal atomic absorption spectrometry (ETAAS), generally in single-element mode and the neutron activation analysis (NAA), while X-ray fluorescence spectrometry and flame AAS are rarely applied because of lack of sensitivity at sub-ppm levels of Au, Pd, and Pt. Some problems of atomic spectrometric quantification techniques and their representative limits of detection are given. Recent applications to geological, industrial, pharmaceutical, biological, and other materials are tabulated. References have been selected mostly from the period 1995 to 2010.     

A fire-assay and wet chemical method for the determination of palladium, platinum, gold, and silver in ores and concentrates

A method is presented for the determination of palladium, platinum, gold and silver in ores and concentrates by a fire-assay and wet chemical technique. After parting of the lead assay button with dilute nitric acid, and separation of the solution from the residue, the palladium and platinum in the solution are precipitated by the addition of stannous chloride, with tellurium as collector. The resulting precipitate is combined with the gold residue and dissolved in aqua regia, then the solution is analysed for palladium, platinum and gold by atomic-absorption spectrophotometry (AAS). Silver is determined in the original solution by AAS before the reduction step.     

Enrichment of trace cerium subgroup rare earths by means of ion flotation

The possibility of ion flotation of cerium subgroup rare earths (Ce-subgroup) wasexplored. Various factors affecting the flotation efficiency were investigated. The results showedthat, by using sodium tetradecyl sulfate as the collector of trace Ce-subgroup and frother, over 95%of Ce-subgroup at ng/g levels could be separated from pH 2.3 media in 10--15 min. The proposedmethod has been applied to the determination of Ce-subgroup in a polluted farmland soil referencematerial (GBW 08303) with satisfactory results.