Platinum Ore Research Articles

‘Irite’ (Hermann, 1836/1841) from the Urals

AbstractA reappraisal of Hermann's ‘irite’, described in 1836 and 1841, has been attempted by examining and analysing three museum samples, accessioned before 1865. The three samples were determined to be mixtures of chromite, native Os and Ir, rutheniridosmine, platinum, laurite, hongshiite, irarsite, cuprorhodsite, iridsite, prassoite, hollingworthite, erlichmannite, several Ru-Ir-Pt-Ti-Cr-Fe oxide/ hydroxide compounds (sometimes well crystallized), Pt-Ir-K chlorocompounds, and Pt-Ir-Ru-K-Clcontaining opal. The latter two are considered as artifacts generated by the hydrometallurgical processes applied to the crude platinum ores. Individual particles of native iridium and osmium display baroque crystal habits (filaments, leafs, blades, hollow crystals) that could be their natural, although rarely observed, states. There is still doubt about the origin (either natural or artificial) of all Ru-Ir-Pt- Ti-Cr-Fe oxides, but they can be compared with those found in several pristine placer and hard-rock deposits worldwide and in the Urals.

Application of potassium tetrafluorobromate to the rapid decomposition and determination of noble metals in chromites and related materials

Described is an effective new procedure for the preparation of chromites and other geological materials for the determination of the noble metals (NM). The procedure is based on the use of a mixture of KBrF 4 and KHF 2 obtained in situ by adding liquid BrF 3 to a mixture of KHF 2 and sample powder. South African Geostandards SARM-7 platinum ore from the Merensky Reef and SARM-65, a platinum-bearing chromite ore, were used for method development. Following fluorinative decomposition of samples, a homogeneous product is obtained which is suitable for instrumental analysis using either atomic absorption or emission spectrometry techniques. Sulfatization of fusion product using H 2SO 4 produces a non-hygroscopic material, which can be easily powdered and sampled directly into the argon plasma. Solution-based analytical techniques can be applied directly after fluorinative decomposition and conversion of resulting fluorides into chlorides by HCl treatment. The proposed new method, combined with spectrometric emission analysis of powders using a double-jet plasmatron dc plasma atomic emission spectrometry (AES) instrument achieved the following limits of detection (LOD) for the noble metals: Ag, Au and Pd: 1–2×10 −2 g/ton; Pt: 5×10 −2 g/ton; Ru, Rh, Ir and Os: 1–3×10 −3 g/ton. Graphic furnace atomic absorption spectrometry (GFAAS) with preliminary extraction, LODs for NMs were: Pt and Ru: 1×10 −2; Pd and Rh: 1×10 −3; Au and Ag: 1–2×10 −4 g/ton. The relative standard deviation of NM determinations was dependent on concentration and sample type but commonly was in the range of 3–15% dc plasma AES and 5–30% for extraction GFAAS.

Complexation and determination of palladium (II) ion with para-Cl-phenylazo-R-acid spectrophotometrically

The complexation of para-Cl-phenylazo-R-acid azo dye with Pd(II) has been studied spectrophotometrically. Protonation constant (p K a) of the ligand has been calculated and the stability conditional constants of para-Cl-phenylazo-R-acid ligand with palladium ion has been determined at a constant temperature (25.0°C), where the molar ratio of this complex is 1:1 (metal:ligand) with log β 1 =3.75, and 1:2 with log β 2 =8.55. Solid complex of para-Cl-phenylazo-R-acid has been prepared and characterized on the basis of elemental analysis and FTIR spectral data. A procedure for the spectrophotometric determination of Pd(II) using para-Cl-phenylazo-R-acid as a new azo chromophore is proposed where it is rapid, sensitive and highly specific. Beer’s law was obeyed in the range 0.50–10.00 ppm at pH 5.0–6.0 to form a violet–red complex ( ε=7.7×10 4 l −1 mol −1 cm −1 at λ max=560 nm). Metal ions such as Cu(II), Cr(III), La(III), Yb(III), Y(III), and Rh(III) interfere with the complex. Ammonium salt of trimellitic acid is used to precipitate some of the interfering ions and a scheme for separation of Pd(II) from a synthetic mixture similar in composition to platinum ore or deposit was made.

Milli-PIXE of coexisting cooperite and braggite – a comparison with electron probe microanalysis

Cooperite and braggite from the Merensky Reef were analyzed by electron probe microanalysis (EPMA) and milli-PIXE to obtain information on the partitioning of minor and trace elements between the two phases. Limitations of the electron microprobe at low concentrations excluded, in most cases, determination of elements such as Cu, Fe and Rh. First results from the PIXE analyses show that the sensitivity to trace elements has not improved. A striking difference between the techniques was the observation of a higher Pd to Pt ratio in PIXE analyses, as well as higher concentrations of Fe than previously observed. The information obtained from this study emphasizes the problem of comparing analytical results which were obtained by different micro-analytical techniques and constitutes an important step to fingerprinting these economically important minerals in platinum ores.

Determination of small amounts of palladium in wastes from reworking of spent catalysts by microwave induced plasma atomic emission spectrometry

Microwave induced plasma atomic emission spectrometry (MIP-AES) was used for analytical control of reworking of catalysts. Palladium was determined in plant wastes after acid digestion in open systems or systems under pressure. The conditions for introduction of analyte solution using ultrasonic nebulisation and excitation of palladium in the low-power argon microwave plasma sustained in the TM 010 Beenakker type resonator were established. The matrix effects of iron and nickel were studied. Palladium was determined using the argon flow-rate of 200 ml min −1 and 130 W of incident power and detection limit of about 65 μg l −1 in the matrix containing up to 5 mg ml −1 of interfering metals was achieved. A matrix matching method to obtain accurate results was finally applied. The wide linear dynamic range obtained (0.3–250 mg l −1) was useful for routine analysis. For samples with higher palladium content a spectrophotometric method was used as reference to assess the accuracy and precision of the determination by the MIP-AES technique. The low Pd level was tested by analysis of the reference material (platinum ore).

Extraction and Spectrophotometric Determination of Palladium with Pyridine-2-acetaldehyde Salicyloylhydrazone

Abstract A simple and rapid method is proposed for the separation by solvent extraction and spectrophotometric determination of palladiuim(II) with pyridine-2-acetaldehyde salicyloylhydrazone (PASH). The optimum conditions were evaluated by studying critically pH, reagent concentration, and period of equilibration. The palladiuim was determined by measuring Pd(II)–PASH extracted complex in chloroform at 425 nm. The proposed method offers excellent separation of Pd(II) from rutheniuim, cobalt, nickel, copper, and rhodium. The method was applied for the analysis of palladium catalyst and platinum ores.

Dry-chlorination inductively coupled plasma mass spectrometric method for the determination of platinum group elements in rocks

A dry-chlorination procedure has been developed for use in the determination of low concentrations of platinum group elements (PGE) and Au in rock pulps. The PGE and Au, present as native metals, natural alloys and as PGE-(or Au-) bearing sulfide group minerals, are converted by dry-chlorination into PGE (or Au) sodium salts. These salts are dissolved in weak HCl. The solutions are analysed for PGE and Au content by inductively coupled plasma mass spectrometry (ICP-MS). Tests on three reference rock pulps [diluted South African Bureau of Standards Reference Material (SARM)-7 Platinum Ore; diluted INCO S-1800; Nevada Bureau of Mines (NBM) 6a Stillwater] and one gabbro rock showed that the dry-chlorination–ICP-MS method produced results that were usually comparable to, and often better than, fire assay techniques. Reagent contamination was extremely low (Pt⩽1 ng g–1; other PGE and Au⩽0.2 ng g–1). The recoveries of PGE obtained by dry-chlorination–ICP-MS were often >90%.

Mineralogy in the evaluation of ore deposits

Abstract Mineralogical characterization of an ore deposit is an essential on-going activity in a continuum of evaluation exercises and decisions which operate from the very first recognition of mineralization to the cessation of mining and beyond. The main input of the mineralogist to ore evaluation is through the provision of a detailed qualitative and quantitative mineralogical representation of an ore that is specifically targeted to the needs of the process engineer in determining metallurgical recovery, especially during the exploration and pre-production stage. This process mineralogical input is often related to fine-tuning in mining and processing resulting from unexpected variations in the mineralogy of the ore to the mill. Mineralogical characteristics of platinum ore, refractory gold ores, and complex Cu-Zn-Pb ores are used to illustrate aspects of process mineralogical input at various stages in the life cycle of a mine. It is concluded that it is difficult for the mineralogist to become established as an essential and ongoing participant of exploration and mine evaluation exercises. It is thus important that both process engineers and geologists are given a better training in process mineralogy than is presently the case. Most mineralogical training and research in geology departments is exclusive of industrial applications.

Ion Pair Extraction and Separation Studies of Palladium

Abstract A simple and rapid method is proposed for the extraction, separation, and spectrophotometric determination of palladium from salicylate media using Aliquat 336 dissolved in xylene as an extractant. The optimum conditions were evaluated from a critical study of pH, salicylate concentration, Aliquat 336 concentration, and period of equilibration. The palladium in the Aliquat 336 phase is determined spectrophotometrically with 4-(2-pyridylazo)resorcinol (PAR) at 530 nm. The proposed method described the scheme for the separation of platinum, nickel, copper, cobalt, zinc, and manganese from binary mixtures. The method was extended to the analysis of palladium catalyst and platinum ores.

Analysis of a rhenium-osmium solid-solution spike by inductively coupled plasma mass spectrometry

The rhenium-osmium decay scheme (187Re →187Os) offers a unique opportunity to investigate the genesis of, and directly date, ultramafic rock, sulphide and platinum ore deposits. Inductively coupled plasma mass spectrometry (ICP-MS) is a viable method for Os isotopic analysis as it provides the high temperatures necessary to ionise Os. The sample can be introduced into the ICP mass spectrometer either by conventional nebulisation or by distillation using an Os “generator.” Generator-mode analysis is superior to nebulisation because (i) the total number of counts is two orders of magnitude higher for a given sample size and (ii) Os oxidises readily to volatile OsO4, which has a boiling-point lower than most Re compounds, so that Os can be efficiently separated from 187Re. The importance of Os loss during sample preparation was minimised by combining the sample powder with a powdered Re-Os isotopic spike prior to any chemical treatment. The spike is in a nickel sulphide matrix and was made by a thioacetamide co-precipitation of Os, Re and Ni followed by a fire assay. The 190Os/192Os ratio in this preparation is 51.5 ± 0.9, the 187Os/188Os ratio is 0.063 ± 0.006 and the 185Re/187Re ratio is 17.04 ± 0.41. These values are within the error limits quoted by the Oak Ridge National Laboratory and Techsnabexport, the suppliers of the metallic spikes. Parameters that significantly influence the Os analyses include the oxidising agent and the run temperature. The oxidising agent H5IO6 is preferred to H2O2 or HNO3 as it has the highest electrode potential, provides a prolonged, consistent reaction and is more stable when stored. Chilling the sample and the H5IO6, initially retards uncontrolled OsO4 emission. Heat applied later in the run releases OsO4 and helps maintain a high count rate. Thus, OsO4 can be generated in a steady, controllable and reproducible manner.

Rapid Spectrophotometric Determination Of Osmium With Cyclohezane 1,3-Dione Bisthiosemicarbazone Monohydrochloride: Simultaneous Determination of Osmium and Platinum

Abstract A simple, sensitive and rapid spectrophotometric method has been developed for the determination of osmium using cyclohexane 1,3-dione bisthiosemicarbazone mono-hydrochloride (1,3-CHDT.HCl). The method is based on the instantaneous colour reaction between 1,3-CHDT. HCl and osmium(VIII) in sodium acetate—acetic acid buffer medium (pH range 3–6). The osmium complex shows maximum absorbance at 375 nm and considerable absorbance at 510 nm. Although the complex formed between platinum(IV) and reagent (1,3-CHDT.HCl) shows maximum absorbance at 375 nm, it does not show any absorbance at 510 nm. Simultaneous determination of osmium and platinum is carried out when present alone and in presence of other foreign (associated) ions. Some physico-chemical and analytical characteristics of osmium and platinum complex are described. Interference of various foreign ions have studied and osmium is estimated selectively in the presence of constituents of platinum ores.

Justus Erich Bollmann and Francisco Antonio Zea

The activities of the German-born physician Justus Erich Bollmann in securing a supply of Colombian platinum ore for the English chemist William Hyde Wollaston is traced from the time Bollmann settled in London in 1816. An account is also given of Bollmann’s efforts in 1820 and 1821 to obtain for sale on the London market some 40,000 pounds of platinum from the Government of the then newly established Republic of Colombia, efforts which involved negotiations with, and financial advances made to, the first Vice-President of that Republic, Don Francisco Antonio Zea.

A critical evaluation of the performance of triphenylphosphine and N, N'-diphenylthiourea in solvent extraction concentration of precious metals for ICAP-AES analysis

In view of the capability of Inductively Coupled Argon Plasma-Atomic Emission Spectrometry (ICAPAES) for simultaneous multi-element analysis group extraction of trace elements is of special importance. Group extraction of precious metals using the complexing agents N, N'-diphenylthiourea (DPTU)and triphenylphosphine (TPP) was systematically investigated. From the results it appeared that platinum, palladium, gold and silver were selectively extracted as a group without the need of a labilizing agent. Direct ICAP-AES analysis of the organic extracts turned out to be feasible, but experimentally the analysis of organic solutions was much less straightforward compared to aqueous solutions. A procedure was tested to transfer the metals back into aqueous solution. The extraction procedure using both DPTU and TPP in solvent extraction of precious metals for ICAP-AES analysis has been applied to a certified platinum ore. The results showed a good agreement with the certificate.

Palladium and Platinum

Palladium and platinum are the longest known and most studied of the six platinum metals [1–11], a reflection of their abundance and consequent availability. Platinum occurs naturally as the element, generally with small amounts of the other platinum metals. It was used as a silver substitute by Colombian Indians and first observed there by Ulloa (1736), who called it platina del Pinto (‘little silver of the Pinto river’) but the first sample was actually brought to Europe in 1741 by Charles Wood, Assay Master of Jamaica. Palladium was isolated in 1803 by W.H. Wollaston, who was studying the aqua regia-soluble portion of platinum ores (he announced his discovery by an anonymous leaflet advertising its sale through a shop in Soho) and named it after the newly discovered asteroid Pallas [12].

A comparison of methods for the determination of platinum in ores

Fire-assay and wet-extraction methods of determining platinum in ores have been evaluated. The fire-assay procedure using lead as a collector was used in combination with flame and flameless atomic-absorption, emission spectroscopy and X-ray fluorescence. In this last method flattened silver beads were analysed directly, whereas for the other methods the beads were dissolved in aqua regia and the solutions made up with concentrated hydrochloric acid before analysis. The wet procedures involved treatment of the ores with acids and subsequent analysis by flame atomic-absorption or by spectrophotometry after treatment with tin(II) chloride. Chromatographic, ion-exchange and solvent-extraction procedures were used to isolate platinum from base metals, the other platinum metals and gold. Results for each ore by fire assay-flame atomic-absorption, fire assay-emission spectroscopy, and wet extraction combined with spectrophotometry, showed no difference at the 99% confidence level. X-Ray fluorescence and flameless atomic-absorption results tended to be high and low respectively. The most precise method was wet extraction followed by spectrophotometric determination. Emission spectroscopy and X-ray fluorescence generally yielded the poorest precision. Wet-extraction methods were time-consuming and since no advantage was gained in accuracy over the fire-assay methods, a combined fire assay-flame atomic-absorption system was the preferred method of analysis.

Use of low energy photon spectroscopy in activation analysis of noble metals with high-energy bremsstrahlung

Noble metals have been analyzed in high purity copper and a platinum ore to be certified as reference materials. Analyses were performed by photon activation analyses using both conventional gamma and low energy photon spectroscopy. Our values agree very well with those of other laboratories using various analysis methods. Low energy photon spectroscopy is more advantageous than gamma spectroscopy from various points of view.

Trace determination of platinum—II. Analysis in ores by pulse polarography after fire-assay collection

A pulse-polarography method is described for the determination of traces of platinum in ores after fire-assay separation and preconcentration. The silver bead from the fire assay is dissolved and treated with ammonia and ethylenediamine to produce a sensitive catalytic polarographic wave. Measurement of the wave by differential pulse polarography allows determination of Pt with a detection limit of 0.0025 ppm. Platinum in ore samples was determined in the range 0.1–0.9 ppm and a correlation coefficient of 0.98 was obtained on comparison with AAS results.

Determination of platinum in ores by a combined fire-assay and flameless atomic-absorption method

A combined fire-assay and flameless atomic-absorption procedure for the determination of platinum in ores is described. Silver beads obtained by cupellation are dissolved in aqua regia and made up to standard volume with 6 M hydrochloric acid, then 50-μl aliquots are injected into a carbon tube. From 0.5 to 5 ppm platinum can be determined with a precision of approximately 5%. The procedure tolerates other platinum metals and gold in the amounts present in the ores analysed.

Determination of platinum in ores by a combined fire assay—X-ray fluorescence method

A combined fire assay—x-ray fluorescence procedure for the determination of platinum in ores is described. Silver beads obtained by cupellation in the classical fire assay process are flattened to constant thickness before placement in the x-ray beam. A standard plot of platinum—silver intensity ratio versus platinum concentration is used to measure the platinum content of ore samples.

Jacob Forster (1739–1806) and his connections with forsterite and palladium

SummaryThe person after whom forsterite was named has been confirmed as Jacob Forster (1739–1806), a mineral collector and dealer of London. The discovery of palladium and rhodium by William Hyde Wollaston and of iridium and osmium by Smithson Tennant appears to have been made on crude platinum ore from South America supplied by Forster.