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 6M hydrochloric acid, then 50-mul 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.     

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.     

An investigation of a flameless atomic-absorption method for determination of aluminium, calcium, iron and magnesium in sewage sludge

The methods currently used for the determination of aluminium, calcium, iron and magnesium in sewage sludge are time-consuming. A rapid flameless atomic-absorption procedure, utilizing homogenization of diluted samples as the only pretreatment, has been compared with wet and dry analytical methods followed by flame atomic-absorption analysis, in a statistically designed experiment. Low-sensitivity (secondary absorption) lines have been used for the flameless analysis. The flameless atomic-absorption method described is better than all the other methods tested, with the exception of the nitric-perchloric-hydrofluoric acid digestion procedure. The time saved is substantial and the method could be used advantageously for routine analysis.     

Determination of silver in ores, concentrates, zinc process solutions, copper metal and copper-base alloys by atomic-absorption spectrophotometry after separation by extraction of the tribenzylamine-silver bromide complex

A method for determining 0.1 μg/g or more of silver in ores and concentrates and 0.001 μg/ml or more of silver in zinc process solutions is described. Silver is separated from the matrix elements by chloroform extraction of the tribenzylamine—silver bromide ion-association complex from 0.08M potassium bromide—2M sulphuric acid and stripped with 9M hydrobromic acid. This solution is evaporated to dryness and organic material is destroyed with nitric and perchloric acids. Silver is determined by atomic-absorption spectrophotometry in an air—acetylene flame, at 328.1 nm, in a 10% v/v hydrochloric acid—1% v/v diethylenetriamine medium. Cadmium, bismuth and molybdenum are partly co-extracted but do not interfere. The method is also applicable to copper metal and copper-base alloys. Results obtained by this method are compared with those obtained by a fire-assay/atomic-absorption method.     

A critical review of the volumetric methods for the platinum metals

The published methods for the volumetric determination of the six platinum metals have been appraised. The lack of generally applicable and accurate methods is emphasized. No volumetric method has been recorded for the direct application to solutions of platinum metals, ores, concentrates or natural alloys, and only a few for determinations in synthetic alloys such as fire assay beads. Volumetric methods for the platinum metals are characterized by the absence of data concerning methods of dissolution.     

Improved tribenzylamine-silver bromide extraction/atomic-absorption spectrophotometric method for the determination of silver in ores, related materials and zinc process solutions

An improved tribenzylamine extraction/atomic-absorption method for the determination of silver in ores, related materials and zinc process solutions is described. The method, which involves the separation of silver by a single methyl isobutyl ketone extraction of the tribenzylamine-silver bromide ion-association complex from ~ 0.5-2M sulphuric acid-0.14M potassium bromide, is simpler and more rapid than a previous method based on a triple chloroform extraction of the complex. Silver is stripped with 12M hydrochloric acid containing 1% thiourea as a complexing agent. Thiourea is destroyed with nitric and perchloric acids and silver is ultimately determined by atomic-absorption spectrophotometry in an air-acetylene flame, at 328.1 nm, in a 10% v v hydrochloric acid-1% v v diethylenetriamine medium. Cadmium and bismuth are partly co-extracted but do not interfere. Results obtained by this method are compared with those obtained previously by the tribenzylamine/chloroform extraction method and with those obtained by a direct acid-decomposition/atomic-absorption method.     

Comparison of silver results for canadian reference ores and concentrates and zinc-processing products by acid decomposition, tribenzylamine/chloroform extraction and fire-assay combined with atomic-absorption spectrophotometry

The results obtained for silver in Canadian reference ores and concentrates and in zinc-processing products by three atomic-absorption spectrophotometric methods are compared. "Wet chemical" methods based on the decomposition of the sample with mixed acids yield more accurate results than those based on fire-assay collection techniques. A direct acid-decomposition method involving the determination of silver in a 20% v/v hydrochloric acid-1% v/v diethylenetriamine medium is recommended for the determination of approximately 10 mug g or higher levels of silver. A method based on chloroform extraction of the tribenzylamine-silver bromide ion-association complex from 0.08M potassium bromide-2M sulphuric acid is recommended for samples containing < 10 mug of silver per g.     

Determination of silver in ores and metallurgical concentrates by a combination of fire-assay preconcentration (using tin as collector) and atomic-absorption spectrophotometry

A new method is described for the determination of silver in ores and metallurgical concentrates. The procedure is based on collection of silver in a tin button during a fire assay fusion, and the subsequent determination by atomic-absorption spectrophotometry. The proposed method is rapid and free from inter-element interferences, and results obtained agree favourably with those obtained by alternative methods.     

Determination of gold, indium, tellurium and thallium in the same sample digest of geological materials by atomic-absorption spectroscopy and two-step solvent extraction

A rock, soil, or stream-sediment sample is decomposed with hydrofluoric acid, aqua regia, and hydrobromic acid-bromine solution. Gold, thallium, indium and tellurium are separated and concentrated from the sample digest by a two-step MIBK extraction at two concentrations of hydrobromic add. Gold and thallium are first extracted from 0.1M hydrobromic acid medium, then indium and tellurium are extracted from 3M hydrobromic acid in the presence of ascorbic acid to eliminate iron interference. The elements are then determined by flame atomic-absorption spectrophotometry. The two-step solvent extraction can also be used in conjunction with electrothermal atomic-absorption methods to lower the detection limits for all four metals in geological materials.     

Interferences and their elimination in the determination of the noble metals by atomic-absorption spectrophotometry

A number of serious interferences in the determination of the noble metals by atomic-absorption spectrophotometry have been investigated, and ways of eliminating them considered. The use of the nitrous oxide and acetylene flame reduced many of the interferences but also reduced the sensitivity. Additions of lanthanum, copper sulphate, copper + cadmium sulphate, uranium, and vanadium as releasing agents were effective in the removal of interferences for one or more of the noble metals in the air-acetylene flame. Uranium additions were found to be effective in removing mutual interferences associated with the noble metals (osmium and indium were not tested) whereas vanadium removed mutual and base-metal interferences. The precision and accuracy of methods of analysis based on the use of uranium and vanadium were acceptable, and the application of these methods to the analysis of noble metals collected by various procedures is briefly discussed.     

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.     

Determination of iridium in mafic rocks by atomic absorption

Iridium is determined in mineralized mafic rocks by atomic absorption after fire-assay concentration into a gold bead. Inter-element interferences in the atomic-absorption determination are removed and Ir sensitivity is increased by buffering the solutions with a mixture of copper and sodium sulphates. Substantial amounts of Ag, Al, Au, Bi, Ca, Cd, Co, Cr, Fe, Ho, Hg, K, La, Mg, Mn, Mo, Ni, Pb, Te, Ti, V, Y, Zn and platinum metals can be tolerated in the atomic-absorption determination. The sensitivity and detection limits are 3.2 and 0.25 ppm of Ir, respectively.     

Fire-assay collection of gold and silver by copper

Gold and silver are very effectively collected in copper after fire-assay fusion at 1200 degrees . The resultant copper button is dissolved in perchloric acid and the parting solution is diluted with an equal volume of water. Both gold and silver are precipitated in the copper perchlorate medium by reduction with formic acid or hydroquinone. The two noble metals are collected, dissolved in acids, and determined by atomic-absorption spectrometry. The proposed procedure is simple, relatively rapid, and has been successfully applied to ores, concentrates, furnace products, and copper alloys. Recoveries compare favourably with those obtained by the classical lead cupellation method.     

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.     

Review of methods for the determination of lanthanides in geological samples

The following methods of determining lanthanides in geological samples are reviewed, together with the separation techniques necessarily associated with them: neutron-activation analysis, atomic-absorption and flame-emission spectrometry, plasma-source emission spectrometry, mass spectrometry, X-ray fluorescence spectrometry, and spectrophotometry.     

Referee analysis of precious metal sweeps and related materials

Sweeps samples are often complex mixtures containing from trace amounts to 20% of one or more precious metals distributed in matrices consisting of widely varying mixtures of base metals or their oxides. Three collection procedures are described that are suitable for the isolation of precious metals from base substances. One is based on direct fusion of the sample (high-grade sweeps) with sodium peroxide, and the others on collection of the precious metals by fire-assay techniques using either nickel sulphide or silver. The precious metals are then determined either gravimetrically or by atomic-absorption or plasma-emission spectrometry.     

Determination of lead in drinking waters by hydride generation and atomic-absorption spectroscopy, and three other methods

Simultaneous presence of copper and nickel in potable waters interferes with the determination of lead at trace levels by the hydride-atomic-absorption spectrophotometric method. This interference is eliminated by co-precipitating lead with manganese dioxide from acidic solution. The precipitate is dissolved in 0.85% nitric acid and analysed by the automated hydride-atomic-absorption method. This method has been applied to 22 representative water samples and results compared with those obtained by using differential pulse anodic-stripping voltammetry, flame atomic-absorption and graphite-furnace atomic-absorption spectrophotometry. The precision of the three methods is reported and their accuracy checked by the analysis of reference standard water samples. The sensitivity of the three methods is of the order of 1 mug/l., compared to 100 mug/l. for flame atomic-absorption. The merits of each method are discussed.     

Analysis of sediments for heavy metals by a rapid electrothermal atomic-absorption procedure

A rapid electrothermal atomic-absorption spectrophotometric procedure with homogenization as the only pretreatment is compared with two wet pretreatment methods followed by flame atomic-absorption, in a statistically designed experiment. Samples from the top 5 cm of sediments at three different points of the Tejo estuary were used for the tests. The results show that the electrothermal procedure performed as well as whichever was the better of the flame methods for the determination of cadmium and nickel, irrespective of the sand content of the samples; although not statistically significant, there was apparently a decrease in recovery for chromium, copper and lead by the electrothermal method as the sand content of the sample increased. For zinc the electrothermal method gave results statistically different from those of the flame procedures when the sand content was high but not when the organic content of the sample was high. Because of the limited degree of replication (5 variates) the relative differences between the average values obtained by the three methods were significant only if they exceeded 15%. The electrothermal method has the advantage of substantially greater speed.     

Determination of lead in gasoline by atomic absorption spectroscopy

A procedure has been developed for the direct determination of lead in gasoline by atomic absorption spectroscopy. This procedure is rapid, does not require expensive equipment, is remarkably free from interference by other trace elements present, and allows considerable variation in the sulfur and nitrogen content of the gasoline. It compares favorably with other existing procedures for this determination, such as X-ray fluorescence, wet chemical methods, and flame photometry.     

Carbon nanotube-based extraction and electrochemical detection of heavy metals

In this mini review, recent trends and challenges in developing carbon nanotube-based extraction and electrochemical detection of heavy metals in water are reviewed. Carbon nanotubes (CNT) have electrical, mechanical, chemical, and structural properties superior to those of conventional materials, for example graphite and activated carbon. CNT-based procedures are also more efficient than traditional techniques and methods, for example liquid?Cliquid extraction, atomic-absorption spectroscopy, flame photometry, and inductively coupled plasma, because they can enable rapid, sensitive, simple, and low-cost on-site detection. Different forms of CNT, including as-grown, oxidised, and functionalised CNT, can be well suited to metal adsorption. The measurement procedure relies on adsorbing the metal on the CNT surface after reasonable contact time, either by applying an electrical potential or under open-circuit conditions, and subsequent quantification. Different types of CNT-based electrode, including composite, paste, and binder-free, can be fabricated and used for metal detection. Application of CNT and their novel properties to the adsorption and detection of heavy metals is discussed in detail.