New chelating sorbents for noble metals

The properties of the new ehelate-forming “POLYORGS” sorbents for concentration of noble metals are discussed. POLYORGS are made from different polymeric matrices (polystyrene, copolymers of styréne with divinylbenzene, fibrous materials). They contain heterocyclic amine and amidoxime groups, and are selective for noble metals. Some methods of noble metal determination after preliminary concentration of POLYORGS sorbents are given.     

Sorption preconcentration in combined methods for the determination of noble metals

Combined methods for the determination of noble metals with the use of sorption preconcentration with complexing, anion-exchange, and other sorbents are reviewed. Characteristics of sorbents, techniques of sorption preconcentration, and techniques for the preparation of a concentrate for determination are considered. Features of instrumental methods for the determination of noble metals in the analysis of different materials are discussed. Examples of the use of sorption preconcentration in combined methods for the determination of noble metals are given from publications between 1996–2005.     

Trends in sorption preconcentration combined with noble metal determination.

Nowadays much attention is being paid to the determination of trace amounts of noble metals in geological, industrial, biological and environmental samples. The most promising techniques, such as inductively coupled plasma atomic emission spectrometry (ICP-AES), inductively coupled plasma mass spectrometry (ICP-MS) and electrothermal atomic absorption spectrometry (ETAAS) are characterized by high sensitivity. However, the accurate determination of trace noble metals has been limited by numerous interferences generated from the presence of matrix elements. To decrease, or eliminate, these interferences, the sorption preconcentration of noble metals is often used prior to their instrumental detection. A great number of hyphenated methods of noble metal determination using sorption preconcentration have been developed. This review describes the basic types of available sorbents, preconcentration procedures and preparations of the sorbent to the subsequent determination of noble metals. The specific features of instrumental techniques and examples of ETAAS, FAAS, ICP-AES, ICP-MS determinations after the sorption preconcentration of noble metals are considered. The references cited here were selected mostly from the period 1996 - 2006.     

POLYORGS as complexing sorbents for preconcentration of trace metals

Summary The main characteristics of the complexing sorbents POLYORGS are reviewed. These sorbents contain pyrazole, imidazole, amidoxime, 2-mercaptobenzothiazole, thioglycolanilide and arsenazo groups and exhibit high selectivity in respect to noble, rare-earth and heavy metals. The sorbents POLYORGS are applied for the preconcentration of these metals to be determined in ores, rocks, natural and waste waters, and industrial products. The metal determinations after preconcentration are carried out by means of different instrumental methods (e.g., AAS, XRFA, ICP-AES, NAA) either directly in the sorbent, after elution of the analytes or decomposition of the sorbent.     

New Complexing Polymer Aminothioether Sorbents in the Analytical Control of Recyclable Metal-Containing Raw Material of Rare and Noble Metals

The development and use of thioether sorbents for the separation and preconcentration of metals from aqueous solutions are described. The possibilities of initial polymer thioethers in selective preconcentration and the acceleration of sorption through the introduction of nitrogen-containing groups into thioethers are considered. The dependence of the selectivity of sorbents on the nature of radical at the nitrogen atom is revealed. The use of aminothioethers with different substituents at the nitrogen atom enables distinguishing the groups of noble metals, toxic elements of arsenic and selenium subgroups, and a number of nonferrous metals in the presence of large excesses of other elements. A high recovery of the elements to be determined into the sorption preconcentrate and the selectivity of the sorbents help to improve the accuracy of the analysis. Prospects for the use of aminothioethers are considered on an example of sewage waters. It is found that the extraction of small concentrations of elements from large volumes of solutions is more convenient to carry out in dynamics, for which powdered aminothioether sorbents are not suitable. To ensure a possibility of using aminothioethers in dynamics, a “snake in a cage” synthesis method is used, in which the inert granular support is modified with aminothioether moieties. The introduction of aminothioethers with different radicals at the nitrogen atom makes it possible to combine sorbents selective with respect to different groups of elements on one carrier and thus to create a universal sorbent with predetermined properties, aimed at extracting certain metals.     

New sorbents based on organosilicon guanidine derivatives

Monomeric and polymeric organosilicon derivatives of 1-acetylguanidine, which exhibits sorption properties, were synthesized. The organosilicon polymers prepared were studied as sorbents for heavy [Hg(II)] and noble [Ag(I), Au(III), Rh(III), Pd(II), Pt(IV)] metals. They actively take up platinum group metals and exhibit metallochromic properties by analogy with the starting compound, 1-acetylguanidine. Their interaction with all the elements studied is accompanied by coloration. The initial monomers exhibit similar metallochromic properties.     

Automated on-line preconcentration of palladium on different sorbents and its determination in environmental samples

The determination of noble metals in environmental samples is of increasing importance. Palladium is often employed as a catalyst in chemical industry and is also used with platinum and rhodium in motor car catalytic converters which might cause environmental pollution problems. Two different sorbents for palladium preconcentration in different samples were investigated: silica gel functionalized with 1,5-bis(di-2-pyridyl)methylene tbiocarbohydrazide (DPTH-gel) and [1,5-Bis(2-pyridyl)-3-sulphophenyI methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex lx8-200)]. The sorbents were tested in a micro-column, placed in the auto-sampler arm, at the flow rate 2.8 mL min(-1). Elution was performed with 4 M HCl and 4 M HNO3, respectively. Satisfactory results were obtained for two sorbents.     

Sorption methods of concentrating noble metals

Summary The possibility of concentrating microamounts of noble metals on inorganic collectors and chelating sorbents has been investigated. Optimum conditions have been found for simultaneous concentration of Pd, Pt, Rh, Ir, Au and Ag from solutions of complicated composition. For trace analysis a method is suggested based on co-precipitation of the noble metals on copper sulphide, with separation from large amounts of Ni, Co, Fe and associated components. For separation of the noble metals from copper, thin-layer chromatography or sorption on a chelating sorbent under static conditions can be used. The purity of the concentrations obtained allows use of various methods of determination: spectral, atomic-absorption, radioactivation etc.

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Zusammenfassung Die Möglichkeit, Edelmetalle in Mikromengen an anorganischen Kollektoren und Chelatbildnern anzureichern, wurde untersucht. Optimale Bedingungen für die gleichzeitige Anreicherung von Pd, Pt, Rh, Ir, Au und Ag aus Lösungen komplizierter Zusammensetzung wurden gefunden. Für spurenanalytische Zwecke eignet sich die Mitfällung von Edelmetallen mit Kupfersulfid, wobei sie von Ni, Co, Fe und sonstigen Begleitstoffen getrennt werden. Zur Trennung von Kupfer kann die Dünnschichtchromatographie oder die Adsorption an Chelatbildnern unter statischen Bedingungen dienen. Die Reinheit der Konzentrate ermöglicht dann die Bestimmung durch Spektralanalyse, Atomarabsorption, Aktivierungsanalyse usw.

     

Ion-exchange resins containing S-bonded dithizone and dehydrodithizone as functional groups : Part 1. Preparation of the Resins and Investigation of the Sorption of Noble Metals and Base Metals

The one-step reaction of dehydrodithizone with chloromethylated polystyrene yields the anion-exchanger P-TD. Reduction of the immobilized tetrazolium groups of P-TD produces a chelating resin, P-D, containing S-bonded dithizone as the functional group. Distribution coefficients as a function of acidity are presented for 27 metal ions, to establish the selectivity of these sorbents for noble metals. For gold and platinum group metals, the ion-exchangers show marked differences in loading capacities, rates of simultaneous sorption in static conditions and efficiencies in column tests. The P-TD anion exchanger seems to be more profitable than the P-D chelating resin for most purposes.     

Sorption Capacity and Selectivity Relative to Metal Ions for Oxidized Carbon Sorbents with Different Numbers of Oxygen-Containing Groups

We have determined the sorption capacity and selectivity for a broad range of metal ions (alkali, alkaline-earth, transition metal, noble metals, etc.) in two-component and multicomponent mixtures of oxidized carbon sorbents with different numbers of oxygen-containing surface functional groups. We discuss the reasons for the observed changes, their connection with the nature and number of oxygen-containing surface functional groups, and the possibilities for practical application.     

New chelating sorbents based on pyrazolone containing amines immobilized on styrene-divinylbenzene copolymer-I Synthesis and analytical characterization

A series of new cheating sorbents has been prepared by modification of styrene-divinylbenzene copolymer with different pyrazolone-containing amines. The substances were characterized by elemental analysis and infared spectroscopy. The complexation ability of the sorbents towards alkali, alkaline-earth, transition and precious metals has been studied. The new sorbents may successfully be applied to the simultaneous preconcentration of alkaline-earth and transition elements in neutral medium and to the selective separation of precious metals in acidic medium.     

Surface Atomic Regulation of Core–Shell Noble Metal Catalysts

Core–shell noble metal catalysts have gained significant attention in the past few decades, as they not only reduce the use of noble metals effectively but also exhibit unique properties derived from the synergistic effect between core and shell metals. In particular, regulating the surface structure of shells to maximize the atomic utilization efficiency of noble metals is critically important. Controlling the shell thickness of noble metal catalysts at the atomic level as an efficient approach to realize this goal has been attracting growing attention; this approach involves the formation of ultrathin shells (typically 2–6 atomic layers), monolayers, or even atomically dispersed noble metals embedded in the host metal. These strategies drive the core/support metals to improve the number of active sites and the intrinsic activity of the deposited noble metals remarkably, meanwhile minimizing the usage of noble metals. Herein, recent advances regarding atomic control of the core–shell noble metal catalysts is reviewed, with focus on the surface regulation. First, synthesis methods and surface structures are summarized, and then catalytic applications of these architectures are highlighted.     

由类水滑石前驱体制备的CuZnAl复合氧化物催化剂催化湿氧化处理苯酚

The efficiency of several noble metals for catalytic wet oxidation (CWO) of various pollutants has been demonstrated[1,2]. However, the noble metals are expensive, affecting greatly the economics of the corresponding process.     

The determination of all the platinum group elements and gold in rocks and ore by neutron activation analysis after preconcentration by a nickel sulphide fire-assay technique on large samples

The noble metals are inhomogeneously distributed in sulphide ores and their host rocks. It is therefore necessary to analyse large sample sizes to obtain representative analyses. A nickel sulphide fire assay technique has been adapted to extract the noble metals from a large sample size (50 g) into a nickel sulphide button. Subsequently the fire assay button is dissolved in hydrochloric acid and the solution is filtered. The noble metal residue retained on the filter paper is analysed quantitatively by i.n.a.a. techniques. This method is rapid, relatively inexpensive and has better sensitivities for all the noble metals than other analytical techniques.     

Metal Sorption by Materials with a Mobile Phase of Extractants

Data on sorption of rare, noble, radioactive, and nonferrous metals from aqueous solutions by impregnates and TVEXs were analyzed. These are materials combining the properties of sorbents and extractants and differing in the production method. Their distinctive feature is that the extractant is not chemically bonded to the solid support, which is responsible for high kinetic characteristics of sorption processes involving these materials, favorably comparing with conventional sorbents. As a mobile phase to be deposited on the carrier (mainly polymeric) in the case of impregnates or to be introduced during synthesis of TVEXs served organophosphorus extractants, amines, quaternary ammonium bases, etc. Information regarding the effect of various parameters (solution acidity, metal concentration, phase ratio, temperature, and concentration of impurity elements) on separating capability and metal sorption capacity and kinetics was provided for this type of materials. Methods used for stabilizing the properties of impregnates with the view to minimize the extractant loss during application were considered.

     

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.     

New potential-energy functions for Cu, Ag and Au solids and their applications to computer simulations on metallic surfaces

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Thermal decomposition study of sewage sludge and of organicwaste used in the sorption of metals

The conventional treatments of effluents containing heavy metals produce significant quantities of byproducts with recalcitrant characteristics, making necessary looking after alternative techniques in order to avoid the production of new contaminated residues. Sorption process of chromium and zinc in vertical columns loaded with sewage sludge and organic solid waste has been studied in this work. The data from the TG curves of the two sorbents presented significant differences when they were submitted to the metal uptake, being noticed the displacement of the thermal events towards lower temperatures for both types of sorbents studied. As it was expected, for both sorbents, an increase in the mass of samples has been observed at the completion of the thermal tests upon metal uptake. Therefore, these facts demonstrate that during the biosorption process a physico-chemical interaction took place between sorbents and metals, as it was evidenced by the more than 100 K increase in the decomposition temperatures as well as the variation of the ΔH values of the samples.     

New organosilicon derivatives of some analytical reagents: sorbents and metallochromic agents

A synthesis of organosilicon monomeric and polymeric derivatives of 1,4-phenylenediamine, 4-aminoantipyrine, and aniline, which are analytical agents possessing sorption properties, was accomplished. The synthesized organosilicon polymers were studied as sorbents of heavy metals Fe^III, Hg^II and noble metals Ag^I, Au^III, Rh^III, Pd^II, Pt^IV. Poly[(3-N-silsesquioxanylpropyl-4aminoantipyrine)] exhibited high sorption activity with respect to platinum group metals in comparison with poly[N,N´-bis(3-silsesquioxanylpropyl)-1,4-phenylenediamine]. The reaction of poly[(3-N-silsesquioxanylpropyl-4-aminoantipyrine)] practically with all the elements under study was accompanied by coloring. The starting monomer exhibited similar metallochromic properties.